Innovation andpractice ofTD-LTEforintelligenttransportation systemsGuide Words: ITS; enhanced TD-LTE; safety-related ITS applicationAbstract: Intelligent transportation system (ITs) has become a popular research topic to meet theincreased demands of transportation safety, traffic efficiency, comfort in the journey and environmentprotection, etc. ITS applications impose higher requirements on wireless communication systems. Forexample, safety-related ITS services must always be low latency and entertainment-related ITSservices need high data rate. The ITS dedicated short-range communications (DSRC) technology tosupport the safety- related application is still under development, while long term evolution (LTE), asthe next generation mobile communication systems, offers an efficient communication platform forITS information exchange, which can meet most ITS services requirements of latency, data rate aswell as communication range. In this paper, based on the time-division duplex (TDD) mode of LTE,i.e. TD-LTE, an enhanced TD-LTE network architecture is introduced to better support safety-relatedITS application with low latency requirement, and some enhanced access schemes of TD-LTE areproposed to improve the performance of supporting the high-speed IP-based ITS applications inhotspots. At last, two practical application scenarios of enhanced TD-LTE systems are givenI.INTRODUCTIONIntelligent transportation system (ITS) has become a popular research topic to meet the increaseddemands oftransportation safety,traffic efficiency,comfort in the journey and environment protectionetc. ITS applications impose higher requirements on wireless communication systems.For example,safety-related ITS services must always be low latency and entertainment-related ITS services needhigh data rate.The ITS dedicated short-range communications (DSRC) technology to support thesafety-related application is still under development, while longterm evolution (LTE),as thenextgeneration mobile communication systems, offers an efficient communication platform for ITSinformation exchange, which can meet most ITs services requirements of latency, data rate as well ascommunication range. In this paper, based on the time-division duplex (TDD) mode of LTE, i.eTD-LTE, an enhanced TD-LTE network architecture is introduced to better support safety-related ITSapplication with low latency requirement, and some enhanced access schemes of TD-LTE areproposed to improve the performance of supporting the high-speed IP-based ITS applications inhotspots. At last, two practical application scenarios of enhanced TD-LTE systems are givenCurrently, there are a variety of wireless communication technologies, such as cellular network
Innovation and practice of TD-LTE for intelligent transportation systems Guide Words：ITS; enhanced TD-LTE; safety-related ITS application Abstract：Intelligent transportation system (ITS) has become a popular research topic to meet the increased demands of transportation safety, traffic efficiency, comfort in the journey and environment protection, etc. ITS applications impose higher requirements on wireless communication systems. For example, safety-related ITS services must always be low latency and entertainment-related ITS services need high data rate. The ITS dedicated short-range communications (DSRC) technology to support the safety- related application is still under development, while long term evolution (LTE), as the next generation mobile communication systems, offers an efficient communication platform for ITS information exchange, which can meet most ITS services requirements of latency, data rate as well as communication range. In this paper, based on the time-division duplex (TDD) mode of LTE, i.e. TD-LTE, an enhanced TD-LTE network architecture is introduced to better support safety-related ITS application with low latency requirement, and some enhanced access schemes of TD-LTE are proposed to improve the performance of supporting the high-speed IP-based ITS applications in hotspots. At last, two practical application scenarios of enhanced TD-LTE systems are given. I. INTRODUCTION Intelligent transportation system (ITS) has become a popular research topic to meet the increased demands of transportation safety, traffic efficiency, comfort in the journey and environment protection, etc. ITS applications impose higher requirements on wireless communication systems. For example, safety-related ITS services must always be low latency and entertainment-related ITS services need high data rate. The ITS dedicated short-range communications (DSRC) technology to support the safety- related application is still under development, while long term evolution (LTE), as the next generation mobile communication systems, offers an efficient communication platform for ITS information exchange, which can meet most ITS services requirements of latency, data rate as well as communication range. In this paper, based on the time-division duplex (TDD) mode of LTE, i.e. TD-LTE, an enhanced TD-LTE network architecture is introduced to better support safety-related ITS application with low latency requirement, and some enhanced access schemes of TD-LTE are proposed to improve the performance of supporting the high-speed IP-based ITS applications in hotspots. At last, two practical application scenarios of enhanced TD-LTE systems are given. Currently, there are a variety of wireless communication technologies, such as cellular network
