GPS World September 2006 - 1

Sept. 2006 The Business and Technology of Global Navigation and Positioning
w w w. g p s w o r l d . c o m Phase Wind-Up Analysis Assessing Real-Time
Kinematic Performance Don Kim, Luis Serrano, and Richard Langley see the
same steady phase wind-up term but circularly polarized antenna's phase
Doppler shift, which alters both the GPS A each channel will have a
different amount depends directly on the antenna's carrier phase and
ranging modulation group of spin modulation phase and amplitude
orientation with respect to the sig- delay. The polarization-induced
frequency determined by the elevation angle. This ad- nal source. As a
result, the observed carrier shift is sometimes called rotational Doppler.
ditional spin modulation cannot be can- phase depends on the relative
orientation of In this article, we will concentrate our celled by the
double-differencing operation. the transmitting and receiving antennas as
discussion on the phase wind-up associated Although the observed carrier
phase from well as the direction of the line of sight be- with rotation of
receiving antennas. non-aligned antennas cannot be cancelled tween them.
Changing the receiver antenna Observable Effects by the
double-differencing operation, it has orientation changes the reference
direction been generally ignored in GPS applications The different effects
of phase wind-up can and thus the measured phase. Similarly, due to the
relatively small effect. However, be observed depending on the
relationship changing the orientation of the transmitting related to our
recent work on an RTK-based between the spin axis of the platform host-
antenna changes the direction of the elec- vehicle navigation system, we
have observed ing the antenna and the antenna boresight. tric field at the
transmitting antenna and A base-mounted antenna the spin axis in a few
cases that the phase wind-up can subsequently that at the receiving
antenna. is aligned with the antenna boresight has a significantly degrade
the performance of the The result is also a change in the measured phase
that depends directly on the antenna's system. In this article, we
introduce three phase. As one or both of the antennas ro- orientation. In
this case, the phase shift is phase wind-up observables and use them to
tate, the phase change accumulates and is common to all signals, from
different satel- demonstrate qualitative assessment of the referred to as
phase wind-up. It has also been lites, simultaneously received and there-
phase wind-up in several test scenarios. called phase wrap-up and the
right-hand fore to all receiver channels. By double- circular polarization
phase component. Phase Wind-up Observables differencing the measurements
between In addition, the rotation of the receiving satellites and between
receivers , therefore, antenna causes an apparent change in the To
validate the effects of the phase wind-up this common phase shift can be
removed. GPS carrier frequency. It is distinguished in the carrier-phase
measurements, we use For a rotating circumference-mounted from the normal
Doppler shift in that phase the phase wind-up observables described in
antenna the spin axis is not aligned with wind-up is carrier-frequency
independent this section. For the present, these observ- the antenna
boresight , however, the phase and does not affect ranging modulation
ables are not used for correcting the effects term appears to be the sum
of the common group delay. Note that Doppler shift is the of the phase
wind-up but for the qualitative phase shift plus some small perturbation
apparent change in carrier frequency caused assessment of its effects on
the carrier-phase that increases as the depression angle devi- by movement
along a receiver's line-of-sight measurements. Potential use of these
observ- ates from the spin axis. All of the channels LOS . A GPS receiver
antenna can sense ables in correcting the effects of the phase         

GPS World September 2006

Table of Contents for the Digital Edition of GPS World September 2006

GPS World September 2006 - 1
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