System and method for single to two-band personal communication service base station conversion

CDMA (Code Division Multiple Access) communications systems and methods for performing a single to multiple frequency band conversion for mobile communications. The systems and methods include mixing a portion of a first CDMA signal in a first frequency band with a reference signal to convert a portion of the first CDMA signal to a second frequency band. The converted portion and the other portion of the first frequency band can then be transmitted. The systems and methods further include filtering a portion of a second CDMA signal having frequency components in multiple frequency bands to provide a filtered CDMA signal in the first frequency band. The filtered CDMA signal is then mixed to convert it to the second frequency band for receiver processing.

TECHNICAL FIELD 
The present invention relates to a CDMA (Code Division Multiple Access) 
communications methods and systems preferably applied to mobile 
communications. 
BACKGROUND ART 
An exemplary Personal Communication Service (PCS) system 20 is shown in 
FIG. 1. PCS system 20 includes wireless terminals 22, base stations 24, 
switches 26, and a fixed network such as a public switched telephone 
network (PSTN) 28. Each base station 24 serves many wireless terminals 22 
simultaneously. Each switch 26 connects many base stations 24 to PSTN 28. 
Wireless terminals 22 and base stations 24 include transmitters and 
receivers to exchange radio frequency (RF) communication signals. 
Code division multiple access (CDMA) is a class of modulation that uses 
specialized codes to provide multiple communication channels in a 
designated segment of the electromagnetic spectrum. With CDMA, there are 
no restrictions on when transmission may take place or what frequency may 
be used in an allocated channel. In short, there are no restrictions on 
time or bandwidth. Each transmitter may transmit whenever it wishes and 
can use any or all of the bandwidth allocated a particular channel. Adding 
additional code sequences simply degrades voice quality. 
CDMA is referred to as spread-spectrum multiple access. Transmissions can 
spread throughout the entire allocated bandwidth spectrum. Transmissions 
are separated through envelope encryption/decryption techniques. That is, 
the transmissions are encoded with a unique binary word called a chip 
code. Each transmitter has a unique chip code. To receive a particular 
transmission, a receiver must know the chip code for the particular 
transmitter. 
CDMA communication systems differ from analog systems in that multiple 
users share one carrier frequency in a frequency band simultaneously. 
There are multiple frequency bands in the electromagnetic spectrum 
available for the use of mobile communications. A problem exists, however, 
that frequency bands are a scare commodity. Consequently, the demand for 
frequency bands is greater than the supply. As a result, service providers 
of mobile communications obtain frequency bands as they become available. 
Typically, the acquired frequency bands are segregated from each other by 
other bands. A given provider is often granted two or more non-contiguous 
or segregated frequency bands. Furthermore, different providers typically 
have their own frequency bands. 
In the past, to operate in a pair of segregated frequency bands, two sets 
of equipment dedicated to each frequency band was required. For instance, 
separate antennas, cables, and radio/signal processing hardware were 
required for each frequency band. What is needed is a system and method 
that would allow operation in multiple segregated frequency bands by one 
set of hardware. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a system 
and method for a single to multiple frequency band conversion for mobile 
communications. 
It is another object of the present invention to provide a system and 
method for a single to two frequency band conversion for transmitting 
signals. 
It is still another object of the present invention to provide a system and 
method for a two to single frequency band conversion for receiving 
signals. 
In carrying out the above objects and other object, the present invention 
provides a CDMA (Code Division Multiple Access) communications method for 
converting a CDMA signal in a single frequency band to two frequency bands 
for transmission. The method includes splitting a CDMA signal into a first 
CDMA signal and a second CDMA signal. The first and the second CDMA 
signals are in a first frequency band. The first CDMA signal is then mixed 
with a reference signal having a predetermined frequency to convert the 
first CDMA signal from the first frequency band to a second frequency 
band. The first and the second CDMA signals are then transmitted. 
Further, in carrying out the above objects and other objects, the present 
invention provides a CDMA communications method for converting a received 
CDMA signal having frequency components in at least two frequency bands to 
a single frequency band. The method includes passing only frequency 
components of a received CDMA signal within first and second frequency 
bands to provide a filtered two frequency band CDMA signal. The filtered 
two frequency band CDMA signal is then split into a first CDMA signal and 
a second CDMA signal. 
