CN108923855B - Heterogeneous network uplink competition access method based on optical communication VLC - Google Patents
Heterogeneous network uplink competition access method based on optical communication VLC Download PDFInfo
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- CN108923855B CN108923855B CN201810736753.7A CN201810736753A CN108923855B CN 108923855 B CN108923855 B CN 108923855B CN 201810736753 A CN201810736753 A CN 201810736753A CN 108923855 B CN108923855 B CN 108923855B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
- H04B10/114—Indoor or close-range type systems
- H04B10/116—Visible light communication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
- H04B10/114—Indoor or close-range type systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access, e.g. scheduled or random access
- H04W74/08—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access]
- H04W74/0808—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using carrier sensing, e.g. as in CSMA
- H04W74/0816—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using carrier sensing, e.g. as in CSMA carrier sensing with collision avoidance
Abstract
The invention discloses a heterogeneous uplink competition access method based on optical communication VLC, which mainly solves the problems of serious uplink and downlink interference, large network delay and high data packet retransmission probability in the VLC technology. The scheme is as follows: constructing a visible light beacon frame to realize the isomerism of VLC and infrared communication; adding the infrared channel busy and idle information into a visible light beacon frame, and increasing the interception range of the infrared channel in a broadcasting mode; judging whether the channel is busy or idle, and executing an improved back-off algorithm; and sending an access request and data after the conditions are met, and finishing the heterogeneous network uplink access based on the optical communication VLC. The invention designs the visible light beacon frame containing the infrared channel information, can realize the separation of uplink and downlink in an optical communication network, avoids mutual interference, improves the existing infrared communication backoff algorithm, provides a nonlinear backoff function, reduces the network delay and the data packet retransmission probability, and better realizes communication. The method is suitable for indoor visible light heterogeneous network communication.
Description
Technical Field
The invention belongs to the technical field of optical communication, relates to an MAC layer competition access mechanism, in particular to an uplink competition access method of a heterogeneous network based on optical communication VLC, and is suitable for an indoor visible light heterogeneous communication network.
Background
Optical Communication (Optical Communication) is a Communication method using light waves as carriers, and mainly includes Communication technologies such as Optical fibers, indoor visible light, and wireless light. In recent years, with the rapid development of solid-state lighting technology, white Light Emitting Diodes (LEDs) have been widely used. Visible Light Communication (VLC) based on white light LEDs has attracted attention of numerous organizations and scholars as an emerging wireless communication technology. VLC is a communication mode in which light in the visible light band is used as an information carrier, and light signals are directly transmitted in the air without a transmission medium such as an optical fiber or other wired channels, combines illumination and communication, adds a data transmission function to an illumination facility, and transmits information by high-speed bright and dark flashing of a light source. VLC utilizes visible light spectrum which is higher than 3THz and still belongs to blank spectrum, and is not limited by use license; visible light cannot penetrate through a building wall, visible light signals in mutually adjacent closed units cannot interfere with each other, and safety and confidentiality are good; VLC transceiver equipment is simple and low in cost; the visible light wavelength belongs to submicron level, and has obvious advantages in accurate direction positioning; VLC can replace the application of radio in certain specific situations where electromagnetic interference is sensitive, such as airplanes, hospitals, nuclear power plants or oil drilling, etc. The advantages make VLC a brand-new broadband access mode for indoor wireless communication networks.
In practical application, if VLC is used as a single wireless communication mode, there are many defects that a light link is easily blocked, a multipath effect is obvious, an uplink communication link is difficult to implement, an LED modulation bandwidth is limited, background light interference is serious, a communication distance is short, and the like. Therefore, more and more researchers are trying to implement heterogeneous convergence of VLC and various communication modes to construct a network system with large system capacity, fast data transmission rate, low access delay, high reliability, high security, support of dense access, and flexible architecture. Infrared technology is a mature communication technology, although the communication distance is only a few meters, infrared light is a communication medium with many advantages, and the infrared technology is small in size and low in cost, is very suitable for being heterogeneous with VLC, and avoids the problem of mutual interference of an uplink and a downlink. Usually, two infrared devices must be directly butted on a sight line to exchange data, and similar to visible light, infrared light can not penetrate through a building wall, so that the transmission safety and the consistency with VLC are ensured.
