JP2006013841A - Wireless communication system, wireless communication apparatus and wireless communication method, and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless communication system, a wireless communication apparatus and a wireless communication method, and a computer program capable of efficiently transmitting data as the entire system by avoiding communication opportunities from being partial due to unreasonable extension of a re-transmission interval of a communication station with a weak reception power. <P>SOLUTION: Each communication station grasps a communication state of its own station on the basis of reception power from an access point and sets a transmission interval in response to the communication state under which its own station is set by increasing the upper limit of the number of retransmission times in response to the increased reception power and decreasing the upper limit of the number of retransmission times in response to the decreased reception power. As a result, when the communication state is not excellent, re-transmission interval is extended every time the number of retransmission times is increased due to collision and lost transmission opportunities can autonomously be avoided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program for performing mutual communication between a plurality of wireless stations such as a wireless LAN (Local Area Network). The present invention relates to a wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program in which a wireless network is operated by performing autonomous distributed communication operations.

  More specifically, the present invention relates to a wireless communication system and a wireless communication apparatus in which each communication station performs autonomous and distributed access control while avoiding a collision in accordance with a CSMA (Carrier Sense Multiple Access Collision Avidance) communication procedure. In particular, the present invention relates to a wireless communication method and a computer program, and in particular, avoids a situation in which a retransmission interval of a communication station with low received power is unduly long and an unfair communication opportunity is avoided to efficiently transmit data as a whole system. The present invention relates to a wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program.

  Information network sharing and device resource sharing can be efficiently realized by computer networking such as a LAN. Here, a wireless LAN is attracting attention as a system for releasing users from the conventional wired LAN connection. According to the wireless LAN, most of the wired cables can be omitted in a work space such as an office, so that a communication terminal such as a personal computer (PC) can be moved relatively easily.

  In recent years, the demand for wireless LAN systems has increased remarkably with the increase in speed and cost. In particular, the introduction of a personal area network (PAN) has been studied in order to construct a small-scale wireless network between a plurality of electronic devices existing around a person and perform information communication. For example, different radio communication systems and radio communication systems are defined using frequency bands that do not require a license from a supervisory agency, such as 2.4 GHz band and 5 GHz band.

  One standard for wireless networks is IEEE (The Institute of Electrical and Electronics Engineers) 802.11 (for example, see Non-Patent Document 1), HiperLAN / 2 (for example, Non-Patent Document 2 or Non-Patent Document 2 or Non-Patent Document 2). Patent Document 3), IEEE 802.15.3, Bluetooth communication, and the like. Regarding the IEEE802.11 standard, there are extended standards such as IEEE802.11a (see, for example, Non-Patent Document 4), b, and g, depending on the wireless communication method and the frequency band to be used.

  Generally, in order to configure a local area network using wireless technology, it is called “access point”, “coordinator”, or “point coordinator (PC)”, which controls the whole area. A method is used in which one communication device is provided and a network is formed under the overall control of the communication device. When a certain communication station performs information transmission, first, a band necessary for the information transmission is reserved at an access point, and a transmission path is used so that a collision with information transmission at another communication station does not occur. That is, synchronous wireless communication is performed in which communication stations in the wireless network are synchronized with each other through the access point.

  Here, in a wireless communication system in which an access point exists, when performing asynchronous communication between a communication device on the transmission side and the reception side, wireless communication via the access point is always required. There is a problem that usage efficiency is halved. On the other hand, as another method of configuring a wireless network, an autonomous distributed communication method in which terminals perform wireless communication directly and asynchronously has been devised.

  For example, in an ad hoc wireless communication system that does not have a central control station, the routing is automatically changed even if one unit fails or power is turned off, so that the network is unlikely to fail, and packets are hopped multiple times between mobile stations. As a result, data can be transmitted to a relatively long distance while maintaining a high data rate. Various development cases are known for ad hoc systems (for example, see Non-Patent Document 5).

