HK1074671B - Gps satellite signal acquisition assistance system and method in a wireless communications network - Google Patents

Description

GPS satellite signal acquisition assistance system and method in a wireless communication network

Background

Related applications:

this application claims priority to U.S. provisional application No. 60/239774 (filed on 12/10/2000).

Background of the invention:

the present invention relates to communication systems. More particularly, the present invention relates to GPS positioning systems and wireless networks.

Description of related art:

the trend in the wireless communications industry is to provide services that generate accurate location information for wireless terminals and provide that information to requesting entities. The demand by public safety service providers in responding to emergency calls in an immediate manner drives this trend to a tremendous extent. In many cases, the caller may be unwilling or unable to provide accurate location information. When such information is automatically provided as in a wired telephone service, public safety authorities can respond quickly and provide services. Generally, the location at which a public safety entity receives a "911" call is referred to as a "public safety answering point" (hereinafter "PSAP").

In a wireless telephone network, such as a cellular or PCS network, the specification of automatic caller location information is more difficult than in a wireline telephone network due to the inherent mobility of wireless telephones. In some wireless systems, the PSAP has location information that identifies which wireless base station or which radio sector within a wireless base station is handling an emergency call. This level of resolution of location information only identifies the location of the calling party in a wide geometric area, so PSAP distributors must rely on the location information given by the calling party's head of mouth before they can respond to emergency service requests.

When the federal communications commission (hereinafter "FCC") adopted an announcement and rules for enhanced E991 wireless services, it forced the market to emphasize the focus on location information regulations released in 1996, month 6. The FCC published a revision of this announcement and rules at 23.12.1997. The main parts are as follows:

the FCC may require that the cellular, broadband PCS and geometry area dedicated mobile radio frequency (hereinafter "SMR") systems deliver all E911 emergency calls to the PSAP from any mobile station that does not transmit a mobile identification number (hereinafter "MIN"), or its functional equivalent, through the carrier's credit check or other validation steps within 12 months after the rule's expiration date.

Beginning twelve months after the rule's expiration date (and completing within eighteen months), the FCC requires cellular, broadband PCS, and regional SMR licenses to provide some E911 enhancements. These E911 enhancements include the ability to relay the caller's telephone number (call back the caller if the call is cut off). Likewise, the carrier must be able to route E911 calls to the appropriate PSAP.

Within five years after the rule validity date, the position (location) of the mobile station making the emergency call must be provided to the qualified PSAP in two dimensions with an accuracy within a 125 meter radius as measured by the Root Mean Square (RMS) method. According to the FCC, a request is qualified if and when (1) the PSAP indicates that it can receive and utilize the number and location transmitted by the wireless carrier together, and (2) a cost recovery mechanism exists.

FCC location accuracy requirements are a minimum value, and therefore vendors and manufacturers of wireless network devices are researching to provide more accurate location data than this minimum value. For example, U.S. patent 6021330, "MOBILE LOCATION establishment IN A WIRELESS system DESIGNATED TIME INTERVALS OF speeded COMMUNICATIONS," assigned to Vanucci OF Lucent Technologies, teaches a system in which the LOCATION OF a MOBILE station is estimated by measuring the differential path delay times OF beacon signals transmitted simultaneously by several base stations. Trilateration is made to determine location.

Patents assigned to Qualcomm Inc: another method OF mobile station POSITION measurement in a wireless system is taught in united states patent No. 6081299 "SYSTEMAND METHOD FOR DETERMINING THE POSITION OF A WIRELESS CDMA TRANSCEIVER" to Soliman et al. Soliman et al teach a more complex method of making a mobile station position decision using global positioning system satellite and terrestrial base station signals. In general, Soliman et al teaches the process of receiving at a base station a first signal transmitted from a first GPS satellite and a second signal transmitted from a second GPS satellite. The mobile station is also operable to receive these GPS signals and transmit a third signal to the base station in response thereto. The base station receives the third signal and uses it to calculate the position of the mobile station. In a particular embodiment, the base station transmits the assistance information to the mobile station. The mobile station uses the assistance information to acquire signals transmitted by the first and second satellites more quickly than without the assistance information.

The use of GPS satellite position and velocity measurements is a good method of wireless terminal position determination since position can be determined within the accuracy requirements of FCC announcements and regulations. It also has other advantages because the new GPS features can be incorporated into the wireless phone once the unit has been added with GPS technology. These premium characteristics can be used to increase the market value of products and increase revenue by providing additional services to the end users of these products.

