Title of Invention	RADIO COMMUNICATION APPARATUS
Abstract	A disclosed radio communication apparatus includes an amplifier configured to amplify a signal received via one of multiple channels including a channel where frequency hopping is conducted; a signal strength measurement circuit configured to measure signal strength of the received signal; and a gain value computation unit configured to compute a gain value for the amplifier based on the signal strength measured by the signal strength measurement circuit. The gain value computation unit is configured to use values specific to the respective channels as coefficients of a function to compute the gain value.

Title of Invention

RADIO COMMUNICATION APPARATUS

Abstract

A disclosed radio communication apparatus includes an amplifier configured to amplify a signal received via one of multiple channels including a channel where frequency hopping is conducted; a signal strength measurement circuit configured to measure signal strength of the received signal; and a gain value computation unit configured to compute a gain value for the amplifier based on the signal strength measured by the signal strength measurement circuit. The gain value computation unit is configured to use values specific to the respective channels as coefficients of a function to compute the gain value.

Full Text	DESCRIPTION Title of the Invention RADIO COMMUNICATION APPARATUS Technical Field The present invention relates to a radio communication apparatus for radio communications of signals modulated in MB-OFDM (Multi Band-Orthogonal Frequency Division Multiplexing) scheme. Background Art UWB (Ultra Wide Band) is a radio communication scheme where a wide frequency band in bandwidth of 7.5 GHz ranging from 3.1 GHz to 10.6 GHz is used. A specification for physical layers in the UWB is standardized in IEEE 802.15.3a by IEEE (The Institute of Electrical and Electronic Engineers) working for defining standard specifications. In the physical layer in the UWB, two modulation schemes MB-OFDM (Multi Band-Orthogonal Frequency Division Multiplexing) and DS-UWB (Direct Spread-UWB) are employed. In the MB-OFDM, the whole band ranging from 3.1 GHz to 10.6 GHz is divided into 14 bands (frequency bands). For each of the divided bands, QPSK (Quadrature Phase Shift Keying) is conducted in primary modulation for carrying digital signals in radio waves, and OFDM (Orthogonal Frequency Division Multiplexing) is conducted in secondary modulation for achieving communications tolerant to interference from other radio waves. In the DS-UWB, a lower band from 3.1 GHz to 4.9 GHz and a higher band from 6.2 GHz to 9.7 GHz are used. For signal transmission, the QPSK or BPSK (Binary Phase Shift Keying) is conducted in the primary modulation and CDMA (Code Division Multiple Access) is conducted in the secondary modulation. Also, a direct frequency spread scheme is used in the DS-UWB in the transmission of signals. In the UWB, these modulation schemes are used to reduce transmission power levels. Specifically, the FCC (Federal Communications Commission) specifies that EIRP (Equivalent Isotropically Radiated Power) indicative of regulated transmission power level per 1 MHz in the UWB be less than or equal to -41.25 dBm. This level corresponds to about 0.5 mW of total power, which may be about 1/20 of total power of the PHS (Personal Handy-Phone System). In the MB-OFDM, each of the 14 bands is assigned to a band group including two or three bands. Bands 1-3 are assigned to band group 1, bands 4-6 are assigned to band group 2, bands 7-9 are assigned to band group 3, bands 10-12 are assigned to band group 4, and bands 13-14 are assigned to band group 5. Also, in the MB-OFDM, frequency hopping is used. The frequency hopping is a technique for communications through continuous transition of a communicating band to other bands as illustrated in FIG. 12. Even in cases where an error occurs in communicated data due to noise having occurred in a certain frequency, the continuous transition between communicating bands could correct the error-occurring data by using data communicated in other bands. In the MB-OFDM, patterns for frequency hopping are defined as TFC (Time Frequency Code) as illustrated in FIG. 13. In FIG. 13, TFC 1 is illustrated to have the frequency hopping pattern "BAND 1 → BAND 2 → BAND 3 → BAND 1 → BAND 2 → BAND 3." Also, TFC 5 is illustrated to use only BAND 1 without frequency hopping. If it is not specified in upper layers which channel is used to transmit what data, the band groups are defined depending on regions in countries. On the other hand, TFCs are selected in the sequence specified in the MB-OFDM. In this manner, the band groups and the TFCs are determined, and accordingly channels are determined. In conventional radio communication apparatuses, AGC (Automatic Gain Control) is conducted for suppressing fluctuation of the amplitude of a received electrical signal and converting it into a signal with a constant amplitude. In AGC, gain (amplification degree) is increased for a small amplitude signal based on RSSI (Received Signal Strength Indicator) while gain is decreased for a large amplitude signal. As one implementation of AGC, Japanese Laid- Open Patent Publication 2002-94408 discloses an arrangement including a first attenuator provided between a front-end or a high frequency amplifier and a mixer, a RSSI circuit for generating a RSSI output signal from a received signal, and a second attenuator provided before the RSSI circuit for adjusting an input signal level. In this arrangement, the RSSI output signal is compared to two thresholds. If it is outside of the thresholds, the attenuation amount of the second attenuator and then the attenuation amount of the first attenuator are adjusted to substantially enlarge a dynamic range of input and output in/from the RSSI circuit and prevent saturation of the mixer, the AGC circuit, and other system circuits in strong electric fields without sacrificing modulation performance in weak electric fields. As another implementation of the AGC, Japanese Laid-Open Patent Publication 2005-534252 discloses an arrangement including a RSSI circuit for measuring the RSSI of a received signal, an analog amplifier for amplifying the received signal, an analog-to-digital converter for converting the amplified signal into a digital signal, a digital AGC loop for determining digital gain based on the converted digital signal, and a digital-to-analog converter for setting the digital gain determined by the digital AGC loop in the analog amplifier. In a spectral spread system, this arrangement enables the system to follow a rapid tracking variation while averaging noise. As another implementation of the AGC, Japanese Laid-Open Patent Publication 2006-229739 discloses an arrangement where gain correction is conducted corresponding to individual bands prior to AGC whenever the frequency hopping causes the bands to be switched. As stated above, the TFC "consists of band groups each including several bands, and in some TFCs, the frequency hopping is conducted through transition between the bands. However, signal strength measurement circuits for measuring the strength of received signals, such as the RSSI circuit, may not have uniform measurement performance over the respective bands. For example, even if received signals have the same strength, a strength value for a certain band measured by the signal strength measurement circuit may be higher than a strength value for another band measured by the signal strength measurement circuit. In conventional radio communication apparatuses as disclosed in Japanese Laid-Open Patent Publications 2002-94408 and 2005-534252, AGC operations in consideration of such measurement errors between bands in the signal strength measurement circuit are impossible. In addition, the band switching period for the frequency hopping is specified to be relatively short, such as 312.5 ns, in the MB-OFDM specification. Thus if the MB-OFDM is applied to a conventional radio communication apparatus as disclosed in Japanese Laid- Open Patent Publication 2006-229739, particularly if analog AGC is conducted in such a conventional radio communication apparatus, the AGC operation may not be able to follow the above-stated fast band switching. Disclosure of Invention The present invention addresses the above- mentioned conventional problems. One object of the present invention is provide a radio communication apparatus for enabling the AGC operation to follow the high-speed band switching in consideration of measurement errors between the respective bands in the signal strength measurement circuit. One feature of the present invention relates to a radio communication apparatus including an amplifier configured to amplify a signal received via one of multiple channels including a channel where frequency hopping is conducted; a signal strength measurement circuit configured to measure signal strength of the received signal; and a gain value computation unit configured to compute a gain value for the amplifier based on the signal strength measured by the signal strength measurement circuit, wherein the gain value computation unit is configured to use values specific to the respective channels as coefficients of a function to compute the gain value. According to this feature, the radio communication apparatus achieves AGC operations allowed to follow fast band switching in consideration of measurement errors between different bands in the signal strength measurement circuit in order to compute a gain value by substituting the signal strength into a function with coefficients specific to different channels. For example, the gain value computation unit may use a linear function to compute the gain value. In one embodiment, the radio communication apparatus may include a register complying with a