Master station of communication system and access control method

ES 2 294 539 T3

DESCRIPTION

Communication system main station, and access control method.

Technical field

The present invention relates to a main station of a communication system, and to an access control method, and more specifically it relates to an access control method that is used in a plurality of communication systems that share the same channel, to prevent interference from occurring between the plurality of communication systems.

Prior art

As a technique for reducing interference between a plurality of communication systems sharing the same channel, there is conventionally an access control method to reduce the influence of interfering signals by controlling the transmission power. For example, there are Japanese Unexamined Patent Publication Number 2002-198 834 (patent document 1), Japanese Unexamined Patent Publication Number 2003-37 556 (patent document 2), or Japanese Unexamined Patent Publication Number 2001-53 745 (patent document 3).

Patent document 1 discloses a method of attenuating a signal power and an interference power, by means of an attenuator provided in a base station, and compensating the power of a wireless signal input into a receiver, with a transmitting power of a transmitter from a terminal station, so that a wireless signal strength level becomes a reference level.

Likewise, patent document 2 discloses a method by which a base station, which has detected interference signals, notifies the interference information to another base station by transmitting the interference signals through a local communication network, to cause that the notified base station reduces a transmit power based on the interference information.

Furthermore, patent document 3 discloses the following method. First a frequency resource is assigned to a wireless station, from which high priority data is transmitted. Furthermore, it is assigned a timing and a frame length in use for the transmission of the high priority data. When high priority data is transmitted from an access point (AP), according to the assigned timing and frequency length, the wireless station verifies the channel availability by performing physical carrier detection before transmission. , and transmits the high priority data only if the channel availability has been verified (that is, the channel is free).

However, in the case where the communication system described above is a power line communication system, depending on the configuration of a device connected to the network, the amount of signal attenuation in a communication system can substantially exceed the amount of signal attenuation that interferes with other communication systems, due to the characteristics of a power line transmission path. That is, in the case where the patent document 1 or the patent document 2 is applied to the power line communication system, and the interference between the communication systems is realized by power control, there is a possibility that Depending on the device configuration, some devices may be unable to perform device communication on the system due to reduced signal strength. Furthermore, in the case of wireless communications the similar phenomenon may occur, that is, the signal strength is suddenly reduced despite the physical proximity, due to the attenuation of the signal strength, which is caused by shielding.

The conventional configuration described above does not allow a communication system to maintain the quality of the communications it carries out, by controlling the transmission power, while reducing interference with other communication systems. Thus, the overall performance of each communication system is substantially reduced due to interference between the communication systems, and it is difficult to carry out a communication bandwidth control.

Furthermore, in the case that the control disclosed in patent document 3 is used, the interference between communication systems can be reduced by virtual carrier or physical carrier detection. However, it is impossible to ensure the quality of service (QoS) of a communication bandwidth.

Document US 2003/128 684 A1 discloses a station in a local area network, the station being capable of transmitting and receiving data using a first modulation scheme, the local area networks further comprising a second station capable of transmitting and receiving data using a second modulation scheme, and an access point for communication with both stations, where the station receives a beacon frame transmitted by the access point, which indicates the beginning of a containment free period followed by a containment period, and the containment free period comprises a secondary containment period, during which the facility is allowed to transmit data according to the first modulation scheme and following a distributed access mechanism with a coordination function.

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Disclosure of the invention

Therefore, the objective of the present invention is to provide a main station and an access control method that are capable of easily avoiding interference between communication systems, while ensuring the QoS of a communication bandwidth of each system. without carrying out transmission power control, in a plurality of communication systems sharing the same channel.

The present invention is directed to a main station used in a communication system, in a system environment in which a plurality of communication systems, each of which consists of at least one secondary station and one main station that manages the secondary station, share the same channel. To solve the above problems, the main station of the present invention includes a communication section, an acquisition section, and a determining section.