(e.g. 2G/3G/4G), wireless LAN, dedicated short-range communications (DSRC) and so on. On onehand, in some countries, many trials have been done to test the DSRC technology to support thesafety-related applications. Though the test results are positive, both the factor of commercial modeand lawful policy are ambiguous. It seems that use of DSRC is still indeterminate. On the other hand,cellular access technology,especially long term evolution(LTE)system,has been proven to satisfy theneed of comfort and some efficiency use cases. In this paper, we propose some enhancements onTD-LTE tech and system to support more applications in ITS areaII. TD-LTE—a strong communication plat-formLTE is the next generation orthogonal frequency division multiple access (OFDMA) basedtechnology of choice for most of the3rd generation partnership project (3GPP)and3rd generationpartnership project2 (3GPP2) operators today, with over100operatorsalready committed to deployLTE startingin2010.TD-LTE is thetime-divisionduplex(TDD)modeandis developed totakeadvantage of the technical advancements as well as numerous similarities with TDSCDMA whichcould enhance the LTE ecosystem. Based on TD- LTE technology, we propose a novel framework fortheorganizationofvehicularnetworks.WechoseTD-LTEforthefollowingreasons[2]:a. high throughput (downlink: 100Mbps, uplink: 50Mbps) ;b. latency targets (control plane: 100ms, user plane: 5ms);5MHz,10MHz,15MHz,c.emphasis on spectrum flexibility(1.4MHz,3.0MHz,20MHz);d.uplink/downlink flexibility's. low cost per bitWith the progress of the standardization in3GPP, TD-LTE provides a global platform to buildnext generations of interactive mobile services that will provide faster data access, enhanced roamingcapabilities, unified messaging and broadbandmultimedia.By integrating and coordinating industry resource, TD- LTE covers end- to- end industrial chainincluding radio access network (RAN), core network(CN), RF devices, antenna, user equipment's(UEs), chipsets, testing instruments, software, service and applications[3] III.TD-LTE enhancementforITSThe enhanced TD-LTE network architecture is aiming to reduce the end- to- end delay betweeninvolved vehicles. As mentioned above, some life safety related ITS applications require very lowdelay communication,e.g., for detecting potential danger, each vehicle needs to periodically transmitits current position/heading/velocityinformation to surroundingvehicles,and atthe same time itreceives those heartbeat messages from other vehicles nearby. With such cooperative- style messageinterchanges, the electronic device on each vehicle could rebuild a full picture of surrounding road
(e.g. 2G/3G/4G), wireless LAN, dedicated short-range communications (DSRC) and so on. On one hand, in some countries, many trials have been done to test the DSRC technology to support the safety-related applications. Though the test results are positive, both the factor of commercial mode and lawful policy are ambiguous. It seems that use of DSRC is still indeterminate. On the other hand, cellular access technology, especially long term evolution（LTE）system, has been proven to satisfy the need of comfort and some efficiency use cases. In this paper, we propose some enhancements on TD-LTE tech and system to support more applications in ITS area II. TD-LTE—a strong communication plat⁃form LTE is the next generation orthogonal frequency division multiple access (OFDMA) based technology of choice for most of the3rd generation partnership project (3GPP) and3rd generation partnership project2 (3GPP2) operators today, with over100operatorsalready committed to deploy LTE starting in 2010.TD-LTE is the time-division duplex (TDD) mode and is developed to take advantage of the technical advancements as well as numerous similarities with TDSCDMA which could enhance the LTE ecosystem. Based on TD- LTE technology, we propose a novel framework for the organization of vehicular networks. We chose TD- LTE for the following reasons [2]: a. high throughput (downlink:100Mbps, uplink:50Mbps）; b. latency targets (control plane:100ms, user plane:5ms); c. emphasis on spectrum flexibility(1.4MHz, 3.0MHz, 5MHz, 10MHz, 15MHz, 20MHz); d. uplink/downlink flexibility’s. low cost per bit. With the progress of the standardization in3GPP, TD- LTE provides a global platform to build next generations of interactive mobile services that will provide faster data access, enhanced roaming capabilities, unified messaging and broadband multimedia. By integrating and coordinating industry resource, TD- LTE covers end- to- end industrial chain, including radio access network (RAN), core network(CN), RF devices, antenna, user equipment’s (UEs), chipsets, testing instruments, software, service and applications [3] III. TD-LTE enhancement for ITS The enhanced TD- LTE network architecture is aiming to reduce the end- to- end delay between involved vehicles. As mentioned above, some life safety related ITS applications require very low delay communication, e.g., for detecting potential danger, each vehicle needs to periodically transmit its current position/heading/velocity information to surrounding vehicles, and at the same time it receives those heartbeat messages from other vehicles nearby. With such cooperative- style message interchanges, the electronic device on each vehicle could rebuild a full picture of surrounding road
