KR100775207B1 - DMV communication system using antenna diversity and DMV communication method using antenna diversity - Google Patents

Abstract

DMB communication system using antenna diversity according to the present invention comprises a plurality of antennas; RF unit for processing the signal transmitted and received through the antenna by the OFDM method; A switch unit selectively connecting the antenna to the RF unit; And an antenna controller configured to control the switch unit by measuring an intensity of a signal received through the antennas and selecting an antenna that receives a signal of the highest electric field in a section in which null time exists among the OFDM signal standards. do.

According to the present invention, since the reception sensitivity of the antenna is sensed and the antenna switching operation is processed using a null time interval of the DMB communication standard, the reception state can be optimally maintained while efficiently using hardware and software resources. In addition, according to the present invention, an antenna having an optimal reception sensitivity can be selected by actively responding to changes in the reception environment, so that a DMB communication system that is strong against fading environments such as a vehicle, a crowded area, and a hardware structure installation area such as a bridge can be developed. Can be.

Description

DMB communication system using antenna diversity and DMB communication method using antenna diversity {Digital Multimedia Broadcasting system using antenna diversity and digital multimedia broadcasting method using antenna diversity}

1 is a block diagram schematically showing the components of a DMB communication system using antenna diversity according to a first embodiment of the present invention.

2 is a block diagram schematically showing the components of a DMB communication system using antenna diversity according to a second embodiment of the present invention;

3 is a data structure diagram exemplarily illustrating a section in which null times exist among OFDM signal standards used in a DMB communication system using antenna diversity according to an embodiment of the present invention.

4 is a diagram illustrating an OFDM signal standard processed in a DMB communication system using antenna diversity according to an embodiment of the present invention on a spectral domain;

FIG. 5 is a data table exemplarily showing a mode-specific OFDM signal standard that can be used in a DMB communication system using antenna diversity according to an embodiment of the present invention. FIG.

6 is a block diagram schematically illustrating components of an antenna control module provided in a DMB communication system using antenna diversity according to an embodiment of the present invention.

7 is a flowchart illustrating a method of switching an antenna in a DMB communication method using antenna diversity according to an embodiment of the present invention.

8 is a flowchart illustrating a method of changing a check time period in a DMB communication method using antenna diversity according to an embodiment of the present invention.

<Explanation of symbols for main parts of drawing>

100: DMB communication system according to the second embodiment

111, 112, 113, and 114: the first to fourth antennas

121, 122, 123, 124: 1st to 4th LNA

130: switch unit 140: RF unit

150: BB unit 160: antenna control module

162: null time management means 164: timer management means

166: signal strength detecting means 168: control signal generating means

The present invention relates to a DMB communication system using antenna diversity and a DMB communication method using antenna diversity.

DMB (Digital Multimedia Broadcasting) refers to high-end broadcasting that encompasses radio (audio) broadcasting, TV broadcasting and mobile communication data. In 2003, "digital audio broadcasting" and "digital video broadcasting" Incorporation has led to the generic term DMB being commonly used.

Since DMB transmits broadcast signals as digital data using all terrestrial, satellite, and radio frequency bands, DMB has a wide range of applications from mobile broadcasting, portable broadcasting, and personal broadcasting, and the development of contents is extensive.

DMB is classified into terrestrial DMB and satellite DMB according to technical standard and network configuration. Terrestrial DMB is based on Orthogonal Frequency Division Multiplex (OFDM), and satellite DMB is code division multiplex (CDM). It uses the same principle as mobile communication technology.

Because of the different frequency bands and system configurations, DMB receivers with various types of platforms are being developed. Typical DMB receivers include antennas, variable filters, low noise amplifiers (LNAs), gain amplifiers, mixers, It consists of a filter and an intermediate frequency amplifier.

The antenna receives a DMB signal, and the variable filter selectively passes channel frequencies. The mixer also produces an intermediate frequency, and the filter removes signal components outside the passband.

The low noise amplifier increases the signal gain by lowering the noise figure of the input signal, and the gain amplifier performs an automatic gain control (AGC) function to automatically adjust the gain of the DMB signal.

The intermediate frequency amplifier adjusts the gain of the intermediate frequency components passed through the mixer and the filter so that the intermediate frequency signal of the DMB signal is finally output.

The conventional DMB receiver has a problem in that the characteristics of the active elements constituting the receiver deteriorate according to the electric field strength of the input signal received through the antenna. For example, when a strong electric field signal is input, the low noise amplifier at the first stage of the receiver The linearity may be distorted. If the linearity of the active elements is deteriorated, the reception sensitivity of the entire receiver may be reduced.

