Baseband Hardware Designs in Modernised GNSS Receivers - Global Navigation Satellite Systems: Signal,Theory and Applications - page 50

Signal /
Component

Correlator
Operating
Frequency
(MHz)

Resource Utilisation Power

estimate
(mW)

Registers Combina-
tional

Memory
(bits)

Galileo E5 100 667 519 - 31.98

Table 3. Resource utilisation and power consumption estimates for the Galileo E5 AltBOC
correlator; the reference signal generation is implemented with the help of AltBOC LUT
(OSSISICD, 2010)

for each channel and the Galileo E5 requires 24 accumulators per channel. Combining
the signal components before the correlation operation is possible but with significant
performance degradation. The performance degradation arises mainly due to the data-bit
ambiguity. Methods that try to avoid the data-bit ambiguity compromise on the performance
parameters of the signal in question. Therefore, again a careful consideration is required to
trade-off the performance vs. resource (or power) consumption advantage.

Table 3 shows the power consumption for the Galileo E5 AltBOC correlator if all the four
signal components are processed simultaneously. In this case there are only six accumulators
required as in the single signal component case. The reference signal in this case is generated
according to the AltBOC LUT provided in the Galileo ICD (OSSISICD, 2010). However,
the presence of data-bits (assuming that the secondary code phase resolution has already
happened) hampers the correlator output and hence the performance. Observe that the power
reduction compared to the correlator processing the signal components separately is about
19% which is a significant reduction. In other words it is possible to reduce the correlator
power consumption without losing the performance if there is a data aiding mechanism.

5.4.4 Optimising the correlator blocks across signals

Correlator design optimisation is a separate topic of itself as there are several ways to tackle
the resource utilisation issue. Moreover the optimisation is often receiver specific. Three
examples are given below where the optimisation is possible in specific correlator blocks.

First, the need for subcarrier NCO can be eliminated (even when the multiplication required
is not a power of two) by implementing clock multipliers with simple gates. For example,
in the case of Galileo E5, the x1.5 clock can be generated by simple gates that implement

2

multiplier.

Second, the carrier and code NCO for different signals from the same satellite can be
combined. This is done by programming and generating the required carrier for one of the
signals and deriving the difference in the relative Doppler for the second signal.

Third, the operating frequency for the signals can be adjusted such that the operating
frequencies can be derived from a single clock with simple dividers. The advantages of such
a clock domain construction are simplification of generation of control and timing signals as
well as ease of data transfers across different correlation stages of different signals.