Method and apparatus for determining remote unit location using phased array antenna elements

An apparatus (100) and method dynamically allocates radio frequency receive path resources as required by a programmable location engine (112). The programmable location engine (112) employs cascaded time of arrival and direction of arrival algorithms to determine per remote unit location data. The apparatus (100) employs a phased array antenna (104) and a programmable receiver switching apparatus (108). A plurality of radio frequency receivers (102a-102n) receive a plurality of different carriers, such as CDMA carriers, on each of a different phased array antenna element (106a-106d). An RF switching matrix (126) and mobile location shared resource controller (110) dynamically switch the plurality of radio frequency receivers (102a-102b) to not only receive the different carriers on each of the different phased antenna radio elements to determine time of arrival information, but alternately receive a same carrier signal over all or a portion of the phased array antenna element to determine direction of arrival information.

CROSS REFERENCE TO RELATED CO-PENDING APPLICATIONS
 This application is a related application to a co-pending application
 entitled "Mobile Unit Location Apparatus and Method for a CDMA Wireless
 System" having inventors Pfeil et al., filed on even date, owned by
 instant assignee and hereby incorporated in its entirety by reference.
 This application is a related application to a co-pending application
 entitled "Method and Apparatus for Determining an Angle of Arrival of a
 Transmitted Signal in a Communication System" having inventors Golovin et
 al., filed on even date, owned by instant assignee and hereby incorporated
 in its entirety by reference.
 This application is a related application to a co-pending application
 entitled "Method and Apparatus for Locating a Remote Unit Within a
 Communication System" having inventors Pfeil et al., filed on even date,
 owned by instant assignee and hereby incorporated in its entirety by
 reference.
 FIELD OF THE INVENTION
 The invention relates generally to methods and apparatus for locating
 remote units, such as remote units in radio frequency wireless systems,
 and more particularly to methods and apparatus that utilize a phased array
 antenna arrangement for determining a location of a remote unit in a
 wireless communication system.
 BACKGROUND OF THE INVENTION
 Many wireless communication systems, such as cellular TDMA radiotelephone
 systems employ some type of mobile unit location apparatus and techniques.
 Multi-lateration mobile unit location techniques are well known which
 employ a plurality of base station receivers to triangulate or otherwise
 determine the location of a mobile unit based on a plurality of different
 sites.
 Other wireless communications systems, such as those employing code
 division multiple access (CDMA) channelization may use a plurality of CDMA
 carriers (e.g., codes) over a plurality of different frequencies. A
 problem can arise with mobile location techniques of CDMA type systems
 since mobile units typically control their output power as a function of
 their proximity to a transmitting antenna. For example, as a mobile unit
 gets closer to a base site antenna, it may lower its output power to allow
 other mobile units to use the same CDMA carrier. This can provide less
 interference for other mobile units using the same CDMA carrier. However,
 as the mobile unit decreases power, the path loss can increase and
 multi-lateration location can become more difficult since other antennas
 at other sites may not be able to detect the mobile carrier of the low
 output power. Accordingly, there is a desire for single site mobile unit
 location techniques.
 Such a single site mobile location system or a multi-site location system
 may not exist on many cellular base stations. Consequently, the addition
 of location finding equipment may be required as add-ons to cellular base
 stations. However, a problem can arise since the addition of single site
 mobile unit location systems can require additional hardware and/or
 antennas such as additional CDMA receivers, local oscillators and other
 front end receiving equipment. This is partly due to the need to provide a
 mobile unit location apparatus that is compatible with different
 manufacturers of cellular base stations. However, the duplication of
 equipment can greatly increase the cost of the overall system.
 In addition, for multi-carrier radio telephone systems, such as that
 defined by IS 95 Proposed EIA/TIA INTERIM STANDARD Wideband Spread
 Spectrum Digital Cellular System Dual Mode Mobile Station Base Station
 Compatibility Standard, Apr. 21, 1992 incorporated herein by reference, it
 is desirable to perform remote unit location determination for many remote
 units within a single carrier as well cases wherein multiple remote units
 are assigned to multiple carriers. However, to locate all remote units on
 traffic channels, duplicate receiver hardware may typically be required to
 acquire baseband data for multiple carriers. Generally, if wideband
 receivers are used, such as scan receivers, multiple digital acquisition
 paths will still be required since remote units to be located may be
 assigned unique carriers. Thus, locating remote units assigned to unique
 CDMA carriers requires observation of baseband data within each carrier,
 which implies the need for digital acquisition paths assigned to each
 carrier. Further, each of these assigned carriers requires either a
 wideband multi-carrier receiver, a plurality of multi-carrier receivers,
 or a plurality of single-carrier receivers.
