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  • 101.
    Ozyagci, Ali
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Association and deployment considerations in dense wireless LANs2014In: Vehicular Technology Conference (VTC Spring), 2014 IEEE 79th, IEEE conference proceedings, 2014Conference paper (Refereed)
    Abstract [en]

    Wireless LANs based on the IEEE 802.11 standard are one of the most commonplace indoor wireless access solutions. As the ever growing demand for data consumption necessitates higher rates and volumes, it is fairly common to observe more and more WLANs being deployed in close proximity to each other. As distances between WLAN installations diminish, the access points (APs) and stations (STAs) in these WLANs create a complex interference environment, which is also compounded by the indoor propagation environment. In this paper, we investigate the impact of two important parameters related to the deployment and operation of densely deployed wireless LANs on the aggregate throughput obtained by all the nodes in these WLANs. The first such operational parameter we investigate is access point and user station association; namely, whether STAs associate with a random ``strong'' AP or the AP from which they obtain the strongest received power. The second operational parameter we consider is the way in which APs are placed in the indoor environment; namely, whether APs are deployed randomly or in a manner to reduce inter-AP interference. In order to account for the complex node interactions in the MAC layer, which is crucial for accurate performance estimation, we perform packet-level simulations using OPNET. Our results show that the type of node association used in densely deployed WLANs has a critical impact on the aggregate throughput. In comparison, the type of AP deployment used is not nearly as significant; varying from moderate to no impact at all.

  • 102.
    Ozyagci, Ali
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Delay bound capacity analysis of dense WLANsManuscript (preprint) (Other academic)
    Abstract [en]

    Indoor WLAN deployments are becoming denser such that it is fairly common to observe several WLANs operating on the same channel. Increasing density creates more congestion and interference on these WLANs, which potentially has a significant impact on the delay and throughput performance of these WLANs. Therefore, we investigate the behavior of MAC layer delay and aggregate throughput in densely deployed WLANs in connection with different traffic arrival rates, propagation environments and deployment choices. The novelty of this work is that such a comprehensive study has not been performed before. We perform an extensive simulation study using OPNET by incorporating in our analysis a realistic MAC model and the impact of indoor propagation environment causing hidden nodes. We identify the relationship between delay and aggregate throughput in a system of densely deployed WLANs and propose guidelines for determining suitable WLAN deployment densities in different propagation environments.

  • 103. Park, J.
    et al.
    Kim, S. -L
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Asymptotic behavior of ultra-dense cellular networks and its economic impact2014In: 2014 IEEE Global Communications Conference, GLOBECOM 2014, 2014, p. 4941-4946Conference paper (Refereed)
    Abstract [en]

    This paper investigates the relationship between base station (BS) density and average spectral efficiency (SE) in the downlink of a cellular network. This relationship has been well known for sparse deployment, i.e. when the number of BSs is small compared to the number of users. In this case the SE is independent of BS density. As BS density grows, on the other hand, it has previously been shown that increasing the BS density increases the SE, but no tractable form for the SE-BS density relationship has yet been derived. In this paper we derive such a closed-form result that reveals the SE is asymptotically a logarithmic function of BS density as the density grows. Further, we study the impact of this result on the network operator's profit when user demand varies, and derive the profit maximizing BS density and the optimal amount of spectrum to be utilized in closed forms. In addition, we provide deployment planning guidelines that will aid the operator in his decision if he should invest in densifying his network or in acquiring more spectrum.

  • 104. Park, Jihong
    et al.
    Kim, Seong-Lyun
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Tractable Resource Management With Uplink Decoupled Millimeter-Wave Overlay in Ultra-Dense Cellular Networks2016In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, no 6, p. 4362-4379Article in journal (Refereed)
    Abstract [en]

    The forthcoming 5G cellular network is expected to overlay millimeter-wave (mmW) transmissions with the incumbent micro-wave (mu W) architecture. The overall mm-mu Wresource management should, therefore, harmonize with each other. This paper aims at maximizing the overall downlink (DL) rate with a minimum uplink (UL) rate constraint, and concludes: mmWtends to focus more on DL transmissions while mu W has high priority for complementing UL, under time-division duplex (TDD) mmW operations. Such UL dedication of mu W results from the limited use of mmW UL bandwidth due to excessive power consumption and/or high peak-to-average power ratio (PAPR) at mobile users. To further relieve this UL bottleneck, we propose mmW UL decoupling that allows each legacy mu Wbase station (BS) to receive mmW signals. Its impact on mm-mu W resource management is provided in a tractable way by virtue of a novel closed-form mm-mu W spectral efficiency (SE) derivation. In an ultra-dense cellular network (UDN), our derivation verifies mmW (or mu W) SE is a logarithmic function of BS-to-user density ratio. This strikingly simple yet practically valid analysis is enabled by exploiting stochastic geometry in conjunction with real three-dimensional (3-D) building blockage statistics in Seoul, South Korea.

  • 105. Piunti, P.
    et al.
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Morosi, S.
    Teka, Kaleab Ejigayehu
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Del Re, E.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Energy efficient adaptive cellular network configuration with QoS guarantee2015In: 2015 IEEE International Conference on Communications (ICC), IEEE conference proceedings, 2015, p. 68-73Conference paper (Refereed)
    Abstract [en]

    Cellular network energy optimization is driven by different factors, namely transmission power and activity of the base stations. Quality of Service (QoS) of users is determined by received power, interference and bandwidth allocation and cannot be neglected. In existing studies, such drivers are treated separately, i.e., bandwidth allocation is fixed while power consumption is a variable to be optimized. This paper proposes a novel optimization framework which is aimed at minimizing the power consumption in cellular networks while affording a minimum bit rate for each mobile terminal by jointly considering energy consumption and QoS drivers. Mixed Integer Quadratic Programming (MIQP) based optimization framework solves the problems of the determination of the user association, the bandwidth allocation, the identification of the active base stations and their transmission power, guaranteeing also a requested service rate for each user. The proposed solution is shown to allow power savings of up to 60%, very close to the optimum lower bound, when the traffic is below the 35% of the maximum load.

