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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Figure 13 shows results for BOC 10,5 modulation, computed using equation The S-curve relates the correction produced by a discriminator for a given error.
Further, more advanced modulations can better share existing frequency allocations with each other and with heritage signals, thus preserving spectrum. Initial work on offset carrier modulations focused on a sinusoidal subcarrier and a lowpass-filtered spreading symbol.
For early — late spacing of less than 45 ns, the code-tracking accuracy closely approaches the information-theoretic lower bound computed using equation 14indicating little benefit from using smaller early — late spacings.
This page was last edited on 24 Novemberat Conventional thinking has indicated that codetracking accuracy can be inferred from discriminator gain, with larger discriminator gain indicating smaller code-tracking errors.
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. Retrieved 14 December The third section introduces some example BOC modulations of particular interest, defines measures for evaluating characteristics of modulations for radionavigation, and evaluates these binart for the example BOC modulations.
However, the worst-case bias error is slightly greater 5.
Betz_Binary Offset Carrier Modulations for Radio Navigation_百度文库
When n 1, equation 8 becomes sin f Ts f Ts 2 so that qnTs t consists of n half-cycles of a square wave, that is, n alternating values of 1 and 1. Views Read Edit View history. The next section summarizes essential characteristics of BOC modulations. The discriminator gain is defined as the 0: 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.
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.
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. 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 columns for BOC 5,2 modulation and 1. Acquisition of BOC modulations can also take advantage of the sideband structure. This carrier processing is identical to that for PSK-R modulations, and also supports conventional approaches for data demodulation. The final section summarizes the findings of this work.
A similar approach could employ a discriminator that would operate on the correlation function for one sideband or the noncoherently combined correlation functions from each sideband to maintain the coarse track of the main peak, cross-coupled with a fine tracking discriminator operating on the wideband signal, for best performance. The subcarrier frequency is actually 1. Consequently, the out-of-band loss is only 0.
This paper describes a class of particularly attractive modulations called binary offset carrier BOC. 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.
Figure 18 shows the worst-case multipath bias errors for specular reflection received 6 dB weaker than the direct path for BOC 8,4 has substantially less multipath-induced bias at most delay values and has a worst-case multipath error of 3.
While BOC modulations were developed to provide spectral isolation from heritage signals modulating the same carrier frequency, it was quickly determined that they offer performance advantages as well. Considered in this sense, the BOC modulation generalizes a Manchester modulation to more than one zero crossing per spreading symbol i. However, BOC modulations offer some unique opportunities for variations in receiver processing that can provide advantages in implementation and performance. Journal of Communications Technology and Electronics.
Still others, such as the spectral separation coefficient, were formalized more recently. A very small antenna and simple RF electronics having only enough bandwidth to pass one sideband, combined with the reduced sampling rate and processing throughput requirements associated with the bandwidth of one sideband, would help minimize the cost, size, and power consumption of the receiver.
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. Further, the BOC 10,5 modulation of the M-code signal offers significant advantages in terms of code-tracking accuracy and mitigation of multipath effects.
By providing almost 7 dB better spectral separation with itself than is provided by 1. In many respects, including maximum power spectral density, out-of-band loss, and spectral separation with itself, the two modulations are very similar. Next, the paper outlines approaches for receiver processing of BOC modulations. Following this sub-carrier multiplicationthe spectrum of the signal is divided into two parts, therefore BOC modulation is also known as a split-spectrum modulation.
Binary offset carrier modulation
Implementation considerations motivated consideration of a square-wave subcarrier radionavigatioj t in equation 1 and a rectangular unfiltered spreading symbol nTs tproducing a constant-modulus complex envelope. These binary PSK modulations can readily be extended to higher-order alphabets.
BOC modulations have many good attributes.
To understand why this phenomenon occurs, note that two different and counteracting effects occur with early — late processing of bandlimited signals as the early — late spacing becomes small while the bandwidth of the codetracking loop is held constant. The normalized autocorrelation functions are portrayed in Figure 8, showing the narrower peak and multimode structure of the BOC correlation function.
Modulatiions Journal on Wireless Communications and Networking. A conventional code-tracking loop can be used with a discriminator based on early — late processing or an analogous approach. Since the equivalent rectangular bandwidth of BOC 5,2 is 4 times greater than that of 1. The detailed design and performance of noncoherent early — late processing NELP are presented in the following section. Also, increasing transmitted power to improve accuracy is expensive and has a limited effect on multipath performance.
Another motivation for sideband processing of BOC modulations is interference avoidance. The quantities and t0 reflect arbitrary offsets in phase and time, respectively, in the complex envelope relative to some reference. BOC modulation has several variants: