Su Wei Tan

Fair subcarrier and power allocation for multiuser orthogonal frequency-division multiple access cognitive radio networks using a colonel blotto game

The problem of subcarrier allocation (SA) and power allocation (PA) for both the downlink and uplink of cognitive radio networks (CRNs) is studied. Two joint SA and PA schemes based on Blotto games are presented for orthogonal frequency-division multiple access (OFDMA)-based CRNs. In this work, the authors consider a more practical scenario by taking into account the correlation between adjacent subcarriers. In the proposed games, secondary users (SUs) simultaneously compete for subcarriers using a limited budget. In order to win as many good subcarriers as possible, the SUs are required to wisely allocate their budget subject to the transmit power, budget and interference temperature constraints. Two PA and budget allocation strategies are derived to enable fair sharing of spectrum among the SUs. It is shown that by manipulating the total budget available for each SU, competitive fairness can be enforced. In addition, the conditions to ensure the existence and uniqueness of Nash equilibrium (NE) in the proposed methods are established and algorithms which ensure convergence to NE are proposed. Simulation results show that the proposed methods can converge rapidly and allocate resources fairly and efficiently in correlated fading OFDMA channels.

Joint channel assignment and routing in multiradio multichannel wireless mesh networks with directional antennas

The aggregate capacity of a wireless mesh network WMN is severely affected by interflow interference. In this paper, we propose a network architecture that incorporates directional antennas with multiple orthogonal channels to effectively enhance the performance of WMNs. First, a sectored connectivity graph is introduced to model multiradio multichannel WMNs with directional antennas. Next we formulate the topology design, directional interface assignment, channel allocation, and routing mathematically as a mixed integer linear programming problem. This problem is solved using an iterated local search algorithm to obtain optimized network resource allocation. Simulation results indicate that the proposed architecture can achieve higher packet delivery ratio while providing better network fairness. Copyright

Discretionary bandwidth granting scheme for homogenous real-time applications

IEEE 802.16e is an advanced wireless access technology that provides high-speed data transmission in long distance and offers quality of service (QoS) to subscribers. The provisioning of QoS is one of the great features by IEEE 802.16 to support both real-time and non-real-time applications. In IEEE 802.16, the common part sublayer in the MAC layer is responsible for maintaining the QoS services. There are many functions in the common part sublayer; the most popular topics discussed by researchers are the uplink and downlink scheduling algorithms. Many discussions had been made and focused on these two classes of schedulers. Another equally important component but overlooked so far is the bandwidth request and grant module. Bandwidth request and grant module arbitrates the amount of bandwidth to be granted, besides handling the bandwidth requests. This bandwidth request and grant process has always been developed in a conventional way, and its importance has been underestimated. In addition, the bandwidth distribution within a same service class or category also attracted little attention thus far. Many algorithms for interclass scheduling have been studied and proposed but not as much for intraclass scheduling. However, in bandwidth request and grant process, constraints on the required knowledge by the schedulers limit the intraclass scheduling algorithms to be applied onto them. We view the bandwidth request and grant process as an important part of the QoS architecture. In this paper, we proposed a new bandwidth granting scheme for the bandwidth request and granting process, which enables bandwidth to be fairly granted based on the necessity to all the requests from the same service class or category. By applying our scheme, significant improvements have been observed and recorded. Experiment results have proven and confirmed the effectiveness of our proposed scheme as compared to the conventional scheme.

An adaptive fuzzy handover triggering approach for Long-Term Evolution network

To cope with the increasing demand for efficient data delivery, self-organizing networks have been introduced in the Long Term Evolution LTE system to provide autonomous and flexible mobility management. The existing handover triggering scheme for LTE is not flexible enough to incorporate new performance metrics, and it introduces handover latency. There are studies on non-conventional handoff algorithms for LTE applications, for instance, the fuzzy logic approach. However, the fuzzy logic approach needs regular manual tuning to constantly produce optimal output. In this paper, we address this issue by proposing an adaptive fuzzy logic-based handoff decision algorithm, which can cope with environmental changes and improve efficiency by reducing human intervention. Performance results show that the proposed algorithm can reduce unnecessary handovers by about 20% compared with the fuzzy logic and conventional LTE handover triggering scheme, leading to reduced packet loss rates.

