Showing papers on "Co-channel interference published in 2009"

Downlink power control in co-channel macrocell femtocell overlay

Abstract: In this paper, interference mitigation through downlink power control is considered for Macrocell Femtocell overlay. Specifically, the strong interference in the downlink from the home base station to a nearby macrocell user should be properly controlled such that the quality-of-service of both the macrocell user and the Femtocell users can be guaranteed. In this work, the fundamental capacity limitation of spatial spectrum sharing among a macrocell user and a Femtocell user is identified. A downlink power control problem is formulated to address the co-channel interference, as well as provide quality-of-service to both the macrocell user and the Femtocell users. The feasibility condition of the problem is derived and both centralized and distributed solutions are provided. Because the co-channel interference are from heterogeneous cells, a joint power control, channel management and admission control procedure is suggested such that the priority of the macrocell users is always ensured. Simulation results demonstrate the effectiveness of the proposed schemes.

Handling CCI and ICI in OFDMA femtocell networks through frequency scheduling

Abstract: Femtocells have a strong potential for increasing the efficiency and coverage of next-generation broadband wireless networks. In this paper, a co-channel framework for the coexistence of orthogonal frequency division multiple access (OFDMA) based macrocell and femtocell wireless networks is proposed. It is based on utilizing the resource blocks of macrocell-associated mobile stations (mMSs) that are far away to a femtocell base station (fBS), therefore avoiding strong interference that may occur between a femtocell and close-by mMSs. An avoidance method that jointly utilizes the spectrum sensing results as well as scheduling information obtained from the macrocell base station (mBS) is introduced. Moreover, the impact of inter-carrier interference (ICI) from the mMSs in the uplink is discussed and evaluated through simulations.

Interference mitigation for control channels in a wireless communication network

Abstract: Techniques for mitigating interference on control channels in a wireless communication network are described. In an aspect, high interference on radio resources used for a control channel may be mitigated by sending a request to reduce interference to one or more interfering stations. Each interfering station may reduce its transmit power on the radio resources, which may then allow the control channel to observe less interference. In one design, a user equipment (UE) may detect high interference on radio resources used for a control channel by a desired base station. The UE may send a request to reduce interference on the radio resources to an interfering base station, which may reduce its transmit power on the radio resources. The UE may receive the control channel on the radio resources from the desired base station and may observe less interference from the interfering base station.

Virtual time-slot allocation scheme for throughput enhancement in a millimeter-wave multi-Gbps WPAN system

Abstract: This paper proposes a virtual time-slot allocation (VTSA) scheme for throughput enhancement to realize a multi-Gbps time division multiple access (TDMA) wireless personal area network (WPAN) system in a realistic millimeter-wave residential multipath environment TDMA system without time-slot-reuse mechanism conventionally allocates one TDMA time-slot to only one communication link at a time In the proposed VTSA scheme, taking advantage on the large path loss in the millimeterwave band, a single TDMA time-slot can be reallocated and reused by multiple communication links simultaneously (hence the name virtual), thus significantly increasing system throughput On the other hand, allowing multiple communication links to occupy the same time-slot causes the generation of co-channel interference (CCI) The cross layer VTSA scheme is therefore designed to be able to maximize the throughput improvement by adaptively scheduling the sharing of time-slots, and at the same time monitor the potential performance degradation due to CCI As a result, it is found that the VTSA scheme is capable of improving system throughput as much as 30% in both AWGN and multipath channels (line-of-sight (LOS) and non-line-of-sight (NLOS) environment) Additionally, by coupling with higher-order modulation schemes, the system is able to achieve up to a maximum throughput of 38 Gbps It is also observed that higher-order modulations although have higher maximum achievable throughput in low CCI environment, the tolerance against increasing CCI is considerably lower than that of the lower-order modulations

A message-passing approach for joint channel estimation, interference mitigation, and decoding

Abstract: Channel uncertainty and co-channel interference are two major challenges in the design of wireless systems such as future generation cellular networks. This paper studies receiver design for a wireless channel model with both time-varying Rayleigh fading and strong co-channel interference of similar form as the desired signal. It is assumed that the channel coefficients of the desired signal can be estimated through the use of pilots, whereas no pilot for the interference signal is available, as is the case in many practical wireless systems. Because the interference process is non-Gaussian, treating it as Gaussian noise generally often leads to unacceptable performance. In order to exploit the statistics of the interference and correlated fading in time, an iterative message-passing architecture is proposed for joint channel estimation, interference mitigation and decoding. Each message takes the form of a mixture of Gaussian densities where the number of components is limited so that the overall complexity of the receiver is constant per symbol regardless of the frame and code lengths. Simulation of both coded and uncoded systems shows that the receiver performs significantly better than conventional receivers with linear channel estimation, and is robust with respect to mismatch in the assumed fading model.

