1 / 10

Content

Multi User Detection and Channel Estimation with Rotated Transforms for MC-CDMA Armin Dammann, Stefan Kaiser, Ronald Raulefs, Stephan Sand Institute of Communications and Navigation, DLR Oberpfaffenhofen Gunther Auer DoCoMo Eurolabs, Munich Zurich, 2nd July, 2003. Content.

sailor
Download Presentation

Content

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Multi User Detection and Channel Estimation with Rotated Transforms for MC-CDMAArmin Dammann, Stefan Kaiser,Ronald Raulefs, Stephan SandInstitute of Communications and Navigation, DLR OberpfaffenhofenGunther AuerDoCoMo Eurolabs, MunichZurich, 2nd July, 2003

  2. Content • Introduction of Rotated Transforms • How to extend the signal space efficiently for low modulation schemes • System Overview of the MC-CDMA System • Results for 4-QAM • Summary/Outlook

  3. 4 -4 -3 -2 -1 1 2 3 Rotated Transforms • Drawback of many orthogonal transforms is ambiguity in one subcarrier Number of sequences “per point”  Ambiguity • “Rotated Transforms” is an add-on technique to overcome this problem Construction: • Let j be the smallest rotation angle (rad), which maps the signal constellation (before spreading) onto itself (e.g. for BPSK: p; for QPSK: p/2) • A “Rotated Transform” is constructed by multiplying the kth data symbol by exp( j·j ·k/N ).

  4. Creation of Non- and Rotated Constellations im re Non-Rotated Rotated 1 -1 exp( j·p ·0/2 ) • 1 • 1 -1 • 1 • 1 -1 exp( j·p ·1/2 ) im 1 im re 1 -1 -2 -1 1 2 re -1

  5. im im re 4 -4 -3 -2 -1 1 2 3 re Comparison of Non- and Rotated Constellations BPSK, Walsh-Hadamard, N = 8

  6. 1 1 … p 1 S/P P/S Spread Rot … … L MOD p Source … OFDM + TG … … 1 … M Rot Spread Q … L Multipath Channel S S Maximum Likelihood Detector with channel state information (CSI) 1 p-1 1 P/S S/P Rot Desp CSI … DMOD p-1 Sink … -TG IOFDM … M Rot Q Desp System Model

  7. MLSE - Rotated • Independent Rayleigh Fading Channel • 4-QAM Modulation • Spreading Length 4 • (Non) Rotated • Uncoded • Perfect Channel Estimation

  8. MLSE - Rotated • 12-Tap Channel • Spreading Length 4 • 4 Active Users • 4-QAM Modulation • (Non) Rotated • Uncoded • Perfect or 2x 1-D Channel Estimation

  9. Summary • Rotated transform extends signal space efficiently • MLSE exploits this even for 4-QAM (3dB gain for full loaded system with 4 Users) • Performance gain applying rotated transforms increases very slightly for real channel estimation • Outlook • Include Coding • Limits for higher modulation schemes or large spreading sequences

  10. Creation of Non- and Rotated Constellations im BPSK alphabet re 1 -1 Rotating Rotated Non-Rotated im Spreading 1 im re 1 -1 -2 -1 1 2 re -1

More Related