HK1021675B - Dual band transceiver - Google Patents

Description

Dual band transceiver

The present invention relates to wireless communication systems, and more particularly, to dual-band mobile stations that must be capable of transceiving in two separate frequency bands used by such systems, such as the two frequency bands used to provide cellular telephone service and Personal Communications Service (PCS), respectively.

The prior art includes cellular radio systems operating since the early eighties of this century that provide telephone service to an increasing number of subscribers, estimated to be more than twenty million today. Cellular telephone service operates much like fixed wire line telephone service in homes and offices, except that telephone calls to and from mobile subscribers are connected using radio waves rather than telephone lines. Each mobile subscriber has a dedicated (10 digit) telephone number, which is billed per month as the "airtime" for the cellular telephone call. Many of the special services available to landline telephone users (e.g., call waiting, call forwarding, three-way calling, etc.) are also commonly available to mobile users.

In the united states, cellular operating licenses are issued by the Federal Communications Commission (FCC) in compliance with a licensing plan that divides the united states into several regional business markets defined by 1980 statistics. The larger metropolitan market is called the metropolitan statistical region (MSA) and the smaller rural market is called the rural statistical Region (RSA). Only two cellular licenses are issued in each market, allowing the system to operate. Originally allocated to these two systems were two distinct Radio Frequency (RF) segments in the 800MHz range, referred to as the "a-band" and "B-band", respectively. The two cellular systems within each market are commonly referred to as the "a system" and the "B system," respectively. To meet the demand of an increasing number of mobile users, the FCC has subsequently released several other frequency bands in the 800MHz range to the a and B systems, referred to as the "a 'and a" frequency bands "(for the a system) and the" B' frequency bands "(for the B system). The A, A 'and a "frequency bands allocated to the a system and the B and B' frequency bands allocated to the B system each actually comprise two respective frequency bands, one for transmission and the other for reception, separated by 45 MHz. The transmit band and receive band are each divided into a series of RF channels spaced 30MHz apart. Thus, each RF channel includes a 39KHz transmit channel and a corresponding 30KHz receive channel separated by 45MHz in the 800MHz range.

The architecture of a typical cellular radio system is shown in figure 1. A regional area, such as a metropolitan area, is divided into smaller contiguous radio coverage areas referred to as "cells," e.g., cells C1-C10. The cells C1-C10 are served by a set of respective fixed radio stations B1-B10, called "base stations". Each base station operates on a subset of the RF channels assigned to the system. Fig. 1 illustrates a case where base stations B1 to B10 are arranged at the centers of cells C1 to C10, respectively, and each is provided with an omnidirectional antenna that radiates uniformly in each direction. However, base stations B1-B10 may also be located at the edges or off-center of cells C1-C10, with cells C1-C10 being directionally illuminated with radio signals (e.g., one base station may be equipped with three directional antennas each covering a 120 sector).

These RF (radio frequency) channels assigned to any given cell (or sector) can be reassigned to distant cells in a frequency reuse pattern; as is well known in the art. In each cell (or sector), there is at least one radio frequency channel used to carry control or supervisory messages, referred to as the "control" or "paging/access" channel. Other channels are used to carry voice calls and are referred to as "voice" or "talk" channels. Cellular telephone users (mobile users) within cells C1-C10 are equipped with hand-held, portable or car-mounted telephones, collectively referred to as "mobile stations," such as mobile stations M1-M5, each communicating with a neighboring base station.

As shown in FIG. 1, the base stations B1-B10 are connected to and controlled by a Mobile Telephone Switching Office (MTSO) 20. The MTSO20 is connected to a central office (not expressly shown in fig. 1) within the landline (wireline) Public Switched Telephone Network (PSTN)30, or to a facility such as an Integrated Services Digital Network (ISDN). MTSO20 switches calls between wireline and mobile subscribers, controls signaling to the mobile stations, compiles accounting statements, stores subscriber service details, and ensures operation, maintenance, and testing of the system.

Access to the cellular system by any of the mobile stations M1-M5 is controlled based on a mobile station identification number (MIN) and an Electronic Serial Number (ESN) stored in the mobile station. The MIN is a numerical representation of the 10-digit telephone number assigned to the mobile station by the home system operator. An Electronic Serial Number (ESN) is specified by the manufacturer and is permanently stored in the mobile station. Such MIN/ESN pairs are transmitted by the mobile station at the time of call origination, and their validity is checked by the MISO 20. If the MIN/ESN pair is determined to be invalid (e.g., where the ESN is blacklisted due to a theft report for the mobile station), the system may deny access to the mobile station. The system also sends the MIN to the mobile station when alerting the mobile station of an incoming call.

After being switched on (powered up), the mobile stations M1-M5 each enter an idle state (dormant mode) and tune to the strongest control channel (typically the control channel of the cell in which the mobile station is currently located) and are constantly monitored. When the mobile station moves between cells while in the idle state, the mobile station will eventually tune to the control channel of the "new" cell "by" losing "the radio connection on the control channel of the" old "cell. Initial tuning to the control channel and subsequent change of control channel is automatically accomplished by scanning all the active control channels in the cellular system to find the "best" control channel (in the united states, there are 21 "dedicated" control channels per cellular system, meaning that the mobile must scan up to 21 RF channels. when a control channel with good reception quality is found, the mobile remains tuned to this channel until the reception quality deteriorates again.

