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Showing papers on "Co-channel interference published in 2001"


Proceedings ArticleDOI
06 May 2001
TL;DR: A linear pre-processing plus encoding scheme is proposed, which significantly enhances cellular downlink performance, while putting the complexity burden on the transmitting end, and approaches those of optimum joint processing at the high SNR region.
Abstract: A linear pre-processing plus encoding scheme is proposed, which significantly enhances cellular downlink performance, while putting the complexity burden on the transmitting end. The approach is based on LQ factorization of the channel transfer matrix combined with the "writing on dirty paper" approach (Caire, G. and Shamai, S., Proc. 38th Annual Allerton Conference on Communication, Control and Computing, 2000) for eliminating the effect of uncorrelated interference, which is fully known at the transmitter but unknown at the receiver. The attainable average rates with the proposed scheme approach those of optimum joint processing at the high SNR region.

535 citations


ReportDOI
24 Jan 2001
TL;DR: This paper considers two fundamentally different ways that receivers measure and report the effect of interference on signal quality, demonstrating that in non-white noise the measures are not the same.
Abstract: : Testing the response of C/A code receivers to partial-band interference (continuous Gaussian interference whose power is concentrated in part of the front-end bandwidth) has included examining how receivers measure and report the effect of such interference. This paper considers two fundamentally different ways that receivers measure and report the effect of interference on signal quality, demonstrating that in non-white noise the measures are not the same. While the effective C/N0 reliably measures the effect of interference on a receiver, the precorrelation C/N0 is not reliable. Specifically, precorrelation estimation of N0 does not properly account for the spectrum of the interference. Depending on the spectrum of the interference, precorrelation estimates may be accurate, or may over-estimate the degradation caused by interference, or may under-estimate the degradation caused by interference. Theoretical and numerical results are provided and compared to some measured data.

116 citations


Patent
18 Apr 2001
TL;DR: In this paper, an unlicensed RF data delivery system uses interference characterization to adapt the RF transmission to accommodate the interferences using at least one detection system to determine the type of interference present in an RF band.
Abstract: An unlicensed RF data delivery system uses interference characterization to adapt the RF transmission to accommodate the interferences It uses at least one detection system to determine the type of interference present in an RF band A channel per channel measurement of interference is made, usually in conjunction with a sweep of the total operating spectrum, generating a picture of the interference over the entire frequency spectrum The system characterizes not only interference levels, but bandwidth of the interference A profile is generated, the response to that interference profile is one of several methods, such as frequency change; changing modulation to higher or lower levels; changing the channel width; changing the code rate; changing antenna polarity; and using hub diversity By first characterizing the type of interference, the system response is tailored to maximize the available interference free spectrum

105 citations


Patent
25 Sep 2001
TL;DR: In this paper, a method for a combined adaptive digital pre-distorter and pre-equalizer apparatus in single and/or multiple-link hopping radio systems including hopping among a plurality of radio links to transmit variable-length bursts of radio signals was proposed.
Abstract: A method for a combined adaptive digital pre-distorter and pre-equalizer apparatus in single- and/or multiple-link hopping radio systems including hopping among a plurality of radio links to transmit variable-length bursts of radio signals on the plurality of radio links. Further, pre-distorting amplitude and phase of transmitted signal constellations based on the inverse AM-to-AM and AM-to-PM characteristics and the operating conditions of the high-power amplifier, respectively. Further, pre-equalizing amplitude and group-delay variations of the transmit RF radio using the pre-stored estimated complex tap coefficient of the pre-equalizer under different frequency bands.

91 citations


Patent
12 Jun 2001
TL;DR: In this article, a communications system network that enables secondary use of spectrum on a noninterference basis is disclosed, which uses high-processing gain probe waveforms that enable propagation measurements to be made with minimal interference to the primary users.
Abstract: A communications system network that enables secondary use of spectrum on a non-interference basis is disclosed. Each secondary transceiver measures the background spectrum. The system uses a modulation method to measure the background signals that eliminates self-generated interference and also identifies the secondary signal to all primary users via on/off amplitude modulation, allowing easy resolution of interference claims. The system uses high-processing gain probe waveforms that enable propagation measurements to be made with minimal interference to the primary users. The system measures background signals and identifies the types of nearby receivers and modifies the local frequency assignments to minimize interference caused by a secondary system due to non-linear mixing interference and interference caused by out-of-band transmitted signals (phase noise, harmonics, and spurs). The system infers a secondary node's elevation and mobility (thus, its probability to cause interference) by analysis of the amplitude of background signals. Elevated or mobile nodes are given more conservative frequency assignments that stationary nodes.

