Showing papers on "Co-channel interference published in 2010"

The investigation of power control schemes for a device-to-device communication integrated into OFDMA cellular system

Abstract: Power control is one of the key functions which are able to co-ordinate the system interference. In this paper, several power control schemes are investigated for a hybrid LTE system, which combines the direct device-to-device (D2D) mode communication and the normal cellular mode communication. In the system study, the power control for the D2D mode communication is emphasized. In general, the utilization of local area transmission for D2D communications provides a better SINR than normal cellular communications. In this case, the proper power control for D2D communications can be a flexible way to improve (and balance) the overall system performance. Naturally, the low power transmission of D2D communications leads to many potential advantages, such as low interference level (to normal cellular users) and low power consumption. From the power control point of view, the low power transmission provides more freedom to tune the Tx power. However, power control is not an efficient solution to avoid the strong mutual (co-channel) interference between different types of UEs. In this case, the join consideration of mode selection, resource scheduling, link adaption and power control is needed.

Performance Analysis of Two Hop Amplify-and-Forward Systems with Interference at the Relay

Abstract: We analyze the performance of a two hop channel state information (CSI)-assisted amplify-and-forward system, with co-channel interference at the relay. The system's outage probability and the average bit error rate (BER) in the presence of Rayleigh faded multiple interferers are investigated. We derive an exact expression for the outage probability and an accurate bound for the system's average BER. Simulation results show the validity of the analysis and point out the effect of interference.

Statistics of Co-Channel Interference in a Field of Poisson and Poisson-Poisson Clustered Interferers

Abstract: With increasing spatial reuse of radio spectrum, co-channel interference is becoming a 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 from an annular field of Poisson or Poisson-Poisson cluster distributed interferers. Poisson and Poisson-Poisson cluster processes are commonly used to model interferer distributions in large wireless networks without and with interferer clustering, respectively. Further, by considering the interferers distributed over a parametric annular region, we derive interference statistics for finite- and infinite- area interference region with and without a guard zone around the receiver. Statistical modeling of interference is a useful tool to analyze outage probabilities in wireless networks and design interference-aware transceivers. Our contributions include: 1) developing a unified framework for deriving interference models for various wireless network environments; 2) demonstrating the applicability of the symmetric alpha stable and Gaussian mixture (with Middleton Class A as a particular form) distributions in modeling co-channel interference; and 3) deriving analytical conditions on the system model parameters for which these distributions accurately model the statistical properties of the interference. Applications include co-channel interference modeling for various wireless networks, including wireless ad hoc, cellular, local area, and femtocell networks.

Measurement of loop-back interference channels for outdoor-to-indoor full-duplex radio relays

Abstract: A full-duplex relay enhances the end-to-end spectral efficiency compared to a half-duplex relay, provided that the loop-back interference at relays is managed well. In order to study the feasibility of the full-duplex relay, it is crucial to measure and model the loop-back interference channels. This paper presents a measurement campaign of these channels for outdoor-to-indoor communications. A compact relay antenna was developed to serve as a signal repeater between outdoor base stations and indoor users, and was used for the loop-back interference channel measurement. The magnitude of the interference was evaluated by the isolation between the transmit and receive antennas. Measurement results revealed that the isolation in multipath environment was 48 dB in the compact relay antenna, and it could be further reduced by placing the outdoor and indoor antennas in a different position referred to as a separate relay. Combined with an appropriate countermeasure to reduce the interference level, such as an interference canceller, the full-duplex operation of indoor compact relay station was found to be feasible.

Performance Analysis of Dual-Hop Relaying Systems in the Presence of Co-Channel Interference

Abstract: -In this paper, we investigate the effect of co-channel interference on the performance of dual-hop communications with amplify-and-forward relaying. Based on the derivation of the effective signal-to-interference-plus-noise ratio (SINR) at the destination node of the system, taking into account co-channel interference, we obtain expressions for the error and outage probabilities. Moreover, we study the performance of the system in the high SINR regime. Monte-Carlo simulations are further provided and confirm the accuracy of the analytical results.

