A subcarrier multiplexed CDM optical local area network, theory andexperiment

A hybrid scheme is proposed for the purpose of suppressing the effects of external modulation and/or laser nonlinearities in subcarrier multiplexing (SCM) fiber optic communications systems. Hybrid CDMA/FDMA combines two schemes in such a way that the resulting hybrid network is robust against interference and is much more spectrally efficient than a CDMA system. Several possible architectures are introduced for the hybrid CDMA/FDMA subcarrier fiber optic local area network (LAN). The networks utilize CDMA and SCM, an asynchronous multiple access scheme. Direct sequence spread spectrum multiple access (DS/SSMA), the most common form of CDMA is employed. It is shown that by using the code sequence sets for which the shift-and-add property holds, intermodulation products (IMPs) and harmonics have a similar interference-like effect as nonmatching sequences do. Owing to the fact that the shift-and-add property holds for conventional spreading sequences, suppression of nonlinear distortions is examined. An average error probability performance evaluation of the selected configuration is presented for a transceiver pair. In analysis of the system, the authors assume the interference term arising from other users is Gaussian distributed. The results are compared to that obtained by exact evaluation of interference distribution using Gauss quadrature rule integration method. The authors compare the performance of this scheme for two different code sequence lengths. They also present some preliminary experimental results on the proposed LAN implementation as well as its measured transmission performance     

Comparison of hybrid FDMA/CDMA systems in frequency selectiveRayleigh fading

A hybrid FDMA/CDMA scheme operating over a frequency selective Rayleigh fading channel is described and analyzed. The performance of the hybrid system is then compared with that of a wideband CDMA system occupying the same total bandwidth. Both coherent and noncoherent modulation formats are investigated; it is found that, for coherent modulation with a RAKE receiver, wideband CDMA has greater capacity than does the hybrid. However, for the noncoherent modulation formats (either DPSK or square-law detected orthogonal signalling), a hybrid system can have a greater capacity if a high channel error rate can be tolerated. Otherwise, a wideband noncoherent system remains optimal     

Interference-Adaptive Fast Dynamic Channel Allocation in TD-SCDMA System

This paper proposes a new priority metric for fast dynamic channel allocation (DCA) in TD-SCDMA system, which reallocates radio resource units (RUs) to bearer services in a cell. It allows for developing a new interference-adaptive fast DCA algorithm, which is more flexible with a non-uniform user distribution. It considers the relative transmission opportunities with respect to the residual capacity and co-channel interference levels for all users, which steadily varies in the real communication environment. The proposed fast DCA algorithm aims to fully utilize the physical resource available in the time-division duplexing (TDD)-based CDMA system subject to the various types of inter-cell interference, as opposed to most existing algorithms in which traffic load and quality of service cannot be jointly balanced among the multiple radio resource units in a flexible manner. The simulation results show that the proposed algorithm improves the outage performance while reducing the average system interference, achieving full utilization of the physical resource, i.e., 48 RUs in TD-SCDMA, over a wide range of acceptable outage performance.     

Effect of nonlinearities on outage performance of fiber-fedmicrocellular networks for GMSK systems

Application of fiber for remoting the complex RF signal processing and control procedures in a microcellular system has attracted much attention. This paper investigates the effect of the laser diode nonlinearities on the outage performance of a Gaussian minimum shift keying (GMSK)-based system in a Rician channel. The analysis presented assumes that in contrast to the rapid (or short-term) fluctuations modeled by the Rician distribution, the slow (or long-term) fluctuations due to shadowing or near-far effects are compensated (in an exact sense) by power control schemes. The nonlinearity of the laser diode is shown to create a tradeoff between the outage and system parameters such as radio capacity and threshold bit-error rate (BER). The optical noises, such as shot noise, thermal noise, and relative intensity noise, are shown to degrade the outage of the system. Also, in addition to the usual improvement of outage with a strong specular component, it is observed that the specularity of the channel in a small measure mitigates the effective nonlinearity of the system and thus increases the dynamic range of the system. Design equations are provided for optimal performance     

