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Showing papers on "Co-channel interference published in 1999"


Proceedings ArticleDOI
01 Jan 1999
TL;DR: To extend this work to OFDM(A) mobile radio systems in the uplink case where many users' contributions to the ICI overlap, the concept of an equivalent single-user which causes the total ICI is introduced in order to use the same analytical framework.
Abstract: We analyze the effects of Doppler spread in mobile channels on orthogonal frequency division multiplex (OFDM) systems. This is important, since channel variations during one OFDM symbol cause inter sub-carrier interference (ICI) in OFDM systems, which degrades the performance, since ICI can be seen as additional near-Gaussian noise. The analysis is outlined, and closed-form results given for numerous important practical Doppler spread encountered in mobile channels. We also show that for the case of asymmetrical Doppler spreads, the frequency correction of the receiver can be adjusted so as to minimize the ICI. To extend our work to OFDM(A) mobile radio systems in the uplink case where many users' contributions to the ICI overlap, we have introduced the concept of an equivalent single-user which causes the total ICI, in order to use the same analytical framework. For some channel examples, we simulated the Doppler spread of this equivalent user. Simulation results confirm our analysis and show the importance of the analytical tool to perform realistic system analysis without having to resort to time consuming time-domain simulations.

240 citations


Patent
Antti Kansakoski1, Jean-Marie Tran1
09 Jul 1999
TL;DR: In this article, a system and method for canceling interference present in a code-division multiple access (CDMA) channel signal received at a CDMA receiver that is caused by multipath components of a transmitted pilot channel signal or by soft handoff conditions is presented.
Abstract: A system and method for canceling interference present in a code-division multiple access (CDMA) channel signal received at a CDMA receiver that is caused by multipath components of a transmitted pilot channel signal or by soft handoff conditions is computationally efficient because it operates at symbol rates. The channel signal from which such multipath interference is canceled can be either a traffic (data) channel or the pilot channel itself. Interference signals are produced in groups corresponding to the fingers of the CDMA rake receiver. The interference signals corresponding to each finger are used to cancel interference in the other fingers.

108 citations


Proceedings ArticleDOI
01 Sep 1999
TL;DR: The system BER performance is shown to be improved by an order of a magnitude due to combining AOFDM with interference suppression, and the subcarrier based signal-to-noise ratio (SNR) is found to be in most cases an effective measure for controlling the modulation mode adaptation.
Abstract: This paper investigates the feasibility of adaptive OFDM (AOFDM) transmissions in co-channel interference limited environments upon invoking the sample matrix inversion (SMI) algorithm. The subcarrier based signal-to-noise ratio (SNR), which can be derived from the SMI algorithm's weights is shown to be in most cases an effective measure for controlling the modulation mode adaptation. A simple pilot based scheme is introduced, which allows channel parameter estimation on an OFDM symbol-by-symbol basis. The system BER performance is shown to be improved by an order of a magnitude due to combining AOFDM with interference suppression.

58 citations


Patent
27 Nov 1999
TL;DR: In this article, the authors proposed a method for cancelling co-channel interference in a multi-carrier communication system, which includes receiving a serial baseband multichannel signal including a desired signal and at least one interference signal over a receiving branch.
Abstract: A method for cancelling co-channel interference in a multi-carrier communication system includes receiving a serial baseband multi-carrier signal including at least one desired signal and at least one interference signal over at least one receiving branch, and converting the received multi-carrier signal into a plurality of baseband sub-carrier signals. Co-channel interference in each sub-carrier signal is cancelled by subtracting an estimated desired received sub-carrier signal and an estimated interference sub-carrier signal from a received sub-carrier signal. The sub-carrier signals are converted to a multi-carrier output signal comprising the desired signal.