  • 106.
    Rasti, Mehdi
    et al.
    Department of Electrical and Computer Engineering, Tarbiat Modares Univesity, Tehran, Iran.
    Sharafat, Ahmad R.
    Department of Electrical and Computer Engineering, Tarbiat Modares Univesity, Tehran, Iran.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    A Distributed and Efficient Power Control Algorithm for Wireless Networks2008In: 2008 IEEE 19TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, IEEE , 2008, p. 1494-1499Conference paper (Refereed)
    Abstract [en]

    In the well-known distributed target-SIR tracking power control algorithm, when the target-SIR requirements are not reachable for all users, all non-supported users (those who do not reach their target SIRs) transmit at their maximum power. Such users inefficiently consume their energies, and introduce unnecessary interference to others, which in turn unnecessarily increases the number of non-supported users. To deal with this, the smallest number of users should be removed due to infeasibility of the system (gradual removal problem). We present a new distributed constrained power control (DCPC) algorithm to address the gradual removal problem. The basic idea is that any transmitting user whose required transmit power for reaching its target-SIR exceeds its maximum power is temporarily removed. Each temporarily removed user resumes its transmission if its required transmit power for reaching its target-SIR goes below a given threshold (lower than its maximum power). This threshold is determined by each removed user in a distributed manner using only local information. We will show that our proposed algorithm has at least one-fixed point (i.e., its convergence can be guaranteed), and at the equilibrium where the algorithm converges, all transmitting users (the users whose transmit powers are greater than zero) reach their target SIRs consuming the minimum aggregate transmit power. Furthermore, in contrast to the existing DCPC algorithms, no user is unnecessarily removed in our proposed scheme, i.e., it is efficient. Our simulation results confirm our analytic developments and show that our scheme outperforms the existing DCPCs in addressing the gradual removal problem, in terms of convergence, outage probability and power consumption.

  • 107. Rasti, Mehdi
    et al.
    Sharafat, Ahmad R.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    A Distributed Dynamic Target-SIR-Tracking Power Control Algorithm for Wireless Cellular Networks2010In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 59, no 2, p. 906-916Article in journal (Refereed)
    Abstract [en]

    The well-known fixed-target-signal-to-interference-ratio (SIR)-tracking power control (TPC) algorithm provides all users with their given feasible fixed target SIRs but cannot improve the system throughput, even if additional resources are available. The opportunistic power control (OPC) algorithm significantly improves the system throughput but cannot guarantee the minimum acceptable SIR for all users (unfairness). To optimize the system throughput subject to a given lower bound for the users' SIRs, we present a distributed dynamic target-SIR tracking power control algorithm (DTPC) for wireless cellular networks by using TPC and OPC in a selective manner. In the proposed DTPC, when the effective interference (the ratio of the received interference to the path gain) is less than a given threshold for a given user, that user opportunistically sets its target SIR (which is a decreasing function of the effective interference) to a value higher than its minimum acceptable target SIR; otherwise, it keeps its target SIR fixed at its minimum acceptable level. We show that the proposed algorithm converges to a unique fixed point starting from any initial transmit power level in both synchronous and asynchronous power-updating cases. We also show that our proposed algorithm not only guarantees the (feasible) minimum acceptable target SIRs for all users (in contrast to the OPC) but also significantly improves the system throughput, compared with the TPC. Furthermore, we demonstrate that DTPC, along with TPC and OPC, can be utilized to apply different priorities of transmission and service requirements among users. Finally, when users are selfish, we provide a game-theoretic analysis of our DTPC algorithm via a noncooperative power control game with a new pricing function.

  • 108.
    Rasti, Mehdi
    et al.
    Department of Electrical and Computer Engineering, Tarbiat Modares Univesity, Tehran, Iran.
    Sharafat, Ahmad R.
    Department of Electrical and Computer Engineering, Tarbiat Modares Univesity, Tehran, Iran.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Improved Distributed Power Control Algorithms with Gradual Removal in Wireless Networks2008In: 2008 EUROPEAN WIRELESS CONFERENCE, IEEE , 2008, p. 165-169Conference paper (Refereed)
    Abstract [en]

    In the well-known distributed target-SIR tracking power control algorithm, when the target-SIR requirements are not reachable for all users (due to heavy load and/or deep fading), some users transmit at maximum power without reaching their target SIR. Such users inefficiently consume their energies, and introduce unnecessary interference to others, which in turn results in more unnecessary non-supported users. To alleviate the situation, a minimal number of users have to be removed (the gradual removal problem). In this paper, we propose improvements to two algorithms that were shown to be the best of the existing distributed power control algorithms for the gradual removal problem, and demonstrate that the improved algorithms have smaller outage probabilities. In addition, we show that the convergence rate for one of our improved algorithms is substantially better than those of both original algorithms.

  • 109.
    Rasti, Mehdi
    et al.
    Department of Electrical Engineering, Shiraz University of Technology, Shiraz, Iran.
    Sharafat, Ahmad R.
    Department of Electrical and Computer Engineering, Tarbiat Modares Univesity, Tehran, Iran.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Pareto and Energy-Efficient Distributed Power Control with Feasibility Check in Wireless Networks2011In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 57, no 1, p. 245-255Article in journal (Refereed)
    Abstract [en]

    We formally define the gradual removal problem in wireless networks, where the smallest number of users should be removed due to infeasibility of the target-SIR requirements for all users, and present a distributed power-control algorithm with temporary removal and feasibility check (DFC) to address it. The basic idea is that any transmitting user whose required transmit power for reaching its target-SIR exceeds its maximum power is temporarily removed, but resumes its transmission if its required transmit power goes below a given threshold obtained in a distributed manner. This enables users to check the feasibility of system in a distributed manner. The existence of at least one fixed-point in DFC is guaranteed, and at each equilibrium, all transmitting users reach their target-SIRs consuming the minimum aggregate transmit power. Furthermore, in contrast to the existing algorithms, no user is unnecessarily removed by DFC, i.e., DFC is Pareto and energy-efficient. We also show that when target-SIRs are the same for all users, DFC minimizes the outage probability. Simulation results confirm our analytical developments and show that DFC significantly outperforms the existing schemes in addressing the gradual removal problem in terms of convergence, outage probability, and power consumption.

  • 110.
    Rosberg, Zvi
    et al.
    IBM, Haifa Research Laboratory.
    Zander, Jens
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Towards a framework for power control in cellular radio systems1998In: Wireless networks, ISSN 1022-0038, E-ISSN 1572-8196, Vol. 4, no 3, p. 215-222Article in journal (Refereed)
    Abstract [en]

    Efficiently sharing the spectrum resource is of paramount importance in wireless communication systems, in particular in Personal Communications where large numbers of wireless subscribers are to be served. Spectrum resource sharing involves protecting other users from excessive interference as well as making receivers more tolerant to this interference. Transmitter power control techniques fall into the first category. In this paper we describe the power control problem, discuss its major factors, objective criteria, measurable information and algorithm requirements. We attempt to put the problem in a general framework and propose an evolving knowledge dashbank to share, study and compare between algorithms.