莱斯衰落信道中混合FDMA/CDMA性能分析

分析混合频分多址／码分多址系统在莱斯多径衰落信道的性能,并与占据相同带宽的宽带ＣＤＭＡ系统进行比较。系统采用二进制ＤＰＳＫ调制和瑞克接收机。结果表明,直达 径分量较强或信噪比较大时,混合系统的性能优于宽带ＣＤＭＡ系统,否则,宽带ＣＤＭＡ系统最优。     

Centralised power control in CDMA cellular mobile systems

Efficient power control is of great importance in the design of high capacity cellular radio systems. Optimum power control scheme, in the sense that it minimises the outage probability, has been fully investigated for FDMA/TDMA cellular systems. The authors propose optimum power control and several centralised power control algorithms for CDMA cellular systems. Simulation results indicate that the optimum power control scheme outperforms the perfect average power control algorithm by ~1.9 dB under the IS-95 defined radio condition     

Capacities of FDMA/CDMA systems in the presence of phase noise andmultipath Rayleigh fading

The effect of phase noise on the capacities of coherently demodulated hybrid frequency-division multiple access/code division multiple-access (FDMA/CDMA) systems operating over a multipath Rayleigh fading channel is investigated. Using an approximate upper bound on the bit-error rate performance, which has been derived and presented in a previous paper, the capacities of the FDMA/CDMA systems are estimated for several combinations of channel and system parameters. Simulation results are also included to show the effect of the bounding error     

The capacity of a spread spectrum CDMA system for cellular mobileradio with consideration of system imperfections

There has been much interest in the use of spread spectrum code division multiple access (CDMA) techniques for cellular mobile radio. To date, spread spectrum has been used mainly for military applications, in which the inherent transmission security and immunity to deliberate jamming are important. Spread spectrum systems, however, possess various other features such as multiple access and multipath rejection capability, which make their use attractive within the mobile radio environment. However, the current interest has been principally motivated by the work of Gilhousen et al. (see IEEE Trans. Vehic. Technol., vol.VT-40, no.2, p.303, 1991) in which it is claimed that the CDMA option may offer capacity improvement over more conventional frequency and time division multiple access, FDMA and TDMA, techniques. Within this paper, the relative capacities of a basic FDMA and CDMA system are examined. It is shown that, in the absence of capacity-enhancing features such as voice activity detection and cell sectorization, the capacity of each system is comparable. The paper then assesses the sensitivity of the CDMA system to typical propagation conditions, power control errors, and realistic antenna patterns and shows that the capacity of a CDMA system may be significantly reduced under nonideal conditions     

Information theoretic considerations for cellular mobile radio

We present some information-theoretic considerations used to determine upper bounds on the information rates that can be reliably transmitted over a two-ray propagation path mobile radio channel model, operating in a time division multiplex access (TDMA) regime, under given decoding delay constraints. The sense in which reliability is measured is addressed, and in the interesting eases where the decoding delay constraint plays a significant role, the maximal achievable rate (capacity), is specified in terms of capacity versus outage. In this case, no coding capacity in the strict Shannon sense exists. Simple schemes for time and space diversity are examined, and their potential benefits are illuminated from an information-theoretic stand point. In our presentation, we chose to specialize to the TDMA protocol for the sake of clarity and convenience. Our main arguments and results extend directly to certain variants of other multiple access protocols such as code division multiple access (CDMA) and frequency division multiple access (FDMA), provided that no fast feedback from the receiver to the transmitter is available     

CDMA卫星通信系统功率控制研究

文章从卫星通信系统的功率控制原理入手,提出了一种适合CDMA卫星通信系统的功率控制方法;给出了精准的功率控制时的系统容量,通过推导给出的中断概率公式和例举的CDMA卫星通信系统实际数据,将功率控制误差对于系统容量的影响进行了仿真.仿真结果表明,当标准方差不断增大,系统的中断概率增大,系统容量随之显著减小;而采用精准的功率控制技术,可以有效改善系统性能.     

