Exploiting Trunked Radio to Support ITS Network Expansion and
Contents
1. Location 1 Location 1 Location 1 Location 2 Location 2 Location 2 Location 3 Location 3 Location 3 Primary Secondary Testing Primary Secondary Testing Primary Secondary Testing Communication Dialup ENCOM NTS Dialup CDMA NTS Dialup CDMA NTS Data rate bps 9600 9600 1200 9600 UDP 1200 9600 UDP 1200 Sign status Avg 60 40 350 69 10 360 71 15 350 Sign status SD 3 32 2 57 3 55 4 52 2 05 3 03 3 10 2 37 3 55 Sign status Max 65 43 357 75 14 366 75 19 357 Post message Avg 65 41 340 66 9 400 75 10 320 Post message SD 5 23 2 14 3 97 4 02 1 73 3 87 4 38 1 79 2 37 Post message Max 73 44 347 75 12 406 82 14 325 Current message Avg 59 35 310 55 5 390 69 9 390 Current message SD 3 03 1 95 3 22 3 46 1 48 3 55 3 16 1 41 2 97 Current message Max 65 38 314 60 8 397 75 12 394 Clear message Avg 55 38 300 70 8 410 68 7 310 Clear message SD 4 71 2 57 3 29 2 61 1 34 2 76 3 13 1 55 3 19 Clear message Max 62 42 305 74 101 414 75 10 315 medium and larger data network applications In order to provided testing equipment reduce the investment cost and improve data reliability and REFERENCES security we have provided a new way use of an existing NTS radio to provide communication to DMSs The results from our tests show that we can use the NTS as network medium to control NTCIP protocol based signs Due to the small size of control messages this data can be sent to through the NTS network using available2. o e r ag Ea m anna TT p Egun Egun n TTE ee PEM oe SE Rae SE E Ke ee HER eH yp eX eK Ree E Re HX HHH KK HX Sign Status Post Message Current Message Clear Message Fig 3 followed by a command to check the current message to verify that the new message was correctly posted to the sign As last step a final command was sent to clear the sign before repeating the test The communication time for the transmission of each DMS command is shown in Figure 3 Results are shown for each of the three locations L1 L2 and L3 using the primary P secondary S and the NTS network tested T methods of communication As expected the secondary communication mechanism was always fastest followed by the primary dial up communication While send ing commands through the NTS network was the slowest method of communication in each test all tests completed in less than 7 minutes While this latency may be unacceptable for many ITS functions it is typically acceptable for the infrequent control of a DMS Note that although the dial up modem operates at 9600 bps 8 times faster than the 1200 bps rate of the tested approach it spends some time waiting in the initial process of original connection Telephone line noise reduces the achieved data rate and can make the initial process unsuccessful When an initial call fails the server will automatically call back In our tests connections were always made after no more then two tries This make the a
3. 40 to 55 degree C Orion 8 ENCOM 9 Motorola Canopy 10 Motorola Canopy 11 Model 900 MHz OFDM COMMPAK IP AP SM or BH 30 60 Mbps Backhaul Operating Frequency 902 928 MHz 902 928 MHz 5 725 GHz to 5 850 GHz 5 47 GHz to 5 725 GHz 4 940 to 4 990 GHz 4 940 to 4 990 GHz Bandwidth 5 10 or 20 MHz N A 2 5 MHz 11 MHz Transmission Method Fixed Frequency Frequency Hopping spread spectrum Fixed Frequency Fixed Frequency Modulation OFDM BPSK or QPSK N A FSK BPSK QPSK 16 64 QAM Data Speed 5 5 11 or 22 mbps 300 bps to 230 4 kbps 10 mbps or 20 mpbs 30 Mbps or 60 Mbps Interface Ethernet RJ 45 Ethernet RJ 45 RS 232 Ethernet RJ 45 Ethernet RJ 45 AES FEC and ARQ 19 dBm to 25 dBm 40 to 60 degree C the same manner as in the small data network applications Because the Canopy provides only an Ethernet interface an Ethernet to serial converter is used to adapt the Canopy for communication with the DMS In one deployment a DMS in Tulsa OK is located roughly 3 miles away from a division office The telephone network does not reach a point close to the DMS As in the application described in Section I A an auto answer dial up modem is installed at the division office A pair of Ethernet to serial converters are used with point to point tunneling Using the first a the regular dial up modem s RS 232 serial signal is converted to an Internet Protocol IP signal that is connected to the Canopy At the DMS site the IP sign
