車用通訊技術

1. 車用通訊技術

3. MAC for Dedicated Short Range Communications in Intelligent Transport System The protocol is optimized by adjusting the CW dynamically to meet predefined requirements, such as maximum saturation throughput, weighted fairness, bounded delay, and differentiated QoS. The challenge is to design an enhanced .11 MAC layer with open interfaces to integrate new solutions. Another challenges to MAC design include a multi-rate environment, shortened connection time and frequent updating of stations in the coverage area. Simply increasing the data rate without reducing overhead leads to bounded throughput. Due to shortened connection time, burst download speeds in DSRC systems should aim for higher rates than current WLAN. • Public safety • to reduce traffic accidents • Traffic management • to improve the flow of traffic, reducing congestion • Traveler information support • to provide a great variety of travel-related timely information, such as electronic maps, and road and weather information • Entertainment/rich media content delivery • Internet access, infotainment (news, sports, movies, etc.) on demand

5. Limitations of 802.11 in DSRC Environments • DCF OVER MULTIHOP • Blocking • Fairness? • DCF/PCF OVER HIGH MOBILITY • 100 km/h (27 m/s) 200 * 2 / 27 = 15 s • A efficient protocol with low overhead is preferred. • PCF mode • High mobility results multirate

6. Predicting the Lifetime of Repairable Unicast Routing Paths in Vehicle-Formed Mobile Ad Hoc Networks on Highways • Intelligent Transportation Systems (ITS) is developed to exchange information between vehicles with dedicated short range communication (DSRC). • provide drivers with timely traffic congestion and road condition information • provide drivers with networking services, such as send/receive emails and browse web pages, etc • Inter-vehicle communications (IVC) used for ITS can be viewed as a type of mobile ad hoc networks. • This paper analyzes the lifetime of repairable unicast routing paths existing in an IVC network.

7. Predicting the Lifetime of Repairable Unicast Routing Paths in Vehicle-Formed Mobile Ad Hoc Networks on Highways • Using a traffic simulator, this paper analyzed the lifetime distribution of unicast paths and the relationships between lifetime and several other performance metrics. • This paper can help these routing protocols to consider whether it is worth initiating a long-lived transfer on a unicast path whose lifetime is predicted to be short.

8. Energy management in the IEEE 802.16e MAC • IEEE 802.16e sleep mode • Minimize MS power • Decrease usage of BS air interface resources • Power Saving class • Connection that have common property • Repeatedly activated and deactivated • Three types of power saving classes Power SavingClass #1 Sleep Listen Sleep Listen Power SavingClass #2 Sleep Listen Sleep Listen MSAvailability Unavailability Availability Unavailability Availability

9. A new QoS architecture for IEEE 802.16 • Original IEEE 802.16 • Containing: • Signaling between BS and SS • The principles for the QoS classes • NOT containing • The service packet scheduler & admission control Performance Analysis of the IEEE 802.16 Wireless Metropolitan Area Network The proposed design • The original design

10. An Opportunistic Uplink Scheduling Scheme to Achieve Bandwidth Fairness and Delay for Multiclass Traffic in WiMAX (IEEE 802.16) Broadband Wireless Networks • The proposed scheme provides fairness in bandwidth allocation while meets the different delay requirements. • Closed-form expressions for the polling interval • low-complexity scheduling algorithm for obtaining good fairness-delay performance with multiclass traffic

11. Operational overview • Scheduling epoch • Polling is performed by the BS, only once every k frames. • An SS is eligible if, at the polling instance, • it has a non-empty queue, and • the SINR of its wireless link to the BS is above a minimum threshold SINRth • Once determined, the membership of the eligible set is frozen for the entire scheduling epoch.

12. Determining the optimal polling interval k • Determine the best choice of the polling interval k by considering • the maximum delay that a set of SSs can tolerate, and • the worst-case relative fairness in their bandwidth allocations To minimize a combination of the worst-case relative fairness in bandwidth plus the normalized delay. The provider may choose the relative weights of the two quantities. cost cost normalized delay worst-case fairness measure

13. IEEE 802.16 scheduling services & QoS architecture • Unsolicited Grant Service (UGS) • Real-time, periodic fixed size packets (e.g. T1 or VoIP) • Real-Time Polling Service (rtPS) • Real-time, periodic variable sizes packets (e.g. MPEG) • Non-Real-Time Polling Service (nrtPS) • Variable sized packets with loose delay requirements (e.g. FTP) • Best Effort Service (BE) • Proposing a polling-based opportunistic deficit round robin (O-DRR) scheduling scheme. • to balance the worst-case unfairness in bandwidth allocation with the delay requirements of multi-class traffic