Visible light has a broadcast nature and is suitable for downlink, and infrared communication generally has the characteristics of point-to-point communication and is therefore suitable for uplink. The beam of the infrared light is narrow, the alignment angle is about 15 degrees, so that the communication range of the infrared light is small, namely the monitoring range is small, when one device occupies the infrared channel, other devices cannot monitor the infrared channel, namely the busy and idle conditions of the infrared channel cannot be detected. The existing infrared uplink contention window CWi is as follows:
CWi＝CW+4i，i＝0，1，2，...m
where i is the backoff order, CW is the initialized backoff window and CWminWhen CW is 8, m is the backoff order corresponding to the maximum backoff window, CWmax256, i.e., m 62.
The existing contention window is slow in growth speed, when the number of mobile terminals is large, the probability of collision is large, the backoff order is high, and the network delay is large.
Disclosure of Invention
The invention aims to provide a heterogeneous network uplink competition access method based on optical communication VLC, which reduces network delay and data packet retransmission probability and is characterized by comprising the following steps:
1) creating a beacon frame applied to the visible light heterogeneous network: periodically broadcasting a beacon frame containing infrared receiver Busy and idle information IR _ Busy by a visible light signal transmitter of a visible light access point AP;
2) detecting and extracting infrared channel busy and idle information: the method comprises the steps that a visible light receiver of the mobile terminal periodically detects a beacon frame and extracts infrared channel Busy and idle information IR _ Busy in the beacon frame in real time;
3) judging whether the infrared channel is busy or idle: when the IR _ Busy field shows Busy, the current mobile terminal needs to wait and continues to monitor the IR _ Busy information; when the IR _ Busy field is idle, the current mobile terminal needs to execute a nonlinear back-off algorithm and set a back-off timer according to the current contention window;
4) in the process of executing back-off by the mobile terminal, continuously monitoring infrared channel Busy and idle information IR _ Busy: when the IR _ Busy shows idle, the back-off timer performs self-subtraction every other time slot; when the IR _ Busy indicates Busy, the back-off timer stops self-decrementing;
5) requesting for access: when the value of the backoff timer is reduced to 0, the infrared transmitter of the mobile terminal immediately sends an access request frame; after receiving an access request frame sent by a mobile terminal, a visible light AP infrared receiver sends an access request response frame to a target mobile terminal through a visible light channel by a visible light emitter;
6) and (3) sending data: if the visible light receiver of the mobile terminal receives the corresponding access request response frame, the data frame is sent by the infrared transmitter through the infrared channel; after receiving the corresponding data frame, the visible light AP infrared receiver sends a data confirmation frame to the target mobile terminal through the visible light channel by the visible light emitter, and executes the step (7); otherwise, judging that collision occurs, the mobile terminal needs to execute the back-off algorithm again, and retransmits the access request frame, and returns to the execution step (4);
7) and completing access: and the mobile terminal receives the corresponding data confirmation frame, the access is successful, and the one-time access of the heterogeneous network uplink competition based on the optical communication VLC is realized.
The competition access method is improved on the basis of the existing advanced infrared carrier sense collision avoidance protocol, realizes uplink competition access of the mobile terminal in a heterogeneous network based on optical communication VLC, enlarges the virtual carrier sense range of uplink infrared communication of the mobile terminal, reduces network transmission delay, reduces the retransmission probability of data packets and improves the channel utilization rate.
Compared with the prior art, the invention has the following advantages:
first, in the existing optical communication technology, a beacon frame applied to a VLC and infrared communication heterogeneous network is not provided, and therefore the invention specially designs the beacon frame applicable to the visible light communication heterogeneous network, the beacon frame is added with information of an infrared channel, and is designed with an infrared receiver ID bound with a visible light AP, and the visible light and infrared heterogeneous communication network is realized by adopting the beacon frame.
