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• 201.
Univ Elect Sci & Technol China, Key Lab Commun, Chengdu 611731, Sichuan, Peoples R China.;Univ Elect Sci & Technol China, Ctr Intelligent Networking & Commun, Chengdu 611731, Sichuan, Peoples R China..
Ericsson Res, S-16483 Stockholm, Sweden.. KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap. Univ Elect Sci & Technol China, Key Lab Commun, Chengdu 611731, Sichuan, Peoples R China.. Univ Elect Sci & Technol China, Ctr Intelligent Networking & Commun, Chengdu 611731, Sichuan, Peoples R China.. Univ Elect Sci & Technol China, Key Lab Commun, Chengdu 611731, Sichuan, Peoples R China..
Decentralized Caching Schemes and Performance Limits in Two-Layer Networks2018Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 67, nr 12, s. 12177-12192Artikel i tidskrift (Refereegranskat)

We study the decentralized caching scheme in a two-layer network, which includes a server, multiple helpers, and multiple users. Basically, the proposed caching scheme consists of two phases, i.e., placement phase and delivery phase. In the placement phase, each helper/user randomly and independently selects contents from the server and stores them into its memory. In the delivery phase, the users request contents from the server, and the server satisfies each user through a helper. Different from the existing caching scheme, the proposed caching scheme takes into account the pre- stored contents at both helpers and users in the placement phase to design the delivery phase. Meanwhile, the proposed caching scheme exploits index coding in the delivery phase and leverages multicast opportunities, even when different users request distinct contents. Besides, we analytically characterize the performance limit of the proposed caching scheme, and show that the achievable rate region of the proposed caching scheme lies within constant margins to the information-theoretic optimum. In particular, the multiplicative and additive factors are carefully sharpened to be 1/48 and 4, respectively, both of which are better than the state of arts. Finally, simulation results demonstrate the advantage of the proposed caching scheme compared with the state of arts.

• 202.
Univ Elect Sci & Technol China, Natl Key Lab Sci & Technol Commun, Chengdu, Sichuan, Peoples R China..
KTH, Skolan för elektro- och systemteknik (EES). Univ Elect Sci & Technol China, Natl Key Lab Sci & Technol Commun, Chengdu, Sichuan, Peoples R China. Univ Elect Sci & Technol China, Natl Key Lab Sci & Technol Commun, Chengdu, Sichuan, Peoples R China.. Univ Elect Sci & Technol China, Natl Key Lab Sci & Technol Commun, Chengdu, Sichuan, Peoples R China.. Univ Elect Sci & Technol China, Natl Key Lab Sci & Technol Commun, Chengdu, Sichuan, Peoples R China.. Univ Elect Sci & Technol China, Natl Key Lab Sci & Technol Commun, Chengdu, Sichuan, Peoples R China..
Outage Probability Analysis and Optimization in Downlink NOMA Systems with Cooperative Full-duplex Relaying2017Ingår i: 2017 IEEE 86th Vehicular Technology Conference (VTC-FALL), Institute of Electrical and Electronics Engineers (IEEE), 2017, Vol. 2017, s. 1-5Konferensbidrag (Refereegranskat)

We study a downlink non-orthogonal multiple access (NOMA) system with cooperative full-duplex relaying, where the near user in terms of the base station (BS) is enabled to act as a full-duplex relay for the far user. In particular, we first derive the outage probability with closed-form expressions when the power allocations at the BS and relay (or the near user) are fixed. Then, we analytically obtain the optimal power allocations with closed-form expressions at the BS and relay to minimize the outage probability. Numerical results validate the correctness of the theoretical analysis and demonstrate the advantages of the proposed algorithms over the state of arts.

• 203. Zhang, Lin
KTH, Skolan för elektro- och systemteknik (EES), Teknisk informationsvetenskap.
A SURVEY OF ADVANCED TECHNIQUES FOR SPECTRUM SHARING IN 5G NETWORKS2017Ingår i: IEEE wireless communications, ISSN 1536-1284, E-ISSN 1558-0687, Vol. 24, nr 5, s. 44-51Artikel i tidskrift (Refereegranskat)

Spectrum efficiency is one of the key performance metrics in 5G communication networks. To enhance spectrum efficiency, advanced spectrum sharing techniques are normally used. In this article, we provide a survey of the recent development of advanced techniques for spectrum sharing. In particular, we elaborate cognitive radio, device-to-device communication, in-band full-duplex communication, non-orthogonal multiple access, and Long Term Evolution on unlicensed spectrum. For each technique, we present the basic principle and research methodology of the state of the art. By considering various promising evolutions in 5G networks, we emphasize challenges to deploy each technique. Finally, we discuss the integration issue of multiple spectrum sharing techniques and identify potential challenges.

