System and method for achieving extended radio coverage and additional capacity using extended frequency bands

System and method for obtaining extended radio coverage and additional capacity by using extended frequency band

This application relates to T. Przelomiec and K Raith's "A Method and Apparatus for Locating a Digital Control Channel in a Downbanded Cellular System" filed on March 27, 1996. The US patent application with serial number 08/622403 and related to T. Przelomiec and T. Brown filed on March 27, 1996, entitled "Control Channel Synthronization Between DBC and Cellular Networks (Control Channel between DBC and Cellular Networks) Synchronous)" U.S. Patent Application No. 08/622631, and related to Thomas A. Przelomiec's serial number entitled "Downbanded Cellular Systems and Methods" filed on March 27, 1996. The US patent application 08/622311, and the publication texts of these related applications are expressly incorporated herein by reference.

The present invention relates generally to radio communication systems, and more specifically to increasing the capacity and/or coverage area of existing communication systems. In one application, the present invention relates to a time/frequency duplex technique to obtain extended radio transceiver frequency band coverage in adjacent frequency bands.

The rapid growth of radio communication systems, such as cellular radio systems, has forced designers to find ways to increase system capacity without reducing communication quality. One way to provide increased capacity is to increase the efficiency of the use of the available cellular spectrum, for example, by changing analog to digital communication technology. In North America, this change was achieved by switching from an analog "AMPS" system to a digital system "DAMPS" standardized to IS-54B and later to IS-136. Other technological improvements, such as the use of time division multiple access instead of frequency division multiple access, have also increased system capacity. Even if more spectrum efficient technologies are adopted, the need for more capacity in cellular communication systems is still a concern.

Another way to increase the capacity of a cellular communication system is to provide additional spectrum. For example, the FCC initially allocated two sets of frequencies (ie, 825-845 MHz (uplink) and 870-890 MHz (downlink)) for cellular services in the United States. In 1987, the FCC allocated an additional 5 MHz to each frequency group to increase capacity. Of course, this solution is limited because the available spectrum is limited and existing communication systems other than cellular systems occupy part of the available spectrum.

The land mobile radio (LMR) system is allocated frequency groups adjacent to the cellular frequency band shown in Figure 1, namely 806-824MHZ (uplink) and 851-869 (downlink). Contrary to the cellular radio system, the LMR system is a transmission relay system, usually used to provide radio communication services between various radio units of a special organization. For example, the police department uses the LMR (commonly referred to as the Public Service Relay (PST) system) scheme to communicate between patrol cars and dispatchers at the police headquarters. The LMR system has historically been implemented as an independent site that covers a relatively large geographic area and is served by one (or some) transmitting base stations. On the other hand, the cellular system covers many smaller "cells or even wider ones. Geographical area, each cell is served by its own transmitting base station. Recently, the LMR multi-site system has been developed and used to expand the geographic coverage in the LMR area. At each LMR site, a part of the LMR spectrum is allocated to the LMR operator. A fixed frequency pair is generally selected as a control channel in this spectrum, and all other frequencies are used for services.

In 1994, the FCC announced that it would uniformly adjust the frequency spectrum allocated to LMR, cellular and personal communication systems, so operators can now use frequencies within the combined bandwidth in any way desired. In connection with other adjustments such as allowing the use of LMR spectrum on a wide area basis instead of on a site-by-site basis, LMR frequencies are now available for cellular communications. The LMR frequency used for cellular communication is referred to herein as "downbanded cellulan- (DBC)".

In order to realize a DBC system compatible with cellular systems, several challenges must first be solved. For example, a conventional LMR system operating in the United States has a 25KHZ channel width, while a cellular system operating in accordance with IS-54B has a 30KHZ channel width. A solution to this problem is provided in the aforementioned U.S. Patent Application No. 08/622311 entitled "Down-band Cellwlar Systems and Methods", in which the conventional channel of the LMR spectrum is redefined in a way with significant advantages.Chemical. More specifically, for every six 25KHZ LMR channels originally specified, five new 30KHZ DBC channels are specified. In this way, full compatibility with the cellular system is obtained, for example, roaming between the cellular and the DBC system is allowed.

