Showing papers on "Co-channel interference published in 2000"

A multi-user precoding scheme achieving crosstalk cancellation with application to DSL systems

Abstract: This paper describes a precoding scheme capable of achieving crosstalk cancellation in scenarios involving communication from a "base station" to a number of geographically dispersed users. We illustrate that joint processing at the "base station" of the transmitted signals of all users can succeed in removing the otherwise resulting crosstalk. The method employed borrows from the concept of the Tomlinson-Harashima (1971, 1972) precoder which is often used for equalization against intersymbol interference (ISI). One possible application of the proposed technique is in digital subscriber line (DSL) systems, where far end crosstalk (FEXT) poses a severe transmission constraint. Simulation results show that significant improvements can be realized in such scenarios.

UWB radio deployment challenges

Abstract: The challenges related to the deployment of ultrawideband (UWB) radios are posed in terms of interference issues that UWB radio systems will encounter. The problem of coexistence with a Global Positioning System (GPS) receiver is used as an experimental example. Calculation of an upper bound to the UWB transmitter power illustrates the effect of one possible type of regulation for a given UWB antenna system. The interference environment for a UWB receiver is used to lower bound the UWB transmitter power necessary for a given data rate. Sample measurements are provided.

Overcoming time-varying co-channel interference using type-2 fuzzy adaptive filters

Abstract: This paper presents a method for overcoming time-varying co-channel interference (CCI) using type-2 fuzzy adaptive filters (FAF). The type-2 FAF is realized using an unnormalized type-2 Takagi-Sugeno-Kang fuzzy logic system. A clustering method is used to adaptively design the parameters of the FAF. We use transversal equalizer and decision feedback equalizer structures to eliminate the CCI. Simulation results show that the equalizers based on type-2 FAFs perform better than the nearest neighbor classifiers or the equalizers based on type-1 FAFs when the number of co-channels is much large than 1.

Effects of CIR selection diversity with two correlated branches in the m-fading channel

Abstract: A number of methods for the measurement of channel impulse response (CIR) (desired signal carrier power to interference ratio) have been proposed in cellular mobile radio systems. The paper estimates the probability of cochannel interference for CIR selection diversity having two correlated branches in the m-fading channel. The advantage of CIR selection diversity over selection diversity based on the desired signal power algorithm is confirmed.

Method and apparatus for measuring co-channel interference

Abstract: A mobile communication system includes cell segments each associated with a base station. The base station includes transceivers capable of communicating over two sets of carriers. A first set of carriers carry circuit-switched traffic, while the second set of carriers carry packet-switched data. Co-channel interference measurements are made by mobile units or by a serving base station in each cell segment during communications of active bursts of traffic or control signaling. Such bursts may include a training sequence that is used by the measuring device to recreate a burst without interference contributions. Co-channel interference is then determined based on the recreated bursts and the received bursts. Multiple interference values may be derived and applied to an averaging filter to calculate the final interference contribution value.

Radio communication method and radio communication apparatus

Abstract: PROBLEM TO BE SOLVED: To enable the simultaneous use of a plurality types of radio communication systems using the same frequency band in the same area. SOLUTION: Communication channel control sections 111 and 121 are provided in a Bluetooth module 11 and a radio LAN module 21 respectively to prevent interference between signals in the IEEE 802.11b standard and the Bluetooth standard both of which use the same radio frequency band. These sections 111 and 121 perform control for searching a radio channel interfering the other radio communication system, based on the respective BERs of communication channels used at present, to stop the use of the communication channel (open the channel to the other radio communication system). COPYRIGHT: (C)2002,JPO

Iterative co-channel interference cancellation in narrowband mobile radio systems

Abstract: In this paper, co-channel interference cancellation using iterative subtraction is proposed for narrow-band QPSK systems. Signal separability is obtained using both the relative timing delay between signals and the decoded bits output from the channel decoder. Cancellation after decoding results in more reliable signal subtraction, at the expense of interleaving delay. Simulation results show that a small number of iterations is required when ideal channel knowledge is assumed. Soft subtraction, where the estimated values are weighted with some reliability measure, leads to significant C/I gains for both coded and uncoded bits.