87 citations


Proceedings ArticleDOI
11 Jun 2001
TL;DR: It is shown that the proposed method can effectively mitigate CCI while preserving the space-time structure, thereby, significantly improving the system's interference suppression ability without significant performance degradation.
Abstract: Space-time coded OFDM is a promising scheme for future wideband multimedia wireless communication systems. The combination of space-time coding (STC) and OFDM modulation promises an enhanced performance in terms of power and spectral efficiency. However, STC transmit diversity impairs the system's interference suppression ability because each transmitter generates multiple signals that appear independent to the receiver antenna arrays. In this paper, we propose a novel CCI cancellation method employing angle diversity based on beamforming. It is shown that the proposed method can effectively mitigate CCI while preserving the space-time structure, thereby, significantly improving the system's interference suppression ability without significant performance degradation.

53 citations


Patent
10 May 2001
TL;DR: In this article, a system for mitigating the effects of interference in an unlicensed RF band for point-to-point data transmissions comprises a multibeam antenna locating interference with transmission to and from data transmission subscribers.
Abstract: A system for mitigating the effects of interference in an unlicensed RF band for point to point data transmissions comprises a multibeam antenna locating interference with transmission to and from data transmission subscribers. A scanner determines the frequency, bandwidth and any periodicity of the interference. Separate scanners can be used for each antenna beam. Nulls are generated in the data transmission antenna pattern in the direction of the interference during periods of interference. Communications with subscribers in a direction of the interference is carried out using a different channel or is scheduled around the interference occurrences. Alternatively, such subscribers are directed to establish data transmissions with an alternate hub antenna.

51 citations


01 Jan 2001
TL;DR: In this paper, the connection between the feedback channel capacity in closed loop modes and the channel coherence time is investigated, and it is shown that in LOS environments, the requirements on the feedback bit rate is lower.
Abstract: Transmit antenna diversity using closed loop and open loop modes are compared in environments with line of sight propagation and spatially and temporally non-white noise. The connection between the feedback channel capacity in closed loop modes and the channel coherence time is investigated. It is shown that in LOS environments, the requirements on the feedback channel bit rate is lower. Furthermore, we derived the beamforming vector in closed loop transmit diversity with directional interference and showed how this gives an equivalent gain in SNR of about 3 dB at the receiver, even at a beamforming weight phase resolution of 90 .

48 citations


Proceedings ArticleDOI
28 Oct 2001
TL;DR: Assessment of the interference caused by UWB signals via analysis and simulations finds the aggregate effect of spatially distributed UWB radios on a receiver, and theoretical BER expressions.
Abstract: Ultra-wideband (UWB) signals will encounter many interference sources, primarily from relatively narrowband (NB) systems. In addition., UWB signals will also affect a large number of NB radios; of critical importance is the potential interference with GPS, E-911, and navigation bands, as well as cellular bands. There is a rich and growing literature on UWB radios; however, issues related to interference measurements have only been partially addressed. Here, we assess the interference caused by UWB signals via analysis and simulations. Analytical results include the aggregate effect of spatially distributed UWB radios on a receiver, and theoretical BER expressions.

47 citations


Patent
05 Dec 2001
TL;DR: In this article, the authors propose a method and apparatus for assigning the data rate and/or power level to the mobile terminals without determining the highest theoretical system throughput, and without determining weighted system throughput.
Abstract: A method and apparatus for assigning the data rate and/or power level to the mobile terminals without determining the highest theoretical system throughput, and without determining the highest weighted system throughput. An order is imposed on the terminals and the data rate and/or power covariance matrices are assigned such that the data rates of the terminals having a lower index in the order will not be decreased due to the presence of the terminals having a higher index in the order, and this is accomplished without changing the power covariance matrixes of the antennas involved in the communication with the lower index terminals. Thus, the assignment is made to the terminals based on the terminals requirements without regard to the interference introduced by the terminals with a higher index in the order since this interference will be compensated for by the compensation technique when the compensation technique process the terminals in accordance with the order. The invention reduces the amount of computation necessary to implement such compensation techniques on an ongoing, real-time basis in a real-world system.

