Ad-Hoc Networks and New GPS Measurement Techniques for Robotic Follower Applications

Transcription

1 Ad-Hoc Networks and New GPS Measurement Techniques for Robotic Follower Applications Syed Masud Mahmud, Ph.D. Electrical and Computer Engg. Dept. Wayne State University, Detroit MI (313) , January 15, rd Annual Winter Workshop U.S. Army Tank-Automotive RD&E Center, Warren, MI Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 1

2 Speaker s Background Received Ph.D. in Electrical Engineering from the University of Washington, Seattle (1984). Worked for Oakland University, Rochester, Michigan, during Has been working for Wayne State University since Published over 70 technical papers in referred journals and conference proceedings. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 2

3 Speaker s Current Areas of Interest Intelligent Vehicles, Intelligent Transportation Systems, In-Vehicle Networking, Time Triggered Protocols for Real- Time Applications, Collision Warning and Collision Avoidance systems, Security in Wireless Communications, and Embedded Systems. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 3

4 Outline of the Talk Why unmanned vehicle? Communication mechanisms of unmanned vehicle (MANET). Introduction to Ad-Hoc Wireless Networks. Introduction to DSSS (Direct Sequence Spread Spectrum) and FHSS (Frequency Hopping Spread Spectrum). Some Wi-Fi Background. Some Bluetooth Background. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 4

5 Outline of the Talk Measurements using GPS Receivers. Measurements using Differential GPS Receivers. Measurements using Cooperative GPS receivers. A Distance Measurement Protocol for Robotic Follower Applications. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 5

6 Why Unmanned Vehicles? Applications of unmanned vehicles can increase combat effectiveness and personnel safety. These include reconnaissance, surveillance, target acquisition, logistics, minefield and other obstacle detection, explosive disposal, physical security, and operations in contaminated environments Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 6

7 Communication Mechanisms for Unmanned Vehicles The only practical communication mechanisms for unmanned vehicles is the wireless communications. A group of unmanned vehicles will be able to work together to achieve common goals and objectives provided each vehicle of the group is equipped with appropriate hardware, software and protocol to form Mobile Ad Hoc Networks (MANET). Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 7

8 Wireless Ad Hoc Networks A wireless ad hoc network is a collection of autonomous nodes that communicate with each other by forming a multihop radio network. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 8

9 Wireless Ad Hoc Networks Connectivity is maintained in a decentralized manner. Links typically have less bandwidth than in a wired network. Each node functions as both a host and a router. The control of the network is distributed among the nodes. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 9

10 Wireless Ad Hoc Networks The network topology is in general dynamic, because the connectivity among the nodes may vary with time due to node departures and new node arrivals. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 10

11 Challenges in Mobile Ad Hoc Networks Power management Bandwidth Interference Routing Security Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 11

12 Ad Hoc Routing Protocols Ad Hoc Routing Protocols Table-Driven Source-Initiated On-Demand DSDV WRP CGSR AODV DSR LMR TORA ABR SSR Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 12

13 Table-Driven Routing Protocols Destination-Sequence Distance-Vector Routing (DSDV)- Every mobile node in the network maintains a routing table in which all possible destinations and the number of hops to each destination are recorded Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 13

14 Destination-Sequence Distance- Vector (DSDV) Routing A destination node broadcasts its route information with a sequence number. The sequence number of the route message, which just arrived at a node, will be used by the receiving node to determine whether this information is already available in its table. If another message, carrying route information of Node 2, comes to Node 1 with a sequence number equal to 45, then Node 1 will not make any changes in its table. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 14

15 Destination-Sequence Distance- Vector (DSDV) Routing Node 6 just joined a group and started broadcasting its route information with a sequence number. Node 1 will receive the information from Node 6 (with the same sequence number) twice Node 1 will ignore the second message from Node Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 15

16 Destination-Sequence Distance- Vector (DSDV) Routing Routing table updates are periodically transmitted throughout the network. To reduce the potentially large amount of network traffic that such updates can generate, route updates can use two types of packets. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 16

17 Destination-Sequence Distance- Vector (DSDV) Routing The first is known as full dump. This type of packet carries all available routing information. During periods of occasional movement, these packets are transmitted infrequently. Smaller incremental packets are used to relay only that information which has changed since the last full dump. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 17

18 Destination-Sequence Distance- Vector (DSDV) Routing Node 4 will send only the information about Node 6 instead of sending the entire table. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 18

