Abstract:
An equalizer circuit includes a carrier sensor, first and second equalizer units, carrier sense controller, and reception signal switching unit. The carrier sensor senses the start of a reception signal on the basis of a signal representing the reception level of the reception signal. The first and second equalizer units equalize the reception signal. The carrier sense controller alternately enables the first and second equalizer units every frame reception in accordance with an output from the carrier sensor. The reception signal switching unit alternately switches between outputs from the first and second equalizer units every frame reception and outputs the selected output as demodulation data.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an equalizer circuit and equalizing method and, more particularly, to an equalizer circuit and equalizing method for preventing waveform distortion and interference waves (noise) in multipath fading. 
   In data transmission of a high-speed radio ATM (Asynchronous Transfer Mode) system for multimedia mobile communication of 20 to 30 Mbps using a 5.2-GHz band, an equalizing function is used to prevent data quality degradation in multipath fading. 
   A technique using this equalizing function has been proposed by the present applicant/assignee. This technique proposes a radio data communication terminal for narrowband modulation system, in which a tap coefficient for an equalizer is set after a frequency offset value for operating a phase rotation means is obtained using, e.g., a shortest preamble. 
   As shown in  FIG. 3 , the equalizer circuit for performing the above equalizing function comprises a carrier sensor  6  for sensing the presence/absence of an input carrier and an equalizer unit  7  for receiving an output from the carrier sensor  6 . The equalizer unit  7  is comprised of a memory unit  8 , phase rotation unit  9 , phase difference detector  10 , average value detector  11 , integrator  12 , vector converter  13 , transmission line characteristic estimating unit  14 , a tap coefficient setting unit  15 , and equalizer  16 . 
   The carrier sensor  6  senses the presence/absence of a carrier in accordance with an RSSI (Received Signal Strength Indicator) signal Q representing the reception level from an RF (Radio Frequency) converter (not shown). The carrier sensor  6  then detects the start of a reception signal and outputs a carrier sense signal R to the equalizer unit  7  for a time interval from a time when detecting the start of reception data to a time when receiving a demodulation data end signal S of a one-pulse signal for stopping the equalizer unit  7 . 
   The memory unit  8  receives a reception data signal P for an arbitrary period to control the output. The phase rotation unit  9  rotates the phase of the output signal from the memory unit  8  through a necessary angle. The phase difference detector  10  obtains the current angle and the angle of a PN (Pseudo Noise) code sequence obtained upon the lapse of one period. The phase difference detector  10  then obtains the difference between these two angles. 
   The average value detector  11  integrates the phase difference from the phase difference detector  10  a predetermined number of times. The average value detector  11  then divides the integrated value by the predetermined number of times to obtain the average value of the average phase difference per symbol. The integrator  12  integrates the average value from the average value detector  11  in units of symbols. The vector converter  13  converts the output from the integrator  12  into a real part amplitude value and an imaginary part amplitude value. The vector converter  13  outputs these amplitude values to the phase rotation unit  9 . 
   The transmission line characteristic estimating unit  14  obtains the transmission line characteristics of the one-period PN code sequence for a preamble period using the signal obtained upon phase rotation in the phase rotation unit  9 . The tap coefficient setting unit  15  obtains a tap coefficient necessary for the equalizer  16  in accordance with the transmission line characteristics obtained by the transmission line characteristic estimating unit  14 . The tap coefficient setting unit  15  then sets the tap coefficient in the equalizer  16 . The equalizer  16  equalizes the output from the phase rotation unit  9  using a filter having the tap coefficient set by the tap coefficient setting unit  15 . The equalizer  16  outputs a demodulation data signal U. Reception processing is performed using this demodulation data signal U. 
     FIGS. 4A  to  4 F show the reception timings of a conventional phase shifter circuit shown in FIG.  3 . In this case, the inactive interval of the reception data signal P is long. 
   The carrier sensor  6  determines the presence/absence of a carrier in accordance with the RSSI signal Q from the RF converter (FIG.  4 B). The carrier sensor  6  then outputs the carrier sense signal R representing the start of the reception data signal P to the equalizer unit  7  (FIGS.  4 A and  4 C). Upon detecting the start of the reception data signal P, the equalizer unit  7  detects the frequency offset, estimates the transmission line characteristics, and sets the tap coefficient. 
   The equalizer  16  stores the preamble signal having the repeated PN code in the memory unit  8  and performs processing for a period of various initial settings ( FIG. 4E ) and has a delay accordingly. Upon completion of various initial settings in the equalizer  16 , the demodulation data signal U is output (FIG.  4 G). Upon completion of demodulation, the demodulation data end signal S is output to the carrier sensor  6  (FIG.  4 F). At this time, the equalizer unit  7  is always operating in response to a system clock signal T ( FIG. 4D ) and therefore consumes power. In addition, a long inactive interval decreases the information bit rate. 
