JP6017946B2 - Time division multiplex array antenna device - Google Patents

Description

  The present invention relates to a time division multiplex array antenna apparatus that performs communication by time division multiplexing using a plurality of antennas arranged in an array.

  In recent years, wireless devices using adaptive array antennas such as wireless local area networks (LANs), mobile phones, and mobile receivers for digital terrestrial broadcasting tend to be used daily. As a result, the low cost of these wireless devices The need for computerization is increasing. However, an adaptive array antenna, in principle, requires analog circuits such as filters, amplifiers, down converters, A / D converters, etc., as many as the number of antennas. For example, the cost is higher than that of a single-antenna wireless device. There was a problem.

  In order to solve this problem, an adaptive array antenna (C-TDM-AAA: Conventional Time-Division Multiplexing Adaptive Array Antenna) has been proposed in the past, for example, by using time-division multiplexing using switches. (See Non-Patent Document 1). In Non-Patent Document 1, the bandwidth used by the wireless device, the switch switching speed, the filter bandwidth, and the conditions to be satisfied by the sampling speed are examined in detail. When switching and sampling are performed at appropriate timing, each antenna is It is shown that the received signal can be completely reproduced.

A CMA Adaptive Array Antenna System with a Single Receiver Using Time-Division Multiplexing, (IEICE Trans. Commun., Vol. E84-B, no. 6, pp. 1637-1646, June 2001.)

  By the way, in this type of time-division multiplex array antenna apparatus, there is a current situation in which the SNR (signal-noise ratio) is reduced to 1 / number of antennas. Therefore, there was a need for technology development to improve the SNR of the time division multiplex array antenna apparatus.

  An object of the present invention is to provide a time division multiple array antenna apparatus capable of improving the SNR.

The time-division multiplex array antenna apparatus that solves the above-described problem is capable of selectively connecting a specific one of a plurality of antennas to an internal signal processing circuit by a switch circuit having a plurality of switches. When a specific one of the antennas is operated as a single antenna in a configuration in which the antenna can be communicated as a time-division multiplex array antenna by selectively connecting to the signal processing circuit in order by the switch A digital filter capable of band-limiting a digital signal of a received radio wave, a reception state determination unit that determines a reception state of a radio wave at the array antenna during communication with the time division multiplex array antenna, and the single When it is preferable to receive radio waves with an antenna, only one specific switch of the plurality of switches is always used. While connecting, the path of the received signal, the by switching a path through the digital filter, and a reception path switching unit for operating the particular one of said antennas as said single antenna, the reception state determination The unit performs monitoring of the reception state of the radio wave at the time of monitoring for monitoring whether or not the radio wave is received, and the reception path switching unit is an antenna having the maximum reception power among the array antennas. The antenna is operated as the single antenna by turning on the switch .

According to this configuration, the reception state of radio waves is monitored, and when it is preferable to receive radio waves with a single antenna, the reception path is switched to the digital filter side while only one specific antenna is always connected. As a result, in A / D conversion, the received signal is digitally processed by band limitation using a digital filter instead of rearranging the signals. For this reason, in a situation where it is preferable to receive radio waves with a single antenna, the time-division multiplex array antenna apparatus can be operated as a single antenna, so that the SNR can be improved accordingly.
In addition, if the reception status of radio waves is monitored during monitoring and it is determined that it is preferable to operate with a time-division multiplex array antenna when detecting radio waves during monitoring, radio reception is performed with a time-division multiplex array and operation is performed with a single antenna. If it is determined that this is preferable, radio waves are received using a single antenna. Therefore, it is possible to smoothly perform the radio wave reception state determination → antenna switching in the process of radio wave reception.

  In the time-division multiplex array antenna apparatus, the reception state is preferably a strength of received power when a radio wave is received by the antenna. According to this configuration, since the reception state of the radio wave is determined based on the strength of the received power, it is possible to accurately identify in what state the antenna is receiving the radio wave.

  In the time division multiplex array antenna apparatus, the reception state determination unit determines a ratio of received power between the antennas during communication with the time division multiplex array antenna, and the reception path switching unit receives the received power. When the ratio is equal to or greater than a threshold value, it is preferable to change the antenna from the time division multiplex array antenna to the single antenna by switching the reception path. According to this configuration, it is determined whether it is better to operate with a time division multiplex array antenna or a single antenna based on the received power ratio between the antennas when receiving radio waves with the time division multiplex array antenna. It is possible to accurately determine which antenna should be operated.

