1. Impulse Burst Position Detection and Channel Estimation Scheme for OFDM Systems 高永安 老師 學生：吳林達 報告日期： 2006/5/18

2. Jukka Rinne, Ali Hazmi, Student Member, IEEE, and Markku Renfors, Senior Member, IEEE,” Impulse Burst Position Detection and Channel Estimation Schemes for OFDM Systems,” IEEE Transactions on Consumer Electronics, Vol. 49, No. 3, AUGUST 2003

3. Outline Introduction Channel estimation step Pre-estimation method MSE analysis Simulation environment(1) Channel model Implementation method Simulation environment(2) Simulation result

4. Introduction(1) Impulse noise is a common impairment in a communications systems arising, e.g., from motors or lightning. Impulse noise ： This model can be physically thought of as each transmitted data symbol being hit independently by an impulse with probability p and with a random amplitude g(gauss). OFDM is inherently more immune to this form of impairment when compared to single carrier modulation.

5. Introduction(2) The idea is to use pilots of the other (previous and future) symbols to construct reliable channel estimates We study the limitations and performances of those approaches in terms of MSE and BER in the case of single frequency network (SFN) hilly terrain static and mobile cases.

6. Channel estimation step1 1. Carry out the channel estimation in time domain. 2. Carry out channel estimation in frequency domain. 3. Compensate channel on data-carriers.

8. Channel estimation step2 pre-estimation: 1. Carry out pre-estimation of pilot of burst contaminated symbol in time or frequency domain using impulse noise free symbols. 2. Use conventional estimation.

9. Method #1: Four Away OFDM Symbols

10. Method #2: Six Pilots Spacing

11. Method #3: Twelve Pilots Spacing

12. MSE analysis environment The symbol contains impulse burst Other symbols are assumed to be impulse free Mean Square Error (MSE) is calculated analytically after pre-estimation

13. In general MSE can be written as:

14. In the case of method #1, For the method #2, the estimate at pilots (of both neighboring symbols) is calculated first by and then pre-estimation interpolation is used. In the above equations, AWGN and ICI exist in the pilots, i.e., before pre- estimation.

15. For method #3, it can be found that where AWGN and ICI are defined after pre- estimation

16. 條件： Assume all the pilots contain the same amount of estimation errors. MSE for method #1 ：

17. for method #2, the MSE at the pilots is given by: The total MSE in the pilot estimates after pre- estimation can be found from: The optimum pre-estimation filter coefficients are given by:

18. For method #3, the MSE at the pilots can be found from: The total MSE for method #3 after combining the pilots is given by:

19. The ICI power used in the above equations can be expressed in the case of wide sense stationary uniformly distributed uncorrelated scatters (WSSUS)

20. Simulation environment(1)

21. MSE vs. Doppler frequency for different pre- estimation methods Interpolator length :91 Max delay of the channel:.

22. Channel model Impulse noise model: A standard Bernoulli-Gaussian process is used to model impulsive noise Burst length L=500 samples corresponding in 8k mode DVB-T system to the duration of 54.5 For easier implementation, we suppose that the impulse burst occurs exactly once in every 8th OFDM symbol.

23. Time-Frequency Selective Channel: SFN configuration, based on DVB-T channel model for hilly terrain reception. Two transmitters, both paths to the receiver are modeled as a hilly terrain, static and mobile reception. Received powers from transmitter were defined relatively to the most powerful signal (and first to arrive). A value of 0 dB for both paths has been chosen. The channel model is mainly parameterized by the delay and the Doppler frequency when we consider an SFN mobile channel.

24. Implementation method(1) Four Away OFDM Symbols (FOA) 適用條件： impulse bursts occur quite rarely. In the case of static single frequency network (SFN), this method is very effective and simple to implement.

25. Implementation method(2) Six Pilot Spacing (SPS) To tolerate larger Doppler frequencies An interpolator designed for a delay spread of 1024 samples is used to interpolate the channel coefficients.

26. Implementation method(3) Twelve Pilot Spacing (TPS) An interpolator designed for a delay spread of 512 samples is used based on the twelve pilot spacing pattern.

27. Simulation environment(2) 8k DVB-T system model Sub-modulation:64QAM Code rate:1/2 or 2/3 Impulse noise burst length : L=500samples(54.5 ) Interpolator length:125 Max delay spread = respectively for method2 and method3 SNR=30dB

28. BER performance for three method in SFN static channel(1)

29. BER performance for three method in SFN static channel(2)

30. BER performance for three method in SFN static channel(3)

31. BER performance for three method in SFN mobile channel(1) code rate:1/2 64QAM-OFDM

32. BER performance for three method in SFN mobile channel(2) code rate:2/3 64QAM-OFDM

33. Tolerability of the three methods in Doppler frequency and delay spread cases