WO2015103834A1

WO2015103834A1 - Method, device and system for realizing vlc dynamic access

Info

Publication number: WO2015103834A1
Application number: PCT/CN2014/078032
Authority: WO
Inventors: 支周; 洪文昕; 陈晓红; 钱晨; 韦玮; 禹忠
Original assignee: 中兴通讯股份有限公司
Priority date: 2014-01-07
Filing date: 2014-05-21
Publication date: 2015-07-16
Also published as: CN104768232A

Abstract

Disclosed are a method, device and system for realizing VLC dynamic access. The method comprises: generating, by a user node, an appointment request frame for appointing an uplink channel and sending same; and after appointment is successful, sending, by the user node, data in an appointed time slot.

Description

Method, device and system for realizing VLC dynamic access

The present invention relates to the field of optical communications, and in particular, to a method, device and system for implementing visible light communication (VLC) dynamic access. Background technique

In recent years, light-emitting diodes (LEDs), which are known as "green lighting", have developed rapidly. LEDs have the advantages of low power consumption, long life, environmental protection, good modulation performance, and high response sensitivity. At present, LEDs can be used as illumination sources, and signals can be modulated onto LED visible beams for VLC.

According to the environment, VLC can be divided into indoor applications and outdoor applications. Outdoor applications include: LED intelligent transportation systems, mines, underwater communication systems, etc. The indoor application replaces the wireless local area network base station with white LED lighting equipment, and can communicate only within the illumination range of the LED light to form a visible-light communication personal area network (VPAN). When the user exceeds the light coverage, Termination of communication, with a high degree of confidentiality. In addition, because VLC completely avoids electromagnetic interference from radio frequency access, it is also very suitable for RF-sensitive areas such as airplanes and hospitals. VLC's communication speed can reach tens of megahertz to hundreds of megabits per second. In addition, the indoor transmission distance is limited (<10111), and the optical pulse delay is small, which can provide high-speed data transmission capability. Therefore, VLC provides a new high-speed data access method for indoor communication, which has great development prospects.

The indoor VLC system belongs to the star network topology. The VLC access point sends data to each user node in a broadcast downlink mode, and each user node is connected to the VLC access point through a point-to-point optical link. This topology structure is characterized in that it is easy to add new nodes in the network. The security and priority of data are easy to control and easy to implement network monitoring. When multiple users have data transmission requests, in order to make better use of channel resources, it is necessary to allocate the uplink channel reasonably. Multi-Access (MA) technology.

Currently, the multiple access methods specified by the MAC protocol are classified into: fixed (resource) access, dynamic (resource) access, and hybrid access. Fixed access methods include Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), and Code Division Multiple Access (CDMA) to provide a reliable, continuous network, but with strong bursts of traffic or long periods of no packet transmission. In this case, channel resources are wasted. Dynamic access can be divided into random contention access and control access. The representative of the random access mode is ALOHA and Carrier Sense Protocol (CSMA), which is suitable for bursty service networks. When the number of users or traffic is small, it is sometimes characterized by small delay and high channel utilization. Controlling access can effectively avoid transmission conflicts, but when the amount of users is small, it generates large overhead and low channel utilization. The hybrid access mode is mainly the reservation type on-demand access, which can be divided into two types: single service packet transmission and multi-service packet transmission.

In the indoor VLC system, due to the limited number of user nodes under the illumination coverage VPAN, each user is independent of each other, randomly transmits transmission data, and cannot detect each other's uplink signals, and the indoor transmission distance is short, and the transmission delay can be can be ignored. Therefore, the uplink access mode of the system is more suitable for random access. The ALOHA protocol in the random access mode is simple to implement and supports data services with burst characteristics. Compared with the fixed access mode, unnecessary overhead can be reduced, but ALOHA will blindly occupy channel resources and cause transmission conflicts. The channel utilization is low. The CSMA protocol is based on the random access mode of listening to the channel state, which can reduce the conflict and improve the channel resource utilization, but the access delay is large and the communication quality is affected. Summary of the invention

In view of this, embodiments of the present invention provide a method, apparatus, and system for implementing VLC dynamic access to reduce the probability of overlapping collisions.

The technical solution of the embodiment of the present invention is implemented as follows:

An embodiment of the present invention provides a method for implementing dynamic access of a visible light communication VLC, the method comprising: The user node generates a reservation request frame for the reserved uplink channel and transmits it; after the reservation is successful, the user node transmits data in the reserved time slot.

