7,937 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
Throughput Maximization for Mobile Relaying Systems
This paper studies a novel mobile relaying technique, where relays of high
mobility are employed to assist the communications from source to destination.
By exploiting the predictable channel variations introduced by relay mobility,
we study the throughput maximization problem in a mobile relaying system via
dynamic rate and power allocations at the source and relay. An optimization
problem is formulated for a finite time horizon, subject to an
information-causality constraint, which results from the data buffering
employed at the relay. It is found that the optimal power allocations across
the different time slots follow a "stair-case" water filling (WF) structure,
with non-increasing and non-decreasing water levels at the source and relay,
respectively. For the special case where the relay moves unidirectionally from
source to destination, the optimal power allocations reduce to the conventional
WF with constant water levels. Numerical results show that with appropriate
trajectory design, mobile relaying is able to achieve tremendous throughput
gain over the conventional static relaying.Comment: submitted for possible conference publicatio
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