20 research outputs found
Capacity scaling law by multiuser diversity in cognitive radio systems
This paper analyzes the multiuser diversity gain in a cognitive radio (CR)
system where secondary transmitters opportunistically utilize the spectrum
licensed to primary users only when it is not occupied by the primary users. To
protect the primary users from the interference caused by the missed detection
of primary transmissions in the secondary network, minimum average throughput
of the primary network is guaranteed by transmit power control at the secondary
transmitters. The traffic dynamics of a primary network are also considered in
our analysis. We derive the average achievable capacity of the secondary
network and analyze its asymptotic behaviors to characterize the multiuser
diversity gains in the CR system.Comment: 5 pages, 2 figures, ISIT2010 conferenc
Extreme Level Crossing Rate: A New Performance Indicator for URLLC Systems
Level crossing rate (LCR) is a well-known statistical tool that is related to
the duration of a random stationary fading process \emph{on average}. In doing
so, LCR cannot capture the behavior of \emph{extremely rare} random events.
Nonetheless, the latter events play a key role in the performance of
ultra-reliable and low-latency communication systems rather than their average
(expectation) counterparts. In this paper, for the first time, we extend the
notion of LCR to address this issue and sufficiently characterize the
statistical behavior of extreme maxima or minima. This new indicator, entitled
as extreme LCR (ELCR), is analytically introduced and evaluated by resorting to
the extreme value theory and risk assessment. Capitalizing on ELCR, some key
performance metrics emerge, i.e., the maximum outage duration, minimum
effective duration, maximum packet error rate, and maximum transmission delay.
They are all derived in simple closed-form expressions. The theoretical results
are cross-compared and verified via extensive simulations whereas some useful
engineering insights are manifested.Comment: Accepted for publication in IEEE TV
Flow Level QoE of Video Streaming in Wireless Networks
The Quality of Experience (QoE) of streaming service is often degraded by
frequent playback interruptions. To mitigate the interruptions, the media
player prefetches streaming contents before starting playback, at a cost of
delay. We study the QoE of streaming from the perspective of flow dynamics.
First, a framework is developed for QoE when streaming users join the network
randomly and leave after downloading completion. We compute the distribution of
prefetching delay using partial differential equations (PDEs), and the
probability generating function of playout buffer starvations using ordinary
differential equations (ODEs) for CBR streaming. Second, we extend our
framework to characterize the throughput variation caused by opportunistic
scheduling at the base station, and the playback variation of VBR streaming.
Our study reveals that the flow dynamics is the fundamental reason of playback
starvation. The QoE of streaming service is dominated by the first moments such
as the average throughput of opportunistic scheduling and the mean playback
rate. While the variances of throughput and playback rate have very limited
impact on starvation behavior.Comment: 14 page
An Analytical Framework for Heterogeneous Partial Feedback Design in Heterogeneous Multicell OFDMA Networks
The inherent heterogeneous structure resulting from user densities and large
scale channel effects motivates heterogeneous partial feedback design in
heterogeneous networks. In such emerging networks, a distributed scheduling
policy which enjoys multiuser diversity as well as maintains fairness among
users is favored for individual user rate enhancement and guarantees. For a
system employing the cumulative distribution function based scheduling, which
satisfies the two above mentioned desired features, we develop an analytical
framework to investigate heterogeneous partial feedback in a general
OFDMA-based heterogeneous multicell employing the best-M partial feedback
strategy. Exact sum rate analysis is first carried out and closed form
expressions are obtained by a novel decomposition of the probability density
function of the selected user's signal-to-interference-plus-noise ratio. To
draw further insight, we perform asymptotic analysis using extreme value theory
to examine the effect of partial feedback on the randomness of multiuser
diversity, show the asymptotic optimality of best-1 feedback, and derive an
asymptotic approximation for the sum rate in order to determine the minimum
required partial feedback.Comment: To appear in IEEE Trans. on Signal Processin
Multiple Access Design for Symbiotic Radios: Facilitating Massive IoT Connections with Cellular Networks
Symbiotic radio (SR) has emerged as a spectrum- and energy-efficient paradigm
to support massive Internet of Things (IoT) connections. Two multiple access
schemes are proposed in this paper to facilitate the massive IoT connections
using the cellular network based on the SR technique, namely, the simultaneous
access (SA) scheme and the selection diversity access (SDA) scheme. In the SA
scheme, the base station (BS) transmits information to the receiver while
multiple IoT devices transmit their information simultaneously by passively
backscattering the BS signal to the receiver, while in the SDA scheme, only the
IoT device with the strongest backscatter link transmits information to the
receiver. In both of the schemes, the receiver jointly decodes the information
from the BS and the IoT devices. To evaluate the above two schemes, in this
paper, we have derived the closed-form expressions of the ergodic rates and the
outage probabilities for the cellular and IoT transmissions. Finally, numerical
results are provided to verify the theoretical analysis and compare the two
proposed multiple access schemes. When the number of IoT devices is small, the
SDA scheme is more appealing since it can significantly reduce the
computational complexity while achieving equivalent performance to the SA
scheme. When the number of IoT devices is large, the SA scheme is preferable
since it guarantees a significantly better rate performance and a lower outage
probability