The user node sends a reservation request frame at a time. When a reservation request frame sent by two or more user nodes collides, the conflicting user node re-attempts the transmission of the reservation request frame.

The embodiment of the invention provides a method for implementing VLC dynamic access, and the method includes:

The VLC access point notifies the status of the current channel by means of downlink broadcast, and the time at which the uplink random signal is allowed to be transmitted; and, by the VLC access point, dynamically allocates the number N of the transport packet slots according to the received reservation request frame.

An embodiment of the present invention further provides an apparatus for implementing dynamic access of a VLC, where the apparatus is a user node, and the user node is configured as:

A reservation request frame for the reserved uplink channel is generated and transmitted; after the reservation is successful, the data is transmitted in the reserved time slot.

The embodiment of the present invention further provides a device for implementing dynamic access of a VLC, where the device is a VLC access point, and the VLC access point is configured as:

Notifying the status of the current channel and the time when the uplink random signal is allowed to be transmitted by means of downlink broadcast; and dynamically allocating the number of transmission packet slots according to the received reservation request frame

The embodiment of the present invention also provides a system for implementing VLC dynamic access, where the system includes a VLC access point and a user node;

The VLC access point is configured to notify the current channel status by means of downlink broadcast, and the time at which the uplink random signal can be sent; and, according to the received reservation request frame, dynamically allocate the number N of the transmission packet slots;

The user node is configured to generate a reservation request frame for scheduling an uplink channel and send the data; after the reservation is successful, the data is sent in the reserved time slot.

Embodiments of the present invention reduce the probability of overlapping collisions. DRAWINGS

Figure 1 is a schematic diagram of a network topology of an indoor VLC system;

2 is a schematic diagram of a relationship between a reserved ALOHA throughput S and a network load G (M=10) according to an embodiment of the present invention;

3 is a schematic diagram of a relationship between a reserved ALOHA normalized delay and a network load G (M=10) according to an embodiment of the present invention;

4 is a schematic diagram of relationship between packet loss rate and network load according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a relationship between a blocking rate and a normalized access density according to an embodiment of the present invention; FIG. 6 is a schematic flowchart of a user node end for implementing VLC dynamic access according to an embodiment of the present invention; FIG. 7 is a schematic diagram of implementing VLC according to an embodiment of the present invention; A flow diagram of a dynamically accessed VLC access point; FIG. 8 is a schematic diagram of a system for implementing VLC dynamic access according to an embodiment of the present invention. detailed description

In general, the VLC network may include a VLC access point and at least one user node, which may be applied to the downlink broadcast channel and the uplink channel when implementing dynamic access.

Both the VLC access point and the user node may divide the uplink channel into N+1 time slots, one of which is used as a reserved time slot for transmitting the reservation request frame, and the other N time slots are used as the transmission packet data. To transmit a packet slot, a simple TDMA (simple-TDMA) protocol can be used. All user nodes share the N time slots, and the VLC access point controls the use of each time slot.

The VLC access point informs the user of the current channel status by means of downlink broadcast, and the time at which the user node can send the uplink random signal.

When the user node has uplink data to be sent, the user node generates a reservation request frame (which may be one packet length) and sends a reservation request including the reservation request frame to the VLC access point to reserve an uplink channel, and the reservation application may adopt an ALOHA method. Competition is sent. After the reservation is successful, the user node can send data in the reserved time slot until the data transfer is completed.

The reserved time slot in the embodiment of the present invention includes the length of time and grouping that the user node will occupy. Number of information.

The user node sends a reservation request frame at a time. When the reservation request frames sent by two or more user nodes overlap (ie, collide) in the reserved time slot, the conflicting user nodes will randomly wait for a period of time and then retry the reservation request. The transmission of the frame.

In practical applications, the channel may be divided into frames according to the size of the user node traffic in the network, and each frame is divided into a reserved time slot of length T1 and a transport packet time slot of length T2.

Each user node can randomly contend for the reserved time slot. Only the user node that has not collided in the reserved time slot can occupy the transmission packet time slot, so no collision occurs in the transmission packet time slot.

The number of transmission packet slots is dynamically allocated by the VLC access point according to the subscription request of the user node.

If no collision occurs within the reserved time slot, the packet data is transmitted in the corresponding transport packet time slot. Obviously, the reserved ALOHA method can greatly improve the throughput S, and the theoretical extreme value is S = N / (N + 1), where N is the number of transmission packet slots in each frame.

