Traffic integration in personal, local and geograhical wireless networks

Currently, users identify wireless networks with the first and second generation of cellular-telephony networks. Although voice and short messaging have driven the success of these networks so far, data and more sophisticated applications are emerging as the future driving forces for the extensive deployment of new wireless technologies. In this chapter we will consider future wireless technologies that will provide support to different types of traffic including legacy voice applications, Internet data traffic, and sophisticated multimedia applications. In the near future, wireless technologies will span from broadband wide-area technologies (such as satellite-based network and cellular networks) to local and personal area networks. Hereafter, for each class of networks, we will present the emerging wireless technologies for supporting service integration. Our overview will start by analyzing the Bluetooth technology that is the de-facto standard for Wireless Personal Area Networks (WPANs), i.e. networks that connect devices placed inside a circle with radius of 10 meters. Two main standards exist for Wireless Local Area Networks (WLANs): IEEE 802. and HiperLAN. In this chapter we focus on the IEEE 802.11 technology, as it is the technology currently available on the market. In this chapter, after a brief description of the IEEE 802.11 architecture, we will focus on the mechanisms that have been specifically designed to support delay sensitive traffics

Analysis and enhancement of wireless LANs in noisy channels

Without a doubt, Wireless Local Area Networks (WLANs) technology has been encountering an explosive growth lately. IEEE 802.11 is the standard associated with this promising technology, which enures shared access to the wireless medium through the distributed coordination function (DCF). Recently, the IEEE 802.11e task group has made extensions to WLANs medium access control (MAC) in order to support quality of service (QoS) traffic. An inherited problem for WLANs, is the volatility of the propagation medium, which is a challenging issue that affects the system performance significantly. Consequently, enhancing the operation of the DCF in noisy environments is of great interest, and has attracted the attention of many researchers. Our first major contribution in the presented thesis, is an analytical and simulation analysis for the binary exponential backoff (BEB) scheme of the DCF, in the presence of channel noise. We show that following the BEB procedure when a host encounters erroneous transmission is needed only if the channel was highly loaded. However, incrementing the contention window (CW) upon each packet failure, whether caused by instantaneous transmission (i.e. collision) or channel noise, will result in the waste of air time if the channel was lightly loaded. Accordingly, we present a hybrid access method that adapts the CW according to the channel load along with the frame error rate (FER). Other means to overcome the channel noise is the adjustment of the transmission rate. Many rate adaptation (RA) algorithms were introduced in the past few years, including the Automatic Rate Fallback (ARF) which is currently implemented in the wireless cards. Yet, many drawbacks are associated with these RA algorithms; specifically, in regard to the techniques and events that should trigger the rate change. Moreover, the IEEE 802.11e QoS flows requirements were not considered with the latter schemes. Accordingly, our next major contribution in this work is the presentation of a novel rate adaptation scheme. The simplicity of the introduced rate adaptation scheme is that it relies on the MAC layer parameters rather than those of the PHY layer when adjusting the rate. Furthermore, our algorithm supports the IEEE 802.11e MAC extensions where QoS traffic requirements were integrated in the procedure of adjusting the bit rate. Hence, strict real-time flow parameters such as delay and maximum drop rate are respected. Finally, we enhance the dynamic assignment of transmission opportunities (TXOPs) in order to offer fair air-time for nodes facing high packet loss rat

Improving aggregate user utilities and providing fairness in multi-rate wireless LANs

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 159-166).A distributed medium access control (MAC) protocol is responsible for allocating the shared spectrum efficiently and fairly among competing devices using a wireless local area network. Unfortunately, existing MAC protocols, including 802.11's DCF, achieve neither efficiency nor fairness under many realistic conditions. In this dissertation, we show that both bit and frame-based fairness,the most widely used notions, lead to drastically reduced aggregate throughput and increased average delay in typical environments, in which competing nodes transmit at different data transmission rates. We demonstrate the advantages of time-based fairness, in which each competing node receives an equal share of the wireless channel occupancy time. Through analysis, experiments on a Linux test bed, and simulation, we demonstrate that time-based fairness can lead to significant improvements in aggregate throughput and average delay. Through a game theoretic analysis and simulation, we also show that existing MAC protocols encourage non-cooperative nodes to employ globally inefficient transmission strategies that lead to low aggregate throughput. We show that providing long-term time share guarantees among competing nodes leads rational nodes to employ efficient transmission strategies at equilibriums.(cont.) We describe two novel solutions, TES (Time-fair Efficient and Scalable MAC protocol) and TBR (Time-based Regulator) that provide time-based fairness and long-term time share guarantees among competing nodes. TBR is a backward-compatible centralized solution that runs at the AP,works in conjunction with DCF, and requires no modifications to clients nor to DCF. TBR is appropriate for existing access point based networks, but not effective when nearby non-cooperative nodes fall under different administrative domains. Our evaluation of TBR on an 802.1lb/Linux test bed shows that TBR can improve aggregate TCP throughput by as much as 105% in rate diverse environments. TES is a non-backward compatible distributed contention-based MAC protocol that is effective in any environment, including non-cooperative environments. Furthermore, the aggregate throughputs sustained with increased loads. Through extensive simulation experiments, we demonstrate that TES is significantly more efficient(as much as 140% improvement in aggregate TCP throughput) and fairer than existing MAC protocols including DCF.by Godfrey Tan.Ph.D