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OFDM(A) Competence Development – Part IV

OFDM(A) Competence Development – Part IV. Per Hjalmar Lehne, Frode Bøhagen , Telenor R&I R&I seminar, 23 January 2008, Fornebu, Norway Per-hjalmar.lehne@telenor.com Frode.bohagen@telenor.com. Outline. Part I: What is OFDM? Part II: Introducing multiple access: OFDMA, SC-FDMA

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OFDM(A) Competence Development – Part IV

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  1. OFDM(A) Competence Development – Part IV Per Hjalmar Lehne, Frode Bøhagen, Telenor R&I R&I seminar, 23 January 2008, Fornebu, Norway Per-hjalmar.lehne@telenor.com Frode.bohagen@telenor.com

  2. Outline • Part I: What is OFDM? • Part II: Introducing multiple access: OFDMA, SC-FDMA • Part III: Wireless standards based on OFDMA • Part IV: Radio planning of OFDMA OFDM Competence Development

  3. OFDMA Radio Planning • No difference in the principal planning procedure compared to GSM and UMTS • Steps in a planning procedure: • Find the input parameters • Define cell edge quality • Calculate coverage • Calculate capacity • Input parameters: • power • frequency reuse scheme • etc… Define edge quality If coverage or capacity do not meet requirements Coverage • Results: • Path loss • Cell range • Results: • Cell capacity • Throughput distributions Capacity Subcarrier orthogonality => OFDMA planning has more resemblance with GSM planning than UMTS planning Done OFDM Competence Development

  4. Frequency Reuse • Frequency reuse is a source to co-channel-interference (CCI) • Traditional GSM planning uses relatively large FRF (Example: FRF = 7) • For new OFDMA systems smaller FRFs are suggested (typical FRFs of 1 or 3) Smaller FRF => Inter cell interference for OFDMA systems closer to UMTS than GSM OFDM Competence Development

  5. Reuse Factor = 1 • Referred to as universal frequency reuse • Reuse 1 => always highest spectral efficiency • Usually combined with interference randomization • Frequency hopping • Frequency domain scrambling OFDM Competence Development

  6. Reuse Factor = 3 • Increased spatial separation between co-channels • Eliminates CCI at the sector boundaries • Significantly decreases CCI between neighbour cells OFDM Competence Development

  7. f1 f2 f3 frequency Fractionally Frequency Reuse • Procedure • Users are designated into multiple classes (e.g. cell centre and cell edge) • Different frequency resources are assigned for different user classes • Transmissions across BSs and sectors are coordinated so that maximal interference avoidance is achieved f1+ f2+ f3 OFDM Competence Development

  8. DL subframe UL subframe Preamble Centre cell with FRF =1 Whole cell with FRF =3 Centre cell with FRF =1 Whole cell with FRF =3 Fractionally Frequency Reuse • Time coordination • Power coordination • Result: Frequency reuse factor between 1 and 3 OFDM Competence Development

  9. Link budget • Studying OFDMA link budgets reveals • No big surprises • Interference margins between 1-6 dB suggested • Example: E-UTRA link budget (outdoor) OFDM Competence Development

  10. Summary: OFDMA radio planning • No principal difference in radio planning for OFDMA compared to existing systems (WCDMA/TDMA/FDMA) • Interference properties of OFDMA • Limited inter-cell-interference due to orthogonal subcarriers (similar to GSM) • Large intra-cell-interference due to small FRF (similar to UMTS) • Interference margins suggested 1 - 6 dB • Fractionally frequency reuse suggested to trade off fairness with efficiency OFDM Competence Development

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