CN102118211A - Timing and synchronization method for media-sharing STDM system - Google Patents
Timing and synchronization method for media-sharing STDM system Download PDFInfo
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Abstract
The invention discloses a timing and synchronization method for a media-sharing STDM (Statistic Time Division Multiplexing) system, which mainly solves the problems in the prior point-to-multipoint network art, such as great expenses for timing and synchronization and complex method for the measurement of round-trip delay. The timing and synchronization method is realized through the following steps: a central station sends a timing and synchronous frame D without timestamp periodically; an auxiliary station adopts the time when the frame D is received as a reference, and sends a frame U for the measurement of round-trip delay at the stipulated offset time; the central station receives the frame U and calculates the round-trip delay through the difference between the offset value generated at the time when the U frame arrives and the stipulated offset value; the central station adopts the time when the frame D is sent locally as a reference, uses the offset value which is relative to the reference to indicate channel planning information and carries out time-delay compensation; and the auxiliary station receives the channel planning information and visits a channel at the offset time stipulated by the central station. The method achieves the advantages of small expenses for timing and synchronization and simple method for the measurement of round-trip delay, and can be applied to the field of media-sharing point-to-multipoint access networks and media-sharing local area networks.
Description
Technical field
The invention belongs to communication technical field, relate to a kind of timing and method for synchronous, be specifically related to a kind of timing and method for synchronous that is used for sharing medium STDM system, can be used for based on the point of sharing medium STDM technology to multiple spot local area network (LAN) and Access Network field.
Background technology
STDM STDM is a kind of channel multiplexing technology commonly used, and in this technology, channel is divided in the mode of time-division and dynamically shared between a plurality of users.This technology when certain user has data to transmit, then is this user's allocation of channel resources may according to user's actual needs dynamic assignment channel resource; When the user suspends transfer of data, then be not this user's allocation of channel resources may, this moment, the transmittability of channel can be used by other users, thereby had higher channel utilization.
This technology is widely used in based in the local area network (LAN) and Access Network of sharing medium, and its common form is a point-to-multipoint network that the center is arranged.In this network, there is a central site unified distribution channel resource, other website except that central site is called the subordinate website, when the subordinate website has data to transmit, to be its allocation of channel resources may at first by central site, typical mode is to send request by the subordinate website to central site, central site permits distributing then, perhaps central site planning a period of time is shared this section channel resource by a plurality of websites in the mode of competition, and the subordinate website must be in strict accordance with the time access channel of central site appointment.
Above-mentionedly in fact channel distribution has been become the time period continuous and not of uniform size by central site based on the mode of STDM technology allocation of channel resources may, each slave station presses the time period of central site appointment and uses channel resource in order.In order to allow above-mentioned shared media system operate as normal based on the STDM technology, at first need to solve two problems, the one, problem regularly, promptly how central site represents the start-stop moment of each time period on the channel time axle of its division; The 2nd, synchronous problem, promptly the clock of subordinate website will be set up synchronously with the clock of central site, so just can make central site and subordinate website based on identical time reference access channel.In addition, in the bigger Access Network of coverage, each subordinate website causes each subordinate website to differ greatly to the signal transmission delay between the central site more greatly to the distance difference of central site, this will cause different subordinate websites different with the synchronization extent between the central site, thereby may cause the signal of different subordinate websites to bump, therefore, also need to solve the problem of synchronous correction, i.e. the influence of erasure signal propagation delay to causing synchronously.
Above-mentioned shared medium STDM technology generally is that channel distribution is become continuous data transfer cycle in actual use, and each data transfer cycle DTC was made up of several time periods, and each time period is a transfer of data chance.The timing of system be by the central site delivery system time synchronously, typical mode is the beacon frame that system timestamp is carried in periodically issue, the subordinate website is according to the system time of the central site issue local timer of resetting, thus set up between each subordinate website and the central site synchronously.The start-stop of each data transfer cycle is constantly with the system clock value representation, and each time period in each data transfer cycle is then represented with relative data transmission cycle starting point deviant constantly.Above-mentioned existing share medium STDM system use existing regularly with the data transfer cycle schematic diagram of method for synchronous as shown in Figure 1, wherein the B frame is the Beacon frame of central site with the fixed cycle issue, it is beacon frame, carry the system timestamp value, the local clock value of replacement oneself when the slave station point is received the B frame, thus clock synchronization set up with central site.The channel allocation of each data transfer cycle DTC is issued by special channel plan frame by central site, the start-stop of the start-stop that the using system time value is represented DTC in the channel plan frame each transmission period constantly and among the DTC constantly, the start-stop of each time period uses relatively the deviant in the initial moment of this DTC to represent constantly.
