William K. Wong

Interference Avoidance with Dynamic Inter-Cell Coordination for Downlink LTE System

The investigation of co-channel interference mitigation techniques (such as, interference cancellation through receiver processing, interference randomization by frequency hopping, and interference avoidance through resource usage restrictions imposed by frequency and power planning) has become a key focus area in achieving dense spectrum reuse in next generation cellular systems such as 3GPP LTE, LTEadvanced, and WiMAX. In this paper, we propose an interference avoidance scheme for LTE downlink that uses dynamic inter-cell coordination facilitated through X2 interface among neighbouring evolved UTRAN nodeBs (eNBs, i.e., LTE base stations). Proposed scheme is evaluated by extensive simulations and compared with a number of reference schemes available in the literature. It has been observed that the proposed scheme attains superior performance in terms of cell-edge and sector throughput compared to those in the reference schemes.

Soft QoS provisioning using the token bank fair queuing scheduling algorithm

Future-generation wireless packet networks will support multimedia applications with diverse QoS requirements. Much of the research on scheduling algorithms has been focused on hard QoS provisioning of integrated services. Although these algorithms give hard delay bounds, their stringent requirements sacrifice the potential statistical multiplexing performance and flexibility of the packet-switched network. Furthermore, the complexities of the algorithms often make them impractical for wireless networks. There is a need to develop a packet scheduling scheme for wireless packet-switched networks that provides soft QoS guarantees for heterogeneous traffic, and is also simple to implement and manage. This article proposes token bank fair queuing (TBFQ), a soft scheduling algorithm that possesses these qualities. This algorithm is work-conserving and has a complexity of O(1). We focus on packet scheduling on a reservation-based TDMA/TDD wireless channel to service integrated real-time traffic. The TBFQ scheduling mechanism integrates the policing and servicing functions, and keeps track of the usage of each connection. We address the impact of TBFQ on mean packet delay, violation probability, and bandwidth utilization. We also demonstrate that due to its soft provisioning capabilities, the TBFQ performs rather well even when traffic conditions deviate from the established contracts.

Token bank fair queuing: a new scheduling algorithm for wireless multimedia services

SUMMARY The token bank fair queuing algorithm (TBFQ) is a novel scheduling algorithm that is suitable for wireless multimedia services. The bandwidth allocation mechanism integrates the leaky bucket structure with priority handling to address the problem of providing quality-of-service (QoS) guarantees to heterogeneous applications in the next generation packet-switched wireless networks. Scheduling algorithms are often tightly integrated with the wireless medium access control (MAC) protocol. However, when heterogeneous wireless systems need to be integrated and interoperate with each other, it is desirable from the QoS provisioning standpoint to decouple scheduling algorithm from the MAC protocol. In this paper we propose a framework of seamless QoS provisioning and the application of TBFQ for uplink and downlink scheduling in wireless networks. We study its performance under a generic medium access framework that enables the algorithm to be generalized to provide QoS guarantees under various medium access schemes. We give a brief analysis of the algorithm and compare its performance with common scheduling algorithms through simulation. Our results demonstrate that TBFQ significantly increases wireless channel utilization while maintaining the same QoS, unlike many fair queuing algorithms, TBFQ does not require timestamping information of each packet arrival}an impractical feature in an already resource scarce environment. This makes TBFQ suitable for wireless multimedia communication. Copyright # 2004 John Wiley & Sons, Ltd.

Scheduling for integrated services in next generation packet broadcast networks

In future wireless packet networks, it is anticipated that a wide variety of applications, ranging from WWW browsing to E-mail service, and real-time services like packetized voice and digital videoconference, will be supported with varying levels of quality of service (QoS). There is a need for packet scheduling schemes that effectively provide QoS guarantees and at the same time are simple to implement. This paper focuses on the scheduling of fixed sized packets or data segments over the downlink of a TDMA/TDD wireless interface. The proposed scheduling mechanism is based on the token bank leaky bucket mechanism, which integrates the policing and servicing functions and keeps track of the potential of each connection. This results in lower packet delay, jitter and violation probability. The performance is evaluated using computer simulations. The performance measures are packet delay, jitter, violation probability, degree of multiplexing, and throughput. The trade-off between these parameters is exploited.

Cross-layer resource scheduling for video traffic in the downlink of OFDMA-based wireless 4G networks

Designing scheduling algorithms at the medium access control (MAC) layer relies on a variety of parameters including quality of service (QoS) requirements, resource allocation mechanisms, and link qualities from the corresponding layers. In this paper, we present an efficient cross-layer scheduling scheme, namely, Adaptive Token Bank Fair Queuing (ATBFQ) algorithm, which is designed for packet scheduling and resource allocation in the downlink of OFDMA-based wireless 4G networks. This algorithm focuses on the mechanisms of efficiency and fairness in multiuser frequency-selective fading environments. We propose an adaptive method for ATBFQ parameter selection which integrates packet scheduling with resource mapping. The performance of the proposed scheme is compared to that of the round-robin (RR) and the score-based (SB) schedulers. It is observed from simulation results that the proposed scheme with adaptive parameter selection provides enhanced performance in terms of queuing delay, packet dropping rate, and cell-edge user performance, while the total sector throughput remains comparable. We further analyze and compare achieved fairness of the schemes in terms of different fairness indices available in literature.

