JP6032543B2 - Antenna switching reception system and corresponding transmission system - Google Patents

Description

  The present invention relates to an antenna switching reception system for switching and receiving an antenna in a wireless communication system.

  In wireless communication systems, level degradation due to multipath fading is one of the problems. Signals received by the receiving antenna include not only signals directly input from the transmitting antenna to the receiving antenna but also signals input through a plurality of different paths. For this reason, signals (multipaths) having different delay times are also input to the receiving antenna, so that the reception level deteriorates by overlapping and canceling signals at the receiving antenna end. This is a phenomenon called level degradation due to multipath fading.

  As a representative measure for avoiding the influence of level deterioration due to multipath fading, there is a multicarrier transmission technique such as OFDM. This is a technology that can reduce the influence of level degradation due to multipath fading because information to be transmitted is divided into a plurality of carriers (subcarriers) and transmitted in a wide frequency band. However, in OFDM transmission, it is difficult to reduce the cost because it requires a complicated configuration for processing by transforming the frequency axis and time axis by inverse Fourier transform and Fourier transform, which increases the circuit scale. was there.

  In addition, there are measures by “switching diversity”, “selective diversity” for switching a plurality of antennas, and “combining diversity” for combining received signals at each antenna. These measures are based on the fact that the effects of multipath fading differ depending on the location of the receiver and the plane of polarization of the radio wave. “Selective diversity” is a technology that monitors reception levels at multiple antennas and receives signals with optimal antennas, but requires as many receivers as the number of antennas, which increases the circuit scale. There were drawbacks. “Combining diversity” is a technology that combines the phases of signals received by multiple antennas, but this also requires as many receivers as the number of antennas and a phase shifter that matches the phases of each signal. There was a drawback that the circuit scale was increased.

  “Switching diversity” is a technique for reducing the influence of multipath fading by switching to the other antenna when one antenna has the influence of multipath fading. In recent years, with the widespread use of portable wireless devices, the antenna switching unit is also required to be downsized and reduced in cost, and can be configured with a single receiver. Diversity "is installed in various radio devices.

  However, in “switching diversity”, the reception level at the switching destination antenna is not known until the antenna is switched. For this reason, if the reception level at the antenna to be switched to is lower, there is a disadvantage that the signal must be received under worse conditions.

  Further, the wireless LAN is based on a system that receives a plurality of packets (frame: a set of signals constituting a preamble, a unique word, and a payload) and switches an antenna when an error is detected over a plurality of packets. In other words, the antenna is switched after an error occurs, and the generated error is dealt with by sending the same packet again from the transmitter (retransmission function). However, in a situation where the communication environment is poor due to multipath fading, the number of retransmissions increases, making it unsuitable for devices that need to communicate with multiple devices and receive new payload signals one after another.

  Various proposals have been made to overcome the above-mentioned drawbacks of “switching diversity”. For example, in Patent Document 1, in an antenna switching reception system that switches a plurality of antennas to receive radio signals, the quality of received radio signals is compared while switching antennas at a predetermined cycle, and an antenna that receives a payload is selected. Techniques to do this have been proposed.

  In Patent Document 1, FIGS. 6 to 9 and the like show that the plurality of unique word detection units individually detect a plurality of types of unique words and execute different antenna selection operations according to the detected unique words. Discloses a technique for selecting an antenna. The plurality of types of unique words UW1 to UW4 are composed of different bit strings, and the plurality of unique word detection units simultaneously wait for the unique words UW1 to UW4 and detect UW1 to UW4 included in the packet.

WO2012 / 028917

  The process of simultaneously waiting for a plurality of types of unique words UW1 to UW4 as described above places a heavy burden on the receiving system, and a plurality of unique word detection units that execute this process are subjected to a corresponding load. Therefore, a CPU (Central Processing Unit) having relatively high specifications is applied to the baseband unit including a plurality of unique word detection units in Patent Document 1. Further, the higher the transmission speed during communication, the more advanced CPU application is required.

  However, since a CPU with high specifications and high specifications has a high cost, it is one factor that hinders the reduction of the manufacturing cost of the wireless communication system. Also, recent wireless communication systems tend to incorporate a wide variety of functions. When a CPU is used to detect a plurality of unique words, execution of other functions is temporarily hindered. There is a fear.

  The present invention has been made to solve the above problems. That is, it is possible to provide an antenna switching reception system and the like that can reduce the influence of level fluctuations due to multipath fading by accurately selecting an antenna with high signal quality with a simple and inexpensive configuration without heavy processing. For the purpose.

In order to achieve the above object, the antenna switching reception system of the present invention searches for an antenna control unit that controls switching of a plurality of antennas and a received radio signal while switching antennas, and is set in advance. A bit string detection unit that detects the same bit string as the bit string of the unique word and a signal quality detection unit that detects the quality of the radio signal received for each antenna, and the bit string detection unit includes a plurality of When any one of the first unique words is detected within the first predetermined time, the signal quality detection unit detects the quality of the received radio signal, and the antenna control unit switches the antenna. Thereafter, the bit string detection unit searches for a first unique word different from any one of the first unique words within a second predetermined time. The signal quality detection unit detects the quality of the radio signal received by the switched antenna, and the antenna control unit selects an antenna having a high signal quality detected by the signal quality detection unit, and then Antenna receiving system, wherein the first unique word is transmitted by twice the number of the plurality of antennas, and each of the plurality of antennas is first detected by the first unique word. Until the first unique word is switched, the preamble is transmitted before the first unique word and the transmission period is twice as long as the transmission period of the first unique word.

  In this invention, after the antenna control unit selects an antenna having a high signal quality, the antenna detects when the bit string detection unit detects a second unique word different from the first unique word within a third predetermined time. The control unit preferably receives the subsequent payload while the antenna is fixed.

  In the present invention, the first predetermined time corresponds to a time corresponding to two cycles of the first unique word and a preamble received before the first unique word, and the second predetermined time is the first unique word. It is preferable to correspond to a time of one cycle or more of the preamble.

  In the present invention, the third predetermined time is one cycle of the preamble received before the second unique word and the second unique word at a time equal to or longer than three cycles of the preamble and the first unique word. It is preferable to correspond to the time added.

  In this invention, it further includes a header detection unit that detects a header included in the payload, and a data detection unit that detects data included in the payload, and the header detection unit detects the header within a fourth predetermined time. It is preferable to return to the detection operation of the first unique word by the bit string detection unit while switching the antenna again without receiving the payload data.

  In this invention, it further includes a reception time update unit that updates a data reception time for detecting the data based on a length included in the header, and the data detection unit is updated by the reception time update unit. When the detection of the data cannot be completed within the reception time, it is preferable to return to the operation of detecting the first unique word by the bit string detection unit while switching the antenna again.