In other words, the signal received through the antenna is weakened due to signal attenuation, multipath loss, interference, Doppler effect, etc., and the recognition rate is changed. It's time.

According to the present invention, an antenna diver having an improved signal processing structure to check a reception electric field in real time using characteristics of an OFDM signal standard and characteristics of a terrestrial DMB communication system and to maintain a recognition rate stably by switching an antenna having the highest electric field. Provides a DMB communication system using a city.

In addition, the present invention by determining the reception sensitivity of a plurality of antennas using the null time of the DMB communication standard, by applying a combination of the check time period, the number of checks, antenna rank alignment, etc. in detecting the reception strength of each antenna The present invention provides a DMB communication method using antenna diversity to reduce an inefficient computational burden of hardware resources and maintain an optimal reception state.

DMB communication system using antenna diversity according to the present invention comprises a plurality of antennas; RF unit for processing the signal transmitted and received through the antenna by the OFDM method; A switch unit selectively connecting the antenna to the RF unit; And an antenna controller configured to control the switch unit by measuring an intensity of a signal received through the antennas and selecting an antenna that receives a signal of the highest electric field in a section in which null time exists among the OFDM signal standards. do.

In addition, the antenna control unit included in the DMB communication system using the antenna diversity according to the present invention is included in the baseband processor or processor unit, the antenna controller is a signal according to the transmission standard corresponding to the transmission mode-1 of the OFDM scheme And control the switch unit on the null time.

In addition, the antenna control unit provided in the DMB communication system using antenna diversity according to the present invention includes a timer to variably set a check time period, record the number of checks according to the check time period, and the number of checks. To control the switch unit.

The DMB communication method using the antenna diversity according to the present invention relates to a DMB communication system using an OFDM signal standard, and measures the signal strength of a plurality of antennas by checking a check time period in a null time domain. Doing; Generating a switching control signal by selecting an antenna that receives a signal of the highest electric field when the signal strength of the antenna is measured; And switching the selected antenna with an RF unit according to the switching control signal.

In the DMB communication method using antenna diversity according to the present invention, the signal strength of the antenna may be measured by changing the check time period in comparison with a reference value having a predetermined grade when the signal strength of the antenna is measured. It further comprises the step.

Hereinafter, a DMB communication system using antenna diversity and a DMB communication method using antenna diversity will be described in detail with reference to the accompanying drawings.

1 schematically illustrates the components of a DMB communication system (hereinafter, referred to as a "DMB communication system according to a first embodiment") 100 using antenna diversity according to a first embodiment of the present invention. The block diagram shown.

Referring to FIG. 1, the DMB communication system 100 according to the first embodiment of the present invention includes a first antenna 111, a second antenna 112, a third antenna 113, a fourth antenna 114, and a fourth antenna. A low noise amplifier (LNA) 121, a second low noise amplifier 122, a third low noise amplifier 123, a fourth low noise amplifier 124, a switch 130, an RF unit 140, and A baseband (BB) unit 150 is formed, and the baseband unit 150 includes an antenna control module 160.

The DMB communication system 100 according to the first embodiment of the present invention processes a transmission / reception signal by the OFDM method, and includes a plurality of antennas 111, 112, 113, and 114 and grasps the antenna having the best reception state in real time. It characterized in that the processing.

In addition, the DMB communication system according to the first embodiment of the present invention includes four LNAs 121, 122, 123, and 124, and the four antennas 111, 112, 113, and 114 each have an LNA 121, It has a configuration connected to the switch unit 130 through 122, 123, 124.

Since the power of the radio wave received through the antennas 111, 112, 113, 114 has a very low power level due to the attenuation and the influence of noise, the low noise amplifiers 121, 122, 123, 124 receive the received signal. Since the received signal contains external noise, the received signal is amplified while suppressing the noise component as much as possible. In other words, an important part of determining the noise figure of the communication system is the noise figure of the early block of the system because the overall noise figure is greatly improved when the early block has a small noise figure and a large gain. Accordingly, the low noise amplifiers 121, 122, 123, and 124 are designed by grabbing the operating point and the matching point so that the noise figure has a small value.

In the first embodiment of the present invention, the antenna control module 160 is provided in the baseband unit 150, the antenna control module 160 is in the interval in which a null time of the OFDM signal standard exists, the The switch unit 130 is controlled by measuring the strength of a signal received through the antennas 111, 112, 113, and 114, and selecting an antenna that receives the signal of the highest electric field.

