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Showing papers on "Co-channel interference published in 2004"


Patent
17 Nov 2004
TL;DR: In this paper, a cancellation device can suppress antenna interference by generating an estimate of the interference signal and subtracting the estimate from the interference signals, based on sampling signals on an antenna that generates the interference or on the antenna that receives the interference.
Abstract: A wireless communication system can comprise two or more antennas that interfere with one another via free space coupling, surface wave crosstalk, dielectric leakage, or other interference effect. The interference effect can produce an interference signal on one of the antennas. A cancellation device can suppress antenna interference by generating an estimate of the interference signal and subtracting the estimate from the interference signal. The cancellation device can generate the estimate based on sampling signals on an antenna that generates the interference or on an antenna that receives the interference. The cancellation device can comprise a model of the crosstalk effect. Transmitting test signals on the communication system can define or refine the model.

288 citations


Journal ArticleDOI
TL;DR: An adaptive detection scheme is developed, which together with a Turbo ST MUD structure offers substantial performance gain over the well-known V-BLAST techniques with coding in this interference-limited cellular environment.
Abstract: The capacity of downlink cellular multiple-input multiple-output (MIMO) systems, where co-channel interference is the dominant channel impairment, is investigated in this paper, mainly from a signal-processing perspective. Turbo space-time multiuser detection (ST MUD) is employed for intracell communications and is shown to closely approach the ultimate capacity limits in Gaussian ambient noise for an isolated cell. Then, it is combined with various multiuser detection methods for combating intercell interference. Among various multiuser detection techniques examined, linear minimum-mean-square-error (MMSE) MUD and successive interference cancellation are shown to be feasible and effective. Based on these two multiuser detection schemes, one of which may outperform the other for different settings, an adaptive detection scheme is developed, which together with a Turbo ST MUD structure offers substantial performance gain over the well-known V-BLAST techniques with coding in this interference-limited cellular environment. The obtained multiuser capacity is excellent in the high to medium signal-to-interference ratio scenario. Nonetheless, numerical results also indicate that a further increase in system complexity, using base-station cooperation, could lead to further significant increases of the system capacity. The asymptotic multicell MIMO capacity with linear MMSE MUD preprocessing is also derived, and this analysis agrees well with the simulation results.

279 citations


Patent
05 Aug 2004
TL;DR: In this article, a crosstalk cancellation device can include a controller that monitors crossstalk-compensated communication signals and adjusts the model to enhance the cancellation performance.
Abstract: Signals propagating in one communication channel can generate crosstalk interference in another communication channel. A crosstalk cancellation device can process the signals causing the crosstalk interference and generate a crosstalk cancellation signal that can compensate for the crosstalk when applied to the channel receiving crosstalk interference. The crosstalk cancellation device can include a model of the crosstalk effect that generates a signal emulating the actual crosstalk both in form an in timing. The crosstalk cancellation device can include a controller that monitors crosstalk-compensated communication signals and adjusts the model to enhance crosstalk cancellation performance. The crosstalk cancellation device can have a mode of self configuration or calibration in which defined test signals can be transmitted on the crosstalk-generating channel and the crosstalk-receiving channel.

126 citations


Proceedings ArticleDOI
17 May 2004
TL;DR: Unusually, it is seen that, with a modification of the MIMO channel matrix to incorporate interference, higher correlation in the channel yields higher capacity rather than the more familiar desire for decorrelated channels.
Abstract: We consider both analytically and via Monte Carlo simulation the variation of the information theoretic capacity of multiple-input, multiple output (MIMO) communication systems. We present a way of explicitly examining the effect of interference on the MIMO sub-channel gains. Using this, we derive asymptotic lower bounds on capacity with many interferers and in high interference-to-noise ratio and present simulation results for them. We also study the behaviour of the capacity as a function of the number of interferers, the interference-to-noise ratio (INR) and the transmit and receive array sizes. It is found that, in interference, the benefit of providing multiple transmit antennas is very small indeed from a capacity perspective, whilst the number of receive antennas is critical both to the capacity and the number of users the system can mitigate interference from. Unusually, it is seen that, with a modification of the MIMO channel matrix to incorporate interference, higher correlation in the channel yields higher capacity rather than the more familiar desire for decorrelated channels.

