JP5842111B2 - Antenna switching reception system - Google Patents

Description

  The present invention relates to an antenna switching reception system for switching and receiving antennas 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.

  Further, 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 there is an influence of multipath fading on one antenna (see, for example, Patent Document 1). 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, so that it is easy to develop and the circuit scale is small and the cost can be reduced. Diversity "is installed in various radio devices.

Japanese Patent Laid-Open No. 06-303218

  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 frames (a lump of payload signals) and switches antennas when an error is detected over a plurality of frames, that is, antenna switching after an error occurs. The generated error is dealt with by sending the same frame again to the transmitter (retransmission function). However, when the communication environment is poor due to multipath fading, the number of retransmissions increases, making it unsuitable for devices that need to receive new payload signals one after another at high speed, such as voice and video.

  The present invention provides an antenna switching reception system that can reduce the influence of level fluctuations due to multipath fading by accurately selecting an antenna having a high reception level even in an environment with many multipaths with a simple configuration. Objective.

To achieve the above object, an antenna switching reception system of the present invention is an antenna switching reception system that receives a radio signal by switching a plurality of antennas.
From the transmission system, a preamble signal, at least one test signal, and a payload signal are transmitted in this order, and the antenna switching timing detection signal included in the preamble signal is transmitted at a lower transmission rate than the payload signal. Sent
It determines that detects that the reception level of the received antennas selected signal is momentarily or continuously for a threshold or more than a predetermined time and the preamble signal is input, detects the antenna switching timing detection signal And
Receiving the at least one test signal by switching the plurality of antennas based on the antenna switching timing detection signal ;
The antenna switching timing detection signal and the test signal are each configured by a specific sequence of signal sequences and transmitted.
A storage unit that stores the same signal sequence as the transmitted antenna switching timing detection signal and the transmitted test signal ;
A correlation value calculation unit that calculates a correlation value between the signal sequence stored in the storage unit, the signal sequence of the received antenna switching timing detection signal , and the correlation value of the signal sequence of the received test signal; ,
Detecting the antenna switching timing detection signal based on the correlation value calculated by the correlation value calculation unit ;
The antenna for receiving the payload signal is selected based on the correlation value of the received signal sequence of the test signal calculated by the correlation value calculation unit .

  According to the present invention, since the antenna that receives the test signal and receives the payload signal is selected before receiving the payload signal, the influence of level fluctuations due to multipath fading can be reduced with a simple configuration. As a result, even in a multipath environment, it becomes easy to avoid the occurrence of an error due to reception level deterioration due to multipath fading.

1 is a block diagram showing a schematic configuration of an antenna switching reception system according to a first embodiment of the present invention. The flowchart which shows operation | movement of the antenna switching reception system of 1st Embodiment. The figure which shows the operation | movement of the said antenna switching reception system when the signal received using two antennas and this signal are received in the antenna switching reception system of 1st Embodiment. The block diagram which shows schematic structure of the antenna switching receiving system by 2nd Embodiment of this invention. The flowchart which shows operation | movement of the antenna switching reception system of 2nd Embodiment. The figure which shows the operation | movement of the said antenna switching reception system when the signal received using two antennas and this signal are received in the antenna switching reception system of 2nd Embodiment. The block diagram which shows schematic structure of the antenna switching receiving system by 3rd Embodiment of this invention. The flowchart which shows operation | movement of the antenna switching receiving system of 3rd Embodiment. The figure which shows the operation | movement of the said antenna switching reception system when the signal received using two antennas and this signal are received in the antenna switching reception system of 3rd Embodiment. The block diagram which shows schematic structure of the antenna switching receiving system by 4th Embodiment of this invention. The flowchart which shows operation | movement of the antenna switching reception system of 4th Embodiment. The block diagram which shows schematic structure of the antenna switching receiving system by 5th Embodiment of this invention. The figure which shows the operation | movement of the said antenna switching reception system when the signal received using two antennas and this signal are received in the antenna switching reception system of 5th Embodiment. The figure which shows the operation | movement of the said antenna switching reception system when the signal received using two antennas and this signal are received in the antenna switching reception system of 6th Embodiment. The block diagram which shows schematic structure of the antenna switching receiving system by 7th Embodiment of this invention. The figure which shows the operation | movement of the said antenna switching reception system when the signal received using two antennas and this signal are received in the antenna switching reception system of 7th Embodiment. The block diagram which shows schematic structure of the antenna switching receiving system by 8th Embodiment of this invention. The flowchart which shows operation | movement of the antenna switching reception system of 8th Embodiment. The figure which shows the operation | movement of the said antenna switching reception system when the signal received using two antennas and this signal are received in the antenna switching reception system of 9th Embodiment. The block diagram which shows schematic structure of the antenna switching receiving system by 10th Embodiment of this invention. The figure which shows the operation | movement of the said antenna switching reception system when the signal received using two antennas and this signal are received in the antenna switching reception system of 10th Embodiment. The block diagram which shows schematic structure of the antenna switching receiving system by 11th Embodiment of this invention. The figure which shows the operation | movement of the said antenna switching reception system when the signal received using two antennas and this signal are received in the antenna switching reception system of 11th Embodiment. The block diagram which shows schematic structure of the antenna switching receiving system by 12th Embodiment of this invention. The figure which shows the operation | movement of the said antenna switching reception system when the signal received using two antennas and this signal are received in the antenna switching reception system of 13th Embodiment.

