5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica Topology Control in Wireless Ad Hoc Networks Paolo Santi Istituto di Informatica e Telematica del CNR, Pisa, ITALY paolo.santi@iit.cnr.it 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica Tutorial outline Introduction – Motivation: the need for Topology Control (TC) in ad hoc networks – An ad hoc network model – Topology control: a taxonomy Stationary networks – The critical transmitting range for connectivity – Energy efficient communications: unicast/broadcast – TC protocols: “ideal” properties and state-of-the-art solutions Mobile networks – Mobility models – The mobile critical transmitting range – Topology control with mobility Open issues – More realistic network and energy models – Is mobility beneficial or detrimental for TC? – Multi-hop data traffic – Topology control in the protocol stack Towards and implementation of TC: the CLUSTERPOW and NTC-PL protocols 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica Motivations for topology control Both energy and capacity are limited resources in ad hoc networks In case of Wireless Sensor Networks (WSN), energy consumption is especially critical The ad hoc network designer should strive for reducing node energy consumption and providing sufficient network capacity The answer: Topology Control (TC) — maintain a topology with certain properties (e.g., connectivity) while reducing energy consumption and/or increasing network capacity Introduction: 1/7 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica Topology control: an informal definition Topology control: the art of coordinating nodes’ decisions regarding their transmitting ranges, in order to generate a network with the desired properties A remark on terminology: – Topology control: a system-level perspective — optimize the choice of the nodes’ transmit power levels to achieve a certain global property – Power control: a wireless channel perspective — optimize the choice of the transmit power level for a single wireless transmission, possibly along several hops Introduction: 2/7 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica An ad hoc network model Introduction: 3/7 The power p i required by node i to transmit data to node j must satisfy p i /δ(i,j) α ≥ β , where δ(i,j) is the distance between i and j, β is the transmission quality parameter, and α is the distance-power gradient Nodes are represented by points in d-dimensional space (d=1,2,3) A range assignment is a function RA that assigns to every node u a transmitting range RA(u) in (0,r max ], where r max is the maximum transmitting range (common to all the nodes) Assuming β =1, the energy cost of a range assignment is defined as ∑ u (RA(u)) α 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica The communication graph Introduction: 4/7 Given node positions and a range assignment RA, the communication graph contains a directed edge (u,v) if and only if v is within u’s transmitting range, i.e. RA(u) ≥ δ(u,v) A range assignment is said to be connecting if it generates a strongly connected communication graph Note: if nodes are mobile, a range assignment which is connecting at time t 1 might become disconnected at a later time t 2 In mobile networks, we have in general a sequence of range assignments RA 1 , RA 2 , , where the transition between the range assignments is determined by the TC protocol 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica The symmetric communication graph Introduction: 5/7 Often, we are only interested in bi-directional (symmetric) links The symmetric communication graph is obtained from the communication graph by deleting unidirectional wireless links 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica An example (Point Graph) Introduction: 6/7 Comm. graph Symmetric Comm. graph 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica Topology control: a taxonomy Introduction: 7/7 Topology control Homogeneous (the CTR) Non homogeneous per-packet TC periodical TC routing graphs level-based 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica The Critical Transmitting Range (CTR) the CTR: 1/12 A range assignment RA is said to be homogeneous if all the nodes have the same transmitting range r, i.e. RA(u)=r for all u, for some r∈(0,r max ] The CTR problem: assume n nodes are placed in a given region R; what is the minimum value of r such that the r-homogeneous range assignment is connecting? This minimum value of r is called the critical transmitting range for connectivity . ITALY paolo.santi@iit.cnr.it 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica Tutorial outline Introduction – Motivation: the need for Topology Control (TC) in ad hoc networks – An ad hoc network. consumption and/or increasing network capacity Introduction: 1/ 7 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica Topology control: an informal definition Topology control: the. atica Motivations for topology control Both energy and capacity are limited resources in ad hoc networks In case of Wireless Sensor Networks (WSN), energy consumption is especially critical The ad hoc network