A performance review of out-of-frame detection schemes for DS1signals

A basic framework is given for performance comparisons of several frame detection schemes used to identify individual channels within a DS1 digital transmission system in either the superframe (SF) or extended superframe (ESF) format. Key criteria include mean misframe times, out-of-frame detection times, reframe times, tolerance to error bursts and application considerations. Through the use of Markov chain models, analytical solutions for the mean misframe and out-of-frame detection times are derived in terms of the bit error ratio and frame period. Performance comparisons of several frame detection schemes in various error conditions are made     

Research on uplink coordinated transmission schemes in LTE-advanced systems

The investigation of inter-cell interference mitigation techniques is a key area in wireless communications.Coordinated multiple points(CoMP) transmission/reception is a candidate technique for interference cancellation in 3GPP LTE-Advanced system.However,the coordination scheme in CoMP remains a key research problem to be solved,which will have a strong influence on the performance of CoMP.In this paper,a novel coordinated transmission scheme is proposed for the uplink LTE-Advanced system.In our scheme,several base transceiver stations(BTS) and users are selected as coordination partners which form a CoMP cluster.Joint processing is used at the receiver to mitigate interference.From the perspective of coordinated partner selection,our scheme can be divided into static and dynamic coordination which are both considered to fully exploit the throughput gain of CoMP.The proposed schemes are evaluated by system level simulation and compared with the conventional LTE system based upon single cell processing.Our simulation results demonstrate that the proposed schemes attain superior performance as opposed to the conventional system in terms of cell average and cell edge throughput.     

ARQ schemes for data transmission in mobile radio systems

An important problem in land mobile radio communications is how to provide reliable data communications to the largest number of users. To explore this problem, several existing ARQ protocols are examined which have application to the land mobile radio channel, as well as some new protocol combinations. All protocols are analyzed for several key system performance measures which are verified by experimental means for static as well as fading channels. Finally, a conclusion is reached regarding a new protocol combination which is found to offer significant advantages over all other protocols explored.     

Joint detection and combining schemes in MIMO-HARQ systems

This article mainly investigates the combining schemes for hybrid automatic retransmission request (HARQ) protocols in multiple-input multiple-output (MIMO) wireless communication systems. A novel scheme, which joins MIMO detection and HARQ combining, called mid-combining, is presented in this article. Based on the position of HARQ combining, we classify the HARQ combining schemes into three types, named pre-combining, mid-combining, and post-combining. The simulation results show that mid- combining can increase the system throughput for all SNRs.     

色散补偿光纤传输系统的最佳补偿方案

研究了采用色散补偿光纤传输系统的最佳补偿方案,经研究发现,混合补偿方案可以大大减小光纤非线性效应的影响,提高系统传输距离.此外,还对非归零码(NRZ)和归零码(RZ)的传输性能进行了比较.     

Antenna-diversity-assisted genetic-algorithm-based multiuser detection schemes for synchronous CDMA systems

A spatial diversity reception assisted multiuser code-division multiple-access detector based on genetic algorithms (GAs) is proposed. Two different GA-based individual-selection strategies are considered. In our first approach, the so-called individuals of the GA are selected for further exploitation, based purely on the sum of their corresponding figures of merit evaluated for the individual antennas. According to our second strategy, the GA's individuals are selected based on the concept of the so-called Pareto optimality, which uses the information from the individual antennas independently. Computer simulations showed that the GAs employing the latter strategy achieve a lower bit-error rate as compared to the former strategy. For a 15-user GA-assisted system employing a spreading factor of 31, a complexity reduction factor of 81 was achieved at a performance identical to that of the optimum multiuser detector using a full search.     

Enhanced detection with new ordering schemes for V-BLAST systems

This letter proposes a new optimal ordering method which minimizes error propagation in the vertical Bell-lab Layered Space-Time (V-BLAST) by exploiting the whole filter output. A suboptimal ordering metric is also proposed which requires much reduced complexity compared to the optimal ordering metric. We also derive a simplified version of the suboptimal ordering metric which achieves a significant performance gain over the conventional ordering with minor additional complexity.     