The transmission system according to the present invention corresponds to the antenna switching reception system, and transmits the first unique word before the payload by twice the number of the plurality of antennas .

  In this invention, it is preferable to transmit the second unique word before the payload after transmitting the plurality of first unique words.

  According to the antenna switching reception system of the present invention, it is not necessary for the bit string detection unit to wait for a plurality of types of unique words at the same time, so the processing load on the bit string detection unit is reduced. As a result, instead of an expensive CPU, a bit string detection unit can be configured with a low-spec IC or the like, and an antenna with high signal quality can be selected accurately. With a simple and inexpensive configuration, multipath fading can be used. The effect of level fluctuation can be reduced. Moreover, since the operation | movement which detects a 1st unique word with the switched antenna is stopped for the 2nd predetermined time, the processing burden of a bit string detection part can be reduced. In addition, even when a signal can be received by only one antenna, it can be handled without any problem. Even if the quality of the radio signal received by the switched antenna does not reach a level at which the first unique word can be detected, the detection of the first unique word is stopped after the second predetermined time has passed, This is because preparation can be made for detection of a unique word.

The block diagram which shows the concept of HEMS to which the antenna switching receiving system by one Embodiment of this invention is applied. The block diagram which shows the schematic structure of the HEMS controller which comprises the antenna switching reception system and its transmission system, and comprises the HEMS, and various household appliances. The block diagram which shows the structure of the antenna switching reception system. The figure which shows the transition of the signal transmitted from the corresponding transmission system in the same embodiment, the antenna switched by the same antenna switching receiving system, the signal received by each antenna, and its reception level. In the same embodiment, another figure which shows the transition of the signal transmitted from the corresponding transmission system, the antenna switched by the same antenna switching reception system, the signal received by each antenna, and its reception level. In the same embodiment, another figure which shows the transition of the signal transmitted from the corresponding transmission system, the antenna switched by the same antenna switching reception system, the signal received by each antenna, and its reception level. In the same embodiment, another figure which shows the transition of the signal transmitted from the corresponding transmission system, the antenna switched by the same antenna switching reception system, the signal received by each antenna, and its reception level. The flowchart which shows operation | movement of the antenna switching reception system. The figure which shows the structure of the payload received by the same antenna switching reception system. 9 is a flowchart showing in detail an example of operations of # 1 to # 7 in FIG. 9 is a flowchart showing in detail an example of operations of # 9 to # 14 in FIG. The flowchart which shows an example of operation | movement of # 20 thru | or # 23 in FIG. 8 in detail. The flowchart which shows an example of operation | movement of # 23 in FIG. 8 in detail. 14 is a flowchart showing an example of the operation of FIG. 13 in more detail.

  An antenna switching reception system according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an energy management system called a HEMS (Home Energy Management System) or the like. HEMS is a system that performs information presentation and automatic control for power saving by connecting home electric appliances in a home via a communication network and performing integrated control together with a switchboard and a home power generation facility. The HEMS 100 includes a HEMS controller 101, various home appliances 102, a solar power generator 103, a fuel cell 104, a storage battery 105, an electric vehicle 106, an information processing terminal 107, a distribution board 108, and the like. The The distribution board 108 incorporates a power measurement communication device 108a. Distribution board 108 is connected to an outdoor smart meter 109. The smart meter 109 is provided from the power company to each user's home, supplies power to the distribution board 108 from the transmission line, and measures the main power in the distribution board 108. Various information (for example, a request for power saving) is input from the power company server 110 to each user's home to the HEMS controller 101 via the smart meter 109 and the power measurement communication device 108a. The power measurement communication device 108a and the smart meter 109 are connected by wire or wirelessly. The power measurement communication device 108a may be provided outside the distribution board 108 and connected to the distribution board 108 by wire or the like. The smart meter 109 is connected to the smart meter 109 of another house and the server 110 of the electric power company by wireless or wired to constitute a smart meter network.

  The HEMS controller 101 is a wireless energy-saving control device, and controls various devices as the core of the network described above. HEMS controller 101 and home appliance 102, solar power generator 103, fuel cell 104, storage battery 105, electric vehicle 106, information processing terminal (monitor device) 107, distribution board 108 and the like (hereinafter referred to as home appliance 102) In this case, two-way communication is established by wire or wireless. Each device may be configured to be connected to the HEMS controller 101 via another device. For example, the fuel cell 104 may be connected to the power measurement communication device 108a of the distribution board 108 by wire, and the power measurement communication device 108a may be connected to the HEMS controller 101 wirelessly. In this case, bidirectional communication is established between the fuel cell 104 and the HEMS controller 101 by wire and wireless via the power measurement communication device 108a.

  FIG. 2 shows a schematic configuration of the HEMS controller 101 and various home appliances 102 in the HEMS 100. In various devices constituting the HEMS 100, devices that perform wireless communication, such as the HEMS controller 101 and the home appliance 102, are each equipped with a corresponding transmission system and reception system. The antenna switching reception system 1 according to an embodiment of the present invention is applied as this reception system, and the transmission system 70 of the present invention is applied as a corresponding transmission system. That is, when the transmission system 70 of the HEMS controller 101 functions, the antenna switching reception system 1 such as the home appliance 102 functions to transmit and receive radio signals. On the other hand, when the transmission system 70 such as the home appliance 102 functions, the antenna switching reception system 1 of the HEMS controller 101 functions to transmit and receive radio signals. 2 illustrates the configuration of the HEMS controller 101 and the home appliance 102, but a device such as the power measurement communication device 108a may be applied instead of the home appliance 102.

  FIG. 3 shows an antenna switching reception system. The antenna switching reception system 1 includes a receiver 2 and a plurality of antennas A and B. The receiver 2 includes an antenna switching unit 3, an RFIC 4, a CPU 5, and the like.

  The antenna switching unit 3 switches the antenna that receives the radio signal among the two antennas A and B in accordance with the control signal output from the CPU 5. The RFIC 4 includes an RF unit (signal quality detection unit) 41, a demodulation unit 42, a synchronization establishment unit 43, a preamble detection unit (bit string detection unit) 44, a unique word (UW) detection unit (bit string detection unit) 45, and the like. Have That is, circuits such as the RF unit 41, the demodulation unit 42, the synchronization establishment unit 43, the preamble detection unit 44, and the unique word detection unit 45 are integrated and mounted on one IC chip.