Distributed energy efficient spectrum access in cognitive radio wireless ad hoc networks

Abstract: In this paper, energy efficient spectrum access is considered for a wireless cognitive radio ad hoc network, where each node is equipped with cognitive radio, has limited energy, and the network is an OFDMA system operating on time slots. In each slot, the users with new traffic demand will sense the spectrum and locate the available subcarrier set. Given the data rate requirement and maximal power limit, a constrained optimization problem is formulated for each individual user to minimize the energy consumption per bit over all selected subcarriers, while avoid introducing harmful interference to the existing users. Because of the multi-dimensional and non-convex nature of the problem, a fully distributed subcarrier selection and power allocation algorithm is proposed by combining an unconstrained optimization method with a constrained partitioning procedure. Due to the non-cooperative behavior among new users, they will execute distributed power control to manage the co-channel interference when needed. Simulation results demonstrate that the proposed scheme performs tightly to the global optimal solution. In addition, the comparison between the proposed energy efficient allocation scheme and the well established rate or power efficient allocation algorithms is carried out to demonstrate the advantage of the proposed scheme in terms of network lifetime.

J-CAR: An efficient joint channel assignment and routing protocol for IEEE 802.11-based multi-channel multi-interface mobile Ad Hoc networks

Abstract: The capacity of an IEEE 802.11-based multi-hop wireless network is limited. By effectively utilizing multiple non-overlapping channels and multiple interfaces, collision and co-channel interference can be reduced. This allows more concurrent transmissions and thus enhances the network capacity. In this paper, we introduce an efficient distributed joint channel assignment and routing protocol, called J-CAR. Unlike existing schemes, J-CAR allows a data interface to dynamically change its routing protocol working mode between send and receive on a call-by-call basis, which distributed joint channel assignment enhances the utilization of both interface and channel. In J-CAR, channels are negotiated and assigned to active links in conjunction with the on-demand routing process. At each hop, J-CAR conducts a local optimization by selecting the least interfered channel according to the channel interference index. The channel interference index is designed by taking both the protocol and physical interference models into consideration. To find the least interfered path for network load balancing on a global scale, J-CAR employs a length-constrained widest-path routing. The ldquowidthrdquo of a path is determined by the interference level of its bottleneck link. With an adjustable threshold on the path length (with respect to the shortest-path), the excessively long path can also be avoided. We show that with a comparable complexity as the existing schemes, J-CAR provides much higher system good puts and shorter end-to-end packet delays.

Apparatus and method for interference cancellation and synchronization maintenance over interference channel estimation in communication system based on full-duplex relay

Abstract: An apparatus and method for interference cancellation and synchronization maintenance over interference channel estimation in a communication system are provided. An interference channel estimator fixes synchronization and estimates an interference signal. An interference signal controller eliminates the estimated interference signal from a received RF signal. A synchronization unit unfixes fixed synchronization and tracks synchronization when the interference signal cancellation is stable. A data buffer stores data from which the interference signal is canceled.

Methods and apparatus for generating, reporting and/or using interference cancellation information

Abstract: Apparatus and methods for power control for mitigation or control of interference in a wireless communications environment. Power control techniques can consider the effectiveness of interference cancellation before making power control determinations. For example, where interference with a base station from an interfering wireless terminal is being canceled such that the effects of that interference are not adversely affecting operations of the base station, the offending terminal can be left unchanged, or its transmit power can be increased. On the other hand, where the interference cancellation operation is not able to cancel the effects of the interfering signal sufficiently, the operation can lower the uplink transmit power of the offending signal so as to not cause interference to the other base station.

Channel estimation in OFDM systems with unknown interference

Abstract: We investigate the problem of channel estimation in an orthogonal frequency-division multiplexing (OFDM) system plagued by unknown narrowband interference (NBI). Such scenario arises in many practical contexts, including cellular applications and emerging spectrum sharing systems, where coexistence of different types of wireless services over the same frequency band may result into remarkable co-channel interference. Estimation algorithms devised for conventional OFDM transmissions are expected to suffer from significant performance degradation in the presence of NBI. To overcome this difficulty, in the present work we follow a novel pilot-aided approach where the interference power on each pilot subcarrier is treated as a nuisance parameter which is averaged out from the corresponding likelihood function. The latter is then maximized in an iterative fashion according to the expectation-maximization (EM) principle or by applying the Jacobi-Newton algorithm. The resulting schemes have affordable complexity and are inherently robust to NBI. Their accuracy is investigated by means of computer simulations and compared with the relevant Cramer- Rao bound.