WiMedia MAC-PHY interface specification; and a MAC unit configured to write a value in the register, wherein the MAC unit is configured to write the coefficients in the register prior to writing in the register a value indicative of the channel via which the signal is received, and the gain value computation unit is configured to use the coefficients written in the register as the coefficients of the function to compute the gain value. According to this embodiment, the radio communication apparatus can be easily implemented by a radio communication apparatus complying with the WiMedia MAC-PHY interface specification to write the coefficients in the register via the MAC unit and compute the gain value based on the coefficients. In one embodiment, the MAC unit may be configured to write the coefficients in a range in the register in the WiMedia MAC-PHY interface specification, the range being where a vendor is allowed to assign proprietary coefficients. According to this embodiment, the radio communication apparatus can be implemented to comply with the WiMedia MAC-PHY interface specification. In one embodiment, the radio communication apparatus may include a table storage unit configured to store a table including correspondence between the channels and the coefficients, wherein the MAC unit is configured to write the coefficients in the register based on the table in the table storage unit. According to this embodiment, the radio communication apparatus can modify coefficients for different channels without modification of hardware, firmware and software by changing the table stored in . the table storage unit. In one embodiment, the radio communication apparatus may include an analog-to-digital conversion unit configured to perform analog-to-digital conversion on the received signal, wherein the signal strength measurement circuit is configured to measure signal strength of the received analog signal, and the amplifier is configured to amplify the received digital signal converted by the analog-to-digital conversion unit. According to this embodiment, the radio communication apparatus can improve AGC characteristics if gain control for a narrow bandwidth is needed to measure the signal strength of a received analog signal and amplify the resulting digital signal. In one embodiment, the signal strength measurement circuit may be configured to measure signal strength of the received analog signal, and the amplifier may be configured to amplify the received analog signal. According to this embodiment, the radio communication apparatus can improve AGC characteristics if a received fast signal with a higher S/N (Signal to Noise) ratio is amplified to measure the signal strength of a received analog signal and amplify the received analog signal. In one embodiment, the radio communication apparatus may include a coefficient determination unit configured to determine a coefficient suitable for a frequency band of a channel where the frequency hopping is not conducted as a coefficient of the channel and determine an average value of coefficients suitable for different hopping frequency bands of a channel where the frequency hopping is conducted as a coefficient of the channel. In one embodiment, the radio communication apparatus may include a coefficient determination unit configured to determine a coefficient suitable for a frequency band of a channel where the frequency hopping is not conducted as a coefficient of the channel and determine a coefficient of a channel where the frequency hopping is conducted based on a sample variance suitable for different hopping frequency bands. According to these embodiments, the radio communication apparatus can compute the gain value in consideration of deviations between coefficients for hopping frequency bands in order to determine coefficients for channels where frequency hopping is conducted based on sample variance among the coefficients suitable for the frequency bands. In one embodiment, the coefficient determination unit may be configured to weight individual terms of the sample variance. According to this embodiment, the radio communication apparatus can prevent a gain value unsuitable for a frequency band if a coefficient suitable for a certain frequency band significantly deviates from coefficients suitable for the other frequency bands in hopping frequency bands. In one embodiment, the radio communication apparatus may include a transmission unit configured to transmit a baseband signal in consecutively changed frequency bands; an attenuator configured to attenuate the baseband signal; and an attenuation rate configuration unit configured to set an attenuation rate of the attenuator, wherein the signal strength measurement circuit is configured to measure signal strength of the baseband signal as the received signal, and the coefficient determination unit is configured to determine a coefficient suitable for each of the frequency bands based on the signal strength. According to this embodiment, the radio communication apparatus can determine coefficients for different channels in consideration of measurement errors due to different instances of the signal strength measurement circuit. According to the above-mentioned features of the present invention, a constant current supply type switching regulator can convert an input voltage into a desired output current without the use of any current detecting resistor, which may reduce the number of elements in the switching regulator and alleviate loss otherwise caused by an incoming current to the resistor. Brief Description of Drawings FIG. 1 is a block diagram illustrating a radio communication apparatus according to one embodiment of the present invention; FIG. 2 is a schematic diagram illustrating an assignment of PHY/RF registers in a radio communication apparatus according to one embodiment of the present invention; FIG. 3 is a schematic diagram illustrating an assignment within TXCHAN and RXCHA registers assigned to a PHY/RF register in a radio communication apparatus according to one embodiment of the present invention; FIG. 4 is a block diagram illustrating a reception unit in a baseband unit in a radio communication apparatus according to one embodiment of the present invention; FIG. 5 is a schematic diagram illustrating an assignment within a AGC_PARAM register assigned to a PHY/RF register in a radio communication apparatus according to one embodiment of the present invention; FIG. 6 is a schematic diagram illustrating a computation operation for a gain value in a gain value computation unit in a radio communication apparatus according to one embodiment of the present invention; FIG. 7 is a flowchart of a reception channel configuration operation in a radio communication apparatus according to one embodiment of the present invention; FIG. 8 is a block diagram illustrating a reception unit in a baseband unit in a radio communication apparatus according to another embodiment of the present invention; FIG. 9 is a schematic diagram illustrating a determination operation for a coefficient referred to by a gain value computation unit in a radio communication apparatus according to one embodiment of the present invention; FIG. 10 is a block diagram illustrating a baseband unit in a radio communication apparatus according to another embodiment of the present invention; FIG. 11 is a flowchart illustrating a coefficient configuration operation in a radio communication apparatus according to one embodiment of the present invention; FIG. 12 is a schematic diagram illustrating frequency hopping; and FIG. 13 is a schematic diagram illustrating relationships between bands and TFCs in the MB-OFDM. Description of Embodiments Embodiments of the present invention will be described with reference to the accompanying drawings in detail below. FIG. 1 is a block diagram illustrating a radio communication apparatus according to one embodiment of the present invention. In this embodiment, a radio communication apparatus 1 is coupled to a host controller 2 via a PCI (Peripheral Component Interconnect)-Express bus 3. The host controller 2 includes a main CPU (Central Processing Unit) 10 and a memory 11. The main CPU 10 uses the memory 11 to run an operating system 12 and to execute a device driver 13 on the operating system 12. The device driver 13 communicates data to the radio communication apparatus 1 via the PCI-Express bus 3 and controls the radio communication apparatus 1 by reading and writing values from/in a register in a MAC (Media Access Controller) unit 22 as described below. The radio communication apparatus 1 includes a sub CPU 20, a memory 21, the MAC unit 22 for generating and/or filtering data frames, a PHY (Physical Layer) unit 23 for signal processing such as frequency conversion and an antenna 24. The sub CPU 20 uses the memory 21 to run a real-time operating system 25 and executes firmware 26 for controlling components in the MAC unit 22 on the real-time operating system 25. The sub CPU 20 may configure a register (not illustrated) in the MAC unit 22 and/or communicate data to the host controller 2 in execution of the firmware 26. Also, the sub CPU 20 may read and/or write values from/in a PHY/RF register 41 as described below in the PHY unit 23 via a WiMedia MAC-PHY interface bus 27 in execution of the firmware 26. The MAC unit 22 and the PHY unit 23 may perform operations based on specifications of WiMedia MAC and MB-OFDM. Communications between the MAC unit 22 and the PHY unit 23 may be specified in conformity with the WiMedia MAC-PHY interface specification. Thus, the MAC unit 22 and the PHY unit 23 distributed by different vendors can be connected to each other and used together. In the WiMedia MAC-PHY interface specification, as illustrated in FIG. 2, a range from a base address (reference address) "0x00" to address "0x20" in the PHY/RF