Anup Thapa

QoS Provisioning in Wireless Body Area Networks: A Review on MAC Aspects

Wireless Body Area Networks (WBANs) deal with variety of healthcare services with diverse Quality of Service (QoS) requirements. However, QoS handling is a challenging problem in such networks. In general, QoS related problems can be addressed from different layers in the networking protocol suite. Design of an efficient QoS aware Medium Access Control (MAC) protocol can address this problem in MAC layer. This paper analyzes the QoS requirements of WBAN, identifies the requisites of QoS handling system, and outlines the trends that are being followed for its advancement with focus on QoS issues at MAC layer. We review some prior works, compare them, and analyze the current research concerned with problem of providing QoS in WBAN. We also explore some open issues and discuss them.

A MAC protocol to select optimal transmission mode in very high throughput WLAN: MU-MIMO vs. multiple SU-MIMO

During some cases, especially when the channel quality varies considerably between the receivers, MU-MIMO transmission may fail to utilize the available MIMO capacity to its full potential. A MAC protocol design that can switch between MU-MIMO and multiple SU-MIMO transmissions after taking into account the achievable performance could be one of the simple yet attractive solutions to address such issue. In this paper, by simply upgrading the WLAN default MAC protocol CSMA/CA, we propose a MAC protocol that is capable of performing such switching task in a forthcoming very high throughput WLAN. The detailed performance analysis demonstrates that the more benefits could be achieved from the proposed scheme in comparison to the conventional MU-MIMO transmission only scheme both in terms of throughput and delay.

An Intelligent Contention Window Control Scheme for Distributed Medium Access

This paper proposes a novel contfntion window control scheme for backoff based CRA (Collision Resolution Algorithm). The proposed scheme demonstrates a distributed way to control random slot selection over the contention window in each contention stage with reference to nomlalized backoff value in the previous contention stage. Such control results an intelligent backoff time distribution over the contention window for each contention stage. Backoff time chosen for every access from such distribution potentially mitigates much collisions along with reduced channel ideal time. Analysis results show that, compared to the performance of legacy scheme incorporating DSSS (Direct Sequence Spread Spectrum) 802.11b system parameters, there is at least 13% normalized throughput enhancement with heavily reduced packet delay in an IBSS (Independent Basic Service Set) with more than 30 stations with saturated traffic.

Utility Based Backoff (UBB) Algorithm for Initial Ranging Procedure in WiBro

In this paper, a contention resolution backoff al- gorithm termed Utility Based Backoff (UBB) is proposed for initial ranging procedure in IEEE 802.16e based WiBro (Wireless Broadband) system. In UBB algorithm, whenever an active Sub- scriber Station (SS) experiences a collision during ranging request transmission, it accomplishes its new contention window size based on the utility (satisfaction) upon its randomly selected backoff value on the previous transmission attempt. Higher the deferred backoff value lower will be the utility and vice versa. The contention window will be larger for higher utility and vice versa. The process is repeated unless the request is transmitted successfully, or until the maximum retransmission attempt is reached. UBB algorithm applied to WiBro reduces the average medium access delay for the successful request transmission compared to Binary Exponential Backoff (BEB). Even more, throughput for lower offered load is higher in UBB than BEB.

Performance characterization of CSMA/CA adapted multi-user MIMO aware MAC in WLANs

To realize the multi-user multiple input multiple output (MIMO) advantage over WLANs, it requires significant changes in the MAC protocol. Either the dominant MAC protocol carrier sense multiple access/collision avoidance (CSMA/CA) needs to be replaced by a novel multi-user MIMO aware MAC protocol or it should be upgraded into multi-user MIMO aware CSMA/CA. Nevertheless, the simplest approach would be upgrading the CSMA/CA. Simple modifications in the control packets format and/or the channel access mechanism can upgrade CSMA/CA into simple, yet practicable, multi-user MIMO aware MAC protocol. By utilizing convenient changes, several modification approaches can be provisioned for this purpose. Hence, it is important to understand their performance benefits and trade-offs. In this article, we discuss some of such modification approaches that best represent the possible modifications. We provide their detail performance analysis based on analytical modeling and derived expressions in terms of throughput and delay. We also derive expressions for achievable performance and present their performance limits too.

Delay efficient emergency access control protocol in medical implant communication

In order to find out current operating channel of the hub during emergency in medical implant communication, an implant node sequentially sends an empty frame in all the available channels until it receives an acknowledgement. The channel scanning process by sending an empty frame in advance, however, adds higher overhead if the probability of transmission in the correct channel is high and/or payload size is small. In such scenario, the direct data transmission technique in which node transmits data directly without empty frame in advance could exhibit better performance. In this paper, to save emergency packet suffering from inappropriate delay, we propose to use these two transmission schemes adaptively. Nodes select their transmission mode by taking into account both the probability of successful transmission and the payload size. We find payload threshold value that serves as switching criterion between two schemes during various network conditions. Through rigorous analysis and simulation, we show that the proposed scheme significantly enhances the delay performance.

Performance analysis of CSMA/CA adapted MIMO aware MAC for multi-user transmission in WLANs

Compared to the traditional SISO system, one of the major benefits of MIMO is to increase spectral efficiency employing spatial multiplexing. However, such an independently increased PHY layer capacity cannot be translated easily to MAC layer capacity gain unless special measures are taken in MAC protocols. For distributed WLANs with MIMO, subtle modifications in dominant MAC protocol CSMA/CA can give rise to a simple, yet practicable, MIMO aware MAC. When employing such MAC for single user spatial multiplexing, throughput is increased linearly with the antenna elements in use; leaving the delay constant. However, for multi-user multiplexing, requirement of more and extended control packets exchange leads higher overhead which ultimately decreases the performance compared to single user multiplexing. But nevertheless, during various network scenarios mutli-user multiplexing, multi-user transmission, is more preferable for its capability to transmit multiple streams of data destined to multiple receivers at one transmission opportunity. In this paper, based on the analytical modeling and derived expressions, we present the performance analysis of CSMA/CA adapted multi-user transmission supporting MIMO aware MAC in terms of average throughput and delay.

Uplink scheduling mechanism for MPEG encoded video in IEEE 802.16 MAN

MPEG coded video consists three types of periodically arranged inter-frame dependent frames: I, P, and B with different level of information and importance. When such encoded frames are transported in any wireless network, all frames are equally prone to loss. However, the effect of loss of frames is not uniform for all frame types. The effect of loss on visual quality depends on the type of the frame and position of the frame inside the GOP. So we extract these frame-position and frame-type information of every frame to develop a priority based opportunistic scheduler. In other words, the priority weight to be assigned to each frame is simply a function of frame-type and frame-position value. Every video with m number of GOPs with GOP dimension of (N, M) are fragmented into N/M + 1 layers and the frames belonging to each layer are tagged with homogeneous priority weight. Hence, this added priority determines the transmission and selective drop order of the frames residing in different layers. Performance analysis carried for this scheduler under IEEE 802.16 based system confirms the less PLR for important frame types. The proposed MPEG scheduling mechanism can be used without modification in other systems as well, provided, there is provision of QoS class based scheduling.