随机M进制正交码混合DS—SFH CDMA扩频通信系统性能分析

本文研究了随机ＭＦ是制正交码混合ＤＳ－ＳＦＨ扩频码分多址信号经过多径瑞利频率非选择性衰落信道，在非相干ＲＡＫＥ接收机中采用最大输出信噪比选择或最大输出选择接收时系统的性能；给出了两种分集接收情况下差错概率表示式。数值计算研究了分集数，Ｍ值，多用户干扰对系统性能的影响，并且对这两种分集接收情况下系统性能进行了比较。     

Capacity of synchronous coded DS SFH and FFH spread-spectrummultiple-access for wireless local communications

The performance of synchronous spread-spectrum multiple-access (SSMA) communications based on direct-sequence (DS), slow frequency-hopped (SFH), and fast frequency-hopped (FFH) systems for wireless local communications of micro-cellular personal communications is analyzed. Using an indoor multipath fading channel model with clusters of arriving rays, we investigate multiuser DS systems with RAKE and diversity reception by selection combining (SC), multiuser SFH systems with equal-gain (EG) diversity reception, and multiuser FFH systems with correlated EG and self-normalization (SN) combining techniques. Reed-Solomon codes are considered to further improve the system performance. Given a fixed available bandwidth with narrow band interference (NBI), capacities and packet error rates are determined under various system configurations. Total capacities of hybrid frequency-division multiple-access (FDMA)/SSMA (DS and SFH) systems are compared with those of wide-band SSMA systems. For high data rate communications, wide-band DS-SSMA systems have larger capacities than hybrid FDMA/DS-SSMA systems. For low data rate communications, a capacity comparison between wide-band DS-SSMA and hybrid FDMA/DS-SSMA systems depends on fading statistics. Hybrid FDMA/SFH-SSMA systems have larger capacities than wide-band DS-SSMA systems, FFH-SSMA systems could not provide satisfactory performance due to correlation among hopping bands     

DS－SFH扩频多址系统在瑞利衰落信道中多径分集的性能研究

本文讨论了混合ＤＳ－ＳＦＨ扩频多址ＳＳＭＡ通信系统在瑞利衰落信道中多径分集接收的性能。基于多径干扰、多址干扰和信道噪声之和为一个高斯随机变量的分析，推导了在等增益组合（ＥＧＣ）和选择最大（ＳＭ）多径分集接收算法下，扩频系统的平均差错概率。理论分析和数值模拟指出：扩频多径分集接收可以明显地改善ＤＳ－ＳＦＨＳＳＭＡ系统的性能，在提高系统性能方面，等增益组合算法优于选择最大分集算法。     

Cellular Efficiency with Slow Frequency Hopping: Analysis of the Digital SFH900 Mobile System

The new digital cellular SFH900 mobile system, based on "mixed" slow frequency hopping (SFH) combined with time division, is described in detail. The system includes Viterbi quasi-coherent demodulation of GMSK for which performance measurements in multipath conditions are presented. A concatenated coding scheme that takes full benefit of built-in frequency diversity and interference diversity is introduced. A model for SFH cellular performance evaluation is presented and the quality-versus-capacity tradeoff for SFH900 is given for various frequency reuse patterns. With advanced 16 kbit/s speech coding techniques, and including a 25 percent overhead for management and signaling, the spectrum efficiency of a many-celled SFH900 network is around 3.5 users/cell/MHz, a significant increase in comparison to conventional analog systems. SFH provides intrinsic adaptability to varying traffic conditions and enhanced flexibility for multiservice operation. The SFH900 principles, which have been recently validated through field tests, are very promising for second generation cellular systems.     