As can be seen from Figure 1, there is only a 2MHZ interval between the largest cellular transmit frequency (849MHZ) and the smallest LMR receive frequency (851MHZ). This small frequency interval is different from the one usually used in DAMPS cellular phones. 20MHZ maximum transmit/minimum receive frequency interval is different. Assuming that the ceramic duplex filter used in the cellular radio system maintains the separation between the transmitted and received signals, this 20MHz frequency interval is satisfactory. However, current filter material technology (including ceramic duplexers) cannot allow a single LMR "plus" honeycomb ceramic to provide ideal in-band "flatness" and out-of-band suppression for such a narrow 2MHZ interval as shown in Figure 1. Duplex filter structure.

Therefore, an object of the present invention is to provide a duplex device that can allow the increased coverage of the conventional separated frequency band to enter the radio communication frequency band.

Another object of the present invention is to provide such a duplex device with transceiver hardware conventionally used in a radio device such as a cellular radio device that transceives in only one frequency band.

The third object of the present invention is to use only a single duplexer in an extended band radio transceiver.

The fourth object of the present invention is to manufacture such an extended band radio device inexpensively without increasing the number of parts or the size of the parts.

The fifth object of the present invention is to apply the duplex circuit system of a cellular radio equipment compatible with the IS-136 specification to a cellular phone and allow additional "lower band" communication in the land mobile radio frequency band.

The present invention provides a radio transceiver with the ability to transmit and receive information through first and second different frequency groups. Each group of frequencies includes a transmitting frequency band and a receiving frequency band. An example of the first and second frequency groups is the allocation of transmission and reception for land mobile cellular radio equipment. The radio transceiver includes a transmitter, a receiver and an antenna, and a duplex circuit is connected between the antenna and the transmitter and the receiver. system. Depending on the operating mode of the radio transceiver used for communication in the first or second group of frequencies, a converter is provided to configure the antenna, duplexer circuitry, receiver, and transmitter differently.

In a preferred embodiment of the present invention, only a single duplexer is used to allow the radio equipment to transmit and receive on the first and second set of frequencies. The converter connects this duplexer to the antenna of the radio equipment and to Receiver and transmitter. In order to work in the first set of transmit/receive frequency bands, the converter is set to connect a duplexer between the antenna and the transmitter and receiver. In order to transmit and receive in another set of transmit/receive frequency bands, set the converter to bypass this duplexer at least when connecting the antenna and the receiver in the receiving channel.

Therefore, the present invention can use only a single cellular duplexer to make the cellular radio equipment that used to transmit and receive on the officially designated cellular transceiver frequency band suitable for land mobile radio (LMR) transmission and reception adjacent to the cellular transmission and reception frequency bands. Send and receive in the frequency band. As always, this duplexer is used to route cellular frequency transmission and reception. LMR frequency transmission can be routed through this duplexer, and LMR is routed through a converter.

In an example application of a time slot-based communication system such as a TDMA system, a control signal generated according to the time slot calibration timing is used to complete the control of the converter in the extended frequency band. When sending and receiving in the cellular frequency band, the static setting is on. In the LMR extended frequency band, the converter is set dynamically. When transmitting radio waves, the antenna is connected to the transmitter through this duplexer during the transmission time slot. During the transmission time slot, the converter effectively separates the antenna from the receiver. During the receiving time slot, the antenna is connected to the receiver, bypassing this duplexer.

In a preferred embodiment, the converters are implemented using gallium arsenide (GaAs) field-effect transistors (FETs) with low insertion loss and fast converter speeds. These converters remain otherwise composed of a second duplexer specifically included for the extended frequency band. Provides the required transmit-receive isolation.

Therefore, the present invention provides radio equipment with geographic coverage and improved system access in congested areas (due to the additional channels provided in the extended frequency band), and in one embodiment does so without adding an expensive second dual The worker handles calls in the extended frequency band. Moreover, the existing transceiver circuitry similar to that in conventional cellular radio telephones can be used for extended frequency band communications.