47 citations


Proceedings ArticleDOI
19 Aug 2001
TL;DR: In this paper, in-band interference caused by different kinds of ultra wideband signals in UMTS frequency bands as a function of UWB pulse width was investigated and shown that one can reduce interference by using different waveforms and pulse widths to avoid UMTS frequencies without any additional filtering.
Abstract: This paper studies in-band interference caused by different kinds of ultra wideband signals in UMTS frequency bands as a function of UWB pulse width. UWB frequency spectra are produced by using several types of narrow pulse waveforms. Due to the extremely wide bandwidth these signals will spread over the frequency bands allocated to other RF-systems. Study revealed that one can reduce interfering UWB power by using different waveforms and pulse widths to avoid UMTS frequencies without any additional filtering. The simulations did not make a significant difference between time hopping and direct sequence concepts when interference was calculated at the UMTS bands.

Proceedings ArticleDOI
06 May 2001
TL;DR: The results from this empirical study are used to substantiate analytical models for interference suppression versus carrier frequency offset and provide insight into the impact of adjacent channel interference from the interfering wireless service.
Abstract: The IEEE 802.11 and Bluetooth (BT) wireless networks can provide complementary services and they are likely to be installed within the same environments. Coexistence between the networks will be impaired if the probability of packet collision between the networks is sufficiently large. This paper presents the results of an empirical study focused on evaluating one aspect of the probability of collision: determining the interference power at which packet retransmission is likely to be required. The results from this empirical study are used to substantiate analytical models for interference suppression versus carrier frequency offset. The empirical study and analytical model are used to provide insight into the impact of adjacent channel interference from the interfering wireless service.

Proceedings ArticleDOI
01 Jan 2001
TL;DR: It is shown that in case of narrowband interference (with respect to the spread spectrum bandwidth), UWB provides more effective interference suppression than DS-SS.
Abstract: In this paper we analyze the performance of ultra-wideband (UWB) communications in the presence interference. The interference is modeled as a zero mean random process with constant power spectral density over a certain bandwidth. Closed-form expressions are developed for the processing gain of a pulse position modulation UWB utilizing rectangular pulses. Simple approximations are obtained for special cases (narrowband and wideband interference). We compare the interference suppression properties of UWB and direct-sequence spread spectrum (DS-SS) under certain assumptions. It is shown that in case of narrowband interference (with respect to the spread spectrum bandwidth), UWB provides more effective interference suppression than DS-SS.

Proceedings ArticleDOI
06 May 2001
TL;DR: Results here show that low power UWB systems operating at the same levels as unintended radiators can comfortably coexist with conventional users of the radio spectrum without significant impact on the performance of those radio services.
Abstract: The noise floor rise in a generic receiver as a basis for the determination of interference levels to a victim receiver is applied to assess interference to systems that are designed to operate in multipath fading environments. The interference levels might be over estimated by as much a 20 dB if fading is not properly taken into account. The impact of potentially interfering sources such as UWB emissions must be treated as an effect on the overall system reliability. Results here show that low power UWB systems operating at the same levels as unintended radiators can comfortably coexist with conventional users of the radio spectrum without significant impact on the performance of those radio services.

