Effective pilot assignment schemes in massive MIMO systems
The explosive growth of mobile applications and services over cellular networks poses new challenges to network operators in upgrading existing cellular networks in order to handle huge wireless data transmission. Nonetheless, the fifth generation (5G) launch holds tremendous potential to address...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
2022
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/114922/1/114922.pdf http://psasir.upm.edu.my/id/eprint/114922/ http://ethesis.upm.edu.my/id/eprint/18211 |
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| Summary: | The explosive growth of mobile applications and services over cellular networks
poses new challenges to network operators in upgrading existing cellular
networks in order to handle huge wireless data transmission. Nonetheless, the
fifth generation (5G) launch holds tremendous potential to address these challenges.
5G uses a powerful massive multiple-input-multiple output (MIMO)
system between the base station (BS) and the users, which promises high
speed, low latency, and massive connectivity. While extremely useful, intercell
interference has been identified as one of the major challenges of massive
MIMO-enabled cellular systems. When the same pilot sets are reused across
adjacent cells to estimate the channel state information (CSI), this causes a
so-called pilot contamination problem that saturates the signal to interference
plus noise ratio (SINR). Furthermore, this problem cannot be mitigated by
increasing the number of serving antennas.
In this thesis, an efficient pilot assignment scheme (EPA) is proposed to tackle
the pilot contamination problem and consequently improve the uplink data
rate of users in multi-cell massive MIMO systems, especially those who suffer
from bad channel conditions. This was achieved by using the large-scale
characteristics of the fading channel to minimize the amount of outgoing intercell
interference at the target cell during the pilot assignment process.
Then, a partial pilot assignment scheme (PPA) is developed to reduce the
time computational complexity accompanied by the EPA scheme. Specifically,
the pilot assignment process is carried out for specific users who are
tagged according to comparing their large-scale channel fading coefficients to
a specific threshold value. This scheme achieves a data rate that is close to
that of the EPA scheme.
Furthermore, an effective pilot reuse-PPA scheme (EPR-PPA) is introduced
to efficiently mitigate the impact of interference. Not only is the uplink data
rate greatly improved, but also the time computational complexity is further
reduced. In the EPR-PPA scheme, two pilot sets are used in the network and
the PPA algorithm is implemented in cells that cause low interference at the
serving cell, which share the same pilot set.
Simulation results showed that the proposed schemes outperformed both the
existing smart pilot assignment (SPA) and conventional schemes. Herein, different
linear receiving detectors are used in evaluating the performance of such
proposed schemes. The obtained results ensure that the proposed schemes
have significantly improved the system performance in terms of achievable
uplink rate and cumulative distribution function (CDF) for both SINR and
uplink rate. In particular, the improvements in the uplink data rate are
roughly [12% – 78%], compared to the SPA schema. Moreover, the results
of the evaluation explain the great improvements in the performance of poor
SINR users, with the probability of achieving a higher SINR increasing almost
by [20% – 37%], compared to the SPA assuming 64 antenna elements
are equipped to the serving BS. The proposed schemes have also proved their
high effectiveness and performance even in severe interference environments.
In addition, the time computational complexity is reduced by approximately
[52% – 72%] compared to the SPA. |
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