     FIGS. 5A  to  5 G show the reception timings of the conventional phase shifter circuit shown in FIG.  3 . This exemplifies a short inactive interval of the reception data signal P. 
   The carrier sensor  6  determines the presence/absence of a carrier in accordance with the RSSI signal Q from the RF converter ( FIG. 5B ) and outputs the carrier sense signal R representing the start of the reception data signal P to the equalizer unit  7  (FIGS.  5 A and  5 C). The equalizer unit  7  detects a frequency offset, estimates the transmission line characteristics, and sets the tap coefficient upon detecting the start of the reception data signal P. 
   The equalizer  16  stores the preamble signal having the repeated PN code in the memory unit  8  and performs processing for a period of various initial settings ( FIG. 5E ) and has a delay accordingly. Upon completion of various initial settings in the equalizer  16 , the demodulation data signal U is output (FIG.  5 G). Upon completion of demodulation, the demodulation data end signal S is output to the carrier sensor  6  (FIG.  5 F). At this time, the equalizer unit  7  is always operating in response to a system clock signal T ( FIG. 5D ) and therefore consumes power. 
   Since the inactive interval of the reception data signal P is short, a carrier detection signal β representing the leading edge of the carrier sense signal R cannot be detected upon receiving the next frame during a carrier sense period α. Therefore, the reception operation is performed every other frame, and the demodulation data signal U cannot normally be output. 
   In the above conventional equalizer circuit, a long inactive interval undesirably decreases the information bit rate. When the next frame is received during the processing period of the demodulation data with a short inactive interval, the carrier sense signal cannot be detected. Data is received every other frame, resulting in a reception error. Since the equalizer unit is always operating in response to the system clock signal, wasteful power is undesirably consumed. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an equalizer circuit and equalizing method capable of normally performing real-time processing even upon receiving a continuous burst signal. 
   It is another object of the present invention to provide an equalizer circuit and equalizing method which can reduce power consumption. 
   In order to achieve the above object of the present invention, there is provided an equalizer circuit comprising carrier sensing means for sensing the start of a reception-signal on the basis of a signal representing a reception level of the reception signal, first and second equalizing means for equalizing the reception signal, control means for alternately enabling the first and second equalizing means every frame reception in accordance with an output from the carrier sensing means, and switching means for alternately switching between outputs from the first and second equalizing means every frame reception and outputting the selected output as demodulation data. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of an equalizer circuit according to an embodiment of the present invention; 
       FIGS. 2A  to  2 N are timing charts showing operation of switching two parallel equalizers according to the embodiment shown in  FIG. 1 ; 
       FIG. 3  is a block diagram of a conventional equalizer circuit; 
       FIGS. 4A  to  4 G are timing charts of conventional operation for a long inactive interval; and 
       FIGS. 5A  to  5 G are timing chats of conventional operation for a short inactive interval. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention will be described in detail with reference to the accompanying drawings. 
     FIG. 1  shows an equalizer circuit according to an embodiment of the present invention. Referring to  FIG. 1 , the equalizer circuit of this embodiment is comprised of a carrier sensor  1  for detecting the carrier of an input signal, a carrier sense controller  2  for receiving an output from the carrier sensor  1 , gate circuits  3   a  and  3   b  for receiving an output from the carrier sense controller  2 , an equalizer unit  4   a  for receiving a reception data signal A and outputs from the carrier sense controller  2  and gate circuit  3   a , an equalizer unit  4   b  for receiving the reception data signal A and the outputs from the carrier sense controller  2  and gate circuit  3   b , and a reception data switching unit  5  for receiving outputs from the equalizer units  4   a  and  4   b  and outputting a demodulation data signal M. Gate signals from the equalizer units  4   a and  4   b  are output to the carrier sense controller  2 . 
   The carrier sensor  1  detects the start of the reception data in accordance with an RSSI signal B from an RF converter  21  and outputs a signal representing this start to the carrier sense controller  2 . The carrier sense controller  2  determines the start of reception data in accordance with a signal from the carrier sensor  1  and detects the end of carrier sensing on the basis of demodulation data gate signals J and K respectively from the equalizer units  4   a  and  4   b . 
   At the start and end of carrier sensing, the carrier sense controller  2  generates active-high carrier sense signals C and D for low-power consumption and real-time processing every other frame. The carrier sense controller  2  outputs the carrier sense signal C to the gate circuit  3   a  and equalizer unit  4   a  and the carrier sense signal D to the gate circuit  3   b  and equalizer unit  4   b . The carrier sense signals C and D serve as enable signals for the equalizer units  4   a  and  4   b.    