To detect an incoming call, the mobile station continually monitors the current control channel to determine whether a paging message addressed to it (i.e., containing its MIN) has been received. When, for example, a normal (landline) subscriber calls the mobile subscriber, a paging message is sent to the mobile station. The call is sent from PSTN 30 to MTSO20 which analyzes the dialed number. If the dialed number is valid, the MTSO20 requests some or all of the base stations B1-B10 to page the called mobile station throughout their respective cells C1-C10. Each base station B1-B10 that receives the request from MTSO20 then sends a paging message containing the MIN for the called mobile station on the control channel of the corresponding cell. Each idle mobile station M1-M5 in the cell compares the MIN in the paging message received on the control channel with the MIN stored in the mobile station. The called mobile station with the matching MIN will automatically send a page response to the base station on the control channel, forwarded by the base station to the MTSO 20. Upon receiving the page response, MTSO20 selects a voice channel available in the cell from which the page response is forwarded (for which reason MTSO20 needs to maintain a free channel list) and requests the base stations in that cell to command the mobile station to tune to the selected voice channel via the control channel. Once the mobile station has tuned to the selected voice channel, a through connection is established.

On the other hand, when a mobile subscriber initiates a call (e.g., by dialing a general subscriber's telephone number and then pressing the "send" button on the mobile station's telephone handset), the dialed number and the mobile station's MIN/ESN are sent to the base station over the control channel and then to the MTSO 20. After the MTSO20 confirms that the mobile station is active, it assigns a voice channel to establish a direct connection for the call, as previously described. If the mobile station moves between cells in a talk state, the MTSO20 performs a "handoff" that transfers the call from the old base station to the new base station. The MTSO20 selects a voice channel available in the new cell and instructs the old base station to send a handoff message to the mobile station on the current voice channel of the old cell informing the mobile station to tune to the selected voice channel of the new cell. The handoff message is sent in an "intermittent and outstanding" manner, the resulting intermittency being hardly noticeable in the call. Upon receipt of the handover message, the mobile station tunes to the new voice channel, thereby establishing a through connection by the MTSO20 through the new cell. This old voice channel in the old cell is marked as a free channel within MTSO20 and can be allocated for use by another call.

As described above, such initial cellular radio systems were compliant with the Advanced Mobile Phone Service (AMPS) standard, employing analog transmission methods, particularly Frequency Modulation (FM) methods, and duplex (bi-directional) RF channels. According to the AMPS standard, each control or voice channel between a base station and a mobile station utilizes a pair of separate frequencies (available in the A, A ', a ", B or B' band) including a forward (downlink) frequency used by the base station to transmit (received by the mobile station) and a reverse (uplink) frequency used by the mobile station to transmit (received by the base station). Thus, the AMPS system is a Single Channel Per Carrier (SCPC) system, with each RF channel allowing only one voice circuit (telephone call). Different users access the same set of RF channels with different RF channels (frequency pairs) designated, a so-called Frequency Division Multiple Access (FDMA) technique. This initial AMPS (analog) architecture forms the basis of the industry standard EIA/TIA-553, initiated by the Electronics Industry Association (EIA) and Telecommunications Industry Association (TIA).

However, in the late eighties, the cellular communications industry in the united states began to move from analog to digital technologies, driven primarily by the increasing demands of users to address the growing problems and expand system capacity requirements. It was earlier recognized that there are three ways in which the capacity improvements sought for next generation cellular systems could be achieved, namely to use "cell splitting" to provide more user channels in certain areas where increased capacity is required, to use more advanced digital radio communication techniques in these areas, or to combine the two. According to the first approach (cell splitting), the area of the corresponding cell (cell radius) is reduced due to the reduction of the transmission power of the base station, thereby reducing the frequency reuse distance, so that more channels can be available per geographical area (i.e. increased capacity). There are other advantages to using smaller cells, such as allowing a user to have a longer "talk-through" because the mobile station can transmit with much less power than is used in larger cells, so that its battery does not need to be charged as often. It is well known in the art that cell splitting creates a series of progressively smaller cells, called "macrocells", "microcells", and "picocells", within the coverage area of a conventional cellular telephone system. In such a hierarchical cellular architecture, a macro cell (typically at least 1km in radius) may, for example, serve fast moving users, covering areas of less than moderate traffic. Micro cells may serve slow moving users, covering high density pedestrian areas (e.g., convention centers or busy city streets) or busy avenues (streets or highways). A pico cell may cover an office aisle or floor of a high-rise building.

In terms of the system (MTSO), the base stations within the microcells and picocells can be considered extension stations for base stations within adjacent or overlapping macrocells. In this case, the base stations of the microcells and picocells may be connected to the macrocell base station by, for example, digital transmission lines. Alternatively, the pico cell and the pico cell may be treated the same as the macro cell and directly connected to the MTSO. The macro, micro and pico cells may be different from each other in terms of radio coverage, or may overlap each other in stages to handle different traffic distribution situations or radio environments. For example, handoff between microcells is sometimes difficult to perform at some street corners, especially where the user is moving quickly enough that the change in signal strength is more than 20dB per second. In this case, a "umbrella" macro cell may be used to serve fast moving users, while a few micro cells may be used to serve slow moving users. Since different types of users are managed separately in this way, handover between microcells can be avoided for fast moving users suffering from severe corner effects. Therefore, the concept of cell splitting is generally useful not only for covering "hot spots" (high traffic areas) but also for covering "dead spots" (terrain, zone of the terrain that blocks radio signal propagation).