environment situation which is used to detect potential danger, and then warn the driver. An enhancednetwork architecture was given [4], which introduced some new ITS related function in the servicelayer. However, the analysis result shows that it cannot support heart beat messagewithlo Hzperiodicity. To address the delay challenge, here another approach is given on TD- LTE system. Fig.1shows the system architecture of enhanced TD-LTE network.Inthisenhanced scheme,threenewfeaturesareproposed intotheTD-LTEsystems.Firstly,inUGu interface, a new transport channel named ITS- B channel is defined, by which the enhancedNode (eNB)could broadcast downlink safety- related ITS message to every vehicles within itscoverage area. The primary characteristic of this broadcasting channel is the short repetition/updatingperiod. Secondly, a new function component is introduced into eNB called ITS- mirror. When eNBreceives the uplink heartbeat messages from vehicles, ITS- mirror could forward such messages backto all nearby vehicles through the ITS- B channel. In such method, the vehicles could see each other.Finally, as people already have noticed, some traffic accidents affect not only nearby neighbors, inmany casesthey also slowdown car speed several kilometers behind.However,the forwardingbehavior within eNB is not enough to help those vehicles get such message. So a new functioncomponent called ITS analyzer is introduced into the core network element, e.g. MME, The analyzerreceives the input message from the ITS-mirror module in eNB, makes the relevant analysis, andfinally forwards relevant message to far-end ends deemed necessary. Those victim ends will theninject received message into the ITS- B channel to indicate underground vehicles. It should bementioned that, direct interchange between ITS- mirrors of nearby ends is of course not precludedwhich seems to haveless transmission delaybut with lack ofknowledge of thewhole area.Core networkTraditionalITSfunctionanalyzereNBeNBITSnotifierITSnotifierITSmirroITSmirreOBUOBUOBUOBUOBUOBUFig.1 Enhanced TD-LTE network architecture for ITS safety-related applicationThegoal folate-Hiistoachievehigherperformanceand lowercost of indoor/hotspotdeployment
environment situation which is used to detect potential danger, and then warn the driver. An enhanced network architecture was given [4], which introduced some new ITS related function in the service layer. However, the analysis result shows that it cannot support heart beat messagewith10 Hz periodicity. To address the delay challenge, here another approach is given on TD- LTE system. Fig.1 shows the system architecture of enhanced TD-LTE network. In this enhanced scheme, three new features are proposed into the TD-LTE systems. Firstly, in UGu interface, a new transport channel named ITS- B channel is defined, by which the enhanced Node (eNB)could broadcast downlink safety- related ITS message to every vehicles within its coverage area. The primary characteristic of this broadcasting channel is the short repetition/updating period. Secondly, a new function component is introduced into eNB called ITS- mirror. When eNB receives the uplink heartbeat messages from vehicles, ITS- mirror could forward such messages back to all nearby vehicles through the ITS- B channel. In such method, the vehicles could see each other. Finally, as people already have noticed, some traffic accidents affect not only nearby neighbors, in many cases they also slow down car speed several kilometers behind. However, the forwarding behavior within eNB is not enough to help those vehicles get such message. So a new function component called ITS analyzer is introduced into the core network element, e.g. MME. The analyzer receives the input message from the ITS-mirror module in eNB, makes the relevant analysis, and finally forwards relevant message to far-end ends deemed necessary. Those victim ends will then inject received message into the ITS- B channel to indicate underground vehicles. It should be mentioned that, direct interchange between ITS- mirrors of nearby ends is of course not precluded, which seems to have less transmission delay but with lack of knowledge of the whole area. Fig.1 Enhanced TD-LTE network architecture for ITS safety-related application The goal folate-Hi is to achieve higher performance and lower cost of indoor/hotspot deployment