The GPS navigation system uses satellites that are in orbit around the earth. Accurate navigation information, including three-dimensional position, velocity, and time of day, is available to any GPS user anywhere on the earth. The GPS system comprises 24 satellites scattered in circular orbits with a radius of 26600 km on three planes inclined 55 ° with respect to the equator and spaced 120 ° apart two by two. Eight satellites are uniformly in each of three orbital paths. Position measurements using GPS are based on measurements of the propagation delay time of GPS signals propagating from orbiting satellites to a GPS receiver. In general, accurate position determination in 4 dimensions (latitude, accuracy, elevation and time) requires reception of signals from 4 satellites. Once the receiver measures the corresponding signal propagation delay, the range of each signal is calculated by multiplying each delay by the speed of light. The position and time are then found by solving a set of four equations with four unknowns incorporating the measured range and the known position of the satellite. The accuracy of the GPS system is maintained by an atomic clock onboard each satellite and by a ground tracking station that continuously monitors and corrects for satellite clocks and orbital parameters.

Each GPS satellite transmits two direct sequence coded spread spectrum signals in the L-band. The L1 signal is at a carrier frequency of 1.57542GHz and the L2 signal is at a carrier frequency of 1.2276 GHz. The L1 signal includes two Phase Shift Keyed (PSK) spread spectrum signals modulated in quadrature phase: p-coded signal (P refers to accuracy) and C/a-coded signal (C/a refers to coarse/acquisition). The L2 signal contains only the P-coded signal. The P and C/a codes are repeating pseudo-random bit sequences (termed "chips" by the spreading engineer) modulated onto a carrier. The receiver uses the clock-like nature of these codes in making time delay measurements. The code for each satellite is unique, allowing the receiver to tell which satellite sent the given code even though all satellites were at the same carrier frequency. A 50 bit/sec data stream is also modulated onto each carrier, which includes information about system state and satellite orbit parameters required for pilot calculation. The P-code signal is encrypted and is generally not available to commercial and private users. The C/a signal is available to all users.

The operations performed in the GPS receiver are largely representative of those performed in any direct sequence spread spectrum receiver. In a process known as despreading, the spreading effect of pseudo-coded modulation is likely to be removed from each signal by multiplying it with a time-aligned, locally generated code replica. Since the appropriate time alignment or coding delay is not necessarily known at the receiver start-up stage, it must be determined by searching during the initial "acquisition" stage of operation of the GPS receiver. Once the proper code time alignment is determined, it is maintained during the "tracking" phase of GPS receiver operation.

Once the received signals are despread, each signal comprises a 50 bit/second PSK signal at the intermediate carrier frequency. The exact frequency of the signal is uncertain due to the Doppler (Doppler) effect and local receiver GPS clock reference error caused by relative motion between the satellite and the terminal unit. During initial signal acquisition, the doppler frequency must also be searched since it is typically not known prior to acquisition. Once the doppler frequency is approximately determined, carrier demodulation continues to be performed.

After carrier demodulation, the data bit timing is obtained through a bit synchronization loop and the data stream is finally detected. Once the signals from the 4 satellites have been acquired and automatically tracked, the necessary time delays and doppler measurements have been made, and a sufficient number of data bits (sufficient to determine GPS time reference and orbit parameters) have been received, navigation calculations can be undertaken.

One drawback of GPS systems for position determination is the long time required for the initial signal acquisition phase. As described above, before four satellite signals can be tracked, they must be searched in a two-dimensional search "space" whose dimensions are code phase delay and doppler frequency offset. In general, if the location of the signal is not known a priori within the search space, i.e. in the case after a "cold start" of the receiver, a large number of code delays (about 2000) and doppler frequencies (about 15) must be searched for each satellite to be acquired and tracked. Therefore, up to 30000 positions within the search space must be examined for each signal. These locations are typically checked one by one in sequence, a process that may take 5 to 10 minutes. The acquisition time is further lengthened if it is considered that the identifiers (i.e., PN codes) of the four satellites in view of the receiving antenna are not known.

In the case where the GPS receiver has acquired satellite signals and is then in a tracking mode, the position decision process is virtually instantaneous. However, in conventional use of the wireless terminal, the user turns on the power and starts operating quickly. This may be the case when aiming for emergency communication. In this case, the time delay associated with a 5 to 10 minute GPS satellite signal acquisition cold start generated by the GPS/wireless terminal unit before a position fix is available limits the response time of the system.

Accordingly, there is a need in the art for a system and method to reduce the time required to acquire GPS satellite signals and provide position location in a GPS/wireless terminal unit.

Summary of the invention

The system and method of the present invention addresses a need in the art. In a first embodiment, a system for transmitting a GPS receiver code-phase search range to an integrated GPS/wireless terminal unit operating in a wireless network is disclosed. The system includes a base station also having a GPS receiver that generates a GPS time reference. And a controller that calculates a GPS code phase search range with respect to the base station geometry plus the radio coverage area and with respect to the GPS time reference plus the estimated radio signal propagation delay within the coverage area. And a transmitter coupled to the controller for transmitting the calculated GPS code search range to the terminal unit. In one specific expression of the above system, the GPS code-phase search range is defined by a center value and a magnitude value.