58 citations


Proceedings ArticleDOI
Z. Kostic1, I. Maric1
16 May 1999
TL;DR: In this paper, the authors examine techniques for increasing spectral efficiency of cellular systems by using slow frequency hopping with dynamic frequency-hop pattern adaptation, driven by rapid frequency quality estimates, and present simulation studies that express system performance by calculating code word error cumulative distribution functions.
Abstract: We examine techniques for increasing spectral efficiency of cellular systems by using slow frequency hopping with dynamic frequency-hop pattern adaptation. The adaptation is driven by rapid frequency quality estimates. We present simulation studies that express system performance by calculating code word error cumulative distribution functions. The impact of path loss, shadowing, Rayleigh fading, co-channel interference, voice activity and occupancy is monitored. Simulations have been done for circuit-switched systems. The paper investigates: (a) full-replacement dynamic frequency hopping (DFH); (b) worst-dwell DFH; and (c) threshold-based DFH. The results show that full-replacement dynamic frequency hopping can support twice as many users as random frequency hopping. The two other techniques perform worse than the full-replacement technique, but better than random hopping.

58 citations


Patent
02 Jul 1999
TL;DR: In this article, a channel selection method is provided to share a frequency band efficiently in local radio communication system and other radio communications systems, based on transmission and reception of control packets and interference wave power.
Abstract: A channel selection method is provided to share a frequency band efficiently in local radio communication system and other radio communications systems. The use of each selectable channel in local radio communications system 10A is examined on the basis of transmission and reception of control packets (step 302). The use of each selectable channel in another radio communication system 10B is examined on the basis of interference wave power (step 303). A channel for use in a radio communication at local radio communication system 10A is selected based on the results of the examinations.

37 citations


Journal ArticleDOI
TL;DR: By opting for channel partitioning, the improvement in spectral efficiency compared to channel sharing is two to three times greater, and the reuse factors in the microcells and macrocells therefore do not need to be increased beyond conventional values.
Abstract: The performance in terms of signal-to-interference ratio (SIR), teletraffic, and spectral efficiency of a combined macrocellular and microcellular network is investigated when either both types of cells share the same channel set, or when the channel set is partitioned between the macrocells and the microcells. The analysis is for time-division multiple access (TDMA) with frequency hopping, power control, and discontinuous transmission, and the radio channel is composed of an inverse fourth-power path loss law with log-normal fading. We commence by introducing a single microcell into a hexagonal cluster of macrocells before considering clustered microcells. Both omnidirectional and sectorized cells are examined. We find that high reuse factors are required when channel sharing is employed. When channel partitioning is used, no co-channel interference occurs between the microcells and the macrocells allowing them to be planned independently. The reuse factors in the microcells and macrocells therefore do not need to be increased beyond conventional values. The outcome is that by opting for channel partitioning, the improvement in spectral efficiency compared to channel sharing is two to three times greater.

33 citations


Patent
Andreas Czylwik1
27 Nov 1999
TL;DR: In this article, an interference cancellation scheme for a digital multi-carrier communication system is proposed, where the effect of the inter-symbol interference is avoided by using a digital multiuser communication system, and the receiver (8) comprises a plurality (L) of interference cancellers (171-17L) each of which is associated to a respective one of subcarrier signals.
Abstract: The present invention relates to an interferance signal cancel ing method, a receiver using the same and a digital multi-carrier communication system comprising such a receiver. A main aspect of the present invention is to apply an interference cancellation scheme to a digital multi-carrier communication system. By using a digital multi-carrier communication system, the effect of the inter-symbol interference is avoided. As a result the receiver (8) comprises a plurality (L) of interference cancellers (171-17L) each of which is assocaiated to a respective one of sub-carrier signals for canceling only co-channel interference.

29 citations


Proceedings ArticleDOI
16 May 1999
TL;DR: Simulations and experimental results for transmission of normal GSM bursts in interference limited scenarios are presented and the advantages of taking the spatial correlation of the co-channel interference into account are examined.
Abstract: In this work, burst oriented data transmission over unknown frequency selective channels is considered. The receiver is assumed to use multiple antennas and the problem of estimating the start position of a data packet in the presence of spatially correlated co-channel interference is addressed. Each burst is assumed to contain a known training sequence, and in the paper metrics for finding the position of this training sequence are studied. More specifically, we examine the advantages of taking the spatial correlation of the co-channel interference into account, as compared with treating it as spatially white. Simulations and experimental results for transmission of normal GSM bursts in interference limited scenarios are presented.

