Location-Aided Routing (LAR) in Mob

Location-Aided Routing (LAR) in Mobile Ad Hoc Network

Organization
• Introduction
• Related Work
• Location-Aided Routing (LAR) protocol
– Route Discovery using Flooding
– Location information
– Expected Zone and Request Zone
– LAR Scheme 1
– LAR Scheme 2
– Error in location estimate
• Simulation Model and Results
• Variations and Optimizations

Introduction
Mobile Ad hoc Network(MANET)
• Node mobility which is the cause of frequent and unpredictable topology changes leads to difficult task of route maintenance in MANET
• Many protocols have been proposed for MANET to achieve efficient routing
• This paper suggest an approach to decrease overhead of route discovery by utilizing location information (GPS or other method to obtain location information)
• Two LAR protocols for route discovery presented in this paper uses location information(may be out of date) to limit search space which results in fewer route discovery messages

Related Work
• Many protocols have been proposed for MANNET such as DSR, AODV, TORA, ZRP
• Existing MANET routing algorithm mentioned do not utilize physical location of a destination node
• Similar idea (utilizing location information) have been applied and developed called “selective paging for cellular PCS (personal communication service) networks
• In selective paging, the system pages a selected subset of cells close to the last known location of mobile host which decrease location tracking cost
• This paper propose and evaluate an analogous approach for routing in MANET

Route Discovery Using Flooding
• This paper discuss the basic flooding algorithm and location-aided route discovery based on limited “flooding”
Basic Flooding Algorithm
– A source node S needs to find a route to destination node D, node S broadcasts a route request to all its neighbors
– Intermediate node X receives a route request and compares the destination with its own identity
– If it does not match, then node X broadcast the request to its neighbors(sequence numbers used to detect duplicate and eliminate/avoid redundant transmissions)
– Node D responds by route reply messages to sender which traverse the path in reverse of the path received by D (route request packet contains path of all nodes traversed starting S)

Route Discovery Using Flooding
Basic Flooding Algorithm
– Timeout scheme is also used to re-initiate route request with new sequence number due to transmission error or node D is unreachable from S

Route Discovery Using Flooding
• In this paper, implementation assumes that node S can know that route is broken only if it attempts to use the route by sending data packet and receiving route error messages – it initiates route discovery for D
• Note that route request may reach every node in the network that is reachable from S (potentially all nodes in the MANET)
• This paper claims that by using location information reduces the number of nodes to whom route request is propagated (limit the scope of route request propagation)

Location Information
• Location information can be obtained by the use of Global Positioning System (GPS)
• With use of GPS, mobile host can know its physical location – note that GPS includes some degree of error compared to the real coordinates and GPS-calculated
– NAVSTAR GPS has positional accuracy of 50-100 meters
– Differential GPS has positional accuracy of few meters
• This paper assumes that each node knows its current location precisely – possibility of error in location are discussed separately in the performance evaluation
• Also assume that the mobile nodes are moving in a two-dimensional plane

Expected Zone
• The Expected Zone is the region where source node S thinks that the destination node D may contained at some time t – only an estimate made by S
– Assume that node S knows that the node D was at location L at time t0 and current time is t1
– From the viewpoint of S, expected zone of node D is the region that node S expects to contain node D at time t1 based on the knowledge that node D was at location L at time t0
• If S knows that D travels with average speed v, then S assumes that the expected zone is the circular region of radius v(t1- t0) centered at location L
• Note that if actual speed is faster than the average, then the destination may be outside the expected zone at t1

Expected Zone
• Without the previous knowledge of the location of D, S will assume that the entire region is the expected zone and implementation uses the basic flooding algorithm
• The size of expected zone can be reduced if node has more information about the mobility of a destination D

Request Zone
• Node S defines (implicitly or explicitly) a request zone for the route request
• Node forwards a route request only if it belongs to the request zone (it does not forward a route request to its neighbor if outside of the request zone)
• Two LAR scheme differ in determining the membership of request zone
• The request zone includes expected zone in addition to (possibly) other surrounding zone around the request zone
• If a route is not discovered within the timeout period, S initiates a new route discovery with expanded request zone – all paths from S to D include nodes that are outside the request zone
• Note that the probability of finding path can increase as size of request zone increases (route discovery overhead also increases with the size of the request zone

