Abstract
Existing medium access control (MAC) schemes for wireless local area networks (WLANs) have been shown to lack scalability in crowded networks and can suffer from widely varying delays rendering them unsuited to delay sensitive applications, such as voice and video communications. These deficiencies are mainly due to the use of random multiple access techniques in the MAC layer. The design of these techniques is highly linked to the choice of the underlying physical (PHY) layer technology. The advent of new PHY schemes that are based on orthogonal frequency division multiple access (OFDMA) provides new opportunities for devising more efficient MAC protocols. We propose a new adaptive MAC design based on OFDMA technology. The design uses OFDMA to reduce collision during transmission request phases and makes channel access more predictable. To improve throughput, we combine the OFDMA access with a carrier sense multiple access (CSMA) scheme. Data transmission opportunities are assigned through an access point that can schedule traffic streams in both time and frequency (subchannels) domains. We demonstrate the effectiveness of the proposed MAC and compare it to existing mechanisms through simulation and by deriving an analytical model for the operation of the MAC in saturation mode.
Highlights
The throughput and scalability of a wireless local area network (WLAN) are greatly dependent on its medium access control (MAC) protocol and its associated multiple access (MA) scheme
The MAC protocol proposed in this article combines orthogonal frequency division multiple access (OFDMA) with carrier sense multiple access (CSMA)/collision avoidance mechanism (CA) mechanisms and significantly increases the performance and utilization efficiency of a WLAN in the MAC layer
Our results indicate that our protocol works best when the ratio of stations to channels is about 4 or 8
Summary
The throughput and scalability of a wireless local area network (WLAN) are greatly dependent on its medium access control (MAC) protocol and its associated multiple access (MA) scheme. The original designs of MAC protocols for WLANs included the CSMA/CA (CSMA with collision avoidance) mechanism in IEEE 802.11 WLANs and time division multiple access (TDMA) in HIPERLAN [1,2,3]. TDMA required complex scheduling in a central node and used fixed time slotbased transmissions, as opposed to variable length packet transmissions Such a scheme had limited flexibility in low cost WLANs that are dominated by bursty data traffic. Another major issue is to improve support for persistent real-time traffic, produced by multimedia applications, while maintaining the random access and variable length packet transmission features of the original MAC To achieve these goals, we utilize the orthogonal frequency division multiple access (OFDMA) scheme [5, 6].
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