  The RF unit 41 down-converts a radio signal received using any one of the antennas A and B, and extracts a baseband signal. When the RF unit 41 receives a radio signal, AFC (Automatic Frequency Control) is generally executed, and a frequency error between transmission and reception is removed. In that case, AFC may be canceled for a predetermined time after the antenna switching unit 3 switches the antenna. This is to avoid the influence of the interference wave, accurately detect the preamble and the unique word, and reduce the packet loss. Further, the RF unit 41 detects the reception level of the radio signal received using any one of the antennas A or B. For example, RSSI (Received Signal Strength Indication) is used to detect the reception level. A signal related to the reception level detected by the RF unit 41 is input to the signal processing unit 51 of the CPU 5 and used for detecting the quality of the radio signal. The demodulator 42 demodulates the baseband signal extracted by the RF unit 41. The synchronization establishment unit 43 establishes bit synchronization of the demodulated baseband signal.

  The preamble detection unit 44 searches for a baseband signal whose synchronization is established by the synchronization establishment unit 43, and detects a bit string of the preamble. A specific example of the preamble bit string is a bit string in which 01 is alternately repeated (hereinafter referred to as 01 alternating). In the preamble detection unit 44, a bit string of a known preamble (same as the preamble transmitted from the transmission system) is set and stored in advance. The preamble is detected by evaluating the degree of coincidence between the bit string of the baseband signal and the bit string stored in advance. When both match completely, it is determined that the preamble has been detected. For example, when the preamble is composed of 01 alternatings, the preamble detecting unit 44 may determine that the preamble has been detected when the 01 alternatings continuously match in a predetermined bit. In this case, the preamble detection timing may be different each time (see FIG. 4 and the like). Furthermore, it may be determined that the preamble has been detected when the error rate of the bit string of the baseband signal with respect to the preamble bit string stored in advance is equal to or less than a predetermined value. This is because even in this case, it can be considered that a bit string substantially identical to the preamble bit string stored in advance is detected from the baseband signal.

  A signal indicating that the preamble detector 44 has detected the preamble is input to the unique word detector 45, the CPU 5, and the like. The signal may be output from the preamble detection unit 44 to the CPU 5 and input to the unique word detection unit 45 or the like via the CPU 5.

  The unique word detection unit 45 searches the baseband signal for which synchronization is established by the synchronization establishment unit 43, and detects a bit string of the unique word. In the unique word detection unit 45, a bit string of a known unique word (same as the unique word transmitted from the transmission system) is set and stored in advance. The unique word is detected by evaluating the degree of coincidence between the bit string of the baseband signal and the bit string stored in advance. When the two match completely, it may be determined that a unique word has been detected, or when the error rate of the bit string of the baseband signal with respect to the bit string of the unique word stored in advance is below a predetermined value, the unique word It may be determined that has been detected. This is because even in the latter case, it can be considered that a bit string substantially identical to the bit string of the unique word stored in advance is detected from the baseband signal. A signal indicating that the unique word detection unit 45 has detected a unique word is input to the signal processing unit 51 of the CPU 5 or the like. The known preamble and unique word described above are shared with the corresponding transmission system, and a packet to which the preamble and unique word are added is transmitted from the transmission system.

  The CPU 5 includes a signal processing unit (signal quality detection unit, header detection unit, data detection unit, reception time update unit) 51, an antenna control unit 52, a counter 53, and the like, and controls the antenna switching reception system 1. The CPU 5 may be configured to detect a preamble or a unique word instead of the preamble detection unit 44 or the unique word detection unit 45. In this case, the preamble detection unit 44 or the unique word detection unit 45 is omitted from the RFIC 4. The signal processing unit 51 performs various processes on the signals input from the RF unit 41, the synchronization establishment unit 43, the preamble detection unit 44, the unique word detection unit 45, and the like. For example, the signal processing unit 51 detects the quality of the radio signal from the signal representing the reception level input from the RF unit 41. At this time, the signal processing unit 51 performs a calculation process on the signal representing the reception level input from the RF unit 41, and calculates a numerical value that serves as a quality signal determination index. More specifically, the signal processing unit 51 calculates an average value for each antenna for the reception level input from the RF unit 41. The antenna control unit 52 evaluates the average value of the reception levels calculated by the signal processing unit 51, selects the antenna that receives the payload, determines whether or not the antenna needs to be switched, and determines the antenna switching unit 3 for the antenna. A control signal for switching is output. The counter 53 functions as the first counter to the fifth counter in FIGS. 4 to 7 and counts time.

  In the present embodiment, two antennas are switched by the antenna switching unit 3 to receive a radio signal, but the number of antennas may be three or more.

  4 to 7 show the signal transmitted from the corresponding transmission system, the antenna switched by the antenna switching reception system 1, the signal received by each antenna, and the transition of the reception level. One packet is composed of a plurality of pairs of preambles and unique words followed by a payload that is transmitted subsequently. In this embodiment, two kinds of unique words UW1 (first unique word) and unique words UW2 (second unique word) are transmitted from the transmission system.

  The unique word UW1 is used for the antenna switching reception system 1 to select an antenna that receives a payload. The unique word UW2 is used to detect the head of the payload (that is, to cue). The preamble transmitted before the unique word UW1 and the preamble transmitted before the unique word UW2 may be composed of the same bit string or may be composed of different bit strings. On the other hand, the preamble, the unique word UW1, and the unique word UW2 are composed of bit strings having a low correlation value so that they are not erroneously detected.

  The unique word UW1 is transmitted twice to each antenna so that it can be received regardless of the timing at which the antennas A and B are switched. A preamble is transmitted before every unique word. Further, dummy data is transmitted after the fourth unique word UW1 and before the preamble transmitted immediately before the unique word UW2. Note that data for giving an antenna switching waiting time may be inserted at the head of the second and subsequent preambles and dummy data as necessary.

  The antenna switching reception system switches radio signals transmitted from the transmission system while switching the antennas A and B at a predetermined period (for example, a period twice the transmission period of the preamble and the unique word UW1: a first predetermined time T1). Receive. The first predetermined time T1 is counted by a counter 53 that functions as a first counter. The received signal is down-converted by the RF unit 41 as described above, demodulated by the demodulation unit 42, and bit synchronization is established by the synchronization establishing unit 43. Then, the preamble is detected by the preamble detector 44, and the unique word UW1 is detected by the unique word detector 45.

  As described above, the preamble and the unique word UW1 are transmitted twice to each antenna so that the preamble and the unique word UW1 can be received regardless of the timing at which the antennas A and B are switched. In this embodiment, since two antennas are used, the preamble and the unique word UW1 are transmitted four times each as shown in FIGS. In this way, the preamble and unique word UW1 twice as many as the number of antennas mounted in the antenna switching reception system are transmitted. Further, until the unique word UW1 is detected for the first time, each antenna is switched at a cycle that is twice the transmission cycle of the preamble and the unique word UW1, that is, the first predetermined time T1. When any one of the unique words UW1 is detected, another unique word UW1 is searched over the second predetermined time T2 after switching the antenna. The second predetermined time T2 is set to be equal to or longer than the time corresponding to the transmission cycle of the preamble and the unique word UW1, and is counted by the counter 53 functioning as a second counter. The time for inserting the dummy data corresponds to the second predetermined time T2. In the present embodiment, the quality of the radio signal received until the first unique word UW1 is detected at the first predetermined time T1 is compared with the quality of the radio signal received over the second predetermined time T2 after antenna switching. And the antenna that receives the payload is selected. When the antenna is selected, the preamble and the unique word UW2 are searched over the third predetermined time T3. The third predetermined time T3 is set to be equal to or longer than a time obtained by adding a time corresponding to one cycle of the preamble and the unique word UW2 to a time corresponding to three cycles or more of the preamble and the first unique word UW1, and functions as a third counter. 53.