register 41 is defined as a range for storing dynamic configurations (dynamic register set) . For example, as illustrated in FIG. 3, a transmitted TFC and a band group are set in a TXCHAN register at address "0x02" while a received TFC and a band group are set in a RXCHAN register at address "0x04". For this reason, the sub CPU 20 for executing the firmware 26 configures a transmission channel by writing the TFC and the band group in the TXCHAN register via the MAC unit 22 and a reception channel by writing the TFC and the band group in the RXCHAN register via the MAC unit 22. Also in the WiMedia MAC-PHY interface specification, a range from address "0x20" to address "0x80" in the PHY-RF register 41 is defined as a range for storing static configurations (static register set) such as communication speed and the number of configurable signal transmission levels supported by the radio communication apparatus 1. Also in the WiMedia MAC-PHY interface specification, a range from address "0x80" to address "OxFF" in the PHY/RF register 41 is defined as a range for storing configurations specific to vendors (vendor range). In FIG. 1, the MAC unit 22 attaches a MAC header to a data frame to be transmitted to the PHY unit 23, encrypts the MAC header attached data frame and transmits the encrypted data frame to the PHY unit 23 via the WiMedia MAC-PHY interface bus 27. Also, the MAC unit 22 decrypts a received data frame from the PHY unit, analyzes the decrypted data frame and filters or extracts data to be further transmitted to an upper protocol from data obtained from the data frame based on the analysis. The PHY unit 23 includes a RF (Radio Frequency) unit 40, the PHY/RF register 41 and a baseband unit 42, and the baseband unit 42 includes a transmission unit 50 and a reception unit 51. The RF unit 40 performs MB-OFDM modulation on a baseband signal supplied from the transmission unit 50 in the baseband unit 42 to transmit the signal as a radio wave via the antenna 24 over the air. Also, the RF unit 40 demodulates the MB-OFDM modulated signal received via the antenna 24 into a baseband signal and supplies the demodulated baseband signal to the reception unit 51 in the baseband unit 42. The transmission unit 50 in the baseband unit 42 D/A (Digital-to-Analog) converts a digital data frame received from the MAC unit 22 via the WiMedia MAC-PHY interface bus 27 into an analog baseband signal and supplies the converted baseband signal to the RF unit 40. The reception unit 51 in the baseband unit 42 A/D (Analog-to-Digital) converts a baseband signal received from the RF unit 4 0 into a digital data frame and transmits the converted data frame to the MAC unit 22 via the WiMedia MAC-PHY interface bus 27. FIG. 4 shows an exemplary arrangement of the reception unit 51 in the baseband unit 42. The reception unit 51 in the baseband unit 42 includes a RSSI circuit 60, a gain value computation unit 61, an A/D converter 62, an amplifier 63 and a signal processing unit 64. The RSSI circuit 60 measures RSSI as received signal strength of an analog baseband signal supplied from the RF unit 40 and supplies a signal indicative of the measured RSSI to the gain value computation unit 61. Note that the RSSI circuit 60 may serve as a signal strength measurement circuit according to an embodiment of the present invention. The gain value computation unit 61 computes a gain value based on the RSSI indicative of the signal supplied from the RSSI circuit 60 and one or more values configured in the PHY/RF register 41 and supplies a signal indicative of the computed gain value to the amplifier 63. The values set in the PHY/RF register 41 herein means one or more gain control parameters (hereinafter referred to as "AGO_PARAM register") written in a certain address, such as address "OxAO" relative to the base address, within the vendor range in the PHY/RF register 41 in FIG. 2. In the AGC_PARAM register, as illustrated in FIG. 5, a coefficient "gradient" indicative of the gradient of a linear function for finding an input signal from the RSSI is located in upper 4 bits, and a coefficient "intercept" indicative of the intercept of the linear function is located in lower 4 bits. The coefficients "gradient" and "intercept" for different channels are associated with each other in a table stored in the memory 21 in advance. In this manner, the memory 21 may serve as a table storage unit according to the present invention. In this embodiment, it is assumed that the coefficients "gradient" and "intercept" for the channels are predetermined through prior measurement. For example, if no frequency hopping is conducted in a channel, the coefficients "gradient" and "intercept" suitable for a band in that channel is stored in the table. On the other hand, if frequency hopping is conducted in a channel, respective average values of the coefficients "gradient" and "intercept" suitable for individual bands are stored in the table. The sub CPU 20 for executing the firmware 2 6 may set the AGC_PARAM register prior to setting the RXCHAN register in the PHY/RF register 41. In FIG. 4, the gain value computation unit 61 computes a gain value based on corrected RSSI (hereinafter referred to as "cRSSI") through substitution of the RSSI into a linear function with the coefficients "gradient" and "intercept" in the AGC_PARAM register. Specifically, as illustrated in FIG. 6, the gain value computation unit 61 may substitute the RSSI (=a) into the linear function with the coefficients "gradient" and "intercept" in the AGC_PARAM register and substitute the cRSSI (=f(a)), which is an output of the linear function, into a predefined linear function g(x) to compute the gain value g(f(α)) for the amplifier 63. For a signal with uniform strength, for example, if the RSSI measured by the RSSI circuit 60 for a certain band is higher than the RSSI measured by the RSSI circuit 60 for a reference band, a linear function f (x) with the coefficients "gradient" and "intercept" at least one of which is smaller than the coefficients of the linear function f(x) for the reference band is used, and thus the cRSSI (=f'(α) ) obtained through substitution of the RSSI (=α) into f (x) would be smaller than the cRSSI (=f(α)) for the reference band. In other words, the gain value computed by the gain value computation unit 61 becomes g(f (α)) by estimating the RSSI measured by the RSSI circuit 60 to be relatively small, resulting in a gain value larger than the gain value g(f(α)). In FIG. 4, the A/D converter 62 converts an analog signal supplied from the RF unit 40 into a digital signal and supplies the digital signal to the amplifier 63. The amplifier 63 amplifies the digital signal supplied from the A/D converter 62 based on the gain value represented by a signal supplied from the gain value computation unit 61 and supplies the amplified digital signal to the signal processing unit 64. For example, the signal processing unit 64 may perform frequency conversion and/or other operations on the amplified digital signal and transmit the resulting signal as a data frame to the MAC unit 22. Exemplary configuration operations of a reception channel in the radio communication apparatus 1 including the above-stated components are described in detail with reference to FIG. 7. The WiMedia MAC-PHY interface specification specifies that if a channel is changed during communication, a beacon frame with "Channel Change Information Element" (hereinafter referred to as "Channel Change IE") may be transmitted to a communicating opponent apparatus. The "Channel Change IE" may include the next new channel and information such as a time period until transition to the new channel. Upon receiving this beacon frame, the communicating opponent apparatus uses a transmission channel or a reception channel as a new channel based on the information in the Channel Change IE. In this manner, the configuration operations of the received channel is performed in response to activation and/or degradation of communication conditions as well as based on the information in the Channel Change IE transmitted by the communicating opponent apparatus. At step S1, the coefficients "gradient" and "intercept" corresponding to a received channel to be configured are identified by the sub CPU 20 in a table stored in the memory 21. At step S2, the identified coefficients "gradient" and "intercept" are set by the sub CPU 20 in the AGC_PARAM register in the PHY/RF register 41 via the MAC unit 22. At step S3, the received channel, that is, a TFC and a band group, are set by the sub CPU 20 in the RXCHAN register in the PHY/RF register 41 via the MAC unit 22. As a result, when the received channel is switched in the PHY unit 23 at step S4, the PHY unit 23 informs the sub CPU 20 via the MAC unit 22 that the received channel has been switched at step S5. In this manner, according to this embodiment of the present invention, the radio communication apparatus 1 computes gain values through substitution of the RSSI into a function with coefficients specific to respective channels. As a result, whenever a band is switched in a channel where frequency hopping is conducted, the radio communication apparatus 1 does not have to change the gain value and can perform AGC operations to enable fast band switching to be followed in consideration of measurement errors between bands in the signal strength measurement circuit. In this embodiment, the amplifier 63 amplifies a digital signal supplied from the A/D converter 62. As illustrated in FIG. 8, in another embodiment, the amplifier 63 may amplify a received analog signal and supply the amplified signal to the A/D converter 62. In this case, the signal strength is measured from the received analog signal, and the received analog signal is amplified. Thus, AGC characteristics can be improved in amplification of the received signal if the