Visible light LEDs, due to their numerous advantages, are expected to become the dominant indoor lighting technology. These lights can also be switched ON/OFF at high frequency, enabling their additional use for wireless communication and indoor positioning. In this article, visible LED light--based indoor positioning systems are surveyed and classified into two broad categories based on the receiver structure. The basic principle and architecture of each design category, along with various position computation algorithms, are discussed and compared. Finally, several new research, implementation, commercialization, and standardization challenges are identified and highlighted for this relatively novel and interesting indoor localization technology.
The objective of this paper is to study the impact of scheduling flexibility on both demand profile flatness and user inconvenience in residential smart grid systems. Temporal variations in energy consumption by end users result in peaks and troughs in the aggregated demand profile. In a residential smart grid, some of these peaks and troughs can be eliminated through appropriate load balancing algorithms. However, load balancing requires user participation by allowing the grid to re-schedule some of their loads. In general, more scheduling flexibility can result in more demand profile flatness, however the resulting inconvenience to users would also increase. In this paper, our objective is to help the grid determine an appropriate amount of scheduling flexibility that it should demand from users, based on which, proper incentives can be designed. We consider three different types of scheduling flexibility (delay, advance scheduling and flexible re-scheduling) in flexible loads and develop both optimal and sub-optimal scheduling algorithms. We discuss their implementation in centralized and distributed manners. We also identify the existence of a saturation point. Beyond this saturation point, any increase in scheduling flexibility does not significantly affect the flatness of the demand profile while user inconvenience continues to increase. Moreover, full participation of all the households is not required since increasing user participation only marginally increases demand profile flatness.
A wireless indoor positioning system using white LED lights is proposed. The time difference of arrival technique is employed and the phase differences between the received signals are determined to develop a positioning algorithm which can estimate the receiver location with a mean localisation error as low as 1 mm in a room of dimensions 5 × 5 × 3 m. Through simulations, it is identified that the optimum receiver height where localisation error gets minimised is between 2.5 and 3 m from the ceiling which corresponds well with the typical dimensions of a room.
The performance of time division multiplexing and frequency division multiplexing protocols for light emitting diode light emitting diode (IPS) designs using visible light emitting diode lights is evaluated. The impact of timing synchronisation errors on the localisation accuracy of IPS designs is also determined.Introduction: In this Letter, we consider a visible light emitting diode (LED) based indoor positioning systems (IPS) design comprising multiple LED panels placed on the ceiling and transmitting their location coordinates to a photodiode receiver whose location coordinates are to be determined. The localisation accuracy provided by such a design is largely dependent on ability of receiver to distinguish individual signals coming from different LEDs. To facilitate the receiver, LED transmissions are multiplexed either in time division multiplexing (TDM) [1] or in frequency division multiplexing (FDM). In this Letter, we always refer to an IPS design using the TDM protocol as 'TDM-IPS', and an IPS design using the FDM protocol as 'FDM-IPS', respectively. We design a fingerprinting algorithm and then determine localisation accuracy of a fully synchronised TDM-IPS. We then consider the impact of timing synchronisation errors between any two transmitting LEDs. We propose a relatively simpler FDM-IPS transmitter and receiver. The localisation accuracy provided by our FDM-IPS is greater than that for TDM-IPS when any two LEDs have a timing synchronisation error of 10%.
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