JP2012049832A - Antenna switching reception system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna switching reception system having a simple structure and capable of accurately selecting an antenna having a high reception level under the environment where multipath is caused many times, to suppress the influence of level variation due to multipath fading.SOLUTION: In an antenna switching reception system that receives a radio signal by switching between a plurality of antennas, each antenna receives a test signal before receiving a payload signal, and an antenna to receive the payload signal is selected.

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.

  In addition, there are measures by “switching diversity”, “selective diversity” for switching a plurality of antennas, and “combined 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 (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 fluctuation due to multipath fading by selecting an antenna having a high reception level accurately even in an environment with many multipaths with a simple configuration. Objective.

  In order to achieve the above object, the antenna switching receiving system of the present invention receives a test signal at each antenna before receiving a payload signal in an antenna switching receiving system that switches a plurality of antennas to receive a radio signal. The antenna that receives the payload signal is selected, and the antenna that receives the test signal is switched based on the antenna switching timing detection signal detected before the test signal.

  In this antenna switching reception system, the antenna switching timing detection signal is constituted by a specific sequence of signal sequences and transmitted, and the signal sequence of the same sequence as the transmitted antenna switching timing detection signals And a correlation value calculation unit for calculating a correlation value of the signal sequence stored in the storage unit and the signal sequence of the received antenna switching timing detection signal, and the antenna switching timing detection It is preferable to detect the signal for use based on the correlation value calculated by the correlation value calculation unit.

  In this antenna switching reception system, it is preferable to detect the antenna switching timing detection signal transmitted at a lower transmission rate than the payload signal.

  In this antenna switching reception system, it is preferable that the antenna switching timing detection signal can be demodulated even in a saturated state without depending on the reception level.

  The antenna switching reception system preferably includes a counter unit that counts time from a specific antenna switching reference timing to the next antenna switching reference timing, and detects the antenna switching reference timing based on the count value of the counter unit. .

  In this antenna switching reception system, the antenna switching timing detection signal is transmitted a plurality of times within one frame, and the antenna switching timing detection signal is transmitted at predetermined intervals of a period that is at least twice the length of the antenna switching timing detection signal. It is preferable to provide an antenna periodic switching control unit that switches between the two.

  In this antenna switching reception system, it is preferable that the antenna switching timing detection signal is not detected for a predetermined period after the antenna switching timing detection signal is detected.

  In this antenna switching reception system, it is preferable that the antenna switching timing detection signal is not detected for a predetermined period after the unique word signal is detected after the antenna switching timing detection signal is detected.

  The antenna switching reception system includes a non-detection time counter unit that counts a time during which the antenna switching timing detection signal is not detected, and the non-detection time counter unit counts a predetermined time during reception by any antenna. When it does, it is preferable to switch to another antenna.

  In this antenna switching reception system, the test signal is configured and transmitted by a specific sequence of signal sequences, and the storage unit further stores a signal sequence of the same sequence as the transmitted test signals. And a second correlation value calculating unit that calculates a correlation value between the signal sequence of the test signal stored in the storage unit and the signal sequence of the received test signal, and the second correlation value calculating unit includes: Preferably, when the test signal is detected based on the calculated correlation value, the payload signal is received without performing antenna switching.

  In this antenna switching reception system, it is preferable to have a plurality of second correlation value calculation units corresponding to the number of the test signals.

  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 an embodiment of the present 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 same antenna switching reception system. The flowchart which shows operation | movement of the antenna switching reception system. The block diagram which shows schematic structure of the modification of the antenna switching receiving system by the said embodiment. The figure which shows the operation | movement of the said antenna switching receiving system when the signal received using two antennas and this signal are received in the modification. The flowchart which shows operation | movement of the modification. The figure which shows the operation | movement of the said antenna switching reception system when receiving the signal received using two antennas in another modification of the same antenna switching reception system, and this signal. The block diagram which shows schematic structure of another modification of the antenna switching reception system. The figure which shows the relationship between the flame | frame received using two antennas, and a counter value in the modification. The figure which shows another relationship between the flame | frame received using two antennas, and a counter value in the modification. The flowchart which shows operation | movement of the modification. The block diagram which shows schematic structure of another modification of the antenna switching reception system. The figure which shows the operation | movement of the said antenna switching receiving system when the signal received using two antennas and this signal are received in the modification. The flowchart which shows operation | movement of the modification. The block diagram which shows schematic structure of another modification of the antenna switching reception system. The figure which shows the operation | movement of the said antenna switching receiving system when the signal received using two antennas and this signal are received in the modification. The flowchart which shows operation | movement of the modification. The block diagram which shows schematic structure of another modification of the antenna switching reception system. The figure which shows the operation | movement of the said antenna switching receiving system when the signal received using two antennas and this signal are received in the modification. The flowchart which shows operation | movement of the modification. The block diagram which shows schematic structure of another modification of the antenna switching reception system. The figure which shows the operation | movement of the said antenna switching receiving system when the signal received using two antennas and this signal are received in the modification. The flowchart which shows operation | movement of the modification.

