Low-complexity cochannel interference cancellation and macroscopicdiversity for high-capacity PCS

More than a factor of three increase in overall personal communication system (PCS) capacity can be achieved in small handheld communication devices with limited battery power or in small low-complexity base stations when incorporating simple interference cancellation techniques without training sequences in the channel-access algorithm that realizes macroscopic selection diversity based on signal quality measurement. The comparison is done with respect to microscopic selection diversity and macroscopic selection diversity based on channel power measurement. Results were obtained by computer simulations     

Adaptive cochannel interference cancellation in space-time coded communication systems

Space-time coding is a powerful scheme that combines channel coding, modulation, and multiple transmit antennas to achieve higher data rates and combat fading in wireless systems. In this letter, we propose a multiple-input multiple-output minimum mean-square error spatial-filtering-based adaptive antenna arrays method to suppress cochannel interference (CCI) in space-time coded systems. It is shown that the proposed method can effectively suppress CCI while preserving the space-time structure, thereby significantly improving the system's interference suppression ability without significant bit error rate performance degradation.     

Improved parallel interference cancellation for CDMA

This paper introduces an improved nonlinear parallel interference cancellation scheme for code-division multiple access (CDMA) that significantly reduces the degrading effect on the desired user of interference from the other users that share the channel. The implementation complexity of the scheme is linear in the number of users and operates on the fact that parallel processing simultaneously removes from each user a part of the interference produced by the remaining users accessing the channel the amount being proportional to their reliability. The parallel processing can be done in multiple stages. The proposed scheme uses tentative decision devices at the multiple stages to produce the most reliably estimated received data for generation and cancellation of user interference. Simulation results are given for a multitude of different situations, in particular, those cases for which the analysis is too complex     

Macrodiversity cochannel interference analysis

A cochannel interference analytical model to evaluate the performance of S+I-macrodiversity to combat shadowing is presented. It was found that the performance difference between the S+I-macrodiversity and S/I-macrodiversity is significant, but the performance with S-macrodiversity is close to the case of S+I-macrodiversity     

Trellis-coded cochannel interference canceller for microcellularradio

Cochannel interference is a major impairment that limits the capacity of microcellular radio systems. This paper proposes a trellis-coded cochannel interference canceller, which uses trellis-coded modulation with maximum likelihood sequence estimation of both the desired signal and cochannel interference. This technique permits operation even when the signal-to-interference ratio is 0 dB. Computer simulation results show that this technique significantly reduces the bit-error rate in microcellular systems with Nakagami-Rice fading, particularly when the average signal-to-interference ratio is 0 dB. However, the technique requires: (1) synchronization of the interference and the desired signal and (2) higher computational complexity than standard techniques     

Diversity MPSK receivers in cochannel interference

The performance of M-ary phase shift keying (MPSK) in the presence of cochannel interference in microcellular radio environments is analyzed. Average bit error rates (BER) of MPSK using both dual-branch equal gain combining (EGG) and dual-branch selection combining (SC) are derived assuming that the desired signal experiences frequency-nonselective Ricean or Nakagami fading and the multiple interferers experience independent frequency-nonselective Rayleigh fading. Nyquist pulses are used, and perfect coherent detection is assumed at the receiver. The accuracy of the Gaussian interference approximation for diversity receivers is also assessed     

Minimising cochannel interference in television reception

A method is proposed for minimising cochannel interference in television reception, by introducing a random change in phase of the vision carrier at the beginning either of each field, or each line, of the television picture. Unlike the present system, in which the carrier frequency offsets are related to the picture line frequency, the benefits to be expected from the method described would apply independent of the number of interfering stations. No practical tests on the proposal have yet been made.     