26 citations


Proceedings ArticleDOI
23 Aug 1999
TL;DR: Experimental results shown that the SVM equalizer outperforms both linear and RBF equalizers, particularly for small training set, in case of time-varying channels.
Abstract: Investigates the application of support vector machines (SVMs) for the equalization of communication systems corrupted with additive white Gaussian noise, intersymbol and co-channel interference. Performance obtained with SVMs for this task is compared to the one obtained with linear and radial basis function (RBF) equalizers. The centers and the weights of the RBF networks are determined by the k-means and LMS algorithms, respectively. Experimental results shown that the SVM equalizer outperforms both linear and RBF equalizers, particularly for small training set. In case of time-varying channels, it is envisaged that the length of the training sequence which needs to be periodically transmitted would be reduced by SVM equalizers.

21 citations


Patent
02 Mar 1999
TL;DR: In this paper, the authors present an interference cancellation for a DS-CDMA communication system and a radio communication device that performs multi-rate transmission and eliminates interference of high-rate channels by a simplified structure.
Abstract: The present invention is directed to an interference canceller for a DS-CDMA communication system and a radio communication device that performs multi-rate transmission and eliminates interference of high-rate channels by a simplified structure. In a DS-CDMA communication system that performs a multi-rate transmission including at least low-rate channels and high-rate channels, there is provided an interference canceller that includes an array antenna interference replicating unit. The interference replicating unit is used in high-rate channels that receive signals received via array antenna elements and creates interference replicas of the high-rate channels. The system also includes an adder 6 , which subtracts the interference replicas from the received signal via the array antenna elements. Further a resultant interference-eliminated signal is applied to receivers for the low-rate and high-rate channels.

Journal ArticleDOI
TL;DR: This work proposes a subspace-based algorithm for blind channel estimation of a synchronous CDMA downlink, and shows that the estimation accuracy can be increased considerably using a decision feedback approach.
Abstract: Synchronous code-division multiple-access (CDMA) techniques possess intrinsic protection against co-channel interference due to the orthogonal spreading codes used. However, in the presence of multipath, the signals lose their orthogonality property, leading to increased cross correlation. In these cases, channel estimation may be needed in order to improve the detection of the desired symbols. We propose a subspace-based algorithm for blind channel estimation of a synchronous CDMA downlink. We compare the channel estimation accuracy with the Cramer-Rao bound, and we show that the estimation accuracy can be increased considerably using a decision feedback approach.

Proceedings ArticleDOI
16 May 1999
TL;DR: For the AWGN channel with and without co-channel interference, the detector is found to be robust to complexity reduction both in the number of states in the Viterbi decoder and in the approximate filter bank.
Abstract: A coherent CPM detector based on a reduced filter bank and a reduced state Viterbi decoder is proposed. Bit error probabilities of this detector for some CPM schemes satisfying a specific narrow spectrum requirement mask are simulated for the AWGN channel. The performance for one of the good candidates is then further evaluated for the case when co-channel and adjacent channel interference is present. For the AWGN channel with and without co-channel interference, the detector is found to be robust to complexity reduction both in the number of states in the Viterbi decoder and in the approximate filter bank. The number of states in the decoder and the complexity of the filter bank can be reduced significantly. It is still possible to reduce the complexity for the AWGN channel with adjacent channel interference, but not to the same extent without loosing significantly in performance.

Journal ArticleDOI
TL;DR: A new approach to interference suppression in code-division multiple-access (CDMA) wireless networks where high bit rate signal due to lower processing gain must use a higher level in order to provide the required quality of transmission.
Abstract: In this paper we present a new approach to interference suppression in code-division multiple-access (CDMA) wireless networks. Depending on the interfering signal, these schemes adaptively change not only their parameters but their structures as well. For the relevant types of the interfering signal, suppression is also possible for the wideband interference occupying the same frequency band as the CDMA signal. Probability of error in these schemes is for several orders of magnitude better than in the existing solutions described in the open literature so far. The main applications are the CDMA overlay type wireless network collocated in the same frequency band with a high bit rate microwave communication system, and the multimedia CDMA network where high bit rate signal due to lower processing gain must use a higher level in order to provide the required quality of transmission.

