482 research outputs found
Green Cellular Networks: A Survey, Some Research Issues and Challenges
Energy efficiency in cellular networks is a growing concern for cellular
operators to not only maintain profitability, but also to reduce the overall
environment effects. This emerging trend of achieving energy efficiency in
cellular networks is motivating the standardization authorities and network
operators to continuously explore future technologies in order to bring
improvements in the entire network infrastructure. In this article, we present
a brief survey of methods to improve the power efficiency of cellular networks,
explore some research issues and challenges and suggest some techniques to
enable an energy efficient or "green" cellular network. Since base stations
consume a maximum portion of the total energy used in a cellular system, we
will first provide a comprehensive survey on techniques to obtain energy
savings in base stations. Next, we discuss how heterogeneous network deployment
based on micro, pico and femto-cells can be used to achieve this goal. Since
cognitive radio and cooperative relaying are undisputed future technologies in
this regard, we propose a research vision to make these technologies more
energy efficient. Lastly, we explore some broader perspectives in realizing a
"green" cellular network technologyComment: 16 pages, 5 figures, 2 table
Energy-Efficient Cooperative Cognitive Relaying Schemes for Cognitive Radio Networks
We investigate a cognitive radio network in which a primary user (PU) may
cooperate with a cognitive radio user (i.e., a secondary user (SU)) for
transmissions of its data packets. The PU is assumed to be a buffered node
operating in a time-slotted fashion where the time is partitioned into
equal-length slots. We develop two schemes which involve cooperation between
primary and secondary users. To satisfy certain quality of service (QoS)
requirements, users share time slot duration and channel frequency bandwidth.
Moreover, the SU may leverage the primary feedback message to further increase
both its data rate and satisfy the PU QoS requirements. The proposed
cooperative schemes are designed such that the SU data rate is maximized under
the constraint that the PU average queueing delay is maintained less than the
average queueing delay in case of non-cooperative PU. In addition, the proposed
schemes guarantee the stability of the PU queue and maintain the average energy
emitted by the SU below a certain value. The proposed schemes also provide more
robust and potentially continuous service for SUs compared to the conventional
practice in cognitive networks where SUs transmit in the spectrum holes and
silence sessions of the PUs. We include primary source burstiness, sensing
errors, and feedback decoding errors to the analysis of our proposed
cooperative schemes. The optimization problems are solved offline and require a
simple 2-dimensional grid-based search over the optimization variables.
Numerical results show the beneficial gains of the cooperative schemes in terms
of SU data rate and PU throughput, average PU queueing delay, and average PU
energy savings
Maximum Throughput of a Secondary User Cooperating with an Energy-Aware Primary User
This paper proposes a cooperation protocol between a secondary user (SU) and
a primary user (PU) which dedicates a free frequency subband for the SU if
cooperation results in energy saving. Time is slotted and users are equipped
with buffers. Under the proposed protocol, the PU releases portion of its
bandwidth for secondary transmission. Moreover, it assigns a portion of the
time slot duration for the SU to relay primary packets and achieve a higher
successful packet reception probability at the primary receiver. We assume that
the PU has three states: idle, forward, and retransmission states. At each of
these states, the SU accesses the channel with adaptive transmission
parameters. The PU cooperates with the SU if and only if the achievable average
number of transmitted primary packets per joule is higher than the number of
transmitted packets per joule when it operates alone. The numerical results
show the beneficial gains of the proposed cooperative cognitive protocol.Comment: Accepted WiOpt 201
Energy-aware cooperative wireless networks with multiple cognitive users
In this paper, we study and analyze cooperative cognitive radio networks with arbitrary number of secondary users (SUs). Each SU is considered a prospective relay for the primary user (PU) besides having its own data transmission demand. We consider a multi-packet transmission framework that allows multiple SUs to transmit simultaneously because of dirty-paper coding. We propose power allocation and scheduling policies that optimize the throughput for both PU and SU with minimum energy expenditure. The performance of the system is evaluated in terms of throughput and delay under different opportunistic relay selection policies. Toward this objective, we present a mathematical framework for deriving stability conditions for all queues in the system. Consequently, the throughput of both primary and secondary links is quantified. Furthermore, a moment generating function approach is employed to derive a closed-form expression for the average delay encountered by the PU packets. Results reveal that we achieve better performance in terms of throughput and delay at lower energy cost as compared with equal power allocation schemes proposed earlier in the literature. Extensive simulations are conducted to validate our theoretical findings
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