226 research outputs found
Optimal Error Correcting Delivery Scheme for an Optimal Coded Caching Scheme with Small Buffers
Optimal delivery scheme for coded caching problems with small buffer sizes
and the number of users no less than the amount of files in the server was
proposed by Chen, Fan and Letaief ["Fundamental limits of caching: improved
bounds for users with small buffers," (IET Communications), 2016]. This scheme
is referred to as the CFL scheme. In this paper, the link between the server
and the users is assumed to be error prone only during the delivery phase.
Closed form expressions for average rate and peak rate of error correcting
delivery scheme for CFL prefetching scheme is obtained. An optimal error
correcting delivery scheme for caching problems employing CFL prefetching is
proposed.Comment: 7 page
Optimal Error Correcting Delivery Scheme for Coded Caching with Symmetric Batch Prefetching
Coded caching is used to reduce network congestion during peak hours. A
single server is connected to a set of users through a bottleneck link, which
generally is assumed to be error-free. During non-peak hours, all the users
have full access to the files and they fill their local cache with portions of
the files available. During delivery phase, each user requests a file and the
server delivers coded transmissions to meet the demands taking into
consideration their cache contents. In this paper we assume that the shared
link is error prone. A new delivery scheme is required to meet the demands of
each user even after receiving finite number of transmissions in error. We
characterize the minimum average rate and minimum peak rate for this problem.
We find closed form expressions of these rates for a particular caching scheme
namely \textit{symmetric batch prefetching}. We also propose an optimal error
correcting delivery scheme for coded caching problem with symmetric batch
prefetching.Comment: 9 pages and 4 figure
Multi-access Coded Caching with Decentralized Prefetching
An extension of coded caching referred to as multi-access coded caching where
each user can access multiple caches and each cache can serve multiple users is
considered in this paper. Most of the literature in multi-access coded caching
focuses on cyclic wrap-around cache access where each user is allowed to access
an exclusive set of consecutive caches only. In this paper, a more general
framework of multi-access caching problem is considered in which each user is
allowed to randomly connect to a specific number of caches and multiple users
can access the same set of caches. For the proposed system model considering
decentralized prefetching, a new delivery scheme is proposed and an expression
for per user delivery rate is obtained. A lower bound on the delivery rate is
derived using techniques from index coding. The proposed scheme is shown to be
optimal among all the linear schemes under certain conditions. An improved
delivery rate and a lower bound for the decentralized multi-access coded
caching scheme with cyclic wrap-around cache access can be obtained as a
special case. By giving specific values to certain parameters, the results of
decentralized shared caching scheme and of conventional decentralized caching
scheme can be recovered.Comment: 26 pages, 6 figures, 6 tables, Submitted to IEEE Transactions on
Communication
Low-latency Networking: Where Latency Lurks and How to Tame It
While the current generation of mobile and fixed communication networks has
been standardized for mobile broadband services, the next generation is driven
by the vision of the Internet of Things and mission critical communication
services requiring latency in the order of milliseconds or sub-milliseconds.
However, these new stringent requirements have a large technical impact on the
design of all layers of the communication protocol stack. The cross layer
interactions are complex due to the multiple design principles and technologies
that contribute to the layers' design and fundamental performance limitations.
We will be able to develop low-latency networks only if we address the problem
of these complex interactions from the new point of view of sub-milliseconds
latency. In this article, we propose a holistic analysis and classification of
the main design principles and enabling technologies that will make it possible
to deploy low-latency wireless communication networks. We argue that these
design principles and enabling technologies must be carefully orchestrated to
meet the stringent requirements and to manage the inherent trade-offs between
low latency and traditional performance metrics. We also review currently
ongoing standardization activities in prominent standards associations, and
discuss open problems for future research
3G Wideband CDMA : packet-based optimisation for high data-rate downlink transmission
A third generation (3G) of mobile communication systems, based on Wideband CDMA, are intended to offer high-speed packet-based services. Network operators wish to maximise the throughput in the downlink of3G systems, which requires efficient allocation ofresources. This thesis considers the problem ofmaximising throughput in an interference dominated channel. Cooperative broadcasting is a theoretical technique to mitigate this problem. Its implementation in practical systems requires efficient resource allocati.on to maximise the thr(oughput whilst meeting system and user-imposed constramts. A resource allocation approach is presented for implementing cooperative broadcasting. Users are paired and a teclmique for allocating resources between the pair is developed. Then, a method for pairing the users is considered. Simulation results are presented, which show a throughput improvement over existing resource allocation approaches. The problem ofcontrolling the distribution ofrandomly arriving data to meet the resource allocation specifications is examined. A single-threshold buffer is proposed, which requires fewer calculations than an existing double-threshold buffer. Simulation results are presented which show a throughput improvement may be realised, greater than that which would achievable using other rate control schemes. Cooperative broadcasting may lead to transmissions to some users being allocated low power. When full channel infonnation is available at the transmitter, a water filling solution may be used to maximise capacity. However, when combined with buffer management, erasure may result. This erasure may be overcome using an erasure protection code. Such a code is examined. When combined with Turbo coding, ajoint detector may be used for providing error and erasure protection. Analysis ofthis detector shows a lower limit on the error rate, dependent on the probability of erasure. Simulation results show that using this approach the error rate is significantly improved. This code can then be used to increase capacity, whilst achieving low error rates.Imperial Users onl
Recent Trends in Communication Networks
In recent years there has been many developments in communication technology. This has greatly enhanced the computing power of small handheld resource-constrained mobile devices. Different generations of communication technology have evolved. This had led to new research for communication of large volumes of data in different transmission media and the design of different communication protocols. Another direction of research concerns the secure and error-free communication between the sender and receiver despite the risk of the presence of an eavesdropper. For the communication requirement of a huge amount of multimedia streaming data, a lot of research has been carried out in the design of proper overlay networks. The book addresses new research techniques that have evolved to handle these challenges
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