Delay analysis of continuous bit rate traffic over an ATM network

A packet multiplexer is modeled for continuous bit rate (CBR) traffic in an asynchronous transfer mode (ATM) network as an nD/D/1 queue. The efficiencies of various algorithms for finding the delay distribution are compared. In particular, a new algorithm is proposed whose time complexity is O(n²), where n is the number of voice sources being multiplexed. The use of the central limit theorem can reduce the time complexity to O(n) for large n . An asymptotic formula is found whose time complexity is independent of n and it works well (for practical purposes) over a wide range of parameter values. The authors examine and comment on the use of the M/D/1 results as an approximation. In addition to comparing the performances of these algorithms, they show that the buffer requirements for such a queue are significantly less than the theoretical maximum (even when the requirement on the call disruption probability is very low). This result has important implications in the design of buffer size. The buffer requirement is relatively insensitive to the design criterion (call disruption probability)     

Exact bit error rate calculations for synchronous MC-CDMA over aRayleigh fading channel

The bit error rate of a synchronous multicarrier code-division multiple-access system operating in a Rayleigh fading channel is calculated based on a moment generating function method, without any assumption on the distribution of multiple access interference. Two closed-form BER expressions are derived. Moreover, the BER can be accurately evaluated by using a Gauss-Chebyshev quadrature rule based numerical approach     

Two-way TCP traffic over rate controlled channels: effects andanalysis

We study the performance of bidirectional TCP/IP connections over a network that uses rate-based flow and congestion control. An example of such a network is an asynchronous transfer mode (ATM) network using the available bit rate (ABR) service. The sharing of a common buffer by TCP packets and acknowledgment (acks) has been known to result in an effect called ack compression, where acks of a connection arrive at the source bunched together, resulting in unfairness and degraded throughput. It has been the expectation that maintaining a smooth flow of data using rate-based flow control would mitigate, if not eliminate, the various forms of burstiness experienced with the TCP window flow control. However, we show that the problem of TCP ack compression appears even while operating over a rate-controlled channel. The degradation in throughput due to bidirectional traffic can be significant. For example, even in the simple case of symmetrical connections with adequate window sizes, the throughput of each connection is only 66.67% of that under one-way traffic. By analyzing the periodic bursty behavior of the source IP queue, we derive estimates for the maximum queue size and arrive at a simple predictor for the degraded throughput, for relatively general situations. We validate our analysis using simulation on an ATM network using the explicit rate option of the ABR service. The analysis predicts the behavior of the queue and the throughput degradation in simple configurations and in more general situations     

A multiscale model for MPEG-4 varied bit rate video traffic

This paper studies modeling approach of MPEG-4 VBR video traffic based on multifractal multiplicative model. Multiscale analysis reveals that the multiplier distribution is different in style on different time scales. Based on statistical characteristics of the multipliers, a composite modeling approach is proposed: Gaussian distribution is used to fit multiplier distribution at large time scales, a new statistical distribution-Symmetric Pareto distribution to fit multiplier distribution at small time scales and a linear model to model frame traffic. Simulations are performed to validate the good effect of this approach.     

Spreading sequences for asynchronous MC-CDMA revisited: accurate bit error rate analysis

The bit error rate (BER) of an asynchronous multicarrier code-division multiple-access system in an additive white Gaussian noise channel is evaluated using Monte Carlo integration and moment-generating function methods. The BER performance for different families of spreading sequences is investigated. Numerical results show that the approach of a recently published paper (see Popovic, B.M., IEEE Trans. Common., vol.47, p.918-26, 1999) cannot give an accurate BER because the interference from other subcarriers has been omitted. Some new findings about the performance of different sequences are also presented.     