For the characteristics of indoor VLC systems, the following conditions can be provided:

(1). The channel is considered to be error-free, that is, the packet loss rate only involves the probability of a transmission failure due to a collision;

(2) The reserved packet in the reserved time slot of the newly arrived network conforms to the Poisson process, and the average arrival rate is averaged to reach S packets within the unit time τ;

(3) The entire process of the reservation packet arriving at the network (including the arrival process of the newly arrived and retransmitted reservation packet) is a Poisson process, and within a unit time T, an average of G packets are reached;

(4) Each user node has at most one reservation packet (including any reservation packets that have previously collided) ready to send;

(5) Since the indoor VLC network topology is star-shaped, as shown in Figure 1, the VLC access point is connected to multiple user nodes, so that the coverage is small, the transmission distance is short, and the optical pulse delay is small. Therefore, the transmission delay is ignored when considering conflicts;

(6). It can be assumed that there are 10 user nodes under a VLC access point, M=10 (the indoor VLC communication range is limited, ^^ has only 10 users under the illumination).

Throughput:

The reserved ALOHA frame length is T0, which is divided into N+1 time slots. The reserved time slot length for reservation is T1, and the transmission packet time slot length for transmitting data packets is Τ2. Then there are Τ1=Τ0/(1+Ν),

, and 1<=Ν<=9 (the number of user nodes <10).

The throughput within the reserved time slot is discussed separately separately. Taking Τ as the unit time, λ is the reservation group arrival rate. According to the Poisson formula, the probability of occurrence of any group other than the reservation group within the time : is:

, (ΛΤ·) ^Κ e— ^Ar

^{F {κ)} = ^ Έ ^ ^{, κ ≥ 0} The newly arrived appointment group is g ^{= XF} , and the average number of reserved packets is G (including the newly arrived and retransmitted reservation packets)

G ^K e- ^G

P(K) = -—— , Κ≥0

number). So have, ! . The probability that a reservation packet can be successfully transmitted is Ρ(Κ二二二e- ^GT , the retransmission probability is: p _r =1— = 0) = l_e_ ^Gr . When the VLC system contains a limited number of user nodes M, each user node is viewed. Frames are randomly transmitted independently, and one frame can be transmitted in length. Let Si be the probability that the user node i successfully transmits one frame in any time slot, then 1-Si is the probability that the user node i does not transmit successfully (send failed or not sent at all) in any time slot.

Gi and 1-Gi are the probability that the user node i transmits and does not transmit one frame in any time slot, respectively. Therefore, for all i, there is Si ≤ Gi, and each user node sends frames is independent, so get:

S] = ^,Π (1 - G!) Assuming that the statistical characteristics of each user node are the same, that is, Si=S/M and Gi=G/M, and S and G are the throughput and network load of the entire system, respectively, the simplification is:

S = G (1-G / M) M-1;

When the reservation packet transmission is successful, the data packet can be correctly transmitted. That is to say, if a data packet is successfully sent, it needs to send 1/S reservation packets on average, and the probability of no collision for each reservation packet is S, the time occupied by the packet data is T2, and the number of user nodes is Μ=10, so the throughput can be Nearly 4 is expressed as:

As shown in Fig. 2, the relationship between the reserved ALOHA throughput S of N=3, N=6, and N=9 and G packets is given.

real-time:

Delay time = ALOHA delay D1 + reservation request frame collision retransmission delay D2+ packet transmission delay D3.

(1) .ALOHA Delay refers to the observation time before the reservation request frame is sent. Although the arrival of each packet data is approximately a Poisson process, since there are different packet data arrival rates due to different channel traffic, each user node waits for an average of T2/2 before transmitting the packet data, and then starts transmitting a reservation request. Frame, ie:

D _l = T ₂ + T ₂ / 2 = 3T ₂ / 2 .

(2) The transmission delay factor is R, that is, after a reservation request frame is sent, the RT1 is passed to receive the confirmation message, and the next frame is sent. Therefore, it takes time T1 (l+R) to send a reservation request frame.

When a collision has occurred and must be retransmitted, it is necessary to wait for a time n times Tl (n is a random positive integer). After the retransmission is completed, it is still necessary to pass RT1 to receive the confirmation message. Therefore, retransmission requires time Tl(l+R+n+R).

The average number of retransmissions is related to n. The smaller n is, the larger the collision probability of the frame during retransmission, and the number of retransmissions. It will also increase; the larger the n, the lesser the collision probability, but the average delay for sending one frame increases. Theoretical analysis shows that choosing n=5 is a better compromise. In this case, the relationship between the number of retransmissions NR and n is not large, and it can be concluded that:

^ I

s ;

In summary, the average delay of the collision retransmission of the reservation request frame is:

Z) ₂ =N _fl (R + ^3⁄4 =(G ' l)[R + ^3⁄4.

