Combat Co-channel Interference Research Articles

Interference-Aware Cooperative Communication in Multi-Radio Multi-Channel Wireless Networks

There are a lot of recent interests on cooperative communication (CC) in wireless networks. Despite the large capacity gain of CC in small wireless networks with its capability of mitigating fading taking advantage of spatial diversity, cooperative communication can result in severe interference in large networks and even degraded throughput. The aim of this work is to concurrently exploit multi-radio and multi-channel (MRMC) technique and cooperative transmission technique to combat co-channel interference and improve the performance of multi-hop wireless network. Our proposed solution concurrently considers cooperative routing, channel assignment, and relay selection and takes advantage of both MRMC technique and spatial diversity in cooperative wireless networks to improve the throughput. We propose two important metrics, contention-aware channel utilization routing metric (CACU) to capture the interference cost from both direct transmission and cooperative transmission, and traffic aware channel condition metric (TACC) to evaluate the channel load condition. Based on these metrics, we propose three algorithms for interference-aware cooperative routing, local channel adjustment, and local path and relay adaptation respectively to ensure high performance communications in dynamic wireless networks. Our algorithms are designed to be fully distributed and can effectively mitigate co-channel interference and achieve cooperative diversity gain. To our best knowledge, this is the first distributed solution that supports cooperative communications in MRMC networks. Our performance studies demonstrate that our proposed algorithms can efficiently support cooperative communications in multi-radio multi-hop networks to significantly increase the aggregate throughput.

Novel femto cooperative scheme with interference mitigation and performance analysis under different fading channels

In femto cell systems, a novel femto cooperative (Fe-COPE) system is proposed to combat co-channel interference from neighbor cells in different fading channel environments. The proposed scheme utilizes each user as a relay in a network system that acquires diversity gain from the interferer user of the Fe-COPE system with feedback cancellation technique. The performance of the proposed Fe-COPE system is analyzed under the Rayleigh, Rician-K, and Nakagami-m fading channels. Closed form expressions for the moment generating function of the received signal-to-noise-ratio (SNR) are derived to evaluate the bit error rate (BER) expressions under the M-QAM modulation scheme. Simulation results show considerable improvement in the curves of BER as a function of SNR. Monte Carlo simulation confirms the correctness of the analytical expressions derived for the Fe-COPE system.

Opportunistic Relay Selection for Cooperative Relaying in Cochannel Interference Contaminated Networks

A multiple-relay assisted cooperative automatic-repeat-request (CARQ) system is proposed in interference-limited scenario, where multiple-user detection (MUD) receivers using successive interference cancellation (SIC) are employed at the relay nodes (RNs) and the destination node (DN) to combat cochannel interference (CCI). We analyze the outage performance and propose a novel best effort-detection-based opportunistic relay selection (BED-ORS) scheme, which achieves significantly better outage performance than the traditional highest SNR-based ORS scheme offered in the literature. Moreover, considering the effects of the outdated channel state information (CSI), an improved-BED-ORS (I-BED-ORS) scheme is proposed to enhance the robustness against CSI imperfections.

Spectrum efficiency of Fixed WiMAX OFDM network in the presence of co-channel interference with diversity combining

WiMAX (Worldwide Interoperability for Microwave Access) is a promising technology which can offer high speed voice, video and data services upto the requirements at the customer's end. The objectives of this paper is the Performance evaluation of a WiMAX system under various diversity schemes (Selection combining, Maximal ratio combining and Equal gain combining), employing different adaptive transmission policies, such as Optimal power and rate adaptation policy, Optimal rate adaptation with constant transmit power policy, Channel inversion with fixed rate policy, and Truncated channel inversion policy, subjected to co-channel interference. The WiMAX system incorporates OFDM with BPSK modulation as the transmission scheme. Simulated results of the estimated spectrum efficiency shows that the implementation of Optimal power and rate adaptation policy is highly effective to combat co-channel interference in the WiMAX communication system, under Selection combining.

Estimation of the output error statistics of space-time equalization in an antenna array EGPRS receiver with soft-decision decoding

The use of antenna arrays can help combat cochannel interference (CCI) in wireless cellular systems. In this paper, we consider an enhanced general packet radio service diversity receiver based on least squares spatio-temporal equalization and soft-decision decoding in the presence of decision feedback and/or asynchronous CCI. We compare known and novel estimators of the error mean and variance at the output of the deterministic space-time equalizer. The collected simulation data indicate that the estimation of the error mean and variance is critical to the performance of soft-in/hard-out Viterbi decoding in the presence of nonstationary input disturbance. Moreover, the use of short-term error statistics provides receiver performance gains of up to 15-20 dB in terms of signal-to-interference ratio, with respect to the use of burst statistics based on the training sequence midamble and tentative decisions on the payload symbols.

Co-channel interference mitigation in GSM networks by iterative estimation of channel and data

In multiple-access communication systems several users share the system resources, thus creating co-channel interference to each other. Multiuser detection, applied at the receiver side, is a powerful technique to combat co-channel interference, in contrast to single-user approaches that treat the interference as additive noise. In this paper, we investigate the feasibility of achieving increased spectral efficiency in GSM-like TDMA networks by applying multiuser detection. We focus on downlink operation and consider two mobile users that share the same physical channel within the same cell or in two adjacent cells. No synchronization between the base stations is assumed. Mobile terminals exploit multiple receiving antennas. We propose a simple iterative receiver algorithm that performs joint channel and data estimation. Results of simulations that evaluate the receiver's performance are presented.

Stationary points of a kurtosis maximization algorithm for blind signal separation and antenna beamforming

Blind source separation has been the subject of extensive research. In particular, blind antenna beamforming is an effective signal separation technique for communication systems to combat co-channel interference. Among many potential candidate approaches, the simple constant modulus algorithm (CMA) has been widely studied and used in practice. The CMA is designed to capture and separate signals with negative kurtosis. However, when some signals have positive kurtoses, the CMA is unable to capture and separate these sources. We show that the kurtosis maximum algorithm (KMA) can capture signals with both the positive and negative kurtoses. Its global convergence proof is presented for noiseless systems with multiple signals sources and for systems with a single source and zero-kurtosis (such as Gaussian) additive noise.

Efficient Spectrum Utilization for Mobile Radio Systems Using Space Diversity

Space diversity combining is a well-known method of smoothing amplitude fluctuations of the received signal in Rayleigh fading environments, such as mobile radio. Perhaps less well known is that space diversity combining can also be an excellent method of combating cochannel interference. In this paper, it is shown that high spectrum efficiencies in mobile radio systems can be achieved with a modest number of space diversity branches. With a large number of diversity branches it is shown that frequency reuse is possible resulting in spectrum efficiencies, as defined herein, greater than 100 percent.