sic hotnets talk
TRANSCRIPT
-
8/13/2019 Sic Hotnets Talk
1/41
Successive Interference Cancellation:A Back of the Envelope Perspective
Souvik Sen, Naveen Santhapuri,
Romit Roy Choudhury, Srihari Nelakuditi
-
8/13/2019 Sic Hotnets Talk
2/41
2
Simple Case of Wireless Transmission
Decoding successful if:
AP
Threshold
Signal =Noise
SNR=
T1
-
8/13/2019 Sic Hotnets Talk
3/41
3
Interferer
What if parallel transmissions?
Decoding successful only if:
T1AP
T2
Signal =
Interference + NoiseSINR =
Threshold
-
8/13/2019 Sic Hotnets Talk
4/41
4
Collision
Collision
Decoding fails because:
Interferer
T1AP
T2
Signal =
Interference + NoiseSINR = Threshold
-
8/13/2019 Sic Hotnets Talk
5/41
5
Successive Interference Cancellation
Interferer
T1AP
T2
Thus, it is as if SIC can uncollide signals,
resulting in two successful transmissions
-
8/13/2019 Sic Hotnets Talk
6/41
6
Capacity with SIC
SNR =
Rblue =Sblue
noiselog 1 +
SINR =
R*green =Sgreen
Sblue +noiselog 1+
T1
T2
Interferer
AP
Strong signal penalized, weak signal gets all the benefits
RSIC =Sblue +Sgreen
noiselog 1+
+
-
8/13/2019 Sic Hotnets Talk
7/417
Channel Capacity w/o SIC
SNR =
Rblue =Sblue
noiselog 1 +
T1
T2
Interferer
AP
SNR =
SgreenRgreen =
noiselog 1 +
Gainsic =
Rsic =Sblue +Sgreen
noiselog 1+
RwoSIC = max( Rblue, Rgreen )
-
8/13/2019 Sic Hotnets Talk
8/418
SIC PHY Capacity Gain
-
8/13/2019 Sic Hotnets Talk
9/419
SIC PHY Capacity Gain
Max SIC gain whenequal signal strengths
-
8/13/2019 Sic Hotnets Talk
10/41
We were tempted to schedule packet
transmissions of similar signal strengths ...
As protocol designers ...
Our interpretation was that ...
maximizing SIC capacity will maximize throughput
But lets verify that ...
-
8/13/2019 Sic Hotnets Talk
11/4111
SIC: A Packet Perspective
!Weaker blue packet can be at a high rate
MAC Layer throughput can actually suffer
T1T2
Interferer
AP
HOLE
!Stronger green packet has to be at low rate
Packet Transmission Time
Rate
-
8/13/2019 Sic Hotnets Talk
12/4112
Mathematically ...
T1T2
InterfererAP
Packet Transmission Time
TimeSIC =
TimewoSIC =
Packet Transmission Time
L
Rblue
L
R*greenmax ,=
L
Rblue
L
Rgreen
+=
SIC Gain=
-
8/13/2019 Sic Hotnets Talk
13/41
13
SIC Throughput Gain
-
8/13/2019 Sic Hotnets Talk
14/41
14
SIC Throughput Gain
Max throughput gain whensignal strengths are 2:1
-
8/13/2019 Sic Hotnets Talk
15/41
15
Why is This Happening?
T1T2
InterfererAP
> T> T =
Rgreen
Rblue
-
8/13/2019 Sic Hotnets Talk
16/41
16
Capacity Vs. Throughput
!We expected:" Maximizing SIC capacity will maximize throughput
!Reality:
"Equal signal strengths maximize capacity but not throughput
Capacity HOLE
-
8/13/2019 Sic Hotnets Talk
17/41
by reducing size of the hole ...Cant we improve MAC layer throughput with SIC
-
8/13/2019 Sic Hotnets Talk
18/41
We study SIC enabled throughput in two scenarios
1. Two transmitters transmitting to a common receiver
2. Two transmitters transmitting to distinct receivers
-
8/13/2019 Sic Hotnets Talk
19/41
We begin with
1. Common receiver
We consider:
1. Power control
2. Scheduling
3. Multirate packetization
4. Packet packing
-
8/13/2019 Sic Hotnets Talk
20/41
20
(1) Power Control
!Reduce power of blue Tx such that
SINR*green=Rgreen
Rblue
= 2 *
Reduce
-
8/13/2019 Sic Hotnets Talk
21/41
21
(2) Client Pairing
T1 T2
T4
T3
T1, T2 T3, T4
-
8/13/2019 Sic Hotnets Talk
22/41
22
(2) Client Pairing
T1 T2
T4
T3
T1, T3 T2, T4
-
8/13/2019 Sic Hotnets Talk
23/41
23
(3) MultiRate Packetization
!Multirate Packetization" Send the strong packet at high rate after weak packet has finished
R*green
RblueRgreen
Rblue
-
8/13/2019 Sic Hotnets Talk
24/41
24
(4) Packet Packing
!Packet Packing" Send multiple packets to fill up the hole
" Hard because stronger signal modeling becomes difficult
R*green
Rblue
-
8/13/2019 Sic Hotnets Talk
25/41
- Perform Monte Carlo Simulations
How Does Adaptation Help?
