1. Feedback-jamming ARQ mechanisms
Mar 09
doc.: IEEE /0290r0
Mar 09
Feedback-jamming ARQ mechanisms
Date:
Authors:
Jochen Miroll et al., Saarland University
Jochen Miroll et al., Saarland University

2. Abstract NACK-jamming leader based Multicast
Mar 09
doc.: IEEE /0290r0
Mar 09
Abstract
NACK-jamming leader based Multicast
Comparison with ACK polling
Pros and Cons
HLBP: Hybrid leader based Multicast protocol
Jochen Miroll et al., Saarland University
Jochen Miroll et al., Saarland University

3. Glossary Synchronisation of Multicast clients, event-driven or clocked
Mar 09
Glossary
Synchronisation of Multicast clients, event-driven or clocked
ACK-polling AP gathers ACK from each client
Jochen Miroll et al., Saarland University

4. 802.11 Template Instructions 2/4
Mar 09
doc.: IEEE /0290r0
Mar 09
Template Instructions 2/4
Step 5. Menu select View, Master, Slide Master. Place the document designator in the right hand side of the header.
Document designator example "doc.: IEEE /9876r0" , or
"doc.: IEEE /9876r2"
Step 6. Menu select View, Header and Footer (5 data fields):
Slide tab:
Header = venue date (as Month Year, e.g. January 2005)
Footer = first author, company
Notes tab:
Data and time, Fixed = venue date (as Month Year, e.g. January 2005)
Header = document designator (e.g. “doc.: IEEE /9876r0”)
Click "Apply to all".
Step 7. Delete the four template instruction slides.
Jochen Miroll et al., Saarland University
Jochen Miroll et al., Saarland University

5. NACK jamming Leader Based Protocol
Mar 09
NACK jamming Leader Based Protocol
Jochen Miroll et al., Saarland University

6. NACK-jamming vs. Block-ACK polling
Mar 09
NACK-jamming vs. Block-ACK polling
Jochen Miroll et al., Saarland University

7. NACK jamming LBP summary (1)
Pros
Scalability: Depending on seq# signalling overhead
Our simulation shows an example for 10-Block-ACK vs. 25 clients
Or from the latency PoV: Maximum delay is constant
Determined by (pre-configured) # of retransmission rounds, independent of # of clients
Event driven, distributed, optimal feedback
NACK+ACK at the same time
ACK polling is TDMA – more strict synchronisation necessary
Purposely jamming the ACK is enforcing a collision – synchronisation need not be as strict as for TDMA
Jochen Miroll et al., Saarland University

8. NACK jamming LBP summary (2)
doc.: IEEE /0290r0
Mar 09
NACK jamming LBP summary (2)
Cons (or are they?)
NACK-jamming still requires synchronisation of individual clients
But: If a client device is “too slow” to jam, it does not affect the others
Scalability may not be an issue at home
But: Other use-cases exist: large audience video broadcast, e.g. at public places like airports, etc.
How to select the leader – a protocol is required
But: ACK polling also requires knowledge at clients about ACK sequence
Not applicable for blocks of frames
But: This is compensated by increased scalability
Jochen Miroll et al., Saarland University
Jochen Miroll et al., Saarland University

9. Synchronisation: jamming vs. ACK
Mar 09
Synchronisation: jamming vs. ACK
Jamming
Collision, Fail!
SIFS
SIFS
ACKReq
Block
AP1
ACK
Block
ACK
STA 1 (leader)
NACK
Block
ACK
STA r-1
NACK
Block
ACK
STA r
NACK Jamming
Block Polling
Jochen Miroll et al., Saarland University

10. Increasing LBP efficiency: HLBP
Mar 09
doc.: IEEE /0290r0
Mar 09
Increasing LBP efficiency: HLBP
NACK-jamming destroys „positive information“
Block-NACK (similar to Block-ACK) is thus not possible
Solution: Apply FEC to a block
Transmit block of frames
Assume at least one client did not receive at least one frame in block
=> ACK gets jammed
Transmit parity frames
Clients try to recover the data from the frames + parity they received
Repeat 2. until ACK does not get jammed anymore
(or retry limit reached)
Problem solved:
The use of parity-retransmission eliminates the need for positive info
Jochen Miroll et al., Saarland University
Jochen Miroll et al., Saarland University

11. Mar 09
HLBP*
* A rateless FEC code is assumed here, for e.g. for RS parity would be parity OR data
Jochen Miroll et al., Saarland University

12. HLBP vs. Block-ACK polling
Mar 09
HLBP vs. Block-ACK polling
Jochen Miroll et al., Saarland University

13. Summary LBP with NACK jamming is feasible
For low jitter, low latency applications
For error tolerant applications
Because it scales better than positive feedback
LBP with NACK jamming might be less feasible
For strong power-saving requirements
Block-ACK polling is more efficient
The CHT is larger since Block-NACK is not possible
HLBP
Block-NACK scheme, comparable to Block-ACK
Most efficient
Most complex due to FEC
Jochen Miroll et al., Saarland University

14. Mar 09
References
Jochen Miroll et al., Saarland University