JP2008228024A - Radio communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication system in which the capability of an error correction code can be altered in accordance with a communication path status for every AP (Access Point) without applying an excessive processing load onto respective APs even in the case where video/audio data are broadcasted/distributed from a distribution server to radio terminals under control via the APs. <P>SOLUTION: In the radio communication system, which comprises a plurality of radio base stations 3 for offering services to radio terminals 4, 5 under control via radio communication paths and a distribution server 1 for generating error correction coded data from data by using an error correction code and for distributing the generated data to the plurality of radio base stations 3, and in which the radio base stations 3 and the distribution server 1 are connected over a trunk local area network (LAN) 2, each of the radio base stations 3 includes:a communication status detecting means for detecting a communication status of the radio communication path in the area where services are offered;and a control means for controlling to delete a part of the error correction coded data based on a result of the communication status detection. The radio base station 3 transmits the controlled error correction coded data to the radio terminals 4, 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wireless communication system that communicates data in units of packets using, for example, a wireless LAN, and in particular, improves communication quality when distributing information such as a video signal over a communication path where communication errors are likely to occur. The present invention relates to a wireless communication system.

  In recent years, wireless communication systems such as IEEE802.11a / b / g are becoming widespread. These are called the wireless local area network (Local Area Network) system or wireless LAN system for short, replacing the equivalent of Ethernet (registered trademark) used in wired LAN systems with wireless. Communication system.

  In particular, in a moving body such as a train or an airplane, use of a wireless LAN has a great advantage because it can immediately respond to a change in seat layout, and can be reduced in cost and weight by cableless. However, in a communication system using a wireless LAN, a data error occurs on the communication path because the radio wave environment of the communication path fluctuates due to various factors. In the case of a data service that does not require real-time performance, if data error occurs and data cannot be received normally, normal data can be received by means such as retransmission. On the other hand, when real-time performance is required as in video and audio distribution services, it is necessary to ensure communication quality using an error correction code or the like.

  The error correction code adds redundant data (hereinafter referred to as “parity”) for detecting and correcting an error to the distribution data. In order to enhance the error correction capability, it is necessary to increase redundant data, and the execution communication speed becomes slow. Therefore, it is important to select an error correction code having an appropriate correction capability. As an error correction code, a Reed-Solomon code having excellent coding efficiency is often used. However, encoding processing of highly efficient error correction codes such as Reed-Solomon codes has a larger processing load than decoding processing, and increases the scale and power consumption of the realized circuit.

  In a system in which video data is broadcasted (broadcasted) from a distribution server to a plurality of wireless terminals as clients via a wireless base station (access point: hereinafter referred to as “AP”), from the AP to the wireless terminal A technique is disclosed in which, when data is transmitted, error correction coding is performed at the AP, and the correction capability of the error correction code is changed depending on the number of retransmissions (for example, see Patent Document 1).

  When the wireless terminal receives the transmission request packet from the AP, it detects the communication environment status (S / N and delay spread) of its own terminal, adds the data to the response packet and sends it back to the transmission side, and then transmits A technique is disclosed in which the side enhances the optimum communication rate and error correction capability based on the communication environment data in the response packet returned from the receiving side (see, for example, Patent Document 2).

Furthermore, the reception line quality status received from each user station is notified to the center station, and the status is judged at the center station, and the mode is switched to an appropriate modulation method or error correction method. A technique is disclosed in which the center station notifies the user station of switching information, and the user station automatically switches to a corresponding method (see, for example, Patent Document 3).
JP 7-336331 A Japanese Patent Application Laid-Open No. 2000-151639 JP 2001-53824 A

  However, in the techniques disclosed in Patent Document 1 and Patent Document 2, the AP performs error correction coding, and changes the coding rate of the error correction code according to the state of the communication path such as a radio wave environment. ing. Therefore, there has been a problem that the processing load on the AP increases, an expensive CPU is required for the AP, and the scale and power consumption of the processing circuit increase.

  In the technique disclosed in Patent Document 3, the center station monitors the reception line status of the user station and transmits the same error correction encoded data to all the user stations. Although the radio wave environment of the area where the service is provided for each AP is different, the central station performs the encoding control centrally, so the control for each AP cannot be performed and the correction capability is insufficient depending on the AP. Or the communication speed is reduced due to excess.