In another embodiment of the system, the base station includes a means for acquiring a time offset of the GPS/wireless terminal unit relative to a GPS time reference, and the controller calculates a GPS code-phase search range with respect to the base station geographic location plus the wireless coverage area and time reference. In a clear expression of this embodiment, the means for obtaining the time offset uses the round-trip radio signal propagation time between the reference and the terminal unit to establish said time offset.

In another embodiment of the system, the base station includes a means for acquiring a position reference for the GPS/wireless terminal unit, and the controller is for calculating a GPS code-phase search range with respect to the position reference in addition to the time reference. In a clear expression of this embodiment, the means for obtaining a position reference uses a terrestrial based measurement method and a covariance matrix to establish said position reference.

In addition to the above-described systems, the present invention discloses several methods of implementing the present invention. In a first method of defining a GPS receiver code-phase search range for an integrated GPS/wireless terminal unit operating in a wireless network with base stations, steps include calculating a GPS code-phase search range with respect to a base station geometric location plus a wireless coverage area and with respect to a base station GPS time reference plus an estimated wireless signal propagation delay within the wireless coverage area. The calculated GPS code phase search range is then transmitted by the base station for reception by the terminal unit. In one explicit expression of the method, the GPS code-phase search range is defined by a center value and a size value.

In another embodiment of the above method, a step is added of acquiring a time reference for a GPS/wireless terminal unit that determines a time offset from a base station GPS time. Next, a GPS code-phase search range is calculated for the base station geometry plus the radio coverage area, as well as a time reference. In another embodiment, the acquiring step uses the radio signal propagation time back and forth between the base station and the terminal unit to determine the time offset.

In a modification of the above embodiment, a step of acquiring a position reference for the GPS/wireless terminal unit is added. Then, a GPS code phase search range is calculated with reference to the position reference and the time offset. In a refinement thereon, the step of obtaining a position reference uses a terrestrial based measurement method and a covariance matrix to establish the position reference.

Brief description of the drawings

FIG. 1 is an exemplary spatial environment diagram over an illustrative embodiment of the invention.

Fig. 2 is a diagram of a sector arrangement of a radio base station.

Fig. 3 is a functional block diagram of a wireless terminal unit.

Fig. 4 is a functional block diagram of a base station.

Fig. 5 is a diagram of an illustrative embodiment of the present invention.

Fig. 6 is a diagram of an illustrative embodiment of the present invention.

Fig. 7 is a diagram of an illustrative embodiment of the present invention.

Fig. 8 is a diagram of an illustrative embodiment of the present invention.

Fig. 9 is a diagram of an illustrative embodiment of the present invention.

Description of the invention

In order to reveal the advantageous teachings of the present invention, illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings. While the present invention is described herein with reference to illustrative embodiments for particular applications, it will be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the invention would be of significant utility.

Reference is made to FIG. 1, which is an illustrative spatial environment in which the present invention may operate. The wireless network is located on the surface of the earth 4 and includes a number of wireless base stations identified as 6, 8, 10, 12 and 14 in fig. 1. Each base station generally defines a coverage area, commonly referred to as a coverage "cell". Mobile terminal unit 2 (or any number of mobile terminal units) operates within the coverage area of the wireless network. The terminal unit 2-generally operates on or near the surface of the earth. In a preferred embodiment, the wireless terminal unit includes a GPS receiver that receives GPS signals from GPS satellites, illustrated by items 16, 18, 20 and 22 in FIG. 1. The wireless termination unit also includes a CDMA transceiver operating in accordance with the EAI-IS-95 standard in the preferred embodiment and thereby communicates with a wireless network base station as described with respect to base station 8 in fig. 1.

Referring to fig. 2, the "cell" coverage of a typical radio base station 24 in the preferred embodiment is illustrated. The base station 24 may include one or more CDMA transceiver systems in the preferred embodiment. There are three transceiver systems in fig. 2 coupled to three antennas illustrated by items 26, 28 and 30 in fig. 2. The antennas 26, 28 and 30 are generally oriented 120 deg. apart from each other and use directional antennas that transmit and receive signals in a 120 deg. wedge shaped radiation pattern. The cell coverage area of each antenna 26, 28 and 30 is thus represented by radiation patterns 34, 32 and 36, respectively. The combination of these figures generally defines the "cell" coverage 38 of the wireless system base station 24. With respect to the present invention, it is noted that the wireless network in the preferred embodiment maintains wireless terminal unit call tracking information that analyzes which area or which base station a particular wireless terminal unit is visiting to place or receive a call. In addition, the wireless network contains data representing the geographic area covered by each base station "cell" and sector. Thus, the location of a wireless terminal unit operating in a call is known, at least within the coverage area of a base station, and possibly to the coverage area of a sector.