These and other objects of the present invention and specific exemplary embodiments of the present invention will now be described with reference to the following drawings, in which the same reference numerals refer to the same elements: Figure 1 shows adjacent transmitting and receiving land in the 800-900 MHz frequency range Mobile radio and cellular frequency bands; Figures 2A and 2B show the concept of a lower-band cellular system used with existing cellular systems; Figure 3 shows a single "network of radio base stations assigned to a single cell and multiple mobile/portable radios" Figure 4 is a functional block diagram of a radio device that is initially configured to operate with a set of frequencies, which is adapted to communicate in an additional extended frequency set according to the first exemplary embodiment of the present invention; Figures 5-8 It is a functional block diagram of a mobile radio telephone configured to communicate on the first set of transmit and receive frequencies, which is adapted to transmit and receive on the second set of adjacent transmit and receive frequencies according to the second preferred exemplary embodiment of the present invention; 9 is a flowchart showing an example of a method for switching the duplexer control by the radio controller according to the operation mode of the radio equipment according to the second preferred embodiment of the present invention; Figs. The time slot calibration signaling generated in the TDMA type cellular system generates a timing diagram of an exemplary technique for converting the conversion control signal of the RF converter according to the present invention; FIG. 11A is a schematic diagram of an exemplary RF converter that can be used according to the present invention; And FIG. 11B is a table showing the characteristics of the RF converter shown in FIG. 11A.

In the following description, specific details such as specific circuits, circuit elements, techniques, etc., are proposed for the purpose of illustration and not limitation, so as to provide a comprehensive understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented in other embodiments different from these specific details. In other cases, detailed descriptions of well-known methods, devices, and circuits are omitted so as not to obscure the description of the present invention with unnecessary details.

In this description, reference is generally made to an example application of the present invention applied to a lower-band cellular application, where the cellular radio is modified to transmit and receive in the cellular and LMR frequency bands. Those skilled in the art will of course realize that this is only an example application and the present invention can be applied to any communication system with reasonably close or adjacent frequency bands in order to provide the communication system with extended coverage and/or additional capacity. Moreover, although the cellular and LMR transmit/receive frequency bands are adjacent, the present invention can also be used to cover adjacent frequency bands that are not necessarily adjacent.

The lower-band cellular system includes an independent DBC system that uses the LMR spectrum and provides enhanced communication services, and a cooperative application of the DBC system and the cellular system. Figure 2A shows a cooperative application of such a DBC system, where the DBC system is positioned adjacent to the cellular system. This DBC system is represented as having multiple cells, and each cell is supported by a mobile switching center (MSC) 10 generally used in existing cellular radio systems. Similarly, a cellular system has multiple cells supported by three such MSs 12, 14, and 16. Each geographic "cell" (represented as a circle or ellipse) includes one or more fixed radio base stations (not shown) connected to the respective MSC for sending radio signals to mobile/portable radio equipment in the cell and Receive radio equipment from mobile/portable radio equipment in the cell. In this example structure, the DBC system provides additional geographic coverage, which will allow operators of, for example, cellular systems to provide greater geographic services to mobile/portable radio users when their mobile/portable radio users "roam" into the cells of the DBC system. Portable radio users.

Another example of cooperation is shown in FIG. 2B. In FIG. 2B, each larger circle and ellipse represents a cellular system, and each smaller circle in the cellular system 20 represents a DBC system. This example shows that the DBC system is the same as the cellular system and can be used to supplement the capacity of the cellular system, that is, to handle more simultaneous calls.

Using these example applications of the DBC system described in the cell standard, some comprehensive details of radio base stations and mobile/portable radio stations are provided to enrich this discussion, but unnecessary details, DBC radio base stations, and radio base stations that may obscure the present invention are not provided. Mobile/portable radio stations can be manufactured using basically the same components as conventional cellular base stations and mobile/portable radio stations with some exceptions. For example, DBC equipment includes radio frequency (RF) communication hardware (and software). Additional information about the more specific details of the example radio mobile station and base station implementation relates to P.Dent and B. The unexamined and commonly assigned US Patent Application Serial No. 07/967027 entitled "Multi-Mode Signal Processing" filed by Elkelund on October 27, 1992, the disclosure of which is incorporated herein by reference. The DBC system can also be implemented according to the D-AMPS specified in EIA/TIA IS-54B and IS-136, the disclosure of which is also incorporated herein by reference.

Figure 3 shows a block diagram of a cell that can be used in a lower-band cellular radio communication system. Cell 30 represents an example radio base station 32 and multiple mobile/portable (M/P) transceivers 38 in cell 30. The radio base station 32 includes a data processing unit 34 connected to a mobile switching center (MSC), which in turn is connected to a public switched telephone network (PSTN) and possibly other networks (not shown).

