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UWB Receiver Algorithm

UWB Receiver Algorithm. 黃璿光 2007/05/28. Outline. Synchronization Time synchronization Packet detection Frame synchronization Frequency synchronization Coarse Frequency synchronization Phase tracking Channel Estimation Zero-Padded Prefix. Receiver. Time Synchronization.

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UWB Receiver Algorithm

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  1. UWB Receiver Algorithm 黃璿光 2007/05/28

  2. Outline • Synchronization • Time synchronization • Packet detection • Frame synchronization • Frequency synchronization • Coarse Frequency synchronization • Phase tracking • Channel Estimation • Zero-Padded Prefix

  3. Receiver

  4. Time Synchronization

  5. PLCP frame format

  6. Standard preamble

  7. Time-Frequency Code (TFC) • MBOA version 0v9 • The proposed UWB system also utilizes a time-frequency code (TFC) to interleave coded data over 3 frequency bands (called a band group). • Four band groups with 3 bands each and one band group with 2 bands are defined, along with four 3-band TFCs and two 2-band TFCs. • ECMA-368 • Two types of TFCs: one where the coded information is interleaved over three bands, referred to as Time-Frequency Interleaving (TFI); and, one where the coded information is transmitted on a single band, referred to as Fixed Frequency Interleaving (FFI). • Within each of the first four band groups, four TFCs using TFI and three TFCs using FFI are defined. For the fifth band group, two TFCs using FFI are defined.

  8. Time-Frequency Codes (MBOA 0v9) • These PLCP preamble sequences are each associated with a particular time-frequency code (TFC).

  9. MB-OFDM Band • There are 5 Band Groups: • Band group #1 is mandatory, remaining (#2 – #5) are optional. • Define 4 Time-Frequency coded Logical Channels for Band groups #1 – #4. • Can avoid Band group #2 when interference from U-NII is present.

  10. Preamble Pattern

  11. Packet detection C0~C7: {＋ － － － ＋ ＋ － ＋} - + + - A0~A15: {＋ ＋ ＋ ＋ － － ＋ ＋ － － ＋ － ＋ － ＋ ＋} - - + - + + + + - + + +

  12. Packet detection {＋ ＋ ＋ ＋－ － ＋ ＋ － － ＋ －＋ － ＋ ＋}

  13. Packet detection {＋ － － － ＋ ＋ － ＋} {＋ ＋ ＋ ＋ － － ＋ ＋ － － ＋ － ＋ － ＋ ＋}

  14. Frame Synchronization

  15. Frame Synchronization • Frame synchronization • Find the precise moment of when individual OFDM symbols start and end. • Typical algorithm • Using know preamble sequences • The refinement is performed by calculating the cross-correlation of the receiver signal and the know preamble sequences • Using the cycle prefixes • This algorithm use maximum likelihood estimation to find the symbol time

  16. PLCP Preamble

  17. Find Boundary • 利用頻率同步的方法，及PS與FS交接處有正負號的差異，會使延遲相關得到的值，在實部會有正負號的差異，藉此將前後兩次得到的值，符號取出來做XOR即可找尋。 + + + + - - -

  18. Frame Synchronization

  19. Frequency synchronization

  20. Coarse Frequency synchronization • Frequency offsets tracking • One of the main drawbacks of OFDM is its sensitivity to carrier frequency offset. The degradation is caused by two main phenomena : • Reduction of amplitude of the desired subcarrier • Inter carrier interference caused by neighboring subcarrier • The frequency offsets must be corrected to compensate these phenomena • Typical algorithm • Data-aided algorithm • These methods are base on preamble embedded into the transmitted signal • Cyclic prefix based algorithm • Use the inherit structure of the OFDM signal provided by the cyclic prefix

  21. Time Domain Approach • TFC = 1 165 495

  22. Cn mn rn C | |2 ( )* Pn ( )2 Z-D P delay correlate • Using correlator: • From the delay correlate structure, the decision is calculate as

  23. Time Domain Approach • Let D be the delay between the identical samples of the two repeated symbols.

  24. Time Domain Approach • Frequency error estimator is formed as • For UWB band#1

  25. Coarse Frequency synchronization • Frequency error estimator is formed as

  26. Coarse Frequency synchronization • Packet Error Rate as a function of for the 200 Mbps data rate of MB-OFDM UWB system with coarse frequency synchronization performance in CM1.