混合DS－SFH扩频多址室内无线数字通信性能分析

本文讨论了ＤＳ－ＳＦＨ扩频多址室内无线通信系统在瑞利多径衰落信道中的平均差错概率和多址容量。基于多径干扰、多址干扰和信道噪声的机理分析，推导了计算平均差错概率的有效近似公式。理论分析和数值模拟指出：混合系统的ＤＳ部分具有良好的多址容量并提供抗来自指定用户的多径干扰能力，混合系统的ＦＨ部分则具有抗来自非指定用户的多址和多径干扰能力。     

A comparison of slow-frequency-hop and direct-sequencespread-spectrum communications over frequency-selective fading channels

Spread-spectrum modulation can provide protection from the selective fading that is typically encountered in mobile radio networks. Because the methods of combating frequency-selective fading are quite different for slow-frequency-hop (SFH) and direct-sequence (DS) spread spectrum systems, these two types of modulation perform very differently. The purpose of this paper is to compare the performance of SFH and DS systems under identical conditions for several models of the wide-band fading channel. Each system has the same bandwidth, transmits over the same frequency-selective Gaussian wide-sense-stationary uncorrelated-scattering channel, and uses error-correction coding to combat thermal noise and fading. The probability of bit error at the output of the decoder is determined for each system by a combination of analysis and simulation. Results are presented for systems with a single transmitter-receiver pair and for networks with multiple simultaneous transmissions (i.e., multiple-access communications). The multiple-access network is distributed, so that control of power by a central terminal, such as a base station, is not possible. The results illustrate the tradeoffs in performance between SFW and DS spread-spectrum systems as a function of the parameters of the signals and the channel model. The performance of the SFH system is shown to be less sensitive to the exact characterization of the channel delay spectrum than the DS system. For most of the channels considered in this paper, SFH spread spectrum gives better performance than DS spread spectrum     

CIRC编码在DS-SFH系统中的应用及性能分析

在Nakagami衰落信道的基础上,对采用DPSK调制方式的混合DS-SFH扩频通信系统进行了差错概率计算,分析了衰落参数对系统性能的影响。为了提高系统在低信噪比下的性能,又采用CIRC码对系统进行编码处理。理论和数值分析显示,CIRC编码作为一种能够有效对付突发差错的编码方式,可以有效地提高系统的抗多径干扰和多址干扰能力。     

Spectral efficiency for a hybrid DS/FH code-divisionmultiple-access system in cellular mobile radio

The spectral efficiency of a hybrid cellular direct-sequence/frequency hopping code-division muItiple-access (DS/FH-CDMA) system operating in a Rayleigh-fading environment is examined. In this work, spectral efficiency is evaluated in terms of the theoretically achievable channel capacity (in the Shannon sense) per user, on the condition that this is estimated in an average sense. The analysis covers the downlink assuming a static model of operation and a direct-sequence/slow-frequency hopping (DS/SFH) as well as a direct-sequence/fast-frequency hopping (DS/FFH) scheme. As it is shown, the spectral efficiency of cellular DS/FFH-CDMA operating in a Rayleigh-fading environment is greater than that of broad-band DS- and DS/SFH-CDMA systems operating under normalized conditions. This is justified by the combination of path-diversity reception as achieved by conventional coherent RAKE receivers and the frequency diversity that is inherently present in FFH transmission     

Optimal SIR for an hybrid cellular DS/SFH CDMA system

A hybrid direct‐sequence/slow frequency hopping code‐division multiple‐access (DS/SFH CDMA) system operating in a Rayleigh fading environment is described and its spectral efficiency is estimated in terms of the theoretically achievable average channel capacity (in the sense of information theory) per user. The analysis covers the operation over a broadcast cellular time‐varying link and leads to a simple novel closed‐form expression for the optimal average spread signal‐to‐interference power ratio (SIR) received by each user based on the maximization of the achieved spectral efficiency. Copyright © 2007 John Wiley & Sons, Ltd.     

混合DS／SFH CDMA扩频通信系统中的自适应跳频

文章基于进一步提高跳扩频通信系统的抗干扰性能，提出了在混合直接序列扩频（DS／SFHCDMA）通信系统中实现自适应跳频（AFH）方式，给出了基于优化考虑的自适应跳频地址编码方法，在给出信道仿真参数的前提下，对自适应跳频系统的误码性能进行了分析。结果表明自适应方式优于传统方式。     

