Showing papers on "Co-channel interference published in 1984"

MMSE Equalization of Interference on Fading Diversity Channels

Abstract: Adaptive equalization is used in digital transmission systems with parallel fading channels. The equalization combines the diversity channels and reduces intersymbol interference due to multipath returns. When interference is present and correlated from channel to channel, the equalizer can also reduce its effect on the quality of information transfer, important applications for interference cancellation occur in diversity troposcatter systems in the presence of jamming, diversity high frequency (HF) systems which must cope with interfering skywaves, and space diversity line-of-sight (LOS) radio systems where adjacent channel interference is a problem. In this paper we develop the general formulation for minimum mean square error (MMSE) equalization of interference in digital transmission diversity systems. The problem formulation includes the use of available receiver decisions to assist in MMSE processing. The effects of intersymhol interference are included in the analysis through a critical approximation which assumes sufficient processor capability to reduce ISI effects to levels small enough for satisfactory communication. The analysis also develops he concept of additional implicit or intrinsic diversity which results from channel multipath dispersion. It shows how the MMSE processor sacrifices diversity to suppress interference even when the interference arrives in the main beams of the receiver antenna patterns. The condition of near synchronous same-path interference is also addressed. Because the spatial angle of arrival of the interference may result in delay differences between interference signals in different antenna channels, interference delay compensation may be required. We show that this effect is compensated for with a small number of appropriately spaced equalizer taps.

Error rate performance of binary DPSK system with multiple co-channel interference in land mobile radio channels

Abstract: The error rate performance of a binary differentially encoded phase-shift keying (DPSK) system in the presence of both thermal noise and multiple co-channel interferers is theoretically analyzed in the fast Rayleigh fading environment encountered in the typical UHF or microwave land mobile radio channels. The main objective is to show the additional degradation of an error rate of a binary DPSK system when undesired multiple co-channel M-ary DPSK interferers are virtually generated in a practical land mobile radio channel. The error probabilities are presented by a simple closed form as a function of noise correlation, interferer correlation, the number of interferers, M-ary modulating phase of interferer, Doppler frequency, carrier-to-noise (CNR) and carrier-to-interference (CIR) average power ratios.

Interference and noise suppressions using spread spectrum systems

Abstract: Reviews strategies of suppressing interference and noise under various circumstances in order to justify the applications of spread spectrum systems. The basic principles of spread spectrum systems are discussed to demonstrate their capabilities of suppressing noise and interference, and other significant advantages of using such systems. The paper is also examines the factors which affect the capability for interference and noise suppressions and the performance of the systems. It is obvious that the systems can suppress various forms of interference and noise effectively and still achieve other significant goals. The ability of suppressing noise and interference depends on the process gain and correlation properties of the codes of the systems. The overall system performance depends on the degree of synchronization which can be accomplished by the systems.

Multiple-User Interference in a Frequency-Hopped Spread-Spectrum Communication System Using Differential Phase-Shift Keying.

Abstract: : A design of short Reed-Solomon hopping sequences which have excellent correlation properties is proposed. Within the design, any two sequences will have at most one partial hit or one full hit when used asynchronously. The behavior of a near-optimum differential phase-shift keying (DPSK) receiver with multiple-user interference over a non-fading channel is discussed. Bit error rates for the receiver with single interference in one chip and the receiver with single interference in J distinct chips are found. Finally, generalization of the multiple-user interference model is considered. Keywords include: Near-optimum FH-DPSK receiver, Reed-Solomon frequency hopping patterns, and multiple-user interference, error probabilities.

Suppression of FM adjacent channel interference

Abstract: Within current RF allocations, increases in communication traffic have resulted in a trend toward spectral crowding. Effects of adjacent channel interference have traditionally been minimized by geographically isolating channel assignments, or by over-spacing channel centers, inefficiencies which will be unacceptable for future needs. As a result of increased density of communication signals, future receiver hardware will require digital signal processing techniques for suppressing adjacent channel interference. Over the last few years, there have been research efforts aimed at solutions for this type of interference, especially in FM communications Of specific interest here is a mathematical structure developed in [7] addressing suppression of such interfering components after discrimination, where bandwidth reduction results in savings in computation requirements. Initial attempts to apply adaptive filtering techniques to this structure indicated that fundamental problems existed with the formulation. In this paper, this technique is closely scrutinized, and we demonstrate that significant baseband improvements are unlikely for general modulating signals, contrary to published claims.