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TR 36.881 (RAN2)
Study on Latency Reduction Techniques for LTE

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Rapporteur:  Mr. Enbuske, Henrik

Potential gains like reduced response time and improved TCP throughput due to latency improvements on typical applications and use cases are identified and documented. In this evaluation, latency reductions due to protocol enhancements as well as shortened TTIs are assumed. Specifically, the following items should apply:
  • Consider the web application (HTTP/FTP+TCP) use case and analyse the possible gains in the performance metrics of delay and perceived data rate for TCP based data transactions.
  • Consider real-time application use case and analyse the possible gains in delay, service coverage and system capacity.
  • Aspects of complexity, energy-consumption, signalling overhead and resource efficiency should be considered.
The evaluations include active UEs and UEs that have been inactive a longer time, but are kept in RRC Connected. Reducing user plane latency for the scheduled UL transmission with resource efficient solution as a result of protocol and signalling enhancements are studied and compared to the pre-scheduling solutions allowed by the standard today.
Specification impact, feasibility and performance of TTI lengths between 0.5ms and one OFDM symbol are studied, taking into account impact on e.g. L2 overhead, reference signals and physical layer control signalling.
Backwards compatibility shall be preserved, i.e. solutions should allow normal operation of pre-Rel 13 UEs on the same carrier.

full Table of Contents for  TR 36.881  Word version:   14.0.0


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1  ScopeWord-p. 6
2  References
3  Definitions, symbols and abbreviationsWord-p. 7
4  Study Objectives
5  Overview of LTE latency
6  Scenarios, Applications and Use Cases
7  Evaluation Structure and AssumptionsWord-p. 15
8  Solutions for latency reduction
9  Performance EvaluationWord-p. 20
9.1  Protocol evaluations on TTI reduction and Fast UL
9.1.1  Simulation 1: TCP slow-start behavior for FTP file download based on reduced TTI and reduced SR periodicity [4]Word-p. 21
9.1.2  Simulation 2: Capacity and throughput gain with 0.5ms TTI [5]Word-p. 24
9.1.3  Simulation 3: Throughput and packet download time with reduced latency in LTE [3]Word-p. 26
9.1.4  Simulation 4: Latency evaluation results for TTI reduction and Fast UL [6]Word-p. 27
9.1.5  Simulation 5: System Performance with TTI shortening [6]Word-p. 34
9.1.6  Simulation 6: Evaluation results for TTI reduction [6]Word-p. 44
9.1.7  Simulation 7: Performance evaluation of latency reduction enhancements [6]Word-p. 46
9.1.8  Simulation 8: TTI reduction gain with additional L1/L2 overhead [6]Word-p. 52
9.1.9  Simulation 9: Effect of UE and eNB processing times on TCP performance [6]Word-p. 54
9.1.10  Simulation 10: System Performance Gain with TTI reduction [6]Word-p. 58
9.1.11  Simulation 11: TTI reduction gain with additional L2 overhead [9]Word-p. 60
9.1.12  Simulation 12: TTI reduction gain with additional L2 overhead [10]Word-p. 61
9.2  Protocol evaluations on Contention based PUSCH transmissionWord-p. 64
9.3  Handover latency [11]Word-p. 74
9.4  Findings from system evaluations on TTI reduction and reduced processing time
9.5  Findings from link evaluations on TTI reduction and reduced processing timeWord-p. 76
10  Conclusion
A  Simulation assumptionsWord-p. 79
B  System evaluation resultsWord-p. 98
C  Link-level evaluation resultsUp
D  Change history

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