Wireless communication device

A wireless communication device capable of restraining interference and thereby improving transmission quality. A wireless controller includes a wireless communication interface, and a baseband controller includes a baseband communication interface for controlling the transfer/reception of baseband signals, a logic circuit, and a memory. The wireless communication interface and the baseband communication interface are connected to each other by a communication line, and the memory stores, with respect to individual radio frequencies of a receive radio signal, bit rates for the communication line at which interference caused by noise produced around the communication line is minimized. When notified of a receive radio frequency, the logic circuit reads, from the memory, an optimum bit rate which corresponds to the receive radio frequency and at which the interference is minimized, and sets the optimum bit rate in the wireless communication interface and the baseband communication interface.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based upon and claims the benefits of priority from the prior Japanese Patent Application No. 2008-075994, filed on Mar. 24, 2008, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication device for performing wireless communication.

2. Description of the Related Art

A mobile phone terminal comprises, as its main components, an RF transceiver (RF-IC) for converting an RF (Radio Frequency) signal to a baseband signal and vice versa, and a baseband processor IC (PHY: physics) for processing the baseband signals. In recent years, the analog interface between the RF-IC and the PHY is being replaced by a digital interface.

As such digital interfaces, DigRF has been standardized for 3G (3rd Generation) applications and JC-61 has been standardized for WiMAX (Worldwide Interoperability for Microwave Access) applications.

These standards permit interconnection between the RF-IC and the PHY, and since hardware connectivity is guaranteed for ICs complying with the standards, the standardization is expected to accelerate liberalization of the digital mobile phone component market.

FIG. 14illustrates a schematic configuration of a mobile phone terminal. The mobile phone terminal5comprises an antenna section50, an RF-IC60, and a PHY70. The illustrated terminal is of a direct conversion type wherein an RF signal with a frequency equal to that of the carrier wave is directly converted to a baseband signal and vice verse without involving an IF (Intermediate Frequency) stage.

The antenna section50includes antennas51and52, a switch53, and band-pass filters54a,55b-1and55b-2. The RF-IC60includes amplifiers61a,61b-1and61b-2, an adder62, mixers63a-1,63a-2and63b-1to63b-4, D/A converters64a-1and64a-2, A/D converters64b-1to64b-4, a multiplexer (MUX)65, a demultiplexer (DEMUX)66, a driver67, a receiver68, and a synthesizer69. The PHY70includes a driver71, a receiver72, a multiplexer73, a demultiplexer74, and a logic circuit75.

When the RF signal is to be received, the switch53switches to a receive side (the antenna51is connected to the input terminal of the band-pass filter55b-1). The RF signal received by the antennas51and52is input to the band-pass filters55b-1and55b-2through which a desired RF frequency is passed to be sent to the RF-IC60.

The RF signal output from the band-pass filter55b-1is applied to the amplifier61b-1in the RF-IC60, and the amplifier61b-1provides differential outputs, which then are supplied to the mixers63b-1and63b-2. Similarly, the RF signal output from the band-pass filter55b-2is applied to the amplifier61b-2in the RF-IC60, and the amplifier61b-2provides differential outputs, which are input to the mixers63b-3and63b-4.

The synthesizer69outputs in-phase (I) local signals I(+) and I(−) having the same frequency as the RF frequency (I(+) and I(−) are opposite in phase), and also outputs quadrature (Q) local signals Q(+) and Q(−) (Q(+) and Q(−) are opposite in phase) with the same frequency.

The mixer63b-1mixes the RF signal (+), which is one of the signals output from the amplifier61b-1, with the local signal I(+) output from the synthesizer69, to generate a baseband signal. Also, the mixer63b-1mixes the RF signal (−), which is the other signal output from the amplifier61b-1, with the local signal I(−) output from the synthesizer69, to generate a baseband signal.

On the other hand, the mixer63b-2mixes the RF signal (+) output from the amplifier61b-1with the local signal Q(+) output from the synthesizer69, to generate a baseband signal. Also, the mixer63b-2mixes the RF signal (−) output from the amplifier61b-1with the local signal Q(−) output from the synthesizer69, to generate a baseband signal. The mixers63b-3and63b-4carry out identical processes.

The analog baseband signals output from the mixers63b-1to63b-4are input to the A/D converters64b-1to64b-4, respectively, which then perform analog/digital conversion to obtain digital baseband signals.

The A/D converter64b-1outputs an I digital baseband signal generated from the RF signal received by the antenna51, and the A/D converter64b-2outputs a Q digital baseband signal generated from the RF signal received by the antenna51.

Also, the A/D converter64b-3outputs an I digital baseband signal generated from the RF signal received by the antenna52, and the A/D converter64b-4outputs a Q digital baseband signal generated from the RF signal received by the antenna52.

The multiplexer65multiplexes the two I baseband signals output from the A/D converters64b-1and64b-3into one baseband signal, and also multiplexes the two Q baseband signals output from the A/D converters64b-2and64b-4into one baseband signal. The two, I and Q digital baseband signals thus obtained are output to the driver67, which then sends the signals to the PHY70.

In the PHY70, the receiver72receives the digital baseband signals and outputs the received signals to the demultiplexer74. The demultiplexer74demultiplexes the baseband signals into a number of signals equal to that before the multiplexing, which signals are sent to the logic circuit75, where a predetermined process is performed on the received baseband signals.

A wireless technology using multiple antennas to transmit and receive data is called MIMO (Multiple Input Multiple Output). In the mobile phone terminal5, the two antennas51and52are used to receive data, and the received data is multiplexed and then demultiplexed, thereby enabling communication tolerant to multipath fading.