A complete error model for free space polarimetric measurements

The authors present a complete 12-term error model for the systematic errors in polarimetric radar and antenna free space measurements for test range and laboratory use. Errors are induced by the frequency response, the channel imbalance, the coupling between the transmit channels, the coupling between the receive channels, the coupling from transmit to receive and by the residual reflections of the environment. The errors are contained in three 2×2 matrices, the isolation matrix, the transmit matrix and the receive matrix. A full polarimetric calibration with the empty room, a sphere, a vertical dihedral corner and a 45° dihedral corner is proposed. The physical understanding is supported by a cubic signal graph for the error terms     

Investigations on bit error performance for video over DAB

The digital audio broadcasting (DAB) system which was originally designed for high quality audio transmission to mobile receivers is investigated for transmission of compressed digital video and multimedia signals. The bit error performance is considered using various levels of error protection provided by the DAB system. As a result, a net bit rate of about 1.5 Mbit/s can be achieved. With additional error correction coding, a bit error ratio (BER) of less than 10^-10 can be realized. This is the requirement for compressed video signals. The SNR per bit is below 16 dB. The results are demonstrated and compared using computer simulations of the complete system     

Trial results of novel bit error rate monitor scheme over skywave HF link

Details are given of an error monitoring technique applicable to any digital communication system. An example application of the technique to a live skywave HF link using parallel-tone modems is described. The performance of the scheme is presented and discussed for this channel.<>     

Dynamics of TCP traffic over ATM networks

Investigates the performance of transport control protocol (TCP) connections over ATM networks without ATM-level congestion control and compares it to the performance of TCP over packet-based networks. For simulations of congested networks, the effective throughput of TCP over ATM can be quite low when cells are dropped at the congested ATM switch. The low throughput is due to wasted bandwidth as the congested link transmits cells from “corrupted” packets, i.e., packets in which at least one cell is dropped by the switch. The authors investigate two packet-discard strategies that alleviate the effects of fragmentation. Partial packet discard, in which remaining cells are discarded after one cell has been dropped from a packet, somewhat improves throughput. They introduce early packet discard, a strategy in which the switch drops whole packets prior to buffer overflow. This mechanism prevents fragmentation and restores throughput to maximal levels     

Approximate average bit error probability for DQPSK over fading channels

The bit error probability (BEP) of DQPSK with Gray coding over an AWGN channel can be computed simply, although it is hard to integrate and derive the average BEP for fading channels. Presented are novel approximations of the average BEP of DQPSK with Gray coding over fading channels. Numerical results show that the novel formulations are quite accurate.     

TCP over wireless with link level error control: analysis anddesign methodology

This paper considers the problem of supporting TCP, the Internet data transport protocol, over a lossy wireless link whose quality varies over time. In order to prevent throughput degradation, it is necessary to “hide” the losses and the time variations of the wireless link from TCP. A number of solutions to this problem have been proposed in previous studies, but their performance was studied on a purely experimental basis. This paper presents an approximate analysis, validated by computer simulations, for TCP performance over wireless links. The analysis provides the basis for a systematic approach to supporting TCP over wireless links. The specific case of a Rayleigh-faded wireless link and automatic repeat request-based link-layer recovery is considered for the purpose of illustration. The numerical results presented for this case show that a simple solution, that of using an appropriately designed link-layer error-recovery scheme, prevents excessive deterioration of TCP throughput on wireless links     

一种基于FPGA的高速误码测试仪的设计

误码测试仪是检测通信系统可靠性的重要设备。传统的误码测试仪基于CPLD和CPU协同工作,不仅结构复杂,价格昂贵,而且不方便携带。基于FPGA的高速误码测试仪,采用FPGA来完成控制和测试模块的一体化设计,提高了系统功能扩展性和系统的集成度,使得各个功能模块在不改动硬件电路的情况下可以相应变化。在发送端发送m序列作为测试数据,其测试速率最高可达到155 Mb/s。由于将物理层上的各协议层的功能集中到FPGA内部实现,减少了硬件和软件的设计复杂度,并且缩短了系统的开发的周期,具有可升级的特点。     

Cell loss analysis of broadband switching systems carrying variable bit rate video traffic

Many different traffic models have been proposed for the data generated by variable bit rate (VBR) video coders. It has been observed in simulation studies that use of different coders results in a wide variation in predicted cell loss statistics. In this paper, several models are studied, and their predictions of network performance compared to those obtained using real data. A quasi-stationary analysis technique is used to obtain analytic approximations for some of these cell loss statistics.     

