KR100836421B1 - Listen before talk system using intermediate frequency - Google Patents

Abstract

An LBT(Listen Before Talk) system using an IF(Intermediate Frequency) is provided to select a signal channel without an interference signal to perform communication to thus stably restore/process a reception signal. The first switch unit(105) switches a plurality of reception antennas(101a-101d). The first and second mixer units(125,160) convert a reception signal into an IF signal. A signal detecting unit(140) detects a power level of the IF signal of the first mixer unit. A comparing unit(145) compares the detected level with one of a plurality of reference voltages, and generate comparison information. A controller(170) determines whether there is an interference signal in the reception signal, controls the first switch unit according to the determination result, selects the reference voltage as a comparison target, and transfers it to the comparing unit. The second switch unit(110) switches the reception signal transferred from the first switch unit to the first or second mixer unit. A demodulating unit(165) including an ADC(Analog to Digital Converter) demodulates a baseband I signal and a baseband Q signal to a digital signal which has plural polarities, and a modulating unit(175) modulates a digital transmission signal to a transmission signal, which is an analog signal, by synthesizing the digital transmission signal transmitted from the demodulating unit with an oscillation frequency signal.

Description

List Before Talk system using Intermediate Frequency}

1 is a block diagram schematically illustrating the components of an LBT system using an IF according to an embodiment of the present invention.

2 is a graph illustrating a form in which a detection level of a received signal is adjusted in an LBT system using an IF according to an embodiment of the present invention.

Figure 3 is a graph measuring the signal received in the LBT system using an IF according to an embodiment of the present invention.

Figure 4 is a graph measuring the signal received by the LBT system for each frequency band using the IF according to an embodiment of the present invention.

5 is a diagram illustrating an exemplary switching time of an LBT system using an IF according to an embodiment of the present invention.

<Explanation of symbols for main parts of drawing>

100: LBT system 101a to 101d: receiving antenna

101e: transmission antenna 105: first switch section

110: second switch unit 115: phase synchronization circuit portion

120: third switch section 125: first mixer section

140: signal detector 145: comparator

150: LNA 160: second mixer

165: demodulation unit 170: control unit

175: modulator 180: PAM

The present invention relates to a List Before Talk (LBT) system using IF (Intermediate Frequency).

Currently, ubiquitous network technology has attracted the attention of many people, ubiquitous network technology means a technology that allows to naturally connect to various networks regardless of time and place.

An example of such ubiquitous network technology is RFID technology, and among them, RFID technology introduced in commerce is representative.

In general, a commercial RFID system consists of a tag attached to a product and a tag with detailed information embedded therein, and a reader that reads information of the tag using RF communication, and the tag attached to the product passes through the region where the reader is located and transmits the information. It provides the basis for efficient logistics / distribution management such as distribution, assembly, price change and sales of goods.

On the other hand, the conventional RFID transmission and reception system is generally implemented through the envelope detection using ASK (Amplitude Shift Keying) modulation method, according to the conventional design method has a disadvantage that the data recognition rate is formed because the bit error rate is lowered.

In particular, in the case of the RFID reader, the radio wave environment is severely changed due to the tag moving at a high speed, and a change in the reception signal is greatly generated according to the external environment change (for example, the tag signal generated when the tag is moved). Phase shift, etc.), in particular frequency interference between RFID readers, has a significant effect on the recognition rate of RFID tags.

For example, when a large number of tags exist in an area where a plurality of RFID readers are installed, tag signals using the same frequency band may be simultaneously received by the RFID readers. In this case, interference between tag signals may occur and the RFID reader may There is a problem that the signal cannot be processed and the data recognition rate is further lowered.

In addition, when the transmission signal of another RFID reader or its own transmission signal is transmitted to the receiving end of the RFID reader, the transmission signal may act as an interference signal, which may make processing of the tag (reception) signal more difficult.

In addition, when the tag is moved, since the supply position of the energy is also changed, this becomes a factor to lower the recognition rate, and there is a problem that the reception sensitivity and the recognition distance are also reduced.

RFID frequencies range from low frequency (LF) such as 125 KHz and 135 KHz, high frequency (HF) such as 13.56 MHz, ultra high frequency (UHF) in the 433 MHz and 900 MHz bands, and microwave in the 2.45 GHz band. The frequency of the 900 MHz band is expected to be widely used due to the advantages of being able to make it small, small, long recognition distance, and distinguishing multiple tags.

