Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2001-03-18
2002-10-29
Blum, Theodore M. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S357490, C701S213000
Reexamination Certificate
active
06473033
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to pseudolite transmitters, or more specifically, to an integrated split spectrum pseudolite/satellite base station transmitter.
2. Discussion of the Prior Art
The Global Positioning System (GPS) is a system of satellite signal transmitters that transmits information from which an observer's present location and/or the time of observation can be determined. Another satellite-based navigation system is called the Global Orbiting Navigational System (GLONASS), which can operate as an alternative or supplemental system.
The GPS was developed by the United States Department of Defense (DOD) under its NAVSTAR satellite program. A fully operational GPS includes more than 21 Earth orbiting satellites approximately uniformly dispersed around six circular orbits with four satellites each, the orbits being inclined at an angle of 55° relative to the equator and being separated from each other by multiples of 60° longitude. The orbits have radii of 26,560 kilometers and are approximately circular. The orbits are non-geosynchronous, with 0.5 sidereal day (11.967 hours) orbital time intervals, so that the satellites move with time relative to the Earth below. Generally, four or more GPS satellites will be visible from most points on the Earth's surface, and can be used to determine an observer's position anywhere on the Earth's surface, 24 hours per day. Each satellite carries a cesium or rubidium atomic clock to provide timing information for the signals transmitted by the satellites. An internal clock correction is provided for each satellite clock.
Each GPS satellite continuously transmits two spread spectrum, L-band carrier signals: an L
1
signal having a frequency f
1
=1575.42 MHz (nineteen centimeter carrier wavelength) and an L
2
signal having a frequency f
2
=1227.6 MHz (twenty-four centimeter carrier wavelength). GPS satellites transmit both a C/A code and a P-code. There are a total of 32 pseudo random (PRN) C/A codes, with each satellite generating a different C/A code. The code modulations that produce either a P-code or a C/A code are impressed onto the L
1
carrier and the L
2
carrier.
The deployment of additional frequencies is being planned by the DOD. More specifically, DOD is exploring several options to maintain, or improve, the performance of civilian applications of GPS without compromising military utilities. Indeed, the civilian community does not have a second frequency. Today, corrections are based upon L
2
, which is a military frequency, and subject to DOD use and control. The addition of L
5
to the GPS constellation on the Block HF satellites would, at a minimum, assure the civilian community of the existence of reliable dual frequency transmissions.
As a result, a new GPS frequency, L
5
, is being considered for civil sector uses in order to reserve L
2
for military purposes. This new frequency is targeted to provide both carrier phase and C/A-code range information. Two frequencies are proposed for L
5
; the first being 1207 MHz yielding a 368 MHz separation from L
1
, and the second being 1309 MHz having a separation of 266 MHz from
The GPS satellite bit stream includes navigational information on the ephemeris of the transmitting GPS satellite (which includes orbital information about the transmitting satellite within next several hours of transmission) and an almanac for all GPS satellites (which includes a less detailed orbital information about all other satellites). The transmitted satellite information also includes parameters providing corrections for ionospheric signal propagation delays (suitable for single frequency receivers) and for an offset time between satellite clock time and true GPS time. The navigational information is transmitted at a rate of 50 Baud.
A second satellite-based navigation system is the Global Orbiting Navigation Satellite System (GLONASS), placed in orbit by the former Soviet Union and now maintained by the Russian Republic. GLONASS uses 24 satellites, distributed approximately uniformly in three orbital planes of eight satellites each. Each orbital plane has a nominal inclination of 64.8° relative to the equator, and the three orbital planes are separated from each other by multiples of 120° longitude. The GLONASS satellites have circular orbits with a radii of about 25,510 kilometers and a satellite period of revolution of 8/17 of a sidereal day (11.26 hours). A GLONASS satellite and a GPS satellite will thus complete 17 and 16 revolutions, respectively, around the Earth every 8 days. The GLONASS system uses two carrier signals L
1
and L
2
with frequencies of f
1
=(1.602+9k/16) GHz and f
2
=(1.246+7k/16) GHz, where k (=1,2, . . . 24) is the channel or satellite number. These frequencies lie in two bands at 1.597-1.617 GHz (L
1
) and 1,240-1,260 GHz (L
2
). The L
1
code is modulated by a C/A-code (chip rate=0.511 MHz) and by a P-code (chip rate=5.11 MHz). The L
2
code is presently modulated only by the P-code. The GLONASS satellites also transmit navigational data at a rate of 50 Baud. Because the channel frequencies are distinguishable from each other, the P-code is the same, and the C/A-code is the same, for each satellite. The methods for receiving and demodulating the GLONASS signals are similar to the methods used for the GPS signals.
The European Union plans to develop by 2008 the system of navigation and positioning by satellite designed exclusively for civil purposes-the GALILEO system. GALILEO should enable each individual, by way of a small, cheap individual receiver, to know his or her position to within a few meters, with guaranteed continuity of transmission of the signal. The GALILEO project, supported by the European Space Agency, aims to launch a series satellites at around 20 000 km to be monitored by a network of ground control stations, in order to provide world cover. GALILEO system should be integrated into the existing GNSS-Global Navigation Satellite System, comprising at present time GPS and GLONASS satellite systems.
Reference to a Satellite Positioning System or SATPS herein refers to a Global Positioning System, to a Global Orbiting Navigation System, to a GALILEO project, and to any other compatible satellite-based system that provides information by which an observer's position and the time of observation can be determined, all of which meet the requirements of the present invention.
A Satellite Positioning System (SATPS), such as the Global Positioning System (GPS) or the Global Orbiting Navigation Satellite System (GLONASS), uses transmission of coded radio signals, with the structure described above, from a plurality of Earth-orbiting satellites. A SATPS antenna receives SATPS signals from a plurality (preferably four or more) of SATPS satellites and passes these signals to an SATPS signal receiver/processor, which (1) identifies the SATPS satellite source for each SATPS signal, (2) determines the time at which each identified SATPS signal arrives at the antenna, and (3) determines the present location of the SATPS satellites.
The range (r
i
) between the location of the i-th SATPS satellite and the SATPS receiver is equal to the speed of light c times (&Dgr;t
i
), wherein (&Dgr;t
i
) is the time difference between the SATPS receiver's clock and the time indicated by the satellite when it transmitted the relevant phase. However, the SATPS receiver has an inexpensive quartz clock which is not synchronized with respect to the much more stable and precise atomic clocks carried on board the satellites. Consequently, the SATPS receiver estimates a pseudo-range (pr
i
) (not a true range) to each satellite.
After the SATPS receiver determines the coordinates of the i-th SATPS satellite by demodulating the transmitted ephemeris parameters, the SATPS receiver can obtain the solution of the set of the simultaneous equations for its unknown coordinates (x
0
, y
0
, z
0
) and for unknown time bias error (cb). The SATPS recei
Blum Theodore M.
Tankhilevich Boris G.
Trimble Navigation Ltd
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