For solving synchronous correction problem mentioned above, need the round-trip delay between measuring center website and the subordinate website.Usually the method for the measurement round-trip delay that adopts as shown in Figure 2, when the slave station point receive that central site sends have the measurement frame of timestamp the time, the replacement local clock is the timestamp value of receiving, wait for a period of time and return one after handling and have the response frame that the local current time stabs, when the center website is received the response frame that the subordinate website sends, will utilize the timestamp value of carrying in this frame to calculate round-trip delay between it and the subordinate website.Round-trip delay equals descending time delay and uplink time delay sum, round-trip delay RTT=T as shown in Figure 2
Down+ T
Up=T
Response-T
Wait for=(t
2-t
0)-(t
1-t
0)=t
2-t
1, promptly round-trip delay equals the difference of timestamp value in the current local clock value of central site and the response frame received.Obtain as stated above after the round-trip delay, the delivery time that central site is adjusted the subordinate website arrives in the orthochronous of central site expectation to guarantee signal, thereby avoids collision.
Above-mentioned timing depends on the timestamp that central site is issued with method for synchronous, and the timing of data transfer cycle need represent that expense is bigger with system time; The measurement of round-trip delay need design special flow process, and is comparatively complicated.
Summary of the invention
The objective of the invention is to avoid the deficiency in the above-mentioned prior art, based on point-to-multipoint network a kind of timing and method for synchronous that is used for sharing medium STDM system proposed, with timing and the synchronization overhead that reduces system, the method for round-trip delay between simplified measurement central site and the subordinate website.
Realize the technical scheme of the object of the invention, comprise the steps:
1) central site sends the timing and synchronization frame D of no-timestamps with fixed cycle length or variable cycle length;
2) the subordinate website with the moment of local timing of receiving no-timestamps and synchronization frame D as time reference, the round-trip delay that sends no-timestamps in the deviant moment corresponding of system's regulation is measured frame U;
3) central site is after the round-trip delay of receiving no-timestamps is measured frame U, the timing that sends no-timestamps with this locality and the moment of synchronization frame D are as time reference, count value with the current time correspondence of receiving the U frame deducts step 2) the middle deviant that sends system's regulation of U frame, draw the round-trip delay between central site and the above-mentioned subordinate website;
4) central site carries out channel plan with the moment of synchronization frame D as time reference with the timing that this locality sends no-timestamps, use with respect to the deviant of benchmark and represent channel plan information, and the round-trip delay that obtains in the use step 3) carries out delay compensation to deviant and handles, again by transmitting channel planning frame E issue channel plan information;
5) the subordinate website is when receiving channel plan frame E, with moment of local timing of receiving no-timestamps and synchronization frame D as time reference, the moment of deviant appointment is carried out data transmit-receive in channel plan frame E.
The timing of described no-timestamps is measured frame U with the round-trip delay of synchronization frame D and no-timestamps, is further used for carrying any useful information as required.
Described " use with respect to the deviant of benchmark and represent channel plan information " is the timing that sends no-timestamps with this locality with the moment of synchronization frame D as benchmark, use represent data transfer cycle with respect to the deviant of benchmark start-stop constantly; With the initial moment of data transfer cycle as benchmark, use represent each time period in this data transfer cycle with respect to the deviant of benchmark start-stop constantly.
Described " delay compensation processing " is meant that central site deducts round-trip delay value between central site and this subordinate website with the planning value of slave station point transmitting-receiving data.
The present invention has following advantage:
1) the present invention is owing to adopt and to set up system synchronization based on the timing of no-timestamps with synchronization frame D, and with initial moment of D as time reference, use and represent channel plan information, thereby can reduce the timing and the synchronization overhead of system with respect to the deviant of benchmark.