Secondly, because the alignment angle of the infrared communication is very small, and the monitoring range of the mobile terminal on the infrared channel is very small, the invention adds the busy and idle information of the infrared channel into the visible light beacon frame and effectively enlarges the virtual carrier monitoring range of the mobile terminal on the uplink infrared communication through periodic broadcasting.
Thirdly, because the existing infrared communication adopts a linear back-off algorithm, the contention window is small, the growth speed is slow, the network delay is large, and the data retransmission rate is high, the invention improves the back-off algorithm of the infrared communication, adopts a nonlinear back-off function, improves the growth speed of the contention window, reduces the network delay, and reduces the data packet retransmission probability.
Drawings
Fig. 1 is a flow chart of the present invention for implementing contention access.
Fig. 2 is a schematic diagram of a beacon frame structure of VLC improved according to the IEEE 802.15.7 standard in the present invention.
Fig. 3 is a graph comparing the network average delay before the backoff algorithm of the present invention is used and improved.
Fig. 4 is a graph comparing the backoff algorithm of the present invention with the probability of retransmission of a data packet before improvement.
Detailed Description
The invention is described in detail below with reference to the following figures and specific examples:
example 1
Visible light communication VLC combines illumination and communication, adds a data transmission function on lighting facilities, and transmits information through high-speed bright and dark flicker of a light source. VLC utilizes the visible light frequency range which is higher than 3THz and still belongs to the blank spectrum, is not limited by a use license, and meanwhile, due to the fact that the VLC cannot penetrate through barriers such as walls, visible light signals in the adjacent closed units cannot interfere with one another, and safety and confidentiality are good. In practical application, the existing VLC technology has the problems of mutual interference between an uplink and a downlink, difficulty in realizing the uplink, large uplink access delay, small data transmission rate and the like, and meanwhile, the conventional VLC adopts a beacon frame of radio frequency communication, so that the requirement of a visible light heterogeneous network cannot be met.
The invention develops research on the method, and provides a heterogeneous network uplink competition access method based on optical communication VLC, which comprises the following steps:
1) creating a beacon frame applied to the visible light heterogeneous network: the visible light access point AP visible light signal transmitter periodically broadcasts a beacon frame containing infrared receiver Busy information IR Busy.
2) Detecting and extracting infrared channel busy and idle information: the visible light receiver of the mobile terminal periodically detects the beacon frame and extracts the infrared channel Busy and idle information IR _ Busy in the beacon frame in real time.
3) Judging whether the infrared channel is busy or idle: when the IR _ Busy field shows Busy, the current mobile terminal needs to wait and continues to monitor the IR _ Busy information; when the IR _ Busy field shows idle, the current mobile terminal needs to execute a non-linear back-off algorithm, and set a back-off timer according to the current contention window.
4) In the process of executing back-off by the mobile terminal, continuously monitoring infrared channel Busy and idle information IR _ Busy: when the IR _ Busy shows idle, the back-off timer performs self-subtraction every other time slot; the back-off timer stops self-decrementing when IR Busy is indicated.
5) Requesting for access: when the value of the backoff timer is reduced to 0, the infrared transmitter of the mobile terminal immediately sends an access request frame; and after receiving the access request frame sent by the mobile terminal, the infrared receiver bound with the visible light AP sends an access request response frame to the target mobile terminal through the visible light channel by the visible light emitter.
6) And (3) sending data: if the visible light receiver of the mobile terminal receives the corresponding access request response frame, the data frame is sent by the infrared transmitter through the infrared channel; after receiving the corresponding data frame, the infrared receiver bound with the visible light AP sends a data confirmation frame to the target mobile terminal through the visible light channel by the visible light emitter, and executes the step (7); otherwise, judging that collision occurs, the mobile terminal needs to execute the back-off algorithm again, and retransmits the access request frame, and returns to execute the step (4).
7) And completing access: the mobile terminal receives the corresponding data confirmation frame, the access is successful, and the one-time access of the heterogeneous network uplink competition based on the optical communication VLC is realized; otherwise, the mobile terminal needs to retransmit the data frame.