  The present invention has been made to solve the above-described problem, and places an excessive processing load on each AP even when video / audio data is broadcast from the distribution server to the subordinate wireless terminal via the AP. It is another object of the present invention to provide a wireless communication system capable of changing the error correction code capability in accordance with the channel condition of each AP.

  In order to solve the above-described problems, a wireless communication system according to the present invention includes a plurality of wireless base stations that provide services via a wireless communication path to subordinate wireless terminals, and an error from data using an error correction code. The wireless base station provides a service in a wireless communication system including a distribution server that generates corrected encoded data and distributes the data to a plurality of wireless base stations, and the wireless base station and the distribution server are connected by a first wired LAN. Communication state detection means for detecting the communication state of the wireless communication path of the area to be controlled, and control means for controlling to delete a part of the error correction encoded data based on the detection result by the communication state detection means The radio base station transmits the error correction encoded data controlled by the control means to the radio terminal. As a result, even if video / audio data is broadcast from the distribution server to the subordinate wireless terminal via the AP, an error may occur depending on the communication path status of each AP without overloading each AP. The ability of the correction code can be changed.

  The wireless communication system of the present invention further includes a reception error rate detection unit for detecting a reception error rate by the wireless terminal, and the communication state detection unit acquires the reception error rate of the wireless terminal from the wireless terminal via the wireless communication path. You may make it do. As a result, the state of the communication path can be accurately grasped almost in real time without providing other special communication means.

  In the wireless communication system of the present invention, the distribution server generates error correction encoded data by adding redundant data for error correction to the data, and the control means deletes part or all of the redundant data. You may control to. As a result, the radio base station can reduce the processing load for changing the correction capability of the error correction code, and the circuit scale and power consumption of the radio base station can be reduced.

  In the wireless communication system of the present invention, the error correction code is a product code composed of an inner code and an outer code, the reception error rate detection means detects the error rate of each of a random error and a burst error, and the control means detects this error rate. The inner code or outer code may be controlled based on the result. As a result, not only random errors in the communication path but also burst errors can be handled accurately.

  In the wireless communication system of the present invention, the error correction code may be a Reed-Solomon code, and the control means may be controlled to delete part or all of the parity of the Reed-Solomon code. This makes it possible to change the error correction capability very easily while maintaining a high error correction coding capability.

  The radio communication system of the present invention further includes control information adding means for adding to the error correction encoded data transmitted from the radio base station to the control information of the control means, and the radio terminal transmits the error correction code based on the control information. You may make it decode. As a result, coding parameters such as code length, number of parity, interleave length, etc. can be transmitted to the wireless terminal side simultaneously with the error correction code, so that it is possible to cope with a change in the state of the communication channel in real time and to transmit the coding parameters A simple system can be constructed without the need for other communication means.

  In the wireless communication system of the present invention, the wireless base station transmits control information of the control means to the distribution server via the first wired LAN, and the distribution server generates error correction encoded data based on the received control information. You may make it do. As a result, the distribution server can configure an error correction code having the minimum necessary error correction capability to cope with the communication path conditions of the entire system, and the burden of the encoding process of the distribution server is minimized. And the bandwidth of the backbone LAN can be saved.

  In the wireless communication system of the present invention, the wireless terminal is connected to the distribution server via the second wired LAN, and the distribution server receives the reception error rate from the wireless terminal via the second wired LAN and receives the received error. Control information may be generated from the error rate and transmitted to the corresponding radio base station. Thereby, since the reception error rate data detected by the wireless terminal is sent to the wireless base station via the wired LAN, the transmission error band data can be stably transmitted and the bandwidth of the wireless communication path can be effectively utilized.

  According to the present invention, even when video / audio data is broadcasted from a distribution server to an underlying wireless terminal via an AP, the communication path status of each AP can be maintained without imposing an excessive processing load on each AP. Accordingly, it is possible to provide a wireless communication system capable of changing the error correction code capability accordingly.

