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  • 1.
    Berggren, Fredrik
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ben Slimane, Slimane
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Linear Successive Interference Cancellation in DS-CDMA Systems2003In: Wireless Communications & Mobile Computing, ISSN 1530-8669, E-ISSN 1530-8677, Vol. 3, no 7, p. 847-859Article in journal (Refereed)
    Abstract [en]

    Successive interference cancellation techniques have the potential to reduce the interference and therefore increase the capacity of cellular radio systems. In this work, we analyze a linear DS-CDMA receiver utilizing soft feedback interference cancellation. To be able to meet diverse QoS requirements, we introduce a power control scheme that takes into account heterogeneous service levels as well as the impact of imperfect interference cancellation. We address the capacity resulting from this receiver and give its user capacity region on closed-form. We show that our results are general and provide a framework for capacity comparison for many proposed linear successive cancellation receiver models. Several receiver modifications are included, partial interference cancellation; when only part of the signal is canceled, and limited cancellation; when not every signal is canceled. We derive the minimum power solution of a single-cell, from which convergent multicellular distributed power control algorithms that iteratively update the powers are suggested. The numerical results show that there are large gains in user capacity from interference cancellation when the Eb/Io requirements are high. However, regardless of the required targets the maximum capacity is always achieved through partial successive interference cancellation. It is also found that the power levels are sensitive to the cancellation effciency and worse performance than single-user detection can occur.

  • 2.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Performance Comparison of Practical Resource Allocation Schemes for Device-to-Device Communications2018In: Wireless Communications & Mobile Computing, ISSN 1530-8669, E-ISSN 1530-8677, article id 3623075Article in journal (Refereed)
    Abstract [en]

    Device-to-device (D2D) communications in cellular spectrum have the potential of increasing the spectral and energy efficiency by taking advantage of the proximity and reuse gains. Although several resource allocation (RA) and power control (PC) schemes have been proposed in the literature, a comparison of the performance of such algorithms as a function of the available channel state information has not been reported. In this paper, we examine which large scale channel gain knowledge is needed by practically viable RA and PC schemes for network assisted D2D communications. To this end, we propose a novel near-optimal and low-complexity RA scheme that can be advantageously used in tandem with the optimal binary power control scheme and compare its performance with three heuristics-based RA schemes that are combined either with the well-known 3GPP Long-Term Evolution open-loop path loss compensating PC or with an iterative utility optimal PC scheme. When channel gain knowledge about the useful as well as interfering (cross) channels is available at the cellular base station, the near-optimal RA scheme, termedMatching, combined with the binary PC scheme is superior. Ultimately, we find that the proposed low-complexity RA + PC tandem that uses some cross-channel gain knowledge provides superior performance.

  • 3. Lee, Chae Y.
    et al.
    Sung, Ki Won
    Dynamic Resource Allocation for CDMA-TDD Indoor Wireless Systems2003In: Wireless Communications & Mobile Computing, ISSN 1530-8669, E-ISSN 1530-8677, Vol. 3, p. 921-931Article in journal (Refereed)
    Abstract [en]

    Future wireless communication systems are expected to provide a broad range of multimedia services that have a significant traffic asymmetry between uplink and downlink. The code division multiple access-time division duplex (CDMA-TDD) system is a promising solution to cope with the problem of traffic asymmetry. However, the TDD system is subject to inter-cell interference compared to frequency division duplex (FDD) system. Since both uplink and downlink share the same frequency in TDD, uplink and downlink may interfere each other especially when neighboring cells require different rates of traffic load. Thus, the resource allocation among cells is an important issue in TDD. In this paper, the resource allocation in the CDMA-TDD is formulated as a mixed integer programming (MIP) problem. A dynamic resource allocation algorithm (DRAA) is provided that effectively solves the traffic asymmetry problem. The MIP problem is also solved by a well-known branch and bound procedure. Both the crossed slot and non-crossed slot allocation are examined and compared to the DRAA. Computational result shows that proposed DRAA gives a good performance as the traffic asymmetry increases between the uplink and downlink. Copyright © 2003 John Wiley & Sons, Ltd.

  • 4.
    Logothetis, Andrew
    et al.
    Ericsson Research, Ericsson AB, Stockholm, Sweden.
    Osseiran, Afif
    Ericsson Research, Ericsson AB, Stockholm, Sweden.
    SINR Estimation and Orthogonality Factor Calculation of DS-CDMA Signals in MIMO Channels Employing Linear Transceiver Filters2007In: Wireless Communications & Mobile Computing, ISSN 1530-8669, E-ISSN 1530-8677, Vol. 7, no 1, p. 103-112Article in journal (Refereed)
    Abstract [en]

    A discrete-time model of DS-CDMA signaling using multiple transmit and receive antennas employing linear transceiver filters is derived. For each link, connecting a base-station to a wireless mobile user, the downlink signal to interference plus noise ratio (SINR) after despreading is derived analytically, and as a by-product an exact closed-form solution of the orthogonality factor is obtained.

    The orthogonality factor is derived for any linear receiver structure that is implemented by a bank of correlators and for any linear combining techniques (such as MRC and MMSE), and for any number of transmit and/or receive antennas that utilize transmit (pre-RAKE) and receive (post-RAKE) filtering.

    The MIMO DS-CDMA model is derived using a filter representation, and is extended to a vector/matrix formulation that permits a systematic and efficient way of computing the SINR in a radio network simulator.

