Francois Pipon

New insights into optimal widely linear array receivers for the demodulation of BPSK, MSK, and GMSK signals corrupted by noncircular interferences-application to SAIC

For nonstationary observations, potentially second-order (SO) noncircular, the SO optimal complex filters are time variant and, under some conditions of noncircularity, widely linear (WL). For more than a decade, there has been an increasing interest in optimal WL filters in radiocommunications contexts involving rectilinear signals such as binary phase-shift keying (BPSK) signals. In particular, it has been pointed out that single antenna interference cancellation (SAIC) may be performed by such filters in the context of BPSK cellular networks. Recently, it has been shown that, by a simple algebraic operation of demodulation on the baseband signal, the minimum shift keying (MSK) and Gaussian MSK (GMSK) modulations can be made to approximately correspond to a BPSK modulation, allowing the application of the SAIC concept to the GSM cellular network at the mobile level, being currently studied for standardization, and offering significant improvements of the networks capacity. Despite the increasing interest in optimal WL filters in rectilinear or quasi-rectilinear contexts, many questions about their behavior and their performance have still arisen. The purpose of this paper is to gain insight into the behavior, properties, and performance of optimal WL array receivers, and thus of the SAIC technology, for the demodulation of BPSK, MSK, and GMSK signals corrupted by noncircular interferences.

MMSE antenna diversity equalization of a jammed frequency-selective fading channel

For digital radiocommunications systems operating on a jammed frequency-selective fading channel, the receiver performance can be improved by using the joint antenna diversity and equalization techniques to combat both time- and frequency-selective fades and jammers effects. The optimum, in the sense of minimum mean-squared error (MMSE), structure of the linear equalizer (LE) and the decision feedback equalizer (DFE) for coherent receiver antenna diversity has been derived for an unjammed environment. The structure of the MMSE antenna diversity equalizer is determined for a jammed multipath channel. We show that is composed of the multidimensional matched filter (MMF) followed by a symbol-rate sampler and the MMSE LE or DFE equalizer for single antenna receivers.

Second-order optimal array receivers for synchronization of BPSK, MSK, and GMSK signals corrupted by noncircular interferences

The synchronization and/or time acquisition problem in the presence of interferences has been strongly studied these last two decades, mainly to mitigate the multiple access interferences from other users in DS/CDMA systems. Among the available receivers, only some scarce receivers may also be used in other contexts such as F/TDMA systems. However, these receivers assume implicitly or explicitly circular (or proper) interferences and become suboptimal for noncircular (or improper) interferences. Such interferences are characteristic in particular of radio communication networks using either rectilinear (or monodimensional) modulations such as BPSK modulation or modulation becoming quasirectilinear after a preprocessing such as MSK, GMSK, or OQAM modulations. For this reason, the purpose of this paper is to introduce and to analyze the performance of second-optimal array receivers for synchronization and/or time acquisition of BPSK, MSK, and GMSK signals corrupted by noncircular interferences. For given performances and in the presence of rectilinear signal and interferences, the proposed receiver allows a reduction of the number of sensors by a factor at least equal to two.

Optimal Array Receiver for Synchronization of a Bpsk Signal Corrupted by Non Circular Interferences

The synchronization problem in the presence of interferences has been strongly studied these last two decades, mainly to mitigate the multiple access interferences from other users in DS/CDMA systems. Most of the available receivers are very specific of the CDMA context and only some scarce receivers may also be used in other contexts such as F/TDMA systems. However, these receivers assume implicitly or explicitly circular interferences and become sub-optimal for non circular (or improper) interferences, characteristic in particular of radiocommunications networks using rectilinear (or monodimensional) modulations such as BPSK modulation. For this reason, the purpose of this paper is to introduce and to analyse the performance of the optimal array receiver for synchronization of BPSK signals corrupted by non circular interferences. This receiver implements an optimal, in a least square sense, widely linear filtering of the data, mainly considered up to now for demodulation purposes of BPSK signals, followed by a correlation operation. Extensions to MSK and GMSK signals are presented elsewhere

Performance of the FASTNET Narrowband VHF Frequency Hopping Tactical Radio in Challenging Multipath Environments

FASTNET is the latest tactical VHF radio from THALES. It offers multiple waveforms in frequency hopping, including a new (time multiplex based) waveform called GEOMUX. Multipath situations had been identified and synchronization multipath related changes had been designed for the previous radio generation for Switzerland. Realistic propagation channels are required for the development and testing of a robust communication systems. Thus, Channel sounding in the 30-88 MHz band has been performed in Switzerland (in Jura and the Alps) and has confirmed the existence of challenging multipath propagation with delay spread up to 80 μs. This results in a dual problem : Inter Symbol Interference (ISI) up to 3 modulated symbols in 25 kHz channel bandwidth and potential problems in hop synchronization strategy. In this article, a highly sensitive multipath detection channel sounder is first introduced. Then, an analysis of the measured channel impulse responses is provided. A method to extract propagation parameters from previous measurements is also described. A realistic and reproducible channel model has been developed and injected into a waveform test environment. FASTNET signal processing has been successfully tested on this test environment. The results were confirmed with dedicated field trials in Switzerland, both for the legacy Combat Net Radio (CNR) mode and the multi-services GEOMUX modes. It shows significant range improvements due to the equalization and synchronization design.