Cellular Networks and Mobile ComputingCOMS 6998-8, Spring 2012
Instructor: Li Erran Li ([email protected])
http://www.cs.columbia.edu/~coms6998-8/1/30/2012: Cellular Networks: LTE
Cellular Networks and Mobile Computing (COMS 6998-8)
2
Outline
• Air interface• Architecture
1/23/12
Cellular Comms Evolution
• 3GPP – collaboration for 3G based on GSM
• 3GPP2 – collaboration for 3G based on IS-95
GSM GPRS EDGE
WCDMA HSPA HSPA+
TD-SCDMA
TD-HSPA
TD-HSPA+
LTE
IS-95 CDMA2000 EV-DO
LTE PHY Basics
• Six bandwidths– 1.4, 3, 5, 10, 15, and 20 MHz
• Two modes – FDD and TDD
• 100 Mbps DL (SISO) and 50 Mbps UL• Transmission technology– OFDM for multipath resistance– DL OFDMA for multiple access in frequency/time– UL SC-FDMA to deal with PAPR ratio problem
Resource grid
• 6 or 7 OFDM symbols in 1 slot
• Subcarrier spacing = 15 kHz
• Block of 12 SCs in 1 slot = 1 RB– 0.5 ms x 180 kHz– Smallest unit of allocation
6 or 7 OFDM symbols
One downlink slot, Tslot
:
:
Transmission BW
Resource block
Resource element
l=0 l=6
12 subcarriers
2-D time and frequency grid
Time
Frequency
1 radio fra
me = 10 mse
c (307200 x
Ts)
#0#1
#2#3
#4#5
#19#18
#17#16
Sub-fr
ame
NBWDL subcarriers
NscRB subcarriers (=12)
Pow
er
1 slo
t =
0.5 m
sec
DL PHY Channels and Signals
• Signals: generated in PHY layers– P-SS: used for initial sync– S-SS: frame boundary determination– RS: pilots for channel estimation and tracking
• Channels: carry data from higher layers– PBCH: broadcast cell-specific info– PDCCH: channel allocation and control info– PCFICH: info on size of PDCCH– PHICH: Ack/Nack for UL blocks– PDSCH: Dynamically allocated user data
DL Channel Mapping
•
64QAM16QAM QPSK
Frequency
Time
P-SCH - Primary Synchronization SignalS-SCH - Secondary Synchronization SignalPBCH - Physical Broadcast ChannelPDCCH -Physical Downlink Control ChannelPDSCH - Physical Downlink Shared ChannelReference Signal – (Pilot)
UL PHY Signals and Channels
• Signals: generated in the PHY layer– Demodulation RS : sync and channel estimation– SRS: Channel quality estimation
• Channels: carry data from higher layers– PUSCH: Uplink data– PUCCH: UL control info– PRACH: Random access for connection
establishment
UL Channel MappingPUSCHDemodulation Reference Signal(for PUSCH)PUCCHDemodulation Reference Signal(for PUCCH format 0 or 1, Normal CP)
64QAM16QAMQPSK
QPSKBPSK
Frequency
Time
MIMO in LTE
• Rel 8 defines MIMO only for DL• 1, 2 and 4 transmit antennas defined for– Transmit Diversity (TxDiv)– Spatial Multiplexing (SpMux)
• Control channels undergo TxDiv based on SFBC• Data channels may undergo TxDiv or SpMux