However, since the frequency of the 900 MHz band has a narrow overall frequency bandwidth and a small number of carriers, the influence of an external interference signal including a transmission signal or interference between the tag signals can be recognized as a more serious problem.

The present invention provides an LBT system using an IF capable of processing a received signal stably by selecting a frequency channel free from interference, and minimizing interference between systems using the same frequency band.

The present invention provides an LBT system using an IF capable of installing / operating a plurality of systems in a limited area by controlling a plurality of antennas through an LBT function and minimizing interference between systems.

The present invention provides an LBT system using an IF capable of accurately determining whether an interference signal exists on a received signal regardless of various signal standards or reception environments.

Listed Before Talk (LBT) system using IF (Intermediate Frequency) according to the present invention comprises a plurality of receiving antennas; A first switch unit for switching the plurality of receive antennas; A first mixer converting the received signal into an intermediate frequency signal; A signal detecting unit detecting a power level of the intermediate frequency signal; A comparator for applying one of a plurality of reference voltages to compare with the sensed power level and generate comparison information; And a control unit which determines whether an interference signal is present in the received signal based on the comparison information, controls the first switch unit according to a determination result, selects a reference voltage as a comparison target, and transmits the reference voltage to the comparison unit.

Hereinafter, the LBT system using the IF according to the present invention will be described in detail with reference to the accompanying drawings. In the embodiment of the present invention, the LBT system using the IF uses a carrier signal in the UHF band as an RFID transmission / reception system.

1 is a block diagram schematically illustrating components of an LBT system 100 using an IF according to an embodiment of the present invention.

1, the LBT system 100 using the IF according to an embodiment of the present invention includes a plurality of receive antennas 101a, 101b, 101c, 101d, a transmit antenna 101e, a first switch unit 105, 2 switch unit 110, the third switch unit 120, the phase synchronization circuit unit 115, the first mixer unit 125, PA (Power Amplifier) 130, the first filter 135, the signal detection unit ( 140, a comparator 145, a low noise amplifier (LNA) 150, a second filter 155, a second mixer 160, a demodulator 165, a controller 170, a modulator 175, A PAM 180 and a third filter 185 are included.

The receiving antennas 101a to 101d are connected to the first switch unit 105 as a plurality.

The first switch unit 105 may be formed of a semiconductor chip such as a single pole throw (SPnT) device, for example, and sequentially switches signals received from the plurality of reception antennas 101a to 101d to switch the second switch unit. Forward to 110.

The second switch unit 110 transmits the received signal transmitted from the first switch unit 105 to the LNA 150 to be processed by the LBT method or to the first mixer unit 125 to transmit the signal power level. By detecting this, the controller 170 can determine whether the interference signal is mixed on the received signal.

Accordingly, the second switch unit 110 may be regarded as a kind of LBT switch, and the first mixer unit 125, the PA 130, the first filter 135, the signal detector 140, and the comparator 145. Can be classified into components for LBT operation.

The phase synchronization circuit 115 generates an oscillation frequency signal in the 900 MHz band, and the third switch unit 120 branches the oscillation frequency signal into two signal paths, with one signal path being the first mixer section 125. The other signal path is connected to the second mixer 155 and the modulator 175.

The second switch unit 110 and the third switch unit 120 may be provided as a switching element such as a single pole double throw (SPDT).

The first mixer 125 may include a mixer, a diode, and the like, and converts the received signal and the oscillation frequency signal transmitted through the second switch unit 110 into an intermediate frequency signal. The PA 130 amplifies the intermediate frequency signal according to the standard (detection level standard) of the signal detection unit 140.

The first filter 135 removes the noise component generated on the intermediate frequency signal in the amplification process and transmits the noise component to the signal detector 140.

The signal detecting unit 140 may be provided as, for example, a log amplifier, and converts the intermediate frequency signal in an analog state into a state capable of detecting a power level by outputting it as a DC voltage signal. ) It extends the signal sensitivity range of the power level that can be received by outputting it as a DC voltage signal proportional to the decibel value.

The generated power level signal may be immediately used by the control unit 170 to determine the presence or absence of the interference signal, but the received signal may be differentiated in signal characteristics according to the state of the receiving environment, the type of RFID radio standard, or the assigned frequency by country. Therefore, an error may occur when the power level signal is interpreted as it is.

