Journal of the Institute of Electronics Engineers of Korea TC (대한전자공학회논문지TC)

The Institute of Electronics and Information Engineers (대한전자공학회)
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Space-Time Concatenated Convolutional and Differential Codes with Interference Suppression for DS-CDMA Systems

간섭 억제된 DS-CDMA 시스템에서의 시공간 직렬 연쇄 컨볼루션 차등 부호 기법

  • Yang, Ha-Yeong (University of Sydney, School of Electrical and Information Engineering) ;
  • Sin, Min-Ho (Dept.of Electric Electronics Engineering, Yonsei University) ;
  • Song, Hong-Yeop (Dept.of Electric Electronics Engineering, Yonsei University) ;
  • Hong, Dae-Sik (Dept.of Electric Electronics Engineering, Yonsei University) ;
  • Gang, Chang-Eon (Dept.of Electric Electronics Engineering, Yonsei University)
  • Published : 2002.01.01
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Abstract

A space-time concatenated convolutional and differential coding scheme is employed in a multiuser direct-sequence code-division multiple-access(DS-CDMA) system. The system consists of single-user detectors (SUD), which are used to suppress multiple-access interference(MAI) with no requirement of other users' spreading codes, timing, or phase information. The space-time differential code, treated as a convolutional code of code rate 1 and memory 1, does not sacrifice the coding efficiency and has the least number of states. In addition, it brings a diversity gain through the space-time processing with a simple decoding process. The iterative process exchanges information between the differential decoder and the convolutional decoder. Numerical results show that this space-time concatenated coding scheme provides better performance and more flexibility than conventional convolutional codes in DS-CDMA systems, even in the sense of similar complexity Further study shows that the performance of this coding scheme applying to DS-CDMA systems with SUDs improves by increasing the processing gain or the number of taps of the interference suppression filter, and degrades for higher near-far interfering power or additional near-far interfering users.

다중 사용자 DS-CDMA 시스템에서 더 좋은 성능을 얻고자 컨볼루션 부호와 시공간 차등 부호의 직렬 연쇄 구조를 제안한다. 본 논문에서 시스템은 다중 접속 간섭(MAI ; Multiple-access Interference) 를 억제하기 위해 다른 사용자의 확산 코드, 동기, 그리고 전력 정보 등을 필요로 하지 않는 단일 사용자 검파기(SUD : Single User Detection) 를 고려한다. 채널 부호로 사용된 부호화율 1 과 메모리 수 1 을 가지는 차등 부호는 부호화로 인한 효율 저하를 가져오지 않으며 최소 상태수를 가지게 된다. 그리고 시공간 블록 부호를 통해 다중 안테나로 인한 다이버시티 이득을 얻게 된다. 이러한 시공간 직렬 연쇄 컨볼루션 차등 부호를 복호함에 있어서 서로간의 정보를 교환하는 반복 복호 처리를 이용한다. 실험 결과로부터 본 시공간 연쇄 부호 기법이 DS-CDMA 시스템에서 기존의 컨볼루션 부호보다 유사한 복잡도에서 더 나은 성능과 유연성을 제공함을 알 수 있다. 또한 제안한 기법이 SUD를 하는 DS-CDMA 시스템에 적용될 때, 처리이득(PG : Processing Gain) 이나 간섭 억제 여파기의 탭 개수의 증가에 따라 성능 향상이 일어나며, 원근 간섭 전력 문제가 심한 경우에 성능 저하가 일어남을 알 수 있다.

Keywords

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