Random Linear Network Coding for Time Division Duplexing (TDD) Lucani, M

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Random Linear Network Coding for Time Division
Duplexing (TDD) Lucani, Médard,
Stojanovic joint with CBMANET

• Novel network coding strategy for TDD
• Use of feedback (ACK) improves delay/energy/
  throughput performance, especially for high
  latency- high errors scenarios
• Random linear coding allows extension to networks

MAIN RESULTS Novel network coding scheme for TDD
channels 1. Delay and Energy Analysis for Link
and Broadcast cases 2. Exists optimal
transmission time in terms of minimizing block
delay, with close-to-optimal energy performance.
3. Outperforms Selective Repeat schemes in high
latency- high error scenarios. Similar
performance otherwise. 4. Delay/throughput
is close to full duplex network coding,
requiring much less energy

• Network coding has studied throughput or delay
  performance considering minimal feedback
• TDD has used ARQ/FEC schemes

1. Use feedback to improve delay performance ACK
states required number of coded packets to decode
data
2. Transmit coded packets for some time, stop to
wait for ACK
HOW IT WORKS 1. Transmission time computed to
minimize delay in data block transmissions, using
ACK and channel conditions 2. Stop transmission
to wait for ACK from receiver (s).
ACK used to update transmission time

• Extend broadcast effect of clusters of
  cooperative nodes
• Sensitivity analysis
• Extend to general network scenario

3. Transmission time depends on ACK and channel
conditions Exists optimal choice
ASSUMPTIONS AND LIMITATIONS Random linear
coding, prior knowledge/estimate of propagation
delay and errors
Feedback, coding and optimal choice of
transmission time minimizes delay, while keeping
throughput performance similar or better than
typical TDD ARQ schemes
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Introduction

• Reliable communication for time division
  duplexing (TDD) channels, i.e. when a node can
  transmit and receive, but not at the same time,
  has been commonly achieved using
• ARQ schemes focuses of retransmission. Typically
  no coding
• FEC schemes focuses on coding. No
  retransmissions.
• Most network coding results focus on throughput
  or delay performance assuming minimal feedback
• Objective Minimize completion time of blocks of
  packets in TDD channels, especially in long
  latency channels
• Key Question How much should we talk before
  stopping to listen?

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Description of Scheme
Erasure Channel
Tx
Rx
ACK i
Receives (M i) random linear coded
packets Acknowledges i missing dofs
Generates N random linear coded packets
M
ACK degrees of freedom required to decode (dofs
reqd) Not particular data packet
Received degrees of freedom
When to stop talking and start listening
Degrees of freedom needed to decode
Degrees of freedom needed by Rx
M
M
i
Choice of Ni, ?i determines performance of scheme
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Minimizing Completion Time or Energy
Full Duplex Minimum Completion

• TDD constraint
• Ni, ?i chosen to minimize
• Mean completion time
• Mean completion energy

e.g M 10, round trip time 250 ms, Rate 1,5
Mbps
Time
Pe 0.8
1.1dB
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Minimizing Completion Time or Energy
Full Duplex Minimum Completion

• TDD constraint
• Ni, ?i chosen to minimize
• Mean completion time
• Mean completion energy

e.g M 10, round trip time 250 ms, Rate 1,5
Mbps
Energy
Pe 0.8
1.15dB
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Throughput
Throughput Metric
? bits / ETime

• Increasing latency,
• favors network coding
• TDD scheme
• Better performance than
• Go-back-N (GBN) and
• Selective Repeat (SR)
• for TDD

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Conclusions

• We have developed a novel network coding strategy
  for TDD channels
• Link
• Broadcast
• Coupling coding and feedback (ACK) improves
  delay/throughput performance, especially for high
  latency- high erasures scenarios
• New Goals

Extension to general networks
Extension to broadcast with cooperative nodes