19 Clusterhead Gateway Switch Routine (CGSR) Routing Clusterhead Gateway Switch Routine (CGSR) The CGSR protocol differs from the DSDV protocol in the type of addressing and network organization. All nodes are grouped into a number of overlapping clusters. All nodes in a cluster execute a distributed algorithm to select a node as the Cluster head. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 19

20 Clusterhead Gateway Switch Routine (CGSR) Routing Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 20

21 Clusterhead Gateway Switch Routine (CGSR) Routing Nodes that are within communication range of two or more cluster heads are called the Gateway nodes. If a node in one cluster wants to send a packet to a node in another cluster, then the source node will first send the packet to its own cluster head. This cluster head will then send the packet to one of its gateway nodes on the path of the packet. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 21

22 Clusterhead Gateway Switch Routine (CGSR) Routing The gateway node will then send the packet to the cluster head of another cluster on the path of the packet. The packet will be moving like this until it goes to the cluster head of the destination cluster. The destination cluster head will then send the packet to the destination node. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 22

23 Clusterhead Gateway Switch Routine (CGSR) Routing In this method, each node keeps a Cluster Member Table where it stores the destination cluster head for each mobile node. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 23

24 Clusterhead Gateway Switch Routine (CGSR) Routing These cluster member tables are broadcast by each node periodically using the DSDV algorithm. Each node must also maintain a routing table which is used to determine the next hop in order to reach the destination. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 24

25 Clusterhead Gateway Switch Routine (CGSR) Routing The disadvantage of having a cluster head scheme is that frequent cluster head changes can adversely affect routing protocol performance because nodes will be busy in reselecting a cluster head instead of relaying the packets. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 25

26 Clusterhead Gateway Switch Routine (CGSR) Routing Hence, instead of invoking cluster head reselection every time the cluster membership changes, a Least Cluster Change (LCC) clustering algorithm is introduced. Using LCC, cluster heads only change when two cluster heads come into contact, or when a node moves out of contact of all other cluster heads. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 26

27 DSDV versus CGSR Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 27

28 Source-Initiated On-Demand Routing Protocols A different approach from table-driven routing is source-initiated on-demand routing. This type of routing creates routes only when desired by the source node. When a node requires a route to a destination, it initiates a route discovery process within the network. This process is completed once a route is found. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 28

29 Source-Initiated On-Demand Routing Protocols Once a route has been established, the route information is kept at the source node until either the destination node is no longer accessible or the route is no longer necessary. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 29

30 Ad Hoc On-Demand Distance Vector (AODV) Routing The AODV routing protocol builds on the DSDV algorithm previously shown. AODV is an improvement on DSDV because it minimizes the number of broadcasts by creating a route ondemand as opposed to maintaining a complete list of routes as in the DSDV algorithm. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 30

31 Ad Hoc On-Demand Distance Vector (AODV) Routing When a source node desires to send a message to some destination node and does not already have a valid route to that destination, it initiates a path discovery process to locate the other node. It broadcasts a route request (RREQ) to its neighbors, which then forward the request to their neighbors and so on, until either the destination or an intermediate node with a fresh enough route to the destination is found. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 31

32 Ad Hoc On-Demand Distance Vector (AODV) Routing 2 3 Source 8 Destination Propagation of RREQ Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 32

33 Ad Hoc On-Demand Distance Vector (AODV) Routing During the process of forwarding the RREQ, intermediate nodes record in their route tables the address of the neighbor from which the first copy of the broadcast packet is received, thereby establishing a reverse path. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 33

34 Ad Hoc On-Demand Distance Vector (AODV) Routing If additional copies of the same RREQ are later received, these packets are discarded. Once the RREQ reaches the destination or an intermediate node with a fresh enough route, the destination/intermediate node sends a route reply (RREP) packet. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 34

35 Ad Hoc On-Demand Distance Vector (AODV) Routing As the RREP is routed back along the reverse path, nodes along this path set up forward route entries in their route tables which point to the node from which the RREP came. 2 3 Source Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 35 8 Destination Propagation of RREP

36 Ad Hoc On-Demand Distance Vector (AODV) Routing As the RREP is routed back along the reverse path, nodes along this path set up forward route entries in their route tables which point to the node from which the RREP came. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 36

