JP2012019459A - Wireless communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wireless communication system which improves transmission efficiency by selecting an optimum modulation system suitably according to the situation of a wireless space beforehand when high-capacity data is transmitted continuously.SOLUTION: In a wireless communication system 1 performing communication by Block Ack system, a transmitter transmits a request frame for requesting execution of Block Ack to a receiver. The receiver determines a modulation system to be used in communication out of a plurality of modulation systems according to the reception state of the request frame thus received. The receiver also sets a determined modulation system in the field of a response frame which responds to the request for executing the Block Ack and transmits the modulation system to the transmitter. The transmitter transmits a data frame by using the modulation system which is set in the field of a response frame thus received.

Description

  The present invention relates to a digital wireless communication system between a plurality of mobile terminals such as a wireless LAN (Local Area Network) and a wireless PAN (Personal Area Network).

  In a physical layer (PHY layer) defined by wireless communication, particularly IEEE802.11 (a standard group of wireless LANs defined by the Institute of Electrical and Electronics Engineers) of a wireless LAN, a plurality of transmission rates are supported by a modulation method. However, IEEE 802.11 does not define a rate adaptation algorithm that is an algorithm for selecting a transmission rate according to channel quality, and implementation of the rate adaptation algorithm is left to the company that manufactures the IEEE 802.11 interface. It has been.

  For this reason, IEEE802.11 provides some provisions to maintain the interoperability of devices that support rate adaptation in the physical layer.

  Current rate adaptation algorithms include a method called ARF (Automatic Rate Fallback) that estimates channel quality from the success and failure of ACK (Acknowledgement) reception performed at the transmitting terminal, and RTS (Request to Send) that is a control frame. : Transmission request) / CTS (Clear to Send: ready to receive) packet, the wireless terminal that has received the RTS packet transmits the transmission rate based on the SNR (Signal-to-Noise Ratio) of the received radio wave For example, there is a method called RBAR (Receiver-Based Autorate).

  The ARF method, which is one of the conventional means for changing the transmission rate, controls the communication rate according to the communication error rate. Therefore, the ARF method is caused by a delay problem that cannot be applied unless an error actually occurs, and a packet collision. Transmission failure is also regarded as a communication error, and there is a problem that the transmission rate is lowered. In addition, in order to control the modulation system by receiving the ARFACK frame, when continuously transmitting data divided into frame units including control information, etc., the communication system must return an ACK frame for each data transmission. There was a problem that it could not be applied.

  The RBAR system, which is another means for controlling the transmission rate, exchanges information on the modulation system and data length between the transmission side and the reception side using RTS / CTS frames before communication. The transmitting side communicates with the modulation method specified by the receiving side, and for the surrounding terminals, it uses RSH (Reservation SubHeader: reservation subheader) using a part of the MAC header of the MAC (Media Access Control) frame. NAV (Network Allocation Vector: a period during which a station other than a terminal having a transmission right suppresses access by a virtual carrier sense function) is notified.

  In the physical layer in the RBAR system, the RSH transmission rate and the data transmission rate are required to transmit data, and it is necessary to notify the reception side of the RSH transmission rate and the data transmission rate. is there. Therefore, an area called SIGNAL in the PLCP header portion of a PLCP (Physical Layer Convergence Protocol) frame is used separately for the RSH transmission rate and the data transmission rate, unlike the conventional wireless LAN usage. Become.

  In the case of the RBAR method, since the communication rate can be set based on the propagation state of the immediately preceding radio space before transmission, it is possible to provide high-rate communication that is more stable than the ARF method. However, when the RBAR method is used as it is, bit information called HCS (Header Check Sequence) is added to the MAC header of the MAC frame when the RSH is used, or the SIGNAL of the physical layer (PHY layer) PLCP frame format. Since it is necessary to divide the area for Data Rate and RSH Rate, the frame configuration needs to be changed for both MAC and PHY.

  Both of the above two conventional examples are systems in which data is transmitted as a single frame without being divided, and there is a problem that it cannot be used as it is when a plurality of frames are transmitted continuously. In particular, when a plurality of frames such as IEEE 802.11e block ack communication are transmitted, there is a problem of occupying more radio space.

JP 2005-236709 A

  In view of such circumstances, the present invention provides a wireless communication system that improves transmission efficiency by appropriately selecting an optimal modulation scheme in advance according to the state of the wireless space when continuously transmitting a large amount of data. To do.