Fading distributions and co-channel interference in wireless systems

Abstract: This paper describes the physical models behind the various fading distributions applicable in wireless-communications systems, and presents the probability density functions, both for the signal envelope and for the power of the mobile radio signal. It addresses the problem of co-channel interference in terms of its mean value, for macrocellular and microcellular structures, and illustrates how the outage probability is influenced by a series of factors such as reuse pattern, modulation scheme, traffic load, and others.

Adaptive co-channel interference (CCI) cancellation for OFDM communication systems

Abstract: This paper proposes a new adaptive co-channel interference (CCI) canceller for an orthogonal frequency division multiplexing (OFDM) scheme. It employs a parametric CCI cancellation scheme, least-mean-squares (LMS) maximum-likelihood estimation (MLE), which simultaneously estimates time-varying channels and transmitted symbols both for desired and CCI signals. Computer simulations were performed on interference canceling characteristics of the proposed CCI canceller both under static and Rayleigh fading conditions, wherein a single CCI is considered. Computer simulations confirm that the proposed canceller attains a BER of 1.5/spl times/10/sup -2/ at a signal-to-interference ratio of -10 dB in Rayleigh fading condition with the maximum Doppler frequency of 52 Hz and average E/sub b//N/sub 0/ of 30 dB.

Co-channel interference cancellation techniques for antenna array assisted multiuser OFDM systems

Abstract: Minimum mean square error (MMSE)-based multiple-antenna assisted co-channel interference suppression/space division multiple access (SDMA) schemes designed for OFDM have drawn wide interest. In this article, parallel interference cancellation (PIC) is proposed and studied in comparison to maximum likelihood sequence estimation (MLSE) based schemes. The best design trade-off was constituted by the successive interference cancellation (SIC) schemes.

A comparison of GSM receivers for fading multipath channels with adjacent and co-channel interference

Abstract: We evaluate and compare several data detection schemes used in GSM systems. In particular, we compare the performance of decision feedback equalization (DFE) and nonlinear data directed estimation (NDDE) to that of maximum likelihood sequence estimation (MLSE). Establishing the performance of the basic NDDE detector is a first step in investigating the applicability of block transmission techniques to GSM systems. Our simulation results, obtained both for fading multipath channels and adjacent- and co-channel interference scenarios, suggest that the NDDE offers certain performance advantages over the DFE, and the performance of both detectors is comparable to that of the MLSE for the SNR region of interest in practical systems. Thus, they both represent viable alternatives to the MLSE detector.

Performance evaluation of a Bluetooth network in the presence of adjacent and co-channel interference

Abstract: The objective of the present paper is to evaluate the impact of interference on the performance of a Bluetooth network. Specifically, the interference analyzed is that from other Bluetooth networks. The study focuses on the impact of adjacent and co-channel interference on the throughput and coverage performance. Analysis and simulation data illustrate the significant difference in performance between synchronous and asynchronous systems. The paper also provides insights on how to design Bluetooth networks for maximum throughput and coverage performance.

Generalized RAKE reception for cancelling interference from multiple base stations

Abstract: A generalized RAKE (G-RAKE) receiver structure is developed to suppress both own-cell and other-cell interference in the downlink of a CDMA system. Interference suppression is achieved by accounting for the interference coloration introduced by the dispersive channel. Compared to the conventional RARE receiver, this G-RAKE receiver may have more fingers and has different finger delays and combining weights. The performance in soft handoff is addressed, and the coding used in the IS-95 and IS-2000 systems is used to study the frame-error-rate (FER) performance. It is shown that with coding, the performance is more limited by other-cell interference than own-cell interference. By using the proposed G-RAKE receiver to suppress own-cell and other-cell interference, a gain of 1-2 dB can be achieved.

