CN107046733B - Visible light full duplex continuous transmission random access method based on channel reservation mechanism - Google Patents
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- 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]
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- H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
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- 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
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- H04W74/0833—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using a random access procedure
Abstract
The invention discloses a visible light full duplex continuous transmission random access method based on a channel reservation mechanism, which is different from a CSMA/CA protocol in the existing IEEE 802.15.7 standard, a user does not directly send a data frame after executing idle channel estimation and detecting that a channel is in an idle state, but firstly sends an RTS frame to reserve the channel, and then sends the data frame after successfully reserving the channel. A full-duplex visible light access point needs to broadcast a busy tone when it receives an RTS frame or a data frame to eliminate hidden nodes. And after the user successfully transmits the data frame once, the user does not perform random backoff again and directly executes CCA, thereby reducing time slot resources consumed by random backoff while preventing data frame collision and improving the throughput and the delay performance. The invention effectively solves the problem of hiding nodes by visible light and simultaneously optimizes the throughput and the time delay performance of the visible light CSMA/CA protocol.
Description
Technical Field
The invention relates to the technical field of visible light communication, in particular to a visible light full-duplex continuous transmission random access method based on a channel reservation mechanism.
Background
In recent years, with the maturity of Light Emitting Diode (LED) technology and the popularization of lighting, Visible Light Communication (VLC) technology developed based on LED lamps has become one of research hotspots in academia and industry because of its advantages of high transmission rate, environmental protection, and the like. In order to promote the development of visible light communication technology, the Institute of Electrical and Electronic Engineers (IEEE) has set the IEEE 802.15.7 standard in 2011[1]The related functions of visible light at a Physical (PHY) layer and a Medium Access Control (MAC) layer are described in detail.
The research on the MAC layer focuses mainly on the protocol of channel resource allocation. Distributed random access is the most important way to solve how multiple users in a wireless local area network compete for access to a channel and share channel resources. A Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) protocol based on half duplex transmission is one of the most mainstream of the current random Access protocols, and is also a channel Access method adopted by most of the conventional wireless communication and the current visible light IEEE 802.15.7 standard.
Due to the limited coverage area (FOV) Of the LED lamp, in a multi-user VLC network, a plurality Of users cannot communicate with each other because they are not within the FOV, which causes the problem Of hiding nodes. For the traditional wireless network, the problem of hidden nodes can be solved by using a channel reservation mechanism, namely a Request To Send/Clear To Send (RTS/CTS) four-way handshake mechanism. However, for the VLC network, the user is not in a state of constantly listening to the CTS frame in order to save energy consumption, and therefore, even if the RTS/CTS channel reservation mechanism is applied to the half-duplex visible light CSMA/CA protocol, the hidden node problem in the VLC network still cannot be solved.
The IEEE 802.15.7 standard does not currently provide a solution to visible light hidden nodes. Part of the literature analyzes the performance of the visible light CSMA/CA protocol based on the assumption that the VLC network has no hidden nodes. Literature reference[2]Analyzing the influence of different loads and different user numbers on the throughput and the delay performance of the visible light CSMA/CA protocol, and obtaining documents[3]A Markov model is established, and system performance indexes such as throughput, collision probability, packet loss probability, time delay and the like of a CSMA/CA protocol in the IEEE 802.15.7 standard are completely analyzed. From the analysis of the existing literature on the visible CSMA/CA protocol, the throughput and delay performance of the CSMA/CA protocol specified in the IEEE 802.15.7 standard is relatively poor, even if the effect of hidden nodes is not considered. Therefore, the hidden node problem caused by the visible light FOV is solved, and meanwhile, the performance of the CSMA/CA protocol is improved, so that the method has important significance for the development and the perfection of the VLC technology in the MAC layer.
Aiming at the problems that the development of the current IEEE 802.15.7 standard is immature, the hidden node cannot be eliminated by a visible light CSMA/CA protocol and the performance is poor, the invention provides a random access method of full-duplex continuous transmission based on an RTS/CTS channel reservation mechanism, which can effectively solve the problem of the visible light hidden node and simultaneously optimize the throughput and the delay performance of the visible light CSMA/CA protocol.
The references are as follows:
[1]IEEE Standard for Local and Metropolitan Area Networks–Part 15.7:Short-Range Wireless Optical Communication Using Visible Light[J].IEEEStandard 802.15.7,2011:1–309.
[2]HWANG J,DO T,YOO M.Performance analysis on MAC protocol based onbeacon-enabled visible personal area networks[C]//2013Fifth InternationalConference on Ubiquitous and Future Networks(ICUFN).2013:384–388.
