Samir N. Al-Ghadhban

Recursive least-squares adaptive channel estimation for spatial modulation systems

In this paper, a recursive least-squares (RLS) adaptive channel estimation scheme is applied for spatial modulation (SM) system over a block fading multiple-input-multiple-output (MIMO) channel. The performance of spatial modulation with channel estimation is compared to vertical Bell Labs layered space-time (V-BLAST) and maximum ratio combining (MRC) transmission schemes for different pilot rates and a fixed 3-b/s/Hz spectral efficiency. Computer simulations carried out demonstrate the superiority of SM over V-BLAST and MRC schemes. In addition, the results in this study show that SM is more robust against channel estimation errors than the other MIMO schemes.

Narrowband Interference Mitigation in SC-FDMA Using Bayesian Sparse Recovery

This paper presents a novel narrowband interference (NBI) mitigation scheme for single carrier-frequency division multiple access systems. The proposed NBI cancellation scheme exploits the frequency-domain sparsity of the unknown signal and adopts a low complexity Bayesian sparse recovery procedure. At the transmitter, a few randomly chosen data locations are kept data free to sense the NBI signal at the receiver. Furthermore, it is noted that in practice, the sparsity of the NBI signal is destroyed by a grid mismatch between the NBI sources and the system under consideration. Toward this end, first, an accurate grid mismatch model is presented that is capable of assuming independent offsets for multiple NBI sources, and second, the sparsity of the unknown signal is restored prior to reconstruction using a sparsifying transform. To improve the spectral efficiency of the proposed scheme, a data-aided NBI recovery procedure is outlined that relies on adaptively selecting a subset of data-points and using them as additional measurements. Numerical results demonstrate the effectiveness of the proposed scheme for NBI mitigation.

Narrow band interference cancelation in OFDM: Astructured maximum likelihood approach

This paper presents a maximum likelihood (ML) approach to mitigate the effect of narrow band interference (NBI) in a zero padded orthogonal frequency division multiplexing (ZP-OFDM) system. The NBI is assumed to be time variant and asynchronous with the frequency grid of the ZP-OFDM system. The proposed structure based technique uses the fact that the NBI signal is sparse as compared to the ZP-OFDM signal in the frequency domain. The structure is also useful in reducing the computational complexity of the proposed method. The paper also presents a data aided approach for improved NBI estimation. The suitability of the proposed method is demonstrated through simulations.

Compressive sensing for feedback reduction in MIMO broadcast channels

We propose a generic feedback channel model, and compressive sensing based opportunistic feedback protocol for feedback resource (channels) reduction in MIMO Broadcast Channels under the assumption that both feedback and downlink channels are noisy and undergo block Rayleigh fading. The feedback resources are shared and are opportunistically accessed by users who are strong (users above a certain fixed threshold). Strong users send same feedback information on all shared channels. They are identified by the base station via compressive sensing. The proposed protocol is shown to achieve the same sum-rate throughput as that achieved by dedicated feedback schemes, but with feedback channels growing only logarithmically with number of users.

Outage capacity comparison of multi-layered STBC and V-BLAST systems

In this paper, we examine the capacity of high data rate open loop MIMO architectures. The focus of the study is to compare the information capacity of multi-layered space time block coded (MLSTBC) systems with V-BLAST and STBCs. MLSTBC combines transmit diversity and spatial multiplexing. The single user data are divided into layers of information and each layer is encoded with a STBC. The result of this study shows that for the same number of transmit-receive antennas, MLSTBC is more power efficient than V-BLAST, since it provides more diversity. Furthermore, at low SNRs and low outage probabilities, MLSTBC is more spectrally efficient. Thus, it is more suitable for low power high data rate wireless applications.

Uplink scheduling criteria comparison for V-BLAST users

We study in this paper uplink scheduling for V-BLAST users. Each user spatially multiplexes his data over multiple transmit antennas. This spatial multiplexing (SM) scheme provides high data rates while multi-user diversity obtained from scheduling improves the performance of the uplink system. The scheduler selects one user at a time based on a criterion that minimizes aggregate BER. The main results of this study show that the scheduler that maximizes the optimal MIMO capacity doesnpsilat work well for a V-BLAST system. Instead, a scheduler that maximizes the V-BLAST capacity is derived specifically from the V-BLAST detection algorithm. Furthermore, we propose and compare suboptimal schedulers that are based on the received MIMO channels before processing.

Performance of Layered Steered Space---Time Codes in Wireless Systems

Layered Steered Space–Time Codes (LSSTC) is a recently proposed multiple-input multiple-output (MIMO) system that combines the benefits of vertical Bell Labs space–time (VBLAST) scheme, space–time block codes (STBC) and beamforming. In this paper, we derive the error performance and capacity of a single-user LSSTC system. The analysis is general enough to any layer ordering and modulation schemes used. In addition, the derived analysis is general for any LSSTC structure in which layers may have different number of antenna arrays and may be assigned power according to any power allocation. Furthermore, we analytically investigate the tradeoff between the main parameters of the LSSTC system, i.e., diversity, multiplexing and beamforming. Our results give recursive expressions for the probability of error for LSSTC which showed nearly perfect match to the simulation results. Results have also revealed the possibility of designing an adaptive system in which it was shown that combining beamforming, STBC, and VBLAST has better performance than VBLAST at high SNR range.

Spatial sequence estimation based decoding algorithm for V-BLAST

In this paper we introduce a novel detection algorithm for V-BLAST (vertical-Bell-Labs layered space-time architecture). The original V-BLAST detector is based on a serial interference cancellation (SIC) algorithm. Although the algorithm is relatively simple to implement, it does not achieve the performance predicted by theoretical analysis. The nulling operation reduces the receive diversity and the serial processing results in unequal diversity advantage for different layers. Also the error propagation severely degrades the performance. A detection algorithm for V-BLAST based on sequence estimation is proposed. The concept of maximum likelihood sequence estimation (MLSE) is applied to combat spatial interference. State reduction techniques are also considered for practical implementation. Simulation results show that the proposed algorithm outperforms interference cancellation based algorithms.

Bayesian narrowband interference mitigation in SC-FDMA

This paper presents a novel narrowband interference (NBI) mitigation scheme for SC-FDMA systems. The proposed scheme exploits the frequency domain sparsity of the unknown NBI signal and adopts a low complexity Bayesian sparse recovery procedure. In practice, however, the sparsity of the NBI is destroyed by a grid mismatch between NBI sources and SC-FDMA system. Towards this end, an accurate grid mismatch model is presented and a sparsifying transform is utilized to restore the sparsity of the unknown signal. Numerical results are presented that depict the suitability of the proposed scheme for NBI mitigation.

Opportunistic round robin scheduling for V-BLAST systems over multiuser MIMO channels

In this paper, we study opportunistic round robin (ORR) uplink scheduling for vertical Bell Labs layered space-time architecture (V-BLAST) systems over multiuser multiple-input multiple-output (MIMO) channels. The proposed ORR scheduling method is compared to greedy scheduling. In greedy scheduling, the base station selects the best user based on a certain criterion without any consideration for fairness. On the other hand, ORR scheduling guarantees full fairness and each user will be served by excluding the previous selected users from the competition in the next round. The selected user spatially multiplexes his data over the transmit antennas. This spatial multiplexing (SM) scheme provides high data rates, while multiuser diversity obtained from scheduling improves the performance of the uplink system. The results show the performance and capacity gains obtained by scheduling. The greedy scheduler captures full multiuser diversity. In contrast, the ORR scheduler provides substantial signal-to-noise ratio (SNR) gains compared to round robin while guaranteeing full fairness to all users.