• 204. Zhang, Lin
KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
Efficient Scheduling and Power Allocation for D2D-Assisted Wireless Caching Networks2016Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, nr 6, s. 2438-2452Artikel i tidskrift (Refereegranskat)

We study a one-hop device-to-device (D2D)-assisted wireless caching network, where popular files are randomly and independently cached in the memory of end users. Each user may obtain the requested files from its own memory without any transmission, or from a helper through a one-hop D2D transmission, or from the base station. We formulate a joint D2D link scheduling and power allocation problem to maximize the system throughput. However, the problem is non-convex, and obtaining an optimal solution is computationally hard. Alternatively, we decompose the problem into a D2D link-scheduling problem and an optimal power allocation problem. To solve the two subproblems, we first develop a D2D link-scheduling algorithm to select the largest number of D2D links satisfying both the signal to interference plus noise ratio and the transmit power constraints. Then, we develop an optimal power allocation algorithm to maximize the minimum transmission rate of the scheduled D2D links. Numerical results indicate that both the number of the scheduled D2D links and the system throughput can be improved simultaneously with the Zipf-distribution caching scheme, the proposed D2D link-scheduling algorithm, and the proposed optimal power allocation algorithm compared with the state of the arts.

• 205. Zhang, Lin
KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
Energy-Efficient Cognitive Transmission With Imperfect Spectrum Sensing2016Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 34, nr 5, s. 1320-1335Artikel i tidskrift (Refereegranskat)

We investigate the energy efficiency (EE) in cognitive radio networks, where cognitive users are allowed to access a licensed frequency band opportunistically, provided that the licensed band is vacant. In particular, we study the impact of imperfect spectrum sensing and formulate the average EE maximization problem in fading channels as a joint optimization problem of the spectrum sensing duration and the transmit power of cognitive users. Meanwhile, we consider the constraints of both the collision probability between the primary and cognitive transmissions and the outage probability of cognitive transmissions. However, the joint optimization problem subject to the constraints is complicated and it is computationally hard to obtain the optimal solution. Alternatively, we develop two algorithms, i.e., a linear search algorithm and an iterative-based algorithm, with considerable complexity to solve the problem. Numerical results verify the correctness of both algorithms and show that the proposed algorithms can achieve the performance close to that of the exhaustive search algorithm and outperform the state of arts.

• 206. Zhang, Lin
KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
Proactive Cross-Channel Gain Estimation for Spectrum Sharing in Cognitive Radio2016Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 34, nr 10, s. 2776-2790Artikel i tidskrift (Refereegranskat)

In an underlay cognitive radio network, the cross-channel gain from a cognitive transmitter (CT) to a primary receiver (PR) is crucial for spectrum sharing. By exploiting the relaying capability of the CT, we propose a proactive estimation scheme for the cross-channel gain. Specifically, the CT proactively acts as a full-duplex amplify-and-forward (AF) relay for primary transceivers to trigger the power adaption of a primary transmitter (PT). By carefully designing the relay signal, the CT is able to obtain an estimation of the cross-channel gain by observing the power adaption. To demonstrate the accuracy of the estimation, we analytically characterize both an upper bound and a lower bound of the estimation performance. Furthermore, we study the impact of CT's relaying on the primary transmission and observe that the impact is related to the CT's location. By introducing a factor phi (0 <= phi <= 1) to denote the probability that the CT's relaying improves the primary transmission instead of causes interference, we design the CT location as a function of f. Numerical results show that the estimation error of the proactive estimation scheme can be as small as 1.7% with success estimation probability around 91%. By comparing with the state of the art, we show the advantages of the proposed estimator.

