瑞利衰落环境下的P-SCDMA系统捕捉性能分析

介绍了分组交换同步码分多址P-SCDMA(Packet-Switch-SynchronousCodeDivisionMul tipleAccess)系统的导频信号模型及其捕捉结构,在给出捕捉性能的理论结果的基础上对其在瑞利衰落环境下进行分析,给出其仿真结果,并和理论结果进行比较。     

The effects of power control on the optical CDMA random access protocol

In this work, the performance of the hybrid system that combines the distributed power control algorithm (DPCA) with the random access protocol as a novel and simple scheme of achieving a high performance in decentralized optical code division multiple access (OCDMA) networks has been investigated. The multiple access interference (MAI) and the near-far problem effects have been considered. The DPCA’s advantage lies in its characteristics being effectively implemented to each node, since only local parameters are necessary. The principal results have shown that the network throughput and delay are strongly affected by the near-far problem and the DPCA works to solve this problem. Hence, the introduction of a certain level of the power control to the random access temporally coded (1D) or the time-wavelength coded (2D) OCDMA networks has demonstrated profitability of the throughput increase and the delay reduction. As a consequence, the proposed system configuration with the DPCA using a very low number of iterations has resulted in a better throughput and simultaneously in a delay decrease when compared to the system without power control mechanisms.     

An effective medium contention method to improve the performance of IEEE 802.11

In this paper, we propose an effective medium access mechanism to enhance performance of the IEEE 802.11 distributed coordination function (DCF). One of the primary issues of 802.11 is a contention-based medium access control (MAC) mechanism over a limited medium, which is shared by many mobile users. In the original 802.11 DCF, the binary exponential backoff algorithm with specific contention window size is employed to coordinate the competition for shared channel. Instead of binary exponential increase, we adopt linear increase for the contention window that is determined according to the competing number of nodes. We also assume that the access point can broadcast the number of mobile nodes to each station through management frames. An analytical model is developed for the throughput performance of the wireless medium. Using simulation results from the NS2 simulator, we show that our model can accurately predict the system saturation throughput, and can obtain better performance in terms of throughput, fairness, and packet drop.     

RS与卷积级联码在Rice信道中的性能分析

针对Rice信道的特性,采用RS码与卷积码进行级联的纠错编码方案,使用matlab对其在Rice信道上的纠错性能进行仿真分析。结果表明,在Rice信道上,RS和卷积的级联码是一种易于实现且性能优越高效的纠错码,有较高的实用价值。     

The effect of correlated errors on the performance of TCP

Wireless channels are known to introduce correlated bursts of errors at the physical layer. Although these errors affect the performance at all layers of a protocol stack, their precise impact, especially at the higher layers, is not completely understood. We study the effect of error correlations on the throughput of a single transport control protocol (TCP) Tahoe connection. We find that TCP Tahoe performs better in the presence of clustered errors. This suggests that techniques that reduce channel memory may be undesirable     

The effect of bandwidth on the performance of a phase-modulated digital channel

The results presented here show that, if identical Gaussian filters are used in the transmitter and receiver of a 2-level coherent-phase-shift-keyed digital channel, the optimum 3-dB bandwidth of each filter is 1.27 times the bit rate.     

The impact of both a priori information and channel estimation errors on the MAP equalizer performance

To combat the effects of intersymbol interference (ISI), the optimal equalizer to be used is based on maximum a posteriori (MAP) detection. In this paper, we consider the case where the MAP equalizer is fed with a priori information on the transmitted data and propose to study analytically their impact on the MAP equalizer performance. We assume that the channel is not perfectly estimated and show that the use of both the a priori information and the channel estimate is equivalent to a shift in terms of signal-to-noise ratio (SNR) for which we provide an analytical expression. Simulation results show that the analytical expression approximates well the equalizer behavior.     

基于System View的比特误码率测试的仿真

比特误码率(R BE)是衡量一个通信系统优劣的重要指标之一。对如何利用System View仿真软件测试和生成一个通信系统的RBE测试曲线的实例进行了研究，并对此次仿真过程中的关键问题加以论述。     

Allocation of resources for the Gaussian multiple access channel with practical partial cooperation

A Gaussian multiple access channel, with partial cooperation between sources, is considered. We develop an encoding scheme in which the transmission is carried out over three orthogonal time phases. The first two phases are exploited such that the two sources can practically and partially exchange their messages. In particular, each phase is terminated when each user can generate the other user’s codeword. Then, the two users can cooperatively transmit in the third phase. This formulation is used to (i) develop the achievable rate region, and (ii) numerically study the importance of each phase’s length and the allocated power to each user in the three characterized transmission phases.     

