We address the problem of designing multirate codes for a multiple-input and multiple-output (MIMO) system by restricting the receiver to be a successive decoding and interference cancellation type, when each of the input signals is encoded independently. It is assumed that the receiver knows the instantaneous fading channel states but the transmitter does not have access to them. We design a multirate coded MIMO system using punctured turbo codes and demonstrate the efficiency of the proposed scheme using simulation results. In particular, the simulation results show performance within 2 dB of MIMO channel capacity.

For a spectrum-efficient, bandwidth-on-demand multiplexer-demultiplexer for a multiuser, multicarrier communication system based on wavelet packet trees for downstream transmission, an innovative scheme for synchronization is proposed which uses a unique sync word at the root of the tree. An example filterbank tree with 8 leaves is used throughout the paper. For this example the creation of the unique 32-bit sync word is described. The multirate signal processing and construction and properties of 25 32/spl times/32 matrices required in the multiplexer to find locations of sync words at input ports to cancel the effects of data and insert the 32-bit sync word in a window in the correct location at the root of the tree is described. The ratio of maximum to minimum absolute values of eigenvalues of the matrices is used to ensure well-conditioning, since they must be inverted in the processing.

Multiple symbol differential detection is known to fill the gap between conventional differential detection of MPSK (M-DPSK) and coherent detection of M-PSK with differential encoding (M-DEPSK). Emphasis has been so far on soft-input/hard-output detectors applied in uncoded systems. In this paper, we investigate a receiver structure suitable for coded DPSK signals on static and time-varying channels. The kernel is an a posteriori probability (APP) DPSK demodulator. This demodulator accepts a priori information and produces reliability outputs. Due to the availability of reliability outputs, an outer soft-decision channel decoder can be applied. Due to the acceptance of a priori information, if the outer channel decoder also outputs reliability information, iterative ("turbo") processing can be done. The proposed "APP DPSK demodulator" uses linear prediction and per-survivor processing to estimate the channel response. The overall transmission scheme represents a type of serial "turbo code," with a differential encoder concatenated with a convolutional code, separated by interleaving. The investigated system has the potential to improve the performance of coherent PSK without differential encoding and perfect channel estimation for fading cases! Only a small number of iterations are required. The receiver under investigation can be applied to several existing standards without changing the transmission format. Results are presented for uncoded and convolutionally coded 4-DPSK modulation transmitted over the Gaussian channel and the Rayleigh flat-fading channel, respectively.

A set of desirable characteristics of a multicarrier spectrum-efficient bandwidth-on-demand multiplexer-demultiplexer pair for use in mobile satellite and personal communication systems is identified and described. New characteristics are the use of single VSB channels, design of multiplexer channels based on wavelet packet trees which have specified stopband attenuation, overlap of the multiplexer channel magnitude frequency responses at the 3-dB points for spectral efficiency, bandwidth on demand, reasonable lengths for the overall equivalent filters for each multiplexer-demultiplexer channel from input to receiver output, and low-complexity receivers. A multirate digital transmultiplexer is proposed consisting of a wavelet packet-based synthesis filter bank tree followed by a DFT polyphase synthesis filter bank at the transmitter, and a matching demultiplexer at the receiver. A simplified receiver for reception of one channel at a time is described. BER performances when there are phase and timing errors are given.

A method for computing the average bit-error probability of binary differential phase-shift keying (DPSK) and frequency shift-keying (FSK) signals transmitted over Nakagami asymptotically slow fading channels with postdetection diversity reception is presented to extend previously published results. The previously published results apply only for maximum ratio combining, i.e., with predetection combining, where phase coherency is necessary. The results for postdetection combining are derived with the explicit expressions for the most practical cases of independent channels and particular cases of correlated channels.

The relationship of filter bank trees to wavelet packet trees for subspaces, decimation operators, and coordinates of the projections of a function onto the subspaces is briefly explained. Two designs for the filter banks are summarized and the equations for the designs are provided. For one of these the prototype filters are all the same, and for the other they are the same at each level of the tree. The best method for spectral factorization of high-order polynomials, needed for the filter designs, is selected. Lattice structures preserving perfect reconstruction with finite word lengths are used in computer simulations to study quantization effects.

