Signal Processing - November 2016 - 128

perspectives corner
applications
Chen Chen, Yi Han, Yan Chen, and K.J. Ray Liu

Indoor global Positioning System
with centimeter accuracy Using Wi-Fi

he global positioning system (GPS) is
a space-based navigation system that
can provide location and time information whenever there is an unobstructed line
of sight (LOS) to four or more GPS satellites [1]. Such a system provides critical capabilities to military, civil, and commercial
applications around the world. On the other
hand, considering the fact that people today
spend more than 80% of their time in indoor environments, accurate indoor localization is highly desirable and has a great
potential impact on many applications.
Unfortunately, the use of GPS satellites to
enable indoor localization is a nonstarter
due to a variety of reasons including poor
signal strength, multipath effect, and limited on-device computation and communication power [2]. Therefore, over the past
two decades, the research community has
Digital Object Identifier 10.1109/MSP.2016.2600734
Date of publication: 4 November 2016

However, when there exist obstacles
between the localized device and the
anchors, the localization performance
degrades significantly. In other words,
the performance of ranging-based systems cannot maintain under non-lineof-sight (NLOS) scenarios, which is
very common for an indoor environment. Such degradation is due to that
the physical ranging rules that translate the collected information into the
distances are impaired by the blockage
and multipath components naturally
existing indoor. Developing a general
physical ranging rule that suits NLOS
conditions is practically difficult, if
not impossible, due to the complicated
indoor environment, which motivates
the development of the fingerprintbased IPSs. A summary of the existing
state-of-the-art capabilities from the
Microsoft-hosted Indoor Localization
Competitions is given in Figure 1, in

Minimum
Anchors

Low Cost?

Res. (m)
LOS

Res. (m)
NLOS

RSSI

1-3

5-10

Active RFID, iBeacon, SPIRIT Navigation,
Modulated LEDs

TOA
TDOA

0.2-0.4

1-5

UWB, Decawave, Time Domain, Zebra,
Nanotron

AOA

0.4

1-5

None

Time
Reversal

0.02

Origin Wireless

Technology

Existing
Hardware?

been urgently seeking new technologies that can enable high-accuracy indoor
localization. However, the results are still
mostly unsatisfactory. Microsoft hosted
Indoor Localization Competitions in recent years and concluded that "the indoor
location problem is not solved" [3].
Many indoor positioning systems
(IPSs) have been developed by leveraging radio wave, magnetic field, acoustic
signal, or other sensory information collected by mobile devices [4]. Most of
these systems are based on the ranging
technique. Ranging is a process to determine the distance from one location
to another by utilizing the collected
information such as the received signal
strength indicator (RSSI) and/or time of
arrival (TOA). Typically, these systems
require multiple anchors at known
locations and dedicated devices to collect fine-grained information for accurate ranging.

Commercial Examples

figure 1. State-of-the-art IPSs.
128

IEEE SIgnal ProcESSIng MagazInE

November 2016

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