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UMTS Signaling FlowContent:
UE State transitionSignaling flow
Classification of Flows In terms of protocol stack, signaling flows can be access layer signaling flows or non-access layer
signaling flows.
In terms of network composition, signaling flows can be categorized as circuit-switched or packet-
switched.
Access layer and non-access layer signaling flows are actually so named from the perspective of
protocol stack.
The flows at the access layer include PLMN selection, cell selection, and radio resource
management flows.
The radio resource management flows are the flows at the RRC layer, including the RRC
connection setup flow, flow of the signaling setup between UEs and CNs, RAB setup flow, call releaseflow, handover flow, and SRNS redirection flow.
UE Working Modes
There are two basic working modes:
Idle
UE stands by without any service. Theres no connection between UE and UTRAN.
Connected
UE transferred to the connected mode after accomplishing RRC Connection Setup.
UE has 4 states under the connected mode:Cell-DCH, Cell-FACH, Cell-PCH, URA-PCH
UE State
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UE States Under the Connected Mode
Cell-DCH
UE is activated, and in service using its dedicated channels.
There are dedicated channels in both uplink and downlink.
UTRAN knows exactly which cell the UE is in. Cell-FACH
UE is activated, but without too much date to transmit, so theres no need to assigndedicated channels to it.
Downlink data transmitted in FACH, while uplink in RACH.
UTRAN knows exactly which cell the UE is in.
Cell-PCH
There is no data transmitted in both uplink and downlink.
UE needs to listen to PICH for paging information.
UE works in discrete receiving, which saves the power effectively.
UTRAN knows exactly which cell the UE is in.
UE needs to do cell update procedure when it passes cells.
URA-PCH
There is no data transmitted in both uplink and downlink.
UE needs to listen to PICH for paging information and receive discretely.
UTRAN only knows which URA (UTRAN Registration Area) UE exists.
UE updates its location information only when its URA changes, which further reducesthe signaling saves resource.
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RRC State Transition (I) Transit from IDLE Mode
After RRC Connection Setup, UE will transit to CELL_FACH or CELL_DCH.
CN indicates UE using dedicated channel (CELL_DCH) or common channel (CELL_FACH)according to the service request.
If there is no service right now, UE will be indicated into PCH mode or release RRC connection
back to IDLE mode.
RRC State Transition (II) Transit from CELL_FACH Mode
UE do not occupy dedicated channels In the mode of CELL_FACH.
UE receives downlink data through FACH(S-CCPCH).
UE transmits uplink data through RACH(PRACH).
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RRC State Transition (III) Transit from CELL_DCH Mode
UE transceives uplink and downlink data through dedicated channels (DPDCHs and DPCCHs).
During the time when there is no data transmitted, CN may indicate UEs transiting to URA_PCH
or CELL_PCH
RRC State Transition (IV)ELL_P H
UR _P H
UE has no activated uplink.
Paging Information makes UE back to CELL_FACH or CELL_DCH mode.
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In CELL_PCH, UE should transit to CELL_FACH first to finish cell updating, and go back if noservice request.
In URA_PCH, if URA changes, UE also transits to CELL_FACH to finish cell updating first beforeit goes back to URA_PCH.
System resource can be saved in these two modes.
Signaling flow
Basic Conception (1) RRC (Radio Resource Control)
provides information transfer service to the NAS (Non Access Stratum).
responsible for controlling the configuration of UMTS radio interface Layers 1 and 2.
RRC Connection
A point to point bi directional connection between the RRC (Radio Resource Control)entities on the UE (User Equipment) and UTRAN (UMTS Terrestrial Radio Access Network).
The UE requires an RRC connection to access the services of the UMTS network.
Basic Conception (2) RAB -Radio Access Bearer
Identify the service the AS (Access Stratum) provides to the NAS (Non Access Stratum)for transfer of user data between the UE (User Equipment) and the CN (Core Network).
RB -Radio Bearer
The service provided by the Layer 2 for the transfer of user data between UE (UserEquipment) and UTRAN (UMTS Terrestrial Radio Access Network).
Basic Conception (3) RL (Radio Link)
RL is a logical association between single UE (User Equipment) and a single UTRAN(UMTS Terrestrial Radio Access Network) access point.
Its physical realization comprises one or more radio bearer transmissions.
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It is possible for a UMTS mobile to have many radio links established, when this occursthe mobile is said to be in a soft handover.
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UE Calling Flow
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UE Initiate Random Access
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Call Setup Flow
CN initiates a paging message to RNC.
RNC judges the paging message from the CN and then sends a paging message to thecorresponding UE.
If no RRC connection is available, UE will send a RRC connection setup request message (RRCConnection Request) to RNC.
RNC determines to set up a RRC connection according to the service request and systemresource occupation then sends a RRC connection setup message (RRC Connection Setup) to UE.
After signaling connection setup, the higher layer of UE (NAS) sends a service request messageto CN through a directly transfer message.
CN sends a RAB assignment message (RAB Assignment Request) to the RNC to allocateresource for UEs request.
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Handover Category
Intra-system handover
Softer handover, soft handover, hard handover
Depending on the Ec/No of CPICH
Inter-system handover
Between FDD and TDD
Handover with different system
2G/3G handover
Compression mode
Softer/Soft Handover Gain and Costs
Softer/Soft Handover Gain:
The optimal fast close loop power control (MS always keep connection with the mostpowerful cell)
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Seamless handover, without RB interruption
When MS moves to the edge of the cell, and could not obtain enough signal power, it canobtain Macro diversity from multiple cells
The UL signaling quality can be improved through obtaining Macro diversity when NodeB (Softer HO) and RNC (Soft HO) combine the receiving signal and lower the required Transport power ofUE.
Softer/Soft Handover Costs:
Additional Rake receiver channel on Node B
Additional DL channelization code
Additional DL power
Additional Rake receiver channel on MS
Additional transport link between Node B and RNC (RNC internal Soft Handover)
Additional transport link between S-RNC and D-RNC (Soft handover between RNCs)
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SRNC Relocation
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DCH-DCH Transport Channel Reconfiguration
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Cell-FACH to Cell-DCH State Transform
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Cell-DCH to Cell-FACH Transform
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RAB Release Flow
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RRC Connection Release
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Call setup flow (1)
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Call setup flow (2)
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Call setup flow (3)
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Call setup flow (4)
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Call setup flow (5)
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Call setup flow (6)
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