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SDR Implementation of WiMax

SDR Implementation of WiMax. Presented by: Sohaib Malik. Software Defined Radio. A radio whose functionality can be changed by changes in only the software Key feature: Reprogramability Reusability of hardware. WiMax : Key Components. Orthogonal Frequency Division Multiplexing (OFDM)

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SDR Implementation of WiMax

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  1. SDR Implementation of WiMax Presented by: Sohaib Malik

  2. Software Defined Radio • A radio whose functionality can be changed by changes in only the software • Key feature: • Reprogramability • Reusability of hardware.

  3. WiMax: Key Components • Orthogonal Frequency Division Multiplexing (OFDM) • Multiple Input Multiple Output (MIMO) • Modern Channel Coding • Receiver Synchronization • Symbol Timing • Carrier Frequency Offset (CFO) • Sampling Frequency Offset (SFO) • MIMO Channel Estimation

  4. OFDM • Spectrum of normal time domain sequence • Spectrum of classical frequency division multiplexing • Spectrum of orthogonal frequency division multiplexing

  5. Simple OFDM System N-Point OFDM System in Time Domain with Cyclic Prefix 256-Point OFDM System for WiMax • Data-carriers 192 & Pilot-carrier 8 • Null Carriers 56: one at Centre, 28 lower freq, 27 high frequency guard carriers

  6. Space-Time Coding for MIMO • Two types of Space-Time codes: Space-Time Block Codes (STBC) and Space-Time Trellis Codes (STTC). STTCs provide both coding and diversity gain but are computationally complex to decode hence are not used in commercial standards till now. STBCs are much more manageable but do not provide coding gain. • Alamouti suggested a simple Transmit diversity scheme for two antennas This is a linear STBC (that can be decoded by linear processing) of rate 1. Linear STBCs of full rate for more than two Tx antennae are known not to exist. Higher order linear block codes are suggested by Tarokh at el in Space-Time Block Codes from Orthogonal Design.

  7. Turbo Codes (Encoder Diagram)

  8. Turbo Decoder

  9. Soft Metric Generation Technique

  10. Transmitter Block Diagram

  11. Receiver Block Diagram

  12. Ideal System Performance QPSK

  13. Ideal system performance 16QAM

  14. Ideal system performance 64QAM

  15. Symbol Timing • Auto-correlation or cross-correlation based • Plateau problem • Low complexity low performance • Maximum likelihood • Additional knowledge of SNR required • Good performance but high complexity

  16. Timing Performance in AWGN Chin-Liang Wang; Hung-Chin Wang, "On joint fine time adjustment and channel estimation for OFDM systems," Wireless Communications, IEEE Transactions on , vol.8, no.10, pp.4940-4944, October 2009

  17. Timing performance in Rayleigh channel with CE

  18. Carrier Frequency Offset • Generated by mismatch between frequency of local oscillator of transmitter and receiver • Causes the time-domain signal to be multiplied by a complex exponential • Causes the frequency domain constellation to rotate. Also adds some ICI

  19. CFO Estimation performance in AWGN

  20. CFO Estimation performance in Rayleigh

  21. Channel Estimation • In OFDM, frequency selective fading channel becomes a frequency non-selective fading channel for each sub-carrier • The channel is multiplicative in nature • Rj(k) = H(k) . Xc(k) + W(k)

  22. Performance of LS Algorithm in AWGN

  23. LS performance in Rayleigh

  24. Total System Performance Without Channel Coding

  25. Questions?

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