Radio Resource RRC

8/3/2019 Radio Resource RRC

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RRC(Radio ResourceControl)

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OUTLINE

RRC Introduction

DRX in RRC_Idle

Analysis

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Radio Resource Control (RRC) UE management and control is handled in the Radio

Resource Control (RRC)

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LTE Protocol Architecture Control Plane

NAS control protocol AS control protocol Between UE and EPC Between UE and eNB

PLMN selection Radio-specific functionality

Tracking area update Interaction with NAS

Paging RRC as main controlling function in AS

Authentication RRC as Layer 3 in AS protocol stack

EPS bearer establishment, modification, release

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RRC Main Functions Broadcast of system information

Including NAS common information

Information applicable for UEs in RRC_Idle and information applicable forUEs in RRC_Connected

Including ETWS(Earthquake and Tsunami Warning System) and

CMAS(Commercial Mobile Alert Service) notifications

RRC connection control Paging

Establishment/modification/release of RRC connection

Initial security activation

RRC connection mobility handover

Establishment/modification/release of RBs carrying user data (DRBs)

Radio configuration control

Assignment/modification of ARQ, HARQ, DRX configurations

QoS control Assignment/modification of semi-persistent scheduling configuration

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Recovery from radio link failure

Inter-RAT(Radio Access Technology) mobility

Measurement configuration and reporting

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RRC state

RRC protocol has two states RRC_Idle

RRC_Connected

When an RRC connection has been establishment, the UE is inRRC_Connected state

Otherwise, the UE is RRC_Idle state

RRC_Idle RRC_Connected releaseentestablishm

Connection

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RRC_IDLE:

A UE specific DRX may be configured by upper layers.

UE controlled mobility;

The UE: Monitors a Paging channel to detect incoming calls, system information change, for

ETWS capable UEs, ETWS notification, and for CMAS capable UEs, CMAS notification

Performs neighbouring cell measurements and cell (re-)selection

Acquires system information.

RRC_CONNECTED:

Transfer of unicast data to/from UE.

At lower layers, the UE may be configured with a UE specific DRX.

Network controlled mobility, i.e. handover

The UE: Monitors a Paging channel and/ or System Information Block Type 1 contents to detect

system information change, for ETWS capable UEs, ETWS notification, and for CMAScapable UEs, CMAS notification;

Monitors control channels associated with the shared data channel to determine if data isscheduled for it;

Provides channel quality and feedback information;

Performs neighbouring cell measurements and measurement reporting;

Acquires system information.

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RRC state characteristics

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Paging

The purpose of paging procedure Transmit paging information provided to upper layers which in

response may initiate RRC connection establishment

e.g. to receive an incoming call

Inform UEs in RRC_Idle and Ues in RRC_Connected about asystem information change

Inform an ETWS notification

Inform a CMAS notification

Initiation E-UTRAN initiates the paging procedure by transmitting the Paging

message at the UEs paging occasion

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RRC Connection Establishment-SRB1

SRB(Signalling Radio Bearer): defined as Radio Bearers (RB) that are used for thetransmission of RRC and NAS messages

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RRC Connection Establishment-SRB2

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DRB Establishment

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RRC Signal Low Layer KeyConfiguration for DRB (1)

MAC : scheduling in eNB Distributes the available radio resources

In one cell among the UEs

Among the bearers of each UEs

Accordance

Downlink data buffered in the eNB

Buffer Status Reports(BSRs), received from the eNB

QoS of each DRB

Scheduling algorithm left to the eNB implementation, signalling tosupport the scheduling standardized

Scheduling mode Dynamic scheduling

Persistent scheduling

Semi-persistent scheduling

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RRC Signal Low Layer KeyConfiguration for DRB (2)

MAC : Discontinuous Reception (DRX) Configured for RRC_Conneted UE

Short-Cycle and Long-Cycle configured tradeoff between batterysaving and latency

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RRC Connection Release

When the UE does not have packets to bereceived/transmitted for an extended period of time The eNB initiates the release of the UEs RRC connection

Request MME to release the UEs S1 connection

eNB removes the UE context MME and SGW only remove the eNB specific part of the UE

context

S1 release procedure

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DRX in RRC_Idle In RRC_Idle state, the discontinuous reception is focus on paging in

order to reduce power consumption

Paging Frame (PF) : One Radio Frame which may contain one or multiple Paging Occasion

Paging Occasion (PO) : A subframe where there may be P-RNTI transmitted on PDCCH addressing

the paging message

PF and PO is determined by using the DRX parameters provided inSystem Information

System Information DRX parameters stored in the UE shall beupdated locally in the UE whenever the DRX parameter values arechanged in SI

When DRX is used the UE needs only to monitor one PO per DRXcycle

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DRX parameters in Idle state DRX parameters

T : DRX cycle of the UE. T is determined by

UE specific DRX cycle if configured by upper layer

Default DRX cycle

nB: 4T, 2T, T, T/2, T/4, T/8, T/16, T/32

N: min(T,nB)

Ns: max(1,nB/T)

UE_ID: IMSI mod 1024

Default DRX cycle broadcast in System Information

UE specific DRX cycle is sent to MME by Attach Request orTracking Area Update Request (NAS control message), thenMME notifies the eNB

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PF is determined by

SFN mod T= (T div N)*(UE_ID mod N)

PO is determinde by

i_s = floor(UE_ID/N) mod Ns

FDD:

Ns PO when i_s = 0 PO when i_s = 1 PO when i_s = 3 PO when i_s = 4

1 9 N/A N/A N/A

2 4 9 N/A N/A

4 0 4 5 9

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Network Re-entry time The UE in RRC_Idle state may be paged by the network

when there is data addressed to that particular UE

Then the UE will returns to RRC_connected state

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Express the network re-entry time as

k

= t0

+ t1

+ t2

+ t3

+ 1

+ 2

+ krtx

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Analytical Result

For simplifying the analysis, assume that

1 (eNB pages UE) is uniform distribution with mean T/2

Paging messages are successfully received by the UE with aprobability of 0.9

The maximum page retransmissions are limited to 4

The preamble detection error rate is 3%

The maximum number of preamble retransmission is 5

UEs preparation time to send the RACH preamble is 2ms

The time to receive RACH response from the eNB is 15ms

RACH transmission backoff time is 6ms

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Multiple pages per paging frame improve the reentry time significant23


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Reference

LTE-Advanced Radio Layer 2 and RRC aspects MagnusLindstrm, Ericsson 3GPP TSG-RAN WG2

Long Term Evolution Protocol Overview freescale

DRX Mechanism forPowe Saving in LTE Chandra S.

Bontu, ED Illidge, IEEE Communication Magazine

3GPP TS 36.331 Radio Resource Control (RRC) Protocolspecification

3GPP TS 36.304 User Equipment (UE) procedures in idle

mode

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Radio Resource RRC

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