2) the present invention is because the subordinate website is to measure frame U at the round-trip delay that the constant offset with respect to the timing of no-timestamps and synchronization frame D sends no-timestamps constantly, central site only needs the difference according to the due in of the due in of U frame and regulation can obtain round-trip delay between central site and the subordinate website, has simplified the measuring process of round-trip delay.
Description of drawings
Fig. 1 be to use existing regularly with the data transfer cycle schematic diagram of method for synchronous;
Fig. 2 is existing round-trip delay method of measurement schematic diagram;
Fig. 3 be to use the present invention regularly with the data transfer cycle schematic diagram of method for synchronous;
Fig. 4 is timing of the present invention and method for synchronous schematic diagram.
Embodiment
Below in conjunction with accompanying drawing content of the present invention is further elaborated.
In the present embodiment, if network environment is a coaxial cable access network, when if the timing of no-timestamps sends with fixed cycle length with synchronization frame D, cycle is 64ms, when sending with variable cycle length, send all period interval minimums and be 64ms to the maximum for 60ms, the transmission skew that the round-trip delay of no-timestamps is measured frame U is 32ms constantly, the clock counter precision of system is 20ns, adopt the access technology of time division duplex and time division multiple access, central site is each subordinate website allocation of channel resources may, the time of each slave station point transmitting-receiving data of unified scheduling.
Referring to Fig. 4, the performing step of present embodiment is as follows:
Step 1, central site send the timing and synchronization frame D of no-timestamps, and the moment that sends this D frame with the local clock counter O reset.
The timing that central site sends no-timestamps and the data transfer cycle of synchronization frame D as shown in Figure 3, D frame wherein is not free to be stabbed, and a plurality of data transfer cycle DTC are arranged between the D frame, each DTC contains the time period of a plurality of transmission data.The timing that central site sends no-timestamps has dual mode with synchronization frame D, a kind of is with fixed cycle 64ms transmission at interval, another kind is to be to send in cycle of 64ms with the minimum interval for the 60ms largest interval, the send mode of each is sending the moment of timing with synchronization frame D, all will be with the local clock counter O reset.
Step 2, the subordinate website is measured frame U at the round-trip delay that the agreement skew sends no-timestamps constantly.
The subordinate website is in the timing of receiving no-timestamps during with synchronization frame D, with the local clock counter O reset, the skew that sends the round-trip delay measurement frame U of no-timestamps according to the present embodiment hypothesis is 32ms constantly, being converted into Counter Value is 32ms/20ns=1600000, therefore, the subordinate website is 1600000 o'clock in the value of waiting until the local clock counter, and the round-trip delay that sends no-timestamps is measured frame U.
Step 3, central site are calculated the round-trip delay value when receiving the U frame.
Central site is with receiving that U frame local Counter Value constantly deducts the transmission U frame Counter Value constantly of agreement, draw and the subordinate website between round-trip delay.With central site local clock Counter Value when receiving the U frame is 1600500 to be example, from step 2 as can be known the corresponding constantly Counter Value of skew of the transmission U frame of system agreement be 1600000, thereby draw round-trip delay RTT=(1600500-1600000) the * 20ns=10us between central site and the subordinate website, the count value of the corresponding counter of this round-trip delay is: 1600500-1600000=500.
Step 4, central site are planned the transmitting-receiving time of each data of subordinate website, and are carried out delay compensation and handle.
Central site distributes channel time according to the resource requirement situation of subordinate website, promptly arrange the time of subordinate website access channel, at first the start-stop of data transfer cycle is used constantly with respect to the deviant in the local initial moment of D frame and represented, deviant with the initial moment of data transfer cycle is a benchmark again, the start-stop of each time period of subordinate website access channel in the data transfer cycle is used constantly with respect to the deviant of benchmark represented; Carry out the delay compensation processing again after drawing above-mentioned deviant information, be about to the Counter Value that deviant deducts the round-trip delay correspondence.With central site certain the data transfer cycle T between two D frames is planned to example, the initial moment with transmission D frame is a benchmark, the start-stop of tentation data transmission cycle T deviant constantly is respectively 8ms and 10ms, planning subordinate website sends data P in data transfer cycle T start offset is 20us constantly, the end skew that sends data P is 220us constantly, and promptly the transmitting time segment length of data P correspondence is 200us.
