CN109067856A - WiFi direct multi-hop mobile device sharing files method and system based on network code - Google Patents
WiFi direct multi-hop mobile device sharing files method and system based on network code Download PDFInfo
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- CN109067856A CN109067856A CN201810795254.5A CN201810795254A CN109067856A CN 109067856 A CN109067856 A CN 109067856A CN 201810795254 A CN201810795254 A CN 201810795254A CN 109067856 A CN109067856 A CN 109067856A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L67/00—Network arrangements or protocols for supporting network services or applications
- H04L67/01—Protocols
- H04L67/06—Protocols specially adapted for file transfer, e.g. file transfer protocol [FTP]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
- H04L65/60—Network streaming of media packets
- H04L65/75—Media network packet handling
- H04L65/765—Media network packet handling intermediate
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Abstract
The present invention discloses a kind of WiFi direct multi-hop mobile device sharing files method and system based on network code, and wherein method includes: that the data of source device selection sharing carry out fragment network-encoding operation to it；Source device waits the question and answer of other mobile devices；Mobile device sends the data packet after recompiling to other mobile devices after being successfully received data；Mobile device can decode to obtain initial data after receiving the data slice of a certain amount of linear independence.The present invention utilizes pattern switching strategy, can save equipment and not stop delay caused by switching, to improve the distribution efficiency of data in system；By using intermediate node active re-encoding strategies, the independence of data packet is enhanced, and reduces system delay using free time, so that the overall performance of system is improved；The present invention has the advantages that data transmission is stable, data sharing rate is high.
Description
Technical field
The invention belongs to wireless communication technology fields, and in particular to a kind of WiFi direct multi-hop based on network code
Mobile device sharing files method and system.
Background technique
File sharing system is the typical case of File Sharing Technique on the internet.The development of mobile device, so that this
The application of sample has vast potential for future development.Now, mobile device-based file sharing system is one and very popular answers
With.However, especially in the case where receiving end is more, communication cost can be very high when transmitting file in business 4G network,
File owners will bear the communication cost of great number.When WiFi direct technology is used, the user positioned at the same area can be with
Save communication cost；In addition, user can obtain shared rate more higher than commercial network.Currently, WiFi direct is mobile
The ideal style of equipment transmission, has obtained the extensive support of many manufacturers.
However, WiFi direct technology is limited by transmission range and number of users.In order to a wide range of interior real
Now large-scale file transmission, introduces network coding technique in the prior art.File point is carried out in traditional communication network
When enjoying, existing safety is poor, bandwidth availability ratio is low problem.It can achieve the stream of theoretically multicast transmission by coding transmission
Amount such as maximizes at the proposition of network codes theory, provides theoretical foundation to improvement traditional file shared system, while but also
Efficiency of transmission, reliability, robustness and the safety for further increasing network are possibly realized.
But currently used passively network code mode is unfavorable for the Dynamic data exchange of each equipment room and handles in real time
The performance of data is to be improved while easy increasing the time delay that generates because intermediate node is encoded；In addition, in the prior art
Mobile device, which expends the time in the different switchings of progress both of which and do not stop to switch to bring, postpones the distribution so that data
It is inefficient.
Summary of the invention
The purpose of the present invention is aim to solve the problem that currently used passively network code mode is unfavorable for each equipment room
The performance of Dynamic data exchange and real-time processing data it is to be improved and meanwhile it is easy increase because intermediate node is encoded generate when
The problem of prolonging provides a kind of WiFi direct multi-hop mobile device sharing files method based on network code.
In order to achieve the above object, the present invention provides provide a kind of WiFi direct multi-hop shifting based on network code
Dynamic device file sharing method, carries out in accordance with the following steps:
Step 1) source device using network code to data carry out slice coding obtain the data slice of k linear independence after
Be converted to the question and answer that wireless access point (Access Point, AP) waits other mobile devices；
Step 2) mobile device sends question and answer request to source device, and source device receives linear by the k after requesting
Unrelated data slice is sent to mobile device；
Step 3) mobile device actively recompile to the data slice received after receiving data slice, while can make
The data slice after recompiling is sent to other mobile devices for source device；
Step 4) is decoded after other mobile devices are successfully received the data slice of the linear independence of predetermined amount and is obtained
Initial data.
It further, include: information source before source device carries out slice coding to data using network code in step 1)
Equipment selection is to sharing data and setting data fragmentation quantity；
Further, middle source device carries out the data after slice coding obtains k coding to data using network code
Network code is generated while piece and describes file (Network Coding Description File, NCD), and the NCD includes
Coding vector and source file fragment quantity.
