JP2008294838A - Communication equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide communication equipment with which a transmission path is efficiently used to keep the number of communicable mobile stations appropriate and successful communication quality is secured in communication between mobile stations without having base stations. <P>SOLUTION: In the communication equipment 1 loaded on each mobile station, a slot timing generation part 11 and a transmission control part 14 detect vacant slots on the transmission path, each mobile station raises transmission rate of data to be transmitted, respectively as the vacant slots decrease on the transmission path, to secure vacancy on the transmission path, and in addition, transmission rate of the data to be transmitted, respectively by the communication equipment loaded on each mobile station is lowered as the vacant slots increase on the transmission path, to effectively use the transmission path. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a communication device.

  Conventionally, as a mobile terminal (mobile station) communication method, a base station that controls communication between mobile stations has been provided. The base station time-divides the time that can occupy a transmission path into slots, and the slots are assigned to each mobile station. There is known a method (time division multiple access method) in which communication is performed by assigning to (for example, see Patent Document 1). The communication method described in Patent Document 1 is a communication method that combines a time division multiplexing method and a variable modulation method that changes the modulation method according to the state of the transmission path, and maintains a substantial information transmission rate. be able to.

  Generally, in a time division communication system transmission line, the number of slots in the communication cycle is determined, so the number of mobile stations that can communicate (the number of accommodated terminals) is determined according to the slot used by each mobile station. Is done. Therefore, if the number of unused slots (empty slots) decreases on the transmission path, the number of mobile stations that can newly participate in communication decreases, and if there are many empty slots on the transmission path, it newly participates in communication. The number of mobile stations that can be increased. Thus, the number of accommodated terminals is determined according to the utilization rate on the transmission path.

On the other hand, it is possible to change the number of slots used by one mobile station by changing the transmission data modulation method. The greater the number of slots used by the mobile station, the longer the transmission time, the less the influence of noise and the like, and the better the communication reliability. Therefore, when the utilization rate on the transmission path is small, the reliability of communication can be improved by increasing the number of slots used by the mobile station.
JP-A-5-130082

  However, since the communication system described in Patent Document 1 is performed via a base station, it cannot be applied to a communication system that directly communicates between mobile stations without going through a base station. In addition, in the communication method in which one of the mobile stations has the function of a base station, the size, shape and density of the mobile station group change according to time, so the control for determining the mobile station to be a base station is complicated. Therefore, smooth communication between mobile stations may be hindered.

  Therefore, the present invention has been made to solve such a technical problem, and in the communication between mobile stations having no base station, the number of mobile stations that can communicate using the transmission path efficiently. It is an object of the present invention to provide a communication device that can easily maintain good communication quality and can easily achieve good communication quality.

  That is, a communication device according to the present invention is mounted on a mobile station, has a transmission means for transmitting transmission data and a reception means for receiving transmission data, and sets a time during which transmission data between mobile stations can occupy a transmission path. Is a communication device that performs transmission / reception under the control of a slot having a time length of, and includes an empty slot detection means for detecting an empty state of a transmission path in units of slots, and a transmission to be transmitted when the number of detected empty slots is smaller Transmission rate changing means for increasing the data transmission rate and decreasing the transmission rate of transmission data to be transmitted as the number of detected empty slots increases.

  In the present invention, the communication device installed in each mobile station detects empty slots on the transmission path, and when there are few empty slots, the transmission rate of data transmitted by each mobile station is increased. For this reason, since other mobile stations can participate in communication, the number of mobile stations capable of communication can be maintained appropriately. In addition, when there are many empty slots in the transmission path, the transmission rate of data transmitted by each communication device mounted on each mobile station is lowered. For this reason, it is possible to ensure communication quality while effectively utilizing the transmission path.

  Here, the empty slot detecting means of the communication device uses a period counter having a period equal to the time length of the slot and a number counter for counting the order of reception of the slots, and an empty slot in a frame consisting of a predetermined number of slots. Detect the situation.

  The communication device installed in each mobile station can recognize the slot timing by synchronizing with a period counter having a period equal to the time length of the slot. Also, the communication device mounted on each mobile station can recognize the slot interval in the frame by recognizing the slot timing, and receives the slot a predetermined number of times using a number counter that counts the order of reception. be able to. As a result, the number of slots corresponding to one frame configured periodically can be obtained, so that the number of empty slots in one frame can be reduced without the base station controlling each mobile station. Can be recognized.

  The transmission rate changing means receives the own occupied slot corresponding to the transmission data transmitted by the transmitting means at the receiving means, and the number of empty slots necessary for lowering the transmission rate is continuous in the slot immediately after the own occupied slot. If the number of empty slots necessary for lowering the transmission rate is continuously present, the transmission rate of the transmission data corresponding to the own slot is reduced. .

  In the present invention, when the transmission rate is lowered and the number of slots used by transmission data is increased, the slot immediately after the self-occupied slot is used, and in the immediately following slot, the empty space necessary for lowering the transmission rate is used. The transmission rate is lowered by checking whether the number of slots exists continuously. For this reason, even if each mobile station independently reduces the transmission rate and increases the number of slots used by one mobile station, it is possible to avoid overlapping slots used by the mobile stations. Therefore, even if the base station does not control each mobile station, it is possible to avoid the transmission data transmitted by each mobile station from overlapping, so that communication quality can be ensured.

  In addition, the communication device is a use slot in which the slot immediately after the own occupancy slot is used by transmission data, the slot immediately before the own occupancy slot is an empty slot, and the transmission data corresponding to the slot before the own occupancy slot Is provided with self-occupied slot changing means for changing the self-occupied slot to a slot before the self-occupied slot when it continues for more than the number of empty slots necessary for lowering the transmission rate.

  In the present invention, even if the slot immediately after the self-occupied slot is a used slot, the slot immediately before the self-occupied slot continues more than the number of empty slots necessary when the data before the self-occupied slot lowers the transmission rate. If it is free, the self-occupied slot is changed to advance the transmission timing. For this reason, since the slot immediately after the self-occupied slot becomes an empty slot, the transmission rate can be changed thereafter. Therefore, even if the base station does not control each mobile station, the transmission path can be used efficiently.

  Further, the transmission rate changing means transmits the transmission rate of the transmission data corresponding to the own occupied slot only when the transmission rate of the transmission data corresponding to the own occupied slot is larger than the transmission rate of the transmission data after the own occupied slot. Is trying to lower.

  As described above, according to the present invention, in addition to the empty state of the slot behind the self-occupied slot, the use state of the transmission path between the mobile stations is controlled using the transmission rate of the transmission data. The operation of decreasing the transmission rate and increasing the number of slots used by transmission data is performed only when the transmission rate is higher than the transmission rate of the rear transmission data. As a result, when there is an empty slot between the transmission data, it is possible to reliably avoid using the same empty slot for both transmission data even if the base station does not control each mobile station.

  The own-occupied slot changing means changes the own-occupied slot when the transmission rate of the transmission data corresponding to the own-occupied slot is larger than the transmission rate of the transmission data before the own-occupied slot. .

  As described above, according to the present invention, in addition to the vacant status in front of the own occupying slot, the usage status of the transmission path between the mobile stations is controlled using the transmission rate of the transmission data. The operation for changing the own slot can be performed only when the transmission rate is higher than the transmission rate of the forward transmission data. As a result, when there is an empty slot between the transmission data, it is possible to reliably avoid using the same empty slot for both transmission data even if the base station does not control each mobile station.

  Advantageous Effects of Invention According to the present invention, in communication between mobile stations that do not have a base station, it is easy to ensure an appropriate number of mobile stations that can communicate efficiently by using a transmission path and to ensure good communication quality. Can be realized.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
1 is a schematic configuration diagram of a communication device according to the first embodiment of the present invention, FIG. 2 is a frame configuration diagram used by the communication device, and FIG. 3 is a packet configuration diagram used by the communication device. The communication device 1 according to the present embodiment is used when communication devices directly communicate with each other in a TDMA (Time Division Multiple Access) communication system. For example, the communication device 1 is mounted on a vehicle (mobile station) and performs broadcast communication. It is a device used for inter-vehicle communication. The communication device 1 is a device that transmits and receives each communication device in units of packets, and transmits and receives at a timing in units of frames configured by a predetermined number of slots. Here, a frame is configured by N slots. Yes. Note that N is an integral multiple of the number of slots used by the packet when the transmission rate is the slowest.