Traffic engineering of the radio interface for cellular mobilenetworks

The paper reviews traffic-related issues in the operation of the radio interface in cellular mobile networks operating with FDMA, TDMA, or CDMA technology. The emphasis is on issues which affect the traffic performance of the network, rather than on transmission technology, or transmission quality measures such as bit error rate. The author reviews the important traffic performance measures for cellular systems and the issues of channel assignment, handoff, access control, traffic modeling, and traffic management. Traffic modeling for all types of networks is considered in some depth, both by drawing analogies with fixed-wire networks, and by considering cellular-specific modeling. From the modeling results, he concludes that reuse-based networks such as FDMA and TDMA possess quite different traffic characteristics from CDMA networks     

A performance comparison of orthogonal code divisionmultiple-access techniques for mobile satellite communications

In recent years, code division multiple-access (CDMA) techniques have received a great deal of attention for mobile terrestrial/satellite communication systems. Primarily considered for the noteworthy features of low power flux density emission and robustness to interference and multipath, CDMA is known to bear reduced bandwidth and power efficiency when compared to traditional TDMA and FDMA due to the intrinsic cochannel self-noise. Early attempts to increase the capacity of CDMA-based systems for commercial applications relied on voice activation and frequency reuse. More recently, practical solutions to implement (synchronous) orthogonal CDMA signaling are being developed independently in Europe and in the USA. This paper is focused on the comparative performance analysis of those two orthogonal CDMA schemes in the operating renditions of a mobile satellite communications system. In particular, the two CDMA systems are compared in the presence of that and frequency-selective multipath fading and a typical satellite transponder nonlinearity. Most numerical results are derived through a time-domain system simulation that confirms and integrates the theoretical findings     

Outage probability of cellular CDMA systems with space diversity,Rayleigh fading, and power control error

It is well known that the capacity of code-division multiple-access (CDMA) systems degrades rapidly with the increase in power control error. The capacity is also affected by small-scale fading such as Rayleigh fading and by the voice activity. The main contribution of this paper is to provide a new simple approximation to the outage probability of the uplink of a CDMA system utilizing an antenna array for space diversity, taking into account stochastic models of the power control error, small-scale fading, and voice activity     

Advantages of CDMA and spread spectrum techniques over FDMA andTDMA in cellular mobile radio applications

A unified theoretical method for the calculation of the radio capacity of multiple-access schemes such as FDMA (frequency-division multiple access), TDMA (time-division multiple access), CDMA (code-division multiple access) and SSMA (spread-spectrum multiple access) in noncellular and cellular mobile radio systems is presented for AWGN (additive white Gaussian noise) channels. The theoretical equivalence of all the considered multiple-access schemes is found. In a fading multipath environment, which is typical for mobile radio applications, there are significant differences between these multiple-access schemes. These differences are discussed in an illustrative manner revealing several advantages of CDMA and SSMA over FDMA and TDMA. Novel transmission and reception schemes called coherent multiple transmission and coherent multiple reception are briefly presented     

SIR-based call admission control for DS-CDMA cellular systems

Signal-to-interference ratio (SIR)-based call admission control (CAC) algorithms are proposed and studied in a DS-CDMA cellular system. Residual capacity is introduced as the additional number of initial calls a base station can accept such that system-wide outage probability will be guaranteed to remain below a certain level. The residual capacity at each cell is updated dynamically according to the reverse-link SIR measurements at the base station. A 2^k factorial experimental design and analysis via computer simulations is used to study the impact of the parameters used in the algorithms. The influence of these parameters on system performance, namely blocking probability and outage probability, is then examined via simulation. The performance of the algorithms is compared together with that of a fixed call admission control scheme (fixed CAC) under both homogeneous and hot spot traffic loading. The results show that SIR-based CAC always outperforms fixed CAC even under overload situations, which is not the case in FDMA/TDMA cellular systems. The primary benefit of SIR-based CAC in DS-CDMA cellular systems, however, lies in improving the system performance under hot spot traffic     