Rate Region Frontiers for n-user Interference Channel with Interference as Noise

Abstract: This paper presents the achievable rate region frontiers for the n-user interference channel when there is no cooperation at the transmit nor at the receive side. The receiver is assumed to treat the interference as additive thermal noise and does not employ multiuser detection. In this case, the rate region frontier for the n-user interference channel is found to be the union of n hyper-surface frontiers of dimension n-1, where each is characterized by having one of the transmitters transmitting at full power. The paper also finds the conditions determining the convexity or concavity of the frontiers for the case of two-user interference channel, and discusses when a time sharing approach should be employed with specific results pertaining to the two-user symmetric channel.

Advanced Signal Processors for Interference Cancellation in Baseband Receivers

Abstract: An interference canceller comprises a composite interference vector (CIV) generator configured to produce a CIV by combining soft and/or hard estimates of interference, an interference-cancelling operator configured for generating a soft projection operator, and a soft-projection canceller configured for performing a soft projection of the received baseband signal to output an interference-cancelled signal. Weights used in the soft-projection operator are selected to maximize a post-processing SINR.

Inter-cell interference control in an uplink multi-carrier radio communications system

Abstract: A multi-carrier cellular radio communication system includes a serving base station associate with a serving cell currently serving a mobile radio and a non-serving base station within range of the mobile radio and associated with a non-serving cell. The mobile radio can transmit to the serving base station at the same time over multiple radio frequency carriers. An estimate is made of inter-cell interference in the non-serving cell caused by uplink transmission by the mobile radio over one or more of the multiple radio frequency carriers over which the mobile radio is currently simultaneously transmitting. If the estimated inter-cell interference in the non-serving cell exceeds a predetermined threshold, then the inter-cell interference in the non-serving cell is reduced or limited by managing radio resources so that the estimated inter-cell interference in the non-serving cell is or becomes less than the predetermined threshold.

Active cancellation of interference in a wireless communication system

Abstract: Various methods and corresponding active interference cancellation units are described. These methods and units can perform active interference cancellation in a system including multiple radios. Notably, signals from a first radio can be received as interference at a second radio. The described methods and units can provide interference conditioning, which manipulates an interference reference of the interference at the first radio to approximate an interference observed at the second radio. After tuning of the interference conditioning, the interference can be removed.

Opportunistic Interference Aligned User Selection in Multiuser MIMO Interference Channels

Abstract: In this paper, we propose a practical interference alignment technique based on an opportunistic user selection in a three-user $2\times 2$ MIMO interference channel where no information is allowed to be shared among transmitters. In the proposed scheme, the user whose interference signals from other transmitters are most aligned with each other is selected at each transmitter. We also investigate optimal and suboptimal beamforming at the selected receiver using extra degrees of freedom by multiple receive antennas. The proposed opportunistic interference aligned user selection (OIAUS) schemes combined with various postprocessing vectors are shown to achieve notable capacity compared to conventional opportunistic user selection schemes while they significantly reduce not only the amount of feedback information but also computational complexity.

Enhancing WLAN performance in the presence of interference

Abstract: A wireless access point coherently receives signals transmitted from client devices and from interfering devices, measures noise and interference capture samples from the received signals, and computes a characterization of noise plus interference. Receive gains and threshold levels are adjusted based on the computed noise plus interference characterization. A set of weights for an interference suppression spatial filter are calculated from the measured noise and interference capture samples and used to produce a filtered signal by spatially filtering the received signals such that interference is spatially nulled in the filtered signal. The method may also include setting PHY parameters at the wireless access point based on the computed noise plus interference characterization. In some embodiments, a protection transmission is transmitted from the wireless access point, requesting connected client devices to suspend transmissions during a specified time period.

Co-Channel Interference in Body Area Networks with Indoor Measurements at 2.4 GHz: Distance-to-Interferer is a Poor Estimate of Received Interference Power

Abstract: Inter-network interference is likely to be a significant source of difficulty for wireless body area networks. Movement, proximity of networks, the large number of nodes per network and the lack of central coordination make cellular approaches to interference modeling ineffective. We examine the interference power of multiple Body Area Networks (BANs) when people move randomly within an indoor office environment. The power-loss trend over 3 m is overwhelmed by random variations in the signal power. Distance-to-interferer is a poor estimate of instantaneous received interference power, and an even less reliable estimate of instantaneous signal-to-interference ratio (SIR). We develop a lognormal statistical model for the signal-to-interference which incorporates the distance effect.