signal is fast and has a high S/N (Signal to Noise) ratio. Also, in this embodiment, the gain value computation unit 61 uses a certain linear function to compute the cRRSI from the RSSI. In another embodiment, the gain value computation unit 61 may use another linear function corresponding to frequency characteristics of the RSSI circuit 60 to compute the cRSSI from the RSSI. Also, in this embodiment, if frequency hopping is conducted in channels, the respective average values of the coefficients "gradient" and "intercept" suitable for individual bands are stored in a table in the memory 21. In another embodiment, as illustrated in FIG. 9, values of the coefficients "gradient" and "intercept" that are suitable for the individual bands and have the smallest sample variance between the coefficients in consideration of deviations for the individual coefficients suitable for the hopping bands may be stored in the table in the memory 21. For example, assuming that coefficients suitable for individual bands are C1, C2 and C3, the coefficient Ca for causing the sample variance V in formula (1) as presented below to be minimized is determined as the coefficient for the channel of interest. In another embodiment, the individual terms (C1-Ca)2, (C2-Ca)2 and (C3-Ca)2 in formula (1) may be weighted, and the coefficient Ca for causing the weighted sample variance V to be minimized may be stored in the table in the memory 21. For example, it is assumed that coefficients suitable for individual bands are C1, C2 and C3. If the gain values are set to be larger in the order of C3, C2 and C1, the coefficient Ca for causing the sample variance V in formula (2) as presented below to be minimized may be determined as the coefficient for the channel of interest. According to this embodiment, if the coefficient suitable for a certain one of hopping bands is further away from the coefficients suitable for the other bands, it is possible to prevent the gain value for that band from being set at an inappropriate value. In this embodiment, the weights 1, 2 and 3 are used in formula (2), but any other weights can be used in formula (2). Also in the above-stated embodiments, the coefficients "gradient" and "intercept" for different channels are predefined through prior measurement. In another embodiment, as illustrated in FIG. 10, an attenuator 52 may be provided for attenuating a baseband signal supplied from the transmission unit 50 in the baseband unit 42 and supplying the attenuated signal to the reception unit 51, and the coefficients "gradient" and "intercept" for different channels may be stored in the table in the memory 21. For example, as illustrated in FIG. 11, upon receiving a request from the host controller 2, the sub CPU 20 selects a band to be measured via the MAC unit 22 at step S11. At step S12, the sub CPU 20 causes the attenuator 52 to attenuate a signal transmitted from the transmission unit 50 such that the strength of the signal received at the reception unit 51 can meet predefined criteria. At step S13, the sub CPU 20 obtains individual RSSIs measured by the RSSI circuit 60. At step S14, steps S12-S13 are repeated through variations of the reference level and attenuation rate for the attenuator 52 until a number of samples corresponding to the number of coefficients of a linear function for correcting the measured RSSIs into cRSSIs can be obtained. For example, if the gain value computation unit 61 uses a linear function to correct the RSSI into the cRSSI, steps S12-S13 may be executed twice. Upon obtaining the corresponding number of samples, at step S15, the sub CPU 20 computes coefficients suitable for the band of interest based on the reference levels and the RSSIs. At step S16, the sub CPU 20 determines whether coefficients suitable for all the bands have been derived. If it is determined that the suitable coefficients have not been derived for all the bands, the process control returns to step Sll. On the other hand, if it is determined that suitable coefficients have been derived for all the bands, the sub CPU 20 determines coefficients for individual channels based on the derived band coefficients at step S17 and stores the determined channel coefficients in the memory 21. In this manner, the sub CPU 20 may serve as a coefficient determination unit according to the present invention. As stated above, the radio communication apparatus according to the present invention may be useful in radio communication systems complying with the MB-OFDM scheme. In particular, if the signal strength measurement circuit has different characteristics for individual bands, the radio communication apparatus may be advantageous. The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention. The present application is based on Japanese Priority Patent Application No. 2008-028922 filed on February 8, 2008, the entire contents of which are hereby incorporated herein by reference. CLAIMS Claim 1. A radio communication apparatus comprising, an amplifier configured to amplify a signal received via one of multiple channels including a channel where frequency hopping is conducted; a signal strength measurement circuit configured to measure signal strength of the received signal; and a gain value computation unit configured to compute a gain value for the amplifier based on the signal strength measured by the signal strength measurement circuit, wherein the gain value computation unit is configured to use values specific to the respective channels as coefficients of a function to compute the gain value. Claim 2. The radio communication apparatus as claimed in claim 1, wherein the gain value computation unit is configured to use a linear function to compute the gain value. Claim 3. The radio communication apparatus as claimed in claim 1, further comprising: a register complying with a WiMedia MAC-PHY interface specification; and a MAC unit configured to write a value in the register, wherein the MAC unit is configured to write the coefficients in the register prior to writing in the register a value indicative of the channel via which the signal is received, and the gain value computation unit is configured to use the coefficients written in the register as the coefficients of the function to compute the gain value. Claim 4. The radio communication apparatus as claimed in claim 3, wherein the MAC unit is configured to write the coefficients in a range in the register in the WiMedia MAC-PHY interface specification, the range being where a vendor is allowed to assign proprietary values. Claim 5. The radio communication apparatus as claimed in claim 3, further comprising: a table storage unit configured to store a table including correspondence between the channels and the coefficients, wherein the MAC unit is configured to write the coefficients in the register based on the table in the table storage unit. Claim 6. The radio communication apparatus as claimed in claim 1, further comprising: an analog-to-digital conversion unit configured to perform analog-to-digital conversion on the received signal, wherein the signal strength measurement circuit is configured to measure signal strength of the received analog signal, and the amplifier is configured to amplify the received digital signal converted by the analog-to- digital conversion unit. Claim 7. The radio communication apparatus as claimed in claim 1, wherein the signal strength measurement circuit is configured to measure signal strength of the received analog signal, and the amplifier is configured to amplify the received analog signal. Claim 8. The radio communication apparatus as claimed in claim 1, further comprising: a coefficient determination unit configured to determine a coefficient suitable for a frequency band of a channel where the frequency hopping is not conducted as a coefficient of the channel and determine an average value of coefficients suitable for different hopping frequency bands of a channel where the frequency hopping is conducted as coefficients of the channel. Claim 9. The radio communication apparatus as claimed in claim 1, further comprising: a coefficient determination unit configured to determine a coefficient suitable for a frequency band of a channel where the frequency hopping is not conducted as a coefficient of the channel and determine a coefficient of a channel where the frequency hopping is conducted based on a sample variance suitable for different hopping frequency bands. Claim 10. The radio communication apparatus as claimed in claim 9, wherein the coefficient determination unit is configured to weight individual terms of the sample variance. Claim 11. The radio communication apparatus as claimed in claim 8, further comprising: a transmission unit configured to transmit a baseband signal in consecutively changed frequency bands; an attenuator configured to attenuate the baseband signal; and an attenuation rate configuration unit configured to set an attenuation rate of the attenuator, wherein the signal strength measurement circuit is configured to measure signal strength of the baseband signal as the received signal, and the coefficient determination unit is configured to determine a coefficient suitable for each of the frequency bands based on the signal strength. ^ A disclosed radio communication apparatus includes an amplifier configured to amplify a signal received via one of multiple channels including a channel where frequency hopping is conducted; a signal strength measurement circuit configured to measure signal strength of the received signal; and a gain value computation unit configured to compute a gain value for the amplifier based on the signal strength measured by the signal strength measurement circuit. The gain value computation unit is configured to use values specific to the respective channels as coefficients of a function to compute the gain value.