The antenna control module 160 will be described in detail below with reference to FIGS. 8 to 10.

The switch unit 130 has four signal paths connecting the four antennas 111, 112, 113, and 114 to the RF unit 140, and controls the signal (voltage) to selectively open and close these signal paths. An applied control voltage terminal and a power supply terminal for supplying power to the switch are provided.

In addition, the switch unit 130 includes a high frequency switching circuit that can be implemented in various forms such as a semiconductor circuit, a microstrip line coupler, a combination circuit of a lumped circuit, and the like, and interprets the control signal and logically controls the switching operation. It includes a decoder.

The RF unit 140 includes a mixer constituting an Rx path, a filter, a PA, a second PA, and four filters constituting a Tx path, a power amplifier module (PAM), a mixer, and a PA.

The RF unit 140 separates the transmission and reception signals into I and Q signals, and processes the separated signals by the OFDM scheme.

The I and Q signals separated through the Rx path of the RF unit 140 are transmitted to the baseband unit 150, respectively, and the analog signals transmitted in the I signal and Q signal states from the baseband unit 150 are RF units ( 140).

The transmitted I and Q signals are synthesized and converted into RF signals.

In addition, the converted signal is amplified into a signal of a size that can be transmitted by the PAM.

The filters are a sort of band pass filter (BPF) and may be provided as SAW filters. When the filters are mixed or amplified, the filters filter signals of mixed noise components.

The PAs amplify the filtered signals into a signal that can be processed by the baseband unit 150, or amplify to a sufficient size so that the signal processed by the baseband unit 150 can be filtered with a linear characteristic.

The baseband unit 150 includes an Rx path stage including an AD converter, a Time Domain Processor (TDP), a Fast Fouriour Transform (FFT), a Frequency Domain Processor (FDP), a Quadrature Phase Shift Keying (QPSK), and a BaseBand Processor (BPB). Tx path stages include DA converter, TDP, Inverse FFT (IFFT), FDP, QPSK, BBP.

The baseband unit 150 processes a signal transmitted and received through a DMB frequency band as a symbolized signal using an orthogonal frequency division multiplexing (OFDM) modulation scheme, and includes a time division technique, a frequency division technique, and a spatial division technique. The signal specification is defined according to the symbology, symbolization, and data frame structure.

In addition, the baseband unit 150 may also use a QPSK modulation scheme.

The QPSK modulation scheme is a form of phase shift keying, in which two bits are modulated at once so that four possible carrier phase shifts (0, 90, 180 or 270 degrees) are selected. Using QPSK, the average PSK can transmit twice the amount of information transmitted using the same bandwidth.

The AD converter provided in the baseband unit 150 converts the intermediate frequency signal in the analog signal state from the RF unit 140 into a digital signal, and the TDP converts a frame synch and a symbol synch. Process the signal in the same time domain.

The FFT converts a signal expressed in the time domain into a signal in the frequency domain, and the FDP performs signal processing on the frequency domain.

The QPSK multiplexes the signal by shifting the phase, and the BBP converts the multiplexed signal into a DMB signal standard for digital processing.

The components of the Tx path stages are components that perform the operation of the components of the Rx path stage in reverse, and thus the detailed description thereof will be omitted.

2 schematically illustrates the components of a DMB communication system (hereinafter referred to as a "DMB communication system according to a second embodiment of the present invention") 200 using antenna diversity according to a second embodiment of the present invention. The block diagram shown.

Referring to FIG. 2, the DMB communication system 200 according to the second embodiment of the present invention includes a first antenna 211, a second antenna 212, a third antenna 213, a fourth antenna 214, and a second antenna. The first low noise amplifier 221, the second low noise amplifier 222, the third low noise amplifier 223, the fourth low noise amplifier 224, the switch unit 230, the RF unit 240, the base band unit 250, and the control unit. 260, and the control unit 260 includes an antenna control module 270.

The DMB communication system 200 according to the second embodiment of the present invention differs from the DMB communication system 100 according to the first embodiment described above in that the antenna control module 270 is implemented on the controller 260. The points are different, and the four antennas 211, 212, 213, and 214, the low noise amplifiers 221, 222, 223, and 224, the switch unit 230, the RF unit 240, and the baseband unit according to the second embodiment. 250 is similar in structure and operation to the first embodiment, and thus a detailed description thereof will be omitted.

