1. OFDMA with Optimized Transmit and Receive Waveforms for Better Interference Immune Communications in Next Generation Radio Mobile Communication Systems Mohamed Siala Professor at SupCom Mohamed.siala@supcom.rnu.tn ITU Workshop on "ICT Innovations in Emerging Economies" (Geneva, Switzerland, 18 September 2013) Geneva, Switzerland, 18 September 2013

2. Presentation Outline Problem statement and proposed solution Overview on single carrier communications Radio Mobile Channel Characteristics: Multipath and Delay Spread Sensitivity to Delay Spread Subcarrier Aggregation: Multicarrier Systems Delay-Spread ISI Immune Communications: Guard Interval Radio Mobile Channel Characteristics: Doppler Spread Considerations on Subcarrier Number Sensitivity to Multiple Access Frequency Synchronization Errors Quality of Service Evaluation and Optimization: SINR Transmit and Receive Waveforms Optimization Results 2 Geneva, Switzerland, 18 September 2013

3. Problem statement and proposed solution Next generation mobile communication systems will operate on highly dispersive channel environments: Very dense urban areas High multipath delay spreads Very high carrier frequencies + high mobile velocities High Doppler spreads OFDMA/OFDM rely on frequency badly localized waveforms High sensitivity to Doppler spread and frequency synchronization errors due to multiple access Increased inter-carrier and -user interference Significant out-of-band emissions Requirement of large guard bands with respect to other adjacent systems Optimization of transmit and receive waveforms for QoS optimization through interference reduction 3 Geneva, Switzerland, 18 September 2013

4. Bandwidth (w) Carrier frequency (fc) Overview on Single Carrier Communications 1/3 4 Frequency (f) Time (t) Power Symbols Symbol duration (T) Symbol rate (R) Geneva, Switzerland, 18 September 2013

5. Bandwidth (w) Symbol duration (T) Overview on Single Carrier Communications2/3 5 Frequency (f) Time (t) Power Symbol rate (R) Geneva, Switzerland, 18 September 2013

6. Overview on Single Carrier Communications3/3 6 Frequency (f) Time (t) Power Symbol duration (T) Bandwidth (w) Geneva, Switzerland, 18 September 2013

7. Radio Mobile Channel Characteristics: Multipath and Delay Spread1/4 Geneva, Switzerland, 18 September 2013 7 Frequency (f) Time (t) Power Transmitted Symbol Shortest path Received symbol replica Received symbol replica Received symbol replica Longest path

8. Radio Mobile Channel Characteristics: Multipath and Delay Spread 2/4 Geneva, Switzerland, 18 September 2013 8 Frequency (f) Time (t) Power Delay spread Shortest path Longest path

9. Radio Mobile Channel Characteristics: Multipath and Delay Spread3/4 Geneva, Switzerland, 18 September 2013 9 Transmitted symbols T Frequency (f) Time (t) w Power fc

10. Radio Mobile Channel Characteristics: Multipath and Delay Spread4/4 Geneva, Switzerland, 18 September 2013 10 Frequency (f) Time (t) w Received symbols Tm Delay spread Time (t) Power Inter-Symbol Interference (ISI) fc

11. Radio Mobile Channel Characteristics: Sensitivity to Delay Spread 1/3 Geneva, Switzerland, 18 September 2013 11 T Frequency (f) Time (t) w Power fc T Frequency (f) Time (t) w Power fc

12. Radio Mobile Channel Characteristics: Sensitivity to Delay Spread2/3 Geneva, Switzerland, 18 September 2013 12 Frequency (f) Time (t) w Tm Delay spread Time (t) Power ISI fc Algiers, Algeria, 8 September 2013 Frequency (f) Time (t) w Tm Delay spread Time (t) Power ISI fc

13. Radio Mobile Channel Characteristics: Sensitivity to Delay Spread3/3 The channel delay spread Tm is independent of the transmission symbol period T Reduced bandwidth w Pro: Increased T Better immunity (reduced sensitivity) to ISI Con: Reduced symbol rate R Aggregate together as many reduced bandwidth F subcarriers as needed to cover the whole transmission bandwidth w: Reduced subcarrier bandwidth F Increased symbol period T = 1/F Reduced sensitivity to ISI Unchanged global bandwidth w Unchanged transmission rate Geneva, Switzerland, 18 September 2013 13

14. Subcarrier Aggregation: Multicarrier Systems T Frequency (f) Time (t) T Frequency (f) Time (t) w fc F=1/T Geneva, Switzerland, 18 September 2013

15. Delay-Spread ISI Immune Communications: Guard Interval 1/6 T Frequency (f) Time (t) w fc F Tg Guard interval insertion Tg Tm Symbol occupancy FT > 1 Reduced symbol rate Geneva, Switzerland, 18 September 2013 15