  The communication device 1 includes a packet receiving unit 10, a demodulating unit 13, a slot timing generating unit 11 (free slot detecting unit, own occupied slot changing unit), a transmission control unit 14 (free slot detecting unit, transmission rate changing unit), a memory 16 , A modulation unit 15 and a packet transmission unit 12 are provided.

  The packet receiving unit 10 receives a packet on the transmission path. As shown in FIG. 3A, the packet received by the packet receiver 10 is composed of a preamble D1, modulation identification information D2, and data D3. Here, the packet before modulation has a fixed length. The packet receiving unit 10 has a function of inputting a packet from a receiving antenna 20 that receives a packet converted into a radio frequency band signal and converting the packet to a low frequency such as an intermediate frequency band or a baseband. The packet receiver 10 has a function of outputting the received packet to the demodulator 13. Further, the packet receiving unit 10 has a function of outputting timing information for detecting a packet to the slot timing generating unit 11.

  The demodulator 13 demodulates the source waveform data. The demodulator 13 has a function of inputting a packet from the packet receiver 10, identifying a signal modulation method from the modulation identification information included in the packet, demodulating with the identified modulation method, and extracting received data Yes. Here, 16QAM, QPSK, or BPSK is used as the modulation method. For example, a packet modulated with BPSK is shown in FIG. 3B, and information indicating that it has been modulated with BPSK is stored in the modulation identification information D23. A packet modulated with BPSK is shown in FIG. 3C, and information indicating that it has been modulated with QPSK is stored in the modulation identification information D22. Further, a packet modulated by 16QAM is shown in FIG. 3D, and information indicating that it is modulated by 16QAM is stored in the modulation identification information D21. The data parts D31, D32, and D33 modulated by the respective modulation schemes use one slot for 16QAM, two slots for QPSK, and four slots for BPSK when the time for occupying the transmission path is time-divided in slot units. That is, 16QAM, QPSK, and BPSK are used in descending order of the modulation multilevel number. When modulated with 16QAM, the transmission rate is larger than when modulated with QPSK and BPSK, and the transmission rate decreases in the order of QPSK and BPSK. Note that the number N of slots forming the above-described frame is an integral multiple of 4 because the number of slots used when modulation is performed with BPSK having the slowest transmission rate. The demodulator 13 has a function of outputting the extracted received data to the data input unit 23 provided in the application or the like. Further, the demodulator 13 has a function of outputting the identified modulation scheme to the transmission controller 14.

  The slot timing generation unit 11 generates slot timing of the communication device 1. The slot timing generation unit 11 has a function of generating slot timing based on the timing information input from the packet reception unit 10. Specifically, the slot timing generation unit 11 has a cycle counter having a cycle equal to the slot length, and the timing at which a packet transmitted by another communication device is detected is set as the start timing of the cycle counter of the communication device 1. It has a function.

  Further, the slot timing generation unit 11 has a number counter with a period N for measuring the number of slots received from the start of reception, and has a function of associating the measured number of slots with a received packet as a slot number. . Hereinafter, the function of associating the slot number with the received packet will be described with reference to FIG. As shown in FIG. 2, it is assumed that terminals A, B, and C equipped with the communication device 1 receive a frame with a period N. As shown in FIG. 2A, it is assumed that the frame is composed of slots indicated by S1 to S (N), terminal A starts receiving from S3, terminal B starts from S5, and terminal C starts receiving from S8. In this case, as shown in FIG. 2 (b), the terminal A adds 1 to the number counter every time it receives a slot in order from the first slot S3, and if there is a received packet, The number counter corresponding to the occupied slot is associated with the received packet as the slot number. Terminals B and C perform the same operation. Thus, for example, since the slot indicated by S9 in FIG. 2A is the seventh slot received from the head in terminal A, slot number 7 is received, and the terminal B is received fifth from the head. Since it is a slot, the slot number is 5, and in the terminal C, it is the slot received second from the head, so that it is a slot number 2. As described above, the slot number is a unique number that each terminal uniquely has for identifying the slot. Further, since the slot number has a period N, it is possible to input a packet for one frame by receiving the Nth slot from the start of reception. Further, the slot timing generation unit 11 has a function of outputting the slot number of the received packet to the transmission control unit 14. Further, it has a function of inputting a slot transmitted by the communication apparatus 1 from the communication control unit 14 and outputting a transmission timing to the packet transmission unit 12.

  The transmission control unit 14 performs control for transmitting a packet. The slot number received from the slot timing generator 11 and the modulation method from the modulator 13 are input and output to the memory 16. Specifically, the transmission control unit 14 sequentially outputs the slot number received from the slot timing generation unit 11 to the memory, and when the modulation scheme is input from the modulation unit 13, the transmission control unit 14 corresponds to the slot number corresponding to the packet. Then, the modulation method is output to the memory 16. Since this operation is repeated up to the slot number cycle N, the memory 16 stores the slot number for one frame, or the slot number and modulation method. By storing in this way, it is possible to determine that a slot number in which no modulation method is stored is an empty slot. The transmission control unit 14 has a function of inputting information for one frame stored in the memory 16 and calculating a ratio of empty slots in one frame. Further, the transmission control unit 14 performs communication based on the calculated ratio of empty slots, the number of empty slots before and after the packet transmitted by the communication device 1, and the modulation scheme of the packets before and after the packet transmitted by the communication device 1. The apparatus 1 has a function of determining a modulation method and a slot of a packet to be transmitted. Further, it has a function of outputting the modulation scheme of the packet to be transmitted to the modulator 15 and the slot of the packet to be transmitted to the slot timing generator 11.

  The modulation unit 15 modulates transmission data. The modulation unit 15 has a function of modulating the transmission data input from the transmission data output unit 24 included in the data output application based on the modulation method input from the transmission control unit 14. The modulation unit 15 has a function of outputting the modulated transmission data to the packet transmission unit 12.

  The packet transmission unit 12 transmits a packet on the transmission path. The packet transmission unit 12 converts transmission data including a low frequency signal input from the modulation unit 15 into a radio frequency band signal, and transmits a radio frequency band signal at the transmission timing input from the slot timing generation unit 11. A function of outputting to the antenna 21 is provided.

  Next, the operation of the communication apparatus according to the first embodiment will be described.

  4 and 6 are flowcharts showing the operation of the communication apparatus 1, and FIG. 5 is a table showing the operation of lowering the transmission rate of the communication apparatus 1. The control process shown in FIG. 4 is repeatedly executed at predetermined intervals, for example, at the timing when the communication device 1 is powered on. Note that the slot timing of the communication device 1 and the slot timing of another communication device that transmits and receives to / from the communication device 1 are assumed to be synchronized using the respective period counters.

  The communication device 1 starts processing from step 10 in FIG. The process of step 10 is a process that is executed by the packet receiver 10 and the slot timing generator 11 and receives a packet on the transmission path. The packet receiver 10 performs a process of receiving a packet, and the slot timing generator 11 performs a process of counting the input slots and outputting them to the transmission control process 14. When the process of step 10 is completed, the process proceeds to a modulation scheme detection process (step 12).

  The process of step 12 is executed by the demodulator 13 and detects the modulation method of the received packet. For example, when the packet shown in FIG. 3B is received, reception synchronization is established by the preamble D11, and D21 modulated by a predetermined modulation scheme is demodulated. Since the modulation method stored in D21 is BPSK, the data of D31 is demodulated by BPSK and the modulation method is output to the transmission control unit 14. Note that the processing of step 10 and step 12 is repeated until reception of a packet corresponding to the period of one frame is completed, and the slot number and modulation scheme for one frame are stored in the memory 16 by the transmission control unit 14. When the process of step 12 is completed, the process proceeds to a calculation process for the availability (step 14).

  The process of step 14 is a process which is executed by the transmission control unit 14 and calculates a free state in one frame. The memory 16 stores the slot number and modulation method in one frame input in the processing of step 10 and step 12, and calculates the ratio of empty slots in one frame based on the data input from the memory 16. To do. Also, the vacant slots before and after the packet output by the communication device 1 are detected. If the vacant slots are available, the number of empty slots is detected. When the process of step 14 is completed, the process proceeds to a free space determination process (step 16).

  The process of step 16 is a process that is executed by the transmission control unit 14 to determine the availability in one frame. This process is a process for determining whether the ratio of empty slots in one frame is equal to or greater than a predetermined value. For example, 40% is set as the predetermined value. When it is determined that the ratio of empty slots in one frame is equal to or greater than a predetermined value, the process proceeds to transmission slot determination processing (step 20).