Referring to fig. 3, there is a functional block diagram of a wireless terminal 2 in a preferred embodiment of the present invention. The CDMA transceiver section 42 and the GPS receiver section 44 are coupled by a common radio frequency circuit 46 coupled to a transmit/receive antenna 48. A controller 40, typically microprocessor based and comprised of associated circuitry including memory, input/output and other peripheral devices, is coupled to and used to control both the CDMA transceiver 42 and the GPS receiver 46. In an alternative embodiment there are two separate controllers that control the CDMA transceiver and the GPS receiver, respectively. The requirements and functionality of the CDMA and GPS portions of the wireless terminal unit of the present invention are well understood by those skilled in the art. In addition, the wireless terminal unit 2 includes a user input/output section 50 which may include a microphone, speaker, display, keypad switch input, and other devices commonly used in wireless transceivers and GPS receivers.

Referring to fig. 4, there is a functional block diagram of a wireless base station 8 in a preferred embodiment of the present invention. The wireless base station 8 includes components typically found in a CDMA base station as understood by those skilled in the art, and typically includes one or more CDMA transceivers 54 and a base station controller 52. The CDMA transceiver 54 is coupled to one or more antennas 55. In the preferred embodiment, the GPS receiver 56 is co-located with conventional base station components. The GPS receiver 56 is coupled to a GPS antenna 57 and to a CDMA controller and a separate position decision device unit 58 (hereinafter "PDE"). The GPS receiver tracks all GPS satellites in its field of view and provides tracking information and ephemeris information to controller 52 and PDE 58 as needed. The PDE 58 may or may not be co-located with other base station equipment. In a typical installation the base station 8 also interfaces with one or more communication networks.

In a preferred embodiment, the wireless terminal unit location determination is made by having the wireless terminal unit include a GPS receiver and using the receiver to receive GPS satellite signals, calculate its location and/or velocity information and transmit the information back to the wireless base station so that the information can be relayed as the wireless terminal unit's entity requesting location information. As previously described, this will occur automatically when the user of the wireless terminal unit places a "911" call, and the location information will be automatically provided to the PSAP.

Position and velocity decisions may occur in many other embodiments of the position decision capability of the present invention. By way of example and not limitation, such applications may include the following:

location sensitive billing: the wireless can set the exact price difference based on the caller location. This enables the wireless carrier to compete with the wired carrier by providing comparable rates when the caller is at home or in the office.

Location-based information services: the user may call a service center to ask for driving directions or to make suggestions for restaurants, hotels, department stores, and gas stations. The service center may also respond to the emergency request by notifying the police/fire department or ordering trailers in the event of a vehicle failure.

Network planning: mobile station location statistics from wireless network operations can be used to plan the expansion and deployment of a completely new network.

Dynamic network control: the collected location statistics may be used to dynamically adjust network parameters to accommodate network load changes caused by the caller's behavior.

Fraud management: fraud can have a devastating impact on wireless carriers by reducing revenue and weakening users' credit. The location information helps the operator to ensure immediate detection and tracking guidance for quickly arresting criminals.

Fleet management and asset tracking: asset tracking enables fleet owners to constantly locate fleets, contact drivers immediately, or update the status of engines, powertrains, door locks, etc. after pushing a button.

Updating the real-time traffic volume: the received information may be sent to a traffic management center to help reduce traffic congestion and speed spread.

In any event, embodiments of the GPS receiver have certain limitations in the wireless network environment. There is market pressure to reduce the cost of GPS implementation compared to stand-alone GPS receiver terminal units. To address this problem, designers have attempted to share CDMA and GPS circuitry components wherever possible. Another way to reduce costs is to remove some of the processing from the wireless terminal unit and move it back to the terminal base station. This is possible in a wireless network environment because of the relatively high-speed communication link between the base station and the terminal unit. For example, it is well known that a base station GPS receiver can track GPS satellites in its field of view, gather pertinent data and provide it to wireless terminal units over CDMA communication links. This functionality eliminates the need for the GPS receiver of the wireless terminal unit to search for available satellites via the PN code and eliminates the need for the wireless terminal unit to maintain a conventional GPS almanac within its memory.

Another fundamental limitation of conventional methods of GPS signal acquisition and measurement is the long time required for the system to acquire and then track the available GPS satellites before a position measurement can be calculated. This is particularly troublesome when the user has an emergency situation that responds by turning on the user's wireless terminal unit to place a "911" call. The cold start time may take 5 to 10 minutes. The cold start time of the wireless terminal unit needs to be reduced to address this lag.

To receive the necessary satellite signals, a standard GPS receiver needs to search all satellite PN code sequences, all PN code phase hypotheses, and all doppler frequency offsets without assistance. This means that the search is performed over 24 satellites, a doppler frequency of 10kHz, and 1023 code hypotheses (requiring 2046 discrete half-chip code drifts and calculations). As described above, the satellite PN codes of geometrically available satellites may be provided to the radioterminal unit over a relatively fast CDMA communications link, which reduces the number of discrete satellite PN code sequences from 24 to the number of a set of satellites that are actually in view, which is typically 8, but may also be 4. The base station continuously monitors the GPS constellation and provides this information to the wireless terminal unit. Thus, the GPS receiver satellite search process in at least the first dimension is greatly reduced. Another aspect is the reduction of the doppler shift frequency search range. At least accounting for the movement of the satellite relative to the stationary base station, the range of the doppler search is thereby reduced to a relative movement between the base station and the terminal unit, such as the speed of a speeding car. However, the tremendous effort to phase align the received satellite PN code sequences with the locally generated PN code sequences is a time consuming process.