Journal ArticleDOI
TL;DR: An analysis of the accuracy of two popular methods for computing the moments of a sum of lognormal random variables, namely Wilkinson's method and Schwartz and Yeh’s method, for the general case when the summands have different mean values and standard deviations in decibel units.
Abstract: Summary Co-channel interference is recognized as one of the major factors that limits the capacity and link quality of a wireless communications system. An appropriate understanding of the statistical behavior of the co-channel interference is therefore required when analyzing and designing techniques that mitigate its undesired effects. The total co-channel interference in a wireless communications system is usually modeled as the sum of lognormally distributed signals, and is generally assumed to be itself lognormally distributed. Based on this assumption, several methods for estimating the moments of the resulting lognormal distribution have been proposed. The accuracy of these methods has been studied in previous works, under the assumption of having all summand signals (individual interference signals) identically distributed. Such an assumption rarely holds in practical cases of emerging wireless communications systems, where co-channel interference may stem from far-away macrocells and nearby transmitters, causing the interference signals to have different moments. In this paper we present an analysis of the accuracy of two popular methods for computing the moments of a sum of lognormal random variables, namely Wilkinson’s method and Schwartz and Yeh’s method, for the general case when the summands have different mean values and standard deviations in decibel units. We show that Schwartz and Yeh’s method provides better accuracy than Wilkinson’s method and is virtually invariant with the difference of the mean values and standard deviations of the summands. Copyright © 2001 John Wiley & Sons, Ltd.

01 Sep 2001
TL;DR: In this paper, the effects of UWB interference on GPS receivers were quantified by inserting increased levels of UB interference until an operating GPS receiver lost lock, and at each interference level leading up to loss of lock, reacquisition time was determined.
Abstract: This addendum to NTIA Report 01-384 describes laboratory measurements on two additional Global Positioning System receivers to quantify the effects of ultrawideband interference on those receivers. The laboratory measurements were performed by inserting increased levels of UWB interference until an operating GPS receiver lost lock. At each interference level leading up to loss of lock, reacquisition time was determined. When possible, fundamental GPS measurements (e.g., pseudorange and carrier phase), status flags (e.g., potential cycle slips), and signal-to-noise ratio were also sampled.

Patent
03 Oct 2001
TL;DR: In this article, a method and apparatus for mitigating co-channel and inter-channel interference in an antenna array system is presented, where the spatial characteristic of the interference is determined and used to obtain a weight that mitigates the interchannel interference.
Abstract: A method and apparatus for mitigating co-channel and inter-channel interference in an antenna array system. According to one aspect, the channel-select filter of a base station or other communication device is modified to detect inter-channel interference on at least one non-primary channel when the transmitter is communicating with a remote user terminal on a primary channel. The spatial characteristic of the interference is determined and used to obtain a weight that mitigates the inter-channel interference. According to another aspect, the spatial characteristic of co-channel and/or inter-channel ghost signal interference caused by a transmitter is determined and used to mitigate the effects of such interference.

Patent
28 Feb 2001
TL;DR: In this article, a more reliable identification property of each co-channel component of the received composite signal is used, namely, the time of arrival of a known part of a signal.
Abstract: Co-channel interference in a wireless network is identified and quantified. Rather that using color code identification, a more reliable identification property of each co-channel component of the received composite signal is used, namely, the time of arrival of a known part of a signal. Detection and timing measurement is performed even in presence of stronger signals by focusing selectively on bursts having fixed contents (e.g., the FCCH burst used in GSM for frequency correction). The repetitive measurements of the time-of-arrival of each of the interfering components of the signal during a drive test enables determination of the geographical location of the interfering co-channel base stations.

Proceedings ArticleDOI
07 Oct 2001
TL;DR: This work investigates the use of smart antennas at both the base and mobile stations, operating jointly, to maximize the SINR of each user before multiuser detection, and finds that the performance of multi-user detection is significantly improved.
Abstract: Indoor wireless communication systems have grown rapidly because of their clear advantages such as mobility, flexibility, and inexpensive network reconfiguration. In order to offer higher data rates approaching those provided by wired LANs, a combined OFDM/SDMA-based approach is an effective solution for increasing the system capacity and spectral efficiency. However, in multi-user environments, the system performance is limited by co-channel interference. Multi-input-multi-output (MIMO) smart antennas with prior knowledge of the channel at the transmitter is another promising technique for providing significant increase in system capacity and performance in wireless communication systems. We investigate the use of smart antennas at both the base and mobile stations, operating jointly, to maximize the SINR of each user before multiuser detection. By doing so, the performance of multi-user detection is significantly improved.

