ETSI TR 102 962 V1.1.1 (2012-02)

Intelligent Transport Systems (ITS); Framework for Public Mobile Networks in Cooperative ITS (C-ITS)

DTR/ITS-0020035

General Information

• Status: Published
• Publication Date: 23-Feb-2012
• Technical Committee: ITS WG2 - Architecture and Cross Layer
• Current Stage: 12 - Completion
• Due Date: 02-Mar-2012
• Completion Date: 24-Feb-2012

Standards Content (Sample)

Technical Report
Intelligent Transport Systems (ITS);
Framework for Public Mobile Networks in
Cooperative ITS (C-ITS)
2 ETSI TR 102 962 V1.1.1 (2012-02)

Reference
DTR/ITS-0020035
Keywords
3GPP, architecture, IPv6, ITS
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3 ETSI TR 102 962 V1.1.1 (2012-02)
Contents
Intellectual Property Rights . 5
Foreword . 5
Introduction . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 6
3 Definitions and abbreviations . 9
3.1 Definitions . 9
3.2 Abbreviations . 9
4 Overview . . 10
5 Communication characteristics and features of cellular networks within C-ITS context . 10
5.1 Introduction . 11
5.1.1 Unicast Scenario . 11
5.1.2 MBMS Scenario (Broadcast Scenario) . 11
5.2 UMTS (HSPA) . 12
Technology Overview . 12
5.2.2 HSPA unicast uplink delay . 14
5.2.3 HSPA Unicast downlink delay . 14
5.2.4 Downlink distribution over HSPA ETWS . 14
5.2.5 CoCar trials and results . 15
5.2.5.1 System overview . 15
5.2.5.2 Unicast Mode . 15
5.2.5.3 Broadcast Mode . 19
5.2.5.4 Final conclusions . 21
5.3 GSM / EDGE . 22
5.3.1 Using GSM / GPRS uplink delay . 22
5.3.2 Downlink distribution over GSM / GPRS ETWS . 22
5.3.3 Downlink distribution over GSM / GPRS in unicast . 23
5.4 LTE . 23
5.4.1 Technology overview . 23
5.4.2 Physical downlink control channel . 24
5.4.3 Physical uplink control channel . 24
5.4.4 CoCarX Results . 24
5.4.4.1 System Overview . 25
5.4.4.2 CAM Scenario . 25
5.4.4.3 DENM Messages . 30
6 Service Enablers in support of C-ITS services . 34
6.1 System Architecture . 34
6.1.1 C-ITS Application Server (C-ITS AS). 37
6.1.2 Geomessaging Enabler . 37
6.1.3 Core Network Infrastructure Nodes . 38
6.1.3.1 Benefits of IMS . 38
6.1.3.1.1 Support for Quality of Service (QoS) . 38
6.1.3.1.2 Differentiated Charging . 38
6.1.3.1.3 Support for Roaming . 39
6.1.4 Warning Areas . 39
6.1.5 Geocast Client . 40
6.1.6 C-ITS applications . 40
6.2 Call flows . 40
6.2.1 Registration and session initiation . 41
6.2.2 C-ITS Application initiation . 42
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4 ETSI TR 102 962 V1.1.1 (2012-02)
6.2.2.1 Subsequent uplink data exchange . 43
6.2.3 Message dissemination (downlink) . 44
6.2.4 Vehicle location update . 44
6.3 Mapping the Geomessaging Enabler to C-ITS architecture . 45
6.3.1 Scalability and handling of multiple Geomessaging Enablers . 46
6.3.2 Handling of multiple cellular networks . 47
7 Identification and enhancements of ITS applications and related use cases . 47
7.1 Introduction . 47
7.2 Use case support . 48
7.2.1 Introduction. 48
7.2.2 DENM . 48
7.2.3 CAM . 48
7.3 BSA Classification . 49
7.3.1 Active road safety and Cooperative traffic efficiency use cases . 49
7.3.2 Co-operative local services and Global internet services use cases . 51
8 Impact on standards for cooperative ITS. 52
8.1 Introduction to standardization for C-ITS . 52
8.2 C-ITS architectures. 52
8.2.1 C-ITS overall architecture . 52
8.2.2 C-ITS communications architecture . 53
8.3 C-ITS commu nicatio ns . 53
8.3.1 Recognition of LTE in an ITS station . 53
8.3.2 ITS station management . 54
8.3.3 Communication profile selection . 54
8.4 C-ITS applications . 54
Annex A: Standard development summary . 55
Annex B: eMBMS for the delivery of vehicular services . 57
B.1 eMBMS characteristics . 57
B.2 Coverage areas associated with eMBMS . 58
B.3 eMBMS channels . 58
B.4 eMBMS performance in LTE . 59
B.5 Evaluation of eMBMS for the delivery of ITS services . 61
Annex C: Bibliography . 62
History . 63

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5 ETSI TR 102 962 V1.1.1 (2012-02)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://ipr.etsi.org).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Technical Report (TR) has been produced by ETSI Technical Committee Intelligent Transport System (ITS).
