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University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr. 2008 Dedicated Short-Range.

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Presentation on theme: "University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr. 2008 Dedicated Short-Range."— Presentation transcript:

1 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Dedicated Short-Range Communications

2 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Abstract In the next decade it is expected that vehicles would become part of the Intelligent Transportation System. The MAC and physical layers of this system would be supported by IEEE p Wireless Access in Vehicular Environments (WAVE) standard. In what follows we give an introduction to IEEE p, showing its PHY and MAC layers as well as research issues connected to each.

3 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Outline Motivation Issues with Vehicle Communications Overview Terminology Physical Layer MAC Layer

4 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Terminology OBE(U) = On-board equipment (unit) RSE(U) = Road side equipment (unit) VII = Vehicle Infrastructure Integration ITS = Intelligent Transportation Services VANET = Vehicular Ad Hoc Network WAVE = Wireless Access in Vehicular Environments AC = Access Category CW = Contention Window

5 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Role of DSRC From Intelligent Transportation System, High Level Architecture Description, [16]

6 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Motivation “Relatively short-range, high-bandwidth, [and] low latency communications technology” for traffic safety. FCC has allocated 75 MHz of bandwidth around 5.9 GHz for VII. VII takes two forms: vehicle-to-vehicle (V2V) vehicle-to-roadside communications (V2R) [1]

7 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Motivation Supporting vehicular wireless communications capabilities within a 1000 m range at highway speeds [3] Standardization efforts include IEEE p  IEEE p also known as Wireless Access in Vehicular Environment (WAVE) Relies on location and timing information from GPS Vehicles will be equipped with OBE to collect sensor information and relay to neighboring vehicles [1].

8 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Applications Applications include: Coordinated traffic control Electronic toll collection Hazard warnings, Road-level weather advisories Different types of safety warnings [1].

9 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Issues with Vehicle Communications Privacy issues Should not divulge identity of vehicle reporting incident Reliability Vehicles are in range for limited period Timely reporting Note: Energy conservation not issue OBE has access to power from car [2]

10 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Physical Layer Variant of IEEE a PHY In North America standard provides seven channels in the 5.9 GHz licensed band [4] Each channel designated for different applications [3] Channels are 10 MHz wide, with 5 MHz margin at lower end of band [4] Central channel is control channel [4] Other channels are service channels [4] Has six (6) service channels and one control channel  Two service channels designated for special safety critical applications [18]

11 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Physical Layer Variant of IEEE a PHY [4]: Uses 64 subcarrier OFDM, 52 subcarriers used for actual transmission;  48 data subcarriers and 4 pilot subcarriers  Pilot signals used to get frequency offset and compute phase noise Training symbols in each packet preamble  Used for signal detection, coarse frequency offset estimation, time synchronization and channel estimation Guard time associated with each OFDM symbol to combat ISI. Data bits are coded and interleaved to combat fading.

12 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Physical Layer Variant of IEEE a PHY [4]: Each vehicle broadcasts status 10 times per second. Lower priority communication is carried out on service channels after negotiation on control channel. Two adjacent service channels may be used together as a single 20 MHz channel Frequency bandwidth is 10 MHz to increase tolerance to multipath propagation effects  Results in reduced Doppler effects  Reduces ISI caused by multipath propagation  Data rate for IEEE p is half that of IEEE a

13 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Physical Layer Channels available for IEEE p [8] Negotiation for service channels is done on control channel From S. Eichler, “Performance Evaluation of the IEEE p WAVE Communication Standard” [8]

14 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr MAC Layer Uses prioritized channel access developed for IEEE e [4]: No frame exchange prior to actual data transmission  Reduces communication overhead Basic Service Set (BSS) is initiated by provide station transmitting service announcement frame regularly  No restrictions on transmission intervals  No authentication or frame exchange needed to join BSS Each station contains four queues representing four different types of traffic Each queue contends independently for medium access

15 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr MAC Layer Uses prioritized channel access developed for IEEE e [4]: Each station maps eight user priorities (UP) into four access categories (AC)  Each AC is modeled as a separate queue contending independently for medium [17]  Each AC has different MAC layer parameters [17]

16 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr MAC Layer Uses prioritized channel access developed for IEEE e [4]: EDCA parameters for IEEE p [8]  Used for access to control channel  aCW min = 15  aCW max = 1023 ACCW min CW max AIFSNtwtw 0aCW min aCW max 9264 μs 1(aCW min + 1)/2 -1aCW min 6152 μs 2(aCW min + 1)/4 -1(aCW min + 1)/ μs 3(aCW min + 1)/4 -1(aCW min + 1)/ μs From S. Eichler, “Performance Evaluation of the IEEE p WAVE Communication Standard” [8]