Further, step 2) specifically includes:
Step 201): mobile device is requested all in reception pattern (Receive Mode, RM) to source device when initial
Send data slice；
Step 202): source device receives the request of several mobile devices, and 3 are selected in the request of several mobile devices
The strongest mobile device of signal, which is sent, agrees to demand file；
Step 203): it receives and agrees to that the mobile device of demand file initiates the connection waiting source device hair to source device
Send data slice；
Step 204): source device sends data slice to M mobile device, includes a NCD in each data slice, and
The data slice sent to each mobile device is up to the 50% of the possessed data slice of information source；
Step 205): being that movement is set when the k number possessed is successfully transmitted completion can then switch to RM by source device according to piece
Standby forwarding data slice.
Further, step 3) the following steps are included:
Step 301): after mobile device is successfully received data slice, the content of each data slice is written to the NCD of oneself；
Step 302): after mobile device successful data reception piece, while a thread being called to generate a new coding square
Battle array is encoded with received all data slices, and the data slice after being re-encoded is put into buffer, waits to be called；
Step 303): mobile device switches to ap mode as source device after having received data slice, waits other equipment
Access；
Step 304): when there is request to generate, it is sent to the encoded data slice of request mobile device.
Still further, mobile device carries out actively again the data slice received after receiving data slice in step 3)
It is specifically included when coding:
After distribution procedure is added in equipment, background thread J will be called to monitor the variation of operative orientation.Once equipment receives
To a new piece of data, thread J will receive the linear combination of all d data slices, and volume is actively generated from finite field gf (256)
Code coefficient [c1,c2,…,cd], with all data slice [Y in mobile devicei1,Yi2,...,Yid]-1It is recompiled to obtain new
Encoder matrix Ynew, expression formula is as follows:
Wherein i represents the length of linear combination in each data slice, and d represents the quantity for recompiling data slice.
By storage into caching.Once request generates, the data slice after encoding in caching is sent to request equipment,
The then thread continuously linear combination of more new piece of data in a device when having continuous request.
Further, all mobile devices can all carry out the conversion of both of which, and specific switchover policy is as follows:
With NCD file FAMobile device A a NCD file F is received from source device BB, r1=rank (FA), r2
=rank (FB∪FA)；Wherein rank represents the order of encoder matrix, r1Represent file FAThe order of middle encoder matrix, r2Represent file FA
With file FBThe order of encoder matrix mutually simultaneously.
1): working as r2> r1When, mobile device A sends data slice and sends a request to source device B, and B agrees to that request sends data
Piece updates NCD file F after receiving data slice to A, AA, then recalculate r1And r2；
2): otherwise, mobile device A is converted into ap mode as source device, waits the connection of other mobile devices；
3): if the waiting time is more than 10 seconds, switching to RM again, an AP connection is selected according to signal strength；
If 4) jumped to 2) without any AP for connection.
On the other hand, the present invention provides a kind of WiFi direct multi-hop mobile device file based on network code
Share system, it is characterised in that: including fragment quantity setting program module, selection coding file routine module, creation connection journey
Linker module and active recodification program module and mobile device mode switching program module is added in sequence module；
The fragment quantity setting program module is used to carry out the file that will share the quantity of slice coding；
The file that the selection coding file routine module is used to select to need to share in source device；
After the creation linker module chooses sharing file with source device, creation connection, source device are clicked
As ap mode, the connection of mobile device is waited；
Link block is added for clicking in the addition linker module, and mobile device be in RM, into sharing state,
AP can be found to be attached；
The active recodification program module carries out the data slice received after receiving data slice for mobile device
Actively recompile；
The mobile device mode switching program module is used to carry out all mobile devices the conversion of both of which.
Further, the active recodification program module executes following procedure:
After distribution procedure is added in equipment, background thread J will be called to monitor the variation of operative orientation.Once equipment receives
To a new piece of data, thread J will receive the linear combination of all d data slices, and volume is actively generated from finite field gf (256)
Code coefficient [c1,c2,…,cd], with all data slice [Y in mobile devicei1,Yi2,...,Yid]-1It is recompiled to obtain new
Encoder matrix Ynew, expression formula is as follows:
Wherein i represents the length of linear combination in each data slice, and d represents the quantity for recompiling data slice.
By storage into caching.Once request generates, the data slice after encoding in caching is sent to request equipment,
The then thread continuously linear combination of more new piece of data in a device when having continuous request.