Introduction
Cooperative Intelligent Transport Systems (C-ITS) applications cover a wide range of different scenarios for road
transport with entities in the infrastructure (already existent or newly to be developed), in vehicles, and in portable
devices. The related functional communication needs demand a multiplicity of communication technologies out of the
classes:
• Ad-hoc communications, e.g. ITS-G5 standardized at ETSI (equivalent to CALM M5 standardized at ISO),
Infra-Red (IR) standardized at ISO, and others such as millimetric waves.
• Cellular network communications, e.g. UMTS, LTE and further generations.
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6 ETSI TR 102 962 V1.1.1 (2012-02)
1 Scope
The present document is based on an analysis of cooperative ITS (C-ITS) services using public mobile cellular
networks for communications between ITS stations in order to:
• identify related functional requirements on the ITS architecture,
• identify required amendments / modifications of existing standards on C-ITS in order to enable usage of public
mobile cellular networks,
• identify functionality to be specified in new ITS standards to be developed under M/453.
The result of the investigations is illustrated in the present document.
2 References
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
reference document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
2.1 Normative references
The following referenced documents are necessary for the application of the present document.
Not applicable.
2.2 Informative references
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
Non-standard references.
[i.1] M/453 EN 2009: "Standardisation mandate addressed to cen, cenelec and etsi in the field of
information and communication technologies to support the interoperability of co-operative
systems for intelligent transport in the european community".
[i.2] Joint CEN and ETSI Response to Mandate M/453.
[i.3] EC/DGINFSO-USDOT/RITA 2009: "EU-U.S. Joint Declaration of Intent on Research
Cooperation in Cooperative Systems".
[i.4] US DoT Research and Innovative Technology Administration, DTFH61-10-F-00045: "Core
System Concept of Operations (ConOps)", 19.4.2011.
[i.5] An Optimized Grid-Based Geocasting Method for Cellular Mobile Networks.
NOTE: Available at: http://docbox.etsi.org/ITS/ITSWG2/05-
CONTRIBUTIONS/2011/ITSWG2(11)0041_An_Optimized_Grid-
Based_Geocasting_Method_for_Cellular_Mobile_Net.pdf
[i.6] Category A Liaison Agreement, ETSI, ISO, 20.5.2008.
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7 ETSI TR 102 962 V1.1.1 (2012-02)
[i.7] EC DG INFSO: "Global Harmonisation of ITS cooperative systems standards", Letter
infoso.g.4(2011)1136082 to ETSI, 10.10.2011.
ETSI standard references
[i.8] ETSI TS 101 539-1: "Intelligent Transport Systems (ITS); V2V Application; Co-operative
Awareness application specification".
[i.9] ETSI TS 101 539-2: "Intelligent Transport System (ITS); V2V Application; Intersection Collision
Risk Warning Specification".
[i.10] ETSI TS 101 539-3: "Intelligent Transport Systems (ITS); V2V Application; Longitudinal
Collision Risk Warning Specification.".
[i.11] ETSI TS 101 556-1: "Intelligent Transport Systems (ITS); I2V Application; Electric Vehicle
Charging Spot Notification Specification".
[i.12] ETSI TS 102 636 (all parts): "Intelligent Transport Systems (ITS); Vehicular Communications;
GeoNetworking".
[i.13] ETSI TS 102 637-1: "Intelligent Transport Systems (ITS); Vehicular Communications; Basic Set
of Applications; Part 1: Functional Requirements".
