User's Manual

Ver.
CHAPTER 2. System Overview
2600-00FKQFGA2
1.0
Discrete Fourier Transform (DFT) is applied to each subscriber in the modulation at the
transmitting side. An inverse Discrete Fourier Transform (IDFT) is applied for minimizing
the Peak to Average Power Ratio (PAPR) at the transmitting side, which allows continuous
allocation of frequency resources available for individual subscribers. As a result, the eNB
can reduce the power consumption of the UE.
Downlink Reference Signal Creation and Transmission
The UE must estimate the downlink channel to perform the coherent demodulation on the
physical channel in the LTE system. The LTE uses the OFDM/OFDMA-based methods for
transmitting and therefore the channel can be estimated by inserting the reference symbols
from the receiving terminal to the grid of each time and frequency. These reference
symbols are referred to as the downlink reference signal. The following reference signals
are defined for the LTE downlink.
 Cell-specific reference signal: The cell specific reference signal is transmitted to every
subframe across the entire bandwidth of the downlink cell. It is mainly used for
channel estimation, MIMO rank calculation, MIMO precoding matrix selection and
signal strength measurement for handover.
Downlink Synchronization Signal Creation and Transmission
The synchronization signal is used for the initial synchronization when the UE starts to
communicate with the eNB. There are two types of synchronization signals: Primary
Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS).
The UE can obtain the cell identity through the synchronization signal. It can obtain other
information about the cell through the broadcast channel. Since synchronization signals and
broadcast channels are transmitted in the 1.08 MHz range, which is right in the middle of
the cell’s channel bandwidth, the UE can obtain the basic cell information such as cell ID
regardless of the transmission bandwidth of the eNB.
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
For the data received over the downlink from the upper layer, the eNB processes it through
the baseband of the physical layer and then 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.
For the data received over the uplink from the UE through a wireless channel, the eNB
demodulates and changes it to the baseband signal to perform decoding.
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