  The present invention is a wireless communication system that performs communication using a block acknowledgment method, wherein a transmission device transmits a request frame requesting execution of the block acknowledgment to a reception device, and the reception device receives a reception state of the received request frame. And determining a modulation scheme to be used for communication from among a plurality of modulation schemes, and setting the determined modulation scheme in a field of a response frame that responds to a request for execution of the block acknowledgment. The transmission apparatus relates to a wireless communication system that transmits a data frame using a modulation method set in a field of the received response frame.

  According to the present invention, there is provided a wireless communication system that performs communication using a block acknowledgment method, wherein the transmission device transmits a request frame requesting execution of the block acknowledgment to the reception device, and the reception device receives the received request frame. A modulation scheme to be used for communication is determined from among a plurality of modulation schemes according to a reception state, and the determined modulation scheme is set in a field of a response frame that responds to a request to execute block acknowledgment. Since the transmission device transmits the data frame using the modulation method set in the field of the received response frame, the appropriate modulation method can be used even when communication occupies a large amount of radio space. Can be used for communication, and by selecting the most suitable modulation method, wireless space is wasted. There is no Rukoto, there is exhibited an excellent effect that it is possible to utilize more of the wireless space.

It is the schematic which shows the radio | wireless communications system based on the Example of this invention. It is a schematic diagram of the baseband part which comprises this radio | wireless communications system. It is the schematic of the MAC layer (wireless) and PHY layer (wireless) which comprise this baseband part. A comparison between the present embodiment and a conventional ADDBA Request frame format is shown, (A) is a schematic diagram of a conventional ADDBA Request frame format, and (B) is a schematic diagram of an ADDBA Request frame format of the present embodiment. The comparison of the principal part of a present Example and the conventional ADDBA frame format is shown, (A) is a schematic diagram of the conventional ADDBA frame format, (B) is a schematic diagram of the ADDBA frame format of a present Example. A comparison between the present embodiment and a conventional ADDBA Response frame format is shown, (A) is a schematic diagram of a conventional ADDBA Response frame format, and (B) is a schematic diagram of an ADDBA Response frame format of the present embodiment. It is a timing chart of a present Example.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 schematically shows a wireless communication system according to an embodiment of the present invention, in which 1 is a wireless communication system, 2 is one of communication networks, Ethernet (registered trademark), 3 Indicates a transmission / reception device. The transmission / reception device 3 mainly includes a baseband unit 4, a radio communication unit (RF unit) 5, and an antenna 6 connected to the radio communication unit 5. The communication units 5 are connected via a coaxial cable 7, and the antenna 6 is connected via an RF coaxial cable 8.

  Next, the flow of communication data in the wireless communication system 1 having the above configuration will be described.

  In the case of transmission data, when data (IP packet) 10 transmitted from a data transmission terminal (not shown) or the like via the Ethernet 2 is input to the baseband unit 4 as input data, the baseband unit 4 In this process, conversion from wired Ethernet 2 MAC frame to wireless MAC frame, access method control, conversion to PLCP frame, error correction, modulation processing, addition of synchronization signal, D / A conversion, etc. are performed. The baseband unit 4 outputs a baseband signal (analog signal) 11.

  A baseband signal 11 output from the baseband unit 4 is input to the wireless communication unit 5 via the coaxial cable 7. The wireless communication unit 5 converts the baseband signal 11 into a wireless signal, performs necessary signal processing such as filtering, amplification, etc., and outputs the signal as a wireless signal 12. A radio signal 12 output from the radio communication unit 5 is transmitted to the radio space from the antenna 6 via the RF coaxial cable 8.

  In the case of received data, when a radio signal is input to the radio communication unit 5 from the antenna 6 via the RF coaxial cable 8, the radio communication unit 5 performs low noise amplification, filtering, demodulation processing, etc. Necessary signal processing is performed and output from the wireless communication unit 5 as a baseband signal (analog signal) 11.

  A baseband signal 11 output from the wireless communication unit 5 is input to the baseband unit 4 through the coaxial cable 7. The baseband unit 4 performs processing such as A / D conversion, correlation detection, equalization processing, synchronization processing, demodulation processing, error correction, PLCP analysis, and MAC frame analysis on the baseband signal 11 as data 10. Is output. Data 10 output from the baseband unit 4 is transmitted to a data receiving terminal (not shown) or the like via the Ethernet 2.

  In the transmission system of the present embodiment, frame conversion processing and modulation processing are executed by a MAC layer (wireless) (described later) and a PHY layer (wireless) (described later) constituting the baseband unit 4.

  Hereinafter, the baseband unit 4 in the present embodiment will be described with reference to FIG.

  The baseband unit 4 includes a PHY layer (wired) 14, a MAC layer (wired) 15, a MAC layer (wireless) 16, and a PHY layer (wireless) 17, and includes the PHY layer (wired) 14 and the MAC layer ( (Wired) 15 constitutes a wired processing system, and the MAC layer (wireless) 16 and the PHY layer (wireless) 17 constitute a wireless processing system.

