Sangchoon Kim

An improved UWB receiver employing generalized normal-Laplacian distribution model

The generalized normal-Laplace (GNL) distribution is employed to reflect the heavy-tailed and impulsive nature of the multiple access interference (MAI) plus AWGN noise in ultra-wideband (UWB) systems. To accurately represent the impulsive feature of the MAI-plus-noise while keeping longer tails, the kurtosis matching (KM) method combined with the method of moments estimation (MME) is proposed for the parameter estimation for time-hopping UWB multiple access communications in AWGN channels. The GNL based UWB receiver using the KM approach outperforms the conventional matched filter receiver, the soft-limiting receiver, the Gaussian-Laplace mixture receiver, and the MME-based GNL receiver in high SNR ranges.

Approximate maximum likelihood approach for code acquisition in DS-CDMA systems with multiple antennas

The problem of estimating code timings in DS-CDMA systems with multiple antennas is considered in the presence of multipath time-varying fading channels and near-far environments. We present an efficient algorithm for an approximate maximum likelihood approach of jointly estimating the multipath timings of a desired user for DS-CDMA systems that consist of multiple antennas either uncorrelated or fully correlated in space. The procedures of the algorithm to estimate code-timings are developed in order to better exploit the time-varying characteristics of the fading process. In the multipath fading channels, the solution of the proposed algorithms is based on successively optimizing the criterion for increasing numbers of multipath delays. It is shown via simulation results that the modified approaches of the approximate maximum likelihood algorithm much more improve its acquisition performance in the time-varying fading channels. It is seen that the acquisition performance of multiple antennas based acquisition scheme is much better than that of a single antenna based timing estimator in the presence of multipath fading channels and the near-far problem. Furthermore, it is observed that the proposed algorithms outperform the correlator and MUSIC estimator in the multiuser environments with near-far situation on time-varying Rayleigh fading channels.

Performance of spatial multiplexing MIMO receivers in frequency selective rayleigh fading channels

In this paper, the error performance of various spatial multiplexing (SM) schemes on frequency selective Rayleigh fading channels is investigated. The work presented here considers several multiple-input multiple-output (MIMO) detection approaches such as zero forcing (ZF), minimum mean square error (MMSE), successive interference cancellation (SIC) and sorted QR decomposition (SQRD) in order to cope with inter-channel interference for the MIMO detection scheme followed by RAKE maximal ratio combining (MRC). The error performance and computational complexity of several detection algorithms are comparatively studied via simulations.

Novel multiuser ultra-wideband receiver based on adaptive modelling of generalised normal-Laplace distribution

This study takes a new receiving approach to detect an ultra-wideband (UWB) signal in the presence of multiple access interference (MAI). A generalised normal-Laplace (GNL) distribution is exploited for designing a novel multiuser UWB receiver. To more accurately comply with real statistical behaviours of the MAI-plus-noise in time-hopping multiple access UWB systems, a modified parameter estimator, which is an adaptive method of moments estimation (aMME), is proposed. In the existing studies, the analysis about GNL model shows appropriate results for UWB simulations, while it requires heavy complexity to obtain the precise distribution because of no existence of a closed-form probability density function (PDF) expression. To practically evaluate the GNL PDF, the fast Fourier transform, which can significantly reduce the computational complexity is considered. The GNL using the aMME outperforms the conventional matched filter UWB receiver, the soft-limiting receiver, the Gaussian–Laplace mixture receiver, the p-order metric receiver and the previous GNL receivers, especially in high SNR ranges. Furthermore, the presented GNL receiving method is applied to each finger of the conventional Rake receiver for signal detection in IEEE UWB multipath channels. The proposed Rake receiver based on the GNL distribution performs better than the conventional Rake receiver in multipath fading channels.

Error Performance of Spatial-temporal Combining-based Spatial Multiplexing UWB Systems Using Transmit Antenna Selection

This paper applies transmit antenna selection algorithms to spatial-temporal combining-based spatial multiplexing (SM) ultrawideband (UWB) systems. The employed criterion is based on the largest minimum output signal-to-noise ratio of the multiplexed streams. It is shown via simulations that the bit error rate (BER) performance of the SM UWB systems based on the two-dimensional Rake receiver is significantly improved by antenna diversity through transmit antenna selection on a lognormal multipath fading channel. When the transmit antenna diversity through antenna selection is exploited in the SM UWB systems, the BER performance of the spatial-temporal combining-based zero-forcing (ZF) receiver is also compared with that of the ZF detector followed by the Rake receiver.