In practical application, visible light serving as a single wireless communication mode has the problems of mutual interference between uplink and downlink and the like. The invention adopts infrared communication as the uplink of the communication system, eliminates the mutual interference of the uplink and the downlink and is easy to realize.
Fig. 1 is a flow chart of the present invention for implementing contention access. Referring to fig. 1, more in detail, the present invention can also be expressed as:
1) the visible light AP periodically broadcasts a beacon frame containing infrared receiver Busy and idle information IR _ Busy, and the beacon frame is suitable for the visible light heterogeneous network.
2) The mobile terminal periodically detects the beacon frame and extracts the infrared channel Busy and idle information IR _ Busy in the beacon frame in real time to acquire the state of the infrared channel, so that the monitoring range of the mobile terminal on the infrared channel is expanded.
3) When the IR Busy field shows Busy, the current mobile terminal needs to wait and continue to listen for IR Busy information.
4) When the IR _ Busy field shows idle, the current mobile terminal needs to execute the non-linear back-off algorithm proposed by the present invention, and sets a back-off timer according to the current contention window.
5) And in the process of executing back-off, the mobile terminal continuously monitors the infrared channel Busy information IR _ Busy.
6) When the IR _ Busy shows idle, the back-off timer performs self-subtraction every other time slot; the back-off timer stops self-decrementing when IR Busy is indicated.
7) When the value of the backoff timer is decreased to 0, the mobile terminal immediately transmits an access request frame.
8) And after receiving the access request frame sent by the mobile terminal, the visible light AP sends an access request response frame to the target mobile terminal through a visible light channel.
9) If the mobile terminal receives a corresponding access request response frame within the designated time, transmitting a data frame through an infrared channel; otherwise, judging that collision occurs, the mobile terminal needs to execute the back-off algorithm again and retransmit the access request frame, and the steps are the same as the step (4).
10) And after receiving the corresponding data frame, the visible light AP sends a data confirmation frame to the target mobile terminal through the visible light channel.
11) If the mobile terminal receives the corresponding data confirmation frame within the appointed time, the access is successful; otherwise, the mobile terminal needs to retransmit the data frame.
Compared with the existing uplink contention access method, the heterogeneous network uplink contention access method based on the optical communication VLC has the advantages that the new beacon frame is used, the heterogeneous structure is formed with the infrared network, the busy and idle information of the infrared channel is released in a downlink visible light broadcasting mode, and the monitoring range of the mobile terminal on the infrared channel virtual carrier wave is enlarged. Meanwhile, by improving the back-off algorithm, the network transmission delay and the data packet retransmission probability are reduced.
The invention is based on an uplink competition access mechanism in a light communication VLC and infrared heterogeneous network, and is suitable for an indoor visible light heterogeneous communication network.
Example 2
In the existing optical communication technology, no beacon frame applied to VLC and infrared communication heterogeneous networks exists, and the invention designs a beacon frame suitable for a visible light communication heterogeneous network.
Similar to embodiment 1, the method for contention based uplink access in heterogeneous network of VLC based on optical communication is applied to a beacon frame of a visible light heterogeneous network, and includes 22 bytes, including a 1byte start flag bit, a 2byte check field, and a 1byte end flag bit, where, referring to fig. 1, the method is sequentially provided after the start flag bit: the heterogeneous network for VLC and infrared communication includes a 1byte frame control bit, a 2byte beacon interval, a 6byte destination address, a 6byte source address, a 1byte infrared receiver identification code, and a 2byte frame body, where the 2byte frame body is connected to a check bit, and is described in detail with reference to fig. 2 as follows:
START is a START flag bit that identifies the START of a frame.
Frame Control is a Frame Control field, where:
firstly, the Type field indicates that the frame Type is management frame (00);
the Subtype field further indicates that the type of the frame is beacon frame (000);
direction field shows whether the frame is the frame (1) sent by AP to terminal;
and fourthly, the Reserved field is a Reserved field and is default to 00.