While cell splitting can improve the capacity and coverage needed to meet the increasing demand of users, the increase in actual capacity using analog AMPS technology is limited. It is generally believed that the desired capacity gain can only be greatly improved by digital techniques, and indeed the benefit of the microcell (cell splitting) that is supposed to increase capacity is obtained. In moving to digital technology, therefore, the EIA/TIA developed a series of wireless interface standards that utilized digital speech coding (analog-to-digital conversion and speech compression) and Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA) technologies to multiply the number of speech circuits (calls) per channel (i.e., increase capacity). These standards include IS-54(TDMA) and IS-95 (CDMA). Both are "dual mode" standards that support the use of both the original AMPS analog voice and control channels, as well as the digital voice channels defined within the existing AMPS framework (thus facilitating the transition from analog to digital and continuing to use existing analog mobile stations). The dual-mode IS-54 standard has become, inter alia, the so-called digital AMPS (D-AMPS) standard. AMPS (D-AMDS) standard. One relevant standard, referred to as IS-55A, specifies minimum performance criteriｃA for IS-54 compliant mobile stations, such as disclosed in EP- ｃA-0621683.

Later, the EIA/TIA established a new specification for D-AMPS, which included a digital control channel adapted to support public or private microcell operation, extend mobile station battery life, and enhance end-user functionality. This new specification builds on the IS-54B standard (the current version of IS-54), referred to as IS-136. A related standard defining the minimum performance level for IS-136 compliant mobile stations IS currently under investigation and IS referred to as IS-137A. All of the above listed EIA/TIA standards are incorporated herein by reference, and may be referred to for a full understanding of the context of development. Copies of these standards are available from the electronics industry association (2001 pennsylvania avenue, n.w., Washington, d.c. 20006).

As digital technology has turned in recent years, there has been an increasing shift to portable telephones for use in homes, offices, public places, and virtually anywhere a user wishes to have telephone service. The cellular telephone system of fig. 1 originates from providing car telephone service. The next stage in the evolution of wireless telephony is the emergence of the concept of "personal communications services" (PCS). The purpose of the PCS is to support communication with users moving in buildings, factories, warehouses, malls, conference centers, airports or any indoor or outdoor area, delivering not only telephone calls but also faxes, computer data, pages and text messages, even television signals to the users. The PCS system employs digital technology (TDMA as specified in IS-136 or the european GSM standard). PCS systems operate at lower power and use smaller cellular structures (i.e., microcells) than conventional large area (mobile) analog cellular systems, and thus can provide the high quality, large capacity radio coverage required for dedicated transactions or other applications. Therefore, PCS systems combine the advantages of both digital technology and microcell architectures, providing a variety of very valuable features. The FCC recently auctioned spectrum in the 1900MHz range for use by PCS systems. Six frequency bands, referred to as "a-F bands," have been defined in the 1900MHz range, each band being divided into a series of duplex RF channels spaced 30KHz apart, similar to the channel allocation for the 800MHz range employed by cellular systems, except that the PCS system has a transmit-receive frequency spacing of 80.04MHz instead of 45 MHz.

Accordingly, it is anticipated that such a wireless environment will include cellular systems operating in the 800MHz range (hereinafter sometimes referred to as the "cell band") and PCS systems operating in the 1900MHz range (hereinafter sometimes referred to as the "PCS band"). Thus, a mobile subscriber desiring service of both systems must use two different mobile stations that are capable of operating in the cell band and the PCS band, respectively, or more preferably, a single "dual-band" mobile station that is capable of operating in both bands. One way to design such dual-band mobile stations is to use completely separate radio hardware for the cell and PCS bands, respectively. Another approach is to use ｃA plurality of synthesis circuits connected to ｃA plurality of frequency multipliers, as disclosed in EP- ｃA-0581573, by selectively setting to operate in different frequency bands. However, these approaches can increase the size and cost of the mobile station. To minimize the size and cost of the mobile station, it is desirable to minimize the hardware used in the cell band to be usable in the PCS band. Furthermore, it is desirable to modify the design of existing D-AMPS mobile stations, for example, in such a way that they can be easily and economically operated in the new PCS band, so that such dual-band mobile stations can be produced early on into the market. These objects are achieved by the present invention.

The present invention allows sharing of most of the radio hardware in the transmit and receive paths between the cell band and the PCS band. A dual-band mobile station constructed in accordance with the present invention can use, for example, a single local oscillator and a single modulator. Furthermore, according to the present invention, the structure of the existing mobile station equipped with hardware operating in the cell band can be slightly modified, and can operate also in the PCS band with a small amount of hardware added.

In one aspect, the present invention provides a dual band transmitter capable of transmitting data signals in a first, lower frequency band, such as the cell band, or a second, higher frequency band, such as the PCS band. Such a dual band transmitter comprises: a first oscillating means for generating a Local Oscillator (LO) signal; a second oscillation device for generating an Offset Frequency (OF) signal; a first mixing means for combining the LO signal and the OF signal into a first transmit signal; a modulation means for modulating the first transmit signal with the data signal to produce a first data modulated transmit signal; a second mixing means for combining the first data modulated transmit signal with the LO signal into a second data modulated transmit signal; a program control means for programming the first oscillation means and the second oscillation means such that the first data modulated transmission signal is in a first frequency band and the second data modulated transmission signal is in a second frequency band; and a transmitting means for transmitting the first data modulated transmission signal when transmitting in the first frequency band and the second data modulated transmission signal when transmitting in the second frequency band.