and meet the demand of the rapid development of mobile Internet data services.Based on the mostadvanced TD-LTE technology, LTE- Hi can support higher transfer rate and high- speed userexperience by carrier aggregation (CA), high order multi- input multi- output (MIMO)and otheradvanced LTE technologies. Considering technical characteristics of the high data rate transmission.LTE- Hi can be applied to the ITS hotspot scene, such as bus, private car, and4Sshop of vehiclemanufacturer. The key technologies of LTE-Hi system that can be applied to ITS include followingaspects.Compared with frequency division duplex(FDD), TDD mode with flexible ratio of uplink anddownlink configuration is more suitablefor the transmission ofasymmetric services, such as IP packetservices. The flexible resource allocation to each direction based on service conditions (Fig.2), caneffectivelyimprovecell anduserthroughput,reducetraffictransmissionlatencyand enhancetheuserexperience. In addition, when the cell traffic load is low, the energy saving of the network can beachieved by configuring more uplink sub-frames.InternetDSUUUDSUUDDSUDDFig.2 Dynamic TDD application in ITSThe MIMO technology is essential to improve the peak rate of the wireless link and systemspectrum utilization, but the existing MIMO technology of LTEsystem is mainly designed for macrocell scenario, and fails to optimize for the high frequency band/indoor/ hotspot environment. Inhotspot cases, particularly in indoor cases, generally there are richer scattering/reflection paths, theSNR is higher compared to the macro cell, and moreover the terminal has lower mobility. Thesefactors for the application of the MIMO technology are very advantageous.Based on MIMO channel characteristics of the hotspot cases and combined with the existingTDLTE MIMO technology framework, the enhancement of the MIMO technology of the hotspotcases is to optimize the design focusing on the following aspects: high- order MIMO, uplink MIMOenhanced, enhanced CSI feedback and other technologies.In ITs hotspot scene, data volume is large and services occur in small and concentrated areas. Ifthe traditional cellular architecture is applied, CN will suffer heavy load. In LTE- Hi, both user planeand control plane adopt local IP access method. The user plane data can directly access the local IPthe control plane data can be simplified with Qu's and mobility based on the requirements of
and meet the demand of the rapid development of mobile Internet data services. Based on the most advanced TD-LTE technology, LTE- Hi can support higher transfer rate and high- speed user experience by carrier aggregation (CA), high order multi- input multi- output (MIMO)and other advanced LTE technologies. Considering technical characteristics of the high data rate transmission, LTE- Hi can be applied to the ITS hotspot scene, such as bus, private car, and4Sshop of vehicle manufacturer. The key technologies of LTE- Hi system that can be applied to ITS include following aspects. Compared with frequency division duplex(FDD), TDD mode with flexible ratio of uplink and downlink configuration is more suitable for the transmission of asymmetric services, such as IP packet services. The flexible resource allocation to each direction based on service conditions (Fig.2), can effectively improve cell and user throughput, reduce traffic transmission latency and enhance the user experience. In addition, when the cell traffic load is low, the energy saving of the network can be achieved by configuring more uplink sub-frames. Fig.2 Dynamic TDD application in ITS The MIMO technology is essential to improve the peak rate of the wireless link and system spectrum utilization, but the existing MIMO technology of LTEsystem is mainly designed for macro cell scenario, and fails to optimize for the high frequency band/indoor/ hotspot environment. In hotspot cases, particularly in indoor cases, generally there are richer scattering/reflection paths, the SNR is higher compared to the macro cell, and moreover the terminal has lower mobility. These factors for the application of the MIMO technology are very advantageous. Based on MIMO channel characteristics of the hotspot cases and combined with the existing TDLTE MIMO technology framework, the enhancement of the MIMO technology of the hotspot cases is to optimize the design focusing on the following aspects：high- order MIMO, uplink MIMO enhanced, enhanced CSI feedback and other technologies. In ITS hotspot scene, data volume is large and services occur in small and concentrated areas. If the traditional cellular architecture is applied, CN will suffer heavy load. In LTE- Hi, both user plane and control plane adopt local IP access method. The user plane data can directly access the local IP, the control plane data can be simplified with Qu’s and mobility based on the requirements of
broadband IP network, and the network can process encryption, authentication and billing of usersbased on the existing IP system and the IP network technologyIV.Application scenarios ofenhancedTDLTE systems inITSWith the enhancement of network architecture and access method, the enhanced TD- LTE systemsprovide a strong communication platform for various ITS applications. Two typical applications aregivenas follows.As in Fig.3, a collision accident occurred on bidirectional four-lane highway.The precedingvehicle uses normal LTE uplink channel to transmit threw message, which includes its position,heading and status, to the nearby enhanced eNB. The enhanced eNB will broadcast a warningmessage via ITS-B channel to vehicles which are in the same enswathe the disabled vehicle, and willdiscontinue to broadcast when the accident is cleared. In