Abstract:
In a data transmission system, a transmitter adds control data to transmission data, and modulates the resultant signal by a predetermined modulation method, and sends the result in a wireless manner. A receiver detects a reception power intensity by use of the control data contained in the transmitted signal. A random pattern is used for a reception-power detecting portion for detecting a reception power intensity, which is contained in the control data.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a data transmission system as a communication system for a mobile communication and a mobile satellite communication, and a data transmitter and a data receiver which are used in the data transmission system.  
           [0003]    2. Discussion of the Prior Art  
           [0004]    In a mobile communication, a receiving signal level is greatly varied (in several tens dB or greater) since when propagating, it is subjected to various interferences, e.g., shadowing, fading and the like. One of the measures possibly taken for this problem is to correct the receiving signal level by the utilization of the AGC (automatic gain control). FIG. 8 shows in block form an overall wireless communication system. FIGS. 9 and 10 show also in block form a prior transmitter and a prior receiver in the mobile wireless communication system, which are prescribed in “TIA/EIA/IS-139.1-A” (TIA/EIA INTERIM STANDARD: TDMACellular/PCS-Radio Interface-Mobile Station-Base Station-Compatibility-Digital Control Channel) or “RCR STD-32”.  
           [0005]    In FIG. 8 showing the communication system, reference numeral  1  is a transmitter for converting a transmission data signal S 1  into a radio signal which is to be transmitted in the form of a transmission signal S 2 ;  2  is a channel for transmitting the wireless signal; and  3  is a receiver for extracting reception data S 4  from a reception signal S 3 . In FIG. 9 showing the transmitter, numeral  11  is a burst generator;  12  is a preamble adder;  13  is a modulator; and  14  is an antenna. The preamble adder  12  generates a transmission burst signal S 12  by use of the transmission data S 1 , an information signal S 11  output from the preamble adder  12 , and the like. A pattern of the preamble is a repetition pattern, e.g., ALLO. The modulator  13  modulates the transmission burst signal S 12  and produces a modulated signal S 13 . The antenna  14  emits a radio wave containing the modulated signal S 13 . In FIG. 10 showing the receiver, numeral  31  is an antenna;  32  is a low noise amplifier (LNA);  33  is an RF/IF portion for frequency converting a signal S 31  output from the low noise amplifier  32 ;  34  is an AGC portion for automatically controlling a low-frequency signal S 32  output from the RF/IF portion  33  so that its output signal level has a fixed value;  35  is a demodulator for demodulating an AGC output signal S 33 ; and  36  is a reception controller for extracting the reception data S 4  from a demodulated signal S 34  output from the demodulator  35 . The wireless communication system thus arranged employs a repetition pattern, e.g., ALLO, for the preamble pattern.  
           [0006]    Description will be given about the operation of the thus arranged mobile wireless communication system when it sends a signal from a mobile station MS to a base station BMI. The wireless communication system used here is prescribed in “TIA/EIA/IS-139.1-A”. In the mobile station MS, the burst generator  11  constructs a transmission burst by adding the bits of a ramp (R), sync words (SYNC= synchronization, SYNC+ = additional synchronization), and an AGC preamble (PREAM= preamble), to data (DATA, already error-correction coded) to be transmitted. A for-mat of the transmission burst is shown in FIG. 11. In the “TIA/EIA/IS-139.1-A”, the preamble consisting of eight symbols of the η/4 shift modulated as a repetition of “1” and “0” is added as the preamble pattern to the transmission data.  