前向纠错改善高速光传送网性能分析研究

分析 FEC两种形式在高速光传送网络系统中的应用与对于系统 Q值改善。比较了两种 FEC在系统中的纠错性能。满足不同速率条件高速光传送网络系统的应用需要 ,可以采用相应的 FEC应用形式。     

The effect of sample timing on bit error rate performance in a multipath fading channel

Digital mobile radio often suffers from fatal effects caused by frequency-selective fading, resulting in severe bit error rate (BER) degradation. The feasibility of digital mobile radio largely depends on the multipath-distortion tolerant capability of modulation technique. The BER performance is compared among four digital modulation techniques in a frequency selective fading channel with large multipath delay spread. In particular, taking the timing fluctuation of eye patterns due to delay distortion of a fading channel into account, the effect of sample timing on BER is analyzed. The analyses have revealed that BER performance markedly depends on the choice of sample timing, and also an interesting fact that BPSK is outstanding in the multipath-distortion tolerance, if coupled with adaptive sampling, and its BER curves remain almost the same as that of frequency-flat fading as long as multipath delay difference is less than a bit interval.     

基于S-CDMA的HFC上行信道接入协议性能仿真分析

讨论了基于S－CDMA的HFC网上行信道的高效接入协议－SAMA，提出了双信道接入机制的工作原理，并对系统性能进行了分析与计算机仿真，得到一些有意义的结论。     

Reducing the effect of pointing errors on the performance of an adaptive array

The effect of pointing errors on the performance of the directional constrained adaptive array using symmetric amplitude control can be reduced by correcting the zeros of the array polynomial. The effect can be further reduced by adding an extra pair of zeros to the array polynomial. Examples are given to illustrate the effectiveness of these methods.<>     

The impact of timing errors on the performance of linear DS-CDMAreceivers

In this paper, an asynchronous direct-sequence code-division multiple-access (DS-CDMA) communication system operating over an additive white Gaussian noise (AWGN) channel is considered. In many applications, the near-far problem can be the limiting factor for the capacity of a DS-CDMA system. Several near-far resistant receivers have, therefore, been proposed (e.g., the decorrelating receiver). These receivers assume perfect knowledge of the propagation delay from all users to the receiver. In practice, the delays are estimated and therefore subject to errors. The performance degradation these errors impose on linear detectors, especially the decorrelating detector, is the topic of this paper     

The effects of channel estimation errors on a nonlinear precoder for multiple antenna downlink channels

The effects of channel estimation errors on the performance of a system employing Tomlinson-Harashima precoding and the QR decomposition, operating over multiple antenna frequency-flat fading channels with decentralized receivers, is evaluated. The QR decomposition of the channel matrix is employed to arrive at an equivalent channel where successive interference cancellation at the transmitter can be used to remove the effect of the multiuser interference. However, in the case of imperfect channel estimation, it is not possible to remove the effect of the multiuser interference due to a mismatch between the precoder and the channel. Consequently, it is necessary to include the estimation error in deriving the probability of symbol error. We also provide simulations to corroborate the analytical results.     

DVB-CI通用接口协议的实现研究

介绍了DVB—CI通用接口在CA系统中的作用,对其接口从应用层到底层的协议特性和功能进行了分析和研究,在此基础上对其协议栈进行了软件实现,并给出了协议的实现框架。     

The performance of trellis coded multilevel DPSK on a fading mobilesatellite channel

The performance of a trellis-coded multilevel differential phase-shift keying (DPSK) modulation over a mobile satellite channel characterized by additive white Gaussian noise (AWGN) and slow Rician fading is presented. Both the optimum and Gaussian (suboptimum) decoding metrics are considered, with performance results given only for the latter. Analytical results (upper bounds on bit error rate) are obtained wherever possible and illustrated by several numerical examples. Also given are simulation results which are more indicative of the exact system performance. Comparisons with results previously obtained for coherent detection of the same coded modulations are presented