Voice capacity in CDMA 2000 1xRTT systems

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Voice capacity in CDMA 2000 1xRTT systems
Term project (COE-543) By S.M.Rehman 230419.
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Outline

• Introduction
• Advantages of CDMA systems
• Propagation Loss Models
• Parameters considered
• Plan of action
• Simulated results
• Future work
• Conclusions

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Introduction.

• Code Division Multiple Access (CDMA) is a viable
  cellular system alternative to both
  frequency-division multiple access (FDMA) and
  time-division multiple access (TDMA) technologies
  .
• CDMA falls under the category of spread
  spectrums.
• Code Division Multiple Access (CDMA) is receiving
  considerable attention as a major contender in
  the upcoming 3G wireless standard development.

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Introduction (Contd)

• CDMA 2000 1xRTT is a 3G wireless technology based
  on CDMA platform. The 1x in 1xRTT refers to 1x
  the number of 1.25MHz channels. The RTT stands
  for Radio Transmission Technology.
• 1xRTT is forward link synchronous with 1.2288 MHz
  chipping, and is an evolution of IS-95.

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Contd.

• 3G systems were also designed to increase voice
  capacity over 2G by various forward and reverse
  link improvements. These include
• fast forward link power control,
• bandwidth efficient modulation,
• lower rate coding and
• reverse link pilot assisted coherent
  demodulation.

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Advantages of CDMA systems

• Universal one-cell frequency reuse
• Narrow band interference rejection
• Inherent multipath diversity
• Soft hand-off capability
• Soft capacity limit
• Improved Channel Capacity.

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Propagation models

• For any wireless communication system , the first
  important step is to design the radio link.This
  is required to determine the base station density
  in different environments as well as the
  corresponding radio coverage.
• One of the most important considerations in the
  radio coverage planning process is the
  propagation model. The accuracy of the prediction
  by a particular model depends on its ability to
  account for the detailed terrain, vegetation, and
  buildings.

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Contd.

• Propagation models are used to determine how many
  base stations are required to provide the
  coverage requirements needed for the network.
• The performance of the network is affected by the
  propagation model chosen because it is used for
  interference predictions.
• The propagation model is also used in other
  system performance aspects including handoff
  optimization, power level adjustments, and
  antenna placements.

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Most important radio propagation characteristics

• Achievable Signal Coverage,
• The maximum data rate that can be supported by
  channel, and
• The rate of fluctuations in the channel.

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Definition

• Propagation models that predict the mean signal
  strength for an arbitrary transmitter-receiver
  separation distance, useful in estimating the
  radio coverage area of a a transmitter are called
  large scale propagation models.
• Propagation models that characterize the rapid
  fluctuations of the RSS over very short travel
  distances or short time durations are called
  small scale or fading models.

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Path Loss

• Radio transmission in a mobile communication
  system often takes place over irregular terrain
  .The terrain profile of a particular area needs
  to be take into account for estimating the path
  loss.
• Path Loss which represents signal attenuation is
  a positive quantity measured in decibels (dB),is
  defined as the difference between the effective
  transmitted power and the received power.

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Path Loss (Contd)

• Some of the commonly used propagation models are
• Longley Rice Model
• Durkins Model
• Okumura Model,
• Hata Model
• PCS extension of Hata model
• Walfisch Bertoni Model
• Wideband PCS micro cell Model.

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Hata model

• For signal strength prediction and simulation in
  macro cellular environments, the Hata Model is
  widely used.
• The Hata model is an empirical formulation of the
  graphical path loss data provided by Okumura, and
  is valid from 150 MHz to 1500 MHz.
• Hata presented the urban area propagation loss as
  a standard formula and supplied correction
  equations for application to other situations.

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Hata formula

• The standard formula for median path loss in
  urban areas is given by
• L50 (urban)dB 69.55 26.16logf c- 13.82
  log(hte) a(hre) 44.9 -6.55 log(hte) log(d) .
• where, fc is the frequency in MHz from 150MHz
  to 1500MHz,
• hte is the effective transmitter antenna
  height(meters) ranging from 30m to 200m, hre is
  the effective receiver antenna height(meters)
  ranging from 1m to 10m,
• d is the T-R separation distance(km) and
  a(hre) is the correction factor for effective
  mobile antenna height which is a function of the
  size of the coverage area .

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Contd..

• For a small or medium sized city the correction
  factor is given by
• a(hre) (1.1log fc 0.7)hre (1.56log
  fc-0.8)dB
• The Free Space Path loss equation is given by
• L (free) 32.4 20logfc 20log (d).
• The average received power at the mobile station
  is calculated as
• Pr(d) EIRP(dBm) - L(urban)(dB) Gr(dB)
• Where EIRP is the Effective Isotropic Radiated
  Power (1 kw) and Gr is the gain of the
• receiving antenna.

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• This model is well suited for large cell mobile
  systems, but not personal communication systems
  which have cells on the order of 1km radius.

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Parameters Considered

• Bandwidth of 1xRTT systems
  1.25MHz.
• Orthogonality factor
  0.8
• Totoal transmitted Power 24
  w
• Fraction of overhead
  0.2
• Eb/No
  7dB
• Number of users between 1 and 50.
• Cell Radius
  1km
• Frequency 1500MHz, Height of base station and
  Height of mobile station equal to 50m 3m
  respectively.

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Simulated Results using Matlab
Frequency Number of users Radius (Km) Eb/No (dB) Rate (kbps)
1500 100 2 7 4.8
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Rate (kbps) Eb/No (dB) Radius (Km) Number of users Frequency (MHz)
4.8 7 6 50 1500
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Results Contd..
Rate (kbps) Eb/No (dB) Radius (Km) Number of users Frequency (MHz)
9.6 7 2 50 1500
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Contd..
Rate (kbps) Eb/No (dB) Radius (Km) Number of users Frequency (MHz)
9.6 7 2 50 200
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Contd..
Rate (kbps) Eb/No (dB) Radius (Km) Number of users Frequency (MHz)
19.2 7 2 50 200
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Scatter plot of path loss and distance for a
macro cell when the base antenna height was 25m.
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Future Work

• It is possible to extend the study by comparing
  other Propagation Loss Prediction Models like the
• Walfisch-Bertoni Model to investigate
  microcellular environments,effects of structure
  of the buildings etc. to get a better
  understanding on the factors effecting system
  design.
• The performance of the variable processing gain
  system can be measured in terms of network
  throughput and can be compared to the performance
  of conventional fixed rate CDMA systems in which
  perfect power control is assumed.

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Acknowledgements

• I convey my deep sense of gratitude to Dr.Ashraf
  who has been helping me through out the project.
• I convey my thankfulness to my compatriots who
  gave a hearing ear to my presentation.