LTE Signaling
R&S
®
CMW-KM5xx/-KS5xx
34
User Manual 1173.9628.02 ─ 16
2.2.10.2
Physical Channel Overview
A downlink physical channel corresponds to a set of resource elements carrying infor-
mation originating from higher layers. Physical channels can be either broadcast chan-
nels or shared channels. Dedicated channels are not used for LTE.
Broadcast channels carry messages that are not directed at a particular UE; they are
point-to-multipoint channels. Shared channels are shared by several UEs. At a given
time, a shared channel is assigned to one UE only, but the assignment can change
within a few timeslots.
An overview of the physical channels of the generated downlink signal is given in the
following table.
Physical DL Channel
Purpose / Type / Modulation Scheme
Physical Broadcast Channel (PBCH)
Provides physical layer information of the cell to be read during
cell search, e.g. system bandwidth, number of transmit anten-
nas, reference signal transmit power
Broadcast; QPSK
Physical Control Format Indicator Chan-
nel (PCFICH)
Carries information about PDCCH format (number of OFDM
symbols in the beginning of a subframe used for PDCCH)
Broadcast; QPSK
Physical Hybrid ARQ Indicator Channel
(PHICH)
Carries ACK/NACK indicators for uplink packets
Shared; QPSK
Physical Downlink Control Channel
(PDCCH)
Carries UE-specific control information, i.e. scheduling infor-
mation or UL power control commands
Shared; QPSK
Physical Downlink Shared Channel
(PDSCH)
Carries user data
Shared; QPSK, 16-QAM or 64-QAM
2.2.10.3
Physical Signal Overview
A downlink physical signal corresponds to a set of resource elements carrying informa-
tion originating from the physical layer. Two types of downlink physical signals are
available: Reference signals and synchronization signals.
Physical DL Signal
Purpose
Reference Signal (RS)
Enables channel estimation
Primary Synchronization Signal (PSS)
Secondary Synchronization Signal (SSS)
Provides acquisition of cell timing and cell identity during cell
search
2.2.11 MIMO and Beamforming
Multiple Input Multiple Output (MIMO) systems are essential for the LTE downlink in
order to achieve the specified throughput and spectral efficiency requirements. The
term MIMO refers to the use of multiple antennas at transmitter side (input to radio
General Description
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