JP2810276B2 - Free channel detection method for time division multiple access communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication device of a time division multiple access communication system in which a communication medium is wireless such as radio waves,
The present invention relates to an empty channel detection method for preventing communication channel interference.

[0002]

2. Description of the Related Art Each communication station at a physically different location
When communicating with a base station or the like by radio waves, a time division multiple access (hereinafter referred to as TDMA) communication method in which all stations share a carrier wave of a single frequency for communication, a frequency band is divided into narrow bands, and There is a frequency division multiple access (hereinafter, referred to as FDMA) communication system in which each divided narrow band is allocated to each station and communication is performed using each frequency carrier. This FDM
In the A-communication system, one carrier is dedicated to one communication channel. Therefore, whether or not there is an empty communication channel can be easily identified by whether or not the carrier of the channel can be received.

However, in the TDMA communication system, a single frequency radio wave is shared by a plurality of stations, the time axis is divided into a certain length, and the divided time (time slot) is allocated to one communication channel. If the management of correctly assigning each communication channel to each communication station is not performed properly, interference will occur. Examples of the channel allocation method include mobile TDMA communication and satellite TDM.
A communication and the like include a pre-assignment method and a demand assignment method. However, even in this channel assignment, when the local clocks provided in the respective communication stations for mobile TDMA communication and the like are different and asynchronous, for example , such as a digital cordless telephone, different communication stations are adjacent due to different clocks. There is a risk that the communication channels may overlap and cause interference. So, before each communication station starts communication,
It is necessary to determine whether the assigned channel is idle.

In the conventional method of confirming this empty channel, the reception level in each time slot is detected, and if the reception level is below a certain value, it is determined that the channel is an empty channel. The level detection method includes the following two methods.

In the first method, the reception level of a received radio wave is compared with a reference level which is a threshold value at an appropriate time within a time slot, and it is determined whether or not the time slot is an empty channel based on the magnitude of the comparison. Is the way. For example,
As shown in FIG. 2, when the reception level at time t ₁ is lower than the reception level of the burst signal 51 transmitted / received by another communication station, the time slot 50 is determined to be an empty channel.

In the second method, as shown in FIG. 3, the envelope of the reception level is time-integrated over the entire time slot, and compared with a reference voltage for detecting an empty channel level. If the voltage is equal to or lower than the reference voltage, the time slot is determined to be an empty channel.

[0007]

However, the above two methods for determining an empty channel have the following disadvantages. First, in the first method, as shown in FIG. 2, the burst signal 51 of another station performing communication is shifted from the slot 50 or shifted from the adjacent slot, and the burst signal 51 Even if the department enters,
Because the reception level at the time the time t ₁ is at the reference level 52 below, resulting in erroneous determination idle channel the slot 50. If the own station burst signal is transmitted under this erroneous judgment, interference occurs with the burst signal 51 which has already communicated, and a communication failure occurs.

In the second method, when the burst signal 51 of the other station performing communication is applied to a part of the time slot 50, the integration of the received signal of the entire time slot 50 may be performed depending on the applied condition. Value is reference level 5
In some cases, it is not possible to determine whether the burst signal 51 exists in the slot 50 exactly as in the first method. As described above, in either of the first and second methods, there is a problem that an erroneous channel determination error that is always erroneously determined as an empty channel occurs unless the majority of the burst signal 51 is included in the slot 50.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a more accurate method for determining whether or not a slot is an idle channel even if a majority of burst signals of other stations do not exist in a time slot. In order to provide a method of detecting an empty channel of the time division multiple access communication system which does not interfere with the communication of other stations.

According to the present invention, a group of bits at the front of a frame,
Report bit group and frame rear bit group in this order.
Time-division multiplexing in which a transmission frame is transmitted in the selected time slot
Applicable to the connection communication method.
How to detect if the time slot is a free channel
The transmission of said group of bits at the beginning of the frame
Required for the first time and transmission of the rear bit group of the frame
The time interval determined from the second time is the reference unit time
The reference unit time from the start of the selected time slot
The received radio wave level at an earlier time
A first determination as to whether the threshold value is equal to or less than a first threshold value,
The reference unit time goes back from the end of the selected time slot
The received radio wave level becomes the second
A second determination is made as to whether the value is equal to or less than the threshold value,
If the second determination result indicates that the received radio wave level is below the threshold value,
Only when there is a vacancy in the selected time slot
The channel is determined.

According to the present invention, the reference unit time is
The first time or the second time, whichever is shorter.
Can be Further, the first determination is based on the selection time.
Made after the start of the slot, the second decision
Be done before the end of the selected time slot.
Can be. Further, the first threshold value and the second threshold value are different from each other.
The threshold can be the same.

