Signal filtering in a transceiver for a wireless telephone system

In a wireless telephone system that utilizes a plurality of remote transceivers to carry telephony signals between wireless telephones and a central transceiver via a broadband distribution network, remote transceiver circuitry is provided to filter telephony signals and control signals from unwanted signals.

FIELD OF THE INVENTION
 The present invention relates to wireless communications systems, and more
 particularly to a remote transceiver that carries telephony communication
 signals between wireless telephones and a central transceiver via a
 broadband distribution network.
 BACKGROUND OF THE INVENTION
 The prior art teaches the use of existing cable television network cables
 to carry telephony signals between a telephone network and remote
 transceiver sites in defined cells or sectors. The transceivers are used
 to establish wireless telephony communication links with wireless
 telephones that are operating within an area covered by each remote
 transceiver. To increase the number of wireless telephone subscribers that
 can use the wireless telephone system it has been suggested to decrease
 the size and operational range of each cell or sector, and to increase the
 number of cells or sectors required to provide wireless telephone service
 to a given area. Having cells or sectors of decreased size permits greater
 reuse of the limited number of frequency channels allocated for wireless
 telephone service because other cells or sectors located at a closer range
 can reuse the same frequency channels for additional calls without signal
 interference. The advantages of reducing cell or sector size to increase
 the call carrying capacity of the wireless telephone network is offset by
 the requirement for additional remote transceivers for the additional
 cells. This offset is minimized by utilizing an existing broadband
 distribution network to provide the communications path between remote
 transceivers in each of the cells or sectors and a central transceiver.
 The base transceiver station acts as the interface between the telephone
 network and the wireless telephone system, and the central transceiver
 acts as the wireless telephone system interface with the broadband
 distribution network.
 To carry wireless telephony signals over a broadband distribution network,
 as described above, a predetermined bandwidth on the network is typically
 allocated for this purpose. However, as required, more bandwidth may be
 allocated to carry wireless telephony signals. To most efficiently use a
 given bandwidth to carry wireless telephony signals between wireless
 telephones and the telephone network, a combination of frequency and time
 division multiplexing is utilized. This requires base transceiver station
 equipment that acts as the interface with the telephone network and the
 wireless telephone system. With the base transceiver station equipment is
 a central transceiver (RASP), also called a Headend Interface Converter
 (HIC), that interfaces with the broadband distribution network, and it
 must function with telephony signals in the wide frequency spectrum of
 radio frequency signals on the telephone network, and up to 1000 Mhz over
 the broadband distribution network. This system also requires a plurality
 of remote transceivers, also called cable microcell integrators (CMI) or
 Remote Antenna Drivers (RADs), in each of the cells or sectors that can
 carry many channels of telephony signals between the wireless telephones
 and the central transceiver via the broadband distribution network,
 without creating signal interference with the telephony signals in
 adjacent cells or sectors. In addition, the remote transceivers (RADs)
 must function with and translate telephony signals in the wide frequency
 spectrums of up to 1000 Mhz on the broadband distribution network and
 between 1850-1990 MHz for the radio link between remote transceivers and
 wireless telephones.
 SUMMARY OF THE INVENTION
 Thus, there is a need in the art for remote transceivers that are
 relatively small and inexpensive, and that can carry a large number of
 communication signals.
 The above described need in the wireless telephone system prior art is
 satisfied by the present invention. A small transceiver is provided which
 is used in a wireless telephone system. This transceiver carries wireless
 telephone signals between wireless telephones and the telephone network
 via a broadband distribution network, such as HFC, fiber optic cable, or
 coaxial cable, on which the transceivers are hung and to which they are
 connected, thus eliminating the need for antenna towers. Further, the
 remotely located transceivers may be interrogated from a central location
 and control signals may be sent to each remote transceiver to change
 internal settings of the transceiver.

DETAILED DESCRIPTION
 In the drawing and the following detailed description, all elements are
 assigned three digit reference numbers. The first digit of each reference
 number indicates in which figure of the drawing an element is located. The
 second and third digits of each reference number indicate specific
 elements. If the same element appears in more than one figure of the
 drawing, the second and third digits remain the same and only the first
 digit changes to indicate the figure of the drawing in which the
 referenced element is located. As used herein the term "telephony signals"
 includes voice, data, fax and any other types of signals that are sent
 over a telephone network now or in the future. Throughout the Figures and
 the following description, reference is made, for one example, to a
 combined band pass filter and amplifier 325a. There are a number of other
 such combined band pass filters and amplifiers. They are shown and
 referenced this way for ease of presentation only. In reality they are
 each a discrete, separate filter the output of which is input to an
 amplifier.
