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OFDMA with Optimized Waveforms for Interference
Immune Communications in Next Generation
Cellular Systems
Mohamed Siala
Pr...
Presentation Outline
Problem statement and proposed solution
Overview on single carrier communications
Radio Mobile Channe...
Problem statement and proposed
solution
Next generation mobile communication systems will
operate on highly dispersive cha...
Bandwidth (w)
Carrier frequency (fc)
Overview on Single Carrier
Communications 1/3
4
Frequency (f)
Time (t)
Power
Symbols
...
Bandwidth (w)
Symbol duration (T)
Overview on Single Carrier
Communications 2/3
5
Frequency (f)
Time (t)
Power

1
w
T
 ...
Overview on Single Carrier
Communications 3/3
6
Frequency (f)
Time (t)
Power
Symbol duration (T)   
1
w T R
T
Bandwidth...
Radio Mobile Channel Characteristics:
Multipath and Delay Spread 1/4
7
Frequency (f)
Time (t)
Power
Transmitted Symbol
Sho...
Radio Mobile Channel Characteristics:
Multipath and Delay Spread 2/4
8
Frequency (f)
Time (t)
Power
Delay spread
Shortest ...
Radio Mobile Channel Characteristics:
Multipath and Delay Spread 3/4
9
Transmitted symbols
T
Frequency (f)
Time (t)
w
Time...
Radio Mobile Channel Characteristics:
Multipath and Delay Spread 4/4
10
Frequency (f)
Time (t)
w
Received symbols
Tm
Delay...
Radio Mobile Channel Characteristics:
Sensitivity to Delay Spread 1/3
11
T
Frequency (f)
Time (t)
w
Time (t)
Power
fc
T
Fr...
Radio Mobile Channel Characteristics:
Sensitivity to Delay Spread 2/3
12
Frequency (f)
Time (t)
w
Tm
Delay spread
Time (t)...
Radio Mobile Channel Characteristics:
Sensitivity to Delay Spread 3/3
The channel delay spread Tm is independent of the
tr...
Subcarrier Aggregation: Multicarrier
Systems
T
Frequency (f)
Time (t)
T
Frequency (f)
Time (t)
wfc
F=1/T
Tunis, Tunisia, 2...
Delay-Spread ISI Immune
Communications: Guard Interval 1/6
T
Frequency (f)
Time (t)
w
fc
F
Tg Guard interval insertion
Tg ...
Delay-Spread ISI Immune
Communications: Guard Interval 2/6
No guard interval insertion 
F = 1/T  Symbol occupancy FT = 1...
Delay-Spread ISI Immune
Communications: Guard Interval 3/6
T
Frequency (f)
Time (t)
w
F
TgTm FT N=4
Total duration
Tunis,...
Delay-Spread ISI Immune
Communications: Guard Interval 4/6
Frequency (f)
Time (t)
w
F
TgTm N=8 
T 
FT 
Total duration...
Delay-Spread ISI Immune
Communications: Guard Interval 5/6
Frequency (f)
Time (t)
w
F
TgTm N=16 
T 
Total duration 
F...
Delay-Spread ISI Immune
Communications: Guard Interval 6/6
Increasing the number of subcarriers N, or equivalently,
reduci...
Radio Mobile Channel Characteristics:
Doppler Spread 1/3
21
Frequency (f)
Time (t)
Power
Transmitted Symbol
Mobile speed
(...
Radio Mobile Channel Characteristics:
Doppler Spread 2/3
22
Subcarrier spacingF
Frequency (f)
Time (t)
w
Power
Frequency (...
Radio Mobile Channel Characteristics:
Doppler Spread 3/3
23
F+Bd
Frequency (f)
Time (t)
Power
Frequency (f)
Received symbo...
Considerations on Subcarrier Number
The Doppler spread Bd is proportional to the mobile speed
v and the carrier frequency ...
Sensitivity to Multiple Access
Frequency Synchronization Errors 1/2
Farthest mobile
Nearest mobilePower
Frequency (f)
Rece...
Sensitivity to Multiple Access
Frequency Synchronization Errors 2/2
Farthest mobile
Nearest mobile
Power
Frequency (f)
Rec...
Quality of Service Evaluation and
Optimization: SINR 1/2
Frequency (f)
Time (t)
F
T
ISI
IUI
User 1
User 2
ICI
SINR: Signal...
Quality of Service Evaluation and
Optimization: SINR 2/2
Signal-to-Interference plus Noise Ratio (SINR):
Conventional mult...
Transmit and Receive Waveforms
Optimization Results 1/6
29
 0.01d mB T
 1.5FT
 30SNR dB