Proceedings ArticleDOI
25 Nov 2001
TL;DR: The statistical distribution of the signal to interference plus noise ratio (SINR) of the optimum combining technique in receive antenna diversity systems is examined and approximations to the distribution are provided along with performance upper and lower bounds.
Abstract: In this paper, we examine the statistical distribution of the signal to interference plus noise ratio (SINR) of the optimum combining (OC) technique in receive antenna diversity systems. The channel is modelled as flat Rayleigh fading, slowly varying and spatially independent. When the number of interferers is less than the number of antennas, our approach considers unequal power interferers and decomposes the SINR into sum of two independent terms by projection onto interference and noise orthogonal subspaces. Following the decomposition, the distributions for these projections are sought. For the case when the number of interferers is larger, approximations to the distribution are provided along with performance upper and lower bounds.

Patent
04 Dec 2001
TL;DR: In this paper, a method for co-channel interference identification and mitigation employs adaptive sequence detection in connection with a model composed of a signal of interest and a combination of other signals which constitute interference in a channel of interest.
Abstract: A method for co-channel interference identification and mitigation employs adaptive sequence detection in connection with a model composed of a signal of interest and a combination of other signals which constitute interference in a channel of interest, wherein the signal of interest is distinguished from the interference by adaptive tracking of signal parameters of all identifiable signals. In a particular embodiment, the process involves estimating the number and time spans of co-channel interference channels based on maximum likelihood estimation and minimum description length from training information derived from a single time division multiple access packet; and then applying the estimate to mitigation of co-channel interference at a receiver. Per-survivor-processing is one technique for adaptive sequence detection.

Patent
Katsuhiko Hiramatsu1
05 Sep 2001
TL;DR: In this paper, transmitting selection diversity is applied in a CDMA radio communication system in which a BS carries out communications with a MS provided with MUD, and interference from other users and fading influences are mitigated.
Abstract: In a radio communication terminal apparatus or an interference cancellation method a known signal is adopted as a common midamble, transmitting selection diversity which applied in a CDMA radio communication system in which a BS carries out communications with a MS provided with MUD, and interference from other users and fading influences are mitigated. The signal transmitted from base station apparatus 101 which is provided with a plurality of antenna branches and performs transmitting selection diversity is received, in symbol power calculating section 150, the symbol power of all codes excluding the code assigned to the radio-communication terminal apparatus is calculated for every antenna branch, in code number detecting section 208, interference code number is detected for every antenna branch based on a known signal included in the receiving signal, in interference code selecting section 209, interference code corresponding to the detected interference code number is selected for every antenna branch based on the calculated symbol power, and interference caused by the selected interference code is cancelled by interference cancellation processing in MUD 210.

Proceedings ArticleDOI
29 Oct 2001
TL;DR: The numerical results show that considerable performance gain can be obtained by transmit diversity when the active user number is relatively small, but as the number of the users increases, the diversity gain will decrease.
Abstract: In this paper, we consider space time spreading in the forward links of a MC-DS-CDMA system when random signature sequences are used. The performance of the system with different diversity order has also been analyzed. The numerical results show that considerable performance gain can be obtained by transmit diversity when the active user number is relatively small. As the number of the users increases, the diversity gain will decrease. It also suggests that it require multiuser interference cancellation when the active user number is relatively large.

Patent
30 May 2001
TL;DR: In this paper, a method for a digital receiver and a receiver exploiting second order statistics for adaptive co-channel interference rejection in wireless communication is presented, which enables to increase the number of communication channels for frequencies used.
Abstract: The present invention relates to a method for a digital receiver and a receiver exploiting second order statistics for adaptive co-channel interference rejection in wireless communication. It uses digitally I, in phase, and Q, quadrature, branches of a received transmitted signal as input to the receiver, a coarse synchronization and a coarse frequency offset compensation have being performed on the signal. It comprises a means for derotation, means for separation, means for filtering, means for estimating and means for detecting transmitted symbols in the received signal. The invention thereby improving co-channel rejection in wireless communication, thus making it possible to increase the number of communication channels for frequencies used.

