Xiangbin Yu

Performance of Variable-Power Adaptive Modulation With Space–Time Coding and Imperfect CSI in MIMO Systems

The performance analysis of multi-input-multi-output (MIMO) systems with M-ary quadrature amplitude modulation (MQAM) and a space-time block code (STBC) over flat Rayleigh fading channels for imperfect channel state information (CSI) is presented. In this paper, the optimum fading gain switching thresholds for attaining maximum spectrum efficiency (SE) subject to a target bit-error rate (BER) and an average power constraint are derived. It is shown that the Lagrange multiplier in the constrained SE optimization does exist and is unique for imperfect CSI and for single-input-single-output (SISO) systems under perfect CSI. On the other hand, the Lagrange multiplier will be unique if the existence condition for MIMO under perfect CSI is satisfied. Numerical evaluation shows that the variable-power (VP) adaptive modulation (AM) with STBC provides better SE than its constant-power (CP) counterpart.

Unified Analysis of Multiuser Scheduling for Downlink MIMO Systems with Imperfect CSI

In this paper, unified BER performance and outage probability analyses of downlink multiuser scheduling for multiple-input multiple-output (MUS-MIMO) transmission/combining (transceiving) systems with imperfect channel state information (CSI) caused by feedback over Rayleigh fading channels is presented. The unified analysis is applicable to MIMO transceiving systems whose received signal-to-noise ratio (SNR) is given as largest order statistic of chi-square distribution. The performance of MUS-MIMO employing selective transmission/selective combining (ST/SC), ST/maximum ratio combining (MRC) and space-time block codes (STBC) can be analyzed by this general framework. Accurate and approximate unified closed-form BER and outage probability expressions of the MUS-MIMO transceiving system with normalized SNR-based scheduling in heterogeneous networks are derived. Based on the approximate BER and outage probability expressions, diversity gains are analyzed at high SNR. The results indicate that the MUS-MIMO for using the three transceiving schemes can achieve full diversity order for perfect CSI, while the diversity gain is degraded differently for the three transceiving schemes under imperfect CSI. Computer simulation shows that the theoretical analysis is in good agreement with simulation results, and the approximate BER expressions are very close to the accurate ones but with lower computational complexity.

Full-Rate Complex Orthogonal Space-Time Block Code for Multiple Antennas

In this paper, full-rate and complex orthogonal space-time block code (STBC) schemes for multiple antennas are proposed, and turbo code is employed as channel coding to improve the proposed STBC schemes performance further. Compared with full-diversity multiple antennas STBC schemes, the proposed schemes can implement full data rate, partial diversity and a smaller complexity. On the condition of the same system throughput and concatenation of turbo code, the proposed schemes have lower bit error rate (BER) than those low-rate and full-diversity code schemes.

Symbol Timing Estimation for Physical-Layer Network Coding

Recently, physical-layer network coding (PNC) has attracted much attention due to its ability to double the throughput in relay-aided communications. However, most research in PNC assumes that the symbol timings of the end nodes are ideally aligned. In fact, they have to be recovered accurately at the relay. In this letter, we present a novel symbol timing error estimator for PNC. It is shown that accurate error estimates can be obtained by the interpolation algorithm based on a small-size Discrete Fourier Transformation (DFT). The Mean Square Error (MSE) performance is one order of magnitude better than that of the conventional maximum likelihood based optimum sample (OS) algorithm for signal-to-noise ratio (SNR) greater than 10 dB.

Performance analysis of variable-power adaptive modulation with antenna selection over Rayleigh fading channels

The performance of multi-input multi-output (MIMO) systems with variable-power (VP) adaptive modulation (AM) and antenna selection (AS) over Rayleigh fading channels for both perfect and imperfect channel state information (CSI) is presented. In this study, the optimum fading gain switching thresholds for attaining maximum spectrum efficiency (SE) subject to a target bit error rate (BER) and an average power constraint are derived. It is shown that the Lagrange multiplier in the constrained SE optimisation is unique if the existence conditions for MIMO systems with transmit AS and receive maximal-ratio combining under perfect or imperfect CSI are satisfied. By using the switching thresholds, we obtain closed-form expressions of the SE and average BER for VP and constant-power (CP) systems. Simulation results for SE and BER are in good agreement with the theoretical analysis. The results show that the VP-AM system using AS with the derived VP control scheme provides better SE than the CP counterpart and the VP-AM system with space-time coding and can fulfil the target BER for different signal-to-noise ratios (SNRs).

