CN108667848B - System for caching, transcoding and transmitting video by using vehicle-mounted AP (access point) and working method thereof - Google Patents
System for caching, transcoding and transmitting video by using vehicle-mounted AP (access point) and working method thereof Download PDFInfo
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- H—ELECTRICITY
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- H04W4/02—Services making use of location information
- H04W4/025—Services making use of location information using location based information parameters
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- H04L65/60—Network streaming of media packets
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- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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- H—ELECTRICITY
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- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
- H04N21/41—Structure of client; Structure of client peripherals
- H04N21/414—Specialised client platforms, e.g. receiver in car or embedded in a mobile appliance
- H04N21/41422—Specialised client platforms, e.g. receiver in car or embedded in a mobile appliance located in transportation means, e.g. personal vehicle
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- H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
- H04N21/43—Processing of content or additional data, e.g. demultiplexing additional data from a digital video stream; Elementary client operations, e.g. monitoring of home network or synchronising decoder's clock; Client middleware
- H04N21/44—Processing of video elementary streams, e.g. splicing a video clip retrieved from local storage with an incoming video stream or rendering scenes according to encoded video stream scene graphs
- H04N21/44004—Processing of video elementary streams, e.g. splicing a video clip retrieved from local storage with an incoming video stream or rendering scenes according to encoded video stream scene graphs involving video buffer management, e.g. video decoder buffer or video display buffer
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/60—Network structure or processes for video distribution between server and client or between remote clients; Control signalling between clients, server and network components; Transmission of management data between server and client, e.g. sending from server to client commands for recording incoming content stream; Communication details between server and client
- H04N21/63—Control signaling related to video distribution between client, server and network components; Network processes for video distribution between server and clients or between remote clients, e.g. transmitting basic layer and enhancement layers over different transmission paths, setting up a peer-to-peer communication via Internet between remote STB's; Communication protocols; Addressing
- H04N21/647—Control signaling between network components and server or clients; Network processes for video distribution between server and clients, e.g. controlling the quality of the video stream, by dropping packets, protecting content from unauthorised alteration within the network, monitoring of network load, bridging between two different networks, e.g. between IP and wireless
- H04N21/64746—Control signals issued by the network directed to the server or the client
- H04N21/64761—Control signals issued by the network directed to the server or the client directed to the server
- H04N21/64769—Control signals issued by the network directed to the server or the client directed to the server for rate control
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- H—ELECTRICITY
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- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
- H04W4/02—Services making use of location information
- H04W4/025—Services making use of location information using location based information parameters
- H04W4/027—Services making use of location information using location based information parameters using movement velocity, acceleration information
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
- H04W4/30—Services specially adapted for particular environments, situations or purposes
- H04W4/40—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P]
- H04W4/48—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P] for in-vehicle communication
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Abstract
The invention discloses a system for caching, transcoding and transmitting videos by utilizing a vehicle-mounted AP (access point) and a working method thereof. The controller collects the position, the speed and the working channel information of the vehicle-mounted AP, responds to a mobile equipment query request, calculates expected throughput between the vehicle-mounted AP and the mobile equipment according to a throughput model, provides a candidate vehicle-mounted AP list, expected throughput and expected communication time for the mobile equipment, selects a proper vehicle-mounted AP for connection according to the candidate vehicle-mounted AP list, and adjusts the code rate of a request video according to the expected average throughput of the connected vehicle-mounted AP by the video client. The system and the working method thereof can fully utilize the vehicle-mounted AP to improve the throughput of the mobile equipment and improve the video watching experience of a user.
Description
Technical Field
The invention belongs to the technical field of networks, and particularly relates to a system for improving network access bandwidth based on a vehicle-mounted network and improving video watching experience of a user through caching and online transcoding and a working method thereof.
Background
With the continuous development of mobile communication technology and the continuous popularization of mobile devices, mobile video traffic volume is huge and grows rapidly, and higher requirements are put forward on network capacity and user experience. The mobile device is mostly equipped with a plurality of network interface cards, such as WiFi, LTE, bluetooth, etc., and can also be expanded through a USB port. The MPTCP protocol enables a mobile device to use multiple radio interfaces simultaneously or alternately, and perform handover in a mobile environment without interrupting the connection, thereby improving throughput and robustness.