A robust coexistence scheme for IEEE 802.15.4 wireless personal area networks

The Industrial, Scientific and Medical (ISM) band is shared among multiple wireless networks such as Bluetooth, wireless local area networks and 802.15.4 low rate wireless personal area networks (LR-WPAN). There are some centralized protocols that may work in this coexistent medium. Since management of these methods is done centrally with the help of configuration messages, their performance is strictly tied to the reliable transmission of these data. Clearly, this required level of reliability is in doubt when these methods are implemented in a heterogeneous environment. In this paper we explore how the performance of these standards is affected when they confront with interference. For this reason, WPAN beacon-enabled mode is selected as a representative of the category of synchronization-based methods, and its performance in a co-located WLAN\WPAN medium is evaluated. Then, a rapid-response and robust interference coexistence scheme is proposed to mitigate the effect of interfering systems on WPANs performance. Simulation results show that the proposed method can be efficiently used to recover an affected WPAN quickly, regardless of the amount of WLAN interference.

Scheduling algorithm in a point-to-multipoint broadband wireless access network

Point-to-multipoint broadband wireless access (BWA) is an attractive solution to provide advanced data services to users who do not have easy access to wireline data services. However, BWA will need to support delay sensitive services as users and applications are becoming increasingly sophisticated. Wireless packet scheduling is an important part of quality-of-service (QoS) provisioning in BWA. The biggest difficulty in wireless packet scheduling is the location-dependent channel errors. Channel condition independent fair scheme (CIF) (T.S. Eugene, et al., March 1998) uses explicit leading/lagging approach to compensate for the erroneous channel state, but is not able to satisfy both rapid convergent guaranteed throughput and fairness. In this paper, we propose to use the token bank fair queuing (TBFQ) scheduling algorithm as a QoS provisioning mechanism for an asymmetric broadband point-to-multipoint wireless LAN. We consider the throughput and fairness performance of TBFQ under location-dependent channel error condition with variable packet length. This work is an extension of our previous work in applying TBFQ in next generation cellular networks.

Scheduling for heterogeneous traffic in next generation wireless networks

Future generation wireless packet networks will support multimedia applications with diverse quality-of-service (QoS) requirements. There is a need to develop a packet scheduling scheme for wireless channels that provides QoS guarantees for heterogeneous traffic and is also simple to implement and manage, This paper focuses on packet scheduling on a reservation-based on-demand TDMA/TDD wireless uplink channel to service integrated real-time traffic. The proposed token bank fair queueing (TBPQ) scheduling mechanism integrates the policing and servicing functions and keeps track of the usage of each connection. This scheme results in lower packet delay, jitters and violation probability. The performance is evaluated using computer simulations. The tradeoffs between the parameters are examined. It is also demonstrated that TBFQ performs rather well even when traffic conditions deviate from the established contracts.

Adaptive Token Bank Fair Queuing Scheduling in the Downlink of 4G Wireless Multicarrier Networks

In this paper we present an efficient cross-layer scheduling algorithm designed for resource allocation in downlink of 4G wireless multicarrier networks. This study focuses on the mechanisms of efficiency, fairness, as well as quality of service (QoS) provisioning and algorithm development for resource allocation in multiuser frequency-selective fading environments. The performance of the proposed scheme is compared to that of the score based (SB) scheduling, which is a variation of the proportional fair (PF) algorithm (the most widely adapted opportunistic scheduling technique), in the presence of interference. It is observed from simulation results that the proposed scheme provides better fairness in terms queuing delays, and dropped packets for various loading factors while the throughput remains comparable. A gain in the performance of cell edge users is also observed for the proposed scheme, this may result in substantial savings in the deployment cost since fewer base stations (BS) will be needed to cover regions.

TBLB algorithm for servicing real-time multimedia traffic streams

In this paper, we propose to use a simple packet servicing algorithm suitable for servicing bursty real-time multimedia traffic streams in packet-switched networks. These real-time multimedia services may include packetized voice and videoconference/playback. The servicing mechanism is an enhancement of the token bank leaky bucket (TBLB) scheme we proposed previously. This new algorithm combines both the servicing and the policing functions, and its performance in accommodating bursty real-time traffic is evaluated by computer simulations. We show that the quality of service (QoS) performance (mean delay and jitter) of TBLB exceeds that of the leaky-bucket constrained generalized processor sharing (GPS). Although GPS has been proven to give bounded delay to a leaky-bucket constrained traffic stream and ensure instantaneous fair allocation of bandwidth, the average delay is often quite large. Also, fairness is not a guarantee of QoS, and is not perceived by users directly. Another property that is often neglected in the analysis of schedulers (but very important to user QoS) is the sensitivity of QoS to deviations of traffic streams from their specified traffic descriptors. We present results to show that our proposed method is relatively robust to such deviations.