The controller 260 may be implemented through a field programmable gate array (FPGA) chip, a digital signal processor (DSP), an ARM-based chip, or the like.

FPGA circuits are gate array circuits (logical integrated circuits) that can add programming as needed when implementing functions related to image inspection outside the chip's production process.The characteristics of gate arrays and programmable logic devices (PLDs) Is implemented. These FPGA circuits have the advantages of being able to use multiple I / Os like a gate array, programmable at a time, and increasing the utility of the gate by 95%.

The ARM 7 or 9 is a type of reduced instruction set computer (RISC) chip. The ARM 7 or 9 has a 32-bit register and an ALU capable of 32-bit operation. ARM also has a 32-bit Booth's multiplier, an instruction decoder, an address register with an incrementer, and is internally connected to a 32-bit address & data bus.

Next, the OFDM technology will be described before explaining the antenna control module 270.

FIG. 3 is a data structure diagram exemplarily illustrating a section in which a null time exists among OFDM signal standards used in a DMB communication system using antenna diversity according to an embodiment of the present invention.

OFDM signals to be processed in the DMB communication system (100, 200) according to the present invention comprises k number of test frames to;; (Time Slot T _S) (T _F Test Frame) as made and the test frames is N time slots again Is done.

Referring to FIG. 3, a form of a test frame T _F including a plurality of OFDM symbols is illustrated. A null time region exists between the test frames T _F , and TFPR ( Time Frequency Phase Reference) block.

The TFPR block distinguishes test frames, contains information about the test frame, and is located next to the TFPR block, which symbolizes data.

OFDM symbol is a time slot; and corresponds to (T _S Time Slot), the time slot are separated by a separator _(△ T), can be exemplified by transmission time base and the modulation frequency axis, as shown in Fig.

The OFDM signal having such a configuration can be represented by the following equation.

k × N × T _S ≒ 1 = constant

(In Equation 1,

"k" means the number of test frames,

"N" means the number of time slots,

"Ts" means a transmission time of an OFDM symbol,

As a constant, "1" means the transmission time (unit "second") of one group of data (full test frame).

According to Equation 1, it can be seen that the number of test frames and the number of time slots can be combined in various forms.

Meanwhile, a probability of identification error is determined according to the three variables "k", "N", and "Ts". The recognition error rate may be determined by the following equation.

(In Equation 2,

“n” means the number of OFDM symbols forming one group,

"k" means the number of test frames.

"N" means the number of time slots)

4 is a diagram illustrating an OFDM signal standard processed in a DMB communication system 100 and 200 using antenna diversity according to an embodiment of the present invention on a spectrum domain, and FIG. 5 is an antenna diver according to an embodiment of the present invention. The data table exemplarily shows a mode-specific OFDM signal standard that can be used in the DMB communication systems 100 and 200 using the city.

4, the frequency spectrum according to the (phase) angular frequency (ω) during OFDM modulation according to the present invention is shown, where "Δf" means spectral width, and "ΔF" of the lower frequency channel. It means an area.

Referring to FIG. 5, an OFDM signal specification for each mode is illustrated, in which a parameter "L" denotes an entire length of an OFDM symbol, "T _F " denotes a length of a test frame, and "Ts" denotes an OFDM unit symbol. Means the length.

In addition, "T _DELTA " means a separator length of an OFDM unit symbol, and "T _NULL " means a null time length.

In the embodiment of the present invention, the antenna control modules 160 and 270 process signals according to a transmission standard corresponding to the transmission mode-1 of the OFDM scheme shown in FIG.

Accordingly, in processing the DMB signal, the antenna control module 160 or 270 recognizes a null time of 1.297 msec every 96 msec, and the first antennas 111 and 211 to the fourth antenna 114 during null time. The signal strength of 214 is selected to select the antenna with the strongest received electric field.

6 is a block diagram schematically illustrating the components of the antenna control module 160 provided in the DMB communication system 100 (described with reference to the first embodiment) using antenna diversity according to an embodiment of the present invention. 7 is a flowchart illustrating a method of switching an antenna in a DMB communication method using antenna diversity according to an embodiment of the present invention, and FIG. 8 is a diagram illustrating antenna diversity according to an embodiment of the present invention. A flowchart illustrating an example of changing a check time period among DMB communication methods.

Referring to FIG. 6, the antenna control module 160 includes a null time managing means 162, a timer managing means 164, a signal strength detecting means 166, and a control signal generating means 168. In describing the components of the control module 160, the DMB communication method using antenna diversity according to an embodiment of the present invention will be described with reference to FIGS. 7 and 8.

