Showing papers on "Co-channel interference published in 1993"

Signal-level-based dynamic power control for co-channel interference management

Abstract: Dynamic power control in cellular systems has long been used for interference reduction, dynamic range control, and terminal battery savings. The analysis and numerical study, in shadow-fading environments, of power control algorithms based on received desired-signal levels are reported. Variational analysis of a simple case shows that compensation for 1/2 the dB value of path-loss variation is the optimal policy for S/I management, rather than the full-compensation algorithm. Simulations of more general cases verify this result and show the degree of robustness to errors and implementation constraints.

Co-channel interference of microcellular systems on shadowed Nakagami fading channels

Abstract: The probability of cochannel interference is evaluated for a microcellular environment with log-normal shadowing and Nakagami fading. For the case when the interfering signals have the same shadowing and fading statistics, an exact mathematical expression is presented for the probability of cochannel interference. For the case when the interfering signals have different shadowing and fading statistics, the probability of cochannel interference is evaluated by approximating the individual interfering signals as having a log-normal distribution, and then applying Schwartz and Yeh's method to obtain a purely log-normal distribution for total interference, while maintaining a composite Nakagami log-normal distribution for the desired signal.

Adaptive co-channel interference reduction system for cellular telephone central base stations

Abstract: A cellular telephone base station (10) uses spatial signal processing to null co-channel (same frequency) interference, such as interference caused by other co-channel radio transmitters and multipath. Radio beams are formed by an antenna array (12) for either or both the transmit and the receive portions of the communications link. Amplitude and phase weighting is applied to inphase and quadrature (I&Q) channels of an array of antenna elements. For the receive portion of the link the weighted signals from these antenna channels are summed to produce a beamsummer output. For the transmit portion of the link the outgoing I&Q signal is amplitude and phase weighted, and then transmitted by the antenna elements in an array to form spatial beams. Antenna array weights are dynamically updated as the angled of arrival of the received signal changes.

Effect of coding in digital microcellular personal communication systems with co-channel interference, fading, shadowing, and noise

Abstract: An analytical model is developed for the performance of a microcellular radio network in the presence of cochannel interference and additive white Gaussian noise. The modulation schemes considered are binary phase-shift keyed (BPSK), binary frequency-shift keyed (BFSK), and quadrature phase-shift keyed (QPSK). The multiple-access channel is statistically modeled by one Rician-distributed desired signal and several uncorrelated Rayleigh plus log-normally shadowed interfering signals, propagating according to dual path loss law with a turning point. The performance is determined in terms of bit error rate (BER), outage probability, block error probability, crosstalk probability, and spectrum efficiency, considering both fast and slow multipath fading. The effect of error correction codes, consisting of blocks with equal number of bits, on the performance parameters is also studied. The computational results show that the propagation loss exponents, Rician factor, turning point, and cell size all plays a major role in the design of an efficient microcellular system. >

Equalization and interference rejection for the terrestrial broadcast of digital HDTV

Abstract: The authors address the problem of transmitting digital HDTV signals in a co-channel interference (CCI) limited environment. A new signal processing technique aimed at rejecting CCI from adjacent analog transmitters is described. The focus is on a receiver structure employing a form of joint decision-feedback equalization (DFE)/trellis coded modulation to combat the interference. DFE is normally not used in coded systems because delay-free decisions are required from the decoder. It is shown that DFE can be used in the application be exploiting the cyclostationary properties of the interference. The technique has several advantages over methods previously proposed: (1) processing is constrained to the receiver; (2) the scheme is able to make use of powerful coding schemes; (3) the scheme is adaptive; and (4) reception of conventional NTSC (National Television Systems Committee) receivers is not affected by this scheme. Simulation results illustrating the performance of this receiver are given. >

Adaptive equalization techniques for multipath fading and co-channel interference

Abstract: The performance of an adaptive fractionally spaced decision feedback equalizer (DFE) in the presence of cyclostationary cochannel interference (CCI) for a frequency-selective quasistatic channel environment is investigated. Simulation and calculation results show that the mean squared error (MSE) convergence for a DFE adapted directly with either the least mean square (LMS) or recursive least squares (RLS) algorithm is prohibitively slow or relatively rapid, respectively. Simulation results also indicate that the performance of an alternative adaptive approach with a computed DFE is limited by its CCI auto-correlation estimation, which requires an unrealistically accurate channel impulse response (CIR) estimate. The preferred approach is to employ an RLS DFE which does not require explicit CIR or CCI autocorrelation estimation.

