Experiment #4: Cooperative Localization Using UWB Ranging
Developed by: Cai Haofan & Jiang Linshan, South University of Science and Technology of China
Acknowledgements: Dr. Wu Guang
Lab Exercise: Cooperative Localization Using UWB Ranging
Experiment Objectives:
The objectives of this lab are to:
1. Learn how to use UWB Two Way Time of Flight range measurement.
2. Develop a better understanding of cooperative localization.
Part 1 - Overview
1.1
Introduction
In this lab we will use a pair of Time Domain P410 UWB transceivers (shown in Figure 1) and the Ranging and
Communications Module Reconfiguration and Evaluation Tool (RCM-RET) software package to measure the
distances between a number of transceivers. We will use the ranging measurements with some additional
algorithms to determine the accurate positions of each node (transceiver) in a system of several nodes.
Fig. 1: Time Domain P410 transceiver with Broadspec antenna.
1.2
Background
1.2.1
Localization Methods
There are many localization methods for wireless ad-hoc or sensor networks and most of them depend on distance
or angle estimation. The most common methods for ranging between two nodes are as followed:

Time-of-Arrival (ToA) or Time-Difference-of-Arrival (TDoA).
This method records the time-of-
arrival or time-difference-of-arrival for received signal. Since the propagation speed of signal can be
known, the distance can be calculated directly from the propagation time.

Received Signal Strength Indication (RSSI) This method measures the power of received signal. The
propagation loss can be calculated based on the transmit power known beforehand and then translated into
distance information using empirical models.

Angle-of-Arrival(AoA) This method measures the angle from which signals are received and then uses
geometric relationships to get the distance information.
Lab Instructions: Experiment #4
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Experiment #4: Cooperative Localization Using UWB Ranging
Developed by: Cai Haofan & Jiang Linshan, South University of Science and Technology of China
Acknowledgements: Dr. Wu Guang

Two Way Time of Flight (TWToF) This method measures the total time required to send a signal from
one unit and receive an echoed response. By knowing the total two way time of travel, the amount of time
required to retransmit the signal, the time when the first arriving energy arrived at both transceivers and the
speed of light it is possible to calculate the separation distance between the two transceivers.
In this lab, we use two Time Domain P410 UWB transceivers to conduct the ranging experiment. The ranging
method used by the P410 is Two Way Time of Flight (TWToF).
1.2.2
Cooperative Multilateration
Consider a system consisting of several P410 transceivers separated by some distance. In this system the locations of
only some of the transceivers or nodes are known. These nodes are called reference, beacon or anchor nodes. The
location of other nodes in the system not known and we will refer to them as unknown nodes. In such a system, it is
possible to compute the location of any given unknown node by measuring the distances between it and at least three
reference nodes.
In an ad-hoc deployment of nodes with a random distribution of reference or anchor node, it is highly possible that a
given unknown node might not be visible from three neighboring anchor nodes. When this occurs, an unknown node
may attempt to estimate its position by considering use of location information over multiple hops in a process we
refer to as collaborative multilateration.
If sufficient information is available to form an over-determined set of equations with a unique solution set, a node
can estimate its position and the position of additional unknown nodes by solving a set of simultaneous quadratic
equations using an optimization algorithm. In this lab we will consider the most basic topology for collaborative
multilateration.
Figure 2 illustrates the most basic topologies for collaborative multilateration. In Figure 2(a), nodes 5 and 6 are
unknown nodes, while nodes 1, 2, 3 and 4 are anchor nodes. In Figure 2(b), nodes A, B and C are unknown nodes,
while nodes 1, 2, 3 are anchor nodes. (We will focus on discussing the localization method of nodes 5 and 6 in (a)
since unknown nodes in (b) can be localized in a similar way.) Because both
Fig. 2: Basic topological structures for collaborative multilateration
Lab Instructions: Experiment #4
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Experiment #4: Cooperative Localization Using UWB Ranging
Developed by: Cai Haofan & Jiang Linshan, South University of Science and Technology of China
Acknowledgements: Dr. Wu Guang
nodes 5 and 6 have three neighbors (degree d = 3) and all the other nodes are anchor nodes with certain location
pi(i=1, 2, 3, 4), we can get the range information of d1, d2, d3, d4 and d5 and therefore form a set of quadratic
equations (see Formula 1) using these locations and distances information .
(1)
A unique position estimate for nodes 5 and 6 can be computed by solving these equations using optimization
algorithm. The optimization solution is found by taking the minimum mean square estimate of a system of
, as the function
. (See Formula 2).
1.2.3
Simulated Annealing Algorithm
The optimization algorithm we use here is the Simulated Annealing (SA) algorithm. It is a generic probabilistic
metaheuristic for the global optimization problem of locating a good approximation to the global optimum of a
given function in a large search space. The algorithm models the physical process of heating a material and then
slowly lowering the temperature to decrease defects, thus minimizing the system energy. (For more information
about the Simulated Annealing algorithm see http://en.wikipedia.org/wiki/Simulated_annealing). In this lab, you
will use the SA algorithm to determine the position of the unknown nodes. This algorithm has been implemented in
MATLAB as A_algorithm_1.m and SA_algorithm_2.m.
Part 2: Localization Experiment
2.1
Required Equipment:
Hardware: Laptop, P410 (at least two), measuring tape
Software: MATLAB


