Combined GPS and wide bandwidth radiotelephone terminals and methods

Wireless mobile terminals include a GPS Radio Frequency (RF) receiver and a wide bandwidth radiotelephone RF receiver having bandwidth that is at least half as wide as the GPS RF signal chip frequency. The wireless mobile terminals also include a shared Intermediate Frequency (IF) section that is responsive to both the GPS RF receiver and to the wide bandwidth radiotelephone RF receiver. A demodulator such as a CDMA despreader is responsive to the shared IF section. Thus, common circuitry may be provided except for the separate GPS RF receiver and wide bandwidth radiotelephone RF receiver. Low cost manufacturing and high efficiency operations may thereby be provided.

FIELD OF THE INVENTION 
The present invention generally relates to wireless communications systems 
and methods, and more particularly, to receivers for wireless mobile 
terminals. 
BACKGROUND OF THE INVENTION 
Wireless communication systems are commonly employed to provide voice and 
data communications to a plurality of subscribers within a prescribed 
geographic area. For example, analog cellular radiotelephone systems, such 
as those designated AMPS, ETACS, NMT-450, and NMT-900, have been deployed 
successfully throughout the world. Recently, digital cellular 
radiotelephone systems such as those designated IS-54B (and its successor 
IS-136) in North America and GSM in Europe have been introduced and are 
currently being deployed. These systems, and others, are described, for 
example, in the book entitled Cellular Radio Systems, by Balston, et al., 
published by Artech House, Norwood, Mass. (1993). In addition to the above 
systems, an evolving system referred to as Personal Communication Services 
(PCS) is being implemented. Examples of current PCS systems include those 
designated IS-95, PCS-1900, and S in North America, DCS- 1800 and DECT 
in Europe, and PHS in Japan. These PCS systems operate at the 2 gigahertz 
(GHz) band of the radio spectrum, and are typically being used for voice 
and high bit-rate data communications. 
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 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, 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 terminals 22 and an 
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 terminals 22 or between a wireless 
mobile terminal 22 and a landline telephone user 32 via a Public Switched 
Telephone Network (PSTN) 34. The base station 26 generally handles the 
radio communications between the cell 24 and the wireless mobile terminal 
22. In this capacity, the base station 26 may function as a relay station 
for data and voice signals. 
FIG. 2 illustrates a conventional celestial wireless communication system 
120. The celestial wireless communication system 120 may be employed to 
perform similar functions to those performed by the conventional 
terrestrial wireless communication system 20 of FIG. 1. In particular, the 
celestial wireless communication system 120 typically includes one or more 
satellites 126 that serve as relays or transponders between one or more 
earth stations 127 and satellite wireless mobile terminals 122. The 
satellite 126 communicates with the satellite wireless mobile terminals 
122 and earth stations 127 via duplex communication links 130. Each earth 
station 127 may in turn be connected to a PSTN 132, allowing 
communications between the wireless mobile terminals 122, and 
communications between the wireless mobile terminals 122 and conventional 
terrestrial wireless mobile terminals 22 (FIG. 1) or landline telephones 
32 (FIG. 1). 
The celestial wireless communication system 120 may utilize a single 
antenna beam covering the entire area served by the system, or as shown in 
FIG. 2, the celestial wireless communication system 120 may be designed 
such that it produces multiple, minimally-overlapping beams 134, each 
serving a distinct geographical coverage area 136 within the system's 
service region. A satellite 126 and coverage area 136 may serve a function 
similar to that of a base station 26 and cell 24, respectively, of the 
terrestrial wireless communication system 20. 
Thus, the celestial wireless communication system 120 may be employed to 
perform similar functions to those performed by conventional terrestrial 
wireless communication systems. In particular, a celestial radiotelephone 
communication system 120 may have particular application in areas where 
the population is sparsely distributed over a large geographic area or 
where rugged topography tends to make conventional landline telephone or 
terrestrial wireless infrastructure technically or economically 
impractical. 
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). Therefore, it would 
be desirable to have a wireless mobile terminal with a GPS receiver 
integrated therein. It will be understood that the terms "global 
positioning system" or "GPS" are used to identify any spaced-based system 
that measures positions on earth, including the GLONASS satellite 
navigation system in Europe. 
