A simple packet-transmission scheme for wireless data over fading channels

In this letter, we present a simplified scheduling scheme for packet transmission over a fading channel which is modeled as a finite-state block channel. We first address the optimal minimum power-transmission policy with constraints on both average delay and packet loss. The optimal policy requires a sophisticated table lookup for implementation. In order to alleviate this problem, we design a simplified transmission policy that is based on checking for three control parameters: a transmission-rate threshold; a channel-state threshold; and the transmission buffer size. Our results show that the minimum average power with the simplified scheme is very close to that achieved by the optimal policy. Further, modeling the simplified scheme via a single-server bulk-service queue, we derive approximations to the quality of service metrics, such as average power and delay, that allow for analytical insights into the policy design.     

A space-time block-coded OFDM scheme for unknownfrequency-selective fading channels

We introduce a space-time block-coded orthogonal frequency-division multiplexing (STBC-OFDM) selective fading channels which does not require channel knowledge either at the transmitter or at the receiver. The decoding algorithm is based on generalized maximum-likelihood sequence estimation. We investigate the performance of the proposed scheme over two-tap Rayleigh fading channels. Simulation results show the performance to be near optimum     

A simple and general parameterization quantifying performance in fading channels

We quantify the performance of wireless transmissions over random fading channels at high signal-to-noise ratio (SNR). The performance criteria we consider are average probability of:error and outage probability. We show that as functions of the average SNR, they can both be characterized by two parameters: the diversity and coding gains. They both exhibit identical diversity orders, but their coding gains in decibels differ by a constant. The diversity and coding gains are found to depend on the behavior of-the random SNR's probability density function only at the origin, or equivalently, on the decaying order of the corresponding moment generating function (i.e., how fast the moment generating function goes to zero as its argument goes to infinity). Diversity and coding gains for diversity combining systems are expressed in terms of the diversity branches' individual diversity and coding gains, where the branches can come from any diversity technique such as space, time, frequency, or, multipath. The proposed analysis offers a simple and unifying approach to evaluating the performance of uncoded and (possibly space-time) coded transmissions over fading channels, and the method applies to almost all digital modulation schemes, including M-ary phaseshift keying, quadrature amplitude modulation, and frequency-shift keying with coherent or noncoherent detection.     

A simple capacity formula for correlated diversity Rician fading channels

Appropriate exploitation of the randomness of multipath propagation in wireless communications can considerably increase the system. capacity. The average capacity of correlated diversity Rician channels, however, is not available in the literature due to the nonlinear log function involved in the conditional channel capacity and to the complicated distribution of correlated Rician channels. Rather than using brute force, we tackle this issue by combining a widely adopted statistical technique with an elegant lemma by Porteous, ending up with a simple and accurate formula for average channel capacity on correlated diversity Rician channels. Numerical results are also presented for illustration.     

Asymmetric diversity modulation scheme in wireless fading relay channels

In this paper, we propose an asymmetric diversity modulation (ADM) scheme for a single-source relay system that utilizes the relay?s higher transmission ability as a form of diversity. To achieve this, the proposed method transmits multiple source bits over a high-order modulating relay as a way to provide additional time diversity. The spatial and time diversity then undergo `bit?-based combining at the destination. Using the proposed `bit?-based channel combining method, we derive the theoretical bit error rate (BER) for such a system. Moreover, we investigate the fact that the proposed scheme shows a performance trade-off between bit power and time diversity resulting from the reduced bit power caused by a high-order modulating relay.     

A coded 16 QAM scheme for fast fading mobile radio channels

An adaptive Viterbi algorithm, derived from a dynamic estimate of the fading channel is used for the decoding of a convolutional coded 16 QAM system in a mobile environment. The estimates are obtained by a sequence of known pilot symbols embedded in the data stream, and perform compensation for Rayleigh fading. The likelihood criterion in the Viterbi decoder is also modified by these channel estimates through a metric weighting function. We demonstrate through computer simulations, that our new technique achieves a BER improvement of 7-10 dB at P_e =10^-3 in a fast flat Rayleigh fading environment compared to an uncoded system. The BER performance of our new technique in a co-channel interference (CCI) controlled environment is also studied, and the results show that it may achieve a 40% to 85% improvement in capacity over the standard modem scheme for the new US digital cellular system, π/4-QPSK     

A simple baseband transmission scheme for power line channels

We propose a simple pulse-amplitude modulation (PAM)-based coded modulation scheme that overcomes two major constraints of power line channels, viz., severe insertion-loss and impulsive noise. The scheme combines low-density parity-check (LDPC) codes, along with cyclic random-error and burst-error correction codes to achieve high-spectral efficiency, low decoding complexity, and a high degree of immunity to impulse noise. To achieve good performance in the presence of intersymbol interference (ISI) on static or slowly time-varying channels, the proposed coset-coding is employed in conjunction with Tomlinson-Harashima precoding and spectral shaping at the transmitter. In Gaussian noise, the scheme performs within 2 dB of unshaped channel capacity at a bit-error rate (BER) of 10/sup -11/, even with (3,6)-regular LDPC codes of modest length (1000-2000 bits). To mitigate errors due to impulse noise (a combination of synchronous and asynchronous impulses), a multistage interleaver is proposed, each stage tailored to the error-correcting property of each layer of the coset decomposition. In the presence of residual ISI, colored Gaussian noise, as well as severe synchronous and asynchronous impulse noise, the gap to Shannon capacity of the scheme to a Gaussian-noise-only channel is 5.5 dB at a BER of 10/sup -7/.     

