Khaled M. F. Elsayed

A Survey on Inter-Cell Interference Coordination Techniques in OFDMA-Based Cellular Networks

Orthogonal Frequency Division Multiplexing Access (OFDMA) has been increasingly deployed in various emerging and evolving cellular systems to reduce interference and improve overall system performance. However, in these systems Inter-Cell Interference (ICI) still poses a real challenge that limits the system performance, especially for users located at the cell edge. Inter-cell interference coordination (ICIC) has been investigated as an approach to alleviate the impact of interference and improve performance in OFDMA-based systems. A common ICIC technique is interference avoidance in which the allocation of the various system resources (e.g., time, frequency, and power) to users is controlled to ensure that the ICI remains within acceptable limits. This paper surveys the various ICIC avoidance schemes in the downlink of OFDMA-based cellular networks. In particular, the paper introduces new parameterized classifications and makes use of these classifications to categorize and review various static (frequency reuse-based) and dynamic (cell coordination-based) ICIC schemes.

Opportunistic scheduling of delay sensitive traffic in OFDMA-based wireless networks

OFDMA is an attractive multiple access technique for packet-based mobile broadband wireless access for beyond 3G and 4G systems. Radio resource allocation in OFDMA can exploit multiuser diversity to increase system capacity by implementing opportunistic scheduling techniques. This paper presents a new opportunistic scheduling scheme for OFDMA-based wireless multimedia networks. We focus the scheduling algorithm on the class of delay-sensitive packets that belong to interactive applications such as telephony and video streaming. We divide the scheduling decision into two sub-problems: the OFDMA subcarrier allocation and subsequently the subcarrier assignment. Both the sub-carrier allocation and assignment algorithms exploit multiuser diversity and are designed to provide fairness with respect to the realizable throughput per user, packet dropping ratios and packet delay distributions. We investigate various performance aspects of the proposed scheduling algorithm using actual MPEG-4 traffic traces under different system loading and requested deadline values. The results show the superiority of the proposed scheduling scheme and its excellent performance with respect to throughput, packet dropping, and delay distributions

Exploiting interference alignment for sum rate enhancement in D2D-enabled cellular networks

Spectrally-efficient and low-latency support of local media services is expected to be provided by enabling underlay direct Device-to-Device (D2D) communication mode in future cellular networks. Interference Alignment (IA) can enhance the capacity of a wireless network by providing more degrees of freedom. In this paper, we propose using IA techniques in a D2D underlay network to enhance spectral efficiency. We compare IA transmission and traditional point-to-point (P2P) transmission from the Bit-Error-Rate (BER) and sum-rate points of view. Furthermore, we propose three grouping schemes for the D2D users into groups of 3-pairs such that IA can be applied using a limited number of signal extensions. Results demonstrate that although traditional P2P transmission can achieve better BER performance; IA transmission is still able to achieve gains in the sum rate. Also, system simulations show that the cell total D2D sum rate can be improved using IA. A gain of up to 31.8% is shown to be attainable at a reasonable transmit signal power level.

ABSF offsetting and optimal resource partitioning for eICIC in LTE-Advanced: Proposal and analysis using a Nash bargaining approach

Almost-blank subframe (ABSF) is a time-domain technique, proposed by the 3GPP to handle Inter-Cell Interference (ICI) in heterogeneous network environments (HetNet). We consider a HetNet environment comprised of a macro-cell and femto-cells distributed across the macro-cell area. We propose a novel approach, called ABSF offsetting, to reduce the blanking rate at the femto-cells while preserving the required optimal blanking rate at the macro-cell. We also study the problem of optimal resource partitioning and offset assignment in the ABSF mode. The proposed solution for the problem is based on multistage Nash bargaining. The performance of the optimal resource partitioning, and ABSF offsetting is evaluated through simulations. The results show that the throughput of the macro-cell is improved, while the degradation in the aggregate femto-cell throughput is reduced due to the reduction in the blanking rate due to offsetting. The simulation results also demonstrate the fairness of the ABSF offsetting with the fairness index approaching 1 among the macro-cell UEs at low loads.

The superposition of discrete-time Markov renewal processes with an application to statistical multiplexing of bursty traffic sources

The main contribution in this paper is the introduction of a methodology for approximately characterizing the superposition process of N>=2 arbitrary (and possibly heterogeneous) discrete-time Markov Renewal Processes (MRP). In this model, the superposition process is characterized by a MRP with a state space that grows exponentially with N. We consider an on/off traffic source model, where the distribution of the on and off periods is arbitrary, as a special case of the general MRP. Subsequently, a queueing model for a FIFO finite-buffer multiplexer with arbitrary on/off input sources is analyzed. We provide numerical results for testing the algorithms introduced in the paper. We also study the effect of some of the statistical properties of on/off input sources on the multiplexers performance.