  The process of step 20 is executed by the transmission control unit 14 and is a process of determining a slot of transmission data and a process of changing a modulation method of transmission data. In the following, considering the ease of understanding the description, the processing of step 20 will be described using the table shown in FIG.

  The transmission data slot determination process and the process of changing the transmission rate are performed by the modulation method of the packet (own packet) transmitted by the transmission apparatus 1, the modulation method of the packets before and after the own packet (forward packet, backward packet), And based on the number of empty slots before and after the slot used by the own packet (self-occupied slot). Specifically, the process for lowering the transmission rate is performed when there is a sufficient space in the rear slot of the own packet, and the slot used by the own packet and the rear slot that is free are used. In the slot determination process, the slot is changed when there is not enough space in the rear slot of the own packet, and the own occupied slot is changed to the front slot. Here, the slot determination process and the modulation scheme change process are performed with priority given to the transmission apparatus 1 that is transmitting by a modulation scheme having a large modulation multi-level number.

  A table shown in FIG. 5 shows the operation of the transmission apparatus 1 in more detail. The table shown in FIG. 5 describes all combinations of modulation schemes and the number of empty slots, and operations at that time. Note that a hatched condition means that the condition is not judged.

  First, a case where the modulation method of the own packet is 16QAM will be described. Numbers 1-1 to 1-5 in FIG. 5 describe combinations when the modulation scheme of the own packet is 16QAM.

  In the case of the number 1-1, that is, regardless of the modulation method of the forward packet and the backward packet, the number of empty slots ahead of the own occupied slot (the number of empty front slots) is 0, and the number of empty slots behind the own occupied slot ( If the number of backward slots is 0), the frame up to a predetermined number of times stored in the memory and the received frame are compared with each other, and it is determined whether there is any change in the slot usage status of other communication devices. to decide. If it is determined that there is no change, it is expected that the frame usage will remain the same, so if there are consecutive vacant slots in the frame, the slot numbers to be transmitted are continuously vacant. Change to slot number. In this way, by changing the slot number, the transmission timing of the packet transmitted from the communication device 1 is changed. On the other hand, when it is determined that there is a change, the slot number to be transmitted and the modulation scheme to be transmitted are not changed.

  In the case of the number 1-2, that is, when the modulation scheme of the front packet is 16QAM, the number of front empty slots is 1, and the number of rear empty slots is 0, the front packet may use the front empty slots. Therefore, the slot number to be transmitted and the modulation scheme to be transmitted are not changed.

  In the case of numbers 1-3, that is, when the modulation scheme of the forward packet is QPSK or BPSK, the front empty slot number is 1 and the rear empty slot number is 0, the front packet can use the front empty slot. Since there is no possibility, the slot number to be transmitted is changed to a number obtained by subtracting 1 from the occupied slot number so that the modulation method can be changed thereafter. In this way, by changing the slot number, the transmission timing of the packet transmitted from the communication device 1 is changed.

  In the case of the numbers 1-4, that is, when the number of free front slots is 2 or more and the number of free back slots is 0 regardless of the modulation method of the front packet and the back packet, the front packet uses the front free slot. Since there is no possibility, the slot number to be transmitted is changed to a number obtained by subtracting 1 from the self-occupied slot number so that the modulation scheme can be changed thereafter. In this way, by changing the slot number, the transmission timing of the packet transmitted from the communication device 1 is changed.

  In the case of numbers 1-5, that is, regardless of the modulation schemes of the front packet and the rear packet, when the number of rear empty slots is 1 or more, the modulation scheme to be transmitted is changed to QPSK in order to effectively use the rear empty slots. change. In this case, the modulation system is changed so that the head slot of the own slot does not change. Further, the transmission rate of transmission is reduced by changing the modulation method to QPSK.

  Next, a case where the modulation method of the own packet is QPSK will be described. Numbers 2-1 to 2-12 in FIG. 5 describe combinations when the modulation scheme of the own packet is QPSK.

  In the case of the number 2-1, that is, when at least one of the modulation schemes of the forward packet and the backward packet is 16QAM, the forward packet and the backward packet may use the forward empty slot and the backward empty slot. Therefore, the slot number to be transmitted and the modulation scheme to be transmitted are not changed.

  In the case of the number 2-2, that is, when the modulation method of the forward packet and the backward packet is QPSK or BPSK, the number of free front slots is 0, and the number of free back slots is 0, the control process of FIG. It is determined whether or not there is a change in the slot of another communication device in the frame after the number of executions. If it is determined that there is no change, the same state is expected to be maintained. Therefore, if there are three or more consecutive slots in the frame, three or more slot numbers to be transmitted are continuously available. Change the slot number. In addition, when there are no three or more consecutive slots in the frame, the slot number to be transmitted and the modulation scheme to be transmitted are not changed. On the other hand, when it is determined that there is a change, the slot number to be transmitted and the modulation scheme to be transmitted are not changed.

  In the case of the number 2-3, that is, when the modulation method of the forward packet and the backward packet is QPSK or BPSK, the number of free front slots is 1 and the number of free back slots is 0, the front packet has a front free slot. Since there is a possibility of use, the slot number to be transmitted and the modulation scheme to be transmitted are not changed.

  In the case of numbers 2-4, that is, when the modulation scheme of the front packet is QPSK, the modulation scheme of the rear packet is QPSK or BPSK, the number of front empty slots is 2 or 3, and the number of rear empty slots is 0 In this case, since there is a possibility that the front packet uses a front empty slot, the slot number to be transmitted and the modulation scheme to be transmitted are not changed.

  In the case of number 2-5, that is, when the modulation scheme of the front packet is QPSK, the modulation scheme of the rear packet is QPSK or BPSK, the number of front empty slots is 4 or more, and the number of rear empty slots is 0 Even if the front packet uses a front empty slot, at least two front empty slots remain, so that the slot number to be transmitted is subtracted from the own slot number so that the modulation scheme can be changed thereafter. Change to a number. In this way, by changing the slot number, the transmission timing of the packet transmitted from the communication device 1 is changed.

  In the case of number 2-6, that is, when the modulation scheme of the front packet is BPSK, the modulation scheme of the rear packet is QPSK or BPSK, the number of front empty slots is 2 or more, and the number of rear empty slots is 0 Since there is no possibility that the front packet uses the front empty slot, the slot number to be transmitted is changed to a number obtained by subtracting 2 from the own occupied slot number so that the modulation scheme can be changed thereafter. In this way, by changing the slot number, the transmission timing of the packet transmitted from the communication device 1 is changed.

  In the case of number 2-7, that is, when the modulation scheme of the front packet and the rear packet is QPSK or BPSK, the number of front empty slots is 0, and the number of rear empty slots is 1, the number of rear empty slots is the modulation scheme. Since there are not enough empty slots necessary to change to BPSK, the slot number to be transmitted and the modulation scheme to be transmitted are not changed.

  In the case of number 2-8, that is, when the modulation scheme of the front packet is QPSK, the modulation scheme of the rear packet is QPSK or BPSK, the number of free front slots is 1, and the number of free back slots is 1. Since there is no possibility that the front packet uses the front empty slot, the slot number to be transmitted is changed to a number obtained by subtracting 1 from the own occupied slot number so that the modulation scheme can be changed thereafter. In this way, by changing the slot number, the transmission timing of the packet transmitted from the communication device 1 is changed.

  In the case of number 2-9, that is, when the modulation scheme of the forward packet is QPSK, the modulation scheme of the backward packet is QPSK or BPSK, the number of free front slots is 2, and the number of free back slots is 1. There is a possibility that the front packet may use a front empty slot, and the number of empty back slots is not enough to change the modulation method to BPSK, so the slot number to be transmitted and the modulation method to be transmitted are changed. do not do.

  In the case of number 2-10, that is, when the modulation method of the front packet is QPSK, the modulation method of the rear packet is QPSK or BPSK, the number of front empty slots is 3 or more, and the number of rear empty slots is 1. Since there is no possibility that the front packet uses the front empty slot immediately before the own occupied slot, the slot number to be transmitted is changed to a number obtained by subtracting 1 from the own occupied slot number so that the modulation scheme can be changed thereafter. . In this way, by changing the slot number, the transmission timing of the packet transmitted from the communication device 1 is changed.

  In the case of numbers 2-11, that is, when the modulation scheme of the front packet is BPSK, the modulation scheme of the rear packet is QPSK or BPSK, the number of front empty slots is 1 or more, and the number of rear empty slots is 1. Since there is no possibility that the front packet uses the front empty slot, the slot number to be transmitted is changed to a number obtained by subtracting 1 from the own occupied slot number so that the modulation scheme can be changed thereafter. In this way, by changing the slot number, the transmission timing of the packet transmitted from the communication device 1 is changed.