Full Text

DESCRIPTION
Title of the Invention
RADIO COMMUNICATION APPARATUS
Technical Field
The present invention relates to a radio
communication apparatus for radio communications of
signals modulated in MB-OFDM (Multi Band-Orthogonal
Frequency Division Multiplexing) scheme.
Background Art
UWB (Ultra Wide Band) is a radio communication
scheme where a wide frequency band in bandwidth of 7.5
GHz ranging from 3.1 GHz to 10.6 GHz is used. A
specification for physical layers in the UWB is
standardized in IEEE 802.15.3a by IEEE (The Institute of
Electrical and Electronic Engineers) working for
defining standard specifications.
In the physical layer in the UWB, two
modulation schemes MB-OFDM (Multi Band-Orthogonal
Frequency Division Multiplexing) and DS-UWB (Direct
Spread-UWB) are employed.
In the MB-OFDM, the whole band ranging from
3.1 GHz to 10.6 GHz is divided into 14 bands (frequency

bands). For each of the divided bands, QPSK (Quadrature
Phase Shift Keying) is conducted in primary modulation
for carrying digital signals in radio waves, and OFDM
(Orthogonal Frequency Division Multiplexing) is
conducted in secondary modulation for achieving
communications tolerant to interference from other radio
waves.
In the DS-UWB, a lower band from 3.1 GHz to
4.9 GHz and a higher band from 6.2 GHz to 9.7 GHz are
used. For signal transmission, the QPSK or BPSK (Binary
Phase Shift Keying) is conducted in the primary
modulation and CDMA (Code Division Multiple Access) is
conducted in the secondary modulation. Also, a direct
frequency spread scheme is used in the DS-UWB in the
transmission of signals.
In the UWB, these modulation schemes are used
to reduce transmission power levels. Specifically, the
FCC (Federal Communications Commission) specifies that
EIRP (Equivalent Isotropically Radiated Power)
indicative of regulated transmission power level per 1
MHz in the UWB be less than or equal to -41.25 dBm.
This level corresponds to about 0.5 mW of total power,
which may be about 1/20 of total power of the PHS
(Personal Handy-Phone System).
In the MB-OFDM, each of the 14 bands is

assigned to a band group including two or three bands.
Bands 1-3 are assigned to band group 1, bands 4-6 are
assigned to band group 2, bands 7-9 are assigned to band
group 3, bands 10-12 are assigned to band group 4, and
bands 13-14 are assigned to band group 5.
Also, in the MB-OFDM, frequency hopping is
used. The frequency hopping is a technique for
communications through continuous transition of a
communicating band to other bands as illustrated in FIG.
12.
Even in cases where an error occurs in
communicated data due to noise having occurred in a
certain frequency, the continuous transition between
communicating bands could correct the error-occurring
data by using data communicated in other bands.
In the MB-OFDM, patterns for frequency hopping
are defined as TFC (Time Frequency Code) as illustrated
in FIG. 13. In FIG. 13, TFC 1 is illustrated to have
the frequency hopping pattern "BAND 1 → BAND 2 → BAND 3
→ BAND 1 → BAND 2 → BAND 3." Also, TFC 5 is
illustrated to use only BAND 1 without frequency hopping.
If it is not specified in upper layers which
channel is used to transmit what data, the band groups
are defined depending on regions in countries. On the
other hand, TFCs are selected in the sequence specified

in the MB-OFDM. In this manner, the band groups and the
TFCs are determined, and accordingly channels are
determined.
In conventional radio communication
apparatuses, AGC (Automatic Gain Control) is conducted
for suppressing fluctuation of the amplitude of a
received electrical signal and converting it into a
signal with a constant amplitude. In AGC, gain
(amplification degree) is increased for a small
amplitude signal based on RSSI (Received Signal Strength
Indicator) while gain is decreased for a large amplitude
signal.
As one implementation of AGC, Japanese Laid-
Open Patent Publication 2002-94408 discloses an
arrangement including a first attenuator provided
between a front-end or a high frequency amplifier and a
mixer, a RSSI circuit for generating a RSSI output
signal from a received signal, and a second attenuator
provided before the RSSI circuit for adjusting an input
signal level. In this arrangement, the RSSI output
signal is compared to two thresholds. If it is outside
of the thresholds, the attenuation amount of the second
attenuator and then the attenuation amount of the first
attenuator are adjusted to substantially enlarge a
dynamic range of input and output in/from the RSSI

circuit and prevent saturation of the mixer, the AGC
circuit, and other system circuits in strong electric
fields without sacrificing modulation performance in
weak electric fields.
As another implementation of the AGC, Japanese
Laid-Open Patent Publication 2005-534252 discloses an
arrangement including a RSSI circuit for measuring the
RSSI of a received signal, an analog amplifier for
amplifying the received signal, an analog-to-digital
converter for converting the amplified signal into a
digital signal, a digital AGC loop for determining
digital gain based on the converted digital signal, and
a digital-to-analog converter for setting the digital
gain determined by the digital AGC loop in the analog
amplifier. In a spectral spread system, this
arrangement enables the system to follow a rapid
tracking variation while averaging noise.
As another implementation of the AGC, Japanese
Laid-Open Patent Publication 2006-229739 discloses an
arrangement where gain correction is conducted
corresponding to individual bands prior to AGC whenever
the frequency hopping causes the bands to be switched.
As stated above, the TFC "consists of band
groups each including several bands, and in some TFCs,
the frequency hopping is conducted through transition

between the bands.
However, signal strength measurement circuits
for measuring the strength of received signals, such as
the RSSI circuit, may not have uniform measurement
performance over the respective bands. For example,
even if received signals have the same strength, a
strength value for a certain band measured by the signal
strength measurement circuit may be higher than a
strength value for another band measured by the signal
strength measurement circuit.
In conventional radio communication
apparatuses as disclosed in Japanese Laid-Open Patent
Publications 2002-94408 and 2005-534252, AGC operations
in consideration of such measurement errors between
bands in the signal strength measurement circuit are
impossible.
In addition, the band switching period for the
frequency hopping is specified to be relatively short,
such as 312.5 ns, in the MB-OFDM specification. Thus if
the MB-OFDM is applied to a conventional radio
communication apparatus as disclosed in Japanese Laid-
Open Patent Publication 2006-229739, particularly if
analog AGC is conducted in such a conventional radio
communication apparatus, the AGC operation may not be
able to follow the above-stated fast band switching.

Disclosure of Invention
The present invention addresses the above-
mentioned conventional problems. One object of the
present invention is provide a radio communication
apparatus for enabling the AGC operation to follow the
high-speed band switching in consideration of
measurement errors between the respective bands in the
signal strength measurement circuit.
One feature of the present invention relates
to a radio communication apparatus including an
amplifier configured to amplify a signal received via
one of multiple channels including a channel where
frequency hopping is conducted; a signal strength
measurement circuit configured to measure signal
strength of the received signal; and a gain value
computation unit configured to compute a gain value for
the amplifier based on the signal strength measured by
the signal strength measurement circuit, wherein the
gain value computation unit is configured to use values
specific to the respective channels as coefficients of a
function to compute the gain value.
According to this feature, the radio
communication apparatus achieves AGC operations allowed
to follow fast band switching in consideration of

measurement errors between different bands in the signal
strength measurement circuit in order to compute a gain
value by substituting the signal strength into a
function with coefficients specific to different
channels.
For example, the gain value computation unit
may use a linear function to compute the gain value.
In one embodiment, the radio communication
apparatus may include a register complying with a
WiMedia MAC-PHY interface specification; and a MAC unit
configured to write a value in the register, wherein the
MAC unit is configured to write the coefficients in the
register prior to writing in the register a value
indicative of the channel via which the signal is
received, and the gain value computation unit is
configured to use the coefficients written in the
register as the coefficients of the function to compute
the gain value.
According to this embodiment, the radio
communication apparatus can be easily implemented by a
radio communication apparatus complying with the WiMedia
MAC-PHY interface specification to write the
coefficients in the register via the MAC unit and
compute the gain value based on the coefficients.
In one embodiment, the MAC unit may be

configured to write the coefficients in a range in the
register in the WiMedia MAC-PHY interface specification,
the range being where a vendor is allowed to assign
proprietary coefficients.
According to this embodiment, the radio
communication apparatus can be implemented to comply
with the WiMedia MAC-PHY interface specification.
In one embodiment, the radio communication
apparatus may include a table storage unit configured to
store a table including correspondence between the
channels and the coefficients, wherein the MAC unit is
configured to write the coefficients in the register
based on the table in the table storage unit.
According to this embodiment, the radio
communication apparatus can modify coefficients for
different channels without modification of hardware,
firmware and software by changing the table stored in
. the table storage unit.
In one embodiment, the radio communication
apparatus may include an analog-to-digital conversion
unit configured to perform analog-to-digital conversion
on the received signal, wherein the signal strength
measurement circuit is configured to measure signal
strength of the received analog signal, and the
amplifier is configured to amplify the received digital

