Decoding of the IS-95A uplink code

This letter considers the decoding of the IS-95(A) uplink code in an effort to assess its best achievable performance. Union bounds on the bit error probability for the IS-95(A) indicate that the interleaver affects significantly system performance. Computer simulation results for iterative decoding show that performance gains in the order of 0.6 dB can be obtained when the sequential interleaver is replaced by a pseudorandom interleaver of same size. Improving iterative decoding for this code while maintaining the original sequential interleaver, results only in minor performance gains over published results     

IS-95与CDMA2000技术的发展

目前,CDMA在成为第三代通信系统最主要的无线接入技术后,技术上出现了突习猛进,本文对现有的CDMA技术IS－95与CDMA2000技术作出比较,简要地介绍了CDMA2000的技术特点和其向3G平滑过度的演进过程,进一步探讨IS－95和CDMA2000在今后的发展趋势。     

CDMA IS-95系统的特点及演进策略

结合中国联通现有的CDMA IS－95网络，介绍了CDMA IS－95系统的网络结构，技术特点及可提供的业务，介绍了DCMA技术的是及各阶段的技术特点，CDMA系统的演进策略，介绍了cdma2000 lx系统在我国的实验情况。     

A decision feedback decorrelator for a dual rate synchronous DS/CDMA system

A dual rate synchronous DS/CDMA system provides service to low bit rate and high bit rate users. In a fixed duration interval, a low rate user transmits one bit while a high rate user transmits M bits. The differences in the bit transmission rates result in different processing gains for each class of user. In this paper, we propose a decision feedback decorrelator for the dual rate synchronous DS/CDMA system which uses modified correlators and initiates the bit decision process at the end of the high rate bit interval. Each step of the decision process is executed by utilizing the decisions of all previously decoded users. This dual rate decision feedback receiver (evaluated by simulation) is found to outperform two types of decorrelators for dual rate CDMA systems. It is also observed that as the interferers grow stronger relative to the desired user, the performance of the decision feedback receiver for decoding the desired user approaches the single user bound. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analysis of peak-to-average power ratio for IS-95 and thirdgeneration CDMA forward link waveforms

The peak-to-average power ratio (PAR) of IS-95-type code division multiple-access (CDMA) forward link waveforms is an important parameter which directly relates to system capacity performance. In this paper, analytical expressions are derived for the PAR. The probability that the instantaneous-to-average power ratio (IAR) exceeds a given value is also derived. The analysis is carried out parametric in 1) the number of active traffic channels; 2) the fractions of power allocated to different forward link channels; and 3) other parameters related to the forward link power budget. An analysis is also given for the distribution of the IAR for the forward link modulation planned for third generation (3G) versions of the IS-95 system and a simple modification to present and future IS-95 modulation schemes is shown that reduces the forward link PAR by up to 3 dB     

Simulation of CDMA system performance with feedback power control

The authors present a summary of the results of a study on CDMA feedback power control in multipath fading radio channels. The signal and interference statistics after power control are presented for a simulated radio system which includes multiple base stations. It is shown that often used analyses based on perfect average power control lead to optimistic capacity results because interference is underestimated by 1-2 dB.<>     

Performance Improvement of IS-95 CDMA Uplink Using Decision Feedback and Sub-Optimal Viterbi Decoding

This paper presents a methodology designed to improve the effectiveness of a non-iterative decision feedback (DF) receiver/decoder for IS-95 Code Division Multiple Access (CDMA) uplink in additive white Gaussian noise (AWGN) and Rayleigh fading. The effectiveness of the DF receiver/decoder is linked to the interleaver specification and the decoding delay of the convolutional decoder. Using sub-optimal convolutional decoding the average decoding delay is reduced resulting in more effective decision feedback decoding (DFD). Simulation results of average decoding delay, bit error rate (BER) and frame error rate (FER) are presented for coherent and noncoherent detection of unfaded single-path and Rayleigh fading multipath signals. Instead of the usual performance degradation these results show that the DF receiver/decoder benefits from some forms of sub-optimal Viterbi decoding. The additional performance gain can further improve the quality of service and/or capacity of a cellular IS-95 system.     