(First embodiment)
An antenna switching reception system according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an antenna switching reception system. The antenna switching reception system includes an antenna switching unit 1 to which two antennas are connected, a radio unit (demodulation unit) 2, an RSSI detection unit 3, an antenna control unit 4, and a unique word detection unit (UW detection unit). 5 etc. The antenna switching unit 1 switches the antenna that receives the radio signal according to the control signal input from the antenna control unit 4. In the following, a case where there are two antennas connected to the antenna switching unit 1 and switched is described, but the number of antennas may be three or more. The radio unit 2 demodulates a signal received by any antenna via the antenna switching unit 1. The RSSI detector 3 detects the RSSI (received signal strength) of a signal received by any antenna via the antenna switching unit 1. The antenna control unit 4 selects an antenna that receives a radio signal based on the RSSI detected by the RSSI detection unit 3 and outputs a control signal to that effect to the antenna switching unit 1. The UW detection unit 5 detects a unique word from a signal received by any antenna via the antenna switching unit 1.

  FIG. 2 shows the operation of the antenna switching reception system of the first embodiment. FIG. 3 shows a signal received using two antennas, that is, antenna A and antenna B in the antenna switching reception system of the first embodiment, and the operation of the antenna switching reception system when receiving this signal. Is shown. In particular, an example in which antenna A is initially selected and a preamble signal is received by the antenna A is shown. The signal shown in FIG. 3 is transmitted from a transmission system corresponding to the antenna switching reception system of this embodiment. From the transmission system, a preamble signal, a test 1 signal, a test 2 signal, a unique word signal, and a payload signal are transmitted. One frame is composed of the preamble signal, test 1 signal, test 2 signal, unique word signal and payload signal. The preamble signal includes, for example, an antenna switching timing detection signal for detecting the timing of switching the receiving antenna to the antenna A or the antenna B when receiving the test 1 signal and the test 2 signal. The test 1 signal and test 2 signal are used to select the antenna that receives the payload signal. The test 1 signal is received by the initially selected antenna, and the test 2 signal is received by the switched antenna. The test signal is added as appropriate according to the number of antennas switched by the antenna switching unit 1. The payload signal includes, for example, data such as a header, video, audio, and temperature, or various control signals.

  The operation of the antenna switching reception system according to the first embodiment will be described with reference to FIGS. First, the RSSI detection unit 3 constantly observes the RSSI value (# 1), and determines that the preamble has been input when detecting that the RSSI level is instantaneously or continuously for a predetermined time or more and is equal to or greater than the threshold (#). YES in 2). Then, the antenna control unit 4 measures the reception level of the currently selected antenna (# 3) and stores it (# 4). In FIG. 3, the test 1 signal is received by the antenna A, and the reception level is detected. Then, the antenna control unit 4 causes the antenna switching unit 1 to switch the antenna, measures the reception level of the antenna (# 5), and stores it (# 6). In FIG. 3, the test 2 signal is received by the antenna B and the reception level is detected (when the antenna B is initially selected, the test 1 signal is received by the antenna B, and the test 2 signal is received by the antenna A. Received). Note that the reception level measurement at # 3 and # 5 is not limited to that by RSSI. For example, the reception level may be measured from the amplification factor when the received signal is amplified by the automatic gain control circuit.

  Thereafter, the antenna control unit 4 compares the two received reception levels (# 7). When the reception level of antenna A is high (YES in # 8), antenna control unit 4 selects antenna A as an antenna for receiving the payload signal. Then, the antenna switching unit 1 is controlled and fixed to the antenna A (# 9), and the unique word and the payload signal are sequentially received (# 11). The example shown in FIG. 3 corresponds to this case. When the reception level of antenna B is high (NO in # 8), antenna control unit 4 selects antenna B as the antenna for receiving the payload signal. Then, the antenna switching unit 1 is controlled and fixed to the antenna B (# 10), and the unique word and the payload signal are sequentially received (# 11). Even when the reception level of antenna A is the same as the reception level of antenna B (NO in # 8), the antenna is not switched (fixed to antenna B that last received the test signal (# 10)). )), A unique word or the like is received (# 11).