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

(Embodiment 1)
FIG. 1 is a configuration diagram of a radio communication system according to Embodiment 1 of the present invention. The wireless communication system according to the present embodiment provides a broadcast service that simultaneously distributes the same video data to all client wireless terminals to be serviced (hereinafter simply referred to as “wireless terminals”). An audio data service can be handled in exactly the same manner, but for the sake of simplicity, the description will be made assuming that only video data is handled. The wireless communication system includes a distribution server 1 for distributing video data, m APs (wireless base stations) 3-1,..., 3-m connected to the distribution server 1 via a backbone LAN 2, respectively. Wireless terminals 4-1 to 4-n1, which are connected to the AP of the mobile terminal and receive services, 5-1 to 5-n2 (the wireless terminals 4-1 to 4-n1 are connected to the AP 3-1. AP3-m is connected with wireless terminals 5-1 to 5-n2. Further, the service ranges of AP3-1,..., AP3-m are referred to as service zone 6-1,. Hereinafter, when it is not necessary to distinguish each AP, it will be referred to as AP3, and similarly referred to as wireless terminals 4, 5 and service zone 6.

  The distribution server 1 is a server for storing video data to be distributed in a HDD (hard disk) or the like and distributing the video data to all the wireless terminals to be serviced via each AP. In the distribution server 1, an error correction encoding process for correcting a communication error occurring on the wireless communication path is also executed simultaneously.

  The backbone LAN 2 is composed of a wide-band LAN such as Gigabit Ethernet, and is a LAN having a sufficiently wide band. All communication data between the distribution server 1 and all APs are communicated via the backbone LAN 2. Although not shown, video data from the VOD server also flows through the backbone LAN 2.

  AP (wireless base station) 3-1,..., AP 3-m transmits video data using a specific channel to all wireless terminals in service zone 6-1,. Send. In addition, each AP monitors the communication channel state such as the radio wave environment in the service zone under its jurisdiction, and controls the ability of the error correction code according to the communication channel state. For this purpose, the AP periodically acquires a reception error rate from the wireless terminals existing in the service zone. And based on this acquired data, the error correction code received from the distribution server 1 is changed and transmitted to the wireless terminal. In a space surrounded by radio wave shielding objects such as trains and airplanes, the problem of fading due to multipath becomes large, and the radio wave environment may change greatly between service zones. Even within the same service zone, the radio wave environment changes with time.

  The wireless terminals 4 and 5 include a wireless adapter unit for transmitting and receiving wireless signals and a reproduction processing unit for viewing video received from the distribution server 1, and the client is a monitor screen of the wireless terminals 4 and 5. Thus, the video service distributed from the distribution server 1 can be enjoyed.

  FIG. 2 is an example of a block diagram inside the distribution server 1 of the present embodiment. The distribution server 1 includes a video data storage unit 20 in which video data to be serviced is stored, a packet division unit 21 for reading out video data and dividing it into packet units, and adding parity for error correction to the video data. An error correction encoding unit 22, a packet division unit 21, a control unit 24 for controlling the error correction encoding unit 22, and a transmission IF unit 23 for sending video data to which error correction parity is added to the backbone LAN 2. I have. The video data storage unit 20 stores compressed video data such as MPEG in order to reduce the transmission band.

  By the way, in the case of a broadcast service, the same video data must be distributed to all APs at the same time, and the error correction capability is changed on the distribution server 1 side according to the radio wave environment of the service zone serviced by each AP. It is difficult. Also, if each AP performs error correction coding processing corresponding to the radio wave environment, the processing load of the wireless adapter unit increases, resulting in increased power consumption and increased costs. Therefore, in the present embodiment, the distribution server 1 performs error correction coding assuming the wireless terminal having the worst environment, and the AP only deletes the parity according to the radio wave environment. As a result, the load on the AP can be reduced and the coding rate corresponding to the radio wave environment of each AP can be achieved. Therefore, the coding rate can be lowered more than necessary to reduce the transmission rate (video quality), or conversely the coding rate. It is possible to avoid the problem that the error cannot be corrected by reducing the value too much.

  The operation of the error correction encoding unit 22 in FIG. 2 will be described with reference to FIG. FIG. 3 is a diagram showing the configuration of an error correction code composed of video data and parity encoded by the error correction encoding unit 22 in the present embodiment. Here, an example is shown in which one Reed-Solomon product code is composed of one packet of 800 bytes of data. The Reed-Solomon product code is a method in which video data is arranged in a square shape composed of rows and columns, and after Reed-Solomon coding is performed in the row direction, Reed-Solomon coding is performed independently in the column direction. The code in the row direction is called an inner code, and the code in the column direction is called an outer code. In the wireless communication system according to the present embodiment, four inner code parities IP1 to IP4 are added to 40-byte data D1 to D40 to generate a 44-byte inner code, and an interleave length of 40 bytes. Are interleaved to add two outer code parities OP1 and OP2 to the 20-byte data B1 to B20 to generate a 22-byte outer code. The video data sequentially read from the video data storage unit 20 is first inner-coded and then outer-coded, so that the outer code is 40-byte interleaved.

