Physical layer aware MAC design for wireless networks

The edge of the Internet continues to spread rapidly over the wireless medium. The coexistence of densely deployed wireless networks demand near-perfect interference management. In this dissertation, we investigate several approaches to mitigate the impact of interference and increase spatial reuse in wireless networks.;Neighbors of both the transmitter and the receiver must keep quiet under 802.11 for the entire duration of the communication, limiting spatial reuse. The nodes reverse their roles as transmitter and receiver for delivering a single data frame. We propose an approach based on piggybacked acknowledgements to alleviate the problem of role reversals and enable more concurrent transmissions. This initial investigation led us towards exploiting physical layer capabilities such as message-in-message (MIM) and successive interference cancellation (SIC) through suitable MAC layer design.;MIM is the ability of a receiver to decode a stronger frame of interest even if its transmission started in the presence of an interfering frame. However, we observed that the frame recovery depends on the relative order of transmissions. Two concurrent transmissions may succeed only if activated in a specific order. With suitable ordering, the number of concurrent transmissions and there by the throughput can be increased. We design MIM-aware MAC protocols for multi-hop mesh networks, and enterprise wireless LANs. Evaluation through simulations and testbed experiments shows that MIM-awareness offers significant performance gains.;SIC is a physical layer technique that allows a receiver to extract a weaker frame of interest from a simultaneous arrival of two or more signals. SIC is feasible because the receiver may be able to decode the stronger signal, subtract it from the combined signal, and extract the weaker one from the residue. While the technique is well known, SIC has not been studied earlier from the perspective of the MAC layer. Taking advantage of software radio platforms such as GNU radio, we investigate the extent of throughput gains possible with SIC and carved out MAC layer opportunities with SIC. We develop an SIC-aware scheduling algorithm that employs client pairing and power reduction to extract the most gains from SIC. We demonstrate the benefits of SIC-aware scheduling on a small testbed of software radios.;Both MIM and SIC make concurrent transmissions feasible. However, a MAC scheme still needs the ability to determine whether another transmission can be concurrent with an on-going transmission. This requires the knowledge of the sender-receiver pair (link) of an on-going transmission. While this information can be gleaned from the frame header, a listener may miss the header as it might be involved in another transmission at that instant. We propose an OFDM based physical layer approach for sensing of active links at any instant. We use a small subset of OFDM subcarriers and assign a unique active/deactive pattern for conveying the signature of the active link. We implement and validate our approach using software radios.