The radio base station 32 of the cell 30 includes multiple voice channels processed by the corresponding voice channel transceivers (36b...36n) controlled by the data processing unit 34. The radio base station 32 also includes control channels that may handle more than one control channel. The channel transceiver 36a and the control channel transceiver 36a are also controlled by the data processing unit 34. Generally, the control channel transceiver 36a uses the mobile station/portable station 38 tuned to that control channel to control information on the control channel of the base station or cell (unless an active call is made through a voice or data channel transceiver). The voice channel transceiver handles the traffic channels that can transmit voice and data information. When the mobile/portable radio 38 enters idle mode for the first time, it locates and tunes to the DBC control channel in order to obtain overhead control information and listen for paging. An example technique for locating the DBC control channel is described in the above-introduced US patent application entitled "A Method and Apparatus for Locating a Digital Control Channel In Downbanded Cellul or System".

Advantageously, the center frequency of the DBC channel can be designated for maximum compatibility with existing cellular systems. For example, the center frequency can be selected according to the harmonics of a known frequency synthesis oscillator generally used in cellular equipment, so that the same oscillator can be used in the DBC equipment to minimize the equipment cost. This is particularly useful when the DBC device can transmit on multiple frequency bands, for example, it can operate in more than one frequency band among the LMR, cellular, and PCS frequency bands.

As mentioned above, one of the most significant hardware challenges in providing cellular transceivers with seamless and compatible transfer and roaming capabilities between land mobile radio (LMR) and cellular frequency bands involves filtering, and in particular, duplex filtering. For the purpose of this description, a duplexer is a filter that functions as a two-channel multiplexer using a transmit-receive converter, so that one antenna can be used for reception and transmission. More specifically, there is only a 2 MHz separation between the maximum cellular transmit frequency of 849 MHz and the minimum land mobile radio reception frequency of 851 MHz. Existing filter materials, such as the current ceramic duplex filter, cannot simultaneously provide the in-band flatness and out-of-band suppression of the cellular and LMR transmit and receive frequency bands, and the necessary isolation between the transmit and receive frequency bands.

Figure 4 shows an example mobile (portable radio transceiver hardware structure that provides extended frequency coverage from one set of transmit/receive (tx/rx) frequencies to two sets of tr/rx frequencies, such as LMR/cellular coverage. Mobile/portable radio The transceiver 38 includes a single antenna 48 connected to the radio receiver and transmitter paths generally shown in FIG. 4, and the duplex circuit system 40 includes a first set of transmit/receive frequencies (such as terrestrial The first duplexer 42 of the mobile radio frequency band) and the RF converter 46 of the second duplexer for duplexing the second set of transmit/receive frequencies (such as the cellular frequency band). The signal received from the RF converter 50 is coupled To the amplifier 52 (this is preferably a low-noise amplifier), its output is routed to the band-pass filter 56 using the RF converter 54. This filter 56 transmits the first group of receiving frequency bands to the band-pass filter 58, this filter 58 transmits the receive frequency band corresponding to the second group. The RF converter 60 couples the output of the receive filter to a down converter and signal processor circuitry 62, which generates a baseband output signal for driving a loudspeaker, for example.

The transmitter includes a signal processor and up-converter 66 for processing the signal to be transmitted and converting the signal into an RF signal. The RF signal to be transmitted is received by the RF converter 68 and appropriately routed to the band pass filter 70 for the transmission band of the first set of frequencies and the band pass filter 72 for the transmission band of the second set of frequencies. The filtered output is transmitted to the RF power amplifier 76 through the RF converter 74, and the power amplifier output can be directly transmitted to the duplex circuit system 40. However, the circulator 78 may be selectively provided to buffer the power amplifier 76 and protect it from reflected antenna waves and provide a stable fixed impedance. The RF converter 80 transmits the amplified RF signal to both the first and second duplexers 42 and 44, which transmit signals in their respective transmission frequency bands to the antenna 48 for transmission through the RF converter 46 .

The control signals for controlling the downconverter/signal processor 60 and the signal processor/upconverter 66 are provided by the controller 64, which may include a suitably programmed microprocessor and/or digital signal processor. The controller also provides additional control signals for controlling the RF converters 46, 50, 54, 60, 68, 74, and 80, as well as the transceiver and duplexer circuitry. In particular, the controller generates a switching and power amplifier control signal, which is used to activate or deactivate the power amplifier and to control the conversion state of each RF converter according to an appropriate timing control signal.