In another embodiment OF the dual band transmitter OF the present invention, the modulating means modulates one OF the LO signal and the OF signal with a data signal to generate a data modulated signal; and the first mixing means combines the other OF the LO signal and the OF signal with the data modulated signal into a first data modulated transmit signal. In each OF the embodiments OF the dual band transmitter described above, the data signal may be selectively transmitted in either the cell band or the PCS band by setting the frequency OF the LO signal between 980MHz to 1050MHz and the frequency OF the OF signal to 155.52MHz when transmitted in the cell band and 190.56MHz when transmitted in the PCS band.

In another aspect, the present invention provides a dual-band mobile station capable of operating in a first, lower frequency band, such as a cell band, or a second, higher frequency band, such as a PCS band. The dual band mobile station includes: a means for detecting an analog speech signal; a means for processing the analog voice signal into a digital baseband data signal; and a dual band transmitting device for transmitting the baseband data signal in the first frequency band or the second frequency band. This dual band transmitting device comprises: a first oscillating means for generating a Local Oscillator (LO) signal; a second oscillation device for generating an Offset Frequency (OF) signal; a first mixing means for combining the LO signal and the OF signal into a first transmit signal; a modulation means for modulating the first transmission signal with the baseband data signal to generate a first data modulated transmission signal; a second mixing means for combining the first data modulated transmit signal with the LO signal into a second data modulated transmit signal; a program control means for programming the first oscillation means and the second oscillation means such that the first data modulated transmission signal is in a first frequency band and the second data modulated transmission signal is in a second frequency band; and a transmitting means for transmitting the first data modulated transmission signal when transmitting in the first frequency band and the second data modulated transmission signal when transmitting in the second frequency band.

In another embodiment OF the dual band mobile station OF the present invention, the modulating means modulates one OF the LO signal and the OF signal with a baseband data signal to generate a data modulated signal; and the first mixing means combines the other OF the LO signal and the OF signal with the data modulated signal into a first data modulated transmit signal. In the above embodiments of the dual-band mobile station, the dual-band mobile station may further comprise a dual-band receiving means for receiving a data modulated signal in the first frequency band or the second frequency band. This dual band receiving apparatus includes: a third mixing means for combining the received first frequency band signal with the LO signal; a frequency multiplier, such as a frequency multiplier, for multiplying the LO signal; and a fourth mixing means for combining the received second frequency band signal with the multiplied LO signal.

In yet another aspect, the present invention provides a method of transmitting a data signal in a first, lower frequency band, such as the cell band, or a second, higher frequency band, such as the PCS band. The method comprises the following steps: generating a Local Oscillator (LO) signal; generating an Offset Frequency (OF) signal; mixing the LO signal with the OF signal to generate a first transmit signal; modulating the first transmit signal with the data signal to produce a first data modulated transmit signal; if the data signal needs to be transmitted in the first frequency band, the LO signal and the OF signal are selected to enable the first data modulation transmission signal to be in the first frequency band, and the obtained data modulation first frequency band signal is transmitted; and if the data signal needs to be transmitted in the second frequency band, mixing the first data modulation transmission signal with the LO signal to form a second data modulation transmission signal, selecting the LO signal and the OF signal to enable the second data modulation transmission signal to be in the second frequency band, and then transmitting the obtained second data modulation transmission signal.

In another embodiment OF the dual band transmission method OF the present invention, one OF the LO signal and the OF signal is modulated with a data signal to generate a data modulated signal, and the other OF the LO signal and the OF signal is mixed with the data modulated signal to generate a first data modulated transmission signal. In the embodiments of the method of the present invention described above, the first data modulated transmit signal may be filtered and then mixed with the LO signal to form the second data modulated transmit signal. This filtering serves to limit spurious emissions when transmitting the second data modulated transmit signal.

The present invention will be more fully understood and appreciated by those skilled in the art from the following detailed description, taken together with the accompanying drawings, in which various objects and advantages of the invention will be apparent. In these drawings:

FIG. 1 illustrates the architecture of a conventional cellular telephone system;

FIG. 2 shows the transmit and receive frequency bands of a cellular telephone system as specified in one known industry standard IS-55A and the transmit and receive frequency bands of a Personal Communications Services (PCS) system as specified in another known industry standard IS-137 currently being developed;

FIG. 3 illustrates a channel allocation within the cellular band of FIG. 2;

FIG. 4 illustrates channel allocation within the PCS band of FIG. 2;

fig. 5 is a block diagram of a mobile station including a dual-band transceiver constructed in accordance with the present invention; and

fig. 6 shows a circuit diagram of the dual band transceiver diagrammatically shown in fig. 5.

Referring to fig. 2, the cell bands are distributed over a range of frequencies from 824MHz to 894MHz, including a transmitting cell band extending from 824MHz to 849MHz and a corresponding receiving cell band extending from 869MHz to 894 MHz. On the other hand, the PCS band is distributed in the frequency range from 1850MHz to 1990MHz, including a transmit PCS band extending from 1850MHz to 1910MHz and a corresponding receive PCS band extending from 1930MHz to 1990 MHz. As shown in fig. 3, the RF channels in the cell band are each associated with a particular channel number, one for one, and each includes a transmit center frequency (mobile to base station) and a corresponding receive center frequency (base to mobile) that are 45MHz apart. As shown in fig. 4, the RF channels in the PCS band are also each associated with a particular channel number, one for one, and each includes a transmit center frequency (mobile to base) and a corresponding receive center frequency (base to mobile) spaced apart by 80.04. It should be noted that while each RF channel used in the cell band falls within a single band in the A, A ', a ", B or B' bands (see fig. 3), some RF channels used in the PCS band (channel numbers 499, 666 and 667, 1166 and 1167, 1333 and 1334 and 1499 and 1501) actually fall within more than one band in the a-F bands (see fig. 4).