  According to the present invention, it is possible to improve SNR in a time division multiplex array antenna apparatus.

The block diagram of the time division multiplex array antenna apparatus of one Embodiment. The time waveform figure of a switch control signal. The rth time waveform figure of a switch control signal. The amplitude spectrum figure of the output signal after passing a 2nd band pass filter. The time waveform figure of a sampling signal. The frequency spectrum figure when communicating by time division multiplexing. The frequency spectrum figure when communicating with a single antenna. The circuit diagram when the reception path is switched to the digital filter side. Explanatory drawing which shows the function of a digital filter.

Hereinafter, an embodiment of a time division multiplex array antenna apparatus will be described with reference to FIGS.
As shown in FIG. 1, the array antenna device 1 includes a plurality of antennas (antenna elements) 2, and the directivity can be electrically switched by adaptively controlling the weight of each antenna 2 according to the propagation environment. It has become. As described above, the array antenna device 1 can remove the beam by directing the beam in the direction of arrival of the desired wave or directing the null in the direction of arrival of the unnecessary radio wave. The array antenna apparatus 1 of this example is also a time division multiplex type in which signals are divided in time units and radio waves are received by one processing circuit.

  In the time-division multiplex array antenna apparatus 1, if the number of antennas 2 is K (K is an arbitrary odd number), the received signal of the k-th antenna 2 is expressed by the following equation (1).

Here, f _k (t) is a baseband signal in the k-th antenna 2. Further, cos (ω _c t) represents a carrier wave, and ω _c represents an angular frequency of the carrier wave.

The receiving circuit 3 of the array antenna apparatus 1 is provided with an analog circuit 4 that performs analog processing on the radio waves received by the antenna 2 and a digital circuit 5 that digitally processes a signal output from the analog circuit 4. The analog circuit 4 is provided with a first bandpass filter 6 having a passband width W for each antenna 2. The first band-pass filter 6, to filter the received signal f _k received by the antenna _{2 (t) cos (ω c} t) in the pass band width W, passing only a frequency that conforms to W. In the time-division multiplex array antenna apparatus 1 of this example, only the first band pass filter 6 is required for each antenna 2, and the subsequent circuit block is shared among the plurality of antennas 2. . The receiving circuit 3 is an example of a signal processing circuit.

The frequency bandwidth W ″ of the received baseband signal f _k (t) is smaller than the pass bandwidth W of the first bandpass filter 6. Therefore, the received signal f _k (t) cos (ω _c t) It passes through the 1 band pass filter 6 as it is.

A plurality of these first band pass filters 6 are connected to a switch circuit 7 that selectively switches the connection of the first band pass filters 6. The switch circuit 7 is one component of the reception circuit 3 and includes a plurality of switches 8 for each first bandpass filter 6. These switches 8 are switch-controlled by a switch control signal g _k (t) input from the clock circuit 9.

Here, as shown in FIGS. 2 and 3, _assuming that the k-th switch 8 is switched with a rectangular-wave-like ON time τ and period T _s , the switch control signal g _k (t) is expressed by the following equation ( It is represented by 2). In the following formula, r is an arbitrary integer.

Here, if the switch switching frequency is W ′ (W ′ = 1 / T _s ), the switch switching frequency W ′ needs to be set appropriately so as to satisfy W ′> W. Expression (2) can be expressed as the following expressions (3) to (5) by the form of Fourier series expansion. In the following equation, n is an integer representing the n-th harmonic component of the switch switching frequency W ′, and Ψ is the ON time ratio of the switch 8.

The reception signal f _k (t) cos (ω _c t) of each antenna 2 is multiplied by the switch control signal g _k (t) when passing through the switch 8 and then the signals from the K antennas 2 are combined. . This synthesized signal h (t) is expressed as the following equation (6).