  For example, in an IEEE802.11 wireless LAN system, networking in IEEE802.11 is based on the concept of BSS (Basic Service Set). The BSS is an “ad-hoc mode” composed of only a BSS defined by an “infrastructure mode” in which a master such as an AP (Access Point) exists and a plurality of mobile stations (Mobile Terminals). IBSS (Independent BSS) defined by

  As a data transmission / access control method in a wireless network, a CSMA (Carrier Sense Multiple Access with Collision Aidance) communication procedure is known. CSMA is a connection method for performing multiple access based on carrier detection. Since it is difficult to receive a signal transmitted by wireless communication by itself, it is confirmed that there is no information transmitted by other communication devices by CSMA / CA (Collision Avoidance) method. Avoid collisions by starting. The CSMA method is an access method suitable for asynchronous data communication such as file transfer and e-mail. For example, IEEE 802.11 employs the CSMA / MA system as a basic data transfer sequence.

  The communication station that owns the transmission data monitors the presence / absence of signals on the wireless medium, and after confirming that the wireless medium is not used for a predetermined frame interval, waits for the back-off time. If the signal does not appear in the wireless medium even during the period, data transmission is started assuming that the own station has acquired the transmission right. When the transmission data is destined for only one specific communication station, the reception destination transmits an acknowledgment signal ACK (Acknowledgement) to the transmission station after receiving the data.

International Standard ISO / IEC 8802-11: 1999 (E) ANSI / IEEE Std 802.11, 1999 Edition, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layers (PH) ETSI Standard ETSI TS 101 761-1 V1.3.1 Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part 1: Basic Control Data ETSI TS 101 761-2 V1.3.1 Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part2: Radio Link Control (LC) Supplement to IEEE Standard for Information technology-Telecommunications and information exchange between systems-Local and metropolitan area networks-Specific requirements-Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5GHZ Band C. K. “Ad Hoc Mobile Wireless Network” written by Thor (Prentice Hall PTR)

  As described above, in an autonomous distributed wireless communication system, it is common for each communication station to perform access control while avoiding a collision based on the CSMA procedure. That is, a communication station with transmission data confirms the use only on the wireless medium for the frame interval, and further waits for the back-off amount, and then acquires the transmission right.

  In such a wireless communication system, each communication station performs back-off control as means for avoiding collisions. That is, a transmitter that intends to transmit a packet generates a random number within a specified contention window, and sets a back-off time based on the random value. The contention window increases twice with each retransmission. In other words, the transmission interval tends to increase with each retransmission. In IEEE 802.11, the minimum value of the contention window is 15 slots and the maximum value is 1023 slots. In such a retransmission control system, unless the communication station sets an upper limit on the number of retransmissions, the contention window continues to increase every time a packet collides and retransmission occurs.

  When a packet transmitted from each communication station to the access point collides, basically, the packet of the communication station with weak reception power at the access point is discarded. Therefore, when there are communication stations with weak reception power and communication stations with strong reception power and each communicates with an access point, when a packet collides, the packet of the communication station with low reception power is always discarded. In other words, the number of retransmissions of a communication station with weak reception power increases unilaterally, resulting in a longer transmission interval. Therefore, such a communication station is discarded due to collision of packets, and the opportunity to transmit data is reduced. Therefore, the communication station hardly falls into a situation. Such a phenomenon that is biased toward a terminal having arbitration of transmission access rights that should be fair is called a capture effect, and has been conventionally cited as a problem of Ethernet (registered trademark).

  Here, a solution in which the communication station sets an upper limit on the number of retransmissions is also conceivable. However, if the upper limit of the number of retransmissions is fixed to an extremely small number, the transmission interval will not be sufficiently long, and when the reception power is strong, the local station will occupy the band. It becomes impossible to share the bandwidth fairly.

  In this way, the phenomenon that the use of the band becomes unfair due to the magnitude of the received power between the communication stations appears remarkably in a state in which each other cannot be recognized, particularly in a hidden terminal state.

  The present invention has been made in view of the technical problems as described above, and its main purpose is that each communication station can perform access control in an autonomous and distributed manner while avoiding a collision according to the CSMA communication procedure. Another object of the present invention is to provide a wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program.

  A further object of the present invention is to avoid the situation where the retransmission interval of a communication station with low received power is unduly long and the communication opportunity is unfair, and can perform data transmission efficiently as a whole system. A wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program are provided.