Method and apparatus that facilitates interference reduction in wireless systems

Abstract: Techniques for managing interference in a wireless communication system are disclosed. In one aspect, an estimated interference associated with data transmission over a plurality of subcarriers on an uplink is determined. The estimated interference may relate to intermodulation products associated with a parallel transmission over the plurality of subcarriers. Based at least partly on the estimated interference, data received on the downlink can be processed, and subcarriers can be selected for data transmission on the uplink. Additionally, resources can be assigned to a wireless device according to the estimated interference.

Pilot aided data transmission and reception with interference mitigation in wireless systems

Abstract: Embodiments disclosed herein reduce interference at pilot symbols and also enable good interference measurements by using a combination pilot tones and null tones along with null tones. In this type of system, the receivers can estimate tile channel state information without any interference from the remaining transmitters and at the same time the receiver can measure either the individual interference channel states or the interference covariances from the silent periods. The groups of transmitters are reused in geographically separated region using a frequency reuse structure. In a preferred implementation, pilot signal is precoded using a multi-antenna precoder. The precoder may be same for pilot and data.

Soft Frequency Reuse in the Uplink of an OFDMA Network

Abstract: The challenges with deploying a cellular wireless communication network with static frequency reuse in an interference limited environment is that for highly loaded cells, significant regions of coverage will experience high interference levels, resulting in unserviceable low signal-to-interference values. Therefore, interference mitigation approaches as adaptive fractional frequency reuse are considered to tackle the problem. In this paper, different strategies for user and resource allocation are evaluated along with fractional frequency reuse schemes. In contrast to downlink scenarios, we investigate the performance of the OFDMA uplink. It is shown that soft frequency reuse is well-performing in the uplink although it is easy to deploy since it does not rely on resource coordination.

The capacity region of Gaussian cognitive radio channels to within 1.81 bits

Abstract: We make use of the deterministic high-SNR approximation of the Gaussian cognitive radio channel to gain insights in deriving inner and outer bounds for any SNR. We show that the derived bounds are at most 1.81 bits apart for any SNR.

Channel capacity of multiple-input multiple-output ultra-wideband systems with single co-channel interference

Abstract: In this paper, the channel capacity of multiple-input multiple-output ultra-wideband (MIMO-UWB) systems with single co-channel interference (CCI) is calculated. A ray-tracing approach is used to calculate the wanted channel frequency response, and the channel frequency response is further used to calculate the corresponding channel capacity. By the ray-tracing approach, two different antenna arrays are applied to our simulation to observe whether MIMO can reduce CCI. Also the effects caused by the two antenna arrays for the desired system and CCI are quantified. Copyright © 2010 John Wiley & Sons, Ltd.

Outage Performance of Dual-Hop Relay Network with Co-Channel Interference

Abstract: In this paper, we investigate the outage performance of dual-hop relay networks with co-channel interference which is a major problem in the cellular radio system. A more realistic channel fading model for micro-cellular radio network is adopted as follows, and the desired signal is assumed to have Rician fading due to the presence of line-of-sight (LOS) propagation and the interfering signals from neighboring cells are assumed to experience Rayleigh fading because of the absence of a LOS propagation. An upper bound of outage probability and the asymptotic expression for amplify-and-forward (AF) protocol are derived. Meanwhile, we also propose the optimal power allocation for dual-hop relay networks in high signal-to-interference ratio (SIR) regime. Computer simulations have been performed to verify the validity and the accuracy of theoretical results.

Co-Channel Interference Cancellation Using Single Radio Frequency and Baseband Chain

Abstract: We present a new architecture for multi-antenna receivers that cancels the co-channel interference (CCI) using a single radio frequency (RF) and baseband (BB) chain, while still achieving nearly the same bit error rate that can be provided by the conventional receiver architecture requiring multiple RF/BB chains. The proposed receiver architecture enables multiple transmitter-receiver pairs to simultaneously communicate in the same frequency band without additional bandwidth, thereby increasing the spectral efficiency or capacity, with significantly reduced receiver complexity and power consumption.