2 is a graph illustrating a form in which a detection level of a received signal is adjusted in an LBT system 100 using an IF according to an embodiment of the present invention.

Referring to FIG. 2, the measurement line "l2" measures a power level signal transmitted from the signal detection unit 140, and the display line "l3" is a reference voltage. If greater than the reference voltage l3, the controller 170 may determine that an interference signal exists.

The display line " l1 " serves as a reference for determining the zero point of the reference voltage (for example, 0 V). The characteristics of the received signal are different depending on the condition of the reception environment, the type of the RFID radio wave standard, or the assigned frequency for each country. If the measurement line "l2" of the power level signal is not synchronized with the display line "l1", the power level signal l2 is difficult to be accurately compared with the reference voltage l3 (an error of "d1-d2" occurs; , About 0.2V).

Accordingly, the comparison function is performed by the comparator 145. The control unit 170 compares the reference voltage differentiated according to the specification such as the type of the RFID propagation standard or the allocated frequency for each country. The comparator 145 compares the reference voltage with the voltage of the power level signal to generate comparison information and transmits the comparison information to the controller 170.

The comparison information is a binary value, for example, may be used as a TTL (Transistor Transistor Logic) signal in the controller 170, and the differentiated reference voltage transmitted by the controller 170 to the comparator 145 is about. It may have a value of 0.2V to 0.4V.

The control unit 170 determines the existence of the interference signal based on the comparison information, and transmits a control signal to the first switch unit 105 to receive the most stable (low influence of the interference signal) antenna 101a To 101d).

In general, in the case of the LBT method, when it is determined that the power of the received signal is greater than -75 dBm, a signal of another channel is selected, and the comparison operation is performed by the comparator 145.

In addition, the controller 170 controls the second switch unit 110 and the third switch unit 120 so that the signal opening paths of the second switch unit 110 and the third switch unit 120 are matched. For example, when the second switch unit 110 selects a path to the first mixer unit 125, the third switch unit 120 also selects a path to the first mixer unit 125.

In general, the RFID channel of the UHF band is composed of 15 channels. When a plurality of readers exist in a limited area, a plurality of tag signals or interference signals are carried on one channel, and in this case, between frequencies Interference occurs.

3 is a graph measuring a signal received by the LBT system 100 using an IF according to an embodiment of the present invention, Figure 4 is a signal received by the LBT system 100 using an IF according to an embodiment of the present invention. Is a graph measured for each frequency band.

Referring to FIG. 3, an interference signal for each channel, including a transmission signal, may be mixed with a reception signal. A signal B between a reference line “C1” and “C2” may be a tag signal, that is, an area of a reception signal. , The upper region of the reference line "C1" and the lower signal A of "C2" are regions of the interference signal.

The interference signal may be a signal transmitted from a transmission path end, a signal transmitted through a transmission antenna 101e and mixed with a reception signal, and may be an interference signal between adjacent channels or an interference signal on the same channel. have.

When the interference signal is a feedback transmission signal, it has a power range of about 30 dBm, and the reception signal has a power range of about -10 dBm, so that the reception signal is buried in the feedback transmission signal as shown in FIG. It will be difficult to restore.

Referring to FIG. 4, a form in which a carrier frequency of an interference signal and a carrier frequency of a received signal are mixed together and transmitted is illustrated in a frequency domain. The "A" signal measures a carrier frequency signal carrying an interference signal. The " B " signal measures a carrier frequency signal carrying a received signal.

When the reception signal and the interference signal are mixed in this way, it is difficult to stably restore the tag signal. However, according to the present invention, it is possible to determine the existence of the interference signal through the LBT operation and to select a channel through the plurality of antennas 101a to 101d. The problem can be overcome.

5 is a diagram illustrating an exemplary switching time of the LBT system 100 using the IF according to an embodiment of the present invention.

Referring to FIG. 5, time points "T1" to "TN" mean a time point at which the corresponding reception antennas 101a to 101d are switched, and section "t1" to "tN" means that the corresponding reception antennas 101a to 101d are made. 1 means a time section connected to the switch 110.

Therefore, signals received through the plurality of receiving antennas 101a to 101d may be sequentially transmitted to the first switch unit 110.

Meanwhile, the LNA 150 suppresses and amplifies the noise component as much as possible when the received signal is transmitted through the second switch unit 110, and the second filter 155 removes the mixed noise component during low noise amplification.