The present invention has been made in consideration of the above problems, and a first aspect thereof is a wireless communication system in which each communication station performs access control in an autonomous and distributed manner while avoiding a collision.
The communication station sets an upper limit value of the number of retransmissions according to the communication state of the local station, and performs retransmission until the upper limit value of the number of retransmissions is reached while increasing the retransmission interval according to the detection of the collision,
Is a wireless communication system.

  However, “system” here refers to a logical collection of a plurality of devices (or functional modules that realize specific functions), and each device or functional module is in a single housing. It does not matter whether or not.

  The present invention relates to a radio communication system in which each communication station performs access control in an autonomous and distributed manner while avoiding a collision according to a CSMA communication procedure. In this type of wireless communication system, there is a problem that the transmission efficiency of the entire system is lowered due to the phenomenon that the retransmission interval of a communication station with low received power becomes unduly long and the communication opportunity becomes unfair.

  In the present invention, each communication station changes the upper limit of the number of retransmissions based on the communication state in which the station is placed, and sets the transmission interval according to the communication state or communication environment in which the station is placed. It is supposed to be. Specifically, based on the received power from the access point (or a specified peripheral station), the communication status of the local station is ascertained, and the received power from the access point or the specified peripheral station increases. Thus, the upper limit value of the number of retransmissions is increased, and the upper limit value of the number of retransmissions is decreased in accordance with the decrease in the received power. As a result, even when the communication state is not good, it is possible to autonomously avoid a situation in which the retransmission interval is extended every time the number of retransmissions overlaps due to a collision, and a transmission opportunity is hardly obtained.

Further, the second aspect of the present invention is described in a computer-readable format so that processing for performing access control in an autonomous and distributed manner while avoiding collision between communication stations on a wireless network is executed on a computer system. Computer program,
A communication state detection step of detecting a communication state of a communication station on the wireless network;
An access control step for performing access control while avoiding a collision with a signal of another station on the wireless network;
A retransmission control step of setting an upper limit value of the number of retransmissions according to the communication state of the communication station, and performing retransmission until reaching the upper limit value of the number of retransmissions while increasing a retransmission interval according to the detection of a collision;
A computer program characterized by comprising:

  The computer program according to the second aspect of the present invention defines a computer program described in a computer-readable format so as to realize predetermined processing on a computer system. In other words, by installing the computer program according to the second aspect of the present invention in the computer system, a cooperative action is exhibited on the computer system, and it operates as a communication device. By activating a plurality of such communication devices to construct a wireless network, the same operational effects as the wireless communication system according to the first aspect of the present invention can be obtained.

  According to the present invention, there is provided an excellent wireless communication system, wireless communication apparatus and wireless communication method, and computer program that each communication station can perform access control in an autonomous and distributed manner while avoiding a collision according to the CSMA communication procedure. Can be provided.

  Further, according to the present invention, it is possible to efficiently perform data transmission as a whole system by avoiding a situation in which a retransmission interval of a communication station with low received power is unduly long and a communication opportunity is unfair. A wireless communication system, a wireless communication device, a wireless communication method, and a computer program can be provided.

  In the wireless communication system according to the present invention, each communication station changes the upper limit of the number of retransmissions based on the received power of the own station, so that the transmission interval depends on the communication state or communication environment in which the own station is placed. Can be set. As a result, even when the communication state is not good, it is possible to autonomously avoid a situation in which the retransmission interval is extended every time the number of retransmissions overlaps due to a collision, and a transmission opportunity is hardly obtained.

  Other objects, features, and advantages of the present invention will become apparent from more detailed description based on embodiments of the present invention described later and the accompanying drawings.

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

  FIG. 1 shows a configuration example of a wireless communication system. The illustrated system includes a plurality of terminal stations and one access point, and performs access control in an autonomous and distributed manner while avoiding collision according to the CSMA communication procedure. In the figure, an access point 10, a terminal station 11, and a terminal station 12 are arranged at positions where they can communicate with each other.