LAR Scheme 1
• The request zone is rectangular in shape
• Assume S knows that the node D was at location (Xd,Yd) at time t0
• Assume S knows the average speed v with which D can move
• From above two, S defines the expected zone at time t1 with radius R = v(t1- t0) centered at location (Xd,Yd)
• The request zone is the smallest rectangle that includes current location S and the expected zone such that the sides of the rectangle are parallel to the X and Y axes
• Node D sends route reply message with its current location and time (may include average speed but simulation assumes all nodes knows each other’s average speed)

LAR Scheme 1
• Size of the request Zone is proportional to
(i)average speed of movement v and
(ii)elapsed time since recorded last location of the destination
• Recall that R = v(t1- t0) is used to determine the size of request zone
• In general, a smaller request zone may be formed at speed that are neither too small nor too large
• For instance, at low speed, factor (i) is small but route discovery occur after long intervals making (ii) larger (t1- t0 is large)

LAR Scheme 2
• Node S includes two pieces of information with its route request
– Assume that S knows the location (Xd,Yd) of D at some time t0 which route discovery is initiated by S at t1 where t1 ³ to
– S calculates its distance from location (Xd,Yd) denoted DISTs and included with the route request
– The coordinate (Xd,Yd) are also included with the route request
• When node I receives the route request from S, node I calculates its distance from (Xd,Yd) denoted DISTi and:
– For some parameter d, if DISTs + d ³ DISTi, then I forwards request to its neighbors – this request includes (Xd,Yd) and DISTi replacing original DISTs and (Xd,Yd) from S
– Else DISTs + d < DISTi, node I discards the route request
• Each intermediate nodes repeat the process above

Error in Location Estimate
• Both LAR schemes assume that each node knows its own location accurately. However, just like GPS, there may be some error in the estimated location
• Let e (location error) denote maximum error in the coordinates estimated by a node
• If a node N believes that it is at location (Xn,Yn), then the actual location of node N may be anywhere in the circle of radius e centered at (Xn,Yn)
• If LAR Scheme 1 is modified to take e into account, then the expected zone is a circle of radius e + v (Xn,Yn) which makes request zone larger since it includes larger expected zone
• No modification is made to the LAR Scheme 2

Performance Evaluation
• The simulation is performed using modified version of MaRS (Maryland Routing Simulator)
• MaRS is discrete-event driven simulator providing a flexible platform for the evaluation and comparisons of network routing algorithm
• Simulations were performed on flooding, LAR scheme 1, and LAR scheme 2
• Simulations are conduct by varying the number of nodes, transmission range of each node, and moving speed

Simulation Model
• Number of nodes in the network was chosen to be 15, 30, and 50 for different simulation runs
• The size of ad hoc network is 1000 unit x 1000 unit square region
• Initial locations of the nodes are obtained using a uniform distribution
• Each node moves continuously without pausing at any location – move with average speed v in the range 1.5 to 32.5 units/sec
• The actual speed is uniformly distributed in the range v – a and v + a units/sec where a=1.5 when v < 10 and a = 2.5 when v ³ 10
• A node travels distance d where d is exponentially distributed with mean 20 units
• The direction of movement for a given move is chosen randomly
• All nodes have the same transmission range

Simulation Model
• Transmission range of 200, 300, 400, and 500 units were used with all wireless links

Kết quả (Việt) 1:

