Emad Alsusa

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Adaptive Code Allocation for Interference
Exploitation on the Downlink of MC-CDMA Systems

• Emad Alsusa Christos Masouros
• Dept. of Electrical Electronic Engineering
• University of Manchester

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Principles of the Proposed Method

• For PSK Modulation, Interference can be Separated
  to Constructive and Destructive
• Interference Depends on Users Crosscorrelations
  as well as the instantaneous Data
• By Reallocating the Codes According to the
  Current Data, the Crosscorrelations and hence
  Interference Amongst Users can be Manipulated
• By Exploiting Constructive Interference the
  Effective SINR can be Increased and Performance
  can be Improved Without the Need to Increase
  Transmitted per-User Power

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MC-CDMA Downlink Employing post-Equalization (K
users)

• Received Signal at the u-th Mobile Unit (MU) at
  the i-th symbol period
• Decision Variable

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Constructive - Destructive Interference
Separation

• User-to-User Constructive MAI

Cumulative Constructive MAI
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Constructive - Destructive Interference
Separation

• Instantaneous per Symbol Effective SINR

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Decision Variables Distributions for pc8
Different Allocation Patterns for K5, L16
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Code-to-User Allocation (CUA) Technique (1/9)

1. Create Code Sets
2. Evaluate Code Sets
3. Select Optimum Code Set
4. Spread and Transmit
5. Transmit SI
6. Detect SI and select the correct code
7. Dispread and Detect

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Code-to-User Allocation (CUA) Technique (2/9)
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Code-to-User Allocation (CUA) Technique (3/9)

• Decision Variables pre-Estimation
• Code Allocation Selection Criteria

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Code-to-User Allocation (CUA) Technique (4/9)

• For Correct Dispreading According to the Updated
  Codes, Transmission of
• SI bits is Necessary
• SI is Common for all Users
• If Code Allocation s7 is 3, 5, 2, 1, 4 then
  User k3 Should Employ Code with Index 2 from the
  reference set for Correct Dispreading

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Code-to-User Allocation (CUA) Technique (5/9)

• Enhanced Received SINR, Improved Reliability
• Data Detection Very Sensitive to SI Errors

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Code-to-User Allocation (CUA) Technique (6/9)

• CUA with MRC, EGC, SU- MMSE post-Equalization

• Performance Improvement of an Order of Magnitude
  Without Increase in Transmitted per-User Power
• Efficiency Reduction to 91 due to Transmission
  of Side Information (SI)

Number of paths4, K20, L32, pc16
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Code-to-User Allocation (CUA) Technique (7/9)

• CUA with EGC post-Equalization and SIC Detection

• Limited Improvement for Increased NC
• Performance Loss for Low SNR due to Unreliable SI

Number of paths4, K20, L32
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Code-to-User Allocation (CUA) Technique (8/9)

• CUA with EGC

• Limited Improvement for Increased Number of
  Available Allocation Patterns (pc)

Number of paths3, K16, L16, SNR7dB
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Code-to-User Allocation (CUA) Technique (9/9)

• CUA with pre-decorrelation employing MRC
  Equalization

• Significant Performance Improvement
• Transmission Efficiency of 32/3494.2

Number of paths3, K32, L32, SNR7dB
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Conclusions

• In Conventional Systems Energy Inherent in the
  System is Wasted due to Data-Code Misalignment
• Part of the Existent Interference can be
  Exploited to Enhance the Received SINR
• By Optimizing the Code Allocation Amongst the
  Users with CUA the Constructive Component of
  Interference can be Maximized
• Improved Received SINR without Transmitted
  per-User Energy Increase
• Application of CUA can Enhance the Performance of
  a Number of Conventional MultiUser Precoding and
  Detection Schemes
• The Dependency on SI Detection Limits the CUA
  Overall Performance for Low Transmitted SNR
• For High SNR Values Performance Improvement of an
  Order of Magnitude is Attained

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Thank you

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