Final Thesis - KReSIT - Indian Institute of Technology, Bombay

4.6. Scheduling 33
is requested from the ST, so the number of slots allocated to downlink are more than the
slots allocated to uplink. Here downlink slots and uplink slots are of contiguous slots. For
making this schedule there are number of scheduling algorithms. We explain two such
algorithms here and also say how we implemented.
4.6.1 Round Robin Scheduling
This is a basic scheduling algorithm. Downlink and Uplink slots can further be divided
into slots. These both are contiguous in a frame. In our protocol as we are following Multi
Sector TDM approach, opposite sectors can be transmitted in parallel. Slots are assigned
STs’s in a round robin fashion. It doesn’t have any priority while scheduling. It is
starvation-free algorithm.
4.6.2 Smoothed Round Robin Scheduling (SRR)
Ordinary round robin schedulers are well known for their burstiness in the scheduling
output. In order to overcome this problem, SRR codes the weights of the flows into
binary vectors to form a Weight Matrix, then uses a Weight Spread Sequence (WSS),
which is specially designed to distribute the output more evenly to schedule. It preserves
Θ(1) time complexity by avoiding the time-stamp maintenance employed in various Fair
Queueing schedulers. The basic idea of SRR is scanning of the WSS and the corresponding
Weight Matrix. The WSS is scanned term by term. When the current term is element
i, column k−i of the Weight Matrix (where k is number of columns of Weight Matrix) is
selected[8].
Table 4.2 are used in the algorithm that is going to be described.
Algorithm There are three asynchronous actions, namely, Schedule, Add flow, and
Del flow. Each action is triggered by some events. The Schedule function is as listed in
Algorithm 4.6.2.
local variable: f, col {f, col are the current row and current column of the M respectively}
P c = 1
P dl = header k−1 → next {initialization}