(3). The minimum delay for transmitting packet data is ^{D3 = 2} ^i; therefore, the average delay of the packet data is: D = 3r ₂ /2 + (G/Sl) [R + ^3⁄4+2R Similarly, in limited In the case of user nodes M, let R=0, η=5,

Τ1=Τ0/(1+Ν), so the normalized delay is:

^=^-[-+(1-^/10)^/ -1]

N+1 2 ;

As shown in Fig. 3, the relationship between the reserved ALOHA normalization delay and G packets of Ν=3, Ν=6, Ν=9 is given.

Packet loss rate:

The packet loss rate is the probability that the reservation request frame will collide within the reserved time slot, and the request is still lost after repeated retransmissions, and the system refuses. Assume that the maximum number of retransmissions of the reservation request frame is M, and the value of M is increased.

1, the delay increases by at least R + T1. Since the retransmission probability of the reservation request frame is ^{= 1_e σ} , the average number of retransmissions is:

M = l + P +Ρ ¹ +Ρ +··· = \Ι {\-P) = e ^GTl

_ _GTi LnM

^ S = gT, =Ge ' -7 =- - so M ;

Assuming that the retransmission is unsuccessful 16 times, the frame is discarded, indicating that the transmission failed and is reported to the upper layer protocol. Therefore, if the retransmission is still unsuccessful for 16 times, the transmission fails, and the probability of transmission failure is:

P _A = P _r ^M+l = (1 _ ) ^M+1 = (1 _ e- ^G ' f . As shown in Fig. 4, the relationship between the reserved ALOHA packet loss rate and G packets is given.

Blockage rate:

For the VLC system, when the number of service channels N is less than the number of users, and the user node requests the request for the frame to be successful, when the system can access the system, all the available resources are in use, and blocking occurs. Obviously, the more resources available by the system, the smaller the blocking probability. Under the assumption that the number of indoor users does not change, the blocking rate is closely related to the number N of data transmission channels.

The Irish B formula indicates the number N of available channel resources, and the relationship between the number of Irish channels p accessed per channel and the blocking rate is:

B(N, p) =

i *

p is the normalized access density of the unit channel, ρ = λ / μ, λ is the access rate of the user's access request, and μ is the service rate of the access procedure. The above equation assumes that λ obeys the Poisson distribution and μ obeys the exponential distribution.

As shown in Fig. 5, the relationship between the reserved ALOHA blocking rate B and the access density p of Ν=3, Ν=6, Ν=9 is given.

Through calculation and image analysis based on the performance of the reservation-based ALOHA-based multiple access method, the conclusions are obtained: (1) The more channel division, the larger the throughput, the larger the relative delay, but the blocking rate will decrease; ). The channel division is small, the throughput performance is degraded, and the delay performance is improved, but the blocking performance is degraded.

It can be seen that the present invention combines fixed allocation with dynamic allocation. The VLC access point in the VLC system divides the number of channels according to the requirements of the specific service of the user, and the allocation is flexible.

As shown in the above description, the embodiment of the present invention implements the VLC dynamic access operation, and the user node can represent the process shown in FIG. 6, and the process includes the following steps: Step 610: The user node generates a reservation request frame for scheduling an uplink channel and sends the reservation request frame.

Step 620: After the reservation is successful, the user node sends data in the reserved time slot.

At the VCL access point, the process shown in FIG. 7 may be performed. The process includes the following steps: Step 710: The VLC access point notifies the status of the current channel by means of downlink broadcast, and the time when the uplink random signal is allowed to be sent.

Step 720: The VLC access point dynamically allocates the number N of the transport packet time slots according to the received reservation request frame.

Correspondingly, the device for implementing dynamic access of the VLC is implemented in the embodiment of the present invention. The device is a user node 81. As shown in FIG. 8, the user node 81 is configured as:

Here, the user node 81 transmits a reservation request frame one time, and when a reservation request frame transmitted by two or more user nodes collides, the transmission of the reservation request frame is retried.

The user node 81 can compete to send the reservation request frame in the manner of ALOHA. The user node 81 is also configured to:

The uplink channel is divided into N+1 time slots, one of which is used as a reserved time slot for transmitting a reservation request frame, and the other N time slots are used as transport packet time slots for transmitting packet data.