In response to the operating mode of the radio device 38 in either the first set of tx/rx frequencies or the second set of tx/rx frequencies, the controller 64 device converters 46, 50, and 80 in order to adopt or the first duplexer 42 or second duplexer 44. These converters are quasi-static, they only change when the transceiver 38 transitions from operation in the first set of tx/rx frequencies to the second set of tx/rx frequencies (or vice versa).

Essentially, in the first example embodiment according to FIG. 4, the interface between the antenna and the transmitter/receiver path includes duplex hardware from two radios in one radio. Assuming appropriate software changes to control the conversion and the transceiver hardware tuned to frequencies in the first and second group of frequency bands, this radio has seamless and compatible roaming into two different radio frequency bands such as cellular and land mobile radio frequency bands. Capacity in the frequency band.

Unfortunately, the extended frequency band radio device according to the first embodiment obtains this extended frequency band at the expense of increased cost, size, and power consumption. The duplexer is a particularly expensive component and is also quite large, occupying a large amount of "real estate" on the printed circuit board on which various radio transceivers and signal processing hardware are installed. The increased cost appears to be undesirable. Since a very important factor in portable telephones is the small size, the increased size is also undesirable. Another disadvantage of the added duplexer is that it causes 1.0-1.5dB loss in the transmit path and 2.5-3.0dB loss in the receive path. These losses reduce the output power and sensitivity, and therefore reduce the effectiveness of the radio equipment. Operating range.

A second preferred embodiment of the present invention which overcomes the disadvantages of the first embodiment will now be described with reference to FIGS. 5-8. In the second preferred embodiment of the present invention, the frequency division duplexer 40 is replaced by a hybrid time/frequency division duplex circuit system 82. Advantageously, the hybrid time/frequency division duplex circuit system 82 includes only one (rather than two) duplexers corresponding to the duplexer 44 in the example of FIG. 5. Even without the duplexer 42, the hybrid time/frequency division duplex circuit system 82 still dynamically converts the RF converters 46 and 50 as described below to provide radio transceiver capabilities in the first and second frequency bands.

Most of the circuitry in the transceiver 38 is the same as described above in connection with FIG. 4 (the same reference numerals always indicate the same components). Therefore, the description of FIGS. 5-8 focuses on the operation of the hybrid time/frequency division duplex circuit system 82. In short, the controller 64 controls the state of the RF converters 46 and 50 according to the operating mode of the transceiver 38. If the radio is operating to transmit and receive on the second set of transmit and receive frequencies, the controller 64 sets the RF converters 46 and 50 to a relatively static state in which the antenna 48 is connected to the receiver and the transmitter through the duplexer 44. In this mode of operation, the duplexer 44 operates as a conventional duplexer, switching transmission signals to and receiving signals from the antenna 48 while maintaining proper isolation between transmission and reception signals.

When the radio device is operating through the first set of tx/rx frequencies to transmit and receive, the controller 64 dynamically operates the RF converters 46 and 50 in time. In this mode of operation, the duplex circuit system 82 performs conversion according to time and frequency so as to connect the signals transmitted and received between the antenna 48 and the receiver and transmitter. When the radio device 38 is transmitting, the RF converter 46 is switched to connect the antenna 48 to the duplexer 44 so that the transmission signal passes through the antenna 48 through the duplexer 44 and the converter 46. The transmission filter in the duplexer 44 has a sufficiently wide passband, for example, like a low-pass filter, enough to transmit the transmission frequencies of the first and second frequency bands. Alternatively, for the received signal, the converters 46 and 50 may be operated by the controller 64 to bypass the duplexer 44 with the signal received on the antenna 48 directly coupled to the receiver.

FIG. 6 shows the converter structure and signal path controlled by the controller 64 when the radio transceiver 38 is transmitting and receiving signals in the second group of transmitting and receiving frequency bands. If the radio device 38 is originally or basically a cellular radio device, the duplexer 44 can correspond to a cellular duplexer designed to duplex the transmission/reception frequency in the cellular frequency band. In that case, the second set of transmission/reception will correspond to the cellular frequency band. For cellular band communication, the controller 64 sets the converters 46 and 50 shown in FIG. 6 to relatively statically (in time) connect the antenna 48 to the duplexer 44 through a full-duplex connection, and the transmitter output signal is directly coupled to The duplexer 44, and the signal received on the antenna 48 is routed to the radio receiver by the duplexer 44 through the converter 50.