When transmitting an RF signal, on the other hand, the switch53switches to a transmit side (the antenna51is connected to the output terminal of the band-pass filter54a). The logic circuit75in the PHY70generates and outputs digital baseband signals, and the multiplexer73multiplexes the received baseband signals. The driver71sends the multiplexed baseband signals to the RF-IC60.

In the RF-IC60, the receiver68receives the multiplexed digital baseband signals and outputs the received signals to the demultiplexer66. The demultiplexer66demultiplexes the baseband signals into the number of signals equal to that before the multiplexing, and outputs the demultiplexed signals to the D/A converters64a-1and64a-2.

The D/A converters64a-1and64a-2each subject the corresponding baseband signal to digital/analog conversion, to generate two analog baseband signals. The mixer63a-1mixes one of the baseband signals output from the D/A converter64a-1with the local signal I(+) output from the synthesizer69, to generate an RF signal. Also, the mixer63a-1mixes the other baseband signal output from the D/A converter64a-1with the local signal I(−) output from the synthesizer69, to generate an RF signal.

On the other hand, the mixer63a-2mixes one of the baseband signals output from the D/A converter64a-2with the local signal Q(+) output from the synthesizer69, to generate an RF signal. Also, the mixer63a-2mixes the other baseband signal output from the D/A converter64a-2with the local signal Q(−) output from the synthesizer69, to generate an RF signal.

The adder62adds together the two signals output from the mixer63a-1and respectively mixed with the local signals I(+) and I(−), and also adds together the two signals output from the mixer63a-2and respectively mixed with the local signals Q(+) and Q(−), to generate I and Q RF signals.

The amplifier61acombines differential inputs, namely, the two RF signals, into one signal, which is sent to the band-pass filter54a. The band-pass filter54apasses a desired RF frequency therethrough, the resulting RF signal being transmitted from the antenna51into the air.

As conventional techniques, a technique has been proposed wherein the interface between the radio portion and the baseband portion employs8B/10B encoding for communication (PCT-based Unexamined Japanese Patent Publication No. 2006-502679 (paragraph nos. [0008] to [0013], FIG. 1)).

The range of bit rates that can be set for the digital interfaces between the RF-IC60and the PHY70of the mobile phone terminal5has its lower and upper limits determined, respectively, by the transmission band and the specifications of high-speed I/O devices (drivers, receivers, etc.). For example, where the RF signal received by the two branches (two antennas51and52) has a frequency bandwidth of 20 MHz, the bandwidth of each of the two branch outputs after the mixing is about 10 MHz.

Also, provided the resolution of the digital signal after the A/D conversion is 10 bits (inFIG. 14, each signal line labeled “10 bits” represents ten 1-bit signal lines), the bandwidth of one A/D output line equals a bit rate of about 20 Mb/s. Accordingly, the lower-limit bit rate of the digital interface between the driver67and the receiver72is derived as 800 Mb/s (=20 Mb/s×10 bits×2 (two I and Q signals)×2 (two branches)).

The bit rate 800 MB/s is, however, a value reckoned taking account only of the I and Q signals; in practice, a minimum of 1 Gb/s is required where control signals, such as those for error correction by redundant encoding, and other header information are taken into consideration (as for the upper-limit bit rate, a maximum of about 3 Gb/s is currently available, depending on the specifications of high-speed I/O devices).

Conventional lower-speed interfaces between the RF-IC and the PHY used to have a bit rate of about 100 Mb/s. The RF frequency at the antenna section is of the order of several GHz (e.g., 1 GHz) and its frequency band is spaced significantly from that of the interface. Accordingly, conventional terminals are not associated with the problem that the transmission quality degrades due to noticeable interference.

In the latest mobile phone terminal5, on the other hand, the digital interface between the RF-IC60and the PHY70has an even higher bit rate because of multiplexing and increased rate per signal line, as stated above.

Consequently, the frequency band of the signal transferred through the digital interface approaches the RF frequency band at the antenna section50, and thus a problem arises in that noise produced at the digital interface leaks into the antenna section50, causing such an interference as to degrade the transmission quality.

FIG. 15is a conceptual diagram illustrating interference between the digital interface and the antenna section50. The figure shows the manner of how noise produced at the digital interface leaks to the antenna section50through a certain isolation and enters the RF-IC60via an input terminal Pin for the RF signal.

Noise is thought to reach the antenna section50mainly through the air, GND (ground) or power supply, and electromagnetic waves generated at the digital interface travel through the air, GND or power supply to the antenna section50. If such a phenomenon occurs, the noise affects the RF frequency and the noise-containing RF signal enters the RF-IC60and is processed, causing degradation of the transmission quality.

The term “isolation” represents an element that causes a change in the amount of interference (the amount of noise leak) and is an index indicating to what extent the interference is reduced. For example, where the signal output from the output terminal of a certain circuit fluctuates by 1 V and if the isolation between the input and output terminals of the circuit is −60 dB, the signal input to the input terminal fluctuates by 1 mV due to the interference. (When converted to antilogarithm, −60 dB equals 10−60/20=0.001, and therefore, a fluctuation corresponding to 1/1000 of 1 V appears at the input terminal. Namely, 1 V×0.001=1 mV.)

Similarly, if the isolation is −80 dB, the signal input to the input terminal fluctuates by 0.1 mV. (When converted to antilogarithm, −80 dB equals 10−80/20=0.0001, and therefore, 1 V×0.0001=0.1 mV.) If the isolation is −100 dB, the signal input to the input terminal fluctuates by 0.01 mV. (When converted to antilogarithm, −100 dB equals 10−100/200=0.00001, and therefore, 1 V×0.00001=0.01 mV.)