(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 10 includes an antenna unit 11 having two antennas, an antenna switching unit 12, an antenna switching timing detection unit 13, an antenna switching determination unit 14, and the like. The antenna switching unit 12 switches from two antennas to one of the antennas. The antenna switching timing detection unit 13 detects the timing at which the antenna switching unit 12 switches the antenna, for example, by detecting a signal of a predetermined level or higher. The antenna switching determination unit 14 selects the antenna that receives the payload signal based on the RSSI (Received Signal Strength) of the signal received by any of the antennas via the antenna switching unit 12, and sends a control signal indicating that. Output to the antenna switching unit 12. In the following, a case will be described where two antennas are connected to the antenna switching unit 12 and switched, but three or more antennas may be used.

  FIG. 2 shows a signal received using two antennas, that is, antenna A and antenna B, in the antenna switching reception system 10, and an operation of the antenna switching reception system 10 when receiving this signal. In particular, an example in which the antenna A is initially selected and the test 1 signal is received by the antenna A is shown. FIG. 3 is a flowchart showing the operation of the antenna switching reception system 10 of the first embodiment.

  The signal shown in FIG. 2 is transmitted from a transmission system corresponding to the antenna switching reception system 10 of the present embodiment. At least a test 1 signal, a test 2 signal, and a payload signal are transmitted from the transmission system. One frame is composed of the test 1 signal, the test 2 signal, and the payload signal. A unique word signal (not shown) for frame synchronization is transmitted before the payload 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. This test signal is added as appropriate according to the number of antennas switched by the antenna switching unit 12. The payload signal includes, for example, various data such as a header, video, audio, air temperature, a known signal sequence for the equalizer to estimate the multipath environment, or various control signals.

  The operation of the antenna switching reception system 10 according to the first embodiment will be described with reference to FIGS. The antenna switching reception system 10 is initially waiting (# 1). When the antenna unit 11 of the antenna switching reception system 10 receives a signal (# 2) and the antenna switching timing detection unit 13 detects the antenna switching timing (YES in # 3), the antenna switching determination unit 14 The reception level is detected (# 4). Here, the detection of the reception level is not limited to that based on RSSI, but may be based on the amplification factor when the received signal is amplified by the automatic gain control circuit. Then, the antenna switching determination unit 14 switches to the antenna B (# 5) and detects the reception level of the antenna B (# 6). The antenna is switched based on the antenna switching timing detected by the antenna switching timing detector 13. Thereafter, the antenna switching determination unit 14 compares the reception level of the antenna A with the reception level of the antenna B (# 7). When the reception level of antenna A is higher (YES in # 8), antenna switching determination unit 14 selects antenna A as an antenna for receiving the payload signal. That is, the antenna switching determination unit 14 outputs a control signal for switching to the antenna A to the antenna switching unit 12 (# 9), and receives a payload signal by the antenna A (# 10). The example shown in FIG. 2 corresponds to this case. When the reception level of antenna B is higher (NO in # 8), antenna B is selected as the antenna for receiving the payload signal. That is, the antenna switching determination unit 14 receives the payload signal by the antenna B while being fixed to the antenna B (# 11). If the reception level of antenna A is the same as the reception level of antenna B, the payload signal is received by antenna B that last received the test signal (# 11).

  According to this antenna switching reception system 10, since the antenna that receives the test signal and receives the payload signal is selected by each antenna before receiving the payload signal, the influence of level fluctuations due to multipath fading is achieved with a simple configuration. 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.