2.2
SA_algorithm_1.m
SA_algorithm_2.m
Before the Experiment
Install the RCM RET, read the RCM RET User’s Guide and P410 RCM Quick Start Guide carefully before the
experiment and pay attention to the use of Calibrate tab, Range tab, Send tab and Logging tab.
Lab Instructions: Experiment #4
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Experiment #4: Cooperative Localization Using UWB Ranging
Developed by: Cai Haofan & Jiang Linshan, South University of Science and Technology of China
Acknowledgements: Dr. Wu Guang
2.3
1.
The Experiment
First use the Calibrate tab RCM RET provides to determine and eliminate the antenna delay between two
RCMs used for ranging. The P410s will measure the distance between the phase center of the antenna on one
unit and the phase center of the antenna on the second unit. (Figure 3 illustrates the location of the phase
center.)
Phase Center
Fig. 3: Location of the antenna phase center.
However, the distance measurement also includes the delay from the electronics, through the cable, to the phase
center of the antenna. This additional delay is not representative of the distance between the two P410s and
needs to be removed through a calibration process.
On the Calibrate tab set the Number of Ranges to 100, separate the two P410s with a distance of about 1 to 2
meters and measure the distance between the phase centers of the antennas with a tape measure. Enter this
measurement into the Measured Distance (mm) field and click on the Calibrate button. RCM-RET will take
100 measurements, compare with the value measured with the tape measure and compute an antenna delay.
When finished, select Write to Flash to save the configuration parameters to the P410 permanent memory.
2.
Set up the rectangular coordinate system on an open, flat floor (plane)
3.
Choose four points on the floor to be the locations of four anchor nodes 1-4, measure and record the
coordinates of these four nodes. Then choose another two points to be unknown nodes and measure these
locations. (The distance between every two nodes must be at least 0.1 m since the required operating distance
of P410 RCM lies between 0.1m and 354m).
4.
Place one node at the first unknown location and the second node at one of the anchor locations such that you
are measuring one of the ranges in Figure 2(a). For example, set the nodes such that you are measuring
distance d15. Note that only one P410 needs to be connected to the laptop and battery while another one just
needs to be connected to the power source.
5.
Open RCM-RET, connect to one of the P410s and begin the experiment after successful connection.
6.
Select the Logging tab so that range measurements taken in the next step will be logged.
Lab Instructions: Experiment #4
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Experiment #4: Cooperative Localization Using UWB Ranging
Developed by: Cai Haofan & Jiang Linshan, South University of Science and Technology of China
Acknowledgements: Dr. Wu Guang
7.
Select the Send tab, click Range Request, enter the node id of the other P410 into the Responder Id field, click
Repeat, click Count, set Count field = 100, set Delay field = 100 and click the Send button. This will take 100
range measurements between the unknown location and an anchor point and log the resultant range
measurements to the log file defined in step 6. When the measurements have been taken, close the log.
8.
Repeat this test for the other unknown ranges in configuration a (d35, d56, d26, and d46.) Repeat this test for
configuration b.
2.4
Lab Report
Prepare a report that 1) computes the location of the unknowns using the Simulated Annealing Algorithm for both
the a and b configurations then 2) compare the results of the SA algorithm with the actual measured locations.
Lab Instructions: Experiment #4
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