  • 5.
    Sung, Ki Won
    et al.
    Korea Advanced Institute of Science and Technology (KAIST).
    Lee, Chae Y
    Korea Advanced Institute of Science and Technology (KAIST).
    Determination of the Multi-slot Transmission in Bluetooth Systems with the Estimation of the Channel Error Probability2006In: Wireless Communications & Mobile Computing, ISSN 1530-8669, E-ISSN 1530-8677, Vol. 6, no 1, p. 61-68Article in journal (Refereed)
    Abstract [en]

    Bluetooth is an open specification for a technology to enable short-range wireless communications that operate in an ad hoc fashion. Bluetooth uses frequency hopping with a slot length of 625 Όs. Each slot corresponds to a packet and multi-slot packets of three or five slots can be transmitted to enhance the transmission efficiency. However, the use of multi-slot packet may degrade the transmission performance under high channel error probability. Thus, the length of multi-slot should be adjusted according to the current channel condition. Segmentation and reassembly (SAR) operation of Bluetooth enables the adjustment of the length of multi-slot. In this paper, we propose an efficient multi-slot transmission scheme that adaptively determines the optimal length of slots of a packet according to the channel error probability. We first discuss the throughput of a Bluetooth connection as a function of the length of a multi-slot and the channel error probability. A decision criteria which gives the optimal length of the multi-slot is presented under the assumption that the channel error probability is known. For the implementation in the real Bluetooth system, the channel error probability is estimated with the maximum likelihood estimator (MLE). A simple decision rule for the optimal multi-slot length is developed to maximize the throughput. Simulation experiment shows that the proposed decision rule for the multi-slot transmission effectively provides the maximum throughput under any type of channel error correlation.

  • 6.
    Sung, Ki Won
    et al.
    Korea Advanced Institute of Science and Technology (KAIST).
    Lee, Chae Y
    Korea Advanced Institute of Science and Technology (KAIST).
    Distributed Timeslot Allocation with Crossed Slots in CDMA-TDD Systems2010In: Wireless Communications & Mobile Computing, ISSN 1530-8669, E-ISSN 1530-8677, Vol. 10, no 3, p. 337-348Article in journal (Refereed)
    Abstract [en]

    Code division multiple access system with time division duplex (CDMA-TDD) is a promising solution to cope with traffic asymmetry of downlink (DL) and uplink (UL) in multimedia services. When a rate of asymmetry is different in each cell, CDMA-TDD system may employ crossed slots, where a timeslot is used for different links in cells. However, it may suffer from base station (BS)-to-BS and mobile station (MS)-to-MS interference problem. Zone division scheme is an efficient way to tackle the crossed slot interference by dividing a cell into inner and outer zones and restricting communication in crossed slots only to inner zone. In this paper, we propose distributed crossed slot resource allocation with zone division in multi-cell CDMA-TDD system. Two conditions for crossed slot resource allocation are defined and the bound on the size of inner zone is analyzed mathematically based on the conditions. Relationship between the capacity of crossed slot and the size of inner zone is also analyzed. Then, numerical results of the mathematical analysis are presented; showing that the proposed crossed slot allocation is effective for traffic asymmetry problem.

  • 7. Yang, Bo
    et al.
    Shen, Yanyan
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Chen, Cailian
    Guan, Xinping
    Opportunistic multichannel access with decentralized channel state information2015In: Wireless Communications & Mobile Computing, ISSN 1530-8669, E-ISSN 1530-8677, Vol. 15, no 2, p. 322-339Article in journal (Refereed)
    Abstract [en]

    This paper considers multiaccess control for the uplink in orthogonal frequency division multiple access wireless networks. To avoid the extensive information exchange associated with centralized approaches, we formulate the decentralized access control problem with the contention power constraint as a Bayesian game, mapping time-varying channel state information into contention strategies. By exploiting the problem structure, a strategy where users access the channels with probability one if the observed channel gain is above a predetermined threshold is shown to be optimal. It is also shown that the energy consumption of the threshold strategy will not exceed that of randomized strategies. The game is then equivalently reformulated as one of finding the threshold value in a distributed manner, and the existence and uniqueness of Bayesian Nash equilibria is established. A distributed algorithm based on Lagrange duality is proposed to approach the unique equilibrium, and the algorithm is shown to be globally stable. In a homogeneous system, the performance loss of the proposed scheme is proved to be bounded compared with a centralized channel allocation scheme. Contrary to other proposals, our method allows for heterogeneous channel state information and achieves a comparable throughput with reduced power.

  • 8.
    Yu, Kai
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Models for MIMO propagation channels: a review2002In: Wireless Communications & Mobile Computing, ISSN 1530-8669, E-ISSN 1530-8677, Vol. 2, no 7, p. 653-666Article in journal (Refereed)
    Abstract [en]

    This paper reviews recently published results on multiple input multiple output (MIMO) channel modeling. Both narrowband and wideband models are considered. We distinguish between two main approaches to MIMO channel modeling, that is,. physically based and nonphysically based modeling. The nonphysical models primarily rely on the statistical characteristics of the MIMO channels obtained from the measured data, while the physical models describe the MIMO channel (or its distribution) via some physical parameters. We briefly review different MIMO channel models and discuss their relationships. Some interesting aspects will be described in more detail and we note areas in which few results are available.

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