37 Ad Hoc On-Demand Distance Vector (AODV) Routing These forward route entries indicate the active forward route. Associated with each route entry is a route timer which will cause the deletion of the entry if it is not used within a specified lifetime. Route Maintenance: If a source node moves, it is able to reinitiate the route discovery protocol to find a new route to the destination. If a node along the route moves, its upstream neighbor notices the move and propagates a link failure notification message to each of its active upstream neighbors to inform them of the erasure of that part of the route. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 37

38 Ad Hoc On-Demand Distance Vector (AODV) Routing These nodes in turn propagate the link failure notification to their upstream neighbors, and so on until the source node is reached. The source node may then choose to reinitiate route discovery for that destination if a route is still desired. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 38

39 Example: Node 3 Departed Node 3 departed from the network. Node 2 detected Node 3 s departure. Node 2 removed the route information from its route table and informed Node 1 about the departure of Node 3. Node 1 also removed the route information from its route table. 2 Source Destination 5 6 Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 39

40 Ad Hoc On-Demand Distance Vector (AODV) Routing Another feature of this protocol is to periodically send a hello message by a node to its neighbor. Using the hello message the nodes maintain their local connectivity. If a node stops receiving the hello message from one of its neighbors, then the node understands that its one particular neighbor moved away. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 40

41 Dynamic Source Routing (DSR) The DSR protocol is an on-demand routing protocol that is based on the concept of source routing. Mobile nodes are required to maintain route caches that contain the source routes of which the mobile is aware. Entries in the route cache are continually updated as new routes are learned. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 41

42 Dynamic Source Routing (DSR) The protocol consists of two major phases: route discovery and route maintenance. When a mobile node has a packet to send to some destination, it first consults its route cache to determine whether it already has a route to the destination. If it has an unexpired route to the destination, it will use this route to send the packet. On the other hand, if the node does not have such a route, it initiates route discovery by broadcasting a route request packet. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 42

43 Dynamic Source Routing (DSR) Each node receiving the packet checks whether it knows of a route to the destination. If it does not, it adds its own address to the route record of the packet and then forwards the packet along its outgoing links. To limit the number of route requests propagated on the outgoing links of a node, a mobile only forwards the route request if the request has not yet been seen by the mobile and if the mobile s address does not already appear in the route record. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 43

44 Dynamic Source Routing (DSR) Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 44

45 Dynamic Source Routing (DSR) A route reply is generated when the route request reaches either the destination, or an intermediate node which contains in its route cache an unexpired route to the destination. By the time the packet reaches either the destination or such an intermediate node, it contains a route record yielding the sequence of hops taken. If the node generating the route reply is the destination, it places the route record contained in the route request into the route reply. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 45

46 Dynamic Source Routing (DSR) If the responding node is an intermediate node, it will append its cached route to the route record and then generate the route reply. To return the route reply, the responding node must have a route to the initiator. If it has route to the initiator in its route cache, it may use that route. Otherwise, if symmetric links are supported, the node may reverse the route in the route record. If symmetric links are not supported, the node may initiate its own route discovery. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 46

47 Dynamic Source Routing (DSR) Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 47

48 Dynamic Source Routing (DSR) Route Maintenance: Route maintenance is accomplished through the use of route error packets and acknowledgments. Route error packets are generated at a node when the data link layer encounters a fatal transmission problem. When a route error packet is received, the hop in error is removed from the node s route cache and all routes containing the hop are truncated at that point. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 48

49 Dynamic Source Routing (DSR) Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 49

50 Introduction to DSSS and FHSS The DSSS and FHSS options were designed specifically to conform to FCC regulations (FCC ) for operation in the 2.4 GHz ISM band. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 50

51 Introduction to DSSS and FHSS Both FHSS and DSSS currently support 1 and 2 Mbps. All 11 Mbps radios are DSSS. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 51

52 The DSSS Technology The DSSS is the same technology used in GPS satellite navigation systems. The data stream is combined via an XOR function with a high-speed pseudorandom numerical sequence (PRN). For 1 and 2 Mbps DSSS the PRN code is the 11-chip Barker sequence, which is Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 52

53 An Example of DSSS Coding Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 53

54 A 0 and a 1 in DSSS Coding Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 54

55 Binary and Quadrature Phase Shift Keying Modulation XOR output is modulated onto a carrier frequency using BPSK and QPSK for 1 and 2 Mpbs signals, respectively. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 55