 In FIG. 1 is shown a simple block diagram of an exemplary broadband
 distribution network 112 integrated with a wireless telephone system which
 include a plurality of remote transceivers known as Remote Antenna Drivers
 (RAD) 118a-i, a central transceiver known as Remote Antenna Signal
 Processor (RASP) 117, and a Base Transceiver Station (BTS) 115. There are
 different types of broadband distribution networks in use. Such networks
 may utilize coaxial cable, fiber optic cable, microwave links, and a
 combination of these. In the embodiment of the invention disclosed herein
 a conventional hybrid fiber coaxial (HFC) cable television signal
 distribution system is utilized. Electrical power is distributed along
 broadband distribution network 112 to power line amplifiers (not shown) of
 the cable television distribution network. This electrical power source,
 or alternate power sources, are used to provide power to RADs 118a-i.
 Integrated with broadband distribution network 112 is a wireless telephony
 system in which the present invention is utilized. One such wireless
 telephony system is taught in U.S. patent application Ser. No. 08/695,175,
 filed Aug. 1, 1996, and entitled "Apparatus And Method For Distributing
 Wireless Communications Signals To Remote Cellular Antennas". The
 telephony system disclosed herein includes a base transceiver station 115
 which is connected to a telephone system 116. Base transceiver station 115
 is also connected to a Remote Antenna Signal Processor (RASP) 117 which is
 the interface to a broadband distribution network 112. Telephony signals
 carried between telephone system 116 and wireless telephones 119 are
 carried via base transceiver station 115, RASP 117, broadband network 112,
 and RADs 118a-i.
 As is known in the prior art, including the above cited prior patent
 application, one or more frequency bands or channels of the broadband
 distribution network 112 are reserved to carry telephony signals between
 telephone system 116 and wireless telephones 119. Telephony signals
 originating from telephone system 116 are transmitted by RASP 117 over
 broadband distribution network 112 in frequency division multiplexing
 format. Telephony signals originating at wireless telephones 119 are
 frequency multiplexed together by RADs 118a-i and transmitted along with
 control and gain tones via broadband network 112 to RASP 117, and thence
 to base transceiver station 115 and telephone system 116.
 In base transceiver station 115 there are a plurality of transceiver
 modules (not shown), as is known in the wireless telephony art, each of
 which operates at a single channel frequency at a time, and which can
 handle a predetermined maximum number of telephone calls from wireless
 telephones. In the wireless telephone system described and claimed herein,
 the frequency that the RADs 118 are assigned to operate at must correspond
 to the operating frequency of the assigned BTS transceiver module. If a
 particular RAD 118 is re-assigned to function with a different transceiver
 module within base transceiver station 115, circuit settings within the
 particular RAD 118 must be changed to function with the different
 transceiver module. In the wireless telephony, art transceiver modules in
 the base transceiver station are also referred to as channel card modules
 and radio modules.
 When wireless telephony traffic in a first sector or cell increases to the
 point where adequate service is not provided to wireless telephone
 subscribers in the first sector or cell, like during rush hour traffic on
 a highway, in accordance with the teaching of the present invention the
 wireless telephone system may be remotely reconfigured by RASP 117 to
 reassign one or more RADs 118 from one or more nearby sectors or cells,
 where those RADs 118 have overlapping signal coverage with the first
 sector or cell, to handle the excess wireless telephony traffic in the
 first sector cell.
 In FIG. 1 are shown three rows of RADs 118. Typically a number of RADs 118
 are spaced along, and connected to, broadband distribution network 112 to
 provide overlapping signal transmission and reception coverage for the
 entire wireless telephone system. Some of the RADs 118 are physically
 located near the boundary between two or more cells or sectors and,
 depending on the frequency of operation they are set to, can be used to
 handle wireless telephony traffic in one or more of the sectors or cells.
 Let us assume that RADs 118g,h,i in the bottom row are physically located
 along broadband distribution system 112 and are configured to handle
 wireless telephony traffic in a first sector that includes a highway.
