Binary Offset Carrier Modulation Technique

By Naitik Nakrani

Kinnal Dhameliya

Binary Offset Carrier

• It is a Spread Spectrum Modulation (such as CDMA)

• It is used in Satelite Navigation System (Galileo)

Spread Spectrum

• How to get ?Answer is By multiplying signal with high frequency code such as PN code

• Why to do so ? As Bandwidth is major limited contraint

PN Code

PN Code

Low Pass Filter

Binary Offset Carrier

• It is a Spread Spectrum Modulation (such as CDMA)

• It is used in Satelite Navigation System (Galileo)

Satelite Navigation System

• Used to find out the location of a Device on earth

• It requires minimum 3 satellite• To Find out Location, Distance from each

satellite is need to know

Distance = Speed X Time

Trilateration Concept

• Its mathematic Concept

Trilateration in 3D

ComparisonSystem GPS GLONASS COMPASS GalileoPolitical entity United States Russia China European UnionCoding CDMA FDMA/CDMA CDMA CDMAOrbital height 20,180 km 19,130 km 21,150 km 23,220 km

Period 11.97 hours 11.26 hours 12.63 hours 14.08 hours

Number ofsatellites At least 24

31, including24 operational1 in preparation2 on maintenance3 reserve1 on tests

5 geostationary orbit (GEO) satellites,30 medium Earth orbit (MEO) satellites

2 test bed satellites in orbit,22 operational satellites budgeted

Frequency1.57542 GHz (L1 signal)1.2276 GHz (L2 signal)

Around 1.602 GHz (SP)Around 1.246 GHz (SP)

1.561098 GHz (B1)1.589742 GHz (B1-2)1.20714 GHz (B2)1.26852 GHz (B3)

1.164–1.215 GHz (E5a and E5b)1.260–1.300 GHz (E6)1.559–1.592 GHz (E2-L1-E11)

Status Operational Operational,CDMA in preparation

10 satellites operational,25 additional satellites planned

In preparation(2014)

Galileo Vs GPS,GLONASS

• Galileo will provide a unique global Search and Rescue (SAR) function.

• Satellites will be equipped with a transponder, which is able to transfer signals from the user's transmitter to the Rescue Co-ordination Centre, which will then initiate the rescue operation.

• At the same time, the system will provide a signal to the user, informing them that their situation has been detected and that help is on the way.

• This feature is new and is considered a major upgrade compared to the existing GPS and GLONASS navigation systems, which do not provide feedback to the user.

Spectrum Interoperability

Binary Offset Carrier

• BOC modulation is used to reduce the interference with BPSK-modulated GPS signal

• where, GPS signals have most of their spectral energy concentrated around the carrier frequency, while BOC signals have low energy around the carrier frequency and two main spectral lobes further away from the carrier (thus, the name of split-spectrum).

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• A BOC-modulated signal consists of a sinusoidal carrier, a sub-carrier, a pseudo-random noise (PRN) spreading code and a data sequence

• The BOC signal is the product in the time domain of these components

• A BOC modulation is denoted BOC(fs,fc), where fs is the subcarrier frequency, and fc is the code rate,defined by

fs = m*f0, fc = n*f0.

• So BOC can also denote as BOC(m,n)

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• Here f0 is C/A (Coarse/Acquisition code) used in GPS

• It is a 1023 bit long PN Othogonal Code• Each code is repeated after every 1ms.• So bit rate is given by 1.023 Mbps• Which means f0 is 1.023 Mhz• So BOC(2,3) means• fs = 2*f0, fc = 3*f0.

BOC generator

Data

Chip Ratefc=n*f0

Sub Carrier fs=m*f0

f0=1.023 MHz

BOC(m,n)

Power Spectrul Density

Application

• The BOC(10,5) modulation used for the M-code signal, the new military signal on GPS carriers L1 and L2.

• A BOC(5,2) modulation that has been suggested as a candidate for a new civil signal on GPS carriers L1 and L2 in addition to the C/A-code or L2C signal, Y-code signal, and M-code signal, and that fits within the existing 24 MHz allocation on these carriers.

• A BOC(8,4) modulation that has very similar spectral properties to a PSK-R modulation with a spreading code rate of 10.23 MHz.

Variants

• Sine BOC (SinBOC) • Cosine BOC (CosBOC)• Alternative BOC (AltBOC)• Multiplexed BOC (MBOC)• Double BOC (DBOC)

Thank you