  The inner code mainly corrects random errors that occur on the communication channel, and the outer code mainly corrects burst errors. By configuring these as product codes, both random and burst errors can be configured. A code resistant to errors can be constructed. For the inner code and the outer code, errors of up to 4 bytes and 2 bytes can be corrected by using erasure correction. By configuring the product code, a burst error of up to 80 bytes can be corrected. This product code has a buffer memory (not shown) of a code length size (800 bytes in this example), and writes to this buffer memory in the order read out from the video data storage unit 20 (in the horizontal direction). It is possible to easily perform interleaving by reading out from the buffer memory in the vertical direction. In general, Reed-Solomon codes have a large processing load for encoding, but can be realized with a relatively small processing load. These processes may be realized by hardware, or may be realized by software processing if a high-performance CPU is installed.

  The code lengths of the inner code and the outer code are not limited to the above values, and may be determined as appropriate depending on the radio wave environment where the system is installed, the encoding capability of the server, and the like.

  In this embodiment, one packet is one error correction code. However, the present invention is not limited to this, and a plurality of correction codes may be configured in one packet, or one correction code. Can also be distributed over a plurality of packets.

  Next, the configuration and operation of the AP and the wireless terminal will be described with reference to FIGS. 4 and 5 are examples of block diagrams of a wireless adapter unit used for the AP and the wireless terminal in the present embodiment, respectively. The AP mainly has a transmission function for transmitting video data received from the distribution server 1 to a subordinate wireless terminal via a wireless LAN. Conversely, the wireless terminal mainly has a reception function for receiving video data transmitted from the AP. Function. The AP reception function and the wireless terminal transmission function are mainly used to transfer communication path state data in the service zone. In addition to the wireless adapter unit, the wireless terminal is provided with a video playback processing unit (not shown) for the client to view received video data. In this video reproduction processing unit, the received compressed video data is returned to the baseband video signal, and display processing on the monitor screen is performed. The video reproduction processing unit is connected to the wireless terminal via the external IF.

  As illustrated in FIG. 4, the AP transmission unit 30 includes a LAN_IF 32 for connecting to a wired LAN, an error correction change unit 33, a wireless packet generation unit 34, a modulation unit 35, and a transmission antenna 36. On the other hand, the AP reception unit 31 includes a reception antenna 37, a demodulation unit 38, a wireless packet extraction unit 39, an error rate data extraction unit 40, a correction capability control unit 41, and a LAN_IF 42.

  First, the operation of the transmission unit 30 on the AP side will be described. The LAN_IF 32 receives the video data packet from the distribution server 1, extracts error correction encoded data from this packet, and outputs it to the error correction change unit 33. The error correction changing unit 33 receives channel state data (for example, reception data error rate) from the wireless terminal, and changes the number of parity of the error correction code based on the channel state data. The wireless packet generation unit 34 divides the output of the error correction change unit 33 into packets that are the minimum unit of wireless communication, and adds a header for identifying the packet. Error correction code parameters (code length, number of parity, interleave length, etc.) are also inserted into this header. The wireless terminal correctly decodes the received error correction code by extracting the parameter carried on the header. The modulation unit 35 modulates packetized transmission data so as to be adapted to the wireless communication path. In IEEE 802.11a, which is assumed to be used in a multipath environment, OFDM that is modulated with a plurality of orthogonal subcarrier signals is used. Finally, the modulated data is transmitted from the transmission antenna 36 to the wireless terminal.

  Next, the operation of the receiving unit 31 on the AP side will be described. A radio signal including information on a reception error rate transmitted from the radio terminal is received by the receiving antenna 37, and then demodulated by the demodulation unit 38 and returned to the baseband signal. A wireless packet extraction unit 39 extracts a wireless packet. Then, the error rate data extraction unit 40 extracts error rate data from the packet data and outputs it to the correction capability control unit 41. The correction capability control unit 41 calculates the required error correction capability from the error rate data, and determines the number of parity deletions of the error correction change unit 33. Further, communication with the distribution server 1 and other APs is possible via the LAN_IF 42 as necessary.