Performance Analysis of Variable-Power Adaptive Modulation With Outdated Feedback for Space–Time Coded MIMO Systems

The performance analysis of a space-time coded multiple-input-multiple-output (MIMO) system that employs different variable-power adaptive-modulation (VP-AM) strategies with outdated channel-state information (CSI) over Rayleigh fading channels is presented. The optimal design of VP-AM with power control (PC) in time (VP-AM-TIME) is first developed. The optimum switching thresholds of VP-AM-TIME for attaining maximum spectrum efficiency (SE) subject to a target bit error rate (BER) and an average power constraint are derived. A closed-form expression of the optimal temporal PC in terms of the Lambert function is obtained. A suboptimal VP-AM-TIME is also developed to further simplify the algorithm. The existence and uniqueness of the Lagrange multiplier that was used in the constrained optimization for the optimal and suboptimal VP-AM-TIME are investigated. By using the switching thresholds, we obtain closed-form expressions of SE and average BER. Then, a VP-AM scheme with joint spatial-temporal power control (VP-AM-JOINT) is developed. The joint spatial-temporal PC problem can be solved by transforming it into an inner-outer optimization problem. Theoretical analysis and simulation results show that the proposed optimal VP-AM-TIME can obtain the same performance as the existing optimal VP-AM-TIME but with much lower computational complexity, and the new suboptimal VP-AM-TIME outperforms the existing suboptimal scheme and obtains a performance closer to the optimal scheme. The results also show that the new VP-AM-JOINT scheme is always superior to the optimal VP-AM-TIME and provides considerable gains in SE over a wide range of feedback delays, although the two schemes have almost the same performance when the feedback delay becomes large.

Adaptive Modulation and Joint Temporal Spatial Power Allocation for OSTBC MIMO Systems with Imperfect CSI

We propose a novel adaptive transmission scheme for space-time coded multiple-input multiple-output beamforming systems with imperfect channel state information at the transmitter, of which the signal constellation, total transmit power (temporal power), and power allocation among eigen-beams (spatial power) are jointly adapted to maximize the average spectral efficiency, subject to a target bit-error-rate and an average power constraint. The power allocation over the spatial and temporal domains makes the traditional approach of partitioning the received signal-to-noise ratio (SNR) inapplicable to the above design problem. By introducing a new variable, called as effective signal-to-noise-to-modulation ratio (ESNMR), we derive a rate-selection policy by partitioning the range of the ESNMR with an optimal set of thresholds. A closed-form temporal power control policy and a simple spatial power allocation algorithm are also obtained. Numerical results demonstrate that the new adaptive transmission scheme yields a significant performance gain over existing adaptation systems.

Performance Analysis of Rate-Adaptive Modulation with Imperfect Estimation in Space---Time Coded MIMO System

Based on the imperfect estimation information, the performance analysis of multi-input multi-out (MIMO) systems with rate-adaptive modulation and space–time coding over flat Rayleigh fading channels is presented in this paper. The fading gain value is partitioned into a number of regions by which the modulation is adapted according to the region the fading gain falls in. Under a target bit error rate (BER) and constant power constraint, the fading gain region boundaries are given. By utilizing the minimum mean squared error estimation, the correlation between the channel gains and their estimates, which contributes to imperfect channel information, is evaluated. With this correlation, the probability density function of fading gain is obtained. Based on these results, the closed-form expressions for the SE and average BER are derived in detail, respectively. The theoretical expressions will be more accurate than the existing schemes, and they include perfect estimation as a special case. Numerical results show that the SE and BER of the system with imperfect estimation are worse than those with perfect estimation due to the estimation error. Moreover, the simulation results for SE and BER are in good agreement with the theoretical analysis.

Performance Analysis of Space–Time Block-Coded MIMO Systems With Imperfect Channel Information Over Rician Fading Channels

The performance analysis of space-time block-coded multiple-input-multiple-output (STBC-MIMO) systems in Rician fading channels for perfect and imperfect channel state information (CSI) is presented in this paper. Accurate expressions of average bit error rate (BER) and symbol error rate (SER) of STBC-MIMO for multiple phase-shift keying (MPSK) and quadrature amplitude modulation (QAM) are derived. Based on asymptotic analysis and Nakagami approximation for Rician fading, closed-form expressions of approximate average BER and SER are obtained for low and high signal-to-noise ratios (SNRs). By combining the error rate expressions of low SNR and SNRs, approximate BER and SER expressions can be obtained for different SNRs. Computer simulation shows that the theoretical analysis is in good agreement with the simulation results, and the approximate expressions derived from the integration of high and low SNR asymptotic analyses are close to the accurate formulas for different SNRs. The asymptotic analysis at high SNR indicates that the coding gain is affected by the Rice factor, transmit and receive antenna numbers, code rate, and modulation, whereas the diversity gain is governed by the transmit and receive antenna numbers. However, the diversity gain will be zero at high SNR in the presence of estimation errors because of the error floor in the error probability curves.

Cross-layer design with feedback delay over MIMO Nakagami-m fading channels

A cross-layer design of packet-data transmission with space-time block coding (STBC) over multiple input and multiple output (MIMO) Nakagami-m fading (NMF) channels is presented. Based on the imperfect channel state information (CSI), the closed-form expressions of average packet error rate (PER) and average spectral efficiency (ASE) of the system with a feedback delay are derived, respectively. Due to the feedback delay, the variable threshold method is employed to reduce the effect of imperfect CSI on the system performance. Numerical results reveal that the derived theoretical expressions can effectively evaluate the performance of the system with the delay. The achieved ASE of the system is higher than that of the system with fixed thresholds, but it will decrease while the error probability increasing when the feedback delay becomes large.