Further, the mobile device mode switching program module specifically executes following switchover policy:
With NCD file FAMobile device A a NCD file F is received from source device BB, r1=rank (FA), r2
=rank (FB∪FA)；Wherein rank represents the order of encoder matrix, r1Represent file FAThe order of middle encoder matrix, r2Represent file FA
With file FBThe order of encoder matrix mutually simultaneously.
1): working as r2> r1When, mobile device A sends data slice and sends a request to source device B, and B agrees to that request sends data
Piece updates NCD file F after receiving data slice to A, AA, then recalculate r1And r2；
2): otherwise, mobile device A is converted into ap mode as source device, waits the connection of other mobile devices；
3): if the waiting time is more than 10 seconds, switching to RM again, an AP connection is selected according to signal strength；
If 4) jumped to 2) without any AP for connection.
The beneficial effects of the present invention are:
1, all the corresponding actively side of recompiling may be arranged as the intermediate node of whole system in each mobile device
Case is conducive to promote the reliability of transmission and the accuracy of data processing；
2, each mobile device describes file with network code, knows AP around when mobile device is converted to RM
The availability of data is conducive to effective transmission of data, reduces system propagation delay time, improves systematic entirety energy；
3, mobile device can carry out the different switchings of both of which, but since different switchings expend the time, in the present system
A kind of switchover policy has been used, the distribution efficiency for not stopping to switch bring delay to improve data is advantageously reduced；
4, the present invention is recompiled by the data of receiving device, is conducive to increase data independence in equipment, is promoted system
The real time data processing performance of system.
Detailed description of the invention:
Attached drawing is used to provide further understanding of the present invention, and constitutes part of specification, with reality of the invention
It applies example to be used to explain the present invention together, not be construed as limiting the invention.In the accompanying drawings:
Fig. 1 is that multi-hop mobile device shares scheme network model schematic diagram；
Fig. 2 is distinct device code efficiency line chart；
Fig. 3, which is that more mobile devices are active, recompiles tactful performance line chart；
Fig. 4 is sharing efficiency line chart in different schemes；
Fig. 5 is that packet fragmentation size can influence line chart to systematic entirety in different schemes.
Specific embodiment
Specific embodiments of the present invention will be described in detail below, it is to be understood that protection scope of the present invention is not
It is restricted by specific implementation.
Unless otherwise explicitly stated, otherwise in entire disclosure and claims, term " includes " or its change
Changing such as "comprising" or " including " etc. will be understood to comprise stated element or component, and not exclude other members
Part or other component parts.
Embodiment one
A kind of WiFi direct multi-hop mobile device sharing files method based on network code, implementation step are as follows:
Step 1): source device selects sharing data and setting data fragmentation quantity, is carried out using network code to data
Slice coding obtains the data slice of k linear independence, while generating a NCD；After source device carries out network code to data
Be converted to the question and answer that AP waits other mobile devices；Slice coding is carried out to data using network code simultaneously and obtains k linearly
Unrelated data slice is not described herein using the prior art.
Step 2): sending question and answer request to source device in mobile device, and source device receives after requesting to mobile device
Send data；
Step 201): when initial, several mobile devices request to send data packet to source device all in RM；
Step 202): source device receives the request of several mobile devices, and M are selected in the request of several mobile devices
The strongest mobile device of signal, which is sent, agrees to demand file；
Step 203): it receives and agrees to that the mobile device of demand file initiates the connection waiting source device hair to source device
Send data slice；
Step 204): source device sends data slice to M mobile device, includes a NCD in each data slice, and
The data slice of transmission is up to the 50% of the possessed data slice of information source；Here the quantity of M be depending on the sum of mobile device,
Mobile device selects source device to send data slice to 3 mobile devices in the present embodiment；
Step 205): being that movement is set when the k number possessed is successfully transmitted completion can then switch to RM by source device according to piece
Standby forwarding data slice.
Step 3): to reduce the time delay that intermediate node carries out re-encoding generation, mobile device is docked after receiving data slice
The data slice received actively recompile, after recompiling at the same time as source device to the transmission of other mobile devices
Data slice；
Step 301): after mobile device is successfully received data slice, the content of each data slice is written to the NCD of oneself；
Step 302): after mobile device successful data reception piece, while a thread being called to generate a new coding square
Battle array is encoded with received all data slices, and the data slice after being re-encoded is put into buffer, waits to be called；
Step 303): at the same time, mobile device switches to ap mode as source device after having received data slice, waits
The access of other equipment；
Step 304): when there is request to generate, it is sent to the encoded data slice of request mobile device.
