Enhanced receivers for High Data Rate CDMA systems

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Enhanced receivers for High Data Rate CDMA systems
Proposed CDMA Receiver
Basic CDMA operation

• Model a symbol-spaced equivalent channel
• Property of G matrix is exploited
• For single user, performance close to Ideal RAKE
  was obtained
• Multi code ISI and Inter Code Interference can
  be model
• Joint Interference suppression will give reduce
  Interference floor
• Published in National Conference on
  Communications 2006, IIT Delhi.

• Message sequence multiplied with a spreading code
  
• Spreading Factor (SF) affects BW increase
• Large processing gain ? interference immunity
• Ratio of bandwidth (W) to information rate
• Low SF ? vulnerable to interference
• Processing Gain 10log10(SF)
• Higher PG 10log10(256) 24dB
• Lower PG 10log10(4) 6dB

Spreading
CDMA System Model
Spreading with code C1(K1)
Spreading with code
Spreading with code C1(K1)
Pulse-shaping filter
Downlink multi-user, multicode CDMA L users, KL
codes/user
Model based Post-Processing
High Data rate CDMA issues
code
code
low data rate user

• Multiple codes to the same user
• Decrease capacity in cell (-)
• Joint Detection possible ()
• Lower spreading factor
• Loss of Orthogonality (-)
• Fewer correlator/receiver ()
• Increases multi-user Interference (-)

Model based Pre-Processing
High data rate user
frequency
frequency
time
time
Current Research Focus
a) Uniform Rate Users
b) Multi Rate Users
Comments
CDMA Receivers
Despreading Correlator
Decision device
Chip Level Equalizer
Frequency spectra of Codes
Single Carrier CDMA code spectrum

• Different codes occupy different bands in
  frequency
• Exploit this selectiveness by coding data across
  a pair of codes
• This improves BER performance and throughput of
  the system

• G-RAKE combining at symbol rate
• optimal combining to improve SINR
• Limited by ISI at low SF
• Chip Level Equalizer operates at chip rate
• In WCDMA its 3.84 Mcps
• Longer filter length improves the performance
• But also introduces filter delay

Generalized RAKE receiver
S. Sendil Kumar PhD. Scholar IIT Madras Chennai,
India.
Web www.iwl.tenet.res.in/ssk Email
sendil_at_iitm.ac.in
Advisor Prof. David Koilpillai IIT
Madras, Chennai, India.
Web www.iwl.tenet.res.in/koilpillai Email
koilpillai_at_tenet.res.in
Split-Band code spectrum approach
S.Sendil Kumar and Prof. David Koilpillai, IIT
Madras, Chennai.