  FIG. 2 shows another configuration example of the wireless communication system. The system configuration shown is different from the system configuration shown in FIG. 1 in that a so-called hidden terminal state exists. That is, although both the terminal station 21 and the terminal station 22 are within the communication range with the access point, they cannot recognize each other due to the influence of obstacles between the terminals and other causes. In such a case, since carrier sense does not operate normally, packets are transmitted at the same time, resulting in frequent collisions. In such a case, when there is a collision between transmission packets from the terminal station 21 and the terminal station 22 at the access point, the stronger reception power controls the competition, and the packet with weak reception power is discarded. Normally, a terminal station whose transmission packet has been discarded (that is, Ack has not returned) performs back-off control to increase the retransmission interval, and tries retransmission.

  FIG. 3 shows the relationship between backoff and packet collision. The terminal station with the transmission data performs carrier sense and acquires the transmission right if it is in the idle state.

  In the example shown in FIG. 3, the three terminal stations 1 to 3 having transmission data each perform back-off control, and since the back-off time of the terminal station 1 is the shortest, the data packet is directed to the access point. To send.

  While the terminal station 1 transmits a packet toward the access point, the other terminal stations 2 and 3 wait. After the terminal station 1 receives the Ack and completes communication, the terminal stations 2 and 3 wait for the carried back-off time and transmit data packets toward the access point.

  In the example shown in FIG. 3, since the back-off times of the terminal stations 2 and 3 at this time are the same, a collision occurs. Next, since the terminal stations 2 and 3 perform retransmission, the back-off time is calculated again from the contention window. Here, since the back-off time of the terminal station 2 is short, the terminal station 2 performs retransmission first.

  The contention window increases with each retransmission. FIG. 4 shows how the contention window increases in IEEE 802.11. In the example shown in the figure, the minimum value of the contention window is 15 slots and the maximum value is 1023 slots, and the contention window is doubled for each retransmission. When retransmitting a packet, the communication station calculates a back-off time from the contention window and a random value.

  FIG. 5 shows an example of a packet sequence when an access point receives packets with different received power from two terminals that are in a hidden terminal state.

  In the example shown in the figure, the transmission packets from the terminals 1 and 2 compete for each other. The reception power of the packet at the access point is higher for the terminal 1, and the reception power of the terminal 2 is lower. Therefore, when both packets collide, the packet of the terminal 2 having a low reception power is basically discarded.

  In the illustrated example, the number of retransmissions is not limited on the terminal 2 side. For this reason, since the reception power is small, the terminal 2 discards its own transmission packet and performs packet retransmission every time the packet collides with the terminal 1. Then, the transmission interval is further increased (see FIG. 4), the transmission opportunities are reduced, and the communication is almost impossible. That is, a capture effect occurs.

  FIG. 6 shows another example of the packet sequence when the access point receives packets with different received power from the two terminals in the hidden terminal state.

  Similarly to the above, the reception power of the packet at the access point is larger in the terminal 1, and the reception power of the terminal 2 is smaller. However, unlike the case of FIG. 5, the terminal 2 with low reception power sets an upper limit of the number of retransmissions according to the communication state of the local station.

  The communication state mentioned here corresponds to the power intensity when a transmission packet from the local station is received at the access point. However, since the received power at the access point cannot be directly measured, the propagation path characteristics are almost reversible, so the transmission power from the access point (or other peripheral station) is based on the received power at the local station. Set the maximum number of retransmissions in.

  The terminal 2 increases the upper limit value of the number of retransmissions according to the increase in the reception power from the access point, while decreasing the upper limit value of the number of retransmissions according to the decrease in the reception power. . As a result, even when the communication state is not good, it is possible to autonomously avoid a situation in which the retransmission interval is extended every time the number of retransmissions overlaps due to a collision, and a transmission opportunity is hardly obtained.

  In the packet sequence example shown in FIG. 6, the terminal 2 sets the upper limit of the number of retransmissions to one. The terminal 2 increases the contention window at each retransmission (see FIG. 4), but the transmission interval is shortened by providing an upper limit on the number of retransmissions. As a result, the transmission opportunity on the terminal 2 side with low reception power increases, and as shown in the figure, a packet enters the transmission interval of the terminal 1 to enable communication.

  FIG. 7 shows still another example of the packet sequence when the access point receives packets with different received power from two terminals in the hidden terminal state. However, in the illustrated example, the received powers of the terminal 1 and the terminal 2 are large, but only the terminal 1 sets the upper limit of the number of retransmissions to one, and the terminal 2 does not provide the upper limit of the number of retransmissions.