Channel selection and interference suppression

Abstract: Several adaptive techniques are described to combat interference in multiple-input multiple-output (MIMO) systems. In addition to adaptive frequency selection, interference suppression techniques for a selected carrier frequency are presented. The interference suppression technique can be adaptively selected based on the availability and quality of channel state information (CSI) and interference statistics. Techniques to estimate interference statistics are also presented. Interference mitigation techniques are also presented for automatic gain control (AGC), intermittent interference, and interference caused to other networks.

Statistical Modeling of Co-Channel Interference

Abstract: With increasing spatial reuse of the radio spectrum, co-channel interference is becoming the dominant noise source and may severely degrade the communication performance of wireless transceivers. In this paper, we consider the problem of statistical-physical modeling of co-channel interference. Statistical modeling of interference is a useful tool to analyze the outage probabilities in wireless networks and to design interference-aware transceivers. Our contributions include (1) developing a unified framework to derive interference models for various wireless network environments, (2) demonstrating the applicability of the symmetric alpha stable and Middleton Class A distributions in modeling co-channel interference in ad-hoc and cellular network environments, and (3) deriving analytical conditions on the system model parameters for which these distributions accurately model the statistical properties of the interference. Simulation results allow us to compare the key properties of empirical co-channel interference and their statistical models under different wireless network environments.

Cognitive Radio Transmission

Abstract: A method, an apparatus, and a computer program for performing cognitive communications in a radio environment are presented. First, a radio communication device estimates a time-varying interference environment in a radio communication channel. On the basis of the estimation, a future interference environment is predicted from time-varying characteristics of the estimated interference. Upon predicting the future interference environment, a radio transmitter is configured to apply transmission parameters to be used in a future transmission time instant for which the interference environment has been predicted. As a consequence, the transmission parameters are selected proactively to match with the predicted interference environment. The transmission parameters may be configured as time-variant.

Multi-Antenna Interference Cancellation Techniques for Cognitive Radio Applications

Abstract: This paper presents a practical method for using multi-antenna radios to cancel interference in cognitive radio systems. Under this method, secondary radio transmitters use beamforming techniques to find antenna weights that place nulls at the primary receivers, and secondary radio receivers use adaptive techniques to decode in the presence of interference from primary users. As an example, we show how this scheme can be leveraged to effectively reuse the uplink band of a cellular network. However, estimating the channel responses, without causing interference and without requiring significant modifications to legacy systems, is a challenging problem. We provide an iterative method for accurate channel estimation in frequency division duplexed networks, where the uplink is independent of the downlink.

Interference Channel aided by an Infrastructure Relay

Abstract: A Gaussian Interference Channel with an Infrastructure Relay (ICIR) is investigated. The relay has finite-capacity links to both sources and destinations that are orthogonal to each other and to the underlying interference channel. A general achievable rate region is presented by using the relay both to convey additional information from the sources (signal relaying) and to ease interference cancelation (interference forwarding). Outer bounds to the capacity region are also derived, and used to determine a number of regimes of interest where either signal relaying only or both signal relaying and interference forwarding are optimal.

Adjacent channel optimized receiver

Abstract: The present invention offers significant improvements in the performance of a radio receiver operating in an environment with high desired band interference. The present invention comprises a high selectivity RF circuit that is located between the antenna and the radio receiver, and utilizes superheterodyne technology to filter adjacent channel interference in the desired band frequency spectrum. This type of interference is problematic for IEEE 802.11 radio receivers that are implemented with the popular direct conversion radio receiver architectures. The present invention may be utilized in many types of radio receivers.