Beacon Interval is a Beacon Interval used to announce the existence of the network, and the AP will send Beacon signals at intervals.
The DA is a destination address (FFFFFFFFFFFF) of frame transmission.
SA is the source address of the frame transmission.
The Infrared _ ID is an identification code of an Infrared receiver bound to the visible light AP.
The Frame Body is a Frame Body for carrying data to be transmitted, wherein:
the IR _ Busy field is used to identify whether the visible AP-bound infrared receiver is Busy;
the Location field is used to identify the AP Location information.
The CRC is a check bit used to detect whether an error frame is erroneous.
STOP is an end flag bit that identifies the end of the frame (7E).
These fields may be periodically broadcast through a beacon frame to transmit information of the infrared receiver bound to the visible light AP to the mobile terminal, and the mobile terminal may parse the relevant information.
The specially designed beacon frame suitable for the visible light communication heterogeneous network is added with the infrared receiver ID bound with the visible light AP, and the visible light and infrared heterogeneous communication network is realized by adopting the beacon frame.
Example 3
Similar to the embodiment 1-2, in the method for contention access to the heterogeneous network based on the optical communication VLC, an IR _ Busy field in a frame body of a beacon frame is used to identify whether an infrared receiver bound to a visible light AP is Busy, that is, whether an infrared channel is occupied, and the infrared receiver broadcasts periodically through the visible light channel. The mobile terminal receives the visible light signal in real time, analyzes the related information and reads the busy and idle information of the infrared channel, so that the state of the infrared channel is virtually intercepted, the interception range of the mobile terminal to the infrared channel is expanded, and the utilization rate of the channel is improved.
Example 4
Heterogeneous network uplink contention access method based on optical communication VLC (visible light communication), as same as embodiments 1-3, the contention window function CW of the nonlinear back-off algorithm provided by the inventioniIs defined as follows
CWi＝CW+2i(i－1)，i＝0，1，2，...11
CWi＝256，i≥12
Where i is the backoff order, CW is the initialized backoff window, CWminWhen CW is 8, m is the backoff order corresponding to the maximum backoff window, CWmax＝256，m＝12。
The initial values of the backoff timer are defined as follows:
Counter＝Random(CWi)
i.e. from 0-CWiWherein an integer is randomly selected by the Random function Random as an initial value of the backoff timer Counter.
By adopting the secondary backoff algorithm, the growth speed of the backoff window is improved, and the backoff times are reduced, so that the network transmission delay and the data packet retransmission probability are reduced.
A more detailed example is given below, further illustrating the invention,
example 5
The heterogeneous network uplink contention access method based on the optical communication VLC is the same as that in embodiments 1 to 4,
1) the visible light AP sends the beacon frame proposed in the present invention to each mobile terminal in a broadcast form through the visible light channel, where the beacon frame includes a state of an infrared receiver bound to the visible light AP, that is, a busy-idle state of the infrared channel.
2) The visible light receiver of the mobile terminal converts the optical signal sent by the visible light into an electric signal, extracts the IR _ Busy information which identifies whether the infrared channel is idle, and judges whether the infrared channel is idle. And if the channel state is idle, executing an improved nonlinear back-off algorithm, setting a back-off timer, and if the channel state is busy, waiting and continuously monitoring.
3) And continuously monitoring the infrared channel while the back-off timer is self-decreasing in the process of executing the back-off algorithm, wherein the timer is self-decreasing if the channel is idle, and the timer stops self-decreasing and waits until the self-decreasing is started when the channel is detected to be idle.
4) When the timer is reduced to 0, the mobile terminal immediately sends an access request frame to the infrared receiver bound with the visible light AP through the infrared channel.
5) When the infrared receiver bound with the visible light AP receives an access request frame sent by a mobile terminal and the infrared channel is idle, sending an access request confirmation frame to a target mobile terminal through the visible light channel, and indicating that the mobile terminal is allowed to send data to the infrared receiver bound with the visible light AP through the infrared channel at the moment; when the visible light AP detects that collision occurs, namely a plurality of terminals send data to one infrared receiver at the same time, the access request confirmation frame is not sent.
