Seyed Amin Hejazi

Relay Selection Strategies for Single-Carrier Frequency-Domain Equalization Multi-Relay Cooperative Networks

In this paper, we investigate several relay selection strategies for cooperative Single-Carrier Frequency-Domain Equalization (SC-FDE) with the amplify-and-forward protocol. We consider both maximum likelihood (ML)-SC-FDE and minimum mean square error (MMSE)-SC-FDE receivers. We provide a novel pairwise error probability (PEP)-based selection criterion (SHARM) for frequency selective channels. We further present several selection strategies for cooperative (C) MMSE-SC-FDE receivers, which are motivated by minimizing the instantaneous error rate. These are, norm-based relay selection (NBRS), instantaneous mutual information-based relay selection (CBRS), singular value based relay selection (SVRS), and equalizer output signal quality-based relay selection (EQRS) strategies. We further propose a novel relay selection strategy, selective-to-flat fading relay selection (SFRS), in which from the effective frequency selective source-relay-destination channel link associated with the selected relay, only the channel tab with highest power is passed to the destination terminal. Additionally, to tackle the multiple relay selection problem considering generic mobile scenarios with moderately fast fading channels, in order to select the near best relay subset within the minimum processing time, we apply estimation of distribution algorithm (EDA) and formulate a modified EDA for the relay selection problem. Our results show promising performance of EDA with comparable computational complexity.

Self-optimising intelligent distributed antenna system for geographic load balancing

Increase in number of mobile users, generates unbalanced load traffic in wireless network. In this study, a load-balancing solution is investigated in order to optimise quality of service. An intelligent distributed antenna system (IDAS) fed by a base transceiver station (BTS) has the ability to distribute the cellular capacity over a given geographic area depending on the time-varying traffic. A virtual cell network is an IDAS with capacity routing capability. To enable load balancing among distributed antenna modules, the authors dynamically allocate the remote antenna modules to the BTS sectors. A self-organised network of virtual cells is formulated as an optimisation problem, which attempts to balance traffic load and minimises the hand-offs as two important cost factors in the network. Two evolutionary algorithms are proposed for optimisation: genetic algorithm and estimation distribution algorithm. Computational results of different traffic scenarios after performing the algorithms, demonstrate that the two algorithms attain excellent key performance indicators for small-scale networks.

Multiuser Two-way relaying with power control for SC-FDE systems

In this paper, we investigate cooperative Single-Carrier Frequency-Domain Equalization (SC-FDE) for two-way relay networks, where multiple users each equipped with multiple antennas exchange their information through a multi-antenna relay node in a bi-directional manner. Under network total power constraint, we present optimal relay beamforming for the multiuser two-way relay system, where the relay transceiver processor is designed based on the minimum mean-square-error (MMSE) criterion. We drive a closed-form expression for the signal-to-interference noise ratio (SEVR) at each of the user terminals, and further present a joint user-relay antenna selection algorithm by applying the estimation of distribution algorithm (EDA). The proposed EDA has a low computational complexity, and its effectiveness is verified through simulation results.

Efficient resource minimization scheme for network coding-assisted multicast system

In this paper, we consider the problem of minimizing the resources used for network coding (MRUNC) while achieving the desired throughput in a multicast system. The problem of minimizing the number of network coding links is NP-hard. In this paper we propose a low-complexity Estimation of Distribution Algorithm (EDA) for MRUNC. Our EDA is applicable to the network with and without cycles. The numerical results show the effectiveness of the proposed method over previously proposed algorithms.

Frequency Reuse Techniques with a Distributed Antenna System

The performance of cellular networks is strongly limited by inter-cell interference. In order to reduce this interference, several techniques have been proposed, e.g., the frequency reuse techniques and distributed antenna system (DAS). This paper investigates the combinations of hard frequency reuse (HFR) and soft frequency reuse (SFR) techniques with DAS in a unique cell architecture, which are called DAS–HFR and DAS–SFR, respectively. This paper analytically quantifies the performance of the downlink multi-cell for DAS–HFR and DAS–SFR in terms of the average spectral efficiency. This also shows, the most appropriate frequency reuse technique depends not only on the average achievable data rate inside the cell, but also on the guaranteed achievable data rate (the minimum achievable data rate which is necessary to be obtained regardless of geographic location). The results show that DAS–SFR improves the achievable data rate of cell edges in a multi-cell environment as compared to a DAS–HFR when frequency reuse factor 1 is utilized. The results also show that DAS–SFR significantly increases the system capacity as compared to the DAS–HFR when frequency reuse factor 3 is utilized.

Low-Complexity Load Balancing with a Self-Organized Intelligent Distributed Antenna System

A high call blocking rate is a consequence of an inefficient utilization of system resources, which is often caused by a load imbalance in the network. Load imbalances are common in wireless networks with a large number of cellular users. This paper investigates a load-balancing scheme for mobile networks that optimizes cellular performance with constraints of physical resource limits and users quality of service demands. In order to efficiently utilize the system resources, an intelligent distributed antenna system (IDAS) fed by a multi base transceiver station (BTS) has the ability to distribute the system resources over a given geographic area. To enable load balancing among distributed antenna modules we dynamically allocate the remote antenna modules to the BTSs using an intelligent algorithm. A self-optimizing network for an IDAS is formulated as an integer based linear constrained optimization problem, which tries to balance the load among the BTSs. A discrete particle swarm optimization (DPSO) algorithm as an evolutionary algorithm is proposed to solve the optimization problem. The computational results of the DPSO algorithm demonstrate optimum performance for small-scale networks and near-optimum performance for large-scale networks. The DPSO algorithm is faster with marginally less complexity than an exhaustive search algorithm.

Swarm based resource minimization in network coded system

In this paper, we present swarm based Resource Minimization Scheme (RMS) for Network-Coding-based Multicast System (NCMS). The main objective of the RMS is to reduce network coding links while maintaining the desired rate of a multicast system. The resource minimization problem in NCMS is NP-Hard. In this paper, we apply the Binary Particle Swarm Optimization (BPSO) algorithm to the resource minimization problem in NCMS. The numerical results show the effectiveness of the proposed BPSO based RMS in comparison to the previously proposed algorithms.