Method for improving coexistence between adjacent tdd and fdd wireless networks

Abstract: A method is provided for reducing interference between FDD and a TDD interfering radio networks. For each of the networks, identifying respective radio entities of a pre-defined type for which the interferences should be reduced; defining a time pattern composed of time slots on each of the interfered FDD and TDD frequency channels, that comprises receive time intervals for radio entities of the pre-defined types that are likely to be interfered; aligning the time patterns so that receive time intervals for the radio entities that are potentially exposed to interferences, overlap each other; defining at least two types of time intervals within the time pattern on each frequency channel, wherein a first type of time intervals enables receiving communications with substantially reduced interference and a second type of time intervals for exchanging communications without mitigating interferences induced by radio entities transmitting during that time intervals. The radio entity that might create interference to the radio entity of the pre-defined type of the other network, is prevented from transmitting communications that might create e substantial interference to the radio entity associated with the other radio network, and communications transmitted to some of radio entities of the pre-defined types that might experience interference are scheduled at intervals of the first type.

Capacity bounds for two-hop interference networks

Abstract: This paper considers a two-hop interference network, where two users transmit independent messages to their respective receivers with the help of two relay nodes. The transmitters do not have direct links to the receivers; instead, two relay nodes serve as intermediaries between the transmitters and receivers. Each hop, one from the transmitters to the relays and the other from the relays to the receivers, is modeled as a Gaussian interference channel, thus the network is essentially a cascade of two interference channels. For this network, achievable symmetric rates for different parameter regimes under decode-and-forward relaying and amplify-and-forward relaying are proposed and the corresponding coding schemes are carefully studied. Numerical results are also provided.

The Diversity Multiplexing Tradeoff for Interference Networks

Abstract: The diversity-multiplexing tradeoff (DMT) for interference networks, such as the interference channel, the X channel, the Z interference channel and the Z channel, is analyzed. In particular, we investigate the impact of rate-splitting and channel knowledge at the transmitters. We also use the DMT of the Z channel and the Z interference channel to distill insights into the "loud neighbor" problem for femto-cell networks.

MIMO rayleigh-product channels with co-channel interference

Abstract: This paper presents an analytical performance investigation of an interference-limited double scattering multiple-input multiple-output (MIMO) channel employing optimum combining. Our main contribution is the derivation of the closed-form expressions for the cumulative distribution function (c.d.f.) and probability density function (p.d.f.) of the maximum eigenvalue of the resultant channel matrix after optimal combining when the transmit, receive and scattering correlation matrices are identities (hence, the channel is referred to as a Rayleigh-product channel). These results allow us to obtain the outage probability of the optimal combining system in a Rayleigh-product channel with co-channel interferences. Furthermore, we investigate, in depth, an important special case of double scattering channel, the keyhole channel, where based on various closed-form expressions for exact and asymptotic measures derived, we examine three key performance metrics, namely, the ergodic capacity, the outage performance and the symbol-error-rate (SER). The analytical results derived are validated by Monte-Carlo simulations.

Interference Alignment and a Noisy Interference Regime for Many-to-One Interference Channels

Abstract: We study the capacity of discrete memoryless many-to-one interference channels, ie, K user interference channels where only one receiver faces interference For a class of many-to-one interference channels, we identify a noisy interference regime, ie, a regime where random coding and treating interference as noise achieves sum-capacity Specializing our results to the Gaussian MIMO many-to-one interference channel, which is a special case of the class of channels considered, we obtain new capacity results Firstly, we extend the noisy interference regime, previously studied for (many-to-one) interference channels with average power constraints on the inputs, to a more general class of inputs This more general class includes the practical scenario of inputs being restricted to fixed finite-size constellations such as PSK or QAM Secondly, we extend noisy interference results previously studied in SISO interference channels with full channel state information (CSI) at all nodes, to MIMO and parallel Gaussian many-to-one interference channels, and to fading Gaussian many-to-one interference channels without CSI at the transmitters While the many-to-one interference channel requires interference alignment, which in turn requires structured codes in general, we argue that in the noisy interference regime, interference is implicitly aligned by random coding irrespective of the input distribution As a byproduct of our study, we identify a second class of many-to-one interference channels (albeit deterministic) where random coding is optimal (though interference is not treated as noise) The optimality of random coding in this second class of channels is due to an interference resolvability condition which precludes interference alignment and hence obviates the need of structured codes

Error performance and throughput evaluation of a multi-Gbps millimeter-wave WPAN system in the presence of adjacent and co-channel interference