Taps Delayed Lines Architecture Based on Linear Transmit Zero-Forcing Approach for Ultra-Wide Band MIMO Communication Systems

In this paper, a transmitter-based multipath processing and inter-channel interference (ICI) cancellation scheme for a ultra-wideband (UWB) spatial multiplexing (SM) multiple input multiple output (MIMO) system is presented. It consists of taps delayed lines and zero-forcing (ZF) filters in the transmitter and correlators in the receiver. For a UWB SM MIMO system with N transmit antennas, M receive antennas, and Q resolvable multipath components, the BER performance of a linear transmit ZF scheme is analyzed in a log-normal fading channel and also compared with that of a receiver-based ICI rejection approach. It is found that when M ≤ N , the transmit ZF processing approach outperforms the ZF receiver while making the mobile units low-cost and low-power.

Performance of Receive Diversity UWB Systems with Pulse Amplitude and Position Modulation

In this paper, we extend ultra-wideband (UWB) single input single output (SISO) systems with a hybrid pulse amplitude and position modulation (PAPM) to single input multiple output (SIMO) systems using receive antenna diversity. The performance of a rake receive diversity combining scheme for UWB SIMO systems with a PAPM is examined in a log-normal multipath fading channel and also compared with that of a time-switched transmit diversity (TSTD) multiple input single output (MISO) system. It is seen that as the number of receive antennas increases, the receive diversity combining system improves the error performance. It is shown that the TSTD UWB MISO systems offer the performance equivalent to the receive diversity combining scheme for SIMO systems.

Performance of decremental antenna selection algorithms for spatial multiplexing MIMO systems with linear receiver over correlated fading channels

This study proposes enhanced suboptimal transmit antenna selection algorithms based on eigenvalue decomposition for spatial multiplexing multiple-input multiple-output (MIMO) systems with linear receivers over correlated MIMO flat fading channels. The suboptimal algorithms presented are based on the n th rooting of maximal ratio combined full channel matrix, in which the condition number significantly decreases, and the decremental selection strategy. The first algorithm exploits channel gains obtained by the channel scaling technique, and is further simplified with much lower complexity in the second algorithm. It is shown that they outperform other suboptimal algorithms in terms of bit error rate minimisation under doubly correlated channels. Moreover, their computational complexities are compared with those of other fast antenna selection algorithms. In addressing channel estimation errors on doubly correlated channels, the proposed decremental selection approaches are shown to offer more robustness than other algorithms.

Transmitter-based Inter-channel Interference Cancellation and Prerake Combining for UWB Spatial Multiplexing MIMO Systems

Abstract In this paper, an ultra-wideband (UWB) spatial multiplexing (SM) multiple input multiple output (MIMO) system exploiting a transmitter-side preprocessing technique is presented. Its transmitter consists of a symbol-based zero-forcing (ZF) inter-channel interference canceller followed by prerake combiners that collect the energies of L resolvable multipath components and its receiver employs correlators. The improved transceiver scheme based on transmit preprocessing and correlation at the receiver is analyzed in a log-normal multipath fading channel. It is shown that it can provide the same diversity order of (LN−M+1) as the UWB SM MIMO system with prerakes in the transmitter and a ZF filter in the receiver for N transmit antennas, M receive antennas, and L resolvable paths. The theoretical and simulated error performances of the presented transmit ZF and prerake combining scheme are also evaluated and compared with those of the UWB SM MIMO systems using prerake combiners at the transmitter and a ZF detector at the receiver.

Spatial Multiplexing Receivers in UWB MIMO Systems based on Prerake Combining

In this paper, various ultra-wideband (UWB) spatial multiplxing (SM) multiple input multiple output (MIMO) receivers based on a prerake diversity combining scheme are discussed and their performance is analyzed. Several UWB MIMO detection approaches such as zero forcing (ZF), minimum mean square error (MMSE), ordered successive interference cancellation (OSIC), sorted QR decomposition (SQRD), and maximum likelihood (ML) are considered in order to cope with inter-channel interference. The UWB SM systems based on transmitter-side multipath preprocessing and receiver-side MIMO detection can either boost the transmission data rate or offer significant diversity gain and improved BER performance. The error performance and complexity of linear and nonlinear detection algorithms are comparatively studied on a lognormal multipath fading channel.