Mohamad Khattar Awad

OFDMA Based Two-Hop Cooperative Relay Network Resources Allocation

In this paper, we focus on the resources allocation for the OFDMA based two-hop relay network which consists of a single base station, dedicated fixed relay stations and subscriber stations. Subscriber stations are allocated the subcarriers and relay stations that are required to satisfy their minimum rate requirements in either non-cooperative mode (i.e., direct communication with the base station) or in cooperative mode with one of the available relay stations. The cooperation is limited to one relay station to reduce the complexity incurred by the need for synchronization with multiple relays and with the base station at the PHY layer. The subcarriers and relay stations allocation problem is formulated as a Binary Integer Programming (BIP) problem with QoS constraints (minimum rate) and a practical synchronization constraint (cooperation with a single relay). Since the formulated problem is NP-complete, a simple sub-optimal algorithm is proposed to manage the multi-service network resources. Simulations and complexity analysis show that the presented algorithm achieves a network near optimal resources allocation with low computational complexity.

A Dual-Decomposition-Based Resource Allocation for OFDMA Networks With Imperfect CSI

This paper presents a novel scheme for the allocation of subcarriers, rates, and power in orthogonal frequency-division multiple-access (OFDMA) networks. The scheme addresses practical implementation issues of resource allocation in OFDMA networks: the inaccuracy of channel-state information (CSI) available to the resource allocation unit (RAU) and the diversity of subscribers quality-of-service (QoS) requirements. In addition to embedding the effect of CSI imperfection in the evaluation of the subscribers expected rate, the resource-allocation problem is posed as a network utility maximization (NUM) one that is solved via decomposing it into a hierarchy of subproblems. These subproblems coordinate their allocations to achieve a final allocation that satisfies aggregate rate constraints imposed by the call-admission control (CAC) unit and OFDMA-related constraints. A complexity analysis shows that the proposed scheme is computationally efficient. In addition, performance evaluation findings support our theoretical claims: A substantial data rate gain can be achieved by considering the CSI imperfection, and multiservice classes can be supported with QoS guarantees.

An Integrated Overview of the Open Literature's Empirical Data on the Indoor Radiowave Channel's Delay Properties

A comprehensive and integrative overview (excluding ultrawideband measurements) is given of all the empirical data available from the open literature on various temporal properties of the indoor radiowave communication channel. The concerned frequency range spans over 0.8-8 GHz. Originally, these data were presented in about 70 papers in various journals, at diverse conferences, and in different books. Herein overviewed are the multipaths amplitude versus arrival delay, the probability of multipath arrival versus arrival delay, the multipath amplitudes temporal correlation, the power delay profile and associated time dispersion parameters (e.g., the RMS delay spread and the mean delay), the coherence bandwidth, and empirically ldquotunedrdquo tapped-delay-line models. Supported by the present authors new analysis, this paper discusses how these channel-fading metrics depend on the indoor radiowave propagation channels various properties, (e.g., the physical environment, the floor layout, the construction materials, the furnishings locations and electromagnetic properties) as well as the transmitted signals carrier-frequency, the transmitting-antennas location, the receiving-antennas location, and the receivers detection amplitude threshold.

Design of Fair Weights for Heterogeneous Traffic Scheduling in Multichannel Wireless Networks

Fair weights have been implemented to maintain fairness in recent resource allocation schemes. However, designing fair weights for multiservice wireless networks is not trivial because users rate requirements are heterogeneous and their channel gains are variable. In this paper, we design fair weights for opportunistic scheduling of heterogeneous traffic in orthogonal frequency division multiple access (OFDMA) networks. The fair weights determine each users share of rate for maintaining a utility notion of fairness. We then present a scheduling scheme which enforces users long term average transmission rates to be proportional to the fair weights. The proposed scheduler takes the advantage of users channel state information and the inherent flexibility of OFDMA resource allocation for efficient resource utilization. Furthermore, using the fair weights allows flexibility for realization of different scheduling schemes which accommodate a variety of requirements in terms of heterogeneous traffic types and user mobility. Simulation based performance analysis is presented to demonstrate efficacy of the proposed solution in this paper.