6) If the mobile terminal receives the corresponding request access confirmation frame, the use right of the infrared channel at the current time is obtained, and the data frame is immediately sent through the infrared uplink channel; if the request access confirmation frame is not received, judging that collision occurs, executing a back-off algorithm again, namely i +1, resetting a back-off timer and retransmitting an access request frame, and the same step as 3), namely continuously monitoring the infrared channel to wait for idling and executing self-reduction of the timer.
7) And after receiving the corresponding data frame, the infrared receiver bound with the visible light AP sends a data confirmation frame to the target mobile terminal through the visible light channel.
8) If the mobile terminal receives the data confirmation frame, the access is successful, and if the data confirmation frame is not received after time out, the data frame needs to be retransmitted.
By adopting the beacon frame provided by the invention, the access of a heterogeneous network with visible light downlink and infrared light uplink is completed at one time, and meanwhile, the virtual interception range of the mobile terminal to the infrared channel is enlarged. By adopting the backoff algorithm, the growth speed of the backoff window is increased, and the maximum backoff order is reduced, so that the network time delay and the data packet retransmission probability are reduced, and the channel utilization rate is improved.
The technical effects of the invention can be further explained by combining the following simulation experiments:
example 6
The heterogeneous network uplink contention access method based on the optical communication VLC is the same as that in embodiments 1 to 5,
simulation conditions are as follows:
in the indoor VLC downlink and infrared uplink heterogeneous network environment, various parameters are set as shown in a table:
total simulation time: 3 x 10^6us
Average arrival time: 2200us
Average packet length: 16384bits
Simulation content and results:
in a network with VLC as a downlink and infrared as an uplink, the beacon frame proposed by the present invention is adopted to simulate the improved and existing infrared contention access methods, respectively, and the network delay and the data packet retransmission probability are adopted as the flag parameters for comparison, and the results are shown in fig. 3 and fig. 4, respectively.
Fig. 3 is a comparison graph of average network delay with the backoff algorithm of the present invention and the conventional backoff algorithm, where the abscissa is the number of users, the ordinate is the network delay, the solid line is a curve generated by the backoff algorithm of the present invention, and the dotted line is a curve generated by the conventional backoff algorithm. As can be seen from fig. 3, as the number of users increases, the delay increases, and the number of users is smaller, the delay difference between the two backoff algorithms is not large, and when the number of users is greater than 12, the delay generated by the backoff algorithm provided by the present invention is smaller than the delay generated by the conventional backoff algorithm, or as the number of users increases, the performance of the backoff algorithm provided by the present invention is better.
Example 7
The heterogeneous network uplink competition access method based on the optical communication VLC is the same as the embodiments 1-6, and the simulation conditions and the contents are the same as the embodiment 6.
Fig. 4 is a comparison graph of the retransmission probability of the data packet under the backoff algorithm of the present invention and the existing backoff algorithm, where the abscissa is the number of users, the ordinate is the retransmission probability of the data packet, the solid line is a curve generated by the backoff algorithm proposed by the present invention, and the dotted line is a curve generated by the existing backoff algorithm. As can be seen from fig. 4, due to the increase of the number of users, the retransmission probability of the network data packet increases, and by using the back-off algorithm of the present invention, the retransmission probability is significantly reduced before improvement, especially after the number of users is greater than 28, and due to the reduction of the maximum back-off times, when the number of users is large, the increase speed of the retransmission probability is significantly reduced.