A GPS system is illustrated in FIG. 3. As is well known to those having 
skill in the art, GPS is a space-based triangulation system using 
satellites 302 and computers 308 to measure positions anywhere on the 
earth. GPS was first developed as a defense system by the United States 
Department of Defense as a navigational system. Compared to other 
land-based systems, GPS may be unlimited in its coverage, may provide 
continuous 24-hour coverage regardless of weather conditions, and may be 
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 302 orbiting the earth 
continually emit a GPS radio frequency signal 304 at a predetermined chip 
frequency. A GPS receiver 306, 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 signals take 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. From additional information provided in the radio 
signal from the satellites, including the satellite's orbit and velocity 
and correlation to its onboard clock, the GPS processor can calculate the 
position of the GPS receiver through a process of triangulation. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide wireless 
mobile terminals having a Global Positioning System (GPS) receiver 
integrated therein. 
It is another object of the invention to provide a wireless mobile terminal 
having a GPS receiver integrated therein that can be inexpensive to 
manufacture and efficient in operation. 
These and other objects are provided, according to the present invention, 
by a combined GPS and wide bandwidth radiotelephone wireless mobile 
terminal that shares many components. In particular, according to the 
present invention, it has been realized that the GPS receiver function and 
some celestial or terrestrial radiotelephone standards share a common IF 
bandwidth. Moreover, some celestial or terrestrial radiotelephone 
standards share a common task to process a signal to find long code 
lengths therein. Thus, the only major remaining difference may be the 
different radio frequencies that are received. 
Wireless mobile terminals according to the present invention include a GPS 
Radio Frequency (RF) receiver and a wide bandwidth radiotelephone RF 
receiver having bandwidth that is at least half as wide as the GPS signal 
chip frequency. The wireless mobile terminals also include a shared 
Intermediate Frequency (IF) section that is responsive to both the GPS RF 
receiver and to the wide bandwidth radiotelephone RF receiver. A 
demodulator is responsive to the shared IF section. Thus, common circuitry 
may be provided except for the GPS RF front end and wide bandwidth 
radiotelephone RF front end, which operate at different frequencies. 
However, both front ends may be manufactured in a single, dual-band front 
end for low cost manufacturing. High efficiency operations may thereby be 
provided. 
In a preferred embodiment of the present invention, the wide bandwidth 
radiotelephone RF receiver is a Code Division Multiple Access (CDMA) RF 
receiver, including a Universal Mobile Terminal System (UMTS), also known 
as wideband CDMA, or a Time Division Multiple Access (TDMA) RF receiver. 
Both CDMA and TDMA RF receivers may have bandwidth on the order of 1 MHz 
wide, which is comparable to GPS bandwidths. Thus, apart from the 
different RF spectra that are received, many components can be shared. For 
CDMA, the demodulator is preferably a CDMA spread spectrum despreader. For 
TDMA, the demodulator is preferably a TDMA demodulator. 
In fact, due to the similar bandwidths, a combined GPS/CDMA receiver can be 
provided wherein the CDMA receiver has the identical bandwidth as the GPS 
receiver. In this case, IF and demodulation can be combined efficiently. 
Portions of the GPS RF receiver and the TDMA/CDMA RF receiver can also be 
combined. For example, a dual band antenna may be provided wherein the GPS 
RF receiver includes a GPS RF filter that is responsive to the dual band 
antenna and wherein the wide bandwidth radiotelephone RF receiver 
comprises a spread spectrum RF filter that is responsive to the dual band 
antenna. A shared wide bandwidth RF amplifier and filter may then be 
provided in the RF section. 
Other embodiments of the present invention may provide separate GPS and 
CDMA/TDMA IF sections wherein all components are separate or wherein some 
components such as a local oscillator are shared. In yet other 
embodiments, a common demodulator such as a despreader is provided, but 
all other components are separate. 
Methods of receiving wireless communications in a mobile terminal according 
to the invention include the steps of receiving GPS RF signals at a 
predetermined chip frequency on a first RF channel and receiving wide 
bandwidth radiotelephone RF signals on a second RF channel, wherein the 
wide bandwidth radiotelephone RF signals have bandwidth that is at least 
half as wide as the GPS RF signal chip frequency. The GPS RF signals and 
the wide bandwidth radiotelephone RF signals are then demodulated in a 
shared demodulator. The demodulator can include a shared mixer. 
Accordingly, high efficiency, low cost wireless mobile terminals and 
wireless communication receiving methods may be provided.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention now will be described more fully hereinafter with 
reference to the accompanying drawings, in which preferred embodiments of 
the invention are shown. This invention may, however, be embodied in many 
different forms and should not be construed as limited to the embodiments 
set forth herein; rather, these embodiments are provided so that this 
disclosure will be thorough and complete, and will fully convey the scope 
of the invention to those skilled in the art. Like numbers refer to like 
elements throughout. 
