155,217 research outputs found
Cooperative Caching and Transmission Design in Cluster-Centric Small Cell Networks
Wireless content caching in small cell networks (SCNs) has recently been
considered as an efficient way to reduce the traffic and the energy consumption
of the backhaul in emerging heterogeneous cellular networks (HetNets). In this
paper, we consider a cluster-centric SCN with combined design of cooperative
caching and transmission policy. Small base stations (SBSs) are grouped into
disjoint clusters, in which in-cluster cache space is utilized as an entity. We
propose a combined caching scheme where part of the available cache space is
reserved for caching the most popular content in every SBS, while the remaining
is used for cooperatively caching different partitions of the less popular
content in different SBSs, as a means to increase local content diversity.
Depending on the availability and placement of the requested content,
coordinated multipoint (CoMP) technique with either joint transmission (JT) or
parallel transmission (PT) is used to deliver content to the served user. Using
Poisson point process (PPP) for the SBS location distribution and a hexagonal
grid model for the clusters, we provide analytical results on the successful
content delivery probability of both transmission schemes for a user located at
the cluster center. Our analysis shows an inherent tradeoff between
transmission diversity and content diversity in our combined
caching-transmission design. We also study optimal cache space assignment for
two objective functions: maximization of the cache service performance and the
energy efficiency. Simulation results show that the proposed scheme achieves
performance gain by leveraging cache-level and signal-level cooperation and
adapting to the network environment and user QoS requirements.Comment: 13 pages, 10 figures, submitted for possible journal publicatio
Cooperative Regions For Coded Cooperation Over Time-Varying Fading Channels
The performance analysis of coded cooperation has been mainly focused on two extreme cases of channel variability, i.e. the block-fading (BF) and the fast-fading (FF) model. In more practical propagation environments the fading correlation across time depends on the level of user mobility. This paper analyzes the effects of time-selective fading on the performance of coded cooperation by providing an analytical framework for the error rate evaluation as a function of the mobility degree of the mobile station (MS) and of the quality of the inter-MS channel. The purpose is to evaluate the conditions on the propagation settings where the additional exploitation of spatial diversity (when time-diversity is available) provided by cooperative transmission is able to enhance substantially the performance of the non-cooperative transmission. We show that coded cooperation can outperform the non-cooperative (coded and bit-interleaved) transmission only up to a certain degree of mobility. The cooperative region is defined as the collection of mobility settings for which coded cooperation can be regarded as a competitive strategy compared to non-cooperative transmission. Contrary to what has been previously shown for BF channels, we demonstrate that the inter-MS channel quality plays a key role in the definition of the cooperative region
Beacon-Assisted Spectrum Access with Cooperative Cognitive Transmitter and Receiver
Spectrum access is an important function of cognitive radios for detecting
and utilizing spectrum holes without interfering with the legacy systems. In
this paper we propose novel cooperative communication models and show how
deploying such cooperations between a pair of secondary transmitter and
receiver assists them in identifying spectrum opportunities more reliably.
These cooperations are facilitated by dynamically and opportunistically
assigning one of the secondary users as a relay to assist the other one which
results in more efficient spectrum hole detection. Also, we investigate the
impact of erroneous detection of spectrum holes and thereof missing
communication opportunities on the capacity of the secondary channel. The
capacity of the secondary users with interference-avoiding spectrum access is
affected by 1) how effectively the availability of vacant spectrum is sensed by
the secondary transmitter-receiver pair, and 2) how correlated are the
perceptions of the secondary transmitter-receiver pair about network spectral
activity. We show that both factors are improved by using the proposed
cooperative protocols. One of the proposed protocols requires explicit
information exchange in the network. Such information exchange in practice is
prone to wireless channel errors (i.e., is imperfect) and costs bandwidth loss.
We analyze the effects of such imperfect information exchange on the capacity
as well as the effect of bandwidth cost on the achievable throughput. The
protocols are also extended to multiuser secondary networks.Comment: 36 pages, 6 figures, To appear in IEEE Transaction on Mobile
Computin
Slotted Aloha for Networked Base Stations
We study multiple base station, multi-access systems in which the user-base
station adjacency is induced by geographical proximity. At each slot, each user
transmits (is active) with a certain probability, independently of other users,
and is heard by all base stations within the distance . Both the users and
base stations are placed uniformly at random over the (unit) area. We first
consider a non-cooperative decoding where base stations work in isolation, but
a user is decoded as soon as one of its nearby base stations reads a clean
signal from it. We find the decoding probability and quantify the gains
introduced by multiple base stations. Specifically, the peak throughput
increases linearly with the number of base stations and is roughly
larger than the throughput of a single-base station that uses standard slotted
Aloha. Next, we propose a cooperative decoding, where the mutually close base
stations inform each other whenever they decode a user inside their coverage
overlap. At each base station, the messages received from the nearby stations
help resolve collisions by the interference cancellation mechanism. Building
from our exact formulas for the non-cooperative case, we provide a heuristic
formula for the cooperative decoding probability that reflects well the actual
performance. Finally, we demonstrate by simulation significant gains of
cooperation with respect to the non-cooperative decoding.Comment: conference; submitted on Dec 15, 201
Exploiting Tradeoff Between Transmission Diversity and Content Diversity in Multi-Cell Edge Caching
Caching in multi-cell networks faces a well-known dilemma, i.e., to cache
same contents among multiple edge nodes (ENs) to enable transmission
cooperation/diversity for higher transmission efficiency, or to cache different
contents to enable content diversity for higher cache hit rate. In this work,
we introduce a partition-based caching to exploit the tradeoff between
transmission diversity and content diversity in a multi-cell edge caching
networks with single user only. The performance is characterized by the system
average outage probability, which can be viewed as the sum of the cache hit
outage probability and cache miss probability. We show that (i) In the low
signal-to-noise ratio(SNR) region, the ENs are encouraged to cache more
fractions of the most popular files so as to better exploit the transmission
diversity for the most popular content; (ii) In the high SNR region, the ENs
are encouraged to cache more files with less fractions of each so as to better
exploit the content diversity.Comment: Accepted by IEEE International Conference on Communications (ICC),
Kansas City, MO, USA, May 201
Dispensing with channel estimation: differentially modulated cooperative wireless communications
As a benefit of bypassing the potentially excessive complexity and yet inaccurate channel estimation, differentially encoded modulation in conjunction with low-complexity noncoherent detection constitutes a viable candidate for user-cooperative systems, where estimating all the links by the relays is unrealistic. In order to stimulate further research on differentially modulated cooperative systems, a number of fundamental challenges encountered in their practical implementations are addressed, including the time-variant-channel-induced performance erosion, flexible cooperative protocol designs, resource allocation as well as its high-spectral-efficiency transceiver design. Our investigations demonstrate the quantitative benefits of cooperative wireless networks both from a pure capacity perspective as well as from a practical system design perspective
- …