  • 111.
    Sanchez, Marvin
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Hagerman, Bo
    A reuse-greedy algorithm for STDMA multihop networks with advanced antennas & rate control2008In: 2008 3rd International Symposium On Wireless Pervasive Computing: Vols 1-2, 2008, p. 575-579Conference paper (Refereed)
    Abstract [en]

    The introduction of multiple discrete transmission rates has been proposed as a promising way to increase the performance of multihop wireless networks. In this paper we will propose a novel, low complexity algorithm for rate selection and scheduling in a Spatial Time Division Multiple Access (STDMA). The throughput performance is evaluated in a network where nodes are equipped with advanced antennas. The results are compared with the (near) optimum performance found by solving a corresponding nonlinear optimization problem. Results show that our proposed algorithm exhibits a throughput performance that significantly exceeds the performance of fixed rate schemes. Further, our evaluation shows that the proposed algorithm achieves a performance that is close (within about 10%) to the performance obtained by the optimization method.

  • 112.
    Schrader, Brooke
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Karlsson, Robert S.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Andrew, Lachlan L.H.
    Zander, Jens
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Power-control-based Band Allocation in Multiband CDMA2001In: Global Telecommunications Conference, 2001. GLOBECOM '01. IEEE, New York: IEEE , 2001, p. 3306-3310Conference paper (Refereed)
    Abstract [en]

    Multiband CDMA is useful for constructing DSCDMA (CDMA) systems over a non-contiguous spectrum. The method by which users are assigned to their respective frequency bands, termed `band allocation', is an important part of assuring good performance in multiband CDMA systems. This paper proposes a novel approach to band allocation based on the transmission power as it is adjusted by power control. We investigate one such power-control-based algorithm that makes use of quality-based power control to switch users to another band when they reach the maximum transmission power. This algorithm is shown to provide a significant increase in capacity for high QoS requirements when compared with both wideband CDMA systems and other proposed band allocation algorithms for multiband CDMA. The capacity gain provided by the investigated algorithm substantiates our claim that power-control-based algorithms are a viable option for band allocation in multiband CDMA.

  • 113.
    Shi, Lei
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Obregon, Evanny
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Boström, Jan
    CellTV - On the Benefit of TV Distribution Over Cellular Networks: A Case Study2014In: IEEE transactions on broadcasting, ISSN 0018-9316, E-ISSN 1557-9611, Vol. 60, no 1, p. 73-84Article in journal (Refereed)
    Abstract [en]

    As mobile IP-access is becoming the dominant technology for providing wireless services, the demand for more spectrum for this type of access is increasing rapidly. Since IP-access can be used for all types of services, instead of a plethora of dedicated, single-service systems, there is a significant potential to make spectrum use more efficient. In this paper, the feasibility and potential benefit of replacing the current terrestrial UHF TV broadcasting system with a mobile, cellular data (IP-) network are analyzed. In the cellular network, TV content would be provided as one of the services (CellTV). In the investigation, we consider typical Swedish rural and urban environments. We use different models for TV viewing patterns and cellular technologies as expected in the year 2020. Results of the quantitative analysis indicate that CellTV distribution can be beneficial if the TV consumption trend goes toward more specialized programming, more local contents, and more on-demand requests. Mobile cellular systems, with their flexible unicast capabilities, will be an ideal platform to provide these services. However, the results also demonstrate that CellTV is not a spectrum-efficient replacement for terrestrial TV broadcasting with current viewing patterns (i.e., a moderate number of channels with each a high numbers of viewers). In this case, it is doubtful whether the expected spectrum savings can motivate the necessary investments in upgrading cellular sites and developing advanced TV receiver required for the success of CellTV distribution.

  • 114.
    Shi, Lei
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Cellular TV Distribution in Heterogeneous EnvironmentsManuscript (preprint) (Other academic)
  • 115.
    Shi, Lei
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Controlling Aggregate Interference under Adjacent Channel Interference Constraint in TV White Space2012In: 2012 7th International Conference on Cognitive Radio Oriented Wireless Networks (CROWNCOM), IEEE , 2012, p. 1-6Conference paper (Refereed)
    Abstract [en]

    TV White space, where secondary systems can be deployed inside the TV coverage area and utilize the geographically unoccupied TV channels, is considered as a promising solution to relieve the spectrum shortage. To utilize this spectrum, the secondary users must ensure the protection of TV receptionfrom harmful interference on both co-channel and adjacent channels. In this paper, we propose an analytical approach to determining the permissible transmit power for short-range secondary users under aggregate adjacent channel interferenceconstraint in TV white space. This approach employs statistical interference modeling which considers random deployment of secondary users, antenna gain pattern, shadow fading, and the cumulative effect of interference from multiple adjacent channels. Numerical results show that the proposed scheme permits significantly higher transmit power than the existing deterministic method does, while at the same time, it keeps the required level of TV protection. Therefore, considerable potential for the shortrange secondary access to TV white space is expected with our approach.

  • 116. Shi, Lei
    et al.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Future TV Content Delivery Over Cellular Networks From Urban to Rural Environments2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 11, p. 6177-6187Article in journal (Refereed)
    Abstract [en]

    With the increasing number of TV channels and the growing need for on-demand services, the traditional digital terrestrial television is becoming a less attractive way of distributing TV content. As an alternative, we discuss a converged platform in the UHF band for TV and mobile broadband provisioning based on LTE cellular technology and infrastructure, which is here referred to as CellTV. The requirement for CellTV is to provide seamless TV coverage from urban to rural environments and to minimize the spectrum requirement so that the leftover can be used for mobile services. We formulate an optimal spectrum allocation problem for CellTV to distribute different TV channels with different transmission modes. Each TV channel is delivered via either unicast links or the broadcast over single-frequency networks of different modulation orders according to the location-dependent viewing demand and the cellular infrastructure availability. Based on a case study of the Greater Stockholm region, we identify that CellTV only requires a small portion of the UHF band to deliver the TV content in urban areas, thus releasing a significant amount of spectra for mobile broadband services. Meanwhile, the spectrum requirement for CellTV is considerably higher in suburban and rural areas due to the transitions of transmission modes. We further generalize these findings to provide a guiding principle for CellTV deployment in mixed environments and to demonstrate the flexibility advantage of CellTV in adapting to the growing diversity of TV content.

  • 117.
    Shi, Lei
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    On the Permissible Transmit Power for Secondary User in TV White Spaces2012In: 2012 7th International Conference on Cognitive Radio Oriented Wireless Networks (CROWNCOM), IEEE , 2012, p. 13-17Conference paper (Refereed)
    Abstract [en]

    Secondary spectrum access to TV white spaces is considered as a promising solution to relieve the spectrum shortage. In Europe, SE43 working group in CEPT is leading the discussion on the technical requirements for exploiting TV white spaces through the recent ECC report 159. Its analytical approach for determining the maximum permissible power for the secondary user, however, overestimates the power level, and leads to significant violation of the interference limit for TV reception. In this letter, we address the problem by proposing a new approach for determining the secondary user transmit power based on the framework established in ECC report 159. Monte Carlo simulation shows that our method keeps the interference close to the target.