Proceedings ArticleDOI
31 Oct 1999
TL;DR: In this paper, co-channel interference in wideband CDMA systems such as W-CDMA and cdma2000 with carrier stealing is evaluated for different CDMA architectures such as microzoning and sectoring.
Abstract: Wideband code-division multiple access (CDMA) systems are interference-limited, and so must utilize some form of interference reduction in order to maintain an acceptable quality of service and capacity. In this paper, co-channel interference for several different CDMA architectures is evaluated. For wideband CDMA systems such as W-CDMA and cdma2000 with carrier stealing, co-channel interference is significantly reduced by the implementation of either microzoning or sectoring. The disadvantage of microzoning is that intra-cell interference is no longer ideally zero on the forward channel, as it is with sectoring and omnidirectional architectures. For wideband CDMA systems such as cdma2000 without carrier stealing, co-channel interference is reduced by both microzoning and sectoring architectures even more than in the case of W-CDMA and cdma2000 with carrier stealing. In this case, since forward channel intra-cell interference remains ideally zero, the significant reduction of co-channel interference by microzoning makes microzoning clearly superior to omnidirectional architectures.

Proceedings ArticleDOI
16 May 1999
TL;DR: In the context of power control in cellular radio systems, it is given proof that, in the presence of auto-interference, the maximum achievable balanced carrier-to-Interference ratio (CIR) is lower than in the case of its absence.
Abstract: In the context of power control in cellular radio systems, we study the effect of auto-interference. This aspect has been neglected in most of the papers related to this subject. Using a basic model, the effect of this interference on power control is analytically studied. We give proof that, in the presence of auto-interference, the maximum achievable balanced carrier-to-interference ratio (CIR) is lower than in the case of its absence. Known power control methods are applied in this hypothesis. Simulation shows that auto-interference, even if it is relatively small, leads to too optimistic results.

Proceedings ArticleDOI
16 May 1999
TL;DR: The advantages of a low rank truncation of the whitened channel in a mobile radio scenario where the S-T diversity of the channel is almost limited and the lower complexity compared to a full-rank solution are illustrated.
Abstract: MMLSE is known to be the most suitable approach for space-time (S-T) receivers that requires the knowledge of the S-T channel response. In general we do not have the knowledge neither of the channel H nor of co-channel interference's (CCI) statistics, these have to be estimated by using training sequences. When short data preambles are available the large variance of the unconstrained estimate of the multichannel H can heavily affect the achievable performance. This paper illustrates the advantages of a low rank truncation of the whitened channel in a mobile radio scenario where the S-T diversity of the channel is almost limited. The benefits achievable with this class of low-rank receivers are the reduction the variance of the multichannel response estimate and the lower complexity compared to a full-rank solution. The performances in realistic scenarios demonstrate the advantages compared to conventional receivers.

Proceedings ArticleDOI
09 May 1999
TL;DR: This paper is the first to propose the implementation of advanced array signal processing methods for interference detection in radio astronomical observations by describing a multichannel interference detector which enables us to reduce the interference by rejecting corrupted time-frequency slots.
Abstract: Radio-astronomical observations are increasingly disturbed by man-made communication signals, satellite and broadcast services. In particular, the GSM band is a highly saturated domain, full with interferers which are much stronger than radio astronomical signals. We propose a strategy to reduce this interference using its non-stationary nature. We describe a multichannel interference detector which enables us to reduce the interference by rejecting corrupted time-frequency slots. The use of multichannel detection greatly improves performance over previously suggested single channel detectors. This paper is the first to propose the implementation of advanced array signal processing methods for interference detection in radio astronomical observations.

Patent
05 Jul 1999
TL;DR: In this paper, a signal parameter of a selected channel is monitored in order to detect interference due to intermodulation products in a radio communications unit with several transceivers communicating in different frequency bands.
Abstract: In a radio communications unit with several transceivers communicating in different frequency bands, a signal parameter of a selected channel is monitored in order to detect interference due to intermodulation products. The select channel is for example used by a long range radio communications link and the interfering channel on a short range radio link. Once the channel causing interference has been identified, transmissions on it are prevented.

