Therefore, L1 band signals, such as the GPS L1 C/A and Galileo E1 signals, are much more interesting on this side, since there is potentially a factor five or ten in the number of samples to process and in the processing speed, thanks to the ratio of the processing and sampling frequencies. This high chipping rate implies a high sampling frequency, which implies itself a significant amount of samples to store and process, and a lower ratio between the clock frequency of the acquisition process and the sampling frequency leading to a longer processing time. For example, L5 band signals, such as the GPS L5 and Galileo E5 signals, have a high chipping rate (10 times higher than L1 frequency signals). The answer to this question is not so simple, because each signal has its own advantages and drawbacks. This paper aims to answer this question, and quantify it with application examples. Therefore, the main question is: “Which signal should be acquired first?”, to then help the acquisition of the other(s) signal(s). However, knowing one gives precious information on the second) the relative speed being the same, the Doppler are proportional with a known factor (even with the offset due to the local oscillator). The path traveled is the same, therefore the code delay is about the same (there is a slight difference due to the ionosphere that affects them differently. Indeed, considering two signals coming from the same satellite (for example Global Positioning System (GPS) L1 C/A and L5 signals): They are synchronized (the primary codes start at the same time, and the data and secondary code transitions are synchronized). There are now several signals available per constellation, and it is not necessary to acquire the different signals coming from one satellite independently. Nowadays, Fast Fourier Transforms (FFT) are omnipresent in acquisition architectures to accelerate the acquisition, and the amount of memory needed is a major factor in a design. This is a computationally demanding operation since there are numerous possibilities to test, and today’s receivers are targeting higher and higher sensitivities and the ability to process more and more signals. The first stage of a Global Navigation Satellite System (GNSS) receiver is the acquisition, whose aim is to detect the signal and roughly estimate the code delay and the carrier frequency. Moreover, precise assistance providing accurate Doppler could significantly reduce the L5 complexity below the L1 complexity. The E5 signal is always more complex to acquire than E1, while the L5 signal can have a complexity close to the L1 C/A in some cases. The results show that overall the L5 band signals are more complex to acquire, but it depends strongly on the conditions. The goal of this paper is therefore to compare the acquisition of L1 and L5 bands signals (GPS L1 C/A and L5, Galileo E1 and E5a/b) to determine which one is more complex and by which factor, in terms of processing time and memory, considering hardware receivers and the parallel code search. Indeed, L5 band signals have several advantages such as stronger power, lower carrier Doppler, or a pilot channel, unlike the Global Positioning System (GPS) L1 C/A signal. Although the common thought would tell the L1 band signals which are narrowband, an accurate comparison has never been done, and the decision is not as easy as it seems. Therefore, the question of which one to acquire first rises naturally. A receiver does not need to acquire independently the signals in both bands coming from a same satellite, since their carrier Doppler and code delay are closely related. Nowadays, civil Global Navigation Satellite System (GNSS) signals are available in both L1 and L5 bands.
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