1. UWB Synchronization Hui-Min Yeh

2. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Outline Introduction Code synchronization Typical acquisition scheme Typical search strategies Definition of Hit set Transmitter design Hybrid TH/DS signal format Receiver design Proposed search algorithms Joint BRS-NCS search Joint RPS-NCS search Proposed acquisition scheme Simulation results Conclusions

3. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Power delay profile Time The objective of the signal synchronization is to properly align the received signal by correctly estimating the random delay

4. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Introduction Code synchronization (TH code; DS code): To enable the lower BER of data demodulation, the template signal should be aligned with the received signal, the code alignment is so-called code synchronization process. Code synchronization can be spilt into two parts Code acquisition It is a coarse code acquisition, to resolve the code phase error within certain range. Code tracking It is a fine tuning process, to guarantee the timing error below an acceptable level.

5. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Acquisition strategy : The search for acquisition is based on the auto- correlation properties of the applied the codes, the auto-correlation is high if the receiver is synchronized and low in other situations [5]. MAX criterion (Maximum selective): TC criterion (Threshold Crossing): MAX/TC criterion:

6. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Before any data can be received in an UWB communication, the receiver must synchronize on the transmission. Receiver structures Noise template signal Reference template signal Packet data Synchronization on (known) code Reception and processing data Preamble Data Sequence for synchronization Data can have specific coding-> communication can not be tapped

7. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Code synchronization Find the best fit between the code and the received signal

8. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Typical acquisition system The receivers reference signal generator will shift and guess the code boundary of received signal, and the AWGN noise will effect the performance. Correlator 3 4 & 5

9. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Why use RAKE receiver? More than one hypothesized phase can be considered as an estimated timing delay for a coarse acquisition

10. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Definition of Hit set Hit set definition: The definition of Hit set is a critical issue. When the threshold setting is low, the noise effect on the false alarm probability will increase. Oppositely, when the threshold setting is high, the mean acquisition time will increase.

11. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Ex: The periodicity of TH code =4, frame duration, that is Nh=128, Tc = 1 nsec, normalized pulse energy =1,CM1(noise free), search space = 512 cells, Th=2, EGC receiver (20 fingers) Peak value Partial correlation energy 12 N True phase Hit set

12. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Rake fingers = 20, search space = 512 cells, CM1

13. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Search strategies What is the efficient search algorithm? Serial or Parallel Typical serial search algorithms [1] Linear Search (LS) Random Permutation Search (RPS) Bit Reversal Search (BRS) Ideal mean stopping time: Linear Search (LS) Random Permutation Search (RPS) Bit Reversal Search (BRS)

14. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Bit Reversal Search The search algorithm is described by assuming that N is a power of 2. The order of search positions in the bit reversal search algorithm is decided by bit reversing For example: Let the integer of N is equal to 8 (2^3) Search locations for N = 2 3 Reorder search locations by bit reversing Bit Reversing Decimal 01234567 Binary000001010011100101110111 Decimal 04261537 Binary000100010110001101011111

15. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. The ideal and normalized mean stopping time vs. the parameter H/N for three serial search algorithms (N=512 cells)

16. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Bit Reversal Search algorithm, code length=4, Nh=128, CM1(noise free), search space = 512 cells, EGC receiver (20 fingers)

17. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Outline Introduction Code synchronization Typical acquisition scheme Hit definition Typical search strategies Transmitter design Hybrid TH/DS signal format Receiver design Proposed search algorithms Joint BRS-NCS search Joint RPS-NCS search Proposed acquisition scheme Simulation result Conclusions

18. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Frame (C 0 )Frame (C 1 ) Frame (C Nth-1 ) (TH-sequence)(Repeat N T times) 1s Symbol (N ds *T f ) TfTf Next symbol Transmitter design: Hybrid TH/DS signal format

19. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. The variation of power spectral density (PSD) between the pure time hopping sequences and hybrid TH/DS signals No TH coding The periodicity of TH code is equal to the number of pulses per symbol The periodicity of TH code is equal to the number of pulses per symbol Hybrid TH/DS signal The hybrid TH/DS signal format method not only speeds up the code acquisition, but also improves the interference to other co-existing systems [7].

20. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. UWB signals with no Time-Hopping coding Parameters: 10 symbols; number of pulses per symbol ( ) =64; pulse repetition time ( ) =10 nsec; chip duration ( ) = 1 nsec The transmitter power is concentrated at multiples of pulse repetition frequency. Time (ns) Amplitude

21. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. UWB signals with Time-Hopping coding Consider the same parameters The periodicity of TH code ( ) is equal to the number of pulses per symbol, that is, The PSD of the signals is composed of spectral lines at the distances of The transmitted power is concentrated at multiples of symbol repetition frequency.

22. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. UWB signals with hybrid TH/DS signals Consider the same parameters a) Short TH code with ; repeat N T =8 It will increase a lot of spectral lines due to the repeat operation b) Short TH code with ; repeat N T =8; The polarity of pulses per symbol is scrambles by DS code

23. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Outline Introduction Code synchronization Typical acquisition scheme Hit definition Typical search strategies Transmitter design Hybrid TH/DS signal format Receiver design Proposed search algorithms Joint BRS-NCS search Joint RPS-NCS search Proposed acquisition scheme Simulation result Conclusions

24. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Proposed Joint Search Algorithms Joint BRS-NCS Search Joint RPS-NCS Search Non consecutive search (NCS) criterion: The non consecutive search strategy is proposed owing to more than one HIT phase in multi-path channel models. The non consecutive search can achieve a rapid acquisition by testing search locations with a step size D which is greater than one cell. The cells in total search space are so called uncertainty region that can be divided into blocks This will reduce the search time required to acquire the location of hit set from an initial search cell, but it could also increase the miss probability.

25. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. LI-NCS (Linear Increasing NCS) In order to avoid the miss search, we propose a linear increasing NCS (LI-NCS) approach. The search equation can be expressed as The LI-NCS approach can be described as following:  Set initial loop =1, and check blocks. The number of test cells are ‚ If the correlation output of each block in this loop is lower than threshold, then go to the step (3). If the correlation output of one block in this loop is higher than threshold. then the search procedure is DONE. ƒ Set loop = loop + 1, and also check blocks, the number of cells are, then go to step (2)

26. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. An example of the LI-NCS search approach Assume that search space N=12, hit set =[7 8 9 10 11], block size D = 4, 0 1 234 5 678 9 10101

27. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Joint BRS-NCS search procedure a) search space N=48, hit set H=8, b) divided into 8 blocks, each block with D = 6 Correct Symbol Boundary D cells =: New search location (a) (b) (0)(4) (2) (6)(3)(1)(5)(7) Search space N

28. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Receiver design : Acquisition scheme Received signal Find DS-boundary (get symbol boundary) Coarse TH-boundary acquisition Fine acquisition (First stage) (Second stage) ACQ1 ACQ2 Two-stage acquisition scheme TH code acquisition DS code acquisition

29. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Set new search location based on Joint Search Algorithm (new shift ) Template signal generator Hit No Hit Z (RAKE receiver with parallel correlators) TC #1 Second Stage First Stage (Coarse Acquisition) One branch correlator Maximum path amplitude selective Roughly find TH-boundary (Fine Acquisition)

30. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Fine Acquisition Procedure: Left directionRight direction Starting point Step1: The terminating point of coarse acquisition process is the starting point of fine acquisition. Step2 : The new search window in fine acquisition process is equal to the double Hit set size. Step3 : The fine acquisition process searches both right and left directions from the starting point of fine acquisition with one branch correlator to acquire the strongest path. The search range of each direction is equal to the size of hit set. Step4 : We utilize the maximum selective criterion to select the strongest path amplitude Step5 : Finally, the fine acquisition process passes the parameter on to the second stage.

31. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Set step size=: time- hopping code length and new search location based on Joint Search Algorithm location (new shift ) Template signal generator Hit No Hit Z (RAKE receiver with parallel correlators) TC #2 Found DS-boundary (Found symbol boundary simultaneously) Second Stage

32. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Outline Introduction Code synchronization Typical acquisition scheme Hit definition Typical search strategies Transmitter design Hybrid TH/DS signal format Power spectral density (PSD) Receiver design Proposed search algorithms Joint BRS-NCS search Joint RPS-NCS search Proposed acquisition scheme Simulation results

33. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Simulation cases Two-stage vs. one stage Comparison of search strategies Two-step approach MAI case

34. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Channel model 1&4 The first path of CM1 we consider has the strongest amplitude gain, and the tenth path of CM4 has the strongest amplitude gain in our simulation. The strongest path

35. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. SNR vs. Detection probability for the second stage in CM1 Assume that the first stage finds the correct boundary.

36. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Mean stopping time of two acquisition schemes as a function of threshold parameter A Simulation parameters:

37. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. The mean stopping time of Joint BRS-NCS /Joint RPS-NCS method versus threshold setting for step size D=4, D=8, and D is approximated to hit set.

38. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Comparison of performance in terms of Mean stopping time versus threshold setting for proposed search algorithms and bit reversal search algorithm.

39. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. A statistical number as function of offset value for 5000 trials, a) SNR = 10 dB, coarse acquisition result, b) considering fine acquisition result, in CM1 Single-user Multi-user

40. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. SNR = 20 dB, 5000 trials, CM4 Single-user Multi-user

41. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. MAI vs Detection probability (CM1) Simulation results for detection probability of the UWB channel model (CM1), as a function of the number of interfering users N u -1

42. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. MAI vs Detection probability (CM4) Simulation results for detection probability of the UWB channel model (CM4), as a function of number of interfering users N u -1

43. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Simulation results of detection probability for different lengths of in UWB channel model (CM1), as a function of interfering users (N u -1), SNR=20dB

44. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Conclusions The mean stopping time of two-stage acquisition scheme is simulated and it is evident to see that the two-stage acquisition scheme outperforms the conventional one stage acquisition scheme. By simulation results, we can see that the Joint Search Algorithms have lower mean stopping time. We propose a two-step approach which is composed of coarse step and fine step to achieve a fine code acquisition in first stage. Adding more users to the systems is investigated by computer simulations.

45. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. References [1] E. A. Homier and R. A. Scholtz, Rapid acquisition of ultra-wideband signals in the dense multipath channel, Proceeding of 2002 IEEE Conference Ultra Wideband Sys. Tech, (Baltimore, MD), pp. 105-109, 2002. [2] J. Oh, S. Yang, and Y. Shin, A Rapid Acquisition Scheme for UWB Signals in indoor wireless channels, IEEE WCNC 04, Wireless Commun. and Networking Conference, vol. 2, 2004. [3] S. Gexici, E. Fishler, F. Kobayashi, H. V. Poor, and A. F. Molisch, A rapid Acquisition Technique for Impulse Radio, in Proc. IEEE Pacific Rim Conference Commun., Comput., Signal Process., pp. 627-630, Aug 2003. [4] L. Reggiani, G. M. Maggio,Rapid Search Algorithms for Code Acquisition in UWB Impulse Radio Communications, IEEE Commun. Journal, vol. 23, pp. 898-908, May 2002. [5] G. E. Corazza, On the MAX/TC criterion for code acquisition and its application to DS-SSMA systems, IEEE Trans. on Commun., vol. 44, pp. 1173-1182, Sept. 1996. [6] M. Z. Win, R. A. Scholtz, Impulse Radio : How It Works, IEEE Commun. Letters, vol. 2, No. 1, pp. 36-38, Jan. 1998.

46. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. [7] S. Aedudodla, S. Vijayakumaran, T. F. Wong, Rapid Ultra-wideband Signal Acquisition, IEEE Wireless Commun. and Networking Conference, vol. 2, pp 1148-1153, March 2004. [8] O. S. Shin and K. B. Lee, Utilization of multi-paths for spread- spectrum code acquisition in frequency-selective rayleigh fading channels IEEE Journal Trans. on Commun., Apr. 2001. [9] S. L. Han, S. O. Hyun, E. K. Chang, Code acquisition for the DS- CDMA RAKE receiver in a multi-path fading channel, Proceeding of IEEE Singapore International Conference, pp. 215-219, July 1995. [10] V. Saravanan, F. W. Tan,Equal gain combining for acquisition of UWB signals, MILCOM 03, IEEE Military Commun. Conference, vol. 2, pp.880-885, Oct. 2003.