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

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

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

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

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

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

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

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

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

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

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

Radio Mobile Channel Characteristics: Sensitivity to Delay Spread2/3 Geneva, Switzerland, 18 September 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Transmit and Receive Waveforms Optimization Results1/ dB Channel spread factor

Transmit and Receive Waveforms Optimization Results2/6 30

Transmit and Receive Waveforms Optimization Results3/6 31

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

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

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