TRANSMISSION POWER CONTROL FOR AD HOC WIRELESS NETWORKS: THROUGHPUT, ENERGY AND FAIRNESS

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TRANSMISSION POWER CONTROL FOR AD HOC WIRELESS
NETWORKS THROUGHPUT, ENERGY AND FAIRNESS

• Lujun Jia Xin Liu Noubir, G. Rajaraman, R.
• Wireless Communications and Networking
  Conference, 2005 IEEE.
• Presenter Han-Tien Chang

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Outline

• Introduction
• Network Models And Assumptions
• d-PCS A Class of Power Control Schemes
• Simulation Results
• Implementation Issues
• Conclusion And Future Work
• Comments

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Introduction

• Introduce a new power control scheme
• Combines collision avoidance and spatial reuse
• Significant improvements for network throughput
  and energy efficiency simultaneously
• Adhere to the single-channel, single-transceiver
  design rule
• Solve the fairness problem

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Introduction (contd)

• Drawbacks of IEEE 802.11
• 802.11 uses maximum transmission power Pmax
  regardless of the distance between the
  transmitter and the receiver
• Spatial channel reuse in IEEE 802.11 is not
  optimized
• One on-going transmission may unnecessarily block
  multiple nearby sessions by transmitting at Pmax
• Fairness problem
• IEEE 802.11 delivers more packets for short
  distance traffic pairs than for long-distance
  traffic pairs
• When the network load increases, the ratio of
  delivered short distance traffic to long-distance
  traffic increases

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Introduction (contd)

• Related power control schemes 13 may suffer
  from
• The scheme improves energy-efficiency but not
  network throughput, or increase the throughput at
  the expense of energy consumption
• Extra hardware and spectrum availability are
  required, i.e., multiple wireless channels and
  transceivers
• Strong assumptions on MAC or physical layers are
  imposed, which are often difficult to implement

13 A. Muqattash and M. Krunz. A single-channel
solution for transmission power control in
wireless ad hoc networks. In ACM MobiHoc, May
2004.
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Introduction (contd)

• d-PCS
• A novel transmission power function P(t)
• to compute an appropriate transmission power, so
  that a better spatial channel reuse is achieved
• Unlike POWMAC 13, no collision avoidance
  information is explicitly advertised in our
  scheme.
• Instead, nodes choose a transmission power level
  based on its traffic distance d, and an estimate
  of the interference level it experiences.

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Introduction (contd)
8 E.S. Jung and N.H. Vaidya. A power control
MAC protocol for ad hoc networks. In ACM Mobicom,
September 2002. 11 J. Monks, V. Bharghavan, and
W. Hwu. A power controlled multiple access
protocol for wireless packet networks. In IEEE
INFOCOM, April 2001.
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Network Models and Assumptions

• P(r) c P(t)/da
• where c is a constant that depends on the antenna
  gains and heights, and carrier frequency,
• d is the distance that the signal travels,
• and a is the power attenuation factor.
• The typical value of a ranges from 2 to 4.
• For our simulation study, we adopt the standard
  two-ray ground model that sets a to be 4 for
  long-range distances and 2 for short-range
  distances.

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Network Models and Assumptions (contd)

• The bit-error rate of a transmission depends on
  the noise power and the interference level at the
  receiver
• Let Xk, k ? T be the set of nodes
  simultaneously transmitting at any time instant.
• Let Xj be the receiver of a transmitter Xi ? T
• For the transmission by Xi to be successfully
  received by Xj
• (1) the received power P(r) at node Xj must
  exceed the receiving threshold, RXth
• (2) the SINR at Xj must exceed the SINR
  threshold, SINRth

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Network Models and Assumptions (contd)

• We use traffic distance or traffic length to
  denote the distance between the transmitter and
  the receiver.
• The transmission range of a certain power level
  P(t)
• denotes the maximum distance at which the
  received signal is right above RXth
• Beyond the transmission range, the signal can
  still be detected (but not decoded) if its
  strength is above the carrier sensing threshold,
  CSth.
• Typically, CSth is several dBs lower than RXth.
• Thus, the sensing range defined by CSth is larger
  than the transmission range

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d-PCS A Class of Power Control Schemes

• Overview of d-PCS
• 1. Given the maximum transmission power level,
  Pmax
• The corresponding maximum transmission range dmax
  satisfies c Pmax/dmaxa RXth.
• 2. Given the distance d between the transmitter
  and receiver,
• the minimum necessary transmission power,
  Pmin(d), for a transmission to be successful
  satisfies c Pmin/da RXth.

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d-PCS A Class of Power Control Schemes

• Let parameter d be any constant between 0 and a
• our power function is the following
• By substituting RXth with c Pmax/dmaxa
• Let dT be the transmission range of P(t).
• By the definition of transmission range,
• the received signal power at dT is equal to the
  receiving threshold,
• i.e., P(r) c P(t)/(dT)a RXth.
• We then have that the transmission range of P(t)
  is dT dd/admax1-d/a .
• Note that d dT dmax, for any d between 0 and
  a.