(Modification)
FIG. 4 shows a schematic configuration of a modified example of the antenna switching reception system 10 of the first embodiment. In this antenna switching reception system 10, a correlation value calculation unit 15 is applied as an example of the antenna switching timing detection unit 13 of FIG. The transmission system transmits an antenna switching timing detection signal composed of a specific sequence of signal strings before the test 1 signal. The antenna switching timing detection signal is a signal for detecting a reference timing for switching the antenna to be used to the antenna A or the antenna B when receiving the test 1 signal and the test 2 signal. The antenna switching timing detection signal is transmitted at a transmission rate lower than the transmission rate of the payload signal. The correlation value calculation unit (storage unit) 15 stores a signal sequence (reference signal) in the same sequence as the antenna switching timing detection signal transmitted from the transmission system. Examples of the signal sequence include a random signal such as 01100101011000101..., An M sequence having excellent correlation characteristics, and a similar signal sequence. The correlation value calculation unit 15 calculates a correlation value between the stored signal sequence and the signal sequence of the received antenna switching timing detection signal. In this modification, the antenna switching timing detection signal is detected based on the correlation value calculated by the correlation value calculation unit 15.

  FIG. 5 shows a signal received using the antenna A and the antenna B in the antenna switching reception system 10 of this modification, and an operation of the antenna switching reception system 10 when receiving this signal. FIG. 6 is a flowchart showing the operation of the antenna switching reception system 10 of this modification. In this modified example, # 12 is executed instead of the process of # 3 shown in FIG.

  From the transmission system, an antenna switching timing detection signal, a test 1 signal, a test 2 signal, and a payload signal are transmitted. Of the antenna switching timing detection signal, the test 1 signal, the test 2 signal, and the payload signal constituting one frame, the antenna switching timing detection signal is transmitted at a lower transmission rate than the other signals. A signal received via any one of the antennas is compared with a reference signal stored by the correlation value calculation unit 15 while shifting by one sample, and a correlation value is calculated by sequentially digitizing the degree of coincidence. If the degree of coincidence is equal to or greater than a predetermined threshold, it is determined that an antenna switching timing detection signal has been detected (YES in # 12), and antenna switching determination unit 14 detects the reception level of antenna A (# 4). The following processing is the same as that in FIG.

  According to this antenna switching reception system 10, since the antenna switching timing is detected by correlation value detection, the antenna switching timing detection signal and the noise can be more clearly distinguished, and the resistance to noise is enhanced. Is possible. In addition, since the antenna switching can be determined at any location simply by inserting the signal sequence of the antenna switching timing detection signal at the location where the antenna switching is desired, the degree of freedom of the frame configuration can be increased.

  In addition, since the antenna switching timing detection signal transmitted at a lower transmission rate than the payload signal is received, the influence of intersymbol interference due to multipath is avoided and the energy of the signal per bit increases. High sensitivity. Therefore, even when an antenna affected by reception level deterioration due to communication environment deterioration such as multipath fading is selected, the antenna switching timing detection signal can be detected without fail. Therefore, even when an antenna affected by reception level deterioration due to deterioration of the communication environment such as multipath fading is selected, an antenna for receiving a payload signal can be selected accurately. . 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.

(Modification)
FIG. 7A shows an example of a signal (modulated signal) transmitted as an antenna switching timing detection signal of still another modified example of the antenna switching reception system 10. FIG. 7B shows an example of a demodulated signal with level adjustment, and FIG. 7C shows an example of a demodulated signal in a saturated state without level adjustment. Signals received and demodulated via the antenna unit 11 and the antenna switching unit 12 are level-adjusted by an automatic gain control unit (not shown) and then input to the correlation value calculation unit 15. Here, when the influence of multipath fading is large, as shown in FIG. 7B, the demodulated signal level after gain control by the automatic gain control unit may be small. In view of this, the present modification is configured such that, for example, the transmission signal is a binary signal such as BPSK, thereby eliminating the need for gain control and allowing demodulation and detection even in a saturated state.

  In this antenna switching reception system 10, when the transmission signal is a binary signal, the reception signal is input to the correlation value calculation unit 15 without performing gain control by the automatic gain control unit, as shown in FIG. As shown, since it does not depend on the reception level, it can be demodulated even in a saturated state. Therefore, it is possible to reduce the influence of multipath fading and suppress the deterioration of the reception level. As a result, it is possible to improve the detection probability of the antenna switching timing detection signal and reduce the probability that the antenna cannot be switched. Also, by fixing the gain by the automatic gain control unit to the maximum, it is possible to demodulate even in a saturated state without depending on the reception level.