Frequency components of the first CDMA signal within the first frequency 
band are then passed to provide a first frequency band CDMA signal. The 
first frequency band CDMA signal is then mixed with a reference signal 
having a predetermined frequency to convert the first frequency band CDMA 
signal from the first frequency band to the second frequency band to 
provide a second frequency band CDMA signal. The second frequency band 
CDMA signal is then combined with the second CDMA signal to provide a 
combined CDMA signal having frequency components in the first and second 
frequency bands. Frequency components of the combined CDMA signal within 
the second frequency band are then passed to provide a combined second 
frequency band CDMA signal. 
Further, in carrying out the above objects and other objects, the present 
invention provides systems for carrying out the above described methods. 
The advantages accruing to the present invention are numerous. For 
instance, the present invention drastically reduces the cost of required 
cell site equipment used to serve mobile communication users. The present 
invention allows a provider to operate in a certain frequency band while 
another provider operates in a different frequency band. The partners can 
share antennas, cables, and radio/signal processing hardware. Existing 
products require at least separate hardware for such a shared carrier 
application. 
These and other features, aspects, and embodiments of the present invention 
will become better understood with regard to the following description, 
appended claims, and accompanying drawings.

BEST MODES FOR CARRYING OUT THE INVENTION 
Referring now to FIG. 2, an electromagnetic spectrum 30 is shown. Spectrum 
30 includes a plurality of frequency bands 32(a-f). Frequency bands 
32(a-f) include: band A 32a, band B 32b, band C 32c, band D 32d, band E 
32e, and band F 32f. Frequency bands 32(a-f) are arbitrarily segregated 
and adjacent as shown in FIG. 2. Each frequency band 32(a-f) is available 
for CDMA communications. Typically, one frequency band such as band 32a is 
used by one provider and another frequency band such as bands 32b or 32d 
is used by another provider. Frequency bands 32(a-f) are preferably in the 
800-100 MHz range of the electromagnetic spectrum or in the range 
typically used for mobile communications. As an example, bands A, B, and F 
have a bandwidth of about 30 MHz and bands D, E, and C have a bandwidth of 
about 10 MHz. 
Referring now to FIG. 3, an exemplary transmitter 40 of a CDMA 
communication system is shown. Transmitter 40 is connected to an antenna 
(not specifically shown) for transmission of data. In operation, the data 
x(t) transmitted with a data rate R is first modulated by a carrier 
f.sub.0 at mixer 42 to form a signal S(t). The signal S(t) is then 
modulated at mixer 44 by a spreading code G(t) to form a direct sequence 
signal S.sub.t (t). The carrier f.sub.0 is in the center of one of the 
available frequency bands 32(a-f). The direct sequence signal S.sub.t (t) 
is then transmitted by an antenna. 
Referring now to FIG. 4, an exemplary receiver 50 for use with transmitter 
40 shown in FIG. 3 is shown. Receiver 50 is connected to an antenna (not 
specifically shown) for reception of the direct sequence signal S.sub.t 
(t). In operation, the received S.sub.t (t) signal is correlated by a 
mixer 52 using the same spreading code G(t) to despread the signal S.sub.t 
(t). The despread signal S(t) is obtained and then demodulated by f.sub.0 
at a mixer 54 to recover the data x(t). 
Referring now to FIG. 5, a transmitter 60 of a CDMA communication system 
according to the present invention is shown. Transmitter 60 is capable of 
enabling providers operating in different frequency bands to share 
antennas, cables, and radio/signal processing hardware for transmitting 
CDMA signals. 
The operation of transmitter 60 for performing a single to two frequency 
band conversion of a CDMA signal will now be described. As an example, 
transmitter 60 converts a CDMA signal in band D 32d to a C and D band CDMA 
signal. Of course, other CDMA signals in different bands, such as bands A, 
B, E, and F, may be converted into other bands. 
Initially, a CDMA signal in band D 32d is applied to input terminal 62 and 
then split by power splitter 64. A portion of the D band CDMA signal 
outputs power splitter 64 and then directly inputs a multiplexer 66 for 
subsequent transmission by an antenna 68. 
Another portion of the D band CDMA signal outputs power splitter 64 and 
then inputs a mixer 70. Mixer 70 mixes the D band CDMA signal with a 
frequency f.sub.LO from a local oscillator (LO) 72 to form a C band CDMA 
signal. Specifically, mixer 70 uses f.sub.LO to convert the D band CDMA 
signal to a C band CDMA signal. The C band CDMA signal is then applied to 
multiplexer 66 such as a duplexer for subsequent transmission by antenna 
68. 