           [0007]    Those symbols of the preamble are phased as shown in FIG. 12. As shown, the preamble portion takes a fixed envelope level. The output signal S 12  of the burst generator  11  is modulated by the modulator  13  and amplified, and then the thus processed signal is radiated from the antenna  14 . When propagating through the channel  2 , the radio signal is greatly affected by fadings (e.g., Rayleigh fading and frequency-selective fading), and its waveform is greatly distorted. Further, the signal level of the radio signal largely varies depending on the distance between the base station BMI and the mobile station MS, shadowing, and fadings. In the base station BMI, the radio signal S 3  thus distorted in waveform and varied in amplitude is received by the antenna  31 ; it is amplified by the LNA  32 ; and it is converted into a low frequency signal by the RF/IF portion  33 . An A/D converter and the like are provided at the input of the demodulator  35 . Therefore, the input signal level must fall within a predetermined range of levels. An output signal of the RF/IF portion  33  has a great level variation. The level variation of the output signal must be removed before it is input to the demodulator  35 . To remove the level variation, the AGC portion  34  is used. An output signal S 34  of the AGC portion  34  is demodulated by the demodulator  35 , and applied to the reception controller  36 . The reception controller  36  extracts the data portion from the burst signal. The demodulated signal S 34  is processed for its error removal, for example, and finally is output as a reception data signal S 4 .  
           [0008]    The operation of the AGC portion  34  for effecting the level correction will be described. FIG. 13 shows a basic arrangement of the conventional AGC portion  34 . In the figure, reference numeral  41  is an AGC amplifier;  42  is a level detector; and  43  is a low-pass filter (LPF). A low-frequency signal S 32  input to the AGC portion  34  contains a great level variation, as mentioned above. The AGC amplifier  41  of the AGC portion  34  amplifies or attenuate the low-frequency signal S 32 , and produces an output signal S 33 . The AGC output signal S 33  is input to the level detector  42 . The level detector compares a signal level of the AGC output S 33  with a reference signal level, and produces a signal representative of a difference between those signal levels. The difference signal is input to the LPF  43 . The LPF removes a minute variation of the difference signal and outputs an AGC amplifier control voltage signal or an RSSI (received signal strength indicator) signal S 40 . The RSSI signal S 40  determines a gain of the AGC amplifier  41 . The AGC amplifier  41  is thus controlled, and through its control, the output signal strength level of the amplifier  41  is approximate to the reference signal level. The operation of the AGC-portion  34  is as described above. A given time is taken till a close loop consisting of the AGC amplifier  41 , level detector  42  and LPF  43  settles down in operation. In the “TIA/EIA/IS-139.1-A”, to secure a satisfactory demodulation, as shown in FIGS. 14A and 14B, the AGC output signal (input to the demodulator) is settled down at the preamble (PREAM) portion (located in the head portion of the reception burst format) of the reception burst, so that the AGC output levels of the SYNC and DATA portions (follows the PREMA portion in the reception burst format) are put within a desired range of signal levels.  
           [0009]    In a case where the fixed repetition pattern is used for the AGC preamble as mentioned, the radio signal having undergone a frequency selective fading channel improperly operates the AGC portion or circuit. This problem is remarkably revealed in particular in a case where a symbol rate is faster than a fading variation rate and a state of fading little varies within the preamble portion. The frequency selective fading will be described. The frequency selective fading occurs where a delay quantity of a delayed wave, reflected by a distant obstacle, e.g., mountain and building, is not negligible when comparing with the symbol period (FIG. 15).  
           [0010]    A fading phenomenon producing a delay quantity of the delayed wave which is at least {fraction (1/10)} as large as the symbol period sometimes is categorized into the frequency selective fading. If no measure is taken for this fading, the preceding wave interferes with the delayed wave, thereby causing a misjudgment of the received signal (FIG. 16). A composite wave of the preceding wave and the delayed wave is depicted in terms of a frequency spectrum in FIG. 17. The graph shows a great distortion of a waveform, which is representative of an intensity variation of a reception signal having undergone the frequency selective fading channel with respect to frequency. In this sense, the fading of this type is called the “frequency selective fading”. Thus, the frequency selective fading is more likely to occur with increase of the information rate, or the symbol rate.  
