Faheem A. Khan

Modeling and Analysis of Cloud Radio Access Networks Using Matérn Hard-Core Point Processes

In this paper, we analyze the performance of a cloud radio access network (CRAN), consisting of multiple randomly distributed remote radio heads (RRHs) and a macro base station (MBS), each equipped with multiple antennas. To model the spatial distribution of RRHs and analyze its performance, we use stochastic geometry tools. In contrast to previous works on CRAN that consider Poisson Point Process (PPP) model for the spatial distribution of RRHs, we consider a more realistic Matérn hard-core point process (MHCPP) model that imposes a certain minimal distance (referred to as hard-core distance) between the two RRHs so that the RRHs are not too close to each other. To compare system performance of CRAN when different transmission strategies are used, three RRH selection schemes are adopted including 1) the best RRH selection (BRS); 2) all RRHs participation (ARP); and 3) nearest RRH selection (NRS). Considering downlink transmission, the ergodic capacity, outage probability, and system throughput of CRAN are analytically characterized for different RRH selection schemes. The presented results demonstrate that compared to PPP model, the increase in hard-core distance will result in a higher outage probability and cause a negative impact on ergodic capacity. Furthermore, when the same total transmit power is consumed, BRS scheme provides the best outage performance while ARP scheme is the best RRH selection scheme when the same transmit SNR at each RRH is assumed. Moreover, it is shown that the hard-core distance has a more significant impact on systems with higher intensity of PPP distributed candidate points and in large hard-core distance regime increasing the intensity of candidate points can only provide a small improvement in outage performance. We extend our work to multiuser case with zero-forcing (ZF) precoding where it is proven that the results in multiuser case reduce to the derived results in this work by substituting K=1 for single-user.

Dynamic LSA for 5G networks the ADEL perspective

Exploiting additional radio spectrum is key to respond to the unprecedented capacity demands of mobile broadband communication systems in recent years. In fact, most of the frequency bands suitable for mobile communications are already in use by other radio services, and spectrum refarming is usually not possible or constitutes a highly time-consuming procedure. At the same time, several field measurement campaigns have shown that the occupied spectrum below 6GHz is severely underutilized, i.e. there exist “spectrum holes” in the time, frequency, and space dimensions, pointing to the possibility of using spectrum sharing as a mean to better exploit additional spectral resources. Licensed shared access (LSA) is a recent spectrum licensing paradigm that allows licensees to share the licensed spectrum of incumbents without causing harmful interference and ensuring a certain quality-of-service (QoS) for both types of players. The EU-funded project ADEL aims to enhance the current LSA paradigm by introducing 1) dynamic radio resource management (RRM), 2) sensing reasoning, based on database-assisted collaborative sensor networking, and 3) an extension to the LSA architecture that allows a more effective RRM, increasing QoS satisfaction and policy enforcement for all players, finally leading to an overall improved spectrum utilization. The key features of ADELs enhanced LSA paradigm are outlined throughout the remainder of this paper.

Energy efficient cloud radio access network with a single RF antenna

This paper studies the energy efficiency (EE) of the cloud radio access network (C-RAN), consisting of multiple remote radio heads (RRHs) equipped with electronically steerable parasitic array radiator (ESPAR) antennas, which provide multiple antenna functionality with a single radio frequency (RF) chain. An EE optimization problem is formulated to obtain the configuration of ESPAR and the closed-form expressions of the voltage feeding and the loadings are derived for signal transmission at each RRH. Specifically, we obtain the closed-form expressions for precoder and power allocation that are applicable not only for the ESPAR based system but also for standard MIMO antenna (SMA) system with multiple RF chains. It is shown that EA system can be configured with less complexity compared with SMA system in block fading channel. Furthermore, symbol error rate (SER) and EE performances are compared for EA and SMA based systems. It is shown that the system with EA provides better EE performance while providing similar SER performance. From our results, it is proved that EA system can provide better performance to satisfy the requirement of 5G wireless communication networks.