Interference occurs to a certain extent, and the amount of interference varies also in accordance with the value of the isolation as mentioned above. (Under the same environmental conditions, the smaller the value of the isolation, the smaller the amount of interference becomes.)

FIG. 16represents frequency spectra of signals traveling through the digital interface, wherein the vertical axis indicates signal strength (mVrms) and the horizontal axis indicates frequency (MHz). The figure represents simulation results obtained with NRZ (non-return to zero) signals transferred through the digital interface between the driver67and the receiver72.

Spectrum g1represents the strength of a signal traveling through the digital interface at a bit rate of 1 Gb/s, and spectrum g2represents the strength of a signal traveling through the digital interface at a bit rate of 1.5 Gb/s.

Where the isolation between the digital interface and the input terminal Pin is −120 dB, the strength of the signal at the digital interface is, in the case of the spectrum g1, equal to 8.6 mVrms at the RF frequency 1.5 GHz, and therefore, noise leaking from the digital interface into the input terminal Pin is equal to 8.6 nVrms (=8.6 mVrms×0.000001).

Usually, the amplitude of the RF signal at the input terminal Pin has a small value of about 1 nV, and when the bit rate of the digital interface is 1 Gb/s as in the spectrum g1, the noise has an amplitude greater than that of the signal (1 nV<8.6 nV). Consequently, the isolation value −120 dB is not small enough, and the isolation needs to be lowered further.

To set the isolation to a desired value, design and implementation may be modified so that the amount of interference may fall within an allowable range (e.g., a multilayer substrate is used to increase the thickness of the GND pattern). This technique, however, leads to increase in cost.

On the other hand, when the bit rate of the digital interface is 1.5 Gb/s as in the spectrum g2, the signal strength at the digital interface is equal to 0.2 mVrms at the RF frequency 1.5 GHz, and therefore, noise leaking from the digital interface into the input terminal Pin is equal to 0.2 nVrms (=0.2 mVrms×0.000001). In this case, the amplitude of the signal is greater than that of the noise (0.2 nV<1 nV).

Accordingly, where the isolation is −120 dB, the amount of noise leak can be reduced by raising the bit rate of the digital interface to 1.5 Gb/s. This holds true, however, only with respect to the RF frequency 1.5 GHz. The RF frequency varies depending on the wireless communication standard and the country where the terminal is used. In practice, therefore, a specific frequency cannot be set, and it is not possible to restrict the amount of noise leak to a fixed level or lower with respect to various RF frequencies.

For example, inFIG. 16, the relationship of signal strength between the spectra g1and g2is reversed at the RF frequency 2 GHz, compared with the relationship at the RF frequency 1.5 GHz. This reveals that for the same isolation (=−120 dB) and at the RF frequency 2 GHz, the amount of noise leak is greater when the bit rate of the digital interface is 1.5 Gb/s (spectrum g2) than when the bit rate of the digital interface is 1 Gb/s (spectrum g1).

In the case of lower RF frequencies represented inFIG. 16, the signal strength at the digital interface is high irrespective of at what bit rate the NRZ signal may be transferred, under the condition that the bit rate of the digital interface is at or above 1 Gb/s, for example. With respect to low RF frequencies, therefore, significant noise is produced at all times.

Thus, with increase in the bit rate of the digital interface between the RF-IC and the PHY, the extent to which the digital interface interferes with the antenna section50increases. Since the amount of noise leak varies depending on the RF frequency, however, the interference cannot be effectively restrained by merely setting the bit rate of the digital interface to a specific value.

Future RF-ICs are required to deal with various RF frequencies on a single chip, and thus it is difficult to restrain noise over the entire RF frequency range with the bit rate between the RF-IC and the PHY fixed.

SUMMARY OF THE INVENTION

The present invention was created in view of the above circumstances, and an object thereof is to provide a wireless communication device capable of adaptively setting the bit rate of a digital interface between RF-IC and PHY to thereby restrain interference and improve transmission quality.

To achieve the object, there is provided a wireless communication device for performing wireless communication. The wireless communication device comprises an antenna section for transmitting and receiving a radio signal, a wireless controller for converting the receive radio signal to a receive baseband signal and converting a transmit baseband signal to the radio signal, the wireless controller including a wireless communication interface for controlling transfer of the receive baseband signal converted from the receive radio signal and reception of the transmit baseband signal, and a baseband controller for processing the transmit baseband signal and the receive baseband signal, the baseband controller including a baseband communication interface connected to the wireless communication interface by a communication line, for controlling transfer/reception of the transmit and receive baseband signals, a memory, and a logic circuit for variably setting a bit rate of the communication line, wherein the memory stores applicable bit rates for the communication line in association with respective different radio frequencies of the receive radio signal, and the logic circuit reads, from the memory, a bit rate corresponding to the frequency of the receive radio signal and sets the read bit rate as a transfer rate between the wireless communication interface and the baseband communication interface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like reference numerals refer to like elements throughout.FIG. 1illustrates the principle of a wireless communication device. The wireless communication device1comprises an antenna section10, a wireless controller20(hereinafter RF-IC20), and a baseband controller30(hereinafter PHY30). The RF-IC20and the PHY30are interconnected by a communication line40.

The antenna section10transmits and receives RF signals through antennas. The RF-IC20includes a wireless communication interface (I/F)2. The wireless communication interface2controls transfer of a baseband signal (receive baseband signal) converted from the RF signal to the PHY30and also controls reception of a baseband signal (transmit baseband signal) from the PHY30.

