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