(Modification)
FIG. 8 shows a schematic configuration of still another modified example of the antenna switching reception system 10 of the first embodiment. The antenna switching reception system 10 is configured by adding a counter unit 16 to the antenna switching reception system 10 of FIG. The counter unit 16 counts the time from a specific antenna switching reference timing to the next antenna switching reference timing. In the antenna switching reception system 10, the next antenna switching timing reference is detected based on the count value of the counter unit 16.

  9 and 10 illustrate signals (frames) received using the antenna A and the antenna B and the operation of the counter unit 16 in the antenna switching reception system 10 of the present modification. In particular, FIG. 9 shows a case where a frame is received at a constant cycle without error, and FIG. 10 shows a case where a frame is not received at a constant cycle with error. FIG. 11 is a flowchart showing an operation (particularly, an operation corresponding to FIG. 10) of the antenna switching reception system 10 of the present modification. In this modified example, # 13 and # 14 are executed instead of the process of # 3 shown in FIG.

  The counter unit 16 starts counting when the antenna switching timing detection unit 13 first detects an antenna switching timing detection signal. And it counts to the count value N corresponding to the timing used as the reference | standard of antenna switching in the following frame, and resets a counter. The start of counting by the counter unit 16 may be a timing determined within each frame, and may be a timing at which synchronization is established by detecting a unique word signal for frame synchronization after the test 2 signal. .

  In FIG. 9, when the frames are received at a constant period, the timing at which the antenna switching timing detection unit 13 detects the antenna switching timing detection signal in the next frame matches the timing at which the counter unit 16 counts the count value N. Can be made. Therefore, when the counter unit 16 counts the count value N, it can be considered that the antenna switching timing detection signal has been detected. This eliminates the need for the antenna switching timing detection signal from the next frame onward, thereby improving the transmission efficiency of the payload signal. The operation in FIG. 9 corresponds to the operation in which the process of # 14 in FIG. 11 is omitted and the process proceeds to # 4.

  On the other hand, in FIG. 10, when the frame cannot be received at a constant period, the antenna switching timing detection unit 13 detects the antenna switching timing detection signal in the next frame while the counter unit 16 supplementarily uses the count value. . That is, a timing that is a rough reference for antenna switching is detected based on the count value of the counter unit 16, and the antenna switching timing detection unit 13 is operated for a predetermined time before and after that. 10 and 11, for example, after the counter unit 16 counts up to N-4 (YES in # 13), the antenna switching timing detection unit 13 is operated for a predetermined time, and the antenna switching timing detection signal is detected. Is detected (# 14). Thus, even when the frame period includes an error, the detection accuracy of the antenna switching timing detection signal can be improved by using the count value of the counter unit 16 as an auxiliary. For example, when the correlation value calculation unit 15 is applied as the antenna switching timing detection unit 13, the antenna switching timing detection signal associated with the calculation of the correlation value is compared with the case where the antenna switching timing detection signal is always detected. The probability of erroneous detection can be reduced. If the antenna switching timing detection signal can be detected in # 14 (YES in # 14), the process proceeds to # 4. If not (NO in # 14), the process returns to # 1.

(Modification)
FIG. 12 shows a schematic configuration of still another modified example of the antenna switching reception system 10 of the first embodiment. This antenna switching reception system 10 is configured by adding an antenna periodic switching control unit 17 to the antenna switching reception system 10 of FIG. The antenna regular switching control unit 17 switches the antenna every predetermined period having a period equal to or longer than the length of the antenna switching timing detection signal. Accordingly, the antenna switching timing detection signal is transmitted over a plurality of times at least twice the number of antennas in one frame.

  FIG. 13 shows a signal received using the antenna A and the antenna B in the antenna switching reception system 10 of the present modification, and an operation of the antenna switching reception system 10 when receiving this signal. In particular, the case where the antenna is switched every cycle that is twice the length of the antenna switching timing detection signal is shown. FIG. 14 is a flowchart showing the operation of the antenna switching reception system 10 of this modification. In this modification, steps # 15 to # 18 are executed in place of the processes of # 2 and # 3 shown in FIG.