Throughput performance of an adaptive ARQ scheme in Rayleigh fading channels

Using a simulation study we analyze the throughput performance of Yao's adaptive ARQ scheme in time-varying channels. The simulation takes into account the Rayleigh amplitude and the fast or the slow fading characteristics of a wireless channel, under a representative M-FSK modulation and Reed-Solomon coding scheme. We show that, for a specific set of design parameters, Yao's adaptive procedure works well for all channel fading rates, except for moderately slow rates. By observing variations of packet error rates at a specified SNR we provide an explanation for these varied behaviors under different channel fading rates.     

Improved space-time trellis coded modulation scheme on slowRayleigh fading channels

It has been established that the appropriate criteria for space-time trellis coded modulation (STTCM) design on slow Rayleigh fading channels are maximisation of the minimum rank and the minimum determinant of the distance matrices. It is demonstrated that when STTCM is used in systems with a large product (>3) of the numbers of transmit and receive antennas, the design of codes with maximum coding gain is governed by the minimum trace of the distance matrices. A number of new codes based on the proposed design criterion have been constructed and shown to be superior to other known codes     

Performance analysis of TAS/MRC-based scheme in time-varying Rayleigh fading channels

This paper investigates a Multiple-Input Multiple-Output (MIMO) scheme combining Transmit Antenna Selection and receive Maximal-Ratio Combining (TAS/MRC) in time-varying Rayleigh fading channels. We first present new closed-form expressions for optimal received Signal-to-Noise Ratio (SNR), which is expressed in polynomial form. These are used to analyze ergodic capacity, outage probability and Bit Error Rate (BER) of TAS/MRC systems. Numerical results are presented to validate the theoretical analysis.     

A two-symbols/branch MBCM scheme based on 8-PSK constellation under fading channels

A two-symbols/branch scheme of multiple block coded modulation (MBCM) is investigated under fading channels. Compared with a conventional scheme of block coded modulation (BCM), this two-symbols/branch MBCM scheme greatly increases the minimum squared Euclidean distance (MSED), minimum symbol distance (MSD), and minimum product distance (MPD). These three distances determine the bit-error-rate (BER) performance under either Gaussian or fading channels. A pilot symbol assisted fading compensation, as well as the techniques of symbol interleaving and branch weighting, are employed to combat the effect of channel fading. Through computer simulations, it is shown that large coding gains are obtained under both Rayleigh and Rician fading channels.     

相关衰落信道下的一种层间联合自适应SR-ARQ传输机制

传统自适应传输机制在相关慢衰落信道下有较差的系统性能.针对相关衰落信道,提出了一种层间联合自适应传输机制.利用有限状态马尔可夫链来描述相关衰落信道,同时通过构建一个多状态马尔可夫系统模型来分析系统吞吐性能,并对调制方式和传输分组大小进行优化.另外,推导了系统平均吞吐性能的表达式.仿真结果显示所提出的自适应传输机制在相关衰落信道上能获得更好的系统性能.     

Suboptimum Viterbi algorithm for trellis-coded QAM scheme inmultipath Rayleigh fading channels

A new suboptimum Viterbi algorithm for trellis-coded quadrature amplitude modulation based on the channel state information of the multipath Rayleigh fading channel is proposed. Simulation results show that the proposed algorithm has merits for applications that require low bit energy-to-noise ratio     

Comparison of diversity with simple block coding on correlatedfrequency-selective fading channels

We investigate the effects of correlation on the performance of diversity systems in wideband wireless radio environments. Specifically, the average bit error rate (BER) performance of M-ary differential phase shift keying (MDPSK) on correlated frequency-selective slow Rayleigh fading channels is analyzed. A two-branch diversity receiver with postdetection equal gain combining is considered. Nyquist pulse shaping is used and differential detection is employed at the receiver. The effects of cochannel interference on the system performance are assessed using a Gaussian interference model. To further enhance the system performance, the effects of combined diversity and forward error correction (FEC) coding on the average BER are investigated. Results using short cyclic block codes with perfect bit interleaving are obtained. The effects of the root mean square (RMS) delay spread, the amount of correlation, and the level of modulation, M, on the average BER are investigated in detail for both coded and uncoded systems. The results show that dual branch diversity combining with a correlation coefficient of 0.5 outperforms (in terms of BER) short block codes with perfect bit interleaving, and that combined diversity and coding strategies are effective in combatting the effects of frequency-selective fading     