Due to the fact that wireless network communication quality is poor in a high-speed mobile environment, an existing public transportation system provides relatively stable and high-speed network access for users through vehicle-mounted WiFi Access Points (APs). However, current implementations do not adapt well to the mobility of the user: when the user leaves the vehicle, the original connection is disconnected, and the service is interrupted. On the other hand, pedestrians outside the vehicle cannot increase their available network capacity through these available resources. And when the user watches the video on the mobile device through the vehicle-mounted AP, the watching experience of the user also faces the following challenges:
1. in order to discover surrounding vehicular APs, the mobile device needs to scan multiple channels, which results in a large time overhead and a reduction in service time.
2. In a mobile environment, the distance between the vehicle-mounted AP and the mobile device may continuously change, and the traditional RSSI-based AP selection strategy does not well characterize the AP performance.
3. The conventional wireless device triggers AP handover only when RSSI is lower than a certain threshold, and in a mobile environment, the handover strategy has obvious hysteresis, and also misses a better connection opportunity, and cannot fully utilize available resources.
4. The network condition fluctuation in a mobile environment is large due to large differences of speeds and directions of different vehicle-mounted APs, the network bandwidth is difficult to accurately predict by a video client, frequent video blocking of a user is easy to cause, and user experience is reduced.
5. When caching a multi-rate video, a conflict between a storage space and cache effectiveness exists. Caching video blocks of all code rates can cause waste of storage space, and storing video blocks of partial code rates can reduce caching effectiveness.
Disclosure of Invention
The purpose of the invention is as follows: in order to solve the problems, the invention provides a system for caching, transcoding and transmitting videos by utilizing a vehicle-mounted AP (access point), which can fully utilize available vehicle-mounted AP resources to improve the network throughput and optimize the video watching experience of users.
Another object of the present invention is to provide a corresponding operating method of the above system for video caching, transcoding and transmission by using an onboard AP.
The technical scheme is as follows: the invention relates to a system for caching, transcoding and transmitting videos by utilizing a vehicle-mounted AP, which comprises the vehicle-mounted AP, mobile equipment, a controller and a video server, wherein,
vehicle-mounted AP: periodically sending the position, the speed and the working channel information of the current vehicle-mounted AP to a controller; the video block cache and transcoding module is responsible for caching and transcoding the video block, and cache updating is carried out by using a cache replacement strategy;
a mobile device: periodically sending the position, the speed and the number of network cards of the current mobile equipment to a controller, inquiring a surrounding available vehicle-mounted AP list, expected throughput and expected communication time of the vehicle-mounted AP list from the controller, and selecting a proper vehicle-mounted AP for connection according to a result returned by the controller; the video client on the mobile equipment determines the requested video code rate according to the expected throughput and the expected communication time of the connected vehicle-mounted AP;
a controller: the controller collects information of the vehicle-mounted AP, responds to a mobile equipment query request, calculates expected throughput according to the position and speed information of the mobile equipment and the vehicle-mounted AP and by combining a throughput model, and returns an available candidate vehicle-mounted AP list, expected throughput and expected communication time to the mobile equipment;
a video server: and cutting the content into video blocks with fixed playing length, and providing versions with different code rates for each block for a user to select.