14. Fast Handover Scheme for Real-Time Downlink Services in IEEE 802.16e BWA System

15. Fast Handover Scheme for Real-Time Downlink Services in IEEE 802.16e BWA System • To reduce handover latency and packet loss ratio for real-time downlink services, we propose an enhanced handover scheme that an MS can receive downlink data through specified message from Target BS just after synchronization with new downlink of Target BS during handover process. • We define a Fast DL_MAP_IE message to support downlink real-time traffic during handover process. • We proposed scheme uses one reserved bit of the generic MAC header and defines this bit as fast downlink indication bit. In original break-before-make handover, an MS is not able to transmit or receive data before handover process is completed. The sensitive traffic might bring out the packet loss due to the transmit delay during handover process. The Fast DL_MAP_IE handover scheme in which MS can receive real-time downlink service from BS during handover process.

16. Utility-based resource allocation scheme This scheme • supports layer-encoded streams and determines the number of layers to be received by each user dynamically. • can be executed periodically or on-demand to reflect user’s time-variant channel condition. • can be applied to WiMAX and all other networks in which users’ channel conditions can be monitored and the transmission rates can be adjusted accordingly. • can improve the total user satisfaction and the system channel utilization. • supports unicast/multicast, single-layer/multi-layer environment • Dynamically provide each user a reasonable amount of resource depending on its channel quality and the popularity of each program, in order to achieve best utilization of the total system.

17. Utility-Based Layer-Encoded Multicast Scheme • The BS picks up group members one by one into service in decreasing order of their channel conditions and use the most robust burst profile among all selected users to transmit data. • Burst profile of WiMAX: a set of codec settings which reflects the channel condition for BS to transmit data to SSs

19. Conclusions • This paper proposes a utility-based resource allocation scheme for layer-encoded multicast streaming service in WiMAX networks. • Under the same conditions, layer-encoded programs have higher total utility than single-layer programs. • The system can tune the allocated resource to users according to the number of subscribers and the utility function of each program. • None of the programs gets starved and thus fairness is maintained.

20. Introduction of CoopMAC • Wireless link is unreliable (broadcast channel ) • Solution: Use another mobile to relay information • Optional function: The destination can process signals from both mobiles • Results in • Higher reliability, higher data rates, extended coverage

21. Introduction of CoopMAC It can be backward compatible with the 802.11 legacy system • The new Cooperative MAC protocol: • Significantly improves the performance of 802.11 • Can be combined to cooperative schemes on the PHY • It is backward compatible with 802.11 • Can be applied on top of 802.11 as an assisting mechanism • Easy to implemented by changing the driver and the firmware of the card

22. CONCLUSIONS • The new Cooperative MAC protocol: • Significantly improves the performance of 802.11 • Can be combined to cooperative schemes on the PHY • It is backward compatible with 802.11 • Can be applied on top of 802.11 as an assisting mechanism • Easy to implemented by changing the driver and the firmware of the card

23. data RTS CTS ack Introduction (1/3) A B Q P • 802.11 • 4-way RTS / CTS-based exchange with no gaps. • Entire neighborhood of both sender and receiver blocked out. • Key Observations • No gap between RTS/CTS and DATA/ACK phases. • Each node involved in a data packet exchange switches roles between a transmitter and a recipient. • Role reversal occurs during both RTS/CTS and DATA/ACK pairs. B Q time

24. MACA-P fundamentals (1/4) • Control phase • MACA-P protocol adds extra information in the RTS and CTS messages to explicitly delineate the intervals for both the DATA and ACK transmissions. • Tdata: indicates the start time of DATA transmission • Tack: indicates the start time of the ACK transmission

25. MACA-P fundamentals (4/4) • Master transmission schedules • A sender/recipient pair can schedule a data transmission only if there is at most one master transmission in the sender’ neighborhood or at most one master reception in the recipient’s neighborhood

26. Conclusions • 802.11 MAC does not permit many feasible concurrent transmissions. • MACA-P: parallelizing MAC • MACA-P relaxes the 802.11 constraint to increase the number of parallel transmissions. • Enhancements to the base MACA-P specifications • Adaptive learning • Choice of control gap length • Capture behavior