17 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr MAC Layer How to communicate: Stations use Enhanced Distributed Contention Access (EDCA) scheme. AIFS[AC] = AIFSN[AC]*aSlotTime + SIFS If frame arrives in an empty AC queue and medium has been idle for more than AIFS[AC] + aSlotTime [17]  Packet is transmitted immediately If frame arrives when medium is busy ([6] and [17])  Wait until medium idle  Defer for AIFS[AC] + aSlotTime  Pick random CW size and countdown to zero [6]  Additional period is given by CW size for this traffic category  Transmit

18 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr MAC Layer How to communicate: If a transmission fails, the station uses the binary exponential back-off (BEB) scheme [8]:  BEB equation: CW = 2*(CW+1) – 1  BEB continues until:  CW = CW max or  maximum number of retries is achieved Station cannot gain access to SCH and CCH for more than 100 ms [8]

19 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr MAC Layer Some IFS Relationships Fig. 9-3 in [6] From IEEE Std , Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, [6]

20 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Implementation Issues How is routing done? Traditional MANET routing protocols cannot be used in VANET  MANET protocols have an explicit route-establishment phase [3] Cannot use traditional routing techniques since message recipients are unknown beforehand [3].

21 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Implementation Issues How is routing done? Direction-aware broadcast forwarding [3]  Vehicle forwards emergency situation message to all cars behind it Naïve broadcast [3]  Vehicle immediately broadcasts message on emergency situation Intelligent broadcast with Implicit Acknowledgement [3]  Vehicle broadcasts emergency situation message to its neighbors  If vehicle eventually receives the same message, it ceases broadcast  Simulations show that scheme shows good performance.

22 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Implementation Issues Improving reliability (from [7]) Lower layers of DSRC are variant of IEEE a  Manages medium poorly for broadcasts. Failed broadcasts are not retransmitted Contention window size is not adjusted for failed broadcasts Suggest using an adaptive scheme  If reception rate exceeds threshold contention window is reduced.

23 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Implementation Issues Providing security [19] Need to provide:  Anonymity  Can be provided by using: Anonymous certificates Random MACs Changing IP addresses when the OBU moves to new RSU  Authentication  Ensure that fake messages cannot be inserted into the system  Prevent eavesdropping  Prevent competitors from eavesdropping on commercial vehicle operations

24 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Implementation Issues Deployment timeline (from [1]) Proof of concept testing in 2007 Decision on deployment by vehicle manufacturers and Department of Transportation by late Potential introduction in vehicles in 201x IEEE completion by 12/31/08 [15]

25 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr References 1.J. McNew et al., “Safe in Traffic,” GPS World, vol. 17, no. 10, pp , Oct M. Conti and S. Giordano, “Multihop Ad Hoc Networking: The Reality,” IEEE Communications Magazine, vol. 45, no. 4, pp , April S. Biswas et al., “Vehicle-to-vehicle Wireless Communication Protocols for Enhancing Highway Traffic Safety,” IEEE Communications Magazine, vol. 44, no. 1, pp , Jan L. Stibor et al., “Neighborhood Evaluation of Vehicular Ad-hoc Network Using IEEE p,” in Proc. 13th European Wireless Conf., Paris, France, S. K. Shanmugam and H. Leung, “A Novel M-ary Chaotic Spread Spectrum Communication Scheme for DSRC System in ITS,” in Proc. 60th IEEE Vehicular Technology Conference, Fall 2004, Los Angeles, CA, USA, vol. 2, pp IEEE Std , Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, IEEE, N. Balon and J. Guo, “Increasing broadcast reliability in vehicular ad hoc networks,” in Proc. 3 rd Int’l Workshop Vehicular Ad Hoc Networks, 2006, Los Angeles, CA, USA, pp S. Eichler, “Performance Evaluation of the IEEE p WAVE Communication Standard,” in Proc. IEEE 66th Vehicular Technology Conference, (VTC-2007 Fall), Baltimore, MD, USA, pp D. Jiang et al. “Design of 5.9 GHz DSRC-based Vehicular Safety Communication,” IEEE Wireless Communications, [see also IEEE Personal Communications], vol. 13, no. 5, pp , Oct M. Torrent-Moreno, D. Jiang, and H. Hartenstein, “Broadcast reception rates and effects of priority access in based vehicular ad-hoc networks,” in Proc. 1 st ACM Int’l Workshop on Vehicular Ad Hoc Networks, 2004, Philadelphia, PA, USA, pp