 Moreover, single site location techniques, or multi-site location
 techniques, may employ time of arrival and direction of arrival
 algorithms. Yes. It is known in the art to use phased array antennas for
 determining direction of arrival of incoming signals from remote units.
 Yes: The use of phased array antennas enables direction of arrival
 detection by collecting identical copies of the remote unit's transmission
 at each antenna element. The arrival of these identical copies will have
 delays at each antenna element that can be evaluated using geometry to
 determine the angle of arrival. Multipath components of a signal can be
 descerned up to the design of the phased array and the capabilities of the
 direction of arrival algorithms.
 In addition, access probe signals are also defined in CDMA IS 95C. These
 access probe signals are typically used by a remote unit to indicate to a
 base station that the remote unit is available. These access probe signals
 are typically also generated when a call is sent to begin call set up and
 use of traffic channels. In the instances where a service, such as an
 emergency service, wants to know the location of a remote unit as fast as
 possible, a call may get blocked during channel set up due to congestion
 or other reasons. This can prevent the location of the remote where only
 traffic channels are used to determine a remote unit's location. It would
 therefore be desirable to provide location data for a remote unit prior to
 traffic channels being used for the communication.
 Consequently, a need exists for a remote unit location system and method
 that can be used in a multicarrier radiotelephone or wireless system while
 reducing the cost of implementation. It would be desirable if such a
 system could be used both for single site remote unit location and multi
 site remote unit location. Such a system and method should also attempt to
 reduce delays required to obtain location data for selected remote units.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Briefly, an apparatus and method determines a location of one or more
 remote units in a wireless communication system by employing a phased
 array antenna and a programmable receiver switching apparatus. A plurality
 of radio frequency receivers receive a plurality of different carriers,
 such as CDMA carriers, on each of a different phased array antenna
 element. An RF switching matrix and controller dynamically switch the
 plurality of receivers to not only receive the different carriers on each
 of the different phased antenna radio elements to determine time of
 arrival information, but alternately receive a same carrier signal over
 all or a portion of the phased array antenna element to determine
 direction of arrival information from received baseband data. The
 apparatus and method dynamically allocates radio frequency receive path
 resources as required by a programmable location engine. The programmable
 location engine employs cascaded time of arrival and direction of arrival
 algorithms to determine per remote unit location data. For those portions
 of the location engine that can be performed simultaneously on multiple
 carriers, receivers are dynamically assigned to unique carriers to
 facilitate parallel processing. For the portion of the programmable
 location engine that requires sampling of the entire antenna array, such
 as for angle of arrival determinations, the receivers are programmed to
 sample all of the given phased array and antennas elements that are
 temporarily assigned to a same carrier for data acquisition and subsequent
 processing.
 In one embodiment, a radio frequency switching matrix provides local
 oscillator frequencies for each of a plurality of RF receivers. A
 programmable local oscillator outputs the desired local oscillator
 frequency to the radio frequency switching matrix. A controller controls
 the radio frequency switching matrix and the programmable local oscillator
 to dynamically switch the plurality of receivers coupled to each of the
 phased array antenna elements to a same carrier frequency or each element
 to a different carrier frequency, depending upon the requirements of the
 programmable location engine. A plurality of mobile location carrier
 buffers, such as CDMA carrier buffers, are provided for each carrier so
 that suitable information received by the receivers can be stored and used
 for multipass evaluation by the programmable location engine.
 In another embodiment, access probe signals are used as the received
 signals from which location data is determined. The receivers are
 controlled (i.e., steered to a given carrier via programmable LO) to
 obtain data for use in determining time of arrival data per remote unit
 assigned to each of a plurality of carriers, and temporarily controlled to
 receive the same carrier over the phased array antenna elements for
 obtaining per remote unit data for angle of arrival calculations.
