Performance of Hybrid ARQ Schemes for the Mobile LEO Satellite Channel

This paper investigates the performance of hybrid ARQ schemes for the mobile Low Earth Orbit (LEO) satellite channel. The proposed schemes adapt their characteristics to the time-varying behavior of the channel. To obtain an unbiased comparison of different ARQ schemes an approximated analytical method is adopted. More precisely, the sphere-packing bound is used to estimate the best possible performance of a hybrid ARQ scheme. To assess the accuracy of the bound, simulation results, based on the use of turbo codes, are also presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Average Error Performance of M-ary Modulation Schemes in Nakagami-q (Hoyt) Fading Channels

Presented are exact-form expressions for the average error performance of various coherent, differentially coherent, and noncoherent modulation schemes in Nakagami-q (Hoyt) fading channels. The expressions are given in terms of the Lauricella hypergeometric function, F_D ⁽ⁿ⁾; for nges1, which can be evaluated numerically using its integral or converging series representation. It is shown that the derived expressions reduce to some existing results for Rayleigh fading as special cases     

Improving Automatic Repeat-Request (ARQ) Performance on Satellite Channels Under High Error Rate Conditions

Large round trip delay associated with satellite channels reduces the throughput for automatic repeat-request (ARQ) system of error control rather drastically under high error rate conditians. Ground segments that usually accompany satellite circuits at both ends introduce bursts of errors, during which block error rates tend to be quite high, bringing down the throughput to very low values. In this paper, some schemes that modify the currently known variations of ARQ (Stop-and-Wait and continuous systems) are suggested with a view to obtaining higher throughput under high block error rate conditions. Specifically, the modified Go-Back-Nsystem appears to be quite attractive, as it gives substantial improvement with little additional complexity in system implementation.     

A Minimum Mean-Square Error Equalizer for Nonlinear Satellite Channels

The problem of designing and evaluating the performance of a minimum mean-square error equalizer (MMSEE) for binary PSK transmission over band-limited nonlinear satellite channels is considered in this correspondence. The effect of intersymbol interference followed by AM/AM and AM/PM conversions are taken into account while optimizing the performance in the presence of the downlink white Gaussian noise. In analyzing the problem, the decision is made on a typical signal in a received sequence taking into account past and future interfering signals, i.e., ISI. As an illustrative example of the receiver, a typical channel model is considered in details. Based on the analysis, an alternative receiver structure which is more suitable for implementation is introduced. The taps gain coefficients for minimum mean-square error, between the received sample and the actual transmitted bit, are obtained using numerical methods. The performance of the equalizer is evaluated using computer simulation techniques and it is shown that significant performance improvement over the single-sample sign detector can be obtained.     

P－TCM在卫星移动通信信道上的性能

实用化网格编码调制（Ｐ－ＴＣＭ）方案能够利用同一芯片实现不同码率的网格码之编译码过程，其性能在加性高斯白噪声信道上与ＵｎｇｅｒｂｏｅｃｋＴＣＭ码相比差别不大。本文针对编码率为２／３的６４状态Ｐ－ＴＣＭ码，从理论上计算了在相干检测和差分检测两种情况下，该码在Ｒｉｃｉａｎ信道上和轻微遮挡的Ｒｉｃｉａｎ信道上的误比特率上、下限或渐进曲线，并且给出了相应的计算机仿真结果。结果表明，当误比特率为１０－３时，该码在上述信道上约有３．４ｄＢ～５．２ｄＢ的编码增益。     

卫星网络管理系统控制信道设计

设计了一套用于卫星网络管理系统的控制信道。采用TDM/TDMA专用控制信道和复接控制信道互为备份的方式保证信息传输的畅通,2种信道都可保证卫星网管所有功能的完成。主用TDM/TDMA专用控制信道,一旦专用信道中断,采用复接控制信道。复接控制信道与业务复接在一起利用业务信道传输网管信息。TDM/TDMA专用控制信道由链路适配器和突发卫星调制解调器组成,重点描述其设计方案。     

Effects of CEE and Feedback Error on Performance for AF-ORS with PSA-CE Schemes Over Quasi-Static Rayleigh Fading Channels

In this paper, we propose the analytical approach for amplify-and-forward (AF) opportunistic relaying schemes (ORS). When operation of AF-ORS consists of relay selection and data transmission phases based on pilot symbol assisted-channel estimation (PSA-CE) methods over quasi-static Rayleigh fading channels, we show that the relay selection phase can be implemented by pilots symbols transmission for source-relay and relay-destination. Moreover, the feedback method for the selected relay index is proposed to have a simple fashion. Then, we investigate the effects of both a channel estimation error and an estimated noise variance, which are obtained by PSA-CE methods, on the received signal-to-noise ratio (SNR). The average SNR loss is also derived in terms with the number of pilots in PSA-CE methods. Moreover, the average symbol error rate, the outage probability, and the normalized channel capacity of the ORS are derived in approximated closed-form expressions for an arbitrary link SNR when the channel state information in the source-relay-destination link is estimated based on transmitted pilots symbols. As the number of pilot symbols, the derived analytical approach is verified, and by comparing it with simulation results, the accuracy is demonstrated. In addition, it is verified that the effect of the feedback error can be neglected for PAS-CE methods over quasi-static fading channels.     

