Boon Hee Soong

An Interference-Minimization Potential Game for OFDMA-Based Distributed Spectrum Sharing Systems

Wireless orthogonal frequency-division multiple-access (OFDMA) networks, where distributed users can access the spectrum dynamically, offer great flexibility and the potential for the efficient utilization of scarce spectrum resources. Despite that, managing such large-scale networks while maintaining fair and efficient spectrum usage poses a great challenge, mainly due to cochannel interference from the spatially reusable subcarrier. This paper considers the problem of interference minimization in such a scenario from a game-theoretical viewpoint. A general framework that defines the distributed OFDMA-based spectrum access problem is presented. Next, our game-theoretical analysis shows that the proposed interference-minimizing utility function exhibits the properties of a potential game. Given a deterministic number of subcarriers by each player, there exists a pure-strategy Nash equilibrium solution, and therefore, convergence can be guaranteed via sequential best-response dynamics. Our simulation results verify the analysis, and at the same time, the fairness and optimality of the solutions obtained through the proposed game are examined.

Performance Analysis of Downlink Multi-Cell OFDMA Systems Based on Potential Game

This paper investigates the subcarrier allocation problem for a downlink multi-cell multiuser OFDMA network using potential game theory. Each player is considered to be a central base station together with all the mobiles distributed within its coverage area. In such a system, co-channel interferences (CCI), if left uncontrolled, could hinder the transmissions and limit the throughputs of the users, especially those near the cell-edge area. Certain remedies, including power control with pricing, did not seem to solve the problem completely. We specifically address this issue from an interference-minimizing approach, where the utility function adopted is meant to minimize the total CCI among players. Under such formulation, we show that the formulated game can be mathematically described by a potential game. Hence, a Nash equilibrium (NE) will be guaranteed for the proposed game and stable solutions can be achieved via myopic gameplays such as the best/better responses. We propose our iterative algorithm for obtaining the NEs and address several performance issues such as fairness for edge-users and the price of anarchy. Numerical results show the improvement in efficiency and fairness using this approach.

A New Lower Bound on Range-Free Localization Algorithms in Wireless Sensor Networks

This letter examines the lower bound on localization error, which is an important performance measure for localization algorithms. Unlike some previous works based on the circular coverage model, we consider a more realistic scenario where radio propagation is subject to log-normal shadow fading. In this letter, we present an analytical expression for the distribution of lower bound on localization error for any range-free localization algorithm in WSNs. Finally, the derivation is validated through simulations.

An Integrated Cluster-Based Multi-Channel MAC Protocol for Mobile Ad Hoc Networks

This paper proposes a novel joint clustering and multi-channel medium access control (MAC) protocol for mobile ad hoc networks, based on a scalable two-phase coding scheme. It employs the first-phase codes for differentiating the clusters and the second-phase codes for distinguishing the nodes in a specific cluster. The proposed protocol effectively integrates the procedure of code assignment with dynamic clustering and henceforth substantially reduces the control overhead of code assignment in a code division multiple access (CDMA) based multi-channel MAC protocol while simultaneously combating the hidden terminal problem. Furthermore, the confliction detection and resolution mechanism for the allocation of the first-phase codes as well as the collision avoidance mechanism for the allocation of the second-phase codes in the control channel are also introduced. Analytical framework and extensive simulation results, in terms of control overhead and delay, are provided and compared to the traditional distributed CDMA based multichannel MAC algorithms with or without clustering.

