The Bridge - Issue 3, 2021 - 29

Feature
Facilitating Satellite-Airborne-Balloon-Terrestrial
Integration for Dynamic and Infrastructure-less Networks
The results in this section are based on optimizing
the station placement (i.e., HAPs and TBs) and the
associations (access and back-hauling associations).
For stations placements, we use a heuristic shrinkand-realign
algorithm to find the optimal placement.
The shrink-and-realign algorithm has several benefits
compared to other heuristic algorithms in the literature:
(i) it has a simple implementation, (ii) it is considered
as low complexity algorithm, and (ii) it is very fast with
quick convergence. The algorithm starts by generating
initial next candidate positions as spheres around
the current position before recursively shrinking the
sphere radius by half to find the best local position
and compare it to the current position. The algorithm
repeats the above process until the sample space size
decreases below a specific limit or no enhancement
can be made. For resource allocations, we formulate a
linear and convex optimization problems for solving the
associations and power allocations based on OFDMA.
Figure 4 plots the achievable average uplink data rate
as a function of transmit power of ground user. The
average uplink data rate is per ground user and equals
to the sum of the total uplink throughput divided by
the total number of ground users. This figure compares
our proposed integration model with two baseline
models. The satellite station is only used for the
uplink transmission, or the satellite and multiple HAPs
are used only (i.e., TBs are excluded) for the uplink
transmission. It is shown that our integrated system
achieves a higher uplink throughput compares to the
two baselines. For example, when the ground user
transmitted power is equal to 20dBm, the achievable
uplink throughput can be improved from around 0.3
Kbits/sec for satellite only solution and 0.3 Mbits/
sec for satellite and HAPs only to around 3 Mbits/
sec by using the proposed integrated system. This is
due to TBs that can help in broadcasting the uplink
signal and mitigating the pathloss and other unfavorite
effects. Further, from the same figure we can show
that the average ground users throughput of proposed
integrated system and satellite and HAPs only increases
as the ground transmit power increases up to a specific
value (~40 dBm) After this value, the performance
remains constant. This is because of the back-handing
limitation in the relay link from TBs to HAPs.
Figure 3: Simulation Setup
Figure 4: Average uplink data rate versus ground user's transmit power.
Figure 5: Average downlink data rate versus HAPs' peak power.
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The Bridge - Issue 3, 2021

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