Near maximum likelihood detection schemes for wireless MIMO systems

In this letter, we propose two near maximum-likelihood detection (MLD) schemes for multiple input-multiple output antenna systems over flat fading channels. The schemes are based on utilizing an initial estimate of the received symbol and improving it by selectively updating various bits within the symbol. Simulation results show that the performance of the proposed schemes can approach that of MLD but with a significant reduction in complexity.     

Statistical property of intra-channel four-wave mixing in RZ-DPSK transmission systems

The statistical property of intra-channel four-wave-mixing (IFWM) is studied numerically for return-to-zero differential-phase-shift keying transmission. The distributions of IFWM-induced pulse power and phase fluctuations depend on the relative strength of pulse broadening and nonlinear interactions, which can be characterized with a dimensionless parameter. We thus offer a general criterion to understand the stochastic nature of IFWM effect.     

Capacity of multiuser diversity systems with adaptive transmission and different MIMO schemes

In this paper, we present a comprehensive capacity analysis of the downlink of multiuser diversity (MD) systems with adaptive transmission over Rayleigh fading channels. First, the exact capacity of the single‐input single‐output (SISO) systems with MD and adaptive transmission technique is derived. The optimal power allocation scheme for such a system is shown to be a water‐filling algorithm. Next, we derive the exact closed‐form capacity expressions for different multiple‐input multiple‐output (MIMO) schemes, including the selective combining (SC), maximum ratio combining (MRC) and space‐time block codes (STBC). In order to avoid the cumbersome numerical root finding techniques in solving the optimal cutoff SNR level below which the channel is not used, we also provide the approximate expressions for the cutoff level. For the MD MIMO systems, it is observed that the optimal power allocation strategy is to focus transmit power on a single transmit antenna (e.g. Tx‐MRC/Rx‐MRC scheme) or selecting the best transmit antennas (e.g. Tx‐SC/Rx‐MRC scheme). Copyright © 2007 John Wiley & Sons, Ltd.     

Congestion control schemes for reverse link data transmission in multimedia CDMA systems

We investigate the congestion control schemes for reverse link in code division multiple access multimedia systems. We propose four schemes according to the control bit setting methods at base and the rate decision schemes in mobiles. With the proposed schemes, all mobiles control their transmission power and rate simultaneously. As the aggregate effect, the cell-wide congestion control is accomplished. The performance of systems with the proposed schemes are evaluated using computer simulation and compared with each other. Under a congested situation, the proposed schemes guarantee the priority of real-time traffic over non-real-time traffic and prevent an excessively high error rate for real-time services. We describe and evaluate the proposed schemes under the system model assumption based on 1xEV-DO and cdma2000. However, the proposed schemes can be also applied to wide-band code division multiple access systems with minor modification.     

Statistical properties of stimulated Raman crosstalk in WDM systems

The crosstalk variance of stimulated Raman crosstalk in wavelength-division-multiplexing (WDM) systems is derived analytically in a closed-form formula for all systems with different walkoff length. The probability density function (pdf) of stimulated Raman crosstalk is found to be lognormal distribution (Gaussian distribution in decibel scale). Both power penalty and power limit induced by Raman crosstalk are evaluated and can be applied to single- and multispan WDM systems     

Capacity analysis for distributed antenna systems using cooperative transmission schemes in fading channels

Wireless systems equipped with distributed antennas can provide enhanced data throughput as well as improved signal quality when appropriate cooperative transmission schemes among antennas are employed. In this paper, the performance of distributed antenna systems (DAS) under the influence of Rayleigh fading and log-normal shadowing effects is investigated for different cooperation strategies, and corresponding statistical distributions for both the signal-to-interference ratio (SIR) and the capacity are presented. Specifically, the ergodic capacity per remote antenna (RA) is determined when n RAs cooperatively transmit the desired signal to the target receiver, which is compared with the non-cooperative single-antenna transmission (SAT) case. Using the results, a preferable mode of operation for given geographic locations of the receiver is determined. We further propose to perform an adaptive operation between the cooperative and non-cooperative modes under the capacity maximization criteria, and quantify exact amounts of capacity gain over individual transmission modes.     