  In the present modification, the frame transmitted from the transmission system includes antenna switching timing detection signals 1 to 4. The antenna switching timing detection signals 1 to 4 are configured by different specific signal sequences. Since the antenna switching reception system 10 switches antennas regardless of the timing at which frames are transmitted from the transmission system, various patterns can be considered as to which signal is received by which antenna. For example, the antenna switching timing detection signal is received at three patterns of reception timing shown in FIG.

  In the reception timing example 1, if the antenna switching timing detection signal 1 cannot be detected due to reception level deterioration or noise, the antenna switching timing detection signal 2 is continuously received. However, since the antenna A is switched to the antenna B during the reception, the antenna switching timing detection signal 2 is not detected. However, in the present modification, the antenna is switched at a period that is twice the length of the antenna switching timing detection signal, so that the antenna is not switched during reception of the next antenna switching timing detection signal 3. Therefore, the antenna switching timing detection signal 3 can be detected by the antenna B.

  In the reception timing example 2, first, since the antenna A is switched to the antenna B during the reception of the antenna switching timing detection signal 1, the antenna switching timing detection signal 1 is not detected. Subsequently, when the antenna switching timing detection signal 2 cannot be detected during reception of the antenna switching timing detection signal 2 due to reception level deterioration or noise, the antenna switching timing detection signal 3 is continuously received. However, since the antenna B is switched to the antenna A during the reception, the antenna switching timing detection signal 3 is not detected. However, in the present modification, the antenna is switched at a period that is twice the length of the antenna switching timing detection signal, so that the antenna is not switched during reception of the next antenna switching timing detection signal 4. Therefore, the antenna switching timing detection signal 4 can be detected by the antenna A.

  Reception timing example 3 shows a case where the timing for starting reception of the antenna switching timing detection signal matches the timing for switching the antenna. In this case, when the antenna switching timing detection signals 1 and 2 cannot be detected by the antenna B due to reception level degradation, noise, or the like, the antenna switching timing detection signal 3 is detected by switching to the antenna A.

  Thus, in this modification, the antenna periodic switching control unit 17 periodically switches the antenna (# 15), and the antenna switching timing detection unit 13 detects the antenna switching timing detection signal (in # 16). YES). Since the antenna switching timing detection signals are composed of different specific signal sequences, the antenna switching timing detection unit 13 specifies which antenna switching timing detection signal the detected antenna switching timing detection signal is. it can. Then, the antenna periodic switching control unit 17 counts the time until the test 1 signal is received according to the antenna switching timing detection signal detected by the antenna switching timing detection unit 13 (# 17). For example, in the case of the reception timing examples 1 and 3 in FIG. 13, the antenna regular switching control unit 17 counts the time corresponding to the antenna switching timing detection signal 4. If the antenna switching timing detection signal 1 is detected, the time corresponding to the antenna switching timing detection signals 2 to 4 is counted. Since it is sufficient that one of the antenna switching timing detection signals is detected, the antenna switching timing detection function by the antenna switching timing detection unit 13 is stopped during the counting by the antenna periodic switching control unit 17. (# 18). Thereafter, when the counting by the antenna periodic switching control unit 17 is finished, the process proceeds to # 4. Since it is the same as that in FIG.

  According to this antenna switching reception system 10, a signal for antenna switching timing detection is received a plurality of times, and the antenna switching timing can be detected by any one of the antennas by switching the antennas at predetermined intervals. For this reason, even if an antenna switching timing detection signal is being received by one of the antennas, the antenna switching timing detection signal can be detected by another antenna even if the detection becomes impossible due to an instantaneous drop in reception level. it can.

(Modification)
FIG. 15 shows a schematic configuration of still another modified example of the antenna switching reception system 10 of the first embodiment. This antenna switching reception system 10 is configured by adding an antenna switching timing detection on / off control unit (antenna switching timing detection on / off control unit) 18 to the antenna switching reception system 10 of FIG. The antenna switching timing detection on / off control unit 18 controls the antenna switching timing detection unit 13 so as not to detect the antenna switching timing detection signal for a predetermined period after detecting the antenna switching timing detection signal.

  FIG. 16 shows a signal received using the antenna A and the antenna B in the antenna switching reception system 10 of the present modification, and an operation of the antenna switching reception system 10 when receiving this signal. FIG. 17 is a flowchart showing the operation of the antenna switching receiving system 10 of the present modification. In this modification, # 19 is performed between the processes of # 2 and # 3 shown in FIG. 3, # 20 is performed between the processes of # 3 and # 4, and # 21 after the processes of # 10 and # 11. The process of # 22 is executed.

