Rate Adaptive MultiCode MultiCarrier CDMA Systems in Multipath Fading Channel

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Rate Adaptive Multi-Code Multi-Carrier CDMA
Systems in Multipath Fading Channel
May 3, 2003

• CDMA Team
• Jaeweon, Taeyoon, Madhulika, Srivatsan
• E-mail cdma_team_at_yahoo.com

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Contents

• Introduction Motivation
• System Description
• Channel Model
• Adaptation Algorithm
• Simulation Set up Results
• Conclusion Future Work

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Introduction

• Future wireless systems
• integration of voice, data, image, video.
• Variety of data rates
• Concerns
• unfriendly wireless channel
• multipath propagation
• doppler shift
• multiple access interference

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Possible Solutions

• Spread Spectrum techniques
• combat fading effects
• Multi-Carrier
• Robustness against multipath and interference
  rejection
• Multi-Code systems
• variable data rate

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Multi Code System

• High data rate stream split into number of
  parallel low-rate streams
• Low-rate streams are spread by different
  sequences and added before transmission
• High and variable data rates

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Multi-Code Sytem(2)

• Multi-Code CDMA with Variable Sequence-Sets,
  H.D.Schotten, H.Elders-Boll, A. Busboom
• Each user has a sequence set of some size M .

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Multi-Code System
M-ary data symbols
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Channel
G1(n) G2(n) G3(n) . . . GM(n)
1111 1010 1100 1001
Cos(wct)
. . .
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Multi-Code System (MTC)

• Performance in AWGN
• Adaptive Algorithm
• Parameters - Min data rate, max BER, max
  transmit power
• Users increase the size of the sequence set to
  achieve the data rate, and the transmit power to
  decrease the BER.

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Motivation Objectives

• Evaluate the performance of Multi-Code System in
  fading channel
• Different codes for the sequence sets - Walsh,
  Gold, Kasami
• Increase capacity
• By using multi-carriers
• Choices - MC-CDMA, MC-DS-CDMA
• Better Adaptive algorithm
• Parameters - channel condition, desired BER, data
  rate

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Multi-carrier System (I)

• Spread spectrum/CDMA with spreading in the
  frequency domain
• DS-CDMA followed by IFFT
• OFDM preceded by orthogonal matrix operation
• Frequency diversity with each bit transmitted
  simultaneously on many sub carriers.

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Multi-Carrier System
Data Stream
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Why Multi-Carrier?

• Channel - multipath fading
• Destructive interference due to multipath causes
  deep nulls in the channel frequency response.
• In case of wideband signals dips in the spectrum
  result in a small loss of signal power.
• Spectral nulls are unlikely to occur at all of
  the subcarrier frequencies.

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System Description
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Multi-code Multi-carrier System(MTC-MC System)
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Multicode Multicarrier DS CDMA System (MTC-MC-DS
System)

• MC-CDMA outperforms MC-DS-CDMA in multipath
  fading channels
• Hence not evaluated
• Overview of Multicarrier CDMA, S.Hara,
  R.Prasad

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Abbreviations

• CDMA Code Division Multiple Access
• MTC CDMA Multi-Code CDMA
• MTC-MC CDMA Multi-Code Multi-
• Carrier CDMA
• MC-CDMA Multi-Carrier CDMA

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Channel Model

• Multipath Rayleigh Fading Channel
• Principles of Mobile Communication by Gordon L.
  Stuber

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Rate Adaptation

• Parameters
• Instantaneous SINR of the channel
• Desired BER
• Maximum data rate

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Rate Adaptation
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Simulations
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Simulation Setup

• L (Length of multicode sequence) 256
• M 2,4,8,16,32,64,128,256
• Speed of vehicle 60 m/s
• Carrier frequency 900 MHz
• Max. Doppler frequency 50 Hz
• No. of subcarriers 16

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Simulations

• Present the performance of MTC CDMA in fading
  channel using different codes.
• Compare MTC CDMA to MTC-MC CDMA in Fading channel
• Compare MTC-MC CDMA with Adaptation to MTC CDMA.
• Compare the MTC-MC CDMA with Adaptation to MTC-MC
  CDMA

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Multi-Code System with different codes
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MTC AWGN vs. MTC Fading
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MTC Adaptation vs. MTC in Fading Channel
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MTC, MTC-MC (w and w/o Adaptation) in Fading
Channel
M2.96
M18.7
M92.0
M161.3
M197.6
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Adaptive Algorithm (MTC)
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Conclusions

• The system capacity in the Multi-Code CDMA is
  improved by use of Multi-Carrier scheme.
• Adaptive algorithm based on instantaneous channel
  condition improves the average data rate without
  decreasing the performance

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Future work

• Mathematical Analysis
• Simulations for the asynchronous case

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References

• 1 T.S. Rappaport, Wireless communications,
  Principles and Practice, 2nd Ed., Prentice Hall
• 2 H.D.Schotten, H.Elders-Boll, A,Busboom,
  Mutli-Code CDMA with variable sequence sets,
  IEEE 6th International Conference on Universal
  Personal Communications 1997, Vol. 2, pp. 12-16,
  Oct. 1997
• 3 D.W.Hsiung, J.F.Chang, Performance of
  multi-code CDMA in a multipath fading channel.,
  IEE Proceedings-Communications, Vol.147 Issue 6,
  Dec. 2000
• 4 S.Hara, R.Prasad, Overview of Multi-Carrier
  CDMA, IEEE 4th International Symposium on Spread
  Spectrum Techniques and Applications Proceedings
  1996, Vol. 1, pp. 22-25, Sep. 1996
• 5 Gordon L. Stuber, Principles of MOBILE
  COMMUNICATION, Klwer Academic Publishers
• 6 A.J. Goldsmith, S.G. Chua, Variable-Rate
  Variable-Power MQAM for Fading Channels, IEEE
  Transactions on Communications, Vol.45, No.10,
  Oct. 1997

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QA
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• Thank you