addition, the enhanced eNB will notify theroadhazardstatus totheITSanalyzerinthe core network,whichwill furtherdeterminetherelevantarea of accident and forward the hazard warning information to other enhanced ends located in therelevant area of accident. Then such enhanced eNB(s) also utilize ITS- B channel to transmit thewarning information to the vehicles in its cell coverage. When a vehicle receives the hazard warninginformation, the in- vehicle application will determine the correlation of the accident and use thisinformation to alert the drivers in order to provide drivers the opportunity to adapt to vehicle speedand inter- vehicle distance timely. Only drivers approaching the hazardous spot will get the warningon their in- vehicle display unit before the driver reaches the hazardous spot.福ITScenteranalvzeFig.3Exampleof road hazardwarningThis will have great benefits in poor visibility and inclement weather situations and may reducethepotential secondarycrashWith the rapid growth of real-time ITS services, such as video-based vehicle scheduling, real-timetraffic information query, and monitoring data reporting in public transport junction, the demand onhigh-speed data transmission in ITS hotspots increases.Fig.4 illustrates the LTE- Hi to provide high speed data transmission in a public transport junctionWhen the bus arrives at the public transport junction, it will use LTE-Hi systems to report itsmonitoring data, vehicle status information (such as engine conditions, brake system status) to
broadband IP network, and the network can process encryption, authentication and billing of users based on the existing IP system and the IP network technology. IV. Application scenarios of enhanced TDLTE systems in ITS With the enhancement of network architecture and access method, the enhanced TD- LTE systems provide a strong communication platform for various ITS applications. Two typical applications are given as follows. As in Fig.3, a collision accident occurred on bidirectional four- lane highway. The preceding vehicle uses normal LTE uplink channel to transmit threw message, which includes its position, heading and status, to the nearby enhanced eNB. The enhanced eNB will broadcast a warning message via ITS-B channel to vehicles which are in the same enswathe the disabled vehicle, and will discontinue to broadcast when the accident is cleared. In addition, the enhanced eNB will notify the road hazard status to the ITS analyzer in the core network, which will further determine the relevant area of accident and forward the hazard warning information to other enhanced ends located in the relevant area of accident. Then such enhanced eNB(s) also utilize ITS- B channel to transmit the warning information to the vehicles in its cell coverage. When a vehicle receives the hazard warning information, the in- vehicle application will determine the correlation of the accident and use this information to alert the drivers in order to provide drivers the opportunity to adapt to vehicle speed and inter- vehicle distance timely. Only drivers approaching the hazardous spot will get the warning on their in- vehicle display unit before the driver reaches the hazardous spot. Fig.3 Example of road hazard warning This will have great benefits in poor visibility and inclement weather situations and may reduce the potential secondary crash. With the rapid growth of real-time ITS services, such as video-based vehicle scheduling, real-time traffic information query, and monitoring data reporting in public transport junction, the demand on high-speed data transmission in ITS hotspots increases. Fig.4 illustrates the LTE- Hi to provide high speed data transmission in a public transport junction. When the bus arrives at the public transport junction, it will use LTE-Hi systems to report its monitoring data, vehicle status information (such as engine conditions, brake system status) to
dispatchcenter.Inaddition,dispatchcenteralsocantransmitthelatestnotificationoroperation&management information, or other advertisement information to the buses wither-Hi systemsDLE-OAMS1-CDS6aMOLECoSAEHSSLTEUE网ES1-UAAASeNTO金S/PGWPCREPieeD国OAMGWVwFig.4LTE-Hisystemstoprovidehighspeeddatatransmissioninapublictransport junctionV.CONCLUSIONIn this paper, the needs of ITS and the requirements of communication systems to support ITSapplication are summarized. Based on TD- LTE, two kinds of enhancements about the networkingarchitecture and access schemes are proposed to better support ITS, and RHW and high speed datatransmission are given as two practical ITS application scenarios
dispatch center. In addition, dispatch center also can transmit the latest notification or operation & management information, or other advertisement information to the buses wither-Hi systems. Fig.4 LTE-Hi systems to provide high speed data transmission in a public transport junction V. CONCLUSION In this paper, the needs of ITS and the requirements of communication systems to support ITS application are summarized. Based on TD- LTE, two kinds of enhancements about the networking architecture and access schemes are proposed to better support ITS, and RHW and high speed data transmission are given as two practical ITS application scenarios