1. Scheduling Scheme for PCF with Diversity
July 2003
Scheduling Scheme for PCF with Diversity
Marc Realp and Ana Pérez-Neira
Telecommunications Technological Center of Catalonia-CTTC
Marc Realp-CTTC

2. Contents Motivation MPR Capability Model Scheduling Procedure
July 2003
Contents
Motivation
MPR Capability Model
Scheduling Procedure
Simulations
Further Work
Marc Realp-CTTC

3. NG MAC protocols must fully exploit
Motivation(1)
July 2003
In PCF of the IEEE , the PC allows transmission of only one STA at a time in order to avoid collisions.
Diversity at physical level allows more than one packet to be transmitted simultaneously. Hence, giving Multi-Packet Reception (MPR) capabilities.
The do not consider MPR capability.
NG MAC protocols must fully exploit
PHY MPR capabilities.
Marc Realp-CTTC

4. How many STAs should the PC poll simultaneously?
Motivation(2)
July 2003
Example Scenarios:
How many STAs should the PC poll simultaneously?
Access Set (AS)
Marc Realp-CTTC

5. July 2003
MPR Capability(1)
The packet success probability will mainly depend on the number of additional packets present at the receiver n-1 (or Multiple Access Interference):
Hence, the MPR capability,
Marc Realp-CTTC

6. MPR Capability(2) Capacity: Maximum expected successfully
July 2003
MPR Capability(2)
Capacity: Maximum expected successfully
received packets
Therefore:
Without diversity (no MPR): Only one packet at a time to achieve maximum capacity. Hence, nmax=1
With diversity (with MPR): More than one packet at a time. Hence, nmax>1.
Marc Realp-CTTC

7. Scheduling Procedure The AS is directly nmax
July 2003
Scheduling Procedure
The AS is directly nmax
If we have a probability q to receive a CF-Poll correctly:
Computation of AS (>nmax) size is based on Modified Dynamic Queue Protocol (MDQP) protocol.
The optimal AS size that minimizes duration of CFP (or maximizes throughput) is computed off- line as a function of the MPR and the estimated probability (q).
CCA.indicate primitive is used as information from PHY layer to determine STAs that did not receive the CF-Poll. (main difference with Dynamic Queue Protocol (DQP))
The PC is capable to distinguish between:
Empty slots.
Successfully received packets in non-empty slots.
Packets lost due to collision in non-empty slots.
STAs that did not receive the CF-Poll in non-empty slots. (Not possible with the DQP)
Marc Realp-CTTC

8. Scheduling Procedure for PCF
July 2003
SIFS
SIFS 3
SIFS
SIFS
5(NULL)
SIFS
PIFS 2 4
Beacon
Poll 1,2,3
1(NULL)
Poll 2,4,5 2
CF-End 1
The PC determines that packet from STA 2 is lost. 2
Access Set Size is 3 2 4 3 5 4 5
Successfully received packet
Packet waiting for transmission
Packet Lost
Empty buffer
Marc Realp-CTTC

9. Scheduling Procedure for PCF with q
July 2003
SIFS
SIFS
SIFS
SIFS
SIFS
PIFS 3 4
Beacon
Poll 1,2,3 2
Poll 2,4,5 2
CF-End 1
The PC determines that STA 1 has not received a CF-Poll and packet from STA 2 is lost. 2
The PC determines that STA 5 has not received a CF-Poll.
Access Set Size is 3 2 4 3 5 4 5
Successfully received packet
Packet waiting for transmission
Packet Lost
CF-Poll lost
Marc Realp-CTTC

10. Access Set Vs User Packet Probability
July 2003
Access Set Vs User Packet Probability
MDQP
DQP
Number of Users (M)=15
SNR=10dB
Spreading Gain (SG)=6
Access Set
Packet Length (pl)=200bits
Receiver type: Matched Filter
CF-Poll Success Probability (q)
Marc Realp-CTTC

11. Throughput Vs User Packet Probability
July 2003
Throughput Vs User Packet Probability
M=10
M=15
SNR=10
Spreading Gain (SG)=6
Packet Length (pl)=200bits
Receiver type: Matched Filter
Throughput
M=5
Ideal case for w/o diversity PCF
MDQP
DQP
w/o Diversity PCF
CF-Poll Success Probability (q)
Marc Realp-CTTC

12. Further work Introduction of diversity at PHY
July 2003
Further work
Introduction of diversity at PHY
Estimate probability of CF-Poll lose (q)
Must consider PC packets (Downlink) in the scheduling.
Marc Realp-CTTC