The communication section divides a communication bandwidth, in a beacon period in which the main stations compete for the transmission of a beacon packet, a first period of carrier detection multiple access (CSMA) in which only allows specific authorized stations to compete for access, and a second CSMA period in which all stations are allowed to compete for access, and to communicate repeatedly on a periodic basis. The acquisition section acquires a state of use of communication bandwidths, in the other communication systems. The determination section calculates an available communication bandwidth in the communication system to which the station belongs, in the first CSMA period, based on the state of use of the communication bandwidths acquired by the acquisition section, and determines whether the communication requested by the secondary station is accepted or rejected, according to the calculated communication bandwidth.

Typically, the beacon packet includes system information that provides at least assigned times of the beacon period, the first CSMA period, and the second CSMA period. The presence or absence of transmission of the beacon packet by another main station is verified after a random power reduction process, for each cycle of the beacon period. If the absence is confirmed, the beacon packet is transmitted. On the contrary, if the presence is confirmed, the beacon packet is not transmitted.

In addition, the acquisition section can acquire a status of use of communication bandwidths in the other communication systems, by exchanging information with the other main stations using the second period CSMA, or it can acquire a status of use of bandwidths of communication. communication band in the other communication systems, from a beacon packet received from any of the other main stations, in the beacon period.

In this case, it is preferable that a total available bandwidth is obtained, with respect to a communication bandwidth in the first CSMA period, based on the efficiency of the CSMA access and the retransmission bandwidth, and that it is limited an access request from the secondary station, so that the communication bandwidth to be calculated by the primary station does not exceed the total available bandwidth. Furthermore, each of the authorized specific stations preferably carries out transmission time management in the first CSMA period, so that a transmission bandwidth does not exceed a previously specified requested bandwidth. Furthermore, an allocated time AT can be calculated in the first CSMA period, using the expression At = (Σ Tn + M) χ a, which is based on the communication bandwidths Tn requested in the communication systems of the other main stations , in a communication bandwidth M requested in the communication system to which the main station belongs, and in a predetermined coefficient a.

Furthermore, the beacon packet may include system information that provides at least a beacon period start time and a beacon period transmission time, in accordance with a timer value of the host station transmitting the beacon packet. . In this case, a transmission time of the beacon packet from the received beacon packet is preferably required, and a time value of this is corrected based on the transmission time of the acquired beacon packet. Especially, it is efficient to calculate an intermediate value between a synchronization value of this and a transmission time of the beacon packet of any of the other main stations, thereby correcting the synchronization value with the intermediate value.

The process carried out by each component of the main station described above, can be considered as an access control method that carries out a series of procedures. This method is provided in the form of a program, which causes a computer to execute the series of procedures. This program can be entered into the computer using a computer-readable recording medium. Furthermore, each component of the main station described above can be realized as an LSI, which is an integrated circuit.

As described above, based on the present invention, a communication bandwidth is divided into the following three periods: a beacon period, a first CSMA period, and a second CSMA period, and an allocation for the first CSMA period is determined. depending on the information on the communication bandwidth currently used, of each communication system. As a result, even if a plurality of communication systems share the same channel, it is possible to easily avoid interference between communication systems, and ensure the QoS of a communication bandwidth of each communication system, without carrying out control of the communication. potency of transmission. Furthermore, the different access modes are not mutually affected.

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Brief description of the drawings

Fig. 1 is an illustration showing, by way of example, an environment of the communication system to which the present invention is applied.

Figure 2 is a block diagram showing, by way of example, a detailed structure of a station.

Fig. 3 is an illustration for describing the period separation of a communication bandwidth.

Fig. 4 is a timing diagram for describing an access control method, according to a first embodiment of the present invention.

Fig. 5 is a flow chart for describing an access control method, according to the first embodiment of the present invention.

Figure 6 is an illustration showing the relationship between traffic and overall performance in a CSMA access.

Figure 7 is a sequence for describing a method using a normal CSMA period.

Fig. 8 is a flow chart for describing the method using a normal CSMA period.

Fig. 9 is an illustration showing a TXOP in a controlled CSMA period.

Fig. 10 is an illustration showing the format of a beacon packet (beacon frame) used for power line communications, for the purpose of storing assignment information and announcing the information to the system.