  According to the antenna switching reception system of the first embodiment, before receiving a payload signal, each antenna receives a test signal and selects an antenna that receives the payload signal. The influence of fluctuation can be reduced. Thereby, even in a multipath environment, it is possible to avoid the occurrence of errors due to reception level deterioration due to multipath fading. Further, near real-time transmission can be realized by reducing the number of retransmissions. Further, when retransmission is unnecessary, it is possible to eliminate the retransmission function and contribute to cost reduction and size reduction.

  In addition, the test signal is received while switching the antenna, triggered by the fact that the RSSI level is instantaneously or continuously longer than a predetermined time and is equal to or higher than the threshold value. Thereby, the timing which detects a reception level can be united with the test signal received in order to judge antenna switching. Therefore, the reception level can be detected more accurately from the test signal at each antenna, and the antenna for receiving the payload signal can be properly selected. In addition, since the reception level of the antenna is used as a trigger for detecting the reception level of the test signal, it is possible to quickly shift to detection of the reception level of the test signal. Further, since the antenna that receives the payload signal is selected based on the RSSI level of the test signal received by each antenna, that is, the reception level, it is possible to accurately select an antenna that has a good reception state. In # 2, the preamble signal is input by detecting RSSI at a level equal to or higher than the threshold. However, the reception level of the antenna selected by another method, for example, the amplification factor of the automatic gain control circuit described above is detected. Alternatively, the threshold values may be compared.

(Second Embodiment)
An antenna switching reception system according to the second embodiment of the present invention will be described. FIG. 4 shows a schematic configuration of the antenna switching reception system of the second embodiment. The antenna switching reception system of the second embodiment is configured by adding a preamble detection unit 6 to the configuration of the antenna switching reception system of the first embodiment. The preamble detector 6 detects a preamble signal from the signal demodulated by the radio unit 2.

  In the antenna switching reception system of the first embodiment, it is determined that a preamble signal is input when it is detected that the RSSI level is equal to or higher than a threshold value. On the other hand, in the antenna switching reception system of the second embodiment, the preamble detection unit 6 is configured to detect a preamble signal from the signal demodulated by the radio unit 2.

  The preamble signal transmitted from the transmission system includes an antenna switching timing detection signal for detecting the antenna switching timing when receiving the test 1 signal and the test 2 signal. The antenna switching timing detection signal is configured, for example, by a signal in which the same code is repeated over a predetermined time corresponding to at least one symbol. When the preamble detection unit 6 detects a signal in which the same code is repeated over a predetermined time corresponding to at least one symbol, it can determine that an antenna switching timing detection signal, that is, a preamble signal has been detected. Based on the antenna switching timing detection signal, the antenna A can receive the test 1 signal or the test 2 signal, and the antenna B can receive the test 2 signal or the test 1 signal.

  FIG. 5 shows the operation of the antenna switching reception system of the second embodiment. FIG. 6 shows a signal received using the antenna A and the antenna B in the antenna switching reception system according to the second embodiment, and an operation of the antenna switching reception system when the signal is received. In particular, an example in which antenna A is initially selected and a preamble signal is received by the antenna A is shown.

  The operation of the antenna switching reception system according to the second embodiment will be described with reference to FIGS. In the antenna switching reception system of the second embodiment, the preamble signal is detected by the preamble detection unit 6 in place of the processes of # 1 and # 2 in the antenna switching reception system of the first embodiment (# 21). When the preamble signal is detected by the preamble detector 6 (YES in # 21), the antenna controller 4 measures the reception level of the currently selected antenna (# 3) and stores it (# 4). In FIG. 6, the test 1 signal is received by the antenna A, and the reception level is detected. The subsequent operation is the same as the operation of the antenna switching reception system of the first embodiment shown in FIGS.

  According to the antenna switching reception system of the second embodiment, the antenna that receives the test signal is switched based on the preamble signal received before the test signal. Thereby, the timing which detects a reception level can be united with the test signal received in order to judge antenna switching. Therefore, the reception level can be detected more accurately from the test signal at each antenna, and the antenna for receiving the payload signal can be properly selected. In addition, as the antenna switching timing detection signal, a signal in which the same code is repeated over a predetermined time corresponding to at least one symbol is used. As a result, the antenna switching timing detection signal can be detected separately from noise.