The working method for carrying out video caching, transcoding and transmission by using the vehicle-mounted AP-based system comprises the following steps:
1) the vehicle-mounted AP periodically reports the current position, the speed and the working channel information to the controller, and the controller receives and stores the information; the vehicle-mounted AP determines the code rate of a cache video according to the maximum communication distance and the speed information and by combining a throughput model, and caches the streaming video;
2) the mobile equipment periodically sends the information of the position, the speed and the network card number of the current mobile equipment to the controller, and requests to inquire a surrounding available vehicle-mounted AP list, expected throughput and expected communication time of the vehicle-mounted AP list;
3) the controller calculates expected throughput rate of connection establishment between the mobile equipment and a certain vehicle-mounted AP according to the position and speed information of the mobile equipment and the vehicle-mounted AP by combining a throughput model, screens and sorts the vehicle-mounted AP according to the expected throughput, and returns a sorted vehicle-mounted AP list, the expected throughput and the expected communication time to the mobile equipment;
4) the mobile equipment selects and switches the vehicle-mounted AP at a proper time according to the candidate vehicle-mounted AP list, the expected throughput and the expected communication time; the video client on the mobile equipment determines the requested video code rate according to the expected throughput and the expected communication time of the connected vehicle-mounted AP and requests a video block from the vehicle-mounted AP;
5) the vehicle-mounted AP determines how to transmit the video block according to the cache condition, and performs cache updating according to a cache strategy, specifically, if the vehicle-mounted AP caches the video block with the code rate requested by the video client, the vehicle-mounted AP directly transmits the video block to the video client; if the vehicle-mounted AP caches the video block requested by the video client but the code rate is greater than that requested by the video client, the vehicle-mounted AP transcodes the video block into a low code rate and transmits the low code rate to the video client, and meanwhile, the cache is updated; if the requested content is not cached by the vehicle-mounted AP or the video block requested by the video client is cached, but the code rate is lower than that requested by the video client, the vehicle-mounted AP downloads the video block with the code rate requested by the video client from the video server, transmits the video block to the video client and updates the cache.
The throughput model in the steps 1) and 3) is obtained by integrating the instantaneous throughput rate with the communication time, and the instantaneous throughput rate is determined by a logarithmic distance path loss model and the Shannon theorem together.
Has the advantages that: compared with the prior art, the invention has the following advantages:
1. by introducing the controller to collect and track the vehicle-mounted AP information, the mobile device can directly inquire the controller about available vehicle-mounted APs around, and time overhead caused by frequent scanning of the available vehicle-mounted APs around is avoided. And the screening and sequencing of the vehicle-mounted AP are carried out in the controller, and the calculation overhead of the mobile equipment is not increased.
2. Through constructing the throughput model, the relative position change of the vehicle-mounted AP and the mobile device is incorporated into the model, the throughput improvement which can be obtained by connecting the vehicle-mounted AP with the mobile device is more accurately described, and the mobile device is helped to select a better vehicle-mounted AP.
3. The mobile equipment periodically inquires available vehicular APs around the controller, and timely finds better vehicular APs for switching according to the available vehicular AP list, expected throughput and expected communication time, so that the resource utilization rate is improved, the hysteresis of a traditional RSSI-based AP switching strategy is avoided, and the service unavailable time is reduced.
4. The video client determines the code rate of the requested video according to the expected throughput and the expected communication time of the connected vehicle-mounted AP, the network bandwidth is fully utilized, the video quality of a user is improved as much as possible, and inaccuracy and hysteresis of a traditional code rate adjusting method based on historical bandwidth information prediction are avoided.
5. By utilizing the storage capacity of the vehicle-mounted AP to provide the cache service, the time delay of a user for acquiring the video block is shortened, and the transmission rate is improved. And the high-code-rate video is transcoded into the low-code-rate video through the storage capacity of the vehicle-mounted AP to meet the request of the video client, so that the utilization value of the cache file is improved, and the transmission burden of a back-end network is reduced.
Drawings
FIG. 1 is a diagram of a mobile device and an in-vehicle AP communication model;
FIG. 2 is a system scenario diagram for video caching, transcoding and transmission using a vehicle AP;
fig. 3 is a data flow diagram based on the system architecture of fig. 2.
Detailed Description
The technical scheme of the invention is further explained by combining the attached drawings.
First, a throughput calculation model in this scenario is constructed based on the communication diagram of the mobile device and the in-vehicle AP shown in fig. 1.
The distance between the mobile device and the onboard AP is determined by both its position and speed, as a function of time. The RSSI is a function of the distance, and the path loss follows a logarithmic distance path loss model, namely:
RSSI＝φ(d)＝r0+10αlog10(d/d0) (1)
where d is the distance from the mobile device to the onboard AP, d0Is a reference distance, r0Is at d0The received signal strength at a location, typically d0α is a path loss exponent, which represents the rate at which path loss increases with distance.
