User's Manual

Ver.
CHAPTER 2. System Overview
2600-00FKQFGA2
1.0
Resource Allocation and Scheduling
To support multiple accesses, the 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 the eNB to communicate with multiple UEs
simultaneously.
The eNB 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 eNB 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. In addition, to reduce interferences with other cells, the
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.
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 64QAM. 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 eNB 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.
© SAMSUNG Electronics Co., Ltd.
page 17 of 72