• 207. Zhang, Yi
KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap. KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
On Precoding and Energy Efficiency of Full-Duplex Millimeter-Wave Relays2019Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 18, nr 3, s. 1943-1956Artikel i tidskrift (Refereegranskat)

With large available bandwidth, millimeter wave (mm-wave) communications have attracted considerable research interests because of their potential to achieve multi-giga bps rates. However, one of the main challenges for mm-wave is high pathloss. To address this problem, full-duplex (FD) relaying can be used to increase the effective transmission distance and the spectral efficiency. Thus, studying the application of FD relaying in mm-wave communications will be of value. However, one of the main challenges in FD mm-wave relaying is the residual self-interference (SI), which includes line-of-sight (LOS) and non-LOS parts. To eliminate the SI and improve the spectral efficiency, we propose an orthogonal matching pursuit-based SI-cancellation precoding algorithm. Then, we propose an energy consumption model and analyze the energy efficiency performance. We formulate the joint spectral efficiency and energy efficiency optimization problem, which can be transformed into a convex problem. The numerical results show that the FD precoding scheme can effectively eliminate the residual SI and achieve approximately twice the spectral efficiency of the conventional half-duplex system. We also show that in low-spectral-efficiency regions, the optimal energy efficiency can be achieved, but the achievable energy efficiency will decrease in high-spectral-efficiency regions.

• 208. Zhang, Zhengquan
KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
Full-Duplex Two-Way and One-Way Relaying: Average Rate, Outage Probability, and Tradeoffs2016Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, nr 6, s. 3920-3933Artikel i tidskrift (Refereegranskat)

In this paper, we systematically study the average rate and outage probability tradeoffs of full-duplex two-way and one-way relaying under residual self-interference. Among various relaying protocols, two common of them are considered: amplify-and-forward (AF) and decode-and-forward (DF). Furthermore, we consider the application of physical-layer network coding (PNC) and analog network coding (ANC) to full-duplex two-way relaying. Novel closed-form expressions for the average rate and outage probability, are presented. The results show that full-duplex two-way relaying can achieve higher rate than one-way relaying in the medium to high signal-to-noise ratio (SNR) region, at the cost of a certain loss in the outage performance. Moreover, DF protocol can achieve better outage performance than the AF one, but it suffers from a certain loss in the rate in the high SNR region. It is also shown that PNC can further improve the rate and outage performance. In addition, the results clearly reveal the effects of time multiplexing, forward protocol, and network coding on relaying systems, which would shed light on designing practical full-duplex relaying schemes.

• 209.
Southwest Jiaotong Univ, Chengdu, Sichuan, Peoples R China..
Southwest Jiaotong Univ, Chengdu, Sichuan, Peoples R China.. Southwest Jiaotong Univ, Chengdu, Sichuan, Peoples R China.;Southeast Univ, Dhaka, Bangladesh.. KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap. Heriot Watt Univ, Edinburgh, Midlothian, Scotland.. Southwest Jiaotong Univ, Inst Mobile Commun, Chengdu, Sichuan, Peoples R China..
POWER DOMAIN NON-ORTHOGONAL TRANSMISSION FOR CELLULAR MOBILE BROADCASTING: BASIC SCHEME, SYSTEM DESIGN, AND COVERAGE PERFORMANCE2018Ingår i: IEEE wireless communications, ISSN 1536-1284, E-ISSN 1558-0687, Vol. 25, nr 2, s. 90-99Artikel i tidskrift (Refereegranskat)

Power domain non-orthogonal transmission is a promising technology for 5G wireless networks and beyond, as it can achieve higher spectrum efficiency than the orthogonal kind by multiplexing multiple users in the power domain. This article studies power domain non-orthogonal transmission for cellular mobile broadcasting to satisfy the increasing demands on multimedia communications in 5G and beyond. We first present two schemes for non-orthogonal transmission-based cellular mobile broadcasting: multi-rate and multi-service superposition transmissions, and then discuss their information-theoretical perspectives. Furthermore, we provide system designs for virtualized network architecture and physical layer processing, and discuss the key elements. We present a general superposition transmission framework to integrate three schemes developed by the 3GPP and to reduce the complexity of implementation, and then study constellation rotation to improve the BER performance of superposition transmission. Finally, we evaluate the SINR coverage performance of the presented schemes, followed by the main challenges and future research directions.