The reserved time slot contains information on the length of time and the number of packets that the user node will occupy. Another embodiment of the present invention is to implement VLC dynamic access, and the device is a VLC access point 82. As shown in FIG. 8, the VLC access point 82 is configured as:

Notifying the status of the current channel and the time at which the uplink random signal can be transmitted by means of downlink broadcast; and dynamically allocating the number of transport packet slots according to the received reservation request frame

The user node 81 and the VLC access point 82 form a VLC dynamic access system. As shown in FIG. 8, the system includes a VLC access point 82 and a user node 81.

The VLC access point 82 is configured to notify the status of the current channel by using a downlink broadcast. And a time for allowing the transmission of the uplink random signal; and, according to the received reservation request frame, dynamically allocating the number N of the transmission packet slots;

The user node 81 is configured to generate a reservation request frame for the reserved uplink channel and send the data; after the reservation succeeds, the data is transmitted in the reserved time slot.

In summary, the present invention will be fixedly distributed regardless of the method, device or system.

TDMA is combined with a dynamic allocation mechanism. The transport packet slot is composed of N time slots of length T2. The simple TDMA method can provide reliable service and high real-time performance. The reserved time slots are transmitted using the ALOHA protocol, which reduces the probability of overlapping collisions and makes full use of channel resources.

Moreover, the disordered contention of the channel resources caused by the packet transmission competition is avoided, and the channel resources can be allocated reasonably according to the actual service requirements of the user nodes, thereby effectively improving the network throughput and reducing the transmission delay.

The above is only the preferred embodiment of the present invention and is not intended to limit the scope of the present invention.

Claims

claims

1. A method for realizing dynamic access of visible light communication VLC. The method includes: the user node generates a reservation request frame for reserving the uplink channel and sends it; after the reservation is successful, the user node sends data in the reserved time slot.

2. The method according to claim 1, wherein,

The user node sends one reservation request frame at a time. When the reservation request frames sent by more than two user nodes collide, the conflicting user nodes retry the sending of the reservation request frame.

3. The method according to claim 1, wherein the reservation request frame is sent in an ALOHA manner.

4. The method according to any one of claims 1 to 3, wherein the method further includes: dividing the uplink channel into N+1 time slots, and using one of the time slots as a time slot for sending the reservation request frame. reserved time slots, and the other N time slots are used as transmission packet time slots for transmitting packet data.

5. The method according to claim 4, wherein the reserved time slot contains information about the length of time that the user node will occupy and the number of groups.

6. A method for realizing VLC dynamic access, wherein the method includes:

The VLC access point notifies the current channel status and the time allowed to send uplink random signals through downlink broadcast; and, the VLC access point dynamically allocates the number N of packet transmission time slots based on the received reservation request frame.

7. The method according to claim 6, wherein the method further includes:

The uplink channel is divided into N+1 time slots, one of the time slots is used as a reservation time slot for sending reservation request frames, and the other N time slots are used as transmission packet time slots for transmitting packet data.

8. A device for realizing VLC dynamic access, the device is a user node; wherein, the user node is configured to: generate and send a reservation request frame for reserving the uplink channel; after the reservation is successful, send data in the reserved time slot.

9. The device according to claim 8, wherein, The user node is configured to send one reservation request frame at a time. When the reservation request frames sent by more than two user nodes collide, the sending of the reservation request frame is retried.

10. The device according to claim 8, wherein the user node is configured to compete to send the reservation request frame in an ALOHA manner.

11. The device according to any one of claims 8 to 10, wherein the user node is further configured to:

12. The device according to claim 11, wherein the reserved time slot contains information about the length of time that the user node will occupy and the number of groups.

13. A device for realizing VLC dynamic access, the device is a VLC access point; wherein, the VLC access point is configured as:

Notify the status of the current channel and the time when uplink random signals can be sent through downlink broadcast; and dynamically allocate the number of transmission packet time slots based on the received reservation request frame

14. The device according to claim 13, wherein the VLC access point is further configured to: divide the uplink channel into N+1 time slots, and use one of the time slots as a reservation for sending a reservation request frame. time slots, and the other N time slots are used as transmission packet time slots for transmitting packet data.

15. A system for realizing VLC dynamic access, wherein the system includes a VLC access point and a user node; wherein,

The VLC access point is configured to notify the status of the current channel and the time allowed to send uplink random signals through downlink broadcast; and, based on the received reservation request frame, dynamically allocate the number N of packet transmission time slots;

The user node is configured to generate and send a reservation request frame for reserving the uplink channel; after the reservation is successful, send data in the reserved time slot.