signal converted by the analog-to-digital conversion
unit.
According to this embodiment, the radio
communication apparatus can improve AGC characteristics
if gain control for a narrow bandwidth is needed to
measure the signal strength of a received analog signal
and amplify the resulting digital signal.
In one embodiment, the signal strength
measurement circuit may be configured to measure signal
strength of the received analog signal, and the
amplifier may be configured to amplify the received
analog signal.
According to this embodiment, the radio
communication apparatus can improve AGC characteristics
if a received fast signal with a higher S/N (Signal to
Noise) ratio is amplified to measure the signal strength
of a received analog signal and amplify the received
analog signal.
In one embodiment, the radio communication
apparatus may include a coefficient determination unit
configured to determine a coefficient suitable for a
frequency band of a channel where the frequency hopping
is not conducted as a coefficient of the channel and
determine an average value of coefficients suitable for
different hopping frequency bands of a channel where the

frequency hopping is conducted as a coefficient of the
channel.
In one embodiment, the radio communication
apparatus may include a coefficient determination unit
configured to determine a coefficient suitable for a
frequency band of a channel where the frequency hopping
is not conducted as a coefficient of the channel and
determine a coefficient of a channel where the frequency
hopping is conducted based on a sample variance suitable
for different hopping frequency bands.
According to these embodiments, the radio
communication apparatus can compute the gain value in
consideration of deviations between coefficients for
hopping frequency bands in order to determine
coefficients for channels where frequency hopping is
conducted based on sample variance among the
coefficients suitable for the frequency bands.
In one embodiment, the coefficient
determination unit may be configured to weight
individual terms of the sample variance.
According to this embodiment, the radio
communication apparatus can prevent a gain value
unsuitable for a frequency band if a coefficient
suitable for a certain frequency band significantly
deviates from coefficients suitable for the other

frequency bands in hopping frequency bands.
In one embodiment, the radio communication
apparatus may include a transmission unit configured to
transmit a baseband signal in consecutively changed
frequency bands; an attenuator configured to attenuate
the baseband signal; and an attenuation rate
configuration unit configured to set an attenuation rate
of the attenuator, wherein the signal strength
measurement circuit is configured to measure signal
strength of the baseband signal as the received signal,
and the coefficient determination unit is configured to
determine a coefficient suitable for each of the
frequency bands based on the signal strength.
According to this embodiment, the radio
communication apparatus can determine coefficients for
different channels in consideration of measurement
errors due to different instances of the signal strength
measurement circuit.
According to the above-mentioned features of
the present invention, a constant current supply type
switching regulator can convert an input voltage into a
desired output current without the use of any current
detecting resistor, which may reduce the number of
elements in the switching regulator and alleviate loss
otherwise caused by an incoming current to the resistor.

Brief Description of Drawings
FIG. 1 is a block diagram illustrating a radio
communication apparatus according to one embodiment of
the present invention;
FIG. 2 is a schematic diagram illustrating an
assignment of PHY/RF registers in a radio communication
apparatus according to one embodiment of the present
invention;
FIG. 3 is a schematic diagram illustrating an
assignment within TXCHAN and RXCHA registers assigned to
a PHY/RF register in a radio communication apparatus
according to one embodiment of the present invention;
FIG. 4 is a block diagram illustrating a
reception unit in a baseband unit in a radio
communication apparatus according to one embodiment of
the present invention;
FIG. 5 is a schematic diagram illustrating an
assignment within a AGC_PARAM register assigned to a
PHY/RF register in a radio communication apparatus
according to one embodiment of the present invention;
FIG. 6 is a schematic diagram illustrating a
computation operation for a gain value in a gain value
computation unit in a radio communication apparatus
according to one embodiment of the present invention;

FIG. 7 is a flowchart of a reception channel
configuration operation in a radio communication
apparatus according to one embodiment of the present
invention;
FIG. 8 is a block diagram illustrating a
reception unit in a baseband unit in a radio
communication apparatus according to another embodiment
of the present invention;
FIG. 9 is a schematic diagram illustrating a
determination operation for a coefficient referred to by
a gain value computation unit in a radio communication
apparatus according to one embodiment of the present
invention;
FIG. 10 is a block diagram illustrating a
baseband unit in a radio communication apparatus
according to another embodiment of the present
invention;
FIG. 11 is a flowchart illustrating a
coefficient configuration operation in a radio
communication apparatus according to one embodiment of
the present invention;
FIG. 12 is a schematic diagram illustrating
frequency hopping; and
FIG. 13 is a schematic diagram illustrating
relationships between bands and TFCs in the MB-OFDM.

Description of Embodiments
Embodiments of the present invention will be
described with reference to the accompanying drawings in
detail below. FIG. 1 is a block diagram illustrating a
radio communication apparatus according to one
embodiment of the present invention.
In this embodiment, a radio communication
apparatus 1 is coupled to a host controller 2 via a PCI
(Peripheral Component Interconnect)-Express bus 3. The
host controller 2 includes a main CPU (Central
Processing Unit) 10 and a memory 11.
The main CPU 10 uses the memory 11 to run an
operating system 12 and to execute a device driver 13 on
the operating system 12.
The device driver 13 communicates data to the
radio communication apparatus 1 via the PCI-Express bus
3 and controls the radio communication apparatus 1 by
reading and writing values from/in a register in a MAC
(Media Access Controller) unit 22 as described below.
The radio communication apparatus 1 includes a
sub CPU 20, a memory 21, the MAC unit 22 for generating
and/or filtering data frames, a PHY (Physical Layer)
unit 23 for signal processing such as frequency
conversion and an antenna 24.

The sub CPU 20 uses the memory 21 to run a
real-time operating system 25 and executes firmware 26
for controlling components in the MAC unit 22 on the
real-time operating system 25.
The sub CPU 20 may configure a register (not
illustrated) in the MAC unit 22 and/or communicate data
to the host controller 2 in execution of the firmware 26.
Also, the sub CPU 20 may read and/or write values
from/in a PHY/RF register 41 as described below in the
PHY unit 23 via a WiMedia MAC-PHY interface bus 27 in
execution of the firmware 26.
The MAC unit 22 and the PHY unit 23 may
perform operations based on specifications of WiMedia
MAC and MB-OFDM. Communications between the MAC unit 22
and the PHY unit 23 may be specified in conformity with
the WiMedia MAC-PHY interface specification. Thus, the
MAC unit 22 and the PHY unit 23 distributed by different
vendors can be connected to each other and used together.
In the WiMedia MAC-PHY interface specification,
as illustrated in FIG. 2, a range from a base address
(reference address) "0x00" to address "0x20" in the
PHY/RF register 41 is defined as a range for storing
dynamic configurations (dynamic register set) .
For example, as illustrated in FIG. 3, a
transmitted TFC and a band group are set in a TXCHAN

register at address "0x02" while a received TFC and a
band group are set in a RXCHAN register at address
"0x04".
For this reason, the sub CPU 20 for executing
the firmware 26 configures a transmission channel by
writing the TFC and the band group in the TXCHAN
register via the MAC unit 22 and a reception channel by
writing the TFC and the band group in the RXCHAN
register via the MAC unit 22.
Also in the WiMedia MAC-PHY interface
specification, a range from address "0x20" to address
"0x80" in the PHY-RF register 41 is defined as a range
for storing static configurations (static register set)
such as communication speed and the number of
configurable signal transmission levels supported by the
radio communication apparatus 1.
Also in the WiMedia MAC-PHY interface
specification, a range from address "0x80" to address
"OxFF" in the PHY/RF register 41 is defined as a range
for storing configurations specific to vendors (vendor
range).
In FIG. 1, the MAC unit 22 attaches a MAC
header to a data frame to be transmitted to the PHY unit
23, encrypts the MAC header attached data frame and
transmits the encrypted data frame to the PHY unit 23

