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Cellular Networks and Mobile Computing COMS 6998-8, Spring 2012. Instructor: Li Erran Li ( lierranli@cs.columbia.edu ) http:// www.cs.columbia.edu /~coms6998-8 / 1 /30/ 2012: Cellular Networks : LTE. Outline. Air interface Architecture. Cellular Comms Evolution. LTE.

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cellular networks and mobile computing coms 6998 8 spring 2012

Cellular Networks and Mobile ComputingCOMS 6998-8, Spring 2012

Instructor: Li Erran Li (lierranli@cs.columbia.edu)

http://www.cs.columbia.edu/~coms6998-8/

1/30/2012: Cellular Networks: LTE

outline
Outline
  • Air interface
  • Architecture

Cellular Networks and Mobile Computing (COMS 6998-8)

cellular comms evolution
Cellular Comms Evolution

LTE

  • 3GPP – collaboration for 3G based on GSM
  • 3GPP2 – collaboration for 3G based on IS-95
lte phy basics
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
frame structure
Frame Structure

Frame Structure Type 1 (FDD)

Frame Structure Type 2 (TDD)

resource grid

:

:

Resource grid

One downlink slot, Tslot

  • 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

Resource block

Transmission BW

Resource element

12subcarriers

l=0

l=6

2 d time and frequency grid
2-D time and frequency grid

#19

#18

#17

#16

1 radio frame = 10 msec (307200 x Ts)

Time

#5

#4

#3

#2

Sub-frame

#1

NscRB subcarriers (=12)

#0

Power

1 slot = 0.5 msec

Frequency

NBWDL subcarriers

dl phy channels and signals
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

QPSK

16QAM

64QAM

P-SCH - Primary Synchronization Signal

S-SCH - Secondary Synchronization Signal

PBCH - Physical Broadcast Channel

PDCCH -Physical Downlink Control Channel

PDSCH - Physical Downlink Shared Channel

Reference Signal – (Pilot)

Time

Frequency

DL Channel Mapping
ul phy signals and channels
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 mapping

PUSCHDemodulation Reference Signal(for PUSCH)

PUCCH

Demodulation Reference Signal(for PUCCH format 0 or 1, Normal CP)

UL Channel Mapping

64QAM16QAMQPSK

QPSK

BPSK

Time

Frequency

mimo in lte
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
orthogonal rs locations
Orthogonal RS locations
  • channel matrix needs to be known in advance for equalization