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- LTE (E-UTRA) Essentials

LTE (E-UTRA) Air Interface Capabilities

Bandwidth support
• Flexible from 1.4 MHz to 20 MHz
Waveform
• OFDM in Downlink / SC-FDM in Uplink
Duplexing mode
• FDD: full-duplex (FD) and half-duplex (HD)
• TDD
Modulation orders for data channels
• Downlink: QPSK, 16QAM, 64QAM
• Uplink: QPSK, 16QAM, 64QAM
MIMO support
• Downlink: SU-MIMO and MU-MIMO (SDMA)
• Uplink: SDMA

UE eNodeB Communication Link

Single (and same) link of communication for DL & UL
Effectively:
• DL serving cell = UL serving cell
• No UL or DL macro-diversity
– UL softer HO reception is an implementation choice
– UE’s “Active Set” size = 1
• Hard-HO-based mobility
– RACH-based mobility procedure to target cell
– Network controlled by default
– UE initiated under RL failure condition
• Load indicator for inter-cell load control

– Transmitted over X2 interface

E-UTRA Air Interface Peak Data Rates

Downlink
• ~300 Mbps in 20 MHz
• Assumptions:
– 4 stream MIMO
– 14.29% Pilot overhead
(4 TX antennas)
– 10% common channel
overhead
􀂋 Note that this overhead
level is adequate to serve
1 UE/subframe.
– 6.66% waveform overhead
(CP + window)
– 10% guard band
– 64QAM code rate ~1

Uplink
• ~75 Mbps in 20 MHz
• Assumptions:
– 1 TX antenna
– 14.3% Pilot overhead
– 0.625% random access
overhead
– 6.66% waveform overhead
(CP + window)
– 10% guard band
– 64QAM code rate ~1

Time Domain Organization

Radio Frame has two Structures:
• Type 1 (FS1) for FDD DL/UL
• Type 2 (FS2) for TDD

This presentation deals only with FS1










Time Domain Organization
Basic unit of time Ts, defined with relation to 20 MHz, 15 KHz inter-subcarrier separation and
2048 FFT size (36.211)
Ts = 1/(15e3*2048) = 32.55 ns 􀃆 Number of samples in 10 ms is 10 ms/32.55 ns=307200
Tf = 307200Ts = 10 ms
Tslot = (307200/20)Ts = 15360Ts
􀁺 Half radio frame = 5 ms
– Contains one sync channel instance
– Tailoring efficient HO from GSM
􀁺 Radio frame = 10 ms
– Periodicity of sync channel
􀁺 PBCH TTI = 40 ms

– Periodicity of primary broadcast channel

Frequency Domain Organization

LTE DL/UL air interface waveforms use a number of orthogonal subcarriers to
send user traffic data, Reference Signals (Pilots), and Control Information.













Channel Bandwidth and Transmission Bandwidth
More information can be found in TS36.101.
􀁺 OFDM uses all the sub carriers for a single user, whereas OFDMA uses different sub carriers
for different users.
􀁺 There are different types of sub carriers: Data, Pilot, Control, Null, etc.
􀁺 There are two guard bands at the edges of the OFDM/OFDMA-signal (no RF transmission in
these sub carriers). Each guard band exists to avoid interference with adjacent bands.
􀁺 Taking into account the guard band sub carriers and the DC sub carrier, the number of
available sub carriers is as shown in the table.

UL/DL Resource Grid Definitions

Resource Element (RE)   
• One element in the time/frequency
resource grid
– One subcarrier in one OFDM/LFDM
symbol for DL/UL
Resource Block (RB)
• Minimum scheduling size for
DL/UL data channels
• Physical Resource Block (PRB)
– 180 kHz x 0.5 ms
􀂋 12 subcarriers x 1 slot for
15 kHz subcarrier spacing
􀂋 24 subcarriers x 1 slot for
7.5 kHz subcarrier spacing