[i.14] ETSI EN 302 637-2: "Intelligent Transport Systems (ITS); Vehicular Communications; Basic Set
of Applications; Part 2: Specification of Cooperative Awareness Basic Service".
[i.15] ETSI EN 302 637-3: "Intelligent Transport Systems (ITS); Vehicular Communications; Basic Set
of Applications; Part 3: Specifications of Decentralized Environmental Notification Basic
Service".
[i.16] ETSI TR 102 638: "Intelligent Transport Systems (ITS); Vehicular Communications; Basic Set of
Applications; Definitions".
[i.17] ETSI ES 202 663: "Intelligent Transport Systems (ITS); European profile standard for the physical
and medium access control layer of Intelligent Transport Systems operating in the 5 GHz
frequency band".
[i.18] ETSI EN 302 665: "Intelligent Transport Systems (ITS); Communications Architecture".
[i.19] ETSI TS 102 860: "Intelligent Transport Systems (ITS); Classification and management of ITS
application objects".
[i.20] ETSI TS 102 890-1: "Intelligent Transport Systems (ITS); Facilities layer function;
Communication Management specification".
[i.21] ETSI TS 102 890-2: "Intelligent Transport Systems (ITS); Facilities layer function; Services
announcement specification".
[i.22] ETSI TS 102 894-1: "Intelligent Transport System (ITS); Users and Applications requirements;
Facility layer structure, functional requirements and specifications;".
[i.23] ETSI DTS/ITS-0010021: "Intelligent Transport Systems; Facilities layer; Communication
congestion control".
[i.24] ETSI EN 302 895: "Intelligent Transport Systems (ITS); Vehicular Communications; Basic Set of
Applications; Local Dynamic Map (LDM) Specification".
IETF standard references
[i.25] IETF RFC 4145: "TCP-Based Media Transport in the Session Description Protocol (SDP)".
CEN/ISO standard references
[i.26] ISO 16444: "Intelligent transport systems - Communications access for land mobiles (CALM)-
Geo-Routing".
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8 ETSI TR 102 962 V1.1.1 (2012-02)
[i.27] ISO 16445: "Intelligent transport systems - Communications access for land mobiles (CALM)-
Handover architecture".
[i.28] ISO 17419: "Classification and management of ITS applications in a global context".
[i.29] ISO 17423: "ITS application requirements for selection of communication profiles".
[i.30] ISO/NP 17427: "European co-operative ITS framework architecture and roles and responsibilities
in the context of co-operative ITS based on architecture(s) for cooperative systems".
[i.31] ISO 17515: "Intelligent transport systems -- Communications access for land mobiles (CALM)-
LTE cellular systems".
[i.32] ISO 21212, "Intelligent Transport Systems - Communications access for land mobiles (CALM)-
2G cellular systems".
[i.33] ISO 21213: "Intelligent Transport Systems - Communications access for land mobiles (CALM)-
3G cellular systems".
[i.34] ISO 21214: "Intelligent Transport Systems - Communications access for land mobiles (CALM)-
Infra-red systems".
[i.35] ISO 21215: "Intelligent transport systems - Communications access for land mobiles (CALM)-
M5".
[i.36] ISO 21217: "Intelligent Transport Systems - Communications access for land mobiles (CALM)-
Architecture".
[i.37] ISO 21218: "Intelligent Transport Systems - Communications access for land mobiles (CALM)-
Medium service access points".
[i.38] ISO 24102-1: "Intelligent Transport Systems - Communications access for land mobiles (CALM)-
ITS station management Part 1: Local management".
[i.39] ISO 24102-2: "Intelligent Transport Systems - Communications access for land mobiles (CALM)-
ITS station management Part 2: Remote management".
[i.40] ISO 24102-3: "Intelligent Transport Systems - Communications access for land mobiles (CALM)-
ITS station management Part 3: Service access points".
[i.41] ISO 24102-4: "Intelligent Transport Systems - Communications access for land mobiles (CALM)-
ITS station management Part 4: Station-internal management communications".
[i.42] ISO 24102-5: "Intelligent transport systems - Communications access for land mobiles (CALM)-
ITS station management Part 5: Fast service advertisement protocol (FSAP)".
[i.43] ISO 29281-2: "Intelligent transport systems - Communications access for land mobiles (CALM)-
Non-IP networking Part 2: Fast networking & transport layer protocol (FNTP)".