Fig. 11 is an illustration showing details of a frame control section of Fig. 10.

Figure 12 is an illustration showing the details of a Variant (VF) field in Figure 11.

Fig. 13 is an illustration showing details of a trailing header section in Fig. 10.

Fig. 14 is an illustration showing the details of the section of the data body in Fig. 10.

Fig. 15 is a flow chart, showing a procedure of an access control method according to a third embodiment of the present invention (main station side).

Fig. 16 is a flow chart, showing a procedure of an access control method according to the third embodiment of the present invention (secondary station side).

Fig. 17 is an illustration showing information and a timing of a beacon packet in a beacon period.

Fig. 18 is an illustration showing, by way of example, a network system in which the access control method of the present invention is applied to a high speed power line transmission.

Best mode of carrying out the invention

In the following, embodiments of the present invention will be described in detail with reference to the drawings.

Fig. 1 is an illustration showing, by way of example, the environment of a communication system to which the present invention is applied. Figure 1 shows, by way of example, an environment that includes three communication systems 11 to 13 that interfere with each other. The communication system 11 includes a main station 111 and a sub station 112, the communication system 12 includes a main station 121 and secondary stations 122 and 123, and the communication system 13 includes a main station 131 and secondary stations 132 and 133 .

Each of the main stations and the secondary stations includes, as shown in Figure 2, a bandwidth management section 21, a control section 22, a data buffer section 23, a frame transmission section 24, a frame reception section 25 and an interface section with the exchange 26. The bandwidth management section 21 manages various information concerning a communication bandwidth. Control section 22 controls the entire station. The data buffer section 23 temporarily stores various packets. The frame transmission section 24 transmits the packet stored in the data buffer section 23. The frame receive section 25 causes the data buffer section 23 to store a received packet. The switch interface section 26 is, for example, an interface to a switch or an interface to another medium (eg, another communication system) such as a bridge configuration. The determination section is made up of the bandwidth management section 21 and the control section 22. Furthermore, the acquisition section is made up of the

ES 2 294 539 T3 data buffer section 23, frame transmission section 24 and frame reception section 25. Furthermore, a communication section is composed of control section 22, frame transmission section 24 and the frame receiving section 25.

One of the characteristics of the present invention is that a communication bandwidth used by communication systems 11 to 13 is previously divided into the following three periods: a beacon period, a controlled CSMA period, and a normal CSMA period. , each of which has a predefined role. During a beacon period all the main stations compete for the transmission of a beacon packet. During a controlled CSMA period (first CSMA period), only specific authorized stations are allowed to compete for access. That is, the controlled CSMA period is a carrier sense multiple access (CSMA) period, to which access restriction is applied. During a normal CSMA period (second CSMA period) all stations are allowed to compete for access. That is, the normal CSMA period is a CSMA period to which no access restriction applies. These three periods repeat periodically (see Figure 3).

The main stations 111, 121 and 131 manage a beacon period, a controlled CSMA period and a normal CSMA period, according to a tuner provided in each control section 22, for example. Typically, system information indicating an allotted time of each period is transmitted as information stored in a beacon packet.

In the following, an access control method using the primary and secondary stations, described above, will be described.

First realization

Fig. 4 is a timing diagram for describing an access control method, according to a first embodiment of the present invention. Note that in the present embodiment, a case will be described where the start times of the beacon periods are the same (that is, the start times of the beacon periods are pre-synchronized). For synchronizing the start and end periods of the beacon periods, for example, a method that will be described in the third embodiment can be used. Furthermore, it is assumed that information about a communication bandwidth used by a communication system is transmitted as information stored in a beacon packet. Fig. 5 is a flow chart for describing the access control method (bandwidth management method), according to the first embodiment of the present invention.