The present invention reduces the time required to phase match PN code sequences by providing a greatly reduced search window parameter range from the base station to the terminal unit based on calculations derived from information of the location and time reference of the wireless terminal unit. This is possible from a rough knowledge of the receiver location and the time offset of the receiver with respect to GPS time. In the preferred embodiment, the CDMA transmitter/receiver is coupled to a GPS receiver, as described above. CDMA hardware and software allows very efficient communication with a network or any device on the internet (as compared to the GPS downlink) or other private network. It also provides the ability to obtain a coarse position estimate by identifying the base station with which the wireless terminal unit is communicating and measuring the time of arrival of the CDMA signal. Because the CDMA wireless terminal unit timing is aligned with the first arriving CDMA signal, and because the CDMA signal is precisely aligned with GPS time, the wireless terminal unit has a very accurate source of GPS time (typically within tens of milliseconds).

The base station generates a mapping between the location of the wireless terminal unit and the received GPS PN code phase. Again, since this is the relative phase delay of the PN code, this can be directly related to the measurement of the pseudorange. Based on the wireless terminal unit position uncertainty area and the mapping, and based on the expected range of clock errors in the terminal unit relative to GPS time, the base station then specifies the GPS PN code phase search window center and size. Alternatively, it may calculate the starting and stopping PN code phase ranges to define the search window.

In the present invention, three basic cases are considered, which represent other possible cases. In the first case, the location of the wireless terminal unit is only analyzed to the wireless network "cell" address or sector, and the time reference is limited in accuracy to the base station GPS receiver time base station, the delay time being the propagation time from the base station to the terminal unit.

In the second case, the location is only analyzed to the "cell" address and there is a more accurate time reference that is determined by correcting the base station GPS receiver time for the propagation delay between the base station and the wireless terminal.

In a third case, as in the second case, a more accurate time reference is known and a more accurate position estimate is available in the case of a ground-based trilateration system.

Each of these cases will be analyzed in detail. All analyses were in meters; provided that conversion to GPS or CDMA chips is possible if necessary. Also, the sign of the GPS code phase would need to be taken in the early to late direction (larger codes correspond to larger distances).

First case-mapping between user position and GPS pseudorange

Referring to fig. 5, there is shown a spatial relationship diagram between base station 8, wireless terminal unit 2 and one GPS satellite 18. The delay of the CDMA signal at the antenna of the base station 8 is defined as c_fThe delay is expressed as time by dividing the number of meters by the speed of light. . This value is obtained by a calibration procedure within the base station 8GPS receiver and stored in the location decision device of each base station in the network. The three-dimensional positions of the user, the base station and the satellite are respectively defined asAndsince the base station 8GPS receiver is typically in tracking mode and therefore aligned in time with GPS time, it can reasonably be assumed that the delay of the wireless terminal unit's 2GPS receiver clock from actual GPS time is equal to the propagation delay from the base station 8 to the terminal unit 2. Thus, the relative offset in satellite pseudoranges due to receiver clock error is:img id="idf0003" file="C0181914600141.GIF" wi="144" he="27" img-content="drawing" img-format="GIF"/the geometric offset of the terminal unit 2 with respect to the base station 8 causes the following pseudo-rangeSurrounding offset:img id="idf0004" file="C0181914600142.GIF" wi="172" he="28" img-content="drawing" img-format="GIF"/in addition, an offset factor ρ inherent in the base station 8_BTSComprises the following steps:img id="idf0005" file="C0181914600143.GIF" wi="188" he="28" img-content="drawing" img-format="GIF"/where Δ t and Δ r are the satellite clock correction (derived from satellite ephemeris information) and the earth rotation correction (accounting for rotation of the earth during signal propagation), respectively, both of which will be appreciated by those skilled in the art.

From the above value calculations, the best estimate of the pseudorange measurement at the terminal unit 2 is:

img id="idf0006" file="C0181914600144.GIF" wi="447" he="28" img-content="drawing" img-format="GIF"/

the terms that vary according to the user's location are:

img id="idf0007" file="C0181914600145.GIF" wi="150" he="29" img-content="drawing" img-format="GIF"/

the search window of the terminal unit 2 at an arbitrary position within the uncertainty area is then defined by the extremum of the function. Since the terminal unit elevation maximum/minimum problem is known within a suitably small range of values based on the terrain in the vicinity of the base station, finding the center and size of the search window is a two-dimensional function.