The DMB communication method using antenna diversity according to an embodiment of the present invention can be classified into two types: a method of switching an antenna and a method of changing a check time period. The two methods may be operated together or processed separately. It is processed in the antenna control module 160 as.

Referring to FIG. 7, first, the null time managing means 162 determines whether a 1.297 msec time located every 96 msec of the transmitted OFDM signal has arrived (S100).

If the null time has not started (NO in S100), the null time managing means 162 monitors the OFDM signal blocks that are continuously transmitted (S105). Operate (YES in S100).

The timer managing means 164 sets a check time when the check time arrives (YES in S110), and operates the signal strength detecting means 166, and when the check time does not arrive (NO in S110). The timer operation is maintained and the check time is monitored (S115).

That is, when the antenna control module 160 satisfies both the null time satisfying condition S100 and the check time satisfying condition S110, the antenna control module 160 may determine the signal received from the first antenna 111 to the fourth antenna 114. It is to measure the intensity.

The signal strength detecting means 166 counts and records the number of checks each time the signal strength of each antenna is measured (S155) or initializes the number of checks recording (S160), which is received from an antenna that is currently switched (set). When the signal strength is measured three times and continuously determined as the weak electric field (YES in S130), another antenna determined as the highest electric field is set.

Since the signal strength changes from time to time depending on the reception environment, the antenna switching is controlled only when exposed to a predetermined time (recovery) weak electric field environment, not based on a single measurement.

First, when the signal strength detecting means 166 is operated by the interrupt signal transmitted from the timer managing means 164, the signal strength detecting means 166 checks the number of checks, and in the case of initial signal measurement (YES in S120), the previous signal (currently set Antenna information) is recorded (S125).

Here, the "first signal measurement" means a case in which the signal from the currently set antenna is not determined to be smaller than the reference electric field value. For example, if the signal from the currently set antenna is determined to be smaller than the reference electric field value, It is determined that the current signal measurement is not the first signal measurement.

If it is not the first signal measurement as described above (No in S120), the signal strength detecting means 166 confirms the number of checks again, and if the number of checks is exceeded three times (YES in S130), In other words, if it is determined that the previous three times the weak weak electric field, the signal strength detecting means 166 changes the current antenna setting.

However, as a result of confirming the number of checks again, if it has not exceeded three times (NO in S130), the signal strength detecting means 166 includes the first antenna 111 to the fourth antenna 114 including the currently set antenna. The signal strength of the signal is detected (S135).

The signal strength detecting means 166 may be implemented using a RSSI (Received Signal Strength Indicator) circuit, and the RSSI circuit means a circuit for measuring the strength of a signal received through an antenna and converting the signal into a predetermined level value. do.

The RSSI circuit is connected on the baseband signal chain in front of the amplifier of the RF unit 140 or in front of the amplifier provided in the baseband unit 150 to couple the signal and measure the electric field of the coupled signal.

The output of the RSSI circuit is a DC analog signal level and can be sampled by an ADC provided in the circuit, and the measurement result code can be directly transmitted or transmitted through an internal processor bus.

The signal strength detecting means 166, when the strength of the signal received from each antenna 111, 112, 113, 114 is measured, ranks the antenna according to the signal strength (S140), the electric field higher than the current signal It is determined whether there is an antenna that receives a signal of (S145).

As a result of the determination, if the signal strength of the currently set antenna is the strongest (No in S145), the current antenna setting is maintained, and the setting of the check time period (hereinafter described in detail with reference to FIG. 8) is also maintained (S150). ).

On the other hand, if there is an antenna that receives a signal stronger than the signal strength of the currently set antenna (YES in S145), the signal strength detecting means 166 records antenna information for receiving the highest electric field signal and checks the number of checks as described above. Record by increasing once (S155).

In addition, if the number of checks is exceeded three times, the signal strength detecting means 166 changes the current antenna setting as described above, and it is measured that the highest electric field signal is received in the signal strength determination process performed immediately before. The setting is changed to the antenna on which the information is recorded (S165).

The control signal generation means 168 stores the changed antenna information in the memory, generates a control signal corresponding to the antenna information and sends it to the control voltage terminal of the switch unit.

In this way, since the change in the antenna setting means that the reception environment is in an unstable state, the check time period of the timer is changed to be shorter to enhance the monitoring function of the null time managing means 162 and the timer managing means 164.