Proceedings ArticleDOI
R.M. Buehrer1
24 Oct 1999
TL;DR: This work examines linear and non-linear multistage versions of parallel and successive interference cancellation for CDMA systems and concludes that the convergence of multistages interference cancellation is convergent.
Abstract: We examine the convergence of multistage interference cancellation for CDMA systems. Specifically, we examine linear and non-linear multistage versions of parallel and successive interference cancellation.

Proceedings ArticleDOI
Li-Chun Wang1, Kin K. Leung2
01 Dec 1999
TL;DR: The results show that in a typical radio environment, the NBQC system with the ICA scheme can achieve a reuse factor N=2 with the 90 percentile of SIR as high as 11 dB, which represents 3 to 5 dB SIR improvement or about at least 40 percent system capacity improvement over current cellular networks.
Abstract: We propose an improved sectorization scheme for cellular networks, called narrow beam quad-sector cell (NBQC), in which each cell is divided into 4 sectors and each sector is covered by a 60/spl deg/ antenna. The NBQC architecture has a better coverage performance than the current 3-sector cellular architecture. More importantly, the NBQC architecture allows easy implementation of the powerful interleaved channel assignment (ICA) scheme. Because of taking full advantage of the antenna directivity, the NBQC architecture with the ICA scheme can improve the signal to interference ratio (SIR) performance, thereby increasing the system capacity significantly. Our results show that in a typical radio environment, the NBQC system with the ICA scheme can achieve a reuse factor N=2 with the 90 percentile of SIR as high as 11 dB, which represents 3 to 5 dB SIR improvement or about at least 40 percent system capacity improvement over current cellular networks.

Proceedings ArticleDOI
31 Oct 1999
TL;DR: The focus of this paper is to show how different interfering signals will affect the performance of a radio system, and the consequences of approximating these interference signals as additive white Gaussian noise are investigated.
Abstract: Transmitters and electrical equipment co-located to a radio system can, due to its radiated electromagnetic interference, cause serious degradation on the system performance. In real system design, when predicting the loss of performance, with a set of interferences of various signal types, there is a need of simple approximations that simultaneously describe the interferences in a proper manner. The focus of this paper is to show how different interfering signals will affect the performance of a radio system. Furthermore, the consequences of approximating these interference signals as additive white Gaussian noise are investigated.

Proceedings ArticleDOI
16 May 1999
TL;DR: For the downlink, a low complexity signal enhancing receiver that will work with a single receive antenna is developed that offers significant gains at high interfering signal powers especially when the channel memory is low.
Abstract: The capacity of TDMA digital cellular systems like IS-136, GSM and their evolution IS-136HS and EDGE is limited by the intersymbol interference (ISI) arising from multipath propagation and co-channel interference (CCI) due to frequency reuse. The focus of this work is to develop for the downlink, a low complexity signal enhancing receiver that will work with a single receive antenna. This paper proposes a technique to combat both ISI and CCI using tentative decisions obtained through a preliminary detector. These decisions are used in mitigating ISI and CCI to produce final decisions. It is shown that the receiver proposed offers significant gains at high interfering signal powers especially when the channel memory is low.

Patent
16 Sep 1999
TL;DR: In this article, the results of measurements of adjacent transmitter signals to be transmitted with the monitored radio communication at the same frequency and in the same time slot are used in making the power regulation decision.
Abstract: The invention concerns a method of power regulation in a radio system including at least two transmitters, e.g. base transceiver stations, transmitting at the same frequency and receivers, e.g. mobile stations, which have set up a radio communication with the former. In the method according to the invention, the results of measurements of co-channel adjacent transmitter signals are used, besides the results of measurements of the radio communication to be relayed, in making the power regulation decision. From the results of measurements of adjacent transmitter signals to be transmitted with the monitored radio communication at the same frequency and in the same time slot, an estimate is determined of that interference caused to the radio communication, which is to be compensated for by a regulation of the transmission power of the desired signal.

