System Description

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Chapter 2 SOL230 Overview

SOL230 System Description v1.0 11

the wireless channel, the system modulates and transmits it on a specific high

frequency bandwidth.

For the data received over the uplink from UE through a wireless channel, the

SmallCell demodulates and changes it to the baseband signal to perform decoding.

Resource Allocation and Scheduling

To support multiple accesses, the SmallCell uses OFDMA for downlink and SC-

FDMA for uplink. By allocating the two-dimensional resources of time and

frequency to multiple UEs without overlay, both methods enable the SmallCell to

communicate with multiple UEs simultaneously.

The SmallCell can mux multiple UE information for the control channel and

allocate signals from multiple UEs to the same time and frequency resources,

which is the orthogonal resource allocation method using the cyclic shift function

of the Zadoff-Chu sequence. 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 the SmallCell allocates resources to maximize the overall

throughput of the cell by considering the channel environment of each UE, the

data transmission volume required, and other QoS elements.

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.

In particular, the Modulation and Coding Scheme (MCS) is used for changing the

modulation method and channel coding rate according to the channel status. If the

channel environment is good, the MCS increases the number of transmission bits

per symbol using a high-order modulation, such as 64 QAM. If the channel

environment is bad, it uses a low-order modulation, such as QPSK and a low

coding rate to minimize channel errors.

In addition, in the environment where MIMO mode can be used, the SmallCell

operates in MIMO mode to increase the peak data rate of subscribers and can

greatly increase the cell throughput.

If the channel information obtained is incorrect or modulation method of higher

order or higher coding rate than the given channel environment is used, errors may

occur.

In such cases, the errors can be corrected by the HARD function.

H-ARQ

The Hybrid Automatic Repeat Request (H-ARQ) is a retransmission method in the

physical layer, which uses the stop-and-wait protocol. The SmallCell provides the

H-ARQ function to retransmit or combine frames in the physical layer so that the

effects of wireless channel environment changes or interference signal level

changes can be minimized, which results in throughput improvement.

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