Referring now to fig. 5, a simplified block diagram of a dual-band mobile station constructed in accordance with the present invention is shown. The mobile station includes a transmitting portion (upper half of fig. 5) and a receiving portion (lower half of fig. 5). The transmitting section includes a microphone 100, a codec 102, a Digital Signal Processor (DSP)104, a sampling interface 106, and a dual-band transmitter 108. The receive section is essentially a mirror image of the transmit section and includes a speaker 110, a codec 112, a DSP 114, a sampling interface 116, and a dual band receiver 118. The DSPs 104 and 114, the sampling interfaces 106 and 116, and the dual-band transceivers 108 and 118 are controlled by a microprocessor 120 having access to a memory 122 in which the mobile station transmit and receive operating software is stored. The dual band transmitter 108 and receiver 118 are coupled to an antenna 126 through an antenna interface 124.

In the transmit section, the audio (analog) signals detected by the pickup 100 are converted to digital speech samples (data) in the transmit codec 102 and sent to the transmit DSP, which performs gain control, filtering, speech compression, channel coding, and any other desired speech and control data processing (e.g., as per IS-136). The processed baseband data is then sent to a transmit sampling interface 106, which forms a modulated waveform composed of an in-phase (I) signal and a quadrature (Q) signal, as is known to those skilled in the art. The baseband I, Q modulated waveform is sent to the dual band transmitter 108, modulated onto an analog carrier signal, upconverted to a desired channel frequency, filtered, amplified, and sent to the antenna 126 via the antenna interface 124 for transmission.

In the receiver portion, the modulated carrier signal received by the antenna 126 is sent to the dual band receiver 118 via the antenna interface 124 for down conversion to an Intermediate Frequency (IF) signal. The IF signal is sampled in amplitude, phase and/or frequency at sampling interface 116 and the resulting sampled data is provided to receive DSP 114 for processing. The DSP 114 demodulates, filters, amplifies/attenuates, channel decodes, and decompresses the sampled data. The demodulated and decompressed data is then sent to the receiving codec 112 to be converted into a baseband audio signal, which is output through the speaker 110.

Figure 6 shows the mobile station RF section (dual band transmitter 108, dual band receiver 118 and antenna interface 124. in the transmit direction, the I and Q signals from the two interfaces 106 (figure 5) are sent to the IQ modulator 130. the other input to the IQ modulator 130 is the output of the mixer 132. the mixer 132 combines the signal from the main (local oscillator) Voltage Controlled Oscillator (VCO)134 with the signal from the bias VCO 136. both the main VCO 134 and the bias VCO 136 are controlled by logic in the microprocessor 120 (figure 5) as shown schematically in figure 6. in a preferred embodiment, the main VCO 134 is designed to be programmable to any frequency (RF channel) between 980MHz and 1050MHz, the channel spacing is 30KHz, and the bias VCO 136 is set to 155.52MHz and 190.56MHz to meet the needs of operating in the cell band and PCS band, respectively.

As further shown in fig. 6, the output of the IQ modulator 130 is provided to a variable gain amplifier 138, also controlled by the microprocessor 120 (fig. 5). The variable gain amplifier 138 is used to control the output level of the transmit signal. Depending on whether the mobile station is operating in the cell band or the PCS band, the output of the variable gain amplifier 138 will be provided by the switch 140 to the corresponding transmit path. For operation in the cell band, the switch 140 passes the signal to a Band Pass Filter (BPF)142 in the cell band transmit path. The BPF 142 filters out any noise or spurious signals and unwanted signal components generated in the mixer 132 from the transmit signal. The output of the BPF 142 is then sent to a power amplifier 144, which increases the power of the transmitted signal to the desired level. The signal level at the output of the power amplifier 144 is detected by a power level sensor 146, which forms a feedback signal to the microprocessor 120 (fig. 5) for adjusting the gain of the variable gain amplifier 138. The output of power amplifier 144 is provided to duplexer 148, to diplexer 150, and finally transmitted via antenna 126 (fig. 5 and 6). The duplexer 148 serves to separate the cell band transmit signal from the incoming cell band receive signal so that the transmit and receive signals can be routed to the respective paths. On the other hand, the diplexer 150 serves to separate the transmission and reception signals of the cell band from the transmission and reception signals of the PCS band so that the signals of the cell band and the PCS band can be supplied to the corresponding paths, respectively. As is known in the art, the duplexer 148 and the diplexer 150 may be implemented with BPFs.