Exact cochannel interference analysis for log-normal shadowedRician fading channels

An exact analytical method is presented for evaluating the probability of cochannel interference for Rician/Rayleigh faded channels with log-normal shadowing. The method requires that at least one signal (desired or interfering) be Rayleigh faded and log-normal shadowed. The Rice factor of the desired signal is shown to have a large effect on the probability of cochannel interference, while the Rice factors of the interfering signals are shown to have little effect     

Correlated interference cancellation for IR-UWB

In this letter, we propose a hybrid analog/digital detection algorithm, the Correlated Interference Cancellation （CIC） algorithm, for Impulse Radio Ultra-WideBand （IR-UWB） system. The CIC algorithm correlates received signal with its delayed versions in the analog domain and samples the correlation output at the symbol rate. The symbol rate samples are processed in the digital domain to perform interference cancellation. Therefore, CIC works for high data rate systems with heavy InterSymbol Interference （ISI）. Simulation results show that CIC achieves good performance in typical UWB channels.     

Turbo soft interference cancellation for coded asynchronous ds/cdma

In this paper we propose a Multiuser receiver architecture which removes the Multiple Access Interference (Mai) by means of a Soft Input Soft Output (siso) multiuser detector followed by a bank of channel decoders. The extrinsic information at the output of the channel decoders are used to estimate the values of the interfering bits and the SISO multiuser detector subtracts the vector of the interfering bits from the incoming signal. The resulting vector is then filtered by an adaptive mmse filter to help remove the residual mai. The paper examines the use of such a receiver in the context of a synchronous awgn channel and then we generalize to the case of asynchronous multipath fading channels.     

Noise subspace approach for interference cancellation

The authors propose an interference cancelling method using the noise subspace of a covariance matrix in which the desired signal is subtracted. A beamformer using the method can generate deep nulls even for the interferences correlated with the desired signal or located close to the look-direction. In addition, the authors consider how the method can be computed efficiently by utilising the minimum eigenvector.<>     

Frequency-hopping versus interference cancellation for TD-CDMA

This work considers asynchronous time division code division multiple access (TD-CDMA) systems with RAKE receivers and one stage of parallel interference cancellation (PIC) or serial interference cancellation (SIC). A general method based on the concept of spherically symmetric signals is presented for the evaluation of the average probability of error of uncoded TD-CDMA systems. Slow frequency-hopping (SFH) with frequency overlap (FO) between adjacent carriers and interference cancellation are also included in the analysis, which considers the multipath Rayleigh fading channel (which models indoor and outdoor vehicular radio propagation). We analyze quadrature phase shift keying (QPSK) modulation with coherent demodulation and multipath (frequency) diversity with maximal ratio combining (MRC). Power control, adaptive SFH, and interference cancellation are employed for improving the bit-error rate (BER) performance. It is found that the scheme with SFH, in spite of the FO, always improves the performance substantially, and interference cancellation, in general, provides the highest BER improvement     

Subarray design for adaptive interference cancellation

A method for designing near optimal, tapered subarrays for adaptive interference cancellation is proposed. The design method simultaneously produces a complete ordered set of fixed beam definitions, or nonadaptive weight vectors. The designer may choose to implement the first K of these if he or she wishes to have exactly K adaptive weights. In other words, the digital-adaptive processing is done in beam space, such that the beams are designed using the proposed method. To facilitate an RF implementation of the nonadaptive beamformer, each auxiliary beam uses only a designer-specified number of the elements in the aperture, thereby reducing the number of waveguide connections required. This design approach is fundamentally different from conventional subarray design approaches in that the new designs utilize cost functions related to interference cancellation.     

Efficient ISI cancellation for STBC OFDM systems using successive interference cancellation

In this letter, we propose an efficient detection scheme for space-time block coded (STBC) orthogonal frequency-division multiplexing (OFDM) with insufficient cyclic prefix (CP). The proposed scheme employs successive interference cancellation (SIC) and cyclic prefix reconstruction (CPR) concepts. Simulation results present that the proposed scheme outperforms the conventional scheme for STBC OFDM systems.     

