4,509 research outputs found
Energy-Efficient Heterogeneous Cellular Networks with Spectrum Underlay and Overlay Access
In this paper, we provide joint subcarrier assignment and power allocation
schemes for quality-of-service (QoS)-constrained energy-efficiency (EE)
optimization in the downlink of an orthogonal frequency division multiple
access (OFDMA)-based two-tier heterogeneous cellular network (HCN). Considering
underlay transmission, where spectrum-efficiency (SE) is fully exploited, the
EE solution involves tackling a complex mixed-combinatorial and non-convex
optimization problem. With appropriate decomposition of the original problem
and leveraging on the quasi-concavity of the EE function, we propose a
dual-layer resource allocation approach and provide a complete solution using
difference-of-two-concave-functions approximation, successive convex
approximation, and gradient-search methods. On the other hand, the inherent
inter-tier interference from spectrum underlay access may degrade EE
particularly under dense small-cell deployment and large bandwidth utilization.
We therefore develop a novel resource allocation approach based on the concepts
of spectrum overlay access and resource efficiency (RE) (normalized EE-SE
trade-off). Specifically, the optimization procedure is separated in this case
such that the macro-cell optimal RE and corresponding bandwidth is first
determined, then the EE of small-cells utilizing the remaining spectrum is
maximized. Simulation results confirm the theoretical findings and demonstrate
that the proposed resource allocation schemes can approach the optimal EE with
each strategy being superior under certain system settings
Green OFDMA Resource Allocation in Cache-Enabled CRAN
Cloud radio access network (CRAN), in which remote radio heads (RRHs) are
deployed to serve users in a target area, and connected to a central processor
(CP) via limited-capacity links termed the fronthaul, is a promising candidate
for the next-generation wireless communication systems. Due to the
content-centric nature of future wireless communications, it is desirable to
cache popular contents beforehand at the RRHs, to reduce the burden on the
fronthaul and achieve energy saving through cooperative transmission. This
motivates our study in this paper on the energy efficient transmission in an
orthogonal frequency division multiple access (OFDMA)-based CRAN with multiple
RRHs and users, where the RRHs can prefetch popular contents. We consider a
joint optimization of the user-SC assignment, RRH selection and transmit power
allocation over all the SCs to minimize the total transmit power of the RRHs,
subject to the RRHs' individual fronthaul capacity constraints and the users'
minimum rate constraints, while taking into account the caching status at the
RRHs. Although the problem is non-convex, we propose a Lagrange duality based
solution, which can be efficiently computed with good accuracy. We compare the
minimum transmit power required by the proposed algorithm with different
caching strategies against the case without caching by simulations, which show
the significant energy saving with caching.Comment: Presented in IEEE Online Conference on Green Communications (Online
GreenComm), Nov. 2016 (Invited Paper
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