Vị trí-hỗ trợ định tuyến (LAR) trong điện thoại di động quảng cáo hocTổ chức• Giới thiệu• Liên quan đến công việcGiao thức định tuyến hỗ trợ vị trí (LAR) •-Tuyến đường khám phá bằng cách sử dụng Flooding-Vị trí thông tin-Dự kiến khu và yêu cầu khu vực-LAR đề án 1-LAR đề án 2-Lỗi ở vị trí ước tính• Mô phỏng mô hình và kết quả• Biến thể và tối ưu hóaGiới thiệuĐiện thoại di động quảng cáo hoc Network(MANET)• Nút di động mà là nguyên nhân gây ra thay đổi thường xuyên và không thể đoán trước cấu trúc liên kết dẫn đến các nhiệm vụ khó khăn của tuyến đường bảo trì trong MANET• Nhiều giao thức đã được đề xuất cho MANET để đạt được hiệu quả định tuyến• Giấy này đề nghị một phương pháp tiếp cận để giảm chi phí của tuyến đường khám phá bằng cách sử dụng thông tin vị trí (GPS hoặc phương pháp khác để có được thông tin vị trí)• Hai LAR giao thức khám phá lộ trình bày trong bài báo này sử dụng thông tin vị trí (có thể được hết hạn) để hạn chế không gian tìm kiếm mà kết quả trong ít hơn định tuyến phát hiện thưCông việc liên quan• Nhiều giao thức đã được đề xuất cho MANNET chẳng hạn như DSR, AODV, TORA, ZRP• Hiện có MANET thuật toán định tuyến đề cập không sử dụng các vị trí thực tế của một nút đích• Ý tưởng tương tự (sử dụng thông tin vị trí) đã được áp dụng và phát triển được gọi là "chọn lọc phân trang cho mạng máy tính (dịch vụ thông tin cá nhân) di động• Trong chọn lọc phân trang, các hệ thống trang một tập hợp con được chọn của các tế bào gần cuối địa điểm nổi tiếng của máy chủ lưu trữ di động đó làm giảm chi phí theo dõi vị trí• Giấy này đề xuất và đánh giá một cách tiếp cận tương tự cho việc định tuyến trong MANETTuyến đường khám phá bằng cách sử dụng lũ lụt• Bài viết này thảo luận về cơ bản các thuật toán lũ lụt và khám phá lộ địa điểm hỗ trợ dựa trên giới hạn "lũ lụt"Thuật toán cơ bản lũ lụt-Một nút nguồn S nhu cầu để tìm một tuyến đường đến đích nút D, nút S chương trình phát sóng yêu cầu đường nước láng giềng-Trung gian nút X nhận được một yêu cầu đường và so sánh điểm đến với bản sắc riêng của mình-Nếu nó không phù hợp, sau đó nút X phát sóng yêu cầu để nước láng giềng (số thứ tự được sử dụng để phát hiện trùng lặp và loại bỏ/tránh truyền dự phòng)-Nút D phản ứng bằng cách định tuyến trả lời thư gửi mà đi qua con đường ngược lại đường dẫn đã nhận được bởi D (tuyến đường yêu cầu gói chứa các đường dẫn của tất cả các nút ngang S bắt đầu)Tuyến đường khám phá bằng cách sử dụng lũ lụtThuật toán cơ bản lũ lụt-Thời gian chờ chương trình cũng được sử dụng để lại bắt đầu tuyến đường yêu cầu với số thứ tự mới do truyền lỗi hoặc nút D là không thể kết nối từ STuyến đường khám phá bằng cách sử dụng lũ lụt• Trong bài báo này, thực hiện giả định nút đó S có thể biết rằng con đường bị hỏng chỉ khi nó cố gắng sử dụng các tuyến đường bằng cách gửi dữ liệu gói và nhận được thông báo lỗi tuyến đường-bắt đầu khám phá ra con đường cho D• Lưu ý định tuyến yêu cầu có thể tiếp cận với mỗi nút trong mạng có thể truy cập từ S (có khả năng tất cả các nút trong MANET)• Giấy này tuyên bố rằng bằng cách sử dụng vị trí thông tin làm giảm số lượng các nút mà tuyến đường yêu cầu là tuyên truyền (giới hạn phạm vi của tuyến đường yêu cầu tuyên truyền)Location Information• Location information can be obtained by the use of Global Positioning System (GPS)• With use of GPS, mobile host can know its physical location – note that GPS includes some degree of error compared to the real coordinates and GPS-calculated– NAVSTAR GPS has positional accuracy of 50-100 meters– Differential GPS has positional accuracy of few meters• This paper assumes that each node knows its current location precisely – possibility of error in location are discussed separately in the performance evaluation• Also assume that the mobile nodes are moving in a two-dimensional planeExpected Zone• The Expected Zone is the region where source node S thinks that the destination node D may contained at some time t – only an estimate made by S – Assume that node S knows that the node D was at location L at time t0 and current time is t1– From the viewpoint of S, expected zone of node D is the region that node S expects to contain node D at time t1 based on the knowledge that node D was at location L at time t0• If S knows that D travels with average speed v, then S assumes that the expected zone is the circular region of radius v(t1- t0) centered at location L• Note that if actual speed is faster than the average, then the destination may be outside the expected zone at t1 Expected Zone• Without the previous knowledge of the location of D, S will assume that the entire region is the expected zone and implementation uses the