  The PHY layer (wired) 14 and the MAC layer (wired) 15 perform frame generation and control on the data 10 input via the Ethernet 2, and the MAC layer (wireless) 16 and the PHY layer (wireless). ) 17 performs frame generation and wireless LAN control.

  Next, the flow of transmission data and reception data in the baseband unit 4 and the processing content in each layer will be described.

  In the case of transmission data, when the data 10 is input to the PHY layer (wired) 14 via the Ethernet 2, the PHY layer (wired) 14 generates a frame for wireless communication from pitch data. The MAC frame 18 is sent to the MAC layer (wired) 15. The MAC layer (wired) 15 analyzes the Ethernet 2 MAC frame, extracts the MAC header, and sends a signal 19 in the form of data transmitted to and received from the upper layer to the MAC layer (wireless) 16.

  The MAC layer (wireless) 16 adds a wireless MAC header to the signal 19 to generate a wireless MAC frame 20. Further, in the transmission process, the PHY layer (wireless) 17 is notified of information such as a modulation method, a data size, a MAC frame generated by itself using a message called a primitive.

  The PHY layer (wireless) 17 generates a PLCP frame based on information notified from the MAC layer (wireless) 16. At this time, the modulation scheme information instructed from the MAC layer (wireless) 16 is stored in the PLCP frame, and is input to the wireless communication unit 5 via the coaxial cable 7 as the baseband signal 11. It has become.

  In the case of received data, when the baseband signal 11 is input to the PHY layer (wireless) 17 via the coaxial cable 7, the baseband signal 11 is transmitted to the PHY layer (wireless) 17. After performing predetermined processing such as A / D conversion, correlation detection, equalization processing, synchronization processing, demodulation processing, error correction, etc., the PLCP frame is finally analyzed, and a message called a primitive is used as in the case of transmission data Information such as the MAC frame, data size, modulation method, reception level, equalization error, etc. is notified to the MAC layer (wireless) 16.

  The MAC layer (wireless) 16 analyzes the wireless MAC frame 20, extracts the MAC header, and sends a signal 19 in the form of data transmitted to and received from the upper layer to the MAC layer (wired) 15.

  In the MAC layer (wired) 15, an Ethernet 2 MAC header is attached to the signal 19, and it is sent to the PHY layer (wired) 14 as an Ethernet 2 MAC frame 18. The PHY layer (wired) 14 analyzes the MAC frame 18 and inputs data 10 as pitch data to the data receiving terminal (not shown) or the like via the Ethernet 2.

  Next, the details of the radio processing system of the baseband unit 4 will be described with reference to FIG.

  Among the wireless processing systems, the MAC layer (wireless) 16 includes a modulation method selection unit 22, an equalization error information processing unit 23, a modulation method setting unit 24, and a reception level processing unit 25.

  The modulation method selection unit 22 selects an arbitrary modulation method when transmitting framed data, notifies the modulation method setting unit 24 of a modulation method setting value 26 corresponding to the selected modulation method, and When receiving data, it has a function of comparing the received data with a preset threshold 27 and selecting a modulation method.

  The modulation scheme setting unit 24 generates an ADDBA Request frame (request frame) and an ADDBA Response frame (response frame) (described later) as MAC frames based on the modulation scheme setting value 26 notified from the modulation scheme selection unit 22. have.

  The equalization error information processing unit 23 and the reception level processing unit 25 are the same as the reception level information notified by the primitive 28 from the PHY layer (wireless) 17 to the MAC layer (wireless) 16 at the time of data reception. It has a function to analyze error information.

  Next, with reference to FIGS. 4A and 4B, the format of the ADDBA Request frame (ADDBA Request frame format) will be described.

  The ADDBA (Add Block Ack) is a process for performing negotiation for setting communication quality such as a modulation method and a transmission rate between the transmission side and the reception side in advance when communication is performed using the Block Ack method, and ADDBA Request is performed. The frame is a request for negotiation from the receiving side.

  In the present embodiment, the ADDBA Request frame is generated as a MAC frame, and includes a MAC header 29a, a frame body 31a, and a Frame Check Sequence (FCS) field 32a. The MAC header 29a and the frame body 31a each include a plurality of fields. It is composed of

  The MAC header 29a includes a frame control field 33a indicating information such as a frame type, a duration field 34a indicating transmission rate information and time information necessary for frame transmission, and a Dest Address (DA) field 35a indicating a transmission destination address. A source address (SA) field 36a indicating a source address, an independent basic service set identification (IBSSID) field 37a indicating an ID for identifying a network that transmits and receives frames in the ad hoc mode, a sequence number of the MAC frame, , And a Sequence Control field 38a indicating a fragment number for the fragment.