  • 118.
    Shi, Lei
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Opportunities and challenges for converged platform for audio-visual and data services in 470-790 MHz UHF broadcasting band2013In: 24th European Regional ITS Conference, Florence 2013, 2013Conference paper (Refereed)
    Abstract [en]

    In this paper, we will investigate the potential opportunities and challenges for deploying a converged platform in the UHF Broadcasting band (470-790 MHz) to replace the legacy systems and provide terrestrial audio-visual and dataservice. As recent development shows, both mobile broadband and terrestrial broadcasting (DTT) now overlap to offer audio-visual services to customers. Whereas DTT is designed only for audio-visual content, mobile broadband systems are converged all-IP platforms that may carry a multitude of services in unified and device-agnostic way. DTT used to be highly effective, when the task was to distribute a few TV channels to large audiences. However, for the rapidly increasing long-trail of niche television channels, each with diminishingly few viewers, DTT is no longer an efficient way of using the spectrum. Progressively re-farming of the UHF broadcasting band for more flexible and efficient use, is high on the list of discussion items in the upcoming World Radio Conference 2015, it is highly relevant to evaluate this option with a holistic view. This paper will present findings from the analysis of the inherent strengths and weaknesses of mobile and broadcasting industries in their new roles in the converged ecosystem. Detailed discussions are focused on identifying the possible benefits and threats from the perspectives of the broadcasters, mobile network operators, digital terrestrial network operators and the society as a whole. Overall we consider such a converged platform is a win-win solution for most of the stakeholders thanks to the increase in spectrum and network efficiency and flexibility improvement in the all-IP network. Nevertheless, there are still challenging issues to be addressed, such as the compensation and new business model for the digital terrestrial network operator and ensuring the quality of service for audio-visual content delivery in cellular network.

  • 119.
    Shi, Lei
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Opportunities and challenges forTV and Mobile broadband in 470-790 MHz (P8)2013Conference paper (Refereed)
  • 120.
    Shi, Lei
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Permissible Transmit Power for Secondary User in TV White Space2012Conference paper (Refereed)
    Abstract [en]

    Secondary spectrum access to TV white spaces is considered as a promising solution to relieve the spectrum shortage. In Europe, SE43 working group in CEPT is leading the discussion on the technical requirements for exploiting TV white spaces through the recent ECC report 159. Its analytical approach for determining the maximum permissible power for the secondary user, however, overestimates the power level, and leads to significant violation of the interference limit for TV reception. In this letter, we address the problem by proposing a new approach for determining the secondary user transmit power based on the framework established in ECC report 159. Monte Carlo simulation shows that our method keeps the interference lose to the target.

  • 121.
    Shi, Lei
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Secondary spectrum access in TV-bands with combined co-channel and adjacent channel interference constraints2012In: 2012 IEEE International Symposium on Dynamic Spectrum Access Networks, DYSPAN 2012, 2012, p. 452-460Conference paper (Refereed)
    Abstract [en]

    The potential of VHF/UHF band as a candidate for secondary spectrum access, so called ”TV white spaces”, has been intensively investigated in recent years. However, the impact of the accumulated interference from multiple secondary users on different adjacent channels has not been well studied thus far, let alone the effect of combined interference from both co-channel and adjacent channels. This paper presents a framework for assessing secondary spectrum reuse opportunities for portable and mobile devices that comply with geo-location database concepts. The opportunity is evaluated in terms of the maximal number of secondary users that can access the ”TV white space” simultaneously. Particular emphasis is given to the protection of TV receiver from harmful aggregate interference originated from not only the secondary users outside the TV coverage on the same channel but also those close to the TV receivers operating on different adjacent TV channels. An optimization problem is solved to maximize the number of secondary users admitted to the available TV channels at different locations. Through in-depth analysis of the interference characteristics of the optimal solution, it is identified that the cumulative effect of adjacent channel interferences has the dominant impact on TV reception, particularly for the case of secondary devices with limited transmit power. This suggests the possibility to achieve near-optimal exploitation of TV-bands for secondary reuse without explicit coordination of co-channel interference from the secondary users deployed over a wide geographical area.

  • 122.
    Shi, Lei
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Spectrum Requirement for Cellular TV distribution in UHF Band from Urban to Rural Environment2014In: 2014 IEEE International Symposium on Dynamic Spectrum Access Networks (DYSPAN), IEEE Computer Society, 2014, p. 362-365Conference paper (Refereed)
    Abstract [en]

    An the number of TV-channels increase and the number of viewers per channel decreases, Terrestrial Broadcasting is becoming a less attractive way to distribute TV. In addition it does not represent a very efficient use of the UHF band (470790 MHz). In this paper we discuss an alternative, converged platform for TV and mobile broadband provisioning based on LTE cellular technology and infrastructure, here referred to as CelITV. The key feature of Cell-TV is the ability to switch between a unicast mode for small viewer populations and broadcast over LTE single frequency networks (SFN) for popular content. The main advantage is that the spectrum can flexibly be shared with LTE mobile data services, effectively freeing significant parts of the UHF spectrum for these purposes. Based on a case study of the greater Stockholm area, significant potential for spectrum saving is identified in urban areas where the need for spectrum is the largest. Meanwhile, only limited spectrum savings are observed in rural areas due to the large user populations in each cell and the long inter-site distance. As most of the TV channels are broadcasted in urban areas but unicasted in rural areas, this switch of transmission modes causes considerably high spectrum demand in suburban areas.

  • 123. Shin, Eun-Hee
    et al.
    Kim, Dongwoo
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Communication Systems, CoS.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Impact of Open-Loop Power Controlled Feedback on Multiuser Capacity in Rayleigh Fading Channels2009In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 13, no 12, p. 932-934Article in journal (Refereed)
    Abstract [en]

    This letter investigates the impact of open-loop power control (OLPC) employed in uplink (UL) feedback channel on the multiuser downlink (DL) capacity. OLPC is used to reduce the capacity loss caused by the feedback outage. Assuming flat Rayleigh channels correlated between DL and UL, we provide probability distributions on the DL SNR that are successfully fed back through UL managed by OLPC. Numerical results are used to verify the accuracy of the analysis and to show the impact of relevant parameters of OLPC on the capacity as a function of DL-UL correlation.

  • 124.
    Somarriba Jarquín, Oscar
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Evaluation of Heuristic Strategies for Scheduling, and Power Allocation in STDMA Wireless Networks2007In: 2007 INTERNATIONAL SYMPOSIUM ON SIGNALS, SYSTEMS AND ELECTRONICS, VOLS 1 AND 2, IEEE , 2007, p. 427-430Conference paper (Refereed)
    Abstract [en]

    A major design issue in wireless multihop networks is the design of the medium access control (MAC) protocols. Spatial TDMA (STDMA) is a "conflict-free" MAC protocol for these networks, thus enabling high spectral utilization. In link-oriented STDMA, the schedule specifies when particular radio links will be activated. Moreover, the use of power control and multiple-rate selection have the potential of improving STDMA network performance. Besides power and traffic adaptive STDMA, in this paper we also, as a comparison, include optimal STDMA. To obtain the optimal scheduling for STDMA, a convex optimization problem is solved using the method reported in [1]. Our results show that the heuristic strategies can provide near optimal solutions regarding end-to-end network throughput.

