R.P. Gooch

Bio: R.P. Gooch is an academic researcher. The author has contributed to research in topics: Spread spectrum & Estimator. The author has an hindex of 1, co-authored 1 publications receiving 113 citations.

Nonlinear techniques for the joint estimation of cochannel signals

Abstract: Cochannel interference occurs when two or more signals overlap in frequency and are present concurrently. Unlike in spread-spectrum multiple-access systems where the different users necessarily share the same channel, cochannel interference is a severe hindrance to frequency- and time-division multiple-access communications, and is typically minimized by interference rejection/suppression techniques. Rather than using interference suppression, we are interested in the joint estimation of the information-bearing narrow-band cochannel signals. Novel joint estimators are proposed that employ a single-input demodulator with oversampling to compensate for timing uncertainties. Assuming finite impulse-response channel characteristics, maximum likelihood (ML) and maximum a posteriori (MAP) criteria are used to derive cochannel detectors of varying complexities and degrees of performance. In particular, a (suboptimal) two-stage joint MAP symbol detector (JMAPSD) is introduced that has a lower complexity than the single-stage estimators while accruing only a marginal loss in error-rate performance at high signal-to-interference ratios. Assuming only reliable estimates of the primary and secondary signal powers, a blind adaptive JMAPSD algorithm for a priori unknown channels is also derived. The performance of these nonlinear joint estimation algorithms is studied through example computer simulations for two cochannel sources.

Performance enhancement through joint detection of cochannel signals using diversity arrays

Abstract: Joint detection based on exploiting differences among the channels employed by several users allows a receiver to distinguish cochannel signals without reliance on spectrum spreading. This paper makes a number of new contributions to the topic; it provides an analytical expression for the union bound on the average symbol-error rate for an arbitrary number of users and diversity antennas in a fading environment, for both perfect and imperfect channel state information (CSI), and it compares the performance of joint detection with diversity antennas against classical minimum-mean-square-error (MMSE) combining. The performance is remarkable. With accurate CSI, several users can experience good performance with only a single antenna; moreover, for perfect CSI, only a 2-dB penalty is incurred for each additional user. With several antennas, many more users than the number of antennas may be supported with a slow degradation in performance for each additional user. Furthermore, high accuracy is not required from the channel estimation process. In all cases, the performance of joint detection exceeds that of MMSE combining by orders of magnitude.

Performance enhancement through joint detection of cochannel signals using diversity arrays

Abstract: Joint detection based on exploiting differences among the channels employed by several users allows a receiver to distinguish cochannel signals without reliance on spectrum spreading. This paper makes a number of new contributions to the topic: it provides an analytical expression for the union bound on average symbol error rate for an arbitrary number of users and diversity antennas in a fading environment, for both perfect and imperfect CSI, and it compares the performance of joint detection with diversity antennas against classical MMSE combining. The performance is remarkable. With accurate CSI, several users can experience good performance with only a single antenna; moreover, for perfect CSI, only a 2 dB penalty is incurred for each additional user. With several antennas, many more users than the number of antennas may be supported with a slow degradation in performance for each additional user. Furthermore, high accuracy is not required from the channel estimation process. In all cases, the performance of joint detection exceeds that of MMSE combining by orders of magnitude.

Methods and system for reducing co-channel interference using multiple sampling timings for a received signal

Abstract: A plurality of timings are estimated for a received signal wherein the plurality of timings correspond to a plurality of transmitted signals. The received signal is then sampled in accordance with the plurality of timings, to produce a plurality of sample streams from the received signal. Channel estimates are produced for the plurality of transmitted signals and metrics are computed using the sample streams and the channel estimates. Information symbols corresponding to the transmitted signals are detected by using the metrics. Accordingly, by using multiple timings for a received signal, rather than using a common timing, the number of channel taps that are used may be reduced and the accuracy of symbol detection may be increased. The channel estimates may be produced by generating pulse-shape information and producing channel estimates for the multiple transmitted signals using the received signal and the pulse-shape information. Channel estimates may be produced that correspond to a plurality of symbol sequence hypotheses. Channel estimates may be updated using an error signal.

Single-antenna co-channel interference cancellation for TDMA cellular radio systems

Abstract: Co-channel interference cancellation is particularly challenging in the downlink of cellular radio systems because usually only one receive antenna is available at the mobile terminal. This tutorial provides an overview of promising a single-antenna co-channel interference cancellation techniques. Focus is on the downlink of time-division multiple access systems. The results may, however, be extended to related applications, including interference suppression in multiple-input multiple-output systems.

Reuse within a cell-interference rejection or multiuser detection?

Abstract: We investigate the use of an antenna array at the receiver in frequency-division multiple-access/time-division multiple-access systems to let several users share one communication channel within a cell. A decision-feedback equalizer (DFE) which simultaneously detects all incoming signals is compared to a set of DFEs, each detecting one signal and rejecting the remaining as interference. We also introduce the existence of a zero-forcing solution to the equalization problem as an indicator of near-far resistance of different detector structures. Near-far resistance guarantees good performance if the noise level is low. Simulations show that with an increased number of users in the cell, the incremental performance degradation is small for the multiuser detector. We have also applied the proposed algorithms to experimental measurements from a DCS-1800 antenna array testbed. The results from these confirm that reuse within a cell is indeed possible using either an eight-element array antenna or a two-branch diversity sector antenna. Multiuser detection will, in general, provide better performance than interference rejection, especially when the power levels of the users differ substantially. The difference in performance is of crucial importance when the available training sequences are short.