14,210 research outputs found
Traffic Driven Resource Allocation in Heterogenous Wireless Networks
Most work on wireless network resource allocation use physical layer
performance such as sum rate and outage probability as the figure of merit.
These metrics may not reflect the true user QoS in future heterogenous networks
(HetNets) with many small cells, due to large traffic variations in overlapping
cells with complicated interference conditions. This paper studies the spectrum
allocation problem in HetNets using the average packet sojourn time as the
performance metric. To be specific, in a HetNet with base terminal stations
(BTS's), we determine the optimal partition of the spectrum into possible
spectrum sharing combinations. We use an interactive queueing model to
characterize the flow level performance, where the service rates are decided by
the spectrum partition. The spectrum allocation problem is formulated using a
conservative approximation, which makes the optimization problem convex. We
prove that in the optimal solution the spectrum is divided into at most
pieces. A numerical algorithm is provided to solve the spectrum allocation
problem on a slow timescale with aggregate traffic and service information.
Simulation results show that the proposed solution achieves significant gains
compared to both orthogonal and full spectrum reuse allocations with moderate
to heavy traffic.Comment: 6 pages, 5 figures IEEE GLOBECOM 2014 (accepted for publication
Traffic-Driven Spectrum Allocation in Heterogeneous Networks
Next generation cellular networks will be heterogeneous with dense deployment
of small cells in order to deliver high data rate per unit area. Traffic
variations are more pronounced in a small cell, which in turn lead to more
dynamic interference to other cells. It is crucial to adapt radio resource
management to traffic conditions in such a heterogeneous network (HetNet). This
paper studies the optimization of spectrum allocation in HetNets on a
relatively slow timescale based on average traffic and channel conditions
(typically over seconds or minutes). Specifically, in a cluster with base
transceiver stations (BTSs), the optimal partition of the spectrum into
segments is determined, corresponding to all possible spectrum reuse patterns
in the downlink. Each BTS's traffic is modeled using a queue with Poisson
arrivals, the service rate of which is a linear function of the combined
bandwidth of all assigned spectrum segments. With the system average packet
sojourn time as the objective, a convex optimization problem is first
formulated, where it is shown that the optimal allocation divides the spectrum
into at most segments. A second, refined model is then proposed to address
queue interactions due to interference, where the corresponding optimal
allocation problem admits an efficient suboptimal solution. Both allocation
schemes attain the entire throughput region of a given network. Simulation
results show the two schemes perform similarly in the heavy-traffic regime, in
which case they significantly outperform both the orthogonal allocation and the
full-frequency-reuse allocation. The refined allocation shows the best
performance under all traffic conditions.Comment: 13 pages, 11 figures, accepted for publication by JSAC-HC
'Slow'- and 'fast'-light in a single ring-resonator circuit: theory, experimental observations, and sensing applications
Transfer matrix method (TMM) was used to study the phenomena of âslowâ- and âfastâ-light in a single two-port ring-resonator (TPRR) circuit theoretically. Their classifications into âslowâ- and âfastâ-light with negative and positive group velocity (v_g), where âslowâ means |v_g|<c and âfastâ means |v_g|>c, will be introduced. The role of such phenomena in controlling light-matter interaction and pulse delay/âadvancementâ will be discussed.
Direct experimental observations on pulse temporal behaviors in the regimes of âslowâ- and âfastâ-light with negative and positive v_g will be demonstrated, showing large and small pulse âadvancementâ and delay, respectively. Pulse splitting phenomenon as a transition from a highly delayed to a highly âadvancedâ pulse and vice versa, will also be experimentally demonstrated. Theoretical simulations on the pulse delay and âadvancementâ based on the TMM and Fourier transform, which show a good qualitative agreement to the experimental results, will also be presented.
The exploitation of âslowâ-light, either with positive or negative v_g for enhancing light-matter interaction will be discussed through evaluating their effects to the performance of integrated-optical refractometric sensor. It will be shown that when the light is âslowâ, either with negative or positive v_g, there is enhancement of the sensor sensitivity. An integrated-optical sensor which exploits such properties and exhibits sensitivity of one order better than the present day state-of-the-art commercial Mach-Zehnder interferometer refractometric sensor, will be presented
Direct experimental observation of pulse temporal behavior in integrated-optical ring-resonator with negative group velocity
We report a direct experimental observation of pulse temporal behavior in an integrated optical two-port ring-resonator circuit as a function of coupling strength, including the transition across the critical coupling point. We demonstrate the observation of pulse âadvancementâ in the negative v_g regime and pulse delay in the positive v_g regime. We also observed a smooth transition of the pulse shape from highly negative to highly positive v_g (or vice versa) through a pulse splitting phenomenon. The observed phenomena agree well to theoretical simulations
Observing 'back to the future' phenomenon with photonic chip
The possibility to engineer the group velocity of light has attracted much attention in the last couple of years. One of the most exotic phenomena in this research field is the negative phenomenon. Negative implies that if we send light pulse into the optical medium, the peak of the output will leave the output before the peak of the input pulse entering the medium, i.e. a pulse 'advancement' or negative delay. This paper will discuss such counter-intuitive 'back-to-the-future' phenomenon and its direct time-domain experimental observations on a real photonic chip using measurement equipments available in a typical optical telecommunication laboratory. Comments on the consistency of the phenomenon with the causality principles as well as possible application will also be briefly discussed
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