Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2002-09-16
2004-03-30
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S357490
Reexamination Certificate
active
06714159
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for performing positioning, comprising the steps of receiving a signal transmitted by satellites and spread spectrum modulated with a repetition code, performing acquisition of the received spread spectrum modulated signal, measuring the code phase of the received spread spectrum modulated signal, and receiving satellite Ephemeris parameters which are used in the positioning. The invention also relates to an electronic device comprising means for performing positioning, comprising means for receiving a signal transmitted by satellites and spread spectrum modulated with a repetition code, means for acquisition of the received spread spectrum modulated signal, means for measuring the code phase of the received spread spectrum modulated signal, and means for receiving satellite Ephemeris parameters to be used in the positioning.
BACKGROUND OF THE INVENTION
In positioning systems based on satellite positioning, a positioning receiver attempts to receive the signals of at least four satellites in order to find out the position of the positioning receiver and the time data. An example of such a satellite positioning system is the GPS system (Global Positioning System), comprising a plurality of satellites orbiting the globe according to predefined orbits. These satellites transmit positioning data, on the basis of which the position of a satellite can be determined at each moment of time, in case the exact time data used in the satellite positioning system is known in the positioning receiver. In the GPS system, the satellites transmit a spread spectrum signal modulated with a code which is individual for each satellite. Thus, the positioning receiver can distinguish the signals transmitted by the different satellites from each other by using a reference code which is generated locally in the positioning receiver and corresponds to the satellite code.
Each operating satellite of the GPS system transmits a so-called L
1
signal at the carrier frequency of 1575.42 MHz. This frequency is also indicated with 154f
0
, where f
0
=10.23 MHz. Furthermore, the satellites transmit another ranging signal at a carrier frequency of 1227.6 MHz called L
2
, i.e. 120f
0
. In the satellite, the modulation of these signals is performed with at least one pseudo sequence. This pseudo sequence is different for each satellite. As a result of modulation, a code-modulated wideband signal is generated. The modulation technique used in the receiver makes it possible to distinguish between the signals transmitted by different satellites, although the carrier frequencies used in the transmission are substantially the same. This modulation technique is called code division multiple access (CDMA). In each satellite, for modulating the L
1
signal, the pseudo sequence used is e.g. a so-called C/A code (Coarse/Acquisition code), which is a code from the family of the Gold codes. Each GPS satellite transmits a signal by using an individual C/A code. The codes are formed as a modulo-
2
sum of two 1023-bit binary sequences. The first binary sequence G
1
is formed with the polynome X
10
+X
3
+1, and the second binary sequence G
2
is formed by delaying the polynome X
10
+X
9
+X
8
+X
6
+X
3
+X
2
+1 in such a way that the delay is different for each satellite. This arrangement makes it possible to generate different C/A codes by using identical code generators. The C/A codes are thus binary codes whose chipping rate in the GPS system is 1.023 MHz. The C/A code comprises 1023 chips, wherein the iteration time (epoch) of the code is 1 ms. The carrier of the L
1
signal is further modulated by navigation information at a bit rate of 50 bit/s. The navigation information comprises information about the “health”, orbit, time data of the satellite, etc.
To detect the signals of the satellites and to identify the satellites, the receiver must perform acquisition, whereby the receiver searches for the signal of each satellite at the time and attempts to be synchronized and locked to this signal so that the information transmitted with the signal can be received and demodulated.
The positioning receiver must perform the acquisition e.g. when the receiver is turned on and also in a situation in which the receiver has not been capable of receiving the signal of any satellite for a long time. Such a situation can easily occur e.g. in portable devices, because the device is moving and the antenna of the device is not always in an optimal position in relation to the satellites, which impairs the strength of the signal coming in the receiver. In portable device, the aim is also to reduce the power consumption to a minimum. Thus, for example, a positioning receiver arranged in connection with a wireless communication device is not necessarily kept in operation all the time, but primarily when there is a need to perform positioning. This causes, e.g., the problem that the time taken for the positioning is relatively long, because the positioning receiver must first perform acquisition, after which it starts to receive navigation information either from the satellite signal or, e.g., from a base station in a mobile communication network. The positioning receiver can perform the positioning first after it has received a sufficient quantity of navigation information. Furthermore, the positioning receiver must take pseudo range measurements which, in receivers of prior art, are started after receiving at least the satellite Ephemeris parameters of the navigation information. This will prolong the time taken from the turning on of the positioning receiver to the completion of the first position-time fix.
In devices which are particularly intended for positioning, positioning is performed continuously, wherein the time taken for obtaining this first location-time fix is not a particularly big problem in view of continuous use under good signal conditions. However, in some portable electronic devices with also other functions than the positioning receiver, the positioning receiver is turned off for a majority of the operating time of the electronic device, to prolong the operating time of the batteries. Thus, there is often a need to perform positioning in a situation in which sufficiently up-to-date previous positioning data or navigation information is not available. Thus, the time taken for the first location-time fix may be inconveniently long. In some situations, for example when making an emergency call from a mobile communication device, it should be possible to determine the position of the mobile communication device quickly and so precisely that help can be directed to the correct location. Thus, the time taken for obtaining the first position time fix may delay the provision of help to a significant degree.
The positioning arrangement has two primary functions:
1. to calculate the pseudo range between the receiver and the different GPS satellites, and
2. to determine the position of the receiver by utilizing the calculated pseudo ranges and the position data of the satellites. The position data of the satellites at each time can be calculated on the basis of the Ephemeris and time correction data received from the satellites.
The distances to the satellites are called pseudo ranges, because the time is not accurately known in the receiver. Thus, the determinations of position and time are iterated until a sufficient accuracy is achieved with respect to time and position. Because time is not known with absolute precision, the position and the time must be determined e.g. by linearizing a set of equations for each new iteration.
The calculation of the pseudo range can be performed, for example, by measuring the code phases of the satellite-signals in the receiver.
The above-mentioned acquisition and frequency control process must be performed for each signal of a satellite which is received in the receiver. Some receivers may have several receiving channels, wherein an attempt is made on each receiving channel to acquire t
Alanen Kimmo
Syrjārinne Jari
Mull F H
Nokia Corporation
Tarcza Thomas H.
Ware Fressola Van Der Sluys & Adolphson LLP
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