28 research outputs found
Generalized Degrees of Freedom of the Symmetric Cache-Aided MISO Broadcast Channel with Partial CSIT
We consider the cache-aided MISO broadcast channel (BC) in which a
multi-antenna transmitter serves single-antenna receivers, each equipped
with a cache memory. The transmitter has access to partial knowledge of the
channel state information. For a symmetric setting, in terms of channel
strength levels, partial channel knowledge levels and cache sizes, we
characterize the generalized degrees of freedom (GDoF) up to a constant
multiplicative factor. The achievability scheme exploits the interplay between
spatial multiplexing gains and coded-multicasting gain. On the other hand, a
cut-set-based argument in conjunction with a GDoF outer bound for a parallel
MISO BC under channel uncertainty are used for the converse. We further show
that the characterized order-optimal GDoF is also attained in a decentralized
setting, where no coordination is required for content placement in the caches.Comment: first revisio
Wyner's Network on Caches: Combining Receiver Caching with a Flexible Backhaul
In this work, we study a large linear interference network with an equal
number of transmitters and receivers, where each transmitter is connected to
two subsequent receivers. Each transmitter has individual access to a backhaul
link (fetching the equivalent of files), while each receiver can cache
a fraction of the library. We explore the tradeoff between the
communication rate, backhaul load, and caching storage by designing algorithms
that can harness the benefits of cooperative transmission in partially
connected networks, while exploiting the advantages of multicast transmissions
attributed to user caching. We show that receiver caching and fetching content
from the backhaul are two resources that can simultaneously increase the
delivery performance in synergistic ways.
Specifically, an interesting outcome of this work is that user caching of a
fraction of the library can increase the per-user Degrees of Freedom
(puDoF) by . Further, the results reveal significant savings in the
backhaul load, even in the small cache size region. For example, the puDoF
achieved using the pair can also be achieved with the pairs and
, showing that even small caches can provide significant
savings in the backhaul load.Comment: 8 pages, 2 figures, submitted to ISIT 201
Content delivery over multi-antenna wireless networks
The past few decades have witnessed unprecedented advances in information technology, which have significantly shaped the way we acquire and process information in our daily lives. Wireless communications has become the main means of access to data through mobile devices, resulting in a continuous exponential growth in wireless data traffic, mainly driven by the demand for high quality content.
Various technologies have been proposed by researchers to tackle this growth in 5G and beyond, including the use of increasing number of antenna elements, integrated point-to-multipoint delivery and caching, which constitute the core of this thesis. In particular, we study non-orthogonal content delivery in multiuser multiple-input-single-output (MISO) systems. First, a joint beamforming strategy for simultaneous delivery of broadcast and unicast services is investigated, based on layered division multiplexing (LDM) as a means of superposition coding. The system performance in terms of minimum required power under prescribed quality-of-service (QoS) requirements is examined in comparison with time division multiplexing (TDM). It is demonstrated through simulations that the non-orthogonal delivery strategy based on LDM significantly outperforms the orthogonal strategy based on TDM in terms of system throughput and reliability. To facilitate efficient implementation of the LDM-based beamforming design, we further propose a dual decomposition-based distributed approach. Next, we study an efficient multicast beamforming design in cache-aided multiuser MISO systems, exploiting proactive content placement and coded delivery. It is observed that the complexity of this problem grows exponentially with the number of subfiles delivered to each user in each time slot, which itself grows exponentially with the number of users in the system. Therefore, we propose a low-complexity alternative through time-sharing that limits the number of subfiles that can be received by a user in each time slot. Moreover, a joint design of content delivery and multicast beamforming is proposed to further enhance the system performance, under the constraint on maximum number of subfiles each user can decode in each time slot. Finally, conclusions are drawn in Chapter 5, followed by an outlook for future works.Open Acces
Fundamental Limits of Wireless Caching Under Mixed Cacheable and Uncacheable Traffic
We consider cache-aided wireless communication scenarios where each user
requests both a file from an a-priori generated cacheable library (referred to
as 'content'), and an uncacheable 'non-content' message generated at the start
of the wireless transmission session. This scenario is easily found in
real-world wireless networks, where the two types of traffic coexist and share
limited radio resources. We focus on single-transmitter, single-antenna
wireless networks with cache-aided receivers, where the wireless channel is
modelled by a degraded Gaussian broadcast channel (GBC). For this setting, we
study the delay-rate trade-off, which characterizes the content delivery time
and non-content communication rates that can be achieved simultaneously. We
propose a scheme based on the separation principle, which isolates the coded
caching and multicasting problem from the physical layer transmission problem.
We show that this separation-based scheme is sufficient for achieving an
information-theoretically order optimal performance, up to a multiplicative
factor of 2.01 for the content delivery time, when working in the generalized
degrees of freedom (GDoF) limit. We further show that the achievable
performance is near-optimal after relaxing the GDoF limit, up to an additional
additive factor of 2 bits per dimension for the non-content rates. A key
insight emerging from our scheme is that in some scenarios considerable amounts
of non-content traffic can be communicated while maintaining the minimum
content delivery time, achieved in the absence of non-content messages;
compliments of 'topological holes' arising from asymmetries in wireless channel
gains.Comment: Accepted for publication in the IEEE Transactions on Information
Theor