Demodulation using the symbol-by-symbol maximum a posteriori probability (MAP) algorithm is presented. The algorithm is derived for the case of continuous phase modulation (CPM) signals transmitted over Rayleigh flat-fading channels, and a corresponding receiver structure is specified. It is shown that the MAP algorithm requires computing, for each trellis branch, the sum of the products of the weights of all paths through the trellis which pass through that branch, and that this generic computational problem can be solved efficiently by an approach that uses a forward and backward recursion through the trellis. Simulation results are presented which show both the hard and soft decision performance of the MAP receiver to be robust, even in the presence of fade rates of up to 30% of the symbol rate. The application of the receiver concept to phase-shift keying (PSK) signals is also discussed, and then evaluated via simulation. The concept of joint demodulation and decoding using iterative processing techniques is introduced. It is shown that the MAP receiver is well suited for iterative processing applications due to its use of a priori symbol probabilities and its production of optimal soft decisions. Simulation results for the reception of quaternary PSK (QPSK) show that the bit error rate (BER) performance of the iterative MAP receiver can approach that of a receiver operating with perfect knowledge of the fading process.

The design of a high speed, real-to-quadrature converter chip set with filtering, decimation, built-in self-test (BIST), and IEEE 1149.1 based boundary scan will be presented. The 15,000 gate application specific integrated circuit (ASIC) implemented in 1.5 /spl mu/m CMOS gate array technology has 3 half-band filters with 3, 7, and 11 taps which can be cascaded in a number of combinations. The intended ASIC application is the processing of narrowband radio signals at IF frequencies. The paper addresses the ASIC's functionality, VLSI implementation and test methodology, and provides both simulation and test data.

A technique for generating narrow-band Gaussian audio noise based on the implementation of the multirate filter is described. The technique allows modification of the bandwidth, central frequency, and amplitude of the noise in real time without interrupting the noise generator. The frequency spectrum of the noise has sharp cutoffs which meet the spectral sensitivities of the human auditory system.

A method for the sequential updating of log-likelihood functions for maximum-likelihood sequence estimation is presented. It is shown that, in a general case, this method can be implemented using Kalman filtering techniques. For the special case of Rayleigh flat fading and continuous phase modulation (CPM) signaling, this approach is shown to lead to an attractive receiver structure. This type of receiver, called the linear predictive receiver, can be implemented in the form of the Viterbi algorithm with the trellis updates being computed using a bank of finite pulse response (FIR) filter and square operations. Simulation results are presented that demonstrate the superiority of the linear predictive receiver over receivers employing differential detection, in the presence of fast fading. It is shown that the optimal linear predictive receiver does not possess an irreducible error rate for a class of Rayleigh fading channels used to model terrestrial mobile channels.>

The authors describe TCMP, a novel modulation strategy for Rician fading channels that multiplexes a time domain pilot sequence with trellis-coded data to permit coherent detection. This technique is shown to provide remarkably robust performance in the presence of fading. It is also shown that, when choosing trellis codes for fading channels, time diversity is of greater important than asymptotic coding gain. The motivation for studying this strategy is to find signaling schemes for transmitting data at a 4.8 kb/s rate over a mobile satellite channel with 5-kHz channel spacing.>

An iterative optimization technique, based on the method of parallel tangents coupled with an efficient line searching technique, is proposed for the design of two-dimensional linear phase FIR digital filters. The performance index for the optimization procedure is shown to be convex and hence this technique will always converge towards the global minimum. An important feature is that the design time increases slowly as the number of filter coefficients increases. To illustrate the technique several circular lowpass filters were designed. These filters compare favourably to filters designed using the minimax technique that was developed by Harris. The technique can also be used for the design of one-dimensional and multi-dimensional linear phase FIR digital filters.