![]() ; ; Ottersten, Björn ![]() in Channel Quantization Design in Multiuser MIMO Systems: Asymptotic versus Practical Conclusions (2011, May) Feedback of channel state information (CSI) is necessary to achieve high throughput and low outage probability in multiuser multi antenna systems. There are two types of CSI: directional and quality ... [more ▼] Feedback of channel state information (CSI) is necessary to achieve high throughput and low outage probability in multiuser multi antenna systems. There are two types of CSI: directional and quality information. Many papers have analyzed the importance of these in asymptotic regimes. However, we show that such results should be handled with care, as very different conclusions can be drawn depending on the spatial correlation and number of users. There fore, we propose a quantization framework and evaluate the tradeoff between directional and quality feedback under practical conditions. [less ▲] Detailed reference viewed: 167 (1 UL)![]() ; ; et al in IEEE Transactions on Signal Processing (2011), 59(3), 1217-1228 Improving channel information quality at the base station (BS) is crucial for the optimization of frequency division duplexed (FDD) multi-antenna multiuser downlink systems with limited feedback. To this ... [more ▼] Improving channel information quality at the base station (BS) is crucial for the optimization of frequency division duplexed (FDD) multi-antenna multiuser downlink systems with limited feedback. To this end, this paper proposes to estimate a particular representation of channel state information (CSI) at the BS through channel norm feedback and a newly developed channel phase codebook, where the long-term channel correlation is efficiently exploited to improve performance. In particular, the channel representation is decomposed into a gain-related part and a phase-related part, with each of them estimated separately. More specifically, the gain-related part is estimated from the channel norm and channel correlation matrix, while the phase-related part is determined using a channel phase codebook, constructed with the generalized Lloyd algorithm. Using the estimated channel representation, joint optimization of multiuser precoding and opportunistic scheduling is performed to obtain an SDMA transmit scheme. Computer simulation results confirm the advantage of the proposed scheme over state of the art limited feedback SDMA schemes under correlated channel environment. [less ▲] Detailed reference viewed: 169 (3 UL)![]() ; Zheng, Gan ![]() in IEEE Transactions on Signal Processing (2011), 59(2), 728-738 This paper studies distributed optimization schemes for multicell joint beamforming and power allocation in time-division-duplex (TDD) multicell downlink systems where only limited-capacity intercell ... [more ▼] This paper studies distributed optimization schemes for multicell joint beamforming and power allocation in time-division-duplex (TDD) multicell downlink systems where only limited-capacity intercell information exchange is permitted. With an aim to maximize the worst-user signal-to-interference-and-noise ratio (SINR), we devise a hierarchical iterative algorithm to optimize downlink beamforming and intercell power allocation jointly in a distributed manner. The proposed scheme is proved to converge to the global optimum. For fast convergence and to reduce the burden of intercell parameter exchange, we further propose to exploit previous iterations adaptively. Results illustrate that the proposed scheme can achieve near-optimal performance even with a few iterations, hence providing a good tradeoff between performance and backhaul consumption. The performance under quantized parameter exchange is also examined. [less ▲] Detailed reference viewed: 173 (0 UL)![]() Garcia Becerro, Frederic ![]() ![]() in 8th IEEE International Conference on Advanced Video and Signal-Based Surveillance (2011) Detailed reference viewed: 208 (3 UL)![]() Chatzinotas, Symeon ![]() ![]() in EURASIP Journal on Wireless Communications and Networking (2011), 132 Detailed reference viewed: 193 (5 UL)![]() Chatzinotas, Symeon ![]() ![]() ![]() in Energy-Efficient MMSE Beamforming and Power Optimization in Multibeam Satellite Systems (2011) Detailed reference viewed: 153 (6 UL)![]() Garcia Becerro, Frederic ![]() ![]() in 2011 7th International Symposium on Image and Signal Processing and Analysis (ISPA) (2011) Detailed reference viewed: 127 (4 UL)![]() Garcia Becerro, Frederic ![]() ![]() in International Conference on Acoustics, Speech and Signal Processing (2011) Detailed reference viewed: 192 (2 UL)![]() Garcia Becerro, Frederic ![]() ![]() in 2011 IEEE Computer Society Conference on Computer Vision and Pattern Recognition Workshops (CVPRW) (2011) Detailed reference viewed: 227 (2 UL)![]() ; ; Zheng, Gan ![]() in Computational Framework for Optimal Robust Beamforming in Coordinated Multicell Systems (2011) Coordinated beamforming can significantly improve the performance of cellular systems through joint interference management. Unfortunately, such beamforming optimization problems are typically NP-hard in ... [more ▼] Coordinated beamforming can significantly improve the performance of cellular systems through joint interference management. Unfortunately, such beamforming optimization problems are typically NP-hard in multicell scenarios, making heuristic beamforming the only feasible choice in practice. This paper proposes a new branch-reduce-and-bound algorithm that solves such optimization problems globally, with a complexity suitable for benchmarking and analysis. Compared to prior work, the framework handles robustness to uncertain intercell interference and numerical analysis shows higher efficiency. [less ▲] Detailed reference viewed: 153 (0 UL)![]() Chatzinotas, Symeon ![]() ![]() in Clustered Multicell Joint Decoding under Cochannel Interference (2011) Detailed reference viewed: 141 (0 UL)![]() Chatzinotas, Symeon ![]() ![]() ![]() in Joint Precoding with Flexible Power Constraints in Multibeam Satellite Systems (2011) Detailed reference viewed: 196 (11 UL)![]() Chatzinotas, Symeon ![]() ![]() in Interference Alignment for Clustered Multicell Joint Decoding (2011) Detailed reference viewed: 155 (1 UL)![]() ; Ottersten, Björn ![]() in Signal Processing Advances in Wireless Communications (SPAWC), 2011 IEEE 12th International Workshop on (2011) We explore a novel approach to perform decoding-order optimization in the vertical Bell Labs layered space-time (V-BLAST) architecture. Allowing for simultaneous transmission of multiple, separately ... [more ▼] We explore a novel approach to perform decoding-order optimization in the vertical Bell Labs layered space-time (V-BLAST) architecture. Allowing for simultaneous transmission of multiple, separately encoded data streams, the V-BLAST transmit-receive scheme applies to the uplink of a multi-user communication system. A multi-antenna receiver decodes data streams successively, dealing with inter-stream interference by means of cancelling and nulling; interference from previously decoded streams is cancelled by subtraction, and remaining interference is nulled by linear equalization. The order in which the streams are decoded can have a noticeable impact on system performance. We consider the optimization of a fixed decoding order in fast Rayleigh fading, based on long-term channel-fading parameters. For a wide range of performance measures, we show that the fast-fading ordering problem can be treated as a classical linear assignment problem, allowing a solution using existing, efficient algorithms. [less ▲] Detailed reference viewed: 173 (1 UL)![]() Shankar, Bhavani ![]() ![]() ![]() in Communications (ICC), 2011 IEEE International Conference on (2011) This paper discusses the performance of Golden codes in a hybrid satellite/terrestrial system framework employing dual polarized MIMO-OFDM transmissions. Although the use of Golden codes in satellite and ... [more ▼] This paper discusses the performance of Golden codes in a hybrid satellite/terrestrial system framework employing dual polarized MIMO-OFDM transmissions. Although the use of Golden codes in satellite and terrestrial scenarios has been studied independently, a realistic performance assessment must involve both components taking into account the relative delay between their reception. In fact, this work exploits the relative delay to create a multipath scenario and further improve the coding gain of the Golden codes, which is otherwise fixed. This is made possible by utilizing the Golden code in a Space-Frequency coding framework instead of the traditional Space-Time paradigm. The separation between the subcarriers constituting a Golden code is shown to be central to the coding gain enhancement and an algorithm to choose this separation is provided. [less ▲] Detailed reference viewed: 186 (1 UL)![]() ; ; Ottersten, Björn ![]() in Acoustics, Speech and Signal Processing (ICASSP), 2011 IEEE International Conference on (2011) Finding the least squares (LS) solution s to a system of linear equations Hs = y where H, y are given and s is a vector of binary variables, is a well known NP-hard problem. In this paper, we consider ... [more ▼] Finding the least squares (LS) solution s to a system of linear equations Hs = y where H, y are given and s is a vector of binary variables, is a well known NP-hard problem. In this paper, we consider binary LS problems under the assumption that the coefficient matrix H is also unknown, and lies in a given uncertainty ellipsoid. We show that the corresponding worst-case robust optimization problem, although NP-hard, is still amenable to semidefinite relaxation (SDR)-based approximations. However, the relaxation step is not obvious, and requires a certain problem reformulation to be efficient. The proposed relaxation is motivated using Lagrangian duality and simulations suggest that it performs well, offering a robust alternative over the traditional SDR approaches for binary LS problems. [less ▲] Detailed reference viewed: 185 (0 UL)![]() Chatzinotas, Symeon ![]() ![]() ![]() in Proceedings of IEEE (2011) Detailed reference viewed: 193 (7 UL)![]() ; Ottersten, Björn ![]() in Communications (ICC), 2011 IEEE International Conference on (2011) We present a novel approach for joint transmitter-receiver design in the uplink of a wireless multiple-input multiple-output communication system. It applies to, e.g., a fast-fading frequency-division ... [more ▼] We present a novel approach for joint transmitter-receiver design in the uplink of a wireless multiple-input multiple-output communication system. It applies to, e.g., a fast-fading frequency-division duplexing system with periodic pilot signaling from each user - a scenario hindering transmitter optimization based on channel state information (CSI), while CSI-based receiver optimization is possible. Each user multiplexes data onto several, independently coded subchannels processed by a linear precoder, and detected at a base station (BS) employing zero-forcing decision feedback (DF) equalization, eliminating all interference prior to detection. We target the problem of jointly designing fixed linear precoders for all users as well as a fixed detection order for the DF receiver based on long-term channel statistics. We propose an efficiently implementable alternating-minimization technique that is verified numerically to converge fast, and to outperform the popular V-BLAST scheme - a computationally more complex ordered-DF receiver with limited applicability by requiring equal-rate subchannels in the system. [less ▲] Detailed reference viewed: 188 (1 UL)![]() Chatzinotas, Symeon ![]() ![]() in Physical Communication (2011) Detailed reference viewed: 239 (4 UL)![]() Christopoulos, Dimitrios ![]() ![]() in Proceeding of IEEE (2011) Detailed reference viewed: 297 (14 UL) |
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