Note RSSIminIn order to transmit the message from the mobile device to the vehicle-mounted AP, the distance between the mobile device and the vehicle-mounted AP is the communication radius R at this time, that is, the vehicle-mounted AP exists in the range of the radius R with the mobile device as the center, so that the message can be transmitted. From equation (1), the communication radius can be found to be:
according to the Shannon theorem in the information theory and the calculation formula of the signal-to-noise ratio:
Capacity＝Blog2(1+S/N) (3)
SNR＝RSSI-b＝10lg(S/N) (4)
where B is the channel bandwidth, S is the signal power, N is the noise power, and B is the noise strength of the receiving end. And combining the formulas (3) and (4), and assuming that the proportion of the actual TCP throughput in the upper limit capacity is omega, obtaining a calculation formula of the instantaneous throughput rate:
according to the position and speed information of the mobile equipment and the vehicle-mounted AP, the distance d (t) between the mobile equipment and the vehicle-mounted AP at the time t can be easily calculated, and the d (t) is less than or equal to R, so that the communication time interval (t) between the mobile equipment and the vehicle-mounted AP can be obtainedstart,tend) Integrating the instantaneous throughput rate in the period of time with the time t to obtain the expected throughput of the communication between the mobile device and the vehicle-mounted AP, namely:
wherein
Is a function of the instantaneous throughput rate over time, determined by d (t) and equations (1) and (5).
The specific processing is described below in conjunction with the system scenario diagram shown in fig. 2. As shown in fig. 2, the system mainly consists of four parts: the system comprises the vehicle-mounted AP, the mobile equipment, the controller and the video server, wherein the mobile equipment can improve the throughput by selecting and connecting the vehicle-mounted AP and request a video block with a proper code rate to optimize the experience of watching the video by a user. The vehicle-mounted AP is a WiFi access point arranged on a vehicle and has certain storage and calculation capabilities. The mobile device is configured with a plurality of network cards or can be expanded through a USB port, and the mobile device uses an MPTCP protocol, so that the plurality of network cards can be used for data transmission at the same time, and the throughput and the robustness are improved. The controller can be deployed at a cloud end to perform centralized management on all vehicle-mounted APs, and can also be deployed on a base station to manage the vehicle-mounted APs within the coverage range of the base station. The functions of the components of the system are as follows:
vehicle-mounted AP: periodically sending the position, the speed and the working channel information of the current vehicle-mounted AP to a controller; the video block cache and transcoding module is responsible for caching and transcoding the video block, and cache updating is carried out by using a cache replacement strategy;
a mobile device: periodically sending the position, the speed and the number of network cards of the current mobile equipment to a controller, inquiring a surrounding available vehicle-mounted AP list, expected throughput and expected communication time of the vehicle-mounted AP list from the controller, and selecting a proper vehicle-mounted AP for connection according to a result returned by the controller; the video client on the mobile equipment determines the requested video code rate according to the expected throughput and the expected communication time of the connected vehicle-mounted AP;
a controller: the controller collects information of the vehicle-mounted AP, responds to a mobile equipment query request, calculates expected throughput according to the position and speed information of the mobile equipment and the vehicle-mounted AP and by combining a throughput model, and returns an available candidate vehicle-mounted AP list, expected throughput and expected communication time to the mobile equipment;
a video server: and cutting the content into video blocks with fixed playing length, and providing versions with different code rates for each block for a user to select.
Fig. 3 is a data flow diagram according to the system architecture of fig. 2. The vehicle-mounted AP reports own information to the controller periodically, the controller collects the vehicle-mounted AP information, the mobile device is helped to screen and sort surrounding vehicle-mounted APs according to the mobile device information, a candidate AP list, corresponding expected throughput and expected communication time are returned to the mobile device, the mobile device selects the vehicle-mounted AP to be connected according to the candidate AP information, the requested video code rate is determined according to the expected throughput and the expected communication time, the vehicle-mounted AP determines transcoding or downloading from a video server according to the caching condition, and caching updating is carried out according to a caching strategy. The specific working process is as follows:
1) the vehicle-mounted AP periodically reports information such as the current position, the speed, the working channel and the like to the controller, and the controller receives and stores the information. And the vehicle-mounted AP determines the code rate of the cache video according to the information such as the maximum communication distance, the speed and the like and by combining a throughput model, and caches the contents of the stream.
