Synchronization for the uplink of OFDMA-based System

Huan Cong Nguyen

Research output: Book/ReportPh.D. thesis

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Abstract

he Orthogonal Frequency Division Multiple Access (OFDMA) has recently emerged as one of the prime multiple access schemes for the future broadband wireless networks. In OFDMA, available subcarriers are grouped into subchannels, which are assigned to different users operating simultaneously. Preserving the orthogonality among these subchannels is essential, as it prevents the inter-carrier interference (ICI), which consequently eliminates multi-user interference (MUI).

While the orthogonality among subchannels can be maintained relatively easily in the downlink, keeping the orthogonality in the uplink is much more difficult. In the uplink, the received signal is the sum of multiple signals coming from different users, each experiences a independent carrier frequency offset (CFO) due  to oscillator instability and / or Doppler shift. Conventional CFO correction method used in the downlink are designed for single-user system, and therefore are not able to correct multiple CFOs in the uplink.

The aim of this thesis is to provide practical solutions  for the synchronization issues occurring in the uplink of the OFDMA-based broadband wireless systems.  Several data-aided CFO estimation algorithms are  proposed to achieve accurate measurements of the multiple  CFOs in different scenarios. Once the estimates are available, novel MUI cancellation schemes are introduced to mitigate the self- and cross-interference occurring due to multiple CFOs. Evaluation results show that the proposed schemes outperform the  existing techniques in literature with comparable
or even lower additional complexity.

Original languageEnglish
ISBN (Print)87-92078-44-3
Publication statusPublished - 2008
SeriesAalborg Universitetscenter. Institut for Elektroniske Systemer. Afdeling for Kommunikationsteknologi. Rapport
ISSN0908-1224

Keywords

  • OFDM
  • OFDMA
  • synchronization
  • frequency offset
  • 4G
  • 4G mobile communication systems
  • uplink

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