  • 125.
    Somarriba, O.
    et al.
    UNI National Engineering University of Nicaragua.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Robust STDMA scheduling in Multi-hop Wireless Networks for single-node position perturbations2009In: 2009 IEEE 20th Personal, Indoor and Mobile Radio Communications Symposium, PIMRC 2009, 2009, p. 566-571Conference paper (Refereed)
    Abstract [en]

    A major design issue in Multi-hop Wireless Networks is the Medium Access Control (MAC) protocols that determine how nodes share the channel to transmit their packets. One type of MAC protocol with efficient spatial reuse characteristics are the Spatial TDMA (STDMA) protocols. STDMA protocols are a class of conflict-free MAC protocols that enable high spectral utilization by scheduling transmissions on the channel. Its main features are high throughput and the possibility of providing delay guarantees. We studied the sensibility of STDMA networks to disruption caused by slow mobility of one "critical" node (single-user perturbation), that causes problems to the schedule maintenance. We assessed a framework that produces robust STDMA scheduling against these topological changes. To do that, we introduced and analyzed heuristic algorithms that mainly exploit capabilities of the physical layer such as power and rate control, and rerouting. We considered the limited-mobility management in STDMA networks to find the ranges where our heuristics will avoid re-scheduling of the whole STDMA frame. We found that a substantial throughput degradation due to slow mobility in STDMA networks can be compensated by means of power or rate control, and rerouting. Our results showed that rate-controlled (RC) STDMA is the most promising scheme to maintain communication under slow mobility.

  • 126. Song, Young-Keum
    et al.
    Kim, Dongwoo
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Pilot Power Adjustment for Saving Transmit Power in Pilot Channel Assisted DS-CDMA Mobile Systems2010In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 9, no 2, p. 488-493Article in journal (Refereed)
    Abstract [en]

    In DS-CDMA systems coherent detection is usually adopted by adding or multiplexing redundant pilot signals with voice or data traffic. The pilot signals need additional transmit power but, at the same time, decrease the power used for traffic channel through facilitating channel estimation, which reduces the bit energy-to-noise density ratio (E-b/N-o) required for delivering the traffic signals. The interdependency between pilot and traffic channel powers has been analyzed in various studies, but has not yet been exploited in existing power control methods. In this letter, we provide a method of using the interdependency to adjust pilot power in the context of the existing power control algorithms, and prove its convergence and that it reduces the total transmit power.

  • 127.
    Stabellini, Luca
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01).
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01).
    Energy-Aware Spectrum Sensing in Cognitive Wireless Sensor Networks: a Cross Layer Approach2010In: IEEE Wireless Communications and Networking Conference, WCNC, NEW YORK: IEEE , 2010Conference paper (Refereed)
    Abstract [en]

    Low-power transmissions of sensor nodes are easily corrupted by interference generated by co-located wireless terminals that leading to packet losses might increase energy consumption and result in unreliable communications. Dynamic spectrum access mechanisms can mitigate these problems allowing cognitive sensor devices to sense the spectrum and access the wireless medium in an opportunistic way. With this respect, energy efficient algorithms for spectrum sensing have to be designed in order to meet the power constraints of wireless sensor networks. In this paper we consider an energy constrained system comprising two sensor nodes that avoid interference by exploiting spectrum holes in the time domain. We design the algorithm used for spectrum sensing so as to minimize the average energy required for the successful delivery of a packet. While carrying our this task we adopt a cross layer approach that accounts for the average channel occupancy and the power of interfering transmissions at the physical layer as well as for the size of packets used by sensors at the transport layer. Our results show that accounting for the short length of packets commonly used in sensor networks can significantly improve energy efficiency leading to gains of up to 50% if compared to other spectrum sensing algorithms envisaged in the literature.

  • 128.
    Stabellini, Luca
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Energy-efficient detection of intermittent interference in wireless sensor networks2010In: International Journal of Sensor Networks, ISSN 1748-1279, Vol. 8, no 1, p. 27-40Article in journal (Refereed)
    Abstract [en]

    Communications of low-power sensor nodes are easily corrupted by transmissions of collocated devices that inducing packet losses might increase data delay and energy consumption. Dynamic Spectrum Access mechanisms can mitigate these problems. These approaches allow frequency agile sensor nodes to avoid frequency bands experiencing high interference and select channels suitable for their transmissions. In this context, detecting interference and identifying spectrum opportunities in a reliable and efficient manner becomes a task of vital importance. In this paper we propose a new interference detection algorithm accounting both for energy and complexity constraints of sensor motes as well as for the intermittent nature of interference typically experienced by sensor networks in unlicensed bands. We develop an analytical framework that allows to explicitly characterise the performance of our algorithm and also implement it on the TMote Sky sensor platform. Experimental results clearly demonstrate the capabilities of the proposed scheme to identify interfered channels.

  • 129.
    Stabellini, Luca
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Interference Aware Self-Organization for Wireless Sensor Networks: a Reinforcement Learning Approach2008In: 2008 IEEE INTERNATIONAL CONFERENCE ON AUTOMATION SCIENCE AND ENGINEERING, VOLS 1 AND 2, NEW YORK: IEEE , 2008, p. 560-565Conference paper (Refereed)
    Abstract [en]

    Reliability is a key issue in wireless sensor networks. Depending on the targeted application, reliability is achieved by establishing and maintaining a certain number of network functionalities: the greatest among those is certainly the capability of nodes to communicate. Sensors communications are sensible to interference that might corrupt packets transmission and even preclude the process of network formation. In this paper we propose a new scheme that allows to establish and maintain a connected topology while dealing with this problem. The idea of channel surfing (already introduced in [1]) is exploited to avoid interference; in the resulting multi-channel environment nodes discover their neighbors in a distributed fashion using a reinforcement learning (RL) algorithm. Our scheme allows the process of network formation even in presence of interference, overcoming thus the limit of algorithms currently implemented in state of the art standards for wireless sensor networks. By means of reinforcement learning the process of neighbor discovery is carried out in a fast and energy efficient way.

