Initial Ranging procedure in WiMAX standard

1. Initial Ranging procedure in WiMAX standard Student:Chung-ming Li

2. Outline • Introduction • WiMAX frame structure • Down-link timing synchronization • Initial ranging • Timing offset • System design • conclusion

3. Introduction • In OFDMA, it is required that all transmission from MS should arrive BS at the same time. • Imagine a cell size of 10Km, we have round trip time of 66.6 us. • UL data must arrive BS within 0 to 66.6 us. • The whole network synchronization refers to BS clock.

4. Introduction • MSs are distributed all over the cell. • A MS at cell edge receive data quite late and transmits data very early , being compared with MS close to BS. • When a new MS is seeking entry into the network, the MS has no idea as to what time or power should be used for transmitting the initial signal.

5. Introduction • This is the BS’s job to detect this new MS. • Find the misalignment between the new MS ,and then send response to correct it. • The following slides start with a brief description about how WiMAX handles this situation.

6. WiMAX frame structure • TTG and RTG are 105.714 μs and 60 μs, respectively.

7. WiMAX frame structure

8. Initialization AGC Stage Normal AGC Stage DL UL DL UL DL UL DL UL DL UL 5ms 5ms 5ms t Power-on happens at a random time Enable a 5ms counter Measure power Energy detection Yes Several tunes Power on AGC Yes Packet Detection ED AGC Yes PKT AGC Enable a 5ms counter Down-link timing synchronization

9. Down-link timing synchronization • Oversampling

10. Down-link timing synchronization • SRRC

11. Down-link timing synchronization

12. Down-link timing synchronization must be integer !!

13. Down-link timing synchronization • Packet detectionby cyclic prefix FFT_size CP CP

14. Down-link timing synchronization

15. Down-link timing synchronization • Matched filter is with an eye to maximizing SNR

16. Down-link timing synchronization

17. Initial ranging • In WiMAX, code division multiple access( CDMA) codes are used to detect new MS. • A new MS will transmit one CDMA code. • The BS is not only to detect the new MS but also to calculate its timing,frequency and power offset.

18. Initial ranging • Code length=144, 256 sets, using BPSK modulation

19. Timing offset Delay Receive data Cyclic Prefix Cyclic Prefix FFT window BS clock

20. Timing offset FFT Signal in

21. Timing offset without timing advance with timing advance

22. System Design

23. Conclusion • The BS detects the new MS and calculates the timing offset, then corrects MS transmitting parameters. • Taking the round trip time intoconsideration,the maximal cell size should be 6.75 Km.