56 Complementary Code Keying is used for 5.5 and 11Mbps Complementary Code Keying (CCK), is a set of 64 eight-bit code words used to encode data for 5.5 and 11Mbps. The code words have unique mathematical properties that allow them to be correctly distinguished from one another by a receiver even in the presence of substantial noise and interference. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 56

57 DSSS Code Length, Modulation and Symbol Rate Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 57

58 Effect of PRN Sequence on Transmit Spectrum Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 58

59 DSSS Receiver The receiver processing of DSSS signals begins with despreading the signals. This is done by mixing the spread signal with the same PRN sequence that was used for spreading. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 59

60 DSSS Receiver Demodulator Barker Sequence Raw bit stream Correlating Process Data Bits Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 60

61 Received Signal is Correlated with the PRN Sequence to Recover Data and Reject Interference Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 61

62 Properties of DSSS Signals Immune to certain amount of noise Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 62

63 Properties of DSSS Signals Immune to certain amount of interference Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 63

64 Properties of DSSS Signals Multiple access using different PRN codes Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 64

65 The FHSS Technology With frequency hopping spread spectrum, the carrier frequency changes (hops) periodically. The frequency hopping technique reduces interference. If the hop sequence of two transmitters are different and never transmit the same frequency at the same time, then there will no interference among them. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 65

66 The FHSS Technology A hopping code determines the frequencies the radio will transmit and in which order. A set of hopping codes that never use the same frequencies at the same time are considered orthogonal. Because of the nature of its modulation technique, frequency hopping can achieve up to 2 Mbps data rates. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 66

67 DSSS versus FHSS Higher cost Higher power consumption Higher data rates Lower aggregate capacity using multiple physical layers. More range DSSS Smaller number of geographically separate radio cells due to a limited number of channels. Lower cost Lower power consumption Lower data rates Higher aggregate capacity using multiple physical layers. Less range FHSS Most tolerant to signal interference Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 67

68 Wi-Fi (IEEE ) Uses DSSS Technology U.S. allows the use of channels 1 thru. 11. U.K. can use channels 1 through 13. Japan allows the use of all 14 channels. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 68

69 Three Non-Overlapping DSSS Channels Each Channel Bandwidth is about 22 MHz. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 69

70 Some Wi-Fi Background The basic access method for Wi-Fi Distributed Coordination Function (DCF) which uses Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA). This requires each station to listen for other users. If the channel is idle, the station may transmit. If the channel is busy, each station waits until transmission stops. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 70

71 Some Wi-Fi Background The period between completion of packet transmission and start of the ACK frame is one Short Inter Frame Space (SIFS). Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 71

72 Some Wi-Fi Background A node must wait at least one DCF inter frame space (DIFS) after ACK frame before transmitting data. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 72

73 Some Wi-Fi Background If a transmitter senses a busy medium, it determines a random back-off period by setting an internal timer to an integer number of slot times. Upon expiration of a DIFS,the timer begins to decrement. If the timer reaches zero, the station may begin transmission. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 73

74 Some Wi-Fi Background Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 74

75 Some Wi-Fi Background However, if the channel is seized by another station before the timer reaches zero, the timer setting is retained at the decremented value for subsequent transmission. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 75

76 Some Bluetooth Background Bluetooth is a short range wireless communication technology. Frequency Hopping Spread Spectrum 1600 Hops/second 79-1MHz Bands in 2.4GHz ISM Spectrum 1Mbs Raw Data Rate ( 721kbs User Data) Objectives Robustness, low complexity, low power and low cost. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 76

77 Bluetooth Range in Relation to Different Power Classes Class Class 1 Class 2 Class 3 Power 100 mw (20 dbm) 2.5 mw (4 dbm) 1mW (0 dbm) Range 100m ( 325ft) 10m ( 32ft) 1m ( 3ft) Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 77

78 Outdoor Range Tests Test results show that in open space the range of Bluetooth Devices far exceeded the specification. (Results reported by P. Murphy, E. Welsh & P. Frantz of Rice University) Class 1 (20 dbm) Class 2 (4 dbm) Maximum Range 250 m ( 820ft) 122 m ( 400ft) Spec. Range 100 m 10 m Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 78

79 Some Bluetooth Background Bluetooth enabled electronic devices connect and communicate wirelessly via short-range range networks called piconets. One unit acts as the master of the piconet, whereas the other unit(s) acts as slave(s). Master Slave A Piconet with one Master and one Slave Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 79