Waveform
Duration T
5.9 dB
Ch...
Transmit and Receive Waveforms
Optimization Results 2/6
30
 30SNR dB

Waveform
Duration T
 0.01d mB T
Transmit and Receive Waveforms
Optimization Results 3/6
31
 0.01d mB T
 30SNR dB
3
Waveform
Duration T
Transmit and Receive Waveforms
Optimization Results 4/6
32
 0.01d mB T
3
Waveform
Duration T
1.25FT 
/ 0.1dB F 
Transmit and Receive Waveforms
Optimization Results 5/6
33
 0.01d mB T
3
Waveform
Duration T
1.25FT 
/ 0.1dB F 
> 40 d...
Transmit and Receive Waveforms
Optimization Results 6/6
34
 0.01d mB T
3
Waveform
Duration T
1.25FT 
/ 0.1dB F 
Transm...
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Presentation at ITU Workshop on "ICT Innovations in Emerging Economies", OFDMA with Optimized Transmit and Receive Waveforms for Better Interference Immune Communications in Next Generation Radio Mobile Communication Systems

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Presentation on transmit and receive waveforms optimization for future 5G cellular communication systems at the ITU Workshop on "ICT Innovations in Emerging Economies", Geneva, Switzerland, 18 September 2013, entitled "OFDMA with Optimized Transmit and Receive Waveforms for Better Interference Immune Communications in Next Generation Radio Mobile Communication Systems."


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Presentation at ITU Workshop on "ICT Innovations in Emerging Economies", OFDMA with Optimized Transmit and Receive Waveforms for Better Interference Immune Communications in Next Generation Radio Mobile Communication Systems