Because the communication radius of the vehicle-mounted AP and the mobile device is R, the maximum communication time of the vehicle-mounted AP and the mobile device is as follows:
where | v | is the moving rate of the in-vehicle AP. The expected throughput during this time can be calculated by equation (6), which is denoted as T, and then the average throughput rate of the mobile device connecting to the in-vehicle AP is:
the onboard AP caches the popular video using a code rate close to the average throughput rate.
2) The mobile equipment periodically sends the information of the current position, the speed, the number of network cards and the like of the mobile equipment to the controller, and requests to inquire the available vehicular AP list around.
3) The controller calculates expected throughput of connection establishment between the mobile equipment and a certain vehicle-mounted AP according to the information such as the positions and the speeds of the mobile equipment and the vehicle-mounted APs and by combining a throughput model, screens and sorts the vehicle-mounted APs, and returns a sorted vehicle-mounted AP list, the expected throughput and the expected communication time to the mobile equipment.
In the screening process, the controller filters the vehicle-mounted AP with too low expected throughput and too short expected communication time, and only returns the vehicle-mounted AP information with better performance to the mobile equipment.
4) And the mobile equipment selects and switches the vehicle-mounted AP at a proper time according to the candidate vehicle-mounted AP list and the throughput model. According to the expected throughput and the expected communication time of the connected vehicle-mounted AP, the video client determines the requested video code rate by using a similar method (refer to equation 8) in the step 1), and requests a video block from the vehicle-mounted AP.
5) If the vehicle-mounted AP caches the video block with the code rate requested by the video client, directly transmitting the video block to the video client; if the vehicle-mounted AP caches the video block requested by the video client but the code rate is greater than that requested by the video client, the vehicle-mounted AP transcodes the video block into a low code rate and transmits the low code rate to the video client, and meanwhile, the cache is updated; if the requested content is not cached by the vehicle-mounted AP or the video block requested by the video client is cached, but the code rate is lower than that requested by the video client, the vehicle-mounted AP downloads the video block with the code rate requested by the video client from the video server, transmits the video block to the video client and updates the cache.
The specific cache update strategy is as follows: for the video block needing to be cached, if enough available space exists, directly adding the video block into the cache; if the space is not available, finding the video block which is accessed Least recently according to an LRU (Least recently used) algorithm, reserving the video block with the highest code rate, and releasing the storage space occupied by the video block with the low code rate until enough space is available for storing the video block; if there is still not enough memory space, the least recently accessed video block is replaced according to LRU.
Claims (6)
1. A system for video caching, transcoding and transmission by using an in-vehicle AP is characterized by comprising the in-vehicle AP, a mobile device, a controller and a video server, wherein,
vehicle-mounted AP: periodically sending the position, the speed and the working channel information of the current vehicle-mounted AP to a controller; the video block cache and transcoding module is responsible for caching and transcoding the video block, and cache updating is carried out by using a cache replacement strategy;
a mobile device: periodically sending the position, the speed and the number of network cards of the current mobile equipment to a controller, inquiring a surrounding available vehicle-mounted AP list, expected throughput and expected communication time of the vehicle-mounted AP list from the controller, and selecting a proper vehicle-mounted AP for connection according to a result returned by the controller; the video client on the mobile equipment determines the requested video code rate according to the expected throughput and the expected communication time of the connected vehicle-mounted AP;
a controller: the controller collects information of the vehicle-mounted AP, responds to a mobile equipment query request, calculates expected throughput according to the position and speed information of the mobile equipment and the vehicle-mounted AP and by combining a throughput model, and returns an available candidate vehicle-mounted AP list, expected throughput and expected communication time to the mobile equipment; the throughput model is obtained by integrating instantaneous throughput rate with communication time, and the instantaneous throughput rate is jointly determined by a logarithmic distance path loss model and Shannon's theorem and has the form:
wherein, Throughput is the instantaneous Throughput rate of the mobile device and the vehicle-mounted AP, B is the channel bandwidth, RSSI is the received signal strength, B is the noise strength of the receiving end, and ω is the proportion of the actual TCP Throughput to the upper limit capacity;
a video server: and cutting the content into video blocks with fixed playing length, and providing versions with different code rates for each block for a user to select.