The present invention stems from the realization that the GPS receiver 
function and some radiotelephone standards share a common IF bandwidth and 
that some of these standards also share a common task to process a signal 
to find a long code length. Accordingly, components of a GPS receiver and 
a wide bandwidth radiotelephone receiver may be efficiently combined to 
produce wireless mobile terminals and receiving methods that are capable 
of efficient, low cost operation. 
The details of GPS systems and wide bandwidth radiotelephone systems such 
as CDMA and TDMA systems are well known to those having skill in the art, 
and need not be described in detail below. Similarly, the subsystems that 
comprise each of these systems are also well known to those having skill 
in the art and need not be described in detail. Accordingly, the present 
Detailed Description will describe, on a block diagram level, various 
embodiments that can illustrate efficient combination of GPS receivers and 
wide bandwidth radiotelephone receivers. 
Referring now to FIG. 4, wireless mobile terminals and wireless 
communication receiving methods according to the present invention are 
shown. As shown in FIG. 4, wireless mobile terminals and methods according 
to the present invention include a GPS RF receiver 410 and a wide 
bandwidth radiotelephone RF receiver 420 having bandwidth that is at least 
half as wide as that of the GPS RF signal chip frequency. A shared IF 
section 430 is responsive to both the GPS RF receiver 410 and to the wide 
bandwidth radiotelephone RF receiver 420. A demodulator such as a 
despreader 450 is responsive to the shared IF section. 
Preferably, the wide bandwidth radiotelephone RF receiver 420 is a CDMA or 
TDMA RF receiver. Also preferably, the GPS RF receiver 410 and the wide 
bandwidth radiotelephone RF receiver 420 have similar bandwidth in 
different RF spectra. Most preferably, the GPS RF receiver 410 and the 
wide bandwidth radiotelephone RF receiver 420 have identical bandwidth in 
different RF spectra. 
More particularly, there are many cellular telephone standards that have IF 
bandwidths of about 30 KHz, such as the AMPS or digital AMPS standard, or 
about 270 KHz, such as the GSM standard. These narrow bandwidths may be 
insufficient for receiving the 1 MHz wide GPS signal. However, there are 
many cellular telephone standards that do have IF bandwidths of at least 1 
MHz. These include the IS-95 CDMA standard with a bandwidth of 1.2 MHz, 
the Digital European Cordless Telephone (DECT) TDMA standard having a 
bandwidth of about 1 MHz and a proposed Japanese CDMA standard having a 
bandwidth of up to 5 MHz wide. Satellite communication systems are also 
being designed and developed having similar wide bandwidths as well as 
CDMA signal processing, such as GLOBALSTAR. Accordingly, the present 
invention can provide shared IF processing of the GPS and wide bandwidth 
radiotelephone signals and a shared despreading process including 
demodulation/correlation/ baseband processing. Accommodation may be made 
for the differing RF frequencies that are received at similar bandwidths. 
In particular, it is known that the correlation loss caused by filtering in 
a GPS receiver is a function of the ratio of bandwidth to frequency. This 
correlation loss rapidly increases for bandwidths that are less than 50% 
of the chip frequency. See FIG. 10, which is a reproduction of FIG. 12 of 
the textbook entitled "Global Positioning System: Theory and Applications, 
Vol. 1", p. 351, the disclosure of which is hereby incorporated herein by 
reference. For example, if the chipping rate is 1.023 MHz, and if up to a 
3 dB loss is acceptable, then the single-sided bandwidth (half bandwidth) 
of the receiver can be 0.25.times.1.023 MHz or about 255 KHz. The total 
bandwidth is then about 511 KHz, or about half the chip rate. As shown in 
FIG. 10, at lower bandwidths, correlation loss increases rapidly. 
FIG. 5 illustrates another general embodiment of the present invention. In 
this embodiment, a separate GPS RF receiver 510 and wide bandwidth 
radiotelephone RF receiver 520 are provided, as well as a separate GPS IF 
section 530 and wide bandwidth radiotelephone IF section 540. A common 
demodulator such as despreader 550 is also provided. This embodiment may 
be desirable where it is preferred to provide separate IF sections. 