80 Some Bluetooth Background Each unit can simultaneously communicate with up to seven other units per piconet. A Piconet with one Master and seven Slaves Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 80

81 Some Bluetooth Background A TDD (Time-Division Duplex) scheme is used where master and slave alternatively transmit Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 81

82 Some Bluetooth Background Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 82

83 Some Bluetooth Background Slaves can participate in different piconets on a time-division multiplex basis. A master in one piconet can be a slave in another piconet. The piconets are established dynamically and automatically as Bluetooth devices enter and leave the radio proximity. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 83

84 Some Bluetooth Background Multiple piconets with overlapping coverage areas form a scatternet. Master Slave Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 84

85 Bluetooth Baseband Layer Controls the Radio layer. Provides frequency hop sequences. Takes care of lower level encryption for secure links. Handles packet over the wireless link. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 85

86 Bluetooth Baseband Layer Two types of links can be established: - SCO: Synchronous Connection Oriented, meant for synchronous data typically voice. - ACL: Asynchronous Connection Less, used for data transfer applications. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 86

87 Bluetooth Baseband Layer SCO Link ACL Link Master Slave Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 87

88 Bluetooth Baseband Layer Synchronizes devices clocks and establish connections. Discovers devices addresses in proximity. Handles error correction for packets. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 88

89 How Are Connections Made Devices Must Discover Other Devices through an Inquiry Process. A potential master goes to a state called the Inquiry State and then sends a Inquiry Message. All nearby devices go to Inquiry Response States to indicate their presence. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 89

90 How Are Connections Made After the Inquiry process, the potential master knows the addresses (48-bit numbers) of the other devices. The potential master then established a connection with another known device using a process call the Paging processing. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 90

91 States of Bluetooth Units Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 91

92 States of Bluetooth Units Connected State: In this state, a device is an active member of a piconet. Transmit State: In this state, a device transmits packets. Park, Hold and Sniff States: These are different low power state of Bluetooth devices. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 92

93 Measuring Distance Between Intelligent Vehicles Advanced positioning systems and wireless technologies can be used in intelligent vehicles to build collision warning, collision avoidance and cooperative driving systems. The cooperative driving system is necessary for Robotic Follower applications. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 93

94 Measuring Distance Between Intelligent Vehicles The cooperative driving system will also allow a convoy to move together keeping safe distance among the vehicles. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 94

95 Measuring Distance Between Intelligent Vehicles The error in position measurement using standard GPS receivers can be in the order of tens and hundreds of feet. Differential GPS (DGPS) receivers can give better accuracy than standard GPS receivers. Even using DGPS receivers it is found that the error in intervehicle distance measurement is in the order of several feet. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 95

96 Measuring Distance Between Intelligent Vehicles Measurement using DGPS receivers requires an infrastructure of GPS ground stations to cover all the highways and freeways. GPS ground stations may not be readily available in a battle field. As a result, measurement using DGPS receivers may not be possible in a battle field. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 96

97 Measuring Distance Between Intelligent Vehicles This talk presents a technique to measure intervehicle distances without using DGPS receivers. The measurement accuracy of the proposed technique can be as good as that of the DGPS technique. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 97

98 Some GPS Background GPS receivers use timing signals from four satellites to determine its position. Each timing signal indicates how long the signal took to travel from the corresponding satellite to the GPS receiver. The distance between the satellite and the GPS receiver is then determined by multiplying the travel time by the velocity of light. dist = velocity x time Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 98

99 Some GPS Background Each timing signal has some errors due to various conditions such as: lack of synchronization between satellite clock and receiver clock, conditions of the earth s atmosphere, receiver noise, multi-path effect, etc. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 99

100 Distances between a GPS receiver and two satellites with no timing errors in the satellite signals. d1 and d2 are distances between the satellites and the GPS receiver. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 100

101 Distances between a GPS receiver and two satellites (S1 and S2) with errors in the satellite timing signals. e1 and e2 are errors in timing signals. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 101

102 Distances between a GPS receiver and three satellites with errors in the satellite timing signals. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 102

103 Actual Distance Between a Satellite and a GPS Receiver Let (x i,y i,z i ) be the actual coordinates of Satellite-i (for i = 1,2,3,.. ). Let (x Gj,y Gj,z Gj ) be the actual coordinates of GPS Receiver-j (for j = 1,2,3,.. ). The actual distance (R ij ) between Satellite-i and GPS Receiver-j, can be expressed as: Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 103