Analysis of hybrid, coherent FDMA/CDMA systems in Ricean multipathfading

This paper extends the analysis presented by Eng and Milstein (see IEEE J. Select. Areas Commun., vol.12, no.5, p.938-951, 1994) of a hybrid frequency division multiple access/code-division multiple-access [FDMA/CDMA (F/CDMA)] system in a Rayleigh fading environment to include the presence of a direct-path component (i.e., Ricean fading). The results show that a “wideband” CDMA system out performs a hybrid system, although the combination of a specular component and an exponentially decaying multipath intensity profile (MIP) with a large decay factor may result in only a minimal degradation of system performance for a hybrid system     

Capacity analysis of a TDMA-based slow-frequency-hopped cellularsystem

Time-division multiple access (TDMA)-based systems have been adopted as the first generation digital cellular standards in North America, Europe, and Japan. The increasing demand for capacity motivates the study of alternate systems and enhancements to the adopted TDMA standards. In particular, CDMA techniques using direct sequence and slow frequency hopping have been suggested. We analyze the capacity of a slow-frequency-hopped TDMA-based cellular system via calculation of the outage probability. Expressions for the outage probability as a function of voice activity, power control, and antenna diversity are provided for mobile-to-base transmission. These expressions are used to evaluate the system capacity (users/MHz/cell) based on simulating mobile locations within 37 hexagonal cells. The sensitivity to power control error, voice activity factor, and soft capacity of the system is investigated     

Fiber-optic subcarrier multiplexed CDMA local-area networks forsubband image transmission

This paper investigates the application of subcarrier multiplexed code-division-multiple-access (CDMA) techniques to image transmission over fiber-optic local-area networks (LANs). In the hybrid scheme, CDMA is used to suppress the interference caused by the laser nonlinearity in the subcarrier multiplexing (SCM) fiber-optic communication systems. Likewise, the SCM scheme is able to increase the channel data rate of CDMA systems. This hybrid system combines the advantages of both schemes and is particularly well suited to subband coding that divides the image information into multiple parallel data streams using an analysis filter bank, each of which is transmitted via a unique subcarrier-code pair, where the spreading code and subcarrier frequency correspond to the image and one of its subbands, respectively. This hybrid scheme also allows more than one image to be transmitted and be accessed simultaneously at the same channel bandwidth, in which each image is assigned a particular spreading code added to its digital data modulating the subcarrier. After transmission, each received signal is independently recovered at a high-Q surface acoustic wave (SAW) receiver with the matching subcarrier-code pair. Other concurrent signals are rejected by the SAW. Then, all the recovered subbands are reassembled by a synthesis filter bank into a close reproduction to the original image. The image quality of subband image transmission via CDMA/SCM fiber-optic channels is evaluated and examined     

CDMA／SDMA系统性能分析

空分多址接入技术（SDMA）可以通过信号不同的空间传播路径来区分用户，从而提高了蜂窝移动通信系统容量．而此技术又可以和其他多址方式相互兼容，比如频分多址，时分多址，码分多址．CDMA／SDMA系统就是码分多址和空分多址两种接入技术相结合的系统．该系统可通过时空编码实现的．文中分析此种系统的性能，并与多用户环境下的CDMA系统进行了比较．     

基于小波包变换的多址通信

新一代无线通信系统要求大容量、高速率、综合业务、适用于各种环境。为满足上述要求,宜采用ＣＤＭＡ／ＴＤＭＡ／ＦＤＭＡ混合多址方式,其中多载波ＣＤＭＡ已成为目前研究热点。本文提出一种基于小波包变换的多载波ＣＤＭＡ或正交小波包分解复用（ＯＷＰＤＭ）－ＣＤＭＡ通信方式,介绍了其基本结构和主要优点。这是一种很有发展前景的多址通信技术。