(Third embodiment)
An antenna switching reception system according to a third embodiment of the present invention will be described. FIG. 7 shows a schematic configuration of the antenna switching reception system of the third embodiment. The antenna switching reception system according to the third embodiment is configured by adding a sleep release unit 7 to the configuration of the antenna switching reception system according to the second embodiment. The antenna switching reception system according to the third embodiment operates in a sleep mode and a normal reception mode with low power consumption. Transition from the sleep mode to the normal reception mode is controlled by the sleep release unit 7.

  FIG. 8 shows the operation of the antenna switching reception system of the third embodiment. FIG. 9 shows a signal received using the antenna A and the antenna B in the antenna switching reception system according to the third embodiment, and an operation of the antenna switching reception system when the signal is received. In particular, an example in which antenna A is initially selected and a preamble signal is received by the antenna A is shown. Also, as a preamble signal, a preamble 1 signal for canceling the sleep mode and a preamble 2 signal for detecting timing for switching the antenna are transmitted. The preamble 1 signal or preamble 2 signal is set with a sufficient time to shift from the sleep mode to the normal reception mode.

  The operation of the antenna switching reception system according to the third embodiment will be described with reference to FIGS. In the antenna switching reception system according to the third embodiment, processes # 20 to # 23 are inserted between the processes # 2 and # 3 in the antenna switching reception system according to the first embodiment. In # 2, if it is detected that the RSSI level is instantaneously or continuously for a predetermined time or more and is equal to or greater than the threshold value, it is determined that the top of the frame has been input (YES in # 2), and the sleep canceling unit 7 sets the sleep mode. Cancel and shift to the normal reception mode (# 20).

  When the preamble signal is detected by the preamble detector 6 (YES in # 21), the antenna controller 4 measures the reception level of the currently selected antenna (# 3) and stores it (# 4). In FIG. 9, the test 1 signal is received by the antenna A, and the reception level is detected. The operation is the same as that of the antenna switching reception system according to the first embodiment shown in FIGS. Even if the preamble signal is not immediately detected in # 21, the preamble signal is continuously detected by the preamble detector 6 until a predetermined time elapses (NO in # 21, NO in # 22). If the preamble signal is not detected by the preamble detector 6 until the predetermined time has elapsed (YES in # 22), the mode again shifts to the sleep mode (# 23).

  According to the antenna switching receiving system of the third embodiment, the sleep mode is canceled in response to the RSSI level instantaneously or continuously exceeding a predetermined time for a predetermined time or more, and the antenna switching is performed with the selected antenna. A timing detection signal is received. Thereby, it is possible to stand by without starting reception of the antenna switching timing detection signal until the antenna reception level becomes equal to or higher than a predetermined level, thereby reducing the power consumption of the antenna switching reception system.

(Fourth embodiment)
An antenna switching reception system according to a fourth embodiment of the present invention will be described. FIG. 10 shows a schematic configuration of the antenna switching reception system of the fourth embodiment. The antenna switching reception system according to the fourth embodiment is provided with a low-speed preamble detection unit 8 instead of the preamble detection unit 6 in the configuration of the antenna switching reception system according to the second embodiment. The low-speed preamble detection unit 8 is configured to detect a preamble signal transmitted at a lower transmission rate than the payload signal.

  FIG. 11 shows the operation of the antenna switching reception system of the fourth embodiment. In the antenna switching receiving system of the fourth embodiment, the process of # 25 is executed instead of the process of # 21 in the antenna switching receiving system of the second embodiment. That is, when a low-speed preamble signal is detected by the low-speed preamble detection unit 8 (YES in # 25), the antenna control unit 4 measures the reception level of the currently selected antenna (# 3) and stores it (# 4). The subsequent operation is the same as the operation of the antenna switching reception system of the second embodiment shown in FIG.

  According to the antenna switching reception system of the fourth embodiment, the preamble signal transmitted at a lower transmission rate than the payload signal is received. Even when an antenna affected by reception level deterioration due to deterioration of the communication environment such as multipath fading is selected, it is possible to detect the preamble signal without fail. Therefore, the reception level can be detected more accurately from the test signal at each antenna, and the antenna for receiving the payload signal can be properly selected. For example, even if the initially selected antenna is affected by level degradation caused by multipath fading, the payload can be received by an antenna with less influence. As a result, it is possible to avoid a reception error due to the level deterioration due to multipath fading.

(Fifth embodiment)
An antenna switching reception system according to a fifth embodiment of the present invention will be described. FIG. 12 shows a schematic configuration of the antenna switching reception system of the fifth embodiment. The antenna switching reception system of the fifth embodiment is configured by adding an averaging unit 9 to the configuration of the antenna switching reception system of the first embodiment. In the antenna switching reception system according to the fifth embodiment, the RSSI detection unit 3 detects RSSI multiple times for the test 1 signal and the test 2 signal received by each antenna. The averaging unit 9 averages the RSSI detected a plurality of times by the RSSI detection unit 3 for each antenna.