 Subsequently, the receivers are reassigned back to different carrier
 frequencies so that more data can be obtained so time of arrival
 calculations can continue. The reassigning of receivers back to different
 carrier frequencies is performed as a function of where remote unit
 identification data, such as mobile identification (MID), is located
 within the remote unit access probe signals.
 FIG. 1 shows one example of an apparatus 100 having a plurality of radio
 frequency receivers 102a, 102b, 102c, 102d-102n for determining a location
 of a remote unit. For purposes of illustration, and not limitation, the
 disclosed invention will be described with respect to a multicarrier CDMA
 wireless communication system, such as an IS95/C wireless system. However,
 it will be recognized that the invention may be employed in any suitable
 wireless communication system. Also, by way of example, the apparatus 100
 will be described with reference to a four carrier multicarrier CDMA
 wireless system. However, it will be recognized that any suitable number
 of carriers or type of channelization may be used. The remote unit may be
 a mobile unit or a stationary unit.
 The apparatus 100 also includes a phased array antenna 104 having a
 plurality of phased array antenna elements 106a-106d, a programmable
 receiver switching apparatus 108, a mobile location shared resource
 controller 110, a programmable location engine 112, and a bank of mobile
 location CDMA buffers 114. For purposes of illustration, the disclosed
 invention will be discussed as though it is integrated into an existing
 base station in a radiotelephone system that includes normal communication
 receiver 116 and normal communication traffic channel demodulators 118, as
 known in the art. In addition, the apparatus may be employed as part of a
 BTS, or any other suitable network element within a wireless communication
 system. As shown here, the apparatus 100 also communicates location data,
 such as the longitude, latitude, TOA data and/or DOA data a location
 services node 120. The LSN 120 provides a list of remote units for which
 location is desired and other information. For example, carrier
 assignment, remote unit identification and queue information 122 is sent
 to the mobile location shared resource controller 110. Priority is
 assigned by the LSN 120 or other network element for each carrier and for
 each remote unit identified, for example, by a mobile ID. As is well known
 for CDMA type communication systems, multiple remote units may be using
 the same carrier and different Walsh codes. Multicarrier CDMA systems
 employ a plurality of carriers for which each carrier may contain a
 number, such as 64, remote units wherein each remote unit is assigned one
 of 64 Walsh codes for a period of time.
 The receiver switching apparatus 108 includes a radio frequency switching
 matrix 126 and a programmable local oscillator 128. The radio frequency
 switching matrix 126 may be a suitable 4.times.4 switching matrix
 integrated circuit, or any suitable switching mechanism. The programmable
 local oscillator 128 may be a combination of separate programmable local
 oscillators, each programmable through a local oscillator control signal
 130 or bus that provides suitable local oscillator frequency signals
 140a-140b at appropriate frequencies for the radio frequency receivers
 102a-102d.
 The plurality of radio frequency receivers 102a-102n are switched by the
 switching matrix 126 to receive the selected local oscillator frequency
 133 (here four signals) from the programmable local oscillator 128 to
 control the receivers to receive a plurality of different carriers on each
 of the different phased array antenna elements 106a-106d in an initial
 data acquisition period. During this initial data acquisition period, the
 acquired data is used for determining time of arrival data for a given
 remote unit. During other data acquisition periods, the plurality of radio
 frequency receivers 102a-102n, or a suitable subset of the receivers, are
 controlled to receive a same local oscillator frequency to allow the
 receivers to receive a same carrier signal for a different period of data
 acquisition, such as to facilitate angle of arrival location calculations
 on a per remote unit basis. In this embodiment, the plurality of radio
 frequency receivers 102a-102n are added receivers to a conventional BTS to
 facilitate remote unit location. Also as shown, one or more of the radio
 frequency receivers may be shared with normal communication paths, such as
 radio frequency receiver 102a to share resources among existing base
 station receivers to the extent possible. The radio frequency receivers
 102a-102d also include suitable CDMA demodulators so that the receivers
 output despread baseband data 132 for the bank of mobile location CDMA
 buffers 114. The despread baseband data is used by the programmable
 location engine to determine location data on a per remote unit basis. The
 mobile location CDMA buffers 114 and their control is described in more
 detail in copending application entitled "Mobile Unit Location Apparatus
 And Method For A CDMA Wireless System", having attorney docket number
 CE03704R, filed on the same date as instant application by J Pfeil et al.,
 owned by instant assignee and incorporated herein in its entirety.