Co-channel interference cancellation with successive cancellation in narrowband TDMA systems

Abstract: In this paper, successive cancellation of co-channel signals is described in the context of TDMA mobile radio systems employing coherent receivers. Both symbol aligned and misaligned co-channel signals are studied. Signal separability, which is a major problem in successive cancellation of co-channel signals, is obtained using the relative timing delay between co-channel signals. Both hard and soft subtractions are examined. Soft subtraction, where the estimated values are weighted with some reliability measure, leads to significant C/I gains for both coded and uncoded bits.

Adaptive interference cancellation for ADSL

Abstract: An ADSL front end is implemented with an adaptive AM interference canceller to cancel out either a carrier signal of an interfering AM radio signal, or a carrier signal and its sidebands of an interfering AM radio signal, from a received ADSL signal. By canceling an interfering AM radio signal rather than simply filtering out the relevant interfered with frequency band, the interfered with frequency band remains useable for ADSL transmission. In one embodiment, a reference AM radio receiver is either fixedly or adaptively tuned to the carrier frequency of an interfering AM radio station, and the received signal in the frequency band surrounding that carrier frequency is digitized and provided to an adaptive interference canceller. The adaptive interference canceller adaptively adjusts a time delay and phase of the generated AM interference signal to optimize cancellation at a hybrid of the same AM radio signal received as interference over a subscriber line. The AM interference canceller may include a Hilbert bandpass filter, tuned to an appropriate carrier frequency by, e.g., an FFT analyzer. An LMS module adaptively adjusts the parameters of the I and Q channels of the Hilbert filter. In another embodiment, instead of including a reference AM radio receiver, only the carrier signal is removed from the received ADSL signal, leaving the presumably less significant sidebands intact. Preferably, a ratio of differential mode coupling to common mode coupling of the interfering AM radio station is determined to result in a better cancellation of the coupled AM interference signal.

Mitigation of co-channel interference in synchronization bursts in a multi-beam communication system

Abstract: In a cellular satellite system such as Astrolink, where same frequency, same polarization (same "color") signals are used in multiple ground cells, there exists the possibility of interference and false reception of uplink Synchronization Bursts (SB) in systems employing TDMA access of the frequency in question. In such systems, a SB transmitted from one terminal may be received in more than one satellite beam. The reception of the signal from a terminal in an undesired beam (330) is erroneous and may adversely impact the time synchronization (360) of the desired terminal. For example, a system may employ Maximal Length (ML) Pseudo-Noise (PN) sequences (410) for its SBs wherein every beam may use the same sequence. To minimize false reception, the ML PNsequences (410) of each SB may be cyclicly shifted a different amount for each beam to generate sequences (410, 420) having low crosscorrelation with each other. By choosing ML PN codes having low crosscorrelation (410, 420) for the different beams, the interference from undesired beams may be minimized (530).

A novel interference resolving algorithm for the TDD TD-CDMA mode in UMTS

Abstract: When comparing UTRA-TDD with UTRA-FDD it can be found that in the UTRA-TDD mode additional interference scenarios exist. Mobile stations (MSs) can interfere with each other and so can base stations (BSs). Since the source and sink of this type of interference are the same we call it same-entity interference. It is shown by a novel interference resolving algorithm that same-entity interference can be constructively exploited to enable asynchronous overlaps in a UTRA-TDD network. Asynchronous overlaps exist when any cell A is transmitting while the neighbour cell B is receiving. It was found that in a network where an asynchronous overlap exists the algorithm proposed reduces outage from 14% to 6%. In contrast, the outage of an ideally synchronised network was found to be 3.5%. In this 'ideal' network asynchronous overlaps are disallowed resulting in a significant drawback. This is that the flexibility of a TDD system to easily adopt different channel asymmetries is significantly limited.

