a generic quantitative approach to the scheduling of synchronous packets in a shared uplink wireless...

A Generic Quantitative Approach to the

Scheduling of Synchronous Packets in a Shared Uplink

Wireless ChannelAuthors: Authors: Reuven Cohen, Liran Katzir

Published: IEEE/ACM Transactions on Networking, August 2007

OutlineOutline

IntroductionIntroduction Quantitative-Based FrameworksQuantitative-Based Frameworks Computing the ProbabilitiesComputing the Probabilities Proposed AlgorithmsProposed Algorithms SimulationSimulation ConclusionConclusion

IntroductionIntroduction

In a In a single channelsingle channel with with single-carrier PHYsingle-carrier PHY by by the the OFDMOFDM PHY, describe a centralization PHY, describe a centralization scheduling scheme for scheduling scheme for uplinkuplink wireless wireless networks.networks.

The proposed scheme follows five scheduling The proposed scheme follows five scheduling considerations.considerations.

Scheduling ConsiderationsScheduling Considerations

SC1: The specific QoS requirements of each call: the grants should meet the negotiated grant size, grant periodicity, and tolerated grant jitter.

SC2: The specific conditions of each uplink channel: basically, if a channel experiences bad SNR, the scheduler will try to delay the grant as much as possible.

Scheduling ConsiderationsScheduling Considerations

SC3: The specific application layer loss recovery mechanism employed by each synchronous call codec. The quality of a synchronous call can therefore be improved by assigning a higher drop priority to the more important packets.

Scheduling ConsiderationsScheduling Considerations

SC4: SC4: The specific MAC layer loss recovery mechanisms employed by the network, and in particular, whether automatic repeat request (ARQ) is employed.

SC5: Adaptive modulation and coding (AMC), along with power control.

Quantitative-Based FrameworksQuantitative-Based Frameworks

Model 1: The base station maintains a profit matrix Φ. Entry Φ[c, t] in this matrix indicates the profit if the first pending packet of call c is transmitted starting from slot t and is correctly received by the base station. Φ[c, t] = the priority of the packet, if success Φ[c, t] = 0, if nonsuccess

Satisfied SC1 and SC3.Satisfied SC1 and SC3.

Quantitative-Based FrameworksQuantitative-Based Frameworks

Model 2: A schedule σ is a transmission vector that indicates which packet should start being transmitted in which slot. If σ(t) = c, then at time slot t, the transmission of the current packet of call c should start. The overall profit gained from a schedule σ is Profit(σ)=

, where [1…T] is the scheduling interval , μ[c, t] = Φ[c, t] *λ(c, t) , and λ(c, t) is the success probability of the transmission fo

r call c in slot t.

T

t

tt1

,

Quantitative-Based FrameworksQuantitative-Based Frameworks

Model 3: Entry μ[c, t, m] in this matrix is set to Φ[c, t, m] *λ(c, t, m) Where λ(c, t, m) is the probability that the packet o

f call c will be transmitted correctly starting from slot t using PHY profile m.

Quantitative-Based FrameworksQuantitative-Based Frameworks

Model 4: The schedule takes into account MAC layer retransmissions.

Where R is the maximum number of transmissions.

Computing the ProbabilitiesComputing the Probabilities

SS((nn) ) {0, 1}, {0, 1}, where 0 represents a good channelwhere 0 represents a good channel and 1 represents a bad channeland 1 represents a bad channel

p = Prob[p = Prob[SS((nn+1)=0 | +1)=0 | SS((nn) = 0]) = 0] q = Prob[q = Prob[SS((nn+1)=1 | +1)=1 | SS((nn) = 1]) = 1] TT((nn) is the probability that the channel is in err) is the probability that the channel is in err

or state at time or state at time nn..

Computing the ProbabilitiesComputing the Probabilities

TT((nn+1)=+1)=qq TT((nn) +(1-) +(1-pp)(1- )(1- TT((nn) )) ) TT((nn+1)=(+1)=(qq++pp-1) -1) TT((nn) +(1-) +(1-pp)) When When TT(0)=(0)=CC

Assuming that Assuming that aa≠1, for ≠1, for nn > 0 we get > 0 we get

And thereforeAnd therefore

1

0

21 ...n

i

innnn abCabbabaCanT

1

1

a

abCanT

nn

2

1111

qp

qppqpCnT

nn

Computing the ProbabilitiesComputing the Probabilities

CC=1=1

CC=0=0

And And

2

1111101Pr

qp

qppqpSnSob

nn

2

111001Pr

qp

qppSnSob

n

2

111100Pr

qp

qqqpSnSob

n

Proposed AlgorithmsProposed Algorithms

Proposed AlgorithmsProposed Algorithms

Proposed AlgorithmsProposed Algorithms

Algorithm 1: Bigger Profit FirstAlgorithm 1: Bigger Profit First Algorithm 2: Algorithm 2:

Earliest Deadline FirstEarliest Deadline First Mack sure the schedule is feasibleMack sure the schedule is feasible

SimulationSimulation

SimulationSimulation

SimulationSimulation

SimulationSimulation

SimulationSimulation

SimulationSimulation

SimulationSimulation

SimulationSimulation

SimulationSimulation

SimulationSimulation

ConclusionConclusion

Presented a generic quantitative-based scheme Presented a generic quantitative-based scheme for scheduling.for scheduling. Select the most important packets for transmissionSelect the most important packets for transmission Increases the number of synchronous packets that Increases the number of synchronous packets that

transmitted on timetransmitted on time Decreases the number of packets that are Decreases the number of packets that are

transmitted when the channel is noisytransmitted when the channel is noisy