4. City metropolitan network of our experimental testing of this approach are provided in Section IV followed by conclusions in Section V Il EXISTING WIRELESS DEVICES IN THE OKLAHOMA ITS Like that of many other states the Oklahoma ITS network is deployed with a fiber optic network backbone and utilizes wireless networks where fiber optic and other wired networks are unavailable The specifications for the wireless equipment in use in the Oklahoma ITS are shown in Table I ENCOM and Orion radio units are operated at lowest data throughput while the Motorola Canopy equipment provides the highest data throughput Note that the 900 MHz and 5 7 GHz frequencies are unlicensed and open to public use Since they can be easily used by the consumer devices these frequencies are broadly used by individuals and are subject to interference In addition to interference and other noise issues security is a significant concern when wireless networking is used for sensitive ITS functions Data encryption is one method to address these security concerns The encryption method used by each wireless device is also shown in Table I The Federal Communications Commission FCC output power limit for each device and their operating temperature are other significant parameters to consider Temperature constraints are of particular concern when wireless devices are selected for use in Oklahoma because its climate faces both harsh winter and summer seasons Equipmen
5. along with the standard deviation for each set of tests and the maximum latency for that set While the standard deviation in the latency of communication through the NTS network is higher than the secondary mode less variation is actually seen in the NTS tests than in utilizing the dial up modem The results from our experiments demonstrate that DMS control using the NTS network is possible This approach provides alternative method of wireless communication to support ITS applications Although the data throughput of this approach is not high as another wireless networking methods it allows low cost deployment of ITS devices at any region statewide Because the NTS network is privately operated for the state s transportation agency there is greater confidence of network availability during the severe weather or disaster relative to wireless services used by the public With the cost shared for operation and maintenance with the existing voice communication application the NTS further makes ITS network extension feasible within a limited budget V CONCLUSIONS Wireless networks are an attractive alternative to wired networks They can bridge wired networks in several different network topologies such as those we have described as small 765 TABLE II SUMMARY OF AVERAGE TIME STANDARD DEVIATION AND MAXIMUM TIME FOR COMMUNICATION TO DIFFERENT SIGN LOCATIONS THROUGH DIFFERENT NETWORK TYPES TIMES IN SECONDS
6. control channels without interrupting the primary voice service However this DMS control is slow due to the maximum data rate at 1200 bps Communication using our presented approach takes longer than that through telephone and CDMA modems where the data speed is 9600 bps While this may appear slow compared to other networks but it is an extremely inexpensive way to implement ITS devices statewide including in rural regions Sharing the NTS network for voice and data traffic also divides the cost of operation and maintenance Other suitable low data rate ITS applications to utilize the NTS network include traffic sensors and portable DMSs Both need only to transfer a few bytes of data to TMC consoles These traffic sensors and portable DMSs also frequently deployed in work zone areas Data from devices monitoring traffic in these temporary locations can be easily communicated to the TMC via the NTS network In the future if the demand of the data is more than the control channel can support it would also be possible to dedicate a voice channel for data use ACKNOWLEDGMENT The authors would like to thank Alan Stevenson ODOT ITS and Fiber Optic Engineering Manager for his continued support of the OU ITS Lab We would also like to thank Ty Todd communication system manager at ODOT who generously provided technical information regarding the NTS network The authors would like express their appreciation to Dave Anderson President CEO at Trid
7. telephone network service B Medium Data Network Applications For the medium data network category of applications the Canopy wireless devices with throughput of 10 or 20 Mbps are used Figure 1 shows an example in this category TMC consoles in Midwest City OK are linked to the fiber optic network using a 20 Mbps Canopy Users at both the 911 center and the sheriff s office can view and control the ITS cameras without network lag In another case a 10 Mbps Canopy is installed to link the main network and an individual user at the Federal Highway Administration FHWA in Oklahoma City OK Because the user is authorized to control both cameras and DMSs the data bandwidth is configured for asymmetric 40 60 uplink downlink throughput In addition to these medium data rate applications there are other situations where 900 MHz radio devices fail to provide adequate communication due to high noise environments with surrounding interference In these locations 10 Mbps Canopy devices are used to connect DMSs to the ITS network in 762 SUMMARY OF WIRELESS DEVICES USING IN THE STATE OF OKLAHOMA FOR ITS APPLICATIONS TABLE I Data Encryption Error Detection Transmission power Operating Temperature Dynamic key N A up to 30 dBm 20 to 55 degree C RS 422 485 DB 9 128 bit WEP 128 bit WPA 256 bit AES 32 bit CRC ARQ 20 dBm to 30 dBm 40 to 75 degree C AES FEC and ARQ 23 dBm to 30 dBm