IEEE standard references
[i.44] IEEE 1609: "Standard for Wireless Access in Vehicular Environments - WAVE" multipart
deliverable.
Other technical references
[i.45] Motorola, EMBMS Performance Evaluation; 3GPP Tdoc R1-071975; April 23-24, 2007.
[i.46] ETSI TS 136 300: "LTE; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved
Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2".
[i.47] Dorbes, G. and Amosse, H. (2008): "Combining web 2.0 and ims: The road to new services and
business models".
NOTE: Available at: http://www.alcatel-lucent.com/enrich/v2i12008/article_c3a2.html
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9 ETSI TR 102 962 V1.1.1 (2012-02)
[i.48] CoCar Consortium, AKTIV-CoCar: "Adaptive and Cooperative Technologies for Intelligent
Traffic - Cooperative Cars", CoCar Feasibility Study Technology, Business and Dissemination.
[i.49] CoCar Consortium: "CoCarX Coperative Cars eXtended ITS services and communication
architecture Deliverable D3".
[i.50] IEEE 802.11: ." Wireless Access in Vehicular Environments (WAVE): IEEE 1609 Standards
Series".
[i.51] ETSI TS 136 211: "LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical
channels and modulation".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in [i.18], [i.36], [i.16] and the following
apply:
geomessaging: application in charge of distribution of ITS messages into a geographical area
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in [i.18], [i.36], [i.16] and the following apply:
Abis Air interface
APDU Application Protocol Data Unit
BSA Basic Set of Applications
BSC Base Station Controller
BM-SC Broadcast Multicast Service Centre
BTS Base Transceiver Station
CHW Cellular Hazard Warning
CELL_DCH Cell Dedicated Channel
CELL_FACH Cell Forward Access Channel
DL Downlink
DRX Discontinuous Reception
DPCH Dedicated physical channel
ETWS Earthquake and Tsunami Warning System
E2E End to End
FACH Forward Access Channel
FTAP Fast traffic access protocol
GC-SAP Geocast Client Service Access Point
HTTP Hyper Text Transfer Protocol
IMS Internet Multimedia Subsystem
Gb/Gn Interface between GGSN Node and Internet
GSM Global System for Mobile Communications
HSPA High Speed Packet Access
HS-DSCH High speed dedicated shared channel
LTE Long Term Evolution
MBMS Multimedia Broadcast and Multicast Services
MCS Modulation and Coding Scheme
MTCH MBMS Traffic Channel
MSCH MBMS Scheduling
MCCH MBMS Control Channel
MICH MBMS Notification Indicator Channel.
MIMO Multiple-input and multiple-output
MSA MBMS Service Area
MS Mobile Station
PDCH Physical Data Channel
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10 ETSI TR 102 962 V1.1.1 (2012-02)
RNC Radio Network Controller
RLC Radio Link Controller
RRC Radio Resource Control
RTT Round Trip Time
RTI Road Traffic Information
RHW Road Hazard Warning
SMSCB Short Message Service Cell Broadcast
S-CCPCH Secondary Common Control Physical Channel
SIP Session Initialization Protocol
TTI Transmission Time Interval
UE User Equipment
UL Uplink
UMTS Universal Mobile T
URA_PCH Utran Registration Area-Paging Channel
UDP User Datagram Protocol
UA User Agent
W-CDMA Wideband Code Division Multiple Access
4 Overview
Starting from the architecture described in the published standards on ITS communication architecture [i.18] and [i.36],
and considering primarily, but not exclusively, the basic set of applications identified in [i.16], a critical assessment of
the applicability of the 3G and 4G mobile network access to support the described application scenarios is given in the
present document. This analysis refers to technical standards developed by 3GPP. This analysis is based on the ITS
station architecture. Additional technical background provided by R&D projects such as:
• CoCAR (http://www.aktiv-online.org/english/aktiv-cocar.html) [i.48],
• CoCARx (the follow-on project including integration between LTE [i.31] and WAVE-DSRC [i.44] access
technologies) [i.49], and
• CVIS (http://www.cvisproject.org/),
is considered for the development of the present document.
Related standards from other SDOs working on C-ITS, e.g. CEN TC278 WG16 / ISO TC204 WG1, WG16, WG18,
also are considered as appropriate.