The analog circuit 4 is provided with a second bandpass filter 10 having a frequency bandwidth of KW ′. Only one second bandpass filter 10 is provided and shared by a plurality of antennas 2 (switches 8). In the case of this example, the second band pass filter 10 is a filter having an ideal frequency characteristic B (ω) as shown in FIG.

  The synthesized signal h (t) passes through the second bandpass filter 10 and is output as an output signal h ′ (t). The output signal h ′ (t) is expressed by the following equations (7) and (8).

The analog circuit 4 includes an amplifier 11 that amplifies the output signal h ′ (t), a converter 12 that down-converts the amplified output signal h ′ (t) to an IF (Intermediate Frequency) frequency, and a signal at the IF frequency. An IF bandpass filter 13 that passes the signal and an orthogonal converter unit 14 that orthogonally downconverts the IF frequency are provided. The quadrature converter unit 14 is connected to a pair of low-pass filters 15 that allow only low frequencies to pass through signals output from the quadrature converter unit 14 whose phases are shifted from each other by 90 degrees.

  The digital circuit 5 is provided with a pair of A / D converters 16 for A / D converting the signal output from the low-pass filter 15. The baseband signal h ″ (t) input by the A / D converter 16 is expressed by the following equation (9) if the amplifier amplification and the filter loss are ignored.

The baseband signal h ″ (t) is sampled at a period T _s in the A / D converter 16. This sampling signal z _i (t) is expressed as the following equation (10).

As shown in FIG. 5, the sampling signal z _i (t) is a signal whose timing is shifted by T _s / K. Actually, the A / D converter 16 performs sampling at z (t) expressed by the following equation (11).

Now, the sample signal x _i (t) generated by sampling the baseband signal h ″ (t) with the sampling signal z _i (t) in the rearrangement unit 17 is expressed by the following equations (12), (13). It is expressed as

The sample signal x _i (t) is obtained in a form in which the reception baseband signals f _k (t) of the antennas 2 are mixed, as can be seen from the equation (13). Here, at first glance, if the ON time τ of the switch 8 is τ <(T _s / K), the two switches 8 are not connected at the same time, and the reception baseband signal f _k (t) is mixed. Although it seems that it does not occur, in reality, mixing of the received baseband signal f _k (t) occurs due to waveform rounding when passing through the filter. In a normal adaptive array antenna, the received baseband signal f _k (t) should be a signal obtained separately.

Accordingly, the digital circuit 5 of this example is provided with a plurality of arithmetic processing units 18 corresponding to each antenna 2 for separating and extracting the received baseband signal f _k (t) from the sample signal x _i (t). ing. The arithmetic processing unit 18 of this example performs an arithmetic operation using the following equations (14) to (16), that is, multiplies a vector X (t) having x _i (t) as an element by a matrix Φ. Thus, an I transmission signal and a Q phase signal are output for each antenna 2.

Expressions (14) to (16) are defined by the following expressions (17) to (26). X _i (ω) is a Fourier transform of x _i (t), and f _k (Δt) is a signal _obtained by sampling the reception baseband signal f _k (t) of each antenna 2 with a period T _s. . Expression (18) is an expression expressing Expression (17) in a matrix format.

The time division multiplex array antenna apparatus 1 is provided with an adaptive processor 19 that adaptively processes the I-phase signal and the Q-phase signal input from the arithmetic processing unit 18. The adaptive processor 19 estimates, for example, the arrival direction of the received radio wave, directs the beam of the antenna 2 in the direction of the desired wave, or directs the null in the target direction by adaptive processing.

Here, how the baseband signal f _k (Δt) included in the sample signal x _i (t) sampled by the A / D converter 16 is determined by τ which is the pulse width of the switch control signal g _k (t). Think about changes. Consider a case where the ON time τ of the switch 8 is very short, that is, τ≈0. At this time, since Ψ = τ / T _s ≈0, a matrix S≈1 is derived from sinc {nπΨ} ≈1. Therefore, Expression (23) is expressed as the following Expression (27).

Therefore, when τ is very small, a vector X (t) that is a sample signal, that is, a vector having the sample signal x _i (t) as an element is equal to the received baseband signal f _k (t) of each antenna 2. It is a scalar multiple of the vector F (Δt). That is, it can be seen that each sample signal x _i (t) includes only one type of received baseband signal f _k (Δt), and is not in a mixed state. In Non-Patent Document 1 described in the background art, the switch control signal g _k (t) is a delta function, which corresponds to the case of τ≈0 in this study. That is, in Non-Patent Document 1 of the background art, it is considered that τ≈0 is intentionally set so that the vector F (Δt) is not mixed in the sample signal vector X (t).