8. translate the control Rs 232 serial data back to the sign s controller Both data and voice are sent using frequency modulation FM on the NTS system For communicating with DMS we use the data channel assigned for messaging control This messaging control channel uses FM 12 5 KHz narrowband 763 Link 4 Trident RTU Link 4 Trident RTU Skyline Server NTCIP Protocol NTS gateway TrAVL Bridge software ITS Private network Fig 2 spacing The channel is calibrated with a 1000 MHz tone for less than a 800 Hz deviation With this bandwidth allocation 9600 bps data transfer should be supported However to ensure reliable data communication between the DMS and the center a 1200 bps data rate is used for DMS control The network diagram of the DMS server software interface to the NTS is shown in Figure 2 The NTS network is used to provide communication between the Skyline software and the DMS in the field using this existing wide area radio network Link 1 is a network link between the Skyline server and the NTS gateway The link establishes IP communication of eXtensible Markup Language XML data Link 2 is a connection between the NTS gateway and the ethernet to serial converter The signal output from the ethernet to serial converter is sent to the NTS network by Link 3 Using this link control data is sent to all main network areas using the available NTS network control channel to transmit the sign contr
9. 2 54 1996 J Grimm M Fitz J Krogmeier T Chen T Magnuse J Gansman and W Kuo High efficiency narrowband wireless modems for ITS applications ITS Journal vol 3 no 4 pp 333 352 1997 Orion 900 MHz OFDM user manual Visited April 2011 Online Available _ http www wirelessinteractive com pdf radios Orion900_manual pdf ENCOM COMMPAK IP 900 MHz and 24 GHz serial ethernet bridge Visited April 2011 Online Available _http www encomwireless com document centre doc_view 142 commpak ip tmpl component amp format raw Canopy backhaul module user manual Visited April 2011 Online Available http www canopy wireless solutions com AppicationNotes BHManuallss5 pdf 4 9 GHz wireless ethernet bridges Visited April 2011 Online Available http www canopy wireless solutions com AppicationNotes MotorolaPTP49400BridgeTechnicalSpecifications pdf Oklahoma departemnt of transporation radio reference Visited April 2011 Online Available http www radioreference com apps db sid 5253 PassPort trunking Visited April 2011 Online Available http www tridentms com Home PassPortTrunking tabid 6 1 Default aspx
10. 2011 IEEE 22nd International Symposium on Personal Indoor and Mobile Radio Communications Exploiting Trunked Radio to Support ITS Network Expansion and Redundancy Ekasit Vorakitolan Joseph P Havlicekt Mohammed Atiquzzaman and Ronald D Barnes tSchool of Electrical and Computer Engineering School of Computer Science The University of Oklahoma Norman Oklahoma 73019 Email ekasitv joebob atiq ron ou edu Abstract Typical intelligent transportation systems ITS are comprised of geographically distributed ITS devices including sensors cameras and dynamic message signs DMS There are several options for providing data communication between these field devices and traffic management centers TMC Wireless networks are attractive due to their relatively lower cost and ease of deployment compared to fixed networks However these face unique security and signal interference problems and de ploying new wireless networks can require significant equipment investment In this work a new extremely low cost wireless strategy for ITS network communication is presented This approach applies control channels of the Network Trunking System NTS a licensed radio frequency to support the voice communication to control DMS operation under the National Transportation Communications for ITS Protocol NTCIP Because the NTS network has already installed in the metropolitan urban and rural areas in Oklahoma it provides a cheap depl
11. 35 and Wilshire Blvd location 3 Each location is equipped with a different DMS model Original communication with the DMS at location 1 was through dial up modem and a 900 MHz radio with a 9600 bps data rate Locations 2 and 3 have dial up modems and CDMA modems as their communication methods Note that while communication through a dial up modem is expected to be slower than each sign s secondary wireless method of communication the wired method is chosen as the primary way of communicating with each DMS because it doesn t require transportation agents to be connected to the Oklahoma ITS network to control a sign Testing was performed at each location to measure the average latency for each communication method to accomplish various tasks Four different types of commands were sent to each DMS First the sign status was polled checking that the sign is operational Polling the sign checks the status of communication main power sign temperature ambient temperature sign controller LED power supplies brightness control mode and door alarm If the sign has no malfunction the message ODOT TEST MESSAGE was sent to the sign 764 450 7 400 2s e Seer e sg 7 e e a oe e sso Le x x a a 4 aaa aa a aa aa A 4 300 a up Lis ALIT a 250 XL2P o xS eT H 20 L3P Bs 150 BT 100 xX x x e x aye x XX x x z x Ree 9 x x y x x R EE ESe ey Sy x SRS E ens yk est lt 50 2 a I ac s x xt t
