Clock Compensation Two-Way Ranging (CC-TWR)
Based on Ultra-Wideband Communication
Yanming Gu
Control and Simulation Center
Harbin Institute of Technology
Harbin, China
YeomanKu@gmail.com
Baoqing Yang
Control and Simulation Center
Harbin Institute of Technology
Harbin, China
ybq@hit.edu.cn
Abstract—High accuracy and precision of positioning in Ultra-
Wideband (UWB) localization system depends on the quality of
clock oscillators, which influences system performance. This is a
very common method of measuring the distance from the target to
the reference node by two-way range (TWR) or symmetric double-
sided two-way ranging (SDS-TWR), and then obtaining a 2D or
3D coordinate through the relevant algorithm. However, these
methods may not meet the high accuracy or real-time requirements
of the occasion. This paper presents a new way named CC-TWR
based on TWR and clock compensation which can effectively
reduce the influence of clock error (clock drift and frequency
drift). UWB Ranging System was implemented and tested in static
and dynamic practical cases based on DW1000 chip. The effects of
clock errors measured by this CC-TWR way greatly is small than
the traditional way from the experimental results. At the same time,
CC-TWR also has the same high refresh rate as TWR.
Keywords—CC-TWR; UWB; DWM1000; Ranging and
Positioning;
I. INTRODUCTION
Indoor wireless positioning is an indispensable way of
positioning in modern society. At present, the common indoor
positioning technology is based on infrared, ultrasonic,
Bluetooth RF technology, wireless LAN, etc. These different
indoor positioning methods have different prices, measurement
accuracy, anti-jamming capability and power consumption [7].
UWB is a relatively new method of local positioning
utilizes. UWB wireless communication technology has a
considerable bandwidth which provides a very high temporal
resolution with improved ranging accuracy [9]. Simultaneously,
UWB has a wide range of applications in the radio high-
precision positioning field because of anti-interference ability,
low power consumption, low price and so on [4].
The common methods based on high precision UWB
positioning are usually TDOA, TOA based on time
synchronization, and TOF (Time of Fight) based on TWR
without time synchronization [1][10]. In many cases, clock
synchronization requires a larger amount of work, and is not so
suitable for small capacity. At this time, high-precision location
information can often be provided through the TOF positioning
way which has simple, practical and more stable performance.
In the traditional way of TWR, there is a distance error due
to clock drift and frequency drift, causing the error between the
measured distance and the true distance changed over time.
Some improved ranging methods such as SDS-TWR are
presented in [1]. This way reduces the effect of the clock on the
ranging error [2]. However, this way reduces the efficiency of
ranging and still retains a large error term relative to the CC-
TWR method proposed in this paper.
This paper presents the advantage of CC-TWR based on
UWB communication ranging. The experimental system of this
paper is DWM1000 module which is based on DecaWave’s
DW1000 transceiver IC with the IEEE 802.15.4-2011 ultra-
wideband standard [3]. The DWM1000 module integrates
onboard antenna, transmit and receive RF circuits, power
management and clock circuit in one module [4].
II. TWR PRINCIPLE
A. System Architecture
The system has been designed for the local positioning
system. In order to explain the principle more easily, we only
consider the distance measurement from a single tag to an
anchor. The simplified system architecture is presented in Fig.1.
Two nodes (tag and anchor) communicate between
themselves, then they can calculate the TOF (time of fight) and
distance between two nodes by exchanging radio messages.
Generally, anchor is a static reference node while tag stands for
locating points.
Fig. 1. Two-way ranging system architecture.
B. Two-way ranging (TWR) with clock drift
The tag transmits a radio message to the anchor and records
its time of transmit timestamp t0. The anchor receives the radio
message and records its time of receiving timestamp t1. After a