 The mobile location shared resource controller 110 communicates location
 engine control data 144 to the programmable location engine 112 to
 indicate to the programmable location engine 112 which location algorithm
 to use when, such as when to use a time of arrival algorithm versus an
 angle of arrival (direction of arrival) algorithm. This is based on
 knowing the current evaluation period, or any other suitable criteria. The
 mobile location shared resource controller 110 generates a switch matrix
 control signal 145 to control the switch matrix 126 so that the switch
 matrix 126 suitably passes the selected local oscillator frequency 133 to
 the appropriate radio frequency receiver 102a-102n during the evaluation
 period. The receiver switching apparatus 108 reassigns the plurality of
 receivers back to different carrier frequencies to obtain additional time
 of arrival data simultaneously for the plurality of different carriers
 during the time of arrival acquisition and evaluation periods typically
 after data for use in direction of arrival has been obtained over multiple
 phased array antenna elements for a same carrier.
 Moreover, the apparatus 100 is preferably, although not necessarily, a
 single site location remote unit location apparatus such that the phased
 array antenna 104 is located at a single site with the plurality of RF
 receivers and other elements of apparatus 100. As such, a single site
 location apparatus is disclosed that utilizes both time of arrival and
 direction of arrival determinations. The controller 110 may be a portion
 of a programmed processing device such as a programmed computer,
 microprocessor, DSP, state machine, discrete logic or other suitable
 structure. The programmable location engine 112 may be a software module,
 hardware configuration or any suitable combination thereof.
 Referring to FIGS. 2-6, in operation as shown in block 200, the carrier
 assignment, remote unit ID and queue information 122 may take the form of
 a table 400 (FIG. 4) and is evaluated by the mobile location shared
 resource controller 110. In addition, other operations of the mobile
 location shared resource controller 110 are also described in the
 aforementioned co-pending application incorporated herein by reference. As
 part of the carrier assignment and remote unit ID information table 400,
 signal type information is also provided to indicate whether the apparatus
 100 should be set in a mode to evaluate traffic channels to determine the
 location of a remote unit, or if the apparatus 100 should be set in a mode
 to analyze access probe signals to determine the location of a remote
 unit. Accordingly, the carrier assignment and remote unit ID information
 table 400 may also include signal type information 402. It will be
 recognized that this information may be eliminated if, for example, the
 carrier assignment and remote unit ID information table 400 is coded or
 sent at a period of time known by the apparatus 100 to be for a given
 signal type. Accordingly, the mobile location shared resource controller
 110 will determine a signal to be analyzed as a traffic channel or an
 access probe signal or other initial acquisition channel. As shown in
 block 202, the method includes programming the programmable local
 oscillator 128 to allow each of the plurality of radio frequency receivers
 102a-102n to receive a different carrier on each of different phased array
 antenna elements 106a-106d based on the assignment information from the
 carrier assignment remote unit ID information table 400.
 The radio frequency switching matrix 126 is coupled to provide local
 oscillator frequency signals 140a-140d for each of the plurality of RF
 receivers 102a-102d. The programmable local oscillator 128 uses the
 programmable oscillator output 131 to output the selected local oscillator
 frequency 133 as an input for the radio frequency switching matrix 126.
 The RF switching matrix 126, under control of the programmable local
 oscillator 128, dynamically switches the plurality of radio frequency
 receivers 102a-102d, which are coupled to each of the different phase
 array antenna elements 106a-106d, to different carrier frequencies. This
 is done during evaluation periods required for time of arrival data
 acquisition. For direction of arrival data acquisition, the RF switching
 matrix under control of programmable local oscillator 128, dynamically
 switches the plurality of radio frequency receivers 102a-102d subsequently
 to a same carrier signal frequency also for use in determining a location
 of the remote unit. As noted in the embodiment as shown in FIG. 1, the
 signals being received are traffic channel signals which are used to
 determine the location of a remote unit.