104 Measured Distance (R ij ) Between Satellite-i and GPS Receiver-j Where,c j is the bias due to lack of synchronization between the clock of Receiver-j and the clock of satellites. And, d i is the bias due to the effect of atmospheric conditions on the signal of Satellite-i. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 104

105 Measured Distance (R ij ) Between Satellite-i and GPS Receiver-j In the above expression, the effects of multipath and receiver noise have not been considered. Effects of multipath and receiver noise are also present in DGPS measurements. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 105

106 Measured Distances Between GPS Receiver-j and Satellites 1, 2, 3 and 4 Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 106

107 Measured Distances in the Absence of any Atmospheric Errors The above equations have four unknowns: x Gj, y Gj, z Gj and c j. (hence, a solution exists). Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 107

108 No Atmospheric Errors No Errors in Position Measurement If there were no atmospheric errors, then there would be no errors in position measurements of GPS receivers. Note: The effects of multipath and receiver noise have not been considered in the above claim. Like in DGPS measurements, the multipath and receiver noise will introduce some errors. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 108

109 Measurements Using GPS Receivers in the presence of atmospheric errors. Eight unknowns (x Gj,y Gj,z Gj,c j, d 1,d 2, d 3, and d 4, ). Hence, no exact solution. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 109

110 Measurements Using DGPS Receivers GPS ground stations calculate the value of d i (i=1,2,3,..) and broadcast to all roving receivers within their range. The roving receivers then plug in the values of d i (i=1,2,3,..) in the following equations. Now, the roving receivers can solve the equations for exact values of x Gj, y Gj, z Gj and c j. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 110

111 Measurements Using DGPS Receivers Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 111

112 An Approximate Solution Using Standard GPS Receivers Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 112

113 Error in Position Calculation using Standard GPS Receivers Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 113

114 Accurate Distance Measurement Without Using DGPS Receivers For collision warning, collision avoidance and cooperative driving systems, we are not interested in absolute locations of the vehicles. Rather, we would be interested in their relative locations (distances between themselves). Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 114

115 Accurate Distance Measurement Without Using DGPS Receivers Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 115

116 Accurate Distance Measurement Without Using DGPS Receivers Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 116

117 Accurate Distance Measurement Without Using DGPS Receivers Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 117

118 Accurate Distance Measurement Without Using DGPS Receivers Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 118

119 Accurate Distance Measurement Without Using DGPS Receivers Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 119

120 Accurate Distance Measurement Without Using DGPS Receivers Equation (8) is valid for any GPS receiver, given that satellites 1 and 2 are used in the distance calculation. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 120

121 Accurate Distance Measurement Without Using DGPS Receivers Now let s consider two GPS receivers (Receiver-1 and Receiver-2 ), which are very close to each other. The values of d i (i=1,2,3,..) will be same for both GPS receivers. Hence, using Equation (8) we can write the next two equations: Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 121

122 Equation for GPS Receiver-1 Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 122

123 Equation for GPS Receiver-2 Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 123

124 Equation for receivers 1 and 2 Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 124

125 Equation for receivers 1 and 2 Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 125

126 Accurate Distance Measurement Without Using DGPS Receivers The left side of Equation (12) depends on the calculated positions of GPS receivers, and the right side of the equation depends on the actual positions of the GPS receivers. The expressions of both sides of Equation (12) are similar. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 126

127 Accurate Distance Measurement Without Using DGPS Receivers Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 127

128 Accurate Distance Measurement Without Using DGPS Receivers Thus, the distance between the actual positions of two GPS receivers is the same as the distance between their calculated positions, provided the same set of satellites are used for position calculations of both receivers. Like the DGPS measurements, the effects of multipath and receiver noise will also introduce errors in this measurement. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 128

129 Positional Errors Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 129

130 Peer-to-Peer Distance Errors Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 130

131 Parameters for Numerical Results Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 131

132 Parameters for Numerical Results Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 132

133 Numerical Results Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 133

134 Numerical Results Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 134

135 Parameters (Satellites are very close to each other) Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 135

136 Numerical Results (Satellites are very close to each other) Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 136

137 Numerical Results (Satellites are very close to each other) Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 137

138 Effect of Precision Error on the Distance Error If a Code-Phase GPS receiver is used, then the distance between the receiver and a satellite can have a precision error in the order of 10 to 20 feet (3 to 6 meters). If a Carrier-Phase GPS receiver is used then the precision error is in the order of a fraction of an inch (3 to 4 millimeters). Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 138

