1、 ETSI TS 102 687 V1.2.1 (2018-04) Intelligent Transport Systems (ITS); Decentralized Congestion Control Mechanisms for Intelligent Transport Systems operating in the 5 GHz range; Access layer part TECHNICAL SPECIFICATION ETSI ETSI TS 102 687 V1.2.1 (2018-04)2 Reference RTS/ITS-00430 Keywords ITS, ra
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7、the written authorization of ETSI. The copyright and the foregoing restriction extend to reproduction in all media. ETSI 2018. All rights reserved. DECTTM, PLUGTESTSTM, UMTSTMand the ETSI logo are trademarks of ETSI registered for the benefit of its Members. 3GPPTM and LTETMare trademarks of ETSI re
8、gistered for the benefit of its Members and of the 3GPP Organizational Partners. oneM2M logo is protected for the benefit of its Members. GSMand the GSM logo are trademarks registered and owned by the GSM Association. ETSI ETSI TS 102 687 V1.2.1 (2018-04)3 Contents Intellectual Property Rights 4g3Fo
9、reword . 4g3Modal verbs terminology 4g3Introduction 4g31 Scope 5g32 References 5g32.1 Normative references . 5g32.2 Informative references 5g33 Definitions, symbols and abbreviations . 6g33.1 Definitions 6g33.2 Symbols 6g33.3 Abbreviations . 6g34 Overview 7g34.1 Introduction 7g34.2 Architecture 7g34
10、.3 DCC_ACC component . 7g35 Algorithms 8g35.1 Introduction 8g35.2 Requirements 8g35.3 Reactive approach 8g35.4 Adaptive approach 9g3Annex A (informative): Parameter setting of reactive approach . 10g3Annex B (informative): Packet handling to meet channel occupancy limit . 11g3Annex C (informative):
11、Bibliography . 12g3Annex D (informative): Change History 13g3History 14g3ETSI ETSI TS 102 687 V1.2.1 (2018-04)4 Intellectual Property Rights Essential patents IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information pertaining to these essenti
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14、hich are, or may be, or may become, essential to the present document. Trademarks The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners. ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, an
15、d conveys no right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks. Foreword This Technical Specification (TS) has been produced
16、by ETSI Technical Committee Intelligent Transport Systems (ITS). Modal verbs terminology In the present document “shall“, “shall not“, “should“, “should not“, “may“, “need not“, “will“, “will not“, “can“ and “cannot“ are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal
17、 forms for the expression of provisions). “must“ and “must not“ are NOT allowed in ETSI deliverables except when used in direct citation. Introduction Decentralized congestion control (DCC) is a necessity in ad hoc networks where the number of communicating stations varies and is not known in advanc
18、e. Vehicular ad hoc network (VANET) presents a challenge because in a few seconds a very high density of vehicles can be in radio range of each other due to for example an accident. A DCC algorithm needs to cope with few as well as many communicating stations within radio range. The medium access co
19、ntrol (MAC) algorithm schedules transmissions to avoid interference between communicating stations. The wireless channel is a finite resource and when the number of required resources exceeds available resources, the DCC algorithm needs to shape the data traffic injected by each communicating statio
20、n to avoid channel congestion. All MAC schemes applied in an ad hoc setting such as the high-speed vehicular environment need to have DCC. However, DCC cannot solely operate on the MAC layer since the MAC layer is not aware of the applications running in the station. DCC is a cross-layer functionali
21、ty and applications need to be aware of the current channel activity to prioritize between different internal data traffic sources once DCC will restrict transmissions. In infrastructure based networks (i.e. networks containing a centralized network controller such as an access point or base station
22、) when the required resources exceed available resources, the centralized network controller can for example decide to not grant access to the network or run certain links with reduced quality of service. But for a VANET, communicating stations are responsible for a graceful degradation of applicati
23、ons, where some might be temporarily shut down while others can continue without disruption when the DCC is active. DCC is also a way to divide the resources among the communicating stations and to restrict that some stations operate using all resources. ETSI EN 302 571 1 put up upper limits on the
24、DCC by using duty cycle requirements. ETSI ETSI TS 102 687 V1.2.1 (2018-04)5 1 Scope The present document describes the means of controlling the data traffic injected to a frequency channel from the access layer perspective. The outlined algorithms are only applicable to ITS-G5 i.4. 2 References 2.1
25、 Normative 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 referenced document (including any amendme
26、nts) applies. Referenced documents which are not found to be publicly available in the expected location might be found at https:/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. The f
27、ollowing referenced documents are necessary for the application of the present document. 1 ETSI EN 302 571 (V2.1.1): “Intelligent Transport Systems (ITS); Radiocommunications equipment operating in the 5 855 MHz to 5 925 MHz frequency band; Harmonised Standard covering the essential requirements of
28、article 3.2 of Directive 2014/53/EU“. 2 ETSI TS 103 175 (V1.1.1): “Intelligent Transport Systems (ITS); Cross layer DCC management entity for operation in the ITS G5A and ITS G5B medium“. 2.2 Informative references References are either specific (identified by date of publication and/or edition numb
29、er or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETS
30、I cannot guarantee their long term validity. 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. i.1 ETSI TS 102 636-4-2 (V1.1.1): “Intelligent Transport Systems (ITS); Vehicular Communica