via the WiMedia MAC-PHY interface bus 27.
Also, the MAC unit 22 decrypts a received data
frame from the PHY unit, analyzes the decrypted data
frame and filters or extracts data to be further
transmitted to an upper protocol from data obtained from
the data frame based on the analysis.
The PHY unit 23 includes a RF (Radio
Frequency) unit 40, the PHY/RF register 41 and a
baseband unit 42, and the baseband unit 42 includes a
transmission unit 50 and a reception unit 51.
The RF unit 40 performs MB-OFDM modulation on
a baseband signal supplied from the transmission unit 50
in the baseband unit 42 to transmit the signal as a
radio wave via the antenna 24 over the air.
Also, the RF unit 40 demodulates the MB-OFDM
modulated signal received via the antenna 24 into a
baseband signal and supplies the demodulated baseband
signal to the reception unit 51 in the baseband unit 42.
The transmission unit 50 in the baseband unit
42 D/A (Digital-to-Analog) converts a digital data frame
received from the MAC unit 22 via the WiMedia MAC-PHY
interface bus 27 into an analog baseband signal and
supplies the converted baseband signal to the RF unit 40.
The reception unit 51 in the baseband unit 42
A/D (Analog-to-Digital) converts a baseband signal

received from the RF unit 4 0 into a digital data frame
and transmits the converted data frame to the MAC unit
22 via the WiMedia MAC-PHY interface bus 27.
FIG. 4 shows an exemplary arrangement of the
reception unit 51 in the baseband unit 42. The
reception unit 51 in the baseband unit 42 includes a
RSSI circuit 60, a gain value computation unit 61, an
A/D converter 62, an amplifier 63 and a signal
processing unit 64.
The RSSI circuit 60 measures RSSI as received
signal strength of an analog baseband signal supplied
from the RF unit 40 and supplies a signal indicative of
the measured RSSI to the gain value computation unit 61.
Note that the RSSI circuit 60 may serve as a signal
strength measurement circuit according to an embodiment
of the present invention.
The gain value computation unit 61 computes a
gain value based on the RSSI indicative of the signal
supplied from the RSSI circuit 60 and one or more values
configured in the PHY/RF register 41 and supplies a
signal indicative of the computed gain value to the
amplifier 63.
The values set in the PHY/RF register 41
herein means one or more gain control parameters
(hereinafter referred to as "AGO_PARAM register")

written in a certain address, such as address "OxAO"
relative to the base address, within the vendor range in
the PHY/RF register 41 in FIG. 2.
In the AGC_PARAM register, as illustrated in
FIG. 5, a coefficient "gradient" indicative of the
gradient of a linear function for finding an input
signal from the RSSI is located in upper 4 bits, and a
coefficient "intercept" indicative of the intercept of
the linear function is located in lower 4 bits.
The coefficients "gradient" and "intercept"
for different channels are associated with each other in
a table stored in the memory 21 in advance. In this
manner, the memory 21 may serve as a table storage unit
according to the present invention. In this embodiment,
it is assumed that the coefficients "gradient" and
"intercept" for the channels are predetermined through
prior measurement.
For example, if no frequency hopping is
conducted in a channel, the coefficients "gradient" and
"intercept" suitable for a band in that channel is
stored in the table. On the other hand, if frequency
hopping is conducted in a channel, respective average
values of the coefficients "gradient" and "intercept"
suitable for individual bands are stored in the table.
The sub CPU 20 for executing the firmware 2 6

may set the AGC_PARAM register prior to setting the
RXCHAN register in the PHY/RF register 41.
In FIG. 4, the gain value computation unit 61
computes a gain value based on corrected RSSI
(hereinafter referred to as "cRSSI") through
substitution of the RSSI into a linear function with the
coefficients "gradient" and "intercept" in the AGC_PARAM
register.
Specifically, as illustrated in FIG. 6, the
gain value computation unit 61 may substitute the RSSI
(=a) into the linear function with the coefficients
"gradient" and "intercept" in the AGC_PARAM register and
substitute the cRSSI (=f(a)), which is an output of the
linear function, into a predefined linear function g(x)
to compute the gain value g(f(α)) for the amplifier 63.
For a signal with uniform strength, for
example, if the RSSI measured by the RSSI circuit 60 for
a certain band is higher than the RSSI measured by the
RSSI circuit 60 for a reference band, a linear function
f (x) with the coefficients "gradient" and "intercept"
at least one of which is smaller than the coefficients
of the linear function f(x) for the reference band is
used, and thus the cRSSI (=f'(α) ) obtained through
substitution of the RSSI (=α) into f (x) would be
smaller than the cRSSI (=f(α)) for the reference band.

In other words, the gain value computed by the
gain value computation unit 61 becomes g(f (α)) by
estimating the RSSI measured by the RSSI circuit 60 to
be relatively small, resulting in a gain value larger
than the gain value g(f(α)).
In FIG. 4, the A/D converter 62 converts an
analog signal supplied from the RF unit 40 into a
digital signal and supplies the digital signal to the
amplifier 63.
The amplifier 63 amplifies the digital signal
supplied from the A/D converter 62 based on the gain
value represented by a signal supplied from the gain
value computation unit 61 and supplies the amplified
digital signal to the signal processing unit 64.
For example, the signal processing unit 64 may
perform frequency conversion and/or other operations on
the amplified digital signal and transmit the resulting
signal as a data frame to the MAC unit 22.
Exemplary configuration operations of a
reception channel in the radio communication apparatus 1
including the above-stated components are described in
detail with reference to FIG. 7.
The WiMedia MAC-PHY interface specification
specifies that if a channel is changed during
communication, a beacon frame with "Channel Change

Information Element" (hereinafter referred to as
"Channel Change IE") may be transmitted to a
communicating opponent apparatus.
The "Channel Change IE" may include the next
new channel and information such as a time period until
transition to the new channel. Upon receiving this
beacon frame, the communicating opponent apparatus uses
a transmission channel or a reception channel as a new
channel based on the information in the Channel Change
IE.
In this manner, the configuration operations
of the received channel is performed in response to
activation and/or degradation of communication
conditions as well as based on the information in the
Channel Change IE transmitted by the communicating
opponent apparatus.
At step S1, the coefficients "gradient" and
"intercept" corresponding to a received channel to be
configured are identified by the sub CPU 20 in a table
stored in the memory 21.
At step S2, the identified coefficients
"gradient" and "intercept" are set by the sub CPU 20 in
the AGC_PARAM register in the PHY/RF register 41 via the
MAC unit 22.
At step S3, the received channel, that is, a

TFC and a band group, are set by the sub CPU 20 in the
RXCHAN register in the PHY/RF register 41 via the MAC
unit 22.
As a result, when the received channel is
switched in the PHY unit 23 at step S4, the PHY unit 23
informs the sub CPU 20 via the MAC unit 22 that the
received channel has been switched at step S5.
In this manner, according to this embodiment
of the present invention, the radio communication
apparatus 1 computes gain values through substitution of
the RSSI into a function with coefficients specific to
respective channels. As a result, whenever a band is
switched in a channel where frequency hopping is
conducted, the radio communication apparatus 1 does not
have to change the gain value and can perform AGC
operations to enable fast band switching to be followed
in consideration of measurement errors between bands in
the signal strength measurement circuit.
In this embodiment, the amplifier 63 amplifies
a digital signal supplied from the A/D converter 62. As
illustrated in FIG. 8, in another embodiment, the
amplifier 63 may amplify a received analog signal and
supply the amplified signal to the A/D converter 62.
In this case, the signal strength is measured
from the received analog signal, and the received analog

signal is amplified. Thus, AGC characteristics can be
improved in amplification of the received signal if the
signal is fast and has a high S/N (Signal to Noise)
ratio.
Also, in this embodiment, the gain value
computation unit 61 uses a certain linear function to
compute the cRRSI from the RSSI. In another embodiment,
the gain value computation unit 61 may use another
linear function corresponding to frequency
characteristics of the RSSI circuit 60 to compute the
cRSSI from the RSSI.
Also, in this embodiment, if frequency hopping
is conducted in channels, the respective average values
of the coefficients "gradient" and "intercept" suitable
for individual bands are stored in a table in the memory
21. In another embodiment, as illustrated in FIG. 9,
values of the coefficients "gradient" and "intercept"
that are suitable for the individual bands and have the
smallest sample variance between the coefficients in
consideration of deviations for the individual
coefficients suitable for the hopping bands may be
stored in the table in the memory 21.
For example, assuming that coefficients
suitable for individual bands are C1, C2 and C3, the
coefficient Ca for causing the sample variance V in

formula (1) as presented below to be minimized is
determined as the coefficient for the channel of
interest.