As shown in Figure 4, each of the control sections 22 included in the respective main stations 111, 121 and 131 carries out a random power reduction process, within a beacon period, to transmit its own beacon. at the start of the beacon period. The control sections 22 of the main stations 111, 121 and 131 carry out a random power reduction process, to transmit beacon packets 401, 404 and 407 respectively. When the random power reduction process has been completed, each of the control sections 22 of the main stations 111,121 and 131 carries out carrier detection, in order to verify (that is, verify in a medium) if it is being transmitted another beacon packet from any of the other main stations, and transmits its own beacon packet only if no other beacon packet is being transmitted from any of the other main stations. That is, only a main station whose random power reduction process completes first can transmit its own beacon packet.

In the example shown in Figure 4, the main station 121 that first completes the random power reduction process, generates the beacon packet 404 in the data buffer section 23, and transmits the generated beacon packet 404, using frame transmission section 24. This beacon packet includes, as system information, a beacon packet transmission time, a start time of a beacon period, a start time of a controlled CSMA period, and a start time of a normal CSMA period. , etc., based on the tuner. Note that the main stations 111 and 131 that detect the transmission of the beacon packet 404 by carrier detection, stop the transmission of the beacon packets 401 and 407 respectively.

When the beacon packet 404 is received from the main station 121, through the frame receiving station 25 (step S501), the main stations 111 and 131 temporarily store the beacon packet 404 in the memory buffer section. data 23. Each of the control sections 22 of the main stations 111 and 131 extracts information about a communication bandwidth used by the communication system 12, from the stored beacon packet, and stores this information in the administration section of bandwidth 12 (step S502). When the new information is stored in the bandwidth management section 21, each of the main stations 112 and 131 determines whether or not it has been generated at a new request in each communication system (step S503). In the case where a new request has been generated, each of the main stations 111 and 131 again calculates a communication bandwidth, available in its own communication system, based on the stored information, and compares it with the sum of the communication bandwidth currently used by your own communication system plus a communication bandwidth of the new request (step S504). As a result of the above comparison, if the sum is less than the newly calculated communication bandwidth, each of the main stations 111 and 131 accepts the new request (step S505). On the other hand, if the sum is greater than the newly calculated communication bandwidth, the new request is rejected (step S506).

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Using a specific example, a method carried out in step S504 will now be described to calculate an available communication bandwidth in a communication system, based on the communication bandwidths used by other communication systems. For example, in the case where the maximum bandwidth in the controlled CSMA period is 30 Mbps, and the sum of the communication bandwidths used by the other communication systems is 6 Mbps, the efficiency of the CSMA is 0.65, and a percentage of a redundant bandwidth (a margin) for retransmission is, for example, 20% based on the characteristics shown in Figure 6. In this case, the total available communication bandwidth in all communication systems (total available bandwidth) is 15.6 Mbps (= 30 x 0.65 x 0.8). Thus, a communication bandwidth available in a communication system is 9.6 Mbps (= 15.6 - 6.0). As a result, in this example a new request is accepted if its communication bandwidth is equal to or less than 9.6 Mbps.

Regarding the method described above, which uses a beacon period, another way to acquire information about communication bandwidths used by other communication systems, is a method that uses a CSMA period. Such a method will be described using Figures 7 and 8.

For example, in the case where the secondary station 122 has to ensure a QoS, the secondary station 122 transmits a QoS request packet 611 to the main station 121 included in the same communication system (step S801). The main station 121, which has received the packet 611 through the frame receive section 25, temporarily stores the received packet 611 in the data buffer section 23. Then, the control section 22 of the main station 121 transmits a status request packet 612 and 614, to the main stations 111 and 131 respectively, whose presence in their proximity is detected by the beacon packet stored in the memory section. data buffer 23 (step S802). Specifically, the control section 22 of the main station 121, generates the packets 612 and 614 in the data buffer section 23, and transmits the generated packets 612 and 614 to the main stations 111 and 131 respectively, through the frame transmission section 24.

