MBOC (multiplexed binary offset carrier)
MBOC (Multiplexed Binary Offset Carrier) is a modulation scheme used in Global Navigation Satellite Systems (GNSS) to transmit navigation signals. It is a combination of two modulation schemes, Binary Offset Carrier (BOC) and Multiplexed BOC (MBOC). MBOC was developed to improve the performance of GNSS signals in challenging environments, such as urban canyons, where signal interference and reflections are common.
The MBOC modulation scheme is designed to provide better signal quality and higher accuracy by reducing the noise and multipath effects on the received signal. It achieves this by using a combination of two spreading codes, namely the primary code and the secondary code. The primary code is a long code that is used to spread the signal in the time domain, while the secondary code is a short code that is used to spread the signal in the frequency domain. The combination of these two codes results in a more robust signal that is less susceptible to interference and multipath.
The MBOC modulation scheme is defined by the following equation:
s(t) = ∑[a_n BOC_n(t-τ_n)] + ∑[a_n MBOC_n(t-τ_n)]
Where s(t) is the MBOC modulated signal, a_n is the amplitude of the n-th satellite signal, BOC_n(t-τ_n) is the BOC signal of the n-th satellite with time offset τ_n, and MBOC_n(t-τ_n) is the MBOC signal of the n-th satellite with time offset τ_n.
BOC modulation is a form of binary modulation that has a higher spectral efficiency compared to other binary modulations. The BOC signal is formed by adding a binary data signal to a carrier signal that has been offset by a specific frequency. The carrier frequency is usually chosen such that it is orthogonal to the GPS L1 or L5 frequency, which reduces the interference from other signals. BOC modulation is known to be highly resistant to multipath interference and noise.
The MBOC modulation scheme uses a combination of BOC and MBOC modulations. The BOC modulation is used for the primary code, and the MBOC modulation is used for the secondary code. The primary code is a long code that is used to spread the signal in the time domain, while the secondary code is a short code that is used to spread the signal in the frequency domain. The combination of these two codes results in a more robust signal that is less susceptible to interference and multipath.
The MBOC modulation scheme has several advantages over other modulation schemes used in GNSS. One of the main advantages is that it provides a higher signal-to-noise ratio (SNR) compared to other modulation schemes. This is because the MBOC modulation scheme uses a combination of BOC and MBOC modulations, which reduces the noise and interference on the received signal.
Another advantage of the MBOC modulation scheme is that it provides better accuracy and precision in challenging environments. This is because the MBOC modulation scheme is less susceptible to multipath interference and reflections, which are common in urban canyons and other challenging environments.
The MBOC modulation scheme is also compatible with other GNSS systems, such as the Galileo and Beidou systems. This means that MBOC signals can be received by a wide range of GNSS receivers, which improves the availability and reliability of the system.
In conclusion, the MBOC modulation scheme is a powerful modulation scheme used in GNSS to improve the performance of navigation signals. It is a combination of BOC and MBOC modulations that provides a higher signal-to-noise ratio, better accuracy, and precision in challenging environments. The MBOC modulation scheme is compatible with other GNSS systems, which enhances the interoperability and availability of the system. The MBOC modulation scheme has been adopted by several GNSS systems, including the GPS L1C, Galileo E1, and Beidou B1I signals.