[3]NOBAR S K,MEHR KA,NIYA J M.Comprehensive Performance Analysis ofIEEE 802.15.7CSMA/CA Mechanism for Saturated Traffic[J].Journal of OpticalCommunications and Networking,2015,7(2):62–73.
disclosure of Invention
The present invention provides a visible light full duplex continuous transmission random access method based on a channel reservation mechanism, in particular, a full duplex visible light access point can broadcast busy tone to other users in its coverage area while receiving user data, so as to prevent collision caused by simultaneous data transmission due to mutual hiding among multiple users. Based on RTS/CTS channel reservation mechanism, a continuous transmission random access method is provided. Unlike the CSMA/CA protocol in the existing IEEE 802.15.7 standard, a user does not directly transmit a data frame after performing Clear Channel Assessment (CCA) and detecting that a channel is in an idle state, but first transmits an RTS frame to make a reservation for the channel. After the channel is successfully reserved, the data frame is transmitted again. And after the data frame is successfully transmitted for one time, the CCA is directly executed without performing random backoff again, so that the time slot resources consumed by the random backoff can be reduced while the data frame collision is prevented, and the throughput and the delay performance are improved.
In order to solve the technical problems, the technical scheme of the invention is as follows:
a visible light full duplex continuous transmission random access method based on a channel reservation mechanism comprises the following specific steps:
s1: a user has data and the like to be sent and carries out random backoff;
s2: when the back-off time is over, the user executes CCA to judge whether the current channel is idle;
s3: if CCA detects that the current channel is in an idle state, the user does not send a data frame directly, but sends an RTS frame to reserve the channel at first;
s4: when receiving an RTS frame, a full-duplex visible light access point needs to send a busy tone to the outside to eliminate hidden nodes; that is, if the other users perform CCA at the current time, the other users receive the busy tone signal sent by the access point, and therefore, the current channel state is considered to be busy, and backoff needs to be performed again to avoid collision;
s5: a user switches from a sending state to a receiving state by using Short Interframe Space (SIFS) time and waits for the arrival of a CTS frame;
s6: after receiving the CTS frame replied by the access point, the user switches back to the sending state from the receiving state and starts to send the data frame;
s7: after the user finishes sending the data frame, the user switches from the sending state back to the receiving state within the state transition time (aTurneronoundime-TX-RX, tTX-RX) and waits for an Acknowledgement (ACK) frame of the access point;
s8: when the full-duplex visible light access point receives the data frame, the full-duplex visible light access point also needs to broadcast busy tone outwards until the data frame is received completely, and replies an ACK frame to the user to indicate that the data frame is received successfully;
s9: after the user successfully receives the ACK frame, if the user still has data to be transmitted after the user successfully transmits the ACK frame, continuous transmission is immediately carried out after waiting for a Long Inter Frame Space (LIFS) time, that is, random backoff is not carried out again, and CCA is directly executed to judge the state of the current channel;
s10: and when the user does not have data waiting for sending, the random access process is ended.
In a preferred scheme, in step S1, when the user has data to send, the user synchronizes with the beacon frame of the access point, and the backoff period boundary is aligned with the access point.
In a preferred embodiment, two variables are initialized in step S1: NB and BE; a variable NB represents the number of backoff, NB being initialized to 0; the variable BE represents a backoff index for calculating the backoff window size, and the initial value is macMinBE, which represents the minimum value of BE specified by the MAC layer.
In a preferred embodiment, the size CW of the backoff window CW is calculated as 2 in step S2 BE1 and from [0, CW)]And randomly selecting an integer backoff window within the range to perform backoff.
In a preferred scheme, in step S2, when the CCA detects that the channel status is busy, the MAC layer increments the variables NB and BE by 1; setting the maximum value of BE not to exceed macMaxBE; judging whether the value of NB exceeds macmaxCSABackofs; if NB exceeds macmaxSMABackofs, that is, the sending fails, the MAC layer sends a failure instruction to the upper layer and discards the data packet; if NB does not exceed macmaxCSABackofs, jumping back to step S2 to enter the next backoff stage, and calculating a backoff window CW; otherwise, if the CCA detects that the channel status is idle, step S3 is executed; wherein, macmaxBE is the BE maximum value specified by the MAC layer, and macmaxCSABackoffs is the CSMA/CA maximum back-off times specified by the MAC layer.
In a preferred scheme, in step S5, if the user does not receive the CTS frame within the macAckWaitDuration time, it indicates that the sent RTS frame collides, and the process goes back to step S2; otherwise, after the CTS frame is successfully received, the process proceeds to step S6; the macAckWaitDuration is a timeout time length specified by the MAC layer for the user to wait for the access point to reply the CTS frame or the ACK frame.
In a preferred scheme, in step S8, if the user does not receive the ACK frame within the macAckWaitDuration time, it indicates that the transmitted data frame is lost, and jumps back to step S2; otherwise, after receiving the ACK frame returned by the access point successfully, the process proceeds to step S9.
In a preferred scheme, in step S9, when the user performs continuous transmission and performs CCA to detect the channel status, if there is exactly another user that has finished the backoff within the LIFS time and performs CCA, the another user may consider that the channel is idle and start to send an RTS frame; the CCA executed by the current user during continuous transmission will detect that the channel status is busy, and needs to perform backoff again, that is, continuous transmission fails; otherwise, if the CCA executed when the current user continuously transmits detects that the channel is idle, the system directly enters the next round of RTS transmission link, that is, the continuous transmission is successful.
In a preferred scheme, after waiting for a LIFS time interval, the variables NB and BE are reinitialized, but the backoff window CW is set to 0, i.e. the random backoff is not performed again, but CCA is performed directly; if the user has data waiting to be sent after the failed sending, the user needs to return to the initialization state again, i.e. jump back to step S1 to re-initialize the variables.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that: aiming at the problems that the development of the IEEE 802.15.7 standard is immature, the hidden node cannot be eliminated by a visible light CSMA/CA protocol and the performance is poor, a random access method for full-duplex continuous transmission is provided based on an RTS/CTS channel reservation mechanism, the problem of the hidden node of visible light can be effectively solved, and the throughput and the delay performance of the visible light CSMA/CA protocol can be optimized.
Drawings
Fig. 1 is a schematic view of a hidden node for visible light communication according to the present invention.
FIG. 2 is a timing diagram of the RTS/CTS-based visible full-duplex CSMA/CA data transmission according to the present invention.
FIG. 3 is a CSMA/CA random access flow chart of continuous visible light transmission based on RTS/CTS according to the present invention.
FIG. 4 is a comparison of the throughput simulation curves of example 1 of the present invention and the IEEE 802.15.7 standard CSMA/CA.
FIG. 5 is a comparison of CSMA/CA delay simulation curves of the IEEE 802.15.7 standard in accordance with embodiment 1 of the present invention.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the patent;
for the purpose of better illustrating the embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product;
it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The CSMA/CA flow chart based on time slot and effective CCA in the visible light random access mechanism is further described below. It should be noted that the full duplex continuous transmission random access method proposed by the present invention is also applicable to optional non-slotted or CCA inactive cases.
Example 1
As shown in fig. 1 to 3, a visible light full duplex continuous transmission random access method based on a channel reservation mechanism includes the following specific steps:
s1: a user has data and the like to be sent and carries out random backoff;
s2: when the back-off time is over, the user executes CCA to judge whether the current channel is idle;
s3: if CCA detects that the current channel is in an idle state, the user does not send a data frame directly, but sends an RTS frame to reserve the channel at first;
s4: when receiving an RTS frame, a full-duplex visible light access point needs to send a busy tone to the outside to eliminate hidden nodes; that is, if the other users perform CCA at the current time, the other users receive the busy tone signal sent by the access point, and therefore, the current channel state is considered to be busy, and backoff needs to be performed again to avoid collision;
s5: a user switches from a sending state to a receiving state by using Short Interframe Space (SIFS) time and waits for the arrival of a CTS frame;
s6: after receiving the CTS frame replied by the access point, the user switches back to the sending state from the receiving state and starts to send the data frame;
s7: after the user finishes sending the data frame, the user switches from the sending state back to the receiving state within the state transition time (aTurneronoundime-TX-RX, tTX-RX) and waits for an Acknowledgement (ACK) frame of the access point;
s8: when the full-duplex visible light access point receives the data frame, the full-duplex visible light access point also needs to broadcast busy tone outwards until the data frame is received completely, and replies an ACK frame to the user to indicate that the data frame is received successfully;
s9: after the user successfully receives the ACK frame, if the user still has data to be transmitted after the user successfully transmits the ACK frame, continuous transmission is immediately carried out after waiting for a Long Inter Frame Space (LIFS) time, that is, random backoff is not carried out again, and CCA is directly executed to judge the state of the current channel;
s10: and when the user does not have data waiting for sending, the random access process is ended.
