OFDM(A) Competence Development – Part IV

OFDM(A) Competence Development – Part IVPer Hjalmar Lehne, Frode Bøhagen, Telenor R&I

R&I seminar, 23 January 2008, Fornebu, Norway

[email protected]

[email protected]

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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

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OFDMA Radio Planning

• No difference in the principal planning procedure compared to GSM and UMTS

• Steps in a planning procedure:

1. Find the input parameters

2. Define cell edge quality

3. Calculate coverage

4. Calculate capacity

Define edge quality

Coverage

Capacity

Done

Input parameters: power frequency reuse

scheme etc…

Results: Path loss Cell range

Results: Cell capacity Throughput

distributions

If coverage or capacity do not meet requirements

Subcarrier orthogonality => OFDMA planning has more resemblance with GSM planning than UMTS planning

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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

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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

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Reuse Factor = 3

• Increased spatial separation between co-channels

– Eliminates CCI at the sector boundaries

– Significantly decreases CCI between neighbour cells

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Fractionally Frequency Reuse

• Procedure

1. Users are designated into multiple classes (e.g. cell centre and cell edge)

2. Different frequency resources are assigned for different user classes

3. Transmissions across BSs and sectors are coordinated so that maximal interference avoidance is achieved

f1 f2 f3

frequency

f1+ f2+ f3

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• Time coordination

• Power coordination

• Result: Frequency reuse factor between 1 and 3

Fractionally Frequency Reuse

PreambleCentre cell

with FRF =1Whole cell

with FRF =3Centre cell

with FRF =1Whole cell

with FRF =3

DL subframe UL subframe

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Link budget

• Studying OFDMA link budgets reveals

– No big surprises

– Interference margins between 1-6 dB suggested

• Example: E-UTRA link budget (outdoor)

Uplink DownlinkData rate kbps 64,0 Data rate Mbps 1,0

Transmitter - UE Transmitter - Node Ba Max. TX power dBm 24,0 a HS-DSCH power dBm 46,0b TX antenna gain dBi 0,0 b TX antenna gain dBi 18,0c Body loss dB 0,0 c Cable loss dB 2,0d EIRP dBm 24,0 =a + b - c d EIRP dBm 62,0 =a + b - c

Receiver - Node B Receiver - UEe Node B noise figure dB 2,0 e UE noise figure dB 7,0f Thermal noise dBm -118,4 = k(Boltzmann) x T(290K) x B(360kHz) f Thermal noise dBm -104,5 = k(Boltzmann) x T(290K) x B(9MHz)g Receiver noise floor dBm -116,4 =e + f g Receiver noise floor dBm -97,5 =e + fh SINR dB -7,0 From simulation (Nokia) h SINR dB -10,0 From simulation (Nokia)i Receiver sensitivity dBm -123,4 =g + h i Receiver sensitivity dBm -107,5 =g + hj Interference margin dB 2,0 j Interference margin dB 3,0k Cable loss dB 2,0 k Control channel overheaddB 1,0l RX antenna gain dBi 18,0 l RX antenna gain dBi 0,0m MHA gain dB 2,0 m Body loss dB 0,0

Maximum path loss dB 163,4 =d - i - j + k + l - m Maximum path loss dB 165,5 =d - i - j + k + l - m

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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