For operation in the PCS band, switch 140 passes the signal from variable gain amplifier 138 to BPF152 in the PCS band transmit path. The BPF152 in the PCS band transmit path performs similar operations as the BPF 142 in the cell band transmit path. The output of the BPF152 is fed to an upconversion mixer 154, the other input of which is provided by the main VCO 134. This second mixing of the signal from IQ modulator 130 with the signal from main VCO 134 (the first mixing provided by mixer 132) up-converts the transmit signal to the desired frequency in the PCS band. The PCS band transmit signal output by the up-conversion mixer 154 is filtered within the BPF156 to remove any unwanted signal components generated in the up-conversion mixer 154. The output of the BPF156 is provided to a power amplifier 158, the output of which is detected by a power level sensor 160. The power amplifier 158 and power level sensor 160 in the PCS band transmit path perform similar operations as the power amplifier 144 and power level sensor 146, respectively, in the cell band transmit path. The output of the power amplifier 158 is provided to a switch 162. Switch 162 provides transmit signals to diplexer 150 during transmit time slots defined in a TDMA system, such as an IS-136 compliant D-AMPS system.

The operation of the cell band and PCS band transmit paths of fig. 6 will now be described by way of example of some of the specific channels listed in fig. 3 and 4. Assume that the mobile station operates on channel 500 of the cell band, with a corresponding transmit frequency of 840MHz (fig. 3). The master VCO 134 is programmed to a frequency of 995.52MHz, while the bias VCO 136 is set to a frequency of 155.52MHz (fig. 6). The two signals are combined in mixer 132 to produce sum and difference frequencies of 1151.04MHz and 840MHz, respectively, as is well known to those skilled in the art. The resulting sum and difference frequency signals are sent to the IQ modulator 130, amplified by the variable gain amplifier 138, and sent to the cell band transmit path by the switch 140. The sum frequency of 1151.04MHz is then filtered by BPF 142, leaving the desired difference frequency of 840MHz for transmission through antenna 126, as previously described.

On the other hand, assuming that the mobile station operates in channel 500 of the PCS band, the corresponding transmit frequency is 1864.98MHz (fig. 4). The master VCO 134 is programmed to a frequency of 1027.77, while the bias VCO 136 is set to a frequency of 190.56MHz (see fig. 6). The two signals are combined in mixer 132 to produce sum and difference frequencies of 1218.33MHz and 837.21MHz, respectively. The resulting sum and difference frequency signals are modulated in IQ modulator 130, amplified by variable gain amplifier 138, and sent to the PCS band transmit path via switch 140. The sum frequency of 1218.33MHz is filtered by the BPF152, and the remaining 837.21MHz difference frequency is fed to the up-conversion mixer 154 to be mixed again with the 1027.77MHz signal output by the main VCO 134. The sum and difference frequencies produced by this second mixing are 1864.98MHz and 190.56MHz, respectively. The 190.56MHz difference frequency is filtered by BPF156 leaving the 1864.98MHz desired sum frequency transmitted through antenna 126 as previously described.

The reception situation in the cell band and the PCS band is to some extent a mirror of the corresponding transmission situation. During cell band reception, the received signal is passed from duplexer 148 to linear amplifier 164 followed by BPF 166. The BPF 166 is used to attenuate out-of-band noise (including noise generated by the linear amplifier 164) and other spurious signals. The output of the BPF 166 is provided to an IF mixer 168 which combines the received cell band signal with the signal output by the main VCO 134. This mixing stage down-converts the received cell band signal to a first IF frequency to the BPF170, which is then processed and down-converted in a manner substantially consistent with fig. 5 to produce a baseband audio signal.

On the other hand, during PCS band reception, the received signal is provided by the switch 162 to the BPF 172, which filters out signal components outside the PCS band. The output of the BPF 172 is provided to a linear amplifier 174 followed by a BPF 176. The BPF 176 is used to further attenuate out-of-band noise (including noise generated by the linear amplifier 174) and other spurious signals. The output of the BPF 176 is provided to an IF mixer 178 that combines the received PCS band signal with the output of a frequency multiplier 180 that doubles the frequency of the LO signal from the main VCO 134. Since the frequency of the received PCS band signal is approximately twice the frequency of the LO signal output by the main VCO 134, this mixing stage down-converts the received PCS band signal to a first IF frequency to the BPF170, and then IF processes and down-converts in a similar manner as performed for the received cell band signal.

It can be seen that the present invention allows a series of radio hardware components (e.g., IQ modulator 130 and its predecessors in the transmit direction and BPF170 and its successors in the receive direction) to be shared when operating in the cell and PCS bands. It can also be seen that with the present invention, a mobile station has the capability to transmit in the PCS band after being reconfigured with the addition of a small amount of hardware (e.g., BPF152 and mixer 154). Another advantage of the present invention, due to the use of the BPF152 prior to the up-conversion mixer 154, is that it facilitates meeting stringent requirements for spurious radiation in the PCS band, since the BPF152 filters the PCS transmit signal at lower frequencies, and thus can be implemented with a smaller band pass filter than would be required for equivalent filtering in the PCS band.

It will also be apparent to those skilled in the art that various modifications in operation or construction may be made to the basic circuit of fig. 6 in accordance with the invention. For example, since the receive and transmit channel spacing is 45MHz in the cell band and 80.04MHz (differing by 35.04MHz) in the PCS band, the frequency of the main VCO 134 or the bias VCO 136 should be changed when switching between cell band operation and PCS band operation. In this preferred embodiment of the invention, the frequency that biases the VCO 136 is varied. Specifically, the frequency of the bias VCO 136 is set to 155.52MHz for operation in the cell band and 190.56MHz for operation in the PCS band (again, 35.04MHz apart). However, it is also possible to fix the frequency of the bias VCO 136 at, for example, 155.52MHz, while compensating for the difference in the transmit-receive channel spacing by correspondingly programming the main VCO 134 (i.e., "hopping" the main VCO 134 rather than biasing the VCO 136).