  The frame body 31a includes a Category field 39a indicating the function of the frame, an Action field 41a indicating details of the function of the frame, a Dialog Token field 42a for identifying a request and a response, and a Block Ack used for negotiation. A Parameter Set field 43a, a Block Ack Timeout Value field 44a indicating a time-out value at the time of frame exchange, and a Block Ack Starting Sequence Control field 45 indicating a sequence number of a MAC frame for starting Block Ack communication. The Parameter Set field 43a is reserved. Field 46a, Block Ack Policy field 47a, TID field 48a, is composed of four sub-fields of Buffer Size field 49a.

  The FCS field 32a stores correction information for detecting errors in the MAC header 29a and the frame body 31a.

  In the case of the conventional ADDBA Request frame, Code = 3 representing the conventional Block Ack is set in the Category field 39a. In the present embodiment, the Category field 39a is used as the RATE field 51a.

  FIGS. 5A and 5B are partial detailed views comparing the conventional example of the ADDBA frame and this embodiment, and FIG. 5B shows a RATE field 51 and subfields of the RATE field 51. The RATE field 51 is composed of three subfields: a Reserve field 52, a modulation method field 53, and a Category Code field 54.

  A FF (hex) fixed value is set in the Category Code field 54, a setting value (3 bits) of a modulation method arbitrarily selected on the transmission side is set in the modulation method field 53, and the Reserve field 52 is set in the Reserve field 52. 0 is set, and as the RATE field 51, the Code value (4-126) of the Reserve field (not shown) of the conventional Category field 39 is used.

  Next, with reference to FIGS. 6A and 6B, the ADDBA Response frame format (ADDBA Response frame format) will be described.

  The basic configuration of the ADDBA Response frame is the same as that of the ADDBA Request frame (see FIG. 4). As a response to the ADDBA Request frame from the transmission side, the reception side sends back an ADDBA Response frame to negotiate with the transmission side. It is supposed to be done.

  The ADDBA Response frame is composed of a MAC header 29b, a frame body 31b, and an FCS 32b. However, the Block Ack Starting Sequence Control field 45 does not exist in the ADDBA Response frame, and instead Block Ack communication succeeded. In the case of failure, it has a Status Code field 55 in which a code indicating the cause is set.

  Similarly to the ADDBA Request frame, the ADDBA Response frame uses the Category field 39b in the conventional ADDBA Request frame as the RATE field 51b.

  Next, processing in the MAC layer (wireless) 16 when performing communication using the Block Ack method will be described.

  When performing transmission using Block Ack communication, first, an arbitrary modulation method is selected by the modulation method selection unit 22 of the MAC layer (wireless) 16 on the transmission side, and the selected modulation method is supported. The modulation scheme setting value 26 is notified to the modulation scheme setting unit 24.

  The modulation scheme setting unit 24 generates an ADDBA Request frame according to the notified modulation scheme setting value 26, is notified to the PHY layer (wireless) 17 as a primitive 28, and outputs the ADDBA Request frame to the receiving side.

  When receiving, the ADDBA Request frame output from the transmission side is input to the PHY layer (wireless) 17, and the PHY layer (wireless) 17 uses the primitive 28 to receive the reception level information of the ADDBA Request frame. Equalization error information is notified to the MAC layer (wireless) 16.

  In the MAC layer (wireless) 16, the received reception level information and equalization error information are analyzed by the reception level processing unit 25 and the equalization error information processing unit 23, and the analysis result is the modulation scheme selection unit 22. Are compared with a preset threshold value 27, and the optimum modulation method is selected. The selected modulation method is set in the RATE field 51b of the ADDBA Response frame, and an ADDBA Response frame is returned to the transmission side as a response to the ADDBA Request frame from the transmission side.

  When the transmission side receives the ADDBA Response frame, the transmission side extracts the modulation scheme set in the RATE field 51b of the ADDBA Response frame, and transmits data as a Data frame (data frame) by the modulation scheme. When transmission of all Data frames is completed, the transmitting side transmits a Block Ack Request frame that is a request for an acknowledgment response to the normally received Data frame to the receiving side, and the receiving side that has received the Block Ack Request frame confirms the response to the normally received frame. Is transmitted to the transmitting side, the communication is completed.

  FIG. 7 is a timing chart of the present embodiment, and a block Ack communication sequence will be described with reference to FIG. The outline of the operation of the Block Ack communication in this embodiment is basically the same procedure as that of the conventional Block Ack communication.