61 citations


Proceedings ArticleDOI
18 May 2004
TL;DR: In this article, the authors analyzed statistically the response of the correlators, including integrate and dump circuits, to desired and un-desired pulse pairs in differential transmitted reference (DTR-UWB) systems.
Abstract: In transmitted reference ultra-wideband (TR-UWB) systems and differential transmitted reference (DTR-UWB) systems, the performance is, besides noise, determined by interference among pulses due to the dispersive multipath radio channel (interframe interference). The multiple access interference is also heavily influenced by multipath propagation. As a first step towards the analysis and optimization of such systems, this paper analyzes statistically the response of the pulse-pair correlators, including integrate and dump circuits which are the basic building blocks of TR-UWB receivers, to desired and un-desired pulse-pairs. Results are given in terms of basic channel parameters like RMS delay spread and Ricean K-factor. As an example for the application of our analysis, we present a novel multiuser DTR-UWB system.

49 citations


Patent
27 Feb 2004
TL;DR: In this article, a radio communication system consisting of a radio receiver including an interference canceller configured to generate a replica of a received signal and remove an interference signal from the received signal is described.
Abstract: A radio communication system comprises: a radio receiver including an interference canceller configured to generate a replica of a received signal and remove an interference signal from the received signal, and a frequency offset estimator configured to estimate a carrier frequency offset between a carrier frequency of the interference signal and a carrier frequency of a desired signal included in the received signal; and a radio transmitter including a frequency controller configured to adjust a carrier frequency of a transmitted desired signal to the carrier frequency of the interference signal based on the carrier frequency offset received from the radio receiver.

47 citations


Proceedings ArticleDOI
Suman Das1, Harish Viswanathan1
29 Nov 2004
TL;DR: The results show that time multiplexed transmissions, despite the bursty OCI power structure, has throughput comparable to an orthogonal multiple user transmission system for small cells.
Abstract: We consider different transmission options for packet data which are classified based on the nature of in-cell interference (ICI) and out-of-cell interference (OCI) power statistics. The categories are: (a) no ICI, averaged OCI; (b) no ICI, bursty OCI; and (c) averaged ICI, averaged OCI. Depending on whether the reverse link transmission is time-multiplexed, one user at a time transmission or simultaneous transmission by multiple users, with or without in-cell orthogonality, the interference structure falls into one of the above three categories. We analyze the throughput performance of the system in each of these cases when incremental redundancy is employed to combat uncertainty in the interference power. We compare the different options, under an in-cell rise-over-thermal (IROT) constraint, and provide some insights for reverse link design for next-generation cellular systems. Our results show that time multiplexed transmissions, despite the bursty OCI power structure, has throughput comparable to an orthogonal multiple user transmission system for small cells.

38 citations


Journal ArticleDOI
TL;DR: An analytical framework for characterizing the average symbol error rate and outage performance of a smart antenna system in cellular mobile radio environments is developed and selected numerical results are presented to demonstrate the utility of the analysis in assessing the selective interference nulling performance in different fading environments.
Abstract: This paper develops an analytical framework for characterizing the average symbol error rate and outage performance of a smart antenna system in cellular mobile radio environments. Specifically, the carrier-to-interference ratio statistics with N remaining (uncancelled) "weakest" cochannel interference (CCI) signals from a total of N/sub I/ signals are derived, given that both the desired user signal and the CCI signal amplitudes are subjected to Rayleigh, Rice, Nakagami-m, or Nakagami-q fading. General expressions for the outage probability and the average symbol-error rate performance of different digital modulation schemes in the presence of CCI signals are derived. Selected numerical results are presented to demonstrate the utility of the analysis in assessing the selective interference nulling performance in different fading environments.

34 citations


Patent
02 Jun 2004
TL;DR: In this article, the authors proposed a method of operation of a filter (12) of a receiver of a mobile station or a base station of a radio access network and corresponding equipment, the method for use in suppressing co-channel interference and based on separating the inphase (I) and quadrature phase (Q) components of the received signal and then performing whitening on a symbol-by-symbol basis, i.e. the whitening operation is done within one symbol.
Abstract: A method of operation of a filter (12) of a receiver (10) of a mobile station or a base station of a radio access network and corresponding equipment, the method for use in suppressing co-channel interference and based on separating the in-phase (I) and quadrature phase (Q) components of the received signal and then performing whitening on a symbol-by-symbol basis, i.e. the whitening operation is done within one symbol. The invention provides a filter (12) including a module (12b) for performing IQ whitening (either according to the invention or otherwise), and also provides a switch (12a) that can be used to enable or disable IQ whitening, depending on the character of the received signal, and in particular based on the noise plus interference correlation matrix ( ).