Evaluation of heuristic path selection algorithms for multi-constrained QoS routing

Multi-constrained quality of service (QoS) routing aims to find a path in a network that satisfies multiple path constraints. It is known to be NP-complete and many heuristic algorithms have been presented to solve it sub-optimally. Recent promising proposals include the TAMCRA and limited path Dijkstras algorithm (LPDA) which are both based on extended Dijkstras algorithms using non-linear path functions, limited path heuristic algorithm (LPHA) which is an extended Bellman Ford algorithm, and improved limited path heuristic algorithm (ILPHA) which improves LPHA using non-linear path functions for path selection. In this paper, we give a simulation study for comparisons of these heuristic path selection algorithms. It is shown that path selection strategy in ILPHA can significantly improve the performance of LPHA and the heuristic algorithms with dominating area non-linear path function (ILPHA-DomArea, LPDA-DomArea) outperform the heuristic algorithms with the max weight based nonlinear path function (ILPHA-MaxXY, TAMCRA).

Energy Efficiency Analysis of Channel Aware Geographic-Informed Forwarding (CAGIF) for Wireless Sensor Networks

This letter analytically examines the achievable energy efficiency of channel aware geographic-informed forwarding (CAGIF) algorithm, which chooses the next hop relay node by taking into consideration the underlying channel conditions, rather than purely maximizing the forwarding progress. The theoretical analysis in terms of the average forward distance is developed and the upper bound and lower bound of the average energy consumption are provided by referring to the retransmission techniques. Numerical results show that CAGIF significantly improves the energy efficiency over the previous geographic information based routing algorithms that ignore the channel conditions.

Optimal channel assignment in cellular systems using tabu search

The channel assignment problem (CAP) in cellular systems has the task of planning the reuse of the limited available frequencies in a spectrum-efficient and interference-minimal way. We adopt an integer programming representation of the static channel assignment (SCA) formulated by Smith and Palaniswami. The tabu search (TS) algorithm is implemented to solve this problem. Ten benchmark problems are tested, and we show that the TS approach significantly outperforms other optimization techniques.

A new multichannel MAC protocol for ad hoc networks based on two-phase coding with power control (TPCPC)

This paper presents a new CDMA-based multichannel medium access control protocol for ad hoc networks, which is named as two-phase coding multichannel protocol with power control. The first phase code is used to broaden the area reuse and the second phase code is employed to distinguish between different nodes in one specific area. This algorithm efficiently eliminates hidden terminal and exposed terminal problems during data transmission and greatly increases the throughput. In addition, it has good scalability and can be easily accomplished with GPS. Although many multichannel MAC protocols adopting CDMA techniques have been presented, few have addressed the near-far problem. We incorporate power control in our algorithm and reduce the near-far interference. The implementation of two-phase coding with power control is discussed, and the primary simulation result demonstrates that the proposed protocol offers better performance.

An efficient heuristic algorithm for multi-constrained path problems

Multi-constrained path problem (MCPP) alms to find a path in a network that satisfies multiple additive path constraints, it has many applications such as route guidance in intelligent transportation systems and quality of service (QoS) routing in integrated networks for voice, data, and multimedia communications. It is well known that MCPP is NP-complete and heuristic or approximate algorithms are required to solve it suboptimally. A heuristic, limited path Dijkstras algorithm (LPDKS), is presented by extension of the conventional Dijkstras algorithm by maintaining a limited number of nondominated paths, say X non-dominated paths, for each node. Three key design problems are investigated for this new algorithm, i.e., how to maintain X non-dominated paths for each node when there are more paths available, how to decide which path to extend first, and how to determine X. We propose path deletion heuristics and path order heuristic to deal with the first two problems, and provide a heuristic value of X that can have very high probability to find a feasible path when one exists. The complexity analysis and extensive experiments are given to show the performance of the proposed algorithm.

Two-phase coding multichannel MAC protocol with MAI mitigation for mobile ad hoc networks

This letter introduces a novel multichannel medium access control (MAC) protocol for mobile ad hoc networks (MANETs) based on a scalable two-phase coding scheme, which eliminates the hidden terminal problem (HTP) without exchange of neighborhood information. Furthermore, power control is incorporated to mitigate multiple-access interference (MAI). Simulation results show that significant improvement can be achieved by the proposed protocol over IEEE 802.11 DCF.