Abstract: This paper investigates the impact of adjacent channel interference (ACI) and co-channel interference (CCI) on error performance and throughput of a multi-Gbps millimeterwave wireless personal area network (WPAN) system in a realistic residential line-of-sight (LOS) and non-line-of-sight (NLOS) multipath environment. The main contribution of this paper is providing a multi-Gbps WPAN system design in the challenging multipath environment in the presence of ACI/CCI. Based on the investigation results, we have provided ACI/CCI rejection as a reference for victim receiver protection design. In the NLOS environment, the ACI rejection (i.e. ACI that causes 0.5 dB degradation in the required signal-to-noise ratio (SNR) to achieve bit error rate (BER) of 10-6) for pi/2-BPSK, QPSK, 8 PSK and 16 QAM are 13, 7, 0 and -6dB respectively. And the CCI rejection for similar modulation schemes are -18, -20, -26 and -29 respectively. Secondly, we have clarified the LOS-NLOS relationship of the ACI/CCI impact to system performance. ACI in multipath NLOS environment causes an additional 5 dB degradation to error performance as compared to ACI in the LOS environment. CCI on the other hand, has similar impact on error performance in both LOS and NLOS environment. Thirdly, we have clarified the relationship between modulation spectral efficiency and robustness against ACI/CCI. In an environment with no or low ACI/CCI, the maximum achievable throughput for pi/2-BPSK, QPSK, 8 PSK and 16 QAM in LOS environment are 1.2, 2.5, 3.8 and 5 Gbps respectively. In NLOS environment, the achievable throughput decreases to 1, 1.9, 2.8 and 3.8 Gbps respectively. As ACI/CCI increases, the throughput of higherorder modulation schemes such as 16 QAM decreases the most rapidly, followed by 8 PSK and QPSK. The throughput for pi/2-BPSK has the highest tolerance against increasing ACI/CCI, at the expense of lower maximum achievable throughput.

Outage Analysis of Wireless Systems over Composite Fading/Shadowing Channels with Co-Channel Interference

Abstract: This paper presents an outage analysis of wireless systems operating in gamma-shadowed Nakagami-faded environments where the desired signal also suffers from co-channel interference. The interfering signals are also subject to fading and shadowing. Based on the obtained signal to interference ratio (SIR) probability density function (pdf), closed-form expressions for the outage probability are obtained in both cases of statistically identical interferers and multiple interferers with different parameters. The effects on the aforementioned performance metric of the reuse distance and of the combined fading, shadowing and co-channel interference are analyzed subsequently. The newly derived closed-form expressions for the outage probability allow as to assess the effects of the different channel and interference parameters easily.

Outage Probability of Dual-Hop Relay Channels in the Presence of Interference

Abstract: In this paper, we address the performance of a dual- hop relay fading channel in an interference-limited environment, in which the destination node is corrupted by co-channel interfer- ence while the relay node is perturbed by only an additive white Gaussian noise We first investigate the scenario with equal-power interferers, under which the analytical expressions for the outage probability of both the amplify-and-forward (AF) and the decode- and-forward (DF) relay channels are derived in closed form We then extend the analysis for the general case with unequal-power interferers Using majorization theory, we show that in terms of outage probability, the worst scenario appears if the interferers are of equal power, for a given total interference power

Collision analysis for coexistence of multiple bluetooth piconets and WLAN with dual channel transmission

Abstract: Co-channel interference (CCI) has become an important problem with the increasing deployment of wireless networks in the unlicensed frequency band. The existing Bluetooth scheme avoids collisions by modifying its hop sequences in the presence of WLAN. We propose a frequency diversity technique, namely dual channel transmission (DCT), which reduces packet error rate (PER) due to CCI when multiple Bluetooth piconets coexist with or without WLAN interference. The idea of DCT is to transmit the same packet on two distinct frequency hopped channels simultaneously and the power used in each channel is half of what would be used in single channel transmission (SCT). Since a packet is successfully received if at least one channel survives, the PER is reduced even when multiple piconets coexist. Further, the two channels of DCT are separated by at least 22 MHz to ensure robustness to WLAN interference. Theoretic analysis and numerical simulations on key metrics - PER, throughput, and transmission time are presented to validate the proposed approach and quantify its advantages. Comparisons to other coexistence mechanisms also demonstrate the effectiveness of DCT.

Symbol-wise beamforming for MIMO-OFDM transceivers in the presence of co-channel interference and spatial correlation

Abstract: In MIMO-OFDM communications over channels subject to co-channel interference, beamforming (BF) is conventionally applied independently to all subcarriers. Whilst this approach maximises mutual information, it is highly computationally complex. Symbol-wise BF considerably reduces the complexity by carrying out BF in the time domain. In this paper, we generalise symbol-wise BF to take co-channel interference into account. Maximising the mutual information is infeasible in this case and instead, we propose a novel iterative algorithm that maximises the SINR before OFDM demodulation. Computer simulations show that the performance loss relative to subcarrier-wise BF reduces with decreasing frequency selectivity or increasing spatial correlation.

