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Analysis of Synchronization Schemes in OFDM-Based Cellular Cooperative Networks

Sharifi, Shahrouz | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41905 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Hossein Khalaj, Babak; Behrouzi, Hamid
  7. Abstract:
  8. In this thesis, the impact of both time offsets (TOs) and carrier frequency offsets (CFOs) on the average output signal-to-interference-plus-noise ratio (SINR) of OFDM systems is investigated with a novel and simple approach. First, TOs are partitioned into five cases based on how they occur. Then the mathematical models for different cases are derived. Considering CFOs and benefiting from the obtained models, closed-form expression for the SINR in each case is derived. It is proved that, SINR is independent of the observed subcarrier for the given TO and CFO. Besides, it is shown that the performance of the affected system deteriorates rapidly as the number of subcarriers increases. It is also revealed that, as far as the guard interval is longer than the channel delay spread, the SINR is not much sensitive to the number of channel taps and power delay profile.
    Afterwards, the effects of offsets are investigated in cooperative cellular networks. considering the quasi-synchronous protocol which is the only applicable solution for time synchronization in such systems, it is shown that even with this protocol there may exist some uncompensated offsets in the systems which can bring some limitations such as decreasing the distance of the users from each other. So, some ideas are provided in which the structure of the system is used for relaxing the problem. The relays in the system are considered as sources for reconstructing the distorted cyclic prefix of the users’ signals. So, the distance of the users can be increased in an extended model. Furthermore, a method regarding the frequency offset estimation in such systems is proposed in which the base stations use the relays’ signals as the copy of the users’ signal in a manner that the accuracy of the estimation is improved
  9. Keywords:
  10. Synchronism ; Frequency Offset ; Orthogonal Frequency Division Multiplexing (OFDM) ; Time offset ; Signal-to-Interference-Plus-Noise Ratio (SINR) ; Cellular Cooperative Network

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