Behavior and performance of power controlled IS-95 reverse-linkunder soft handoff

The power controlled IS-95 reverse-link is studied. It is observed that received signals from multiple links under soft handoff and power control are not independent but anticorrelated. The cause of the anticorrelation is investigated through analysis and simulation. It is shown that due to this anticorrelation, the required signal-to-interference ratio (SIR) to achieve a given frame error rate can be ~0.7 dB less than previously estimated based on the independence assumption. Such an observation also leads to a more accurate reverse-link capacity estimate. Finally, it is pointed out that by using a postselection power control configuration an additional capacity increase of up to 11% is obtained     

蜂窝系统覆盖范围与容量的折衷──AMPS系统与IS－95CDMA系统的比较

本文介绍了蜂窝系统的性能，评估了一种无负载蜂窝系统的覆盖范围，并且探讨了负载逐步增加与覆盖范围缩减之间的关系。比较了现有模拟高级移动电话服务（ＡＭＰＳ）系统和新型数字ＩＳ－９５码分多址（ＣＤＭＡ）系统。     

浅述IS-95 CDMA网络的射频规划与设计(下)

介绍了IS－95CDMA的特点和无线网络的设计目标；提出了在规划和设计IS－95CDMA网络时，进行射频设计（如链路设计、基站设置和计算机仿真）的基本理论和方案流程。     

Impact of pointing errors on performance of a ground-to-satellite laser uplink communication system based on M-ary pulse position modulation

The laser beam propagating in the ground-to-satellite laser communication system is affected by intensity scintillation due to atmospheric turbulence and pointing errors due to beam wander. These effects would greatly degrade the system performance. Pulse position modulation (PPM) is a power-efficient modulation scheme to overcome this problem. The effect of pointing errors on the performance of a ground-to-satellite laser uplink communication system with M-ary PPM is analyzed in this paper. The results show that pointing error degrades the system performance, and the effect is more significant for a shorter work wavelength. This work benefits the ground-to-satellite laser uplink communication system with M-ary PPM design.     

浅述IS-95CDMA网络的射频规划与设计(上)

介绍IS－95CDMA的特点和无线网络的设计目标；提出了在规划和设计IS－95CDMA网络时，进行射频设计（如链路设计、基站设置和计算机仿真）的基本理论和方案流程。     

IS-95码分多址系统上行信道接收机捕获单元的设计及FPGA实现

捕获是扩频通信系统的关键技术之一，本文针对ＩＳ－９５码分多址蜂窝通信系统标准，给出了一种适合于上行信道接收机的捕获方案，分析了虚警概率和检测概率，并介绍了该方案的ＦＰ－ＧＡ实现。该方案简单可行，采用并行结构，具有捕获时间短，硬件资源消耗少的特点。     

多载波CDMA系统仿真与性能分析

多载波CDMA是OFDM和CDMA结合的综合技术,兼有OFDM和CDMA的优点,可以在无线信道中传送高速数据流,在频谱效率、频率分集、抗多径干扰等方面都能获得较大好处。首先介绍了OFDM的基本原理,给出MC-CDMA的系统模型,然后通过仿真,比较了OFDM系统和MC-CDMA系统的误码性能。结果表明,MC-CDMA系统性能优于OFDM系统,说明了OFDM和CDMA技术结合的必要性。     

利用公共信道部分反馈信道信息的多用户分集方案及其性能

通过定量分析利用随机波束成型技术的多用户分集系统的吞吐率性能,在此基础上提出利用公共信道部分反馈信道信息的多用户分集方案并分析了它的性能,证明通过设置合理的门限,部分反馈信道度量几乎不降低系统吞吐率,但可以大量节省上行反馈的开销,当采用合适的多址方式,在一定带宽下,系统可以容纳更多的用户。     

