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Delay Aware Link Scheduling for Multi-Hop TDMA Wireless Networks
Petar Djukic* and Shahrokh Valaee+
*University of California+University of Toronto, Toronto, ON, Canada
IEEE/ACM TRANSACTIONS ON NETWORKING, VOL. 17, NO. 3, JUNE 2009
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Outline
Introduction Network and transmission model TDMA scheduling Minimum length TDMA scheduling TDMA delay aware scheduling Simulation Conclusion
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Introduction
An important goal for TDMA scheduling algorithms is to find the minimum number of slots required to schedule requested end-to-end rates.
Although previous TDMA scheduling approaches can find minimum length schedules, they do not account for TDMA scheduling delay.
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Introduction
Scheduling delay occurs when packets arriving on an inbound link must wait for the subsequent frame to be transmitted on the outbound link.
Scheduling delay accumulates at every hop in the network, so end-to-end delay experienced on a path can be large.
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Introduction_ goal
Given an assignment of link bandwidths, what is the minimum length TDMA schedule that also minimizes end-to-end scheduling delay?
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Network and transmission model
TDMA network can be represented with a directed connectivity graph
is the set of nodes is the set of directed links
Network and transmission model
Notation:Ts is the duration of each slot.Nc slots reserved for the control traffic.Nd slots reserved for data traffic.
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Network and transmission model
Notation: rj is link rateP is the set of all paths found by the routing algorithmI(.) is the indicator functiongl is the requested end-to-end rate of connection
Notation:cj is capacity.h is the spacing between transmissions of different links.
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Network and transmission model
Notation: nj is the number of times the link transmits in the frame.
The actual rate
The request rate
Conflict-Free Scheduling for Fixed Transmission Orders
Even though the general scheduling problem is NP-complete,if the transmission order is fixed, the scheduling problem haspolynomial complexity.
MINIMUM LENGTH TDMA SCHEDULING_ Linear Search Algorithm
Input : the number of slots in the data sub-frametopology information, link durations, slot duration
TDMA DELAY AWARE SCHEDULING_ End-to-End Scheduling Delay
if the conflict is traversed in the opposite direction
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Simulation
802.16 frame duration is 10ms giving a total of 800 Orthogonal Frequency Division
Multiplexing(OFDM) symbols in each frame. 70 OFDM symbols are for the control sub-frame, 730
symbols for the data sub-frame. Each link transmission has an overhead of h=3 slots. the percentage of the frame used for centralized
scheduling to
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Conclusions
This paper introduces TDMA delay aware scheduling for multi-hop wireless networks.
The proposed polynomial time algorithm that finds one-frame scheduling delay transmission orders on overlay tree topologies.
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