![]() ; Shankar, Bhavani ![]() in A Game Theoretic Approach to Multi-User Spectrum Allocation (2009) Detailed reference viewed: 182 (0 UL)![]() ; ; et al in Signal Processing Advances in Wireless Communications, 2009. SPAWC '09. IEEE 10th Workshop on (2009) This paper proposes a new codebook-based SDMA scheme, which employs a variable number of active beams, i.e., a dynamic multiplexing order, to target a good tradeoff between the multiplexing gain and the ... [more ▼] This paper proposes a new codebook-based SDMA scheme, which employs a variable number of active beams, i.e., a dynamic multiplexing order, to target a good tradeoff between the multiplexing gain and the inter-user interference. The new transmit scheme consist of a modification of the conventional feedback information and the development of a novel scheduling algorithm, where the new scheduling algorithm utilizes a merging of the channel correlation with limited feedback information, and is based on a proposed ML estimate of the possible user interferences. Simulation results demonstrate that in sparse networks the proposed SDMA scheme considerably outperforms some conventional SDMA schemes in terms of the sum throughput, with a comparable feedback overhead. [less ▲] Detailed reference viewed: 118 (0 UL)![]() ; ; et al in Global Telecommunications Conference, 2009. GLOBECOM 2009. IEEE (2009) This paper considers downlink multiantenna communication with base stations that perform cooperative precoding in a distributed fashion. Most previous work in the area has assumed that transmitters have ... [more ▼] This paper considers downlink multiantenna communication with base stations that perform cooperative precoding in a distributed fashion. Most previous work in the area has assumed that transmitters have common knowledge of both data symbols of all users and full or partial channel state information (CSI). Herein, we assume that each base station only has local CSI, either instantaneous or statistical. For the case of instantaneous CSI, a parametrization of the beamforming vectors used to achieve the outer boundary of the achievable rate region is obtained for two multi-antenna transmitters and two single-antenna receivers. Distributed generalizations of classical beamforming approaches that satisfy this parametrization are provided, and it is shown how the distributed precoding design can be improved using the so-called virtual SINR framework. Conceptually analog results for both the parametrization and the beamforming design are derived in the case of local statistical CSI. Heuristics on the distributed power allocation are provided in both cases, and the performance is illustrated numerically. [less ▲] Detailed reference viewed: 173 (0 UL)![]() ; ; et al in Signal Processing Advances in Wireless Communications, 2009. SPAWC '09. IEEE 10th Workshop on (2009) This paper deals with the practical precoding design for a two-hop downlink with MIMO amplify-and-forward relaying. A novel scheme of codebook-based joint precoding at both the base station and the relay ... [more ▼] This paper deals with the practical precoding design for a two-hop downlink with MIMO amplify-and-forward relaying. A novel scheme of codebook-based joint precoding at both the base station and the relay station is first presented, in which a distributed codeword selection is proposed to concurrently choose two joint precoders such that the feedback delay is considerably reduced. Then, the joint codebook design in such a joint precoding system is analyzed, revealing that independent codebook designs at the base station and relay station using the conventional Grassmannian subspace packing method is able to guarantee that the overall performance improves with either size of two codebooks. The excellent performances of the proposed scheme, in terms of both the sum rate and the BER, are finally confirmed with computational simulations. [less ▲] Detailed reference viewed: 152 (1 UL)![]() ; Ottersten, Björn ![]() in Handbook on Advancements in Smart Antenna Technologies for Wireless Networks (2009) Detailed reference viewed: 149 (1 UL)![]() ; ; et al in Wireless Communications & Signal Processing, 2009. WCSP 2009. International Conference on (2009) This paper studies the use of amplify-and-forward (AF) relays for robust beamforming, with the aid of imperfect channel state information (CSI) at the sender. In particular, the maximization of the worst ... [more ▼] This paper studies the use of amplify-and-forward (AF) relays for robust beamforming, with the aid of imperfect channel state information (CSI) at the sender. In particular, the maximization of the worst-case signal-to-noise ratio (SNR) at the destination terminal is studied under a bounded spherical region for the norm