Sudip Biswas

On the Performance of Relay Aided Millimeter Wave Networks

In this paper, we investigate the potential benefits of deploying relays in outdoor millimeter-wave (mmWave) networks. We study the coverage probability from sources to a destination for such systems aided by relays. The sources and the relays are modeled as independent homogeneous Poisson point processes (PPPs). We present a relay modeling technique for mmWave networks considering blockages and compute the density of active relays that aid the transmission. Two relay selection techniques are discussed, namely best path selection and best relay selection. For the first technique, we provide a closed form expression for end-to-end signal-to-noise ratio (SNR) and compute the best random relay path in a mmWave network using order statistics. Moreover, the maximum end-to-end SNR of random relay paths is investigated asymptotically by using extreme value theory. For the second technique, we provide a closed form expression for the best relay node having the maximum path gain. Finally, we analyze the coverage probability and transmission capacity of the network and validate them with simulation results. Our results show that deploying relays in mmWave networks can increase the coverage probability and transmission capacity of such systems.

Performance Analysis of Large Multiuser MIMO Systems With Space-Constrained 2-D Antenna Arrays

Massive multiple-input-multiple-output (MIMO) systems deploying a large number of antennas at the base station (BS) have been shown to produce high spectral and energy efficiency (EE) under the assumptions of increasing BS physical space and critical antenna spacing. We examine the deployment of massive MIMO systems and resulting EE with a more realistic scenario considering a 2-D rectangular array with increasing antenna elements within a fixed physical space. Mutual coupling and correlation among the BS antennas are incorporated by deriving a practical mutual coupling matrix which considers coupling among all antenna elements within a BS. We also provide a realistic analysis of the energy consumption using a model, which takes into account the circuit power consumptions as a function of the number of BS antennas and then present a performance analysis of two practical low complexity detectors/receivers keeping EE into consideration. The simulation results obtained show that EE does not monotonically increase with the number of BS antennas. On the contrary, it is a decreasing concave or quasi-concave function of the number of BS antennas depending on the detection technique used at the receiver. We also show that with decreasing spacing between the antennas, mutual coupling increases, contributing toward reduction in EE. Our analysis thus shows that EE does not increase infinitely in a massive MIMO system when the increasing number of antennas are to be accommodated within a fixed physical space and the total power consumed is considered to be a function of the antennas. Accordingly, closed-form expressions for the optimum number of antennas to attain maximum EE for zero forcing (ZF) are obtained.

An Analysis on Secure Communication in Millimeter/Micro-Wave Hybrid Networks

The secrecy outage of millimeter wave (mmWave) overlaid micro-wave (μWave) networks under the impact of blockages is analyzed, and closed form as well as integral expressions are provided. Specifically, using a network model that accounts for uncertainties both in node locations and blockages, we characterize the conditional connection outage probability and the secrecy outage probability of hybrid networks with multiple eavesdroppers under basic factors, such as density of eavesdropping nodes, antenna gain, and blockage density. The upper and lower bounds of the conditional secrecy outage probability for both the line-of-sight and non-line-of-sight links are derived. As a desirable side effect, certain factors, such as blockages and reduced antenna gain, can decrease the secrecy outage probability in mmWave networks. This can be considered as a tradeoff between outage capacity and secrecy outage capacity with respect to blockages. Hence, blockages that have been proved to be detrimental to achieving higher data rates in mmWave systems, can be helpful for systems with secrecy constraints. Finally, we have shown the coexistence of mmWave and μWave networks from a secrecy perspective.

Robust Transceiver Design for Full Duplex Multiuser MIMO Systems

We consider a weighted sum-rate maximization problem for a multiuser multiple-input multiple-output (MIMO) cellular system where a full-duplex (FD) base-station (BS) serves multiple half-duplex (HD) uplink (UL) and downlink (DL) users simultaneously while taking the imperfect channel knowledge into consideration. By exploiting the relationship between weighted sum-rate and weighted minimum-mean-squared-error problems, joint design of transceiver matrices can be obtained through an iterative convergent algorithm. Simulation results confirmed the importance of accurate channel estimation in FD systems.