  1. 1. OFDMA with Optimized Waveforms for Interference Immune Communications in Next Generation Cellular Systems Mohamed Siala Professor at Sup’Com Mohamed.siala@supcom.rnu.tn ITU Workshop on "ICT Innovations in Emerging Economies" (Tunis, Tunisia, 28 January 2014) Tunis, Tunisia, 28 January 2014
  2. 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 2Tunis, Tunisia, 28 January 2014
  3. 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 3Tunis, Tunisia, 28 January 2014
  4. 4. Bandwidth (w) Carrier frequency (fc) Overview on Single Carrier Communications 1/3 4 Frequency (f) Time (t) Power Symbols Symbol duration (T)  1 w T  1 R T Symbol rate (R) Tunis, Tunisia, 28 January 2014
  5. 5. Bandwidth (w) Symbol duration (T) Overview on Single Carrier Communications 2/3 5 Frequency (f) Time (t) Power  1 w T    1 w T R T  1 R T Symbol rate (R) Tunis, Tunisia, 28 January 2014
  6. 6. Overview on Single Carrier Communications 3/3 6 Frequency (f) Time (t) Power Symbol duration (T)    1 w T R T Bandwidth (w) Tunis, Tunisia, 28 January 2014
  7. 7. Radio Mobile Channel Characteristics: Multipath and Delay Spread 1/4 7 Frequency (f) Time (t) Power Transmitted Symbol Shortest path Received symbol replica Received symbol replica Received symbol replica Longest path Tunis, Tunisia, 28 January 2014
  8. 8. Radio Mobile Channel Characteristics: Multipath and Delay Spread 2/4 8 Frequency (f) Time (t) Power Delay spread Shortest path Longest path Tunis, Tunisia, 28 January 2014
  9. 9. Radio Mobile Channel Characteristics: Multipath and Delay Spread 3/4 9 Transmitted symbols T Frequency (f) Time (t) w Time (t) Power fc Tunis, Tunisia, 28 January 2014
  10. 10. Radio Mobile Channel Characteristics: Multipath and Delay Spread 4/4 10 Frequency (f) Time (t) w Received symbols Tm Delay spread Time (t) Power Inter-Symbol Interference (ISI) fc Tunis, Tunisia, 28 January 2014
  11. 11. Radio Mobile Channel Characteristics: Sensitivity to Delay Spread 1/3 11 T Frequency (f) Time (t) w Time (t) Power fc T Frequency (f) Time (t) w Time (t) Power fc Tunis, Tunisia, 28 January 2014
  12. 12. Radio Mobile Channel Characteristics: Sensitivity to Delay Spread 2/3 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 Tunis, Tunisia, 28 January 2014
  13. 13. Radio Mobile Channel Characteristics: Sensitivity to Delay Spread 3/3 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 13Tunis, Tunisia, 28 January 2014
  14. 14. Subcarrier Aggregation: Multicarrier Systems T Frequency (f) Time (t) T Frequency (f) Time (t) wfc F=1/T Tunis, Tunisia, 28 January 2014
  15. 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 15Tunis, Tunisia, 28 January 2014
  16. 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 16Tunis, Tunisia, 28 January 2014
  17. 17. Delay-Spread ISI Immune Communications: Guard Interval 3/6 T Frequency (f) Time (t) w F TgTm FT N=4 Total duration Tunis, Tunisia, 28 January 2014
  18. 18. Delay-Spread ISI Immune Communications: Guard Interval 4/6 Frequency (f) Time (t) w F TgTm N=8  T  FT  Total duration  Tunis, Tunisia, 28 January 2014
  19. 19. Delay-Spread ISI Immune Communications: Guard Interval 5/6 Frequency (f) Time (t) w F TgTm N=16  T  Total duration  FT  Tunis, Tunisia, 28 January 2014
  20. 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 20Tunis, Tunisia, 28 January 2014
  21. 21. Radio Mobile Channel Characteristics: Doppler Spread 1/3 21 Frequency (f) Time (t) Power Transmitted Symbol Mobile speed (v) w Received symbol replica -fd -fd Received symbol replica 0 Received symbol replica +fd +fd
  22. 22. Radio Mobile Channel Characteristics: Doppler Spread 2/3 22 Subcarrier spacingF Frequency (f) Time (t) w Power Frequency (f) Transmitted symbols Tunis, Tunisia, 28 January 2014
  23. 23. Radio Mobile Channel Characteristics: Doppler Spread 3/3 23 F+Bd Frequency (f) Time (t) Power Frequency (f) Received symbols ICI Bd = 2 fd Doppler spread Tunis, Tunisia, 28 January 2014
  24. 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. 25. Sensitivity to Multiple Access Frequency Synchronization Errors 1/2 Farthest mobile Nearest mobilePower Frequency (f) Received symbols: Perfect user synchronization Large Power gap Perfect synchronization  No Inter-User Interference (IUI) 25Tunis, Tunisia, 28 January 2014
  26. 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 26Tunis, Tunisia, 28 January 2014
  27. 27. Quality of Service Evaluation and Optimization: SINR 1/2 Frequency (f) Time (t) F T ISI IUI User 1 User 2 ICI SINR: Signal-to-Noise Plus Interference Ratio 27Tunis, Tunisia, 28 January 2014
  28. 28. Quality of Service Evaluation and Optimization: SINR 2/2 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    Useful signal power ( )S SINR ISI ICI IUI 28
  29. 29. Transmit and Receive Waveforms Optimization Results 1/6 29  0.01d mB T  1.5FT  30SNR dB  Waveform Duration T 5.9 dB Channel spread factor
  30. 30. Transmit and Receive Waveforms Optimization Results 2/6 30  30SNR dB  Waveform Duration T  0.01d mB T
  31. 31. Transmit and Receive Waveforms Optimization Results 3/6 31  0.01d mB T  30SNR dB 3 Waveform Duration T
  32. 32. Transmit and Receive Waveforms Optimization Results 4/6 32  0.01d mB T 3 Waveform Duration T 1.25FT  / 0.1dB F 
  33. 33. Transmit and Receive Waveforms Optimization Results 5/6 33  0.01d mB T 3 Waveform Duration T 1.25FT  / 0.1dB F  > 40 dB Transmit Waveform
  34. 34. Transmit and Receive Waveforms Optimization Results 6/6 34  0.01d mB T 3 Waveform Duration T 1.25FT  / 0.1dB F  Transmit Waveform

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