The Carrier-Sense Multiple Access with Transmission Acquisition (CSMA/TA) Protocol

Marcelo Carvalho
Professor Adjunto
University of Brasilia
SERC 306
Thursday, November 1, 2018 - 11:00
In this talk, I will present the Carrier-Sense Multiple Access with Transmission Acquisition (CSMA/TA) protocol for wireless local area networks (WLANs), where it is assumed that stations are endowed with half-duplex radios operating with a single antenna over a single channel. In contrast to traditional contention-based channel-access methods, CSMA/TA seeks to increase the likelihood of having the last transmission from a group of colliding transmissions to succeed. To accomplish this goal, a station senses the channel before sending a pilot packet. After finishing the transmission of the pilot packet, the station is required to wait for a certain amount of time before sensing the channel again. If the channel is sensed to be idle again, the station understands that "it has acquired its right to transmit a data frame" and proceeds with that. The throughput computation of CSMA/TA will be presented and compared with the throughput of CSMA and CSMA/CD. An important feature of the analysis is the consideration of the impact of the receive-to-transmit and transmit-to-receive turnaround times. In fact, the approach adopted in CSMA/TA leverages the short transmit-to-receive (TX/RX) and receive-to-transmit (RX/TX) turnaround times of modern half-duplex radios, since these turnaround times can be of the same order of magnitude or even smaller than the maximum propagation delay in some WLAN scenarios, especially those seeking long-range coverage (e.g.: IEEE 802.11ah). It is shown that CSMA/TA performs better than ideal CSMA and CSMA/CD if the propagation delays in the network are larger than turnaround times, and its performance can still surpass CSMA/CD and CSMA if turnaround times are larger than propagation delays, but not too much larger.