Interference-limited Communication Research Articles

On the Capacity of Communication Channels With Memory and Sampled Additive Cyclostationary Gaussian Noise

In this work we study the capacity of interference-limited channels with memory. These channels model non-orthogonal communications scenarios, such as the non-orthogonal multiple access (NOMA) scenario and underlay cognitive communications, in which the interference from other communications signals is much stronger than the thermal noise. Interference-limited communications is expected to become a very common scenario in future wireless communications systems, such as 5G, WiFi6, and beyond. As communications signals are inherently cyclostationary in continuous time (CT), then after sampling at the receiver, the discrete-time (DT) received signal model contains the sampled desired information signal with additive sampled CT cyclostationary noise. The sampled noise can be modeled as either a DT cyclostationary process or a DT almost-cyclostationary process, where in the latter case the resulting channel is not information-stable. In a previous work we characterized the capacity of this model for the case in which the DT noise is memoryless. In the current work we come closer to practical scenarios by modelling the resulting DT noise as a finite-memory random process. The presence of memory requires the development of a new set of tools for analyzing the capacity of channels with additive non-stationary noise which has memory. Our results show, for the first time, the relationship between memory, sampling frequency synchronization and capacity, for interference-limited communications. The insights from our work provide a link between the analog and the digital time domains, which has been missing in most previous works on capacity analysis. Thus, our results can help improving spectral efficiency and suggest optimal transceiver designs for future communications paradigms.

Reconfigurable Intelligent Surface in Wireless-Powered Interference-Limited Communication Networks

The commercialization of future wireless communication systems faces crucial problems in terms of reduced network cost of deployment and high power consumption. As a result, reconfigurable intelligent surfaces (RIS) have been suggested as a promising approach to overcome these existing challenges. In this paper, the performance of RIS in a wireless-powered interference-limited communication network is investigated. In this network, an energy-constrained access point (AP) is powered by a dedicated multiantenna power beacon (PB) and communicates to a destination limited-interference node via the RIS. It is assumed that the RIS experiences generalized-K fading distribution while the PB and interferers links are subjected to Nakagami-m fading distributions. To evaluate the system performance, the analytical closed-form expression of the probability distribution function (PDF) for the concerned system is derived. Through this, the exact closed-form expressions of the systems outage probability, average delay-tolerance throughput and average bit error rate are obtained. The analysis quantifies the effects of the number of reflecting elements in the RIS, number of interferer nodes, fading parameters on the AP and interferer links and number of antennas on the PB. It is deduced from the results that there is a kind of symmetry relationship between the analytical and simulation results. Additionally, the results illustrate that the proposed system with an RIS outperforms the conventional system without an RIS. Finally, the accuracy of the derived analytical expressions is validated through a Monte-Carlo simulation.

Stochastic Delay Guarantee of Wireless Dual-Hop Networks With Interference-Limited Relay

In the interference-limited communication scenarios, the interference impairs the data transmission and further degrades the delay performance. In this letter, the stochastic delay guarantee for a wireless dual-hop network with an interference-limited relay is investigated. Considering the randomness of wireless fading in both data links and interference links, the stochastic service process provided by the network is characterized in terms of the moment generation function (MGF). Due to the stochastic service process, the delay should be a random variable (RV). The delay-outage probability is defined as the probability that the actual transmission delay exceeds a threshold value. To evaluate the stochastic delay guarantee, we derive an upper bound on the minimum acceptable delay threshold and a lower bound on the maximum supportable transmitted data size with the constraint of the delay-outage probability, respectively. Simulation results show that the bounds obtained by the theoretical analysis are reasonably tight and well reflect the effect of the interference on the stochastic delay guarantee.

A Journey From Improper Gaussian Signaling to Asymmetric Signaling

The deviation of continuous and discrete complex random variables from the traditional proper and symmetric assumption to a generalized improper and asymmetric characterization (accounting correlation between a random entity and its complex conjugate), respectively, introduces new design freedom and various potential merits. As such, the theory of impropriety has vast applications in medicine, geology, acoustics, optics, image and pattern recognition, computer vision, and other numerous research fields with our main focus on the communication systems. The journey begins from the design of improper Gaussian signaling in the interference-limited communications and leads to a more elaborate and practically feasible asymmetric discrete modulation design. Such asymmetric shaping bridges the gap between theoretically and practically achievable limits with sophisticated transceiver and detection schemes in both coded/uncoded wireless/optical communication systems. Interestingly, introducing asymmetry and adjusting the transmission parameters according to some design criterion render optimal performance without affecting the bandwidth or power requirements of the systems. This dual-flavored article initially presents the tutorial base content covering the interplay of reality/complexity, propriety/impropriety and circularity/noncircularity and then surveys majority of the contributions in this enormous journey.