Improving the Performance of Spatial Modulation Schemes for MIMO Channels

Spatial modulation (SM) is a recent MIMO transmission concept that holds the potential to increase the spectral efficiency over wireless links using low-complexity transceivers. In this paper, an overview and performance analysis on the key issues of this emerging technology is presented. Based on this analysis, a performance enhancement is suggested by introducing an improved spatial modulation (ISM) scheme that retains the SM key advantages. It is observed that transmitting the same data symbol from more than one antenna at a time has a positive effect in terms of spectral efficiency but, on the other hand, it degrades the bit error rate (BER) performance. In this sense, a more general SM mapping rule is introduced aiming to provide a criterion for choosing an effective performance/rate/complexity trade-off according to the system requirement. An upper bound on the BER performance for ISM is derived and compared to Monte Carlo simulation results. In addition, a two-stage adaptive detector is also presented to enhance further the performance/complexity trade-off at the receiver for SM-based techniques.     

Error Control Codes for Parallel Asymmetric Channels

We consider transmission of messages encoded into binary matrices to be send over a parallel asymmetric channel. Two different channel models are introduced. They depend on the conditions on errors in the subchannels. For each channel model codes are constructed for error correction and for error detection and bounds are derived.     

Performance of Hybrid ARQ Schemes for OFDM Systems

In this paper,four schemes of Hybrid Automatic-Repeat-Request(HARQ)for Orthogonal Frequency DivisionMultiplexing(OFDM)systems are evaluated when they are used in different channel environments.The AccumulativeCorrect Packet Reception Rate(ACPRR)performance of four HARQ schemes is compared in order to verify which ARQschemes are more suitable for different mobility OFDM systems.Computer simulation results show that the maximal ratiocombining frequency diversity ARQ scheme and type Ⅲ HARQ with frequency diversity is more suitable for low mobilityOFDM system.However the type Ⅲ HARQ without frequency diversity is more suitable for high mobility OFDM systembecause of the remarkable time diversity which reduces the required retransmission number to about 2 at the ACPRR of0.96.     

移动卫星信道中的MPSK网格编码调制特性

基于Rice－Lognormal联合分布的两种信道模型，定性地分析了移动卫星信道中的MP－SK－TCM恃性。推导出了适合这两种模型的Chernoff界和另一种新的特性界表达式，计算了8U-TC－MPSK方案的误比特概率。计算机模拟显示出，本文得到的特性界不仅简单、方便，而且比已有的界紧，能够较好地反应这类信道的TCM特性。     

移动卫星信道中的TC-MDPSK特性界

本文基于Ｒｉｃｒ－Ｌｏｇｎｏｒｍａｌ联合分布的两种信道模型,定性地分析了移动卫星信道中的ＴＣ－ＭＤＰＳＫ特性界,推导出了适合这两种信道模型的一种新的特性表达式,讨论了８Ｕ－ＴＣ－ＭＤＰＳＫ方案的误比特率,计算机模拟显示出,本文推导的方法不仅简便,而且得到的特性界比已有的界紧,能够较好地反应这类信道的ＴＣ－ＭＤＰＳ特性。     

Forward Error Correction Coding for Fading Compensation in Mobile Satellite Channels

Fading in mobile satellite communications severely degrades the performance of data transmission. The channel is modeled with nonfrequency selective Rice and Rayleigh fading. Also, stored channel simulation is used for hardware data transmission. FEC coding with Viterbi decoding of convolutional codes, and Berlekamp-Massey decoding of Reed-Solomon codes, are used to compensate for the fading. In addition to interleaving, channel state and erasure information improve the performance of the decoder. The BER after decoding is calculated for specific codes on several channels and for different transmission schemes. Using very simple channel state and erasure information gives 2-7 dB additional coding gain. These gains have been verified by hardware data transmission on synthetic fading channels and stored mobile satellite channels.     

Performance Modeling for Packet Networks with Satellite Overflow Channels

In a packet network using medium speed terrestrial connectivity, average end-to-end delay can be reduced by using highspeed satellite overflow channels despite their propagation delay. To investigate networks of this type analytically, we derive a new basic queueing model for overflow systems with buffered traffic. The simple, closed-form expressions facilitate analysis. Approximations are developed for multiple primary systems with a single overflow channel; these agree with simulation. Using the overflow model analysis indicated the following. The reduced queueing delay to the high capacity overflow channel more than compensated for propagation delay. Inherent, broadcast transmission capabilities of satellite channels reduced overall network delay. The high capacity overflow channels permit networks to withstand substantial nodal imbalance and overloads.     

Performance Evaluation of Combined Coding and Modulation Schemes for Nonlinear Channels

The performance of combined coding and modulation schemes in channels with intersymbol interference and nonlinearities is studied using an analytical approach. The class of possible receivers is presented, and a generalization of the minimum Euclidean distance used for the asymptotic analysis of the performance of combined coding and modulation schemes on AWGN channels is introduced. Numerical results are presented for coded 16-PSK modulation.     

卫星ATM宽带网络及其差错控制技术

介绍了卫星ATM宽带网络的结构和特性,并讨论了应用于透明卫星ATM网络的自适应差错控制技术.     

天气影响下Ka频段移动卫星通信系统的性能

本文建立了ka频段移动卫星通信系统模型,并利用计算机进行仿真给出了不同天气时信号的误码率,为实际的系统设计提供了理论基础。在本文中信道模型建立为雨衰和多径阴影衰落信道。在该模型中,雨衰信道服从高斯分布,阴影衰落信道服从Nakagami-Rayleigh分布。与现在广泛应用的Loo模型相比,此阴影模型能够更好地利用计算机进行仿真,并能提供较清晰的数学表达式,对陆地移动卫星系统进行定性定量的性能预测。     

RS编码UEP M—QAM方案的性能分析

提出基于Reed-Solomon(RS)码的不等差错保护（UEP）MQAM（正交幅度调制方案,并研究其在瑞利平坦衰落和加性白高斯噪音下的性能。计算结果表明,该UEP MQAM方案具有很高的频谱利用率,而且重要数据相对于非重要数据的编码增益可以通过调整RS编码的差错纠正能力来灵活地改变。