First case-base station of uncertain zone center

Referring to fig. 6, there is illustrated the spatial environment in the case where the base station 8 is located at the center of the position uncertainty area of the terminal unit 2. Let plane P be a plane parallel to the earth's tangent plane through the serving base station location. In this case, it is assumed that the terminal unit 2 uncertainty region is on the plane PA circular disc 60 of radius R, centred on the base station 8. The problem can be solved analytically if it is assumed that the uncertainty region is limited to a maximum radius R of 20km, which is reasonable for a typical CDMA "cell" service area. It is further assumed that terminal unit 2 is located on the same earth-tangent plane P as base station 8. It is worth noting that this will introduce a small amount of error since the base station 8 is typically placed at a higher elevation angle than the terminal unit 2. Due to this assumption, an approximation of the geometric offset with respect to the base station 8 causes the following pseudo-range differences at the terminal unit:img id="idf0008" file="C0181914600146.GIF" wi="260" he="29" img-content="drawing" img-format="GIF"/the last term of the equation is the unit vector from the satellite 18 to the base station 8:img id="idf0009" file="C0181914600147.GIF" wi="84" he="53" img-content="drawing" img-format="GIF"/

thus, it is possible to provideThe term that varies in the pseudo-range measurement estimate as a function of the terminal unit 2 is:img id="idf0010" file="C0181914600148.GIF" wi="183" he="30" img-content="drawing" img-format="GIF"/

the distance between the position of terminal unit 2 and base station 8 is defined as d, and * as a unit vectorAnd the vector from the base station 8 antenna to the terminal unit 2 position. Logically, the ranges of these two parameters are as follows:where theta is the elevation angle of the satellite 18 relative to the plane P60. After the use of these parameters, the user can,can be rewritten as: f (d, *) ═ d (cos (*) -1). And, directly available: -R (cos (θ) +1) is not less than f (d, *) is not less than 0. Therefore, the estimated pseudorange at any point inside the uncertainty region will be within this interval: rho_BTS-c_f-R·(cos(θ)+1)≤ρ_user≤ρ_BTS-c_f。

The search window center and size will therefore be:

img id="idf0014" file="C0181914600152.GIF" wi="248" he="42" img-content="drawing" img-format="GIF"/

ρ_Size＝R·(cos(θ)+1)

first case-general case

Reference is made to fig. 7, which is a spatial diagram of a general case where the uncertainty region is not centered around the base station 8. Let P66 be a plane parallel to but not necessarily passing through the plane of the earth at the location of the base station 8 antenna (which is generally below the base station antenna). Likewise, assume that the satellite 18 is above plane P66 and the base station 8 antenna is also above plane P66. The terminal unit 2 is located in plane P66 and assumes that the terminal unit uncertainty region a, 68 or 70 is a smoothly connected region on plane P66. Since EIA IS-801 defines the uncertainty region as an ellipse, a must be confined to a circle with a maximum radius of 50km in order to make the coplanar terminal unit location assumptions described above. This is consistent with the 20km assumption described above regarding the size of the CDMA "cell" service area.

The desired result is again a function found for the user of any terminal unit 2 within the uncertainty area a 68 or 70img id="idf0015" file="C0181914600153.GIF" wi="143" he="29" img-content="drawing" img-format="GIF"/Minimum and maximum values of. Let C (coordinate be)69 is the intersection of the plane P66 with a line 67 passing through the position of the base station 8 antenna and the position of the satellite 18. Two assumptions are considered below:

c ≧ A case:

in this case, the function gets its minimum and maximum values on the boundary of the uncertainty area a 70. Since they are known to be on the boundary, the boundary of a 70 is sampled and the function f is valued at each location. Let f_minAnd f_maxF the resulting minima and maxima at all selected sample locations. The center and size of the search window is then given by the following equation:

img id="idf0017" file="C0181914600155.GIF" wi="220" he="38" img-content="drawing" img-format="GIF"/

ρ_Sixze＝f_max-f_min

c ∈ A case:

in this case, the function gets its maximum at the base station 8 location and its minimum somewhere on the circumference of the uncertainty area a 68. Thus.img id="idf0018" file="C0181914600156.GIF" wi="92" he="22" img-content="drawing" img-format="GIF"/Since f is known_minAt the boundary of a 68, the boundary is sampled and the value of the function f is calculated at each selected location. Likewise, let f_minIs the minimum value derived from all selected sample positions. The center and size of the search window is then given by the following equation:

img id="idf0019" file="C0181914600161.GIF" wi="220" he="37" img-content="drawing" img-format="GIF"/

ρ_Size＝f_max-f_min

the number of sample points obtained on surface a depends on the degree of smoothness of the uncertainty region. The smoother the region, the fewer the number of points needed. In the case of an ellipse 20, the sampling point is sufficient. Obviously, the selected size corresponds to the minimum acceptable guarantee that the terminal unit will be within the search window in a virtually noise-free situation. Some margin may be added when noise is present.