Each of the frame receiving sections 25 of the main stations 111 and 131, which have received the packets 612 and 614 respectively, stores the received packet in the data buffer section 23. Then, the control sections 22 of the main stations 111 and 131 transmit to the main station 121, respectively, a status response packet 613 and 615, which includes the information about the communication bandwidth currently used, stored in the section bandwidth management 21. Specifically, the control sections 22 of the main stations 111 and 131 respectively generate the packets 613 and 615 in the data buffer section 23, and transmit the generated packets to the main station 121 through the frame transmission section. 24.

When packets 613 and 615 are received from main stations 111 and 131 respectively (step S803), control section 22 of main station 121 determines whether or not the request from secondary station 122 is acceptable based on to the information of the communication bandwidth currently used, included in the packets, based on the maximum bandwidth, described above, of the controlled CSMA period, and based on the margin (step S804). Then, based on the results of the determination, the control section 22 of the main station 121 generates a QoS response packet 616, which indicates the acceptance or rejection of the request in the data buffer section 23, and transmits to secondary station 122 through frame transmission section 24 (steps S805 and S806).

The control section 22 of the secondary station 122, which has received the packet 616 indicating acceptance of the request, transmits a data packet through a typical CSMA process during a controlled CSMA period. That is, a transmitting station transmits a data packet upon carrier detection, and a receiving station that has received the data packet returns an acknowledgment packet. In the event that the transmitting station cannot receive the acknowledgment packet due to collision or error, etc., a random power reduction process is carried out, and a data packet is retransmitted. Specifically, when data such as an IP (Internet Protocol) packet is stored in the data buffer section 23 through the exchange interface section 26, the control section 22 of the secondary station 122 determines whether the stored data is, or is not, QoS. In the case where the stored data is QoS data, the control section 22 of the secondary station 122 verifies that there is no other data frame, etc., by carrier detection, after carrying out a random reduction process. power over a controlled CSMA period, and transmits a data frame using the same 24 frame transmission section. Note that in the case where the stored data is not QoS data, the control section 22 of the secondary station 122 carries out a similar process during a normal CSMA period, and transmits a data frame.

Even if the control section 22 of the secondary station 122 has many data transmission pieces, the control section 22 limits the maximum amount of data transmission in the controlled CSMA period. For example, if a speed has been calculated in the system periods, the maximum amount of data transmission is limited to 20% greater than the requested bandwidth. Furthermore, as shown in figure 9 a limitation is imposed, for example by setting the maximum transmission opportunity (TXOP, Transmission Opportunity). In the case where a TXOP is set as shown in FIG. 9, the control section 22 sequentially transmits a data packet. In this case, the control is carried out so that the minimum packet interval is maintained, and other stations cannot carry out the transmission unless an interval longer than the minimum packet interval is detected.

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Note that the control section 22 can include a typical RTS (Request To Send) or CTS (Clear To Send) process before transmitting a data packet, by means of which it is possible to solve a problem of hidden terminal. Furthermore, the virtual carrier duration information, etc., can be included in a packet to carry out virtual carrier detection, thereby reducing the collision frequency. In addition, a master station may transmit an invitation-to-transmit packet, during a controlled CSMA period, to set a TXOP whereby a secondary station transmits a data packet in response to the invitation to transmit. It will be understood that an RTS / CTS sequence may be included. In the event that in response to the invitation to transmit, a data packet, an acknowledgment packet or an RTS packet is not returned, the retransmission of an invitation to transmit packet, or the invitation to transmit, to a next station.

Second realization

In a second embodiment, with reference to Figures 10 to 14, a concrete example will be described, of a case in which the access control method described in the first embodiment is applied to a power line communication system. Figures 10 to 14 are illustrations showing the format of a beacon packet (beacon frame) used for power line communications to store assignment information and announce the information to the system.

It is assumed that the TINF information included in the VF (Variant Field) in the frame control, stores information about communication bandwidths T1 to Tn, which are necessary to ensure QoS and are accepted by a plurality of main stations 1 to n (n is an arbitrary integer), respectively. In addition, as shown in Figure 14 the SI schedule information included in the section of a beacon packet, stores information about a time assigned to a beacon period, an AT assigned time of a controlled CSMA period, and an assigned time of a normal CSMA period. In the present embodiment, a beacon cycle is assumed from 50 ms.