On the Performance of Cooperative Spectrum Sensing in Random Cognitive Radio Networks

This paper investigates the performance of cooperative spectrum sensing in cognitive radio networks using the stochastic geometry tools. In order to cope with the diversity of received signal-to-noise ratios at secondary users, a practical and efficient cooperative spectrum sensing model is proposed and investigated based on the generalized likelihood ratio test detector. In order to investigate the cooperative spectrum sensing system, the theoretical expressions of the probabilities of false alarm and detection of the local decision are derived. The optimal number of cooperating secondary users is then investigated to achieve the minimum total error rate of the final decision by assuming that the secondary users follow a homogeneous Poisson point process. Moreover, the theoretical expressions for the achievable ergodic capacity and throughput of the secondary network are derived. Furthermore, the technique of determining an appropriate number of cooperating secondary users is proposed in order to maximize the achievable ergodic capacity and throughput of the secondary network based on a target total error rate requirement. The analytical and simulation results validate the chosen optimal number of collaborating secondary users in terms of spectrum sensing, achievable ergodic capacity, and throughput of the secondary network.

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

A new LSA-based approach for spectral coexistence of MIMO radar and wireless communications systems

k

On the capacity of correlated massive MIMO systems using stochastic geometry

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.

Interference Alignment in Two-Tier Randomly Distributed Heterogeneous Wireless Networks Using Stochastic Geometry Approach

Recently, the new concept of Licensed Shared Access/Authorized Shared Access (LSA/ASA) has emerged as a feasible commercial version of dynamic spectrum reuse based on Cognitive Radio (CR) technologies, e.g., via spectrum sensing or by exploiting geo-location information. This paper considers the problem of effective spectrum sharing between a colocated Multiple-Input-Multiple-Output (MIMO) radar that monitors the existence of a target and a wireless communications system. More specifically, the investigated scenario considers the downlink of a communications system represented by a Base Station (BS) trying to reuse the spectrum allocated for a colocated MIMO radar in order to communicate with an assigned terminal, in the vicinity of the radar system. We present an accurate model for the operation of the wireless system in the downlink, while the MIMO radar tries to maintain an acceptable detectability level of a target in the far field. The target detection problem is reformulated using a sensing approach based on energy detection, while the BS applies beamforming to null the interference created at the radar receiver. Based on the theory of Hermitian quadratic forms and with the aid of the Linearly Constrained Minimum Variance (LCMV) beamforming solution, the performance of target detection, when the MIMO radar coexists with the data transmission is quantified and numerical results show that spectral coexistence is feasible.

Outage Probability Analysis of Shared UE-Side Distributed Antenna System Based Cooperative AF Relaying Network for 5G Systems

In this paper, we use stochastic geometry to characterize spatially distributed multi-antenna users within a cell that consists of a single multiple-input multiple-output (MIMO) base station (BS) equipped with a large antenna array. We also use large dimensional random matrix theory (RMT) to achieve deterministic approximations of the sum rate of this system. In particular, we consider the users inside the cell to follow a Poisson point process (PPP). The sum rate of this system is analyzed with respect to (i) the different number of antennas at the BS as well as (ii) the intensity of the users within the coverage area of the cell. We obtained closed-form approximations for the deterministic rate at low signal-to-noise ratio (SNR) and high SNR regimes, which have very low computational complexity. We also derive the deterministic rate corresponding to a general user who is chosen from a set of users ordered in accordance with PPP.

Measurement, simulation and optimization of wideband log-periodic antennas

With the massive increase in wireless data traffic in recent years, multi-tier wireless networks have been deployed to provide much higher capacities and coverage. However, heterogeneity of wireless networks bring new challenges for interference analysis and coordination due to spatial randomly distributed transmitters. In this paper, we present a distance-dependent interference alignment (IA) approach for a generic two-tier heterogeneous wireless network, where transmitters in the first and second tiers are distributed as poisson point process (PPP) and poisson cluster process, respectively. The feasibility condition of the IA approach is used to find upper bound of the number of interference streams that can be aligned. The proposed IA scheme maximizes the second-tier throughput by using the tradeoff between signal-to-interference ratio and multiplexing gain. It is shown that acquiring accurate knowledge of the distance between the receiver in the second-tier and the nearest cross-tier transmitter only brings insignificant throughput gain compared with statistical knowledge of distance. Furthermore, the remaining cross-tier and intercluster interferences are modeled and analyzed using stochastic geometry technique. Numerical results validate the derived expressions of success probabilities and throughput, and show that the distance-dependent IA scheme significantly outperforms the traditional IA scheme in the presence of path-loss effect.