The PHY30includes a baseband communication interface3, a logic circuit31, and a memory32. The baseband communication interface3controls transfer of the baseband signal received from the logic circuit31to the RF-IC20and also controls reception of the baseband signal from the RF-IC20. The logic circuit31performs a process of generating and receiving baseband signals and also variably sets the bit rate of the communication line40.

When a signal is transferred at high speeds through the communication line40, noise is produced around the communication line40interconnecting the wireless communication interface2and the baseband communication interface3and interferes with the antenna section10as well as with the junction between the antenna section10and the RF-IC20.

The expression “around the communication line40” signifies not only a region surrounding the communication line40itself, which is a signal line interconnecting the wireless communication interface2and the baseband communication interface3, but also a region surrounding the circuitry of the wireless communication interface2and a region surrounding the circuitry of the baseband communication interface3.

To restrain such interference, the memory32stores a table showing a plurality of different bit rates for the communication line40in association with different RF frequencies of the RF signal received by the antenna section10in such a manner that the RF frequencies are associated with their respective bit rates at which the amount of noise leak is minimized.

When notified of a receive RF frequency to be received (base station notifies in advance the device1of the RF frequency to be used), the logic circuit31reads, from the memory32, an applicable bit rate (optimum bit rate) which corresponds to the receive RF frequency and at which the amount of noise leak is minimized, and sets the optimum bit rate in the wireless communication interface2and the baseband communication interface3(e.g., the frequency of the PLL (Phase Locked Loop) in each of the wireless communication interface2and the baseband communication interface3is set to the optimum bit rate).

The wireless communication interface2and the baseband communication interface3carry out signal transfer via the communication line40at the optimum bit rate set in this manner. Thus, the bit rate of the communication line40interconnecting the wireless controller20and the baseband controller30is adaptively set in accordance with the receive RF frequency, thereby restraining the interference and improving the transmission quality.

FIG. 2is a flowchart illustrating the manner of how the optimum bit rate is set, wherein Step S1is executed before factory shipment and Steps S2to S5are executed when the wireless communication device is actually used.

S1: A table, which indicates the correspondence between RF frequencies and bit rates at which noise produced from the communication line40at the respective RF frequencies is minimized, is written in the memory32(specific table configuration will be explained later with reference toFIG. 5).

S2: The logic circuit31in the PHY30identifies the receive RF frequency.

S3: The logic circuit31reads, from the memory32, the optimum bit rate of the communication line40that corresponds to the receive RF frequency.

S4: The logic circuit31notifies the wireless communication interface2and the baseband communication interface3of the optimum bit rate.

S5: The wireless communication interface2and the baseband communication interface3(i.e., the RF-IC20and the PHY30) perform signal transfer via the communication line40at the optimum bit rate.

The configuration and operation of the wireless communication device1will be now described.FIGS. 3 and 4are block diagrams of the wireless communication device1. The wireless communication device1comprises the antenna section10, the RF-IC20, and the PHY30and carries out wireless communication according to direct conversion scheme.

The antenna section10includes antennas11and12, a switch13, band-pass filters14a,15b-1and15b-2, and a power amplifier16. The antenna11is used for both transmission and reception, while the antenna12is used for reception only.

The switch13connects the antenna11to the output terminal of the band-pass filter14awhen data is to be transmitted, and connects the antenna11to the input terminal of the band-pass filter15b-1when data is to be received.

The band-pass filter14ais an RF filter for transmission and is connected between the output terminal of the power amplifier16and the switch13. The band-pass filters15b-1and15b-2are each an RF filter for reception. The band-pass filter15b-1is inserted between the switch13and the RF-IC20, and the band-pass filter15b-2is inserted between the antenna12and the RF-IC20.

The wireless communication interface2comprises a wireless communication multiplexer2-1and a wireless communication demultiplexer2-2. The wireless communication multiplexer2-1includes a multiplexer2aand a driver2b, and the wireless communication demultiplexer2-2includes a receiver2cand a demultiplexer2d.

The PHY30comprises the baseband communication interface3, the logic circuit31, and the memory32. The baseband communication interface3includes a baseband communication multiplexer3-1and a baseband communication demultiplexer3-2. The baseband communication multiplexer3-1includes a multiplexer3aand a driver3b, and the baseband communication demultiplexer3-2includes a receiver3cand a demultiplexer3d.

The communication line40comprises a transmitting line41and a receiving line42(the transmitting and receiving lines41and42are both digital interface lines). The driver2bin the wireless communication interface2and the receiver3cin the baseband communication interface3are connected to each other by the receiving line42of the communication line40. The driver3bin the baseband communication interface3and the receiver2cin the wireless communication interface2are connected to each other by the transmitting line41of the communication line40.

The process of receiving an RF signal will be now described. When data is to be received, the switch13switches to a receive side (the antenna11is connected to the input terminal of the band-pass filter15b-1). The RF signal received by the antennas11and12is passed through the band-pass filters15b-1and15b-2to extract a desired RF frequency and then sent to the RF-IC20.

The RF signal output from the band-pass filter15b-1is supplied to the amplifier21b-1in the RF-IC20, which amplifier provides differential outputs to the mixers23b-1and23b-2. The RF signal output from the band-pass filter15b-2is supplied to the amplifier21b-2in the RF-IC20, and the amplifier21b-2provides differential outputs to the mixers23b-3and23b-4.

The synthesizer27outputs in-phase (I) local signals I(+) and I(−) having the same frequency as the RF frequency (I(+) and I(−) are opposite in phase), and also outputs quadrature (Q) local signals Q(+) and Q(−) (Q(+) and Q(−) are opposite in phase) with the same frequency.