12. al received from the Canopy is connected through the second Ethernet to serial converter to change the IP signal back into an RS 232 signal that is sent to the sign controller C Large Data Network Applications Canopy 60 Mbps equipment is used to bridge metropolitan or other urban area to the main backbone network in the large data network application As an example the ITS devices in the Midwest City OK area consisting of 4 analog cameras 16 digital web cameras 3 permanent DMSs and TMC consoles as shown in Figure 1 A Canopy 60 Mbps wireless link is used to bridge the data communication between this spur network and the ITS backbone network In this case the Canopy s data throughput is configured as symmetric 50 50 uplink downlink since video streams are transmitted back and forth between the main ITS network and the spur based on user request This allows TMC console users in Oklahoma City and other ares on the network to control and view camera video in the Midwest City area and vice versa Wireless ITS deployments in Oklahoma have typically depended on public mobile network services and license free frequency devices While private wireless networking using 900 MHz radio or Canopy links are the most reli able redundant network connection for DMS devices these approaches unfortunately can only extend to limited areas Since the fiber optic network does not reach the majority of rural areas in the state public network services
13. are the only available form of secondary communication between rural DMSs and TMC consoles This is a significant issue as these DMSs are increasingly being used to improve public safety through communication to travelers In the next section we provide a novel wireless communication strategy that is used to link otherwise wirelessly unreachable DMSs using an existing private voice communication network II DMS CONTROL USING AN EXISTING NETWORK TRUNKED RADIO SYSTEM ODOT s 150 MHz frequency band NTS network has been deployed statewide covering metropolitan urban and rural areas with 96 base stations around the state Each base station utilizes a dipole omni directional antenna Coverage varies by station with a maximum range of approximately 20 miles The state is divided into eight geographical regions 12 and frequency channels are assigned to each region The backbone network for NTS for each region is connected together using a wired network such as fiber optic or T 1 leased line services The NTS is based on the Passport protocol a standard for the Logic Trunked Radio LTR developed by Trident Micro Systems 13 Unlike other states that have invested in dedi cated private ITS radio networks such as 220 MHz systems we have utilized the NTS gateway software TrAVL Bridge to connect a Skyline DMS server s Rs 232 serial interface to the NTS network Trident RTU units with quarter wave dipole antennae are installed at each sign to
14. elephone networks offers easy deployment as long as the device is located in a service area However recurring 978 1 4577 1348 4 11 26 00 2011 IEEE service fees can become expensive for large numbers of widely deployed devices They suffer from copper wire line noise due to weather and humidity Additionally telephone service is not readily available at every roadside location Limitations of wired networks can constrain the deployment of ITS devices 2 3 For these reasons wireless tech nologies including microwave and mobile telecommunications networks are frequently used as part of ITS networks Public mobile telecommunications networks provide a quick and easy wireless solution as service providers have already designed and installed networks that are typically shared with mobile phone users Service providers are responsible for the network operation and maintenance Use of these public wireless network also incurs monthly service fees and they can suffer from a lack of security and limited coverage The availability of these services is also not guaranteed during disasters and severe weather Typical networks also provide greater data download bandwidth than upload making it impossible to send the high resolution video streams back from fields to the TMC 3 4 Private wireless network offer many advantages for ITS applications Both devices operating under licensed frequen cies e g ITS narrow band 220 MHz and 4 9 GH
