Random Access on Multipacket Reception Channel with Applications to Satellite Communications

  • Author / Creator
    Ghanbarinejad, Majid
  • In the field of multiple-access systems, multipacket reception (MPR) is defined as the capability of the receiver to successfully receive/decode concurrent packets from multiple transmitters. While physical-layer capabilities and limitations of MPR-capable systems using technologies such as code-division multiple-access (CDMA) and multiple-antenna communications are well studied in the literature, an important question is how this capability affects the performance at the medium-access control (MAC) layer. Random access on the MPR channel is studied in this thesis. First, we study throughput of Aloha random access with Poisson arrivals and highlight the throughput advantage of the MPR channel compared to the conventional collision channel. The analysis shows that Aloha performs more efficiently on the MPR channels where the maximum number of concurrent transmissions that can be received by the receiver is larger providing that the aggregate traffic on the medium is controlled and maintained below a threshold. If the average number of transmissions exceeds this threshold, however, the system throughput declines rapidly, which motivates efficient control mechanisms on top of random access. Bounds on the throughput performance of random access are examined and a closed-form approximation for throughput of genie-aided random access with Poisson arrivals is derived. A method of computing the optimal access probability is, then, presented for the cases where only partial information about contention on the medium is available. Next, we examine a finite-size multiple-access system where the incoming traffic is the aggregate of interrupted on/off Markov sources. The resulting system is a Markov decision process for which the optimal access algorithm is provided and compared to lower and upper bounds. A new rate/burstiness model of an on/off Markov source is proposed, which is used to present where the throughput curves lay compared to the computed bounds. Furthermore, it is shown that the gap between the upper and lower bounds reduces as the maximum number of packets that can be received increases. Queuing analysis is provided and closed-form equations for queuing delay as a function of throughput are derived. While the above algorithm requires prior knowledge of traffic parameters, we also propose a framework for more practical random access systems where no prior knowledge of traffic and node population is available. The proposed scheme uses the theory of extended Kalman filters in order to track the contention on the medium and select the near-optimal access probability. The proposed scheme is shown to stabilize the operating point of the multiple-access system close to the point where throughput of Aloha takes its maximum. This scheme is also examined for unideal cases such as delayed acknowledgement channel and shown to be a robust access scheme on the MPR channel. Finally, we study two aspects of random access on the MPR channel that are related to satellite communications. First, a repetition random access scheme that employs transmission diversity and iterative collision resolution is analyzed for the case of MPR channels. Asymptotic analysis for this generalized model is provided and it is shown that larger loads can be supported in smaller frames. Next, throughput-delay tradeoff of random access over delayed links is analyzed and scaling laws are derived for the cases of the collision channel and the MPR channel as well as repetition random access. It is shown that multiuser detection and repetition schemes improve the multiple access performance in the sense that the inevitable compromise between throughput and delay is mitigated by joint detection capabilities and/or repetitions.

  • Subjects / Keywords
  • Graduation date
    Fall 2014
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.