Full length article: Ergodic mutual information of OFDMA-based Selection-Decode-and-Forward cooperative relay networks with imperfect CSI

This paper presents a novel approach to investigate ergodic mutual information of OFDMA Selection-Decode-and-Forward (SDF) cooperative relay networks with imperfect channel state information (CSI). Relay stations are either dedicated or non-dedicated (i.e., subscriber stations assisting other subscriber stations). The CSI imperfection is modeled as an additive random variable with known statistics. Numerical evaluations and simulations demonstrate that by considering the CSI imperfection based on a priori knowledge of the estimation error statistics, a substantial gain can be achieved in terms of ergodic mutual information which makes channel adaptive schemes closer to practical implementations.

Downlink Resource Allocation for OFDMA-Based Multiservice Networks with Imperfect CSI

This paper addresses practical implementation issues of resource allocation in OFDMA networks: inaccuracy of channel state information (CSI) available to the resource allocation unit (RAU) and diversity of subscribers quality of service (QoS) requirements. The resource allocation problem in the considered point-to-multipoint (PMP) network is modeled as a network utility maximization (NUM) problem that allocates subcarriers, rate and power while satisfying orthogonal frequency division multiple access (OFDMA) constraints and QoS constraints defined in the service level agreement. Performance evaluation findings support our theoretical claims: a substantial data rate gain is achieved by considering the CSI imperfection and multiservice classes are supported with QoS guarantees by coordinating with a call admission control (CAC) scheme.

Uplink Ergodic Mutual Information of OFDMA-Based Two-Hop Cooperative Relay Networks with Imperfect CSI

This paper analyzes the ergodic mutual information of OFDMA cooperative relay networks when the Channel State Information (CSI) imperfection is considered at resource allocation unit. Based on the derived ergodic mutual information, a quantitative characterization of the impact of CSI inaccuracy on the ergodic mutual information is presented. A network with multiple subscriber stations, relay stations and one base station that employ a Selection-Decode-and-Forward (SDF) relaying scheme is considered in the uplink mode. Subscriber stations act as relay stations to assist other transmitting subscriber stations. Numerical evaluations illustrate that considering the CSI imperfection based on priori knowledge of the error statistics brings substantial gain to the network in terms of ergodic mutual information, and takes the MAC layer resource allocation algorithms a step ahead towards practical implementations.

Source Tracking with Multiple-Forgetting-Factor RLS Using a Vector-Hydrophone Away From or Near a Reflecting Boundary

A vector-hydrophone (a.k.a. acoustic vector-sensor) is composed of two or three spatially collocated but orthogonally oriented velocity-hydrophones, possibly plus a collocated pressure-hydrophone. A vector-hydrophone may form azimuth-elevation spatial beams that are invariant with respect to the sources frequencies, bandwidths and radial locations (i.e., in near field as opposed to the far field). This paper adopts a multiple-forgetting-factor recursive-least-squares (RLS) adaptive algorithm to a single vector-hydrophone for source tracking, without needing any prior knowledge of the source power and/or the noise powers.

Impact of imperfect channel state information on cooperative communications

Although cooperative diversity (CD) systems are widely considered in recent wireless communications standards, little research has been undertaken on their performance under practical conditions. In this study, we study the impact of the channel estimation error on the performance of the multilevel quadrature amplitude modulation (M-QAM) based regenerate-and-forward CD systems. In addition, we investigate the effect of user mobility on channel estimation. After a pilot symbol assisted modulation is proposed for CD systems, the analytical BER performance of the proposed CD system is derived and results are verified via simulations. Numerical results demonstrate that estimation error degrades the performance of CD systems. Furthermore, the inter-user channel estimation error has greater impact on the performance of CD systems than that of the user-to-base station channel. Moreover, the choice of pilot symbol insertion period is crucial and it trades effective data rate for BER performance.

Maintaining Utility Fairness Using Weighting Factors in Wireless Networks

Maintaining fairness using weighting factors is a common approach in resource allocation. However, computing weighting factors for multiservice wireless networks is not trivial because users rate requirements are heterogeneous and their channel gains are variable. In this paper, we propose weighting factor computation and scheduling schemes for orthogonal frequency division multiple access (OFDMA) networks. The weighting factor computation scheme determines each users share of rate for maintaining a utility notion of fairness. We then present a scheduling scheme which takes the users weighting factors into consideration to allocate sub-carriers and power in OFDMA networks. The simulation results demonstrate that the proposed scheduling scheme outperforms an opportunistic scheme in terms of fairness performance in different scenarios, where the users are fixed or mobile.