The conversion of the D band CDMA signal into the C band CDMA signal may 
either be an up or a down frequency conversion depending on where the 
bands are to each other in the spectrum. As shown in FIG. 6, the frequency 
f.sub.LO is approximately the difference in frequency between the center 
frequencies of the frequency bands 32(a-b). The conversion of frequency 
band D 32d into frequency band C 32c would be an up conversion as shown in 
FIG. 6. 
Referring now to FIG. 7, a receiver 80 of a CDMA communication system 
according to the present invention is shown. Receiver 80 is capable of 
enabling providers operating in different frequency bands to share 
antennas, cables, and radio/signal processing hardware for receiving CDMA 
signals. 
Initially, a received CDMA signal is applied to input terminal 82 from an 
antenna 84. The received CDMA signal may include different components in 
different frequency bands. For instance, the received CDMA signal may have 
frequency components in each of the A, B, C, D, E, and F frequency bands. 
The received CDMA signal is then applied to a first bandpass filter 86. 
Bandpass filter 86 rejects all frequency components of the received CDMA 
signal not in the C and D frequency bands. Accordingly, bandpass filter 86 
passes all frequency components of the received CDMA signal in the C and D 
frequency bands. 
The filtered C and D band CDMA signal inputs power splitter 88. A portion 
of the C and D band CDMA signal inputs a second bandpass filter 90. 
Bandpass filter 90 rejects the frequency components of the C and D band 
CDMA signal in the D frequency band. Consequently, the frequency 
components in the C frequency band pass through bandpass filter 90. 
The C band CDMA signal enters a mixer 92 after passing through bandpass 
filter 90. Mixer 92 mixes the C band CDMA signal with a frequency f.sub.LO 
from a local oscillator (LO) 94 to form a D band CDMA signal. 
Specifically, mixer 94 uses f.sub.LO to convert the C band CDMA signal to 
a D band CDMA signal. With reference to FIG. 6, the conversion of the C 
band CDMA signal to the D band CDMA signal is a down conversion. 
The converted D band CDMA signal is then combined with the other portion of 
the C and D band CDMA signal from power splitter 88 in a power combiner 
96. The combined C and D band CDMA signal is then filtered by a third 
bandpass filter 98. Bandpass filter 98 filters out the frequency 
components in the C band such that a D band CDMA signal outputs the 
bandpass filter. The D band CDMA signal may then be processed further by 
standard receiver equipment. 
The operation of receiver 80 has been described with reference to 
converting a C and D band CDMA signal to a D band CDMA signal. Of course, 
like transmitter 60, receiver 80 may convert other CDMA signals in 
different bands into other bands. 
Transmitter 60 and receiver 80 are incorporated in a base station between 
the antenna and transceiver circuitry. The advantage of the present 
invention is that the transceiver circuitry of the base station is unaware 
that signals in two different frequency bands are being transmitted and 
received. The transceiver circuitry only sees signals from one frequency 
band. Thus, transmitter 60 and receiver 80 may be added on to an existing 
base station and they are technology/vendor independent. 
Referring now to FIG. 8, a block diagram illustrating a two band (D and C), 
two cable standard minicell sector base station conversion unit 100 is 
shown. Base station conversion unit 100 includes equipment such as that 
shown in FIG. 6 for converting a single band frequency signal into a two 
band frequency signal for transmission. Similarly, base station conversion 
unit 100 includes equipment such as that shown in FIG. 8 for converting a 
received two band frequency signal into a single band frequency. 
Conversion unit 100 includes a standard minicell multiplexer 102 for 
connection to standard transceiver circuitry (the connection is not 
specifically shown in FIG. 8). Similarly, conversion unit 100 includes a 
pair of antennas 104(a-b) for transmitting and receiving CDMA signals. Of 
course, only one antenna may be used with more advanced circuitry as known 
to those of ordinary skill in the art. 
It should be noted that the present invention may be used in a wide variety 
of different constructions encompassing many alternatives, modifications, 
and variations which are apparent to those with ordinary skill in the art. 
Accordingly, the present invention is intended to embrace all such 
alternatives, modifications, and variations as fall within the spirit and 
scope of the appended claims. 
For instance, while the embodiments have been described particularly in 
reference to non-contiguous frequency bands that are within standard PCS 
spectrums, the present invention is equally applicable to other 
non-contiguous frequency bands. A particular example is the mobile 
cellular spectrums. Although the cellular frequency bands are contiguous, 
a provider may share or own one or more bands with a common receiver to 
save on infrastructure costs. Another example of where the present 
invention can be used is within the Global Station Management (GSM) 
spectrum.