However, looking at equation (27), it can be seen that the magnitude of the vector F (Δt) included in the vector X (t) is proportional to τ. From this, it is predicted that in order to suppress the power loss in the switch 8, it is desirable to increase τ as much as possible, that is, the switch 8 is always connected to any one of the antennas 2. For this reason, the adaptive processor 19 of this example sets the ON time τ of the switch control signal g _k (t) as long as possible within a range not overlapping with τ of the next signal. Thus, this example is considered effective in that the ON time τ (or the ON time ratio Ψ) can be set arbitrarily.

  FIG. 6 shows a frequency spectrum of a radio wave received by time division multiplexing. As shown in the figure, the frequency band width of the second bandpass filter 10 is set to KW ′ in the time division multiplexing method, for example, if the number of antennas K = 3, the desired wave 20 to be received is This is because the signal is received as a signal having three spectrums 21a to 21c. In this case, the spectra 21b and 21c appearing symmetrically on both sides with respect to the spectrum 21a at the center fundamental frequency are copies of the spectrum 21a. In the frequency bandwidth KW ', a signal passing through a band other than the desired wave is thermal noise.

  By the way, as shown in FIG. 7, depending on the received radio waves, SNR (S / S / S / R) is more likely to be received with a single antenna that receives radio waves with only one antenna 2 than with a time division multiplex array antenna. N ratio) may be good. As shown in the figure, if the SNR is good, radio waves can be acquired with a spectrum 22 having a high amplitude. Therefore, in this example, the received power at each antenna 2 is monitored, and when the ratio of received power is large, the time division multiplex array antenna apparatus 1 is operated as a single antenna instead of the time division multiplex array antenna. And

  As shown in FIG. 1, a digital filter 25 is connected to the pair of A / D converters 16 via a pair of switches 23 and 24. The digital filter 25 can band-limit the digital signal after passing through the A / D converter 16 in the received radio wave, and allows only a digital signal in a specific frequency band to pass.

  The digital circuit 5 includes a power ratio determination unit 26 that determines the ratio of reception power in each antenna 2 and a reception path switching unit 27 that switches the reception path of the reception circuit 3 based on the determination result of the power ratio determination unit 26. Is provided. The power ratio determination unit 26 measures the received power of the received radio wave at each antenna 2 and calculates, for example, the ratio between the maximum value and the minimum value. Then, the power ratio determination unit 26 compares the received power ratio with a threshold value and monitors the magnitude of the received power ratio. The reception path switching unit 27 selects a reception path in the reception circuit 3 based on the determination result of the reception power ratio. The power ratio determination unit 26 is an example of a reception state determination unit.

Next, the operation of the time division multiplex array antenna apparatus 1 will be described with reference to FIGS.
As shown in FIG. 1, the time division multiplex array antenna apparatus 1 performs a monitoring operation (reception standby operation) for monitoring whether or not a radio wave is received when waiting for radio wave reception. At this time, the radio wave reception path in the receiving circuit 3 is selected as the path 28 passing through the rearrangement unit 17 by connecting the switches 23 and 24 to the rearrangement unit 17 side. During monitoring, the presence or absence of radio wave reception is monitored by time division multiplexing in which the switches 8 are selectively connected in order.

  As illustrated in FIG. 8, when the power ratio determination unit 26 receives a radio wave during monitoring and starts receiving a radio wave, the power ratio determination unit 26 confirms that the reception power ratio is large and the reception power ratio is greater than or equal to a threshold value with a specific antenna 2. The route switching request Sa is output to the receiving route switching unit 27. The route switching request Sa includes a request for switching the reception route, information for notifying which antenna 2 has the maximum reception power, and the like.

