Wireless Broadband – The New Category
3GPP Standard
3GPP LTE objectives
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Scalable bandwidth : 1.25, 2.5, 5, 10, (15), 20MHz
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Peak data rate (scaling linearly with the spectrum allocation)
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DL (2 Rx @ UE) : 100Mb/s for 20MHz spectrum allocation
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UL (1 Tx @ UE) : 50Mb/s for 20MHz spectrum allocation
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Spectrum efficiency
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DL : 3-4 times HSDPA for MIMO (2,2)
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UL : 2-3 times HSUPA for MIMO(1,2)
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Reference Antenna configurations (targets)
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DL : 2Tx and 2 Rx
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UL : 1 Tx and 2 Rx
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Latency
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C-plane : < 50-100ms to establish U-plane
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U-plane : < 10ms from UE to server
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Capacity
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200 users for 5MHz, 400 users in larger spectrum allocations (active state)
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Mobility
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LTE is optimised for low speeds 0-15km/h but mobility is maintained for speeds up to 350km/h
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OFDMA
High PAPR
• Need for PAPR reduction scheme especially for UL
> Various mappings from Nu data symbols to Nu subcarriers among Nc subcarriers
>Receiver is based on FFT
OFDM / MIMO
> OFDM – robust in dense environments
> OFDM / MIMO perfect long term marriage
> Achieves considerable increase in capacity, peak rates & coverage
UL: Single Carrier (SC)-FDMA
> DFT-spreading of data symbols in frequency domain
> Low PAPR
> Subcarrier mapping
• Distributed mapping
• Frequency diversity
• Transmit signal similar to IFDMA
• Localized mapping
• Multi-user diversity (frequency domain scheduling)
• transmit signal similar to narrowband single-carrier
> MMSE equalization to restore code orthogonality
UL: Interleaved FDMA (IFDMA)
> known as distributed SC-FDMA
Also SC > Hybrid of single-carrier and OFDM concepts
• Low PAPR (same as single carrier)
> Orthogonal uplink as each user is assigned set of sub-carriers orthogonal
to other users
> Receiver is based on FDE (e.g. MMSE).
Localized vs. Distributed
Frame structure
> sub-frame = 0.5ms
• 6 LB (Long Block) for user / control data transfer
• 2 SB (Short Block) for pilot / control data transfer
Cluster structure, Localized FDMA
Cluster structure, Interleaved FDMA
Simulation Parameters
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Frequency hopping used on a TTI basis
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MCS: QPSK rate ¼, ½, ¾ & 16 QAM rate ½, ¾
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1 transmit, 2 receive antennas (uncorrelated)
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ITU PB channel@3 km/hr
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One turbo block per TTI
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TTI=0.5ms
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Both ideal and estimated channel running side by side
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Pilot overhead: 1/7
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Sampling Rate = 15.359 MHz (=4*3.84MHz)
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Pilot power boost = 3dB (i.e. pilot signal amplitude = sqrt(2)*data signal amplitude), QPSK modulation with constant modulus in the frequency domain.
Results for Loc.FDMA, v=3km/h
Results for IFDMA , v=3km/h
iFDMA/Loc.FDMA with real channel estimation , v=3km/h
