1. Delay Sensitive TDMA Slot Assignment in Ad hoc Wireless Networks National Conference on Communication IIT Bombay, India 27 – 28 March 2015 Naresh Vattikuti, Himanshu Sindhwal, Mallesham Dasari Bheemarjuna Reddy Tamma Uurmi Systems Pvt. Ltd. Department of CSE, IIT Hyderabad, India. Hyderabad, India. Email: {vvsnaresh, himanshus, malleshamd}@uurmi.com tbr@iith.ac.in

2. Introduction State of the art Problem statement Delay vs. Spatial reuse of slots Proposed Delay sensitive slot assignment Performance Evaluation Conclusions Outline

3. TDMA slot assignment Multi hop topology - Flows from A - F and C - G Spatial reuse Introduction

4. Delay vs. Spatial reuse Spatial reuse approach Minimum possible delay approach Need to strike the balance between the two

5. Delay analysis Affect is more with longer hop flows

6. Selection of efficient slot based on the previous node’s slot so that the end-to-end delay in a long hop flow is minimized. Strike the balance between the delay and spatial reuse slots, given the Maximum delay for flow is known. Problem Statement

7. Centralized: GSM, PDC, iDEN, PHS etcetera. Distributed: –USAP, USAP/MA –DRTDMA –STDMA algorithms –Applications??? Many algorithms: Effective handling of slot conflict, selection of best slot? Opportunism with the cross layer advantage State of the art

8. The Algorithm restricts each node to select a slot such that it doesn’t breach D max /N (per hop-delay limit), where N is the number of hops in the flow. Once delay for all the slots in S spatial is calculated, we will find a slot which gave minimum delay and call it SspatialMin and the corresponding delay as spatialMin. If this slot is inducing a delay less than D (=D max /N) then this slot will be selected and the algorithm completes else we will move to set S other and repeat the process to find the slot in S other which will give minimum delay among all the slots in S other, we will call it S min and the corresponding delay as фmin. If ф min < spatialMin then we will select the slot S min (the idle slot giving minimum possible delay on this node) otherwise S spatialMin (the idle slot giving minimum possible delay on this node and also spatially reused in the flow) will be chosen. Proposed Algorithm

9. S spatial = getIntersection(Sprev,Sidle) S other = S idle - S spatial D = Dmax/n; For each S i in S spatial if S i >P then ∆ i = S i - P else ∆ i = f- P+S i end if end for ∆ spatial_min = findMinimumOfAll∆ i ’s() S spatial_min = slotCorrespondingTo∆ spatial_min () if ((∆ spatial_min * Slot_dur) <= D) then S selected = S spatial_min else for each S i in S other set if S i >P then ∆ i = S i - P else ∆ i = f- P+S i endif end for ∆ min = findMinimumOfAll∆ i ’s() S min = slotCorrespondingTo∆ min () if ∆ min < ∆ spatial_min then S selected = S min else S selected = S spatial_min endif Slot Selection Algorithm I/P: Previous slots in the flow and idl slots. O/P: Minimal delay aware slot

10. Experimental Setup ParameterValue Number of Nodes20 Number of Slots32 Slot duration1ms Number of Seeds15 Average Dmax200ms Transmission Range1.5units Area20x20units We have analyzed three types of experimental results 1. End-to-end delay with varying load 2. Call acceptance ratio with varying load 3. Call acceptance ratio with different values of D max by keeping the load fixed

11. Load Balancing approach proposed in [3], which is a traditional slot selection method - Get the first available idle slot for reservation MPD approach - Get the minimal delay aware slot out of all the idle slots available in the frame. Delay Sensitive approach - Strike the balance between delay and spatial reuse. Algorithms for Performance Comparison

12. Call Acceptance vs. Load Random Topology Call Acceptance vs. Load (Random Topology) Load = arrival rate *duration Comparison of delay sensitive algorithm with Minimum possible delay approach and load balancing approach.

13. Call Acceptance vs. Load (String Topology) The curve of ’Delay Sensitive’ approach shows that, it achieves greater call acceptance ratio than MPD approach, because of spatial reusability. Call Acceptance vs. Load String Topology

14. Delay vs. Load (Random Topology) And also, the ’Delay Sensitive’ approach’s curve shows that the delay with the increased load is as good as MPD approach and outperforms ’Load Balancing’ approach in the case of random topology. Delay vs. Load Random Topology

15. Delay vs. Load (String Topology) The ’Delay Sensitive’ approach’s curve shows that the delay with the increased load is as good as MPD approach and outperforms ’Load Balancing’ approach in the case of string topology. Delay vs. Load String Topology

16. Delay vs. Hop count (String Topology) Furthermore, the curves show that our approach giving better results in case of flows with more hop count as the probability of tradeoff between delay and spatial reuse happens more frequently. Delay vs. Hop Count Random Topology

17. Call Acceptance vs. D max (String Topology) Additionally, we calculated the call acceptance with varying the Dmax value. The curve shows that, the Delay Sensitive approach gives more call acceptance with the increased Dmax, as the increase in Dmax lead to increase in maximum delay at each hop which will further enhance the spatial reuse. Call Acceptance vs. D max

18. In this paper, an end-to-end delay sensitive approach is provided for slot selection by exploiting the spatial reusability in multi hop AWNs. The results show that the developed algorithm balances well between the delay and spatial reusability metrics. It is also shown from the results that, it performs well for long hop flows. The tradeoff between the two metrics proposed in this paper can be expanded to other QoS metrics in distributed TDMA slot assignment process. Conclusion

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