Online traffic smoothing for delivery of variable bit rate media streams

Traffic smoothing for delivery of online variable bit rate (VBR) media streams is one of the most important problems in designingmultimedia systems. Given an available client buffer, a window size, and a window-sliding size, previous window-based online smoothing methods have tried to reduce the peak bandwidth allocated in each window. However, as bandwidths allocated in different windows are minimized independently, these methods require a large peak bandwidth for transmitting an entire stream. In this paper, a new window-based method is proposed. It introduces two new ideas, the dynamic windowsliding size and the aggressive workahead, for delivery of online VBR media streams. Our aggressive and dynamic window sliding (ADWS) method can automatically decide on the suitable window-sliding sizes for different windows. Thus, the allocated peak bandwidth can be further reduced. By examining various media streams, ADWS is shown to be effective and efficient. Considering the online transmission of the movieStar Wars with a 90-kB client buffer, ADWS yields 13% less in peak bandwidth, compared with the bestknown window-based online smoothing algorthm SLWIN(1). Its computation cost (the window-sliding number) is 75% of that required by SLWIN(1).This work was partially supported by NSC, Taiwan, under grants. NSC88-2213-E-001-011, NSC88-2213-E-001-012, and NSC88-2213-E-001-025. A primitive version of this work appeared in IEEE INFOCOM'99 [7].     

半导体激光器辐射损伤对空间光通信误码率的影响

为了提高空间光通信系统的抗辐射性能,研究了半导体激光器的辐射损伤效应对空间光通信系统误码率的影响.在此基础上,进一步推导了半导体激光器辐射损伤对空间光通信系统误码率的影响模型.通过仿真研究,其结果表明:辐射对半导体激光器的输出光功率线性下降.误码率在1000Gy之前可以忽略影响,辐射至3000Gy之后对误码率的影响迅速...     

基于误码率分析的通信抗干扰能力预测研究

通信系统抗干扰能力预测是进行作战指挥部署的重要前提之一,其难点在于如何量化抗干扰能力的强弱并确定通信压制区域。文中利用MATLAB建立了基于BPSK调制方式的跳频与直扩通信系统仿真模型,并考虑其受宽带与部分频带干扰的情况,首先利用接收机输出端误码率求得各系统信噪比门限,其次依据超短波信号在接收机内部的处理过程进行适当的增益补偿,提出了一种对通信干扰方程进行修正的方法,即用信噪比门限等效替代压制系数,达到计算压制范围并量化预测抗干扰能力的目的。     

最低误码率非线性均衡器的快速自适应学习算法

针对最低误码率非线性均衡器的参数在线自适应学习问题,本文提出基于拟牛顿方法的快速自适应学习算法。采用Parzen窗函数方法估计误码率,通过设定切换条件,使参数学习在滑窗随机梯度法与滑窗拟牛顿法之间切换。这既增加了新算法的数值稳定性,又可提高收敛速度。通过对拟牛顿方法进行修改,还使新算法既可以在线自适应学习,也可用于高维参数的快速学习。仿真采用最低误码率非线性均衡器对通信系统进行干扰抑制和信道均衡,结果表明了新算法的高效性。     

A general analysis of bit error probability for reference-basedBPSK mobile data transmission

Unified analysis of the performance of binary phase shift keying (BPSK) under static and mobile operating conditions is presented for the case in which a separate reference tone is used for channel sounding and subsequent `coherent' data detection. It is shown that under both Rician and Rayleigh fading conditions, the use of a reference can eliminate the irreducible error rate phenomenon, with minimal sacrifice in bit error rate performance over an ideal BPSK system     

TH-CDMA/PPM的比特误码率分析与研究

对采用二元脉冲位置调制的超宽带跳时多路无线电网络的误码率进行了分析。在矩形脉冲的前提下,可以得到关于TH-CDMA/PPM信号在高斯白噪声信道存在k个干扰时错误比特的概率。通过概率的表达式来评定类高斯噪声的准确性,从而可以对超宽带脉冲无线电网络的类高斯噪声性能进行分析。通过大量的仿真结果可以看到,由类高斯噪声产生的比特误码率要低于高斯噪声产生的。对于每个信息比特有较少的脉冲的系统来说,类高斯噪声所产生的错误就变得非常重要。