Second case

Referring to fig. 8, it is a space diagram of the second case. In this case there is a more accurate estimation of the terminal unit 2 clock reference. Variables ofIs defined as an estimate of the receiver time offset obtained from the network. From this estimate of the terminal unit 2 time offset, the offset in the code phase due to the terminal unit 2 clock error is:img id="idf0021" file="C0181914600163.GIF" wi="81" he="18" img-content="drawing" img-format="GIF"/the three-dimensional positions of the terminal unit 2, the base station 8 and the satellite 18 are respectively determined byAndit is given. The geometrical offset with respect to the base station 8 causes the following code phase offsets:img id="idf0024" file="C0181914600166.GIF" wi="171" he="28" img-content="drawing" img-format="GIF"/from these two values, the best estimate of the pseudorange measurement at the location of the terminal unit 2 is:

img id="idf0025" file="C0181914600167.GIF" wi="384" he="28" img-content="drawing" img-format="GIF"/

the items that vary according to the position of the terminal unit 2 are:img id="idf0026" file="C0181914600168.GIF" wi="99" he="29" img-content="drawing" img-format="GIF"/the search window for the position of the terminal unit 2 at any position within the uncertainty area 72 is then defined by the extremum of the function. Finding the search window center and size is therefore a two-dimensional function (since the elevation angle of the terminal unit 2 is known within a very small and statistically insignificant range) maximum/minimum problem.

In this case, the functionimg id="idf0027" file="C0181914600169.GIF" wi="88" he="28" img-content="drawing" img-format="GIF"/Clearly less complex than in the first case. Because of the large distance of the satellites 18, the following simplification is reasonable:img id="idf0028" file="C01819146001610.GIF" wi="183" he="32" img-content="drawing" img-format="GIF"/whereinimg id="idf0029" file="C01819146001611.GIF" wi="73" he="54" img-content="drawing" img-format="GIF"/Is the unit vector from the satellite 18 to the base station 8. The pseudorange interval is thus the projection of the uncertainty region 72 onto the unit vector from the satellite 18 to the base station 8. To illustrate this, a simple case is taken in which the uncertainty region 72 is a circle of radius R in a plane parallel to the tangent plane of the earth 4 at the base station 8 and having a center 74 at the coordinates ofAt the point of (a). Function(s)Is defined by the following values:img id="idf0032" file="C01819146001614.GIF" wi="337" he="29" img-content="drawing" img-format="GIF"/the corresponding search window center and size are:

img id="idf0033" file="C0181914600171.GIF" wi="231" he="26" img-content="drawing" img-format="GIF"/

ρ_Size＝2R·cos(θ)

third case

Referring to fig. 9, it is a space diagram of a third case. In this case, base station 8 has a more accurate estimate of both the time (as in the second case) and the location of terminal unit 2. Definition ofimg id="idf0034" file="C0181914600172.GIF" wi="135" he="17" img-content="drawing" img-format="GIF"/Andrespectively, an estimate of the user's position within an ECEF frame (earth-centric, earth-fixed) and an estimate of the receiver's time bias, both of which are obtained in advance (likely from network measurements). In addition to these estimates, an estimated covariance matrix may be obtained from pre-acquired information about measurement statistics. One row (and the same column) in the matrix corresponds to the time offset estimate. The matrix may be represented by a particular frame, but it is typically rotated so that the x-axis is parallel to the unit vector from the base station 8 to the satellite 18. After this is done, the variance v of the position error to the satellite G along the LOS direction_GAre known. In this regard, the covariance matrix provides the variance v of the time offset estimation error T_TAnd the cross-correlation K between T and G_GT。

The positions of the terminal unit 2, the base station 8 and the satellite 18 are respectively determined byAndand (4) giving. According to these definitions and assumptions, the offset in code phase due to receiver clock offset and position offset is:img id="idf0038" file="C0181914600176.GIF" wi="99" he="18" img-content="drawing" img-format="GIF"/andimg id="idf0039" file="C0181914600177.GIF" wi="205" he="28" img-content="drawing" img-format="GIF"/from these two values, the best estimate of the pseudorange measurement at the terminal unit 2 location is:

img id="idf0040" file="C0181914600178.GIF" wi="448" he="29" img-content="drawing" img-format="GIF"/

the terms that vary with a particular statistic are: f (G, T) ═ G-T.