  In FIG. 17, when the antenna unit 11 receives a signal (# 2), when the signal output from the antenna switching timing detection on / off control unit 18 is on (YES in # 19), the process proceeds to # 3. When the antenna switching timing detection unit 13 detects the antenna switching timing (YES in # 3), the signal output from the antenna switching timing detection on / off control unit 18 is turned off (# 20). Thereby, as shown in FIG. 16, the antenna switching timing detection function is turned off. Thereafter, the processing from # 4 to # 10 or # 11 is executed in the same manner as in FIG. 3, and the payload signal is received by one of the antennas (YES in # 21), and then output from the antenna switching timing detection on / off control unit 18. After the signal to be turned on is turned on (# 22), the process returns to # 1. If the signal output from the antenna switching timing detection on / off control unit 18 is not on (NO in # 19), the process returns to # 1.

  According to the antenna switching reception system 10, after the antenna switching timing is detected, the antenna switching timing is not detected during a predetermined period including the reception time of the payload signal. As a result, it is possible to suppress erroneous detection of the antenna switching timing with respect to a payload signal or noise that becomes a random signal. Therefore, it is possible to prevent an error associated with switching the antenna during reception of the payload signal (because a physical switching time is required for switching the antenna and the payload cannot be received during that time). In addition, when only one of the antennas can be received, it is possible to prevent occurrence of a reception error due to unnecessary antenna switching. Furthermore, even in a system that is equipped with an equalizer or the like and needs to fix a multipath environment for transmission and reception during transmission and reception of payload signals, errors due to antenna switching during transmission and reception of payload signals can be suppressed. That is, it is possible to prevent the multipath environment from being suddenly changed during transmission / reception of the payload signal and the multipath cancellation function by the equalizer from operating normally. As a predetermined period during which the antenna switching timing is not detected, a period from when the reception of the payload signal of the current frame is completed to immediately before the reception of the antenna switching timing detection signal of the next frame may be set. In this case, erroneous detection of antenna switching timing with respect to noise after completion of reception of the payload signal of the current frame can also be suppressed.

  In this modification, even when noise is erroneously detected as the antenna switching timing detection signal, the detection function of the antenna switching timing detection signal is stopped for a predetermined period. Thus, after detecting the antenna switching timing detection signal, the antenna switching timing detection signal may not be detected for a predetermined period when a unique word signal transmitted thereafter is detected. In this case, for example, the unique word signal is transmitted following the antenna switching timing detection signal, the test 1 signal, and the test 2 signal (see paragraph (0023)). If a unique word can be detected after detecting the antenna switching timing detection signal, it can be determined that the previously detected antenna switching timing detection signal is correct. On the other hand, if the unique word signal cannot be detected, it can be determined that the previously detected antenna switching timing detection signal is incorrect, and the detection of the antenna switching timing detection signal is continued. According to this configuration, since the detection of the unique word signal is used in combination with the detection of the antenna switching timing detection signal, it is possible to reduce the possibility of misidentifying noise as the antenna switching timing detection signal.

(Modification)
FIG. 18 shows a schematic configuration of still another modified example of the antenna switching reception system 10 of the first embodiment. This antenna switching reception system 10 is configured by adding a non-detection time counter unit 20 to the antenna switching reception system 10 of FIG. The non-detection time counter unit 20 counts the time during which no antenna switching timing detection signal is detected. In this antenna switching reception system 10, when the non-detection time counter unit 20 counts a predetermined time during reception by any of the antennas, the antenna switching is performed.

  FIG. 19 shows a signal received using the antenna A and the antenna B in the antenna switching reception system 10 of this modification, and the operation of the antenna switching reception system 10 when receiving this signal. FIG. 20 is a flowchart showing the operation of the antenna switching reception system 10 of this modification. In this modified example, when NO in # 12 shown in FIG. 6, the processes of # 25 to # 28 are executed.