• 210. Zhang, Zhengquan
KTH, Skolan för elektro- och systemteknik (EES), Teknisk informationsvetenskap. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
Full-Duplex Device-to-Device-Aided Cooperative Nonorthogonal Multiple Access2017Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 66, nr 5, s. 4467-4471Artikel i tidskrift (Refereegranskat)

This paper presents a full-duplex device-to-device (D2D)-aided cooperative nonorthogonal multiple access (NOMA) scheme to improve the outage performance of the NOMA-weak user in a NOMA user pair, where the NOMA-weak user is helped by the NOMA-strong user with the capability of full-duplex D2D communications. The expressions for the outage probability are derived to characterize the performance of the proposed scheme. The results show that the proposed cooperative NOMA scheme can achieve superior outage performance compared to the conventional NOMA and orthogonal multiple access (OMA). In order to further improve the outage performance, an adaptive multiple access (AMA) scheme is also studied, which dynamically switches between the proposed cooperative NOMA, conventional NOMA, and OMA schemes, according to the level of residual self-interference and the quality of links. The results show that the AMAscheme outperforms the above multiple access schemes in terms of outage performance.

• 211. Zhang, Zhengquan
KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
Two-Timeslot Two-Way Full-Duplex Relaying for 5G Wireless Communication Networks2016Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, nr 7, s. 2873-2887Artikel i tidskrift (Refereegranskat)

We propose a novel two-timeslot two-way full-duplex (FD) relaying scheme, in which the access link and the backhaul link are divided in the time domain, and we study the average end-to-end rate and the outage performance. According to the user equipment capability and services, we investigate two scenarios: three-node I-and four-node Y-relaying channels. Among various relaying protocols, the well-known amplify-and-forward and decode-and-forward are considered. Closed-form expressions for the average end-to-end rate and the outage probability, under the effect of residual self-interference and inter-user interference, are presented. The results show that the proposed two-timeslot two-way FD relaying scheme can achieve higher rate and better outage performance than the half-duplex one, when residual self-interference is below a certain level. Therefore, this relaying scheme presents a reasonable tradeoff between performance and complexity, and so, it could be efficiently used in the fifth-generation wireless networks.

• 212. Zhang, Zhengquan
KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Teknisk informationsvetenskap.
Modeling and Analysis of Non-Orthogonal MBMS Transmission in Heterogeneous Networks2017Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 35, nr 10, s. 2221-2237Artikel i tidskrift (Refereegranskat)

Multimedia broadcast/multicast service (MBMS) transmission, which distributes the media content to multiple users on the same radio resources by using point-to-multipoint communications, is a highly spectrum efficient mechanism for multimedia communications. In this paper, we study the application of power domain non-orthogonal transmission to MBMS enhancements in a K-tier heterogeneous network, in order to satisfy the ever-increasing demands for emerging applications and performance requirements. Then, we present non-orthogonal multi-rate MBMS transmission (NOMRMT) and non-orthogonal multi-service MBMS transmission schemes and investigate their performance by using stochastic geometry. A tractable mode is developed to analyze the performance of asynchronous and synchronous non-orthogonal MBMS transmission. Based on this model, analytical expressions for the signal-to-interference-plusnoise ratio coverage probability, average number of served users, and sum rate are derived. The results demonstrate that non-orthogonal MBMS transmission can achieve better performance than the orthogonal one, while synchronous non-orthogonal MBMS transmission is superior to the asynchronous one.

• 213. Zhang, Zhengquan
KTH, Skolan för elektro- och systemteknik (EES), Teknisk informationsvetenskap.
Non-Orthogonal Multiple Access for Cooperative Multicast Millimeter Wave Wireless Networks2017Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 35, nr 8, s. 1794-1808Artikel i tidskrift (Refereegranskat)

Millimeter wave (mmWave) wireless networks can operate in single-cell point-to-multipoint mode to provide local multicast services efficiently. In this paper, the performance of multicast mmWave wireless networks is studied, through stochastic geometry. Then, the use of power domain non-orthogonal multiple access (NOMA) for enhancing mmWave multicasting is also investigated. Furthermore, we study multicasting in twotier mmWave heterogeneous networks, and propose a novel cooperative NOMA multicast scheme. Analytical expressions for the signal-to-interference-plus-noise ratio coverage probability, the average number of served users, and the sum multicast rate are derived, in order to assess the performance of these schemes. Finally, we discuss the maximum sum multicast rates, by formulating them as optimization problems, and also develop efficient golden section search algorithms to solve them. The offered solutions reveal the impact of data transmission rate and power allocation on the sum multicast rate. Both analytical and numerical results demonstrate that NOMA can significantly improve the mmWave multicasting, while the proposed cooperative NOMA mmWave multicast scheme can further improve the NOMA mmWave multicasting.