16. Delay-Spread ISI Immune Communications: Guard Interval 2/6 No guard interval insertion F = 1/T Symbol occupancy FT = 1 No symbol rate loss Still some ISI which can be reduced by reducing F, or equivalently, increasing T = 1/F or equivalently, increasing the number of subcarriers N = w/F ISI immune communications Perfectly ISI immune communications T = 1/F+Tg FT > 1 Symbol rate loss Symbol rate loss reduced by reducing F, or equivalently increasing N Geneva, Switzerland, 18 September 2013 16

17. Delay-Spread ISI Immune Communications: Guard Interval 3/6 T Frequency (f) Time (t) w F Tg Tm FT N=4 Total duration Geneva, Switzerland, 18 September 2013

18. Delay-Spread ISI Immune Communications: Guard Interval 4/6 Frequency (f) Time (t) w F Tg Tm N=8 T FT Total duration Geneva, Switzerland, 18 September 2013

19. Delay-Spread ISI Immune Communications: Guard Interval 5/6 Frequency (f) Time (t) w F Tg Tm N=16 T Total duration FT Geneva, Switzerland, 18 September 2013

20. Delay-Spread ISI Immune Communications: Guard Interval 6/6 Increasing the number of subcarriers N, or equivalently, reducing the subcarrier spacing F: (Pro) Increases spectrum efficiency (FT ) for a given tolerance to channel delay spread (Tg Tm) (Pro) Increases tolerance to multiple access time synchronization errors (Tg ) for a given spectrum efficiency (FT unchanged) (Con) Increases sensitivity to propagation channel Doppler spread Bd Increase Inter-Carrier Interference (ICI) (Con) Increase sensitivity to multiple access frequency synchronization errors Geneva, Switzerland, 18 September 2013 20

21. Radio Mobile Channel Characteristics: Doppler Spread1/3 21 Frequency (f) Time (t) Power Transmitted Symbol Mobile speed (v) w Received symbol replica -fd Received symbol replica 0 Received symbol replica +fd

22. Radio Mobile Channel Characteristics: Doppler Spread2/3 22 Subcarrier spacing F Frequency (f) Time (t) w Power Frequency (f) Transmitted symbols Geneva, Switzerland, 18 September 2013

23. Radio Mobile Channel Characteristics: Doppler Spread3/3 23 F+Bd Frequency (f) Time (t) Power Frequency (f) Received symbols ICI Bd = 2 fd Doppler spread Geneva, Switzerland, 18 September 2013

24. Considerations on Subcarrier Number The Doppler spread Bd is proportional to the mobile speed v and the carrier frequency fc Any increase in carrier frequency leads to an increase in Doppler spread Any increase in the number of subcarriers: Increases the guard interval Tg and the symbol period T for a constant spectrum efficiency 1/FT (Pro) Better tolerance to channel delay spread Reduced ISI (Pro) Slight decrease in spectrum efficiency due to the insertion of a guard interval Decreases the subcarrier spacing F (Con) Increased sensitivity to the Doppler spread Bd Increased ICI (Con) Reduced tolerance to multiple access frequency synchronization errors 24

25. Sensitivity to Multiple Access Frequency Synchronization Errors 1/2 Farthest mobile Nearest mobile Power Frequency (f) Received symbols: Perfect user synchronization Large Power gap Perfect synchronization No Inter-User Interference (IUI) Geneva, Switzerland, 18 September 2013 25

26. Sensitivity to Multiple Access Frequency Synchronization Errors 2/2 Farthest mobile Nearest mobile Power Frequency (f) Received symbols: Imperfect user synchronization Large IUI Imperfect synchronization Large Inter-User Interference (IUI) Large Power gap Geneva, Switzerland, 18 September 2013 26

27. Quality of Service Evaluation and Optimization: SINR1/2 Frequency (f) Time (t) F T ISI IUI User 1 User 2 ICI SINR: Signal-to-Noise Plus Interference Ratio Geneva, Switzerland, 18 September 2013 27

28. Quality of Service Evaluation and Optimization: SINR2/2 Signal-to-Interference plus Noise Ratio (SINR): Conventional multicarrier use badly frequency localized waveforms: (con) High sensitivity to Doppler spread and frequency synchronization errors (con) Out-of-band emissions Large guard band to protect other systems Transmit and receive waveforms optimization through SINR maximization: (pro) Minimized ISI + ISI + IUI Better transmission quality Reduced out-of-band emissions Small guard bands required to protect other systems 28

29. Transmit and Receive Waveforms Optimization Results1/6 29 5.9 dB Channel spread factor

30. Transmit and Receive Waveforms Optimization Results2/6 30

31. Transmit and Receive Waveforms Optimization Results3/6 31

32. Transmit and Receive Waveforms Optimization Results4/6 Geneva, Switzerland, 18 September 2013 32

33. Transmit and Receive Waveforms Optimization Results5/6 Geneva, Switzerland, 18 September 2013 33 > 40 dB Transmit Waveform

34. Transmit and Receive Waveforms Optimization Results6/6 Geneva, Switzerland, 18 September 2013 34 Transmit Waveform