Journal ArticleDOI
TL;DR: An adaptive channel estimation approach is developed which improves the performance through interference cancellation and significant performance gains are demonstrated for the Digital Advanced Mobile Phone Service (D-AMPS) (IS-136) digital cellular system.
Abstract: The performance of multichannel coherent maximum-likelihood sequence estimation (MLSE) reception in the presence of co-channel interference is limited by the channel estimation accuracy. An adaptive channel estimation approach is developed which improves the performance through interference cancellation. Significant performance gains (up to 8 dB) are demonstrated for the Digital Advanced Mobile Phone Service (D-AMPS) (IS-136) digital cellular system.

Proceedings ArticleDOI
19 Sep 1999
TL;DR: The effects of adjacent channel interference on WCDMA capacity are studied for two adjacent frequency operators as well as for a hierarchical cell structure to be used by one operator at adjacent frequency channels.
Abstract: In this paper the effects of adjacent channel interference on WCDMA capacity are studied for two adjacent frequency operators as well as for a hierarchical cell structure to be used by one operator at adjacent frequency channels. The effect of adjacent channel interference on the system capacity is studied with practical loading of the WCDMA system. Also a new model for adjacent channel interference in the uplink is introduced taking into account the behaviour of a practical WCDMA terminal power amplifier. A goal of this paper is to find out the adjacent channel interference requirements for the WCDMA system.

Proceedings ArticleDOI
16 May 1999
TL;DR: This paper analyses the combined application of "smart antennas" (narrowbeam antennas) and the fractional loading factor to explore the effect of reducing the total co-channel interference, while simultaneously adjusting the cellular cluster size.
Abstract: It is well known that cellular capacity can be increased by reducing cell cluster size, since more channels may then be assigned to each cell. However, this reduction of cluster size leads to increased co-channel interference, requiring the use of some cochannel interference control techniques at the base stations or in the air interface. In this paper we analyse the combined application of "smart antennas" (narrowbeam antennas) and the fractional loading factor. We explore the effect of reducing the total co-channel interference, while simultaneously adjusting the cellular cluster size.

Journal ArticleDOI
TL;DR: In this article, the interference power is suppressed by a factor greater than the spreading factor of the spreading code in a wireless DS-CDMA system and its simple frequency domain expressions for other user interference from the same system and other systems are derived.
Abstract: In a wireless DS-CDMA system, the interference power is suppressed by a factor greater than the spreading factor of the spreading code. An investigation onto the interference suppression factor is presented and its simple frequency domain expressions for other-user interference from the same system and other systems are derived. Some numerical results are presented for two spectrally overlapped systems with different raised cosine Nyquist filters.

Proceedings ArticleDOI
16 May 1999
TL;DR: A system that uses a RAKE receiver along with a weighted iterative interference cancellation (IC) scheme to combat both ISI and co-channel interference and the resultant decoding scheme offers significant performance improvement over a conventional RAke receiver with a complexity much less than that of maximum-likelihood decoding.
Abstract: The performance of CDMA systems can be severely degraded by interference, including both intersymbol interference (ISI) and the interference between users (co-channel interference) due to the non-orthogonality of the PN codes. We consider a system that uses a RAKE receiver along with a weighted iterative interference cancellation (IC) scheme to combat both ISI and co-channel interference. The resultant decoding scheme offers significant performance improvement over a conventional RAKE receiver with a complexity much less than that of maximum-likelihood decoding. We discuss the features and advantages of our proposed scheme and also provide simulation results for its BER performance for different numbers of users and weighting factors.

Proceedings ArticleDOI
16 May 1999
TL;DR: A semi-blind approach for cancelling asynchronous interference using generalized per-survivor processing for channel acquisition and tracking using symbol-asynchronous co-channel signals assuming knowledge of the signal structure is considered.
Abstract: Co-channel interference is a major impairment for IS-136 handsets. Joint estimation of cochannel signals can be used to minimize this effect, but traditional approaches require transmissions from different base-stations to be synchronized. In this paper, we consider a semi-blind approach for cancelling asynchronous interference using generalized per-survivor processing for channel acquisition and tracking. Signal delays and medium responses are jointly estimated for symbol-asynchronous co-channel signals assuming knowledge of the signal structure. Simulation results are presented that show C/I gains of 15 dB in the presence of one interferer.