  4 and 5 show an antenna switching operation and the like when the unique word UW1 is detected by the antennas A and B. FIG. Of the received signal, the solid line portion is the signal received by each antenna. In the following description, for the sake of convenience, when the preamble detection unit 44 and the unique word detection unit 45 first detect the preamble and the unique word UW1, the antenna that has received the radio signal (is active) is referred to as the antenna A. To do. 4 shows that when the reception level of the radio signal received by antenna A is higher than the reception level of the radio signal received by antenna B, FIG. 5 shows the radio signal received by antenna A when the reception level of the radio signal received by antenna B is high. The cases where the reception level is higher than the above are shown.

  4 and 5, the preamble transmitted for the first time cannot be detected by switching the antenna during reception, and the preamble transmitted for the second time is received by the antenna A and detected by the preamble detection unit 44. The When the preamble is detected, the RF unit 41 starts detecting the reception level. Thereafter, the reception level is detected at a predetermined sampling period. Further, the unique word UW1 transmitted following the preamble is detected by the unique word detecting unit 45. The detection of the reception level is continued until the unique word UW1 is detected, and information regarding the detected reception level is sequentially stored in the signal processing unit 51. The signal processing unit 51 calculates an average value (assumed as RA) from the stored reception level.

  When the unique word UW1 is detected, a signal to that effect is output from the unique word detection unit 45 and input to the signal processing unit 51. A signal indicating that the unique word UW1 has been detected is transferred from the signal processing unit 51 to the antenna control unit 52, and the antenna control unit 52 outputs a command to switch the antenna to the antenna switching unit 3, and the antenna is connected to the antenna B. Can be switched to. Thereafter, the preamble transmitted for the third time is received by the antenna B and detected by the preamble detector 44. When the preamble is detected, the reception level is detected at a predetermined sampling period as in the case of the antenna A, and the unique word UW1 is detected. The information regarding the reception level at the antenna B is sequentially stored in the signal processing unit 51 separately from the information regarding the reception level at the antenna A described above, and the signal processing unit 51 determines the average value (RB) from the stored reception level. ) Is calculated.

  The RA and RB calculated by the signal processing unit 51 are input to the antenna control unit 52. The antenna control unit 52 selects an antenna that can obtain higher signal quality by comparing the RA and the RB calculated by the signal processing unit 51 as an antenna that receives the payload.

  In FIG. 4, since the reception level at antenna A is higher than the reception level at antenna B and RA> RB, the quality of the radio signal received at antenna A is higher than the quality of the radio signal received at antenna B. it is conceivable that. Therefore, the antenna control unit 52 compares the RA and RB calculated by the signal processing unit 51 and selects the antenna A having a higher reception level as an antenna that receives the payload. Thereby, the antenna is switched to the antenna A again, and is fixed to the antenna A until the reception of the packet is completed. Therefore, the preamble, unique word UW1 and dummy data transmitted for the fourth time are received by the antenna A, and the subsequent preamble, unique word UW2 and payload are also received by the antenna A.

  In FIG. 5, since the reception level at antenna B is higher than the reception level at antenna A and RB> RA, the quality of the radio signal received at antenna B is higher than the quality of the radio signal received at antenna A. it is conceivable that. Therefore, the antenna control unit 52 compares the RA and RB calculated by the signal processing unit 51 and selects the antenna B having a higher reception level as an antenna that receives the payload. Accordingly, the antenna is fixed to the antenna B without being switched until the reception of the packet is completed. Therefore, the preamble, unique word UW1 and dummy data transmitted for the fourth time are received by the antenna B, and the subsequent preamble, unique word UW2 and payload are also received by the antenna B.

  In FIG. 6, the preamble transmitted for the second time is received by the antenna A, detected by the preamble detection unit 44, etc., and switched to the antenna B, and then the preamble transmitted for the third time is detected by the preamble detection unit 44. The case where it was not done is shown. When the unique word UW1 transmitted for the second time is detected, it is switched to the antenna B immediately after that, so that the preamble transmitted for the third time is substantially received by the antenna B from the head. Therefore, the minimum time required to detect a preamble or the like from the radio signal received by the antenna B is equal to the time for transmitting a set of preambles and the unique word UW1. Therefore, if the preamble transmitted at the third time is not detected, the preamble transmitted at the fourth time may be received by the antenna B, or the antenna is immediately switched to the antenna A as shown in FIG. Also good. In the former case, the second predetermined time T2 is set to a time corresponding to twice the transmission period of the preamble and the unique word UW1, and the opportunity to detect the preamble or the like using the antenna B is obtained twice. Therefore, the opportunity to detect the reception level at the antenna B increases, and the antenna can be selected more appropriately. In the latter case, the second predetermined time T2 may be set to a time corresponding to the transmission cycle of the preamble and the unique word UW1, and the length of the dummy data may be set short to increase the proportion of the payload in the packet. it can. The reason why the length of the dummy data can be set short is as follows. For example, when the fourth unique word UW1 is first detected by the antenna A (see FIG. 7), the antenna is switched to the antenna B and dummy data is received. At this time, if the preamble or the like is detected twice using the antenna B as in the former case, dummy data for two cycles of the preamble and the unique word UW1 is required. On the other hand, by limiting the opportunity to detect a preamble or the like using the antenna B at one time as in the latter case, dummy data for one cycle of the preamble and the unique word UW1 is sufficient.

  In the latter case, since the preamble or the like has not been detected from the radio signal received by the antenna B, it is considered that the signal quality is not sufficient for receiving the payload. It can also be considered that RB = 0. Therefore, the antenna control unit 52 selects the antenna A that provides sufficiently high signal quality as the antenna that receives the payload, and the antenna is switched to the antenna A again and fixed to the antenna A until the reception of the packet is completed. Is done. Even when RB = 0 is considered, an equivalent operation is performed. Further, even if the preamble can be detected by the antenna B, if the UW1 cannot be detected, the antenna A is switched to the same manner as described above. The subsequent operation is the same as that in FIG.

  FIG. 7 shows a case where the preamble or the like transmitted for the fourth time is received by the antenna A and detected by the preamble detection unit 44 or the like as the first preamble or the like in the packet. In this case, after the unique word UW1 transmitted for the fourth time is detected, the antenna B is switched to receive the dummy data.