           [0011]    In the wireless communication system of the type in which a simple repetition pattern is used for the AGC preamble pattern, when the signal is distorted by frequency selective fading channel, an average reception power of the preamble portion greatly varies depending on a relative phase of the preceding wave to the delayed wave and vice versa. FIG. 18 is a vector diagram showing relative phases of the preceding wave to the delayed wave, and the composite waves of those waves at the relative phases. In the figure, times  1  to  3  indicate consecutive three symbols. In case where the fixed repetition pattern is used for the preamble, a relative phase of the preceding wave to the delayed wave is invariable, and therefore, if the fading rate is sufficiently lower than the data transmission rate, the fixed relative phase will be maintained during the-preamble reception. The diagram of FIG. 18 shows three cases: a first case where the preceding wave and the delayed wave cancel out (vector diagrams ( 1 ), ( 2 ) and ( 3 )); a second case where those waves a little interact with each other (vector diagrams ( 4 ), ( 5 ) and ( 6 )); and a third case where those waves additively act (vector diagrams ( 7 ), ( 8 ) and ( 9 )). The relative phase of preceding wave to the delayed wave varies depending on a delay quantity of the delayed wave. Therefore, the relative phase randomly varies with the movement of the mobile station MS. And the average reception power varies with time.  
           [0012]    When a random pattern is received (in this case, the data portion will take a substantially random pattern by scramble and the like), the relative phase of the preceding wave to the delayed wave varies also within the burst. Therefore, the preceding wave and the delayed wave additively and subtractively act within the same burst, and the average reception power is uniform over the entire range of the burst, as shown in FIG. 19.  
           [0013]    In the wireless communication system where the AGC output signal is settled down at the preamble portion and its intensity level is kept substantially constant in the subsequent data portion, the reception power difference between the preamble portion and the data portion is great, entailing a poor modulation. The operation of the AGC circuit in connection with this is shown in FIGS. 20A and 20B. In this case, viz., the large-reception power difference is present between the preceding wave and the subsequent delayed wave (including the SYNC portion), if the AGC output signal is settled down at the preamble portion (( 1 ) in FIGS. 20A and 20B), there is produced an improper output level at the in the data portion. The AGC output signal must be settled down again (( 3 ) in FIGS. 20A and 20B) till the AGC output signal is approximate to the reference value. Thence, the demodulator continues its improper demodulation of the data (( 2 ) in FIGS. 20A and 20B) till the AGC output signal is settled down again.  
         SUMMARY OF THE INVENTION  
         [0014]    The present invention has been made to solve the above problems, and has an object to provide a data transmission system, and a data transmitter and a data receiver, which can secure a satisfactory level control (AGC) and a proper level detection under the frequency selective fading environment, whereby a good communication is secured.  
           [0015]    To achieve the above object, according to the invention, there is provided a data transmission system in which a transmitter side adds control data to transmission data, and modulates the resultant signal by a predetermined modulation method, and sends the-result in a wireless manner, and a receiver side detects a reception power intensity by use of the control data contained in the transmitted signal, the improvement being characterized in that a random pattern is used for a reception-power detecting portion for detecting a reception power intensity, which is contained in the control data.  
           [0016]    In the data transmission system, the reception-power detecting portion is located preceding to the transmission data, and in the receiver side, a reception power intensity of the reception-power detecting portion is detected, and the reception power intensity of the subsequent transmission data portion is adjusted.  
           [0017]    In the data transmission system, the reception-power detecting portion is located preceding to the transmission data, and in the receiver side, an antenna selection diversity is realized which detects a reception power intensity of the reception-power detecting portion, and selects a receiving antenna for the subsequent transmission data portion.  
           [0018]    In the data transmission system, the reception-power detecting portion is located preceding to the transmission data, and in the receiver side, a reception power intensity is detected during the reception-power detecting portion, and a hand-over function is realized which selects a transmitter station.  
           [0019]    In the data transmission system, the reception-power detecting portion is located preceding to the transmission data, and in the receiver side, a reception power intensity is detected during the reception-power detecting portion, and a hand-over function-is--realized which selects a transmitter station of the subsequent transmission data portion.  
           [0020]    In the data transmission system, the random pattern is an M-sequence data pattern.  