 Referring to FIGS. 3, 5 and 6, a mobile location shared resource controller
 controls the programmable local oscillator 128 to provide selected local
 oscillator frequencies 132 to the appropriate radio frequency receivers
 102a-102d via the switching matrix 126 as shown, for example, by column
 600. As shown by way of example, the RF receivers 102a-102d are suitably
 controlled via local oscillator frequency signals 140a-140d from the
 switching matrix 126 to each receive a different carrier signal from each
 of the different phased array antenna elements 106a-106d during a first
 period to obtain data for use in TOA calculations. For example, receiver
 102a is programmed with local oscillator frequency signal 140a to receive
 a first carrier C1 which contains data for remote units 1010, 7777, 2345,
 4768 and 3465. Similarly, RF receiver 102b receives a local oscillator
 frequency signal 140b to allow the RF receiver 102b to receive a different
 carrier C2, which contains remote units 1234, 6543, 3453, and so on for
 other remaining carriers. Hence, these radio frequency receivers receive
 the plurality of different carriers on each of the different phased array
 antenna elements for a first period of time 602. The receiver switching
 apparatus 108, under control of the mobile location shared resource
 controller 110, dynamically changes the local oscillator frequencies
 associated with each of the plurality of radio frequency receivers to
 different frequencies.
 FIGS. 3.1 and 3b illustrate examples of dynamic switching control to
 provide four channel acquisition and reassignment of receivers to provide
 data acquisition of a same channel over multiple phased array antenna
 elements. As shown, where a four by four switching matrix is used, the
 mobile location shared resource controller 110 sets the RF switching
 matrix 126 to obtain data from different carriers, each in a different
 phase array element by control signal 145 controlling the switching matrix
 126 to output the appropriate local oscillator frequency signals 140a-140b
 by selecting appropriate switch control to output the local oscillator
 frequency 133 to the appropriate radio frequency receiver 102a 102d. The
 time of arrival data can be obtained by having the radio frequency
 receivers 102a-102b each receive a different local oscillator frequency
 selected by the mobile location shared resource controller 110 to provide
 four carrier acquisition. As shown in FIG. 3.2, the RF switch matrix 126
 is controlled to set switches for single or same channel acquisition to
 obtain data for direction of arrival calculations for remote unit assigned
 to a selected carrier.
 As shown in block 204, also during this first period of time 602, the RF
 receivers perform synchronization algorithms which align signal recovery
 processes to the proper timing offsets, hence allowing signal recovery and
 location algorithms, as known in the receiver art. Synchronization
 procedures such as these typically achieve increasing accuracy as remote
 unit data arrives at the station and coherency is obtained. The
 synchronization and search process involves determining timing, frequency,
 and other channel offsets. This is accomplished by comparing a known
 sequence to the information transmitted by the mobile and received by the
 remote site. This search achieves coherency as the signal acquisition
 procedures transition from an uncalibrated state to a synchronized state.
 In other words, as described in "CDMA Principles of Spread Spectrum
 Communication" by Andrew J. Viterbi, Addison-Wesley Publishing Company,
 1995 ISBN 0-201-63374-4, which is incorporated by reference herein, known
 sequence re-modulation produces a signal which is then correlated with the
 remote site received baseband data to produce timing offsets. The known
 sequence of data is compared to the information received by remote unit
 within the search window to determine the timing difference relative to
 the remote unit's internal reference, and subsequently the propagation
 delay and hence the distance between the mobile and the remote unit. It
 will be recognized that if the radio frequency receivers 102a-102n are not
 embedded as part of an existing BTS, for example, it may be necessary to
 provide channel modem demodulator hardware and/or software to generate
 suitable synchronization information. The radio frequency receivers are
 dynamically allocated to provide per remote unit data acquisition from
 different carriers. In the second data acquisition and evaluation period
 602, the radio frequency receivers are assigned to the carriers that have
 the highest priority assignments.
 As shown in block 206, during the evaluation and data acquisition period
 602, a local copy of demodulated data 142 is obtained through another
 antenna system 148 and different receivers and demodulators, to provide a
 copy of received demodulated data for use in comparison by the
 programmable location engine 112. Preferably, the demodulated data is
 obtained through an antenna other than the phased array antenna 106a-106d.
