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."

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. Subcarrier Aggregation: Multicarrier
Systems
T
Frequency (f)
Time (t)
T
Frequency (f)
Time (t)
wfc
F=1/T
Tunis, Tunisia, 28 January 2014

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. 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. 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. 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. 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. 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. 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. 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. 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. 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 mobilePower
Frequency (f)
Received symbols: Perfect user synchronization
Large
Power gap
Perfect synchronization
 No Inter-User Interference (IUI)
25Tunis, Tunisia, 28 January 2014

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. 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. 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. 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. Transmit and Receive Waveforms
Optimization Results 2/6
30
 30SNR dB

Waveform
Duration T
 0.01d mB T

31. Transmit and Receive Waveforms
Optimization Results 3/6
31
 0.01d mB T
 30SNR dB
3
Waveform
Duration T

32. Transmit and Receive Waveforms
Optimization Results 4/6
32
 0.01d mB T
3
Waveform
Duration T
1.25FT 
/ 0.1dB F 

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. Transmit and Receive Waveforms
Optimization Results 6/6
34
 0.01d mB T
3
Waveform
Duration T
1.25FT 
/ 0.1dB F 
Transmit Waveform