32 citations


Proceedings ArticleDOI
27 Jun 2004
TL;DR: The main point of the paper is that the time-sharing of Sato's region exceeds the convex closure of a sub-region of Han and Kobayashi for symmetric interference channel under moderate interference, and also the achievable rate region by TDM/ FDM.
Abstract: This paper analyzes achievable rate regions for the Gaussian IFC (interference channel). The achievable rate region is based on reducing one user's transmit power to a point such that its message is decodeable to both receivers. The second receiver then does interference reduction. The main point of the paper is that the time-sharing of Sato's region exceeds the convex closure of a sub-region of Han and Kobayashi for symmetric interference channel under moderate interference, and also the achievable rate region by TDM/ FDM. It follows that on degraded Gaussian IFC, the sum-capacity is achieved with the stronger user transmitting at its maximum rate (ignoring the interference), while the weaker user treats the stronger user as interference. For a one-sided Gaussian IFC with weak or moderate interference, the sum-capacity is achieved if the transmitter, which is not interfered sends its data at the maximal achievable rate of a single-user, and the second transmitter sends its data at the maximal possible rate where the interfering signal is treated as an additive Gaussian noise. We show that the sum-capacity of a one-sided Gaussian IFC implies the upper bound on the sum-capacity of a two-user Gaussian IFC.

24 citations


Journal ArticleDOI
TL;DR: It is shown that the proposed receiver is effective in reducing significantly the effects of Multiple Access Interference (mai) compared to other interference cancellation systems.
Abstract: This paper investigates the Parallel Interference Cancellation technique in Direct Sequence Optical Code Division Multiple Access (ds-ocdma) system. In the proposed system, the estimated interference is removed from the received signal. We have developped a new approach to obtain the analytical expression of error probability in chip synchronous case, for Optical Orthogonal Codes (ooc). We have shown that under specific conditions between codes parameters and users’ number, the interference can be completely neutralized. Simulation results have validated the theoretical analysis. It is shown that the proposed receiver is effective in reducing significantly the effects of Multiple Access Interference (mai) compared to other interference cancellation systems.

Patent
23 Jul 2004
TL;DR: In this article, a method and apparatus for uniquely identifying signal sources in a multisource signal was proposed based on an area-measurement approach and relies on relative time-of-arrival (RTOA) measurements of the signal components impervious to the existence of the phase drift between the scanner and base stations.
Abstract: A method and apparatus for uniquely identifying signal sources in a multisource signal. True levels of signal components transmitted by each of the co-channel base stations in the area under test in a wireless network are measured and associated with the appropriate (originating) base station in presence of co-channel and adjacent-channel interference without interrupting service. The present invention is based on an 'area-measurement' approach and relies on relative time-of-arrival (RTOA) measurements of the signal components impervious to the existence of the phase drift between the scanner and base stations.

28 Jan 2004
TL;DR: The paper discusses the effect of various interference signals on noise power, signal to noise ratio and effect of coherent/non-coherent integration times on the acquisition process.
Abstract: Intentional or unintentional interference and jamming is one of the major concerns in using the Global Positioning System (GPS) in various critical applications. In spite of the GPS frequency bands being protected by International and Federal Communication Commission (FCC) frequency assignments, there is always a chance of disruption of the GPS signal availability in critical times and applications. The GPS system has advantages over narrow-band navigation systems as the signals are spreadspectrum and receiver design techniques can eliminate most of the interference signals. The various sources of unintentional jamming are out-of-band interference caused by nearby transmitters, harmonics of ground transmitters, signals from nearby platforms, pulsed interference and accidental transmission of signals in the wrong frequency band. Any signal or its harmonics near the GPS L1 and L2 frequencies are a potential source of interference. The aim of this paper is to analyze the effect of some interference sources on the GPS spectrum during the acquisition process. The acquisition process determines the signal peak after correlation and then compares it with a detection threshold to determine the success of acquisition. Interference signals cause distortion in the GPS signal resulting in an incorrect, or no correlation peak, during acquisition. The interference signals analyzed in this paper are the continuous wave interference, broadband noise and pulsed interference signals. A GPS simulator (GSS 6560) was used along with a signal generator (E 4431B) and an interference combiner (GSS 4766) to generate the interference signals. The signals were collected using a GPS front end (Signal Tap) data logger. The paper discusses the effect of various interference signals on noise power, signal to noise ratio and effect of coherent/non-coherent integration times on the acquisition process.