Main station 111 receives a beacon packet from other main stations 121 and 131, and stores the received packet in data buffer section 23. Main station 111 analyzes the beacon period stored in data buffer section. data 23, extracts the TINF information and stores a set composed of a main station address 121 or 131, and the TINF information, in the bandwidth management section 21. In the case where the TINF information already exists, the information is updated. In the present embodiment, the TINF information of the main station 121 is assumed to be 5 ms, and the TINF information of the main station 131 is 8 ms. Note that TINF information is not updated in the case where a beacon packet is not detectable due to collision, error, etc. Thus, the control section 22 uses the previously received TINF information. In this case, it is preferable to set a period of time during which the data is valid.

The main station 111 generates a beacon packet in which a bandwidth N requested by its communication system is set. As in this example, in the case where a request for communication bandwidth is not accepted from the secondary station 112 belonging to the same communication system, the bandwidth M is 0 ms. Thus, the main station 111 generates a beacon packet in which an M communication bandwidth is set to "0". Main station 111 determines an assigned time AT of the controlled CSMA period, using TINF information from main stations 121 and 131, and its own communication bandwidth information. For example, in the case where a predetermined coefficient α is 1, 3, the assigned time AT of a controlled CSMA period is calculated as follows: (Σ Tn + M) χ α = (5 + 8 + 0) x 1.3 = 16.9 ms, and is set as YES programming information.

Similarly, each of the main stations 121 and 131 determines an assigned time AT of a controlled CSMA period, using the TINF information acquired from other main stations, stores it in the SI schedule information and generates a beacon. Note that the coefficient α and the expression described above are only illustrative and another expression can be used, for example in the case where RTS / CTS sequence or invitation to transmit is used.

Next, a sequence in the case where a bandwidth request is sent from the secondary station 112 to the master station 111 will be described.

Before sending a request for communication bandwidth, the control section 22 of the secondary station 112 sends a test pattern to the communication destination station, to verify the channel conditions between the two, thereby determining a speed of transmission. Specifically, a test pattern is set in the data buffer section 23, and a channel check frame is transmitted using the frame transmission section 24. When the channel check frame is received, the frame receiving section 25 of the destination station determines an optimal modulation scheme, and an optimal transmission rate for the channel, based on the SNR (Signal to Noise Ratio, signal-to-noise ratio), and so on. The control section 22 of the communication destination station generates a frame of the channel verification result, based on the previous determination results, in the data buffer section 23 and transmits it to the secondary station 112. When the frame of the channel verification result is received, the secondary station 112 analyzes the frame and acquires the modulation scheme and the transmission speed, necessary for the communication.

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The transmission speed is assumed to be for example 48 Mbps. In this case, if the secondary station 112 has to ensure a bandwidth of 6 Mbps, the control section 22 of the secondary station 112 generates a request frame for bandwidth, which includes a transmission rate and a requested bandwidth, and transmits it to the main station 111. In the case where the transmission speed is less than the requested bandwidth, the bandwidth request frame is not transmitted, since allocation is impossible. In this example, a 6 Mbps bandwidth is requested out of the 48 Mbps transmission speed. Thus, bandwidth is assured if 6.25 ms is allocated to each 50 ms beacon cycle. Note that this calculation can be carried out by the control section 22 of the main station 111, or it can be carried out by the control section 22 of the secondary station 112, and notified to the main station 111.

When the bandwidth request frame is received, the main station 111 stores it in the data buffer section 23. The control section 22 of the main station 111 recalculates an allocated time AT of a controlled CSMA period , using data in the bandwidth request frame, and you get AT = 25.025 (= 1.3 x (5 + 8 + 6.25)). The upper limit of a controlled CSMA period is assumed to be 40 ms. In this case, it is determined that the request is acceptable, since the assigned time AT obtained by the previous calculation is less than 40 ms. Thus, the control section 22 of the main station 111 generates a request acceptance completion frame, and transmits it to the secondary station 112. In the case where the request is rejected, similarly the control section 22 of main station 111 transmits a request rejection frame.

