WWRF WG4 – White Paper: Multi-hop Protocols for Relay-based Deployment Concepts

1. WWRF WG4 – White Paper:Multi-hop Protocols for Relay-based Deployment Concepts Editors: D.Schultz, B.Walke ComNets, Faculty 6, RWTH Aachen University

2. Contributors

3. Motivation • Relays are seen as essential part of next generation mobile radio network to allow cost efficient and fast network rollout. First concept and performance evaluations for existing system have proven the value of the concept as shown in the WWRF White Paper “Relay-based deployment “. • The integration of relays as inherent part of the system concept is expected to increase the performance compared to the results shown in WWRF White Paper “Relay-based deployment“ at reasonable (low) node complexity

4. Scope • Relay-based B3G mobile radio network deployment concepts • Layer 1-3 • Physical Layer - PHY (L1) • Medium Access Control - MAC (L2) • Radio Link Control - RLC (L2) • Radio Resource Control - RRC (L3)

5. Objectives The white paper should • provide an outline on how relaying can be integrated in B3G systems as inherent part of it to • Optimise the capacity distribution in a given area • Cover otherwise shadowed areas • Extend the coverage of a B3G BS • Show the traffic performance of multi-hop capable protocols to assess the protocol efficiency • Provide an overview of the complexity of RNs

6. Current Contributions • Requirements and scope have been defined • Multi mode reference architecture • MAC frames based approaches • Frame in frame • Frame by frame • RLC: Relaying ARQ frame work presented • RRM/RRC: Outlook about resource partitioning  further details needed

7. I. INTRODUCTION A. Requirements on Multi-hop Protocols B. Relays in Infrastructure Based Deployment Concepts 1) Relays to extend the service range of a BS (service area size optimization) 2) Optimized Cell Capacity and Minimum Tx Power 3) Coverage of shadowed areas C. Outline II. STATE OF THE ART A. Protocols for central control B. Decentralised protocols III. REFERENCE PROTOCOL ARCHITECTURE IV. RADIO RESOURCE MANAGEMENT A. Resource Reservation B. Mobility Support C. Eval. of Routing and Forwarding Methods 1) Architectural and Algorithmic Characteristics D. Tech. Characteristics of Routing & Fwd. 1) Supporting advanced com. techniques 3) Multiple access method 4) Integration into other RRC functionality 5) Similarity to existing standards 6) Exploiting multi-user diversity E. Resource Partitioning (new from WWRF#16 paper) V. RADIO LINK CONTROL RLC A. Retransmission Protocols 1) Hop-by-Hop vs. End-to-End ARQ 2) ARQ Framework 3) Layered ARQ for error recovery 4) Relay-ARQ for error recovery 5) ARQ in the context of Cooperative relaying B. Segmentation/Reassembly C. Multi-hop Flow Management and Control (New - open for contribution) 1) Flow Set-up 2) Flow control VI. MEDIUM ACCESS CONTROL MAC A. Link adaptation control B. Resource Scheduling C. Frame Descriptor Table (new) C. Multi-user Diversity in Multi-hop Cellular Networks 1) Feeding Phase 2) Delivery Phase VII. COOPERATIVE RELAYING PROTOCOLS VIII. SPECTRUM ISSUES A. Frequency Re-use B. Spatial diversity/Spatial Re-use 1) Tx gain vs. Rx gain between RAPs C. Interference Control D. Coordination Across BS and RN IX. CONCLUSION AND OUTLOOK REFERENCES Table of Contents

8. Definition of Fixed Relay-based Deployment Concepts Capacity Optimisation • L2-Relays in REC • don’t need a wired backbone access (lowers CAPEX and OPEX) • Full flexibility of relays (re-)positioning • Relays support • fast network rollout, • outdoor to indoor service • Exploitation of macrodiversity (co-operative relaying) One-hop Cell Area Optimisation Coverage of shadowed areas

9. The WINNER Multi-mode Protocol Architecture control - plane Configuration andinformation transfer We can have alternatively have (1) a generic Management More flexible or (2) a Management that is specifically optimised for the mode1and mode2 in use  probably more efficient RRC - g RRC - s 2 RRC - s 1 t n e m e g The Multi-mode protocol architecture, facilitating transition (switching) between modes (inter-mode handover) and coexistence of modes (e.g. in relay stations connecting different modes) by way of the cross-stack management supported by the modes convergence manager of a layer or stack a RLC - g n a M k c a t S PHY - g MAC - g c i r MAC - s 2 e n MAC - s 1 e G mode - switching and PHY - g PHY - g - coexistence PHY - s 2 PHY - s 2 PHY - s 2 PHY - s 1 management control user

10. Relay ARQ • Relay ARQ for high reliability and efficient retransmissions • One ARQ process with multiple multi-hop ARQ peers • ARQ responsibility is delegated to next hop on Relay ACK (temporary responsibility) • All multi-hop peers involved in same multi-hop ARQ chain • Ultimate ARQ responsibility remains at the sender. ARQ window only advances on Final ACK from Receiver • Conclusion • Relay ARQ is a solution for the described problem ! Hey, I have received this packet. But I am not the final receiver. Anyway, don’t worry, I will take care of it! Hey, I have received this packet. But I am the final receiver. So you can now delete this packet from your buffer. ACK L3 L3 RACK L2 L2 Relay L2 L1 L1 L1 L1 Relay Node Receiver Sender

11. Multi-hop MAC • In Frame Relaying: • Short delays • BS controlled • Frame-by-Frame Relaying: • High throughput (low protocol overhead)

12. Identified Research Areas • Protocols for FDD Relaying • Relaying optimized MAC • Distributed RRM protocols for coordination across RAPs to improve the mutual interference situation • Protocol support for cooperative relaying • Multi-hop flow set-up • QoS control in multi-hop links

13. Common Goals • Maximize Frequency Reuse • Allow efficient exploitation / fair sharing of the available spectrum, esp. in unlicensed case • Guarantee QoS, since delay can be expected to be a crucial issue in relay-based networks. • Minimize Multiple-Access Interference (MAI), probably making use of advanced coordination across base stations in the system and of cooperation between base stations of different access technologies. • Provide seamless mobility in heterogeneous networks consisting of different radio access technologies. • Sequential coupling of different air interfaces to enable heterogeneous tandem-links. • Important either in the context of wireless connection of Base Stations to core network or in the case of relaying in unlicensed frequency bands.

14. Contact: Daniel C. Schultz Chair of Communication Networks RWTH Aachen University, Faculty 6 Tel.: +49 241 8025828 E-Mail: dcs@comnets.rwth-aachen.de