In the implementation, in step S1, when the user has data to send, the user synchronizes with the beacon frame of the access point, and aligns the backoff period boundary with the access point.
In the implementation, two variables are initialized in step S1: NB and BE; a variable NB represents the number of backoff, NB being initialized to 0; the variable BE represents a backoff index for calculating the backoff window size, and the initial value is macMinBE, which represents the minimum value of BE specified by the MAC layer.
In a specific implementation, the size CW of the backoff window CW is calculated to be 2 in step S2 BE1 and from [0, CW)]Randomly selecting an integer backoff window within the range to carry out backoff; .
In a specific implementation process, in step S2, when the CCA detects that the channel status is busy, the MAC layer increments the variables NB and BE by 1 respectively; setting the maximum value of BE not to exceed macMaxBE; judging whether the value of NB exceeds macmaxCSABackofs; if NB exceeds macmaxSMABackofs, that is, the sending fails, the MAC layer sends a failure instruction to the upper layer and discards the data packet; if NB does not exceed macmaxCSABackofs, jumping back to step S2 to enter the next backoff stage, and calculating a backoff window CW; otherwise, if the CCA detects that the channel status is idle, step S3 is executed; wherein, macmaxBE is the BE maximum value specified by the MAC layer, and macmaxCSABackoffs is the CSMA/CA maximum back-off times specified by the MAC layer.
In the specific implementation process, in step S5, if the user does not receive the CTS frame within the macAckWaitDuration time, it indicates that the sent RTS frame collides, and the process goes back to step S2; otherwise, after the CTS frame is successfully received, the process proceeds to step S6; the macAckWaitDuration is a timeout time length specified by the MAC layer for the user to wait for the access point to reply the CTS frame or the ACK frame.
In the specific implementation process, in step S8, if the user does not receive the ACK frame within the macAckWaitDuration time, it indicates that the transmitted data frame is lost, and it jumps back to step S2; otherwise, after receiving the ACK frame returned by the access point successfully, the process proceeds to step S9.
In a specific implementation process, in step S9, a user performs continuous transmission, and when performing CCA to detect a channel state, if there is exactly another user that has finished backoff and performed CCA within the LIFS time, the another user may consider that the channel is idle and start sending an RTS frame; the CCA executed by the current user during continuous transmission will detect that the channel status is busy, and needs to perform backoff again, that is, continuous transmission fails; otherwise, if the CCA executed when the current user continuously transmits detects that the channel is idle, the system directly enters the next round of RTS transmission link, that is, the continuous transmission is successful.
In a specific implementation process, after waiting for a LIFS time interval, the variables NB and BE are reinitialized, but the backoff window CW is set to 0, that is, the random backoff is not performed again, and the CCA is performed directly; if the user has data waiting to be sent after the failed sending, the user needs to return to the initialization state again, i.e. jump back to step S1 to re-initialize the variables.
To more fully illustrate the beneficial effects of the present invention, the following description will further illustrate the effectiveness and advancement of the present invention in comparing the throughput and delay performance of the CSMA/CA protocol of the IEEE 802.15.7 standard with the actual simulation results. The simulation scenario assumes that the user is in a saturated state, i.e., the user always has a data packet to send to the access point.
Fig. 4 compares the throughput curve of the scheme of the present invention with the CSMA/CA protocol in the IEEE 802.15.7 standard without considering hidden nodes. With the increase of the number of users, even if the hidden node problem is not considered, the throughput performance of the CSMA/CA protocol in the IEEE 802.15.7 standard is gradually reduced, and the scheme of the invention not only solves the hidden node problem, but also avoids the collision of data frames. The throughput performance is better than the current CSMA/CA protocol of the IEEE 802.15.7 standard. And when the number of users is large, the throughput performance of the scheme of the invention can be kept basically constant.
Fig. 5 compares the delay curve of the scheme of the present invention with the CSMA/CA protocol in the IEEE 802.15.7 standard without considering hidden nodes. As the number of users increases, the delay consumed by the successful transmission of data packets by both random access methods increases gradually. Although RTS/CTS overhead is introduced, the time consumed by the back-off of the user can be shortened under the condition of not additionally introducing conflicts by a continuous transmission scheme based on a channel reservation mechanism, namely combining RTS/CTS four-way handshake. Therefore, the time delay performance of the scheme of the invention is better than the CSMA/CA protocol of the current IEEE 802.15.7 standard.
The simulation results show that the performance of the scheme of the invention is better than the CSMA/CA protocol of the existing IEEE 802.15.7 standard in the aspects of throughput and delay performance, and the advancement of the scheme of the invention is illustrated.