A New Frame Synchronization Algorithm for Linear Periodic Channels With Memory

Identifying the start time of a sequence of symbols received at the receiver, commonly referred to as frame synchronization, is a critical task for achieving good performance in digital communications systems employing time-multiplexed transmission. In this work we focus on frame synchronization for linear channels with memory, in which the channel impulse response is periodic and the additive Gaussian noise is correlated and cyclostationary. Such channels appear in many communications scenarios, including narrowband power line communications and interference-limited wireless communications. We derive frame synchronization algorithms based on simplifications of the optimal likelihood-ratio test, assuming the channel impulse response is unknown at the receiver, which is applicable to many practical scenarios. The computational complexity of each of the derived algorithms is characterized, and a procedure for selecting nearly optimal synchronization sequences is proposed. The algorithms derived in this work achieve better performance than the noncoherent correlation detector, and, in fact, facilitate a controlled tradeoff between complexity and performance.

Interference Mitigation via Relaying

This paper studies the effectiveness of relaying for interference mitigation in an interference-limited communication scenario. We are motivated by the observation that in a cellular network, a relay node placed at the cell edge observes a combination of intended signal and inter-cell interference that is correlated with the received signal at a nearby destination, so a relaying link can effectively allow the antennas at the relay and at the destination to be pooled together for both signal enhancement and interference mitigation. We model this scenario by a MIMO Gaussian relay channel with a digital relay-to-destination link of finite capacity, and with correlated noise across the relay and destination antennas. Assuming a compress-and-forward strategy with Gaussian input distribution and quantization noise, we propose a coordinate ascent algorithm for obtaining a stationary point of the non-convex joint optimization of the transmit and quantization covariance matrices. For fixed input distribution, the globally optimum quantization noise covariance matrix can be found in closed-form using a transformation of the relay's observation that simultaneously diagonalizes two conditional covariance matrices by congruence. For fixed quantization, the globally optimum transmit covariance matrix can be found via convex optimization. This paper further shows that such an optimized achievable rate is within a constant additive gap of the MIMO relay channel capacity. The optimal structure of the quantization noise covariance enables a characterization of the slope of the achievable rate as a function of the relay-to-destination link capacity. Moreover, this paper shows that the improvement in spatial degrees of freedom by MIMO relaying in the presence of noise correlation is related to the aforementioned slope via a connection to the deterministic relay channel.

V2V Cooperative Relaying Communications Under Interference and Outdated CSI

In this paper, we study a cooperative vehicle-to-vehicle (V2V) interference-limited communication system with decode-and-forward relaying operating over double-Nakagami (DN) fading channels. This distribution has been proposed as a fading model for scenarios where both the transmitter and the receiver are in motion, as is the case in V2V communications. For the purposes of our analysis, we introduce the bivariate DN distribution and derive statistical metrics for this distribution, such as the probability density function, the cumulative distribution function, and the moments. The new expressions have been employed to model the outdated channel state information (CSI) that is due to the fast time-varying nature of the wireless medium and the delay naturally existing between relay selection and data transmission instances. The analysis considers two relay selection schemes, according to the relay-destination channel quality, namely the well-known best relay selection (BRS) and a new one termed as threshold-based relay selection, which offers lower complexity than BRS. Using our analytical framework, exact and asymptotic performance results are obtained for the outage and the average symbol error probabilities, while the diversity order has been also evaluated. The numerical and simulation results corroborate our theoretical ones and quantify the impact of the outdated CSI, level of interference, and varying distances between the relay nodes and the final destination on the system's performance.

Joint Estimation of Carrier Frequency Offset and Channel Impulse Response for Linear Periodic Channels

In many communications scenarios, the channel exhibits periodic characteristics, e.g., power line communications and interference-limited communications. Additionally, certain approximations for mobile radio channels over finite time intervals may result in periodic channel models. In this paper, we study pilot-aided joint estimation of the channel impulse response (CIR) and of the carrier frequency offset (CFO) for linear periodic channels, in which both the CIR and the noise statistics vary periodically in time. We first consider the joint maximum likelihood estimator (JMLE) for the CIR and the CFO, and discuss the practical drawbacks associated with this estimator. When the coefficients of the delay-Doppler spread function of the CIR are approximately sparse, we propose two estimation schemes with higher spectral efficiency and lower computational complexity compared with the JMLE, which are obtained by exploiting both the periodicity and the sparsity of the channel, without requiring a priori knowledge of the sparsity pattern. Finally, we study the design of pilot sequences aimed at improving the estimation performance in sparse periodic channels. Simulation studies corresponding to practical scenarios of the proposed estimators demonstrate that substantial benefits can be obtained by properly accounting for the sparsity and periodicity in the design of estimation schemes.