Figures 7 and 8 show the hybrid time/frequency division duplex circuit when the radio transceiver 38 is operating in the first tx/rx frequency band corresponding to the LMR tx/rx frequency band connected to the cellular tx/rx frequency band in an example application. The converter configuration and signal path of the system 82 (shown as thick lines in the figure). FIG. 7 particularly shows the structure of the converter that uses the duplexer 44 and the converter 46 to transmit signals from the transmitter. Note: In Figure 7, the receive path is separated from the transmit signal by converters 46 and 50. When a signal is received in the first receiving frequency band, FIG. 8 shows that the controller 64 dynamically triggers the converter to the opposite position in time to bypass the duplexer 44 and directly transmit the signal from the antenna 48 to the receiver.

The operating mode of the radio transceiver 38 can be set by the operator through a switch/button. Alternatively, the radio transceiver 38 may automatically change the operation mode using, for example, a detected signal strength/quality signal or a control signal from a radio base station, such as a transfer control signal.

FIG. 9 shows a flowchart of the general operation outline of the operation of the control converters 46 and 50 executed by the controller 64. Although the converters 54, 60, and 74 are also controlled by the controller 64, the main conversion control discussed is the conversion control of the converters 46 and 50. Therefore, the controller inputs the duplexer switching routine 100 and proceeds to the decision block 102 to determine the current operating mode of the radio transceiver 35. If the radio equipment is operating in the cellular frequency band (only one example), the controller determines the cellular system Type (block 104). Since most digital cellular radio equipment operates in analog or digital mode in order to regulate communication between the older analog cellular system and the newer digital cellular system, if the cellular system is analog, the controller 64 sets the RF converter to pass A single duplexer 44 transmits the communication, and the controller 64 starts radio operation in frequency division multiple access (FDMA) mode (block 106). If the system type is a digital slot-based system, the controller 64 sets the RF converter to route the transmission and reception signals through a single duplexer 44, and starts radio operation in a time division multiple access (TDMA) mode.

If the radio is operating in the land mobile radio (LMR) band (in this non-limiting example), the controller 64 initiates hybrid time-frequency multiplexing by triggering the RF converter for the transmit and receive time slots (block 110). As known in the art, a time division multiple access (TDMA) system multiplexes multiple channels onto a single frequency, where each channel corresponds to a time slot, and the time slots are combined into frames, and each frame transmits, for example, two or three Time slot type channels. The time slot alignment and synchronization between the transmitting and receiving time slots between the mobile/portable radio equipment and the fixed base station are specifically specified in the IS-54 and IS-136 standards. The timing signal generated by the base station for controlling the time slot alignment and time slot synchronization can be easily used by the controller 64 to adjust the duplexer switching operation according to the present invention. Although the timing control signal for performing duplexer conversion is described in the content of a time division multiple access system, the present invention is not limited to a time slot environment, and the present invention can be applied to other types of communication systems including analog systems, as long as appropriate timing The signal informs the controller when to perform proper control of converters 46 and 50.

An existing timing signal in IS-136 is a signal provided by the controller 64 to the power amplifier 76, specifically the drain voltage of the power amplifier. Figure 10(A) shows a typical full-rate TDMA frame including six time slots (TS1-TS6). These six time slots are generally constructed as receiving (Rx) time slots or radio equipment for radio equipment to receive information (no transmission occurs) The transmit (Tx) time slot for sending information (no reception occurred). A specific allocation of receiving and transmitting time slots according to IS-136.1 (Revision 0) on May 17, 1995 is shown in Figure 10(B). Time slots 1, 3, 4, and 6 are used for reception, and time slots 2 and 5 are used for transmission. Therefore, as shown in FIG. 10(C), the transmitter power amplifier drain voltage is only "on" during time slots 2 and 5 (resulting in an appropriate voltage level to turn on the power amplifier transistor). Therefore, the controller 64 also controls the duplexer converter to switch the converter to the appropriate receiving and transmitting state of the appropriate time slot shown in FIG. 10(D).