  Next, the configuration and operation of the wireless adapter on the wireless terminal side will be described. As shown in FIG. 5, the transmission unit 50 of the wireless terminal includes an external IF 52 that receives data from another processing unit (not shown) of the wireless terminal, and error rate data for transmitting its own reception error rate to the AP side. An insertion unit 53, a wireless packet generation unit 54, a modulation unit 55, and a transmission antenna 56 are provided. On the other hand, the reception unit 51 of the wireless terminal is connected to the reception antenna 57, the demodulation unit 58, the wireless packet extraction unit 59, the error correction decoding unit 60, the error rate calculation unit 61, and other processing units (not shown) of the wireless terminal. An external IF 62 for outputting video data is provided. Here, the other processing of the wireless terminal is processing for expanding the compressed video data transmitted from the distribution server 1 and displaying the expanded video signal on the display unit for viewing by the client. .

  Next, the operation on the wireless terminal side will be described. Since the reception function is the main function on the wireless terminal side, the reception side is described first, and then the transmission side is described. The error correction coded video data extracted by the receiving antenna 57, the demodulating unit 58, and the wireless packet extracting unit 59 is subjected to error correction decoding by the error correction decoding unit 60 using the parity added by the error correction coding unit 22. This is executed, and random errors and burst errors generated during communication are corrected to restore video data free from errors. Then, it is sent to the video decoding circuit and the display processing circuit outside the wireless adapter via the external IF 62 so that the client can enjoy the video.

  On the other hand, the error correction decoding unit 60 detects an error during communication using the parity added by the error correction coding unit 22 or a CRCC check code added separately for error detection, etc., and this output is calculated as an error rate. The error rate calculation unit 61 calculates the error rate of the transmission path. As this error rate, the average value of the error rate for each packet may be taken, or the worst value may be taken. Then, the error rate value is transmitted to the AP side, and the error correction change content at the AP is determined.

  Next, the operation on the transmission side will be described. The error rate data insertion unit 53 inserts the error rate data acquired from the error rate calculation unit 61 into the transmission data, and then transmits the signal to the AP side via the radio packet generation unit 54, the modulation unit 55, and the transmission antenna 56. To do. The external IF 52 is an interface for exchanging data with an external processing unit (not shown) of the wireless terminal. When the communication path state monitoring for transmitting an error rate to the AP in response to a transmission request from the AP, the external IF 52 is externally connected. Data exchange with is not performed.

  FIG. 6 shows the data structure of the wireless packet in this embodiment. The video data read from the video data storage unit 20 of the distribution server 1 is divided into 800-byte packets. Next, after being divided into 20 blocks for every 40 bytes of the inner code unit of the Reed-Solomon product code described in FIG. 3, 4-byte parity is added to each block, and at the end of the data block, 2 bytes are added. The outer code parity of the block is added. Then, a packet header indicating a packet delimiter is added to the packet to create a wireless packet. As described above, the error correction coding parameter is inserted into the packet header, and the wireless terminal side can read the error correction coding parameter in the header and perform appropriate decoding. In this example, all the parities added by the distribution server 1 are transmitted as they are as wireless packets. If unnecessary parity is deleted in the AP, the parity number of the inner code and the parity number of the outer code in this drawing also change. These wireless packets are sent to the communication path, and the data is extracted by detecting the header on the wireless terminal side.

  FIG. 7 is a flowchart for explaining in more detail the operation of the wireless adapter unit on the AP side in the present embodiment. First, the error correction encoded data that has been error correction encoded by the distribution server 1 and packetized is received via the backbone LAN 2 (step S70). Next, error correction encoded data is extracted from the received packet (step S71), and the number of parity is changed based on the control from the correction capability control unit 41 (step S72). Thereafter, it is converted into a wireless packet and a header is added (step S73). The error correction code parameter is inserted into this header. The wireless packetized data is transmitted to the wireless terminal via the transmission antenna 36 (step S74). At the same time, the AP monitors the communication channel status of the service area under its control at a predetermined cycle during transmission of video data to the wireless terminal. This monitoring is managed by a timer that measures the time from the start of transmission. In step S75, it is checked whether or not it is the monitoring time. If it is the monitoring time (Yes), the process proceeds to step S77. If it is not the monitoring time (in the case of No), it is determined whether or not the service is terminated (step S76). If the service is not terminated (in the case of No), the process returns to step S70 to receive a new video data packet from the distribution server 1. The operation of receiving and transmitting the wireless packet to the wireless terminal is repeated.