The second mixer 160 generates a baseband signal by synthesizing the oscillation frequency signal transmitted through the third switch unit 120 and the received signal transmitted through the second filter 155. ), A first mixer 164, and a second mixer 166.

The balloon circuit 162 separates the phase-inverted received signal into an I signal (eg, "E sin ωt") and a Q signal (eg "E cos ωt") (ie, converting a single input signal into a differential signal). Output).

The output terminal of the balloon circuit 162 is connected to the first mixer 164 and the second mixer 166. The mixers 164 and 166 are dual mixers, and the first mixer 164 has a 90 degree phase difference. The I baseband signals (I ⁺ signal and I ⁻ signal) having the signal are synthesized, and the second mixer 166 synthesizes the Q baseband signals (Q ⁺ signal and Q ⁻ signal) having a phase difference of 90 degrees.

The demodulator 165 includes an analog to digital converter (ADC) to demodulate the baseband I signal and the baseband Q signal into digital signals having a plurality of polarities.

The control unit 170 has a communication protocol to control wireless communication with the tag, and process the signal transmitted from the demodulator 165 as a digital signal (data coding / decoding, format conversion, filtering operation, etc.) The digital signal (for example, command data) is transmitted to the modulator 175. The controller 170 may be implemented using a field programmable gate array (FPGA) circuit or a digital signal processing (DSP) circuit.

The modulator 175 may include a mixer, a diode, and the like, and synthesizes a digital transmission signal transmitted from the control unit 170 with an oscillation frequency signal transmitted from the third switch unit 120 to perform an analog signal state. Modulation is performed on the transmitted signal.

At this time, the modulator 175 modulates according to a pulse-interval encoding (PIE) signal standard according to the UHF RFID Protocol such as ISO 18000-6A, ISO 18000-6B, ISO 18000-6C, and the like.

The PAM 180 includes a driving amplifier, an intermediate amplifier, a power amplifier, a bias circuit, and the like, and amplifies a transmission signal to a state in which it can be output, and the amplified signal is removed through the third filter 185. And then transmitted to the tag via the transmit antenna 101e.

Although the present invention has been described above with reference to the embodiments, these are only examples and are not intended to limit the present invention, and those skilled in the art to which the present invention pertains may have an abnormality within the scope not departing from the essential characteristics of the present invention. It will be appreciated that various modifications and applications are not illustrated. For example, each component specifically shown in the embodiment of the present invention can be modified. And differences relating to such modifications and applications will have to be construed as being included in the scope of the invention defined in the appended claims.

According to the LBT system using the IF according to the present invention, it is possible to implement the LBT operation circuit with the minimum number of components using the switch structure.

In addition, according to the present invention, since communication can be performed by selecting a signal channel that is not mixed with interference signals, the received signal can be stably restored / processed, and the recognition distance, reception sensitivity, and recognition rate of the communication target can be improved. It works.

In addition, according to the present invention, since the detection level can be set according to a specification such as a kind of radio wave standard or an assigned frequency for each country, the power level of the received signal can be accurately interpreted.

Claims (5)

A plurality of receive antennas; A first switch unit for switching the plurality of receive antennas; A first mixer and a second mixer for converting the received signal into an intermediate frequency signal; A signal detector for sensing a power level of the intermediate frequency signal of the first mixer; A comparator for applying one of a plurality of reference voltages to compare with the sensed power level and generate comparison information; A control unit which determines whether an interference signal is present in the received signal based on the comparison information, controls the first switch unit according to a determination result, selects a reference voltage as a comparison target, and transmits the reference voltage to the comparison unit; Listen Before Talk (LBT) system using an IF (Intermediate Frequency) including a second switch unit for switching the received signal transmitted from the first switch unit to the first mixer or the second mixer. The method of claim 1, LBT system using an IF including a demodulator for converting the intermediate frequency signal of the second mixer unit into a digital signal and transmitting to the control unit. The method of claim 1, A phase synchronization circuit unit generating an oscillation frequency signal; And LBT system using an IF including a third switch unit for switching the oscillation frequency signal to the first mixer or the second mixer. The method of claim 3, And a modulator for modulating the digital signal transmitted from the controller. And the third switch unit uses an IF to switch the oscillation frequency signal to the first mixer unit and the modulation unit. The method of claim 1, wherein the plurality of reference voltages LBT system using IF, characterized in that set according to the type of RFID radio standard or the assigned frequency by country.

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