Rajitha Senanayake

Optimal multiuser detection in a cooperative two-cell network

We derive new theoretical bounds on the minimum bit error probability (BEP) of optimal multiuser joint detection in the uplink of a cooperative cellular network. To identify key insights, we consider the basic two-cell cooperative scenario where the signals transmitted by two users are jointly detected at two base stations. For such a network, we derive closed-form expressions for upper and lower bounds on the minimum BEP with independent Rayleigh fading and path loss between the users and the base stations. We further evaluate these expressions asymptotically to characterize the diversity order at high signal-to-noise ratios (SNRs). We observe that the lower bound accurately approximates the BEP simulation at low SNRs while the upper bound is accurate in the medium to high SNRs.

On the Bit Error Probability of Optimal Multiuser Detectors in Cooperative Cellular Networks

In this paper, we present new theoretical analysis on the uncoded bit error probability (BEP) of optimal multiuser detectors in cooperative cellular networks. We consider the uplink of a cooperative network where an arbitrary number of receivers jointly detect the signals transmitted from multiple transmitters. For such a network, we derive accurate upper and lower bounds on the BEP with independent Rayleigh fading and arbitrary path loss. We observe that our lower bound accurately approximates the BEP at low signal-to-noise ratios (SNRs), whereas the upper bound is accurate at high SNRs. We further evaluate our bounds asymptotically to explicitly characterize the cooperative diversity order and array gains in the high-SNR regime.

An SNR Approximation for Distributed Massive MIMO With Zero Forcing

In this letter, we present a new theoretical analysis of the performance of a massive MIMO network with distributed receive antennas. We consider the uplink of a cooperative cellular network that jointly detects signals from multiple transmitters with a large number of distributed antennas. Applying zero-forcing (ZF) across the receivers, we present our accurate approximation for the signal-to-noise ratio (SNR) of an arbitrary user with Rayleigh fading, path loss and shadowing. We further derive easy-to-evaluate closed-form expressions for the symbol error probability (SEP) and the achievable rate of an arbitrary user. Numerical examples highlight that our novel results provide accurate approximations for the performance of a distributed massive MIMO network.

Error probability bounds for interference-limited cooperative networks

We consider a multi-cell cooperative network where a cluster of base stations jointly detect the signals from multiple users transmitting within the cluster. Different from previous works, we examine the impact of interference from out-of-cluster users whose transmit power scales with that of the in-cluster users. For such a network, we derive new upper and lower bounds on the uncoded bit error probability (BEP) of the in-cluster users with independent Rayleigh fading and arbitrary path loss. We observe that our lower bound accurately approximates the BEP at low signal-to-noise ratios (SNRs), whereas the upper bound is accurate at high SNRs. Our analytical bounds accurately characterize the impact of out-of-cluster interference and cluster size on the BEP. Specifically, we highlight that out-of-cluster interference results in a BEP saturation regime when the transmit power is large. We also show that the saturation threshold increases with the cluster size.

Analytical handle for ZF reception in distributed massive MIMO

This paper considers distributed massive MIMO networks where a large number of antennas, either collocated or geographically scattered over a region, communicate with mobile users. This communication is impaired by interference from similar transmissions in adjacent regions and by noise. Focusing on zero-forcing (ZF) reception, we derive simple expressions that very accurately approximate the instantaneous signal-to-interference-plus-noise ratio (SINR) and the ergodic spectral efficiency of an arbitrary user. These expressions enable short-cutting any assessment of the network-level performance, either analytical or simulation-based.

Performance Analysis of Centralized and Partially Decentralized Co-Operative Networks

We consider cellular networks with co-operative clusters of neighboring base stations detecting multiple in-cluster users subject to interference from out-of-cluster users. We assume that the base stations, equipped with multiple antennas, are connected to a central processor in each cluster. For such a network, we first consider centralized processing where all the in-cluster user signals are sent to the central processor for linear minimum mean squared error (LMMSE) estimation. Next, we consider partially decentralized processing where the in-cluster user signals are locally estimated at each base station, and the local estimates are combined at the central processor. For both processing architectures, we derive new expressions for the achievable rate of an in-cluster user when the channels between the users and base stations are subject to independent Rayleigh fading and distance-dependent path loss. The solutions are based on accurate approximations we derive for the characteristic function (CF) and the probability density function (PDF) of each users signal-to-interference-plus-noise ratios (SINRs). Numerical examples highlight the accuracy of the analysis and compare the performance of centralized and partially decentralized processing under different cluster scenarios.

Decentralized relay selection in two-user multihop decode-and-forward relay networks

In this paper, we analyze the outage and diversity performance of a low-complexity relay selection routing algorithm which applies to large-scale distributed decode-and-forward relay networks with two source-destination user pairs. We analyze a suboptimal decentralized relay selection (DRS) strategy that only utilizes local channel state information of the relays within a given hop, to select distinct multihop paths for each user pair. Specifically, we derive exact closed-form expressions for the outage probability and diversity order of the DRS algorithm which prove that the full diversity order is achieved with complexity that is quadratic with the number of relays in each hop. Illustrative analytical results are accurately validated by numerical simulations.

Performance Analysis of Reconfigurable Antenna Arrays

Reconfigurable antenna arrays provide a means for efficient use of the spatial domain in wireless communication systems. Despite its potential, the topic is only briefly explored in the literature. In this paper, we present a comprehensive theoretical analysis of the performance of reconfigurable systems. We consider a receiver equipped with multiple reconfigurable antennas that pick the best state based on the channel between the transmitter and the receiver. For such a system, we derive a new expression for the moment generating function (MGF) of the received signal-to-noise ratio by employing maximal ratio combining. Based on the MGF, we analyze three important performance measures, specifically, achievable rate, error probability, and outage probability. Furthermore, we conduct an asymptotic analysis incorporating the correlation between reconfigurable states and show that a reconfigurable system can achieve a diversity order of the number of antennas times the number of reconfigurable states. Finally, we discuss the applicability of reconfigurable antennas in novel wireless networks with large antenna arrays and distributed antenna systems, highlighting the performance gains and requirement for fewer RF chains.

Symbol Error Probability of Cluster-Based Cooperative Cellular Networks

This paper analyzes the symbol error probability (SEP) of cluster-based cooperative networks where a finite cluster of base stations jointly detect multiple in-cluster users in the presence of out- of-cluster interference. For such a network, we derive new accurate upper and lower bounds on the SEP of the in-cluster users with Rayleigh fading, arbitrary path loss, and M-ary phase-shift keying modulation. We further derive new asymptotic expressions to accurately characterize the SEP saturation limit arising from out-of-cluster interference. To obtain deeper insights, we extend our analysis to consider Rician fading with line- of-sight paths from the in-cluster users to their nearest base stations. Numerical examples illustrate the accuracy of our results and highlight novel aspects of fading channels, path loss, cluster configurations, and user locations on the SEP of cluster-based cooperative cellular networks.

Error Probability Bounds for Multiuser Detection in Cooperative Cellular Networks

We present new analytical expressions for optimal multiuser detection in the uplink of a cellular network with base station cooperation. We consider a cooperative multicell scenario where multiple base stations jointly detect the signals from multiple users distributed throughout the network. For such a network, we derive new upper and lower bounds on the uncoded bit error probability (BEP) with independent Rayleigh fading and arbitrary path loss between the users and the base stations. Our analytical results are further simplified to produce closed-form bounds on the BEP when the path loss from a given user to each base station is distinct. We demonstrate that the lower bound is accurate at low signal-to-noise ratios (SNRs) while the upper bound is accurate at medium to high SNRs.