Co-channel Interference Assessment for Line-of-Sight and Nearly Line-of-Sight Millimeter-Waves Cellular LMDS Architecture

Abstract: Behavior of co-channel interference in fixed wireless cellular systems, such as millimeter-waves Local Multipoint Distribution Service (LMDS), is different compared to what has been established for mobile microwave systems. This is due to utilization of a high-gain antenna for the subscriber. In this paper, first the analysis of signal-to-interference ratio (SIR) is presented for line-of-sight and nearly line-of-sight LMDS architecture. In this analysis, the effects of precipitation and foliage attenuation and depolarization have been considered. These two parameters have negligible effect on the microwave mobile systems but in millimeter-wave range are among the most important factors in the link budget. To mitigate the fading due to shadowing by buildings and trees, a highly overlapped architecture and macro-diversity are proposed. After analysis of downlink SIR in previously proposed cellular systems, a cellular architecture is proposed based on polarization interleaving and frequency segmentation which has a much higher SIR yield. The statistical assessment of SIR is accomplished by assuming lognormal distribution for the received signals.

On the performance of interference canceller based I/Q imbalance compensation

Abstract: In quadrature receivers, unavoidable imbalances in the analog front-end between the I- and Q-branches result in finite and usually insufficient rejection of the image frequency band. This causes the image signal to appear as interference on top of the desired signal. Both analog and digital techniques to compensate the effects of I/Q imbalance have been presented in the literature. In this paper, we carry out a detailed performance analysis of the interference cancellation based imbalance compensation structure utilizing baseband digital signal processing. Also simulation results are provided for comparison. The results indicate that the interference canceller based solution can offer adequate performance for most communication applications.

Performance analysis of link adaptation in wireless data networks

Abstract: We analyze the performance of a link adaptation scheme in which a user, based on his SIR estimate, either transmits using a given modulation and coding scheme or does not transmit (backs off). The impact of channel correlation on the optimal back off SIR threshold is studied for a co-channel interference limited cellular system. Expressions are derived for the average packet waiting time given the basic system parameters like packet arrival statistics, channel fade statistics, number of users per cell, and link adaptation thresholds. Analysis results are shown to be in good agreement with the simulation results. We show that the optimal back-off threshold crucially depends on the channel correlation, a fact not considered by the formulae suggested in literature for determining the link adaptation thresholds. For channel correlation /spl rho/=0.82, the back-off mechanism could reduce average packet delay by up to 15%, as compared to the no back-off case. No such improvement was found for /spl rho/=0.41.

Anti-jamming solution to narrowband CDMA interference problem

Abstract: The main objective of this paper is to describe and simulate an adaptive interference cancelling technique named amplitude domain processing (ADP). The ADP filter will improve the GPS receiver's robustness against all types of interference (coherent CW pulsed or continuous, chirp interference, etc). The ADP filter is designed in Matlab (Simulink) to show its performance and how it can be applied as an adaptive interference canceller to estimate and remove GPS jammers in a real time basis.

An Interference Cancellation Technique for the Use in Multiband Software Radio Frontend Design

Abstract: A fundamental step towards the design of multiband radios is the replacement of fixed frequency components, like duplexers. For solving the arising problems we started with the development of an analog frontend incorporating a technique to suppress one of the main interference effects, namely the coupling of the transmitted signal into the receiving path. This has been accomplished using an active cancellation technique built into a wideband demonstrator operating in the frequency range from 800 to 2200 MHz and for radio channel bandwidths up to 5 MHz. Using the proposed cancellation technique we achieved a total interference suppression of up to 60 dB.

Subband CMA Adaptive Arrays in Multipath Fading Environment

Abstract: SUMMARY CMA (Constant Modulus Algorithm) adaptive arraysare considered a promising method in mobile communica-tions to mitigate multipath fading and to suppress co-chan-nel interference signals. However, since a CMA adaptivearray assumes no a priori information of the desired signal,it is difficult to separate and combine the multipath rays ofthe desired signal. Therefore, when CMA is applied, theinput signal power of the multipath rays cannot be effi-ciently utilized. Moreover, since suppressing the multipathrays requires many degrees of freedom (DOFs) of the array,the array system becomes complicated. In this paper we propose the subband CMA adaptivearray which enhances the signal correlation between themultipath rays in each subband, as such the multipathfading effect can be greatly mitigated. By using thismethod, the multipath rays of the desired signal are equal-ized and combined, whereas an interference signal withmultipath rays can be suppressed by using a single DOF.' 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(11):43Œ54, 2000Key words: CMA adaptive array; multipath fading;co-channel interference; filter banks; blind signal process-ing.