[0012]

Next, an embodiment of the present invention will be described below with reference to the drawings. Figure 1 is a diagram showing a block configuration diagram of a vacant channel detection circuit for implementing the present invention. In FIG. 1, an antenna 2 is connected to a high-frequency amplifier 3, and an incoming radio wave 1 received by the antenna 2 is received.
Are amplified and modulated by the amplifier 3 and connected to the envelope detector 5 for output. The envelope detector 5 is connected to two comparison circuits 7, 8 such as comparators.
Each of these two comparison circuits 7 and 8 compares the reference level 9 separately connected and input with the envelope detection signal 6. The output of the comparison circuit 7 is a D flip-flop (hereinafter referred to as D−
FF) 12 is connected and input to the data input terminal.
The output of the comparator circuit 8 Ru is connected to the data input terminal of the D-FF13. Also, of these two D-FF12,13
The clock pulses 15 and 16 generated by the timing generation circuit 14 are connected and input to the trigger input terminal of the first embodiment. The outputs of the D-FFs 12 and 13 are connected and input to respective input terminals of the OR circuit 19, and the detection output 2 of the OR circuit 19
0 is connected to the input to the control circuit 21. This control circuit 21
Is a central processing unit (CPU) or a digital signal processor (DSP) that performs various controls by a storage program. The following description is based on the generation timing of the trigger signal 16 of the timing generation circuit 14 and the output of the OR circuit 19. Processing such as judgment to be performed is performed.

Here, the TDMA communication format used in the present invention will be briefly described with reference to FIG. FIG.
Shows an example of the format of a basic frame. In order from the front of the basic frame, a 4-bit transient response ramp time R, a 2-bit start symbol SS and a 6-bit preamble PR, and a 16-bit unique Word UW and 196-bit communication information I
And a 16-bit guard bit G at the end. The bit sum of these signals is 240 bits. Of each signal, particularly important are the unique word UW for establishing frame synchronization and the communication information I, which are the effective information. Also, the ratio of the total time of the ramp time R from the front of the frame to the valid information, the start symbol SS and the preamble PR occupies about 1/20 of the entire frame, and the ratio of the guard bit G occupying the entire frame is about 1/20. , One-fifteenth. The common time of these time widths is 1/20, and the 1/2 time width of this frame time length is defined as unit L.

The operation of the above configuration will be described below with reference to FIGS. FIG. 4 illustrates a state in which the burst signal 51 of another station is applied in the latter half of the time slot 50. The generation timing of the pulses 15 and 16 is controlled by the timing generation circuit 14 so as to be within the time widths 30 and 31 equal to the unit L. The received radio wave 1 is amplified by the high frequency amplifier 3, and the envelope is detected by the envelope detector 5 from the amplified received signal.
The envelope detection signal 6 is input to the comparison circuits 7 and 8, and the magnitude thereof is compared with the reference level 9. The result of this comparison is obtained at the timing of the pulses 15 and 16 by the D-FF1
2 and 13 and the OR circuit 1 as signals 17 and 18
9 is output. That is, a magnitude comparison result between the reception level of the received radio wave and the reference level 9 when the pulses 15 and 16 are generated is obtained. For example, in FIG. 4, at the timing of the pulse 15, since the envelope detection signal 6 is lower than the reference level 9, the signal 17 output from the D-FF 12 is at a low level. At the timing of the pulse 16, the presence of the burst signal 51 causes the envelope detection signal 6 to be higher than the reference level 9, and the signal 18 output from the D-FF 13 to be at a high level. Therefore, the detection output 20 output from the OR circuit 19 that takes the logical sum of these two signals 17 and 18 becomes high level. Since the signal 20 is at the high level, the control circuit 21 determines that the burst signal 51 is present in the slot 50, and determines that the slot 50 is not an empty channel. When the burst signal 51 is applied to the first half of the time slot 50, the signal 17 at the timing of the pulse 15 becomes high and the signal 18 becomes low, and the detection output 20 becomes high. It is determined that the slot 50 is not a free channel. When it is determined that the time slot 50 is not a free channel, the control circuit 21 controls the timing generation circuit 14 to generate pulses 15 and 16 in another time slot so as to search for another free channel. .

Conversely, when the burst signal 51 is applied only to the rear part of the time width 31 as shown in FIG.
As a result of the level comparison at the timing of the pulses 15 and 16, both the signals 17 and 18 are at the low level and the detection output 20 is at the low level. As a result, the control circuit 21
0 is determined as an empty channel. That is, pulses 15, 1
When both the reception levels of the envelope detection signal 6 at the timing of the timing 6 are equal to or lower than the reference level 9, the slot 50 is determined as an empty channel for the first time. At this time, FIG.
As shown in the figure, even if the other station burst signal 51 is applied to the rear part of the time slot 50, the guard bit G portion of the own station burst signal has the ramp time R, the start symbol SS and the preamble PR portion of the other station burst signal 51. Duplicate only in. The guard bit G is used in TDMA communication to prevent the other station signal from being affected even if the burst signal is shifted back and forth on the time axis. Therefore, the unique word UW and the information, which are effective information of the other station burst signal, are used. I is not destroyed, and there is no risk of causing interference. As described above, the time widths 30 and 31 do not affect the effective information of the own-station burst signal and the other-station burst signal even if other-station burst signals exist before and after a part of the time slot detected as an empty channel. The time unit is L.