The mixer23b-1mixes the RF signal (+) output from the amplifier21b-1with the local signal I(+) output from the synthesizer27, to generate a baseband signal. Also, the mixer23b-1mixes the RF signal (−) output from the amplifier21b-1with the local signal I(−) output from the synthesizer27, to generate a baseband signal.

On the other hand, the mixer23b-2mixes the RF signal (+) output from the amplifier21b-1with the local signal Q(+) output from the synthesizer27, to generate a baseband signal. Also, the mixer23b-2mixes the RF signal (−) output from the amplifier21b-1with the local signal Q(−) output from the synthesizer27, to generate a baseband signal. The mixers23b-3and23b-4carry out identical processes.

The analog baseband signals output from the mixers23b-1to23b-4are input to the low-pass filters24b-1to24b-4for filtering, respectively, and the filtered baseband signals are supplied to the A/D converters25b-1to25b-4, respectively.

The low-pass filters24b-1to24b-4preceding the respective A/D converters25b-1to25b-4are anti-aliasing filters for passing only signal frequencies up to ½ of the sampling frequency before the analog signals are converted to digital signals, in order to prevent the occurrence of aliasing (folding noise-induced distortion).

The A/D converters25b-1to25b-4carry out analog/digital conversion to obtain digital baseband signals, which are then filtered by the respective low-pass filters26b-1to26b-4.

The multiplexer2amultiplexes the received baseband signals and outputs the multiplexed signals to the driver2b. The driver2bsends the digital baseband signals to the PHY30through the receiving line42.

In the PHY30, the receiver3creceives the digital baseband signals and outputs the received signals to the demultiplexer3d. The demultiplexer3ddemultiplexes the baseband signals into the number of signals equal to that before the multiplexing and sends the demultiplexed signals to the logic circuit31, where a predetermined process is performed on the received baseband signals.

The process of transmitting an RF signal will be now described. When transmitting data, the switch13switches to a transmit side (the antenna11is connected to the output terminal of the band-pass filter14a). The logic circuit31in the PHY30generates and outputs digital baseband signals, and the multiplexer3amultiplexes the received baseband signals. The driver3bsends the multiplexed baseband signals to the RF-IC20through the transmitting line41.

In the RF-IC20, the receiver2creceives the multiplexed baseband signals and outputs the received signals to the demultiplexer2d. The demultiplexer2ddemultiplexes the baseband signals into the number of signals equal to that before the multiplexing, and outputs the demultiplexed signals to the D/A converters25a-1and25a-2.

The D/A converters25a-1and25a-2each subject the corresponding baseband signal to digital/analog conversion, to generate two analog baseband signals. The analog baseband signals are then filtered by the low-pass filters24a-1and24a-2.

The mixer23a-1mixes one of the baseband signals output from the low-pass filter24a-1with the local signal I(+) output from the synthesizer27, to generate an RF signal. Also, the mixer23a-1mixes the other baseband signal output from the low-pass filter24a-1with the local signal I(−) output from the synthesizer27, to generate an RF signal.

On the other hand, the mixer23a-2mixes one of the baseband signals output from the low-pass filter24a-2with the local signal Q(+) output from the synthesizer27, to generate an RF signal. Also, the mixer23a-2mixes the other baseband signal output from the low-pass filter24a-2with the local signal Q(−) output from the synthesizer27, to generate an RF signal.

The adder22adds together the two signals output from the mixer23a-1and respectively mixed with the local signals I(+) and I(−), and also adds together the two signals output from the mixer23a-2and respectively mixed with the local signals Q(+) and Q(−), to generate I and Q RF signals.

The amplifier21acombines its differential inputs, namely, the two RF signals, into one signal, which is sent to the band-pass filter14a. The band-pass filter14apasses a desired RF frequency therethrough, the resulting RF signal being transmitted from the antenna11into the air.

The table registered in the memory32will be now described with reference toFIG. 5. The table T1includes columns labeled RF frequency and digital interface bit rate. With respect to various RF frequencies to be received, bit rates for the receiving line42are registered at which noise produced around the receiving line42at the respective RF frequencies can be minimized (the amount of noise leak that interferes with the antenna section10can be minimized).

The values registered in the table T1bear a relationship such that an integer multiple of each bit rate falls within the corresponding range of RF frequencies. Specifically, in the case of group G1of bit rates ranging from 0.50 Gb/s to 1.90 Gb/s as indicated in the table T1, the bit rate values “0.50” to “1.90” themselves fall within the respective ranges of RF frequencies (e.g., the bit rate value “0.50” (0.50 Gb/s) times “1” is “0.50”, and the value “0.50” falls within the RF frequency range from 0.45 GHz to 0.55 GHz).

Also, in the case of group G2of bit rates ranging from 1.00 Gb/s to 1.95 Gb/s, the twofold values of the bit rates 1.00 Gb/s to 1.95 Gb/s fall within the respective ranges of RF frequencies (e.g., the bit rate value “1.00” (1.00 Gb/s) times “2” is “2.00”, and the value “2.00” falls within the RF frequency range from 1.95 GHz to 2.05 GHz).

Further, with respect to group G3of bit rates ranging from 1.00 Gb/s to 1.80 Gb/s, the fourfold values of the bit rates 1.00 Gb/s to 1.80 Gb/s fall within the respective ranges of RF frequencies (e.g., the bit rate value “1.00” (1.00 Gb/s) times “4” is “4.00”, and the value “4.00” falls within the RF frequency range from 3.95 GHz to 4.10 GHz).

