Field of the Invention: The present invention relates to communications systems, and more particularly to electronic paging systems.

Background of the Invention; The radio common carrier (RCC) pager industry began in the mid-1940s when the Federal Communications Commission (FCC) began allocating frequencies for local communication services. Several different types of electronic paging systems have been developed and several different types of systems are in widespread use. The need for standards is well recognized and several different competing standards have been developed.

One of the most commonly used formats is the POCSAG coding format. This format was developed by the British Post Office "Post Office Codes Standardization Advisory Group". Other existing formats are the GOLAY sequential code format (sometimes called GSC) which was developed by Motorola, the Dl and D2 formats which were developed by the NEC Corporation, and the FM subcarrier protocol which is shown in U.S. Patent 4,713,808 (Gaskill) .

No single protocol has been able to capture universal or near universal acceptance. The reason for this is that

each protocol generally has advantages and disadvantages. For example, the GOLAY protocol requires more air time per message than does the POCSAG protocol; however, the POCSAG protocol does not support voice paging, whereas the GOLAY does support most voice paging. The GOLAY protocol provides a greater degree of error correction because the messages are encoded with more redundancy than are the POCSAG messages. However, this added redundancy is the reason that the GOLAY protocol requires more airtime. Thus, in each application the advantages and disadvantages of each protocol must be balanced to achieve optimum performance.

In addition to using various possible transmission protocols, pagers may operate at any one of a variety of frequencies. The Federal Communications Commission (FCC) has set aside several parts of the radio frequency spectrum for use by RCC radio paging systems. More recently, the Federal Communication Corporation began allocating frequencies in the 900 MHz for use by nationwide paging systems. The frequencies set aside by the FCC are: a) 30-50 MHz (low band VHF) b) 148-174 MHz (high band VHF) c) 450-512 MHz (UHF) d) 900-950 MHz (900 MHz space band) f) 88-108 MHz (FM-SCA or FM-Subcarrier or Subcarrier Communication Authorization )

In order to accommodate the various protocols, sophisticated paging devices have been developed which can accommodate multiple protocols. For example, U.S. Patent 4,518,961 (Davis), which is assigned to Motorola, describes a battery-powered pager which is capable of processing detected signals in accordance with plurality of de-coding schemes. This pager includes a micro- processor which detects which coding scheme is being used, and then de-codes the message in accordance with the appropriate protocol.

Some pagers can handle signals on more than one frequency. For example, an FM-subcarrier (SCAG) pager being marketed by the CUE Paging Corporation (formerly called DiversiCom) scans the FM frequencies to find a frequency which has an FM-SCA signal of the type broadcast the CUE system. When the pager determines an appropriate signal on one of the FM frequencies, it stays tuned to that frequency and receives the paging message.

None of the prior art systems can receive messages which are transmitted both on an FM-SCA system and messages transmitted over an RCC system using the POCSAG or the GOLAY protocol. Likewise, none of the systems can receive signals on the VHF-UHF or 900 mega-hertz band and also detect signals in the FM-SCA band.

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One of the problems encountered by systems using FM-SCA signals that are transmitted over commercial FM stations is that certain areas are "dead-spots" where signals can not be received. The cost of installing additional FM transmitters which operate using the FM-SCA system to cover dead spots is generally prohibitive, hence, it is desirable to utilize existing or new RCC systems in areas where transmissions dead spots occur. However, no existing pagers can accept both FM-SA signals and RCC signals.

The present invention provides a system which includes a plurality of transmitters operating at different frequencies and using different protocols and an improved pager which can automatically accept both RCC and FM-SA signals. Furthermore the present invention provides a low cost, compact highly efficient pager.