  In the case of number 2-12, that is, when the modulation scheme of the front packet and the rear packet is QPSK or BPSK and the number of rear empty slots is 2 or more, the modulation scheme to be transmitted in order to effectively use the rear empty slots To BPSK. In this case, the modulation system is changed so that the head slot of the own slot does not change. Further, the transmission rate of transmission is reduced by changing the modulation method to BPSK.

  Next, a case where the modulation method of the own packet is BPSK will be described. Numbers 3-1 and 3-2 in FIG. 5 describe combinations when the modulation scheme of the own packet is BPSK.

  In the case of number 3-1, that is, when the modulation scheme of the forward packet is 16QAM or QPSK, the forward packet may use a front empty slot, so the slot number to be transmitted and the modulation scheme to be transmitted are not changed. .

  In the case of number 3-2, that is, when the forward packet modulation scheme is BPSK and the number of front empty slots is an integer n, n is set to BPSK in order to make the empty channel continuous and to make it easy to use the transmission path. The slot number to be transmitted is a value obtained by dividing the number of occupied slots by 4 and subtracting the remainder from the occupied slot number. In this way, by changing the slot number, the transmission timing of the packet transmitted from the communication device 1 is changed.

  This completes the transmission slot determination process and the modulation scheme change process, which are the processes of step 20 in FIG. Returning to FIG. 4, when the processing of step 20 is completed, the routine proceeds to transmission data input processing (step 26).

  The process of step 26 is executed by the modulation unit 15 and is a process for inputting transmission data from the transmission data output unit 24. When the process of step 26 is completed, the process proceeds to a transmission data modulation process (step 28).

  The process of step 28 is a process which is executed by the modulation unit 15 and modulates transmission data by the modulation method determined in step 20 or step 24 (described later). When the process of step 28 is completed, the process proceeds to a packet transmission process (step 30).

  The process in step 30 is executed by the packet transmission unit 12 to transmit a packet. In the process of step 30, the modulation number information including the modulation method used in step 28 and the preamble that is the synchronization signal are added to the data modulated in step 28, and the slot number used in step 20 or the previous packet transmission process This is a process for transmitting a packet. When the process of step 30 ends, the communication device 1 ends the control process of FIG.

  On the other hand, when it is determined in the process of step 16 that the ratio of empty slots in one frame is equal to or greater than a predetermined value, the process proceeds to an empty state determination process (step 22).

  The process of step 22 is executed by the transmission control unit 14 and is a process for determining the availability of one frame. This process is a process for determining whether or not the ratio of empty slots in one frame is equal to or less than a predetermined value. For example, 10% is set as the predetermined value. When it is determined that the ratio of empty slots in one frame is equal to or less than a predetermined value, the process proceeds to transmission slot determination processing and modulation scheme change processing (step 24).

  The process of step 24 is executed by the transmission control unit 14 and is a process of changing the modulation method so as to increase the transmission rate in order to increase the number of accommodated terminals in one frame. Further, it is a process for determining a transmission slot. As shown in FIG. 6, this process is executed from the BPSK confirmation process (step 32). The process of step 32 is a process of determining whether or not the modulation method of the communication apparatus 1 is BPSK. When the modulation method of the communication apparatus 1 is BPSK, the process shifts to QPSK change processing in order to increase the transmission rate (step 34).

  The process of step 34 is a process of changing the modulation scheme to be transmitted to QPSK. When the processing of step 34 is completed, the routine proceeds to transmission slot determination processing (step 40).

  The process of step 40 is a process in which the head slot number of the slot to be transmitted next time is set to the head number of the slot transmitted last time. When the process of step 40 is finished, the transmission slot determination process and the modulation scheme change process are finished.

  On the other hand, if it is determined in step 32 that the modulation method of the communication apparatus 1 is not BPSK, the process proceeds to QPSK confirmation processing (step 36). The process of step 36 is a process of determining whether or not the modulation method of the communication apparatus 1 is QPSK. When the modulation method of the communication apparatus 1 is QPSK, the process shifts to 16QAM change processing to increase the transmission rate (step 38).

  The process of step 38 is a process of changing the modulation scheme to be transmitted to 16QAM. When the processing of step 38 is completed, the routine proceeds to transmission slot determination processing (step 40).

  On the other hand, if it is determined in step 36 that the modulation method of the communication apparatus 1 is not QPSK, the transmission rate is 16QAM, which is the highest, and the transmission rate cannot be increased any more. (Step 40).

  Thus, the transmission slot determination process and the modulation scheme change process in step 24 in FIG. 4 are completed. Returning to FIG. 4, when the processing of step 24 is completed, the routine proceeds to transmission data input processing (step 26).

  On the other hand, if it is determined in step 22 that the ratio of empty slots in one frame is not less than or equal to a predetermined value, the current transmission timing and modulation scheme are efficiently communicated using the transmission path. The process proceeds to the transmission data input process (step 26).

  Thus, the operation of the communication device 1 ends. By performing the above operation, the mobile station on which the communication device 1 is mounted can autonomously check the free state on the transmission line and change the transmission rate by changing the modulation method. It is possible to ensure good communication quality while using it efficiently.

  Next, the effect of the communication apparatus according to the first embodiment will be described.

  FIG. 7 is a schematic diagram showing the frame usage status, and shows the usage status of a frame composed of 24 slots in the order of (a) to (i). In FIG. 7, in consideration of easy understanding of the explanation, it is assumed that the slot numbers uniquely possessed by the communication devices installed in the respective mobile stations are the same.

  As shown in FIG. 7A, mobile stations C1 to C8 each equipped with a communication device 1 communicate using a transmission path. The mobile station C1 packetizes data modulated by 16QAM and transmits it using slot number 4. The mobile station C2 packetizes data modulated by 16QAM and transmits it using the slot number 5. The mobile station C3 packetizes data modulated by 16QAM and transmits it using the slot number 9. The mobile station C4 packetizes data modulated by 16QAM and transmits it using the slot number 11. The mobile station C5 packetizes the data modulated by 16QAM and transmits it using the slot number 13. The mobile station C6 packetizes the data modulated by 16QAM and transmits it using the slot number 15. The mobile station C7 packetizes data modulated by 16QAM and transmits it using the slot number 16. The mobile station C8 packetizes the data modulated by 16QAM and transmits it using the slot number 22. Each of the mobile stations C1 to C8 receives the frame shown in FIG. 7A and performs the control process shown in FIG.

  In (a) of FIG. 7, since the empty situation in the frame is about 67%, each mobile station performs control according to the table shown in FIG. Focusing on the mobile station C1, its own packet is 16QAM, the forward packet is 16QAM (mobile station C8), the backward packet is 16QAM, the number of free front slots is 5, and the number of free back slots is 0. Corresponds to table numbers 1-4. Therefore, the communication device 1 of the mobile station C1 changes the transmission start slot number from 4 to 3 and transmits in the next frame.

  Further, focusing on the mobile station C2, since the own packet is 16QAM, the forward packet is 16QAM, the backward packet is 16QAM, the number of free front slots is 0, and the number of free back slots is 3, the number of the table shown in FIG. It corresponds to 1-5. Therefore, the communication device 1 of the mobile station C2 changes the modulation method to QPSK and transmits in the next frame.

  Focusing on the mobile station C3, since the own packet is 16QAM, the forward packet is 16QAM, the backward packet is 16QAM, the number of free front slots is 3, and the number of free back slots is 1, the number of the table shown in FIG. It corresponds to 1-5. Therefore, the communication device 1 of the mobile station C3 changes the modulation method to QPSK and transmits in the next frame.

  Focusing on the mobile station C4, since the own packet is 16QAM, the forward packet is 16QAM, the backward packet is 16QAM, the number of free front slots is 1, and the number of free back slots is 1, the number of the table shown in FIG. It corresponds to 1-5. Therefore, the communication device 1 of the mobile station C4 changes the modulation method to QPSK and transmits in the next frame.

  Focusing on the mobile station C5, since the own packet is 16QAM, the forward packet is 16QAM, the backward packet is 16QAM, the number of free front slots is 1, and the number of free back slots is 1, the number of the table shown in FIG. It corresponds to 1-5. Therefore, the communication device 1 of the mobile station C5 changes the modulation method to QPSK and transmits in the next frame. Here, it is assumed that the mobile station C5 has moved to a range where the transmission path shared by the mobile stations C1 to C8 does not reach before the next frame, or cannot communicate due to power OFF. In this case, the packet transmitted by the communication device 1 of the mobile station C5 does not exist on the next frame (disappears).