  FIG. 13 shows a signal received using the antenna A and the antenna B in the antenna switching reception system of the fifth embodiment, and an operation of the antenna switching reception system when the signal is received. In particular, an example in which antenna A is initially selected and a preamble signal is received by the antenna A is shown. Antenna A receives the test 1 signal following the preamble signal. In measuring the reception level of the test 1 signal by the antenna A, the RSSI detection unit 3 detects the RSSI a plurality of times, and the value averaged by the averaging unit 9 is used as the reception level of the antenna A. The antenna is then switched and antenna B receives the test 2 signal. Also in the measurement of the reception level of the test 2 signal by the antenna B, the RSSI detection unit 3 detects the RSSI a plurality of times, and the value averaged by the averaging unit 9 is set as the reception level of the antenna B. Since subsequent operations are the same as those of the antenna switching reception system of the first embodiment, the description thereof is omitted.

  According to the antenna switching reception system of the fifth embodiment, the antenna that receives the payload signal is selected based on the average value of RSSI detected a plurality of times from the received test signal. As a result, it is possible to prevent the wrong antenna from being selected due to noise instantaneously mixed when the test signal is received. That is, the influence of sudden noise can be reduced and the accuracy of antenna selection can be improved.

(Sixth embodiment)
An antenna switching reception system according to the sixth embodiment of the present invention will be described. The configuration of the antenna switching receiving system according to the sixth embodiment is the same as that of the antenna switching receiving system according to the first embodiment shown in FIG.

  FIG. 14 shows a signal received using the antenna A and the antenna B in the antenna switching reception system of the sixth embodiment, and an operation of the antenna switching reception system when the signal is received. In particular, an example in which antenna A is initially selected and a preamble signal is received by the antenna A is shown. In the antenna switching reception system of the sixth embodiment, the signal transmitted from the transmission system is configured by a preamble signal, a test 2 signal, a unique word signal, a payload signal, and the like without the test 1 signal.

  In the sixth embodiment, when the preamble signal is received by the antenna A, and the RSSI detection unit 3 detects an RSSI equal to or greater than a predetermined threshold, the antenna control unit 4 determines the reception level of the test signal by the antenna A. Save as. Then, switching to the antenna B starts measurement of the reception level of the test 2 signal. Since subsequent operations are the same as those of the antenna switching reception system of the first embodiment, the description thereof is omitted. In this embodiment, instead of detecting RSSI above a predetermined threshold shown in FIG. 14, a preamble signal is detected by the method shown in the second embodiment, and the RSSI value at that time is tested by antenna A. You may preserve | save as a reception level of a signal.

  According to the antenna switching reception system of the sixth embodiment, the reception level of the preamble signal received by the antenna selected before receiving the test signal is set as the reception level of the test signal by the antenna. As a result, transmission of the test signal to the antenna that has received the preamble signal can be made unnecessary, and the communication packet length can be shortened to improve the transmission efficiency.

(Seventh embodiment)
An antenna switching receiving system according to a seventh embodiment of the present invention will be described. FIG. 15 shows a schematic configuration of the antenna switching reception system of the seventh embodiment. The antenna switching reception system of the seventh embodiment is configured by adding an antenna switching counter unit 10 to the configuration of the antenna switching reception system of the first embodiment.

  A certain time is required to actually switch the antenna. During the switching, the reception level may become unstable, and accurate RSSI may not be measured. Therefore, in the antenna switching reception system of the present embodiment, the antenna switching counter unit 10 is provided so that RSSI is not detected for a certain time after the antenna switching. That is, the antenna switching counter unit 10 counts a predetermined time after the antenna is switched until the reception level of the received signal is stabilized.

  FIG. 16 shows a signal received using the antenna A and the antenna B in the antenna switching reception system according to the seventh embodiment, and an operation of the antenna switching reception system when the signal is received. In particular, an example in which antenna A is initially selected and a preamble signal is received by the antenna A is shown. In the case shown in FIG. 16, the antenna is switched twice. That is, after the reception level of the test 1 signal is detected by the antenna A, the antenna B is switched to the antenna B (first time). After the reception level of the test 2 signal is detected by the antenna B, the antenna A having a higher reception level Switched (second time). At the time of switching between these antennas, the antenna switching counter unit 10 starts counting. Then, the antenna control unit 4 controls the RSSI detection unit 3 so as not to detect the reception level until the antenna switching counter unit 10 counts a predetermined time (in FIG. 16, the blacked time).

  The antenna switching reception system according to the seventh embodiment is configured to detect RSSI after the reception level of the received signal is sufficiently stabilized by the count of the antenna switching counter unit 10. As a result, accurate RSSI level detection is possible, and the accuracy of antenna selection can be further improved.