Patent
14 Jul 2004
TL;DR: In this paper, a transmission side radio station transmits a radio packet by using a radio channel judged to be empty by both of a physical carrier detection judging whether busy state or empty state according to the reception power and a virtual carrier detecting busy state during a set transmission suppression period.
Abstract: A transmission side radio station transmits a radio packet by using a radio channel judged to be empty by both of a physical carrier detection judging whether busy state or empty state according to the reception power and a virtual carrier detection judging busy state during a set transmission suppression period. Here, a transmission suppression period used for the virtual carrier detection is set for a radio channel forming a pair and affected by leak from the transmission radio channel. Thus, even when normal reception cannot be performed in the radio channel affected by the leak from the transmission radio channel, a transmission suppression period can be set for the radio channel affected.

Proceedings ArticleDOI
05 Sep 2004
TL;DR: In a time-division-duplex (TDD) system, the channel state information can be easily obtained at the transmitter side due to channel reciprocity and it can be used to dramatically increase the spectral efficiency of a MIMO system, but the interference structure between transmission directions does not necessarily correlate at all.
Abstract: In a time-division-duplex (TDD) system, the channel state information can be easily obtained at the transmitter side due to channel reciprocity and it can be used to dramatically increase the spectral efficiency of a MIMO system. However, the interference structure between transmission directions does not necessarily correlate at all. In such a case, the modulation/coding parameters assigned based on the reverse link measurements may lead to excessively high frame error rates. If the interference structure between transmission directions differs significantly, A simple closed-loop method to compensate the non-reciprocity between uplink and downlink interference structure is introduced. The simulation results clearly show that in the presence of non-reciprocal interference, some feedback to the transmitter is always needed in order to maintain the desired quality of service at the receiver. The gain from the fast feedback depends on the interference structure and the number of transmitter and receiver antennas.

Proceedings ArticleDOI
24 Aug 2004
TL;DR: In the case of GSM 1800 systems, the proposed ETSI emission limits are found to be offering sufficient protection whereas the current FCC regulations would result in significant interference.
Abstract: The effects of UWB interference on GSM 900 and GSM 1800 systems are considered for current FCC regulations as well as proposed ETSI emission limits for the criteria of either a 1 dB loss in the SINR or a loss leading to the minimum required SINR at the cell edge. UWB densities are computed for different GSM reuse factors and the results show that no harmful interference is to be expected for GSM 900 systems. In the case of GSM 1800 systems, the proposed ETSI emission limits are found to be offering sufficient protection whereas the current FCC regulations would result in significant interference.

Proceedings ArticleDOI
26 Apr 2004
TL;DR: The interference assessment methodology is extended to include the effect of signal imperfections, adding consideration of different types of signalperfections and evaluating their effect on intrasystem and intersystem interference.
Abstract: Analytical techniques have been developed and accepted as effective ways to assess the approximate effects of interference from Global Navigation Satellite System (GNSS) signals to the reception of signals from the same or other GNSSs. The methodology has been used to determine the effects of interference from different signals transmitted by the same system (intrasystem interference) and interference from signals transmitted by other systems (intersystem interference). However, the current methodology assumes that the set of transmitted signals is merely the superposition of ideally specified signals. In fact, transmitted signals have imperfections, and these imperfections can affect the level of interference. This paper extends the interference assessment methodology to include the effect of signal imperfections, adding consideration of different types of signal imperfections and evaluating their effect on intrasystem and intersystem interference.