Apparatus and method for reducing co-channel interference from a radio frequency signal

Abstract: A system for reducing co-channel interference includes a power spectrum analyzer which provides a spectral signal representative of an intermediate frequency signal from the receiver of a direction finding system The system further includes threshold/window logic that, responsive to the comparison of threshold levels and spectral windows to the interfering signals, will provide stop and continue signals to an integrator The integrator receives signals from the direction finding system and stops and starts integration of the output signal responsive to the threshold logic In so doing, co-channel interference is substantially reduced

Planning methods for a national single frequency network for DAB

Abstract: The transmission system developed within Eureka 147 for DAB is known as coded orthogonal frequency division multiplex (COFDM). By dividing the digital data amongst a very large number of low bit rate carriers the COFDM system provides a very high degree of tolerance towards multipath interference. It follows from this that a national network of cochannel transmitters can be developed such that not only do neighbouring transmitters cause mutual interference but can combine in a constructive manner. This is the principle of the single frequency network (SFN). The paper describes the structure and operation of the computerised prediction methods developed by the BBC for the modelling and planning of COFDM single frequency networks, and presents some of the results obtained to date. >

A unique, robust low-rate HF radio modem

Abstract: Military HF radio modems are required to operate over a broad range of adverse channel conditions such as severe multipath and fading, partial-band and carrier-wave interference as well as Gaussian and impulsive noise. The theory of operation and simulation results for a modem capable of providing reliable, low error rate performance in the presence of these harsh forms of interference and distortion is described. The detection is maximum likelihood and is based on a partial-band noise/interference model and the assumption of slow fading. Rejection of interference is facilitated by processing in time and frequency domains. An implementation, allowing a data rate of 75 bits/s, which uses a PSK modulated carrier swept over a 3 kHz bandwidth is described in detail. Simulation results with carrier wave (CW) interference, multipath distortion, Gaussian and impulse noise conditions are presented, demonstrating the exceptional detection performance attainable. >

A performance analysis of PRMA considering speech/data traffic, co-channel interference and ARQ error recovery

Abstract: PRMA (packet reservation multiple access) is a multiple access protocol proposed for use in advanced TDM-based radio systems. While the basic properties of such a protocol are understood, a comprehensive analysis of the protocol performance under realistic operation conditions is missing. The authors consider aspects which are key to a comprehensive analysis, such as traffic source interference, mixture of services (voice and data) and ARQ (automatic repeat request) functions. >

Traffic Analysis of Co-Channel Interference in TDMA Personal Communications Systems: Theoretical Framework

Abstract: This paper presents an analytical modeling framework for studying the impact of co-channel interference on traffic performance in TDMA digital portable radio systems. The theoretical approach is based on a two-dimensional finite state Markov chain description of a base station which tracks both the number of active calls and the number of time slots unusable because of excessive co-channel interference. By suitably choosing certain key model parameters a variety of different radio environments could be studied. Typical of the traffic performance measures that can be obtained with this methodology are new call blocking probabilities, call dropping rates, and the distribution of unusable time slots resulting from co-channel interference (a measure of reduced service capacity). Example numerical calculations illustrating this approach are presented.