In the above embodiment, the empty channel detecting circuit of the digital cordless telephone has been described.
It can also be used for a communication device of the A communication system. In the above example, the envelope detection signal 6 is obtained by using the two comparison circuits 7 and 8.
And the reference level 9 are triggered by the D-FFs 12 and 13 at the timing of the generation of the pulses 15 and 16, respectively, and this is used as one comparison circuit, and the output of this one comparison circuit is used as the D-FFs 12 and 13. May be input in parallel to the data input terminal. The time slot 50 may be determined to be an empty channel when the output of the OR circuit 19 is at a low level using a NAND circuit. Further, as for the level comparison method between the reference level 9 and the received signal, the received signals within the time widths 30 and 31 are integrated with respect to time, and the integrated value is compared with the reference voltage.
If the integrated value is equal to or less than the reference voltage, it may be determined that the channel is an empty channel, and the configuration of the comparison circuit is not particularly limited.

Further, in the above example, the generation timing of the pulses 15 and 16 is set at an arbitrary time within the time widths 30 and 31 which are 1/20 of the slot length, but is not particularly limited to 1/20. For example, if the information I is shorter than 196 bits and a signal that is not particularly important is further added to the front part of the frame, or if there is a unique word UW in the middle of the information I, the time widths 30 and 31 are changed to the next. May be determined as follows. That is, the time widths 30 and 31 are the common time lengths of the time length from the frame start point to the effective information start point of the unique word UW or the information I and the time length from the effective information end point to the frame end point. That is, when the front part and the rear part of the two burst signals overlap, any time width may be used as long as it does not interfere with the respective effective information. Embodiment described above
According to the above, the unique word UW and the communication
A start symbol at the front of the frame excluding the communication information I,
Time width of header part such as preamble and valid information end point
Common with guard bit G time width from frame to frame end
Using the time width as unit L, before and after each time slot
If both the received radio wave levels within the unit L of the
Only if the time slot is a free channel.
It was to so. As a result, in the past, other station burst signals
If the number is out of the time slot,
System slot can be prevented from being erroneously determined as an empty channel.
You. In addition, a tie detected as an empty channel according to the embodiment.
Part of the front or rear part of the
Transmit the own station burst signal while the signal is on
Also, the unique words UW and
Communication does not interfere with communication I
Harm can also be prevented.

[0018]

As described above , according to the present invention,
More than half of burst signals of other stations exist in time slot
Whether the slot is a free channel
Is more accurate and less likely to interfere with other station communications.
There is no available channel detection method for time division multiple access communication.
I can.

[Brief description of the drawings]

FIG. 1 relates to one embodiment of the present invention and is a block diagram showing the configuration thereof.

FIG. 2 is an explanatory diagram of erroneous judgment by a conventional empty channel detection circuit.

FIG. 3 is an explanatory diagram of erroneous judgment by a conventional empty channel detection circuit.

FIG. 4 is a time slot diagram for explaining an operation according to an embodiment of the present invention.

FIG. 5 is a time slot diagram for explaining operation according to an embodiment of the present invention.

FIG. 6 is a diagram showing an example of a frame format of a TDMA communication system used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Received radio wave 2 Antenna 3 High frequency amplifier 5 Envelope detector 6 Envelope detection signal 7, 8 Comparison circuit 9 Reference level 10, 11 Comparison result signal 12, 13 D flip-flop 14 Timing generation circuit 15, 16 Clock pulse 17, 18 Signal 19 OR circuit 20 Detection output 21 Control circuit 30, 31 Time width 50 Time slot 51 Burst signal 52 Reference level

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-22243 (JP, A) JP-A-5-145460 (JP, A) JP-A-5-206942 (JP, A) JP-A-2-206 312417 (JP, A) JP-A-2-222226 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04J 3/00 H04B 7/24 H04Q 7/28

Claims (4)

(57) [Claims] The present invention is applied to a time division multiple access communication system in which a communication frame arranged in the order of a frame front bit group, a valid information bit group, and a frame rear bit group is transmitted in a selected time slot. A method for detecting whether a selected time slot is an empty channel or not, comprising: a first time required for transmission of the frame front bit group;
A time interval determined from a second time required for transmission of the frame rear bit group is set as a reference unit time, and a reception radio wave level is a time earlier than the reference unit time from the start of the selected time slot. A first determination is made as to whether or not the received radio wave level is equal to or less than a first threshold value. At a time after the reference unit time from the end of the selected time slot, the received radio wave level is equal to or less than a second threshold value. A free channel detection method for determining whether or not the selected time slot is a free channel only when both the first and second determination results indicate that the received radio wave level is equal to or lower than a threshold value. 2. The free channel detecting method according to claim 1, wherein the reference unit time is a shorter time of the first time or the second time. 3. The free channel detecting method according to claim 1, wherein said first determination is made after a start point of said selected time slot, and said second determination is made before an end point of said selected time slot. 4. The free channel detecting method according to claim 1, wherein said first threshold value and said second threshold value are the same.