This approach is coherent with the spirit of the "Joint CEN and ETSI Response to Mandate M/453" [i.2], with specific
reference to clause 3.3 "Standardisation for Co-operative systems covering other media", and clause 4.2.3. "National
R&D projects including national FOTs".
As result, the present document illustrates usage of cellular network technology for C-ITS.
Clause 5 presents communication characteristics and features of cellular networks.
Clause 6 identifies ITS applications and related use cases applicable over cellular networks communications, and their
possible enhancements.
Clause 7 explains special features of cellular networks in support of C-ITS services.
Clause 8 illustrates the impact of cellular networks in C-ITS on the ITS communication architecture, and the required
ITS station management, and further procedures.
5 Communication characteristics and features of
cellular networks within C-ITS context
This clause describes the communication characteristics of cellular networks as considered to be applicable for C-ITS.
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11 ETSI TR 102 962 V1.1.1 (2012-02)
5.1 Introduction
Cellular networks offer two modes of data transportation that can be used for V2V or V2I communications. Both modes
require a backend network server that intercepts traffic from vehicles or traffic infrastructure and redistributes traffic to
vehicles and traffic infrastructure after processing. To allow the backend server to redistribute traffic to the concerned
vehicles, moving vehicles need to send location information to the backend server with a reasonable update rate. The
following is a brief overview of these modes in more details.
5.1.1 Unicast Scenario
The unicast scenario is used both for uplink and downlink distribution. In the uplink case, vehicles send the message to
the network. For downlink distribution, vehicles are addressed individually. In this case, the backend server (Traffic
Information Server) sends the same message individually to all concerned vehicles and infrastructure nodes. This is
illustrated in the exemplary Figure 5.1, and where upon "Transmit Trigger Events" (TTE) the moving road works
vehicle sends its identification, type, speed, heading, and position via the cellular network to a traffic information
server. This information is then distributed to all service users in the vicinity.
In order to identify users (approaching vehicles) that move towards the moving road works vehicle, the server also
needs context information about every single user. One approach to realize such a user context is that all equipped cars
regularly send their status, containing identification, location, heading, speed, etc. to the server. Another approach is for
cars to make use of network-based positioning servers to obtain location information. This enables the server to track
the vehicles and to identify those vehicles approaching the moving road works vehicle for which the Moving Road
Works Warning is relevant. Accordingly, the service addresses single approaching vehicles by unicast communications
and informs them about hazards or obstacles ahead.
Note that unicast scenario is always used for uplink regardless of the mode used in downlink distribution.

Figure 5.1: Unicast scenario example "Moving Road Works Warning"
5.1.2 MBMS Scenario (Broadcast Scenario)
This scenario is used exclusively for downlink distribution of messages, and where all vehicles belonging to a broadcast
area are addressed collectively, rather than individually. In the exemplary broadcast scenario depicted in Figure 5.2, the
authorized server (Traffic Information Server) addresses the "Broadcast Multicast Service Centre" (BM-SC) to
distribute the data via "Multimedia Broadcast and Multicast Services" MBMS. MBMS can maintain different broadcast
areas, one of which in this exemplary case would be the highway area with the road works. One broadcast area can
consist of any set of cells specified by the cellular operator.
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12 ETSI TR 102 962 V1.1.1 (2012-02)

Figure 5.2: MBMS scenario
One main difference to the unicast scenario is that no single user but the whole broadcast area is addressed. This means
that it is not necessary to keep a complete user profile in the server that includes the rough position of the user. Thus,
scalability and privacy are less critical in the MBMS scenario.
Furthermore, core network resources are saved, because every message is only transmitted once reaching all vehicles in
the cell using the broadcast channel. If several vehicles are located in one cell, the broadcast solution is also more
resource efficient on the radio interface.
This scenario also means that the received information is not that much personalized according to one certain user
context. Here, the vehicle has to filter out relevant information itself. The larger the broadcast area the more processing
has to be done in the vehicle.
Another variation of broadcast specified by 3GPP for 2G and 3G systems is the broadcast on the "Earthquake and
Tsunami Warning System" (ETWS).
5.2 UMTS (HSPA)
This clause presents a brief overview of the UMTS (HSPA) technology, its key characteristics and suitability for C-ITS.
In addition, the results and conclusions from the CoCar project which used this technology are presented.
