Multichannel Adaptive Polarization Mode Dispersion Compensation with One Compensator in Dense Wavelength Division Multiplexing Transmission Systems

A simple two-section polarization mode dispersion(PMD) compensator is proposed for multichannel PMD compensation, which can compensate two or even more channels simultaneously. Because of the statistical characteristics and the frequency-dependence of PMD, for current single mode fiber with moderate PMD, the probability that all channels are severely degraded at the same time is extremely small, which makes it possible to compensate a dense wavelength division multiplexing(DWDM) transmission system with moderate PMD using this compensator. It is shown that the outage probability of a 40×43 Gb/s DWDM transmission system using this compensator is decreased significantly from 3.6×10-3 to 3.6×10-5.     

Performance Study of DS—SFH ／SSMA Communication with Multipath Diversity

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Cross-layer in MIMO-OFDM System with Adaptive Modulation and Coding：Design and Analysis

The queuing performance of the cross-layer system with Space-time block code （STBC） over Multi- input-multi-output （MIMO） channel is analyzed. The Adaptive modulation and coding （AMC） in physical layer and finite length of buffer in data-link layer are combined with this model. A simple cross-layer design and the queue state process are proposed based on finite state 1V[arkov channel model~ which is to solve the service process. The proposed cross-layer design is also incorporated with STBC to further improve the system performance. Simulation results illustrate the dependence of system performance on various parameters, and quantify the performance gain due to cross-layer optimization. The adjustment of target packet loss rate of adaptive modulation coding in physi- cal layer can maximize average throughput of the system, meanwhile a significant improvement of the system perfor- mance is brought.     

Multiple Working Points in Multichannel ALOHA with Deadlines

This paper addresses the problem of maximizing the capacity of multichannel slotted ALOHA networks subject to a user-specified deadline and a permissible probability of exceeding it. A previous paper proposed to transmit a non-decreasing number of copies of a message in successive rounds until success or deadline. This yielded a low probability of failure due to the large maximum number of copies per message, with only minimal pollution due to the small mean number of copies. In this paper, we examine another way of implementing variable resource expenditure in different rounds: the channels are partitioned into groups, one for each round, and the channels used in later rounds are operated with lower offered loads, i.e., at different working points. The delay-constrained capacity with these Single-Copy Multiple-Working-Point (SC-MWP) policies is shown to be substantially higher than that with conventional ALOHA, but lower than with the optimal Multicopy Single-Working-Point (MC-SWP) scheme. Combining the two to form an MC-MWP scheme only slightly improves capacity over MC-SWP. The SC-MWP approach can be more attractive when using a single transmitter per station because, unlike with multiple copies, transmission time is not prolonged. Therefore, multiple-working-point policies become more attractive when propagation delay is lower (e.g., low orbit satellites).     

Performance evaluation of random power capture on mobile communications

Power assignment schemes are man‐made methods to enhance the capture effect of radio communications. In a previous study, Wen and Yang investigated the combined capture effect of the fixed power assignment scheme, Rayleigh fading, and near–far effect on the performance of packet radios. The performance analysis was limited to an infinite population environment. This assumption is reasonable for a conventional packet radio system with a vast service area. However, for a cellular mobile system, a finite population model should be used. In this paper, we analyse the combined natural and man‐made capture effect on the performance of a cellular system with finite population in each cell. A random power assignment scheme is adopted to produce the man‐made capture. The system throughput and delay are carried out by a Markov model. Some numerical calculations are used to demonstrate the degree of performance improvement. Copyright © 2001 John Wiley & Sons, Ltd.     

具有多重码的预约Slotted ALOHA协议性能分析

本文对具有多重码的预约Slotted ALOHA协议进行了性能分析。它是基于帧的协议且在一个时隙内有多重码可用来传输分组信息。文中利用离散时间,离散状态和Markov链来分析一个小区上行链路的话音分组吞吐量和数据分组延时性能,并提出了两种改进碰撞解决的方法,得到了较好的系统特性。     

ALOHA脉冲超宽带网络的性能分析

脉冲超宽带(IR-UWB)系统的脉冲宽度极窄,脉冲占空比极低,使用跳时和时间分集传送。该文分析了分布式脉冲超宽带网络中采用ALOHA 方式共享信道时帧传送失败的原因,推导出帧传送失败的概率,通过分析数据帧产生-缓冲-传送的M/G/1 排队过程,得到了网络吞吐、帧传送延时的公式。仿真结果说明,ALOHA脉冲超宽带网络的吞吐,帧传送延时和网络稳定性能远远优于ALOHA 载波调制技术网络。     

扩频ALOHA多址系统吞吐量和时延性能分析

该文深入地研究了扩频ALOHA多址(SAMA)系统的信道接入性能,推导了通用的扩频ALOHA多址系统平均误比特率公式,给出了扩频ALOHA系统吞吐量和时延性能表达式,同时还分析了信道编码对系统性能的改进,给出了相应的仿真和数值结果。结论表明,扩频ALOHA多址系统可以显著提高传统ALOHA系统的吞吐量和时延性能,提高程度随扩频增益增加而增加,引入信道编码可以进一步提高网络性能。     

卫星分组话音／数据扩频时隙ALOHA的性能分析

本文讨论了卫星分组话音／数据综合的扩频时隙ＡＬＯＨＡ的性能，并认为该协议较适合于卫星分组话音／数据综合的通信网中，给出了在扩频多址干扰为改进型高斯分布和某一时隙用户数有限的前提下，系统吞吐量的近似解析表达式和平均时延表达式，这比通常的标准高斯分布和无限用户的假设更精确，模拟说明结果性能是优越的。     

低轨卫星移动通信中扩频S—ALOHA协议吞吐性能分析

由于扩频具有良好的抗多径干扰的能力，因此，在地面移动无线系统中被认为是一种较好的多址方式。但在低轨卫星移动系统中，其传播条件恶劣，各种因素对系统的吞吐性能的影响各不一样，本文分析了多径衰落，扩频增益，同步捕获等因素对吞吐性能的影响，得出了解析式，计算了数值曲线并进行了讨论     

Analysis of Channel-aware Multichannel ALOHA in OFDMA Wireless Networks

Orthogonal frequency division multiple access (OFDMA) systems provide multiple channels that can be accessed via random access schemes. In this paper a channel-aware multichannel random access, based on local channel state information (CSI), was investigated and a multichannel slotted ALOHA scheme was proposed accordingly. Also an analytical investigation of total system throughput and the queue state evolution of generic node in the network were present by assuming the channel has been modeled by means of a two state Markov chain. Through the theoretical model and simulation results, we confi rm that the proposed algorithm has the advantage of high throughput and low access delay.     

Performance of Slotted ALOHA Random Access with Delay Capture and Randomized Time of Arrival

The application of the slotted ALOHA random access technique to a system using a spread spectrum waveform is described and analyzed. The technique takes advantage of the delay capture properties of spread spectrum waveforms and is shown to achieve excellent delay and throughput performance. System stability is maintained even in the face of severe fluctuations in user population or traffic loading such as may occur in a large population of mobile users.     

A Scheme to Increase Throughput in Framed‐ALOHA‐Based RFID Systems with Capture

In this paper, a scheme to increase the throughput of RFID systems is presented, which considers the capture effect in the context of framed ALOHA protocol. Under the capture model in which the probability of one tag is identified successfully depending on the number of tags involved in the collision, two probabilistic methods for estimating the unknown number of tags are proposed. The first method is the maximum likelihood estimation method, and the second method is an approximate algorithm for reducing the computational time. The optimal frame size condition to maximize the system throughput by considering the capture effect is also presented.