Department Publications

In this paper, we focus on the ergodic downlink sum-rate performance of a system consisting of a set of heterogeneous users. We study three user selection schemes to group near-orthogonal users for simultaneous transmission. The first scheme is a random selection policy that achieves fairness, but does not exploit multi-user diversity. The second scheme is a greedy selection policy that fully exploits multi-user diversity, but does not achieve fairness, and the third scheme achieves fairness while partially exploiting multi-user diversity. We also consider two beamforming methods for data transmission, namely, maximum-ratio transmission and zero-forcing beamforming. In all scheduling schemes studied in the paper, there is a key parameter that controls the degrees of orthogonality of channel directions between co-scheduled users. We focus on optimally setting this parameter for each scheduling scheme such that …

This paper studies the outage capacity of a network consisting of a multitude of heterogeneous mobile users and operating according to the classical opportunistic beamforming framework. The base station is located at the center of the cell, which is modeled as a disk of finite radius. The random user locations are modeled using a homogeneous spatial Poisson point process. The received signals are impaired by both fading and location dependent path loss. For this system, we first derive an expression for the beam outage probability. This expression holds for all path loss models that satisfy some mild conditions. Then, we focus on two specific path loss models ( i.e. , an unbounded model and a more realistic bounded one) to illustrate the applications of our results. In the large system limit, where the cell radius tends to infinity, the beam outage capacity and its scaling behavior are derived for the selected specific …

In this paper, we consider a cellular network operating according to the classical opportunistic beamforming and scheduling scheme. In a multi-cell network, interference is the main bottleneck on the communication rate, compared to noise. In this paper, we focus on deriving the ergodic downlink sum-rate scaling law for the system of interest considering an interference-limited regime (i.e., the high SNR region). More specifically, through deriving the moment generating function of the sum-rate, we show that the ergodic downlink sum-rate scales logarithmically as the number of users grows large. This result is different from the well-known double logarithmic sum-rate growth with increasing number of users due to the interference-limited assumption. Finally, numerical results are also presented to validate our analysis and provide further insights.

The outage probability of a multiuser two-hop amplify-and-forward relaying system employing opportunistic scheduling is investigated. A practically important case where there are cochannel interference signals present at the network is considered for the analysis. Exact expressions and closed-form lower bounds are derived for the outage probability. Exact closed-form expressions are derived for the system outage probability when interference signals are present at the relay and at the destination separately. A closed-form lower bound is derived for the outage probability when the relay and the destination nodes are affected by interference simultaneously. The effects of channel state information feedback delay are investigated for special cases. In addition, asymptotic outage probability results are derived to obtain useful insights on the effects of interference and feedback delay. The novel expressions can be …

The performance of a random vector quantization based transmit precoding distributed antenna system is investigated in terms of the achievable ergodic rate. An approximate expression is derived for the ergodic rate of the system considering the effects of path loss, Rayleigh fading and out-of-cell interference. A moment matching technique is used to approximate the desired signal power and the total interference power distributions of the system using a Gamma distribution. The proposed approximation estimates the performance of the system accurately and saves computational time in simulations.

The outage probability of a recently proposed relay network with multiple antennas at the relay is analyzed. The relay uses maximal ratio combining to combine the received signals, while it uses maximal ratio transmission for the transmission. It is assumed that the reception at the relay and the destination are corrupted by multiple co-channel interfering signals. Closed-form outage probability expressions are derived when the relay is operated in the amplify-and-forward mode with fixed gain. Both cases of equal power and unequal power interferers are considered.

The outage probability of a multiuser amplify-and-forward relaying protocol is investigated. The practical case where there are co-channel interference signals present at the network is considered for the analysis. Exact expressions and closed-form lower bounds are derived for the outage probability. Three network configurations are analyzed based on the presence of co-channel interference in the system.

A novel single-integral representation for the bivariate Rician distribution was presented in a recent letter in this Transactions (ibid., vol. 59, no. 11. pp. 2951-2954, Nov. 2011). The expression given for the bivariate Rician probability density function (PDF) [1, eq. (12a)] contains a typographical error. The correct expression for the bivariate Rician PDF is presented here.

Novel single-integral representations for the multivariate probability density functions and cumulative distribution functions of Gaussian class distributions (Rayleigh, Rician, Weibull, Nakagami- m , and generalized Rician) are derived. The solutions are expressed in terms of well-known functions which are available in common mathematical software. The marginal random variables are not necessarily identically distributed as is the case for some past solutions. A generalized correlation structure based on a special linear transformation of independent Gaussian random variables is used in this study. The advantage of the new representation is that only a single-integral computation is needed to compute an N -dimensional distribution.