Secrecy Capacity Scaling in Large Cooperative Wireless Networks

We investigate large wireless networks subject to security constraints. In contrast to point-to-point, interference-limited communications considered in prior works, we propose active cooperative relaying-based schemes. We consider a network with $n_{l}$ legitimate nodes, $n_{e}$ eavesdroppers, and path loss exponent $\alpha \geq 2$ . As long as $n_{e}^{2}\big (\log (n_{e})\big )^{\gamma }=o(n_{l})$ , for some positive $\gamma $ , we show that one can obtain unbounded secure aggregate rate. This means zero-cost secure communication, given fixed total power constraint for the entire network. We achieve this result through: 1) the source using Wyner randomized encoder and a serial (multi-stage) block Markov scheme, to cooperate with the relays and 2) the relays acting as a virtual multi-antenna to apply beamforming against the eavesdroppers. Our simpler parallel (two-stage) relaying scheme can achieve the same unbounded secure aggregate rate when $n_{e}^{\alpha /{2}+1}\big (\log (n_{e})\big )^{\gamma +\delta ({\alpha }/{2}+1)}=o(n_{l})$ holds, for some positive $\gamma ,\delta $ . Finally, we study the improvement (to the detriment of legitimate nodes) that the eavesdroppers achieve in terms of the information leakage rate in a large cooperative network in the case of collusion . We show that again the zero-cost secure communication is possible, if $n_{e}^{(2+{2}/{\alpha })}\big (\log n_{e}\big )^{\gamma }=o(n_{l})$ holds, for some positive $\gamma $ ; that is, in the case of collusion slightly fewer eavesdroppers can be tolerated compared with the non-colluding case.

Advanced interference management technique: potentials and limitations

Interference management has the potential to improve spectrum efficiency in current and next generation wireless systems (e.g., 3GPP LTE and IEEE 802.11). Recently, new paradigms for interference management have emerged to tackle interference in a general class of wireless networks: interference shaping and interference exploitation. Interference shaping is a technique that creates a particular linear combination of interference signals when transmitters propagate signals to minimize the aggregated interference effect at each receiver. Interference exploitation is a method that harnesses interference in decoding as side information to improve data rates. Both approaches offer better performance in interference-limited communication regimes than traditionally thought possible. This article provides a high-level overview of several different interference shaping and exploitation techniques for single-hop, multihop, and multi-way network architectures with graphical illustrations. The article concludes with a discussion of practical challenges associated with adopting sophisticated interference management strategies in the future.

Multi-objective resource allocation in interference-limited M2M communication networks

In this paper, we propose a multi-objective optimisation-based solution to the problem of resource allocation in interference-limited machine to machine M2M communication. We consider machine type communication devices MTCDs in a clustered network structure, where they are divided into clusters and the devices belonging to a cluster communicate to cluster head or controller. The cluster head aggregates the traffic and relays from MTCDs to eNB and vice versa. We maximise the number of admitted MTCD controllers and throughput with least interference caused to conventional primary users. We formulate the problem as a mixed-integer nonlinear problem with multiple objectives and apply meshed adaptive direct search MADS algorithm which gives guaranteed convergence. Simulation results show the effects of varying different parameters on cumulative throughput and the number of admitted MTCD controllers.

Succesive Co-Channel Interference Cancellation

In this work, a successive four-stage interference cancellation model to unwrap and remove two co-channel interference signals is introduced and successfully tested. This model utilizes the second order statistics of the co-channel interference signals in an interference limited communication environment for interference cancelation. In this model, interferers and the signal of interest (SOI) are considered as multiple inputs of a multiple-input multiple-output (MIMO) system. Therefore, MIMO equalizers and blind MIMO channel estimator are employed for the corresponding tasks. At any stage of equalization in this model, a single signal is equalized and recovered. Later, a replica of the captured signal is cancelled from the received signal mixture. The remaining signal is fed to the next stage for equalization. The benefit of using this scheme is mainly improving the quality of the SOI by re-equalizing after interferers are completely removed. In the results section, 16 dB interference cancellation gain is shown where interferers are as strong as signal (SIR=0) and SNR is 30 dB. A Rayleigh fading (iid) channel is used for simulation.