31、tions; GeoNetworking; Part 4: Geographical addressing and forwarding for point-to-point and point-to-multipoint communications; Sub-part 2: Media-dependent functionalities for ITS-G5“. i.2 ETSI TR 101 612: “Intelligent Transport Systems (ITS); Cross Layer DCC Management Entity for operation in the I
32、TS G5A and ITS G5B medium; Report on Cross layer DCC algorithms and performance evaluation“. i.3 G. Bansal, J. B. Kenney, and C. E. Rohrs: “LIMERIC: A Linear Message Rate Control Algorithm for DSRC Congestion Control,“ in IEEE Transactions on Vehicular Technology, vol. 62, no. 9, pp. 4182-4197, July
33、 2013. i.4 ETSI EN 302 663 (V1.2.1): “Intelligent Transport Systems (ITS); Access layer specification for Intelligent Transport Systems operating in the 5 GHz frequency band“. ETSI ETSI TS 102 687 V1.2.1 (2018-04)6 3 Definitions, symbols and abbreviations 3.1 Definitions For the purposes of the pres
34、ent document, the following terms and definitions apply: channel busy ratio (CBR): time-dependent value between zero and one representing the fraction of time that a single radio channel is busy with transmissions duty cycle: defined as the ratio, expressed as a percentage of the transmitter total “
35、on“ time on one carrier frequency, relative to 1 second period 3.2 Symbols For the purposes of the present document, the following symbols apply: CBR_L_0_Hop Local channel busy ratio for a specific frequency channel for ego ITS station CBR_G Global channel busy ratio for a specific frequency channel
36、 CBR_L_0_Hop_Previous the second most recent CBR_L_0_Hop CBR_G_Previous the second most recent CBR_G CBRITS-Smoving average of measured CBR values CBRtargetcontrol parameter g1833g3040g3028g3051g2878control parameter g1833g3040g3028g3051g2879control parameter TCBRperiod of time Tonduration of a tran
37、smission Ton_ppduration of the previous transmission Toffminimum time between two transmissions Ton/(Ton+ Toff) control parameter control parametermaxmaximum value of minminimum value of offsetoffset value of t current system time tgotime when gate keeper opens tpgtime when the gate keeper closes 3.
38、3 Abbreviations For the purposes of the present document, the following abbreviations apply: CBR Channel Busy Ratio DCC Decentralized Congestion Control DCC_ACC DCC component of the ACCess layer DCC_FAC DCC component of the FACilities layer DCC_NET DCC component of the NETwork layer ITS Intelligent
39、Transport Systems ITS-S ITS Station MAC Medium Access Control TDC Transmit Datarate Control TPC Transmit Power Control TRC Transmit Rate Control UTC Coordinated Universal Time VANET Vehicular Ad Hoc NETworks ETSI ETSI TS 102 687 V1.2.1 (2018-04)7 4 Overview 4.1 Introduction The objective of the pres
40、ent document is to describe the decentralized congestion control (DCC) algorithms fulfilling the requirements described in clause 4.2.10 of ETSI EN 302 571 1 and in clause 7.2 of ETSI TS 103 175 2. In order to conform to the present document either the algorithm specified in clause 5.3 or the algori
41、thm specified in clause 5.4 shall be implemented. 4.2 Architecture The DCC architecture is shown in Figure 1. It consists of the following DCC components: DCC_ACC located in the access layer; DCC_NET i.1 located in the networking DCC_FAC 2 located in the facilities layer; and DCC_CROSS 2 located in
42、the management layer. The DCC_ACC component is specified in the present document and belongs to a DCC framework covering all parts of the architecture. Figure 1: DCC Architecture 4.3 DCC_ACC component The DCC_ACC component provides the local channel busy ratio (CBR) value to the DCC algorithm. If in
43、formation sharing for DCC is supported through ETSI TS 102 636-4-2 i.1, then the global CBR, CBR_G, value shall be used. NOTE: The global CBR value can be received from the GeoNetworking header if ETSI TS 102 636-4-2 i.1 is supported. ETSI ETSI TS 102 687 V1.2.1 (2018-04)8 5 Algorithms 5.1 Introduct
44、ion Different techniques exist for controlling the network load: Transmit power control (TPC) Transmit rate control (TRC) Transmit datarate control (TDC) One or several techniques combined can be used by the DCC algorithm for controlling the network load. In Table 1, the different techniques are bri
45、efly described. Table 1: Different DCC access mechanisms described. Technique Description TPC In TPC, the output power is altered to adjust the current channel load. For example, during high utilization periods the ITS-S can reduce its output power and thereby, is a reduction in interference range a
46、chieved. This results in that ITS-Ss further away will experience a reduced CBR. TRC TRC regulates the time between two consecutive packets from an ITS-S. During high utilization periods, the TRC increases the time between two packets for the ITS-S, Toff time. TDC TDC is a mechanism that can be used
47、 by wireless systems offering several transfer rate options. During high utilization periods and depending on application, a higher transfer rate can be used to decreased the Ton time. An introduction to reactive and adaptive DCC algorithms is provided in Annex C of ETSI TS 103 175 2 and Annex A of
48、ETSI TR 101 612 i.2. 5.2 Requirements The DCC algorithm is subject to the following requirements: The algorithm shall run on each frequency channel specified in ETSI EN 302 571 1 independently. The algorithm shall run in an infinite loop. The algorithm shall be activated at least every 200 ms. The a
49、lgorithm shall not exceed the limits provided in clause 4.2.10 in ETSI EN 302 571 1 and in clause 7.2 in ETSI TS 103 175 2. The CBR assessment shall be according to clause 4.2.10 in ETSI EN 302 571 1. 5.3 Reactive approach The reactive approach consists of several states reached depending on the current CBR. The evaluation of state is performed every TCBR. Every state can control the network load using one or a combination of the techniques described in clause 5.1. One state can only be reached
