User's Manual

Confidential
Chapter 2 LTE eNB Overview
LTE eNB System Description v2.0 16
Copyright © 2017, All Rights Reserved.
system, MBSFN reference signal of MBSFN sub-frame in addition to the cell-
specific reference signal and UE-specific reference signal used by the existing
unicast. These both reference signals are used to estimate the downlink physical
channel by inserting the reference symbols that can be recognized by the reception
layer MBSFN reference signal.
The MBSFN reference signal is provided in 15 MHz subcarrier spacing in case of
extended CP to antenna port number 4.
Channel Encoding/Decoding
The eNB is responsible for channel encoding/decoding to correct the channel
errors that occurred on a wireless channel. In LTE, the turbo coding and the 1/3
tail-biting convolutional coding are used. Turbo coding is mainly used for
transmission of large data packets on downlink and uplink, while convolutional
coding is used for control information transmission and broadcast channel for
downlink and uplink.
Modulation/Demodulation
In case of data received over downlink from the upper layer, eNB processes it
through baseband of the physical layer and transmits it via a wireless channel.
At this time, to transmit a baseband signal as far as it can go via the wireless
channel, the system modulates and transmits it on a specific high frequency
bandwidth.
In case of data received over uplink from UE through a wireless channel, eNB
demodulates and changes it to baseband signal to perform decoding.
Resource Allocation and Scheduling
To support multiple accesses, eNB uses OFDMA for downlink and SC-FDMA for
uplink. By allocating the 2-dimensional resources of time and frequency to
multiple UEs without overlay, both methods enable eNB to communicate with
multiple UEs simultaneously.
When eNB operates in MU-MIMO mode, the same resource also may be used for
multiple UEs simultaneously. Such allocation of cell resources to multiple UEs is
called scheduling, and each cell has its own scheduler for this function.
The LTE scheduler of eNB allocates resources to maximize the overall throughput
of the cell by considering channel environment of each UE, the data transmission
volume required, and other QoS elements. In addition, to reduce interferences with
other cells, eNB can share information with the schedulers of other cells over the
X2 interface.
Link Adaptation
The wireless channel environment can become faster or slower, better or worse
depending on various factors. The system is capable of increasing the transmission
rate or maximizing the total cell throughput in response to the changes in the
channel environment, and this is called link adaptation.