OFDMA with Optimized Transmit and Receive Waveforms for Better Interference Immune Communications in Next Generation Radio Mobile Communication Systems Mohamed Siala Professor at Sup’Com [email protected]ITU Workshop on "ICT Innovations in Emerging Economies" (Geneva, Switzerland, 18 September 2013) Geneva, Switzerland, 18 September 2013
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OFDMA with Optimized Transmit and Receive Waveforms for Better Interference Immune Communications in Next Generation Radio Mobile Communication Systems.
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OFDMA with Optimized Transmit and Receive Waveforms for Better Interference Immune
Communications in Next Generation Radio Mobile Communication Systems
ITU Workshop on "ICT Innovations in Emerging Economies"
(Geneva, Switzerland, 18 September 2013)
Geneva, Switzerland, 18 September 2013
Presentation Outline
Problem statement and proposed solutionOverview on single carrier communicationsRadio Mobile Channel Characteristics:
Multipath and Delay SpreadSensitivity to Delay Spread
Subcarrier Aggregation: Multicarrier SystemsDelay-Spread ISI Immune Communications: Guard IntervalRadio Mobile Channel Characteristics: Doppler SpreadConsiderations on Subcarrier NumberSensitivity to Multiple Access Frequency Synchronization ErrorsQuality of Service Evaluation and Optimization: SINRTransmit and Receive Waveforms Optimization Results
2Geneva, Switzerland, 18 September 2013
Problem statement and proposed solution
Next generation mobile communication systems will operate on highly dispersive channel environments:
Very dense urban areas High multipath delay spreadsVery 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
3Geneva, Switzerland, 18 September 2013
Bandwidth (w)
Carrier frequency (fc)
Overview on Single Carrier Communications 1/3
4
Frequency (f)
Time (t)
Power
Symbols
Symbol duration (T)
1
wT
1
RT
Symbol rate (R)
Geneva, Switzerland, 18 September 2013
Bandwidth (w)
Symbol duration (T)
Overview on Single Carrier Communications 2/3
5
Frequency (f)
Time (t)
Power
1
wT
1
w T RT
1
RT
Symbol rate (R)
Geneva, Switzerland, 18 September 2013
Overview on Single Carrier Communications 3/3
6
Frequency (f)
Time (t)
Power
Symbol duration (T) 1
w T RT
Bandwidth (w)
Geneva, Switzerland, 18 September 2013
Radio Mobile Channel Characteristics: Multipath and Delay Spread 1/4
Geneva, Switzerland, 18 September 2013 7
Frequency (f)
Time (t)
Power
Transmitted Symbol
Shortest path
Receivedsymbol replica
Receivedsymbol replica
Receivedsymbol replica
Longest path
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
Radio Mobile Channel Characteristics: Multipath and Delay Spread 3/4
Geneva, Switzerland, 18 September 2013 9
Transmitted symbolsT
Frequency (f)
Time (t)
w
Time (t)
Power
fc
Radio Mobile Channel Characteristics: Multipath and Delay Spread 4/4
Geneva, Switzerland, 18 September 2013 10
Frequency (f)
Time (t)
w
Received symbols TmDelay spread
Time (t)
Power
Inter-Symbol Interference(ISI)
fc
Radio Mobile Channel Characteristics: Sensitivity to Delay Spread 1/3
Geneva, Switzerland, 18 September 2013 11
T
Frequency (f)
Time (t)
w
Time (t)
Power
fc
T
Frequency (f)
Time (t)
w
Time (t)
Power
fc
Radio Mobile Channel Characteristics: Sensitivity to Delay Spread 2/3
Geneva, Switzerland, 18 September 2013 12
Frequency (f)
Time (t)
w
TmDelay spread
Time (t)
Power
ISI
fc
Algiers, Algeria, 8 September 2013
Frequency (f)
Time (t)
w
TmDelay spread
Time (t)
Power
ISI
fc
Radio Mobile Channel Characteristics: Sensitivity to Delay Spread 3/3
The channel delay spread Tm is independent of the transmission symbol period TReduced bandwidth w
Pro: Increased T Better immunity (reduced sensitivity) to ISICon: 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 ISIUnchanged global bandwidth w Unchanged transmission rate
No guard interval insertion F = 1/T Symbol occupancy FT = 1 No symbol rate lossStill some ISI which can be reduced by
reducing F,or equivalently, increasing T = 1/For equivalently, increasing the number of subcarriers N = w/F
ISI immune communications Perfectly ISI immune communicationsT = 1/F+Tg FT > 1 Symbol rate lossSymbol rate loss reduced by reducing F, or equivalently increasing N
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
Radio Mobile Channel Characteristics: Doppler Spread 1/3
21
Frequency (f)
Time (t)
PowerTransmitted Symbol
Mobile speed(v)
w
Receivedsymbol replica
-fd
-fd
Receivedsymbol replica
0
Receivedsymbol replica
+fd
+fd
Radio Mobile Channel Characteristics: Doppler Spread 2/3
22
Subcarrier spacingF
Frequency (f)
Time (t)w
Power
Frequency (f)
Transmitted symbolsGeneva, Switzerland, 18 September 2013
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
Geneva, Switzerland, 18 September 2013
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 spreadAny 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
Sensitivity to Multiple Access Frequency Synchronization Errors 1/2
Farthest mobile
Nearest mobile Power
Frequency (f)
Received symbols: Perfect user synchronization
LargePower gap
Perfect synchronization No Inter-User Interference (IUI)
Geneva, Switzerland, 18 September 2013 25
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)
LargePower gap
Geneva, Switzerland, 18 September 2013 26
Quality of Service Evaluation and Optimization: SINR 1/2
Frequency (f)
Time (t)
T
ISI
IUI
User 1
User 2ICI
SINR: Signal-to-Noise Plus Interference Ratio
Geneva, Switzerland, 18 September 2013 27
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 ( )SSINR
ISI ICI IUI
28
Transmit and Receive Waveforms Optimization Results 1/6
29
0.01d mB T
1.5FT
30SNR dB
Waveform
Duration T
5.9 dBChannelspread factor
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
Geneva, Switzerland, 18 September 2013 32
0.01d mB T
3
Waveform
Duration T
1.25FT
/ 0.1dB F
Transmit and Receive Waveforms Optimization Results 5/6
Geneva, Switzerland, 18 September 2013 33
0.01d mB T
3
Waveform
Duration T
1.25FT
/ 0.1dB F
> 40 dB
Transmit Waveform
Transmit and Receive Waveforms Optimization Results 6/6