Uplink Co-Channel Interference Analysis and Cancellation in Femtocell Based Distributed Antenna System

Abstract: In wireless systems, coverage and capacity is a major challenge especially in high buildings. The need to reuse the limited available spectrum results in cochannel interference. Cochannel interference is a very critical factor affecting system performance. It limits the uplink coverage and capacity of wireless networks such as femtocells. Joint processing of the received signal among cochannel receivers has recently been shown to be very beneficial from an interference cancellation point of view. This paper proposes a femtocell based distributed antenna system (DAS) for uplink transmission in high buildings where distributed antenna units deployed on each floor of the building are connected to femto base stations (BS). The femto BSs can cooperate through joint signal processing for all cells in order to estimate the received signal, reduce cochannel interference introduced by frequency reuse among the femtocells and maintain high spectral efficiency. Analysis and numerical results show remarkable gains especially when interference cancellation is employed at each cooperative femto BS, leading to many more simultaneous users being supported on the same frequency and resulting in large capacity increase when compared with the traditional system with no interference cancellation technique.

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.

Asymptotically optimal low-complexity SC-FDE in data-like co-channel interference

Abstract: In this paper, the design of a low-complexity linear equalizer is considered for single-carrier (SC) block transmission in the presence of inter-symbol interference (ISI) and data-like co-channel interference (CCI). Unlike the linear minimum mean-squared error (LMMSE) frequency-domain equalizer (FDE) designed to suppress ISI only, the LMMSE FDE suffers from high computational complexity due to the CCI component in the signal correlation matrix. Motivated by the fact that the double Fourier transform of the autocorrelation function of a wide-sense cyclostationary process consists of impulse fences with equal spacing, a low-complexity FDE is proposed that approximates the frequency-domain correlation matrix of the CCI plus noise by a block matrix with diagonal blocks. It is shown that the proposed FDE is asymptotically optimal in the sense that the average mean-squared error (MSE) converges to that of the LMMSE FDE as the block length tends to infinity. It is also shown that the proposed FDE is more numerically stable than the LMMSE FDE when the receive filter is matched to the transmit filter and its output is over-sampled to better capture the cyclostationarity of the CCI. Discussions and numerical results include SC block transmission systems with unique word instead of cyclic prefix, and systems with multiple receive antennas.

Distributed Cooperative Precoder Selection for Interference Alignment

Abstract: This paper presents a distributed, low-feedback, linear-precoding technique to completely cancel interference in the presence of colored Gaussian noise. The selection of the precoder is based only on locally available channel-state information (CSI) at the receiver. We consider the downlink of a cellular broadband wireless system where base stations and user equipment are assumed to have at least two antennas each, and users are scheduled based on fractional frequency reuse. We present a distributed algorithm that helps the interfering base station (BS) to simultaneously beamform to its own user while still minimizing the interference on the unintended user. Simulation results show that the proposed scheme considerably improves the performance of the cell-edge users while causing only a mild degradation in the performance of the in-cell users, thereby leading to an increase in the overall system throughput.

Throughput analysis of interference-limited MIMO-based cellular systems

Abstract: Cell-wide mean throughputs on cellular system downlinks using multiple-input/multiple-output (MIMO) techniques is a topic of interest to researchers, cellular operators and equipment manufacturers. In previous work, the authors have tested the validity of the noise model (in the MIMO context) for the co-channel interference (CCI), wherein multipath-averaged CCI powers are added to the thermal noise power that results in an overall interference-plus-noise floor. This approximation simplifies throughput computation with only a minor loss of accuracy, while allowing the cell-wide mean throughput per user to be derived analytically. The key to the analysis is (i) the invocation of the noise model for CCI, and (ii) the demonstration that the overall CCI power has a distribution that is log-normal for any user distance from the base station (BS). This enables us to extend a previous analysis for single-cell (noise-only) MIMO systems to the interference-limited case.We present the analytical method and demonstrate its accuracy.