 The local copy of the demodulated data 142 is provided for all carriers of
 interest either through different receivers, or if desired, using the
 location dedicated receivers. Where the radio frequency receivers
 102a-102n are used, additional baseband buffers similar to mobile location
 CDMA buffers 114 would store and provide the copy of demodulated data 142
 to the programmable location engine 112. While the local copy of the
 demodulated data is being obtained, as shown in block 208, the apparatus
 stores samples of demodulated baseband data from each CDMA carrier in the
 bank of mobile location CDMA buffers 114 for use by the programmable
 location engine 112. The demodulated baseband data stored in the bank of
 mobile location CDMA buffers is baseband data that has been despread, as
 known in the art.
 As shown in block 210, also during the evaluation and data acquisition
 period 602, the programmable location engine 112 performs time of arrival
 analysis for each remote unit by obtaining data on a per remote unit basis
 from the appropriate mobile location CDMA buffer assigned to a remote
 unit. As such, the programmable location engine 112 determines time of
 arrival data on a per remote unit basis from each of a plurality of
 different carriers from each of the different phased array antenna
 elements. The baseband data 132 is CDMA carrier data, such as despread
 baseband data, stored on a per carrier basis in the bank of CDMA carrier
 buffers as described in more detail in co-pending application entitled
 "Mobile Unit Location Apparatus And Method For A CDMA Wireless System",
 having attorney docket number CE03704R, previously referenced herein.
 Where desired, time stamps may also be used and assigned to the received
 baseband data 132 so that multipass processing may be performed by the
 programmable location engine for non-real time data, if desired multi-pass
 processing involves multiple evaluations (either serially or in parallel)
 to be performed on a common set of acquired baseband sample data.
 Once the time of arrival data has been determined by the programmable
 location engine 112 for all remote units assigned to a given carrier, the
 programmable location engine sends a signal 146 indicating that it has
 completed the time of arrival determination on a per remote unit basis, to
 the mobile location shared resource controller 110.
 As shown in block 212, once the time of arrival data has been determined
 for the designated remote units on the designated carriers, the method
 includes dynamically switching the plurality of radio frequency receivers
 that are coupled to each of the different phased array antenna elements,
 to receive the same carrier signal. This is to provide data for use in a
 direction of arrival calculation for a remote unit assigned to this
 carrier. As such, the mobile location CDMA buffers obtain data for use in
 determining direction of arrival data, and the programmable location
 engine 112 determines direction of arrival data per remote unit assigned
 to the same carrier signal in response to the mobile location shared
 resource controller 110 dynamically switching the receivers to a same
 carrier signal.
 More specifically, the mobile location shared resource controller 110 sends
 a local oscillator control signal 130 to the programmable local oscillator
 indicating the local oscillator frequency to be used commonly for all of
 the desired RF receivers 102a-102n to obtain data for determining
 direction of arrival data on a per remote unit basis. The switching of the
 plurality of receivers to receive the same carrier signal via a common
 local oscillator is shown, for example, during period 604 in FIG. 6. As
 shown, this period signifies the data acquisition and evaluation period
 for the direction of arrival calculation. By way of example, during this
 time period, carrier C2 is received by each of radio frequency receivers
 102a-102d at the same time such that the receiver resources are
 temporarily reassigned to a single carrier, in this case carrier C2 since
 the highest priority remote unit shown in the list of FIG. 4 was assigned
 to carrier C2. Given prior synchronization values stored from the first
 evaluation period 602, the acquisition across the four element based
 antenna array can be significantly shorter and still provide suitable
 accuracy. The acquisition and evaluation period 602 is likely to be longer
 than the acquisition and evaluation period 604, 606 and 608 since these
 later acquisition periods are used to perform single carrier acquisition
 and some joint time of arrival and direction of arrival processing by the
 programmable location engine 112. The TOA process on a per-carrier basis
 is typically a longer process because of the significant acquisition and
 processing requirements involved. The DOA algorithms re-use the
 synchronization determinations made during the TOA determination periods.