  The dummy data is data composed of a bit string different from the preamble, and is transmitted from the transmission system in order to give the antenna switching reception system 1 time delay when switching from the antenna B to the antenna A again. . Accordingly, the data length of the dummy data is set to be equal to or longer than the sum of the data length of the preamble and the data length of the unique word UW1, that is, the second predetermined time T2.

  The dummy data is composed of a preamble and the unique words UW1 and UW2 by bit strings having a low correlation value. This is to prevent the preamble detection unit 44 and the unique word detection unit 45 from erroneously detecting the dummy data as the preamble and the unique words UW1 and UW2. Each bit string is preferably set so that the correlation value between the dummy data and the preamble, the correlation value between the dummy data and the unique word UW1, and the correlation value between the dummy data and the unique word UW2 are the lowest. However, if the correlation value is low enough to prevent erroneous detection by the preamble detection unit 44 and the unique word detection unit 45, that is, if the correlation value is less than a predetermined value, there is no practical problem.

  As shown in FIG. 7, when dummy data is received by the antenna B, the preamble is not detected by the preamble detector 44 and the unique word UW1 is not detected by the unique word detector 45. In addition, since the preamble or the like transmitted for the second time is received by the antenna B but the preamble or the like is not detected by the preamble detection unit 44 or the like, it is considered that the quality of the signal received by the antenna B is not high. It is done. Therefore, the antenna control unit 52 selects the antenna A that provides sufficiently high signal quality as the antenna that receives the payload, and the antenna is switched to the antenna A again and fixed to the antenna A until the reception of the packet is completed. Is done. The subsequent operation is the same as that in FIG.

  FIG. 8 shows the operation of the antenna switching reception system 1. First, before detecting the unique word UW1, the antennas A and B are alternately switched at a predetermined period (# 1). The predetermined cycle for switching the antenna is, for example, a cycle of two times of the preamble and the unique word UW1, that is, a first predetermined time T1. When the antenna is switched, detection of the preamble and the bit string of the unique word UW1 is reset (# 2). The detection of the detection of the bit string of the preamble and the unique word UW1 is a process of stopping the detection of the bit string and restarting the detection from the first bit. At this time, the unique word UW1 is set as a bit string to be detected by the unique word detection unit 45. That is, the detection of the unique word UW1 is started. The preamble detection unit 44 and the unique word detection unit 45 reset the detection of the bit string for the following reason. That is, since the RFIC 4 cannot recognize which part of the received signal input from the antenna switching unit 3 is received by which antenna, it prevents the antenna that has received the preamble and the unique word from being mistaken. Because. For example, when the antenna A is switched to the antenna B near the end of the bit string of the unique word, the entire bit string is received by the antenna B that has received the last part even though the most part of the bit string is received by the antenna A. This is to prevent misidentification that the message is received.

  A radio signal is received by the antenna activated in the switching, and the preamble is searched by the preamble detector 44 (# 3). When the preamble is detected by the preamble detector 44 (YES in # 4), reception level detection is started (# 5). At this time, an antenna that receives a radio signal is referred to as an antenna A. The reception level is detected at a predetermined sampling period, and the value is sequentially stored in the signal processing unit 51 (the same applies to # 12). In # 4, the preamble detection is continued for the first predetermined time after resetting the bit string detection in # 2, and if the preamble is not detected within the first predetermined time (NO in # 4), # Return to 1. Here, the first predetermined time is a time corresponding to two cycles of the preamble and the unique word UW1, and after the bit string detection is reset in # 2, counting is started. When the unique word UW1 is detected after the preamble is detected (YES in # 6), the detection of the reception level is ended (# 7). In # 6, the detection of the unique word UW1 is continued for a first predetermined time calculated after resetting the bit string detection in # 2. When the unique word UW1 is not detected within the first predetermined time (NO in # 6), the detection of the reception level is terminated and the process returns to # 1.

  When the detection of the reception level at the antenna A is completed, the signal processing unit 51 calculates an average value (RA) from the stored reception level (# 8), and the antenna control unit 52 switches the antenna to the antenna B. (# 9). When the antenna is switched, the detection of the preamble and the bit string of the unique word UW1 is reset as in # 2 (# 9A). Then, the radio signal is received by the antenna B after switching, and the preamble is searched by the preamble detector 44 (# 10). When the preamble is detected by the preamble detector 44 (YES in # 11), reception level detection is started (# 12). In # 11, the preamble detection is continued for the second predetermined time after resetting the bit string detection in # 9A, and as shown in FIG. 6 or FIG. 7, the preamble is not detected within the second predetermined time. In the case (NO in # 11), the process proceeds to # 19. This is because it can be determined that sufficient signal quality cannot be obtained with the antenna B. Here, the second predetermined time is a time corresponding to one cycle of the preamble and the unique word UW1, and the count is started after resetting the detection of the bit string in # 9A. When the unique word UW1 is detected after the preamble is detected (YES in # 13), the detection of the reception level is ended (# 14). In # 11, the detection of the unique word UW1 is continued for a second predetermined time calculated after the bit string detection is reset in # 9A. If the unique word UW1 is not detected within the second predetermined time (NO in # 13), the detection of the reception level is terminated and the process proceeds to # 19. This is because it can be determined that sufficient signal quality cannot be obtained with the antenna B.

  When the detection of the reception level at the antenna B is completed, the signal processing unit 51 calculates an average value (RB) from the stored reception level (# 15), and the antenna control unit 52 is calculated by the signal processing unit 51. The average values RA and RB of the received levels are compared (# 16). As shown in FIG. 5, when RA <RB (YES in # 17), antenna control unit 52 selects antenna B as the antenna that receives the payload. That is, the detection of the bit string is reset (# 20) while the antenna is fixed to the antenna B (# 18). At this time, the unique word UW2 is set as a bit string to be detected by the unique word detection unit 45. That is, the detection of the unique word UW2 is started. On the other hand, as shown in FIG. 4, when RA> RB (NO in # 17), antenna A is selected as the antenna that receives the payload. That is, the antenna is switched to antenna A (# 19), and the process proceeds to # 20.

  When a radio signal is received by the selected antenna A or B and the preamble is detected by the preamble detector 44 (YES in # 21), the process proceeds to detection of the unique word UW2 (# 22). When the unique word UW2 is detected by the unique word detector 45 (YES in # 22), the cueing of the payload is completed, and the payload is subsequently received (# 23). The received payload is processed by the signal processing unit 51. In # 21, the preamble detection is continued for a third predetermined time after resetting the bit string detection in # 20, and when the preamble is not detected by the preamble detection unit 44 within the third predetermined time (# 21 NO) returns to # 1. Here, the third predetermined time corresponds to a time obtained by adding two periods of the preamble and the unique word UW1, a dummy data, and one period of the preamble and the unique word UW2, and after resetting the detection of the bit string in # 20. Start counting. In # 22, the detection of the unique word UW2 is continued for a third predetermined time calculated after resetting the bit string detection in # 20. If the unique word UW2 is not detected by the unique word detector 45 within the third predetermined time (NO in # 22), the process returns to # 1.

