Request PDF on ResearchGate | Binary Offset Carrier Modulations for Radio Navigation | Current signaling for GPS employs phase shift keying (PSK). Abstract: Current signaling for GPS employs phase shift keying (PSK) modulation using conventional rectangular (non – return to zero) spreading symbols. The first model defines the BOC modulation as the result of . The Binary Offset Carrier Modulation can be expressed as a BCS sequence . [J.W. Betz, a] J.W. Betz, Binary Offset Carrier Modulations for Radionavigation.
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Maxima of the mainlobes occur at frequencies radionwvigation below the subcarrier frequency because of the coherent interactions between the upper and lower sidebands. However, the worst-case bias error is slightly greater darrier. Conventional thinking has indicated that codetracking accuracy can be inferred from discriminator gain, with larger discriminator gain indicating smaller code-tracking errors. While the signals are designed to occupy the 24 MHz allocation, the 30 Binzry bandlimiting approximates that which occurs radionavigatiom GPS satellites.
This carrier processing is identical to that for PSK-R modulations, and also supports conventional approaches for data demodulation. Simpler receivers can process only one sideband of the signal, using front-end bandwidths as low as 2 MHz.
While the 90 percent power bandwidth of BOC 10,5 is much wider than that of This class of offset carrier modulation has been termed linear offset carrier, since its modulus takes on a continuum of values. Since it would serve as a new civil signal within L1 and L2, Vol. The locations of spectral peaks and their maximum power spectral densities are selfexplanatory.
Again, while the discriminator gain becomes smaller for early — late spacings of greater than 40 ns, the effect of early — late spacing on code-tracking accuracy cannot be inferred from this behavior. Blind estimation of sy Retrieved from modulationw https: Through the continuing development of innovative modulations and prudent use of modulation attributes such as those employed in this paper, there will be ongoing opportunities to design signals that can be readily implemented, efficiently share spectrum with other signals used for radionavigation, and provide opportunities for enhanced performance.
For a given relative amplitude of the specular reflection, the bias error introduced into code tracking can be computed for a given multipath delay d. This paper has provided two categories of fundamental results in modulation design. The resulting complex envelope was not constant modulus. In contrast, n 5 for a BOC 5,2 modulation, and its spectrum has three sidelobes between the two mainlobes, while n 10 for a BOC 5,1 modulation, and its spectrum has eight sidelobes between the two mainlobes.
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As long as the subcarrier frequency is not excessive e. Since n 5 for BOC 5,2there is a spectral sidelobe at the band center. Figure 7 portrays the spectra of BOC 8,4 and Yet the BOC 8,4 modulation provides slightly 0. To distinguish between the two, equation 13 defines the RMS bandwidth using the normalized bandlimited power spectral density, and the loss of power is accounted for separately through equation Figure 9 shows the cumulative spectra of the five specific modulations being considered.
The curves are well-behaved for early — late spacings of less than ns, but the slope reverses for early — late spacings of — ns. In many respects, including maximum power spectral density, out-of-band loss, and spectral separation with itself, the two modulations are very similar.
Based on similar results for code-tracking accuracy in Figures 15 and 16, it is clear that BOC 5,2 allows reduced receiver front-end bandwidths with less receiver complexity, with very little effect on performance. When code-tracking errors are small so that a linearized analysis applies, the variance of the code-tracking error for NELP in Betz: But bandwidth limitations preclude further improvements that might be obtained using PSK-R modulations with faster keying rates.
Binary offset carrier modulation
A BOC modulation is denoted BOC fs,fcwhere fs is the subcarrier frequency, and fc is the ofdset rate, defined by carroer 1 2Ts 2 Consistent with the convention introduced in  and followed subsequently in work on GPS and elsewhere, the designation BOCused in this paper is an abbreviation.
This approach can provide substantial immunity to some types of interference without the complexity of interference mitigation circuitry.
Even BOC 5,2 has better code-tracking accuracy than Modupations page was last edited on 24 Novemberat Journal of The Institute of Navigation Vol. For example, when the subcarrier frequency is much greater perhaps by more than a factor of 10 than the spreading code rate, the correlation function has many closely spaced in amplitude and delay peaks that can introduce anomalous effects in code tracking.
For BOC 5,1n 10, and the correlation function has 19 peaks, as predicted. Considered in this sense, modulstions BOC modulation generalizes a Manchester modulation to more than one zero crossing per spreading symbol i. More recent work suggests that BOC modulations may allow yet another signal, in addition to heritage signals modupations the new military signal, to be added to currently allocated GPS bands .
The resulting binary-valued modulation, referred to as binary offset carrier, is the subject of this racionavigation. While the discriminator gain becomes smaller for early — late spacing greater than 30 ns, the effect of early — late spacing on code-tracking accuracy cannot be inferred from this behavior, as seen later in this section. Examples of this point are provided in the next section.
BOC modulations have many good attributes.
Figure 20 shows similar results for BOC 5,2 and 1. For BOC 5,2n 5, and the correlation function has 9 peaks, as predicted. Receiver design strategies such as very wide-bandwidth receiver front ends and very small early — late spacing in code-tracking discriminators provide diminishing returns at increasing cost. While the discriminator gain becomes smaller for early — late oftset of greater than 60 ns, the effect of early — late spacing on code-tracking accuracy cannot be inferred from this behavior.
Sideband processing is straightforward to implement and has been demonstrated in hardware . Other practical factors that preclude use of excessive subcarrier frequencies include difficulty in acquiring the correlation function peak and sensitivity to channel imperfections, such as dispersive effects of the ionosphere and RF hardware, including antennas.
This lower bound is based on the performance of a maximum-likelihood estimator of time of arrival using T seconds of data, driving a tracking loop.
For early — late spacing of less than 80 ns, the code-tracking accuracy closely approaches the information-theoretic lower bound computed using equation 14indicating little benefit from using smaller early — late spacings.
Figure 17 compares code-tracking accuracy for the set of modulations considered in this paper, using a 24 MHz front-end bandwidth, a code-tracking loop with equivalent rectangular bandwidth of 0. For early — late spacing of less than 50 ns, the code-tracking accuracy closely approaches the information-theoretic lower cwrrier computed using equation 14indicating little benefit from using smaller early — late radionavigafion.
There is a very close relationship between these variations of offset carrier modulations; in fact, a linear offset carrier modulation can be processed by a receiver using a BOC reference signal having the same subcarrier frequency and code rate with very little effect on performance.