Abstract
In this paper, we present and evaluate an ultra-wideband (UWB) indoor processing architecture that allows the performing of simultaneous localizations of mobile tags. This architecture relies on a network of low-power fixed anchors that provide forward-ranging measurements to a localization engine responsible for performing trilateration. The communications within this network are orchestrated by UWB-TSCH, an adaptation to the ultra-wideband (UWB) wireless technology of the time-slotted channel-hopping (TSCH) mode of IEEE 802.15.4. As a result of global synchronization, the architecture allows deterministic channel access and low power consumption. Moreover, it makes it possible to communicate concurrently over multiple frequency channels or using orthogonal preamble codes. To schedule communications in such a network, we designed a dedicated centralized scheduler inspired from the traffic aware scheduling algorithm (TASA). By organizing the anchors in multiple cells, the scheduler is able to perform simultaneous localizations and transmissions as long as the corresponding anchors are sufficiently far away to not interfere with each other. In our indoor positioning system (IPS), this is combined with dynamic registration of mobile tags to anchors, easing mobility, as no rescheduling is required. This approach makes our ultra-wideband (UWB) indoor positioning system (IPS) more scalable and reduces deployment costs since it does not require separate networks to perform ranging measurements and to forward them to the localization engine. We further improved our scheduling algorithm with support for multiple sinks and in-network data aggregation. We show, through simulations over large networks containing hundreds of cells, that high positioning rates can be achieved. Notably, we were able to fully schedule a 400-cell/400-tag network in less than 11 s in the worst case, and to create compact schedules which were up to 11 times shorter than otherwise with the use of aggregation, while also bounding queue sizes on anchors to support realistic use situations.
Highlights
Background on UWB Positioningwe introduce the architecture of a typical positioning system relying on ranging measurements
The ranging measurements performed by multiple anchors for a specific tag are forwarded to a central Localization engine that applies a trilateration algorithm to estimate the position of that tag
Channel-hopping is used in this mode to increase the robustness to interference. This scheme can be adapted to the UWB physical layer (PHY), as we have shown in UWB-time-slotted channel-hopping (TSCH) [17]
Summary
We introduce the architecture of a typical positioning system relying on ranging measurements. To perform localization we consider two types of nodes. Anchors are fixed nodes with known positions that are part of the positioning infrastructure. Determining the position of tags is performed by exchanging specific messages with anchors. We rely on ranging techniques to estimate the distance between one tag and one anchor. The result of such an estimation is called a ranging measurement. The ranging measurements performed by multiple anchors for a specific tag are forwarded to a central Localization engine that applies a trilateration algorithm to estimate the position of that tag. A tag that moves from cell to cell will be located through ranging measurements with different anchors
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