  FIG. 9 shows the structure of the payload transmitted from the corresponding transmission system 70. The payload is received by the antenna A or B selected by the antenna control unit 52. The payload is composed of a header and data. Additional information necessary for receiving and processing the packet itself, such as the length, device ID, and packet type, is added to the header. The data is the main body of the data that is originally desired to be transmitted and received between the transmission system 70 and the antenna switching reception system 1. A length is inserted at the beginning of the header. The length is information regarding the length of data transmitted following the header. The header (length) and data are detected and processed by the signal processing unit 51 of the CPU 5. Note that the header may be detected by the RFIC 4.

  The header is searched over a fourth predetermined time T4. The fourth predetermined time T4 is set according to the length of the header transmitted from the transmission system 70, and is counted by the counter 53 that functions as a fourth counter. When the header is not detected within the fourth predetermined time T4, the signal processing unit 51 stops detecting the header and detects the first unique word UW1 in the next transmitted packet while switching the antenna again. (See FIGS. 4 to 7).

  When the length is detected, the length of the data is known, so the signal processing unit (reception time update unit) 51 sets the data reception time T5 and receives data over the data reception time T5. The data reception time T5 is counted by the counter 53 that functions as a fifth counter. Since the data reception time T5 is different for each packet, the signal processing unit 51 updates the data reception time T5 based on the detected length every time the length is detected. Even if the data detection is not completed, the signal processing unit 51 stops detecting the data when the data reception time T5 elapses. Then, while switching the antenna again, the operation returns to the operation of detecting the first unique word UW1 in the packet to be transmitted next (see FIGS. 4 to 7).

  FIG. 10 shows an example of the operations of # 1 to # 7 in FIG. 8 in detail. In # 2, when the detection of the preamble and the bit string of the unique word UW1 is reset, the count of the counter 53 is reset. The resetting of the count means a process of stopping detection of the time count and restarting the time count from zero. Here, the counter 53 functions as a first counter and starts counting (# 2B). Then, when a radio signal is received (# 3) and the preamble is detected by the preamble detector 44 within the first predetermined time T1 (YES in # 4), detection of the reception level is started (# 5). When the preamble is not detected (NO in # 4), the count value of the counter 53 is compared with the first predetermined time T1 (# 4A). If the count value of the counter 53 is less than the first predetermined time T1 (NO in # 4A), after incrementing the count of the counter 53 (# 4B), the process returns to # 3 and the search for the preamble is continued from the received signal. Is done. When the count value of counter 53 reaches or exceeds first predetermined time T1 (YES in # 4A), the operation returns to the antenna switching operation (# 1).

  If the unique word UW1 is detected after the start of detection of the reception level in # 5 (YES in # 6), detection of the reception level is ended (# 7). When unique word UW1 is not detected (NO in # 6), the count value of counter 53 is compared with first predetermined time T1 (# 6A). If the count value of counter 53 is less than first predetermined time T1 (NO in # 6A), after incrementing the count of counter 53 (# 6B), the process returns to # 6 and the search for unique word UW1 is continued. . When the count value of counter 53 reaches or exceeds first predetermined time T1 (YES in # 4A), the operation returns to the antenna switching operation (# 1).

  FIG. 11 shows an example of the operations of # 9 to # 14 in FIG. 8 in detail. In this operation example, after the first unique word UW1 is detected in the packet, a timeout time (second predetermined time T2) is set when the antenna is switched to detect another unique word UW1. When the antenna is switched in # 9, detection of the preamble and the bit string of the unique word UW1 is reset (# 9A), and the count of the counter 53 is reset. Here, the counter 53 functions as a second counter and starts counting (# 9B). When a radio signal is received (# 10) and the preamble is detected by the preamble detector 44 within the second predetermined time T2 (YES in # 11), detection of the reception level is started (# 12). When the preamble is not detected (NO in # 11), the count value of the counter 53 is compared with the second predetermined time T2 (# 11A). If the count value of the counter 53 is less than the second predetermined time T2 (NO in # 11A), after incrementing the count of the counter 53 (# 11B), the process returns to # 10 and the search for the preamble is continued from the received signal. Is done. When the count value of counter 53 reaches or exceeds second predetermined time T2 (YES in # 11A), the process proceeds to # 19 and the antenna is switched.

  When the unique word UW1 is detected after the start of detection of the reception level in # 12 (YES in # 13), the detection of the reception level is ended (# 14). When the unique word UW1 is not detected (NO in # 13), the count value of the counter 53 is compared with the second predetermined time T2 (# 13A). If the count value of counter 53 is less than second predetermined time T2 (NO in # 13A), after incrementing the count of counter 53 (# 13B), the process returns to # 13 and the search for unique word UW1 is continued. . When the count value of counter 53 reaches or exceeds second predetermined time T2 (YES in # 13A), the process proceeds to # 19 to switch the antenna.

  FIG. 12 shows an example of the operations of # 20 to # 23 in FIG. 8 in detail. In this operation example, a timeout time (third predetermined time T3) is set when the unique word UW2 is detected after the antenna that receives the payload is selected. When the detection of the bit string is reset and the unique word UW2 is set as the detected bit string (# 20), the count of the counter 53 is reset. Here, the counter 53 functions as a third counter and starts counting (# 20A). When a wireless signal is received and the preamble is detected by the preamble detector 44 within the third predetermined time T3 (YES in # 21), the process proceeds to detection of the unique word UW2 (# 22). When the preamble is not detected (NO in # 21), the count value of the counter 53 is compared with the third predetermined time T3 (# 21A). If the count value of the counter 53 is less than the third predetermined time T3 (NO in # 21A), after incrementing the count of the counter 53 (# 21B), the process returns to # 21 and the search for the preamble is continued from the received signal. Is done. When the count value of counter 53 reaches or exceeds third predetermined time T3 (YES in # 21A), the operation returns to the antenna switching operation (# 1).

  If the unique word UW2 is detected by the unique word detection unit 45 within the third predetermined time T3 after detection of the preamble in # 21 (YES in # 22), the process proceeds to payload reception (# 23). When unique word UW2 is not detected (NO in # 22), the count value of counter 53 is compared with a third predetermined time T3 (# 22A). When the count value of the counter 53 is less than the third predetermined time T3 (NO in # 22A), the count of the counter 53 is incremented (# 22B), then the process returns to # 22 and the search for the unique word UW2 is continued. . When the count value of counter 53 reaches or exceeds third predetermined time T3 (YES in # 22A), the operation returns to the antenna switching operation (# 1).