On the spectral efficiency of wideband CDMA systems

The reverse-link spectral efficiency is evaluated for a direct-sequence (DS) code division multiple access (CDMA) cellular communication system that employs rapid closed-loop power control and coding with interleaving on channels that exhibit doubly selective Rician fading. The focus of the paper is the effect of the chip rate of the DS spread-spectrum signal on the spectral efficiency of the system. Performance is considered for systems with different numbers of demodulators in the RAKE receiver and for systems both with and without antenna diversity. Channels with different delay spectra and Doppler spreads are used to examine the performance of the system in various operating conditions. The implications of the results for the design of wideband CDMA are discussed     

Time division multiple access methods for wireless personalcommunications

Time division multiple access (TDMA) is a classic approach to multiple access in digital cellular wireless communications systems. The authors summarize a number of frequency and time slot allocation techniques for enhancing the capacity and flexibility of TDMA-based systems. They also describe how the problems of fading, delay spread, time variability and interference affect TDMA systems, and how they may he countered and even exploited by appropriate techniques of detection, diversity, coding, adaptive equalization and slow frequency hopping (FH). It is worth emphasizing that the use of one of these techniques, slow random FH, results in a system that is in effect a hybrid of TDMA and code division multiple access (CDMA)     

Packet CDMA versus dynamic TDMA for multiple access in anintegrated voice/data PCN

A comparative evaluation of dynamic time-division multiple access (TDMA) and spread-spectrum packet code-division multiple access (CDMA) approaches to multiple access in an integrated voice/data personal communications network (PCN) environment are presented. After briefly outlining a cellular packet-switching architecture for voice/data PCN systems, dynamic TDMA and packet CDMA protocols appropriate for such traffic scenarios are described. Simulation-based network models which have been developed for performance evaluation of these competing access techniques are then outlined. These models are exercised with example integrated voice/data traffic models to obtain comparative system performance measures such as channel utilization, voice blocking probability, and data delay. Operating points based on typical performance constraints such as voice blocking probability 0.01 (for TDMA), voice packet loss rate 10^-3 (for CDMA), and data delay 250 ms are obtained, and results are presented     

Hybrid slow frequency hopping/ direct sequence spread spectrum indoor communication systems with QPSK modulation

This paper analyses the performance of a spread-spectrum multiple access system based on hybrid direct sequence/slow frequency hopping techniques with QPSK modulation. The performance is analyzed considering multipath and multiple access interferences and an indoor channel having Rician distributed path gains. The system performance is investigated for 2 diversity techniques and compared, for given delay spread, bandwidth and bit rate, with the performance provided by bpsk modulation. It is shown that the larger symbol duration of QPSK is favorable to combat the effect of multipath propagation.     

Multicarrier DS/SFH-CDMA systems

Multicarrier direct-sequence/slow-frequency-hopping (MC DS/SFH) code-division multiple-access (CDMA) systems are proposed, in which multiple carriers are modulated by the same DS waveform and hopped in frequency according to a random hopping pattern. The receiver dehops the received signal with the same pattern, provides RAKE receivers for each carrier, and combines the outputs with a maximal ratio combiner (MRC). The performance of the proposed system is investigated over a frequency-selective Rayleigh-fading channel and compared to that of the MC DS-CDMA systems. It is shown that for the same diversity order, the MC DS/SFH-CDMA systems are superior in reducing multiple-access interference (MAI) while preserving the good capability of narrowband interference suppression, when the system parameters are selected properly.     

Space and network diversity combination for masked node collision resolution in wireless ad hoc network

In wireless ad hoc networks, the traditional carrier sensing multiple access/collision avoidance protocol cannot solve the masked node problem, which affects the network performance greatly. Our proposed collision separation technique overcomes the shortcoming of the IEEE 802.11 request-to-send-clear-to-send handshake by combining the space diversity provided by the antenna array and network diversity provided by the medium access control layer. In this work, the colliding packets caused by masked nodes are not discarded but stored and combined with the selected retransmission packets to separate the data from different nodes. The steady states of the nodes in the network are analyzed via a Markov chain model. The network throughput and delay performance are also investigated. Compared to network assisted diversity multiple access, our proposed method can provide significantly higher throughput and lower delay     

Performance of a cellular hybrid C/TDMA mobile radio systemapplying joint detection and coherent receiver antenna diversity

