Indoor Positioning with GNSS-Like Local Signal Transmitters - Global Navigation Satellite Systems: Signal,Theory and Applications - page 328

infrastructure is still required, although using only one signal distributed to all the
transmitters clearly constitutes a huge improvement (also in terms of synchronisation). On
another hand, multipath mitigation with the SMICL has shown impressive results that have
been validated experimentally, as can be seen through the experimental results. But even
with the SMICL, the repeater approach has two major limitations: the difficulty to carry out
carrier phase measurement, hence limiting the accuracy attainable (although this is
sufficient for the continuity with GNSS outdoors), and poorer performance in dynamic
modes. The goal of the next step presented is to propose a synthesised approach that could
be the way to overcome these last limitations.
5. The repealite concept: Mixing the advantages of both pseudolites and
repeaters
The cycling approach, implemented until now, has a great disadvantage: carrier phase
measurements are almost impossible. In order to improve the indoor accuracy, a new
approach is proposed based on the so-called “repealites 26 ” approach which tries to cumulate
the advantages of both repeaters and pseudolites (i.e. carrier phase measurements and same
signal transmitted through all the transmitters). First theoretical works have shown a
potential of less than one metre accuracy by implementing classical code measurement
smoothing techniques using carrier phase measurements. The remaining problem is that
repealites are now transmitting simultaneously, which leads to the near-far effect. Thus
works have also been carried out concerning this effect.
5.1 Introduction to the idea
It is rather simple in principle: synchronisation is advantageously carried out when the same
single signal is transmitted by all the repealites and simultaneous transmissions allow us to
implement carrier phase measurements (Vervisch-Picois et al. 2010). Multipath is always a
problem but the SMICL, developed in the context of the repeater system, appears to be quite
an efficient answer. The pseudolite double differencing approach is probably a little bit too
complex for mass market devices (this could be discussed) thus the goal is simply to smooth
the code phase measurements with carrier phase measurements, following the classical way
of many current GNSS receivers.
The only remaining difficulty is now the near-far effect: a solution to this problem is
proposed. Note that when both multipath effects and near-far effects have found a solution,
one could consider that the pseudolite system is well suited, since two major problems are
solved. As a matter of fact, this is quite true except for synchronisation purposes. Thus, the
repealite approach seems to be rather an acceptable compromise.
5.2 The proposed system architecture
The proposed method comes from the transmitting approach of the repeated system, but
instead of the sequential mode, the transmission on each antenna is delayed in such a way
that the transmitted signals on each repealite do not interfere once they arrive at the receiver
26 Repealite is a contraction of Repeater and Pseudolite.