Chin Choy Chai

Performance Analysis of Prerake DS UWB Multiple Access System Under Imperfect Channel Estimation

In this paper, the performance of Prerake DS UWB multiple access system under imperfect channel estimation is studied. The signal model of the system is derived in matrix form, which clearly shows the components of inter-chip interference, inter-symbol interference and multiple access interference. The BER formula is derived based on this signal model and validated by simulations. We highlight that the BER performance does not monotonically decrease with the growth of data rate under imperfect channel estimation. The effect of imperfect channel estimation in different cases is also discussed.

A Novel High Data Rate Prerake DS UWB Multiple Access System: Interference Modeling and Tradeoff Between Energy Capture and Imperfect Channel Estimation Effect

A novel high data rate (HDR) Prerake DS UWB multiple access system is proposed, in which the number of taps in the Prerake filter is set to a large value while keeping the number of taps in a chip sufficiently small. Thus high data rate can be achieved via superposition of the chip waveforms, where the inter-chip interference introduced is small due to signal energy focusing. We derive the higher order moments of Multiple Access Interference (MAI) and fit the distribution of MAI using a generalized Gaussian distribution. Numerical results show that the generalized Gaussian distribution is a more appropriate statistical model for the distribution of MAI than the Gaussian distribution. Using the characteristic function (CF) method, an accurate BER formula is derived and validated by numerical results. The effect of imperfect channel estimation is discussed in detail. We highlight that under imperfect channel estimation, there is a tradeoff between the signal energy captured and the channel estimation noise introduced.

Exact BER Analysis of DS PAM UWB Multiple Access System in Lognormal Multipath Fading Channels

We derive exact BER formula for DS PAM UWB multiple access (MA) system using the characteristic function (CF) method. Exact BER analysis has been reported in some earlier works only for AWGN channels. In contrast to previous study, we adopt lognormal multipath fading channel model, which is more practical for real UWB applications. We use the CF method to deal with the exact probability distribution function (PDF) of total noise without making any approximations on the PDF of interference. In applications where the number of interference sources is small, we show that BER obtained by the GA method is less accurate than the CF method in large SNR range. Discussions about the BER results based on the characteristic functions are also provided.

Exact BER analysis of DS-UWB multiple access system under imperfect power control

Ultra-wideband technology is characterized by the transmission of extremely short impulses. To improve its multiple access (MA) capability, UWB technology can be combined with traditional spread spectrum techniques. So far, lot of research on UWB has focused on employing time-hopping spread-spectrum with impulse radio using pulse-position modulated signals. However, direct-sequence (DS) UWB has the potential to provide high data rate service (compared with TH UWB, which is suitable for low data rate applications) as well as narrow band interference rejection capability. Most of the research on UWB bit error probability performance evaluation has employed some approximations. In this paper, a method based on Characteristic Function (CF) is proposed to derive exact bit error probability of DS UWB systems in the presence of multiple access interference (MAI) under imperfect power control. In sharp contrast with widely used Gaussian Approximation (GA) method, CF method deals with the exact distribution of total noise (including MAI and AWGN noise) other than making any assumptions on the distribution of total noise. As a result, CF method offers more accurate BER evaluation than GA method does. Our analytical derivations are validated by simulation results.

On the Multiple Access Performance of Prerake DS UWB System

In this paper, we study the multiple access performance of a Prerake DS UWB system. Prerake technique not only simplifies the receiver structure significantly, but also provides low probability of detection and spatial security in communication. These features are very desirable in military/commercial applications. We present the system signal model in presence of inter-chip interference and inter-symbol interference. The bit error rate (BER) formula is derived based on this signal model. A degradation factor is defined to investigate the multiple access performance of the system. The relationship between the degradation factor and the number of users/bit rate are derived. We also explore the multiple access capacity per user. The BER formula is validated by simulation results in various UWB channel models. In numerical analysis, we highlight the tradeoff between the bit rate and BER performance. The plots on degradation factor vs number of users/bit rate further reveal the constraint between the bit rate and the number of users

WLC28-1: On the Tradeoff between Data Rate and BER Performance of Pre-RAKE DS UWB System

A pre-RAKE system is proposed for the direct sequence (DS) UWB communications to capture the energy effectively in multipath channels. Based on the pre-RAKE technique, the equivalent performance of RAKE with MRC can be achieved using a receiver with only one finger. Compared to the previous research on Pre-RAKE UWB, we consider continuous chip transmission and study the effect of inter-chip interference under lognormal multipath fading channels. Numerical results are provided for cases with and without inter-chip interference to show the tradeoff between the data rate and the BER performance.

Exact BER analysis of DS PPM UWB multiple access system under imperfect power control

Bit error rate (BER) performance of various UWB systems has been analyzed in numerous literatures. Most of the BER evaluation in these publications is based on some approximations. In this paper, we propose a method based on characteristic function (CF) to derive exact BER of DS UWB systems using pulse position modulation (PPM) under imperfect power control. In contrast to the widely used Gaussian approximation (GA) method, CF method deals with the exact distribution of total noise (including multiple-access interference and AWGN noise) other than making any assumptions on the distribution of total noise. Therefore CF method offers much more accurate BER prediction than GA method does. Our analytical derivations are validated by simulation results

A Novel High Data Rate Prerake DS UWB Multiple Access System and its Accurate Interference Model

A novel high data rate (HDR) prerake DS UWB multiple access system is proposed, in which the number of taps in the prerake filter is set to a large value while keeping the number of taps in a chip sufficiently small. Hence high data rate is achieved without sacrificing signal energy captured. We derive the higher order moments of multiple access interference (MAI) and fit the distribution of MAI using a generalized Gaussian distribution. Numerical results are provided to show that generalized Gaussian distribution is a more appropriate model for the distribution of MAI. Next, accurate BER formula is derived using the characteristic function (CF) method. Numerical results show that the HDR Prerake DS UWB system outperforms the conventional partial-prerake DS UWB system.

WLC23-2: Exact BER Analysis of DS PPM UWB Multiple Access System in Lognormal Multipath Fading Channels

We derive exact BER formula for DS PPM UWB multiple access (MA) systems using the Characteristic Function (CF) method. All previous exact BER analysis were carried out in AWGN channels. Here we adopt the lognormal multipath fading channel model, which is more practical for real UWB applications. We derive the exact probability distribution function (PDF) of total noise using characteristic function instead of making any approximations on the PDF of interference. Numerical results clearly show that the BER obtained by CF method is more accurate than the GA method in large SNR range. We also plot the characteristic functions of the statistic decision variables to provide more insight into the numerical results.