4a) calculate the corresponding constantly Counter Value of data transfer cycle T start-stop, the count value of the initial moment correspondence of T is 8ms/20ns=400000 in the present embodiment, and stopping corresponding constantly count value is 10ms/20ns=500000; With the initial moment of data transfer cycle T be benchmark, calculate the corresponding constantly count value of start-stop of each time period that the subordinate website sends in a transfer of data period T, the count value of the initial moment correspondence of time period of subordinate website transmission data P is 20us/20ns=1000 in the present embodiment, and it is 220us/20ns=11000 that this time period stops corresponding constantly count value;
4b) deviant that the start-stop of subordinate website transmitting time section is constantly corresponding deducts the count value of round-trip delay correspondence, draw delay compensation time period deviant afterwards, the value that the deviant that in the present embodiment subordinate website is sent time period in the initial moment of data P is carried out after the delay compensation is 1000-500=500, and it is 11000-500=10500 that this time period stops the value that deviant constantly carries out after the delay compensation;
4c) with step 4a) and 4b) in planning deviant information be encapsulated among the channel plan frame E, the timing that contains in the E frame with this locality transmission no-timestamps is a benchmark with synchronization frame D, the start-stop deviant of data transfer cycle constantly, and with the initial moment of this data transfer cycle be benchmark, the start-stop deviant in this data transfer cycle after each time period passes delay compensation is constantly; Because the interval in the present embodiment between two D frames is 64ms to the maximum, its corresponding count value is 3200000, so needs 22 binary bits can express above-mentioned planning deviant information in the present embodiment in channel plan frame E at most.
Step 5, subordinate website are after receiving channel plan frame E, by the moment access channel of appointment.
5a) send the corresponding constantly Counter Value of start-stop according to each time period in the deviant information calculations data transfer cycle in the E frame, the count value that sends the initial moment is the deviant in the initial moment of data transfer cycle and the initial moment deviant sum of interior each the transmitting time section of data transfer cycle, and the count value that sends the finish time is the deviant and interior each the transmitting time section deviant finish time sum of data transfer cycle in the initial moment of data transfer cycle; The count value of the initial moment correspondence of subordinate website transmission data P is 400000+500=400500 in the present embodiment, and the count value that sends the correspondence finish time is 400000+10500=410500;
5b) 5a set by step puts in slave station) in the Counter Value access channel that obtains, the subordinate website is to begin to send data P at 400500 o'clock at its Counter Value in the present embodiment, is to finish to send data P at 410500 o'clock at its Counter Value.
In the present embodiment, above-mentioned D frame and U frame except that be used for regularly with synchronously, can be according to the further any useful information of carrying of system's needs, such as D frame and U frame are used for the Bearer Channel training information.
Below only be a preferred embodiment of the present invention, do not constitute any limitation of the invention, obviously design those skilled in the art according to the present invention all can make different modifications and displacement, but these are all at the row of protection of the present invention.
Claims (4)
1. a timing and a method for synchronous that is used for sharing medium STDM system comprises the steps:
1) central site sends the timing and synchronization frame D of no-timestamps with fixed cycle length or variable cycle length;
2) the subordinate website with the moment of local timing of receiving no-timestamps and synchronization frame D as time reference, the round-trip delay that sends no-timestamps in the deviant moment corresponding of system's regulation is measured frame U;
3) central site is after the round-trip delay of receiving no-timestamps is measured frame U, the timing that sends no-timestamps with this locality and the moment of synchronization frame D are as time reference, count value with the current time correspondence of receiving the U frame deducts step 2) the middle deviant that sends system's regulation of U frame, draw the round-trip delay between central site and the above-mentioned subordinate website;
4) central site carries out channel plan with the moment of synchronization frame D as time reference with the timing that this locality sends no-timestamps, use with respect to the deviant of benchmark and represent channel plan information, and the round-trip delay that obtains in the use step 3) carries out delay compensation to deviant and handles, again by transmitting channel planning frame E issue channel plan information;
5) the subordinate website is when receiving channel plan frame E, with moment of local timing of receiving no-timestamps and synchronization frame D as time reference, the moment of deviant appointment is carried out data transmit-receive in channel plan frame E.