 The evaluation periods 610-614 illustrate the time of arrival and
 direction of arrival processing performed by the apparatus 100 for remote
 units assigned to carriers five and six (C5 and C6). The dynamic receiver
 assignment allows for fewer lengthy time synchronization acquisition and
 processing periods since it takes less time to take acquisition snapshots
 across the phased array antenna for the direction of arrival processing
 periods since synchronization information is obtained in previous time
 periods during the time of arrival data acquisition periods.
 Referring back to FIG. 2, as shown in block 214, the method includes
 storing the perceived baseband data for use in determining direction of
 arrival data by the programmable location engine 112. As shown in block
 216, the method includes performing the direction of arrival analysis by
 the programmable location engine 112 and again sending a completion signal
 146 to the mobile location shared resource controller 110 when the
 direction of arrival data, determined on a per remote unit basis, is
 complete. As shown in block 212, the apparatus is controlled to obtain the
 data from the same carrier signal for use in a direction of arrival
 determination for each desired carrier. Accordingly, the process may be
 repeated for additional carriers. For example, an additional step of
 obtaining or determining direction of arrival data for other remaining
 carriers of the plurality of different carriers is accomplished by
 dynamically switching the receivers to commonly receive each of the
 remaining carriers in a sequential manner. This is shown for example, in
 periods 606,608 and 610 of FIG. 6.
 Referring to FIG. 5, the evaluation periods used by the programmable
 location engine 112 may be controlled by the assigned priority level of a
 given carrier. For example, as shown in evaluation period 500, carrier C2
 is first carrier detected since carrier C2 has the highest priority as
 shown in the queue information table 400 (FIG. 4). These evaluations may
 be, for example, the time of arrival evaluations. As shown in evaluation
 period 502, the programmable location engine may next evaluate the carrier
 C4, since this carrier has a second level priority and fewer remote units
 to analyze. Depending upon the system, it is likely that evaluation
 periods may require six sets of frames and duration, one set of frames per
 carrier with the number of frames required in a set for evaluation
 processing predominated by the time required for synchronization. Multiple
 location determinations for a selected remote unit can be performed over
 the same set of acquired channel data.
 FIG. 7 illustrates an alternative embodiment where the apparatus 700
 evaluates access probe signals instead of, or in addition to, traffic
 channel signals. The apparatus 700 is substantially the same as the
 apparatus 100 shown in FIG. 1, except that the mobile location shared
 resource controller 110 sends location engine control data 144, local
 oscillator control signal 130, and switch matrix control data 145 to the
 requisite elements as a function of where remote unit identification data,
 such as mobile ID data, is located within the remote unit access probe
 signals. As such, the initial assigning of receivers to obtain the time of
 arrival data and the reassigning of the receivers to receive a same
 (common) carrier for DOA data and the reassigning of receivers back to
 receive different carrier frequencies is performed as a function of where
 the remote unit identification data is located within the remote access
 probe signals. For example, where access probe signals including mobile ID
 data located after a preamble, such as the access probe signals described,
 for example, in IS95/C, the mobile location shared resource controller 110
 switches the radio frequency receivers 102a-102d from the time arrival
 acquisition period to a direction of arrival acquisition period and back
 to a time of arrival acquisition period, before mobile ID data is received
 after the preamble, so that the apparatus 700 can acquire the mobile ID
 data. Accordingly, a location of the remote unit may be performed in an
 efficient manner prior to set up being complete. This may provide useful
 location information in emergency situations where a call cannot be
 completed due to various reasons, and may also find advantages in other
 situations.
 Moreover, the access probe signals are typically shorter in duration than
 communications over traffic channels. Accordingly, the programmable
 location engine 112 utilizes a time of arrival algorithm primarily during
 the access probe duration. A time of arrival determination is performed on
 the same or slightly less than the full access probe. The direction of
 arrival calculation can be performed using a smaller sample set, namely a
 shorter duration.
 It will be recognized by those of ordinary skill in the art that the
 programmable local oscillator and the local oscillators of the receivers
 have sufficient retune specifications to not interfere with direction of
 arrival acquisition. Coherent sampling of each of the antenna elements is
 completed during a snapshot sufficient to perform array analysis.