For future mobile radio systems, an appropriately chosen multiple access technique is a critical issue. Multiple access techniques presently under discussion are code division multiple access (CDMA), time division multiple access (TDMA), and hybrids of both. In the paper, a hybrid C/TDMA system using joint detection (JD-C/TDMA) with coherent receiver antenna diversity (CRAD) at the base station (BS) receiver is proposed. Some attractive features of the JD-C/TDMA system are the possibility to flexibly offer voice and data services with different bit rates, soft capacity, inherent frequency and interferer diversity, and high system capacity due to JD. Furthermore, due to JD, a cluster size equal to 1 can be realized without needing soft handover. The single cell E_b/N₀ performance and the interference situation in a cellular environment of the uplink of a JD-C/TDMA mobile radio system with CRAD is investigated in detail. It is shown that the cellular spectrum efficiency is remarkably high, taking values up to 0.2 bit/s/Hz/BS in the uplink, depending on the actual transmission conditions     

Transmitter-based processing for down-link DS/CDMA systems with multiple transmit antennas

In cellular wireless communication systems, there have been various receiver-based techniques for performance improvement. However, it may be desirable to use transmitter- based techniques to improve the down-link capacity, since the implementation complexity is less critical at a base station (BS) than at a mobile station (MS). This paper presents a transmitter- based processing for the down-link direct-sequence code-division multiple-access (DS/CDMA) systems with multiple transmit antennas. We propose a combined pre-rake/pre-decorrelating approach. This approach combines the advantage of pre-rake scheme, to achieve diversity gain and average received signal-to- noise ratio (SNR) gain, with that of pre-decorrelating scheme, to suppress multiple access interference (MAI) and multipath interference (MPI). Furthermore, to make the total transmit power the same as that without pre-rake/pre-decorrelating processing, two power normalization methods are presented. Simulation results show that the proposed schemes significantly outperform the conventional transmitter-based techniques. The effects of the number of users and the block size on the bit error rate (BER) performance are also investigated.     

Adaptive Retransmission Diversity with Packet Combining for Slotted DS/CDMA Packet Radio Networks

A time diversity automatic repeat-request (ARQ) scheme is investigated for slotted random access direct-sequence code-division multiaccess (DS/CDMA ALOHA) wireless packet radio networks on multipath Rayleigh fading channels. The receiver retains and processes all the retransmissions of a single data block (packet) using predetection diversity combining, instead of discarding those which are detected in error. This effectively improves the system throughput and delay characteristics especially at small values of signal-to-noise ratio (SNR) per bit. A simple and practical selection combining rule is proposed, which lends itself to a low-complexity receiver structure and specifically suitable for high data rate transmissions. Owing to the stochastic nature of the multiple access interference, the new maximum output selection diversity (MO/SD) system yields superior performance in comparison to the traditional maximum SNR selection diversity (SNR/SD) model. The bit error rate performance, throughput and the average number of transmissions required to transmit a packet successfully with and without forward error correction (FEC) are evaluated. Numerical results reveal that the proposed adaptive retransmission diversity with packet combining provides a considerable advantage over the conventional slotted DS/CDMA ALOHA without incurring a substantial penalty in terms of cost or complexity.     

An analysis of the performance of ARQ schemes for integrated traffic satellite-switched SFH and DS CDMA networks

The delay and throughput performance of satellite-switched Slow Frequency Hopping CDMA network for simultaneous voice and data transmission is analyzed and compared to that of a DS-CDMA system. Two ARQ schemes are suggested for data while Forward Error Correction using the same encoder is used for voice packets. The queueing analysis assumes priority for voice and two models for voice traffic are used (Markovian and IPP). The probability of successful packet transmission is derived for all systems as a function of traffic load allowing us to evaluate the systems using delay, throughput, and voice packet loss as figures of merit. Numerical results show that while voice delay is minimal DS CDMA is much more effective then SFH CDMA in all cases. One interesting result is that SFH systems perform better with S/W schemes and achieve a higher maximum throughput. It is also observed that the IPP and Markovian models gave similar results.This work was supported by an NSERC CRD (Collaborative Industrial Research and Development grant,) with Spar Aerospace, Quebec, Canada