ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Thu, 20 Jun 2024 12:16:38 GMT2024-06-20T12:16:38Z50101- Novel joint strength and SIR based CDMA reverse link power control with variable target SIRhttps://scholarbank.nus.edu.sg/handle/10635/72810Title: Novel joint strength and SIR based CDMA reverse link power control with variable target SIR
Authors: Zhang, D.; Zhang, Q.T.; Ko, C.C.
Abstract: The use of power control to achieve the desired signal-to-interferences ratio (SIR) is a crucial issue to ensure the quality of service of a code division multiple access (CDMA) cellular system. Power control based on SIR alone, however, often leads to the problem of vicious circle such that all mobile stations reach their power limits and yet, fail to achieve the desired SIR. In this paper, we present a novel power control scheme, which can significantly reduce the possibility of vicious circle. The new scheme is based on two observations. First, control of the target function SIR must take the signal power into account so as to avoid the problem of trivial optimization. Second, for a given channel operational environment, it is unnecessary and also impossible to pursue an unreasonably high SIR using brute force. The basic philosophy behind the new technique is therefore to define an acceptable SIR region over the entire SIR axis instead and use adaptive technique for two purposes. Namely, adaptively adjust both the target SIR and the step size to approach it according to the changing channel characteristics. The new scheme is essentially a Markov system with adaptive control.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/728102000-01-01T00:00:00Z
- A simple adaptive up-link power control algorithm for DS/CDMA systemhttps://scholarbank.nus.edu.sg/handle/10635/72449Title: A simple adaptive up-link power control algorithm for DS/CDMA system
Authors: Ye, F.; Zhang, Q.T.; Ko, C.C.
Abstract: Power control is a fundamental process in direct sequence coded-division multiple-access (DS/CDMA) system. Proper algorithm must be employed on both transmitter and receiver to mitigate near-far problem and prevent fading while maintaining sufficient transmission quality. This paper presents a simple adaptive up-link power control algorithm with simple yet effective features implemented on mobile handsets as well as on base stations. Simulation results show the improved performance of the proposed algorithm over current fast feedback closed-loop power control (FPC) algorithm[1].
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/724492000-01-01T00:00:00Z
- A simple approach to probability of error for equal gain combiners over rayleigh channelshttps://scholarbank.nus.edu.sg/handle/10635/61711Title: A simple approach to probability of error for equal gain combiners over rayleigh channels
Authors: Zhang, Q.T.
Abstract: A new technique for determining the probability of error of a general equal gain (EG) combiner over Rayleigh channels is presented in this paper. Unlike the existing methods, the new procedure takes a single step and directly derives the error performance from the characteristic function of the decision variable, thereby avoiding the lengthy process of deriving the distribution of the sum of Rayleigh variâtes and thus eliminating all approximations required therein. The new solution is exact and much simpler compared to the existing results. It takes the form of a one-fold integral, which can be easily evaluated by using the Hermite's numerical method. Index Terms- Cellular mobile systems, diversity reception, equal gain combining, Rayleigh fading channels. © 1999 IEEE.
Fri, 01 Jan 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/617111999-01-01T00:00:00Z
- Outage performance of cellular systems over arbitrary lognormal shadowed Rician channelshttps://scholarbank.nus.edu.sg/handle/10635/62570Title: Outage performance of cellular systems over arbitrary lognormal shadowed Rician channels
Authors: Zhang, Q.T.; Tjhung, T.T.
Abstract: Techniques for analysing the outage performance for lognormal shadowed Rician fading channels are becoming of increasing importance as the concept of micro-cells is introduced into wireless personal communications. A general solution, however, has not yet been developed except for some special cases. The authors present an exact solution which takes the form of two-fold integrals, and is applicable to general situations without any restrictions.
Thu, 22 Jul 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/625701999-07-22T00:00:00Z
- A general AR-based technique for the generation of arbitrary gamma VBR video traffic in ATM networkshttps://scholarbank.nus.edu.sg/handle/10635/80273Title: A general AR-based technique for the generation of arbitrary gamma VBR video traffic in ATM networks
Authors: Zhang, Q.T.
Abstract: Modeling variable-bit-rate (VBR) video source traffic is a crucial issue to evaluate the end-to-end performance of transmitting video signals over asynchronous transfer mode (ATM) networks. Difficulties in source modeling arise from the fact that VBR video source traffic usually follows a gamma distribution with high correlation among adjacent data. Many researchers adopt autoregressive (AR) models driven by a Gaussian error process to account for such correlation. The problem is: due to the closure property of the Gaussian distribution, the traffic so generated is Gaussian rather than gamma. As a remedy, some researchers directly consider gamma AR models instead. Unfortunately, the trouble arises from the fact that the closure property does not apply to gamma distributions, and thus, the linear operation performed by an AR model fails to produce a gamma traffic. In this paper, we present a new technique that is capable of generating gamma-distributed traffic with arbitrary correlation while retaining the computational efficiency of Gaussian AR models. The central idea is to decompose a given gamma traffic into a linear combination of a number of χ 2(1) sequences, and each of these latter processes can be easily obtained from a Gaussian AR process through a simple nonlinear operation. Results based on actual video teleconference data are presented to verify the validity of the new algorithm. © 1999 IEEE.