As another example of possible modifications made to the circuit of fig. 6, also belonging to the present invention, the mixer 132 may be moved from the input to the output of the IQ modulator 130 (for example before the variable gain amplifier 138) without affecting the operation of the circuit in the dual band. In this case, the IQ modulator 130 would receive either the signal from the master VCO 134 or the signal from the bias VCO 136 (and receive the IQ signal), while the mixer 132 would receive the other VCO signal (and receive the modulated signal from the IQ modulator 130). Preferably, the signal from the main VCO 134 is provided to the mixer 132 and the signal from the bias VCO 136 is provided to the IQ modulator 130 so that the modulation of the IQ signal occurs at a lower frequency (thereby producing less unwanted signal components).

As a further example of possible modifications to the circuit of fig. 6, the mixer 132 may be implemented as an image reject mixer, so that only the required difference frequency is applied from the mixer 132 to the IQ modulator 130. Alternatively, an appropriate filter may be added to the output of the mixer 132 to filter out unwanted sum frequencies.

In general, those skilled in the art will readily recognize that many modifications and variations may be made to the embodiments of the invention disclosed herein without departing substantially from the spirit and scope of the invention. Accordingly, the forms of the invention herein disclosed are to be taken as illustrative and not restrictive, and the scope of the invention is defined only by the appended claims.

Claims (30)

1. A dual band transmitter (108) capable of transmitting data signals in a first, lower frequency band or a second, higher frequency band, said dual band transmitter comprising:

a first oscillator means (134) for generating a local oscillator signal;

a second oscillating means (136) for generating a bias frequency signal;

a first mixing means (132) for combining said local oscillator signal and said offset frequency signal into a first transmit signal;

a modulation means (130) for modulating said first transmit signal with said data signal to produce a first data modulated transmit signal;

-a second mixing means (154) for combining said first data modulated transmission signal with said local oscillator signal into a second data modulated transmission signal;

a programming means (120) for programming said first oscillating means (134) and said second oscillating means (136) such that said first data modulated transmission signal is in said first frequency band and said second data modulated transmission signal is in said second frequency band; and

-a transmitting means (140) for transmitting said first data modulated transmission signal when transmitting in said first frequency band and for transmitting said second data modulated transmission signal when transmitting in said second frequency band.

2. A dual-band mobile station (100.. 126) equipped with the dual-band transmitter of claim 1, the dual-band mobile station comprising:

-means (100) for detecting an analog speech signal; and

means (102, 104, 106) for processing said analog speech signal into said data signal.

3. The dual-band mobile station of claim 2 wherein said processing means comprises a codec (102).

4. The dual-band mobile station of claim 3 wherein said processing means further comprises a digital signal processor (104).

5. The dual-band mobile station of claim 2, said dual-band mobile station further comprising a dual-band receiver (118) capable of receiving data modulated signals in either said first frequency band or said second frequency band, said dual-band receiver (118) comprising:

a third mixing means (168) for mixing said received first frequency band signal with said received first frequency band signal

Combining the local oscillator signals;

a frequency multiplier (180) for up-converting said local oscillator signal; and

a fourth mixing means (178) for combining said received second frequency band signal with said upconverted local oscillator signal.

6. The dual-band mobile station of claim 5, wherein said first frequency band comprises a transmit frequency band and a receive frequency band allocated to a cellular system, and said second frequency band comprises a transmit frequency band and a receive frequency band allocated to a personal communications services system.

7. The dual-band mobile station of claim 6, wherein said cellular transmission frequency band extends from 824MHz to 849MHz, said cellular reception frequency band extends from 869MHz to 894MHz, said personal communication service system transmission frequency band extends from 1850MHz to 1910MHz, and said personal communication service system reception frequency band extends from 1930MHz to 1990 MHz.

8. The dual-band mobile station of claim 7, wherein said frequency multiplier (180) is a frequency multiplier.

9. The dual band mobile station of claim 7, wherein the frequency of said local oscillator signal is selectively set between 980MHz and 1050MHz, and the frequency of said offset frequency signal is set to 155.52MHz when said cellular transmit or receive frequency band is transmitting or receiving and is set to 190.56MHz when said personal communication services system is transmitting or receiving frequency is transmitting or receiving.

10. The dual band mobile station OF claim 7, wherein a frequency OF said OF signal is set to 155.52MHz when said cellular or said human communication service system transmission or reception band is transmitting or receiving.

11. A dual band transmitter capable of transmitting data signals in a first lower frequency band or a second higher frequency band, said dual band transmitter comprising:

a first oscillator means (134) for generating a local oscillator signal;

a second oscillating means (136) for generating a bias frequency signal;

a modulation means (130) for modulating one of said local oscillator signal and said offset frequency signal with said data signal to produce a data modulated signal;

a first mixing means (132) for combining the other of said local oscillator signal and said offset frequency signal with said data modulation signal to form a first data modulated transmit signal;

-a second mixing means (154) for combining said first data modulated transmission signal with said local oscillator signal into a second data modulated transmission signal;

a programming means (120) for programming said first oscillating means (134) and said second oscillating means (136) such that said first data modulated transmission signal is in said first frequency band and said second data modulated transmission signal is in said second frequency band; and

-a transmitting means (140) for transmitting said first data modulated transmission signal when transmitting in said first frequency band and for transmitting said second data modulated transmission signal when transmitting in said second frequency band.