Summary of the Invention The present invention.provides a pager system which integrates a plurality of transmitters which operate at different frequencies and which transmits messages using a variety of protocols. The receiver includes a front end that can receive messages over a very wide band of frequencies. The frequency of the signal which the system receives at any particular time is controlled by a microprocessor which is a part of the system. The base band audio signal generated by the radio receiver is

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sampled and provided as the input of a Finite Impulse Response (FIR) filter which is controlled by the data in any one of a plurality of ROM's. The output of the FIR filter is provided to a protocol decoder that is in turn controlled by data in a second set of ROM's. The same signal that controls the frequency received by the front end of the system also controls which of the ROM's provides data to the FIR filter and the protocol decoder. By storing appropriate data in the RO 's, the system can accommodate both RCC paging signals and FM-SCA signals. Futhermore the system can handle protocols that require scanning or switching between a number of different frequencies.

The foregoing and other objects, features and advantages of the invention will be apparent from the more particular description of preferred embodiments of the invention, hereinafter described and illustrated in the accompanying drawing. While the invention will be described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit, scope, and teaching of the invention.

From the following description of preferred embodiments of the invention, those skilled in the art will recognize a wide variety of. applications for the method and

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apparatus is possible without departing from the spirit, scope and teaching of the invention.

Description of the Ficrures; Figure 1 is an overall block diagram of a receiver built in accordance with the present invention.

Figure 2 is a block diagram of a system of transmitters designed to operate in accordance with the present invention.

Figure 3 is an illustrative example of a pattern of coverage of several transmitters which could be used with a system operating in accordance with the present invention.

Figure 4 is a block diagram of an alternative embodiment of a receiver built in accordance with present invention.

Detailed Description of the Invention

The embodiment of the invention shown in Figure 1 includes a frequency agile receiver 101 which is capable of receiving signals in the VHF frequency range 30 to 174 MHz. The frequency of receiver 101 is controlled by a signal on line 135 which comes from a microprocessor 106. The system also includes a high frequency receiver 102

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which is designed to receive signals in the 450-950 MHz region.

Frequency agile receiver 101 is capable of receiving the following signals: a) RCC signals in the 30-50 MHz range (VHF) b) RCC signals in the 148-174 MHz band (hi-band VHF) c) FM-Stereo signals in the 88-108 MHz band.

High frequency receiver 102 is capable of receiving: a) RCC signals in the 450-512 MHz (UHF region) and b) RCC signals in the 900-950 MHz UHF band.

Gate 103 gates the output of either receiver 101 or receiver 102 to a finite impulse response (FIR) filter 104. The pass band of filter 104 is controlled by a signal on line 133. Line 133 is activated by data from read only memories (ROMS) 110A to 110F. The output of ROMS 110A to 110F are gated to FIR filter 104 by a gate 115. Gate 115 is in turn controlled by a signal on line 130 from microprocessor 106.

The output of FIR filter 104 is passed to a protocol decoder 105. Protocol decoder 105 can, for example, be a microprocessor which is controlled by programs stored in ROMS 121A to 12IF. The output from ROMS 121A to 12IF is gated to protocol decoder 105 by gate 126 in response to a signal on line 130 from microprocessor 106.

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Microprocessor 106 gates the data from the appropriate ROM 101A to 110F, to FIR filter 104, such that filter 104 passes the appropriate band of frequencies to protocol decoder 105. Protocol decoder 105 is in turn programmed by the appropriate data from ROMS 121A to 12IF so that it decodes the appropriate protocol. The output of the decoder is in turn passed to microprocessor 106 which provides data on output line 136.

The same signal that controls the frequency received by the front end of the system also controls which of the ROM's provides data to the FIR filter and the protocol decoder. By storing appropriate data in the ROM's 110A to 12IF, the system can accommodate various frequency bands and various protocols.

The system shown in Figure 1 operates as follows: in one mode of operation, frequency agile receiver 101, FIR filter 104, protocol decoder 105 and microprocessor 106 operate according to the time multiplex system shown in U.S. Patent 4,171,808 by Gaskill et. al. issued December 15, 1987 and/or the systems shown in co-pending application serial no. 07/121,139 filed November 16, 1987. In another mode of operation, high frequency receiver 102 receives RCC paging signals that are decoded by decoder 105 and microprocessor 106.