Step 4): it can decode to obtain after the data slice that mobile device is successfully received the linear independence of predetermined amount
Initial data.
In the methods of the invention, mobile device can carry out the switching of both of which, to prevent the frequent switching of mode from causing
The decline of system performance proposes a kind of switchover policy on the basis of the above fact Example, advantageously reduces not stop to switch and bring
Delay to improve the distribution efficiency of data, switchover policy is as follows:
With NCD file FAMobile device A a NCD file F is received from source device BB, r1=rank (FA), r2
=rank (FB∪FA)；Wherein rank represents the order of encoder matrix, r1Represent file FAThe order of middle encoder matrix, r2Represent file FA
With file FBThe order of encoder matrix mutually simultaneously.
1): working as r2> r1When, mobile device A sends data slice and sends a request to source device B, and B agrees to that request sends data
Piece updates NCD file F after receiving data slice to A, AA, then recalculate r1And r2；
2): otherwise, mobile device A is converted into ap mode as source device, waits the connection of other mobile devices；
3): if the waiting time is more than 10 seconds, switching to RM again, an AP connection is selected according to signal strength；
If 4) jumped to 2) without any AP for connection.
It should be noted that the above switchover policy can be used alone in mobile device sharing files method, effect can
To reduce delay and improve the distribution efficiency of data.
In the present embodiment, the present invention is that the active for the time delay introducing that reduction intermediate node carries out re-encoding generation is compiled again
The specific method is as follows used by code strategy:
After distribution procedure is added in equipment, background thread J will be called to monitor the variation of operative orientation.Once equipment receives
To a new piece of data, thread J will receive the linear combination of all d data slices, and volume is actively generated from finite field gf (256)
Code coefficient [c1,c2,…,cd], with all data slice [Y in mobile devicei1,Yi2,...,Yid]-1It is recompiled to obtain new
Encoder matrix Ynew, expression formula is as follows:
Wherein i represents the length of linear combination in each data slice, and d represents the quantity for recompiling data slice.
By storage into caching.Once request generates, the data slice after encoding in caching is sent to request equipment,
The then thread continuously linear combination of more new piece of data in a device when having continuous request.
True experiment porch is built when the method for the present invention is embodied, for testing the fortune of this document share system
Row processing.
The experiment is made of 20 mobile devices based on Andriod system, wherein a mobile phone is as source device.Its
In, each mobile device has both of which: AP and RM, so these mobile devices not only send data possessed by oneself
Piece, but also receive the data slice of other equipment.
All mobile devices are all sending and receiving by WiFi direct technical support data piece.Most start by believing
Source mobile terminal sends coded data piece, and source device reaches transmitting data optimal solution when at most sending the 50% of data slice, each
Mobile device can only connect 3 mobile devices as AP node simultaneously and it is outside to be re-used as AP after other mobile devices are received
Constantly expand and send.Do not stop to switch with all mobile device both of which, finally realizes that the data slice of all mobile devices is complete
Transmission.
Based on this, the test analysis of the feasibility of the program, reliability and delay performance is carried out.
One, feasibility
In Fig. 2, commercial mobile device can provide acceptable coding mode for this system, moreover, with fragment number
The increase of k is measured, efficiency reduces.
In Fig. 3, for each request, the data for generating 3.3MB are taken around 1 second, and intermediate node is using actively rearranging
Time consumed by code strategy, which compares passive recodification strategy, can reduce an order of magnitude.When using copy mode, equipment exists
It does not need to perform the encoding operation after receiving request, the data packet in memory is directly sent to receiving device, the reaction time is fast
Speed.When using passive recodification strategy, equipment can just generate re-encoding file upon receiving a request, then be loaded into
It sends in buffer area, this needs one section of operating time and the reaction time is longer.When recoding tactful with active, equipment is being received
With regard to immediately carrying out recodification operation when to a new data slice.Tactful principle of actively recoding is that free time is utilized to carry out
Coding, and with increasing for user is received, free time is reduced, and the processing time improves.
In Fig. 4, in these three schemes, the average time expense of this system has higher than traditional two schemes
Sharing efficiency, and all devices in this system can restore original document in 4.5 minutes.Two, reliability
In experimental situation, the signal strength of Radio Link is always because of a variety of causes, and such as position, preceding there are obstacle, transmittings
The influence of the unlike signals intensity such as power AP generates the received uncertainty of data packet naturally.