 Calibration of the phased array antenna is updated as necessary to
 compensate for any phase imbalance between the phased array antenna
 element receive paths. This calibration is typically performed via an
 injected signal at the array, but may also be performed via other external
 stimulus such as a reference remote unit.
 FIG. 8 illustrates a table showing the dynamic allocation of receiver
 assignment for an access probe signal. As shown, time of arrival data is
 acquired and analyzed during periods 800 and 810. As shown by acquisition
 periods 800, the mobile location shared resource controller 110 controls
 the receiver switching apparatus 108 to detect the access probes for four
 carriers to obtain baseband data for time of arrival calculations. The
 time of arrival (TOA) of an access probe's prompt ray is determined by the
 programmable location engine 112 in a conventional manner as known in the
 art. Preferably a time of arrival algorithm that may also be used may be
 found in co-pending application entitled "Method and Apparatus for
 Determining an Angle of Arrival of a Transmitted Signal in a Communication
 System" having inventors Golovin et al., attorney docket number CE08217R,
 filed on even date, owned by instant assignee and hereby incorporated in
 its entirety by reference. After the receivers are coupled to receive a
 plurality of different carriers on each of the different phased array
 antenna elements 106a-106d for the access probe signal, the mobile
 location shared resource controller 110 controls the receiver switching
 apparatus 108 to control the plurality of RF receivers 102a-102n to
 receive a same carrier during the time period 810 for access probe signals
 to obtain baseband data for direction of arrival calculations by the
 programmable location engine 112. The TOA algorithm is cascaded with a DOA
 algorithm by using the timing reference of the access probe's prompt ray
 provides an index into the stored baseband data used for the direction of
 arrival calculations. Any suitable phased array direction of arrival
 algorithm, as known in the art may be used. Subsequently, the mobile
 location shared resource controller 110 reassigns the RF receivers
 102a-102n to continue time of arrival data acquisition for four carriers
 prior to the detection of the mobile identification data embedded in the
 access probe signal.
 The programmable location engine, is programmable since the controller may
 control which algorithm may be used to switch time. For example, a time of
 arrival algorithm is used to evaluate baseband data stored in the location
 CDMA buffers. The controller may then program the programmable location
 engine to then later perform direction of arrival calculations on baseband
 data stored when the phased array antenna elements are programmed through
 receipt of the same carrier signal over the plurality of different phased
 array antenna elements. One example of suitable cascaded time of arrival
 and direction of arrival algorithms may operate as follows. For a given
 set of remote units on a given set of carriers, the channel parameters
 (timing offsets, energy measurements, frequency offsets) are determined
 and stored for each remote unit. The channel parameter determination can
 be accomplished through a variety of means, such as storing communication
 modem parameters, detecting the correlation peak of the highest energy
 arriving ray, detecting the correlation peak of the earliest arriving ray,
 etc. Once the receivers have been steered to a common carrier via a common
 LO reference, the DOA processing can begin. Immediately following a
 settling time for the receivers (typically the propagation time of the
 signal through the filter response), the acquisition of common carrier
 phased array baseband data can begin. Using the channel parameters
 discovered during the TOA algorithm processing, DOA algorithms a performed
 on the phased array data. This typically involves a dot-product operation
 yielding complex-valued results for each antenna element. These can then
 be evaluated for an angle of arrival determination. A common technique
 involves the zero-padding of the array `signature` (i.e., the dot product
 results). The zero-padded vector is then passed through a spectral
 analysis (typically an fast Fourier transform), the peak spectral energy
 proportional to the angle of arrival.
 It will also be recognized, for example, that the controller need not be a
 shared resource controller but may be a stand alone processing device with
 any other suitable component. In addition, it will be recognized that the
 functionality described herein may be performed by other elements of the
 apparatus 100 as desired. In addition any number of suitable phased array
 antenna elements, either in a linear array, non-linear array or suitable
 combination thereof may be used. Moreover, it should be understood that
 the implementation of other variations and modifications of the invention
 in its various aspects will be apparent to those of ordinary skill in the
 art, and that the invention is not limited by the specific embodiments
 described. It is therefore contemplated to cover by the present invention,
 any and all modifications, variations, or equivalents that fall within the
 spirit and scope of the basic underlying principles disclosed and claimed
 herein.