  When the path switching request Sa is input from the power ratio determination unit 26, the reception path switching unit 27 switches the switch circuit 7 and the switches 23 and 24 based on the path switching request Sa. At this time, the reception path switching unit 27 turns on the switch 8 having the maximum received power among the plurality of switches 8 of the switch circuit 7 and connects the switches 23 and 24 to the digital filter 25 side. As a result, the array antenna apparatus 1 operates as a single antenna instead of a time division multiple array antenna by switching the reception path to the path 29 passing through the digital filter 25. Therefore, the time division multiplex array antenna apparatus 1 receives radio waves with only one antenna 2 having the maximum received power.

  FIG. 9 shows the frequency spectrum of the received radio wave when the proposed method of this example is adopted. As shown in the figure, even when the antenna 2 is switched from the time division multiplex array antenna to the single antenna, the thermal noise assumed to be included in the received radio wave at this time is removed by the digital filter 25. Therefore, even when switching to a single antenna, it is possible to receive radio waves while suppressing thermal noise.

  As shown in FIG. 1, the adaptive processor 19 outputs a reception end notification Sb to the reception path switching unit 27 when it is confirmed that the communication ends (no longer receiving radio waves). When receiving the reception end notification Sb from the adaptive processor 19, the reception path switching unit 27 releases the state in which only the switch 8 of the antenna 2 having the maximum reception power is always connected, and switches the switches 23 and 24 to the rearrangement unit 17. Connect to the side. Thereby, the array antenna apparatus 1 is returned to the time division multiplexing array by switching the reception path to the path 28 passing through the rearrangement unit 17 side.

  This switching operation is repeated each time the received power increases at the specific antenna 2 to receive radio waves. That is, when the reception power ratio of each antenna 2 is less than the threshold during radio wave reception during monitoring, the subsequent reception operation is performed with the time division multiplex array antenna, and the reception power ratio of each antenna 2 is equal to or greater than the threshold. The operation in which the subsequent reception operation is performed with a single antenna is repeatedly executed every time radio waves are received.

According to the configuration of the present embodiment, the following effects can be obtained.
(1) The reception path switching unit 27 operates the antenna 2 as a time division multiplex array antenna by connecting the switches 23 and 24 to the rearrangement unit 17 side during reception monitoring. When the reception path switching unit 27 detects radio wave reception in monitoring, if the reception power ratio between the antennas 2 is equal to or greater than the threshold, only the switch 8 of the antenna 2 having the maximum reception power is always connected, and the switch 23 , 24 are connected to the digital filter 25 side, so that the path of the receiving circuit 3 is switched to the path 29 passing through the digital filter 25. For this reason, in a situation where it is preferable to perform a reception operation with a single antenna, the time division multiplex array antenna apparatus 1 can be operated as a single antenna, so that the SNR can be improved accordingly.

(2) Since the component to be added is the digital filter 25, the circuit configuration of the time division multiplex array antenna apparatus 1 can be simplified even if measures for improving the SNR are taken.
(3) The reception power ratio of each antenna 2 is monitored during monitoring. If the reception power ratio is less than the threshold value during radio wave detection during monitoring, the subsequent radio wave reception is performed as it is with the time-division multiplex array antenna. If the ratio is equal to or greater than the threshold, the subsequent radio wave reception is performed by switching to a single antenna. Therefore, the radio wave reception state determination → antenna switching can be performed smoothly during the radio wave reception process.

(4) Since the determination of the reception state is performed based on the strength of the reception power (reception power ratio), it is possible to accurately identify in what state the antenna 2 is currently receiving radio waves.
(5) Since the reception status of radio waves is determined based on the ratio of received power, what is the current reception status, that is, whether time-division multiplex array antennas or single antennas are used when receiving radio waves It is possible to accurately determine whether it should be.

Note that the embodiment is not limited to the configuration described so far, and may be modified as follows.
The power supply of the digital circuit 5 may be turned off during reception radio wave monitoring, and the power supply of the digital circuit 5 may be switched on when radio wave reception is detected. In this case, the effect of suppressing power consumption in the time division multiplex array antenna apparatus 1 is enhanced.

The reception path may be returned to the original path 28 on the rearrangement unit 17 when it is confirmed that the reception power ratio is less than the threshold.
The receiving circuit 3 is not limited to the configuration in which the baseband signal is sampled by the A / D converter 16. For example, the configuration in which the IF signal is sampled or the RF (Radio Frequency) signal output from the second bandpass filter 10 is sampled. The structure to do may be sufficient. Thus, the receiving circuit 3 can employ various circuit configurations.