Thus, the main timing signal from the radio base station is used to apply an appropriate drain voltage to the power amplifier 76 to turn on the power amplifier during the transmission time slot and turn off the power amplifier (12) during the reception time slot to conserve battery power. The same timing signal can be used by the controller 64 to control the conversion states of the RF converters 46 and 50. During the LMR transmission time slot, the transmitter path is connected to the duplexer 44, and the appropriate switching settings of the converters 46 and 50 are used to isolate/disable the receiver. For the LMR reception time slot, the converter is set to its opposite setting in order to bypass the duplexer 44.

Of course, the present invention can be easily applied to other non-slot systems and systems including analog and digital. All that is needed is to properly indicate to the controller when the transceiver is transmitting or receiving in a specific frequency band so that the RF converter can be set to its proper state.

In a preferred embodiment of the present invention, the RF converter may be a gallium arsenide (GaAs) field effect transistor (FET) microwave monolithic integrated circuit (MMIC). FIG. 11A shows an example gallium arsenide FET converter 150 available from Alpha Industries, Inc., for example. The input terminal (I/P) and the drain voltage input terminal (VDD) are both connected to the common drain of FETs 152 and 154. The control voltages V1 and V2 are applied to the gates of FETs 152 and 154 through bias resistors to drive the conversion output O/ P1 and O/P2. In essence, the converter 150 is a single-pole single-throw converter.

The benefits of using GaAs FET converter 150 include low insertion loss, very fast conversion speed and simple control. Specifically, each GaAsFET 150 has an insertion loss of the order of 0.5 dB, and the MMIC conversion speed is of the order of 10 nanoseconds. These benefits, combined with the very small size and high linearity of the converter, help to form a perfect converter, which is easily controlled by the control signal from the controller 64 that is synchronized with the transmit/receive mode of the radio transceiver. As described above, the control signal can be taken from the transmit synchronous drain bias voltage applied to the power amplifier 76, which is high or zero voltage level when the transceiver is transmitting and low or zero voltage at the end of the time slot. Level. FIG. 10B shows the relationship between the isolation of the output O/P1 and O/P2 and the insertion loss of the FET converters 152 and 154 in a simple graph format.

Therefore, the present invention has been described with the contents of the exemplary embodiment. In summary, the present invention beneficially increases the capacity and coverage of the mobile/portable radio communication system by providing or adopting mobile/portable radio equipment capable of communicating on adjacent or connected frequency bands without actually using additional hardware. In the example of connected LMR and cellular frequencies, only minor modifications to the hardware and software of the cellular radio device are required to make that radio device also have the ability to communicate on the LMR frequency band. The second embodiment of the present invention is preferable because it uses only one duplexer to achieve lower cost and smaller size. By effectively converting two RF converters, the need for a duplexer for each set of adjacent frequency bands is eliminated. Two converters are used in the LMR path to maintain transmission and reception isolation, and since the cellular and LMR transmission signals pass through the cellular duplexer, the low-pass filtering service for the transmission of the two frequency bands reduces the harmonic parasitic content to an acceptable level level. In addition, the third-stage intermodulation performance of the MMIC converter is high enough to maintain the transmission and reception distortion drive requirements.

The above-described exemplary embodiments are illustrative rather than restrictive embodiments of the present invention in all aspects. Although the foregoing exemplary embodiments have been described in terms of base stations and mobile stations, the present invention can be applied to any kind of radio communication system. For example, satellites can send and receive data in communication with DBC remote devices including portable units, personal digital assistants, and the like.

Moreover, although the present invention has been described mainly in terms of communication in the LMR spectrum, the present invention is also intended to be used in multiple hyperbands, such as dual-mode DBC and cellular band mobile phones. For example, the mobile station can be implemented to operate in the A-side cellular frequency band and a portion of the LMR frequency band. This DBC mobile station has the advantage of being able to use the existing cellular network that allows DBC network operators to provide a nationwide roaming footprint. Readers who are interested in a system capable of multiple hyperband operations can refer to the U.S. Patent Application Serial No. 08/425051 entitled "Multiple Hyperband Mobile and Base Stations" filed on April 19, 1995 by krister Raith, which is jointly assigned. The text is incorporated here as a reference. Therefore, the present invention can make many changes in specific implementations that can be derived from the description contained herein by those skilled in the art, and all such changes and modifications are considered to be within the scope and spirit of the present invention defined by the following claims.