Improved topology control for multiradio multichannel wireless mesh networks with directional antennas

There are five interdependent aspects which affect the performance of multiradio multichannel wireless mesh networks with directional antennas, namely topology control, interface assignment, channel assignment, antenna orientation and routing strategies. In this work, we present an improved version of an existing topology control algorithm. We show that proper topology control scheme improves the routing decisions and results in higher packet delivery ratio, lower end to end delay and better fairness.

Collaborative mesh networking for low cost wireless coverage in rural areas

This paper proposes collaborative mesh networking as an alternative to the conventional multi-hop mesh networks for wireless connectivity in rural areas. The proposed method integrates a collaborative transmit beamforming technique in a wireless mesh network. As opposed to the approach of multi-hop mesh, where each node takes turn as a relay station to forward messages to the next node, collaborative mesh elects a few nodes to collaboratively relay a message synchronously. This provides increased receive power at the receiving end, thereby enabling better receive signal quality and longer transmission range. End-to-end performance comparisons in terms of bit error rate and packet loss probability under different scenarios are presented. Results show that collaborative mesh networks can achieve better performance and wider coverage as compared to the conventional multi-hop mesh networks.

Medium access control for collaborative transmit beamforming in wireless networks

A new medium access control (MAC) scheme to enable collaborative transmit beamforming in IEEE 802.11 based wireless networks is proposed. The proposed scheme allows information sharing and simultaneous transmission in collaborative transmit beamforming, and is compatible with the existing distributed coordination function protocol. Performance comparisons with multi-hop and direct communications of the IEEE 802.11g wireless standard employing carrier sense multiple access with collision avoidance MAC are made. Results show that the proposed approach provides better throughput when greater distances or more hops are needed to complete communications, especially in a noisy environment.

Blotto game-based low-complexity fair multiuser subcarrier allocation for uplink OFDMA networks

This article presents a subcarrier allocation scheme based on a Blotto game (SABG) for orthogonal frequency-division multiple access (OFDMA) networks where correlation between adjacent subcarriers is considered. In the proposed game, users simultaneously compete for subcarriers using a limited budget. In order to win as many good subcarriers as possible in this game, users are required to wisely allocate their budget. Efficient power and budget allocation strategies are derived for users for obtaining optimal throughput. By manipulating the total budget available for each user, competitive fairness can be enforced for the SABG. In addition, the conditions to ensure the existence and uniqueness of Nash equilibrium (NE) for the SABG are also established. An low-complexity algorithm that ensures convergence to NE is proposed. Simulation results show that the proposed low-complexity SABG can allocate resources fairly and efficiently for both uncorrelated and correlated fading channels.

Joint resource allocation in multi-radio multi-channel wireless mesh networks with practical sectored antennas

The aggregate capacity of wireless mesh networks is severely affected by interflow interference. Directional antennas and multiple channels are two well known techniques which can be applied to mitigate interflow interference. In this work, a network architecture is proposed to incorporate directional antennas with multiple orthogonal channels effectively to enhance the performance of wireless mesh networks. We first introduce a sectored connectivity graph to model multi-radio multi-channel wireless mesh networks with directional antennas. We then proceed to formulate the topology design, directional interface assignment, channel allocation and routing mathematically as a mixed integer programming problem. This problem is solved using an iterated local search algorithm to obtain optimized resource allocation in the network. Simulation results indicate that the proposed architecture can achieve higher packet delivery ratio. It also provides better fairness among the flows in the network by proper resource allocation, load balancing and capacity planning.

A Coalitional Game-Based Algorithm for OFDMA Resource Allocation in Multicast Cognitive Radio Networks

This letter investigates resource allocation for orthogonal frequency division multiple access (OFDMA)-based multicast cognitive radio networks (MCRNs) under the consideration of primary users’ activities. Due to the heterogeneity of channel gains among secondary users (SUs), the existing multicast schemes are highly conservative and spectrally inefficient. To address this issue, we formulate a novel multicasting problem for MCRNs. This new formulation optimally and adaptively exploits multiuser diversity of OFDMA through dynamic group formation, which clusters SUs within a multicast group into multiple smaller subgroups (coalitions) based on their channel gains. Subcarriers and power are then allocated to these subgroups to maximize aggregate data rate (ADR) of the system. A coalitional game theory is adopted to model the group formation where SUs are allowed to form coalitions to compete for resources. A novel cognitive multicast coalitional game (CMCG) is proposed for SUs to self-organize to reach multi-coalitional equilibrium where optimality can be obtained. Simulation results show that the proposed CMCG algorithm significantly improves the system ADR as compared to the conventional unicast and multicast schemes.