           [0021]    In the data transmission system, the random pattern contains an M-sequence data pattern of 7 bits or longer.  
           [0022]    In the data transmission system, the random pattern is a random pattern of which one period is longer than a distance corresponding to the number of bits representative of the maximum delay quantity of a delayed wave that is prescribed in the channel model for the wireless communication system.  
           [0023]    In the data transmission system, when the transmission data is transmitted, the control data of one burst is added every one or a plural number of transmission data.  
           [0024]    The invention provides a data transmitter in use with a data transmission system in which a transmitter side adds control data to transmission data, and modulates the resultant signal by a predetermined modulation method, and sends the result in a wireless manner, and a receiver side detects a reception power intensity by use of the control data contained in the transmitted signal, the data transmitter comprises random pattern adding means for adding a random pattern to a reception-power detecting portion for detecting a reception power intensity, which is contained in the control data.  
           [0025]    In the data transmission system, the random pattern added by the random pattern adding means is an M-sequence data pattern.  
           [0026]    In the data transmission system, the random pattern added by the random pattern adding means contains an M-sequence data pattern of 7 bits or longer.  
           [0027]    In the data transmission system, the random pattern added by the random pattern adding means is a random pattern of which one period is longer than a distance corresponding to the number of bits representative of the maximum delay quantity of a delayed wave that is prescribed in the channel model for the wireless communication system.  
           [0028]    In the data transmission system, the random pattern adding means operates such that when the transmission data is transmitted, the control data of one burst is added every one or a plural number of transmission data.  
           [0029]    The invention further provides a data receiver in use with a data transmission system in which a transmitter side adds control data to transmission data, and modulates the resultant signal by a predetermined modulation method, and sends the result in a wireless manner, and a receiver side detects a reception power intensity by use of the control data contained in the transmitted signal, the data receiver comprises a reception-power intensity adjusting means for detecting a reception power intensity in the reception-power detecting portion and adjusting a reception power intensity of the subsequent transmission data portion when a random pattern is added to a reception-power detecting portion for detecting a reception power intensity, which is contained in the control data, and the reception-power detecting portion is located preceding to the transmission data.  
           [0030]    The present invention also provides a data receiver in use with a data transmission system in which a transmitter side adds control data to transmission data, and modulates the resultant signal by a predetermined modulation method, and sends the result in a wireless manner, and a receiver side detects a reception power intensity by use of the control data contained in the transmitted signal, the data receiver comprises antenna select diversity means for detecting a reception power intensity in the reception-power detecting portion and for selecting a receiving antenna, when a random pattern is added to a reception-power detecting portion for detecting a reception power intensity, which is contained in the control data, and the reception-power detecting portion is located preceding to the transmission data.  
           [0031]    Additionally, the invention provides a data receiver in use with a data transmission system in which a transmitter side adds control data to transmission data, and modulates the resultant signal by a predetermined modulation method, and sends the result in a wireless manner, and a receiver side detects a reception power intensity by use of the control data contained in the transmitted signal, the data receiver comprises antenna select diversity means for detecting a reception power intensity in the reception-power detecting portion and for selecting a receiving antenna for the subsequent transmission data portion, when a random pattern is added to a reception-power detecting portion for detecting a reception power intensity, which is contained in the control data, and the reception-power detecting portion is located preceding to the transmission data.  
