Jean Conan

The Weight Spectra of Some Short Low-Rate Convolutional Codes

This paper reports the results of a computer analysis of the distance properties of some of the best known rate 1/2, 1/3, and 1/4 codes to constraint length 14. The data include the truncated weight distributions of the codewords belonging to the incorrect subset which specifies the performance of the Viterbi algorithm as well as the minimum asymptotic growth rate of the weights of unmerged codewords which has been conjectured to be related to the length of error events produced by Viterbi decoders.

Structural properties and enumeration of quasi cyclic codes

Given any finite fieldFq, an (N, K) quasi cyclic code is defined as aK dimensional linear subspace ofFqN which is invariant underTnfor some integern, 0 <n ≦N, and whereT is the cyclic shift operator. Quasi cyclic codes are shown to be isomorphic to theFq[λ]-submodules ofFqN where the productμ(gl)·ν is naturally defined asμ0ν+μ1νTn+...+μmνTmnifμ(λ)= μ0+μ1+...+μmλm.In the case where (N/n, q)=1, all quasi cyclic codes are shown to be decomposable into the direct sum of a fixed number of indecomposable components called irreducible cyclicFq[λ]-submodules providing for the complete characterisation and enumeration of some subclasses of quasi cyclic codes including the cyclic codes, the quasi cyclic codes with a cyclic basis, the maximal and the irreducible ones. Finally a general procedure is presented which allows for the determination and characterisation of the dual of any quasi cyclic code.

Joint Estimation of Channel Parameters for MIMO Communication Systems

In the next generation mobile communication systems, high data rates and high capacity are expected if multiple antennas are used at both receive and transmit sides. Such a radio propagation channel constitutes a multiple-input multiple-output (MIMO) system. In a wireless MIMO system, it is possible to estimate channel parameters in a multipath environment by extending the classical parameter estimation methods to the joint space and time domain. In this paper, we propose a subspace-based approach to jointly estimate the angle-of-arrival (AOA), angle-of-departure (AOD) and delay-of-arrival (DOA) of digitally modulated multipath signals in MIMO communication systems. The novel approach uses a collection of estimates of a space-time manifold vector of the channel which utilizes a Khatri-Rao product to transfer the estimated channel response matrix to the classical model. Simulation results show that the proposed methods can achieve high resolution of channel parameters and resolve more multipath components than the number of array elements

Mobile Terminal Location for MIMO Communication Systems

We propose a novel approach in the context of multiple-input multiple-output communication systems to determine the position of mobile terminals based on estimated multipath signal parameters such as angle-of-arrival, angle-of-departure and delay-of-arrival using only one base station. This approach minimizes the errors occurring from the estimation of multipath parameters and gives the position of the mobile terminal by simultaneously resolving a set of algebraic location equations. The root-mean-square (RMS) errors are measured and compared with the Cramer-Rao lower bound to demonstrate the performance of the proposed method.

A transform approach to Goppa codes

Based on a finite Fourier transform of codewords over the finite field GF (q^{m}) , some basic properties of the class of Goppa codes are presented. A new lower bound on the minimum distance for these codes is derived and applied to a subclass of Goppa codes which is. in fact. equivalent to a subset of punctured reversible cyclic codes. Furthermore. it is shown how the class of Goppa codes can be easily decoded in the context of this transformation by using the Berlekamp-Massey decoding algorithm. Through a slight extension of the procedure, it is also shown how this algorithm may be used m decode alternant codes up to their guaranteed error-correction capability.

A [55,16,19] binary Goppa code (Corresp.)

A [55, 16, 19] binary Goppa code and some related codes are described. These codes are found to contain more codewords than any previously known codes of the same length and minimum distance.

Mobile Station Location Estimation for MIMO Communication Systems

Wireless location is the procedure that determines the position of the mobile station in a wireless network. The traditional mobile location systems such as direction finding and ranging are based on trilateration/multilateration techniques. In wireless MIMO communication systems which utilize antenna array at both transmit and receive sides, the redundancy of multipath signals can be exploited to extract more parameters such as angle-of-arrival, angle-of-departure and delay-of-arrival using advanced array signal processing techniques. In this paper, based on estimated multipath signal parameters in the context of MIMO communication systems, we propose a novel approach to determine the position of mobile stations using only one base station. This approach minimizes the errors occurring from the estimation of multipath parameters and gives an optimal estimation of the position of the mobile station by simultaneously resolving a set of algebraic location equations. The mean-square errors are measured and compared with the Cramer-Rao lower bound to demonstrate the performance of the proposed method. This solution breaks the bottleneck of conventional mobile positioning systems which have to require multi-lateration of at least three BSs.

Error correction/masking for digital voice transmission over the land mobile satellite system

The development of a 2400-b/s speech digitizer which provides an acceptable level of intelligibility and quality over land mobile satellite channels is described. Performance tests over simulated channels in the UHF band (800 MHz) are presented. The voice digitizer is a linear prediction (LPC) vocoder which uses a channel error correction and concealment procedure tailored to error statistics for a minimum-shift keyed (MSK) downlink to a moving vehicle. The error-handling technique is based on perceptual criteria and utilizes the parametric nature of LPC representation of speech. A single-error-correcting, single-burst-detecting (28, 20) fire code is shown to be the best choice for the application. The intelligibility of the vocoder is measured and compared to the standard LPC-10 algorithm. The major remaining sources of speech quality degradation due to channel errors are determined and ranked. >

Deterministic Approach for Spatial Diversity Analysis of Radar Systems Using Near-Field Radar Cross Section of a Metallic Plate

A deterministic analysis of spatial diversity is presented in connection with radar systems. A numerical technique based on physical optics is used for our analysis. Contrary to statistical models, the proposed technique takes into account accurate near-field radar cross section of the target, and radiation characteristics of transmitting and receiving antennas. The power scattered by the target and received by multiple antennas as a function of the target aspect angle and distance is analyzed. Two combining methods of received powers are tested and statistical analysis is performed showing that, using spatial diversity, the angular range can be increased significantly and the standard deviation of the target response can be reduced. In order to validate our analysis and proposed scheme, experimental measurements were carried out using a metallic plate and a car as targets. This work has potential applications in automotive collision warning/avoidance radar systems.

Multicast Capacity of Wireless Ad Hoc Networks with Hierarchical Routing

The focus of this paper is on presenting new results on throughput capacity of wireless ad hoc networks with multicast traffic. In seminal works, Gupta and Kumar introduced a new line of research. It is about the asymptotic throughput capacity of dense wireless ad hoc networks as a function of the number of nodes in the network. In this paper, we present an upper bound on the throughput capacity of an ad hoc network with multicast traffic using a hierarchical routing strategy. We start first by generating the upper bound and the strategy gain for the 2-level hierarchical strategy. Then, we generalize the result for multi-level hierarchical routing by giving the recurrence expression of the multicast gain. Finally, we apply the basic result to a broadcast traffic in the network