 During early morning and late afternoon every work day there is rush hour
 traffic that creates peak wireless telephone traffic that causes
 unacceptable service delays in the first sector. Let us also assume that
 the RADs 118d,e,f in the middle row in FIG. 1 are configured and located
 to handle wireless telephone traffic in a second, adjacent sector but they
 each have an area of signal operation that overlaps the highway in the
 first sector.
 One or more of RADs 118d,e,f may be dynamically reassigned by RASP 117 to
 the first sector to handle the increased telephony traffic originating
 from the highway. In addition, as necessary, additional RASP 117 channels
 may be assigned, and additional modules in base transceiver station 115
 may be assigned to handle the excess wireless telephony traffic from the
 first sector. To do this RASP 117 sends control signals to the selected
 remote RADs d,e,f which will cause the frequency at which they operate to
 be changed to match the frequency of RADS 118g,h,i that are normally
 assigned to handle wireless telephone traffic in the first sector. At the
 end of the peak traffic period RASP 117 may send control signals to the
 previously reallocated ones of RADs 118d,e,f to change the frequency at
 which they operate back to their original settings so they are reassigned
 to handle wireless telephony traffic in the second sector. However, the
 re-assignment may be permanent depending on traffic patterns encountered.
 Typically there are a number of RADs 118a-i spaced along, and connected to,
 broadband distribution network 112 to provide overlapping wireless
 telephony signal transmission and reception coverage for the entire
 wireless telephone system in a number of cells or sectors. In this
 arrangement individual RADs 118 may be re-assigned to handle wireless
 telephony signals from an adjacent cell or sector with which it provides
 overlapping signal coverage. Each RAD 118a-i has antennas 120, 121, 122
 used to transmit to and receive signals from remote wireless telephones
 119. Antenna 120 is used to transmit telephony signals to wireless
 telephones 119, while antennas 121 and 122 are used to receive telephony
 signals from wireless telephones 119. Antenna 121 is called the primary
 antenna, and antenna 122 is called the diversity antenna. Antennas 121 and
 122 are physically spaced and cooperate to minimize signal fading and
 thereby provide continuous signal reception from wireless telephones 119.
 In FIG. 2 is shown a general block diagram of a Remote Antenna Driver (RAD)
 218. There is a first circuit 208 of RAD 218, that is shown in detail in
 FIG. 4, that receives telephony signals originating at telephone system
 116 and carried via base transceiver station 115, RASP 117, and broadband
 distribution network 212, and then re-transmitted via antenna 220 of a RAD
 118 to a wireless telephone 119 (not shown). There is also a second
 circuit 209 of RAD 218, that is shown in detail in FIG. 3, that receives
 wireless telephony signals originating from a wireless telephone 119, and
 transmits them via broadband network 212 to RASP 117, and via base
 transceiver station 115 to telephone system 116.
 RAD circuitry 208 and 209 are connected to and controlled by a
 microprocessor 210. Frequency multiplexed with the wireless telephony
 signals carried between RASP 117 and RAD 218 are operational signals of
 different types that are used for controlling the operation of each RAD
 218. These operations include circuit monitoring, gain control, circuit
 operation, and setting the frequency of operation, of each RAD 218.
 The first of the control operations listed in the previous paragraph is
 gain control to compensate for losses and gains in a RAD 218 and broadband
 distribution network 112. As one part of this gain control operation RASP
 117 sends a frequency multiplexed control signal to RAD 218 that is
 received by microprocessor 210 on leads CTRL from circuit 208. Responsive
 thereto microprocessor 210 sends a signal via leads AGC to circuit 209
 which causes the output of a gain tone oscillator 342, with known signal
 level, to be inserted into the signal path, along with telephony signals,
 and be returned to RASP 117 via broadband distribution network 112. The
 signal level output from gain control oscillator 342 (FIG. 3) is of a low
 enough amplitude that it does not interfere with telephony signals passing
 through RAD 218, but is separated from the telephony signals at RASP 117.
 RASP 117 analyzes the amplitude of the gain control oscillator 342 signal
 received at the RASP, which will reflect gains and losses in RAD 218 and
 broadband distribution network 212, as part of a determination whether or
 not to change gain control attenuators in RAD 218.
 As part of monitoring circuit gain levels, as requested by a control signal
 received from RASP 117, microprocessor 210 receives information from RAD
 circuits 208 and 209 on leads MON indicating the gain level of signals
 only within these circuits, and reports this information to RASP 117 as
 described in the last paragraph. Using this circuit gain level
 information, and the gain tone information described in the previous
 paragraph, RASP 117 can determine gains and losses introduced in broadband
 distribution network 212.
