Wireless Ad Hoc and Sensor Networks

206 Wireless Ad Hoc and Sensor NetworksA new link is not added to the system if one of these is satisfied: (1)when the transmitter power of an active link is in danger of exceedingp max ; (2) when the link takes a greater amount of time than the “admissiontime,” T i ; and (3) when the link’s rate of increase of power is morethan a certain predefined value. This constraint rate of increase in poweris necessary because (1) the drastic increase in power of the new linkcreates a large interference on the nearby active links, making it necessaryfor them to increase their power levels to maintain the predefined SIRlevel and (2) the increase of power levels by the active links drain theirbattery power. If a link wants to terminate, its transmitter power is madezero so that it does not cause any interference to other active links. A link,if it were not added because of these reasons, would try to get admissioninto the network after a certain predefined amount of backoff-time B i . TheDPC/ALP with admission control scheme is presented in the followingsubsection.5.3.2 DPC/ALP and Admission Controller AlgorithmThe proposed distributed algorithm with power control can be itemizedas:1. New links trying to gain access to the channel start with a minimumpower p min .2. The interference experienced by all links existing in the networkn Gijκiis calculated as Ii() l = ( ∑ j≠iPj* +G G ).ii ii3. All links in the network calculate their SIR according to Equation5.2 and check against threshold γ i .4. If SIR of a link is greater than the threshold value γ i , the link isdeclared active. The link thus gains access to the network andstarts communicating with the receiver.5. A new link trying to gain access to the network is dropped if:a. Its transmitter power exceeds p max .b. The rate of increase of power exceeds a certain threshold. (Todrop new links that cause large amount of interference toalready existing nodes.)c. The rate of increase of SIR is less than a given threshold. (Toprevent SIR saturation.)d. The amount of time for a link to gain access to the networkexceeds maximum admissible delay. (To prevent SIR saturation.)6. A dropped link, if it has waited for dormant or backoff period B i ,is added to the set of existing new links.