Bandwidth support
โข Flexible from 1.4 MHz to 20 MHz
Waveform
โข OFDM in Downlink / SC-FDM in Uplink
Duplexing mode
โข FDD: full-duplex (FD) and half-duplex (HD)
โข TDD
Modulation orders for data channels
โข Downlink: QPSK, 16QAM, 64QAM
โข Uplink: QPSK, 16QAM, 64QAM
MIMO support
โข Downlink: SU-MIMO and MU-MIMO (SDMA)
โข Uplink: SDMA
UE eNodeB Communication Link
Single (and same) link of communication for DL & UL
Effectively:
โข DL serving cell = UL serving cell
โข No UL or DL macro-diversity
โ UL softer HO reception is an implementation choice
โ UEโs โActive Setโ size = 1
โข Hard-HO-based mobility
โ RACH-based mobility procedure to target cell
โ Network controlled by default
โ UE initiated under RL failure condition
โข Load indicator for inter-cell load control
โ Transmitted over X2 interface
E-UTRA Air Interface Peak Data Rates
Downlink
โข ~300 Mbps in 20 MHz
โข Assumptions:
โ 4 stream MIMO
โ 14.29% Pilot overhead
(4 TX antennas)
โ 10% common channel
overhead
๔ Note that this overhead
level is adequate to serve
1 UE/subframe.
โ 6.66% waveform overhead
(CP + window)
โ 10% guard band
โ 64QAM code rate ~1
Uplink
โข ~75 Mbps in 20 MHz
โข Assumptions:
โ 1 TX antenna
โ 14.3% Pilot overhead
โ 0.625% random access
overhead
โ 6.66% waveform overhead
(CP + window)
โ 10% guard band
โ 64QAM code rate ~1
Time Domain Organization
Radio Frame has two Structures:
โข Type 1 (FS1) for FDD DL/UL
โข 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 ๔ Number of samples in 10 ms is 10 ms/32.55 ns=307200
Tf = 307200Ts = 10 ms
Tslot = (307200/20)Ts = 15360Ts
๔บ Half radio frame = 5 ms
โ Contains one sync channel instance
โ Tailoring efficient HO from GSM
๔บ Radio frame = 10 ms
โ Periodicity of sync channel
๔บ PBCH TTI = 40 ms
โ 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.
๔บ OFDM uses all the sub carriers for a single user, whereas OFDMA uses different sub carriers
for different users.
๔บ There are different types of sub carriers: Data, Pilot, Control, Null, etc.
๔บ 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.
๔บ 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)
โข One element in the time/frequency
resource grid
โ One subcarrier in one OFDM/LFDM
symbol for DL/UL
Resource Block (RB)
โข Minimum scheduling size for
DL/UL data channels
โข Physical Resource Block (PRB)
โ 180 kHz x 0.5 ms
๔ 12 subcarriers x 1 slot for
15 kHz subcarrier spacing
๔ 24 subcarriers x 1 slot for
7.5 kHz subcarrier spacing