Technology Overview
UMTS was first standardized by 3rd Generation Partnership Project (3GPP) in 1999. UMTS is based on Direct
Sequence Code Division Multiple Access (DS-CDMA), which means that every signal of a physical channel is spread
over the whole carrier bandwidth by multiplying it with a certain channelization code, the Orthogonal Variable
Spreading Factor (OVSF, short: SF) code. Thus, with the W-CDMA technology, a unique code identifies each physical
channel, and the SF of the code determines the bit rate.
UMTS has undergone several enhancements over the years that can be briefly summarized as follows:
HSDPA
The first enhancement to UMTS was introduced with High Speed Downlink Packet Access (HSDPA) in 3GPP
Release 5. HPDPA increases the downlink data rates up to 14,4 Mbit/s. Work on this standard enhancement started in
2003 and the technology was finally commercially available in late 2005.
HSUPA
High Speed Uplink Packet Access (HSUPA) was introduced to UMTS Release 6, improved uplink data rates up to 5,7
Mbit/s are possible. It can be seen as the counterpart to HSDPA. First networks have been rolled out using this Release
6 technology in 2007. HSUPA actually implements the same sort of techniques already used by HSDPA.
HSPA
High Speed Packet Access (HSPA) is referred to as the combination of HSDPA and HSUPA.
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13 ETSI TR 102 962 V1.1.1 (2012-02)
UE RRC states
The Radio Resource Control (RRC) defines protocol states that describe which processes should be active in the UE
and whether a common or a dedicated/shared channel is used. The different sub-states are illustrated in Figure 5.3.
Connected
CELL_DCH
data
timeout A
buffer size > x
Idle
CELL_FACH
timeout B
CELL_PCH URA_PCH
Figure 5.3: RRC States
Typically, an inactive UE would camp in RRC Idle mode, which is a power saving mode with very rare signalling
traffic. In this mode, the UE is known by the network on routing area level, i.e. the responsible Radio Network
Controller (RNC) is known. When the UE has uplink data to send, it initiates a connection setup using the Random
Access Channel (RACH) to enter the Connected mode. If downlink data is addressed to the idle UE, the network pages
the UE (paging period assumed to be 640 ms) in the cells of the routing area. In response, the UE initiates a connection
setup and accordingly enters Connected mode.
In Connected mode, there are four different states which are described in the following.
CELL_DCH: A dedicated or shared channel is allocated to the UE. Depending on the WCDMA network this channel
can either be a Dedicated Channel (DCH), High Speed Downlink Shared Channel (HS-DSCH) or an Enhanced DCH
(E-DCH). In this state messages can be transmitted and received with a minimal delay. As depicted in Figure 5.3, the
UE stays in CELL_DCH as long as it sends and receives data. After a certain inactivity time A, the UE transits to
CELL_FACH. The timeouts mentioned in the illustration are network parameters and can differ between operators and
regions. A typical value for A is 2 seconds as implemented in the MNO network used for the trials.
CELL_FACH: Common channels, i.e. RACH and Forward Access Channel (FACH), are established and can be used
to exchange control information and small amounts of user data. When the buffers in UE or RNC exceed a certain
threshold, the UE sends an RRC measurement report and thus initiates a channel type switch to CELL_DCH. The
threshold takes place when the CELL_FACH transmission delay exceeds the delay of the channel switch to
CELL_DCH plus data transmission delay using dedicated channels, i.e. about 220 bytes in uplink. If the UE is not
active at all for a certain time B, the state can be changed to CELL_PCH, URA_PCH or Idle. Figure 5.3 only shows the
change to Idle because this is the procedure used in the live network in which our measurements were performed.
In CELL_FACH the signalling is reduced to the already mentioned measurement reports and cell updates. These cell
updates are sent every time the UE changes the serving cell and generate control signalling traffic. The UE listens to the
Broadcast Channel (BCH) transport channel of the serving cell as well as those from neighbouring cells. When it moves
from one cell to the other it notifies the network about the change triggering a cell location update.
CELL_PCH: The UE sends regular cell updates as in CELL_FACH and is thus known on cell level. In this state,
Discontinuous Reception (DRX) can be performed to save battery power. Thus, a paging message has to be sent to
make the UE switch to CELL_FACH state and listen to the FACH. In uplink, no additional delay compared to
CELL_FACH is expected.
