Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2000-02-15
2002-08-06
Beaulieu, Yonel (Department: 3661)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S357490, C701S213000, C701S215000
Reexamination Certificate
active
06429811
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to location services in radio communication systems. More particularly, the present invention relates to a method and apparatus for assisting a mobile handset in determining its location using assisted global positioning system (Assisted GPS) location determination capabilities in a radio communication system.
BACKGROUND OF THE INVENTION
A GPS receiver determines its position on Earth by using the GPS constellation of twenty-four satellites orbiting twice a day at an altitude of approximately 20,183.61 kilometers above Earth's surface. These satellites provide navigation references to allow triangulation with three to four satellites acting as precise reference points to determine position (latitude, longitude, altitude, and in some applications velocity) at the GPS receiver. The GPS satellites are provided in six orbital planes, at 55 degree inclination. Each orbital plane contains four satellites. The GPS constellation should provide a GPS receiver with four to twelve satellites being visible from any point on Earth having a clear view of the sky.
Traditionally, GPS satellites transmit ephemeris and clock correction parameters directly to GPS receivers. The ephemeris and clock correction data gives a GPS receiver all the information it needs to compute the satellite position as a function of time, and to compute the satellite clock error parameter, also as a function of time. A GPS satellite transmits the data in a broadcast mode from the satellite to the ground at a slow 50 bit per second (BPS) rate. It takes between eighteen and thirty seconds for a single GPS satellite broadcast message to be transmitted one time, depending on when the GPS receiver synchronizes with the transmitted broadcast message. The specification for the over-the-air protocol for the satellite-to-ground message is published in ICD-GPS-200 Specification, published by Rockwell Corporation.
FIG. 1
details a prior art GPS satellite broadcast message
100
. Each message
100
has five subframes, subframe
1111
, subframe
2112
, subframe
3113
, subframe
4
114
, and subframe
5115
. Each subframe
111
,
112
,
113
,
114
,
115
has ten words
120
,
121
,
122
,
123
,
124
,
125
,
126
,
127
,
128
,
129
of thirty bits each. Each thirty-bit word has twenty-four information bits and six bits of parity. For the first word in each sub-frame, the telemetry (TLM) word
120
, there is a fixed eight-bit preamble
131
, a six-teen-bit data section
132
, and the six-bit parity
133
. For the second word in each sub-frame, a hand-over word (HOW)
121
, there is a seventeen-bit time of week (TOW) parameter
141
, a seven-bit data section
142
containing a three-bit subframe identification, and the six-bit parity
143
. Because GPS satellite data messages are transmitted at 50 BPS, it takes precisely six seconds to transmit each 300-bit subframe
111
,
112
,
113
,
114
,
115
and thirty seconds to transmit the entire 1500-bit message
100
. Refer to ICD-GPS-200 Specification for complete details on the GPS satellite broadcast message content and format.
The message transmission is precisely synchronized with GPS time, and the message
100
is such that each bit of the 50 BPS sequence is precisely known in GPS time coordinates. Each bit represents 0.02 seconds additionally-elapsed time since midnight of the previous Saturday in Greenwich, England. The GPS system keeps track of this elapsed time by the TOW parameter
141
. The GPS clock starts at midnight Saturday in Greenwich, England and counts seconds until the next Saturday at midnight. There are 604,800 seconds contained in one GPS week, then the clock is reset to begin the next week. A GPS Week counter is then used to keep track of time outside of one week. Within one data bit, time is known to within 0.001 seconds, because each data bit of the 50 BPS message is also coherent and synchronized with the 1023-bit spread spectrum spreading code. It takes precisely twenty repeats of the signal spreading code to create one data bit. Thus, time is known to under 20 millisecond accuracy by a GPS receiver counting the integer number of pseudo random noise (PRNY code repeats.
Finally, time is known to one millisecond accuracy by a GPS receiver measuring the fraction of one PN code repeat interval (also known as the code phase at the measurement time). Consequently, the 50 BPS message and underlying PN spreading code is used by every GPS receiver built today to obtain a measure of the time as transmitted from the GPS satellite, effectively translating the precise clock in the satellite to the ground-based GPS receiver by adding the propagation delay from the satellite to the receiver to the time indicated by the 50 BPS message.
In any implementation in which a GPS receiver (or sensor) is in embedded into a cellular phone for location purposes, the slow 50 BPS data rate is a problem because it slows the availability of position coordinates and thus slows down a response to the location determination request. In addition, the data transmitted at 50 BPS can become difficult to demodulate in weak signal conditions such as in a building or under heavy foliage. To combat this problem, the idea of Assisted GPS was created.
In Assisted GPS, communications network infrastructure is used to assist the mobile GPS receiver, which can be implemented as a standalone device or integrated with a radiotelephone handset. Assisted GPS establishes a GPS reference network (or a wide-area DGPS network, explained in further detail below) whose reference GPS receivers have clear views of the sky and can operate continuously to monitor the real-time GPS constellation status. The GPS reference network thus provides precise data for each GPS satellite at a particular epoch time. This GPS reference network is also connected with the cellular infrastructure.
At least three modes of Assisted GPS operation can be supported: “MS-assisted,” “MS-based,” and “autonomous.” For MS-assisted GPS, the mobile station (MS) GPS receiver position is calculated at the network. Typically, the mobile station receives assistance data, such as GPS time, Doppler, and code phase search window, and transmits pseudo range data back to the network. For MS-based GPS, the mobile station GPS receiver's position is calculated at the handset. Typically, the mobile station receives assistance data, such as GPS time, ephemeris, and clock correction, and transmits the calculated position back to the network if required. For autonomous GPS, the mobile station GPS receiver's position is calculated at the handset with very limited assistance from the network (or no assistance at all). Autonomous GPS can be loosely characterized as MS-based, although typically for autonomous GPS, the mobile GPS receiver's position is determined independently without network assistance.
For any GPS application, position errors are contributed by the satellite clock, satellite orbit, ephemeris prediction, ionospheric delay, tropospheric delay, and selective availability (SA), which is an accuracy degradation scheme designed to reduce the position accuracy available to civilian users. To reduce these errors, range and range-rate corrections can be applied to the raw pseudo range measurements in order to create a position solution that is accurate to a few meters in open environments. One such correction technique is differential GPS (DGPS), which uses a reference GPS receiver at a surveyed position to send correcting information to a mobile station GPS receiver over a communication link. For MS-assisted GPS, corrections can be applied directly at the network or a server to the pseudo ranges and pseudo range-rates received from the mobile GPS receiver. For MS-based GPS, corrections must be transmitted to the mobile GPS receiver either via “point-to-point” or “broadcast” (“point-to-multipoint”) transmissions. Note that Assisted GPS may operate with or without differential GPS corrections; the corrections are generally required, however, for those location applicat
Geier George J.
King Thomas M.
Zhao Yilin
Beaulieu Yonel
Bowler II Roland K.
Chen Sylvia Y.
LandOfFree
Method and apparatus for compressing GPS satellite broadcast... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for compressing GPS satellite broadcast..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for compressing GPS satellite broadcast... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2928675