  In this modification, as shown in FIG. 20, when the antenna switching timing detection signal that should be received by the antenna A cannot be received over the frames 1 and 2 (NO in # 12), the following operation is performed. Do. That is, if the non-detection time counter unit 20 is not counting time (NO in # 25), the non-detection time counter unit 20 starts counting (# 26) and returns to # 1. If the non-detection time counter unit 20 is counting (YES in # 25) and the count value of the non-detection time counter unit 20 is not equal to or greater than the specified value (NO in # 27), the process returns to # 1. If the count value of the non-detection time counter unit 20 is equal to or greater than the specified value (YES in # 27), the count is stopped, and it is switched to another antenna B assuming that a predetermined time has elapsed (# 28). Here, the predetermined time means a time sufficient to detect the antenna switching timing signal at least once if the antenna and the communication environment are normal. For example, in FIG. 19, the specified value is set so as to be longer than the time required for the communication of frame 1 and frame 2.

  According to this antenna switching reception system 10, when a signal train of antenna switching timing detection signals is not obtained even if a signal is received for a predetermined period, switching to another antenna is performed. Therefore, one antenna does not continue to wait for the antenna switching timing detection signal. Therefore, even when one antenna is broken or temporarily malfunctioned, the antenna switching timing detection signal can be received by another antenna.

(Modification)
FIG. 21 shows a schematic configuration of still another modified example of the antenna switching reception system 10 of the first embodiment. This antenna switching reception system 10 is configured by adding a second correlation value calculation unit 22 and a second correlation value calculation unit 23 to the antenna switching reception system 10 of FIG. Further, a test signal composed of a signal sequence in a specific sequence different from the antenna switching timing detection signal is transmitted from the transmission system. The second correlation value calculation unit (storage unit) 22 stores a signal sequence (reference signal) in the same sequence as the transmitted test 1 signal. The second correlation value calculation unit 22 detects the test 1 signal based on the correlation value by calculating the correlation value between the stored signal sequence and the signal sequence of the received test 1 signal. Similarly, the second correlation value calculation unit (storage unit) 23 stores a signal sequence (reference signal) in the same sequence as the transmitted test 2 signal. The second correlation value calculation unit 23 detects the test 2 signal based on the correlation value by calculating the correlation value between the stored signal sequence and the signal sequence of the received test 2 signal. As a result, even if the antenna switching timing detection signal cannot be detected due to instantaneous reception level deterioration or instantaneous noise mixing, the frame can be detected by detecting the test 1 signal or the test 2 signal. The payload signal can be received.

  FIG. 22 shows a signal received using the antenna A and the antenna B in the antenna switching reception system 10 of the present modification, and an operation of the antenna switching reception system 10 when the signal is received. FIG. 23 is a flowchart showing the operation of the antenna switching receiving system 10 of this modification. In the present modification, the processes of # 31 to # 32 are executed when NO in # 12 shown in FIG. When YES at # 12, the process at # 33 is executed.

  The calculation of the correlation value by the second correlation value calculation unit 22 and the second correlation value calculation unit 23 is performed in parallel with the calculation of the correlation value by the correlation value calculation unit 15. As shown in FIG. 22, the test 1 signal and the test 2 signal are transmitted following the antenna switching timing detection signal. When the correlation value calculation unit 15 detects the antenna switching timing (YES in # 12), the function is stopped so that the second correlation value calculation units 22 and 23 do not detect the test 1 signal or the test 2 signal. (# 33). Thereafter, as in FIG. 6, the processing after # 4, that is, the antenna that receives the payload signal is determined by comparing the reception level detected by each antenna while switching the antenna. Thus, when the correlation value calculation unit 15 detects the antenna switching timing detection signal, the correlation detection by the second correlation value calculation unit 22 using the test 1 signal is not performed or is invalid even if performed. To do. In this case, after receiving the payload signal at # 10 or # 11, the second correlation value calculating units 22 and 23 are operated again in preparation for reception of the next frame.

  When the correlation value calculation unit 15 cannot detect the antenna switching timing (NO in # 12), if the test 1 signal is detected by the second correlation value calculation unit 22 (YES in # 31), the current antenna A A payload signal is received (# 10). Even if the test 1 signal is not detected by the second correlation value calculator 22 (NO in # 31), if the test 2 signal is detected by the second correlation value calculator 23 (YES in # 32), the current The payload signal is received by the antenna A (# 10). When the second correlation value calculation unit 23 does not detect the test 2 signal within a predetermined time (NO in # 32), the process returns to # 1. As described above, when the second correlation value calculation unit 22 detects the test 1 signal, the antenna switching operation is not executed, and another process can be performed during the time during which the test 2 signal is transmitted. For example, when the payload signal is not binary and the reception level needs to be adjusted, it can be assigned to the gain adjustment time of automatic gain control. When the second correlation value calculation unit 23 detects the test 2 signal, the antenna switching operation is not executed, and the payload signal is received with the current automatic gain control value.