12. A dual-band mobile station (100.. 126) equipped with the dual-band transmitter of claim 11, the dual-band mobile station comprising:

-means (100) for detecting an analog speech signal; and

means (102, 104, 106) for processing said analog speech signal into said data signal.

13. The dual-band mobile station of claim 12, wherein said processing means comprises a codec (102).

14. The dual-band mobile station of claim 13, wherein said processing means further comprises a digital signal processor (104).

15. The dual-band mobile station of claim 12, said dual-band mobile station further comprising a dual-band receiver (118) capable of receiving data modulated signals in either said first frequency band or said second frequency band, said dual-band receiver (118) comprising:

-third mixing means (168) for combining said received first frequency band signal with said local oscillator signal;

a frequency multiplier (180) for up-converting said local oscillator signal; and

a fourth mixing means (178) for combining said received second frequency band signal with said upconverted local oscillator signal.

16. The dual-band mobile station of claim 15, wherein said first frequency band comprises a transmit frequency band and a receive frequency band allocated to a cellular system, and said second frequency band comprises a transmit frequency band and a receive frequency band allocated to a personal communications services system.

17. The dual-band mobile station of claim 16, wherein the cellular transmit frequency band extends from 824MHz to 849MHz, the cellular receive frequency band extends from 869MHz to 894MHz, the personal communication service system transmit frequency band extends from 1850MHz to 1910MHz, and the personal communication service system receive frequency band extends from 1930MHz to 1990 MHz.

18. The dual-band mobile station of claim 17, wherein said frequency multiplier (180) is a frequency multiplier.

19. The dual-band mobile station of claim 17, wherein the frequency of said local oscillator signal is selectively set between 980MHz and 1050MHz, and the frequency of said offset frequency signal is set to 155.52MHz when said cellular transmit or receive frequency band is transmitting or receiving and is set to 190.56MHz when said personal communication services system transmit or receive frequency band is transmitting or receiving.

20. The dual band mobile station of claim 17, wherein a frequency of said offset frequency signal is set to 155.52MHz when transmitting or receiving in a transmission or reception band of said cellular or said personal communication service system.

21. A method of transmitting data signals in a lower first frequency band or an upper second frequency band, said method comprising the steps of:

generating a local oscillator signal;

generating a bias frequency signal;

mixing said local oscillator signal with said offset frequency signal to produce a first transmit signal;

modulating said first transmit signal with said data signal to produce a first data modulated transmit signal;

if the data signal needs to be transmitted in the first frequency band, selecting the local oscillator signal and the offset frequency signal to enable the first data modulation transmission signal to be in the first frequency band, and then transmitting the data modulation first frequency band signal; and

if the data signal needs to be transmitted in the second frequency band, the first data modulation transmission signal and the local oscillator signal are mixed to form a second data modulation transmission signal, the local oscillator signal and the offset frequency signal are selected to enable the second data modulation transmission signal to be in the second frequency band, and then the second data modulation transmission signal is transmitted.

22. The method of claim 21, wherein said first data modulated transmit signal is filtered and mixed with said local oscillator signal to produce said second data modulated transmit signal.

23. The method of claim 22, wherein the first frequency band is in the 800MHz range and the second frequency band is in the 1900MHz range.

24. The method of claim 23, wherein the frequency of said local oscillator signal is selectively set between 980MHz and 1050MHz, and the frequency of said bias frequency signal is set to 155.52MHz when transmitting in said first frequency band and is set to 190.56MHz when transmitting in said second frequency band.

25. The method of claim 23, wherein the frequency of said bias frequency signal is set to 155.52MHz when transmitted in said first frequency band or said second frequency band.

26. A method of transmitting data modulated signals in a first lower frequency band or a second higher frequency band, said method comprising the steps of:

generating a local oscillator signal;

generating a bias frequency signal;

modulating one of said local oscillator signal and said bias frequency signal with said data signal to produce a data modulated signal;

mixing the other of said local oscillator signal and said offset frequency signal with said data modulation signal to produce a first data modulated transmit signal;

if the data signal needs to be transmitted in the first frequency band, selecting the local oscillator signal and the bias frequency signal to enable the first data modulation transmission signal to be in the first frequency band, and then transmitting the data modulation first frequency band signal; and

if the data signal needs to be transmitted in the second frequency band, the first data modulation transmission signal and the local oscillator signal are mixed to form a second data modulation transmission signal, the local oscillator signal and the offset frequency signal are selected to enable the second data modulation transmission signal to be in the second frequency band, and then the second data modulation transmission signal is transmitted.

27. The method of claim 26, wherein said first data modulated transmit signal is filtered and mixed with said local oscillator signal to produce said second data modulated transmit signal.

28. The method of claim 27, wherein the first frequency band is in the 800MHz range and the second frequency band is in the 1900MHz range.

29. The method of claim 28, wherein the frequency of said local oscillator signal is selectively set between 980MHz and 1050MHz, and the frequency of said bias frequency signal is set to 155.52MHz when transmitting in said first frequency band and is set to 190.56MHz when transmitting in said second frequency band.

30. The method of claim 28, wherein the frequency of said bias frequency signal is set to 155.52MHz when transmitted in said first frequency band or said second frequency band.