Referring now to FIG. 6, a more detailed embodiment of combined GPS/wide 
bandwidth radiotelephone terminals and methods is illustrated. As shown in 
FIG. 6, a GPS RF section includes GPS antenna 612, RF filter 614, RF 
amplifier 616 and RF filter 618. The wide bandwidth radiotelephone RF 
section includes cellular antenna 611, RF filter 613, RF amplifier 615 and 
RF filter 617. A separate GPS mixer 630 and wide bandwidth radiotelephone 
mixer 640 is provided, each of which uses a separate local oscillator 632 
and 642 respectively. A switch 644 is provided to switch between the GPS 
and wide bandwidth radiotelephone systems. A shared IF filter 646 and a 
shared demodulator such as despreader 650 (demodulator/correlator/base 
band processor) is provided. Similarly, a common microprocessor 652 and 
memory 654 is provided. 
It will be understood by those having skill in the art that the terminals 
and methods of FIG. 6 may be obtained by adding GPS antenna 612, RF filter 
614, RF amplifier 616, RF filter 618, mixer 630, local oscillator 632 and 
switch 644 to a conventional CDMA cellular telephone terminal, to permit 
the combined unit to act in a dual mode GPS/CDMA mode depending on the 
setting of switch 644 and the digital processing of the signal in the 
correlator/base band processor 650 and microprocessor 652. The software 
may need to be adjusted to search for different codes and slightly 
different code chip rates, and then use that information appropriately for 
either task. 
For GPS reception, the code phase shifts may be found for each satellite 
that is visible, and data demodulation may permit time and ephemeris data 
to be obtained. Within the microprocessor 652, the data is combined to 
determine location. In cellular telephone usage, the code polarity is data 
that is further processed in a CODEC to produce voice reception. It will 
also be understood that, for clarity, FIG. 6 does not illustrate the 
transmit path that is used in a CDMA cellular telephone terminal. 
It will also be understood that in the terminals and methods of FIG. 6, 
code phase shifts may be obtained for each satellite that is visible, as 
determined from an internal almanac or from information supplied via a 
cellular telephone link. That information may be stored in the memory 654, 
and then modes may be switched from GPS reception to CDMA cellular 
telephone usage. That code phase shift information may be sent over the 
cellular telephone link to a server where the location is determined using 
additional information that is obtained at a central point. 
Referring now to FIG. 7, an alternate embodiment of the present invention 
is illustrated. The elements of FIG. 7 correspond to those of FIG. 6 
except that a common oscillator 732 is used for both the GPS mixer 630 and 
the wide bandwidth radiotelephone mixer 640. The use of a common local 
oscillator in a dual mode GPS/radiotelephone terminal is described in 
Application Ser. No. 08/925,566, entitled "Systems and Methods for Sharing 
Reference Frequency Signals Within a Wireless Mobile Terminal Between a 
Wireless Transceiver and a Global Positioning System Receiver", to 
coinventors Horton and Camp, Jr., assigned to the assignee of the present 
invention, the disclosure of which is hereby incorporated herein by 
reference. In the embodiment of FIG. 7, the circuit that controls the 
oscillator 732 may be adjusted to supply the appropriate frequency signal 
and permit reception of either GPS or wide band radiotelephone signals. 
FIG. 8 illustrates another embodiment wherein a common mixer 830 and a 
common local oscillator 832 are provided. Thus, switch 844 is used to 
switch the two RF signals into the mixer 830. As with FIG. 7, the 
oscillator may be readjusted to supply the appropriate frequency signal. 
Similar architectures may be used for GPS/DECT and GPS/WCS terminals and 
methods. In DECT, which does not have a correlator function, digital 
hardware may need to be supplied with a firmware/software program to 
perform correlation within the digital resources. 
Referring now to FIG. 9, terminals and methods that share portions of the 
RF system are shown. As shown in FIG. 9, a dual band GPS and cellular 
antenna 910 can receive both GPS and wide band radiotelephone signals. A 
pair of switches 911 and 912 may be used to switch an appropriate GPS RF 
filter 914 or cellular filter 913. Although these filters are shown as 
being separate filters, they may be embodied as a shared filter with 
variable or switched elements. A wide band RF amplifier 915 is then 
provided, along with a mixer 830. Oscillator 832, IF filter 646, 
despreader 650, microprocessor 652 and memory 654, are also provided as 
was already described. It will also be understood that separate GPS and 
cellular antennas may be used rather than a dual band GPS and cellular 
antenna, in combination with a common wide band amplifier. 
In the drawings and specification, there have been disclosed typical 
preferred embodiments of the invention and, although specific terms are 
employed, they are used in a generic and descriptive sense only and not 
for purposes of limitation, the scope of the invention being set forth in 
the following claims.