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

2. Outline Synchronization Channel Estimation Zero-Padded Prefix
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
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. delay correlate Using correlator:
From the delay correlate structure, the decision is calculate as
Z-D
( )* C P
| |2
( )2 mn Cn Pn rn

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 a.

32. Phase Tracking The received pilot subcarrier where
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 : CM1 CM2 CM3 CM4 Characteristics LOS
AWGN : No channel estimation
CM1
CM2
CM3
CM4
Characteristics
LOS
(0-4m)
NLOS
(4-10m)
(Extreme)
RMS delay
5.28 ns
8.03 ns
14.28 ns
25 ns
Number of paths 24
36.1
61.54
122.8

47. Link budget of MB-OFDM system
Information data rate
53.3 80
106.7
160
200
320
480
Mb/sec
Average Tx power
-10.3
dBm
Tx antenna gain
dBi
geometric center frequency of waveform
3882
MHz
Path loss at 1 meter
44.2 dB
distance 10 4 3 2
meters
Path loss at d meter 20 12 6
Rx antenna gain
Rx power
-74.5
-66.5
-64.0
-60.5
Average noise power per bit
-96.7
-95.0
-93.7
-92.0
-91.0
-88.9
-87.2
Rx Noise Figure Referred to the Antenna Terminal
6.6
-90.1
-88.4
-87.1
-85.4
-84.4
-82.3
-80.6
Required Eb/N0
4.1
4.2
4.7
4.9
Implementation Loss
2.5
Link Margin
9.0
7.2
6.0
10.7
11.1
12.2
Proposed Min. Rx Sensitivity Level(sensitivity)
-83.5
-81.7
-80.5
-78.7
-77.2
-75.1
-72.7

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)

51. Conclusion
The baseband signal processing algorithms include time domain synchronization, frequency domain synchronization, and channel estimation, and zero padded process.
The platform of MB-OFDM system with mandatory data rate (53.3, and 200 Mb/s) has been developed. Also, it approached the sensitivity of MB-OFDM proposal of version 0v9 by MATLAB verification.
The simulations incorporate losses due to packet detection, carrier frequency offset, phase tracking and channel effect.