• 214.
Southwest Jiaotong Univ, Chengdu, Sichuan, Peoples R China..
Southwest Jiaotong Univ, Chengdu, Sichuan, Peoples R China.. Southwest Jiaotong Univ, Sch Informat Sci & Technol, Chengdu, Sichuan, Peoples R China.. KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap. Univ Manchester, Commun, Manchester, Lancs, England.. Southwest Jiaotong Univ, Sch Informat Sci & Technol, Chengdu, Sichuan, Peoples R China.. Aristotle Univ Thessaloniki, Elect & Comp Engn Dept, Thessaloniki, Greece.;Aristotle Univ Thessaloniki, Digital Telecommun Syst & Networks Lab, Thessaloniki, Greece.. Southwest Jiaotong Univ, Chengdu, Sichuan, Peoples R China..
6G WIRELESS NETWORKS Vision, Requirements, Architecture, and Key Technologies2019Ingår i: IEEE Vehicular Technology Magazine, ISSN 1556-6072, E-ISSN 1556-6080, Vol. 14, nr 3, s. 28-41Artikel i tidskrift (Refereegranskat)

A key enabler for the intelligent information society of 2030, 6G networks are expected to provide performance superior to 5G and satisfy emerging services and applications. In this article, we present our vision of what 6G will be and describe usage scenarios and requirements for multi-terabyte per second (Tb/s) and intelligent 6G networks. We present a large-dimensional and autonomous network architecture that integrates space, air, ground, and underwater networks to provide ubiquitous and unlimited wireless connectivity. We also discuss artificial intelligence (AI) and machine learning [1], [2] for autonomous networks and innovative air-interface design. Finally, we identify several promising technologies for the 6G ecosystem, including terahertz (THz) communications, very-large-scale antenna arrays [i.e., supermassive (SM) multiple-input, multiple-output (MIMO)], large intelligent surfaces (LISs) and holographic beamforming (HBF), orbital angular momentum (OAM) multiplexing, laser and visible-light communications (VLC), blockchain-based spectrum sharing, quantum communications and computing, molecular communications, and the Internet of Nano-Things.

• 215.
Southwest Jiaotong Univ, Chengdu, Sichuan, Peoples R China..
KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap. Southwest Jiaotong Univ, Chengdu, Sichuan, Peoples R China.;Sch Informat Sci & Technol, Stockholm, Sweden.. KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap. Univ Lancaster, Lancaster, Lancs, England.. Southwest Jiaotong Univ, Inst mobile Commun, Chengdu, Sichuan, Peoples R China..
Heterogeneous Ultradense Networks with NOMA System Architecture, Coordination Framework, and Performance Evaluation2018Ingår i: IEEE Vehicular Technology Magazine, ISSN 1556-6072, E-ISSN 1556-6080, Vol. 13, nr 2, s. 110-120Artikel i tidskrift (Refereegranskat)

Heterogeneous ultradense networks (H-UDNs) are one key enabler for fifth-generation (5G) wireless networks and beyond to satisfy the explosive growth of mobile data traffic, which exploits spatial reuse of scarce spectrum by deploying massive base stations (BSS) to boost network capacity and enhance network coverage. In this article, we present the system architecture for 5G H-UDNs, consisting of virtualized integrated ground-Air-space radio access networks (RANs) and core networks and study network coordination for virtualized H-UDN to efficiently manage computing resources and intercell interference. We look at a cloud-fog-computing coordination framework for efficient computing resource management by achieving reasonable computing task distribution and transfer; computing load balance for computing tasks among virtual computing resources to improve network performance and computing resource efficiency; and a macro-small cell coordination framework for virtualized H-UDN with nonorthogonal multiple access (NOMA) to efficiently manage intercell interference and improve network performance. The joint macro-small enhanced intercell interference coordination (eICIC) and small-small coordinated multipoint joint transmission (CoMP-JT) scheme can efficiently eliminate macro-small intercell interference and utilize small-small intercell interference.

