P-TDMA-SYS: A TDMA System over Commodity 802.11 Hardware for Mobile Ad-Hoc Networks

—In some scenarios such as catastrophes and military operations, there is a need for communication without an infrastructure. In urgent cases, in-time and reliable channel access must be ensured. However, the channel access delay in widely used CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) network increases unpredictably when the channel is sensed busy. Therefore, TDMA (Time Division Multiple Access) gets more and more attention in mobile ad-hoc network research. This paper presents a TDMA network system (named as P-TDMA-SYS) that is designed to support real-time applications in mobile ad-hoc networks (MANETs) and successfully works on commodity 802.11 hardware. The key feature of P-TDMA-SYS is its microsecond synchronization and adaptive medium access policy. P-TDMA-SYS’s implementation contains two major modules. One is the PKER-MAC, a TDMA-based MAC protocol, running over commodity 802.11 hardware. The other is P-TCP, a cross-layer TCP congestion control algorithm specifically for P-KER-MAC. The presented TDMA-based MAC over commodity 802.11 hardware has been tested with a detailed accounting of the hardware and operation system overheads. Furthermore, PTDMA-SYS has been compared with 802.11 CSMA/CA-based network in the single-hop/multi-hop scenarios. The test results show that our implementation achieves reliable throughput and low delay/jitter for supporting real-time applications.