  Focusing on the mobile station C6, since the own packet is 16QAM, the forward packet is 16QAM, the backward packet is 16QAM, the number of free front slots is 1, and the number of free back slots is 0, the table number shown in FIG. It corresponds to 1-2. Therefore, the communication device 1 of the mobile station C6 transmits without changing the modulation scheme and the slot number in the next frame.

  Focusing on the mobile station C7, since the own packet is 16QAM, the forward packet is 16QAM, the backward packet is 16QAM, the number of free front slots is 0, and the number of back free slots is 5, the number of the table shown in FIG. It corresponds to 1-5. Therefore, the communication device 1 of the mobile station C7 changes the modulation method to QPSK and transmits in the next frame.

  Focusing on the mobile station C8, since the own packet is 16QAM, the forward packet is 16QAM, the backward packet is 16QAM (mobile station C1), the number of free front slots is 5, and the number of free back slots is 5, FIG. Corresponds to the numbers 1-5 in the table shown in FIG. Therefore, the communication apparatus 1 of the mobile station C8 changes the modulation method to QPSK and transmits in the next frame.

  As described above, the mobile stations C1 to C8 that have received the frame shown in FIG. 7A operate as described above to form the next frame shown in FIG. 7B.

  Next, the operation of each mobile station that has received the frame shown in FIG. In FIG. 7B, since the empty state in the frame is 50%, each mobile station performs control according to the table shown in FIG. Focusing on the mobile station C1, since its own packet is 16QAM, the forward packet is QPSK (mobile station C8), the backward packet is QPSK, the number of forward empty slots is 1, and the number of backward empty slots is 1, it is shown in FIG. Corresponds to table numbers 1-5. Therefore, the communication device 1 of the mobile station C1 changes the modulation method to QPSK and transmits in the next frame.

  Further, focusing on the mobile station C2, since the own packet is QPSK, the forward packet is 16QAM, the backward packet is QPSK, the number of free front slots is 1, and the number of free back slots is 2, the number of the table shown in FIG. It corresponds to 2-1. Therefore, the communication device 1 of the mobile station C2 transmits the next frame without changing the modulation scheme and the slot number. Here, it is assumed that the mobile station C2 moves to a range where the transmission path shared by each mobile station does not reach before the next frame, or becomes incapable of communication when the power is turned off. In this case, the packet transmitted by the communication device 1 of the mobile station C2 does not exist on the next frame (disappears).

  Focusing on the mobile station C3, since the own packet is QPSK, the forward packet is QPSK, the backward packet is QPSK, the number of free front slots is 2, and the number of free back slots is 0, the table number shown in FIG. It corresponds to 2-4. Therefore, the communication device 1 of the mobile station C3 transmits without changing the modulation scheme and the slot number in the next frame.

  Focusing on the mobile station C4, since the own packet is QPSK, the forward packet is QPSK, the backward packet is 16QAM, the number of free front slots is 0, and the number of free back slots is 2, the table numbers shown in FIG. It corresponds to 2-1. Therefore, the communication device 1 of the mobile station C4 transmits without changing the modulation scheme and the slot number in the next frame.

  Focusing on the mobile station C6, since the own packet is 16QAM, the forward packet is QPSK, the backward packet is QPSK, the number of free front slots is 2, and the number of free back slots is 0, the table number shown in FIG. It corresponds to 1-4. Therefore, the communication device 1 of the mobile station C6 changes the transmission start slot number from 15 to 14 and transmits in the next frame.

  Focusing on the mobile station C7, since the own packet is QPSK, the forward packet is 16QAM, the backward packet is QPSK, the forward empty slot number is 0, and the backward empty slot number is 4, the number of the table shown in FIG. It corresponds to 2-1. Therefore, the communication device 1 of the mobile station C7 transmits without changing the modulation scheme and the slot number in the next frame.

  Focusing on the mobile station C8, since the own packet is QPSK, the forward packet is QPSK, the backward packet is 16QAM (mobile station C1), the number of free front slots is 4, and the number of free back slots is 3, FIG. Corresponds to the number 2-1 in the table shown in FIG. Therefore, the communication device 1 of the mobile station C8 transmits without changing the modulation scheme and the slot number in the next frame.

  As described above, each mobile station that has received the frame shown in (b) of FIG. 7 operates as described above to form the next frame shown in (c) of FIG.

  Next, the operation of each mobile station that has received the frame shown in FIG. In FIG. 7 (c), since the empty state in the frame is 54%, each mobile station performs control according to the table shown in FIG. Focusing on the mobile station C1, since its own packet is QPSK, the forward packet is QPSK (mobile station C8), the backward packet is QPSK, the number of free front slots is 4, and the number of free back slots is 4, it is shown in FIG. Corresponds to table number 2-12. Therefore, the communication device 1 of the mobile station C1 changes the modulation method to BPSK and transmits in the next frame.

  Focusing on the mobile station C3, since the own packet is QPSK, the forward packet is QPSK, the backward packet is QPSK, the forward empty slot number is 4, and the backward empty slot number is 0, the table number shown in FIG. It corresponds to 2-5. Therefore, the communication device 1 of the mobile station C3 changes the transmission start slot number from 9 to 7 and transmits in the next frame.

  Further, focusing on the mobile station C4, since the own packet is QPSK, the forward packet is QPSK, the backward packet is 16QAM, the forward empty slot number is 0, and the backward empty slot number is 1, the number of the table shown in FIG. It corresponds to 2-1. Therefore, the communication device 1 of the mobile station C4 transmits without changing the modulation scheme and the slot number in the next frame.

  Focusing on the mobile station C6, since the own packet is 16QAM, the forward packet is QPSK, the backward packet is QPSK, the forward empty slot number is 1, and the backward empty slot number is 1, the number of the table shown in FIG. It corresponds to 1-5. Therefore, the communication device 1 of the mobile station C6 changes the modulation method to QPSK and transmits in the next frame.

  Focusing on the mobile station C7, since the own packet is QPSK, the forward packet is 16QAM, the backward packet is QPSK, the number of forward empty slots is 1, and the number of backward empty slots is 4, the number of the table shown in FIG. It corresponds to 2-1. Therefore, the communication device 1 of the mobile station C7 transmits without changing the modulation scheme and the slot number in the next frame. Here, it is assumed that the mobile station C7 has moved to a range where the transmission path shared by each mobile station does not reach before the next frame, or cannot communicate due to power OFF. In this case, the packet transmitted by the communication device 1 of the mobile station C7 does not exist on the next frame (disappears).

  Focusing on the mobile station C8, since the own packet is QPSK, the forward packet is QPSK, the backward packet is QPSK (mobile station C1), the number of free front slots is 4, and the number of free back slots is 3, FIG. Corresponds to the number 2-12 of the table shown in FIG. Therefore, the communication device 1 of the mobile station C7 changes the modulation method to BPSK and transmits in the next frame. Here, it is assumed that the mobile station C8 has moved to a range where the transmission path shared by each mobile station does not reach before the next frame, or cannot communicate due to power OFF. In this case, the packet transmitted by the communication device 1 of the mobile station C8 does not exist on the next frame (disappears).

  As described above, each mobile station that has received the frame shown in FIG. 7C operates as described above to form the next frame shown in FIG.

  Next, the operation of each mobile station that has received the frame shown in FIG. In FIG. 7 (d), since the empty state in the frame is 58%, each mobile station performs control according to the table shown in FIG. Focusing on the mobile station C1, since its own packet is BPSK, the forward packet is QPSK (mobile station C6), the backward packet is QPSK, the forward empty slot number is 11 and the backward empty slot number is 0, it is shown in FIG. Corresponds to table number 3-1. Therefore, the communication device 1 of the mobile station C1 transmits without changing the modulation scheme and the slot number in the next frame.

  Focusing on the mobile station C3, since the own packet is QPSK, the forward packet is BPSK, the backward packet is QPSK, the forward empty slot number is 0, and the backward empty slot number is 2, the table number shown in FIG. It corresponds to 2-12. Therefore, the communication device 1 of the mobile station C3 changes the modulation method to QPSK and transmits in the next frame.