  In step S77, a transmission request is transmitted from the AP to all wireless terminals under its control so that its own reception error rate is transmitted to the AP side. When error rate information is received from all wireless terminals (step S78), an error correction capability (additional parity number) is determined using a reference table or the like based on the received error rate of each terminal having the worst error rate (step S79). ). The method for determining the correction capability will be described in detail later. The period for monitoring the reception error rate may be appropriately determined according to the installation status of the AP or wireless terminal and the status of the content to be transmitted. Further, when the change in the radio wave environment is small, the required number of parity may be determined by receiving only once before the start of communication. Further, instead of the AP side issuing a transmission error rate request to the wireless terminal side, the reception error rate may be transmitted from the wireless terminal side to the AP side only when the reception error rate exceeds a predetermined value. . By doing this, the number of times of transmission / reception of the reception error rate is reduced, so that the communication path can be used effectively.

  Next, the operation on the wireless terminal side will be described. FIG. 8 is a flowchart showing the operation on the wireless terminal side in the present embodiment. First, in step S80, the wireless adapter determines whether or not there has been a transmission error rate data transmission request from the AP side. If there is no transmission request (No), a wireless packet of video data is received from the AP (step S81). Then, video data that has been subjected to error correction coding is extracted from the received packet described with reference to FIG. 6 (step S82). At the same time, the encoding parameter of the received video data is extracted from the header (step S83). Then, in the next step S84, error correction decoding is performed based on the extraction parameter, the error generated in the communication path is corrected, and the original video data is restored. Next, in step S85, the compressed video signal is expanded and returned to the original video signal, and this video signal is displayed on the display unit of the client (step S86). Finally, it is determined whether or not the service is finished (step S87). If the service is not finished (No), the process returns to step S80 and the above operation is repeated.

  On the other hand, if it is determined in step S80 that there is a transmission request (in the case of Yes), the wireless terminal calculates the error rate of the received data (step S88) and transmits the data of this reception error rate to the AP side (step S88). S89). The error rate to be transmitted to the AP side may be the error rate of the packet immediately before accepting the transmission request, or the average error rate of a predetermined number of received packets in the past or the worst value of the error rate in order to improve the accuracy. May be used.

  Here, the error rate that can be detected by performing error correction decoding on the received video data is used as the channel state data. However, the present invention is not limited to this, and in order to measure more strictly, the error rate measurement A signal may be separately received from the AP side, and the error rate measured with this signal may be returned. Further, the communication path state may be measured by a radio wave intensity received by the terminal other than the error rate, for example. This eliminates the need for extra processing such as error rate calculation, thereby enabling faster processing. Further, for error detection, an error rate at the packet level may be calculated using FCS added in the MAC layer without being detected by an error correction code, and this value may be used as a reception error rate. .

  FIG. 9 is a diagram showing an example of a reference table for determining the parity number of the error correction code from the reception error rate in the present embodiment. For example, the quality grade is set to five levels based on the reception error rate. The relationship between the error rate and the quality grade is separately determined with reference to not only the error rate but also the occurrence status of random errors and burst errors. The parity of the inner code and outer code of the error correction product code is determined as shown in the table of FIG. 9 according to each quality grade. When the parity number is determined, the coding rate can be calculated. Grade 5 is the case where the error rate is the highest (when the radio wave environment is bad). In this case, parity is not deleted and the parity added by the distribution server 1 is transmitted as it is. In this case, the error correction capability is maximized, but the coding rate is 0.83, which is the lowest, and the transmission speed is decreased. As shown in FIG. 9, grade 2 deletes one outer code parity, grade 3 deletes two inner code parities, grade 4 deletes two inner code parities, and two outer code parities. In grade 5, the error rate is the lowest, and error correction is performed when the error is corrected only by the convolutional code of the physical layer of the wireless LAN. In this case, since redundancy is not added, the coding rate is 1.00 and the transmission speed is maximized. The grade is determined in consideration of not only the error rate but also the error occurrence status. That is, grade 2 and grade 3 have the same coding rate, but grade 2 is selected when random errors are dominant, and grade 3 is selected when there are many burst errors. In this way, it is possible to configure an optimum error correction code depending on the error occurrence situation at that time. This table may be appropriately determined depending on the error correction code to be used and the fluctuation status of the radio wave environment.

