الفهرس 
Long Term Evolution
Quadrature Amplitude ModulationOnly 14 pages are availabe for public view
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Abstract
Long Term Evolution (LTE), developed by Third Generation Partnership
Project (3GPP), is the access part of the Evolved Packet System (EPS). LTE
physical layer is based on Orthogonal Frequency Division Multiple Access
(OFDMA) with Quadrature Amplitude Modulation (QAM). Although there
have been lots of enhancements in the LTE physical layer, yet higher order
modulation schemes were not introduced in the specification until Release 12.
This thesis investigates the performance of LTE with 256-QAM. At the start
of this work, the 3GPP didn’t introduce higher order modulation scheme
(256-QAM) in LTE-A (LTE-Advanced) specification. It wasn’t until release
12.3 that such an enhancement has been introduced. Adopting a higher order
modulation scheme aims to enhance the spectral efficiency of the system and
increase the peak user data rates. This is one of the various aspects that targets
to fulfill the massively increasing demand in the transmitted data volume over
mobile networks.
When proposing higher order modulation to an existing standard, a question
arises regarding the efficiency of the transmission and whether the error
protection and correction techniques that are defined in the standard will have
the ability to mitigate the increased BER in the system. In addition, and in
light of this question, it is also needed to quantify the gain of the proposed
modification. Quantifying such gain is essential when making decisions of
investment in new systems.
The first part of the study is based on a MATLAB system model simulation.
Channel models that were tested included Additive White Gaussian Noise
(AWGN), Pedestrian B (PedB) and Vehicular A (VehA) channels, which are
ITU standardized modeling channels. Bit Error Rate (BER) values were
populated for the probable Signal to Noise Ratio (SNR) operating ranges. The
minimum required SNR for the operation of different Modulation and Coding
Schemes (MCS) was identified, having the criteria of achieving a maximum
of 10-6 BER for reliable transmission. In addition, a capacity and coverage
study has been conducted to quantify the cell capacity gain and the coverage
range for each modulation scheme.
Results demonstrate that LTE-A can adopt the 256-QAM higher order
modulation and have its main gain of enabling a 33% increase in the user’s
maximum allowed bit rate, although a relatively few users will be able to
enjoy this throughput upsurge. Nomadic users are more likely to enjoy the
enhanced user experience, although vehicular users have the privilege as well
in the case of facing good radio conditions that can be mapped to having good
v
coverage in a non-busy hour case to avoid exposure to high system
interference.
The analysis over the cell level has also shown that cell capacity gain reaches
up to 1.5%, while the cell coverage range and expected footprint falls in a
140m coverage area. The capacity gain is not high when inspected on a cell
level basis, where this is a consequence of the small coverage range. This
may stand as a challenging deal for operators who seek to enhance the user
experience while direct revenues (expected from the higher users
consumption rates, i.e due to their use of 256-QAM) may not cover the
incurred expected costs of the upgrades to LTE-A release 12.3.
It is thus recommended to implement the modulation upgrade on specific
cells that serve open areas, which have hot spots close to the cell site location,
in a relatively low to medium data rate consumption urban/suburban
locations. Typical applications target airports, railway stations, football
stadiums and similar zones.
Keywords:
256-QAM, Bit Error Rate (BER), Long Term Evolution (LTE), Long Term
Evolution Advanced (LTE-A), Modulation, Physical Layer, Quadrature
Amplitude Modulation (QAM), Throughput