chapter 10 cooperation link level retransmission in wireless networks m dianati x shen and k naik
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Chapter 10 Cooperation Link Level Retransmission in Wireless Networks M. Dianati, X. Shen, and K. Naik. Scope. Link and MAC layer for fading channels. Two parts: Cooperative Scheduling Cooperative ARQ. Introduction. Sample fading process. Challenges in wireless domain: Fading

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chapter 10 cooperation link level retransmission in wireless networks m dianati x shen and k naik

Chapter 10Cooperation Link Level Retransmission in Wireless NetworksM. Dianati, X. Shen, and K. Naik

scope
Scope
  • Link and MAC layer for fading channels
  • Two parts:
    • Cooperative Scheduling
    • Cooperative ARQ
introduction
Introduction

Sample fading process

  • Challenges in wireless domain:
    • Fading
    • Interference
    • Limited bandwidth
  • Potentials:
    • Again, fading
    • Spatial diversity
introduction stochastic model of flat fading process
Introduction:Stochastic model of flat fading process:

Power spectrum density

Complex envelope of

fading process:

Power spectrum density:

Fading process is a non-white stochastic process with relatively slow variations.

introduction spatial diversity
Introduction: Spatial diversity
  • Using independent transmission paths to increase:
    • Capacity
    • Reliability
    • Both
  • Examples:
    • Multiple antenna systems
    • Cooperative communications
    • Multiuser diversity
cooperative arq motivations
Cooperative ARQ: Motivations
  • ARQ: link level retransmission
    • Is de facto part of wireless link layer protocols
  • Cooperative ARQ uses:
    • Channel state info. (since fading is a non-white process)
    • Spatial diversity
  • To improve:
    • Throughput
    • Delay
cooperative arq basic idea
Cooperative ARQ: Basic idea
  • Let neighbor nodes assist the retransmission trials

Transmission

X

cooperative arq basic idea1

NAK

Cooperative ARQ: Basic idea
  • Let neighbor nodes join retransmission

Negative or positive ACK

cooperative arq basic idea2
Cooperative ARQ: Basic idea
  • Let neighbor nodes join retransmission

Retransmission

cooperative arq basic idea3
Cooperative ARQ: Basic idea
  • Assuming that the physical layer can handle multiple receptions, node cooperation:
    • Mitigates the impact of deep fading on the primary path from the sender to the receiver
    • Improves the chance of successful retransmission
cooperative arq system model
Cooperative ARQ: System model
  • Network model
  • A single cooperation
  • group
cooperative arq basic scheme
Cooperative ARQ: Basic scheme
  • Sender and receiver nodes perform their normal operations.
cooperative arq basic scheme1
Cooperative ARQ: Basic scheme
  • Neighbor nodes:
    • Decode and store a copy of each frame.
    • Drop the frame if ACK is received.
    • Transmit the frame in NAK is received.
  • Neighbors cooperate if
    • They will to cooperate
    • They have enough resources
cooperative arq analytical model1
Cooperative ARQ: Analytical model
  • Three steps:
    • Model cooperation of a single node
    • Combine multiple nodes into a super node
    • Obtain the protocol model
cooperative arq cooperation model of a single neighbor node
Cooperative ARQ: Cooperation model of a single neighbor node
  • A tagged neighbor can help if:

1. It has correctly received the previously transmitted frame

AND

2. Its channel to the receiver node is in good condition.

cooperative arq cooperation model of multiple neighbor node
Cooperative ARQ: Cooperation model of multiple neighbor node
  • What if there are two neighbor nodes?
    • Model as a single node with a better cooperation capability
  • More than two neighbor nodes:
    • Iterative combination of all neighbor nodes into a super node
cooperative arq the protocol model
Cooperative ARQ: The protocol model
  • The cooperation group is either in Transmission state (T) or Retransmission state (R).

O(k): Status of the protocol at discrete time k

P(k): Status of the primary channel

N(k): Status of the super node

G: Good state

B: Bad state

C: Cooperative state

NC: Non Cooperative state

cooperative arq application of the model
Cooperative ARQ: Application of the model
  • Throughput:
  • Delay:
    • Definition of delay: the total time required to transmit a single packet from the network layer
  • Average delay:
cooperative arq application of the model1
Cooperative ARQ: Application of the model
  • For a packet with np fragments:
  • Delay jitter:
cooperative arq simulations1
Cooperative ARQ: Simulations
  • The definition of the normalized inverse fading margin

Normalized inverse fading margin:

cooperative arq summary and further direction
Cooperative ARQ: Summary and further direction
  • Cooperation of few nodes can improve performance of ARQ scheme significantly.
  • Cooperative ARQ is backward compatible.
  • There is not much signaling or maintenance overhead.
  • Further extensions:
    • Non-ideal feedback channels
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