Successive interference cancellation in multicarrier DS/CDMA

In this paper, we present a successive interference cancellation (SIC) scheme for a multicarrier (MC) direct-sequence code-division multiple-access (CDMA) system, using band-limited spreading waveforms to prevent self-interference. In every subband, the SIC receiver successively detects the interferers' signals and substracts them from the user-of-interest. A comparison is made among SIC, a minimum mean-squared error (MMSE) receiver, and matched filter (MF) detection with maximal-ratio combining (MRC). We also consider suboptimal combining using pilot symbol-assisted modulation (PSAM) to make the system more realistic. Analytic bit-error probabilities for SIC, MMSE, and MF in correlated Rayleigh fading channels are derived. The theoretical results for SIC, MMSE, and MF are shown to agree well with simulations. In particular, SIC and MMSE are shown to achieve better performance than MF with MRC; when the number of users is small, SIC provides better performance than does MMSE. Further, the correlation among different subcarriers is studied, and only large subcarrier correlation coefficients result in an obvious worsening of performance. Finally, we derive results for the performance degradation that an SIC scheme experiences in MC CDMA due to phase and timing tracking errors. It is shown that SIC can still retain a performance advantage over MF-MRC, although the advantage of SIC decreases with increasing tracking errors, especially when subcarrier correlation coefficients are small     

Distributed cochannel interference control in cellular radiosystems

Distributed power control algorithms that use only the carrier-to-interference ratios (C/I ratios) in those links actually in use are investigated. An algorithm that successfully approximates the behavior of the best known algorithms is proposed. The algorithm involves a novel distributed C/I-balancing scheme. Numerical results show that capacity gains on the order of 3-4 times can be reached also with these distributed schemes. Further, the effects of imperfect C/I estimates due to noise vehicle mobility, and fast multipath fading are considered. Results show that the balancing procedure is very robust to measurement noise, in particular if C/I requirements are low or moderate. However, for required high C/I levels or for a rapidly changing path loss matrix, convergence may be too slow to achieve substantial capacity improvements     

Spatial-temporal processing for wireless systems with intersymbol and cochannel interference

In this paper, spatial-temporal receive filters for multiple receiver systems with intersymbol interference (ISI), cochannel interference (CCI), and additive white Gaussian noise (AWGN) are investigated. An optimal spatial-temporal filter that is optimal for any following baud-rate processor with any reasonable criterion of goodness is found. Therefore, it allows CCI suppression and equalization to be treated separately. Furthermore, it is shown in this paper that, under certain conditions, the baud-rate samples of the optimal spatial-temporal filter output form a set of sufficient statistics for the following baud-rate signal detector for channels with ISI, CCI, and AWGN, which is very similar to the traditional matched filter for AWGN channels with only ISI. Thus, the optimal spatial-temporal filter is also called an analogical spatial-temporal matched filter.     

Access algorithm for packetized wireless transmission in thepresence of cochannel interference

Packetized access has some potential advantages over conventional circuit-switched-based access methods because several signal sources can share the same radio channel using statistical multiplexing. We consider radio resource assignment algorithms for packetized access based on the packet-reservation multiple-access (PRMA) protocol in the presence of cochannel interference. The statistical multiplexing gain of packet access is limited by frequency reuse, especially when the reuse factor is low or duality requirement is high. We propose a fuzzy logic-based adaptive medium-access control (MAC) algorithm to improve packet-access efficiency. Computer simulations based on the example of packetized voice have confirmed that the proposed packet-access protocol can support a higher number of active users per radio port than that supported by random slot assignment     

Trickle-based interference cancellation schemes for CDMA systems

In this paper, we introduce a novel approach to interference cancellation (IC) for code division multiple access (CDMA) uplink transmission. Several models combining principles of serial (SIC) and parallel (PIC) interference cancellation are discussed. The proposed scheme is derived from the analysis of these hybrid models and applies a user configuration algorithm (termed “trickle”) in order to provide improved bit-error-rate (BER) performance. The algorithm utilizes an adaptive matrix to compute the required configuration to be used for the subsequent interference cancellation stage. We demonstrate that significant performance improvements can be achieved over various hybrid schemes. A reduced-complexity version of the trickle algorithm is also introduced where the processing delay is greatly reduced while maintaining similar performance. We present several numerical examples through which we demonstrate the efficacy of the proposed algorithms relative to existing interference cancellation algorithms.