Mohsen Eslami

Rake-MMSE-equalizer performance for UWB

The performance of a joint rake and minimum mean square error (MMSE) equalizer receiver for high data rate ultra-wideband communications is studied in this paper. The proposed receiver combats inter-symbol interference by taking advantage of the rake and equalizer structure. The receiver performance is investigated using a semianalytical approach and Monte-Carlo simulation. The effects of the number of rake fingers and equalizer taps on the error performance are examined.

A Closed-Form Mutual Information Approximation for Multiple-Antenna Systems With Spatial Modulation

In this letter, a low-complexity approximation for instantaneous mutual information (IMI) of spatial modulation multiple-input single-output systems is presented. Based on this low-complexity approximation, a closed-form approximation for the average mutual information (MI) is derived. The approximation closely follows exact average MI values for different numbers of antennas and a wide range of signal-to-noise ratios. The proposed approximation for the IMI has a considerably lower computational complexity compared to previously proposed bounds. Also, the closed-form approximation of the average MI is considerably less complex than previously proposed bounds that require numerical averaging over randomly generated channel realizations.

Relay Pre-Selection for Reducing CSI Transmission in Wireless Sensor Networks

Relay selection requires collection and transmission of channel state information (CSI) to a central node. When all relay nodes contribute in CSI transmission, the amount of power required for signaling the CSIs linearly increases with the number of relays. A central node should determine the proper number of pre-selected relays by aid of channel statistics and a decision criterion. We derive an upper bound on this number when end-to-end bit error rate is considered as the decision criterion and the source-relay channels are time-varying fading channels.

Zero-Forcing Precoding with Partially Outdated CSI over Time-Varying MIMO Broadcast Channels

Updating channel state information at the transmitter (CSIT) in time varying channels, is one of the main bottlenecks in wireless communication systems. In MIMO broadcast channels CSIT is required for user scheduling and precoder design. A time varying MIMO broadcast channel with limited-capacity feedback links is considered. An efficient threshold-based feedback technique based on allowing CSIT errors only for certain users is proposed. In the proposed scheme, the frequency of CSI feedback for different users is set to be proportional to their channel strength. Hence, CSI feedback is substantially reduced. Analysis and simulation results show net throughput superiority of the proposed scheme over the case of perfect CSIT. For large numbers of users, it is shown that how increase in the number of users can compensate the sum rate loss due to errors caused by partially outdated channel.

Efficient Suboptimal Resource Allocation Algorithms for Multiuser MIMO-OFDMA Systems

Multiple-input multiple-output (MIMO) wireless communication systems in combination with orthogonal frequency division multiple access and space division multiple access are flexible, spectrally efficient and of high capacity. These systems can allocate frequency, time, and space resources adaptively among mobile stations. Optimal resource allocation (RA) for maximizing the sum rate is usually too complex for practical applications, hence suboptimal algorithms are required. The performance of RA algorithms are degraded due to imperfections in channel state information at transmitter (CSIT). Thus, techniques that make the RA algorithm, robust against CSIT errors are favorable. In this paper, two novel suboptimal grouping algorithms are introduced that are shown to achieve better sum rate-complexity and fairness-complexity performances. A novel index is proposed to measure the efficiency of RA algorithms, which takes into account sum rate and complexity simultaneously. Moreover, the effect of erroneous CSIT on sum rate is investigated and it is shown that performance of the proposed RA algorithms with erroneous CSIT are superior to the existing schemes. Finally, fairness performance of the proposed RA algorithms are evaluated, which are shown to be the same if not superior to other existing algorithms.

A novel subcarrier allocation algorithm for throughput improvement of OFDMA femtocell networks in suburban areas

Femtocell networks provide a good opportunity to satisfy increasing user demand for high data rate services. One of the most important challenges in femtocell networks is interference which degrades the overall system throughput considerably. In order to successfully deploy a femtocell network, efficient resource allocation algorithms and interference mitigation techniques should be deployed. In this paper, a novel algorithm is proposed for subcarrier allocation of a two-tier network in suburban areas. Simulation results show that the proposed algorithm improves throughput of a single femtocell in comparison with other methods considered in this paper. In addition, the proposed algorithm improves average overall throughput of users and guarantees the highest throughput among all other methods.

Efficiency, robustness, and fairness of suboptimal RA algorithms for MIMO-OFDMA systems

Due to their lower complexity that make them affordable for practical applications, suboptimal MIMO-OFDMA downlink resource allocation (RA) algorithms have attracted significant attention. In this paper, a novel suboptimal RA algorithm is introduced and shown to achieve higher efficiency performance in comparison with other existing techniques. RA algorithms that are robust against CSIT imperfections, are favorable. The effect of erroneous CSIT on average sum rate of the proposed algorithm is investigated and shown to be superior to the existing schemes. Finally, fairness performance of the proposed RA algorithm is investigated and shown to achieve a remarkable performance.

Threshold-based CSI feedback reduction for time-varying multiple-input multiple-output broadcast channels

In many modern wireless systems that operate based on availability of channel state information at transmitter (CSIT), one of the main bottlenecks is updating CSIT of the time varying channel. In multiple-input multiple-output (MIMO) broadcast channels, CSIT is required for user scheduling and precoding. Most existing CSI feedback reduction techniques reduce the number of feedback terms by allowing only a limited number of users to feedback CSI, or allowing only partial/limited information of user channels to be send back to the transmitter. In this work, CSI is reduced over several time-slots of transmission, and not in a single snapshot at the beginning of each time-slot. A time-varying MIMO broadcast channel with limited-capacity feedback links is considered. An efficient threshold-based feedback technique that maximises net-throughput is proposed. The proposed scheme assigns different CSI feedback rates over several time-slots to different groups of users proportional to their channel strength. Analysis and simulation results for zero-forcing beamforming precoding show net-throughput superiority of the proposed scheme over the case of perfect CSI.

Simplified SVD-BD technique for cellular downlink with coordinated multi-point transmission

In this paper MIMO downlink with base station coordination in a cellular network is considered. Singular value decomposition-block diagonalization (SVD-BD) is a suboptimum method for precoding matrix, but it is computationally inefficient. The SVD-BD uses water-filling power allocation. We have proposed a reduced complexity technique for SVD-BD method based on sum rate maximization. Simulation results show that proposed scheme decreases computational complexity in comparison with SVD-BD. As a result proposed scheme can be considered as a simple and superior practical approach for complexity/throughput trade off in SVD-BD technique in cellular downlink.