The function f (G, T) ═ G-T is treated as a random variable, with a mean of 0 and a variance of:

E[f(G，T)]＝E*(G-T)²*＝E[G²]-2·E[G·T]+E[T²]＝v_G-2·K_GT+v_T·

the corresponding standard deviations are:img id="idf0041" file="C0181914600179.GIF" wi="171" he="24" img-content="drawing" img-format="GIF"/according to the sum of the miss probabilityA compromise of the size of the search window, the factor a is chosen as the number of standard deviations that should be included in the search window. The final search window center and size are:

img id="idf0042" file="C01819146001710.GIF" wi="229" he="29" img-content="drawing" img-format="GIF"/

img id="idf0043" file="C01819146001711.GIF" wi="209" he="24" img-content="drawing" img-format="GIF"/

accordingly, the present invention has been described herein with reference to particular embodiments for particular applications. Those having ordinary skill in the art and access to the teachings of the present invention will recognize additional modifications, applications, and embodiments within the scope thereof. For example, although the present invention is described herein with reference to CDMA, those skilled in the art will appreciate that other techniques may be used. Additionally, the satellite may be a pseudo-light source or other mobile platform operating at low or high elevation angles without departing from the scope of the present principles.

It is therefore intended that the appended claims encompass any and all such applications, modifications, and embodiments within the present invention.

Claims (16)

1. A system for transmitting a GPS receiver code-phase search range to an integrated GPS/wireless terminal unit operating in a wireless network, said system comprising:

a receiver for generating a GPS time reference;

a controller for calculating a GPS code phase search range with reference to base station geographic location, wireless coverage area, angle between a vector from a base station to a GPS satellite and a vector from a base station to a GPS/wireless terminal unit, said GPS time reference, and estimated wireless signal propagation delay within said coverage area, an

A transmitter coupled to the controller for transmitting the calculated GPS code search range.

2. The invention of claim 1 wherein said GPS code-phase search range is defined by a center value and a size value.

3. A system for transmitting a GPS receiver code-phase search range to an integrated GPS/wireless terminal unit operating in a wireless network, said system comprising:

a GPS receiver for generating a GPS time reference;

means for acquiring a time offset for a GPS/wireless terminal unit relative to said GPS time reference;

a controller for calculating a GPS code phase search range with reference to a base station geographic location, a radius of a wireless coverage area served by the base station, an elevation angle of a GPS satellite, and the time reference; and

a transmitter coupled to the controller for transmitting the calculated GPS code search range.

4. The invention of claim 3 wherein said GPS code-phase search range is defined by a center value and a size value.

5. The invention of claim 3 wherein said means for obtaining a time offset uses round-trip radio signal propagation time between said base station and a terminal unit to determine said time offset.

6. A system for transmitting a GPS receiver code-phase search range to an integrated GPS/wireless terminal unit operating in a wireless network, said system comprising:

a GPS receiver for generating a GPS time reference;

means for acquiring a time offset for a GPS/wireless terminal unit relative to said GPS time reference;

means for obtaining a position reference for the GPS/wireless terminal unit;

a controller for calculating a GPS code phase search range with reference to a change in position error of the position reference and the time reference; and

a transmitter coupled to the controller for transmitting the calculated GPS code search range.

7. The invention of claim 6 wherein said GPS code-phase search range is defined by a center value and a size value.

8. The invention of claim 6 wherein said means for obtaining a position reference uses means for providing ground-based trilateration to determine said position reference.

9. A method for defining a GPS receiver code-phase search range for an integrated GPS/wireless terminal unit operating in a wireless network with a base station, said method characterized by the steps of:

calculating a GPS code phase search range with reference to the base station geographic position plus the wireless coverage area, the angle between the vector from the base station to the GPS satellite and the vector from the base station to the GPS/wireless terminal unit, and with reference to the base station GPS time reference plus the estimated wireless signal propagation delay within the coverage area, an

Issuing the calculated GPS code phase search range.

10. The invention of claim 9 wherein said GPS code-phase search range is defined by a center value and a size value.

11. A method for defining a GPS receiver code-phase search range for an integrated GPS/wireless terminal unit operating in a wireless network with a base station, said method characterized by the steps of:

acquiring a time offset for the GPS/wireless terminal unit that determines the time offset relative to the base station GPS time;

calculating a GPS code phase search range with reference to the base station geographic location plus the radius of the wireless coverage area served by the base station, the elevation angle of the GPS satellite, and the time reference, and

issuing the calculated GPS code phase search range.

12. The invention of claim 11 wherein said GPS code-phase search range is defined by a center value and a size value.

13. The invention of claim 11 wherein said acquiring step uses the round-trip radio signal propagation time between said base station and terminal unit to determine time offsets.

14. A method for defining a GPS receiver code-phase search range for an integrated GPS/wireless terminal unit operating in a wireless network with a base station, said method characterized by the steps of:

acquiring a time offset for the GPS/wireless terminal unit that determines the time offset relative to the base station GPS time;

acquiring a position reference for the GPS/wireless terminal unit;

calculating a GPS code phase search range with reference to the change in the position error of the position reference and the time reference; and

sending out the calculated GPS code phase search range through a base station.

15. The invention of claim 14 wherein said GPS code-phase search range is defined by a center value and a size value.

16. The invention of claim 14 wherein said step of obtaining a position reference uses ground-based trilateration techniques to determine said position reference.