In this manner, the values registered in the table T1are in the relationship such that integer multiples of the bit rates fall under the respective ranges of RF frequencies, and therefore, when the table is created, the values obtained by dividing the receive RF frequencies by the respective integers have only to be registered as the bit rates. Also, as seen from the illustrated table T1, the bit rates to be set may be restricted to those not higher than 3 Gb/s in conformity to the existing digital interface standards.

The process of setting the optimum bit rate will be now described with reference toFIGS. 3 and 4. When notified of the receive RF frequency that the device is to receive, the logic circuit31reads, from the table T1stored in the memory32, a bit rate (optimum bit rate) corresponding to the receive RF frequency.

The read bit rate is set basically in the following manner. For the wireless communication interface2, the optimum bit rate is set with respect to the multiplexer2aand the demultiplexer2d, and for the baseband communication interface3, the optimum bit rate is set with respect to the multiplexer3aand the demultiplexer3d.

Noise produced around the receiving line42of the communication line40strongly interferes with the receiving system of the antenna section10, as stated above with reference toFIG. 16. Accordingly, setting the transfer bit rate of the receiving line42to an optimum bit rate in accordance with the receive RF frequency is effective in restraining such interference.

In the case of the transmitting system of the antenna section10, on the other hand, the transmit power is high, and therefore, it is unlikely that noise, if produced to a certain degree around the transmitting line41and leaks into the junction of the transmitting system between the antenna section10and the RF-IC20, causes such an interference as to substantially lower the transmission quality.

Accordingly, the bit rate selected for the receiving line42need not necessarily be set with respect to the transmitting line41. For the transmitting line41, a fixed lower-limit bit rate calculated from the transmission band may be set in advance, and only the bit rate of the receiving line42may be variably set.

Thus, where wireless communication is performed according to TDD (Time Division Duplex: a communication scheme wherein time is allocated separately to transmission and reception; the antenna section10is configured to carry out TDD communication), data transmission is not executed during data reception, and therefore, the fixed bit rate is set with respect to the transmitting line41, as stated above, while the bit rate of the receiving line42is variably set in accordance with the receive RF frequency.

During the data reception, the RF-IC20transfers data to the PHY30via the receiving line42at the optimum bit rate. Accordingly, noise leak from around the receiving line42is restrained, and also since no data transmission is executed during the data reception, no noise leaks from the transmitting line41.

On the other hand, during the data transmission, data reception is stopped, and therefore, no noise leaks from the receiving line42. Although the RF-IC20and the PHY30communicate via the transmitting line41at the fixed bit rate, degradation of the transmission quality due to noise leak does not occur because the transmit power of the transmitting system of the antenna section10is high.

Also in the case of performing TDD communication, a bit rate corresponding to the RF frequency may be set with respect to both the transmitting and receiving lines41and42. Further, where the device is configured so as to carry out communication other than TDD communication, a bit rate corresponding to the RF frequency may be set for both the transmitting and receiving lines41and42, and if noise produced around the transmitting line41causes only a low level of interference, a fixed bit rate may be set with respect to the transmitting line41.

Bit rate setting according to another embodiment of the invention will be now described.FIG. 6illustrates the configuration of a wireless communication device. The wireless communication device1acomprises the antenna section10, an RF-IC20a, and a PHY30a. The RF-IC20aand the PHY30aare interconnected by the communication line40.

The antenna section10transmits and receives RF signals through antennas. The RF-IC20aincludes a signal receiver/processor20a-2, the wireless communication interface2, an amplitude detector28, and a controller29.

The signal receiver/processor20a-2performs frequency conversion as well as A/D conversion on the received RF signal to obtain a baseband signal. The wireless communication interface2controls transfer of the baseband signal converted from the RF signal to the PHY30aand also controls reception of a baseband signal from the PHY30a.

The controller29carries out overall control of the elements in the RF-IC20a. For example, the controller29sets communication frequencies for the individual elements in the RF-IC20a, generates a dummy signal, and variably sets the bit rate of the communication line40.

The PHY30aincludes the baseband communication interface3and the logic circuit31. The baseband communication interface3controls transfer of the baseband signal received from the logic circuit31to the RF-IC20aand also controls reception of the baseband signal from the RF-IC20a. The logic circuit31performs the process of generating and receiving RF signals.

At the startup of the device, the controller29outputs a dummy signal at a certain bit rate to be transferred along the communication line40via the wireless communication interface2. At this time, since the dummy signal travels along the communication line40, noise is produced around the communication line40. The noise thus produced leaks through the air, GND, power supply or the like to the input terminal Pin of the RF-IC20ato which the RF signal from the antenna section10is input, and enters the signal receiver/processor20a-2.

The amplitude detector28detects, on the output side of the signal receiver/processor20a-2, the amplitude (power) indicative of the strength of the interference caused by noise produced around the communication line40. The controller29determines whether or not the detected amplitude is greater than a prescribed value set in advance and, if the prescribed value is exceeded, outputs again the dummy signal with the bit rate changed.

If, as a result of the above control, an amplitude not greater than the prescribed value is detected, a bit rate identical with that of the dummy signal at which the detected amplitude was obtained is set in the wireless communication interface2and the baseband communication interface3.

FIGS. 7 and 8are block diagrams of the wireless communication device1a. The data transmission and reception processes are identical with those explained above with reference toFIGS. 3 and 4; therefore, description of the processes is omitted and only the configuration of the device1awill be explained. The antenna section10comprises the antennas11and12, the switch13, the band-pass filters14a,15b-1and15b-2, and the power amplifier16. The RF-IC20acomprises a signal transmitter/processor20a-1, the signal receiver/processor20a-2, the wireless communication interface2, the synthesizer27, the amplitude detector28, and the controller29.