In Fig. 5, when fragment size k is between 2-10, the influence to sharing efficiency is not significant.In all experiments
In, the shortest time of shared file is 2.85 minutes, this is realized using network code.When k is greater than 6,
Performance based on vandermonde scheme is slightly better than network code, reason first is that concurrent request number is high, therefore active recodification plan
Processing slightly postpones to increase.When many of network mobile device, transmission hop count can be very high in logic, then more equipment
It can execute and recompile operation, this will provide more performance gains.
Three, delay analysis
In systems in practice, delay is likely to occur in the different phases such as transmission delay, I/O processing delay and coding delay,
The delay distribution in file sharing process is assessed herein.Table is first is that time delay analytical table in this scheme, such as 1 institute of table
Show,
One distribution delay of table
| Operation | Time (s) | Duplication | Vandermonde | Network code |
| AP to OM | 4.4 | √ | √ | √ |
| OM to AP | 2.3 | √ | √ | √ |
| It is sliced (33MB) | 3.3 | √ | √ | √ |
| It encodes (33MB, k=4) | 5.6 | × | √ | √ |
| It reads (10MB) | 0.1 | √ | √ | √ |
| It re-encodes (2.5MB) | 0.61 | × | × | √ |
| It transmits (2.5MB) | 0.58 | √ | √ | √ |
| It decodes (10MB) | 1.4 | × | √ | √ |
| It engages (33MB) | 0.5 | √ | √ | √ |
| Write (10MB) | 1.13 | √ | √ | √ |
After WiFi direct technology, RM is switched to from ap mode and averagely needs 4.4 seconds, is switched to ap mode from RM
Need 2.3 seconds.Recompile the section that one section of size is 2.5MB and 0.58 second needs 0.61 second that transmits this section.Using actively
It recodes after strategy, may be performed simultaneously and recompile operation and transmission.Therefore, time delay and base based on network coding scheme
In vandermonde scheme time delay relatively.
Compared with the scheme based on duplication, encoding operation can introduce additional processing delay, and encoding operation, which can increase, to be set
The standby probability that Line independent data packet is received from its neighbour, so that the sharing efficiency of whole system is improved, accordingly, it is considered to coding
The overall performance gain that can be obtained is operated, processing delay is acceptable caused by encoding operation.
The foregoing is only a preferred embodiment of the present invention, is not intended to restrict the invention, although referring to aforementioned reality
Applying example, invention is explained in detail, for those skilled in the art, still can be to aforementioned each implementation
Technical solution documented by case is modified or equivalent replacement of some of the technical features.It is all of the invention
Within spirit and principle, any modification, equivalent replacement, improvement and so on be should all be included in the protection scope of the present invention.
Claims (10)
1. a kind of WiFi direct multi-hop mobile device sharing files method based on network code characterized by comprising
Step 1) source device convert after slice coding obtains the data slice of k linear independence to data using network code
The question and answer of other mobile devices are waited for ap mode；
Step 2) mobile device sends question and answer request to source device, and source device receives the k linear independence after requesting
Data slice be sent to mobile device；
Step 3) mobile device actively recompile to the data slice received after receiving data slice, at the same time as letter
Source device sends the data slice after recompiling to other mobile devices；
Step 4) decoded after other mobile devices are successfully received the data slice of the linear independence of predetermined amount obtain it is original
Data.
2. mobile device sharing files method according to claim 1, which is characterized in that source device uses in step 1)
Network code carries out including: source device selection before slice coding to sharing data and setting data fragmentation quantity to data.
3. mobile device sharing files method according to claim 1, which is characterized in that source device uses in step 1)
Network code carries out data to generate NCD while slice coding obtains the data slice of k linear independence, and the NCD includes compiling
Code vector and source file fragment quantity.
4. mobile device sharing files method according to claim 1, which is characterized in that step 2) specifically includes:
Step 201): mobile device requests to send data slice to source device all in RM mode when initial；
Step 202): source device receives the request of several mobile devices, and M signal is selected in the request of several mobile devices
Strongest mobile device, which is sent, agrees to demand file；
Step 203): it receives and agrees to that the mobile device of demand file initiates the connection waiting source device to source device and sends number
According to piece；
Step 204): source device sends data slice to preset M mobile device, includes a NCD in each data slice,
And the 50% of the possessed data slice of information source is up to the data slice that each mobile device is sent；
Step 205): RM can then be switched to for mobile device turn when the k number possessed is successfully transmitted completion according to piece by source device
Send out data slice.