  FIG. 10 is a diagram showing the configuration of the Reed-Solomon error correction product code when grades 2, 3, and 4 are selected in the present embodiment. FIG. 10A shows product codes generated by the distribution server 1, and FIGS. 10B, 10C, and 10D show grade 2, 3, and 4 code configurations, respectively.

  Thus, in the present embodiment, the configuration of the error correction code of data to be transmitted wirelessly is determined based on the reception error rate of the terminal having the largest reception error rate among the wireless terminals, and the AP is based on that. Delete unnecessary parity on the side. As a result, the correction capability and transmission speed can be optimized for each AP (for each radio zone), and the heavy encoding processing is performed on the distribution server 1 side to minimize the processing load on the AP side. it can.

  In the above description, the Reed-Solomon code has been described as an example of the error correction code, but the error correction code is not limited to the Reed-Solomon code. For example, an LDPC code (Low Density Parity-check Code), a BCH code, or the like may be used. In addition, the error correction code is not only a systematic code in which video data and parity that is redundant data for error correction are completely separated, such as a Reed-Solomon code, but also a single code for data and redundant data. There are also unorganized codes that have a mixed configuration. Such an unstructured code can also be used as the error correction code. In the case of a systematic code such as a Reed-Solomon code, only the parity is deleted according to the communication channel state by the AP, but in the case of a non-systematic code, data including redundant data is deleted. Also in this case, since the encoding is performed on the delivery server side, the load on the AP side is hardly applied.

  Also, when using an error correction code other than the Reed-Solomon code, these error correction codes may be used alone. For example, these error correction codes are used as inner codes, and Reed-Solomon codes are used as outer codes. Then, the above description can be applied as it is.

(Embodiment 2)
Next, a second embodiment will be described. The difference between the second embodiment and the first embodiment is an error correction coding process in the distribution server. In the first embodiment, the parity to be added is determined in advance assuming the worst value of all wireless terminals that provide the service. In the second embodiment, the distribution server acquires the encoding parameters from each AP. Thus, the encoding is realized. FIG. 11 is a block diagram inside the distribution server 7 in the present embodiment. Constituent blocks having the same functions as those of the first embodiment are denoted by the same reference numerals and description thereof is omitted. The distribution server 7 acquires the encoding parameter at that time from all APs via the backbone LAN 2 by the reception IF unit 26. Then, the control unit 25 instructs the error correction coding unit 22 to perform error correction coding at a value with the smallest coding rate among the obtained coding rates of all APs. In the first embodiment, the distribution server 1 must always perform coding processing with the heaviest load assuming the worst value. By doing so, the burden of coding processing of the distribution server 7 is necessary. The bandwidth can be reduced to the minimum, and the bandwidth of the basic LAN 2 can be saved.

(Embodiment 3)
Next, Embodiment 3 will be described. The difference between the third embodiment and the first embodiment is a method in which the AP side acquires error rate information of the wireless terminal. In the first embodiment, the AP side issues a transmission request to the wireless terminal, and the wireless terminal that has received the transmission request transmits the video data to the AP side while receiving video data. For this reason, transmission / reception of redundant data occurs on the wireless transmission path, or extra processing occurs in both the AP and the wireless terminal, which causes a decrease in transmission speed.

  In the third embodiment, the error rate information of the receiving terminal is transmitted to the distribution server via the wired LAN connected to the distribution server, and the distribution server determines the encoding parameter based on this information. FIG. 12 is a configuration diagram of the wireless communication system in the present embodiment. The constituent blocks having the same functions as those of the first embodiment are denoted by the same reference numerals and description thereof is omitted. All wireless terminals that receive the distribution service are connected to the distribution server 1 via the wired LAN 8. By doing so, the error rate information from the wireless terminal can be sent stably via the wired LAN 8, and there is no need to send redundant data by wireless communication, so there is no fear of lowering the communication speed. Further, the distribution server 1 determines the encoding parameter at each AP using the reference table of FIG. 9 from the error rate information acquired from each wireless terminal. Separately from the video data, each parameter is transmitted to each AP via the backbone LAN 2, and each AP deletes the parity according to the received parameter. Thereby, the minimum necessary parity can be added and the transmission speed is not impaired.

  As described above, according to the wireless communication system of the present invention, even when video / audio data is broadcast from the distribution server to each wireless terminal via the base station, an excessive burden is placed on each base station. In addition, it is possible to provide a radio communication system capable of optimizing communication performance and quality for each base station.

