Hongwen Yang

Diversity order of decode-and-forward MIMO relaying with transmit antenna selection

This article analyzes the diversity order of several proposed schemes, where the transmit antenna selection (TAS) strategies are combined with low-complexity decode-and-forward (DF) protocols in the multiple-input multiple-output (MIMO) relaying scenario. Although antenna selection is a suboptimal form of beamforming, it enjoys the advantages of tractable optimization and low feedback overhead. Specifically, this article proposes schemes that combine TAS strategies with fixed decode-and-forward (FDF) and selection decode-and-forward (SDF) protocols. Following that, the asymptotic expressions of outage probabilities are derived and the diversity order of the proposed schemes analyzed. These kinds of combination of transmit antenna selection strategies and low-complexity decode-and-forward protocols can achieve partial diversity order in the MIMO relaying scenario. The numerical simulations verify the analysis.

A New Reduced-Complexity Decoding Algorithm for LDPC Codes

This letter proposes a new algorithm for the check node update in the decoding of low-density parity-check (LDPC) codes. The proposed algorithm is based on a new approximation formula of standard sum-product algorithm (SPA) which can reduce the approximation error of min-sum algorithm (MSA) and has almost the same performance as sum-product algorithm (SPA) under both floating precision operation and fixed-point operation. Besides, the new approximation formula can be implemented in simple structures competitive with MSA.

Closed-form expressions for outage probability of decode-and-forward relaying over Nakagami-m fading channels

Abstract In this article, an exact closed-form expression is derived for outage probability of decode-and-forward (DF) cooperative communications over independent identically distributed Nakagami- m fading channels. Simulation results verify that the theoretical expressions for the outage probability are correct. The optimal power allocation based on the derived outage probability is also studied.

Ergodic capacity of switch-and-examine combining under flat Rayleigh fading channels

Switch-and-examine combining (SEC) is an interesting diversity technique that is simpler than selection combining (SC), whereas its performances is similar in terms of bit error rate (BER) and diversity order. As ergodic capacity is also a key performance index in modern wireless systems, this article analyzes the ergodic capacity of the SEC system. The numerical results show that the ergodic capacity of SEC with optimal threshold is similar to that of SC for arbitrary number of diversity branches.

Adaptive STBC-VBLAST transmission for mobile WiMAX

Abstract Multiple-input multiple-output (MIMO) technology can provide high data rate and substantial diversity. Space time block code (STBC) provides diversity gain and obtains signal of better quality even under bad channel conditions. However, it has no contribution to system average throughput. Vertical-bell laboratory layered space-time (VBLAST) improves peak data rate but leads to higher packet error rate (PER) at cell edge when the channel condition is poor. To get both higher system average throughput and cell edge throughput, an adaptive STBC-VBLAST transmission for downlink mobile WiMAX system is proposed and analyzed through system-level simulation in this article. The proposed approach compares the effective capacity of two candidate MIMO modes (STBC or VBLAST) and reports its decision to the base station with only one extra signaling bit. The simulation results show that the proposed approach can attain a balance between STBC and VBLAST. Besides, the cell throughput approximates that of pure VBLAST and the cell edge throughput is close to that of pure STBC.

Pilot power based rate control in CDMA 2000 1x EV-DO Rev-A

Abstract This article proposes a new algorithm to improve the rate control efficiency of enhanced reverse link medium access control (RLMAC) in the code division multiple access (CDMA) Ix EV-DO release A (Rev. A) system. The new algorithm brings reverse access terminal (AT) pilot power to the RLMAC rate control procedure and makes it easier for a low pilot power user to increase its data rate when the system is slightly loaded and harder to decrease its date rate when the system is heavily loaded. Numerical results of system level simulations show that the new algorithm can bring higher system throughput, lower AT transmission power, and lower system load.

Improvement of a MIMO antenna structure with combination of transmit beamforming and spatial multiplexing

Abstract Downlinks of the cellular systems generally have more transmit antennas than receive antennas. To efficiently exploit all antenna resources, a technique that combines the advantage of beamforming and spatial multiplexing has been proposed, which partitions the transmit antennas into neighboring sub-groups. In this article, this technique is further improved by Eq. (1) allowing non-contiguous antenna grouping, and Eq. (2) adopting two new grouping criteria: minimum signal distance maximization (MSDM) criterion and maximum correlation coefficient minimization (MCCM) criterion. Simulation results indicate that these improvements can bring noticeable gains in the Rayleigh flat fading channel environment.