           [0032]    Further, the invention provides a data receiver in use with a data transmission system in which a transmitter side adds control data to transmission data, and modulates the resultant signal by a predetermined modulation method, and sends the result in a wireless manner, and a receiver side detects a reception power intensity by use of the control data contained in the transmitted signal, the data receiver comprises hand-over control means for detecting a reception power intensity in the reception-power detecting portion and for selecting a transmitter station for the subsequent transmission data portion, when a random pattern is added to a reception-power detecting portion for detecting a reception power intensity, which is contained in the control data, and the reception-power detecting portion is located preceding to the transmission data.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]    [0033]FIG. 1 is a block diagram showing a transmitter in a wireless communication system which is an embodiment 1 of the present invention;  
         [0034]    [0034]FIGS. 2A and 2B are explanatory diagrams useful in explaining the structure of a transmission burst generated in the transmitter;  
         [0035]    [0035]FIG. 3 is a graph showing a probability density distribution of reception power obtained when two QPSK modulated waves interfere with each other in random phase-differences;  
         [0036]    [0036]FIG. 4 is a block diagram showing a transmitter of a wireless communication system, which is an embodiment 2 of the present invention;  
         [0037]    [0037]FIG. 5 is a block diagram showing an arrangement of an AGC portion of the receiver in the second embodiment;  
         [0038]    [0038]FIG. 6 is a block diagram showing a receiver of a wireless communication system, which is an embodiment 3 of the present invention;  
         [0039]    [0039]FIG. 7 is a diagram showing a burst format used in the embodiment 4;  
         [0040]    [0040]FIG. 8 shows in block form an overall wireless communication system;  
         [0041]    [0041]FIG. 9 shows in block form a conventional transmitter in the wireless communication system;  
         [0042]    [0042]FIG. 10 shows in block form a conventional receiver in the wireless communication system;  
         [0043]    [0043]FIG. 11 is a diagram showing a burst format containing an AGC preamble added thereto;  
         [0044]    [0044]FIG. 12 is a diagram showing the phases of those symbols of the preamble;  
         [0045]    [0045]FIG. 13 is a block diagram showing an arrangement of the conventional AGC portion;  
         [0046]    [0046]FIGS. 14A and 14B are diagrams useful in explaining an AGC processing procedure;  
         [0047]    [0047]FIG. 15 is a diagram useful in explaining a frequency selective fading;  
         [0048]    [0048]FIG. 16 is a set of waveforms for explaining the occurrence of an error when the radio signal undergoes a frequency selective fading;  
         [0049]    [0049]FIG. 17 is a diagram showing frequency spectra of a preceding wave and a delayed wave when the radio wave distorted by a frequency selective fading channel;  
         [0050]    [0050]FIG. 18 is a vector diagram showing relative phases of the preceding wave to the delayed wave, and the composite waves of those waves at the relative phases;  
         [0051]    [0051]FIG. 19 is a vector diagram useful in explaining a case where the preceding wave and the delayed wave additively and subtractively act within the same burst; and  
         [0052]    [0052]FIGS. 20A and 20B are diagrams showing a case where a reception power level difference is present between the preamble portion and the subsequent data portion in the burst.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0053]    The preferred embodiments of the present invention will be described with reference to the accompanying drawings.  
       &lt;Embodiment 1&gt;  
       [0054]    [0054]FIG. 1 is a block diagram showing a transmitter in a wireless communication system which is an embodiment 1 of the present invention. Like reference numerals are used for designating like or equivalent portions in FIG. 9 showing the prior transmitter already described. In the figure, reference numeral  11  is a burst generator;  13  is a modulator;  14  is an antenna; and  51  is a preamble adder. The burst generator  11  receives transmission data S 1  and an information signal S 11  from the preamble adder  51 , and generates a transmission burst S 52  by use of those signals. The modulator  13  modulates the transmission burst S 52  derived from the burst generator  11 . The antenna  14  emits a modulated signal S 53 . The arrangements of the wireless communication system and the receiver are substantially the same as those of the prior ones described in connection with FIGS. 8 and 10. In the embodiment 1, the channel  2  (FIG. 8) is a channel suffering from the frequency selective fading channel.  