  The present invention is, for example, a wireless communication system that communicates data in units of packets using a wireless LAN, and particularly wireless communication that distributes information such as video signals through a communication path that is highly likely to cause a communication error. It can be used for the system.

Configuration diagram of radio communication system according to Embodiment 1 of the present invention Block diagram inside distribution server according to Embodiment 1 of the present invention The figure which shows the structure of the error correction code | cord | chord which consists of the video data and parity which are encoded in the error correction encoding part in Embodiment 1 of this invention. The block diagram of the radio | wireless adapter part used for AP in Embodiment 1 of this invention. Block diagram of a wireless adapter unit used in the wireless terminal according to Embodiment 1 of the present invention The figure which shows the data structure of the radio | wireless packet in Embodiment 1 of this invention. The flowchart for demonstrating operation | movement of the wireless adapter part by the side of AP in Embodiment 1 of this invention The flowchart which shows operation | movement of the radio | wireless terminal in Embodiment 1 of this invention. The figure which shows an example of the reference table for determining the parity number of an error correction code from the reception error rate in Embodiment 1 of this invention. The figure which shows the structure of the Reed-Solomon error correction product code | cord | chord when the grade 2, 3, 4 in Embodiment 1 of this invention is selected. Block diagram inside distribution server in embodiment 2 of the present invention Configuration diagram of radio communication system according to Embodiment 3 of the present invention

Explanation of symbols

1,7 Distribution server 2 Core LAN
3,3-1 to 3-m AP (radio base station)
4,4-1 to 4-n1,5,5-1 to 5-n2 wireless terminal 6,6-1 to 6-m service zone 8 wired LAN
20 video data storage unit 21 packet division unit 22 error correction encoding unit 23 transmission IF unit 24, 25 control unit 26 reception IF unit 30, 50 transmission unit 31, 51 reception unit 32, 42 LAN_IF
33 Error correction change unit 34, 54 Radio packet generation unit 35, 55 Modulation unit 36, 56 Transmission antenna 37, 57 Reception antenna 38, 58 Demodulation unit 39, 59 Radio packet extraction unit 40 Error rate data extraction unit 41 Correction capability control unit 52,62 External IF
53 Error rate data insertion unit 60 Error correction decoding unit 61 Error rate calculation unit

Claims (8)

A plurality of radio base stations that provide services to the subordinate radio terminals via a radio communication path;
A server for generating error correction encoded data from data using an error correction code and distributing to the plurality of radio base stations;
In the wireless communication system in which the wireless base station and the distribution server are connected by a first wired LAN,
The wireless base station detects a communication state of the wireless channel in an area providing the service, and a part of the error correction encoded data based on a detection result by the communication state detection unit. Control means for controlling to delete,
The wireless communication system, wherein the wireless base station transmits the error correction encoded data after the control by the control means to the wireless terminal. The wireless terminal has reception error rate detection means for detecting a reception error rate, and the communication state detection means acquires the reception error rate of the wireless terminal from the wireless terminal via the wireless communication path. The wireless communication system according to claim 1. The distribution server generates the error correction encoded data by adding redundant data for error correction to the data, and the control means controls to delete part or all of the redundant data The wireless communication system according to claim 1 or 2. The error correction code is a product code composed of an inner code and an outer code, the reception error rate detection means detects each error rate of a random error and a burst error, and the control means determines the inner error based on the detection result. The radio communication system according to any one of claims 1 to 3, wherein the code or the outer code is controlled. The error correction code is a Reed-Solomon code, and the control unit performs control so as to delete a part or all of the parity of the Reed-Solomon code. Wireless communication system. The radio base station further includes control information adding means for adding control information of the control means to the error correction encoded data to be transmitted, and the radio terminal decodes the error correction code based on the control information The wireless communication system according to any one of claims 1 to 5. The radio base station transmits control information of the control means to the distribution server via the first wired LAN, and the distribution server generates the error correction encoded data based on the received control information. The wireless communication system according to claim 1. The wireless terminal is connected to the distribution server via a second wired LAN, the distribution server receives the reception error rate from the wireless terminal via the second wired LAN, and the received reception error rate. 2. The radio communication system according to claim 1, wherein the control information is generated from the base station and transmitted to the corresponding radio base station.

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