System Description

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Chapter 2 SOL230 Overview

SOL230 System Description v1.0 10

For uplink SC-FDMA, which is similar to OFDMA modulation and demodulation,

a 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 SmallCell can reduce the

power consumption of the UE.

Downlink Reference Signal Creation and Transmission

The UE must estimate the downlink channel to perform coherent demodulation on

the downlink physical channel in the LTE system. The LTE uses OFDM/OFDMA-

based methods for transmission, making it possible to estimate the channel by

inserting the reference symbols from the receiving terminal into the grid for each

time and frequency. These reference symbols are called downlink reference signals;

there is one type of reference signals defined in 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 SmallCell. 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 SmallCell.

Channel Encoding/Decoding

The SmallCell 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. The 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 SmallCell

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

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