  Further, focusing on the mobile station C4, since the own packet is QPSK, the forward packet is QPSK, the backward packet is QPSK, the forward empty slot number is 2, and the backward empty slot number is 1, the number of the table shown in FIG. It corresponds to 2-9. Therefore, the communication device 1 of the mobile station C4 transmits without changing the modulation scheme and the slot number in the next frame.

  Focusing on the mobile station C6, since the own packet is QPSK, the forward packet is QPSK, the backward packet is BPSK (mobile station C1), the number of free front slots is 1, and the number of free back slots is 11, FIG. Corresponds to the number 2-12 of the table shown in FIG. Therefore, the communication device 1 of the mobile station C6 changes the modulation method to BPSK and transmits in the next frame.

  As described above, each mobile station that has received the frame shown in FIG. 7D operates as described above to form the next frame shown in FIG.

  Next, the operation of each mobile station that has received the frame shown in FIG. In FIG. 7 (e), since the free space in the frame is 41%, each mobile station performs control according to the table shown in FIG. Focusing on the mobile station C1, since its own packet is BPSK, the forward packet is BPSK (mobile station C6), the backward packet is BPSK, the number of free front slots is 9, and the number of free back slots is 0, it is shown in FIG. Corresponds to table number 3-2. Therefore, the communication device 1 of the mobile station C1 changes the slot number and transmits in the next frame. Since the current number of free slots is 9, the value obtained by subtracting the remainder 1 obtained by dividing 9 by 4 from the self-occupied slot number 3, that is, the slot number at the start of transmission is changed to 2, and transmitted.

  Focusing on the mobile station C3, since the own packet is BPSK, the forward packet is BPSK, the backward packet is QPSK, the forward empty slot number is 0, and the backward empty slot number is 0, the table number shown in FIG. This corresponds to 3-2. Therefore, the communication device 1 of the mobile station C3 changes the slot number and transmits in the next frame. Since the current number of free slots is 0, the value obtained by subtracting the remainder 0 obtained by dividing 0 by 4 from the self-occupied slot number 7, that is, the slot number at the start of transmission is changed to 7, and transmission is performed. In this case, the result is that there is no change in the slot number for starting transmission.

  Focusing on the mobile station C4, since the own packet is QPSK, the forward packet is BPSK, the backward packet is BPSK, the forward empty slot number is 0, and the backward empty slot number is 1, the number of the table shown in FIG. Corresponds to 2-7. Therefore, the communication device 1 of the mobile station C4 transmits without changing the modulation scheme and the slot number in the next frame.

  Focusing on the mobile station C6, since the own packet is BPSK, the forward packet is QPSK, the backward packet is BPSK (mobile station C1), the number of free slots is 1, and the number of free slots is 9, FIG. Corresponds to the number 3-1 in the table shown in FIG. Therefore, the communication device 1 of the mobile station C6 transmits without changing the modulation scheme and the slot number in the next frame.

  As described above, each mobile station that has received the frame shown in FIG. 7E operates as described above to form the next frame shown in FIG.

  Next, the operation of each mobile station that has received the frame shown in FIG. In (f) of FIG. 7, since the empty situation in the frame is 41%, each mobile station performs control according to the table shown in FIG. Focusing on the mobile station C1, since its own packet is BPSK, the forward packet is BPSK (mobile station C6), the backward packet is BPSK, the number of free front slots is 1, and the number of free back slots is 1, as shown in FIG. Corresponds to table number 3-2. Therefore, the communication device 1 of the mobile station C1 changes the slot number and transmits in the next frame. Since the current number of free slots is 8, the value obtained by subtracting the remainder 0 obtained by dividing 8 by 4 from the self-occupied slot number 3, that is, the transmission start slot number is changed to 3, and transmission is performed. In this case, the result is that there is no change in the slot number for starting transmission.

  Focusing on the mobile station C3, since the own packet is BPSK, the forward packet is BPSK, the backward packet is QPSK, the forward empty slot number is 1, and the backward empty slot number is 0, the number of the table shown in FIG. This corresponds to 3-2. Therefore, the communication device 1 of the mobile station C3 changes the slot number and transmits in the next frame. Since the current number of forward empty slots is 1, the value obtained by subtracting the remainder 1 obtained by dividing 1 by 4 from the self-occupied slot number 7, that is, the slot number at the start of transmission is changed to 6, and transmission is performed.

  Focusing on the mobile station C4, since the own packet is QPSK, the forward packet is BPSK, the backward packet is BPSK, the forward empty slot number is 0, and the backward empty slot number is 1, the number of the table shown in FIG. Corresponds to 2-7. Therefore, the communication device 1 of the mobile station C4 transmits without changing the modulation scheme and the slot number in the next frame.

  Focusing on the mobile station C6, since the own packet is BPSK, the forward packet is QPSK, the backward packet is BPSK (mobile station C1), the number of free front slots is 1, and the number of free back slots is 8, FIG. Corresponds to the number 3-1 in the table shown in FIG. Therefore, the communication device 1 of the mobile station C6 transmits without changing the modulation scheme and the slot number in the next frame.

  As described above, each mobile station that has received the frame shown in (f) of FIG. 7 operates as described above to form the next frame shown in (g) of FIG.

  Next, the operation of each mobile station that has received the frame shown in FIG. In (g) of FIG. 7, since the empty situation in the frame is 41%, each mobile station performs control according to the table shown in FIG. Focusing on the mobile station C1, since its own packet is BPSK, the forward packet is BPSK (mobile station C6), the backward packet is BPSK, the forward free slot number is 8, and the backward free slot number is 0, it is shown in FIG. Corresponds to table number 3-2. Therefore, the communication device 1 of the mobile station C1 changes the slot number and transmits in the next frame. Since the current number of free slots is 8, the value obtained by subtracting the remainder 0 obtained by dividing 8 by 4 from the self-occupied slot number 3, that is, the transmission start slot number is changed to 3, and transmission is performed. In this case, the result is that there is no change in the slot number for starting transmission.

  Focusing on the mobile station C3, since the own packet is BPSK, the forward packet is BPSK, the backward packet is QPSK, the forward empty slot number is 0, and the backward empty slot number is 1, the number of the table shown in FIG. This corresponds to 3-2. Therefore, the communication device 1 of the mobile station C3 changes the slot number and transmits in the next frame. Since the current number of free slots is 0, the value obtained by subtracting the remainder 0 obtained by dividing 0 by 4 from the self-occupied slot number 6, that is, the slot number at the start of transmission is changed to 6, and transmission is performed. In this case, the result is that there is no change in the slot number for starting transmission.

  Focusing on the mobile station C4, since the own packet is QPSK, the front packet is BPSK, the back packet is BPSK, the number of free front slots is 1, and the number of back free slots is 1, the number of the table shown in FIG. Corresponds to 2-8. Therefore, the communication device 1 of the mobile station C4 changes the transmission start slot number from 11 to 10 and transmits in the next frame.

  Focusing on the mobile station C6, since the own packet is BPSK, the forward packet is QPSK, the backward packet is BPSK (mobile station C1), the number of free front slots is 1, and the number of free back slots is 8, FIG. Corresponds to the number 3-1 in the table shown in FIG. Therefore, the communication device 1 of the mobile station C6 transmits without changing the modulation scheme and the slot number in the next frame.

  As described above, each mobile station that has received the frame shown in (g) of FIG. 7 operates as described above to form the next frame shown in (h) of FIG.

  Next, the operation of each mobile station that has received the frame shown in FIG. In (h) of FIG. 7, since the empty situation in the frame is 41%, each mobile station performs control according to the table shown in FIG. Focusing on the mobile station C1, since its own packet is BPSK, the forward packet is BPSK (mobile station C6), the backward packet is BPSK, the number of free front slots is 8, and the number of free back slots is 0, it is shown in FIG. Corresponds to table number 3-2. Therefore, the communication device 1 of the mobile station C1 changes the slot number and transmits in the next frame. Since the current number of free slots is 8, the value obtained by subtracting the remainder 0 obtained by dividing 8 by 4 from the self-occupied slot number 3, that is, the slot number at the start of transmission is changed to 3, and transmission is performed. In this case, the result is that there is no change in the slot number for starting transmission.

  Focusing on the mobile station C3, since the own packet is BPSK, the forward packet is BPSK, the backward packet is QPSK, the forward empty slot number is 0, and the backward empty slot number is 1, the number of the table shown in FIG. This corresponds to 3-2. Therefore, the communication device 1 of the mobile station C3 changes the slot number and transmits in the next frame. Since the current number of free slots is 0, the value obtained by subtracting the remainder 0 obtained by dividing 0 by 4 from the self-occupied slot number 6, that is, the slot number at the start of transmission is changed to 6, and transmission is performed. In this case, the result is that there is no change in the slot number for starting transmission.