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The receiver system shown in Figure 1 is designed to operate in an overall system that has a plurality of transmitters such as the system shown in Figure 2. As shown in Figure 2 the system include three FM transmitters 202, 203 and 204 which are designed to transmit data using an FM subcarrier technique such as described in the previously referenced patent. The system also includes (a) a VHF RCC transmitter 205 which operate at 150.5 MHz, (b) a VHF RCC transmitter 206 which operates at 150.6 MHz and (c) a UHF RCC transmitter which operates at 900 MHz. Messages are directed to transmitters 202 to 205 from a message clearing house 201 in the same way that messages are directed to the transmitters in the previously referenced patent.

The transmitters shown in Figure 2 transmit signals over the area shown in Figure 3. Transmitters 202, 203 and 204 generally provide signals of appropriate strength in the area 10. In area 10, the system operates as described in the previously referenced patent and patent applications.

The problem to which the present invention is directed is that transmitters 202, 202 and 203 do not provide appropriate signals in geographical areas designated 11, 12, and 13 in Figure 3. This would generally be due to buildings or due to various geographical features such as hills.

In accordance with the present invention each of the areas 11, 12, and 13 is provided with its own transmitter. Three such area are shown herein; however, it should be understood that this is merely for the purpose of illustration and a system could include many or as few as one such transmitter. Transmitters 205, 206 and 207 which are designed to cover specific area operate on different frequencies than FM SCA transmitters 202, 203 and 204 which broadcast information signals as a sub- carrier on a commercial FM broadcast station. For the purposes of illustration, herein, (a) area 11 is shown as having RCC transmitters operating in the 150.5 MHz region (b) area 12 is shown as having an RCC transmitter operating in the 150.6 MHz region and (c) region 13 is shown as having a transmitter operating in the 900 MHz region.

Receiver 101 can receive the signals from FM stations, 202, 203 and 204 and,it can also receive the RCC signals from stations 205 and 206 even though the data is encoded using different protocols in these stations. Receiver 101 cannot receive the high frequency signals from transmitter 207. Such signals are received by high frequency receiver 102.

Processor 106 controls the frequency that the system is set to at any time using the same technique as that

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described in the previously referenced patent application. In this system when the microprocessor selects a frequency it also (a) gates the contents of the appropriate ROM 110A to 110F to FIR filter 104 (b) gates the contents of the appropriate ROM 121A to 12IF to Protocol decoder 105 and (c) selects the appropriate receiver 101 or 102.

With the system shown a wide variety of frequencies and protocols can be. ^' accomodated. Thus protocols and frequencies which can be used most economically in several areas can be combined into one unified system. In some situatiions the protocol may be directly related to the signal frequency which is being used, in other situations the same protocol may be used with a variety of frequencies.

An alternative embodiment of the invention is shown in Figure 4. In the embodiment of the invention shown in Figure 4, all signals go to frequency agile receiver 402. However, high frequency signals pass through a frequency converter 401 prior to being gated to frequency agile receiver 402. Microprocessor 106 provides a signal on line 412 which allows signal from the antenna to go directly to receiver 402 for cases where the received signal is within the range of receiver 402. For frequencies above the capability of receiver 402, the signals are first gated through frequency divider 401.

In another alternate embodiment, data can be stored in the ROM for the protocol decoder such that the protocol decoder will send signals to the system under certain circustances which cause the system to perform an automatic frequency selection based upon the information stored in the ROM.

Still another alternate embodiment which could operate in substantially the same manner as the embodiments described herein would have two receivers or more receivers, each with differenct frequency characteristics. Gating would be connected between the receivers and the remainder of the system so that only one of the receivers would be operable in the system at any one time.

It should be understood that changes may be made in the combination and arrangement of steps and apparatus heretofore set forth in the specification and drawings. It should also be understood that changes may be made in the embodiments disclosed without departing from the spirit and scope of the invention as defined in the following claims.

What is claimed is:

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