DESCRIPTION
IEEE Globecom 2010 Workshop on Pervasive Group Communications ( PerGroup 2010). Overlapped NACKs: Improving Multicast Performance in Multi-access Wireless Networks. Authors : Luca Canzian , Andrea Zanella , Michele Zorzi. - PowerPoint PPT PresentationTRANSCRIPT
Email: [email protected], [email protected], [email protected]
Overlapped NACKs: Improving Multicast Performance in Multi-access
Wireless Networks
IEEE Globecom 2010 Workshop on Pervasive Group Communications (PerGroup 2010)
Authors : Luca Canzian, Andrea Zanella, Michele Zorzi
• Basic problem• Our approach• Case study: Bluetooth• Performance comparison• Conclusion
2
Outline
• Basic problem• Our approach• Case study: Bluetooth• Performance comparison• Conclusion
3
Outline
Multicast: only 1 transmission!!!-> resource saving (time/frequency, power) Increasing rate More bandwidth for other devices/applications
4
Multicast communicationWireless network
5
ACK based reliability
ACK
ACK
ACKACK
Devices send ACKs if the packet is correctly received Reliability Scalability Coordination mechanism
6
NACK based reliability
NACK
Devices send NACKs if the packet is NOT correctly received Scalability Reliability Coordination mechanism
NACK
• Basic problem• Our approach• Case study: Bluetooth• Performance comparison• Conclusion
7
Outline
8
Overlapping NACKs
NACK
NACKs sent in the same resource!! (-> collisions) Scalability No coordination mechanism? Reliability
NACK
1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1
Nack slave 1 Nack slave 2
Resulting Nack
9
DPSK exampleQ
I
Q
I
After 1 symbol period
Q
I
-120°
120°120°
240°
0
10
Double-NACK structure
1 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 1
Q
I
Q
I
11 1 1 1 1 1 1 0 1 0 1 1 1 1 1 1 1
I
Q
I
Q
00
10
01
11
DQPSK phase-shifts
First NACK Second NACKPhase displacement
SLA
VE 1
SLA
VE 2
• Basic problem• Our approach• Case study: Bluetooth• Performance comparison• Conclusion
11
Outline
Bluetooth technology
• Ad-hoc Personal Area Network (PAN)
• Direct communication only between master and slaves
• Time-Division Duplexing (TDD) communication
• Packets last 1, 3 or 5 slots
• GFSK (1 Mbps), π/4-DPSK (2 Mbps), 8DPSK (3 Mbps)
• No multicast (multi-unicast) !!!-> SIG proposal
12
13
ACK and NACK based protocols
SIG (Special Interest Group) proposal
Our proposalOverlapped NACKs
• Basic problem• Our approach• Case study: Bluetooth• Performance comparison• Conclusion
14
Outline
15
Throughput vs slaves
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Throughput vs BER& 3-DH5
17
Reliability
BER=1E-5 BER=1E-4
DH1 6.9E-11 / 2.1E-10 6.3E-09 / 1.9E-08
DH3 3.0E-09 / 9.0E-09 1.7E-07 / 4.9E-07
DH5 9.7E-09 / 2.9E-08 3.5E-07 / 1.0E-06
2-DH1 2.7E-10 / 8.2E-10 2.3E-08 / 6.8E-08
2-DH3 1.1E-08 / 3.4E-08 3.8E-07 / 1.1E-06
2-DH5 3.4E-08 / 1.0E-07 6.6E-07 / 1.9E-06
3-DH1 6.4E-10 / 1.9E-09 4.9E-08 / 1.4E-07
3-DH3 2.4E-08 / 7.1E-08 5.5E-07 / 1.6E-06
3-DH5 6.9E-08 / 2.0E-07 9.9E-07 / 2.8E-06
On average 1 packet every 625000 is lost !!!
Average PER / Worst case PER
• Basic problem• Our approach• Case study: Bluetooth• Performance comparison• Conclusion
18
Outline
19
Conclusion
1. New simple NACK based protocol for reliable multicast communications
2. NACK structure to be robust to collisions
3. Comparison with an ACK based protocol for Bluetooth
4. Results show:
• Little reliability loss
• High throughput gain
Email: [email protected], [email protected], [email protected]
Overlapped NACKs: Improving Multicast Performance in Multi-access
Wireless Networks
IEEE Globecom 2010 Workshop on Pervasive Group Communications (PerGroup 2010)
Authors : Luca Canzian, Andrea Zanella, Michele Zorzi
21
Time synchronization
1 1 1 1 1 1 1 11 1
Q
I
Q
II
Q
11 1 1
1 1 1 11 1 1 1 1 111 1 1
OVERLAPPING INTERVAL
22
Time synchronization
1 1 1 1 1 1 1 11 1
Q
I
Q
II
Q
11 1 1
1 1 1 11 1 1 1 1 111 1 1
OVERLAPPING INTERVAL
0
0
1
0
23
Time synchronization
1 1 1 1 1 1 10 10 1
OVERLAPPING INTERVAL 1
1 1 1 1
1 1 1 1 1 1 10 11 1 1 1 1 1
1
Q
I
Q
I
Q
I
1
OVERLAPPING INTERVAL 2I
Q
00
10
01
11
DQPSK phase-shifts
24
Frequency offsetEqual amplitude case
Red turns of 0°Blue turns of 60°
Green turns of 30°
Green turns of 210°!!!-> discontinuity of 180°
Conclusion:• Most time high SNR and constant phase drift
-> it can be compensated • Some time SNR drastically decreases and phase discontinuity
-> this must be taken into account to set correlator threshold
25
Frequency offset1 signal much stronger than the other
Red turns of 0°Blue turns of 60°
Conclusion:SNR of the received signal decreases a little
Green ~ Red + noise Max phase error
Max amplitudeerror
26
b: average number of bits transmitted in a cycle d: average duration of a cycle
N N-1 1 0. . .
Pe N
N (1-P )e
N-1 (1-P )e
1-P e
PePe N-1
1
(N-1) (1-P ) P
N (1-P ) P
e e
N-1
N-2
ee
N (1-P ) P N-1ee
Markov model Nbite BERP 11
Renewal Process:db
ttuntildtransmittebitsTh
t
lim
Nji
otherwise
ijPPji
Pji
eje
ji ,...,1,0,0
1,
Markov model
27
Probability that the master does not recognize the overlapping of i double NACKs (missed detection probabilities)
N N-1 1
0
. . .
PeN
PePe N-1
1
(N-1) (1-P ) P
N (1-P ) P
e e
N-1
N-2
ee
N (1-P ) PN-1
ee
L L L
[1-P (N-1)]
[1-P (1)]
[1-P (1)]
(N-1) (1-P ) Pe e
N-2P (1)
[1-P (1)][1-P (N-1)]
N N-1 1
(1-P )eN
(1-P )eN-1
1-P e
[1-P (N)]
PeN
P (N)
N (1-P ) PN-1
ee P (N-1)
Pe N-1
P (N-1)
N (1-P ) PN-1
ee P (1)
nr
nr
nr
nr
nr
nr
nrnr
nr
nr
nr
Pe P (1)nr
1 1 1
. . .
)(iPnr
N
iLiP
NiPER
1
N
iLiPB
1
Probability to be absorbed in Li
iLP