(Eighth embodiment)
An antenna switching reception system according to the eighth embodiment of the present invention will be described. FIG. 17 shows a schematic configuration of the antenna switching reception system of the eighth embodiment. The antenna switching reception system of the eighth embodiment is configured by eliminating the RSSI detection unit 3 and adding a correlation value calculation unit 11 from the configuration of the antenna switching reception system of the second embodiment.

  The test 1 signal and the test 2 signal are configured by a signal sequence of a specific sequence and transmitted from the transmission system, and the correlation value calculation unit (storage unit) 11 has the same sequence as the transmitted test 1 signal and test 2 signal. Are stored. The correlation value calculation unit 11 calculates a correlation value between the stored signal sequence and the signal sequence of the test signal demodulated by the radio unit 2, and the antenna control unit 4 calculates the correlation calculated by the correlation value calculation unit 11. Select an antenna to receive the payload signal based on the value.

  FIG. 18 shows the operation of the antenna switching reception system of the eighth embodiment. In the antenna switching reception system of the eighth embodiment, processes # 31 to # 36 are executed instead of the processes of # 3 to # 8 in the antenna switching reception system of the second embodiment. First, when the preamble signal is detected (YES in # 21), the test 1 signal is received by the currently selected antenna, the correlation value is calculated by the correlation value calculation unit 11 (# 31), and the maximum correlation value is Saved (# 32). The correlation value is calculated by the following procedure. That is, when the received signal is demodulated by the radio unit 2, the correlation value calculation unit 11 shifts the demodulated test signal signal sequence bit by bit with respect to the stored signal sequence. The correlation value is calculated by sequentially digitizing.

  When the correlation value of one antenna is calculated, the antenna is switched under the control of the antenna control unit 4, the test 1 signal is received, the correlation value is calculated by the correlation value calculation unit 11 (# 33), and the maximum correlation is obtained. The value is saved (# 34). Then, the maximum correlation values of the respective antennas are compared (# 35). If the correlation value of antenna A is large (YES in # 36), the process proceeds to # 9, and if the correlation value of antenna A is not large (# The process proceeds to NO) # 10 in 36. The operation is the same as that of the antenna switching reception system according to the first embodiment shown in FIG. Note that the processing of # 25 shown in FIG. 11 may be performed instead of the processing of # 21.

  According to the antenna switching reception system of the eighth embodiment, the antenna that receives the payload signal based on the signal sequence stored in the correlation value calculation unit 11 and the correlation value calculated from the signal sequence of the received test signal. select. Accordingly, it is possible to select an antenna that receives a payload signal without requiring a configuration for detecting the reception level of the test signal (for example, the RSSI detector 3). Therefore, the configuration of the antenna switching reception system can be made simple and inexpensive.

(Ninth embodiment)
An antenna switching receiving system according to the ninth embodiment of the present invention will be described. The configuration of the antenna switching reception system of the ninth embodiment is equivalent to the configuration of the antenna switching reception system of the first embodiment.

  FIG. 19 shows a signal received using the antenna A and the antenna B in the antenna switching reception system of the ninth embodiment, and an operation of the antenna switching reception system when receiving this signal. In particular, an example is shown in which the antenna A is initially selected, a preamble signal is received by the antenna A, and the length for measuring the reception level of the antenna corresponds to 2 symbols. The antenna A and the antenna B are switched every predetermined time (a time corresponding to 1/2 symbol in FIG. 19) when receiving the test signal.

  First, after the preamble signal is received and detected by the antenna A, the test 1 signal is received by the antenna A and the measurement of the reception level is started. When the reception level of the antenna A is measured and stored, it is switched to the antenna B, and the antenna 1 also receives the test 1 signal and starts measuring the reception level. When the reception level of antenna B is measured and stored, it is switched back to antenna A, and the test 2 signal is received by antenna A and measurement of the reception level is started. When the reception level of the antenna A is measured and stored, the antenna B is switched to the antenna B again. The antenna B receives the test 2 signal, and the measurement of the reception level is measured and stored. The reception levels obtained in this way are averaged and compared for each antenna.

  According to the antenna switching reception system of the ninth embodiment, the respective antennas are alternately switched every predetermined time when receiving the test signal. Thereby, it is possible to prevent erroneous determination due to fluctuations such as a momentary drop in reception level due to the occurrence of fading and the like, and to improve the accuracy of antenna selection. In measuring the reception level of the antenna, a length of 3 symbols or more may be used. In this case, the reception level can be determined more accurately over a long time. Further, the selection of the antenna is not limited to the average value of the reception level, and may be based on the maximum correlation value according to the antenna switching reception system of the eighth embodiment.