Novel single-integral representations for the bivariate probability density function and cumulative distribution function of two correlated Rician random variables are derived. The solutions are expressed in terms of well known functions which are available in common mathematical software. The two random variables are not necessarily identically distributed as required by some past solutions. The new form of the bivariate Rician cumulative distribution function is applied to give a new expression for the outage probability of dual selection combining diversity operating in correlated Rician fading.

Novel representations for the multivariate probability density function and cumulative distribution function of the non-central chi-square distribution are derived. The solutions are expressed in terms of well known functions which are available in common mathematical software. When the number of degrees of freedom, m, is even, the new representation has the advantage that only a single-integral computation is needed to compute a N-dimensional distribution. The new representations are used to numerically evaluate the outage probability of multiple input multiple output systems with receiver antenna selection, operating in correlated Rician fading. The well known equal correlation model, which is considered to be a useful model for a closely placed set of antennas, is used for the analysis.

Novel single-integral representations for the multivariate probability density functions (PDFs) and cumulative distribution functions (CDFs) of the Gaussian class Weibull distribution are derived. The solutions are expressed in terms of familiar mathematical functions which are available in common mathematical software. The well known equal (constant) correlation model is considered. A special linear transformation of independent Gaussian random variables is used to generate correlated Weibull random variables. The advantage of the new representation is that only a single integral computation is needed to compute a N-dimensional distribution. The new representation of the CDF is used for the performance evaluation of a selection diversity combiner operating in equally correlated Weibull fading channels. The new PDF representation is also used for an analysis of the moments of the output signal-to-noise ratio …

An analytical framework to evaluate the exact performance of multihop amplify-and-forward relaying in the presence of co-channel interference is presented. The new results are formulated based on the recently introduced generalized transformed characteristic function method. The new framework is used to evaluate the exact performance measures such as average symbol error probability, outage probability and ergodic capacity, when the multihop relaying system is operating in identically distributed fading channels with equal power interferers at the relays and the destination.

Novel representations for the multivariate probability density function (PDF) and cumulative distribution function (CDF) of the equi-correlated non-central chi-square (χ 2 ) distribution are derived. The new representations are given as single integral solutions in terms of well known mathematical functions which are available in common mathematical software packages. The advantage of the new representations is that only a single integral computation is needed to evaluate the PDF and CDF for an arbitrary number of dimensions. The new representations are used to numerically evaluate the outage probability of a single user multiple input multiple output system with receiver antenna selection diversity, operating in correlated Rician fading channels. The well known constant (equal) correlation model, which is considered to be a useful model for a closely placed set of antennas, is used for the analysis in this paper. A …

Simple expressions for the symbol error rate of some coherent and noncoherent modulation schemes with dual maximal ratio combining operating in identically distributed correlated Nakagami-q fading are derived. The new expressions are derived based on a decorrelation transformation applied to the correlated branches. New expressions are given as both closed-form and finite range single integrals of elementary mathematical functions, which can be easily evaluated using mathematical software.

Novel single integral representations for the multivariate probability density function and cumulative distribution function of Rayleigh and Rician distributions are derived. A generalized correlation structure is used in this analysis. The derived novel representations are used to evaluate the outage probability of N-branch selection diversity operating in correlated Rayleigh and Rician fading channels modeled by the generalized correlation model.

Novel simple forms for the probability density function (PDF) and the cumulative distribution function (CDF) of two correlated Rician random variables (RVs) are derived. The new representations for the bivariate Rician PDF and CDF are given in the form of single integral solutions in terms of well known functions that are available in common mathematical software packages. The general case of non-identically distributed Rician RVs is considered in this analysis. The new form of the bivariate Rician cumulative distribution function is applied to give a new expression for the outage probability of dual selection combining diversity operating in correlated Rician fading.

Novel single integral representations for the multivariate probability density function (PDF) and cumulative distribution function (CDF) of the Nakagami-m distribution with integer and identical fading severity parameter m are derived. A generalized correlation structure is used in this model. The single integral solutions for the PDF and the CDF are given in terms of well known mathematical functions which are available in common mathematical software packages. The novel representation derived for multivariate CDF is used to evaluate the outage probability of N-branch selection diversity combining operating in correlated Nakagami-m fading modeled by the generalized correlation model.