Progressive MIMO-OFDM reception over time-varying underwater acoustic channels

Abstract: MIMO-OFDM has been actively studied for high data rate communications over the bandwidth-limited underwater acoustic (UWA) channels Unlike existing receivers that treat the intercarrier interference (ICI) as additive noise, in this paper we deal with ICI explicitly together with the co-channel interference (CCI) due to parallel transmissions in MIMO-OFDM The proposed receiver has the following components: 1) compressed-sensing (CS) based sparse channel estimation, 2) soft-input-soft-output MMSE/Markov Chain Monte Carlo (MCMC) detector for interference mitigation, and 3) nonbinary LDPC decoding These components are integrated under a progressive receiver framework, where the receiver starts with low-compleixty ICI-ignorant processing, and then progresses to ICI-aware processing with increasing ICI levels In addition to simulation, we use real data from the MACE10 experiment, in which the transmitter was slowly moving, to verify the system performance Simulation and experimental results show that explicitly addressing ICI and CCI significantly improves the performance of MIMO-OFDM in underwater acoustic systems

Interference Cancellation Technique for MIMO MB-OFDM UWB Cognitive Radio

Abstract: This paper presents an interference mitigation algorithm for coexistence of Multiple-Input Multiple-Output (MIMO) Multiband OFDM ultra wideband (MB UWB) Cognitive Radio systems with other wireless communication systems While other interference cancellation algorithms are applied for SISO system, an improved Active Interference Cancelation algorithm for MIMO MB-UWB systems is proposed with aims to generate sufficiently deep spectral notch and minify excess transmit power of AIC tones The efficiency of the algorithm in terms of several parameters, such as interference bandwidth, notch depth and optimization parameters is evaluated The simulation results show that a spectral notch depth of - 70 dB and a power peak of 1 dB are achievable

Interference mitigation through limited transmitter cooperation

Abstract: Interference limits performance in wireless networks, and cooperation among receivers or transmitters can help mitigate interference by forming distributed MIMO systems. Earlier work [1] shows how limited receiver cooperation helps mitigate interference. The scenario with transmitter cooperation, however, is more difficult to tackle. In this paper we study the two-user Gaussian interference channel with conferencing transmitters to make progress towards this direction. We characterize the capacity region to within a constant number of bits regardless of channel parameters. Based on the constant-to-optimality result, we show that there is an interesting reciprocity between the scenario with conferencing transmitters and the scenario with conferencing receivers, and their capacity regions are within a constant gap to each other. Hence in the interference-limited regime, the behavior of the benefit brought by transmitter cooperation is the same as that by receiver cooperation.

A stochastic association mechanism for macro-to-femtocell handover

Abstract: In this paper, we consider a macrocell site underlaid with self-organizing stand-alone femtocells and propose a mechanism for macro-to-femtocell handover, inspired by multi-stage Dutch auctions The proposed solution introduces a new distributed handover procedure, which does not rely on any centralized coordination typically performed by the macro base stations in existent cellular systems The applicability of this solution is assessed through system-level simulations using the Monte Carlo approach When considering the duration of association procedures, results have shown that the distributed mechanism scales well with increasing density of femtocell sites Additionally, macrocell users benefit from better link quality and less uncoordinated interference generated by the underlay femtocell tier To illustrate, after performing handover, the co-channel interference experienced by a tagged macrocell user becomes less than one tenth of that in full interference scenario

Effects of Co-channel Interference in WLAN and Cognitive Radio Based Approach to Minimize It

Abstract: WLAN uses frequency spectrum for providing wireless access to nomadic nodes which is in fact a very scarce resource. One common issue in deployment of a multi-channel multi-AP wireless network is interference. One of the reasons why theoretical throughput (54 Mbps for 802.11g) can’t be achieved is co-channel interference. In this paper, the effect of co-channel interference on data throughput has been studied in a practical multiple AP (access point) scenario. Interference can be minimized by adjusting the transmission power. This paper also provides an algorithm for transmission power adjustment of APs by using the concept of cognitive radio, which eventually helps in minimizing co-channel interference.

Femtocell Frequency Planning Scheme in Cellular Networks Based on Soft Frequency Reuse

Abstract: Femtocell is an attractive solution for operators to overcome the indoor coverage problem and to offload the growing traffic within macro cells. However, when femtocells are deployed in the existing macro cell environments, co-channel interference (CCI) may occur between the macro cell and femtocells. This CCI severely degrades the performance of femtocell and macro cell. Therefore, we propose a femtocell frequency allocation method in the macro cell network based on soft frequency reuse (SFR) scheme in downlink. We investigate the performance of macro cell and femtocell according to the power ratio in SFR scheme. Simulation results show that the proposed femtocell deployment does not affect the performance of macro cell users.