• 216.
KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
On the achievable degrees of freedom of partially cooperative X networks with delayed CSIT2012Ingår i: 2012 IEEE Global Communications Conference (GLOBECOM), New York: IEEE , 2012, s. 2450-2454Konferensbidrag (Refereegranskat)

We investigate the achievable degrees of freedom (DoF) in K-user X networks (K × K X networks) with delayed channel state information at transmitters (CSIT), where partial cooperation (i.e. message sharing) is potentially allowed among transmitters. We consider two possible cooperation scenarios. In the first scenario one of the transmitters serves as a super node which can obtain the messages of the other transmitters. By proper interference alignment (IA) design, we prove that a DoF 2K over K+1 can be achieved almost surely. In the second scenario, there is no super node but each transmitter shares its message to its left-side neighbor. We show that when K = 3, DoF 7 over 5 is achievable. In both cases, the achieved DoF are shown to be improved compared with non-cooperative X networks. Moreover, we use a simple example to show that sharing a subset of messages may also improve DoF.

• 217.
KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
The two-hop MISO broadcast network with quantized delayed CSIT2013Ingår i: 2013 IEEE Wireless Communications and Networking Conference (WCNC), IEEE Communications Society, 2013, s. 3022-3027Konferensbidrag (Refereegranskat)

We consider a downlink two-hop MISO broadcast network with a 2-antenna source communicating to 2 singleantenna destinations, assisted by 2 single-antenna intermediate relays. We investigate spectrally efficient transmission schemes and their achieved sum degrees of freedom (DoF), with quantized delayed channel state information (CSI) feedback. Assuming Grassmannian vector quantization, we study two feedback scenarios according to the feedback range limit, namely global-range feedback, i.e., the source can receive the feedback signals from both the relays and the destinations, and one-hop-range feedback, i.e., each node can only attain the feedback information of its upcoming hop. We establish a sum DoF lower bound for each case. Our results reveal that when the quantization rate at relays BR= α1log2(SNR) and at destinations BD = α2log2(SNR) for min 1, α2} ≥ 1, the optimal sum DoF 4/3 can be achieved with finite-rate delayed feedback.

• 218.
KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. Princeton University.
Secrecy degrees of freedom of wireless X networks using artificial noise alignmentManuskript (preprint) (Övrigt vetenskapligt)

The problem of transmitting confidential messages in $M \times K$ wireless X networks is considered, in which each transmitter intends to send one confidential message to every receiver. In particular, the secrecy degrees of freedom (SDOF) of the considered network achieved by an artificial noise alignment (ANA) approach, which integrates interference alignment and artificial noise transmission, are studied. At first, an SDOF upper bound is derived for the $M \times K$ X network with confidential messages (XNCM) to be $\frac{K(M-1)}{K+M-2}$. By proposing an ANA approach, it is shown that the SDOF upper bound is tight when either $K=2$ or $M=2$ for the considered XNCM with time/frequency varying channels. For $K,M \geq 3$, it is shown that an SDOF $\frac{K(M-1)}{K+M-1}$ can be achieved, even when an external eavesdropper appears. The key idea of the proposed scheme is to inject artificial noise to the network, which can be aligned in the interference space at receivers for confidentiality. Moreover, for the network with no channel state information at transmitters, a blind ANA scheme is proposed to achieve the SDOF $\frac{K(M-1)}{K+M-1}$ for $K,M \geq 2$, with reconfigurable antennas at receivers. The proposed method provides a linear approach to handle secrecy coding and interference alignment.

• 219.
KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
Degrees of freedom of two hop MISO broadcast network with mixed CSIT2014Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 13, nr 12, s. 6982-6995Artikel i tidskrift (Refereegranskat)

A downlink two-hop MISO broadcast network is considered, with a two-antenna source communicating to 2 single-antenna destinations, via multiple single-antenna relays in between. The sum degrees of freedom (DOF) of the network with mixed channel state information at the transmitter (CSIT) is investigated. The mixed CSIT consists of accurate delayed CSIT and inaccurate instantaneous CSIT, and its availability is limited within each hop, i.e. the source is oblivious to the channels of the second hop. Given a transmission power P and a real value α in [0,1], if the variance of the error for instantaneous CSIT decreases as O(P-α), it is shown that the sum optimal DOF of the considered network is d = $\frac{4+2\alpha}{3}$when there exist at least 3 intermediate relays. The result can be extended to the MIMO and multiple-hop cases. The proposed achievable schemes essentially combine the concept of retrospective interference alignment based on delayed CSIT and linear beamforming based on inaccurate instantaneous CSIT into an integrated form. Our results show that, in multi-hop MISO broadcast networks, delayed CSIT and inaccurate instantaneous CSIT can be exploited simultaneously to benefit network DOF.

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