5. mobile device sharing files method according to claim 1, which is characterized in that step 3) the following steps are included:
Step 301): after mobile device is successfully received data slice, the content of each data slice is written to the NCD of oneself；
Step 302): after mobile device successful data reception piece, while call thread generate a new encoder matrix with
Received all data slices are encoded, and the data slice after being re-encoded is put into buffer, are waited to be called；
Step 303): mobile device switches to ap mode as source device after having received data slice, waits the visit of other equipment
It asks；
Step 304): when there is request to generate, it is sent to the encoded data slice of request mobile device.
6. according to claim 1, which is characterized in that mobile device receives after data slice to receiving in step 3)
Data slice progress specifically includes when actively recompiling:
After distribution procedure is added in equipment, background thread J will be called to monitor the variation of operative orientation；Once equipment receives one
A new piece of data, thread J will receive the linear combination of all d data slices, and coding system is actively generated from finite field gf (256)
Number [c1, c2..., cd], with all data slice [Y in mobile devicei1, Yi2..., Yid]-1It is recompiled to obtain new
Encoder matrix Ynew, expression formula is as follows:
Wherein i represents the length of linear combination in each data slice, and d represents the quantity for recompiling data slice.
7. mobile device sharing files method described in any one claim according to claim 1~6, which is characterized in that
All mobile devices can all carry out the conversion of both of which, and specific switchover policy is as follows:
With NCD file FAMobile device A a NCD file F is received from source device BB, r1=rank (FA), r2=
rank(FB∪FA)；Wherein rank represents the order of encoder matrix, r1Represent file FAThe order of middle encoder matrix, r2Represent file FAWith
File FBThe order of encoder matrix mutually simultaneously；
1): working as r2> r1When, mobile device A sends data slice and sends a request to source device B, B agree to request send data slice to
A, A update NCD file F after receiving data sliceA, then recalculate r1And r2；
2): otherwise, mobile device A is converted into ap mode as source device, waits the connection of other mobile devices；
3): if the waiting time is more than 10 seconds, switching to RM again, an AP connection is selected according to signal strength；
If 4) jumped to 2) without any AP for connection.
8. a kind of WiFi direct multi-hop mobile device file sharing system based on network code, it is characterised in that: including dividing
Piece quantity setting program module, selection coding file routine module, creation linker module, be added linker module and
Active recodification program module and mobile device mode switching program module；
The fragment quantity setting program module is used to carry out the file that will share the quantity of slice coding；
The file that the selection coding file routine module is used to select to need to share in source device；
After the creation linker module chooses sharing file with source device, creation connection is clicked, source device becomes
Ap mode waits the connection of mobile device；
Link block is added for clicking in the addition linker module, and mobile device is in RM, into state is shared, can seek
AP is looked for be attached；
The active recodification program module carries out actively the data slice received after receiving data slice for mobile device
It recompiles；
The mobile device mode switching program module is used to carry out all mobile devices the conversion of both of which.
9. mobile device file sharing system according to claim 8, it is characterised in that:
The active recodification program module executes following procedure:
After distribution procedure is added in equipment, background thread J will be called to monitor the variation of operative orientation；Once equipment receives one
A new piece of data, thread J will receive the linear combination of all d data slices, and coding system is actively generated from finite field gf (256)
Number [c1, c2..., cd], with all data slice [Y in mobile devicei1, Yi2..., Yid]-1It is recompiled to obtain new
Encoder matrix Ynew, expression formula is as follows:
Wherein i represents the length of linear combination in each data slice, and d represents the quantity for recompiling data slice.
10. mobile device file sharing system according to claim 8, it is characterised in that: the mobile device mode is cut
It changes program module and specifically executes following switchover policy:
With NCD file FAMobile device A a NCD file F is received from source device BB, r1=rank (FA), r2=
rank(FB∪FA)；Wherein rank represents the order of encoder matrix, r1Represent file FAThe order of middle encoder matrix, r2Represent file FAWith
File FBThe order of encoder matrix mutually simultaneously；
1): working as r2> r1When, mobile device A sends data slice and sends a request to source device B, B agree to request send data slice to
A, A update NCD file F after receiving data sliceA, then recalculate r1And r2；
2): otherwise, mobile device A is converted into ap mode as source device, waits the connection of other mobile devices；
3): if the waiting time is more than 10 seconds, switching to RM again, an AP connection is selected according to signal strength；
If 4) jumped to 2) without any AP for connection.
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