Patent
29 Sep 2004
TL;DR: In this article, the authors proposed two space-time filters, which can be operated sequentially to cancel unknown co-channel interference (CCI) from external interferers as well as inter symbol interference (ISI) cancellation.
Abstract: Recently, the multiple-input multiple-output system has been investigated. This provides a considerable increase in throughput at relatively small cost in terms of bandwidth. However, the processing overhead for this type of communication technique is significant. In addition, this type of system involves considerable processing overhead in tying to remove inference both from unknown co-channel interference (CCI) from external interferers as well as inter symbol interference (ISI). The scheme of the invention contains two space-time filters, which can be operated sequentially. The primary purpose of the first filter is CCI cancellation whereas the primary purpose of the other filter is ISI cancellation. This separation of processing the ISI and CCI whilst operating an integrated channel estimation scheme provides considerable improvements over the prior art systems. Each filter can be optimised to the removal of the specific type of interference.

Patent
10 Feb 2004
TL;DR: In this article, an enhanced radio receiver detects and attenuates a signal from the transmitter, without attenuation or interference with other desired signals, when both are located in the same aircraft.
Abstract: Systems and methods for reducing interference in an enhanced radio receiver from a transmitter when both are located in the same aircraft are provided. The enhanced radio receiver detects and attenuates a signal from the transmitter, without attenuation or interference with other desired signals. An enhanced radio transmitter may inform the enhanced radio receiver of the frequency of transmission via a data communication path such that the enhanced radio receiver attenuates the transmitted frequency for the duration of transmission.

Proceedings ArticleDOI
05 Apr 2004
TL;DR: An estimate of the achievable performance in a suburban ad-hoc network is presented and the impact of using omnidirectional antennas on routing performance where different networks, using overlapping frequency channels, exist within each other's transmission ranges are discussed.
Abstract: A suburban ad-hoc network (SAHN) interconnects a cooperative group at broadband speed using wireless links. The nodes are stationary. A SAHN involves low installation and service costs for SAHN specific traffic. Some current routing solutions for mobile ad-hoc networks may be used in the SAHN after certain optimizations. Efficiency can be improved by using smart directional antennas. Neighboring nodes falling outside the transmission region of a directional antenna are less vulnerable to co-channel interference. Additionally, increased transmission range can be achieved by reducing noise, interference and multipath fading. We emphasize the interference reduction capability of directional antennas and investigate the routing performances using three antenna schemes; multiple fixed directional, multiple omnidirectional and single omnidirectional antennas. We present an estimate of the achievable performance in a SAHN through extensive simulations. We also discuss the impact of using omnidirectional antennas on routing performance where different networks, using overlapping frequency channels, exist within each other's transmission ranges.

Patent
Sami Aromaa1, Pertti Henttu1
12 Feb 2004
TL;DR: In this article, the authors proposed a method for suppressing interference and arrangement for same, and radio communications receiver, which includes computing at least one transform of a received, analogue-to-digital converted radio signal, computing metrics defining the concentration of the interference present both for the transformed radio signal and the non-transformed radio signal.
Abstract: Method for suppressing interference and arrangement for same, and radio communications receiver. The method includes: computing at least one transform of a received, analogue-to-digital converted radio signal; computing metrics defining the concentration of the interference present both for the transformed radio signal and the non-transformed radio signal; selecting the transform whose metrics indicate the highest concentration of the interference in the transfer domain as the transform to be used, or selecting no transform if the metrics indicate the highest concentration of the interference for the non-transformed signal; suppressing the localized interference from the transformed radio signal by using weighting and computing inverse transform of the transformed radio signal if the transform was selected, or suppressing the localized interference from the non-transformed radio signal by using weighting if no transform was selected; and detecting and decoding the interference suppressed radio signal.

Proceedings ArticleDOI
17 May 2004
TL;DR: In this paper, the performance of OFDMA in a cellular environment with frequency reuse of one and non-perfect frequency synchronization is investigated, in particular the effects of co-channel interference (CCI) in the uplink is analyzed.
Abstract: OFDM is a potential candidate for next generation air-interfaces. The intrinsic property of OFDM ensures that it can be used in a multiuser application to produce a highly flexible and cost-efficient communication system. In particular, the FDMA technique in combination with OFDM (OFDMA) is assumed in this paper. This allows for a high degree of bit-granularity, which is desirable for packet data services. In the past, the performance of such an air-interface was primarily investigated for a single cell scenario (hot spot). In this investigation the performance of OFDMA in a cellular environment with frequency reuse of one and non-perfect frequency synchronization is investigated. In particular the effects of co-channel interference (CCI) in the uplink is analysed since primarily this link direction is affected by asynchronous transmissions. Two kinds of power control methods have been implemented in this paper in order to combat the CCI and improve the spectrum efficiency. One is constant received power control (CRPC); the other is step removal algorithm C/I balancing power control (SRAPC). The performance measure is outage. The results show that outage probability is significant (up to 55%) for a two-cell case with CRPC. The results for a multiple-cell cluster are also shown in this paper.