2. timing described in claim 1 and method for synchronous, wherein the timing of no-timestamps is measured frame U with the round-trip delay of synchronization frame D and no-timestamps, is further used for carrying any useful information as required.
3. timing described in claim 1 and method for synchronous, step 4) described " use with respect to the deviant of benchmark and represent channel plan information " wherein, be the timing that sends no-timestamps with this locality with the moment of synchronization frame D as benchmark, use represent data transfer cycle with respect to the deviant of benchmark start-stop constantly; With the initial moment of data transfer cycle as benchmark, use represent each time period in this data transfer cycle with respect to the deviant of benchmark start-stop constantly.
4. timing described in claim 1 and method for synchronous, step 4) described " delay compensation processing " wherein is meant that central site deducts round-trip delay value between central site and this subordinate website with the planning value of slave station point transmitting-receiving data.
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| CN103220115A (en) * | 2013-05-05 | 2013-07-24 | 西安电子科技大学 | Time division duplex/time division multiple access channel plan frame encoding method |
| CN104348561A (en) * | 2013-08-07 | 2015-02-11 | 中国科学院声学研究所 | Synchronizing method of underwater communication network based on centralized topology structure |
| CN106707738A (en) * | 2017-02-10 | 2017-05-24 | 广东大仓机器人科技有限公司 | Method for calibrating clocks of two ultrasonic modules |
| CN107819563A (en) * | 2017-08-30 | 2018-03-20 | 悦享趋势科技（北京）有限责任公司 | The measuring system of time synchronism apparatus and pulse wave conduction speed |
| WO2018068180A1 (en) * | 2016-10-10 | 2018-04-19 | 海能达通信股份有限公司 | Master node, slave node, and synchronization information self-correction method |
| WO2018085989A1 (en) * | 2016-11-08 | 2018-05-17 | 武汉芯泰科技有限公司 | Channel allocation and frame transmission controller |
| CN108064044A (en) * | 2016-11-08 | 2018-05-22 | 武汉芯泰科技有限公司 | A kind of channel distribution and frame transmission control unit (TCU) |
| CN109691191A (en) * | 2016-09-14 | 2019-04-26 | 华为技术有限公司 | A kind of method and apparatus that clock is synchronous |
| CN113993009A (en) * | 2020-07-27 | 2022-01-28 | 上海诺基亚贝尔股份有限公司 | Method and device for multi-domain transmission by time synchronization, OLT and ONU |
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| CN103220115A (en) * | 2013-05-05 | 2013-07-24 | 西安电子科技大学 | Time division duplex/time division multiple access channel plan frame encoding method |
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| CN104348561A (en) * | 2013-08-07 | 2015-02-11 | 中国科学院声学研究所 | Synchronizing method of underwater communication network based on centralized topology structure |
| CN104348561B (en) * | 2013-08-07 | 2017-08-25 | 中国科学院声学研究所 | The synchronous method of subsurface communication net based on Centralized Topology |
| CN109691191A (en) * | 2016-09-14 | 2019-04-26 | 华为技术有限公司 | A kind of method and apparatus that clock is synchronous |
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| CN108064044A (en) * | 2016-11-08 | 2018-05-22 | 武汉芯泰科技有限公司 | A kind of channel distribution and frame transmission control unit (TCU) |
| CN106707738A (en) * | 2017-02-10 | 2017-05-24 | 广东大仓机器人科技有限公司 | Method for calibrating clocks of two ultrasonic modules |
| CN107819563A (en) * | 2017-08-30 | 2018-03-20 | 悦享趋势科技（北京）有限责任公司 | The measuring system of time synchronism apparatus and pulse wave conduction speed |
| CN113993009A (en) * | 2020-07-27 | 2022-01-28 | 上海诺基亚贝尔股份有限公司 | Method and device for multi-domain transmission by time synchronization, OLT and ONU |
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Application publication date: 20110706 |