  When both packets collide, there is no difference in received power, so both packets are discarded. At this time, since the upper limit of the number of retransmissions is 1 on the terminal 1 side, the transmission interval does not become long. On the terminal 2 side, since there is no upper limit on the number of retransmissions, the contention window increases with each retransmission (see FIG. 4), and the transmission interval becomes longer.

  As a result of controlling the number of retransmissions different for each terminal as described above, the terminal 1 occupies the band. In other words, the terminal 2 has fewer transmission opportunities and falls into a state in which almost no communication is possible as in the case shown in FIG.

  FIG. 8 shows still another example of the packet sequence when the access point receives packets with different received power from two terminals in the hidden terminal state. However, in the illustrated example, the received power of the terminal 1 and the terminal 2 is large with each other, but on the terminal 1 side, the number of retransmissions is increased in accordance with the large received power of the own station.

  When both packets collide, there is no difference in received power, so both packets are discarded. At this time, both the terminal 1 and the terminal 2 increase the contention window every time they are retransmitted (see FIG. 4), and the transmission interval becomes longer. Can be shared.

  Of course, the terminal 1 does not increase the number of retransmissions according to the reception power of the own station being large, but the terminal 2 also sets the upper limit of the number of retransmissions according to the fact that the transmission opportunity of the own station is unreasonably small. Similarly, it is possible to obtain the effect of sharing the bandwidth fairly between terminals.

  FIG. 9 schematically shows a configuration of a wireless communication apparatus that operates as a terminal station in the wireless communication system according to the present invention. This wireless communication apparatus can perform access control in an autonomous and distributed manner while avoiding collision according to the CSMA communication procedure. In addition, this wireless communication device can autonomously avoid falling into a situation where a transmission opportunity is hardly obtained due to the capture effect by setting an appropriate number of retransmissions according to the communication state of the local station. it can.

  The wireless communication apparatus 100 includes an antenna 101 for transmitting / receiving a radio signal, an RF unit 102 for processing a high-frequency signal, a digital signal processing, up-conversion to a high-frequency signal, and down to an intermediate frequency signal. A baseband unit 103 that performs conversion is configured.

  The baseband unit 103 includes a modulation unit 131 and a demodulation unit 132 that perform digital modulation / demodulation such as OFDM modulation, a MAC processing unit 133 that performs processing of a MAC (Media Access Control) frame in a radio signal, and a CPU 134 that controls the MAC processing unit. A ROM (Read Only Memory) 135 for storing a program describing processing operations in the CPU 134, and a RAM (Random Access) for use in data expansion such as loading of the program stored in the ROM 135 and temporary storage of work data. memory) 136.

  The MAC processing unit 133 mainly performs access control in the wireless transmission path. In the present embodiment, access control is performed in an autonomous and distributed manner while avoiding collision according to the CSMA communication procedure, and retransmission control at the time of packet collision is performed. Access control and retransmission control are realized in such a manner that the CPU 134 develops and executes the control program in the ROM 135 in the RAM 136.

  Each communication station generally performs back-off control as means for avoiding collisions. That is, when a packet is to be transmitted, a random number is generated within a specified contention window, and a back-off time based on the random value is set. In such a retransmission control method, unless the communication station sets an upper limit on the number of retransmissions, the contention window continues to increase every time a packet collides and a retransmission occurs, and a capture effect that a transmission opportunity cannot be obtained occurs. there is a possibility.

  Therefore, in this embodiment, by setting an appropriate number of retransmissions according to the communication state of the own station, it is autonomously avoided that a transmission opportunity is hardly obtained due to the capture effect. ing. Setting the upper limit of the number of retransmissions shortens the transmission interval, so that the communication station can appropriately acquire a transmission opportunity.

  The communication state mentioned here corresponds to the power intensity when a transmission packet from the local station is received at the access point. However, since the reception power at the access point cannot be directly measured, the propagation path characteristics are almost reversible, so the reception power at the local station of the transmission packet from the access point (or other peripheral station) is used. .

