Multiuser Channel Estimation for Ultra-Wideband Systems Using up to the Second-Order Statistics

Abstract

<p/> <p>In a pulse-position modulation-based ultra-wideband (UWB) communication system, multiple access is enabled by assigning unique time-hopping sequences to different users. Each user's data information is carried by positions of short pulses which are directly transmitted through an unknown and possibly dense multipath channel. Single-user channel estimation methods have been proposed by maximum likelihood optimization that treats multiple access interference as Gaussian noise. In this paper, multiuser channel estimation methods are proposed based on a pulse-rate discrete-time system model and up to the second-order statistics of the channel outputs. The model can be regarded in a trilinear structure and also resembles a code-division multiple-access (CDMA) system with newly defined hopping-code dependent matrices and inputs for each user. Considering that either the mean or covariance of received signals contains sufficient information for all unknown channels, least squares and covariance matching ideas are successfully applied to estimate all channels blindly. Accordingly, closed-form solutions are derived. Those channel estimates can be used to design typical linear receivers. Performance of each proposed estimator is analyzed and also verified by computer simulations. Corresponding receivers' performance is also studied numerically.</p

POR-based channel estimation for UWB communications

“…We can conclude that BER = BER 0 = BER 1 . Moreover, according to (15), we have ∆f 1 = 2 h 1,1 . After examining BER 0 , it is found that BER depends on the SINR of the receiver ∆f 1 .…”

“…This has been observed in subspace techniques [11], [12] and the minimum-variance technique [13], or even mean and covariance-based channel-estimation methods [14], [15]. Therefore, for convenience, zero-mean data is obtained after subtracting the estimated mean from directly received data.…”

Performance Study of A Near-Optimum Modulation Diversity Assisted Ultra-Wideband Receiver

“…It has been observed PPM signals have a nonzero mean [10]. Thus a first-order blind estimator is constructed to obtain an estimate of the reference signal w.…”

“…It will be used to construct correlation templates for symbol detection. The detection process is similar to (7), with w0 being replaced by the improved waveform w1 b°O) = sgn ((4wI)'r12,i), b$j) = sgn(Wlr,2)- (9) In order to further improve system performance, we may continue to update the estimate of w in an adaptive way for n > N as more data are received [12], [13] Wn-N+1 = 1Wn-N + Yn + an(y -Yn) + bnj)rn,2, (10) 448 (5) and perform symbol detection using this updated w each time. Here, ,u < 1 is a forgetting factor, which can be set to a constant value or adjusted dynamically to achieve optimal performance.…”