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4. Dynamic Resource Allocation
Mobile communication systems exhibit significant variation in the
number of UEs in a given cell, and in their time-varying channel conditions.
Moreover, with the expansion
of mobile applications, different UE have
different requirements. Thus, resource allocation
became more complex as
flexibility and dynamicity is required, while
maintaining a resource and
energy efficient system. This is done using the scheduler, implemented in the
eNodeB in LTE, which allocates the available resource blocks according to
the UE’s need and condition. [10] [11] [13]
This chapter introduces the frame structure behind scheduling, and how
the current scheduler manages the resources between all active users. Finally,
MCS selection in LTE/NR 3GPP is explained in detail.
4.1. Frame Structure
In LTE, like several communication systems, data is exchanged in frames.
A radio frame, depicted in Fig. 11, is composed of 10 subframes each of 1
ms. This composition enables the synchronization
of data between the
eNodeB and the UE, where each transmitted packet contains the frame and
subframe number.
Fig. 11. Radio frame structure.
The fundamental transmission schemes are the same for DL and UL in LTE,
given that OFDM is used in the DL and SC-FDMA in the UL, with 15 kHz
subcarrier separation in both links.
Although both FDD and TDD operations
are supported in LTE, two
frame structures,
with the same frame length, are available due to the
differences between the TDD and FDD versions.
Frame 1
Frame 2
Frame 3
Frame 1
Subframe 1
Subframe 2
Subframe 3
Subframe 10
10 ms
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