Performance of an adaptive successive serial-parallel CDMAcancellation scheme in flat Rayleigh fading channels

The performance of a successive concatenated cancellation scheme for code-division multiple-access (CDMA) uplink transmission in cellular mobile radio is presented. Both serial and parallel cancellation stages are employed. The serial cancellation stage is first used to obtain initial data estimates followed by the parallel cancellation stages to enhance the accuracy of the estimates. The performance of this scheme is evaluated via analysis and simulation. In our analysis, we develop a model to consider the impact of wrongly estimating the phase and amplitude of the channel impulse response on the successive concatenated cancellation scheme. Analysis and simulation results in flat Rayleigh fading asynchronous channels with both perfect and nonperfect channel estimation and with perfect ranking confirms the accuracy of our analytical model as well as the significant improvement in performance compared to the conventional single-user matched filter (MF) detection and the stand-alone parallel cancellation schemes. Analytical results also show that the concatenated scheme has the potential to reach the single-user performance bound for a wide range of user base size, up to K=120 users, with a processing gain of 127 using one serial and three parallel cancellation stages. Finally, we propose a method whereby the receiver adapts with the number of users in order to retain the bit error ratio (BER) performance while decreasing the processing delay     

瑞利衰落信道中可变包长可变调制方式SR-ARQ系统性能研究

提出了可变包长可变调制方式的选择重传自动重传请求系统(VS-AM-SR-ARQ),研究了其在瑞利衰落信道下的性能,推导出吞吐量的一般表达式,并提出了用两步法求出最佳的切换门限值.理论分析和数值计算结果表明,可变包长可变调制方式的ARQ系统可以更好地适应衰落信道,其吞吐量性能要优于普通的ARQ系统.     

An adaptive modulation scheme for simultaneous voice and datatransmission over fading channels

We propose a new adaptive modulation technique for simultaneous voice and data transmission over fading channels and study its performance. The proposed scheme takes advantage of the time-varying nature of fading to dynamically allocate the transmitted power between the inphase (I) and quadrature (Q) channels. It uses fixed-rate binary phase shift keying (BPSK) modulation on the Q channel for voice, and variable-rate M-ary amplitude modulation (M-AM) on the I channel for data. For favorable channel conditions, most of the power is allocated to high rate data transmission on the I channel. The remaining power is used to support the variable-power voice transmission on the Q channel. As the channel degrades, the modulation gradually reduces its data throughput and reallocates most of its available power to ensure a continuous and satisfactory voice transmission. The scheme is intended to provide a high average spectral efficiency for data communications while meeting the stringent delay requirements imposed by voice. We present closed-form expressions as well as numerical and simulation results for the outage probability, average allocated power, achievable spectral efficiency, and average bit error rate (BER) for both voice and data transmission over Nakagami-m fading channels. We also discuss the features and advantages of the proposed scheme. For example, in Rayleigh fading with an average signal-to-noise ratio (SNR) of 20 dB, our scheme is able to transmit about 2 bits/s/Hz of data at an average BER of 10 ^-5 while sending about 1 bit/s/Hz of voice at an average BER of 10^-2     

A simple and effective precoding scheme for noise whitening onintersymbol interference channels

A precoding scheme for noise whitening on intersymbol interference (ISI) channels is presented. This scheme is compatible with trellis-coded modulation and, unlike Tomlinson precoding, allows constellation shaping. It can be used with almost any shaping scheme, including the optimal SVQ shaping, as opposed to trellis precoding, which can only be used with trellis shaping. The implementation complexity of this scheme is minimal-only three times that of the noise prediction filter, hence effective noise whitening can be achieved by using a high-order predictor     

An ICI reduction scheme for OFDM system with phase noise over fading channels

Orthogonal Frequency Division Multiplexing has become a key element of todays wireless communication systems. However, its sensitivity to oscillator phase noise is responsible for common phase error (CPE) and inter-carrier interference (ICI) which greatly degrades the overall system performance. In this contribution, we address the problem of reducing the effects of phase noise in an OFDM system operating over a frequency selective fading channel. We propose a method for jointly estimating the channel and CPE in a first step and removing ICI in a second step, using a power series expansion of the phase noise process. The algorithm is simulated on both coded and uncoded systems with phase noise over a fading channel.     

New selection diversity reception scheme effective for both frequency-flat and selective fading channels

A new selection diversity reception scheme is proposed, which combines and takes advantage of the maximum signal envelope branch selections (MEBS) and the minimum delay-spread branch selection (MDBS) schemes. The performance of the proposed scheme is theoretically investigated under frequency-flat and frequency-selective fading channel conditions and the improvement over the MEBS and the MDBS schemes is confirmed.<>