PHY-MAC Dialogue with Multi-Packet Reception
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PHY-MAC Dialogue PHY-MAC Dialogue with Multi-Packet Receptionwith Multi-Packet Reception
Workshop on Broadband Wireless Ad-Hoc Networks and Services
12th-13th September 2002ETSI, Sophia Antipolis, France
Marc Realp-CTTC/Ana I. Pérez-Neira-UPCwww.cttc.es www-tsc.upc.es
IST-2001-38835 ANWIRETIC2002-04594-C02-02 GIRAFA
ContentsContents
Motivation Cross-Layer Design
MPR matrix. PHY-MAC dialogue. Parameters Exchange.
PHY level Matched Filter. Activity User Detection.
MAC level Dynamic Queue Protocol-DQP. Modified Dynamic Queue Protocol-
MDQP. Simulations Conclusions & Further Work
MotivationMotivation
In wireless systems a common channel is shared by many users.
Traditionally, information is lost when a collision occurs, i.e., when two or more packets are sent trough the channel.
Diversity at physical level allows more than one packet to be transmitted simultaneously.
Conventional MAC algorithms do not consider Multi-Packet Reception (MPR) capability.
CROSS-LAYER DESIGNMAC fully exploits PHY reception capabilities.
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions &
Further Work
MPR matrixMPR matrix
The probability of a packet to be correctly received is:
Hence,
,
1 (num. of users) ; 0
[ packets are correctly received | packets are transmitted]
( , , ( ))n k
n M k n
C P k n
B k n Ps n
0
Pe(n) Bit error probability in the presence of 1 interferers
e=number of correctable errors in a packet
pl=packet length
( ) ( , , ( ))e
t
n
Ps n B t pl Pe n
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions &
Further Work
MPR matrixMPR matrix
The MPR matrix is defined as:
Expected number of correctly received packets when n packets have been transmitted:
1,0 1,1
2,0 2,1 2,2
,0 ,
0 0
0
0
M M M
C C
C C C
C
C C
,1
n
n n kk
C kC
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions &
Further Work
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions &
Further Work
PHY-MAC DialoguePHY-MAC Dialogue
Cross-Layer design reduces PHY-MAC dialogue to a BER exchange.
Should other parameters be considered in order to improve system performance?
SchedulingFairness
Traffic Modelling
Throughput
Delay
PER BER
ModulationScheme
Power Tx/Rx
TransceiverArchitecture
Diversity
Channel &Signal
Estimation
BatteryLife
Bit Rate
MAC Layer PHY Layer
Error Correcting Code
(Binomial)
Numberof Users
QoS
?
?
?
?
Parameters ExchangeParameters Exchange
Information flows between PHY and MAC levels:
BER is used for MPR computation. Active Users used for MAC efficiency. Access Set used for PHY efficiency.
MAC
PHY
BERACT.US.
ACC.SET
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions &
Further Work
PHY LevelPHY Level
CDMA System Model
Receiver Structure
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions &
Further Work
e(t)
1
21 2 M
M
d
de Ad n a a a n
d
(.)T
o
dt
(.)T
o
dt
Detection of
Active Users
Set of Active Users
^
1d
^
Md
1a
Ma
PHY LevelPHY Level
Data Demodulator Matched Filter
Active Users Detector
Motivation Cross-Layer
Design PHY level MAC level Simulation Conclusions &
Further Work
MF ||•||2 State Estimatione
( )1kn
( )kn
( )kn
Power detectionDecision based on Traffic Information
: Indicator function that takes value 1 if the kth user is active and 0 otherwise
^T T
MF Ad A Ad A n R d z
ka
Third TPL3=5
Second TPL2=7
First TPL1=4
Dynamic Queue Protocol-DQPDynamic Queue Protocol-DQP System with M users to transmit data to a
central controller. Time axis is divided into transmission periods
(TP). A TP ends when all packets generated in the
previous TP are successfully transmitted. The basic structure is a waiting queue where
all users in the system are processed in groups of Access Set size.
Based on packet user probability in one TP (qi) and the MPR matrix, the size of the access set which contains users who can access the channel in the ith TP is chosen optimally.
Transmit packets generated before 0
Transmit packets generated in (0,4]
Transmit packets generated in (4,11]
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions &
Further Work
DQP Vs MDQPDQP Vs MDQP
MDQP stands for Modified Dynamic Queue Protocol.