Error Performance and Throughput Evaluation of a Multi-Gbps Millimeter-Wave WPAN System in Multipath Environment in the Presence of Adjacent and Co-Channel Interference

Abstract: This paper investigates the impact of adjacent channel interference (ACI) and co-channel interference (CCI) on the error performance and throughput of a multi-Gbps millimeter-wave wireless personal area network (WPAN) system in both residential multipath line-of-sight (LOS) and non-LOS (NLOS) environment. It is found that the ACI that causes 0.5dB degradation in signal-to-noise ratio (SNR) for BPSK, QPSK, 8-PSK and 16-QAM systems are 13, 7, 0 and -6 dB respectively. And the CCI that causes similar SNR degradation for BPSK, QPSK, 8-PSK and 16-QAM are -18, -20, -26 and -29 dB respectively. Additionally, multipath NLOS environment in the presence of ACI is found to cause an extra 5 dB degradation on error performance as compared to ACI in LOS environment. On the other hand, CCI in both LOS and NLOS environment display approximately similar impact on error performance. In extremely low ACI/CCI environment, the maximum achievable throughput for BPSK, QPSK, 8-PSK and 16-QAM in NLOS environment are 1.1, 2.2, 3.4 and 4.6Gbps respectively. Then as ACI/CCI increases, the throughput of 16-QAM decreases the most rapidly, followed by 8-PSK, QPSK and pi/2-BPSK. It is also found that system tolerance against ACI/CCI can be increased by employing modulation schemes with lower modulation level, at the expense of lower maximum achievable throughput.

Bypassing method for co-channel interference between base stations, control apparatus and base station device

Abstract: The invention discloses an method for evading co-channel interference between basic stations, which includes following steps: periodically measures co-channel interference power of each up-link subchannel; classifies the codes in the time slot whose interference power exceeds the preset threshold in the protection code field; then makes the codes outside the protection code field as the adjusting and distributing resource when adjusting and distributing resources. The invention also discloses a control device which includes a measuring unit which is used for measuring co-channel interference power of each up-link subchannel; an identifying unit which is used for identifying the codes corresponding to the time slot whose interference power exceeds the preset threshold; and an adjusting and distributing unit which is used for resource adjusting and distributing. Meanwhile, the invention also discloses a basic station device. Through calculating the interference power of each time slot, the invention identifies the codes corresponding to the time slot whose interference power exceeds the preset threshold as the unusable resource and does not regards the codes as the adjusting and distributing resource; therefore can evade the co-channel interference from other basic stations.

Multiple Antennas Selection for Linear Precoding MISO Cognitive Radio

Abstract: Using multiple antennas in coexisting radio systems can cancel or control the co-channel interference (CCI), hence improve the overall spectrum efficiency. However, one of the drawbacks of such techniques is the hardware complexity. Antenna selection technology may reduce such costs while partly keeping the advantages of multiple antennas. In this paper, we focus on the downlink of a linear precoding multiple input single output (MISO) cognitive radio (CR) system and apply antenna selection techniques in the transmitter side of the secondary system. We discuss the optimal, maximum norm, and our proposed subset optimal selection strategy, which has a lower computational complexity and reduces feedback information compared to the optimal method. The simulation results show that our proposed methods achieve near optimal performance in terms of SNR.

Turbo Packet Combining for Broadband Space-Time BICM Hybrid-ARQ Systems with Co-Channel Interference

Abstract: In this paper, efficient turbo packet combining for single carrier (SC) broadband multiple-input--multiple-output (MIMO) hybrid--automatic repeat request (ARQ) transmission with unknown co-channel interference (CCI) is studied. We propose a new frequency domain soft minimum mean square error (MMSE)-based signal level combining technique where received signals and channel frequency responses (CFR)s corresponding to all retransmissions are used to decode the data packet. We provide a recursive implementation algorithm for the introduced scheme, and show that both its computational complexity and memory requirements are quite insensitive to the ARQ delay, i.e., maximum number of ARQ rounds. Furthermore, we analyze the asymptotic performance, and show that under a sum-rank condition on the CCI MIMO ARQ channel, the proposed packet combining scheme is not interference-limited. Simulation results are provided to demonstrate the gains offered by the proposed technique.