Wireless Ad Hoc and Sensor Networks

Distributed Fair Scheduling in Wireless Ad Hoc and Sensor Networks 3077.3.1 Fluctuation Constrained and Exponentially Bounded FluctuationThe variable rate service models for wireless ad hoc networks have to bedefined to incorporate the channel- and contention-based protocols. An FCservice model for wireless networks in the interval [ t1, t2]has two parameters,average rate λ( t1, t2)bps and variations parameter ψλ ( ) givenby ψλ ( ) = χλ ( ) + δλ ( ) + ωλ ( ), where χλ ( ) is the reduction in wireless channelcapacity due to channel uncertainties, ωλ ( ) is the variation due tobackoff interval, and δλ ( ) is the burstiness in bits.FC service model (Goyal et al. 1997): A wireless node follows thefluctuation constrained (FC) service model with parameters( λ( t1, t2 ), ψ( λ)), if for all intervals [ t1, t2]in a busy period of thenode, the work done by the node, denoted by Wt ( , t), satisfies1 2Wt ( , t) ≥λ( t, t)( t −t) −ψ( λ)1 2 1 2 2 1(7.5)The EBF service model is a stochastic relaxation of FC service model.Intuitively, the probability of work done by a wireless node followingEBF service model deviating from the average rate bymore than γ , decreases exponentially with γ .EBF service model (Goyal et al. 1997): A wireless node follows theEBF service model with parameters ( λ( t1, t2), B, ω, ψ( λ)), if for allintervals [ t1, t2]in a busy period of the node, the work done bythe node, denoted by Wt ( , t), satisfies1 2PWt ( ( , t) < λ( t , t )( t −t ) −ψ( λ) −γ)≤Be1 2 1 2 2 1−ωγ(7.6)NOTE From now, the weight of a packet of flow f at node l is denotedas φ f, l , and it is given by φf, l=σ fφf.The proposed scheme from Regatte and Jagannathan (2004) workswell even with variable rate wireless nodes. From now on, we definea variable rate wireless node with the proposed scheme as an ADFSwireless node. The ADFS scheme satisfies the fairness criterion givenin Equation 7.3. The description of the scheme and the MAC protocolis given next.The main goal of the ADFS protocol is to achieve fairness in wirelessad hoc networks. To accomplish this, the protocol has to be implementedboth at the queuing algorithm level, for proper scheduling, and at theMAC protocol level, to control the dynamic backoff algorithm for accessingthe channel.