11,283 research outputs found
Optimal Joint Power and Subcarrier Allocation for MC-NOMA Systems
In this paper, we investigate the resource allocation algorithm design for
multicarrier non-orthogonal multiple access (MC-NOMA) systems. The proposed
algorithm is obtained from the solution of a non-convex optimization problem
for the maximization of the weighted system throughput. We employ monotonic
optimization to develop the optimal joint power and subcarrier allocation
policy. The optimal resource allocation policy serves as a performance
benchmark due to its high complexity. Furthermore, to strike a balance between
computational complexity and optimality, a suboptimal scheme with low
computational complexity is proposed. Our simulation results reveal that the
suboptimal algorithm achieves a close-to-optimal performance and MC-NOMA
employing the proposed resource allocation algorithm provides a substantial
system throughput improvement compared to conventional multicarrier orthogonal
multiple access (MC-OMA).Comment: Submitted to Globecom 201
The Approximate Optimality of Simple Schedules for Half-Duplex Multi-Relay Networks
In ISIT'12 Brahma, \"{O}zg\"{u}r and Fragouli conjectured that in a
half-duplex diamond relay network (a Gaussian noise network without a direct
source-destination link and with non-interfering relays) an approximately
optimal relay scheduling (achieving the cut-set upper bound to within a
constant gap uniformly over all channel gains) exists with at most active
states (only out of the possible relay listen-transmit
configurations have a strictly positive probability). Such relay scheduling
policies are said to be simple. In ITW'13 we conjectured that simple relay
policies are optimal for any half-duplex Gaussian multi-relay network, that is,
simple schedules are not a consequence of the diamond network's sparse
topology. In this paper we formally prove the conjecture beyond Gaussian
networks. In particular, for any memoryless half-duplex -relay network with
independent noises and for which independent inputs are approximately optimal
in the cut-set upper bound, an optimal schedule exists with at most
active states. The key step of our proof is to write the minimum of a
submodular function by means of its Lov\'{a}sz extension and use the greedy
algorithm for submodular polyhedra to highlight structural properties of the
optimal solution. This, together with the saddle-point property of min-max
problems and the existence of optimal basic feasible solutions in linear
programs, proves the claim.Comment: Submitted to IEEE Information Theory Workshop (ITW) 201
Recommended from our members
Directed Placement for mVLSI Devices
Continuous-flow microfluidic devices based on integrated channel networks are becoming increasingly prevalent in research in the biological sciences. At present, these devices are physically laid out by hand by domain experts who understand both the underlying technology and the biological functions that will execute on fabricated devices. The lack of a design science that is specific to microfluidic technology creates a substantial barrier to entry. To address this concern, this article introduces Directed Placement, a physical design algorithm that leverages the natural "directedness" in most modern microfluidic designs: fluid enters at designated inputs, flows through a linear or tree-based network of channels and fluidic components, and exits the device at dedicated outputs. Directed placement creates physical layouts that share many principle similarities to those created by domain experts. Directed placement allows components to be placed closer to their neighbors compared to existing layout algorithms based on planar graph embedding or simulated annealing, leading to an average reduction in laid-out fluid channel length of 91% while improving area utilization by 8% on average. Directed placement is compatible with both passive and active microfluidic devices and is compatible with a variety of mainstream manufacturing technologies
- …