On the effect of antenna correlation and coupling on energy-efficiency of massive MIMO systems

Massive Multiple-Input-Multiple-Output (MIMO) systems deploying a large number of antennas at the base station (BS) have been shown to produce high spectral and energy efficiencies (EE) under the assumptions of increasing BS physical space and critical antenna spacing. We propose a more realistic system model considering a fixed physical space: incorporating coupling and correlation among the BS antennas while providing a realistic analysis of the power consumption using a new power consumption model, taking into account the circuit power consumptions as a function of the number of BS antennas. We also touch on the performance analysis of two practical low complexity detectors keeping EE into consideration. The simulation results obtained show that EE does not monotonically increase with the number of BS antennas. On the contrary, it is a decreasing concave or quasi concave function of the number of BS antennas depending on the detection technique used at the receiver. Also shown is that with decreasing spacing between the antennas, mutual coupling increases contributing towards reduction in EE. Our analysis thus shows that EE does not increase in a massive MIMO system when a large number of antennas are to be accommodated within a fixed physical space and the total power consumed is considered to be a function of the antennas.

Performance Analysis of Correlated Massive MIMO Systems With Spatially Distributed Users

In this paper, we analyze the performance of an uplink large-scale multiple-input-multiple-output system with a single base station (BS) serving spatially distributed multiantenna user devices (UDs) within a fixed coverage area. Stochastic geometry is used to characterize the spatially distributed users while large dimensional random matrix theory is used to achieve deterministic approximations of the sum rate of the system. In particular, the users in the vicinity of the BS are considered to follow a Poisson point process within the fixed coverage area. The sum rate of this system is analyzed with respect to different number of antennas at the BS as well as the intensity of the users within the coverage area of the cell. Closed-form approximations for the deterministic rate at low and high signal-to-noise ratio regimes are derived that have very low computational complexity. The deterministic rate for a general

Transceiver design of optimum wirelessly powered full-duplex MIMO interference channel

k

Robust transceiver design in full-duplex MIMO cognitive radios

th ordered user is also derived. It is shown that the deterministic approximations offer a reliable estimate of the ergodic sum rate obtained by Monte Carlo simulations. We also briefly touch on the growing issue of power consumption in wireless systems by analyzing the energy efficiency of the system using a power consumption model, taking into consideration the circuit power consumption, which is a function of the number of antennas of the BS and UDs.

On the security region of best source indices in random wireless networks

In this paper, the energy harvesting (EH) technique is investigated by designing transceivers for a K link multiple-input multiple-output (MIMO) interference channel. Each link consists of two full-duplex (FD) nodes exchanging information simultaneously in a bi-directional communication technique. All the nodes suffer interference, such as strong self-interference because of operating the FD mode and inter-user interference from other links due to simultaneous transmission at each link. The received signal at each node is divided into two parts - one for information decoding and the other for EH. By minimizing the total transmission power of the system subjected to both signal-to-interference-plus-noise ratio (SINR) and EH threshold constraints, the transmit and receive beamforming vectors and receive power splitting (PS) ratios are jointly designed. Furthermore, the case of multiple-input single-output (MISO) interference channel is also included for the sake of comparison. Simulation results show that FD MIMO systems work efficiently and the EH technique can support power consumption limited devices with a certain guaranteed transmission quality.

Beamforming Design for Full-Duplex MIMO Interference Channels–QoS and Energy-Efficiency Considerations

We consider a full duplex (FD) multiple-input multiple-output (MIMO) underlay cognitive radio cellular network, in which an FD secondary base-station (BS) serves multiple half-duplex uplink (UL) and downlink secondary users (SUs) at the same time and frequency. We assume that the channel state information (CSI) available at the transmitters is imperfect, and the errors of the CSI are assumed to be norm bounded. Under the impact of channel uncertainty, we address the sum mean-squared-errors minimization problem subject to individual power constraints at the UL SUs, a total power-constraint at the secondary BS, and the interference constraints on the primary users by the secondary network. By transforming the problem into an equivalent semidefinite programming (SDP), we propose an iterative alternating algorithm to compute the transceiver matrices jointly. Moreover, to reduce the high computational complexity of the SDP method, we develop a cutting-set method, which solves the problem by alternating between an optimization step (transceiver design) and a pessimization step (worst-case channel analysis). Numerical results are presented to show the effectiveness and robustness of the proposed algorithms.