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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All have most or all of their power contained within 24 MHz, but the different locations of large slopes show that their power is located in different portions of the band. In addition, a smaller spectral separation coefficient indicates the ability of a modulation to provide enough processing gain against multipleaccess interference from similar signals so that it can support higher data rates.
While the signals are designed to occupy the 24 MHz allocation, the 30 MHz bandlimiting approximates that which occurs at GPS satellites. Acquisition architectures have been developed that process each sideband separately . By providing almost 7 dB better spectral separation with itself than is provided by 1.
Receiver radiknavigation 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.
However, studies and hardware testing have demonstrated that the BOC modulation designs described in this section provide robust and practical performance. For first-order performance analysis of codetracking error in white noise, let the correlation integration time within the discriminator raadionavigation T units of secondsand let BL units of hertz be the one-sided noise-equivalent rectangular bandwidth of the code-tracking loop. One example in which single-sideband processing might be useful is in a portable wireless device, such as a cellular telephone, that includes a radio navigation satellite service RNSS receiver.
In some applications, however, the implementation simplicity afforded by the opportunity to process narrower bandwidths may offset these disadvantages. BOC modulation has several variants: Furthermore, the redundancy in the upper and lower sidebands of BOC modulations offers practical advantages in receiver processing for signal acquisition, code tracking, carrier tracking, and data demodulation. The calculation assumes the receiver has a 24 MHz front-end bandwidth, and that NELP uses good choices of early — late spacing — 0.
The correlation function from sidelobe processing is a bandlimited version of the correlation function for a PSK-R binwry at the spreading code rate of the BOC modulation — a much broader correlation function than that of the dual-sideband BOC modulation.
The columns for BOC 5,2 modulation and modulatiobs. The spectral separation coefficient, defined in equation 16indicates the extent to which signals interfere with each other. The curves are well-behaved for early — late spacings of less than 60 ns, but the slope reverses for early — late spacings of 60 — 70 ns. Engineering judgment is still needed in selecting practical BOC modulations.
The binary offset carrier BOC modulation was developed for this purpose . Packet Switching in Ra Simple logic indicates whether the prompt tap is no longer tracking the main peak and directs how to maintain track of the main peak. Further, more advanced modulations forr better share existing frequency allocations with each other and with heritage signals, thus preserving spectrum. The final section summarizes the findings of this work. Implementation considerations motivated consideration of a square-wave subcarrier cTs t in equation 1 and a rectangular unfiltered spreading symbol nTs tproducing a constant-modulus complex envelope.
Another motivation for sideband processing of BOC modulations is interference avoidance. While the set of measures does not completely define the design space, it does provide important insights into the suitability of a modulation for radionavigation.
The zero crossings nearest the radionavifation peak occur at approximately 54 ns.
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Considered in this sense, the BOC modulation generalizes a Manchester modulation to more than one zero crossing per spreading symbol radionavigztion.
The maximum of the power spectral density for offsdt BOC 5,2 modulation is more than 6 dB lower than that for 1. To examine the effect of multipath on the code tracking of different modulations using NELP, consider a simple model of multipath as a specular reflection having some amplitude relative to the direct path, arriving at some phase and delay, with all values time-invariant over the time period of interest.
Simpler receivers can process only one sideband of the signal, using front-end bandwidths as low as 2 MHz. Before being selected, it was radiionavigation to rigorous scrutiny, ranging from analysis to hardware demonstrations, as were other candidate modulations. For example, n 4 for both BOC 10,5 and BOC 8,4 modulations, and their spectra modulatios two sidelobes between the two mainlobes.
BOC 5,2 has substantially less multipath-induced bias at most multipath delays. The normalized autocorrelation functions are portrayed in Figure 6, showing the narrower peak and multimode structure of the BOC correlation function. Comparing the code-tracking errors in the preceding figures with corresponding discriminator gains plotted earlier reveals an important insight.
Binary offset carrier modulation
This paper describes a class of particularly attractive modulations called binary offset carrier BOC. However, the worst-case bias error is slightly greater 5. If desired, filtering can be used to select only the desired sideband and prevent aliasing at lower sampling rates. BOC raidonavigation have many good attributes.
As in conventional PSK, the zero crossings of each mainlobe are spaced by twice the code rate, while the zero crossings of each sidelobe are spaced at the code rate. The subcarrier frequency is actually 1. The main idea behind BOC modulation is to reduce the interference with BPSK -modulated signal, which has a sinc function shaped spectrum.
In fact, use of a BOC 5,1 or BOC 5,2 modulation allows high-performance receivers to employ front-end bandwidths as narrow as 12 MHz with almost no performance degradation as compared with wider bandwidths, offering the opportunity for exceptional performance with compact antennas and lower-power electronics. The normalized autocorrelation functions are portrayed in Figure 8, showing the narrower peak and multimode structure of the BOC correlation function.
Generation of data, spreading code, subcarrier, and RF uses a common clock so that zero crossings are aligned. Figure 19 shows the worst-case multipath bias errors for specular reflection received 6 dB weaker than the direct path for 1.
The resulting binary-valued modulation, referred to as binary offset carrier, is the subject of this paper. Current signaling for GPS employs phase shift keying PSK modulation using conventional rectangular non — return to zero spreading symbols.
Even with these advantages, the M-code signal is almost as separated from this new modulation as from heritage signals using 1. The support of the BOC 5,2 autocorrelation function is half that of the autocorrelation function for 1.
The error becomes very large for early — late spacing near 70 ns, corresponding to the slope reversal in the S-curves observed in Figure 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. As other sources of error diminish, contributions from noise and multipath start to dominate. BOC 10,5 provides slightly better spectral separation with itself, allowing more signals with greater power variation.
Figure 20 shows similar results for BOC 5,2 and 1.