Central controller in DQP is capable to distinguish between: Empty slots. Successfully received packets in non-empty
slots. Central controller in MDQP is capable to
distinguish between: Empty slots. Successfully received packets in non-empty
slots. Packets lost due to collision in non-empty
slots. Nodes with empty buffers in
non-empty slots.
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions &
Further Work
45
12345
12 5
Non-empty slot. Node 3 packet
successfully received.Node 2 packet lost.
Empty slot
Non-empty slot.Nodes 2 and 4 packets successfully received.
Access Set=35
2
12345
24
Non-empty slot. Node 2 packet lost.
Node 3 packet successfully received.
Node 1 empty
Successfully received packet Packet waiting for transmission
Empty bufferPacket Lost
1
423
23 4
2
Non-empty slot.Nodes 2 and 4 packets successfully received.
Node 5 empty.
Central controller do not know whether packets from nodes 1 and 5 have collided or the buffers of these nodes were empty.
Central controller determines that nodes 1 and 5 have empty buffers.
DQP MDQP
MDQP Optimal Access SetMDQP Optimal Access Set
Ni is chosen in order to minimise the absorbing time of a finite state discrete Markov chain.
Each state (j,k) defines: j=number of unprocessed users in one slot k=number of packets sent in one slot
2,2
2,1
2,0
1,1
1,0
0,0
C2,2
C2,1
C1,1
C1,0
1
C2,0
C1,0
C1,1
1
1
Number of Users(M)=2
Access Set (N)=2
1,..,arg min [ | , ]i i i
N MN E L q N
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions &
Further Work
Access Set Vs User Packet ProbabilityAccess Set Vs User Packet Probability
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions &
Further WorkA
ccess S
et
User Packet Probability (qi)
Number of Users (M)=15SNR=10Spreading Gain (SG)=6
Packet Length (pl)=200bitsNumber of Correcting Errors(e)=2Receiver type: Matched Filter
MDQP
DQP
Throughput Vs User Packet ProbabilityThroughput Vs User Packet Probability
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions &
Further Work
SNR=10Spreading Gain (SG)=6
Packet Length (pl)=200bitsNumber of Correcting Errors(e)=2Receiver type: Matched Filter
User Packet Probability (qi)
Th
rou
gh
pu
t
MDQP
DQP
M=15
M=10
M=5
Packet Delay Vs User Packet ProbabilityPacket Delay Vs User Packet Probability
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions &
Further Work
User Packet Probability (qi)
SNR=10Spreading Gain (SG)=6
Packet Length (pl)=200bitsNumber of Correcting Errors(e)=2Receiver type: Matched Filter
Packet
Dela
y
MDQP
DQP
M=15
M=10
M=5
ConclusionsConclusions
Cross-Layer design concept. New idea of PHY-MAC dialogue.
Number of active users used as an additional parameter exchange between layers.
Proposal of a centralised system PHY layer with active users detector.
MAC layer with MDQP.
System improvements in terms of throughput and packet delay.
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions
& Further Work
MPR matrix for Ad-Hoc NetworksMPR matrix for Ad-Hoc Networks
MPR must be modified considering communications in Ad-Hoc scenarios. Communications are Half-Duplex.
A node can not receive a packet while is transmitting.
A node might successfully receive a packet not intended for it.
Packet might be lost due to collision of many packets.
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions
& Further Work
1
3
2
4
5
Packet intended for that node
Packet not intended for that node
PHY-MAC Dialogue in the IEEE802.11bPHY-MAC Dialogue in the IEEE802.11b
CSMA/CA is used. Medium is sensed by means of active user detection mechanism.
Medium is determined IDLE when Number of users sensed < Nopt for a period longer than DIFS.
After deferral, Back-off procedure adjusted depending on Number of users sensed.
Busy Medium(N. Users>=Nopt)
Back-Offprocedure
Contention Period (CP)
SIFS
PIFS
DIFS
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions
& Further Work
PHY-MAC Dialogue in the IEEE802.11bPHY-MAC Dialogue in the IEEE802.11b
Analytical throughput expression Nopt for throughput maximisation
Modifications on the current 802.11 standard. Additional information flows:
PHY->MAC: Number of current active users. MAC->PHY: Number of users (Nopt) to consider
busy medium. Additional field in Beacon frames or broadcast
message to transmit Nopt. Carrier sense mechanism modifications
User activity detection and MUD at PHY level. Possible change in back-off procedure for
better performance. Simulations
Motivation Cross-Layer
Design PHY level MAC level Simulations Conclusions
& Further Work
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