27. Sensor Measurements for Wi-Fi Location with Emphasis on Time-of-Arrival Ranging • WLAN location sensor measurement • Signal strength (SS) • Time difference of arrival (TDOA) • Time of arrival (TOA) • Angle of arrival (AOA) • shortcomings of GPS • Do not work indoors • accuracy • Application for indoor location • Indoor navigation • Printer finding • Location-based security • Digital home • Location aware tag a small modification to the WLAN physical layer, one can provide accurate location to the WLAN system. The performance of the TOA is significantly better than SS

28. Self-learning Collision Avoidance for Wireless Networks • The sender queries RSS_RS_LookUP • Suspend its backoff timer when its RSS suggests low channel access ratio • Resume the timer when its RSS is high enough for high channel access ratio. • The idea of busy channel is now changed • Either the Sender’s or Receiver’s channel is not available.

29. Self-Learning Collision Avoidance • The sender directly builds the mapping between the RSS & success ratio. • Maintain the record and look it up • To decide if it can make the channel access. • RSS_SR_Update( rss, sf ) • RSS_SR_LookUp( rss ) • Dividing the RSS range into N intervals • N tuples of (Si, Fi, Ti) • Use aging factor to remove outdate data.

30. Upd_RSS_SR • Si: The number of successful channel access attempts • Fi: The number of failed channel access attempts • Ti: The last time Si & Fi were updated

31. Upd_RSS_SR

32. Conclusion • The advantages of SELECT are • Simple design and implementation • Not affecting 802.11 much • Adaptive to the environmental change • Treat the system as a black box, and react to the observing input-output. • Reduce complexity & achieve substantial gain

33. Max-min Fairness We need to prove that Algorithm 1 can allocate a feasible fair share vector φthat each flow has a bottleneck clique with respect to φ. • PROPOSITION 1. The fair share allocation obtained when Algorithm 1 finishes verifies the max-min fairness criterion defined earlier. • PROPOSITION 2. [11] A feasible rate vector r is max-min fair if and only if each session has a bottleneck link with respect to r. • PROPOSITION 2.1. A feasible fair share vector φis max-min fair if and only if each flow has a bottleneck clique with respect to φ. 33

34. Rate-Adaptive Framing for Interfered Wireless Networks • Frame loss in wireless networks • environmental and thermal noise • interference from other wireless stations • Majority of existing wireless rate controls generally reduce the channel rate on frame losses. • In highly interfered wireless networks, simply reducing the channel rate would • prolong the frame transmission time • aggravate frame loss rate • RAF maintains the history of the physical carrier sense. • Multiple series of idle and busy intervals

35. Exploiting Medium Access Diversity in Rate Adaptive Wireless LANs • The highest feasible rate is ultimately bounded by the channel signal to noise ratio, - encouraging the multi-rate adaptations • Medium Access Diversity (MAD) scheme: a rate adaptation schemes by exploiting multiuser diversity. • Selectively transmit data to a receiver that improves the overall throughput of the network, while maintaining temporal fairness. • The sender broadcasts a query message including the list of potential receivers for channel condition probing. • Each receiver sends its own reply message back to the sender in the corresponding time slot. • The sender chooses the receiver that maximizes potential throughput gain and begins its data transmission. The chosen receiver will reply with an ack message if it receives the data packet(s) correctly.

36. MAD SCHEDULING • As to improve the utilization of the channel while maintaining temporal fairness • Focus on a given sender • Maximum relative gain scheduling policy: • chooses a node with maximum gain relative to others φi :perceived signal reception power Γi ci = Γi/ φi :the expected power of the additive white Gaussian noise ci :a positive (nonzero) relative scaling factor for receiver i

37. Proposition 2. With independent Rayleigh fading channels, the difference between asymptotic throughput produced by optimal temporal fair scheduling and that by maximum relative gain scheduling is upper bounded by where W is the bandwidth of the communication channel

38. A Beacon Selection Algorithm for Bounded Error Location Estimation in Ad hoc Networks • We have proposed in this work an intelligent beacon selection algorithm for computing the location of a node in an ad hoc network. • We show that given a maximum of ±ε error in the location of each of the beacon nodes and a maximum error of ±δ in each of the measured ranges along either axes. • The location of a node can be computed within an error bound of ±[3ε(1+√2)+2δ] to ±(3ε+2δ) along the x-axis and within ±[2δ(1 +√2)+3ε] to ±(3ε+2δ) along the y-axis.

