Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is a technique used in wired networks like Ethernet (IEEE 802.3) to improve network performance by efficient medium access. When a collision is detected, the colliding nodes terminate their transmissions to keep the collision time as short as possible. This effectively improves the utilization of the transmission medium, since less time is spent in collisions and the time between transmission attempts is reduced.

In wireless networks, however, CSMA/CD is generally assumed to be impractical due to the physical characteristics of the wireless channel. In fact, the power of a signal degrades by orders of magnitudes on its way from transmitter to receiver due to free space path loss and signal propagation effects, such as attenuation and reflections. Therefore, even if a transmitter was equipped with a separate receive antenna, its own transmission would typically drown out the weak signals from other transmitters, which would render the detection of weak signals impossible. Nevertheless, recent research has demonstrated that self-interference cancellation techniques become feasible, which allows to design full-duplex radios [1]. This might effectively be key to the design of CSMA/CD for IEEE 802.11-based networks, allowing for enhanced network performance under high load conditions [2].

[1] Mayank Jain, Jung Il Choi, Taemin Kim, Dinesh Bharadia, Siddharth Seth, Kannan Srinivasan, Philip Levis, Sachin Katti, and Prasun Sinha. “Practical, Real-Time, Full Duplex Wireless”, 17th annual international conference on Mobile computing and networking (ACM MobiCom '11). Las Vegas, Nevada, USA, 2011, pp. 301-312.

[2] Konstantinos Voulgaris, Athanasios Gkelias, Imran Ashraf, Mischa Dohler and A. H. Aghvami. “Throughput Analysis of Wireless CSMA/CD for a Finite User Population”, IEEE Vehicular Technology Conference, Montreal, Quebec, CA, 2006, pp. 1-5.


  • Literature review: Review different self-interference cancellation techniques and assess their suitability for 802.11-based networks. Also review literature relating to channel access techniques.
  • CSMA/CD design: Make a conceptual design of a fully-fledged CSMA/CD mechanism, which also takes practical limitations into account, such as settling times of gain controls. Your design may also employ correlation techniques to detect weak signals from far-away nodes.
  • Implementation: Implement your CSMA/CD design on a software-defined radio. Self-interference cancellation might require a combination of well-considered antenna placement on the device, analog cancellation in the RF band, and digital cancellation in the baseband. Your implementation may be based on GNU Radio and USRP, or on WARP.
  • Evaluation: Evaluate the performance of individual components of your implementation (e.g., the self-interference cancellation gain), as well as the overall performance of CSMA/CD nodes in a real network, as compared to conventional CSMA/CA.