 Responsive to the gain level information described in the previous two
 paragraphs RASP 117 can send other control signals back to RAD 218 which
 are received by microprocessor 210 on leads CTRL. Microprocessor 210 uses
 the control information received from RASP 117 to send signals via leads
 AGC to RAD circuits 208 and 209 which results in adjustments being made to
 attenuators to adjust the signal gain levels in these circuits.
 RAD 218 receives an interrogation control signal, as previously described,
 which cause microprocessor 210 to send back information about RAD circuit
 208 (FIG. 4) and circuit 209 (FIG. 3). This information indicates the
 settings of attenuator pads, the temperature at which each RAD 218 is
 operating, and the frequency of local oscillators within RAD circuits 208
 and 209.
 Microprocessor 210 may receive other control signals from RASP 117 and
 respond thereto to change the frequency of some of the local oscillators
 within RAD circuitry 208 and 209 to change the frequency on which
 telephony signals and control signals are carried over broadband
 distribution network 112 to and from RASP 117. In this manner the sector
 which each RAD 118 is assigned to may be changed to handle peak traffic
 loads and for other reasons.
 In FIG. 3 is shown a detailed block diagram of circuit 309 within Remote
 Antenna Driver (RAD) 118 that carries telephony signals from a wireless
 telephone 119, via broadband communications network 112, to central
 transceiver RASP 117. This is the circuit shown as RAD circuit 209 in FIG.
 2.
 Briefly, primary receive antenna 321 is connected to a first portion of the
 circuitry in FIG. 3, and that circuitry is identical to a second portion
 of the circuitry that is connected to diversity receive antenna 322. The
 telephony signals received by both antennas 321 and 322 from a wireless
 telephone 119 (not shown in FIG. 3) are initially processed in parallel,
 then the two signals are frequency multiplexed together and are both
 returned via broadband distribution network 112 (shown in FIG. 1) to
 remote RASP 117 and base transceiver station 115 (FIG. 1) to be processed.
 Built into RAD circuitry 309 in FIG. 3 is circuitry which is enabled by
 microprocessor 210 in FIG. 2, responsive to a control signal received from
 remote RASP 117, to provide gain control for the telephony signal as it
 appears at the input of RASP 117. Further, RASP 117 can send other
 frequency multiplexed control signals to each RAD 118 which microprocessor
 210 responds to and changes the frequency at which RAD 118 transmits and
 receives telephony signals over broadband distribution network 112 to and
 from RASP 117, and can also change the frequency at which each RAD 118
 communicates with wireless telephones.
 Telephony signals from a wireless telephone 119 (not shown in FIG. 3)
 operating in a sector assigned to one or more RAD 118s are received by
 primary receive antenna 321. These signals are input to an isolator 323a
 which isolates antenna 321 from RAD circuit 309. The telephony signal is
 then input to directional coupler 324a that has a second signal input
 thereto from power divider 343 which is used for the aforementioned gain
 control purposes.
 The telephony signal (modulated RF carrier) received from remote wireless
 telephone 119, and the gain tone, low level signal, are applied via
 directional coupler 324a to a combined band pass filter and amplifier
 325a. The signals are amplified and extraneous signals are filtered from
 the received telephony signal by bandpass filter 325a. The operation just
 described also applies to isolator 323b, coupler 324b and bandpass filter
 and amplifier 325b.
 The amplified and filtered telephony signal is then input to mixer 326a
 which is used along with SAW filter 329a primarily to assist in filtering
 of the spread spectrum, digital telephony signal in accordance with the
 teaching of present invention. Mixer 326a also has input thereto a signal
 from local oscillator 327. This signal from local oscillator 327 is input
 to power divider 328 which applies the signal to both mixers 326a and 326b
 while providing isolation between these two mixers.
 The frequency of local oscillator 327 is digitally controlled and is
 determined by a binary control word applied to its control input 327a from
 microprocessor 210 (FIG. 2), responsive to control signals received from
 RASP 117. Similarly, control signals from remote RASP 117 causes
 microprocessor 210 to set the frequency of digitally controlled local
 oscillators 333a and 333b.