  • 130.
    Sunell, Kai-Erik
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Zander, Jens
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Power Control for Coded Frequency Hopping Cellular Systems1998Conference paper (Refereed)
    Abstract [en]

    Transmitter power control has proven to be a powerful technique to control interference  and improve the performance of wireless networks. Efficient power control normally re­  quires fast and reliable quality measurements. In cellular systems where propagation and  interference conditions vary rapidly, such real­time measurements cannot be obtained. In­  stead, diversity techniques can be useful. Frequency hopping combined with error control  coding is an example how this diversity can be implemented. These systems effectively  ''average'' the interference. How power control should be applied in these systems is,  however, not obvious.  In this paper, we show that symbol error performance in the uplink of a coded fre­  quency hopping cellular system is, at least in principle, minimized by maintaining the  received signal power at a constant level, provided that accurate instantaneous measure­  ments are available. When such instantaneous measurements are not available, but only  time averages this is no longer the optimum strategy. Therefore, also some signal­level  based power control schemes are analyzed with respect to their interaction with the error  control coding schemes used. Results show that power control schemes designed for static  channel allocation (without interference randomization) may give rise to severe fairness  problems in coded frequency hopping systems. It is also found that changing the code  parameters does not significantly affect the choice of power control policy.

  • 131.
    Sung, Ki Won
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Kim, Seong-Lyun
    Yonsei University.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Temporal Spectrum Sharing Based on Primary User Activity Prediction2010In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 9, no 12, p. 3848-3855Article in journal (Refereed)
    Abstract [en]

    In this paper we investigate the opportunistic spectrum access in temporal domain where a secondary user shares a radio channel with a primary user during the OFF period of the primary user. We consider practical ON/OFF traffic models whose bursty natures are not properly described by a Markovian assumption. An optimal strategy to determine the transmission power of the secondary user is proposed, which can be adapted to any source traffic model of the primary user. This strategy will maximize the spectrum utilization of the secondary user while keeping interference violations to the primary user below a threshold. Numerical results show that the transmission power of the secondary user depends on the probability distribution of the primary traffic as well as the elapsed time of the OFF period.

  • 132.
    Sung, Ki Won
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Obregon, Evanny
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    On the requirements of secondary access to 960-1215 MHz aeronautical spectrum2011In: 2011 IEEE International Symposium on Dynamic Spectrum Access Networks, DySPAN 2011, IEEE , 2011, p. 371-379Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate the spectrum sharing requirements of secondary access to 960-1215 MHz band which is primarily allocated to aeronautical usage. Primary system of interest is distance measuring equipments (DME) aiding navigation of airplanes. We consider a scenario where indoor femtocells share the spectrum as secondary users. For the protection of the primary system, each secondary user decides whether to transmit or not depending on an interference threshold established by a central network. We provide a simple mathematical framework for analyzing the aggregate interference generated by multiple secondary users spreading in a large area. Requirement for the secondary access is established in terms of the size of exclusion region depending on the density of secondary users. Numerical results suggest the use of adjacent DME channel is required for a dense deployment of the secondary users. We discuss the challenges and implementation issues of practical secondary access, and suggest the directions of further research.

  • 133.
    Sung, Ki Won
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Shi, Lei
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Coexistence of LTE femtocells with GSM cellular network2010In: 2010 IEEE 21st International Symposium on Personal Indoor and Mobile Radio Communications, PIMRC 2010, IEEE , 2010, p. 1556-1560Conference paper (Refereed)
    Abstract [en]

    In this paper we investigate the deployment of LTE indoor femtocells on the frequency band currently used by GSM cellular network. We consider a scenario where the LTE femtocells share GSM uplink spectrum provided that the legacy GSM users are not harmed by interference from the femtocells. Difference in the characteristics of GSM and LTE technologies is exploited to enable the spectrum sharing. The performance of both systems is analyzed mathematically in terms of average SINR. Simulation is employed to support the analysis. Numerical results show that the availability of the spectrum sharing depends on the number of femtocells in each GSM cell and the locations of femtocells.

  • 134.
    Sung, Ki Won
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Tercero Vargas, Miurel
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Aggregate Interference in Secondary Access with Interference Protection2011In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 15, no 6, p. 629-631Article in journal (Refereed)
    Abstract [en]

    This paper presents a derivation of the probability distribution function (pdf) of the aggregate interference in a secondary access network where multiple secondary users cause interference to a single primary user. The derivation considers a practical interference protection mechanism that the transmission of each secondary user is regulated by an interference threshold. Analytic pdf of the interference from a secondary user is obtained. Then, the distribution of the aggregate interference is approximated based on its cumulants. The derived pdf shows a good agreement with Monte Carlo simulation.

  • 135.
    Sung, Ki Won
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Aeronautical Communication Systems as Potential Primary Users in Secondary Spectrum Access2011In: 10th Scandinavian Workshop on Wireless Ad-hoc Networks (ADHOC 11), Stockholm, Sweden, May 2011, 2011Conference paper (Refereed)
    Abstract [en]

    Secondary spectrum access emerges as a meansto increase spectrum utilization significantly in a near future.However, the technical availability and the economic value of thesecondary access have not been fully investigated. Particularly,the impact of the secondary access on the real-life primary systemsremains mostly unaddressed. Among the primary systemsof interest are aeronautical communication systems operating inthe radio frequencies under 6 GHz. In this paper, we presentan overview of various aeronautical communication systems asthe potential primary users. We describe the purposes, characteristics,and operational facts of not only existing but alsofuture aeronautical systems. We also discuss the opportunitiesand challenges of secondary access to aeronautical spectrumand suggest a secondary use case suitable for the aeronautical spectrum.

  • 136.
    Sung, Ki Won
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Coordination of Clusters for Inter-Cell Scheduling2011In: 2011 IEEE 73RD VEHICULAR TECHNOLOGY CONFERENCE (VTC SPRING), IEEE , 2011, p. 1-5Conference paper (Refereed)
    Abstract [en]

    Coordination of base stations is essential in the mitigation of inter-cell interference in cellular communication systems. One of practical solutions is a cluster-based inter-cell scheduling where base stations in each cluster determine their transmissions in cooperative fashion. In spite of potential performance improvement, the inter-cell scheduling may result in conflict between clusters. However, a dynamic coordination in the cluster level is difficult due to the prohibitive burden of inter-cluster communication. In this paper, we address the coordination of clusters in the downlink of cellular networks. We propose a rule of inter-cluster coordination, namely nominal scheduling order with penalty (NSOP) which does not require communication between the clusters. Dynamic system level simulations are performed to examine the performance of the NSOP in various interference scenarios. It is observed that the proposed NSOP effectively strikes a balance between the inter-cluster interference avoidance and the intra-cluster multi-user diversity by means of a simple penalty factor.