Also, in the case where the request is accepted, the control section 22 of the main station 111 updates the data in the bandwidth management section 21, sets the TINF information to 6.25 ms, generates the packet beacon in which the SI programming information is updated to 25.025 ms, and periodically transmitted. When the beacon packet is received, secondary station 12 analyzes the data in the packet. Secondary station 112 acquires the SI schedule information and detects a controlled CSMA period, thereby transmitting a data frame requiring bandwidth assurance, using a CSMA process for a period of 25.025 ms stored in the schedule information. YES programming. Note that a data frame that does not need bandwidth assurance is transmitted during a normal CSMA period.

Third realization

In a third embodiment, a process for synchronizing the start and end times of the beacon periods will be described, the process being usable in combination with the access control method described in the first embodiment. Fig. 15 is a flow chart showing a procedure of an access control method according to the third embodiment of the present invention (main station side). Fig. 16 is a flow chart showing a procedure of an access control method according to the third embodiment of the present invention (secondary station side).

Each main station individually determines whether or not it has just received a beacon packet (step S1501). In the case where a beacon packet has not been received, the main station acquires a value of its own timer (step S1502). The main station determines whether or not the acquired timer value reaches a start time of a beacon period (step S1503). If a start time is not reached, the process returns to step S1501. If a start time is reached, the main station starts a random power reduction process (step S1504).

In the case where the beacon packet has been received from another main station, in the course of the random power reduction process (step S1505, SI), the main station acquires a value of its own timer (step S1508). The master station then extracts a beacon period start time from the received beacon packet and adds a predetermined offset time (Delay Offset) to this beacon period start time, thereby obtaining a time transmission of the beacon packet in another main station (step S1509). See figure 17. Then, the main station calculates an intermediate value between the obtained beacon packet transmission time and its own timer value, and sets the timer to the intermediate value (step S1510). For example, in the case where a value of the beacon packet transmission time in another main station is "1200" and the value of its own timer is "1300", the timer value is set to "1250" , which is an intermediate value between the two.

On the other hand, in the case where a random power reduction process is completed without receiving a beacon packet from any of the other main stations (step S1506, SI), the main station generates a beacon packet to which the start time of the beacon period based on its own timer, and a predetermined offset time is added and transmitted to the other main stations (step S1507).

Each master station acquires a beacon period start time, a controlled CSMA period start time and a normal CSMA period start time, which are included in a beacon packet, and detects a synchronization. Note that a start time of a next beacon period is acquired by adding a System Period, which is a cycle of generation of a beacon period, to an initial time of the beacon period.

When each slave station receives a beacon packet from a main station, from a communication system to which it belongs (step S1601), the secondary station extracts a transmission time from the packet.

Beacon ES 2 294 539 T3, from the received beacon packet (step S1602). Then, each secondary station sets a timer value to the transmission time of the retrieved beacon packet (step S1603).

Thus, based on the access control method according to the present invention, a communication bandwidth is divided into the following three periods: a beacon period, a controlled CSMA period and a normal CSMA period, and an allocation of the CSMA period controlled based on information about a currently used communication bandwidth of each communication system. As a result, even if a plurality of communication systems share the same channel, it is possible to easily avoid interference between communication systems, and ensure the QoS of a communication bandwidth of each communication system, without carrying out power control. of transmission. Furthermore, the different access modes do not affect each other.

Furthermore, a timer of each station is corrected based on a transmission time of the beacon packet, whereby it is possible to synchronize the systems with each other. Especially, a system time of each station is corrected, by obtaining an intermediate value between a transmission time of the beacon packet of any of the other stations, and its own timer value. Thus, even if there may be a station whose timer is out of sync, it is possible to synchronize the systems by repeatedly carrying out a process.