Performance of optimum diversity combining and equalization with co-channel interference in mobile radio channel

Abstract: The paper presents a statistical and theoretical analysis of Nth-order diversity reception combined with equalization in a mobile radio channel. The diversity paths are statistically independent and each is characterized by the sum of multiple delayed and independent Rayleigh-fading beams. In modeling the multi-path radio performance, the authors take into account co-channel interference (CCI) generated by frequency reuse and additive white Gaussian noise (AWCN). The performance evaluations are made of average error probability and outage probability. The average error rate is determined by using a Monte Carlo simulation for a set of channel parameters such as signal-to-noise ratio (SNR), signal-to-CCI ratio (SIR) and equalization coefficients determined for this channel, etc. A quadrature amplitude modulation (QAM) is used in the signal analysis. Equalization-taps are determined by using minimum mean-squared error (MSE) criterion and it is expressed directly in terms of the channel parameters and modulation characteristics of the signal. >

Recent results concerning the benefit of joint detection in CDMA systems

Abstract: CDMA is a potential multiple access method for third generation cellular mobile radio systems. If accurate power control and soft handover have to be avoided, adequate CDMA system capacity can only be guaranteed by applying methods of interference suppression, which can be subdivided into interference cancellation and joint detection (JD). The basic principle of IC relies on the fact that the user signals radiated by different users arrive with unequal power levels at the receiver. These differences of power levels make it possible to detect, as a first step, the strongest user signal by, for example, a RAKE receiver, and to eliminate this signal from the total received signal. In subsequent steps, by repetition of this procedure all the other user signals can be detected in decreasing order of power levels. In the case of JD, the a-priori knowledge about the CDMA codes of the different users is exploited when separating the user signals simultaneously in the receiver. JD can only be performed if sufficient knowledge about the impulse responses of the involved radio channels is provided in the receiver. >

Channel allocation system for radio communication system

Abstract: PURPOSE:To provide the channel allocation system for the radio communication system capable of sufficiently displaying the effect of the dynamic channel allocation system even in a sector configuration. CONSTITUTION:Sector antennas 31-34 connecting to reception sections of base stations 11-14 in the radio communication system cover sector cells 41-44 respectively. Radio terminal equipments 21-26 are located to any of the sector cells 41-43. The base station 11 measures an interference level as to channels CH1-CH15 to decide the selection order of the communication channel to a radio terminal equipment 21. A maximum level among interference wave levels of all sector antennas 31a-31d is adopted for the interference wave level. The interference wave level has a high correlation with the interference wave level measured by the radio terminal equipment 21.

Co-channel interference modelling for spectrally efficient cellular mobile radio systems

Abstract: A comparative study of six different co-channel interference models is presented. Three geographical models and three statistical models are studied. In comparing the advantages and disadvantages of each model, the most appropriate model is recommended to establish the relationship between the protection ratio of a modulation technique and the number of cells per cluster needed in a cellular system in order to maintain a given voice quality. Hence, the spectral efficiency can be evaluated.

High capacity cell configuration strategy in ACI and CCI conditions

Abstract: A cell allocation strategy in both adjacent channel interference (ACI) and cochannel interference (CCI) conditions is proposed to increase the system capacity of digital cellular systems. Attention is focused on the effects of ACI on such parameters as the antenna directivity, the channel separation, and the number of cell sites in a cell cluster. The results show that careful selection of these parameters can result in a system capacity approximately 50% higher than US digital cellular systems.

Criteria of the possibility of multipath interference cancellation

Abstract: A case exists in which cancellation of interference is not possible with an interference canceler which cancels the interference wave from ground radio stations mixing into the ground station for the satellite communication. It is found experimentally that this is caused by the difference in the frequency characteristics of the input signals to the two antennas by the multipath effects. Further, a method is proposed to discriminate whether the arriving interferences can be cancelled. Its effectiveness is confirmed experimentally. Whether or not the interferences can be cancelled can be determined by the amount of variation of the received electric field intensity of the interferences. If there is a signal with a constant-shaped spectrum, the distortion of the shape can be used for discrimination. As a result, the condition and limit of applications of the interference canceler are found.