of CSI error vector. We show that under a condition on the estimated CSI quality, the robust-optimal collaborative-relay beamforming (CRBF) can be obtained by S-Procedure and rank relaxation techniques. In addition, a distributed algorithm is proposed by examining the structure of the optimal CRBF. [less ▲] Detailed reference viewed: 188 (0 UL)![]() ; Ottersten, Björn ![]() in Acoustics, Speech and Signal Processing, 2009. ICASSP 2009. IEEE International Conference on (2009) The symbol error performance of spatially correlated multi-antenna systems is analyzed herein. When the transmitter only has statistical channel information, the use of space-time block codes still ... [more ▼] The symbol error performance of spatially correlated multi-antenna systems is analyzed herein. When the transmitter only has statistical channel information, the use of space-time block codes still permits spatial multiplexing and mitigation of fading. The statistical information can be used for precoding to optimize some quality measure. Herein, we analyze the performance in terms of the symbol error rate (SER). It is shown analytically that spatial correlation at the receiver decreases the performance both without precoding and with an SER minimizing precoder. Without precoding, correlation should also be avoided at the transmitter side, but with an SER minimizing precoder the performance is actually improved by increasing spatial correlation at the transmitter. The structure of the optimized precoder is analyzed and the asymptotic properties at high and low SNRs are characterized and illustrated numerically. [less ▲] Detailed reference viewed: 154 (0 UL)![]() ; Shankar, Bhavani ![]() in EURASIP Journal on Advances in Signal Processing (2009) Detailed reference viewed: 188 (1 UL)![]() ; Ottersten, Björn ![]() in Acoustics, Speech and Signal Processing, 2009. ICASSP 2009. IEEE International Conference on (2009) Training-based estimation of channel state information in multi-antenna systems is analyzed herein. Closed-form expressions for the general Bayesian minimum mean square error (MMSE) estimators of the ... [more ▼] Training-based estimation of channel state information in multi-antenna systems is analyzed herein. Closed-form expressions for the general Bayesian minimum mean square error (MMSE) estimators of the channel matrix and the squared channel norm are derived in a Rayleigh fading environment with known statistics at the receiver side. When the second-order channel statistics are available also at the transmitter, this information can be exploited in the training sequence design to improve the performance. Herein, mean square error (MSE) minimizing training sequences are considered. The structure of the general solution is developed, with explicit expressions at high and low SNRs and in the special case of uncorrelated receive antennas. The optimal length of the training sequence is equal or smaller than the number of transmit antennas. [less ▲] Detailed reference viewed: 153 (0 UL)![]() ; Ottersten, Björn ![]() in Wireless Communications & Signal Processing, 2009. WCSP 2009. International Conference on (2009) Cooperative precoding is an attractive way of improving the performance in multicell downlink scenarios. By serving each terminal through multiple surrounding base stations, inter-cell interference can be ... [more ▼] Cooperative precoding is an attractive way of improving the performance in multicell downlink scenarios. By serving each terminal through multiple surrounding base stations, inter-cell interference can be coordinated and higher spectral efficiency achieved, especially for terminals at cell edges. The optimal performance of multicell precoding is well-known as it can be treated as a single cell with distributed antennas. However, the requirements on backhaul signaling and computational power scales rapidly in large and dense networks, which often makes such fully centralized approaches impractical. In this paper, we review and generalize some recent work on multicell precoding with both centralized and distributed cooperation. We propose practical precoding strategies under Rician channel conditions, and illustrate how the major gain of multicell precoding originates from having good base station synchronization and not from making centralized precoding decisions. [less ▲] Detailed reference viewed: 142 (0 UL)![]() ; ; Ottersten, Björn ![]() in IEEE Transactions on Signal Processing (2008), 56(3), 11881204 In the design of next-generation multiuser communication systems, multiple-antenna transmission is an essential part providing additional spatial degrees of freedom and allowing efficient use of resources ... [more ▼] In the design of next-generation multiuser communication systems, multiple-antenna