(10th Embodiment)
An antenna switching receiving system according to the tenth embodiment of the present invention will be described. FIG. 20 shows a schematic configuration of the antenna switching reception system of the tenth embodiment. The antenna switching reception system of the tenth embodiment is configured by adding a payload length counter unit 12 to the configuration of the antenna switching reception system of the first embodiment. When receiving the payload signal, the payload length counter unit 12 counts a time corresponding to the length of the payload signal of the received packet so that the antenna is not switched.

  FIG. 21 shows a signal received using the antenna A and the antenna B in the antenna switching reception system of the tenth embodiment and the operation of the antenna switching reception system when receiving this signal. In particular, an example in which antenna A is initially selected and a preamble signal is received by the antenna A is shown.

  In FIG. 21, after being fixed to the antenna 1, until the unique word signal is detected, an operation equivalent to that of the antenna switching receiving system of the first embodiment shown in FIG. 3 is performed. When the unique word signal is detected, the payload length counter unit 12 starts counting time corresponding to the length of the payload signal. Then, for a certain period of time (payload reception time), the antenna switching function (that is, detection of a preamble signal (RSSI) serving as the trigger) is stopped.

  According to the antenna switching reception system of the tenth embodiment, antenna switching is not performed when a payload signal is received based on the count of the payload length counter unit. As a result, it is possible to prevent a reception error that occurs when the antenna is erroneously switched during reception of the payload signal.

(Eleventh embodiment)
An antenna switching reception system according to the eleventh embodiment of the present invention will be described. FIG. 22 shows a schematic configuration of the antenna switching receiving system of the eleventh embodiment. The antenna switching reception system of the eleventh embodiment is configured by adding a switching stop threshold setting unit 13 to the configuration of the antenna switching reception system of the first embodiment. In the antenna switching reception system according to the eleventh embodiment, when a sufficiently strong RSSI level is detected so that it is not necessary to switch the antenna in receiving the preamble signal, the antenna switching function is stopped. Therefore, the switching stop threshold value setting unit 13 is used when setting a threshold value of the RSSI level that is a reference for stopping the antenna switching function. The threshold set by the switching stop threshold setting unit 13 is set to a value larger than the thresholds described in # 2 of FIG. 2 and FIG. 3 of the first embodiment.

  FIG. 23 shows a signal received using the antenna A and the antenna B in the antenna switching reception system of the eleventh embodiment and the operation of the antenna switching reception system when receiving this signal. In particular, an example in which antenna A is initially selected and a preamble signal is received by the antenna A is shown. In FIG. 23, first, a preamble signal is received and its RSSI is detected. At this time, when the RSSI is larger than the threshold set by the switching stop threshold setting unit 13, the antenna is not switched. That is, the antenna 1 continues to receive the test 1 signal, the test 2 signal, the unique word signal, and the payload signal.

  According to the antenna switching reception system of the eleventh embodiment, when the reception level of the initially selected antenna is equal to or higher than the predetermined threshold, it is determined that the antenna can receive the payload signal without any problem, and the antenna is switched. Not performed. Thereby, it is possible to reduce the possibility of malfunction of antenna selection accompanying the occurrence of reception level detection error or the like.

(Twelfth embodiment)
An antenna switching receiving system according to the twelfth embodiment of the present invention will be described. FIG. 24 shows a schematic configuration of the antenna switching receiving system of the twelfth embodiment. The antenna switching reception system of the twelfth embodiment is configured by adding a communication cycle counter unit 14 to the configuration of the antenna switching reception system of the first embodiment. In wireless communication, usually, regular communication is performed between devices, for example, every few minutes to several hours in order to check the state of each device. In the twelfth embodiment, the antenna is switched according to whether or not regular communication is possible. Specifically, when the unique word for regular communication is not detected within a predetermined time with the selected antenna, the antenna is switched to the other antenna. The communication cycle counter unit 14 starts counting when the unique word detection unit 5 detects a unique word in the packet.

  FIG. 25 shows a signal received using the antenna A and the antenna B in the antenna switching reception system of the twelfth embodiment and the operation of the antenna switching reception system when receiving this signal. In particular, an example in which antenna A is initially selected and a preamble signal is received by the antenna A is shown. 25, from the transmission system, the regular communication packet 1, the regular communication packet 2, the regular communication packet 3, the regular communication packet 4.. . . Will be sent periodically. These regular communication packets are appropriately transmitted between normal data transmission signals and control signals. When the periodic communication packet 1 is received by the antenna A, the communication cycle counter unit 14 starts counting when the unique word detection unit 5 detects the unique word in the packet. Thereafter, when a failure or the like occurs in the antenna A, the antenna switching reception system cannot receive the periodic communication packet 2 even if the count value of the communication cycle counter unit 14 exceeds a certain value. At this time, the antenna control unit 4 determines that there is a possibility that a failure or the like has occurred in the antenna A, switches to the antenna B, and receives the periodic communication packet 3 and thereafter.