Fri, 01 Jan 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/802731999-01-01T00:00:00Z
- Maximal-ratio combining over Nakagami fading channels with an arbitrary branch covariance matrixhttps://scholarbank.nus.edu.sg/handle/10635/62399Title: Maximal-ratio combining over Nakagami fading channels with an arbitrary branch covariance matrix
Authors: Zhang, Q.T.
Abstract: The error probability of maximal ratio combiners (MRC's) in a correlated Nakagami environment with an arbitrary branch covariance matrix is not available in the literature although some work has been done for two special cases with constant and exponential correlations. Correlation structures of this type, though of theoretical interest, may not match to practical situations, even for an antenna array of a totally symmetrical configuration. In this paper, we tackle the general problem by virtue of characteristic functions, avoiding the difficulty of explicitly obtaining the probability density function (PDF) for the signal-to-noise ratio (SNR) at the MRC output. We derive a simple closed-form solution for arbitrarily correlated channels with an integral fading parameter and a solution in the form of a one-fold integral for a fading parameter of nonintegral values. Simple algorithms have also been developed for their efficient implementation. The formulas are then used to analyze two possible antenna configurations for a base station, ending up with some findings of interest to system design.
Fri, 01 Jan 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/623991999-01-01T00:00:00Z
- Co-channel interference analysis for mobile radio suffering lognormal shadowed Nakagami fadinghttps://scholarbank.nus.edu.sg/handle/10635/61942Title: Co-channel interference analysis for mobile radio suffering lognormal shadowed Nakagami fading
Authors: Zhang, Q.T.
Abstract: Determination of the outage performance of a cellular mobile system in lognormal shadowed Nakagami fading environments has been the focus of many researchers. However, general results are not available in the literature. The difficulty arises from the philosophy which attempts to determine first the outage probability for Nakagami fading and then average it over lognormal distributions. The consequence is outage expressions in the form of an intractable multi-fold integral. By formulating the problem in the framework of characteristic functions and naturally combining the two separated steps in a single one, the author obtains an expression for outage probability always in the form of a two-fold integral no matter how many co-channel users are in operation. The outage probability so obtained can be accurately and efficiently evaluated by using the Hermite and Gaussian quadrature. It thereby provides a general analysis tool for lognormal shadowed Nakagami channels with arbitrary parameters. Numerical results are also presented to illustrate the theory.
Fri, 01 Jan 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/619421999-01-01T00:00:00Z
- Outage performance of cellular systems over arbitrary lognormal shadowed Rician channelshttps://scholarbank.nus.edu.sg/handle/10635/80924Title: Outage performance of cellular systems over arbitrary lognormal shadowed Rician channels
Authors: Zhang, Q.T.; Tjhung, T.T.
Abstract: Techniques for analysing the outage performance for lognormal shadowed Rician fading channels are becoming of increasing importance as the concept of micro-cells is introduced into wireless personal communications. A general solution, however, has not yet been developed except for some special cases. The authors present an exact solution which takes the form of two-fold integrals, and is applicable to general situations without any restrictions.
Thu, 22 Jul 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/809241999-07-22T00:00:00Z
- Maximal-ratio combining over Nakagami fading channels with an arbitrary branch covariance matrixhttps://scholarbank.nus.edu.sg/handle/10635/80700Title: Maximal-ratio combining over Nakagami fading channels with an arbitrary branch covariance matrix
Authors: Zhang, Q.T.
Abstract: The error probability of maximal ratio combiners (MRC's) in a correlated Nakagami environment with an arbitrary branch covariance matrix is not available in the literature although some work has been done for two special cases with constant and exponential correlations. Correlation structures of this type, though of theoretical interest, may not match to practical situations, even for an antenna array of a totally symmetrical configuration. In this paper, we tackle the general problem by virtue of characteristic functions, avoiding the difficulty of explicitly obtaining the probability density function (PDF) for the signal-to-noise ratio (SNR) at the MRC output. We derive a simple closed-form solution for arbitrarily correlated channels with an integral fading parameter and a solution in the form of a one-fold integral for a fading parameter of nonintegral values. Simple algorithms have also been developed for their efficient implementation. The formulas are then used to analyze two possible antenna configurations for a base station, ending up with some findings of interest to system design.
Fri, 01 Jan 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/807001999-01-01T00:00:00Z
- Novel joint strength and SIR based CDMA reverse link power control with variable target SIRhttps://scholarbank.nus.edu.sg/handle/10635/81617Title: Novel joint strength and SIR based CDMA reverse link power control with variable target SIR
Authors: Zhang, D.; Zhang, Q.T.; Ko, C.C.
Abstract: The use of power control to achieve the desired signal-to-interferences ratio (SIR) is a crucial issue to ensure the quality of service of a code division multiple access (CDMA) cellular system. Power control based on SIR alone, however, often leads to the problem of vicious circle such that all mobile stations reach their power limits and yet, fail to achieve the desired SIR. In this paper, we present a novel power control scheme, which can significantly reduce the possibility of vicious circle. The new scheme is based on two observations. First, control of the target function SIR must take the signal power into account so as to avoid the problem of trivial optimization. Second, for a given channel operational environment, it is unnecessary and also impossible to pursue an unreasonably high SIR using brute force. The basic philosophy behind the new technique is therefore to define an acceptable SIR region over the entire SIR axis instead and use adaptive technique for two purposes. Namely, adaptively adjust both the target SIR and the step size to approach it according to the changing channel characteristics. The new scheme is essentially a Markov system with adaptive control.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/816172000-01-01T00:00:00Z