In summary, the heterogeneous uplink contention access method based on the VLC in the invention mainly solves the problems of serious uplink and downlink interference, large network delay and high data packet retransmission probability in the VLC technology. The scheme is as follows: 1. constructing a visible light beacon frame to realize the isomerism of VLC and infrared communication; 2. adding the infrared channel busy and idle information into a visible light beacon frame, and increasing the interception range of the infrared channel in a broadcasting mode; 3. judging whether the channel is busy or idle, and executing an improved back-off algorithm; 4. and sending an access request and data after the conditions are met, and finishing the heterogeneous network uplink access based on the optical communication VLC. The invention designs the visible light beacon frame containing the infrared channel information, can realize the separation of uplink and downlink in an optical communication network, avoids mutual interference, improves the existing infrared communication backoff algorithm, provides a nonlinear backoff function, reduces the network delay and the data packet retransmission probability, and better realizes communication. The method is suitable for indoor visible light heterogeneous network communication.
Claims (4)
1. A heterogeneous network uplink competition access method based on optical communication VLC is characterized by comprising the following steps:
(1) creating a beacon frame applied to the visible light heterogeneous network: periodically broadcasting a beacon frame containing infrared receiver Busy and idle information IR _ Busy by a visible light signal transmitter of a visible light access point AP;
(2) detecting and extracting infrared channel busy and idle information: the method comprises the steps that a visible light receiver of the mobile terminal periodically detects a beacon frame and extracts infrared channel Busy and idle information IR _ Busy in the beacon frame in real time;
(3) judging whether the infrared channel is busy or idle: when the IR _ Busy field shows Busy, the current mobile terminal needs to wait and continues to monitor the IR _ Busy information; when the IR _ Busy field is idle, the current mobile terminal needs to execute a nonlinear back-off algorithm and set a back-off timer according to the current contention window;
(4) in the process of executing back-off by the mobile terminal, continuously monitoring infrared channel Busy and idle information IR _ Busy: when the IR _ Busy shows idle, the back-off timer performs self-subtraction every other time slot; when the IR _ Busy indicates Busy, the back-off timer stops self-decrementing;
(5) requesting for access: when the value of the backoff timer is reduced to 0, the infrared transmitter of the mobile terminal immediately sends an access request frame; after receiving an access request frame sent by a mobile terminal, an infrared receiver bound with a visible light AP sends an access request response frame to a target mobile terminal through a visible light channel by a visible light emitter;
(6) and (3) sending data: if the visible light receiver of the mobile terminal receives the corresponding access request response frame, the infrared transmitter sends a data frame through the infrared channel, after the infrared receiver bound with the visible light AP receives the corresponding data frame, the visible light transmitter sends a data confirmation frame to the target mobile terminal through the visible light channel, and step (7) is executed; otherwise, judging that collision occurs, the mobile terminal needs to execute the back-off algorithm again, and retransmits the access request frame, and returns to the execution step (4);
(7) and completing access: and the mobile terminal receives the corresponding data confirmation frame, the access is successful, and the one-time access of the heterogeneous network uplink competition based on the optical communication VLC is realized.
2. The heterogeneous network uplink contention access method based on optical communication VLC of claim 1, wherein the beacon frame applied to the visible light heterogeneous network has 22 bytes, and includes a 1byte start flag bit, a 2byte check field, and a 1byte end flag bit, and is sequentially set after the start flag bit: the system comprises a 1byte frame control bit, a 2byte beacon interval, a 6byte destination address, a 6byte source address, a 1byte infrared receiver identification code and a 2byte frame body, and is used for a heterogeneous network of VLC and infrared communication.
3. The heterogeneous network uplink contention access method based on optical communication VLC as claimed in claim 2, wherein: an IR _ Busy field in a frame body of the beacon frame is used to identify whether an infrared receiver bound by the visible light AP is Busy, i.e., whether an infrared channel is occupied.
4. The heterogeneous network uplink contention access method based on the optical communication VLC as claimed in claim 1, wherein: in step (4), the contention window CWiThe function is defined as follows
CWi＝CW+2i(i-1)，i＝0，1，2，…11
CWi＝256，i＝12
Where i is the backoff order, CW is the initialized backoff window, CWminWhen CW is 8, m is the backoff order corresponding to the maximum backoff window, CWmax256, i.e., m is 12.
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| CN109474338B (en) * | 2019-01-22 | 2021-05-28 | 重庆邮电大学 | Access selection method for indoor VLC-WiFi hybrid communication system |
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