The signal transmitter/processor20a-lincludes the amplifier21a, the adder22, the mixers23a-1and23a-2, the low-pass filters24a-1and24a-2, the D/A converters25a-1and25a-2, and the low-pass filters26a-1and26a-2.

The signal receiver/processor20a-2includes the amplifiers21b-1and21b-2, the mixers23b-1to23b-4, the low-pass filters24b-1to24b-4, the A/D converters25b-1to25b-4, and the low-pass filters26b-1to26b-4.

The wireless communication interface2comprises the wireless communication multiplexer2-1and the wireless communication demultiplexer2-2. The wireless communication multiplexer2-1includes the multiplexer2aand the driver2b, and the wireless communication demultiplexer2-2includes the receiver2cand the demultiplexer2d.

The PHY30acomprises the baseband communication interface3and the logic circuit31. The baseband communication interface3includes the baseband communication multiplexer3-1and the baseband communication demultiplexer3-2. The baseband communication multiplexer3-1includes the multiplexer3aand the driver3b, and the baseband communication demultiplexer3-2includes the receiver3cand the demultiplexer3d.

The communication line40comprises the transmitting line41and the receiving line42(the transmitting and receiving lines41and42are both digital interface lines). The driver2bin the wireless communication interface2and the receiver3cin the baseband communication interface3are connected to each other by the receiving line42of the communication line40. The driver3bin the baseband communication interface3and the receiver2cin the wireless communication interface2are connected to each other by the transmitting line41of the communication line40.

The following describes in detail the manner of how the optimum bit rate is set in the wireless communication device1a.FIGS. 9 and 10are flowcharts illustrating the optimum bit rate setting process, wherein all steps are executed when the device is actually used.

S11: The logic circuit31identifies the receive RF frequency to be received.

S12: The switch13in the antenna section10is set in a mode in which no RF signal is received. For example, the switch13is set to the transmit side (the antenna11is connected to the output terminal of the band-pass filter14a) or is opened (the antenna11is connected neither to the band-pass filter14anor to the band-pass filter15b-1).

S13: The controller29sets the communication frequency (RF frequency) with respect to the individual filters and the synthesizer27in the RF-IC20a.

S14: The controller29sets the bit rate for the dummy signal to the lower-limit bit rate that can be set with respect to the receiving line42.

S15: The controller29outputs the dummy signal to the four input terminals of the multiplexer2ain the wireless communication interface2. The dummy signal output from the controller29is transferred to the PHY30athrough the multiplexer2a, the driver2b, and the receiving line42.

S16: The amplitude detector28detects, on the output side of the signal receiver/processor20a-2, the amplitude indicative of the strength of the interference caused by noise produced around the receiving line42, and notifies the controller29of the detection result. Specifically, the amplitude detector28detects the amplitudes of the signals output from the respective low-pass filters26b-1to26b-4, then obtains a sum of the detected amplitudes, and notifies the controller29of the obtained sum.

S17: The controller29determines whether or not the detected amplitude (sum) is greater than the prescribed value. If the prescribed value is not exceeded by the detected amplitude, the flow proceeds to Step S18; if the prescribed value is exceeded, the flow proceeds to Step S20.

S18: A bit rate identical with that of the dummy signal at which the amplitude detected in Step S16was obtained is set with respect to the multiplexer2aand the demultiplexer2din the wireless communication interface2as well as the multiplexer3aand the demultiplexer3din the baseband communication interface3.

S19: The wireless communication interface2transfers data to the baseband communication interface3through the communication line40at the thus-set optimum bit rate.

S20: The controller29raises the currently set bit rate α of the dummy signal by ΔM.

S21: The controller29determines whether or not the set bit rate (α+ΔM) assumes a value smaller than or equal to the upper-limit bit rate of the receiving line42. If the set bit rate is lower than or equal to the upper-limit bit rate (α+ΔM≦upper-limit bit rate), the flow returns to Step S15; if the upper-limit bit rate is exceeded (upper-limit bit rate<α+ΔM), the flow proceeds to Step S22.

S22: The controller29notifies the logic circuit31that there is no bit rate that can be set for the receiving line42in order to reduce the noise interference to a desired level, whereupon the logic circuit31generates an alarm.

Thus, when setting the optimum bit rate, the dummy signal is output with its bit rate successively varied from the lower-limit bit rate to the upper-limit bit rate of the receiving line42, and the amplitude indicative of the extent of noise leak from the receiving line42is detected. Then, it is determined whether or not the detected amplitude is greater than the prescribed value, and if a bit rate at which the amplitude does not exceed the prescribed value is detected, this bit rate is set with respect to the receiving line.

According to the aforementioned control procedure, if an amplitude not exceeding the prescribed value is detected in the process of sweeping the bit rate of the dummy signal from the lower-limit bit rate to the upper-limit bit rate, the sweeping is instantly suspended, and a bit rate identical with that of the dummy signal at which the detected amplitude was obtained is set in the wireless communication interface2and the baseband communication interface3.

As an alternative control procedure, all bit rates that can be set for the receiving line42may be swept from the lower-limit bit rate to the upper-limit bit rate, and a plurality of amplitudes which are judged to be smaller than or equal to the prescribed value may be stored in memory. After the sweeping is finished, the smallest value among the stored amplitudes may be extracted.