  The CPU 134 may use the RSSI (Received Signal Strength Indicator) obtained in the RF unit 112 for calculating the received power, or may have a device other than the RSSI (Received Signal Strength Indicator). Based on the calculated received power value, the CPU 134 changes the upper limit value of the number of retransmissions.

  FIG. 10 shows, in the form of a flowchart, an operation procedure for setting the upper limit value of the number of retransmissions of the own station in accordance with the received power intensity in the wireless communication apparatus.

  When the wireless communication station receives data from the access point (or other peripheral station) (step S1), the wireless communication station calculates the value of the received power (step S2). And it is discriminate | determined whether the value exceeds a threshold value (step S3).

  Here, if the calculated received power is equal to or less than the threshold, the upper limit value of the number of transmissions is reduced (step S4). If the calculated received power is equal to or greater than the threshold, the upper limit value of the number of transmissions is increased (step S5).

  As described above, each communication station operating in the wireless communication system autonomously sets the upper limit value of the number of transmissions according to the received power, so that transmission opportunities can be evenly obtained. , You will be able to share the same bandwidth fairly. Note that a plurality of threshold values may be set so that a plurality of upper limit values of the number of transmissions can be set.

  In the above embodiment, when the received power is large, the bandwidth is shared fairly. Therefore, the upper limit of the number of retransmissions is increased. However, when the received power is large, the bandwidth is intentionally occupied. A method of reducing the number of retransmissions is also conceivable. Thus, it should be fully understood that the gist of the present invention includes all retransmission control methods for setting the upper limit value of the number of retransmissions from the received power.

  Further, FIG. 11 shows, in the form of a flowchart, an operation procedure for the wireless communication apparatus to perform retransmission control using the upper limit value of the number of retransmissions set by itself based on the received power.

  After transmitting the packet (step S11), the wireless communication apparatus receives the Ack or the corresponding reception confirmation response signal from the transmission destination (step S12), and transmits the next packet (or the transmission data is lost). (Sometimes, the transmission operation is terminated) (step S13)

  On the other hand, when Ack cannot be obtained from the transmission destination, it is recognized that the packet has collided with a transmission packet from another communication station (or the packet reception processing has failed at the transmission destination due to other reasons).

  In this case, it is determined whether or not the current number of retransmissions has reached the upper limit value of the number of retransmissions set based on the received power (step S14).

  Here, if the current number of retransmissions has not yet reached the upper limit, the back-off time is calculated in the same manner as in the normal retransmission operation (step S15), and data retransmission is performed based on the packet retransmission timing obtained thereby. Is attempted (step S16).

  On the other hand, when the current number of retransmissions reaches the upper limit, the packet is retransmitted and the next packet is transmitted (step S13).

  By limiting the number of retransmissions to the upper limit value in this way, the contention window is increased every time retransmission is performed, and the situation where the transmission interval becomes longer is avoided. As a result, the wireless communication apparatus can obtain a transmission machine at an appropriate transmission interval even when the received power is small, and can share the band fairly with other communication stations. It becomes possible.

  The present invention has been described in detail above with reference to specific embodiments. However, it is obvious that those skilled in the art can make modifications and substitutions of the embodiment without departing from the gist of the present invention.

  In the present specification, the embodiment in which the present invention is applied to an autonomous distributed wireless network has been mainly described. However, the gist of the present invention is not limited to this. For example, the present invention can be similarly applied to a communication system that performs access control by collision detection or collision avoidance and performs retransmission control according to the occurrence of a collision even in a wireless network other than autonomous distribution or a wired network. Needless to say.

  In short, the present invention has been disclosed in the form of exemplification, and the description of the present specification should not be interpreted in a limited manner. In order to determine the gist of the present invention, the claims section described at the beginning should be considered.