In another embodiment, the individual terms
(C1-Ca)2, (C2-Ca)2 and (C3-Ca)2 in formula (1) may be
weighted, and the coefficient Ca for causing the
weighted sample variance V to be minimized may be stored
in the table in the memory 21.
For example, it is assumed that coefficients
suitable for individual bands are C1, C2 and C3. If the
gain values are set to be larger in the order of C3, C2
and C1, the coefficient Ca for causing the sample
variance V in formula (2) as presented below to be
minimized may be determined as the coefficient for the
channel of interest.

According to this embodiment, if the
coefficient suitable for a certain one of hopping bands
is further away from the coefficients suitable for the
other bands, it is possible to prevent the gain value
for that band from being set at an inappropriate value.
In this embodiment, the weights 1, 2 and 3 are
used in formula (2), but any other weights can be used
in formula (2).

Also in the above-stated embodiments, the
coefficients "gradient" and "intercept" for different
channels are predefined through prior measurement. In
another embodiment, as illustrated in FIG. 10, an
attenuator 52 may be provided for attenuating a baseband
signal supplied from the transmission unit 50 in the
baseband unit 42 and supplying the attenuated signal to
the reception unit 51, and the coefficients "gradient"
and "intercept" for different channels may be stored in
the table in the memory 21.
For example, as illustrated in FIG. 11, upon
receiving a request from the host controller 2, the sub
CPU 20 selects a band to be measured via the MAC unit 22
at step S11.
At step S12, the sub CPU 20 causes the
attenuator 52 to attenuate a signal transmitted from the
transmission unit 50 such that the strength of the
signal received at the reception unit 51 can meet
predefined criteria. At step S13, the sub CPU 20
obtains individual RSSIs measured by the RSSI circuit 60.
At step S14, steps S12-S13 are repeated
through variations of the reference level and
attenuation rate for the attenuator 52 until a number of
samples corresponding to the number of coefficients of a
linear function for correcting the measured RSSIs into

cRSSIs can be obtained. For example, if the gain value
computation unit 61 uses a linear function to correct
the RSSI into the cRSSI, steps S12-S13 may be executed
twice.
Upon obtaining the corresponding number of
samples, at step S15, the sub CPU 20 computes
coefficients suitable for the band of interest based on
the reference levels and the RSSIs.
At step S16, the sub CPU 20 determines whether
coefficients suitable for all the bands have been
derived. If it is determined that the suitable
coefficients have not been derived for all the bands,
the process control returns to step Sll.
On the other hand, if it is determined that
suitable coefficients have been derived for all the
bands, the sub CPU 20 determines coefficients for
individual channels based on the derived band
coefficients at step S17 and stores the determined
channel coefficients in the memory 21.
In this manner, the sub CPU 20 may serve as a
coefficient determination unit according to the present
invention.
As stated above, the radio communication
apparatus according to the present invention may be
useful in radio communication systems complying with the

MB-OFDM scheme. In particular, if the signal strength
measurement circuit has different characteristics for
individual bands, the radio communication apparatus may
be advantageous.
The present invention is not limited to the
specifically disclosed embodiments, and variations and
modifications may be made without departing from the
scope of the present invention.
The present application is based on Japanese
Priority Patent Application No. 2008-028922 filed on
February 8, 2008, the entire contents of which are
hereby incorporated herein by reference.

CLAIMS
Claim 1. A radio communication apparatus
comprising,
an amplifier configured to amplify a signal
received via one of multiple channels including a
channel where frequency hopping is conducted;
a signal strength measurement circuit
configured to measure signal strength of the received
signal; and
a gain value computation unit configured to
compute a gain value for the amplifier based on the
signal strength measured by the signal strength
measurement circuit, wherein
the gain value computation unit is configured
to use values specific to the respective channels as
coefficients of a function to compute the gain value.
Claim 2. The radio communication apparatus as
claimed in claim 1, wherein
the gain value computation unit is configured
to use a linear function to compute the gain value.

Claim 3. The radio communication apparatus as
claimed in claim 1, further comprising:
a register complying with a WiMedia MAC-PHY
interface specification; and
a MAC unit configured to write a value in the
register, wherein
the MAC unit is configured to write the
coefficients in the register prior to writing in the
register a value indicative of the channel via which the
signal is received, and
the gain value computation unit is configured
to use the coefficients written in the register as the
coefficients of the function to compute the gain value.
Claim 4. The radio communication apparatus as
claimed in claim 3, wherein
the MAC unit is configured to write the
coefficients in a range in the register in the WiMedia

MAC-PHY interface specification, the range being where a
vendor is allowed to assign proprietary values.
Claim 5. The radio communication apparatus as
claimed in claim 3, further comprising:
a table storage unit configured to store a
table including correspondence between the channels and
the coefficients, wherein
the MAC unit is configured to write the
coefficients in the register based on the table in the
table storage unit.
Claim 6. The radio communication apparatus as
claimed in claim 1, further comprising:
an analog-to-digital conversion unit
configured to perform analog-to-digital conversion on
the received signal, wherein
the signal strength measurement circuit is
configured to measure signal strength of the received

analog signal, and
the amplifier is configured to amplify the
received digital signal converted by the analog-to-
digital conversion unit.
Claim 7. The radio communication apparatus as
claimed in claim 1, wherein
the signal strength measurement circuit is
configured to measure signal strength of the received
analog signal, and
the amplifier is configured to amplify the
received analog signal.
Claim 8. The radio communication apparatus as
claimed in claim 1, further comprising:
a coefficient determination unit configured to
determine a coefficient suitable for a frequency band of
a channel where the frequency hopping is not conducted
as a coefficient of the channel and determine an average

value of coefficients suitable for different hopping
frequency bands of a channel where the frequency hopping
is conducted as coefficients of the channel.
Claim 9. The radio communication apparatus as
claimed in claim 1, further comprising:
a coefficient determination unit configured to
determine a coefficient suitable for a frequency band of
a channel where the frequency hopping is not conducted
as a coefficient of the channel and determine a
coefficient of a channel where the frequency hopping is
conducted based on a sample variance suitable for
different hopping frequency bands.
Claim 10. The radio communication apparatus
as claimed in claim 9, wherein
the coefficient determination unit is
configured to weight individual terms of the sample
variance.

Claim 11. The radio communication apparatus
as claimed in claim 8, further comprising:
a transmission unit configured to transmit a
baseband signal in consecutively changed frequency
bands;
an attenuator configured to attenuate the
baseband signal; and
an attenuation rate configuration unit
configured to set an attenuation rate of the attenuator,
wherein
the signal strength measurement circuit is
configured to measure signal strength of the baseband
signal as the received signal, and
the coefficient determination unit is
configured to determine a coefficient suitable for each
of the frequency bands based on the signal strength. ^

A disclosed radio communication apparatus includes an amplifier configured to amplify a signal received via one
of multiple channels including a channel where frequency hopping is conducted; a signal strength measurement circuit configured
to measure signal strength of the received signal; and a gain value computation unit configured to compute a gain value for the
amplifier based on the signal strength measured by the signal strength measurement circuit. The gain value computation unit is
configured to use values specific to the respective channels as coefficients of a function to compute the gain value.

Documents:

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Patent Number

278859

Indian Patent Application Number

2490/KOLNP/2010

PG Journal Number

01/2017

Publication Date

06-Jan-2017

Grant Date

31-Dec-2016

Date of Filing

08-Jul-2010

Name of Patentee

RICOH COMPANY, LTD.

Applicant Address

3-6, NAKAMAGOME 1-CHOME, OHTA-KU, TOKYO, 1438555 JAPAN

Inventors:

#	Inventor's Name	Inventor's Address
1	EJIMA, TAKESHI	2-1-2-302, MINAMINARUSE 1-CHOME, MACHIDA-SHI, TOKYO, 1940045 JAPAN

PCT International Classification Number

H04B 1/16

PCT International Application Number

PCT/JP2009/051682

PCT International Filing date

2009-01-27

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2008-028922	2008-02-08	Japan