2. The system for video caching, transcoding and transmission using an in-vehicle AP as claimed in claim 1, wherein the in-vehicle AP is a WiFi access point installed on a vehicle with storage and computing capabilities.
3. The system for video caching, transcoding and transmission using an in-vehicle AP as claimed in claim 1, wherein the mobile device supports MPTCP protocol and is equipped with multiple network cards or is extended to multiple network cards through USB ports.
4. A method of operating a system for video caching, transcoding and transmission using an onboard AP according to any one of claims 1 to 3, characterized in that it comprises the following steps:
1) the vehicle-mounted AP periodically reports the current position, the speed and the working channel information to the controller, and the controller receives and stores the information; the vehicle-mounted AP determines the code rate of a cache video according to the maximum communication distance and the speed information and by combining a throughput model, and caches the contents of the stream;
2) the mobile equipment periodically sends the information of the position, the speed and the network card number of the current mobile equipment to the controller, and requests to inquire a surrounding available vehicle-mounted AP list, expected throughput and expected communication time of the vehicle-mounted AP list;
3) the controller calculates expected throughput of connection establishment between the mobile equipment and a certain vehicle-mounted AP according to the position and speed information of the mobile equipment and the vehicle-mounted AP by combining a throughput model, screens and sorts the vehicle-mounted AP according to the expected throughput, and returns a sorted vehicle-mounted AP list, the expected throughput and expected communication time thereof to the mobile equipment, wherein the throughput model is obtained by integrating instantaneous throughput with communication time, and the instantaneous throughput is determined by a logarithmic distance path loss model and a Shannon theorem together and has the form:
wherein, Throughput is the instantaneous Throughput rate of the mobile device and the vehicle-mounted AP, B is the channel bandwidth, RSSI is the received signal strength, B is the noise strength of the receiving end, and ω is the proportion of the actual TCP Throughput to the upper limit capacity;
4) the mobile equipment selects and switches the vehicle-mounted AP at a proper time according to the candidate vehicle-mounted AP list, the expected throughput and the expected communication time; a video client on the mobile equipment determines a requested video code rate according to the expected throughput and the expected communication time of the connected vehicle-mounted AP, and requests a video block from the vehicle-mounted AP;
5) and the vehicle-mounted AP transmits the requested video block to the video client, and performs cache updating according to the cache strategy.
5. The operating method according to claim 4, characterized in that said step 5) comprises: if the vehicle-mounted AP caches the video block with the code rate requested by the video client, directly transmitting the video block to the video client; if the vehicle-mounted AP caches the video block requested by the video client but the code rate is greater than that requested by the video client, the vehicle-mounted AP transcodes the video block into a low code rate and transmits the low code rate to the video client, and meanwhile, the cache is updated; if the requested content is not cached by the vehicle-mounted AP or the video block requested by the video client is cached, but the code rate is lower than that requested by the video client, the vehicle-mounted AP downloads the video block with the code rate requested by the video client from the video server, transmits the video block to the video client and updates the cache.
6. The method of claim 5, wherein the cache update policy is: for a video block needing to be cached, directly adding the video block into the cache under the condition that a storage space is available; if the storage space is unavailable, finding the video block which is accessed least recently according to the LRU algorithm, reserving the video block with the highest code rate, and releasing the storage space occupied by the video block with the low code rate until enough space is available for storing the video block which needs to be cached; if there is still not enough memory space, the least recently accessed video block is replaced according to LRU.
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