Ultra-wide Bandwidth Channel Research Articles

Reduced-Rank Adaptive Least Bit-Error-Rate Detection in Hybrid Direct-Sequence Time-Hopping Ultrawide Bandwidth Systems

The design of high-efficiency low-complexity detection schemes for ultrawide bandwidth (UWB) systems is highly challenging. This paper proposes a reduced-rank adaptive multiuser detection (MUD) scheme that is operated in least bit-error-rate (LBER) principles for hybrid direct-sequence time-hopping UWB (DS-TH UWB) systems. The principal component analysis (PCA)-assisted rank-reduction technique is employed to obtain a detection subspace, where the reduced-rank adaptive LBER-MUD is carried out. The reduced-rank adaptive LBER-MUD is free from channel estimation and does not require knowledge about the number of resolvable multipaths and the multipaths' strength. In this paper, the BER performance of the hybrid DS-TH UWB systems using the proposed detection scheme is investigated, assuming communications over UWB channels modeled by the Saleh-Valenzuela channel model. Our studies and performance results show that, given a reasonable rank of the detection subspace, the reduced-rank adaptive LBER-MUD can efficiently mitigate both multiuser and intersymbol interference (ISI) and achieve the diversity gain promised by the UWB systems.

A Novel Approximation of NDA ML Estimation for UWB Channels

Novel non-data-aided near-maximum-likelihood estimators for the delays and the attenuations in an ultra-wide bandwidth channel are proposed by using an approximation to the maximum likelihood equation. Numerical results show that these new estimators outperform previous approximate non-data-aided maximum likelihood channel estimators reported in the literature. Moreover, in some cases, the performances of the new non-data-aided estimators approach those of the data-aided estimators, enabling a reduction in the overhead expense of pilot symbols.

Performances of EGC and MRC diversity for UWB PAPM systems in IEEE channel models

Accurate approximations to the bit error rates of equal gain combining and maximal ratio combining diversity are obtained for pulse-amplitude-and-position-modulation operating in IEEE ultra-wide bandwidth (UWB) channel models. Numerical results are presented to show the accuracy of the approximations for the IEEE CM1 and CM3 UWB channel models. Results for pulse amplitude modulation and pulse position modulation are obtained as special cases of the more general results. Precise estimates of the loss of equal gain combining relative to maximal ratio combining are obtained for both line-of-sight CM1 and non-line-of-sight CM3 channels. Noteworthy, while the performance loss of equal gain combining with respect to maximal ratio combining is less than 0.4 dB for the non-line-of-sight channel, it can be as much as 2 dB for the line-of-sight channel.

Ultra-wide bandwidth in-vehicle channel measurements using chirp pulse sounding signal

A novel ultra-wide bandwidth (UWB) channel measurement approach based on chirp pulse sounding signal in an automotive vehicle is proposed. An UWB channel impulse response (CIR) estimator using de-convolution technique is constructed to verify that the chirp pulse sounding signal generated with rectangular window is 12.71 dB better in accuracy than the Gaussian pulse sounding signal to measure the CIR of the UWB channel. The UWB channel measurement in the frequency band of 4.25–4.75 GHz is carried out inside an automotive vehicle. The experimental results validate the correctness of using chirp pulse sounding signal to measure the UWB channel inside an automotive vehicle with windows closed through the root mean square delay spread for Cases A and B radio propagation channel models of IEEE 802.15.3a UWB standard when the threshold is properly chosen. Also, test results show that opening the vehicle's window may change the channel characterisation.

Interference analysis of uwb systems for IEEE channel models using first- and second-order moments

Statistical moments of the inter-path interference, the inter-chip interference and the intersymbol interference in a direct-sequence binary phase shift keying ultra-wide bandwidth (UWB) system are analyzed for the IEEE UWB channel models. Exact expressions for the first- and second-order moments are derived. The effects of the duration of the monocycle pulse, the spreading gain, and the number of interfering symbols on the average powers of the interferences are examined.

Designing Time-Hopping Ultrawide Bandwidth Receivers for Multiuser Interference Environments

The multiple-user interference (MUI) in time-hopped impulse-radio ultrawide bandwidth (UWB) systems is impulse-like and poorly approximated by a Gaussian distribution. Therefore, conventional matched filter receiver designs, which are optimal for Gaussian noise, are not fully efficient for UWB applications. Several alternative distributions for approximating the MUI process and the MUI-plus-noise process in UWB systems are motivated and compared. These distributions have in common that they are more impulsive than the Gaussian approximation, with a greater area in the tails of the probability density function (pdf) compared to a Gaussian pdf. The improved MUI and MUI-plus-noise models are utilized to derive new receiver designs for UWB applications, which are shown to be superior to the conventional matched filter receiver. Multipath propagation is abundant in UWB channels and is exploited by a Rake receiver. A Rake receiver uses multiple fingers to comb the multipath rays with a conventional matched filter implemented in each finger. Rake structures utilizing the new receiver designs that are suitable for reception of UWB signals in multipath fading channels are provided. An optimal performance benchmark, based on an accurate theoretical model for the interference that fully explains the features of the MUI pdf, is also presented. Analysis and simulation results are shown for the novel receivers, which demonstrate that the new designs have superior performance compared to the conventional linear receiver when MUI is significant. Several adaptive receivers are shown to always match or exceed the performance of the conventional linear receiver in all MUI-plus-noise environments. Parameter estimation for the new receivers also is discussed.

A MAP Estimator for the m Parameter in Nakagami Fading Ultra-Wide Bandwidth Indoor Channels

A maximum a posteriori (MAP) estimator for the Nakagami m parameter in an ultra-wide bandwidth (UWB) indoor channel is proposed. Previous work exclusively studies maximum likelihood (ML) estimation and moment method (MM) estimation of the Nakagami m parameter. This letter derives the MAP estimator for the Nakagami m parameter by using the a priori probabilities of the Nakagami fading parameters in an indoor UWB channel. The performance of the MAP estimator is examined and compared with those of the ML estimator and the MM estimator. Numerical results demonstrate that the new MAP estimator is superior to the ML estimator and the MM estimator in an indoor UWB channel, especially when the sample size in the estimation is small

Analytical study of maximum likelihood delay and gain estimators for UWB channels

The performances of data-aided maximum likelihood estimators for the delay and the gain in an ultra-wide bandwidth channel are analysed. The probability density functions of the estimates are derived. The root mean squared errors of the estimators are examined analytically. Simulation results are provided to verify the analysis.

CRLBs for NDA ML estimation of UWB channels

The Cramer-Rao lower bounds for non-data-aided maximum likelihood channel gain and delay estimation in an ultra-wide bandwidth communication system are derived. These bounds serve as useful benchmarks for non-data-aided ultra-wide bandwidth channel estimators.