  FIG. 13 shows in detail an example of the receiving operation of # 23 in FIG. 8, that is, the payload. In this operation example, a timeout time (fourth predetermined time T4) is set for header detection. When the unique word UW2 is detected in # 22, the count of the counter 53 is reset. Here, the counter 53 functions as a fourth counter and starts counting (# 23A). When a radio signal is received, the header is detected by the signal processing unit 51, and detection of the header is completed within the fourth predetermined time T4 (YES in # 23B), the process proceeds to data reception (# 23E). When the detection of the header is not completed (NO in # 23B), the count value of the counter 53 is compared with the fourth predetermined time T4 (# 23C). If the count value of the counter 53 is less than the fourth predetermined time T4 (NO in # 23C), the count of the counter 53 is incremented (# 23D), and then the process returns to # 23B and the header search is continued from the received signal. Is done. When the count value of counter 53 reaches or exceeds fourth predetermined time T4 (YES in # 23C), the operation returns to the antenna switching operation (# 1).

  FIG. 14 shows in more detail an example of the reception operation of # 23 in FIG. 8, that is, the payload. In this operation example, a timeout time (fourth predetermined time T4A and T4B) is set for detection of the length and the header. Here, the fourth predetermined time T4B is equivalent to the fourth predetermined time T4 in FIG.

  In this operation example, a timeout time (data reception time T5) is also set for data detection. Since the data length differs for each packet, the signal processing unit 51 dynamically changes the time spent for data detection by updating the setting of the data reception time T5 each time a length is detected.

  When the unique word UW2 is detected in # 22, the count of the counter 53 is reset. Here, the counter 53 functions as the fourth counter A and the fourth counter B, and starts counting (# 23A). When the wireless signal is received and the length is detected by the signal processing unit 51 and the length detection is completed within the fourth predetermined time T4A (YES in # 23F), the process proceeds to header detection (# 23B). When the length detection is not completed (NO in # 23F), the count value of the counter 53 is compared with the fourth predetermined time T4A (# 23G). If the count value of the counter 53 is less than the fourth predetermined time T4A (NO in # 23G), the counter 53 is incremented (# 23H), then returns to # 23F, and the search for the length from the received signal continues. Is done. When the count value of counter 53 becomes equal to or longer than the fourth predetermined time T4A (YES in # 23G), the operation returns to the antenna switching operation (# 1).

  When the length detection in # 23F is completed, the header is detected by the signal processing unit 51 (# 23B). When the detection of the header is completed within the fourth predetermined time T4B (YES in # 23B), the signal processing unit 51 updates the setting of the data reception time T5 based on the length detected in # 23F. As a result, the time spent for data detection by the signal processing unit 51 is dynamically optimized for each packet, and the processing load on the CPU 5 is reduced. Further, even when the noise included in the received radio signal is mistaken as a signal such as a unique word, it is possible to quickly return to the operation of searching for the unique word UW1 or the like. When the detection of the header is not completed (NO in # 23B), the count value of the counter 53 is compared with the fourth predetermined time T4B (# 23C). If the count value of the counter 53 is less than the fourth predetermined time T4B (NO in # 23C), after incrementing the count of the counter 53 (# 23D), the process returns to # 23B and the header search is continued from the received signal. Is done. When the count value of counter 53 is equal to or longer than the fourth predetermined time T4B (YES in # 23C), the operation returns to the antenna switching operation (# 1). The counter 53 functioning as the fourth counter B may be set to reset after the detection of the length in # 23F (YES in # 23F) and start counting the fourth predetermined time T4B. Good. In this case, the fourth predetermined time T4B is a time obtained by subtracting the fourth predetermined time T4A corresponding to the length length from the fourth predetermined time T4 in FIG.

  When the head detection is completed at # 23B and the setting of the data reception time T5 is updated at # 23I, the count of the counter 53 is reset. Here, the counter 53 functions as a fifth counter and starts counting (# 23J). When a radio signal is received, data is detected by the signal processing unit 51, and data detection is completed within the data reception time T5 (YES in # 23K), the operation returns to the antenna switching operation (# 1). When the data detection is not completed (NO in # 23K), the count value of the counter 53 is compared with the data reception time T5 (# 23L). If the count value of the counter 53 is less than the data reception time T5 (NO in # 23L), the count of the counter 53 is incremented (# 23M), then the process returns to # 23K and the search for data from the received signal is continued. The When the count value of counter 53 is equal to or longer than data reception time T5 (YES in # 23L), the operation returns to the antenna switching operation (# 1).

  As described above, according to the antenna switching reception system 1 of the present embodiment, the unique word detection unit 45 does not have to wait for a plurality of types of unique words at the same time. That is, in FIG. 8, only the unique word UW1 needs to be waited for and detected only at # 6 and # 13, and only the unique word UW2 at # 22, so that the processing burden on the unique word detector 45 is greatly reduced. The In recent years, ICs that do not reach the CPU have been promoted to be multi-functional, and such a process of waiting for and detecting a single unique word can be realized by using a function provided in the RFIC 4. As a result, it is possible to accurately select an antenna with high signal quality while configuring the unique word detection unit 45 using the bit string detection function provided in the RFIC 4. Even if the CPU 5 is configured to detect a preamble or unique word instead of the preamble detector 44 or the unique word detector 45, the processing load on the CPU 5 is still reduced. Therefore, the influence of level fluctuations due to multipath fading can be reduced with a simple and inexpensive configuration without using a high-spec CPU 5. The processing capability of the CPU 5 can be allocated to functions other than bit string detection, and the multifunctional antenna switching reception system 1 can be constructed without increasing costs.

  In addition, since the operation of detecting the unique word UW1 with the switched antenna is held for the second predetermined time T2, the processing load on the CPU 5 can be reduced. Even if the quality of the radio signal received by the switched antenna does not reach a level at which the unique word UW1 can be detected, the detection of the unique word UW1 is stopped after the second predetermined time T2 has elapsed, and the unique word UW2 This is because it is possible to shift to preparation for detection. (See Figure 6.)

  Further, the unique word UW2 is received by the antenna selected by the antenna control unit 52 as an antenna having a high signal quality, and the leading bit of the payload is detected, so that the payload can be properly cued. Further, since the payload is received while being fixed to the antenna selected by the antenna control unit 52, a high-quality payload signal can be acquired.

  In addition, since the operation of detecting the unique word UW2 is limited to the third predetermined time T3 after the antenna is selected, the processing load on the CPU 5 can be reduced. After the properly set third predetermined time T3 has elapsed, the unique word UW2 in the packet is not transmitted from the transmission system 70, so detection of the unique word UW2 is stopped and reception of the next packet is received. It is because it can move to preparation.

