Fine-Grained Channel Access in Wireless LAN

With the increasing of physical-layer (PHY) data

rate in modern wireless local area networks (WLANs) (e.g.,

802.11n), the overhead of media access control (MAC) progressively

degrades data throughput efficiency. This trend reflects a

fundamental aspect of the current MAC protocol, which allocates

the channel as a single resource at a time. This paper argues

that, in a high data rate WLAN, the channel should be divided

into separate subchannels whose width is commensurate with

the PHY data rate and typical frame size. Multiple stations can

then contend for and use subchannels simultaneously according

to their traffic demands, thereby increasing overall efficiency. We

introduce FICA, a fine-grained channel access method that embodies

this approach to media access using two novel techniques.

First, it proposes a new PHY architecture based on orthogonal

frequency division multiplexing (OFDM) that retains orthogonality

among subchannels while relying solely on the coordination

mechanisms in existing WLAN, carrier sensing and broadcasting.

Second, FICA employs a frequency-domain contention method

that uses physical-layer Request to Send/Clear to Send (RTS/CTS)

signaling and frequency domain backoff to efficiently coordinate

subchannel access. We have implemented FICA, both MAC and

PHY layers, using a software radio platform, and our experiments

demonstrate the feasibility of the FICA design. Furthermore,

our simulation results show FICA can improve the efficiency of

WLANs from a few percent to 600% compared to existing 802.11.

 

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