时分导频位CDMA系统上行链路阵列接收到部分多址干扰抑制技术

针对时分导频位CDMA系统上行链路,本文提出了导频位辅助LMS－DRMTA算法加上部分多址干扰对消的空时联合干扰抑制接收方案,由于阵列的干扰抑制作用,其输出信号中只剩下少量强的多址干扰信号,部分干扰对消法只对阵列输出中的强多址干扰信号进行干扰估计并抑制,这样一方面大大降低了系统处理的运算量及缓存空间,另一方面又消除了因弱多址干扰估计的不准确而民的系统性能下降,并且相对于自适应全多址干扰对消有更好的系统稳定性,仿真实验表明该方案比全干扰用户对消法具有更好的干扰抑制效果。     

SAC OCDMA系统FOC地址码设计及性能研究

设计了一种新的适合同步光谱幅度编码光码分变址(Spectral-amplitude coding optical code division multiple access,SAC OCDMA)系统的地址码,能够使多址干扰产生的误码率为0.且该地址码的互相关限为1,在给定码重和用户数的情况下能够得到较小码长,便于系统的编解码。利用OptiSys 7.0设计出仿真系统,分析比较用波分复用器和光纤光栅作为编解码器适用的不同系统,在考虑散弹噪声、相位引起的强度噪声(PIIN)和热噪声的情况下,根据该地址码的特点分析整个编解码系统的信噪比和误码率,并与现有的SAC地址码性能进行比较.结果表明:选用该地址码的SAC OCDMA系统得到的眼图更为理想,在系统误码率、编解码实现,及系统性能上都有了很大的提高。     

OCDMA系统中二维变重光正交码的设计及性能分析

以单重合序列作为波长跳频序列,严格变重光正交码作为时间扩频序列,构造一种新的跳频/扩时二维变重光正交码。对所构造二维码的自相关和互相关性能进行了详细地分析,得出互相关均值的表达式,并对该二维地址码的多址干扰误码率进行了仿真比较和理论分析。结果表明,确定严格变重光正交码的参数和单重合序列的长度,增加波长数会增加码字容量并会降低系统的误码率;确定单重合序列的参数和严格变重光正交码的码重和码字个数,增加码长将降低系统的误码率。     

A comparison of system performance using two different chip pulsesin multiple-chip-rate DS/CDMA systems

This paper describes a comparison of system performance using two different chip waveforms of spreading sequences in multiple-chip-rate (MCR) direct-sequence (DS)/code-division multiple-access (CDMA) systems. The chip pulses used in this study are closely related to the characteristics of output filter employed at transmitter. In general, the chip waveform is an important factor to determine the link performance. The raised cosine chip pulse with a roll-off factor of α will be adopted for IMT-2000 systems in order to reduce both the intersymbol effect and the spectral width of the modulated signal. However, due to the complexity of obtaining quantitative results on the performance of MCR-DS/CDMA systems, rectangular chip pulses are mainly utilized in performance analysis. Therefore, it is necessary to investigate the effect of the chip pulses used, i.e., a rectangular and a raised cosine chip pulses on system performance in order to evaluate MCR-DS/CDMA systems accurately. Thus, the effect of the chip pulses used on the performance in MCR-DS/CDMA systems is investigated in terms of the system capacity and blocking probability. It is shown that the system using a raised cosine chip pulse (i.e., RC system) supports at least 80% more capacity and 57% more traffic than that using a rectangular chip pulse (i.e., R system)     

A new family of 2-D optical orthogonal codes and analysis of its performance in optical CDMA access networks

A new family of two-dimensional optical orthogonal code (2-D OOC), one-coincidence frequency hop code (OCFHC)/OOC, which employs OCFHC and OOC as wavelength hopping and time-spreading patterns, respectively, is proposed in this paper. In contrary to previously constructed 2-D OOCs, OCFHC/OOC provides more choices on the number of available wavelengths and its cardinality achieves the upper bound in theory without sacrificing good auto-and-cross correlation properties, i.e., the correlation properties of the code is still ideal. Meanwhile, we utilize a new method, called effective normalized throughput, to compare the performance of diverse codes applicable to optical code division multiple access (OCDMA) systems besides conventional measure bit error rate, and the results indicate that our code performs better than obtained OCDMA codes and is truly applicable to OCDMA networks as multiaccess codes and will greatly facilitate the implementation of OCDMA access networks.