  According to the antenna switching reception system 10, when the antenna switching timing detection signal cannot be detected, the second correlation value calculation unit 22 or the second correlation value calculation unit 23 detects the test 1 signal or the test 2 signal. Therefore, it is possible to detect the head of the payload signal in two or three stages. As a result, even when noise or a momentary drop in level occurs during reception of the antenna switching timing detection signal, the head of the payload signal can be detected by the test 1 signal or the test 2 signal. The probability of losing the payload signal can be reduced. Note that the second correlation value calculation unit for detecting the test signal can be further added according to the number of test signals to be transmitted (that is, the number of antennas).

  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 receiving system which combined the characteristic of each embodiment mentioned above suitably may be sufficient.

DESCRIPTION OF SYMBOLS 10 Antenna switching reception system 11 Antenna part 12 Antenna switching part 13 Antenna switching timing detection part 14 Antenna switching judgment part 15 Correlation value calculation part 16 Counter part 17 Antenna regular switching control part 18 Antenna switching timing detection ON / OFF control part 20 Non-detection Time counter unit 22 Second correlation value calculation unit 23 Second correlation value calculation unit

Claims (11)

  In an antenna switching reception system that switches a plurality of antennas and receives a radio signal, before receiving the payload signal, the antenna receives the test signal by each antenna, selects the antenna that receives the payload signal, and receives the test signal. The antenna switching receiving system, wherein the antenna to be switched is switched based on an antenna switching timing detection signal detected before the test signal. The antenna switching timing detection signal is configured and transmitted by a specific sequence of signal trains,
A storage unit for storing a signal sequence in the same sequence as the antenna switching timing detection signal to be transmitted;
A correlation value calculation unit that calculates a correlation value between the signal sequence stored in the storage unit and the signal sequence of the received antenna switching timing detection signal;
The antenna switching reception system according to claim 1, wherein the antenna switching timing detection signal is detected based on the correlation value calculated by the correlation value calculation unit.   The antenna switching reception system according to claim 1 or 2, wherein the antenna switching timing detection signal transmitted at a lower transmission rate than the payload signal is detected.   The antenna switching reception system according to any one of claims 1 to 3, wherein the antenna switching timing detection signal can be demodulated even in a saturated state without depending on a reception level.   A counter unit that counts time from a specific antenna switching reference timing to a next antenna switching reference timing is provided, and the antenna switching reference timing is detected based on a count value of the counter unit. Item 5. The antenna switching reception system according to any one of items 4 to 4. The antenna switching timing detection signal is transmitted a plurality of times within one frame,
6. The antenna periodic switching control unit for switching an antenna every predetermined period having a period equal to or longer than a length of the antenna switching timing detection signal. The described antenna switching reception system.   The antenna switching reception system according to any one of claims 1 to 6, wherein the antenna switching timing detection signal is not detected for a predetermined period after the detection of the antenna switching timing detection signal. .   8. The detection of the antenna switching timing detection signal is not performed for a predetermined period after the detection of the antenna switching timing detection signal and further detection of the unique word signal. The antenna switching receiving system according to one item.   A non-detection time counter unit that counts a time during which the antenna switching timing detection signal is not detected, and when the non-detection time counter unit counts a predetermined time during reception by any antenna, another antenna The antenna switching reception system according to any one of claims 1 to 8, wherein the antenna switching reception system is switched to. The test signal is composed of a specific sequence of signal sequences and is transmitted,
The storage unit further stores a signal sequence in the same sequence as the transmitted test signal,
A second correlation value calculating unit that calculates a correlation value between the signal sequence of the test signal stored in the storage unit and the signal sequence of the received test signal;
The said 2nd correlation value calculation part receives a payload signal, without performing antenna switching, when the said test signal is detected based on the calculated correlation value, Any one of Claim 1 thru | or 9 characterized by the above-mentioned. The antenna switching receiving system according to claim 1.   The antenna switching reception system according to claim 10, further comprising a plurality of the second correlation value calculation units corresponding to the number of the test signals.

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