   The gate circuit  3   a  masks a system clock signal E and the carrier sense signal C and outputs an active-high clock gate signal F to the equalizer unit  4   a . The gate circuit  3   b  masks the system clock signal E and the carrier sense signal D and outputs an active-high clock gate signal G to the equalizer unit  4   b . 
   The equalizer unit  4   a  detects the frequency An offset, estimates the transmission line characteristics, and sets the tap coefficient upon receiving the carrier sense signal C. The equalizer unit  4   a  outputs the demodulation data gate signal J and the demodulation data signal H to the reception data switching unit  5  upon initial setting of an internal equalizer  41   a.    
   The equalizer unit  4   b  detects the frequency offset, estimates the transmission line characteristics, and sets the tap coefficient upon receiving the carrier sense signal D. The equalizer unit  4   b  outputs the demodulation data gate signal K and the demodulation data signal L to the reception data switching unit  5  upon initial setting of an internal equalizer  41   b.    
   The reception data switching unit  5  alternately receives the demodulation data gate signal J from the equalizer unit  4   a  and the demodulation data gate signal K from the equalizer unit  4   b . The reception data switching unit  5  switches (selects) between the demodulation data signal H from the equalizer unit  9 a and the demodulation data signal L from the equalizer unit  4   b  in response to the demodulation data gate signals J and K and outputs the selected demodulation data signal as the demodulation data signal M. Reception processing is performed in accordance with the demodulation data signal M from the reception data switching unit  5 . 
     FIGS. 2A  to  2 N show the switching operation for the two parallel equalizers shown in FIG.  1 . The reception data signal A is made up of preamble signals for performing various training operations and information data, as shown in FIG.  2 A. 
   The preamble signals are received by repeating a PN code for a predetermined period. The carrier sensor  6  determines the presence/absence of a carrier in accordance with the RSSI signal B from the RF converter  21  (FIG.  2 B). The carrier sensor  6  then outputs the carrier sense signals C and D representing the start of the reception data signal A to the gate circuits  3   a  and  3   b  and equalizer units  4   a  and  4   b  (FIGS.  2 C and  2 H). Upon outputting the carrier sense signals C and D from the carrier sense controller  2 , the equalizer units  4   a and  4   b  detect the frequency offset values, estimate the transmission line characteristics, and set the tap coefficients using a PN-code one-period signal. 
   The equalizer units  4   a  and  4   b  store the PN codes in an internal memory  42   a  during the respective initial setting periods ( FIGS. 2E and 2J ) and has delays accordingly. At the end of the demodulation data signals H and L from the equalizer units  4   a  and  4   b , the carrier sense controller  2  stops outputting the carrier sense signals C and D, as will be described later. 
   The operation of the gate circuits  3   a  and  3   b , equalizer units  4   a  and  4   b , and reception data switching unit  5  will now be described in detail below. 
   The gate circuits  3   a  and  3   b  control to gate the system clock signal E using the carrier sense signals C and D as gate signals ( FIGS. 2C ,  2 H, and  2 N). While receiving the carrier sense signals C and D, the gate circuits  3   a  and  3   b  output the clock gate signals F and G (FIGS.  2 D and  2 I). While receiving the carrier sense signals C and D, the equalizer units  4   a  and  4   b  perform the above-mentioned processing using the reception data signal A and clock gate signals F and G. As a result of processing, the equalizer units  4   a  and  4   b  output the demodulation data signals H and L to the reception data switching unit  5  (FIGS.  2 H and  2 L). At the same time, the equalizer units  4   a  and  4   b  output the demodulation data signals J and K synchronized with the demodulation data signals H and L (FIGS.  2 F and  2 K). 
   The reception data switching unit  5  selects the demodulation data signal H or L in accordance with the demodulation data gate signals J and K and outputs the demodulation data signal M (FIG.  2 M). At this time, the carrier sensor  2  stops outputting the carrier sense signals C and D upon receiving the demodulation data gate signals J and K. 
   Since the equalizer units  4   a  and  4   b  construct a parallel circuit, these equalizer units can alternately be switched in real time to allow reception processing even if the next frame is received during the carrier sense period. Since the clock gate signals F and G are supplied to the equalizer units  4   a  and  4   b , power consumption can be reduced. 
   According to the present invention, the two parallel equalizers  41   a  and  41   b  in the equalizer units  4   a  and  4   b  are alternately switched every frame and operate for reception during only the clock gate period, thereby reducing the power consumption. Real-time processing is allowed even with delays in initial settings for the equalizers in the equalizer units  4   a  and  4   b.    
   The two parallel equalizers (equalizers in the equalizer units  4   a  and  4   b ) are alternately switched every frame reception. Even if a continuous burst signal having a short inactive interval is input, normal processing can be performed in real time. In addition, since the equalizer units  4   a  and  4   b  operate for reception during only the carrier sense period, power consumption can be reduced.