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 model

Cooperative ARQ: Analytical model

  • Fading channel model


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 the protocol model1

Cooperative ARQ: The protocol model


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 simulations

Cooperative ARQ: Simulations


Cooperative arq simulations1

Cooperative ARQ: Simulations

  • The definition of the normalized inverse fading margin

Normalized inverse fading margin:


Cooperative arq simulation results normalized throughput

Cooperative ARQ: Simulation results: Normalized throughput

  • N=2 (number of neighbor nodes)


Cooperative arq simulation results normalized throughput1

Cooperative ARQ:Simulation results: Normalized throughput

Lp=-1 dB

Lp=-1 dB

N=2


Simulation results delay and jitter

Simulation results: Delay and Jitter

N=2

np=20


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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