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Future 3GPP Radio Technologies for IMT-Advanced

This document discusses LTE-Advanced technologies and their objectives, improvement for nomadic environments, peak rate/throughput, cell edge performance improvement, improved support of MBMS, and enabling technologies for LTE-Advanced.

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Future 3GPP Radio Technologies for IMT-Advanced

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  1. REV-080037 Future 3GPP Radio Technologies for IMT-Advanced Source: Samsung Agenda Item: 3 3GPP IMT-Advanced Workshop 7-8 April 2008 Shenzhen, China

  2. Discussion on LTE-advanced • Driver for LTE-advanced • Demand for ubiquitous mobile broadband access • Objectives for LTE-advanced technologies • Improvement for nomadic environments • Improvement of peak rate/throughput • Cell edge performance improvement • Improved support of MBMS • Schedule of study/work item for LTE-advanced

  3. Enabling Technologies for LTE-Advanced • Peak Data Rate improvement • DL 4x4 : LTE baseline 2x2 • UL 2x4 : LTE baseline 1x2 • 8 Tx antennas at eNode-B including 8x8 MIMO spatial multiplexing is also considered • Sector/cell throughput improvement • Advanced Downlink MU-MIMO: 8 Tx beam-forming • Uplink SU-MIMO • Hybrid OFDMA and SC-FDMA in uplink • Multi-stream MIMO SFN broadcast • Superposition of unicast and broadcast traffic • Cell edge performance improvement • Multi-hop relay – coverage extension • Multi-cell MIMO (Network MIMO) – toward a cell without cell edge?

  4. Uplink Improvements: Hybrid OFDMA and SC-FDMA Uplink SU-MIMO

  5. Hybrid SC-FDMA/OFDMA Uplink 64-QAM, 2/3 coding rate • At higher SNR, SC-FDMA suffers from loss of orthogonality leading to performance degradation • The PAPR/CM gain of SC-FDMA over OFDMA reduces for higher order modulations • It is advantageous to not use FFT-precoding at higher SNR for higher order modulations and MIMO • Higher order modulations and MIMO skip FFT-precoding • The link loss for SC-FDMA using 64-QAM is more than the PAPR/CM gain which results in overall loss of performance • Hybrid scheme is a simple and straightforward enhancement to the LTE system 64-QAM, 1/3 coding rate

  6. Uplink SU-MIMO • Various configurations • UL antenna selection • UL beamforming / transmit diversity • UL Spatial multiplexing • UL SU-MIMO was discussed in LTE study item • But, not included in LTE spec • UE cost was one major concern • Feasible for LTE-advanced • Reducing pilot overhead is one key issue • Pilots on separate locations –more overhead • Pilots on same location, but with CDM • More complicated for OFDMA with distributed transmission

  7. Advanced MIMO Technology:8Tx beam-forming Multi-cell MIMO

  8. Advanced MU-MIMO: 8Tx Beam-forming • 8Tx beam-forming provides • Higher beam resolution, increased coverage, larger beam forming gain and larger number of simultaneous beams in one sector • Both throughput and coverage gain • Cell edge performance gain of up to150% against 4x2 case with 12 UEs/cell • Issue: pilot provisioning 5%-tile UE throughput Sector throughput

  9. Multi-cell Network MIMO • Less co-channel interference, more signal • Better cell edge performance • Requirements: • Increased uplink feedback overhead • Synchronization to more than one cell Data S1,S2 Channel Info feedback Precoding Network backhaul Zero forcing example:

  10. Relay Technologies: Full duplex Relay Subcarrier Duplexed Relay Superposition Relay Collaborative mobile relay

  11. Relay Technology RS Providing Coverage Extension Relays beneficial for low SINR (cell-edge) UEs* *F. Khan, Capacity and Range Analysis of Multi-Hop Relay Wireless Networks, IEEE Vehicular Technology Conference Fall 2006. Relays also useful for coverage holes, indoor coverage and underground tunnels etc.

  12. TDD and FDD Relaying • TDD relaying suffers from link budget limitation because only a single node transmits at a given time. • In FDD relaying, two nodes can transmit simultaneously but the scheme does not allow power and resource sharing between eNB-Relay and Relay-UE links.

  13. Subcarrier Division Duplexed Relaying • Subcarrier division duplexed relaying allows power and resource sharing between eNB-Relay and Relay-UE links. • The number of orthogonal subcarriers on these links can be dynamically varied • Both eNB and UE can transmit when relay is receiving data • Greater coverage relative to a TDD scheme

  14. Full Duplex Relay (TDD Example) Half Duplex Relay Full Duplex Relay • Benefits: • Able to Tx/Rx in same BW resource • Better use of power and BW • Challenge: inter-antenna interference • Interference suppression • Isolation of Tx/Rx components

  15. Superposition Relay • An example using hierarchical modulation • Relay decodes the signal as a higher constellation • UE decodes the signal as a lower constellation • Relay forwards the difference constellation An example of transmission of sequence “0010” from eNB to the UE

  16. MS_R1 MS_R1 MS Coverage hole Collaborative Communication: Emergency MS Relay • Emergency call situation • Emergency caller is located in the outside of coverage • The service is absent or the signal is insufficient to support a call • Only possible to connect the emergency call through the MS Relay • Emergency call features • Not frequent, no prior information when will happen • Hard to constantly monitoring the Emergency Call • Battery consumption problem • Efficiency protocol needed • how the MS relay search for emergency UE • How the emergency UE select the MS relay within the available pool

  17. MBSFN Enhancements: Multi-stream MIMO for MBSFN Superposition of MBSFN and unicast

  18. MBSFN Spatial Multiplexing • MBSFN system is bandwidth limited particularly in smaller cells • MBSFN signals received from multiple antennas from multiple cells are decorrelated • Potential for performance improvement using MIMO spatial multiplexing • Base layer is carried with more robustness (better coding, modulation and/or higher power). • UEs with good channel conditions can also decode the enhanced layer by canceling the base layer signal • Allows differentiated QoS

  19. MBSFN/Unicast Superposition Free MBMS Capacity Unused Cancelled SFN Node-B Total MBMS MBMS Power Node-B signal Power Unicast Unicast Unicast • Unicast traffic is (often) interference limited; broadcast is not. • Borrow some unicast power without affecting unicast performance and use this power for MBSFN superposition • Greater than 2b/s/Hz MBSFN (20Mb/s in 10MHZ bandwidth) throughput without degrading unicast performance • System simulations according to case-1 in LTE TR 25.814.

  20. Summary • Driver for LTE-advanced is expected demand on ubiquitous broadband access • Key enabling technologies identified and discussed

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