 The operation of mixer 326a results in multiple frequencies being output
 from the mixer as is known in the art, but due to the frequency of
 oscillator 327, most of the signals present at the input of RAD circuit
 309 from antenna 321 are shifted far outside the band of frequencies which
 can pass through SAW filter 329. Only the desired signals can pass through
 SAW filter 329. This frequency shift also helps to prevent leak through of
 unwanted signals present at the front end of circuit 309 because they are
 blocked by narrow bandpass filter 325 which is passing signals of a
 frequency far from the signals applied to SAW filter 329a. Due to the
 sharp filtering action of SAW filter 329a, even spurious signals close to
 the desired telephony and control tone signals are removed. The same
 filtering operation applies to mixer 326b and SAW filter 329b.
 The filtered telephony signal is then amplified by amplifier 329a and input
 to step attenuator 330a which is used to adjust the gain level of the
 signal in one-half dB steps. The amount of attenuation provided by step
 attenuator 330a is controlled by a binary word at its control input 331 a
 from microprocessor 210. The control of step attenuators 330a, 330b, and
 336 is all accomplished responsive to control signals from RASP 117 as
 part of the gain control operation that assures that the signal level of
 telephony signals appearing at the input to RASP 117 from all RADs 118a-i
 are within an acceptable range. Attenuator 330b in the parallel channel
 handling the telephony signals from diversity antenna 322 performs the
 same function.
 The telephony signal that is output from step attenuator 330a is input to
 mixer 332a along with a fixed frequency signal from local oscillator 333a.
 Mixer 332a is used to shift the frequency of the telephony and gain tone
 signals to the frequency required to apply the signals to broadband
 distribution network 112. This same operation applies to the telephony and
 gain tone signals output from mixer 332b.
 The frequency of oscillators 333a and 333b is determined by binary words
 applied to their control input 333c. A control signal is sent from RASP
 117 which causes microprocessor 210 to set the frequency of local
 oscillators 333a and 333b. The frequency of the telephony signal output
 from step attenuator 330a is the same as the frequency of the telephony
 signal output from step attenuator 330b. However, the frequency of local
 oscillator 333a is different from the frequency of local oscillator 333b.
 The result is that the carrier frequency of the telephony and gain tone
 signals output from mixer 332a is different than the carrier frequency of
 the telephony and gain tone signals output from mixer 332b. This is done
 so that both primary antenna 321 and diversity antenna 322 signals are
 both sent to RASP 117 and base transceiver station 115 for processing.
 However, all carrier frequencies are within the assigned wireless
 telephony channel on broadband distribution network 112.
 The telephony signals received by primary antenna 321 and diversity antenna
 322 are frequency multiplexed together and sent via broadband network 112
 to RASP 117. To accomplish this, combiner 334 is utilized. Combiner 334
 has the telephony and gain tone signals output from both mixers 332a and
 332b input thereto. As described in the previous paragraph these two
 telephony signals modulate carriers that are at different frequencies, but
 both frequencies are in an assigned channel of broadband distribution
 network 112. Combiner 334 combines the two sets of signals so they are all
 frequency multiplexed together.
 The combined signal is input to bandpass filter and amplifier 335 which
 removes spurious frequencies created by the mixing action in circuits 332a
 and 332b, and amplifies the signals that pass through the filter. The
 combined and filtered telephony and gain tone signals are input to step
 attenuator 336 to adjust the gain level of signals. Similar to the
 operation of the previously described step attenuators, this digitally
 controlled attenuator is set responsive to control signals received from
 remote RASP 117 as part of the gain control operation.
 The frequency multiplexed telephony and gain tone signals output from step
 attenuator 336 are input to signal combiner 337 which has a second input
 from control signal oscillator 338. The frequency of control signal
 oscillator 338 is set responsive to a binary signal on its control leads
 338a from microprocessor 210. RASP 117 is the origin from which the
 control signal is received to set the frequency of control signal
 oscillator 338. The frequency chosen is different than the frequencies
 used for the telephony signals received via the primary and the diversity
 antennas and for the gain tone signal.
 Responsive to different control signals received from RASP 117,
 microprocessor 210 (FIG. 2) sends signals on control inputs 338a. These
 microprocessor 210 signals cause control signal oscillator 338 to produce
 an information signal. The information signal indicates various
 information about RAD 218, but particularly including the settings of step
 attenuators 330a, 330b and 336, to RASP 117 as part of the novel gain
 control operation. RASP 117 uses this information to keep an updated
 status regarding each of the RADs 118a-i.