139 Effect of Precision Error on the Distance Error Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 139

140 Effect of Precision Error on the Distance Error Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 140

141 Effect of Precision Error on the Distance Error Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 141

142 Effect of Precision Error on the Distance Error Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 142

143 In a real system, the effect due to precision error will be very small. The results of the previous two slides were determined assuming that the precision error is about 6 inches. But, if we use carrier-phase GPS receivers then the precision error is about 0.4 inch. Hence, the distance error will be very small compared to that shown in the previous two slides. It will be 0.18ft and 0.35ft instead of 2.65ft and 5.21ft, respectively. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 143

144 Setup for Collecting Test Data Initial Budget: Under $500 Two low-cost GPS receivers. Two 900MHz Multi- Protocol Wireless Links. Help from Philip Sokolowski, a student. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 144

145 Setup for Collecting Test Data Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 145

146 Setup for Collecting Test Data Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 146

147 Setup for Collecting Test Data Due to lack of sufficient budget we bought two very low-cost GPS receivers, which have very limited programming features. We could not program the GPS receiver to look at a particular set of satellites. We were blocking the satellite signals manually using aluminum foils. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 147

148 Distance Between Points P1(lat1,lon1) and P2(lat2,lon2) Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 148

149 Actual Data from the Field Test Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 149

150 Actual Data from the Field Test Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 150

151 Actual Data from the Field Test Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 151

152 Actual Data from the Field Test Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 152

153 Manually shielding the satellites was very time consuming It took too much time to manually setup receivers for looking at the same set of four satellites. We bought two new GPS receivers which can be programmed to look at only a particular set of satellites. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 153

154 Automating Data Collection Process Philip Sokolowski, a graduate student, is developing the necessary hardware and software to automate the data collection process. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 154

155 Wireless Protocol for Distance Measurement 1. The Lead Vehicle selects four good satellites and broadcasts a message to all other vehicles informing them about the set of four satellites to use. 2. All vehicles in the convoy use the same set of four satellites to calculate their own positions. 3. All vehicles exchange their position information among themselves. 4. All vehicles computer their distance from other vehicles. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 155

156 Wireless Protocol for Distance Measurement 5. If the lead vehicle changes any satellite in the set of four satellite, then it informs all other vehicles about the change. 6. If 10Hz GPS receivers are used, then the vehicles will be able to broadcast new position information every 100 msec. 7. However, the vehicles will be able broadcast other dynamic information such as speed, acceleration, jerk and direction more frequently (for example, every 10 msec even using Bluetooth technology). Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 156

157 Wireless Protocol for Distance Measurement 8. In between two successive GPS updates, the vehicles will be able to keep track of their distance from other vehicles using their real-time dynamic information. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 157

158 Distance Estimation Between two Successive GPS Readings Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 158

159 Bluetooth bandwidth is sufficient for exchanging vehicles dynamic information. The master vehicle (lead-vehicle) will be able to send data after every two time slots (1.25 msec). Every slave vehicle (followers) will be able to send data after every 14 time slots (8.75 msec.) M: Master S1, S2, S3,... : Slaves Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 159

160 Vehicles Dynamic Parameters All parameters will fit in one small packet. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 160

161 Secure Communications among the Vehicles of a Convoy The vehicles must have secure wireless links to communicate among themselves. Otherwise, hackers may change the contents of the intervehicle messages. All the vehicles of a convoy must be preloaded with a set of secret keys so that they can securely exchange messages. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 161

162 References 1. Elizabeth M. Royer and Chai-Keong Toh, A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks, IEEE Personal Communications, April 1999, pp Syed Masud Mahmud and Shobhit Shanker, An Architecture for Intelligent Automotive Collision Avoidance Systems, Proceedings of the 3rd Annual Intelligent Vehicle Systems Symposium of NDIA, National Automotive Center and Vectronics Technology, June 9 12, 2003, Traverse City, Michigan, pp IEEE Tutorial by Jim Zyren and Al Petrick. 4. Brief Tutorial on IEEE Wireless LANs by Jim Zyren and Al Petrick. Ad-Hoc Networks & GPS Measurements for Robotic Followers by Syed M. Mahmud 162