  Focusing on the mobile station C4, since the own packet is QPSK, the forward packet is BPSK, the backward packet is BPSK, the forward empty slot number is 0, and the backward empty slot number is 2, the number of the table shown in FIG. It corresponds to 2-12. Therefore, the communication device 1 of the mobile station C4 changes the modulation method to BPSK and transmits in the next frame.

  Focusing on the mobile station C6, since the own packet is BPSK, the forward packet is QPSK, the backward packet is BPSK (mobile station C1), the number of free front slots is 2, and the number of free back slots is 8, FIG. Corresponds to the number 3-1 in the table shown in FIG. Therefore, the communication device 1 of the mobile station C6 transmits without changing the modulation scheme and the slot number in the next frame.

  As described above, each mobile station that has received the frame shown in (g) of FIG. 7 operates as described above to form the next frame shown in (i) of FIG.

  As shown in FIG. 7, the communication apparatus 1 provided in each mobile station autonomously determines the transmission timing and modulation scheme. Even when the transmission rate is lowered, it is possible to prevent the transmission packets from overlapping and interfering with each other by checking the modulation schemes and empty slots of the packets before and after the own packet. When the packet shown in (i) of FIG. 7 is received, the vacant state in the frame is 33%, so that the transmission rate is increased in order to increase the number of accommodated terminals in one frame. When the transmission rate is increased in this way, the operation is performed without changing the head of the transmission slot. For example, when the modulation method is QPSK and the own packet is transmitted using slot numbers 1 and 2, even if the modulation method is changed to 16QAM, the slot number of the own packet is 1, The timing of is not changed.

  As described above, according to the communication device 1 according to the first embodiment, the communication device 1 installed in each mobile station detects empty slots on the transmission path, and when there are few empty slots on the transmission path, The transmission rate of data transmitted by each mobile station is increased. For this reason, since other mobile stations can participate in communication, the number of mobile stations capable of communication can be maintained appropriately. Further, since the utilization rate of the transmission path decreases as the number of empty slots increases in the transmission path, the number of slots used by each mobile station is increased, and the data transmitted by the communication device 1 mounted on each mobile station is transmitted. The rate is falling. For this reason, it is possible to ensure communication quality while effectively utilizing the transmission path.

  In addition, according to the communication device 1 according to the first embodiment, the empty slot detection unit of the communication device 1 includes the period counter having a period equal to the time length of the slot and the number counter that counts the received order of the slots. In order to detect the vacant state in a frame composed of a predetermined number of slots, the number of vacant slots in one frame can be recognized without the base station controlling each mobile station.

  Further, according to the communication device 1 according to the first embodiment, when the transmission rate changing means of the communication device 1 decreases the transmission rate and increases the number of slots used by the transmission data, immediately after the own occupied slot. In the immediately following slot, it is used by checking whether there are consecutive empty slots necessary for lowering the transmission rate. For this reason, even if each mobile station independently reduces the transmission rate and increases the number of slots used by one mobile station, it is possible to avoid overlapping slots used by the mobile stations. Therefore, even if the base station does not control each mobile station, it is possible to avoid the transmission data transmitted by each mobile station from overlapping, so that communication quality can be ensured.

  Further, according to the communication device 1 according to the first embodiment, even if the slot immediately after the own occupancy slot is a used slot, the data immediately before the own occupancy slot indicates that the data before the own occupancy slot has a transmission rate. When the number of empty slots necessary for lowering is continuously available, the self-occupied slot is changed to advance the transmission timing. For this reason, since the slot immediately after the self-occupied slot becomes an empty slot, the transmission rate can be changed thereafter. Therefore, even if the base station does not control each mobile station, the transmission path can be used efficiently.

  Further, according to the communication device 1 according to the first embodiment, in addition to the availability of the slot behind the own slot, the usage status of the transmission path between the mobile stations is controlled using the transmission rate of the transmission data. To do. The operation of decreasing the transmission rate and increasing the number of slots used by transmission data is performed only when the transmission rate is higher than the transmission rate of the rear transmission data. As a result, when there is an empty slot between the transmission data, it is possible to reliably avoid using the same empty slot for both transmission data even if the base station does not control each mobile station.

  Furthermore, according to the communication apparatus 1 according to the first embodiment, in addition to the empty status of the slot ahead of the own slot, the usage status of the transmission path between the mobile stations is controlled using the transmission rate of the transmission data. To do. The operation for changing the own slot can be performed only when the transmission rate is higher than the transmission rate of the forward transmission data. As a result, when there is an empty slot between the transmission data, it is possible to reliably avoid using the same empty slot for both transmission data even if the base station does not control each mobile station.

(Second Embodiment)
Next, a communication apparatus according to the second embodiment of the present invention will be described.

  The communication device 2 according to the second embodiment is configured in the same manner as the communication device 1 according to the first embodiment shown in FIG. 1, and the transmission slot determination process and the modulation scheme change process when the transmission rate is lowered are performed. Is different. Therefore, the constituent elements are denoted by the same reference numerals as in the first embodiment, and the description thereof is omitted. Hereinafter, the transmission slot determination process and the modulation scheme change process of the communication apparatus 2 according to the second embodiment will be described with reference to FIG. explain.

  FIG. 8 is a table showing the operation of lowering the transmission rate of the communication apparatus 1 as in FIG. 5, and represents the processing of step 20 in FIG. The table shown in FIG. 8 is used, for example, when the communication status deteriorates due to the influence of fading or the like in mobile communication using radio and the modulation schemes of the preceding and succeeding packets cannot be grasped. Even in such a case, since it is possible to predict the usage status of the slot from the observation value of the received power, as shown in FIG. 8, the determination of the transmission slot and the modulation scheme based only on the number of empty slots Make changes.

  The table shown in FIG. 8 describes all combinations of the modulation scheme of the own packet and the number of empty slots, and the operation at that time. It should be noted that a condition with a single oblique line means that the condition is not judged, and a condition with a double oblique line means that the condition cannot be judged due to deterioration of the communication status.

  First, a case where the modulation method of the own packet is 16QAM will be described. Numbers 4-1 to 4-3 in FIG. 8 describe combinations when the modulation scheme of the own packet is 16QAM.

  In the case of the number 4-1, that is, when the number of front empty slots is 0 or 1, and the number of rear empty slots is 0, assuming that the modulation method of the front packet is 16QAM, the front packet can use the front empty slot. Therefore, the communication device 2 does not change the slot number to be transmitted and the modulation scheme to be transmitted.

  In the case of number 4-2, that is, when the number of front empty slots is 2 or more and the number of rear empty slots is 0, there is no possibility that the front packet uses the front empty slot immediately before the own occupied slot. The communication device 2 changes the slot number to be transmitted to a number obtained by subtracting 1 from its own slot number so that the modulation method can be changed. Thus, by changing the slot number, the transmission timing of the packet transmitted from the communication device 2 is changed.

  In the case of the number 4-3, that is, when the number of back empty slots is 1 or more, the communication device 2 changes the modulation scheme to be transmitted to QPSK in order to effectively use the back empty slots.

  Next, a case where the modulation method of the own packet is QPSK will be described. Numbers 5-1 to 5-7 in FIG. 8 describe combinations when the modulation scheme of the own packet is QPSK.

  In the case of number 5-1, that is, when the number of front empty slots is 0 to 3 and the number of rear empty slots is 0, if the modulation method of the front packet is QPSK, the front packet is changed from QPSK to BPSK. Since it is possible to change and use two empty slots, the communication apparatus 2 does not change the slot number to be transmitted and the modulation scheme to be transmitted.

  In the case of number 5-2, that is, when the number of front empty slots is 4 or more and the number of rear empty slots is 0, the modulation method of the front packet is QPSK, and the modulation method is changed to BPSK and two empty slots are assigned. Even if it is used, since at least two empty slots remain, the communication apparatus 2 changes the slot number to be transmitted to a number obtained by subtracting 2 from its own slot number so that the modulation method can be changed thereafter. . Thus, by changing the slot number, the transmission timing of the packet transmitted from the communication device 2 is changed.

  In the case of number 5-3, that is, when the number of front empty slots is 0 to 2 and the number of rear empty slots is 1, assuming that the modulation method of the front packet is QPSK, the modulation method of the front packet is changed to BPSK. Since two empty slots can be used, the communication device 2 does not change the slot number to be transmitted and the modulation scheme to be transmitted.

