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Modeling the Effect of Transmit Power and Physical Carrier Sense in Multi-hop Wireless Networks. Yong Yang , Jennifer C. Hou and Lu-chuan Kung Department of Computer Science University of Illinois at Urbana-Champaign. Carrier Sensing Range d cs. Carrier Sensing Range d cs. Motivation.

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modeling the effect of transmit power and physical carrier sense in multi hop wireless networks

Modeling the Effect of Transmit Power and Physical Carrier Sense in Multi-hop Wireless Networks

Yong Yang, Jennifer C. Hou and Lu-chuan Kung

Department of Computer Science

University of Illinois at Urbana-Champaign

Y. Yang, J. Hou and L.-C. Kung

motivation

Carrier Sensing Rangedcs

Carrier Sensing Range dcs

Motivation
  • Single-hop / Single-cell wireless networks

s1

r1

s2

r2

Y. Yang, J. Hou and L.-C. Kung

motivation1

Interfernce Range din

Motivation
  • Single-hop / Single-cell wireless networks

s1

r1

s2

r2

Y. Yang, J. Hou and L.-C. Kung

motivation2

dcsdind

Tx Power, CS Threshold

Motivation
  • Single-hop / Single-cell wireless networks
  • Multi-hop / Multi-cell wireless networks

s1

r1

s2

r2

  • Objective: study the effect of Transmit Power and Carrier Sensing on Network Throughput

Y. Yang, J. Hou and L.-C. Kung

contributions

s1

r1

s2

r2

s3

Contributions
  • Model IEEE 802.11 based multi-hop networks
    • Incorporate important MAC/PHY attributes
      • Transmit Power, Carrier Sense Threshold
    • Consider accumulated signal effect
  • Analyze the effect of MAC/PHY attributes on network throughput

Y. Yang, J. Hou and L.-C. Kung

outline
Outline
  • Motivation
  • Contributions
  • Accumulated Signal Effect
  • Analytical Model
  • Effect of Tx. Power and Carrier Sensing
  • Conclusions and Future Work

Y. Yang, J. Hou and L.-C. Kung

accumulated signal effect

Consider a thin ring Ri outside dcs of width Dr:

      • Inner radius:
      • Signal level at s:
      • node together can make s sense busy
      • Effective contenting nodes

ri

Accumulated Signal Effect
  • Accumulated signals outside dcs may exceed CSth
  • Assumptions
    • Nodes are distributed by a Poisson point process with d
    • Nodes always have packet to transmit
  • Effective number of contenting nodes within dcs :

s

dcs

Y. Yang, J. Hou and L.-C. Kung

accumulated signal effect contd
Accumulated Signal Effect (contd.)
  • Thus, the total effective contenting nodes:
  • Equivalently, we can use an effective carrier sense threshold
  • Similarly, we can obtain the effective SIR threshold

s

dcs

Y. Yang, J. Hou and L.-C. Kung

model overview

Idle

Busy

Collision

Success

Model Overview
  • The MAC layer throughput of each sender s:
  • Tv: expected length of a slot
    • Four types of activities in a slot with respective to s
  • Pa: transmission attempt probability in a slot
  • Pc: collision probability given a transmission attempt

Y. Yang, J. Hou and L.-C. Kung

model transmission attempt prob
Model: Transmission Attempt Prob.
  • Bianchi models the back-off process of a node as a discrete-time Markov process
    • The unit of time is the virtual slot time
    • The key assumption: for each transmission attempt, it incurs a collision with a constant and independently probability Pc
  • This can be applied to multi-hop networks
    • The only different is the virtual slot time

Y. Yang, J. Hou and L.-C. Kung

model virtual slot time
Model: Virtual Slot Time
  • A virtual slot could be
    • Successful transmission:
      • Sender s transmits, and no collision
    • Collision:
      • Sender s transmits, but runs into a collision
    • Idle:
      • No node in CSsU{s} attempts to transmit
    • Busy:
      • Sender s is backing off, while at least one in CSs transmit
  • Expected length of a virtual slot

Tsucc, Tcol, Tidleand Tbusy can be determined given MAC/PHY parameters

Y. Yang, J. Hou and L.-C. Kung

model collision probability

s

r

Model: Collision Probability

Tp

  • A transmission is corrupted if
    • Any node in CSs INrstarts to transmit at the beginning of the transmission
    • Any node in INr \ CSsstarts to transmit at or even after the beginning of the transmission
  • The collision probability:

t

CSs

INr

d

din

dcs

Y. Yang, J. Hou and L.-C. Kung

fixed point analysis
Fixed Point Analysis
  • A set of fixed point equations:
  • We prove that a unique solution exists to this equations
  • But hard to find explicit formulas

Y. Yang, J. Hou and L.-C. Kung

effect of tx power

Area

1000m1000m

Payload

2048B

Rate

36Mbps

4

Effect of Tx Power
  • The per-node throughput S decreases with the increase of d
  • Adjust transmit power to control d
    • Subject to connectivity constraint

Y. Yang, J. Hou and L.-C. Kung

effect of carrier sense

d

din

dcs

s

r

Effect of Carrier Sense
  • When dcs > d + din, the per-node throughput S decreases with the increase of dcs
  • The optimal dcs* exists in [0, d + din]

Y. Yang, J. Hou and L.-C. Kung

conclusions and future work
Conclusions and Future Work
  • Model IEEE 802.11 based multi-hop networks
  • Analysis and simulation show
    • Use power control to decrease d to improve MAC layer throughput
    • Adjust carrier sensing threshold s.t. dcs < d + din
  • Future Work
    • Online power control algorithm joint with carrier sense threshold adjustment
    • End-to-end throughput

Y. Yang, J. Hou and L.-C. Kung

thank you and questions
Thank You and Questions?

Y. Yang, J. Hou and L.-C. Kung