  27. Phase Tracking

  28. Tracking • Frequency estimation is not a perfect process, so there is always some residual frequency error. The main problem of the residual frequency offset is constellation rotation.

  29. Tracking • Transmission signal : • Receiver signal : : frequency offset

  30. Tracking • After CFO : : residual frequency offset • 非常小且會隨 n 而變的值，但因為變化非常緩慢，所以我們可以在一個OFDM symbol內視為是一個常數。

  31. Phase Tracking • Carrier phase tracking • Frequency estimation is not prefect process, so there is always some residual frequency error. The main problem of the residual frequency offset is constellation rotation • Typical algorithm • Data-aided carrier phase tracking • These special subcarriers are referred to as pilot subcarriers • Twelve predefined subcarriers among the transmitted data are referred as pilots in 802.15.3a.

  32. Phase Tracking • Thereceived pilot subcarrierwhere • n : OFDM symbol index • k : Sub-carrier index • : Channel frequency response • : Pilot sub-carrier • : Residual frequency error

  33. Data-aided carrier phase tracking • phase compensate :

  34. Phase Tracking

  35. Phase Tracking • Packet Error Rate as a function of for the 200 Mbps data rate of MB-OFDM UWB system with/without phase tracking performance in CM1.

  36. Channel Estimation

  37. Singal Model • 如果假設有i個通道與N個估測信號，我們可以做下面的運算來達成目標，令 為接收的N個估測符元(Channel Estimation Symbols)經過傅氏轉換後的訊號， 為發送之連續符元， 為第i個通道之頻率響應， 為第i個通道第n個符元之雜訊，接收的信號可表示成下式 其中 ， ， ， ，皆為頻域上l點的一維矩陣，l表示IFFT與FFT的點數

  38. LS Algorithm • LS algorithm

  39. Compensation • 現在我們所使用的方式 : 因為系統是QPSK的系統，所以在演算法的設計上，我們採用只補償相位的方式即在接收信號經過FFT後再乘上一個

  40. Channel Estimation

  41. Channel Estimation • Packet Error Rate as a function of for the 200 Mbps data rate of MB-OFDM UWB system with Channel Estimation performance in CM1.

  42. Zero-Padded Prefix • Using a zero-padded (ZP) prefix instead of a cyclic prefix is a well-known and well-analyzed technique. • Recall that the OFDM with cyclic prefix is created by pre-appending the last 32 samples of IFFT output: • A ZP-OFDM signal is created by pre-appending 32 zeroes to the IFFT output.

  43. Zero-Padded Prefix • A Zero-Padded MB-OFDM has the same multi-path robustness as a system that uses a cyclic prefix (60.6 ns of protection). • The receiver architecture for a zero-padded multi-band OFDM system requires only a minor modification.

  44. Zero-Padded Prefix • Zero padded prefix removes the structure in the transmitted signal No Ripples in the PSD. • Power spectral density for a ZP-OFDM signal: • Hence, a Zero-padded Multi-band OFDM system does NOT require any back-off at the transmitter.

  45. Zero-Padded Prefix • Packet Error Rate as a function of copy sample for the 200 Mbps data rate of MB-OFDM UWB system with Zero-Padded Prefix performance in CM4 and .

  46. Channel Model • Environment setup : AWGN : No channel estimation

  47. Link budget of MB-OFDM system

  48. Simulation Result(53.3 Mbps) • For a packet error rate of less than 8% with a PSDU of 1024 bytes

  49. Simulation Result(106.7 Mbps)

  50. Simulation Result(200 Mbps)

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