  In the case of number 5-4, that is, when the number of front empty slots is 3 or more and the number of rear empty slots is 1, the modulation method of the front packet is QPSK, and the modulation method is changed to BPSK and two empty slots are assigned. Even if it is used, since at least one free slot remains, the communication apparatus 2 changes the slot number to be transmitted to a number obtained by subtracting 1 from its own slot number so that the modulation scheme can be changed thereafter. . Thus, by changing the slot number, the transmission timing of the packet transmitted from the communication device 2 is changed.

  In the case of number 5-5, that is, when the number of front empty slots is 0 to 2 and the number of rear empty slots is 2, if the modulation method of the front packet is QPSK, the front packet changes the modulation method to BPSK. Therefore, the communication apparatus 2 does not change the slot number to be transmitted and the modulation scheme to be transmitted. Since the number of free rear slots is 2, even if the modulation method is changed to BPSK, it does not interfere with the rear packets, but importance is placed on avoiding duplication of slots, and no change is made with a margin.

  In the case of number 5-6, that is, when the number of front empty slots is 3 or more and the number of rear empty slots is 2, the modulation method of the front packet is QPSK, and the modulation method is changed to BPSK and two empty slots are assigned. Even if it is used, since at least one free slot remains, the communication apparatus 2 changes the slot number to be transmitted to a number obtained by subtracting 1 from its own slot number so that the modulation scheme can be changed thereafter. . Thus, by changing the slot number, the transmission timing of the packet transmitted from the communication device 2 is changed.

  In the case of numbers 5 to 7, that is, when the number of rear empty slots is 3 or more, the modulation scheme to be transmitted is changed to BPSK in order to effectively use the rear empty slots.

  Next, a case where the modulation method of the own packet is BPSK will be described. The number 6-1 in FIG. 8 describes a combination when the modulation method of the own packet is BPSK.

  In the case of the number 6-1, that is, when the number of front empty slots is a number n of 3 or more, the communication device 2 uses the number of slots occupied by BPSK to effectively use the front empty slots. A value obtained by dividing by 4 and subtracting the remainder from the self-occupied slot number is used as a transmission slot number. Thus, by changing the slot number, the transmission timing of the packet transmitted from the communication device 2 is changed.

  Thus, in the process of FIG. 4, the transmission slot determination process and the modulation scheme change process using the table shown in FIG. 8 are completed.

  As described above, according to the communication device 2 according to the second embodiment, the communication device 2 mounted in each mobile station detects empty slots on the transmission path, and when there are few empty slots on the transmission path, The transmission rate of data transmitted by each mobile station is increased. For this reason, since other mobile stations can participate in communication, the number of mobile stations capable of communication can be maintained appropriately. Further, since the utilization rate of the transmission path decreases as the number of empty slots increases in the transmission path, the number of slots used by each mobile station is increased, and the data transmitted by the communication device 2 mounted on each mobile station is transmitted. The rate is falling. For this reason, it is possible to ensure communication quality while effectively utilizing the transmission path.

  Further, according to the communication device 2 according to the second embodiment, the empty slot detection means of the communication device 2 includes the period counter having a period equal to the time length of the slot and the number counter for counting the order of receiving the slots. In order to detect the vacant state in a frame composed of a predetermined number of slots, the number of vacant slots in one frame can be recognized without the base station controlling each mobile station.

  Further, according to the communication device 2 according to the second embodiment, when the transmission rate changing means of the communication device 2 decreases the transmission rate and increases the number of slots used by the transmission data, immediately after the own occupied slot. In the immediately following slot, it is used by checking whether there are consecutive empty slots necessary for lowering the transmission rate. For this reason, even if each mobile station independently reduces the transmission rate and increases the number of slots used by one mobile station, it is possible to avoid overlapping slots used by the mobile stations. Therefore, even if the base station does not control each mobile station, it is possible to avoid the transmission data transmitted by each mobile station from overlapping, so that communication quality can be ensured.

  Further, according to the communication device 2 according to the second embodiment, even if the slot immediately after the own occupancy slot is a used slot, the data immediately before the own occupancy slot indicates that the data before the own occupancy slot has a transmission rate. When the number of empty slots necessary for lowering is continuously available, the self-occupied slot is changed to advance the transmission timing. For this reason, since the slot immediately after the self-occupied slot becomes an empty slot, the transmission rate can be changed thereafter. Therefore, even if the base station does not control each mobile station, the transmission path can be used efficiently.

  Furthermore, according to the communication device 2 according to the second embodiment, since the modulation scheme and the transmission slot can be determined based only on the number of front empty slots and the number of rear empty slots in the own packet, Even when the modulation method cannot be recognized due to fading or the like, communication quality can be ensured while efficiently using the transmission path.

  Each embodiment described above shows an example of a communication apparatus according to the present invention. The communication device according to the present invention is not limited to the communication device according to each of these embodiments, and the communication device according to each embodiment may be modified or otherwise changed without changing the gist described in each claim. It may be applied to the above.

  For example, in the first and second embodiments, the case where modulation is performed using three modulation schemes of 16QAM, QPSK, and BPSK has been described. However, it is not always necessary to perform the modulation using the three modulation schemes. When two modulation schemes are used, two modulation schemes of QPSK and BPSK may be used, and two modulation schemes of 16QAM and BPSK may be used.

  In the first and second embodiments, the example in which the modulation scheme is changed as a means for changing the transmission rate has been described. However, the modulation scheme is not limited to 16QAM, QPSK, and BPSK, but FSK, 64QAM, and 256QAM. In short, anything can be used as long as it can change the transmission rate.

It is a block diagram which shows the structure outline | summary of the communication apparatus which concerns on 1st Embodiment of this invention. It is a frame block diagram which the communication apparatus of FIG. 1 uses. It is a packet block diagram which the communication apparatus of FIG. 1 uses. It is a flowchart which shows operation | movement of the communication apparatus of FIG. 3 is a table showing an operation for lowering the transmission rate of the communication apparatus of FIG. 1. It is a flowchart which shows operation | movement of the communication apparatus of FIG. It is a schematic diagram which shows the use condition of the flame | frame used by the communication apparatus of FIG. 1 in time series. It is a table which shows the operation | movement which reduces the transmission rate of the communication apparatus which concerns on 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,2 ... Communication apparatus, 11 ... Slot timing production | generation part (free slot detection means, self-occupied slot change means), 14 ... Transmission control part (Transmission rate change means, empty slot detection means).

Claims (6)

A mobile station is equipped with a transmission means for transmitting transmission data and a reception means for receiving transmission data. The time during which transmission data between mobile stations can occupy the transmission path is controlled by a slot having a predetermined time length. A communication device for performing transmission and reception,
Empty slot detecting means for detecting the empty state of the transmission path in slot units;
Transmission rate changing means for increasing the transmission rate of the transmission data to be transmitted when the number of detected empty slots is small and decreasing the transmission rate of the transmission data to be transmitted when the number of detected empty slots is large ,
A communication apparatus comprising: The empty slot detecting means detects an empty state in a frame composed of a predetermined number of slots using a period counter having a period equal to the time length of the slot and a number counter for counting the order of receiving the slots. ,
The communication apparatus according to claim 1. The transmission rate changing means includes
The receiving unit receives a self-occupied slot corresponding to the transmission data transmitted by the transmitting unit,
In the slot immediately after the self-occupied slot, check whether the number of empty slots necessary for lowering the transmission rate exists continuously,
If the number of empty slots necessary for lowering the transmission rate is continuously present, lowering the transmission rate of the transmission data corresponding to the own occupied slot;
The communication apparatus according to claim 1 or 2, characterized by the above. The slot immediately after the self-occupied slot is a used slot used by transmission data, the slot immediately before the self-occupied slot is the empty slot, and the transmission data corresponding to the slot before the self-occupied slot is Self-occupied slot changing means for changing the own-occupied slot to a slot before the own-occupied slot when the number of empty slots necessary for lowering the transmission rate is continuous.
The communication device according to claim 3. The transmission rate changing means corresponds to the self-occupied slot only when the transmission rate of the transmission data corresponding to the self-occupied slot is larger than the transmission rate of transmission data after the self-occupied slot. Reducing the transmission rate of transmission data;
The communication device according to claim 3 or 4, characterized by the above. The own-occupied slot changing means changes the own-occupied slot only when the transmission rate of the transmission data corresponding to the own-occupied slot is larger than the transmission rate of transmission data before the own-occupied slot. thing,
The communication device according to claim 5.

Images