Then, a bit rate identical with that of the dummy signal at which the smallest value was obtained may be set in the wireless communication interface2and the baseband communication interface3.

The following describes the case where the bit rate setting control of the wireless communication device1ais applied to a superheterodyne (double conversion) type device.FIGS. 11 to 13are block diagrams illustrating such a wireless communication device.

The wireless communication device1a-1comprises the antenna section10, an RF-IC200and the PHY30a, and is of a superheterodyne type in which, when data is transmitted, the baseband signal is first up-converted to IF frequency band and then to RF frequency band, and when data is received, the received RF frequency is first down-converted to the IF frequency band to obtain a baseband signal.

The illustrated blocks are identical with those illustrated inFIG. 7except that the RF-IC200is configured differently from the RF-IC20a. In the following, therefore, the RF-IC200will be explained. The RF-IC200comprises a signal transmitter/processor201, a signal receiver/processor202, the wireless communication interface2, VCOs (Voltage Controlled Oscillators)2g-1and2g-2, the amplitude detector28, and the controller29.

The signal transmitter/processor201additionally includes a mixer2e-1connected between the amplifier21aand the adder22. The signal receiver/processor202additionally includes a mixer2f-1connected between the amplifier21b-1and the mixers23b-1and23b-2, as well as a mixer2f-2connected between the amplifier21b-2and the mixers23b-3and23b-4.

The VCO2g-1outputs local signals f(+) and f(−) for the frequency conversion between RF and IF frequencies. The VCO2g-2outputs I local signals I(+) and I(−) having the same frequency as the IF frequency, and also outputs Q local signals Q(+) and Q(−) of the same frequency. In other respects, the configuration of the RF-IC200is identical with that of the RF-IC20a.

The conversion between RF and IF frequencies will be explained. When an RF signal is received, the mixer2f-1mixes the two RF signals output from the amplifier21b-1with the local signals f(+) and f(−), to generate IF signals. The IF signals are then mixed with the local signals I(+) and I(−) by the mixer23b-1to be converted to baseband signals, and also mixed with the local signals Q(+) and Q(−) by the mixer23b-2to be converted to baseband signals. The mixer2f-2operates in the same manner.

When an RF signal is to be transmitted, the mixer23a-1mixes the baseband signals with the local signals I(+) and I(−) to convert the baseband signals to IF signals, and the mixer23a-2mixes the baseband signals with the local signals Q(+) and Q(−) to convert the baseband signals to IF signals. The IF signals output from the adder22are mixed with the local signals f(+) and f(−) by the mixer2e-1, thus generating an RF signal.

To give concrete values, where the frequency of the RF signal to be received is 4.5 GHz and the frequency of the local signals f(+) and f(−) is 3.5 GHz, for example, the output frequency of the mixers2f-1and2f-2is 1 GHz (=4.5 GHz−3.5 GHz) and the frequency of the local signals I(+), I(−), Q(+) and Q(−) is equal to the output frequency of the mixers2f-1and2f-2, namely, 1 GHz.

The bit rate is set in the same manner as in the wireless communication device1a. Specifically, when the device1a-1is started, the dummy signal is output at a certain bit rate to be transferred over the communication line40, and the amplitude indicative of the strength of the interference induced by noise produced around the receiving line42is detected. Then, it is determined whether or not the detected amplitude is greater than the prescribed value set beforehand, and if it is judged that the amplitude is not greater than the prescribed value, a bit rate identical with that of the dummy signal at which the detected amplitude was obtained is set in the wireless communication interface2and the baseband communication interface3.

In the case of the direct conversion type wireless communication device in which the receive RF frequency is directly converted to baseband signals, noise produced around the receiving line42and leaking into the input terminal Pin interferes with the RF frequency that is to be subjected to the mixing prior to the generation of baseband signals, and thus the RF frequency alone needs to be given attention as a frequency liable to be affected by the interference. Accordingly, the direct conversion type device may have a configuration wherein a table showing the correspondence between RF frequencies and applicable bit rates is prepared so that an optimum bit rate can be selected in accordance with the receive RF frequency, as described above with reference toFIG. 5.

On the other hand, in the superheterodyne type wireless communication device in which baseband signals are obtained after the receive RF frequency is converted to IF frequency, the IF-stage processing is performed prior to the mixing process and the subsequent generation of the baseband signals. Thus, the interference exerts an influence not only on the RF frequency but on the IF frequency and the frequencies (LO frequencies) of the local signals output from the VCOs. In the case of the superheterodyne type device, therefore, an optimum bit rate fails to be set if the RF frequency alone is taken into consideration, unlike the direct conversion type device.

Accordingly, when an optimum bit rate is to be set, the method is employed in which the dummy signal is made to travel through the wireless communication interface2and the receiving line42, and the amplitude influenced by actually occurring noise interference is measured with the bit rate of the dummy signal varied successively, to find a bit rate at which the amplitude remains at or below the allowable level. In this case, since the optimum bit rate is derived with the use of transfer paths through which leakage noise actually passes, noise interference attributable not only to the RF frequency but to the IF and LO frequencies can virtually be taken into account when the optimum bit rate is set, and therefore, the bit rate setting method can be effectively applied to superheterodyne type wireless communication devices. Also, since the optimum bit rate is set with the dummy signal passed through individual devices to actually cause noise interference, it is possible to set the optimum bit rate that may vary from device to device depending on the configuration of packaged elements.

According to the present invention, the bit rate of the communication line interconnecting the wireless controller and the baseband controller is variably set in accordance with the receive radio frequency, whereby the occurrence of interference can be restrained, making it possible to improve the transmission quality.