Performance evaluation of an adaptive GSM receiver with frequency‐selective fading and adjacent‐ and co‐channel interference

Abstract: This study represents the sequel and conclusion of a previous one already published in this Journal a few issues ago.1 In that article, we tackled the problem of evaluating theoretically the performance of an adaptive MLSE receiver for MSK signals on a frequency-selective stationary radio propagation channel, and we validated the theoretical findings (in the form of upper and lower bounds to the BER of the receiver) by means of computer simulations. In the present paper, we report on the performance of the very same scheme of channel-estimator-plus-Viterbi-equalizer receiver for mobile communications in a more realistic operating environment. In particular, we completely encompass here the groupe special mobile (GSM) transmission format, based on the Gaussian minimum shift keying (GMSK) modulation scheme and on narrowband time-division multiple access (TDMA) transmission. Also, we remove the assumption of a time-invariant propagation channel, assuming the recommended standard GSM channels as benchmark transmission conditions. Finally, with the aid of extensive computer simulations, we analyse the sensitivity of the MLSE receiver to unwanted co-channel and adjacent-channel interference coming from other users of the mobile cellular GSM system.

A fundamental approach to communications in a hostile environment

Abstract: The authors outline an approach to detector design to achieve good communications performance in severe channel environments. A transmitted radio signal may undergo distortion, and be modified by interference and noise. By using a stochastic model of the channel, the essential design criterion for optimality namely, maximization of the probability of correct detection, may be proposed from fundamentals, taking into consideration as best as is known, the nature of the noise, interference and distortion. In support of this approach, two examples demonstrate how improved detector performance may be achieved. The examples detail detectors for impulsive noise and narrowband interference based on a simple model. >

Methods for ascertaining radar interference into high capacity radio relay receivers

Abstract: The operational surveillance of radio relay equipment carrying normal traffic has become common within many administrations. The parity check feature of the radio frame is exploited to derive an estimate of the bit error rate (BER) and subsequently the number of events (seconds) when a certain BER is exceeded is cumulated. Thus one may estimate whether the performance of a particular transceiver/radio hop will meet the requirements of CCIR Rec. G.821. The function described is performed by the supervisory system for all radio channels and all hops of a particular transmission system. Some methods for ascertaining the occurrence of radar EMI, and for extracting some of the characteristic features of an interfering radar are presented.

Effect of obstacles on interference between slant paths and terrestrial links, as a function of frequency

Abstract: Questions related to interference between radio communication systems are becoming more and more crucial as both terrestrial and satellite radio services are rapidly expanding. This interference can be reduced by several techniques, in particular site shielding (COST Project 210). In this method, an obstacle is used in the vicinity of an earth station to be protected against unwanted signals produced by terrestrial links. >

Optimum Detection of Antipodal Signals Disturbed by Partly Known Co-Channel Interference and Gaussian Noise - Asymptotic Results

Abstract: Optimum Detection of Antipodal Signals Disturbed by Partly Known Co-Channel Interference and Gaussian Noise - Asymptotic Results

Transmitter Power Control for Co-Channel Interference Management in Cellular Radio Systems - An Overview and some Recent Results

Abstract: Transmitter Power Control for Co-Channel Interference Management in Cellular Radio Systems - An Overview and some Recent Results

Capacities of simplex and duplex VHF air/ground mobile radio communication systems employing cylindrical cells

Abstract: The channel capacities of simplex and duplex VHF air/ground (A/G) mobile radio communication systems employing cylindrical cells are compared considering co-channel and adjacent channel interferences criteria currently adopted by the International Civil Aviation Organization (ICAO) and the Federal Aviation Administration (FAA). According to ICAO recommendations, the co-channel interference source must be beyond the radio line-of-sight (RLOS) of the receiver. The FAA co-channel interference criterion requires a signal-to-interference ratio of at least 14 dB or beyond RLOS protection. Capacity depends mainly on the frequency reuse distance. In order to prevent air-to-air interference, simplex systems using the same frequency for air-to-ground and ground-to-air require a larger frequency reuse distance than duplex systems which do not require air-air interference since different frequency bands are used for uplink and downlink communications. A comparison is presented between the capacities of the two systems. It is shown that the capacity ratio of the two systems depends on the cell dimensions. It is concluded that the duplex system has more capacity than the simplex system for cells of large radii and small heights.