basic flooding algorithm• The size of expected zone can be reduced if node has more information about the mobility of a destination DRequest Zone• Node S defines (implicitly or explicitly) a request zone for the route request• Node forwards a route request only if it belongs to the request zone (it does not forward a route request to its neighbor if outside of the request zone)• Two LAR scheme differ in determining the membership of request zone• The request zone includes expected zone in addition to (possibly) other surrounding zone around the request zone• If a route is not discovered within the timeout period, S initiates a new route discovery with expanded request zone – all paths from S to D include nodes that are outside the request zone• Note that the probability of finding path can increase as size of request zone increases (route discovery overhead also increases with the size of the request zone LAR Scheme 1• The request zone is rectangular in shape• Assume S knows that the node D was at location (Xd,Yd) at time t0 • Assume S knows the average speed v with which D can move• From above two, S defines the expected zone at time t1 with radius R = v(t1- t0) centered at location (Xd,Yd) • The request zone is the smallest rectangle that includes current location S and the expected zone such that the sides of the rectangle are parallel to the X and Y axes• Node D sends route reply message with its current location and time (may include average speed but simulation assumes all nodes knows each other’s average speed)LAR Scheme 1• Size of the request Zone is proportional to (i)average speed of movement v and (ii)elapsed time since recorded last location of the destination• Recall that R = v(t1- t0) is used to determine the size of request zone• In general, a smaller request zone may be formed at speed that are neither too small nor too large• For instance, at low speed, factor (i) is small but route discovery occur after long intervals making (ii) larger (t1- t0 is large) LAR Scheme 2• Node S includes two pieces of information with its route request– Assume that S knows the location (Xd,Yd) of D at some time t0 which route discovery is initiated by S at t1 where t1 ³ to– S calculates its distance from location (Xd,Yd) denoted DISTs and included with the route request– The coordinate (Xd,Yd) are also included with the route request• When node I receives the route request from S, node I calculates its distance from (Xd,Yd) denoted DISTi and:– For some parameter d, if DISTs + d ³ DISTi, then I forwards request to its neighbors – this request includes (Xd,Yd) and DISTi replacing original DISTs and (Xd,Yd) from S– Else DISTs + d < DISTi, node I discards the route request• Each intermediate nodes repeat the process aboveError in Location Estimate• Both LAR schemes assume that each node knows its own location accurately. However, just like GPS, there may be some error in the estimated location• Let e (location error) denote maximum error in the coordinates estimated by a node• If a node N believes that it is at location (Xn,Yn), then the actual location of node N may be anywhere in the circle of radius e centered at (Xn,Yn)• If LAR Scheme 1 is modified to take e into account, then the expected zone is a circle of radius e + v (Xn,Yn) which makes request zone larger since it includes larger expected zone• No modification is made to the LAR Scheme 2 Performance Evaluation• The simulation is performed using modified version of MaRS (Maryland Routing Simulator)• MaRS is discrete-event driven simulator providing a flexible platform for the evaluation and comparisons of network routing algorithm• Simulations were performed on flooding, LAR scheme 1, and LAR scheme 2• Simulations are conduct by varying the number of nodes, transmission range of each node, and moving speedSimulation Model• Number of nodes in the network was chosen to be 15, 30, and 50 for different simulation runs• The size of ad hoc network is 1000 unit x 1000 unit square region• Initial locations of the nodes are obtained using a uniform distribution• Each node moves continuously without pausing at any location – move with average speed v in the range 1.5 to 32.5 units/sec• The actual speed is uniformly distributed in the range v – a and v + a units/sec where a=1.5 when v < 10 and a = 2.5 when v ³ 10• A node travels distance d where d is exponentially distributed with mean 20 units
• The direction of movement for a given move is chosen randomly
• All nodes have the same transmission range

Simulation Model
• Transmission range of 200, 300, 400, and 500 units were used with all wireless links