RAN Efficiency Improvement Scheme for Diverse Data Applications

3GPP TSG-RAN WG2 Meeting #75

[R2-114273]Signalling Overhead of Diverse Data Applications over LTE (Intel)

[R2-114274]Traces of Diverse Data Applications over LTE network for eDDAEvaluation Framework (Intel)

[R2-114308]RAN Efficiency Improvement Schemes (Renesas Mobile Europe)

Tzu-Chun Luo

2011.10.19

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Outline

• Introduction

• Signalling Overhead Calculation

• Trace Analysis

• Potential Scheme

• Conclusion

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Introduction

• Diverse data application(DDA) : Many devices(e.g. smartphone, tablet) are capable of running a wide variety of data applications, often in parallel. Such a diversity in device and application type creates a corresponding diversity in the traffic profiles that must be efficiently supported by the radio access networks(RAN) on which they run

• Numerous applications require that an always-on experience is seamlessly delivered and presented to the end user

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DDA work item

• Those applications may be designed without consideration of the characteristics of cellular networks, and consequently may exhibit traffic profiles not well suited to those connections.

• Objective

– Identify and specify mechanisms at the RAN level that enhance the ability of LTE to handle diverse traffic profiles.

– Enhancements may be applicable to E-UTRAN, the UE or both, and should encompass both FDD and TDD modes

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Signalling Overhead Calculation

• One of the key metrics of the evaluation for eDDA WI is the signalling overhead(for RRC connection)

• To get an understanding of the signalling overhead seen over LTE networks, we followed the following methodology

– Measure the number of RRC messages exchanged by an LTE modem when setting up an RRC connection

– Collect sample traces of packet arrival patterns over LTE network

– Apply a range of values of Idle inactivity timer to the traces to obtain rate of RRC state change events and the ratio of data exchanged to the signalling overhead 5

Details of over-the-air RRC messages exchanged

RRC message exchanged during RRC_Idle → RRC_Coonected

Length in bytes

Service Request 18

RRC Connection Setup 51

RRC Connection Request 31

RRC Connection Setup Complete 32

Security Mode Command 28

Security Mode Complete 27

RRC Connection Reconfiguration 81

RRC Connection ReconfigurationComplete

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Total 295

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Signalling Overhead Calculation

• The messages exchanged over the EMM and between packet gateway do not include

RRC message exchanged during RRC_Connection → RRC_Idle

Length in bytes

RRC Connection Release 28

Total 28

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Trace Analysis

• Experimental setup consisted of an LTE smart phone device and a software tool installed on the phone to capture layer 3 packets exchanged through the phone’s LTE interface

• Background traffic : Skype, Gtalk, Stock update, Twitter, Weather and News

• Active session : Safari, Android Market App and YouTube

• All the different traces were obtained from the same location with no mobility

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Active user traffic vs. background traffic

• It doesn’t make much difference when applications run in background with an active session

0 20 40 60 80 100 120 140 160 180 2000

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Interarrival Time(ms)

CD

F

CDFs of Packet Interarrival Times

Active User

Only Background Traffic

Active User + Background Traffic

0 500 1000 15000

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Packet Size (bytes)

CD

F

CDFs of Packet Sizes

Active User

Only Background

Active User + Background Traffic

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Trace for background traffic

0 100 200 300 400 500 600 700 800 900 10000

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Interarrival Time (ms)

CD

F

CDF Packet Interarrival Times

CDF Points Inter Arrival Times (ms) (+/-

5%)

10% 1

30% 7

50% 60

70% 200

90% 925

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Trace for multiple background applications

• The packet sizes are generally very small ranging from 68 to 100 bytes for 90% of all the packets

0 100 200 300 400 500 600 700 800 900 10000

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Packet Size (bytes)

CD

F

CDF of Packet Sizes

CDF Points Packet Size (bytes)

90% 100 (+/- 5%)

minimum 68

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Analysis of Specific background application traffic

• Single vs. multiple background application makes a big difference in the CDF of packet inter-arrival times

0 20 40 60 80 100 120 140 160 180 2000

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Interarrival Time (ms)

CD

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CDF of Packet Interarrival Times

All Background

Skype

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Impact of Signalling Overhead

• For a user running a active session using Safari

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Impact of Signalling Overhead

• For a user running multiple apps in background

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Impact of Signalling Overhead

• For a user running an active session with multiple apps in background

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Potential Scheme

• R2-114308 discusses low data rate application and MTC(Machine Type Communication) small data transmission

• Potential schemes to improve the LTE RAN efficiency

– Always-On in RRC_Connected State

– Making use of RRC_Idle mode Tx/Rx

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Always-On in RRC_Connected State

• Straightforward : to keep UE always in RRC_Connected State and never release the UE to RRC_Idle State

• Advantage : reduce the signalling overhead between RRC_Connected and RRC_Idle transitions

• Drawback :

– RAN resource(e.g. C-RNTI resources, CQI/SR/SRS resources, memory used for UE context) are reserved

– Power consumption to keep RRC_Connected(e.g. PDCCH monitoring, radio link monitoring, time/frequency synchronization, RRM/CSI measurement, UL TA maintenance)

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Always-On in RRC_Connected State• Solution : DRX, s-Measure

– In DRX mode, UE is allowed to decrease the frequency of PDCCH monitoring

– S-Measure allows such control over RRM/CSI management can be configured to be aperiodical

• But UE still needs to retain downlink timing/frequency synchronization and possible uplink timing, Since there can be a relatively long interval between packet transmission, the cost seems not so desirable

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Making use of RRC_Idle mode Tx/Rx

• Transmit and receive data in RRC_Idle state

• UL transmission : use RACH Msg3 to carry a small packet, then eNB can directly reject the RRC connection setup request

• Advantage : the security activation procedure, SRB/DRB setup procedure, and RRC connection release procedure will not be needed

• Drawback :

– No integrity protection and ciphering

– Delay due to RACH contention

– No ack, the applications need to be based on UDP 19

RACH procedure with small data transmission

MTC Device eNB

Random Access Preamble1

Random Access Response 2

Scheduled Transmission3

Contention Resolution 4

Implicit or explicit infrequent small data

transmission indication of the MTC

device: e.g. priority, size, type etc.

Implicit or explicit indication

on the data source and type

etc. Upon receiving the infrequent small data

transmission from the MTC devices, eNB

sends the RRC connection rejection message

to UE with cause value of the offline small

data transmission. It also acknowledges the

MTC’s small data transmission at eNB.

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Making use of RRC_Idle mode Tx/Rx

• DL transmission : MBMS service can be reused

• Advantage : DL data transmission could for group of UEs and more signalling are saved

• Drawback :

– eNB can not transmit DL data to individual UEs

– No ack

– No integrity protection and ciphering

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Conclusion• R2-114273:Signalling Overhead of DDA over LTE

– Proposal 1: We propose to investigate and develop efficient mechanisms to reduce the signalling overhead when running background traffic

• R2-114274:Traces of DDA over LTE network for eDDAevaluation framework– Proposal 1: The data shows that background traffic is significantly

different from active user traffic (HTTP, FTP etc.). We recommend either using traces or developing a model based upon traces for multiple applications running in the background.

– Proposal 2: We recommend using Table 1 and Table 2 as a baseline to compare against any other sample traces for the case of user running background traffic.

– Proposal 3: For eDDA simulation framework, a specific mix of background applications must be decided to obtain consistent traces.

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