Journal ArticleDOI
TL;DR: Based on the pairwise probability of error analysis, a new design criterion is developed that determines the code robustness to CCI (CCI diversity gain), and an algebraic framework for constructing space-time codes that jointly optimize the fading and CCI diversity gains is developed.
Abstract: We consider the design of space-time codes for multiple-input multiple-output (MIMO) systems operated in the presence of co-channel interference (CCI). Based on the pairwise probability of error analysis, we develop a new design criterion that determines the code robustness to CCI (CCI diversity gain). We further develop an algebraic framework for constructing space-time codes that jointly optimize the fading and CCI diversity gains. The proposed framework is general for arbitrary numbers of transmit antennas and quadrature amplitude modulation constellations. Numerical results that quantify the performance gains offered by the proposed techniques are also presented.

24 Sep 2004
TL;DR: The preliminary result showed that the MOP method can effectively mitigate all three types of interference at all power levels if a single interference source is present, which is consistent with simulation results which show that for the SCORE algorithm to generate satisfactory results, sufficient number of antenna elements is necessary even if there is no interference source present.
Abstract: This paper presents the performance analysis of two digital beam forming techniques used in conjunction with a software GPS receiver to mitigate interference to GPS signals in interference environment. The first method is the constrained minimum power (MOP) method. The second method is the so-called self-coherence restoral (SCORE) method. Both experimental and simulation data are used in the study. The study was performed using experiment data collected in an anechoic chamber to obtain GPS and interference signals. A two by two GPS antenna array and a four channel radio frequency front end were used to collect simulated GPS data generated using hardwarebased simulator in controlled interference environment. Three types of interference signals are deployed in the experiments: FM chirp, binary phase shift key, and broadband. The interference power levels used were +20, +30, and +40 dB above GPS signal power. A software GPS receiver was used to perform acquisition of GPS signals to evaluate the performance of the beam forming algorithms. The preliminary result showed that the MOP method can effectively mitigate all three types of interference at all power levels if a single interference source is present. Experiments using multiple broadband interference sources were also analyzed and our results shown that the effectiveness of the MOP method diminishes as the interference signal power increases and ceases to function at the +40 dB level. The SCORE method does not exhibit consistent performance for the experimental data. This is consistent with our simulation results which show that for the SCORE algorithm to generate satisfactory results, sufficient number of antenna elements is necessary even if there is no interference source present. The number of antenna element is determined by the number of satellites available, as well as the number of interference sources. The experimental and simulation results are discussed in this paper.

Patent
Dagnachew Birru1, Jeff Bennett1
09 Feb 2004
TL;DR: In this paper, a pseudo-random frequency sequence is used to reduce pico-net interference in a multi-band ultra wideband network, such that neighboring nodes using the same technique can reduce band overlap thereby reducing mutual interference.
Abstract: A wireless communication system and method is provided that uses a pseudo-random frequency sequence to reduce pico-net interference in a multi-band ultra wideband network. Pulse are transmitted using a pseudo-random sequence of frequencies such that neighboring pico-nets using the same technique can reduce band overlap thereby reducing mutual interference.

Proceedings ArticleDOI
17 May 2004
TL;DR: It is shown by means of simulation in TDMA and OFDM environments that the regularized semi-blind solution significantly outperforms the conventional estimators and demonstrates performance close to the LR based benchmark.
Abstract: An asynchronous interference cancellation problem is addressed when training and working intervals are available, containing the desired signal and arbitrary overlapping interference. A likelihood ratio (LR) maximization approach is developed for estimation of the structured correlation matrices over both training and working intervals for the Gaussian data model and exploited to obtain a performance benchmark for ad-hoc estimators. A regularized non-iterative estimation of the antenna array coefficients is proposed, which employs the autocorrelation matrix estimation as a weighted sum of the autocorrelation matrices estimated over the training and working intervals. It is shown by means of simulation in TDMA and OFDM environments that the regularized semi-blind solution significantly outperforms the conventional estimators and demonstrates performance close to the LR based benchmark.