Minimum mean-squared error decision-feedback equalization fordigital subscriber line transmission with possibly correlated line codes

The author presents a theory on MMSE (minimum mean-squared error) decision-feedback equalization which augments previously published results by allowing both a correlated symbol sequence and a fractionally spaced DFE (decision-feedback equalizer) forward filter. This theory facilitates calculating the potential DSL (digital subscriber line) transmission performance in cases of correlated line codes, especially for situations where one or both of the DFE filters are infinite in length. The situation of an infinite-length DFE is of interest because it provides information on the limit of MMSE equalization and can thus serve as a benchmark against which the performance of a finite-length DFE may be compared. The author also presents a few numerical examples of the performance of MMSE decision-feedback equalization in DSL transmission at ISDN (integrated services digital network) basic access rates with several well-known line codes     

An evaluation of error performance estimation schemes for DS1transmission systems carrying live traffic

Under the memoryless binary symmetric channel assumption, the author evaluates performance estimation schemes for DS1 transmission systems carrying live traffic. Bipolar violations, framing bit errors, and code-detected errors are commonly used to estimate bit error ratios and the respective numbers of errored seconds and severely errored seconds that are fundamental parameters in characterizing the performance of DS1 transmission systems. A basic framework based on the coefficient of variation is proposed to evaluate several estimation schemes. Serious drawbacks of the existing estimation schemes based on the superframe (D4) format are identified. A new method for estimating the number of errored seconds is proposed. A computer simulation shows that this proposed method performs much better than the conventional counting method. The performance of the cyclic redundancy check (CRC) code of the extended superframe (ESF) format is also evaluated through the use of a computer simulation model. The simulation results show that all the errored seconds are detected by the CRC code. This is a welcome feature of the code for real-time performance monitoring. Furthermore, the results suggest a new threshold of 326 CRC errors per second for determining severely errored seconds     

网络编码双向机会协作系统无线传输方案频谱效率比较分析

文章对放大转发双向机会协作通信系统(OR-TW-AFNC)的频谱效率进行了详细地研究,运用适当的数学证明和近似分析获得了OR-TW-AFNC系统两时隙、三时隙和四时隙传输方案平均“和速率”的近似封闭解析解。数值分析结果表明,对于OR-TW-AFNC系统的三种不同传输方案,依不同的信道实现和信噪比范围,这三种系统的频谱效率是不同的;特别是在低信噪比区域,由于三时隙方案有效地利用了直径传播信号,其相应的频谱效率要高于两时隙方案。与此同时,比较分析结果也表明文章所得近似封闭解析解是正确的、可靠的。      

Minimum mean-square error echo cancellation and equalization fordigital subscriber line transmission. I. Theory and computation

An integral part of an ISDN (integrated services digital network) is the provision of full-duplex digital transmission capability over voice-grade metallic subscriber lines with all the associated disturbances from echo, intersymbol interference, and crosstalk, among other things. The author presents a theory for analyzing the optimal performance, in the MMSE (minimum-mean-squared error) sense, of full-duplex transceiver structures incorporating echo cancelers and decision-feedback equalizers. The theory augments previously published results by allowing a colored input signal and a fractionally spaced multitap MMSE forward filter in the decision-feedback equalizer. The properties of and efficient ways of calculating the MMSE solutions for various types of line codes, including the precoded partial-response codes and the block codes, are investigated. The author discusses how the MMSE is related to the ubiquitous SNR (signal-to-noise ratio) measure and the concerns associated with using it to gauge the transmission performance     

空时分组码分块传输系统中的Turbo检测译码

将基于MMSE的Turbo检测译码方案应用于空时分组码分块传输系统。利用信道矩阵的循环特性，Turbo检测算法可以用FFT/IFFT可快速实现，并且矩阵求逆运算量非常低。仿真结果表明，无论是采用Turbo码还是LDPC码，提出的接收机的性能明显优于传统非迭代的接收机，有1∽2dB的增益。