26 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr References 11.Q. Xu et al., “Layer-2 protocol design for vehicle safety communications in dedicated short range communications spectrum,” in Proc. 7th Int’l IEEE Conf. Intelligent Transportation Systems, 2004, pp F. Yu and S. Biswas, “Self-Configuring TDMA Protocols for Enhancing Vehicle Safety With DSRC Based Vehicle-to-Vehicle Communications,” IEEE Journal on Selected Areas in Communications, vol. 25, no. 8, pp , Oct J. Zhu and S. Roy, “MAC for Dedicated Short Range Communications in Intelligent Transport System,” IEEE Communications Magazine, vol. 41, no. 12, pp , Dec M. D. Dikaiakos et al., “Location-Aware Services over Vehicular Ad-Hoc Networks using Car-to-Car Communication,” IEEE Journal on Selected Areas in Communications, vol. 25, no. 8, pp , Oct IEEE Official Timelines, Mar. 2008, 16.Intelligent Transportation System, High Level Architecture Description, Feb Q. Ni, L. Romdhani, and T. Turletti, “A Survey of QoS Enhancements for IEEE Wireless LAN,” Journal of Wireless Communications and Mobile Computing, vol. 4, no. 5, pp , Aug M. Weigle, “Standards: WAVE/ DSRC/ p,” class notes CS 795/895, Old Dominion University, Spring W. Whyte, “Safe at Any Speed: Dedicated Short Range Communications (DSRC) and On-road Safety and Security,” presented at RSA Conference 2005.

27 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Backup Slides

28 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Physical Layer Research Issues: Using a chaotic spread spectrum modulation scheme [5]  Baseband symbols split into in-phase and quadrature phase components and each is modulated with chaotic parameter modulation.  Proposed system achieves the same performance as a conventional M-ary QAM system with a relatively low complexity receiver.

29 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr MAC Layer Research issues (from [8]) Recall WAVE has control channel and six service channels  Each station would use both control channel and service channel for no more than 100 ms. Contention mechanism in WAVE uses specific parameters Simulation results show that number of received messages for all AC decreases linearly due to more collisions on channel.

30 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr MAC Layer Research issues (from [8]) Suggests using mechanism to reduce number of high priority messages  Will result in slightly shorter message queues Suggest using different EDCA parameters to minimize effects of high collision probability

31 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr MAC Layer Research issues (from [9]) Congestion control mechanism necessary in DSRC.  Vehicles could regulate message generation rates and transmission powers according to context. Propose using Piggybacked Acknowledgement protocol for performance feedback. Propose ECHO protocol to proactively forward other nodes’ messages

32 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr MAC Layer Research issues (from [10]) Assume VANETs will operate in saturated state  Need to determine network parameters to reduce probability of collision  Propose priority access scheme Simulation results show that decreasing AIFS and CW size results in higher packet reception probability  AIFS has larger effect on probability

33 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr MAC Layer Research issues (from [11]) Develop MAC protocol that can meet latency and reliability requirements for safety messages, while making economical use of the control channel. Propose new MAC protocols that have lower probability of reception failure and occupy the channel less than IEEE

34 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr MAC Layer Research issues (from [12]) Introduces Vehicular Self-Organizing MAC (VeSOMAC)  TDMA protocol which copes with vehicular topology changes Simulations show that VeSOMAC has smaller packet latency than IEEE  Results in fewer vehicles colliding in a VANET

35 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr MAC Layer Research issues (from [13]) Presents state of art on IEEE , and how that applies to VANETs. State that most current research on multi-hop networks assumes slowly-changing topology.  Not necessarily case for VANETs.  MAC design for DSRC complicated by shortened connection time and frequent topology changes  Must support higher data rates due to shorter connection time.

36 University of Kansas | School of Engineering Department of Electrical Engineering and Computer Science Daniel T. Fokum Apr Application Layer Research issues (from [14]) Introduces Vehicular Information Transfer Protocol (VITP)  VITP is stateless and analogous to HTTP VITP architecture consists of  VITP peers  Location encoding scheme and  Additional protocol features VITP performance depends on return condition for VITP requests


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