Analysis and optimization of caching techniques in eireless networks : reactive and proactive paradigm / Ahmed Mohamed Magdy Ahmed

Supervisor: Mohammed Nafie

Thesis (M.A.)—Nile University, Egypt, 2017 .

"Includes bibliographical references"

Contents:
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Main Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Dynamic Proactive Caching in Relay Networks . . . . . . . . . . . . . . 9
2.1 System Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2 Problem Formulation . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3 Lower Bound and Proposed Policy . . . . . . . . . . . . . . . . . . 16
2.4 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.4.1 Impact of number of files on the cost reduction gain . . . . 23
2.4.2 Impact of Zipf parameter on cost reduction gain . . . . . . . 25
2.4.3 Comparison with caching at end user . . . . . . . . . . . . . 26
2.4.4 Impact of prediction window size on the expected cost . . . 29
3. On Optimal Dynamic Caching in Relay Networks . . . . . . . . . . . . . 31
3.1 System Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.2 Problem Formulation . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.3 Lower Bound and Proposed Policy . . . . . . . . . . . . . . . . . . 36
3.4 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.4.1 Time average cost across time horizon . . . . . . . . . . . . 41
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3.4.2 Impact of block size on time average cost . . . . . . . . . . 43
3.4.3 Impact of number of files on time average cost . . . . . . . . 43
3.4.4 Impact of Zipf parameter on time average cost . . . . . . . 45
3.4.5 Impact of relative channel cost on time average cost . . . . 46
3.4.6 Comparison with no caching and LRU schemes . . . . . . . 47
4. Towards Optimal Resource Allocation in Caching Relay Networks . . . . 49
4.1 System Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.2 Problem Formulation . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.2.1 Main Problem . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.2.2 Optimal Service Portion . . . . . . . . . . . . . . . . . . . . 53
4.2.3 Final Problem . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.2.4 Proposed Caching Technique . . . . . . . . . . . . . . . . . 58
4.3 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.1 Finding and Observations . . . . . . . . . . . . . . . . . . . . . . . 65
5.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Bibliography . . . . . . . . . .

Abstract:
In this work, we explore the performance of caching in relay networks. First, we
investigate the idea of proactive caching in relay networks. Second, we investigate
dynamic content caching in non-proactive networks. Third, we investigate the optimal
time average transmission energy resulting from caching in non-proactive relay
networks.
In the first part of this work, we investigate the performance of dynamic proactive
caching in relay networks where an intermediate relay station caches content for
potential future use by end users. A central base station proactively controls the
cache allocation such that cached content remains fresh for consumption for a limited
number of time slots called proactive service window. With uncertain user demand
over multiple data items and dynamically changing wireless links, we consider the
optimal allocation of relay station’s cache to minimize the time average expected
service cost. We characterize a fundamental lower bound on the cost achieved by
any proactive caching policy. Then we develop an asymptotically optimal caching
policy that attains the lower bound as the proactive caching window size grows. We
provide numerical simulations to validate our analytical findings and demonstrate
performance merits.
In the second part, we investigate dynamic content caching in relay networks where
an intermediate relay station (RS) can adaptively cache data content based on their
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varying popularity. With the objective of minimizing the time average cost of content
delivery, we formulate and study the problem of optimal RS cache allocation when
the popularities of data content are unknown apriori to the network. While optimal
dynamic cache control suffers the curse of dimensionality, we develop a fundamental
lower bound on the achievable cost by any caching policy. Inspired by the structure of
such lower bound, we develop a reduced-complexity policy that is shown numerically
to perform close to the lower bound.
In the third part of this work, we investigate the performance of caching in relay
networks where an intermediate relay station (RS) caches content for future demand
by end users. With uncertain user demand over multiple data items and dynamically
changing wireless links, we characterize the optimal transmission time for serving data
items, cached data portion allocation of relay station and optimal service portion, as
a part from the cached portion, to minimize the total average transmission energy.
We argue that under several settings fully caching the higher popular items is the
optimal caching policy which minimizes the total expected transmission energy.

Text in English, abstracts in English.