On the relay placement problem in a multi-cell LTE-Advanced system with co-channel interference

One of the main problems in LTE-A networks is the small rates achieved by cell-edge users. This is due to the adoption of a frequency reuse factor of 1, which aims at increasing the overall capacity. This occurs, however, at the expense of increasing the interference level for cell-edge users. Cooperative communication through the use of relays is an efficient technique to solve this problem. However, careful placement of the relays is a crucial factor in determining the expected capacity gain. In this paper, the relay placement problem in an LTE-A network is studied, taking into consideration the effect of co-channel interference. An optimization framework is proposed to maximize either the total cell capacity or the total cell-edge capacity. Simulation results show a capacity gain factor of 8.027 for cell-edge users due to relay deployment, under 100% cell load in center cell and adjacent cells.

Adaptive Fractional Frequency Reuse (AFFR) scheme for multi-cell IEEE 802.16e systems

In this paper we present a new Adaptive Fractional Frequency Reuse scheme (AFFR) for multi-cell OFDMA based IEEE 802.16e network. The Adaptive Fractional Frequency Reuse (AFFR) scheme is managed by the Access Service Network Gateway (ASN-GW) which coordinate a set of BSs (one cluster). To make better usage of radio resources; we assume that the cell area is virtually divided into two different zones: the fractional frequency reuse (FFR) zone which includes all users who are suffering from high Inter-Cell Interference ICI from neighbouring cells and the Full Usage (FU) zone where Inter-Cell Interference ICI can be neglected. The base station BS assigns users to each zone dynamically based on their channel state information. ASN-GW decides the set of subcarriers assigned to the FFR zone within each BS. In the FU zone; all subcarriers available in the system can be used. We provide simulation results comparing our AFFR scheme with different schemes. We examine the effect of the choice of the major system design parameters on the performance. The simulation results illustrate the superiority of the proposed scheme for multiple values of system design parameters.

Shrinking the reuse distance: Spectrally-efficient radio resource management in D2D-enabled cellular networks with Interference Alignment

Enabling underlay direct Device-to-Device (D2D) communication mode in future cellular networks has good potential for spectrally-efficient and low-latency support of local media services. Recently, it has become evident that shrinking the reuse distance over which wireless resources are reused is a key enabler for achieving high spectral efficiency. Moreover, Interference Alignment (IA) based transmission can enhance the capacity of a wireless network by providing more degrees of freedom. In this work, we exploit clustering of D2D users, frequency reuse over clusters and then using IA to enhance the sum rate. Specifically, we show that in a D2D environment, it is possible to achieve significant gains in attainable rates by constructing clusters of D2D pairs and reuse the available radio resources over the clusters. Moreover, within a cluster, it is possible to further enhance the spectral efficiency by constructing small-sized groups of D2D pairs over which IA is applied to offer additional degrees of freedom. We show that resource reuse over the clusters offer overall rate increase proportional to the number of formed clusters. In addition, interference alignment offers up to 33% increase in the overall rates in the high transmission power regimes compared to the normal Point-to-Point (P2P) communication.

Network design methods for mitigation of intentional attacks in scale-free networks

Network robustness and network reliability are important issues in the design of Internet Service Providers’ topologies. In this paper, we examine the structural characteristics of network topologies that affect robustness and reliability. We examine the interplay between the structural characteristics of network topologies and the resource capacity over-provisioning strategies when the network breakdowns subject to practical constraints (router technology) and economic considerations (link costs). We study the robustness of the Internet connectivity under node intentional harmful attack using two attacks strategies: static degree-based and static load-based. We find that the robustness of network topologies is affected by the variation of their structural characteristics. In our proposed approach, we show that highly-heterogeneous topologies have less robustness compared with lightly-heterogeneous topologies. The observations from the robustness study provide us useful insights for proposing multiple efficient preventive resource capacity over-provisioning strategies for mitigation of intentional attacks. The proposed strategies utilize the structural properties by calculating the excess traffic in case of single global cascading failure for each node and measure its influence on the other nodes as well as locally. The results show that our proposed strategies can significantly enhance the robustness and increase the resilience of network topology. We also show that highly-heterogeneous topologies have high resilience compared with lightly-heterogeneous topologies. By using real data from the Sprint network at the router level, we provide further empirical evidence in support of the proposed approach.

Directional antenna with busy tone for capacity boosting and energy savings in wireless ad-hoc networks

Directional antennas are well known for being capable of performance improvement in wireless ad-hoc networks. In the IEEE 802.11 MAC protocol when two nodes are communicating with each other, all other nodes in the transmission zone are required to remain idle. With the use of directional antennas, it is possible to have two pairs of nodes located in each others transmission range to communicate simultaneously; this increases the spatial reuse of the wireless channel. However, directional antennas suffer from deafness and hidden terminal problems and therefore new mechanisms are required for exploitation of the directional antennas in an intelligent manner. In this paper we present a scheme based on switched beam directional antenna with busy tone for controlling the directional antenna beams for maximum spatial reuse and saving in energy consumption. The purpose of the busy tone signal is to inform nodes in the transmission zone about the current transmission which helps solving hidden terminal and deafness problems. We present performance evaluation results which confirm the significant improvement in both throughput and energy consumption. We also study the effect of the number of beams on the throughput and energy consumption.