  • 137.
    Sánchez Garache, Marvin
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Hagerman, Bo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Radio Resource Allocation in Spatial TDMA Multihop Networks with Advanced Antennas2007Conference paper (Refereed)
    Abstract [en]

    Advanced Antenna Systems (AAS) have the potential of significantly improving the performance in Wireless Multihop Networks. Critical for achieving performance gains is the proper design of radio resource management (RRM) schemes. In this paper RRM for networks utilizing Beam-Steering Circular Arrays in combination with Spatial Time Division Multiple Access  is studied. A heuristic, low complexity, RRM scheme based on the algorithm in [1] is proposed. Its network throughput performance is compared to the (near) optimum performance of the convex optimization method proposed in [2] extended to be utilized with  AAS. Both a constant transmission power scheme as well as SINR balancing power control are studied for various antenna beamwidths. The proposed AAS scheme is shown to improve the throughput performance significantly (up to 5 times in our experiments) compared to systems with omnidirectional antennas. Our heuristic scheme exhibits a throughput performance that in most cases lies within 10-15% of the one obtained by the convex optimization method.

  • 138. Sánchez Garache, Marvin
    et al.
    Zander, Jens
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Adaptive Antennas in Spatial TDMA Multihop Packet Radio Networks1999Conference paper (Refereed)
    Abstract [en]

    Multihop Packet Radio Networks (MHPRN) is an alternative for reliable rural data transmission where no telecommunication infrastructures exist. A key issue in designing such networks is the selection of Medium Access Control (MAC) strategy. Spatial TDMA is a MAC protocol proposed for MHPRN where links are pre-assigned time-slots according to a schedule in such way that interference is avoided allowing dense reuse of time slots within the network. Terrain obstacles act as shields to interference and may produce better performance. In this paper it is shown that use of simple adaptive directional antennas in rough terrain considerably improve the throughput and delay performance of MHPRN using STDMA. Using fourelement linear antenna arrays at both transmitter and receiver ends of a link controlled to maximize the received power, provide a significantly reduction in the average packet delay and up to 70% capacity improvement respect to a reference system using omnidirectional antennas.

  • 139.
    Sánchez Garache, Marvin
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Hagerman, Bo
    On the Performance of Power and Rate Control in STDMA Multihop Networks With Advanced Antennas2008In: ICN 2008: SEVENTH INTERNATIONAL CONFERENCE ON NETWORKING, PROCEEDINGS / [ed] Bi J; Gyires T; PozniakKoszalka I, LOS ALAMITOS: IEEE COMPUTER SOC , 2008, p. 105-110Conference paper (Refereed)
    Abstract [en]

    The introduction of advanced radio resource management features such as directional antennas, power control and variable data rates have been proposed to increase the performance of multihop wireless networks. In this paper we will study the combined effects of adaptive rate selection and power control in Spatial Time Division Multiple Access (STDMA) networks where nodes are equipped with advanced (beamforming) antennas. In our evaluation, the rates are selected from a discrete set. To assess the optimum performance of the various techniques, joint scheduling, rate and power control is done by solving a non-linear optimization problem. The results show that variable rates schemes can significantly improve the end-to-end network throughput compared to fixed rate schemes, whereas power control adds only a limited additional gain. The latter effect becomes even more pronounced as more narrow-beam antennas are used.

  • 140.
    Sánchez, Marvin
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Zander, Jens
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Giles, Tim
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Combined Routing & Scheduling for Spatial TDMA in Ad hoc Networks2002Conference paper (Refereed)
  • 141.
    Sánchez, Marvin
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Zander, Jens
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Giles, Tim
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Combined Routing & Scheduling for Spatial TDMA in Multihop Ad hoc Networks2002In: 5TH INTERNATIONAL SYMPOSIUM ON WIRELESS PERSONAL MULTIMEDIA COMMUNICATIONS, VOLS 1-3, PROCEEDINGS, New York: IEEE , 2002, p. 781-785Conference paper (Refereed)
    Abstract [en]

    Spatial Time Division Multiple Access(STDMA) is a conflict free MAC protocol for multihop ad hoc networks where links or nodes are scheduled to transmit in periodical slots. This paper analyzes the performance of a novel routing and scheduling strategy to create the schedule in STDMA, named Reuse Adaptive Minimum Hop Algorithm (RA-MHA). RA-MHA uses the set of minimum hop paths between sources and destinations as well as previously suggested schedule strategies in order to assign link transmissions. The results show that when directional antenna patterns are used, RA-MHA produces substantial improvement in throughput and packet delay.

  • 142.
    Tercero, Miurel
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Aggregate Interference from Secondary Users with Heterogeneous Density2011In: 2011 IEEE 22nd International Symposium On Personal Indoor And Mobile Radio Communications (PIMRC), IEEE , 2011, p. 428-432Conference paper (Refereed)
    Abstract [en]

    This paper presents an analytical model to approximate the probability distribution function of the aggregate interference that a primary user receives from multiple secondary transmitters. In particular, we consider heterogeneity in spatial distribution of secondary users such that there are several sites with densely populated secondary users in the whole area. The concentration of secondary users is modeled as an annulus sector with higher user density, which is termed hot zone. The mathematical framework presented in this paper can readily be adapted to various existing interference models. It is observed that the heterogenous user distribution has a considerable impact on the aggregate interference if the hot zone is near the primary receiver, while hot zones over a certain distance is well approximated by a homogeneous secondary user distribution. The aggregate interference also depends on the shape of the hot zone and the interference threshold imposed on the secondary users.

  • 143.
    Tercero, Miurel
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Exploiting Temporal Secondary Access Opportunities in Radar Spectrum2013In: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 72, no 3, p. 1663-1674Article in journal (Refereed)
    Abstract [en]

    In this paper, we quantify the temporal opportunities for secondary access to radar spectrum. Secondary users are assumed to be WLANs which opportunistically share the radar frequency band under the constraint that the aggregate interference does not harm radar operation. Each WLAN device employs dynamic frequency selection (DFS) as a mechanism to protect the radar from the interference. We also consider an advanced interference protection mechanism, which is termed temporal DFS. It exploits the temporal variation of interference power due to the periodic rotation of radar antenna. It is observed that the probability of accessing the radar spectrum is significantly higher when the temporal DFS is used compared to the conventional DFS. As a consequence, more WLANs can utilize the radar spectrum when the temporal DFS mechanism is considered. This shows that having better knowledge of the primary user activity can bring about the increased opportunity of secondary spectrum access to radar band, and thus improve the spectrum utilization.