  First, a modulation scheme arbitrarily selected by the modulation scheme selector 22 (see FIG. 3) for negotiation of Block Ack scheme from the transmitting station 56 is selected by the modulation scheme setting section 24 (see FIG. 3). The RATE field 51 a (see FIG. 4B) is set, and an ADDBA Request frame is transmitted to the receiving station 57.

  In the receiving station 57, the reception level and equalization error information of the ADDBA Request frame sent from the transmitting station 56 are acquired from the PHY layer (wireless) 17 (see FIG. 3) and the RATE field of the ADDBA Request frame. The modulation scheme set in 51a is acquired. The modulation scheme selection unit 22 compares the reception level and equalization error information acquired from the PHY layer (wireless) 17 with the threshold 27 (see FIG. 3), and determines the final modulation scheme as the RATE of the ADDBA Response frame. The field 51b (see FIG. 5B) is set and returned to the transmitting station 56.

  The transmitting station 56 acquires the modulation scheme from the RATE field 51b of the ADDBA Response frame, and the subsequent Data frames are transmitted from the transmitting station 56 by the modulation scheme set in the RATE field 51b of the ADDBA Response frame.

  After transmitting all the Data frames, the transmitting station 56 transmits a Block Ack Request frame to the receiving station 57, and the receiving station 57 that has received the Block Ack Request frame returns a Block Ack frame to the transmitting station 56. The transmitting station 56 analyzes the returned Block Ack frame, and if all the Data frames have been transmitted normally, the communication is terminated. If there is a Data frame that could not be transmitted normally, the Data frame that could not be transmitted is transmitted again, and after the transmission of the Data frame is completed, a Block Ack Request frame is transmitted to the receiving station 57, and the Block Ack returned Analyze the frame. As a result of the analysis, if the retransmitted Data frame is normally transmitted, the communication is terminated. If there is a Data frame that cannot be transmitted, the above process is repeated until the Data frame is normally transmitted, and the communication is terminated. To do.

  As described above, before transmitting data from the transmission side to the reception side, the transmission side transmits an ADDBA Request frame generated as a MAC frame, and the reception side selects a modulation scheme selected based on the reception level and equalization error information Since the transmission side transmits the Data frame with the modulation method acquired from the ADDBA Response frame, the transmission side transmits the MAC frame again after receiving the ADDBA Response frame. Negotiation is not necessary, the communication process can be simplified, and communication can be performed with an appropriate modulation method even when a large amount of radio space is occupied.

  In addition, since the present embodiment can be implemented only by changing the Category field 39 of the conventional ADDBA Request frame and the ADDBA Response frame to the RATE field 51, the conventional frame configuration may be changed slightly and easily. Can be implemented.

  Furthermore, by selecting an optimum modulation method, it is possible to use more radio space without wastefully occupying the radio space.

(Appendix)
The present invention includes the following embodiments.

  (Supplementary note 1) In a plurality of wireless terminals that perform data transmission / reception, in the case of a one-to-one transmission, before the transmission side transmits transmission data, the reception side of the reception side such as the reception quality and reception level from the reception side. Considering the status information, select the modulation method from the transmission side and notify the reception side. The reception side examines whether the modulation method specified by the transmission side is possible, and determines the final modulation method from the transmission side. The wireless communication system is characterized in that the transmission side that has received the response from the reception side transmits the transmission data by the final modulation scheme designated by the reception side.

  (Supplementary note 2) The wireless communication system according to supplementary note 1, wherein the selection of a modulation scheme is controlled in a baseband one-layer / MAC layer (Media Access Control Layer).

DESCRIPTION OF SYMBOLS 1 Wireless communication system 2 Ethernet 3 Transmission / reception apparatus 4 Baseband part 5 Wireless communication part 6 Aerial line 10 Data 11 Baseband signal 12 Wireless signal 14 PHY layer (wired)
15 MAC layer (wired)
16 MAC layer (wireless)
17 PHY layer (wireless)
18 MAC frame 19 Signal 20 MAC frame 29 MAC header 31 Frame body 51 RATE field

Claims (1)

  A wireless communication system that performs communication using a block acknowledgment method, wherein a transmission device transmits a request frame for requesting execution of the block acknowledgment to a reception device, and the reception device has a plurality of frames depending on a reception state of the received request frame. A modulation method to be used for communication is determined from among the modulation methods, and the determined modulation method is set in the field of the response frame in response to the request for execution of the block acknowledgment, and transmitted to the transmission device, The wireless communication system, wherein the transmitting apparatus transmits a data frame using a modulation method set in a field of the received response frame.

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