The same or similar reference numerals correspond to the same or similar parts;
the terms describing positional relationships in the drawings are for illustrative purposes only and are not to be construed as limiting the patent;
it should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (1)
1. A visible light full duplex continuous transmission random access method based on a channel reservation mechanism is characterized by comprising the following specific steps:
s1: a user has data and the like to be sent and carries out random backoff;
in step S1, when the user has data to send, synchronizing with the beacon frame of the access point, and aligning the backoff period boundary with the access point;
two variables are initialized in step S1: NB and BE; a variable NB represents the number of backoff, NB being initialized to 0; the variable BE represents a backoff index and is used for calculating the size of a backoff window, and the initial value is macminBE and represents the minimum value of BE specified by the MAC layer;
s2: when the back-off time is over, the user executes CCA to judge whether the current channel is idle;
in step S2, the size CW of the backoff window CW is calculated to be 2BE1 and from [0, CW)]Randomly selecting an integer backoff window within the range to carry out backoff;
in step S2, when the CCA detects that the channel status is busy, the MAC layer increments the variables NB and BE by 1, respectively; setting the maximum value of BE not to exceed macMaxBE; judging whether the value of NB exceeds macmaxCSABackofs; if NB exceeds macmaxSMABackofs, that is, the sending fails, the MAC layer sends a failure instruction to the upper layer and discards the data packet; if NB does not exceed macmaxCSABackofs, jumping back to step S2 to enter the next backoff stage, and calculating a backoff window CW; otherwise, if the CCA detects that the channel status is idle, step S3 is executed; wherein, macmaxBE is the BE maximum value specified by the MAC layer, and macmaxCSABackoffs is the CSMA/CA maximum back-off times specified by the MAC layer;
s3: if CCA detects that the current channel is in an idle state, the user does not send a data frame directly, but sends an RTS frame to reserve the channel at first;
s4: when receiving an RTS frame, the full-duplex visible light access point sends a busy tone to the outside to eliminate hidden nodes; that is, if the other users perform CCA at the current time, the other users receive the busy tone signal sent by the access point, and therefore, the current channel state is considered to be busy, and backoff needs to be performed again to avoid collision;
s5: the user switches from a sending state to a receiving state by using short frame interval time and waits for the arrival of a CTS frame;
in step S5, if the user does not receive the CTS frame within the macAckWaitDuration time, it indicates that the RTS frame sent conflicts, and the process returns to step S2; otherwise, after the CTS frame is successfully received, the process proceeds to step S6; wherein, macAckWaitDuration is the time-out time length specified by the MAC layer for the user to wait for the access point to reply the CTS frame or the ACK frame;
s6: after receiving the CTS frame replied by the access point, the user switches back to the sending state from the receiving state and starts to send the data frame;
s7: after the user finishes sending the data frame, switching from the sending state to the receiving state within the state transition time and waiting for an access point to reply an ACK frame;
s8: when the full-duplex visible light access point receives the data frame, the full-duplex visible light access point also needs to broadcast busy tone outwards until the data frame is received completely, and replies an ACK frame to the user to indicate that the data frame is received successfully;
in step S8, if the user does not receive the ACK frame within the macAckWaitDuration time, it indicates that the transmitted data frame is lost, and it jumps back to step S2; otherwise, after receiving the ACK frame replied by the access point successfully, the process proceeds to step S9;
s9: after the user successfully receives the ACK frame, if the user still has data to be transmitted after the user successfully transmits the ACK frame, continuous transmission is immediately carried out after the user waits for a long frame interval time, namely random backoff is not carried out again, and CCA is directly executed to judge the state of the current channel;
in step S9, when the user performs continuous transmission and performs CCA to detect the channel status, if there are other users that have already been evacuated within the LIFS time and performed CCA, the other users will consider the channel to be idle and start sending an RTS frame; the CCA executed by the current user during continuous transmission will detect that the channel status is busy, and needs to perform backoff again, that is, continuous transmission fails; on the contrary, if the CCA executed when the current user continuously transmits detects that the channel is idle, the next round of link for sending the RTS is directly entered, namely the continuous transmission is successful;
after waiting for a LIFS time interval, the variables NB and BE are reinitialized, but the backoff window CW is set to 0, i.e. the CCA is performed directly without performing a random backoff again; if the user has data to be sent after the sending fails, the user needs to return to the initialization state again, namely, the user jumps back to the step S1 to initialize the variables again;
s10: and when the user does not have data waiting for sending, the random access process is ended.
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