  • 144.
    Tercero, Miurel
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. National University of Engineering (UNI), Nicaragua.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Impact of aggregate interference on meteorological radar from secondary users2011In: IEEE Wireless Communications and Networking Conference (WCNC), IEEE , 2011, p. 2167-2172Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate the impact of aggregate interference in a secondary spectrum access system. Particularly, meteorological radar operating in 5.6 GHz band is considered to be a primary user. Secondary users are WLAN devices spreading in a large area which induce aggregate interference to the radar. We develop a mathematical model to derive the robability distribution function (PDF) of the aggregate interference. The derivation considers dynamic frequency selection (DFS) mechanism for the protection of the radar such that the transmission of each WLAN is regulated by an interference threshold. Numerical experiments are performed with various propagation environments and densities of WLAN devices. It is observed that the effect of aggregate interference is severe in a rural environment. The interference threshold for individual WLAN should be much lower than the maximum tolerable interference at the radar. Thus, only a limited number of WLANs can transmit at the same time. On the other hand, adverse effect of the aggregate interference is not shown in an urban environment, where up to 10 WLANs per square kilometer can use the radar spectrum without considering the aggregate interference. The framework discussed in this paper can readily be adapted to assess the aggregate interference for other types of radars.

  • 145.
    Tercero, Miurel
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Temporal secondary access opportuities for WLAN in radar bands2011In: Wireless Personal Multimedia Communications (WPMC), 2011 14th International Symposium on, Elsevier, 2011, p. 6081515-Conference paper (Refereed)
    Abstract [en]

    In this paper we quantify the temporal opportunities for secondary access in radar bands. In our study, WLANs are secondary users homogeneously or heterogeneously distributed, which opportunistically access the radar spectrum. Each WLAN employs dynamic frequency  selection (DFS) as a mechanism to protect the radar from interference. We also consider an interference protection mechanism based on DFS and the prediction of the radar’s antenna pattern, which is termed Temporal DFS. We have the most of the time the probability of accessing the radar band are higher when Temporal DFS is used. As a consequence, there are more active WLANs when Temporal DFS mechanism is considered compare with normal DFS mechanism. This, shows once more that by having knowledge of the primary users activity secondary users can increase the probability of accessing the spectrum and improve spectrum utilization.

  • 146.
    Tercero Vargas, Miurel
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    González Sánchez, Pamela
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Ileri, Ömer
    The Scientific and Technological Research Council of Turkey.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Distributed spectrum access with energy constraint for heterogeneous channels2010In: 2010 Proceedings of the 5th International Conference on Cognitive Radio Oriented Wireless Networks and Communications, CROWNCom 2010, Cannes, 2010Conference paper (Refereed)
    Abstract [en]

    The demand for wireless communications services has increased the amount of spectrum resources required, promoting research interest in dynamic spectrum allocation schemes. There exist many promising solutions to allocate spectrum on a dynamic basis in order to get an efficient spectrum usage. One particular form is auction mechanism, tailored for allocating transmission rights on a short term basis to provide efficient allocation of scarce resources. However, most existing approaches are focused on homogeneous settings where all channels are treated as if they have the same propagation characteristics. In this work we consider two distributed auction schemes; sequential and concurrent, based on sequential ascending and combinatorial bidding, respectively, taking into account the propagation conditions of the channels (heterogeneous settings). The performance of these schemes is compared to two reference cases: (i) distributed homogeneous channels allocation (channel-agnostic case), and (ii) the centralized allocation scheme. Experimental results suggest that auction mechanisms which take into account the channel characteristics improve spectrum utilization under energy constraint. For wireless cellular networks with high unit energy cost (low coverage) concurrent access gives a better utilization of the spectrum and energy resources with higher service providers utility.

  • 147.
    Timus, Bogdan
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Soldati, Pablo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Kim, Dongwoo
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Cross-Layer Resource Allocation Model for Cellular-Relaying Network Performance Evaluation2011In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 60, no 6, p. 2765-2776Article in journal (Refereed)
    Abstract [en]

    The enhancement of cellular networks with relaying technologies is expected to bring significant technoeconomic benefits at the expense of more complex resource allocation. Suitable models for solving network dimensioning problems in cellular-relaying networks must handle radio resource allocation among hundreds of links and tackle interactions between networking layers. For this purpose, we propose a novel cross-layer resource allocation model based on average interference and ideal rate adaptation for the physical layer (PHY), time shares for the medium access layer, and fluid flows for the transport and network layers. We formulate a centralized social welfare maximization problem. When the routes are selected with an a priori algorithm, we show that the resource allocation problem admits an equivalent convex formulation. We show a numerical example for how to use the proposed framework for configuring the backhaul link in a practical relaying network. The overall problem of selecting routes and allocating time shares and link rates is nonconvex. We propose an iterative suboptimal algorithm to solve the problem based on a novel approximation of PHY. We state and prove several convergence properties of the algorithm and show that it typically outperforms routing based on signal-to-noise ratio only.

  • 148.
    Timus, Bogdan
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Soldati, Pablo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Implications of fairness criteria on the techno-economic viability of relaying networks2009In: 2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, 2009, p. 3050-3054Conference paper (Refereed)
    Abstract [en]

    The introduction of relaying techniques into cellular networks is expected to reduce the total infrastructure cost, especially when coverage extension is sought. With the advent of networks such as LTE, guaranteeing high data-rate coverage may become a challenge even for incumbent operators which nowadays provide full coverage for voice service. However it is not straightforward that operators will be able (or want) to guarantee coverage for the high data-rates. In this paper we study how the techno-economic viability of the relaying solution depends on the type of service to be provided by the operator. We exemplify the trade off between coverage and system throughput with two fairness criteria: perfect fairness (coverage guarantee) and proportional fairness. We show that relays provide advantages when the operator is interested in providing bit-rate/QoS guarantees. When maximizing the system throughput or cell capacity, relays are of less value.

  • 149.
    Timus, Bogdan
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Communication Systems, CoS.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Communication Systems, CoS.
    Incremental Deployment with Self-backhauling Base Stations in Urban Environment2009In: 2009 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATION WORKSHOPS, NEW YORK: IEEE , 2009, p. 541-545Conference paper (Refereed)
    Abstract [en]

    High capacity mobile broadband access requires a dense infrastructure of base stations. The costs associated with the backhaul transmission for these base stations is often a significant part of the total cost of the access network. It has been proposed to use part of the available spectrum to route data between base stations, so-called in-band relaying or self-backhauling. Although self-backhauling may result in a lower total system capacity, we will in this paper show examples where temporary use of in-band relaying postpones investments in fixed backhaul connections. This reduces the total (life-time) cost of the access network. In our incremental strategy example the total cost savings are in the order of 5 to 10%, depending on the relation between the additional equipment cost and the cost of leasing the fixed backhaul. Self-backhauling is not worth implementing when the entire network capacity needs to be achieved up-front, but the savings are significant when service uptake is slow or difficult to predict. The discount rate used in the investment analysis has only a minor impact on the results.

  • 150.
    Tombaz, Sibel
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Han, Sang-Wook
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    An Economic Viability Analysis on Green Solutions for Wireless Access NetworksManuscript (preprint) (Other academic)
12345 101 - 150 of 222
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