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Saturation Throughput Analysis of a Cognitive WLAN Overlaid on a Primary Network with Time-Scheduled Users

Rahimzadeh, Parisa | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43282 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Ashtiani, Farid
  7. Abstract:
  8. The activity status of primary users in a cognitive network scenario is a key parameter in saturation throughput of the secondary users. In this respect, usually a simple on-off traffic model with exponentially distributed intervals is exploited. For time-scheduled users in modern common standards like WiMAX or LTE this traffic model is not valid anymore. In this thesis, we focus on the saturation throughput analysis of a cognitive network scenario, comprised of a WLAN overlaid on a network with time-scheduled primary users like WiMAX. In this scenario, the cognitive nodes (CNs) hear downlink map (DL-MAP) and thus, know the frequency and time locations of all allocated slots at each downlink subframe. Analysis of the occupancy distribution of empty slots in the downlink subframe of the primary network is done with a finite state discrete-time Markov chain. Different phases of packet transmission procedure in a secondary IEEE 802.11-based WLAN are modeled with an ∞ queue in an open queueing network. The duration of sending a secondary users packets in empty slots of WiMAX frames is a parameter of this queueing network. In order to evaluate this parameter, we follow a three-step modeling approach. At first we use the average number of empty slots to estimate transmission time of the secondary users packets. Although this method results in an accurate model in FDD mode, percentage of error is unacceptable in TDD mode. In the second step we use another queuing network for a more accurate calculation of transmission time of the packet in TDD mode. In this network we use the probability mass function of empty slots in consecutive frames of WiMAX. However uniform assumption of starting time of the packet transmission over a frame is still applied. In the third step we use a queuing network to find the probability mass function of starting time of the packet transmission during a frame. By some modifications in the queueing network of the secondary nodes, we are able to follow time sequence of packet transmission with multi-class queuing network. Finally, comparison of the results obtained in these three steps shows that we finally reach an accurate estimation for calculating the saturation throughput of the secondary network (less than 4% error). We evaluate the saturation throughput of cognitive network versus the number of CNs as well as the data arrival rate at WiMAX in downlink direction and confirm our analytical results by simulation
  9. Keywords:
  10. Queueing Network ; Wordwide Interoperability for Microwave Access (WIMAX)Networks ; Cognitive Radio ; Wireless Local Area Network ; Saturation Throughput

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