-
8/13/2019 Sic Hotnets Talk
26/41
26
Considerable Improvement with Adaptation
Upload Performance with MAC Modifications
SIC
PacketPacking
Power
Control
Rate
-
8/13/2019 Sic Hotnets Talk
27/41
2. Distinct Recievers
T1
T2 R1R2
Situations much less favorable to SIC
-
8/13/2019 Sic Hotnets Talk
28/41
2. Distinct Recievers
T1
T2 R1R2
Main Concern:
T1 will transmit at best possible bit-rateto R1
R2 has to decode T1s signal at this bit rate...-Despite the presence of T2s signal
-
8/13/2019 Sic Hotnets Talk
29/41
2. Distinct Recievers
T1
T2 R1R2
Thus, necessary (but not sufficient) condition:
R2s interferer(T1) must be closer than its own transmitter(T2)
T1s own receiver(R1) must be further than interfered receiver(R2)
-
8/13/2019 Sic Hotnets Talk
30/41
T1
T2 R1R2
Gains available when all conditions hold
-
8/13/2019 Sic Hotnets Talk
31/41
T1
T2
R1
R2
Gains available when all conditions hold
How often do these SIC permissible
topologies occur?
-
8/13/2019 Sic Hotnets Talk
32/41
32
Gain with SIC in less than 10% of the cases
Monte Carlo Simulation
(AP Transmission Range)
-
8/13/2019 Sic Hotnets Talk
33/41
Can protocol adaptation help?
1. Power control
2. Scheduling
3. Multirate packetization
4. Packet packing
-
8/13/2019 Sic Hotnets Talk
34/41
34
Not many topologies support SIC
thus limited scope for protocols
Does MAC Adaptation Help?
-
8/13/2019 Sic Hotnets Talk
35/41
Implication on Network Architecture?
-
8/13/2019 Sic Hotnets Talk
36/41
Residential WLANs:
Neighbors AP may be strongerSome SIC scenarios possible
Enterprise WLANs:
Clients likely to associate with stronger APSuch scenarios unlikely
T1
T2
R1
R2
-
8/13/2019 Sic Hotnets Talk
37/41
T1
T2
R1
R2
Of course:
SIC throughput gains will increase if bit rate T1->R1 is sub optimal
However, rate adaptation schemes such as SoftRate andAccuRate approaching optimality ... little room for SIC
-
8/13/2019 Sic Hotnets Talk
38/41
38
Mismatch with Literature?
Interference cancellation has been shown to be beneficial ...Our observations are not in conflict
In existing schemes, interfering bits are known
ZigZag, ANC, CSMA/CN, Full Duplex ...
This paper investigates the case ofUnknown Interference Cancellation
-
8/13/2019 Sic Hotnets Talk
39/41
39
Conclusion
!Successive Interference Cancellation" A PHY layer capability to uncollide transmissions
!Throughput gain is not immediate from SIC
" Permissible bit rates impact the length of packet transmission times" Creates under-utilization of the channel
!Protocol adaptations possible to cope with problem
" Some gains available for common receiver scenario" However, limited gains for networks with distinct receivers
-
8/13/2019 Sic Hotnets Talk
40/41
SIC aware protocol design fraught
with pitfalls
Consider doing a back-of-the-envelope calculation
before plunging into system design
40
Takeaway Message
-
8/13/2019 Sic Hotnets Talk
41/41
Questions,
comments?Thank you
Duke SyNRG Research Grouphttp://synrg.ee.duke.edu