Proceedings ArticleDOI
17 May 2004
TL;DR: Results indicate that the performance gain compared to SIC and PIC is even greater in the multipath scenario and in the presence of channel estimation imperfections, while benefits of using BSS exists.
Abstract: In this paper we consider DS-CDMA uplink interference cancellation based on the blind source separation (BSS) technique. While BSS assisted interference suppression compared to linear receivers is quite well reported, a comparison of BSS with nonlinear receivers is overlooked in the literature. Huovinen (2003) was the first one to make this comparison in the AWGN channel with perfect channel information. In this paper we make further evaluation. In particular, the effects of multipaths, related channel estimation errors and additional external interference (like adjacent channel interference or intentional jamming) are examined and compared to conventional successive interference cancellation (SIC) and M-stage parallel interference cancellation (PIC) schemes. We demonstrate by numerical experiments that benefits of using BSS exists. Moreover, results indicate that the performance gain compared to SIC and PIC is even greater in the multipath scenario and in the presence of channel estimation imperfections.

Journal ArticleDOI
TL;DR: An empirical bound is provided on the difference between the minimal number of channels required based only on geographic reuse distance versus the cumulative interference case in the context of linearly increasing demand.
Abstract: This paper studies the problem of centralized dynamic channel assignment (DCA) in wireless cellular systems under space and time-varying channel demand. The objective is to minimize the number of channels required to satisfy demand while also satisfying co-channel interference constraints. Cumulative co-channel interference constraints govern channel reuse, via a threshold decision criterion based on the carrier-to-interference ratio. The paper makes two contributions. First, it provides an empirical bound on the difference between the minimal number of channels required based only on geographic reuse distance versus the cumulative interference case in the context of linearly increasing demand. The bound is characterized using only the reuse distance. It is obtained with an Integer Programming (IP) based strategy that uses channel assignments for one demand state to assign channels for the next state. Geographic locality constraints are applied to limit reassignments. The impact of cumulative interference constraints is observed to be small for small geographic localities. Second, the paper presents a new, fast DCA heuristic that is based on the characteristic channel reuse patterns used by the IP-based strategy. The heuristic and IP-based method yield similar results for the zero blocking condition. The DCA heuristic is applied to the problem of estimating the blocking probabilities of call arrivals modeled by a two state discrete-time Markov chain and uniformly distributed holding times. The blocking performance for an ensemble of spatial load imbalance distributions is uniquely characterized using the heuristic and IP solutions.

Proceedings ArticleDOI
27 Jun 2004
TL;DR: Single antenna co-channel interference cancellation for cellular TDMA networks by means of joint delayed-decision feedback sequence estimation is proposed and can be increased by a novel adaptive state allocation technique.
Abstract: Single antenna co-channel interference cancellation for cellular TDMA networks by means of joint delayed-decision feedback sequence estimation is proposed. The performance can be increased by a novel adaptive state allocation technique.

Proceedings ArticleDOI
17 May 2004
TL;DR: A code acquisition scheme employing parallel interference cancellation (PIC) for DS-CDMA systems is investigated and it is found that the proposed scheme outperforms the conventional method by producing higher values of P/sub d/ for a particular value of P-sub fa/.
Abstract: A code acquisition scheme employing parallel interference cancellation (PIC) for DS-CDMA systems is investigated. The scheme employs PIC to remove the multiple access interference (MAI) from the synchronized users in the system. The interference cancelled signal is used to acquire the code phase of a new unsynchronized user entering the system. The performance of the new scheme is compared to the conventional method (of using the received signal to perform acquisition) in terms of the probabilities of detection (P/sub d/) and false alarm (P/sub fa/). From simulation results, it is found that the proposed scheme outperforms the conventional method by producing higher values of P/sub d/ for a particular value of P/sub fa/. A mathematical expression is derived for evaluating P/sub d/ at each stage of the PIC and is verified with the simulation results.