Proceedings ArticleDOI
25 Nov 2001
TL;DR: The minimum interference dynamic channel assignment algorithm is employed, while simple Kalman filters are designed to provide the predicted measurements of both the channel gains and the interference levels, which are then used to update the power levels.
Abstract: We propose a distributed dynamic channel and power allocation (DCPA) scheme based on a novel predictive power control algorithm. The minimum interference dynamic channel assignment algorithm is employed, while simple Kalman filters are designed to provide the predicted measurements of both the channel gains and the interference levels, which are then used to update the power levels. Extensive computer simulations are carried out to show the improvement in performance, under the dynamics of user arrivals and departures and user mobility. It is shown that the number of dropped calls and the number of blocked calls are decreased while, on average, fewer channel reassignments per call are required.

Proceedings ArticleDOI
11 Jun 2001
TL;DR: Serial and parallel interference cancellation techniques, which were originally developed for CDMA multiuser techniques, can be used for OFDM equalization and are much more efficient than a brute force inversion of the channel matrix.
Abstract: Intercarrier interference can be a dominant source of errors in OFDM-systems, requiring some sort of equalization. We show that serial and parallel interference cancellation techniques, which were originally developed for CDMA multiuser techniques, can be used for OFDM equalization and are much more efficient than a brute force inversion of the channel matrix. Maximum excess delays of up to 70% of the OFDM block duration can be handled without loss of performance.

Proceedings ArticleDOI
07 Oct 2001
TL;DR: The peak interference-to-carrier ratio (PICR) can be reduced by coding to select only those messages with low PICR as valid codewords, and a new ICI reduction scheme, called tone reservation, that inserts optimized pilot tones in the data frame.
Abstract: Orthogonal frequency division multiplexing (OFDM) is sensitive to the carrier frequency offset (CFO). We introduce the peak interference-to-carrier ratio (PICR) to measure the resulting intercarrier interference (ICI). This paper shows that the PICR can be reduced by coding to select only those messages with low PICR as valid codewords. While explicit constructions of higher-rate, ICI-suppressing codes are rather difficult, we propose two new codes that map data onto three and four adjacent subcarriers. We also propose a new ICI reduction scheme, called tone reservation, that inserts optimized pilot tones in the data frame. Computing these pilot tones at the transmitter is a simple optimization technique.

Proceedings ArticleDOI
01 Jan 2001
TL;DR: In this article, a superresolution method was used to identify as many multipath components as possible in the spatial mobile radio channel and a solution to the "pairing problem" was proposed to match the underlying physical propagation path connecting them.
Abstract: The spatial mobile radio channel contains delay information and angular information about the multipath components (mpcs) Signal delay and ensuing intersymbol interference has played an important role since the inception of digital mobile radio systems like GSM The multipath signals impinging from different directions of arrival (DOAs) at an antenna array received quite some attention in the past few years We call this a directional channel The investigation of smart antennas has lead to better understanding of the radio channel itself and to more accurate and realistic spatial channel models The identification of useful mpcs and the suppression of undesired co-channel interference has great potential in smart antennas The paper describes the use of a superresolution method to identify as many mpcs as possible We offer also a novel solution to the "pairing problem", ie which DODs and DOAs match the underlying physical propagation path connecting them Though the measurements we describe were made, for practical reasons, in predominantly static environments, we aim at mobile radio applications

Proceedings ArticleDOI
01 Jan 2001
TL;DR: This work considers the application of interference avoidance to multiaccess dispersive channels corresponding to the uplink of a CDMA system in which the channel between each user and the base station is assumed to be known.
Abstract: We consider the application of interference avoidance to multiaccess dispersive channels corresponding to the uplink of a CDMA system in which the channel between each user and the base station is assumed to be known. By using a symbol transmission interval long enough a common set of signal space basis functions (sinusoids) is shared by all users at the base. Each user sends frames containing multiple symbols (as many as there are signal space dimensions) and each symbol is assigned a signature waveform. Optimal signature waveforms which achieve sum capacity are obtained through iterative application of interference avoidance. Such optimal signature waveforms provide to each user a uniform signal-to-interference plus noise-ratio (SINR) for all its symbols, and the optimal linear detector for each symbol is a matched filter.