Space-time filtering with suppression of asynchronous co-channel interference

Abstract: The problem of suppression of asynchronous co-channel interference (CCI) is classified as a "threshold" problem where even a small amount of additional information about the part of the CCI without overlapping with the training sequence of the desired signal can significantly improve the performance. A training-like extension of the training sequence can be applied in this kind of problem. The known structure of a timeslot is exploited to select the appropriate positions of information symbols which can be used as the training-like ones. The estimation algorithms based on the training-like approach are proposed. The efficiency is demonstrated by means of simulations in a GSM system.

Performance of a MAC protocol with smart antennas in a multicellular environment

Abstract: We present a study of the signal-to-interference-plus-noise ratio and throughput efficiency achievable in a multicellular environment in the presence of smart antennas at the base station receivers. Interference is explicitly taken into account, and different cases are compared. It is seen that the system operates most efficiently with full frequency reuse, even though this requires network-wide synchronism. The effect of lack of synchronization is also studied.

Capacity and quality enhancement for ANSI-136 downlink using interference cancellation and beamforming

Abstract: In this paper, we investigate the capacity and quality gains for the downlink of an ANSI-136 system when handsets equipped with co-channel interference cancellation are deployed together with base stations employing array antennas. We find that the two capacity-enhancing techniques complement each other very well. Cell sectorization and beamforming increase interferer strength disparity which is exploited by an interference cancelling receiver Compared to a 7/21 re-use system with conventional receivers, the capacity can be almost tripled by means of four fixed beams per sector and two-user joint detection receivers for a slowly-varying flat fading environment.

MC-CDMA uplink-blind carrier frequency offset estimation

Abstract: In order to reduce multiuser and self interference to improve system performance in multicarrier-CDMA (MC-CDMA), accurate carrier references are necessary. This paper presents a low complexity blind carrier offset estimator that simultaneously estimates the carrier offsets of multiple users.

The effect of blanking of TDMA interference on radio-astronomical observations: experimental results

Abstract: The fast growth of the wireless communication industry poses severe limitations on radio-astronomical observations. This is largely due to the fact that in radio astronomy, in contrast to communication systems, the signals of interest are many orders of magnitude below the receiver noise power levels. The structure of some communication signals opens the possibility to reduce the effect on radio-astronomical observations using advanced array processing techniques. One such structure is time slots, used in TDMA communication systems such as the Iridium system and the GSM system. We present the results of blanking of time-slotted interfering signals measured at the Westerbork Synthesis Radio Telescope.

Performance evaluation of cellular mobile systems with successive co-channel interference cancellation

Abstract: This paper presents an analytical framework for the performance evaluation of cellular mobile radio systems equipped with smart antenna systems. In particular, the paper focuses on low-complexity systems which are able to successively suppress the strongest active interferers. The desired user fading statistics is assumed to be flat Rayleigh, Rician, or Nakagami, whereas the interfering signals are assumed to be independent and subject to slow flat Rayleigh fading. The paper starts by presenting generic closed-from expressions for the the carrier-to-interference ratio probability density function after interference cancellation. Based on that, exact closed-form expressions for the outage probability and average error rate formulas are derived. Finally, the impact of some practical considerations on the performance of successive interference cancellation are investigated. More specifically, the effect of traffic loading, the overall spectral efficiency gain, and the impact of time delay are studied.

Forward link capacity based on interference characteristics in CDMA systems

Abstract: Interference is one of the key factors in determining the capacity and performance of CDMA (code division multiple access) systems. In the forward link, the interference consist of a non-stationary process from the multipath of the same cell and stationary Gaussian process resulting from the background noise and interfering signals of other cells, which vary according to the number of multipaths and mobile's position. We investigated the interference characteristics and the required E/sub b//I/sub t/ in WCDMA environments adopting the described interference model. The forward link capacity can be obtained from the results under uniform user distribution throughout the cell. The effect of outer loop power control on the capacity, by which the received E/sub b//I/sub t/ is set exactly to the target value at each position, is also investigated.