Adaptive Medium Access Control

Reference#: P02860

Wireless communication is a critical enabling technology for many applications in commercial, scientific, government, and military environments. Design choices made at the lower layers of the communication stack have major implications on the overall performance of applications when communicating over shared wireless channels, particularly in multi-hop wireless networks. More specifically, data link layer Media Access Control (MAC) designs should enable efficient use of the RF spectrum, support network scalability to large numbers of mobile nodes and traffic flows, and provide responsive and adaptive fair allocation of bandwidth among the connected mobile devices while minimizing adverse cross-layer interactions.

The most common wireless MAC designs in deployment are the Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA). Unfortunately, these MAC techniques do not offer sufficiently fine grained adaptability to adjust to varying traffic loads; they offer limited scalability and suffer from plethora of adverse cross-layer interactions that limit their suitability for many applications in multi-hop wireless network deployments.

Researchers at the Johns Hopkins University Applied Physics Laboratory have developed the Adaptive Medium Access Control (AMAC) protocol which integrates the TDMA and CSMA/CA channel access approaches and incorporates new adaptive congestion and collision avoidance schemes to reduce bandwidth wastage and diminish adverse cross-layer interactions within the multi-layer TCP/IP protocol stack.

The AMAC systemís decentralized methods provide a common synchronized periodic epoch, alternating Contention Free Periods (CFPs) and Contention Periods (CPs) in a periodic schedule, adaptive and guaranteed access to the media using short Contention Free Periods (CFPs), and adaptive collision avoidance schemes for both broadcast and unicast packets.

AMACís unique combination of features alleviates the intractable problem of unfair distribution of bandwidth among competing TCP traffic flows that traverse varying length paths in multi-hop ad-hoc wireless networks. It improves support for multi-media traffic while allowing higher transmission incidents from a large number of transmitting devices sharing a common channel and delivers a significant end-to-end performance improvement for both constant and variable bit rate traffic.

Patent Status: U.S. patent(s) 8,675,678 issued.

Dr. G. R. Jacobovitz
Phone: (443) 778-9899

Additional References:

Link to U.S. Patent and Trademark Office