Note that each of the embodiments described above is carried out by means of a CPU that carries out the interpretation and execution of predetermined program data, which is stored in a storage device (a RAM, a ROM, a hard disk, etc. .) of the procedure described above, and that they are executable. In this case, the program data can be input to the storage device through a recording medium, or it can be directly executed from the recording medium. Note that the recording medium includes a ROM, a RAM, a semiconductor memory such as flash memory, a magnetic disk memory such as a floppy disk and a hard disk, an optical disk such as a CD-ROM, a DVD, and a BD, a memory card, and so on. Furthermore, the recording medium is a concept that includes a communication medium such as a telephone line and a carrier line.

Furthermore, all or a part of the functional blocks that make up the main station of the present invention are constructed as an LSI (referred to as an IC, an LSI system, a super-LSI, an ultra-LSI, etc., depending on the degree of integration), which is typically an integrated circuit. Each functional block can be built separately in the form of a chip, or it can be constructed in the form of a chip so that part or all of it is included.

Furthermore, an integration method is not limited to LSI, and can be obtained by means of a dedicated circuit, or by means of a general-purpose processor. In addition, an FPGA (Field Programmable Gate Array) can be programmed, which is an LSI that can be programmed after its manufacture, or a reconfigurable processor can be used that allows reconfiguration of the connections and parameters of the circuit cells, in the LSI.

In addition, if another integration technology is available to replace the LSI, thanks to advances in semiconductor technology or due to the appearance of another technology derived from it, the integration of the functional blocks can be carried out using the new integration technology indicated above. For example biotechnology can be applied to the integration described above.

In the following, an example will be described, in which the invention described in the above embodiments is applied to a real network system. Fig. 18 is an illustration showing an exemplary network system in which the present invention is applied to high-speed power line transmission. In figure 18, a power line is connected to an IEEE1394 interface and a USB interface, etc., provided in a multimedia device such as a personal computer, a DVD recorder, a digital television and in a home server system, at through a module that has the function of the present invention. As a result, it is possible to configure a network system that is capable of transmitting digital data, such as multimedia data, at high speed through the power line. This system increases the ease of use due to a reduced cost and a simple installation, since it is possible to use a power line that has already been installed in a home, in an office, etc., as a network line without the need installing the required network cable in a conventional wired LAN.

In the configuration described above, an example has been described in which an existing device is applied to a communication by power line, through an adapter that converts a signal interface of the existing multimedia device, to an interface of communication by power line. However, it will be possible to carry out data transmission between devices, through a power cord of a multimedia device, by manufacturing a multimedia device having a built-in function of the present invention. As shown in Figure 18, this eliminates the need for the adapter, the IEEE1394 cable, and the USB cable, simplifying cabling. In addition, it is possible to connect to the Internet through a router and connect to a wired / wireless LAN using a central station, etc., whereby a LAN system using the high-speed line transmission system can be extended. feed, of the present invention. In addition, by a power line transmission method, the transmission data flows through a power line, thereby eliminating data loss and interception, which become a problem with wireless LANs. Thus, the power line transmission method is effective in protecting data due to

ES 2 294 539 T3 to your enhanced security. It will be understood that data transmitted over a power line is protected by IPSec, which is an extended IP protocol, by content encryption, by another DRM scheme, and so on.

Thus, it is possible to carry out a high-quality transmission of AV content by power line, by carrying out a copyright protection function through content encryption, and a QoS function that includes a performance of the present invention (improved overall performance and bandwidth allocation, responding flexibly to increased retransmission and traffic fluctuations).

Industrial applicability

The control method according to the present invention can, for example, be applied to a case where a plurality of communication systems share the same channel. Especially the control method is effective, for example, in a case where the interference between communication systems is easily avoided, and the QoS of a communication bandwidth of each communication system is ensured without carrying out power control. of transmission.

References cited in description

The list of references cited by the applicant is for the convenience of the reader only. It is not part of the European Patent document. Even though special care has been taken in compiling the references, errors or omissions cannot be ruled out and the EPO disclaims all responsibility in this regard.

Patent documents cited in the description • JP 2002198834 A [0002] • JP 2003037556 A [0002] • JP 2001053745 A [0002] • US 2003128684 A1 [0009]