When the antenna setting is maintained at the current setting or changed to another antenna setting, the time counted by the timer and the check count recording area are initialized (S160).

Subsequently, a method of changing the check time period will be described with reference to FIG. 8, which relates to a method of changing the check time period shorter for a weak electric field and longer for the strong electric field based on signal strength.

The method of changing the check time period may be performed in a separate process from the method of switching the antenna described with reference to FIG. 7. For example, the process of detecting the signal strength of the antenna or setting the antenna to the antenna of the highest electric field. In the process of changing to and changing the timer period may be processed together.

The timer managing means 164 initializes the check time period, and the signal strength detecting means 166 grasps the electric field of the signal received from the currently set antenna.

As the received electric field is grasped, the signal strength detecting means 166 compares the grading level with a predetermined level at predetermined numerical intervals and changes the check time period accordingly.

For example, reference level 1 may be rated at intervals of 10 dBm, such as "-85 dBm" and reference level 2 "-95 dBm," and a check time of about 3 minutes if the current reception field corresponds to reference level 1 If the period is set or the current reception electric field corresponds to the reference level 2, a check time period of about 30 seconds may be set.

In this way, the DMB communication system 100 using antenna diversity according to the present invention uses the null time of the DMB transmission mode-I, changes the check time period according to the received electric field, and sets the antenna setting according to the number of counts. This change allows for real-time adaptation to the receiving field environment to maintain the most optimal antenna sensitivity.

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 DMB communication system using the antenna diversity according to the present invention, since the reception sensitivity of the antenna is sensed and the antenna switching operation is processed using a null time interval of the DMB communication standard, the reception state is efficiently used while using hardware and software resources. It is effective to keep the optimum.

According to the DMB communication method using the antenna diversity according to the present invention, it is possible to actively respond to changes in the receiving environment to switch the antenna having the optimal reception sensitivity in real time, so that the installation of hardware structures such as vehicles, population areas, piers Develop a DMB communication system that is strong against fading environments such as regions.

Claims (12)

A plurality of antennas; RF unit for processing the signal transmitted and received through the antenna by the OFDM method; A switch unit selectively connecting the antenna to the RF unit; And And an antenna controller configured to measure the strength of a signal received through the antennas and select an antenna that receives a signal of the highest electric field in a section in which a null time exists among the OFDM signal standards to control the switch unit. DMB communication system using antenna diversity. The method of claim 1, wherein the antenna control unit DMB communication system using the diversity, characterized in that included in the baseband processor or processor. The method of claim 1, wherein the antenna control unit A DMB communication system using antenna diversity, characterized in that the signal is interpreted according to a transmission standard corresponding to the transmission mode-1 of the OFDM scheme, and the switch unit is controlled on the null time. The method of claim 1, wherein the antenna control unit And a timer to variably set a check time period, record the number of checks according to the check time period, and control the switch unit according to the number of checks. The method of claim 4, wherein the antenna control unit DMB communication system using antenna diversity characterized in that the check time period is set variably by comparing the reference signal strength divided by a predetermined class and the signal strength of the currently switched antenna. The method of claim 4, wherein the antenna control unit For each period of the check time, the strength of the signal received through the antennas is compared and the antenna for receiving the signal of the highest electric field is recorded.If the number of checks exceeds a predetermined number, the currently set antenna is set as the recorded antenna. DMB communication system using diversity, characterized in that for changing. The method of claim 1, A DMB communication system using diversity further comprising a low noise amplifier between the antenna and the switch unit. In the DMB communication system using the OFDM signal standard, Measuring signal strength of a plurality of antennas by checking a check time period in a null time region; Generating a switching control signal by selecting an antenna that receives a signal of the highest electric field when the signal strength of the antenna is measured; And And switching the selected antenna with an RF unit according to the switching control signal. The method of claim 8, wherein measuring the signal strength of the antenna And counting the number of measurements of the signal strength when the check time arrives. The method of claim 9, wherein generating the switching control signal And the switching control signal is generated when the number of times of measurement exceeds a predetermined number of times. The method of claim 10, wherein generating the switching control signal Arranging the antennas whose signal strengths are measured in electric field order; Recording antenna information for receiving the highest electric field signal among the aligned antennas; And And generating the switching control signal according to the recorded antenna information when the number of times of measurement is greater than or equal to a predetermined number of times. The method of claim 8, wherein measuring the signal strength of the antenna And changing the check time period in comparison with a reference value having a predetermined class when the signal strength of the antenna is measured.

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