Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2000-01-21
2001-09-25
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C701S213000
Reexamination Certificate
active
06295023
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to position computation methods and systems, and more particularly, to methods and systems for obtaining assistance information from a communication network for use in position computation. Wireless communication systems (networks) are commonly employed to provide voice and data communications to subscribers. For example, analog cellular radiotelephone systems, such as those designated AMPS, ETACS, NMT-450, and NMT-900, have long been deployed successfully throughout the world. Digital cellular radiotelephone systems such as those conforming to the North American standard IS-54 and the European standard GSM have been in service since the early 1990's. More recently, a wide variety of wireless digital services broadly labeled as PCS (Personal Communications Services) have been introduced, including advanced digital cellular systems conforming to standards such as IS-136 and IS-95, lower-power systems such as DECT (Digital Enhanced Cordless Telephone) and data communications services such as CDPD (Cellular Digital Packet Data). These and other systems are described in
The Mobile Communications Handbook,
edited by Gibson and published by CRC Press (1996).
FIG. 1
illustrates a conventional terrestrial wireless communication system
20
that may implement any one of the aforementioned wireless communications standards. The wireless system may include one or more wireless mobile terminals (stations)
22
that communicate with a plurality of cells
24
served by base stations
26
and a mobile telephone switching office (MTSO)
28
. Although only three cells
24
are shown in
FIG. 1
, a typical cellular radiotelephone network may comprise hundreds of cells, and may include more than one MTSO
28
and may serve thousands of wireless mobile terminals
22
.
The cells
24
generally serve as nodes in the communication system
20
, from which links are established between wireless mobile stations (terminals)
22
and a MTSO
28
, by way of the base stations
26
servicing the cells
24
. Each cell
24
will have allocated to it one or more dedicated control channels and one or more traffic channels. The control channel is a dedicated channel used for transmitting cell identification and paging information. The traffic channels carry the voice and data information. Through the communication system
20
, a duplex radio communication link
30
may be effected between two wireless mobile stations
22
or between a wireless mobile station
22
and a landline telephone user
32
via a public switched telephone network (PSTN)
34
. The function of the base station
26
is commonly to handle the radio communications between the cell
24
and the wireless mobile terminal
22
. In this capacity, the base station
26
functions chiefly as a relay station for data and voice signals.
As the wireless communication industry continues to advance, other technologies will most likely be integrated within these communication systems in order to provide value-added services. One such technology being considered is a global positioning system (GPS). Briefly, as illustrated in
FIG. 2
, GPS is a space-based triangulation system using satellites
52
and computers
58
to measure positions anywhere on the earth. GPS was first developed by the United States Department of Defense as a navigational system. The advantages of this navigational system over other land-based systems are that it is not limited in its coverage, it provides continuous 24-hour coverage, regardless of weather conditions, and is highly accurate. While the GPS technology that provides the greatest level of accuracy has been retained by the government for military use, a less accurate service has been made available for civilian use. In operation, a constellation of 24 satellites
52
orbiting the earth continually emit a GPS radio signal
54
. A GPS receiver
56
, e.g., a hand-held radio receiver with a GPS processor, receives the radio signals from the closest satellites and measures the time that the radio signal takes to travel from the GPS satellites to the GPS receiver antenna. By multiplying the travel time by the speed of light, the GPS receiver can calculate a range for each satellite in view. Ephemeris information provided in the satellite radio signal typically describes the satellite's orbit and velocity, thereby generally enabling the GPS processor to calculate the position of the GPS receiver
56
through a process of triangulation.
The startup of a GPS receiver typically requires the acquisition of a set of navigational parameters from the navigational data signals of four or more GPS satellites. This process of initializing a GPS receiver may often take several minutes.
The duration of the GPS positioning process is directly dependent upon how much information a GPS receiver has initially. Most GPS receivers are programmed with almanac data, which coarsely describes the expected satellite positions for up to one year ahead. However, if the GPS receiver does not have some knowledge of its own approximate location, then the GPS receiver cannot find or acquire signals from the visible satellites quickly enough, and, therefore, cannot calculate its position quickly. Furthermore, it should be noted that a higher signal strength is needed for capturing the C/A Code and the navigation data at start-up than is needed for continued monitoring of an already-acquired signal. It should also be noted that the process of monitoring the GPS signal is significantly affected by environmental factors. Thus, a GPS signal which may be easily acquired in the open typically becomes harder to acquire when a receiver is under foliage, in a vehicle, or worst of all, in a building.
Recent governmental mandates, e.g., the response time requirements of the FCC Phase II E-9 11 service, make it imperative that the position of a mobile handset be determined accurately and in an expedited manner. Thus, in order to implement a GPS receiver effectively within a mobile terminal while also meeting the demands for fast and accurate positioning, it has become desirable to be able to quickly provide mobile stations with accurate assistance data, e.g., local time and position estimates, satellite ephemeris and clock information, and visible satellite list (which generally varies with the location of the mobile station). The use of such assistance data can permit a GPS receiver that is integrated with or connected to a mobile station to expedite the completion of its start-up procedures. It is, therefore, desirable to be able to send the necessary GPS assistance information over an existing wireless network to a GPS receiver that is integrated with or connected to a mobile station.
Taylor et al., U.S. Pat. No. 4,445,118, discusses the concept of aiding or assisting GPS receivers. The method described uses a single transmitter, such as a geosynchronous satellite, to provide a single assistance message for a wide geographical area. The assistance data includes a list of GPS satellites in view, the respective satellite positions, and predicted Doppler shifts on the satellite signals. This structure of this message permits the position computation function (PCF) to be done in the user receiver.
Krasner, U.S. Pat. No. 5,663,734, describes another GPS receiver approach. The patent is mainly related to the receiver architecture, but discusses how the receiver performance can be improved by assistance. The patent mentions “data representative of ephemeris” and expected Doppler shifts as possible contents of the assistance message.
Lau, U.S. Pat. No. 5,418,538, describes a system and method for aiding a remote GPS/GLONASS receiver by broadcasting “differential” information from a like receiver in a “reference station”. The reference station broadcasts a visible satellite list and also the associated ephemeris, in one embodiment. The advantage to the remote receiver is three-fold: reduced memory requirements, lower-cost frequency reference, and faster acquisition. The discussion describes the benefit of be
Ericsson Inc.
Myers Bigel & Sibley & Sajovec
Phan Dao
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