         [0055]    The operation of the transmitter of the embodiment 1 will be described. The burst generator  11  generates a transmission burst S 52  by adding bits of the ramp (R) and the sync word (SYNC) and an AGC preamble (random pattern) to data (DATA) to be transmitted (FIGS. 2A and 2B). The transmission burst S 52  is modified by the modulator  13 , and emitted from the antenna  14 , in the form of a transmitting radio signal S 2 . The transmitting radio signal S 2  undergoes a frequency selective fading channel  2 , and reaches the antenna  31  of the receiver. In the receiver, the received signal is amplified by the LNA  32 , and converted into a low-frequency signal S 32  by the RF/IF portion  33 . The output signal of the RF/IF portion  33  contains a great variation of signal level. The AGC portion  34  then removes signal level variation from the incoming signal, and applies its output signal to the demodulator  35 . The reception controller  36  extracts the data portion from the burst of the demodulated signal, and outputs a reception data signal S 4 .  
         [0056]    A probability density distribution of reception power obtained when two QPSK modulated waves (preceding wave power=  1  (normalized value) and delayed wave= 0.5) interfere with each other in random phase-differences, is shown in terms of normalized anti-logarithm in FIG. 3. In the graph, an M-sequence is employed for a random pattern. As seen from the graph, the reception power of the random pattern is substantially constant, but the reception power of the ALLO (repetition pattern) greatly varies. Therefore, the former reception power will be incoincident with the latter one highly probably.  
         [0057]    In the embodiment 1, it is noted that the random pattern is used for the preamble. Therefore, there is no chance that a great difference of reception power is produced between the preamble portion and the data portion in the burst. The AGC portion  34  settles down a signal level variation of the reception signal having undergone the frequency selective fading into a proper signal level (( 1 ) in FIGS. 2A and 2B) in the preamble portion of the burst signal, whereby it adjusts the signal level of the subsequent data portion to the reference value or its near value.  
         [0058]    The random pattern, which is added, as the preamble, in forming the burst by the preamble adder  51 , is not limited to that of the M-sequence, but may take any other random pattern if the preamble pattern is not a repetition pattern of which one period is shorter than a distance corresponding to the number of bits representative of the maximum delay quantity of the delayed wave. In other words, any random pattern may be used if it causes the modulated signal of the preamble portion whose spectrum is not a line spectrum but a broad spectrum.  
       &lt;Embodiment 2&gt;  
       [0059]    A transmitter of a wireless communication system, which is an embodiment 2 of the present invention, is shown in FIG. 4 which uses like reference numerals for designating like or equivalent portions in FIG. 1 showing the embodiment 1. An arrangement of an AGC portion of the receiver in the wireless communication system of the second embodiment is shown in FIG. 5 which uses like reference numerals for designating like or equivalent portions in FIG. 13 of the prior AGC portion. In FIG. 4, reference numeral  60  is a data burst generator;  61  is a random pattern generator;  62  is an AGC burst generator; and  63  is a burst-select switch. The data burst generator  60  generates a data burst signal S 62 . The random pattern generator  61  generates an AGC random pattern S 60 . The AGC burst generator  62  generates an AGC burst signal S 61 . The burst-select switch  63  selects a burst signal to be transmitted, an AGC burst signal S 61  or a data burst signal S 62 . In FIG. 5, reference numeral  70  is a memory for storing an output signal S 40  of the LPF  43  in the form of an AGC-amplifier control voltage S 40 A; and  71  is a switch to determine as to whether or not the output signal S 40  of the LPF  43  is to be stored into the memory  70 . The arrangements of the wireless communication system and the receiver, which are used for this embodiment, are substantially the same as those in FIGS. 8 and 10.  
         [0060]    The operation of the transmitter of the second embodiment will be described. In the transmitter, the AGC burst generator  62  generates an AGC burst signal S 61  by use of an AGC random pattern S 60  output from the random pattern generator  61 . Further, the data burst generator  60  generates a data burst signal S 62  by use of the transmission data S 1 . The burst-select switch  63  selects one of those bust signals in accordance with a predetermined procedure, the modulator  13  modulates the selected burst signal, and the modulated signal is emitted from the antenna  14 , in the form of a transmitting radio signal S 2 . The signal S 2  experiences a frequency selective fading and enters the receiver  3 . In the receiver, the received signal is processed for amplification and frequency-conversion-into an AGC input signal S 3 .  