  The first predetermined time T1 is set to a time corresponding to two cycles of the preamble and the unique word UW1, and the second predetermined time T2 is set to a time longer than one cycle of the preamble and the unique word UW1. Therefore, any preamble and unique word UW1 can be awaited in a reception state regardless of the timing at which the antenna is switched for a packet transmitted from the transmission system 70.

  The third predetermined time T3 is set to a time obtained by adding a time corresponding to one cycle of the preamble received before the unique word UW2 and the unique word UW2 to a time equal to or longer than three cycles of the preamble and the unique word UW1. Yes. Therefore, even if the antenna is switched at any timing for the packet transmitted from the transmission system 70, the unique word UW2 can be waited in the reception state after the antenna is selected.

  Further, when the signal processing unit 51 cannot complete the header detection within the fourth predetermined time T4, the unique word UW1 is detected by the unique word detection unit 45 or the like while switching the antenna again without receiving the payload data. Return to operation. Thereby, the processing load of the CPU 5 can be further reduced. Further, even when the noise included in the received radio signal is mistaken as a signal such as a unique word, it is possible to quickly return to the operation of searching for the unique word UW1 or the like.

  When the signal processing unit 51 cannot complete the detection of data within the updated data reception time T5, the unique word UW1 is returned to the operation of detecting the unique word UW1 while switching the antenna again. Thereby, the processing load of the CPU 5 can be further reduced. Further, since the data reception time T5 is dynamically updated and optimized for each packet based on the length included in the header, the processing load on the CPU 5 can be further reduced.

  In addition, a wireless transmission / reception system corresponding to the antenna switching reception system 1 can be constructed by a transmission system that transmits a plurality of unique words UW1 before the payload. Further, a wireless transmission / reception system that is more compatible with the antenna switching reception system 1 can be constructed by a transmission system that transmits the unique word UW2 before the payload after transmitting a plurality of unique words UW1. Further, a radio transmission / reception system that is more compatible with the antenna switching reception system 1 can be constructed by a transmission system that transmits a preamble before each unique word UW1.

  The present invention is not limited to the configuration of the above embodiment. When the unique word detection unit 45 detects any one of the plurality of unique words UW1 within the first predetermined time T1 while switching the antenna, the signal processing unit 51 detects the quality of the received radio signal. After the antenna control unit 52 switches the antenna, the unique word detection unit 45 searches for another unique word UW1 within the second predetermined time T2, so that the antenna control unit 52 is detected by the signal processing unit 51. It is only necessary to select an antenna having a high signal quality and receive the subsequent payload.

  The present invention can be variously modified. For example, the quality of the signal received by each antenna may be detected based on the reception level at a certain point in time without calculating the average value of the reception levels. For example, the signal quality may be detected based on the reception level when the preamble is detected by each antenna, after a predetermined time has elapsed since the detection of the preamble, or when the unique word UW1 is detected. In this case, the processing load on the signal processing unit 51, that is, the processing load on the CPU 5 is further reduced.

  Further, the first predetermined time T1, the second predetermined time T2, the third predetermined time T3, the fourth predetermined time T4, and the data reception time T5 are set including a slight margin time (margin) in addition to the above-described time. May be. This is because it is possible to avoid problems associated with clock lag between terminals.

  The quality of the signal received by each antenna can be detected not only by the reception level but also by the error rate of the bit string of the baseband signal with respect to the bit string of the unique word stored in advance.

  In addition, the antenna switching reception system 1 and the transmission system 70 of the present invention are not limited to the HEMS 100, and can be widely applied to other wireless systems using “switching diversity”.

DESCRIPTION OF SYMBOLS 1 Antenna switching reception system 3 Antenna switching part 41 RF part (signal quality detection part)
44 Preamble detector (bit string detector)
45 Unique word detector (bit string detector)
51 Signal processing unit (signal quality detection unit, header detection unit, data detection unit, reception time update unit)
52 Antenna control unit 70 Transmission system UW1 Unique word (first unique word)
UW2 unique word (second unique word)

Claims (8)

An antenna control unit that controls switching of a plurality of antennas, and a bit string detection unit that searches a wireless signal received while switching antennas alternatively and detects a bit string that is the same as a bit string of a preset unique word ,
A signal quality detection unit that detects the quality of the radio signal received for each antenna;
When the bit string detection unit detects any one of the plurality of first unique words composed of the same bit string within a first predetermined time, the signal quality detection unit determines the quality of the received radio signal. Detect
After the antenna control unit switches the antenna, the bit string detection unit searches for a first unique word different from any of the first unique words within a second predetermined time, so that the signal quality detection unit , Detect the quality of the radio signal received by the switched antenna,
The antenna control unit is an antenna switching reception system that selects an antenna having a high signal quality detected by the signal quality detection unit and receives a subsequent payload,
The first unique word is transmitted by twice the number of the plurality of antennas,
Each of the plurality of antennas is switched at a cycle that is twice the transmission cycle of the preamble and the first unique word transmitted before the first unique word until the first unique word is detected for the first time. An antenna switching receiving system. After the antenna control unit selects an antenna having a high signal quality, the bit string detection unit detects a second unique word different from the first unique word within a third predetermined time.
The antenna switching reception system according to claim 1, wherein the antenna control unit receives a subsequent payload while the antenna is fixed.   The first predetermined time corresponds to a time corresponding to two cycles of the first unique word and a preamble received before the first unique word, and the second predetermined time includes the first unique word and the preamble. The antenna switching reception system according to claim 1, wherein the antenna switching reception system corresponds to a time of one period or more.   The third predetermined time is obtained by adding a time corresponding to one period of the preamble received before the second unique word and the second unique word to a time equal to or longer than three periods of the preamble and the first unique word. 4. The antenna switching receiving system according to claim 3, which is dependent on time. When a header detection unit that detects a header included in the payload and a data detection unit that detects data included in the payload are further included, and the header detection unit cannot complete detection of the header within a fourth predetermined time ,
5. The detection of the first unique word by the bit string detection unit is resumed while the antenna is switched again without receiving payload data. 6. Antenna switching reception system. A reception time update unit for updating a data reception time for detecting the data based on a length included in the header;
When the data detection unit cannot complete detection of the data within the data reception time updated by the reception time update unit,
6. The antenna switching reception system according to claim 5 , wherein the first unique word detection operation by the bit string detection unit is restored while the antenna is switched again. The transmission system corresponding to the antenna switching reception system according to claim 1 , wherein the first unique word is transmitted before the payload by twice as many as the number of the plurality of antennas .   The transmission system corresponding to the antenna switching reception system according to claim 2, wherein after transmitting the plurality of first unique words, the second unique word is transmitted before the payload.

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