Novel single integral representations for the multivariate probability density function (PDF) and cumulative distribution function (CDF) of Gaussian class Weibull distributions are derived. A special linear transformation of independent Gaussian random variables is used to generate correlated Weibull random variables. The solutions are expressed in terms of familiar functions which are available in common mathematical software. The well known equal (constant) correlation model is used in this paper. The advantage of the new representation is that only a single integral computation is needed to compute a L-dimensional distribution. Some applications of the new distribution representations are also given.

Multivariate statistics play an important role in performance analysis of wireless communication systems in correlated fading channels. This thesis presents a framework which can be used to derive easily computable mathematical representations for some multivariate statistical distributions, which are derivatives of the Gaussian distribution, and which have a particular correlation structure. The new multivariate distribution representations are given as single integral solutions of familiar mathematical functions which can be evaluated using common mathematical software packages. The new approach can be used to obtain single integral representations for the multivariate probability density function, cumulative distribution function, and joint moments of some widely used statistical distributions in wireless communication theory, under an assumed correlation structure. The remarkable advantage of the new …

Designing a PABX system using the existing power line infrastructure as the transmission medium is an effective method of implementing a fast and easily installable communication solution. The scope of this research is to develop such a system for a small scale organizational environment to avoid the complexities and time consumption of cable installation. As the power line transmission technique, we used narrowband frequency shift keying to counter the noise disturbances in power line. In addition we used a novel communication protocol to further reduce the effects of noise and to achieve reliable transmission. We integrated the switching function into the central unit which is the central control element in the system. We were able to achieve voice communication at the rate of 2kbps and to switch between four extensions. Further improvements in the voice quality can be achieved by using advanced noise …

This paper presents a coherent demodulation scheme that reduces the multiple-access interference (MAI) considerably in a band-limited direct-sequence code-division multiple-access system. The despreading signal is obtained from a combination of the conventional despreading signal and its weighted early and late versions that are used in the delay-locked loop (DLL). It is shown that with appropriate choice of the weighting parameter of the early-late signals of the DLL, the signal-to-interference-plus-noise ratio of the decision variable is increased, which leads to improvement in the bit-error performance and hence the potential increase in the system capacity by about 25%. The analyses are performed in the frequency domain. The effect of imperfect synchronization on the system performance is also analyzed.

The thesis presents the development of a simple technique for remote reading of utility meters using the low voltage power distribution network. Remotely reading electricity, gas and water meters have distinct advantages over traditional metering methods. Several communication technologies have been designed and implemented for this purpose using wireless techniques, telephone lines, power transmission and distribution lines. In this study, the last one has been selected as the basis for the development of a remote meter reading system applicable to Sri Lanka.

The performance of a coherent delay-locked tracking scheme for direct-sequence/spread-spectrum systems using half-sine or triangular chip waveforms for early and late despreading sequences is analyzed. The effect of band-limiting on the received signals is considered. Mean time to lose lock (MTLL) and root mean square (rms) tracking error of the delay-locked loop (DLL) are compared with that of a conventional DLL which uses rectangular chip despreading waveforms. Linear and nonlinear (based on the renewal process approach) analyses are employed to evaluate the performance of the DLL. Results show that the use of either the half-sine or triangular chip waveform reduces the rms tracking error and increases the MTLL considerably when the early-late spacing is approximately between 0.7-1.3 chip times. The results apply in particular to the commonly used DLL using one chip early-late spacing …

HKU Scholars Hub: Delay-locked loop techniques in direct sequence spread-spectrum receivers Skip navigation HKU Login Guest Login Home Publications Researchers Staff Research Postgraduates Organizations Grants Datasets Deposit Data HKUL Research Data Management Theses Patents Community Service File Download FullText.pdf Links for fulltext (May Require Subscription) DOI: 10.5353/th_b3124104 Supplementary Appears in Collections: HKU Theses Online Electrical & Electronic Engineering: Theses postgraduate thesis: Delay-locked loop techniques in direct sequence spread-spectrum receivers Show simple item record Show full item record Export item record Title Delay-locked loop techniques in direct sequence spread-spectrum receivers Authors Thayaparan, Subramaniam. Issue Date 1999 Publisher The University of Hong Kong (Pokfulam, Hong Kong) Citation Thayaparan, S.. (1999). Delay-…