39. A Routing Metric for Load-Balancing in Wireless Mesh Networks • Some of the challenge in WMNs are load balancing, optimal routing, fairness, network auto-configuration and mobility management. • Focus on routing and load balancing. • Existing solution in mobile ad-hoc and sensor networks can not be applied to WMNs due to the difference in traffic patterns, mobility scenarios, gateway functionalities and bandwidth requirements. • We proposed a routing metric that provides load balancing at mesh router. • We introduce a dynamic traffic splitting algorithm to balance load distribution among mesh routers.

40. Sensor Measurements for Wi-Fi Location with Emphasis on Time-of-Arrival Ranging • shortcomings of GPS • Do not work indoors • accuracy • Application for indoor location • Indoor navigation • Printer finding • Location-based security • Digital home • Location aware tag • This paper shows that with a small modification to the WLAN physical layer, one can provide accurate location to the WLAN system. • The performance of the TOA is significantly better than SS

41. Time of Arrival (TOA) _1 • The TOA system likes the RADAR • The time-difference is related linearly to the distance to the object • Problem: the AP does not have a deterministic delay • Measure and sent back to the client

42. Time of Arrival (TOA) _2

43. Projection Based Location System via Multiple Discriminant Analysisin 802.11 WLAN environment End User: Mobile client WLAN Network Location Server WLAN access point RSS statistic model request Radio map WLAN access point Data collection

44. IP and Above Multi-Path Routing JMM Multi-Channel Link Layer 802.11 MAC Single Radio … … Channel 1 Channel 2 Channel N Joint Multi-Channel Link Layer and Multi-Path Routing Design for Wireless Mesh Networks • Assuming that each node has only one single interface, we show that multi-path routing, when being harmonized with multi-channel capability, has great potential to achieve good performance for WMNs. • We design the JMM protocol by: • routing on dual (master and slave) paths • partitioning each superframe into two (RF/TF) parts • forwarding packets alternatively on first and second parts alone each path • Our scheme efficiently and intelligently decomposes contending traffics over different channels, different time, and different paths, and hence leads to significant throughput improvement.

45. Overview: Wireless Multihop Relay Networks • Mobile Ad Hoc Networks (MANET) • Mobile • Ad hoc (peer-to-peer) • Wireless Mesh Networks (WMN) • Infrastructure multihop relay • Wireless Sensor Networks (WSN) • Sensor • Collecting data + data processing • Power-efficient • Vehicular Ad Hoc Networks (VANET) • Vehicle-to-vehicle

46. Classification : multihop-relay networks • Which nodes do relay for others? • Mobility? • Static with wireless connections • Low mobility • High mobility (e.g. vehicular) • Battery driven? • Does power efficient design a critical issue? • Example(i): sensor node with limited battery power • Example(ii): wireless mesh router (powered by electric wires) • Architecture • Pure peer-to-peer • Limited infrastructure • Some centralized control

47. Classifications of Routing Protocols • On-demand routing protocol • Also know as reactive routing protocol • Discover route “on-demand” (when needed) • Example • AODV (Ad hoc On-Demand Distance Vector Routing) • DSR (Dynamic Source Routing Protocol) • Proactive routing protocol • Actively maintain valid routes • Example • OLSR (Optimized Link State Routing) • Hybrid routing protocol • Mixture of proactive and on-demand protocol • Example • ZRP (The Zone Routing Protocol)

48. Introduction to Mobile Wireless Sensor Networks Hung-Yu Wei National Taiwan University

49. MANET and WSN Introduction to Mobile Wireless Sensor Networks • Mobile Ad Hoc Network (MANET) • Mobile • Peer-to-peer paradigm • Routing issues • Wireless Sensor Networks (WSN) • Sensing • Data-centric • Sensors to sink model • New trend: mobile wireless sensor network • MANET + WSN = MWSN?

50. Using Mobile Sensor • Improving wireless sensor network with mobile nodes • Adaptation to events • Resilient to failures • Reconfigure for disparate application support • System scalability and flexibility • Energy saving • Some mobile sensors may be more powerful and without energy constraint • Heterogeneous sensor network design • Mobile phones • Robots