         [0061]    During the reception of the AGC burst, the switch  71  is turned on in the AGC loop, and the AGC-amplification control voltages (RSSI) S 40  and S 40 A control the AGC amplifier  41  so that the output signal of the amplifier has the reference value. In the reception of the data burst signal, the switch  71  is turned off, a value which was stored in the memory  70  when the AGC burst signal is received is used as the RSSI voltage S 40 A.  
         [0062]    In the second embodiment 2, when the AGC burst signal and the data bust signal are received, if a variation in a state of the channel  2  is small, the RSSI S 40  of the equal value may be used for the data burst receiving process, and hence the AGC amplifier produces an AGC output signal S 33  at a proper level from the start of the burst during the data burst reception. Therefore, the subsequent signal processings by the demodulator  35  and the reception controller  36  will be performed normally, whereby good data reception is effected on the basis of the proper demodulation. Also in the data burst reception, the value of the RSSI40A may be corrected by turning on the switch  71 .  
       &lt;Embodiment 3&gt;  
       [0063]    [0063]FIG. 6 is a block diagram showing a receiver in a wireless communication system, which is an embodiment 3 of the present invention. In FIG. 6, like reference numerals are used for designating like or equivalent portions in FIG. 10. The receiver consists of two signal routes ranging from the antenna  31  to the level detectors. The circuit components in those signal routes are distinguished from each other by affixing letters A and B at the ends of reference numerals. In the figure, reference numerals  80 A and  80 B are level detectors;  81  is a selector; and  82  is a switch. The level detector  80 A ( 80 B) measure a reception power level and produces a reception level information signal S 80 A (S 80 B). The selector  81  receives the reception level information signals S 80 A and S 80 B, and selects the level information signal of better reception state among from those received signals. The switch  82  is driven in response to a control signal S 81  from the selector  81 . Signals S 82 A and S 82 B are output from the level detectors  80 A and  80 B. The arrangements of the wireless communication system and the transmitter, which are used for this embodiment, are substantially the same as those in FIGS. 8 and 1.  
         [0064]    The operation of the embodiment 3 will be described. The antennae  31 A and  31 B receive a radio wave from the transmitter. The signals, received by those antennae, are amplified and frequency-converted, and input to the level detectors  80 A and  80 B. The level detectors  80 A and  80 B detects power levels of the signals S 32 A and S 32 B, and outputs the reception-level information signals S 80 A and S 80 B to the selector  81 . The level detectors  80 A and  80 B may take any of various forms. In case where those are constructed with the AGC circuits, the RSSI signals are used as the reception-level information signals.  
         [0065]    The selector  81  compares the reception-level information signals S 80 A and S 80 B from the level detectors  80 A and  80 B, and outputs a control signal S 81  as the result of the comparison to the switch  82 . In turn, the switch  82  allows the signal, which is received by the antenna  31 A or  31 B and selected by the selector  81 , to pass therethrough and go to the demodulator  35 . When the burst format shown in FIG. 11 is used, the selector  81  is operated during the receiving of the AGC preamble to operate the switch  82 . By so doing, a reception signal is more suitable for the receiving of the data portion, improving the receiving performance of the receiver. Also in the embodiment 3, it is essential to predict a reception power intensity during the processing of the preamble portion.  
       &lt;Embodiment 4&gt;  
       [0066]    [0066]FIG. 7 shows a burst format used in an embodiment 4 of the present invention. In a wireless communication system where the RSSI for the AGC is determined by use of reception power information of a burst signal received in the past, the AGC pattern may be located at the middle or the end of the burst format (midamble and postamble). The preamble, midamble and postamble may properly be combined.  
       &lt;Embodiment 5&gt;  
       [0067]    In a mobile station which receives radio waves from a plural number of base stations, the present invention may be used for selecting a-desired base station from among those base stations. Specifically, a reception level is detected by use of the AGC preamble of a random pattern or the AGC burst signal, and the best base station is determined by the detected reception level and sets up a related channel. This selection may be performed during the receiving through a specific channel.