 The output from combiner 337 now has five signals frequency multiplexed
 together to be returned via broadband network 112 to RASP 117. The signals
 are the telephony signal received by primary antenna 321, the telephony
 signal received by diversity antenna 322, the gain tone signal output from
 gain tone oscillator 342 as applied to both primary and diversity paths,
 and the system information signal output from control signal oscillator
 338. This frequency multiplexed signal output from combiner 337 is input
 to band pass filter and amplifier 339 to remove any extraneous signals and
 amplify the desired signals before they are input to broadband
 distribution network 112 and sent to RASP 117.
 Transformer and coupler 340 is used to couple the frequency multiplexed
 signals described in the previous paragraphs to broadband distribution
 network 112. The transformer is an impedance matching transformer having
 50 ohm primary and 75 ohm secondary windings. When broadband distribution
 network 112 uses coaxial cable, the secondary winding of transformer 340
 is wired in series with the center conductor of the video distribution
 coaxial cable. As previously described, RAD 118 hangs from the coaxial
 cabling of the broadband distribution network 112 to which it is
 connected. In other applications, such as with fiber optic cable, other
 well known frequency conversion and signal coupling techniques are used.
 A small portion of the frequency multiplexed signals passing through
 transformer and coupler 340 is coupled to Built In Test (BIT) and power
 monitor 341. Monitor 341 samples the signal level of the combined signals
 that are being input to broadband distribution network 112 and reports
 this information to RASP 117 via control signal oscillator 338 which has
 been previously described. If the output signal level is too high and the
 level cannot be corrected, microprocessor 210 will shut down RAD 118 and
 report this to RASP 117.
 In FIG. 4 is shown a detailed block diagram of circuit 408 in RAD 118 that
 carries telephony signals originating at RASP 117 via broadband
 distribution network 112 and circuit 408 to wireless telephones 119 (not
 shown). As previously described, RAD 118 hangs from and is connected to
 broadband distribution network 112. Transformer 442 is an impedance
 matching transformer having 75 ohm primary and 50 ohm secondary windings.
 When broadband distribution network 112 is coaxial cable, the primary
 winding of transformer 442 is wired in series with the center conductor of
 the coaxial cable. Transformer 442 is used to connect frequency
 multiplexed telephony and control signals carried on broadband
 distribution network 112 to the input of RAD circuit 408. Only the RADs
 118, the receive frequency which has been tuned to the particular
 frequency of telephony and control signals on broadband distribution
 network 112 can actually receive and forward the telephony signals to a
 wireless telephone 119.
 All RADs 118 assigned to a sector receive control signals directed toward
 any one of the RADs in the sector. However, each RAD 118 has a unique
 address that prefixes each control signal and is used by the RAD 118 to
 accept only control signals directed specifically to it by RASP 117.
 The frequency multiplexed telephony and control signals received by RAD
 circuit 408 from broadband distribution network 112 are input to band pass
 filter and amplifier 443. The combination of mixers 444 and 447, and
 filters 443, 446 and 451 are primarily used to provide filtering of the
 digital, spread spectrum telephony signal in accordance with the teaching
 of present invention.
 Filter 443 passes all possible frequency multiplexed telephony and control
 signals that are carried on broadband distribution network 112, and
 excludes most other unwanted signals carried on broadband distribution
 network 112. Circuit 443 also amplifies the signals that pass through the
 filter.
 The signals output from filter 443 are input to mixer 444 along with a
 signal from local oscillator 445. Alike the local oscillators shown in
 FIG. 2 and described with reference to that Figure, the frequency of local
 oscillator 445 is digitally controlled at its input 445a by microprocessor
 210 in FIG. 2 responsive to control signals received from RASP 117.
 The operation of mixer 444 results in multiple frequencies being output
 from the mixer as is known in the art and unwanted frequencies are blocked
 by band pass filter 446 which passes only desired signals. The selected
 set of telephony and control signals are now input to mixer 447. Alike
 other local oscillators in FIGS. 3 and 4, oscillator 449 is digitally
 controlled at its control input 449a by microprocessor 210 responsive to
 control signals received from RASP 117. In a manner well-known in the art,
 mixer 447 combines the signals input to it and provides a number of output
 signals at different frequencies. All these frequencies are input to an
 attenuator 450 which is used to adjust the gain level of the signals.
 Attenuator 450 is part of the gain control system and is digitally
 controlled at its input 450a in 1/2 dB steps by microprocessor 210,
 responsive to control signals received from RASP 117, alike the digitally
 controlled attenuator 336 in FIG. 3.
