Ger man Aerospace Center Gothenburg, April, 2007 High Spectral Efficient and Flexible Next Generation Mobile Communications Simon Plass, Stephan Sand, Mikael Sternad, and Arne Svensson

2 Ger man Aerospace Center Motivation  What are the requirements and challenges for next generation communications systems?  How can these technical challenges be solved? Remark: The focus is on the physical layer (PHY) in this presentation

3 Ger man Aerospace Center Evolution of Mobile Communications Analog systems 1G GSM 2G UMTS 3G ??? 4G Digital systems

4 Ger man Aerospace Center 4G GMC Scenarios 0, Mbit/s mobility high speed/ wide area medium speed/ within a city walking speed/ within a limited areas portable/ indoor 2G TDMA FDMA 3G CDMA WLAN (IEEE ) OFDM data rate

5 Ger man Aerospace Center Main Requirements for 4G  Efficient use of the valuable spectrum  Flat IP architecture for low operational expenditure and less capital expenditure  Flexible spectrum allocation and sharing has to be included  New services based on real time applications, e.g., gaming or new trends of Web 2.0

6 Ger man Aerospace Center Cyclic prefix IFFT Cyclic prefix IFFT Basic Transmission Technique: Generalized Multi Carrier (GMC)  Robust to multi-path environments  Efficient use of the available spectrum  Flexible allocation of user data to sub-carriers  Includes all OFDM based transmission techniques such as OFDMA, MC-CDMA, SS-MC-MA, IFDMA, etc. Data symbols Space- Time- Frequency Precoding

7 Ger man Aerospace Center Advanced Techniques for the PHY  Adaptive functionalities at the transmitter and receiver exploiting channel state information and user demands  Transmitter: Adaptive bit-interleaved coded modulation (BICM) Adaptive Space-time-frequency (STF) precoding Coding  Mod Adaptive BICM Predicted CSI Cyclic prefix IFFT Cyclic prefix IFFT Data symbols adaptive Space- Time- Frequency Precoding Predicted MIMO-CSI

8 Ger man Aerospace Center Advanced Techniques for the PHY  Receiver: Iterative channel estimation, demodulation, and decoding Improve bit estimates by toggle until regeneration brings optimality (TURBO) principle Decod  -1 Demod STF Decod Channel Estimation CSI Prediction SISO CSI MIMO CSI Inverse OFDM converted signals sink

9 Ger man Aerospace Center Technical Highlights for 4G Systems  Spectrum Flexibility  Inter-cell Interference Handling  Relaying Concepts

10 Ger man Aerospace Center Spectrum Flexibility – Spectrum Assignment Concepts  Definition of new spectrum assignment at the World Radiocommunications Conference (WRC) in Oct/Nov MHz2.6 GHz3.4 GHz5 GHz 2G & 3G bands 4G Candidate band Cand. band I 900 MHz2.6 GHz3.4 GHz5 GHz 2G & 3G bands 4G Cand. band Candidate band Shared by 4G II 900 MHz2.6 GHz3.4 GHz5 GHz 2G & 3G bands Shared by 4G Candidate band Cand. band Candidate band Shared by 4G Narrowband 4G III

11 Ger man Aerospace Center Spectrum Flexibility – Spectrum Sharing Mechanisms  Sharing and Co-existence (spectrum sharing with fixed satellite systems (FSS)) Use of geographical ‚exclusion zones‘ Use of directional antennas and beamforming to avoid LOS transmissions towards FSS ground stations  Flexible Spectrum Usage Long-term spectrum assignment Short-term spectrum assignment Resource partitioning

12 Ger man Aerospace Center Inter-cell Interference Problem  Goal: High overall spectral efficiency in combination with high flexibility for packet data traffic  Method: Frequency reuse of one and generalized multi-carrier system  Result: Inter-cell interference problem at the cell borders

13 Ger man Aerospace Center Inter-cell Interference Handling  Difficulties: Fast and tight inter-cell coordination is required for maximal gains in interference avoidance Complication with packet-switched channel-aware scheduled transmission  Possible approaches: For high loads, allocate low SINR user to a separated frequency pool with frequency reuse of three, the others with reuse of one For low loads, dynamic frequency assignment and/or coordinated beamforming can be used of the lower fraction of low SINR users Inter-cell interference cancellation schemes at the receiver, if resources at receiver available

14 Ger man Aerospace Center Conclusions We have shown:  The needs of next generation communications systems  The underlying transmission technique GMC  The adaptive components of the PHY  The need of spectrum flexibility and its mechanisms  The need of inter-cell interference handling and possible approaches

15 Ger man Aerospace Center Thank you!