transmission is an essential part providing additional spatial degrees of freedom and allowing efficient use of resources. A major limiting factor in the resource allocation is the amount of channel state information (CSI) available at the transmitter, particularly in multiuser systems where the feedback from each user terminal must be limited. Herein, we show that the Euclidean norm of the instantaneous channel, when combined with long-term channel statistics provides sufficient information for the transmitter to efficiently utilize multiuser diversity in time, frequency, and space. We consider the downlink of a communication system where the base station has multiple transmit antennas whereas each user terminal has a single receive antenna. The CSI provided by channel statistics and feedback of the norm of the instantaneous channel vector is studied in depth for correlated Rayleigh and Ricean fading channels, within a minimum mean-square error (MMSE) estimation framework. An asymptotic analysis (high instantaneous SNR) is presented which shows that channel realizations with large channel norm provide additional spatial CSI at the transmitter. This makes the proposed scheme ideal for multiuser diversity transmission schemes, where resources are only allocated to users experiencing favorable channel conditions. [less ▲] Detailed reference viewed: 189 (0 UL)![]() ![]() ; Ottersten, Björn ![]() in EURASIP Journal on Wireless Communications and Networking (2008) Detailed reference viewed: 142 (1 UL)![]() ![]() ; ; Ottersten, Björn ![]() in IEEE Transactions on Wireless Communications (2008), 7(11), 40584063 Detailed reference viewed: 58 (0 UL)![]() ![]() Devarakota, Pandu Ranga Rao ![]() ![]() in Pattern Recognition Letters (2008), 29(3), 243253 Detailed reference viewed: 41 (1 UL)![]() ![]() ; ; Ottersten, Björn ![]() in IEEE Transactions on Vehicular Technology (2008), 57(2), 9861000 Detailed reference viewed: 53 (0 UL)![]() ![]() ; ; Ottersten, Björn ![]() in IEEE Transactions on Signal Processing (2008), 56(8), 36783689 Detailed reference viewed: 65 (0 UL)![]() ![]() ; ; Ottersten, Björn ![]() in EURASIP Journal on Applied Signal Processing (2008) Detailed reference viewed: 136 (0 UL)![]() ![]() ; ; Ottersten, Björn ![]() in IEEE Transactions on Signal Processing (2008), 56(7), 32783293 Detailed reference viewed: 40 (0 UL)![]() ![]() ; ; Ottersten, Björn ![]() in IEEE Wireless Communications (2008) In this paper the autocorrelation properties of shadow fading and angle spread at both the base station (BS) and at the mobile station (MS) are analyzed using urban macro cellular measurement data. The ... [more ▼] In this paper the autocorrelation properties of shadow fading and angle spread at both the base station (BS) and at the mobile station (MS) are analyzed using urban macro cellular measurement data. The shadow fading parameter is shown to have a longer decorrelation distance than the angle spread at both the BS and at the MS. Furthermore, we observe variations in the shadow fading that depend on the direction of the MS movement. The same dependence is not observed in the angle spreads. These results indicate that the origin of the angle spread is local to the transmitter and receiver, while the shadow fading depends on the intermediate environment. [less ▲] Detailed reference viewed: 148 (1 UL)![]() ![]() ; Ottersten, Björn ![]() in Proceedings IEEE International Conference on Acoustics, Speech, and Signal (ICASSP) (2008) In wireless multiple antenna and multi-user systems, the spatial dimensions may be exploited to increase the performance by means of antenna gain, spatial diversity, and multi-user diversity. A limiting ... [more ▼] In wireless multiple antenna and multi-user systems, the spatial dimensions may be exploited to increase the performance by means of antenna gain, spatial diversity, and multi-user diversity. A limiting factor in such systems is the channel information required by the transmitter to control the intra-cell interference. Herein, the properties of spatially correlated channels with longterm statistical information at the transmitter and fixed-rate feedback of the quantized Euclidean channel norm are analyzed using a spectral subspace decomposition framework. A spatial division multiple access scheme is proposed with interference suppression at the receiver and joint scheduling and zero-forcing beamforming at the transmitter. Closed-form expressions for first and second moments of the feedback conditional channel statistics are derived. It is shown that only a few bits of feedback are required to achieve reliable rate estimation and weighted sum-rate maximization. [less ▲] Detailed reference viewed: 132 (0 UL) |
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