  In the antenna switching receiving system according to the twelfth embodiment, after the unique word is detected by the unique word detector 5, the unique word for the next periodic communication cannot be received until the communication cycle counter 14 counts a predetermined value. When switching to another antenna. Thereby, since it can detect that malfunctions, such as a failure, have occurred in the selected antenna and switch to another antenna, it is possible to prevent a state in which reception is not possible from continuing.

  Note that the present invention is not limited to the configuration of the above-described embodiment, and at least before receiving a payload signal, the antenna may be configured to receive a test signal with a plurality of antennas and select an antenna that receives the payload signal. That's fine. Moreover, the antenna switching reception system which combined the characteristic of each embodiment mentioned above suitably may be sufficient.

  The present invention can be modified in various ways. For example, in each embodiment, the preamble signal and the test signal may be configured by the same signal sequence. In this case, the preamble signal and the test signal can be generated by a single configuration. Thereby, the structure of the transmission system which produces | generates and transmits a preamble signal and a test signal can be simplified.

  In addition, the test signal may be configured to include a pseudo-random signal sequence that imitates the payload signal, and further includes a signal sequence that is the same as a part of the signal sequence included in the payload signal. May be. In this case, the antenna that receives the payload signal can be selected based on the result of receiving the test signal of the signal sequence close to or identical to the payload signal. Thereby, the accuracy of antenna selection can be further improved.

  In addition, by configuring to receive the test signal transmitted from the transmission system at the same transmission rate as the payload signal, the test signal is received in a state close to the state in which the payload signal is actually received, and the antenna is You can choose. Thereby, the accuracy of antenna selection can be further improved. Further, the time required for transmitting / receiving the test signal can be shortened.

  The preamble signal detection (# 21 in FIGS. 5 and 18) in the second and eighth embodiments may be configured to be performed by calculating a correlation value. In this case, the preamble signal including the antenna switching timing detection signal is configured by a specific sequence of signal sequences and transmitted from the transmission system. The preamble detection unit (storage unit, correlation value calculation unit) 6 stores a signal sequence in the same sequence as the preamble signal. Further, the preamble detector 6 calculates a correlation value between the stored signal sequence and the signal sequence of the received preamble signal. The correlation value is calculated by the following procedure. That is, when the received signal is demodulated by the radio unit 2, the preamble detection unit 6 shifts the demodulated preamble signal sequence by 1 bit from the stored signal sequence, and increases the degree of coincidence between them. Correlation values are calculated by digitizing sequentially. According to this configuration, the preamble signal and the noise can be more clearly distinguished, and the resistance to noise can be enhanced. The preamble signal detection (# 25 in FIG. 11) in the fourth embodiment is the same as described above.

1 Antenna switching unit 2 Radio unit (demodulation unit)
DESCRIPTION OF SYMBOLS 3 RSSI detection part 4 Antenna control part 5 Unique word detection part 6 Preamble detection part 7 Sleep cancellation | release part 8 Low speed preamble detection part 9 Averaging part 10 Antenna switching counter part 11 Correlation value calculation part 12 Payload length counter part 13 Switching stop threshold value setting 14 Communication cycle counter

Claims (1)

In an antenna switching reception system that receives a radio signal by switching a plurality of antennas,
From the transmission system, a preamble signal, at least one test signal, and a payload signal are transmitted in this order, and the antenna switching timing detection signal included in the preamble signal is transmitted at a lower transmission rate than the payload signal. Sent
It determines that detects that the reception level of the received antennas selected signal is momentarily or continuously for a threshold or more than a predetermined time and the preamble signal is input, detects the antenna switching timing detection signal And
Receiving the at least one test signal by switching the plurality of antennas based on the antenna switching timing detection signal ;
The antenna switching timing detection signal and the test signal are each configured by a specific sequence of signal sequences and transmitted.
A storage unit that stores the same signal sequence as the transmitted antenna switching timing detection signal and the transmitted test signal ;
A correlation value calculation unit that calculates a correlation value between the signal sequence stored in the storage unit, the signal sequence of the received antenna switching timing detection signal , and the correlation value of the signal sequence of the received test signal; ,
Detecting the antenna switching timing detection signal based on the correlation value calculated by the correlation value calculation unit ;
An antenna switching receiving system, wherein an antenna for receiving the payload signal is selected based on a correlation value of a signal sequence of the received test signal calculated by the correlation value calculation unit .

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