The receiving circuit 3 may be a circuit that downconverts a signal by a normal converter instead of the orthogonal converter unit 14.
The number of antennas 2 is not limited to an arbitrary odd number, and may be an arbitrary even number.

The ON time τ (ON time ratio Ψ) of the switch 8 may be appropriately changed to a time width other than the value described in the embodiment.
Sample signal x received signal from the _{i (t) f k (t} ) cos (ω c t) play (separation) computing is not limited to the method of multiplying the matrix Φ to the sample signal x _i (t). In short, if the received signal f _k (t) cos (ω _c t) can be reproduced (separated) from the sample signal x _i (t), it can be changed to various calculation methods.

The frequency bandwidth of the second bandpass filter 10 may be a value obtained by multiplying the frequency band of the first bandpass filter 6 by a coefficient K, for example.
The time division multiplex array antenna apparatus 1 is not limited to a receiver, and may be a transmitter or a transceiver.

The determination of switching of the reception path is not limited to the power ratio of the received radio wave, and may be performed using another index such as an amplitude ratio or amplitude difference of the received radio wave.
The determination of whether or not radio waves are received is not limited to the reception signal strength (reception power ratio), and various methods can be adopted as long as it can be determined whether radio waves can be received.

  ・ Changes in the reception path are not limited to the case of monitoring / radio wave reception. For example, the reception path may be switched appropriately while reading the received radio wave.

The single antenna 2 connected during single antenna operation is not limited to the antenna having the maximum received power, but may be an antenna suitable for other communications.
The time division multiplex array antenna apparatus 1 is not limited to being used as a receiver for a vehicle or an electronic key, but can be appropriately applied to other devices and apparatuses.

Next, technical ideas that can be grasped from the above-described embodiment and other examples will be described below together with their effects.
(A) In the time-division multiplex array antenna, the power loss due to switching of the switch is suppressed by increasing the ON time of the switch, and even if reception signals of each antenna are mixed by this processing, Separating the superimposed signal into received signals of each antenna by performing an operation on the superimposed signal. According to this configuration, since the received signal of each antenna can be separated from the superimposed signal, the signal can be acquired with high accuracy.

  DESCRIPTION OF SYMBOLS 1 ... Time division multiplexing array antenna apparatus, 2 ... Antenna, 3 ... Reception circuit as a signal processing circuit, 7 ... Switch circuit, 8 ... Switch, 25 ... Digital filter, 26 ... Power ratio determination part as a reception state determination part, 27: Reception path switching unit, 28, 29: Reception path.

Claims (3)

A specific one of a plurality of antennas can be selectively connected to an internal signal processing circuit by a switch circuit having a plurality of switches, and the plurality of antennas are selectively connected to the signal processing circuit by the switches in order. By doing so, in the time division multiplex array antenna device capable of communicating the antenna as a time division multiplex array antenna,
When make operating the particular one of said antennas as a single antenna, and a digital filter capable of band-limited radio digital signal received,
A reception state determination unit that determines the reception state of radio waves in the array antenna during communication with the time division multiplex array antenna;
When it is preferable to receive the radio wave with the single antenna, by switching the path of the received signal to the path through the digital filter while always connecting only one specific one of the plurality of switches. A reception path switching unit that operates a specific one of the antennas as the single antenna ,
The reception state determination unit performs monitoring of the reception state of the radio wave at the time of monitoring to monitor whether or not the radio wave is received,
The reception path switching unit is configured to operate the antenna as the single antenna by turning on the switch of the antenna having the maximum reception power among the array antennas. apparatus. 2. The time division multiplex array antenna apparatus according to claim 1, wherein the reception state is a strength of received power when radio waves are received by the antenna. The reception state determination unit determines a ratio of received power between the antennas during communication with the time division multiplex array antenna, and the reception path switching unit, when the received power ratio is equal to or greater than a threshold, 3. The time division multiplex array antenna apparatus according to claim 2 , wherein the antenna is changed from the time division multiplex array antenna to the single antenna by switching a reception path.