,d ? 0, a
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d-PCS A Class of Power Control Schemes
How the transmission power changes as a function
of the traffic distance d, under different d-PCS
The transmission range d-PCS that lies between d
and dmax
Main Goal identify a good d value such that
the corresponding power control scheme yields
performance improvement in network throughput,
energy efficiency and fairness simultaneously
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d-PCS A Class of Power Control Schemes

• Analysis of d-PCS
• analyze the fairness behavior of d-PCS,
• the fairness for different traffic distance is
  closely related to the aggregate throughput
• Assumptions
• Each source node is located independently and
  uniformly in the Euclidean plane
• For each source, its destination is located at a
  distance chosen independently and uniformly at
  random from 0, dmax.
• N 0 in our following derivation for simplicity

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d-PCS A Class of Power Control Schemes

• Consider an on-going transmission from a node Xi
  to node Xj
• For any other transmitting node Xk, k?i, let Xk
  be the receiver.
• In order for the transmission from Xi to Xj to be
  successful, we need SINRj to exceed SINRth.
• We determine the value d that minimizes
  E1/SINRj.
• We note that minimizing E1/SINRj is only an
  approximation for maximizing the aggregate
  throughput.

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d-PCS A Class of Power Control Schemes

• Lemma 3.1
• The minimum of this equation is achieved at
• dOPT(dij) 1/ (ln dmax - ln dij)-1
• We can thus infer the following
• (1) This equation is a decreasing function of d
  on -8, dOPT, and an increasing function of d on
  dOPT,8
• (2) dOPT is an increasing function of dij
• (3) There exist threshold distances d, d with
  dOPT(d) 0 and dOPT(d) a

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d-PCS A Class of Power Control Schemes

• Three observations (????????)
• Observation 1
• For 0 lt dij d, dOPT(dij) lt 0, which implies
  that E1/SINRj increases as d increases from 0
  to a
• Thus, the throughput of the traffic pairs with 0
  lt dij ddecreases when d increases from 0 to a
• Observation 2
• For dltdij d, 0 dOPT(dij) a, which implies
  that E1/SINRj first decreases then increases
  when d increases from 0 to a.
• This indicates that the throughput of the traffic
  pairs with d dij d first increases then
  decrease when d increases from 0 to a.
• Observation 3
• For dlt dij , dOPT(dij) gt a, which implies that
  E1/SINRj decreases when d increases from 0 to
  a.
• This indicates that the throughput of the traffic
  pairs with dij gt d increases when d increases
  from 0 to a.

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Simulation Results

• Simulation model
• GloMoSim-2.03
• Physical layer
• Application layer
• CBR traffic model (pkt size 512 bytes)

Parameter Value
Bandwidth 2Mbps
Receiving Threshold -64dBm
Carrier sensing threshold -71dBm
Pmax 25dBm
dmax 250m
Carrier sensing range 550m
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Simulation Results (contd)

• Topology and traffic
• Generate random topologies with 200 stationary
  nodes distributed on a 2000 2000m2 area
• Select randomly located single-hop
  transmitter-receiver pairs
• also referred to as traffic pairs
• Select random traffic pairs from 0 to 250m
• Performance metrics
• Aggregate and normalized throughput
• Energy efficiency (Mb/Joule)
• Throughput achieved in different destination
  ranges

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Simulation Results (contd)

• Random topologies with varying number of traffic
  pairs

Normalized throughput under varying number of
traffic pairs with fixed data rate of 1.0Mbps.
Aggregate throughput under varying number of
traffic pairs with fixed data rate of 1.0Mbps.
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Simulation Results (contd)
Distance in m
0-50 5-100 100-150 150-200 200-250

1. The preference is slowly inversed when d
   increases from 0 to 4, with 4-PCS showing a
   strong preference for long traffic pairs.
2. for destination range 100-150m, the achieved
   throughput first increases then decreases
3. for destination range 200-250m, the achieved
   throughput increases
4. When d is equal to 2 or 2.5, the achieved
   throughputs on each range are close to the
   average, thus a fair allocation of the channel
   capacity is observed

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Simulation Results (contd)
Data delivered per unit energy under varying
number of traffic pairs
Normalized bit-meter/sec measurement under
varying number of traffic pairs
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Simulation Results (contd)

• Random topologies with varying data rate

Achieved throughput on different destination
ranges (30 traffic pairs at data rate 600Kbps)
Aggregate throughput under varying data rate. The
total number of pairs is 30
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Simulation Results (contd)
Data delivered per energy unit under varying data
rate. The total number of pairs is 30.
Normalized bit-meter/sec under varying data rate,
where the total number of pairs is 30.
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Implementation Issues

• Power function implementation
• Within the RTS/CTS handshake protocol
• the communicating nodes can estimate the channel
  gain. We propose to convert the distance variable
  of the power function into a gain variable.
• RTS/CTS power level update
• In a mobile network the channel characteristics
  change as the nodes move, therefore the
  transmission power levels have to be updated.
• We propose to use a technique similar to the
  closed-loop power control used in CDMA cellular
  systems.

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Conclusion And Future Work

• Propose d-PCS
• a class of power control schemes for ad hoc
  wireless networks, based on a novel transmission
  power function
• Compared with IEEE 802.11
• achieves up to 40 throughput increase
• improves energy efficiency by a factor of 3
• shows better fairness with respect to the traffic
  length distribution.
• Future work
• plan to integrate our power control scheme within
  a resource efficient multi-hop routing protocols

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Comments

• Experiment Discussion
• We should know what we want to find out in this
  experiment or prove the hypothesis
• Analysis ? Experiment