 The gain adjusted signal output from attenuator 450 is input to SAW filter
 and amplifier 451. Due to the sharp filtering action of SAW filter 451,
 even spurious signals close to the desired telephony and control tone
 signals are removed. Control signals frequency multiplexed with the
 telephony signal do not pass through SAW filter 451. Instead, the control
 signals are input to mixer 448 as is described further in this
 specification.
 The telephony signals passed through SAW filter 451 are input to digitally
 controlled attenuator 452 to adjust the gain level of the signal before it
 is input to mixer 453 along with the output of digitally controlled local
 oscillator 454. Attenuator 452 is part of the gain control system and is
 digitally controlled at its control input 452a in 2 dB steps by
 microprocessor 210, responsive to control signals received from RASP 117.
 The amplitude adjusted telephony signal output from attenuator 452 is input
 to mixer 453 along with a signal from digitally controlled 454a oscillator
 454. Oscillator 454 is controlled by microprocessor 210, responsive to
 control signals received from RASP 117, in the same manner as local
 oscillators 445 and 449. Mixer 453 combines the two signals in a manner
 well-known in the art to produce several output signals, one of which is
 the telephony signal now having the desired carrier frequency for
 transmission of the communications signal to a remote wireless telephone
 119. The signals output from mixer 453 are input to band pass filter and
 amplifier 455. Band pass filter 455 passes only the desired carrier
 frequency. The signal is also amplified before being input to signal
 divider 456.
 A portion of the telephony signal input to divider 456 is divided and input
 to bit and power monitor 457, while the remainder of the signal is input
 to band pass filter and amplifier 458. Bandpass filter 458 assures that
 there are no extraneous signals combined with the desired telephony
 signal, amplifies same, and applies it to power amplifier 459. Power
 amplifier 459 amplifies the telephony signal and couples it to transmit
 antenna 420. The signal is transmitted within the physical area of the
 cell or sector covered by this RAD 118 and is received by a remote
 wireless telephone 119 which is in the area covered by this RAD 118.
 The telephony signal input to bandpass filter 458 is sampled by divider 456
 and the sample is input to BIT and Power Monitor 457. The level of signal
 is reported by microprocessor 210 to RASP 117. In addition, the output of
 power amplifier 459 is also sampled and input to BIT and Power Monitor
 457. A signal level measurement is used in concert with attenuators 450
 and 452, as commanded by RASP 117, to adjust the power level of the
 telephony signal to be applied to transmit antenna 420. If the signal
 level output from power amplifier 459 is too high microprocessor will shut
 down this RAD 118.
 A portion of the signal output from bandpass filter and amplifier 446, and
 still including any control signals, is input to mixer 448 along with a
 signal from local oscillator 460. The output of mixer 448 is input to
 reference channel oscillator 462 and forward control channel circuit 461.
 Circuit 461 accepts only control signals sent from RASP 117 and sends them
 to microprocessor 210. Control signals have a prefix RAD address as part
 of the control signals and each RAD 118 has a unique address. Therefore,
 microprocessor 210 in each RAD 118 can recognize and accept only control
 signals directed to it.
 When a RAD 118 receives control signals directed to it, microprocessor 210
 responds thereto to perform the action required by RASP 117. The control
 signal may ask for the settings of the local oscillators and attenuators,
 and this information is returned to RASP 117 using control signal
 oscillator 338 as previously described. The control signal from RASP 117
 may also indicate revised settings for local oscillators and attenuators.
 Microprocessor 210 makes the required changes and then sends a
 confirmation signal back to RASP 117 indicating that the requested changes
 have been made. As part of the gain control operation the control signal
 from RASP 117 may also request information concerning the outputs from bit
 and power monitors 341 and 457, and request that the output from gain tone
 oscillator 342 be added to the telephony communications signals.
 Responsive to any of these control signals, microprocessor 210 performs
 the requests.
 Reference channel oscillator 462 processes the output of mixer 448 to
 generate a phase lock loop reference signal that is used to provide a
 master frequency to all local oscillators within all RAD 118s to match
 their frequency of operation with RASP 117.
 While what has been described hereinabove is the preferred embodiment of
 RAD 118, it can be understood that numerous changes may be made to the
 signal filtering disclosed herein by those skilled in the art without
 departing from the scope of the invention.