Improper Signaling for Symbol Error Rate Minimization in <inline-formula> <tex-math notation="TeX">$K$</tex-math></inline-formula>-User Interference Channel

The rate maximization for the K-user interference channels (ICs) has been investigated extensively in the literature. However, the practical problem of minimizing the error probability with given signal modulations and/or data rates of the users is less studied. In this paper, by utilizing additional degrees of freedom from the improper signaling (versus the conventional proper signaling) , we seek to optimize the precoding matrices for the K-user single-input single-output (SISO) ICs to minimize pair-wise error probability (PEP) and symbol error rate (SER) with two proposed algorithms, respectively. Compared with conventional proper signaling and other state-of-the-art improper signaling designs, our proposed improper signaling schemes achieve notable error rate improvement in SISO-ICs under both the additive white Gaussian noise (AWGN) and cellular system setups with or without channel coding. Our study provides another viewpoint for optimizing transmissions in ICs and further justifies the practical benefit of improper signaling in interference-limited communication systems.

Cross Layer Interference Management in Wireless Biomedical Networks

Interference, in wireless networks, is a central phenomenon when multiple uncoordinated links share a common communication medium. The study of the interference channel was initiated by Shannon in 1961 and since then this problem has been thoroughly elaborated at the Information theoretic level but its characterization still remains an open issue. When multiple uncoordinated links share a common medium the effect of interference is a crucial limiting factor for network performance. In this work, using cross layer cooperative communication techniques, we study how to compensate interference in the context of wireless biomedical networks, where many links transferring biomedical or other health related data may be formed and suffer from all other interfering transmissions, to allow successful receptions and improve the overall network performance. We define the interference limited communication range to be the critical communication region around a receiver, with a number of surrounding interfering nodes, within which a successful communication link can be formed. Our results indicate that we can achieve more successful transmissions by adapting the transmission rate and power, to the path loss exponent, and the selected mode of the underline communication technique allowing interference mitigation and when possible lower power consumption and increase achievable transmission rates.

Analysis of routing protocols and interference-limited communication in large wireless networks via continuum modeling

The evaluation and assessment of the design of large wireless networks is an important problem in numerous applications. Direct simulation is a traditional approach for studying such networks but is severely limited in its utility as the size of the network increases. This necessitates other means for studying large networks, one of which is the modeling of large networks with continuum models. In this paper, we introduce nonlinear partial differential equations whose solutions approximate the expected behavior of large networks governed by probabilistic communication rules. The relative speed at which solutions can be obtained from the continuum models allows for the investigation of routing protocols and communication limitations due to interference—a feat that is not feasible via simulation methods. Specifically, we investigate the effects of a directed diffusion routing protocol and explore communication limitations in an interference-sensitive network. Network design studies using the approximating continuum models are then presented.

Interference Minimization Approach to Precoding Scheme in MIMO-Based Cognitive Radio Networks

A precoding scheme based on the interference minimization is proposed for an interference-limited communication system such as multiple-input multiple-output (MIMO)-based cognitive (CR) networks. The proposed precoder is to maximize the sum capacity through the minimization of interference power. By selecting a channel with the minimum singular value of the interference channel, the transmitter with the proposed precoder sends the information signals through the channel which produces the minimum interference in the system. Simulation results show that the proposed precoding scheme has the best performance in terms of the sum capacity in a MIMO-based CR network.

Spectrum management for interference-limited multiuser communication systems

Consider a multiuser communication system in a frequency selective environment whereby users share a common spectrum and can interfere with each other. Assuming Gaussian signaling and no interferen...

Beam-selection performance analysis of a switched multibeam antenna system in mobile communications environments

The probability of incorrect beam selection (PIBS) with a switched multibeam antenna system is theoretically analyzed under power-limited and interference-limited mobile communication environments. Periodic transmission of a unique word sequence followed by the information symbol sequence is assumed. The model of beam selection used is based upon a simple three-stage mechanism: (1) signal validation; (2) averaging; and (3) selection of the largest output. Complex correlation peaks corresponding to the unique words, detected by the matched filter for the signal validation are averaged over several consecutive unique words, and a beam having the largest output is selected. Equally weighted noncoherent integration is assumed for the averaging process. The beam selection takes place frame-by-frame. The paper discusses the PIBS derivation for a simple switched two-beam antenna system. Numerical calculation results are then presented. It also investigates the impact of the incorrect beam selection on the overall average signal-to-noise (SNR) power ratio and signal-to-interference (SIR) power ratio. The amount of the overall SNR (or SIR) improvement over the omnidirectional antenna depends on the propagation conditions. In general, larger improvements can be achieved by smaller values of the PIBS.