15. ent Micro Systems who permitted us to disclose the experimental results of communication with DMSs through the NTS network and 1 2 3 4 5 6 7 8 9 10 11 12 13 766 Columbia Telecommunications Corporation Brief engineering assess ment Efficiencies available through simultaneous construction and co location of communication conduit and fiber The National Association of Telecommunications Officers and Advisors and The City and Country of San Francisco Tech Rep August 2009 Intelligent transportation systems its operations Visited April 2011 Online Available http www wsdot wa gov Operations ITS A Amanna Assessment of current and emerging broadband wireless technologies for VDOT s operations program Virginia Tech Trans portation Institute Tech Rep Jun 2008 B Kilani E Vorakitolan J Havlicek M Tull and A Stevenson Distributed ITS control and the oklahoma virtual TMC in Proceedings of the 12th International IEEE Conference on Intelligent Transportation Systems Missouri USA Oct 2009 pp 785 790 FCC rules for unlicensed wireless equipment operating in the ISM bands Visited April 2011 Online Available http www afar net tutorials fcc rules M Fitz J Krogmeier J Grimm J gansman T Chen and T Mag nusen The 220 MHz ITS spectral allocation Potential pitfalls and applications IEEE Communicaitons Magazine pp 4
16. oller commands to DMSs At the sign an RTU unit coverts the data back to RS 232 serial data which controls signs via Link s 4 The basic idea of this approach is to construct a system that allows the DMS server and distant clients to operate as though they were directly connected using a virtual communication port utilizing a point to multipoint network Regardless of direction data is presented to the NTS Network in its native form NTCIP protocol conditioned for transport by the NTS Network and finally delivered by the NTS Network to the target after being restored to its native NTCIP data package The NTS gateway identifies sign addresses in the message from the Skyline software and performs a database lookup to RCC Emission Designator 11KOF9W narrowband data Link 4 Trident RTU Trident RTU NTS network Link 3 Ethernet to Serial Network interface through NTS associate the target sign with a radio The exchange is then initiated with the correct sign IV TESTING RESULTS OF UTILIZING THE NTS NETWORK A testing network was setup at the ODOT central office by installing the NTS gateway and connecting it to the DMS server controller The controller did not require any special setup since the NTS gateway software was configured to utilize a virtual serial port Three RTU units are installed at DMSs in Oklahoma City I 40 and Choctaw Road location 1 I 35 and 19th Street location 2 and I
17. oyment solution requiring only additional adapter devices Long term operation and maintenance costs can further be amortized between voice and data services The proposed technique is compared to the existing ITS wireless networking strategies and hybrid network strategies merging wired and wireless networks deployed in Oklahoma Details of the strategy for using wireless networking in the Oklahoma ITS and experiences with wireless ITS device deployment are also provided I INTRODUCTION This paper presents the use of the Oklahoma Department of Transportation ODOT licensed 150 MHz frequency band NTS This network has already been deployed across the state for voice communication thus our approach avoids the expense of the deployment of a new dedicated network while still providing reliable communication with low bandwidth ITS devices This network can be used in conjunction with the wired wireless and hybrid networks that already support Oklahoma s ITS Communication networks play an important role in ITS linking traffic monitoring and traveller feedback devices to TMCs There are distinct tradeoffs in the choice of platform for these networks Fiber optic networks provide the highest throughput and data security but are prohibitively expensive to be deployed outside densely populated areas For example the cost in 2009 to install a fiber optic network in San Francisco was between USD 95 000 and USD 240 000 per mile 1 The use of t
18. t must be able to operate in a wide range of temperature Each of wireless units described in Table I have both advantages and disadvantages for particular ITS applications The remainder of this section describes how each wireless devices are deployed in three different categories of ITS application within the Oklahoma ITS network A Small Data Network Applications The small data network category of applications is specified to support devices at the end of the network branch These are typically low data transmission rate devices such as DMS or traffic sensors In the Oklahoma ITS a typical deployment in this category utilizes 900 MHz radio devices Figure 1 shows one such deployment In this case the DMSs in the Midwest City OK area communicate with the Oklahoma ITS network using 900 MHz radio This radio link is operated in a point to multipoint configuration This can be seen in this example with the radio link between the I 40 amp 29th Street location the DMS at J 40 amp Sooner Road east bound and I 40 amp Sooner Road west bound For the DMSs at the I 40 amp Post Road and I 40 amp Choctaw Road the point to point topologies of 900 MHz radio are used to carry the control data traffic Because of the limitation of the line of sight between the radio links a repeater is installed where obstructions occur between them For example the repeater at the I 40 amp Anderson Road is used to retransmit the signal between the signs on Choc
