Xiaoyu Dang

BER constraint based power allocation for downlink MC-CDMA systems with linear MMSE receiver

Power allocation plays a crucial role in wireless communications. To facilitate the efficient allocation of limited transmit power, in this paper, a bit error rate (BER) constraint based power allocation scheme is proposed for the downlink of multi-carrier code division multiple access (MC-CDMA) systems with linear minimum mean square error (MMSE) receiver. According to the instantaneous path gains, the proposed scheme can determine the required minimum transmit power on each channel to meet the BER constraint. The simulation results show that the proposed scheme can consistently provide high-quality solutions with a very few iteration time, and also prove that it is efficient in reducing the transmit power while meeting BER constraint, and thereby improves the system performance.

Aeronautical telemetry using offset QPSK in frequency selective multipath

The impact of frequency selective multipath fading on the bit error rate performance of ARTM Tier-1 waveforms (FQPSK and SOQPSK) is derived and analyzed. In the presence of a strong specular reflection with relative magnitude |/spl Gamma//sub 1/|, the ARTM Tier-1 waveforms suffer a loss in performance of (1 - |/spl Gamma//sub 1/|)/sup -4/spl radic/|/spl Gamma///sub 1/| for |/spl Gamma//sub 1/| < 0.5 and a relatively high error floor at approximately 10/sup -2/ for |/spl Gamma//sub 1/| /spl ges/ 0.5. The ARTM Tier-1 waveforms possess twice the spectral efficiency of PCM/FM, but exhibit a greater loss and higher error floors than PCM/FM for the same multipath conditions and signal-to-noise ratio.

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.

System Outage Probability Analysis of Uplink Distributed Antenna Systems over a Composite Channel

This paper studies the system uplink outage probability in distributed antenna systems (DAS). Firstly, owing to the complexity of actual wireless environments, this paper establishes a composite channel model which takes path loss, lognormal shadowing and Rayleigh fading into account. Then, the probability density function (PDF) of the output signal-to-noise ratio (SNR) is derived. After that, an analytical expression of the uplink outage probability for the MS over a given position is obtained after employing the selective transmission (ST) scheme. Further, considering the distribution of MSs in the cell, a closed-form expression of the system outage probability is derived. Numerical results show that the closed-form expression of the system outage probability can provide sufficient precision for evaluating the outage performance of DAS.

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.

System capacity analysis of downlink distributed antenna systems over composite channels

This paper focuses on the downlink system capacity in distributed antenna systems (DAS). Firstly, this paper establishes a composite channel model which takes path loss, lognormal shadowing and Rayleigh fading into consideration. Then, to facilitate the analysis, the distribution of the output SNR is approximated by a lognormal distribution. After that, by making use of selective diversity (SD) scheme for distributed antennas, an approximate analytical expression of the capacity for a mobile station (MS) over a given position is derived. Further, considering the distribution of MSs in the system, a closed-form expression of the system capacity is obtained. Numerical results show that the closed-form expression can provide sufficient precision for evaluating the system capacity performance of DAS.

Noncoherent Multiple-Symbol Detector of Binary CPFSK in Physical-Layer Network Coding

It is well known that the binary continuous phase frequency shift keying (CPFSK) signal is power efficient with constant envelope, because it allows transmission with inexpensive and energy efficient nonlinear amplifiers. Recently, physical-layer network coding (PNC) using the binary CPFSK is considered as a potentially attractive solution to the dual needs of high throughput and high power efficiency in two-way relay wireless network. However, most recent studies on PNC have assumed that the carrier phases of the two transmitted signals arriving at the relay are ideally aligned. In fact, the carrier phase offset between the two node-signals always exists in practice. In this letter, a noncoherent multiple-symbol detector of binary CPFSK signals with unknown carrier phase offset in physical-layer network coding is proposed, which is based on the log-likelihood ratio test. It is shown by simulation that the algorithm with five symbol observation interval achieves 6.7 dB performance gain, compared with only one symbol observation interval.

An analysis of FQPSK and SOQPSK in frequency selective multipath

The performance of FQPSK and SOQPSK-TG in frequency selective multipath is analyzed in this paper. It is shown that these waveforms, called the advanced range telemetry (ARTM) tier-1 waveforms, behave the same in the presence of multipath interference. In the presence a strong specular multipath reflection with relative amplitude |/spl Gamma/| > 0.5, the phase averaged bit error rate exhibits a floor at approximately 10/sup -2/. When the amplitude |/spl Gamma/| is less than 0.5, the loss in performance relative to the AWGN case is approximately (1 - |/spl Gamma/|)/sup -4//spl radic/(|/spl Gamma/|). The ARTM tier-1 waveforms possess twice the spectral efficiency of PCM/FM, but exhibit a greater loss and higher error floors than PCM/FM for the same multipath conditions and signal-to-noise ratio. Given the bandwidth of the ARTM tier-1 waveforms is half that of PCM/FM, the time-varying multipath interference effects the waveform half the time thus improving the overall link availability.

Performance analysis of cross-layer design with average PER constraint over MIMO fading channels

In this article, a cross-layer design (CLD) scheme for multiple-input and multiple-output system with the dual constraints of imperfect feedback and average packet error rate (PER) is presented, which is based on the combination of the adaptive modulation and the automatic repeat request protocols. The design performance is also evaluated over wireless Rayleigh fading channel. With the constraint of target PER and average PER, the optimum switching thresholds (STs) for attaining maximum spectral efficiency (SE) are developed. An effective iterative algorithm for finding the optimal STs is proposed via Lagrange multiplier optimisation. With different thresholds available, the analytical expressions of the average SE and PER are provided for the performance evaluation. To avoid the performance loss caused by the conventional single estimate, multiple outdated estimates (MOE) method, which utilises multiple previous channel estimation information, is presented for CLD to improve the system performance. It is shown that numerical simulations for average PER and SE are in consistent with the theoretical analysis and that the developed CLD with average PER constraint can meet the target PER requirement and show better performance in comparison with the conventional CLD with instantaneous PER constraint. Especially, the CLD based on the MOE method can obviously increase the system SE and reduce the impact of feedback delay greatly.

Performance of Cross-Layer Design with Antenna Selection and Imperfect Feedback Information in MIMO Systems

By combining adaptive modulation and automatic repeat request, a cross-layer design (CLD) scheme for MIMO system with antenna selection (AS) and imperfect feedback is presented, and the corresponding performance is studied. Subject to a target packet loss rate and fixed power constraint, the variable switching thresholds of fading gain are derived. According to these results, and using mathematical manipulation, the average spectrum efficiency (SE) and packet error rate (PER) of the system are further derived. As a result, closed-form expressions of the average SE and PER are obtained, respectively. These expressions include the expressions under perfect channel state information as special cases and provide good performance evaluation for the system. Numerical results show that the proposed CLD scheme with antenna selection has higher SE than the existing CLD scheme with space-time block coding, and the CLD scheme with variable switching thresholds outperforms that with conventional-fixed switching thresholds.