FIG. 1 is a diagram illustrating a configuration example of a wireless communication system. FIG. 2 is a diagram illustrating another configuration example of the wireless communication system. FIG. 3 is a diagram illustrating the relationship between backoff and packet collision. FIG. 4 is a diagram showing an increase in contention windows in IEEE 802.11. FIG. 5 is a diagram showing an example of a packet sequence when an access point receives packets with different received power from two terminals in a hidden terminal state. FIG. 6 is a diagram illustrating another example of a packet sequence when a packet with different reception power is received from two terminals in the hidden terminal state at the access point. FIG. 7 is a diagram showing still another example of a packet sequence when a packet with different reception power is received from two terminals in the hidden terminal state at the access point. FIG. 8 is a diagram showing still another example of a packet sequence when a packet with different reception power is received from two terminals that are in a hidden terminal state at the access point. FIG. 9 is a diagram schematically showing a configuration of a wireless communication apparatus operating as a terminal station in the wireless communication system according to the present invention. FIG. 10 is a flowchart showing an operation procedure for setting an upper limit value of the number of retransmissions of the own station in the wireless communication apparatus. FIG. 11 is a flowchart showing an operation procedure for the wireless communication apparatus to perform retransmission control using the upper limit value of the number of retransmissions set by itself.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,20 ... Access point 11, 21, 12, 22 ... Terminal 100 ... Wireless communication apparatus 101 ... Antenna 102 ... RF unit 103 ... Baseband unit 131 ... Modulation unit 132 ... Demodulation unit 133 ... MAC processing unit 134 ... CPU
135 ... ROM
136 ... RAM

Claims (10)

A wireless communication system in which each communication station performs autonomous and distributed access control while avoiding collisions,
The communication station sets an upper limit value of the number of retransmissions according to the communication state of the local station, and performs retransmission until reaching the upper limit value of the number of retransmissions while increasing the retransmission interval according to the detection of the collision,
A wireless communication system. The communication station grasps its own communication state based on the received power from an access point or a predetermined peripheral station,
The wireless communication system according to claim 1. The communication station increases the upper limit of the number of retransmissions according to the increase in received power from the access point or a predetermined peripheral station, and the upper limit of the number of retransmissions according to the decrease in the received power. Decrease,
The wireless communication system according to claim 1. A wireless communication device that performs access control in an autonomous and distributed manner while avoiding collision between communication stations on a wireless network,
Communication means for transmitting and receiving wireless signals on the wireless network;
Communication state detecting means for detecting the communication state of the own station on the wireless network;
Access control means for performing access control while avoiding a collision with a signal of another station on the wireless network;
A retransmission control means for setting an upper limit value of the number of retransmissions according to the communication state of the local station, and performing retransmission until the upper limit value of the number of retransmissions is reached while increasing the retransmission interval according to the detection of a collision;
A wireless communication apparatus comprising: The communication state detection means detects the communication state of the own station based on the received power from the access point or a predetermined peripheral station,
The wireless communication apparatus according to claim 4. The retransmission control means increases an upper limit value of the number of retransmissions according to an increase in received power from an access point or a predetermined peripheral station, and an upper limit value of the number of retransmissions according to a decrease in the received power. Decrease the value,
The wireless communication apparatus according to claim 5. A wireless communication method for performing access control in an autonomous and distributed manner while avoiding collision between communication stations on a wireless network,
A communication state detection step of detecting a communication state of a communication station on the wireless network;
An access control step for performing access control while avoiding a collision with a signal of another station on the wireless network;
A retransmission control step of setting an upper limit value of the number of retransmissions according to the communication state of the communication station, and performing retransmission until reaching the upper limit value of the number of retransmissions while increasing a retransmission interval according to the detection of a collision;
A wireless communication method comprising: In the communication state detection step, the communication state of the communication station is detected based on received power from an access point or a predetermined peripheral station.
The wireless communication method according to claim 7. In the retransmission control step, the upper limit of the number of retransmissions is increased in accordance with an increase in received power from an access point or a predetermined peripheral station, and an upper limit of the number of retransmissions in accordance with the decrease in the received power. Decrease the value,
The wireless communication method according to claim 8. A computer program written in a computer-readable format so as to execute processing for autonomously distributed access control on a computer system while avoiding collision between communication stations on a wireless network,
A communication state detection step of detecting a communication state of a communication station on the wireless network;
An access control step for performing access control while avoiding a collision with a signal of another station on the wireless network;
A retransmission control step of setting an upper limit value of the number of retransmissions according to the communication state of the communication station, and performing retransmission until reaching the upper limit value of the number of retransmissions while increasing a retransmission interval according to the detection of a collision;
A computer program comprising:

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