19. taw Road and Post Road to overcome a large hill In general the 900 MHz radio provides a low data transfer speed that is not suitable to carry traffic camera video However for small spur network tasks such as DMS control the 900 MHz radio is a suitable as communication medium because the DMS control commands are small data transfers In fact for permanent DMSs in Oklahoma dial up modems are used the main control wireless networks are used for redundant back up Existing wireless network devices providing communication backup for DMSs in the Oklahoma ITS consist of CDMA modems Motorola 10 Mbps Canopy and 900 MHz radio devices In some circumstances wired and wireless devices applied in a hybrid network branch For example a permanent DMS on the I 44 Turnpike between Oklahoma City and Tulsa required constructing an initial telephone cable at a cost of USD 40 000 to connect the DMS to the telephone network at the tollbooth approximately 2 miles away Instead a dial up modem was installed at the tollbooth with an auto answer mode configuration This modem was in turn connected to a 900 MHz radio The radio pair linking the phone network at the tollbooth and the DMS is configured for point to point tunneling bridging the data between the DMS and dial up modem The small data network application configuration has been extremely useful in the Oklahoma ITS network It has allowed expansion with devices at the edge of the fiber optic network and
20. verage time for the dial up modem up to about one minute for each category of command sent to the sign Unlike dial up modem the ENCOM 900 MHz radio is operated at 9600 bps does not requires an initial process to originate call Hence the communication time interval for sending message to signs is shorter than utilizing the dial up modem The NTS network can provide maximum speed at 1200 bps and needs at least 5 to 7 minutes for each transaction to complete It does not require a initial process to originate call but it does require a process for NTS gateway to search the database for the sign address multi drop address and find an available control channel to send to data to appropriate locations To achieve stronger signal levels we also found Latency of sending various commands to message signs during our experiments that the RTU unit antenna needed to be installed outside of the sign When the signal strength is weak this directly effects data transition speed causing communication delays and timeouts Little latency variation is seen between test performing each of the various DMS commands However as the slowest method of communication sending the message though the NTS network was slightly more dependent on the type and the length of the command being sent As shown in Figure 3 each test was repeated 10 times for each sign The results of these experiments are shown in Figure 3 and the average latency is reported in Table II
21. z band for public safety and unlicensed frequencies e g Industrial Scientific and Medical ISM band 900 MHz and 5 7 GHz are utilized in the ITS applications 5 These private wireless solutions provide more reliability throughput and security than public services The use of licensed wireless device can reduce the problem of signal interference compared to unlicensed band because only authorized users can propagate that frequency into the air The 220 MHz band serves data transfer for traffic sensors changeable message signs and incident response vehicles 6 However seperate wireless solutions require significantly more network investment and maintenance than public telecommunication services Addi tionally although the 220 MHz is used successfully in lower data rate ITS applications high efficiency wireless devices are required due to the limitation of bandwidth and problems such as fading and multi path signal propagation 7 The unlicensed frequency devices used in the Oklahoma ITS are described in Section II Building our experiences in wireless ITS deployments our novel use of a 150 MHz trunked wireless network is described in Section III Results 761 lt lt 10 Mbps Canopy 1 mile jouglas 4PTZC 40 amp Post 900 MHz Orion 900 MHz ENCOM 2miles 1 mile 1 408 amp Anderson 10 MHz ENCOM 2miles 40 amp Choctaw Fig 1 The wireless network link between Oklahoma City main ITS network and Midwest
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