URA_PCH: This state is similar to CELL_PCH, but the UE sends URA updates instead of cell updates, i.e. the serving
RNC is known. That means that much less control signalling is necessary, but also that the UE has to perform a cell
update for data transmission. The UE has to be paged for downlink transmissions, but the cell update procedure is faster
than the complete bearer setup from Idle state. This state is not implemented in the measured network.
For an RTI service supporting hazard warnings, the timeouts for state transition could be optimized specially for a
certain user group. A simple way to force the UE to stay in a certain state without changing network parameters is to
send small dummy messages to restart the timers, e.g. the implementation of the CoCar prototype uses such keep-alive
messages. These keep-alive messages can be created by the application, but obviously generate unwanted transmission
overhead.
ETSI
14 ETSI TR 102 962 V1.1.1 (2012-02)
5.2.2 HSPA unicast uplink delay
The UE can be in either Idle state (power saving state) or "Radio Resource Control (RRC) Connected" state. In Idle
state, which is a power saving state, the connection setup will require 2 seconds to 2,5 seconds which disqualifies this
state from further discussions as the total latency should not exceed one second. "RRC connected" includes three sub
states that are to be considered, namely CELL_DCH (shared or dedicated channel) sub state, CELL_FACH (common
channel) sub state and URA_PCH sub state.
• If the UE is in CELL_DCH or CELL_FACH sub state the total uplink transmission time is 100 ms to 178 ms.
• If the UE is in URA_PCH sub state about 300 ms has to be added to the above due to state channel switching
to CELL_FACH sub state before start of transmission, i.e. the total time is 400 ms to 500 ms in total.
5.2.3 HSPA Unicast downlink delay
Similar to the above case, only UEs in "RRC connected" state have to be considered, as idle state is disqualified already
on its uplink performance.
For UEs in CELL_DCH and CELL_FACH sub state values are similar to those for uplink transmission presented
above. Furthermore:
• For networks based on R6 and later releases as many as about 1 000 UEs per cell in CELL_DCH sub state can
be reached with a message.
• For networks based on R7 and later releases up to 2 000 UEs can be reached with a message.
For UEs in URA_PCH, state channel switching requires 300 ms similar to the uplink case. Furthermore, paging is
required and that takes another 160 ms (average value).
However, there are severe snags associated with the use of the CELL_DCH and CELL_FACH sub state:
• Continuous camping on CELL_DCH sub state can be allowed for a very limited number of devices depending
on the product specification. Furthermore, switch down from CELL_DCH to CELL_FACH sub state normally
takes place after a few seconds of no data transmission.
• The situation for CELL_FACH sub state is somewhat better than for CELL_DCH sub state. The maximum
number of UEs allowed to remain in the CELL_FACHs sub-state is higher than the previous case but it is
shared amongst all RBSs connected to the "Radio Network Controller" (RNC) node which controls the RBSs.
This will anyway prevent a widespread use of it for unicast ITS message distribution. Switching down to
URA_PCH sub state or idle state takes place typically after ~30 seconds of "quietness".
• Finally, the number of stations being simultaneously in the URA_PCHs sub-state has also an upper limit.
In conclusion, provided that UEs are permanently in CELL_DCH or CELL_FACH sub-state, the total latency for
unicast V2V or V2I is not an issue. The issue is rather the limitations imposed on the number of UEs simultaneously in
CELL_DCH and CELL_FACH.
5.2.4 Downlink distribution over HSPA ETWS
ETWS in WCDMA shows a couple of major obstacles for using it for C-ITS purposes:
• Reception of ETWS notification in CELL_FACH and CELL_DCH sub-state is not standardized and is up to
UE implementation/capability and operator support.
• The ETWS primary notification carries no data and a secondary notification will always be required for any
message.
The first obstacle could be removed by a minor change in the standard if major operators would drive the issue but the
second is worse as the lowest possible total latency will be around two seconds. Whether an extended primary
notification able to forward a message would be possible to introduce, technically and standardization wise, has not
been investigated.
ETSI
15 ETSI TR 102 962 V1.1.1 (2012-02)
5.2.5 CoCar trials and results
5.2.5.1 System overview
The CoCar project aimed at assessing cellular technology for the use in low latency vehicular communication focusing
on using the public cellular network for transportin
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