SC-FDMA for 3GPP LTE uplink. Hong-Jik Kim, Ph. D.

Transcription

1 SC-FDMA for 3GPP LTE uplink, Ph D

2 Wireless Broadband The New Category Mobil ile Local Area Fixe ed Cellular Cordless POTS UMTS / WCDM A HSDPA 3GPP LTE Wireless Broadband 1xEV-DO WiMAX 80216e WiFi n a/b/g WiMAX 80216d NG DSL / Cable / DSL / DLC Fiber Voice & Messaging Broadband Existing Rollout

3 3GPP Standard 2G 2,5G 3G 3,5G 4G? Japan PDC Europe GSM GPRS WCDMA HSDPA R99 Rel 5 HSUPA Rel 7 Rel 6 Rel 6 LTE North America TDMA EDGE DL Shared CH HARQ AMC UL Shared CH HARQ AMC Multi-Carrier DL MIMO OFDMA DL/UL MIMO 3

4 3GPP LTE objectives > Scalable bandwidth : 125, 25, 5, 10, (15), 20MHz > Peak data rate (scaling linearly with the spectrum allocation) DL (2 UE) : 100Mb/s for 20MHz spectrum allocation UL (1 UE) : 50Mb/s for 20MHz spectrum allocation > Spectrum efficiency DL : 3-4 times HSDPA for MIMO (2,2) UL : 2-3 times HSUPA for MIMO(1,2) > Reference Antenna configurations (targets) DL : 2Tx and 2 Rx UL : 1 Tx and 2 Rx > Latency C-plane : < ms to establish U-plane U-plane : < 10ms from UE to server > Capacity 200 users for 5MHz, 400 users in larger spectrum allocations (active state) > Mobility LTE is optimised for low speeds 0-15km/h but mobility is maintained for speeds up to 350km/h 4

5 OFDMA Nu Nc Nc Np+Nc Bit Stream Constellation mapping S/P converter Symbol to Nc-point Subcarrier IFFT Cyclic P/S Mapping Prefix converter > 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 5

6 OFDM / MIMO > OFDM robust in dense environments > OFDM / MIMO perfect long term marriage > Achieves considerable increase in capacity, peak rates & coverage Multi-Element Transmitter A B C Tx Encode er 1 N T na Tx Anten Space-Time QAM Symbol Symbol MIMO Channel Matrix, H t 0 t 1 t 2 Space-Time Codeword 1 N R Decoder Rx Multi-Element Receiver A B C 25GHz, 10MHz,TDD OFDMA MIMO (Tx:Rx) 1x1 1x2 2x2 2x4 4x2 4x4 Bits/Sec/Hz/Sector Cornerstone Technology for WiMAX, 3GPP LTE, 3GPP2 Evol and Practical Deployments with 2X4 Configurations Cable &Antenna Solutions 6

7 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 user diversity (frequency domain scheduling) transmit signal similar to narrowband single-carrier > MMSE equalization to restore code orthogonality 7

8 UL: Interleaved FDMA (IFDMA) 2π j kt T e can be used by different users comb-shaped spectrum > Also known as distributed SC-FDMA > 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 (eg MMSE) 8

9 Localized vs Distributed 5/4 = 125 MHz Localized Less frequency diversity Higher FER for narrowband users Time domain channel has larger power fluctuations Difficult to choose appropriate MCS due to rapid channel fluctuations Less accurate power control Low-rate user may block a high-rate (broadband) user from the channel, especially if channel dependent scheduling is used Narrowband filter has longer impulse response reduces effective CP length (IFDMA only) Channel estimation not degraded at low bandwidths 5 MHz Distributed, RF = 4 Larger frequency diversity Low-rate and high-rate h users coexist peacefully Time domain channel has less power fluctuation More stable MCS selection More accurate power control Channel estimation becomes degraded for very large repetition factors Tighter frequency synchronization may be required 9

10 Frame structure 1 sub-frame = 05 msec CP LB#1 CP SB CP LB #2 CP LB #3 CP LB #4 CP LB #5 CP SB CP #1 #2 LB#6 > 1 sub-frame = 05ms 6 LB (Long Block) for user / control data transfer 2SB(Sh (Short tblock) k)for pilot t/ control ldata transfer 10

11 Cluster structure, Localized FDMA 10 data sub-carriers + 5 pilot sub-carriers 1 short block 1 long block 1 TTI Data sub-carrier Pilot sub-carrier Unobserved sub-carrier, short blocks 11

12 Cluster structure, Interleaved FDMA 10 data sub-carriers + 5 pilot sub-carriers per user 1 TTI Data sub-carrier of user 1, 2,3,4 Pilot sub-carrier of user 1, 2,3,4 Unobserved sub-carrier carrier, short blocks 12

13 Simulation Parameters Frequency hopping used on a TTI basis MCS: QPSK rate ¼, ½, ¾ & 16 QAM rate ½, ¾ 1 transmit, 2 receive antennas (uncorrelated) ITU PB channel@3 km/hr One turbo block per TTI TTI=05ms Both ideal and estimated channel running side by side Pilot overhead: 1/7 Sampling Rate = MHz (=4*3 384MHz) Pilot power boost = 3dB (ie pilot signal amplitude = sqrt(2)*data signal amplitude), QPSK modulation with constant modulus in the frequency domain 13

14 Results for LocFDMA, v=3km/h 10 0 LocFDMA, v=3km/h 10-1 BL LER -2 QPSK 1/4, Perfect IR 10 QPSK 1/4 QPSK 1/2, Perfect IR QPSK 1/2 QPSK 3/4, Perfect IR QPSK 3/4 16QAM 1/2, Perfect IR 16QAM 1/2 16QAM 3/4, Perfect IR 16QAM 3/ SNR 14

15 Results for IFDMA, v=3km/h ifdma, v=3km/h BLER QPSK 1/4, Perfect IR QPSK 1/4 QPSK 1/2, Perfect IR QPSK 1/2 QPSK 3/4, Perfect IR QPSK 3/4 16QAM 1/2, Perfect IR 16QAM 1/2 16QAM 3/4, Perfect IR 16QAM 3/ SNR 15

16 ifdma/locfdma with real channel estimation, v=3km/h SUBBAND/DIVERSITY, Estimated channel, v=3km/h BLER 10-2 ifdma QPSK 1/4 LocFDMA QPSK 1/4 ifdma QPSK 1/2 LocFDMA QPSK 1/2 ifdma QPSK 3/4 LocFDMA QPSK 3/4 ifdma 16QAM 1/2 LocFDMA 16QAM 1/2 ifdma 16QAM 3/4 LocFDMA 16QAM 3/ SNR 16

17 Thank you