CN1249942C - Random access method utilized in orthographic frequency division multiple access (OFDM) system - Google Patents
Random access method utilized in orthographic frequency division multiple access (OFDM) system Download PDFInfo
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Abstract
The present invention relates to a random access method for an OFDM honeycomb mobile communication system. A user terminal of an OFDM system can complete initial registration for logging on, the transmission of signals in a stand-by state and the transmission of bursted short grouped data packs by the access method. The access method achieves an access process of a mobile terminal through an access probing step and an access message transmission step. The present invention is mainly characterized in that (1), an access probing time slot and an access message transmission time slot are separately arranged, which enables access prefixes and access messages of multiple users to be respectively and independently processed without mutual influence; (2), a synchronization method suitable for an OFDM system is used, which enables the system to carry out effective estimation and correction on the timing and the frequency deviation of the mobile terminal when the system treats the access process; (3), the access conflicts of multiple users are detected by a method for detecting errors and judging conflicts of CRC. The present invention is a random access method which is suitable for the OFDM system, and is simultaneously a method for primarily estimating the timing and the frequency deviation of the OFDM system.
Description
Technical field
The present invention relates to a kind ofly move the accidental access method that uses in the communication system at the OFDM honeycomb, in particularly a kind of radio honeycomb mobile communication system based on the OFDM mode, the multi-user is in the implementation method of sharing the Random Access Channel random access system.
Background technology
Along with the fast development of mobile communication technology and the appearance of multimedia application, people have higher requirement to cell mobile communication systems Radio Transmission Technology of new generation and wish, meanwhile, wideband OFDM (OFDM) more and more is subjected to people's attention as a kind of new mode of dealing with problems on the stage of cell mobile communication systems of new generation.
OFDM is a kind of parallel transmission technology, it is provided with K equally spaced orthogonal sub-carriers on assigned frequency band, each subcarrier is modulated separately, symbol period is K a times of same rate single-carrier system, sensitiveness to intersymbol interference reduces greatly than single-carrier system, thereby can more effective anti-multipath be disturbed.Usually, adopt the cellular mobile telecommunication system of OFDM technology to have the following advantages: (1) has effective ability of anti-multipath; (2) can effectively eliminate intersymbol interference (ISI) at interval by inserting protection at each intersymbol; (3) be fit to high speed data transfer; (4) wireless frequency service efficiency height; (5) has powerful noise resisting ability.
Ofdm system has and a lot of different characteristics of mobile communication system in the past, and these characteristics also make the access way at random that is applied in the ofdm system that own unique one side is arranged.We know, when OFDM has above-mentioned superior function, also have some self shortcoming, one of them is exactly responsive especially to frequency deviation, this is because each subcarrier in the ofdm system is an orthogonal division, in case the orthogonality between subcarrier can not get guaranteeing that then performance can rapid deterioration.Therefore, when ofdm system is applied to mobile communication system, in the uplink and downlink link, all need to guarantee Frequency Synchronization preferably.Also must consider these problems for the access way at random in the ofdm system equally.Because good synchronization policy can guarantee that not only Access Preamble has the correct reception of bigger detection probability and access message under as far as possible little void inspection probability in the random access procedure, simultaneously, also can timing and frequency departure be controlled within the scope of system's permission by timing and frequency offset estimating value are fed back to mobile terminal adjustment.
The multiple access access mechanism that often uses mainly contains three classes at present: compete class at random, as Aloha series; The distribution according to need class is as token ring; The fixed allocation class is as FDMA, TDMA, CDMA etc.This three classes multiple access technique is respectively applied for different communication services.Along with development of Communication Technique, in order to obtain high throughput, lower time delay and less overhead, among various access waies are in continuous improvement and merge.As CDMA is exactly the combination of fixed allocation mode and Random assignment mode, it has zero channel access delay, bandwidth availability ratio is high and good advantages such as statistic multiplexing characteristic, but also there are shortcomings such as the limited and base station complexity height of transmission rate in it, makes this access way be not suitable for ofdm system.
Carrier sense multiple access CSMA technology makes whole channel width share for all users, has only when channel idle, just allows the user to send information, and this mode has reduced the probability that collision takes place.802.11a adopt the CSMA/CA agreement, this agreement is closely linked the division and the frame format of time-domain, guarantee that a certain moment has only terminal to send, realized the centralized control of network system, this mode has solved problems such as time delay, concealed terminal and exposed terminal by adopting RTS/CTS (Request To Send/Clear To Send) short message handshake mechanism.But this access way is not suitable for containing the mobile communication system of voice service greatly because of access delay.
Access way is a kind of multiple access technique of competitive way at random, is suitable for strong bursts of traffic, and ALOHA is exactly a kind of access way simply at random.But the Business Stream collision takes place in pure ALOHA easily when traffic carrying capacity is heavier.For reducing conflict, use the time slot A LOHA mode after improving usually.Time slot A LOHA mode is that the time is divided into isometric time slot (slot), and inserting application can only just can send when each time slot begins.The advantage of this mode is to use family random access system and reduced the probability of multi-user conflict to a certain extent at any time, and have only when same time slot has two or more users and arrive, just can clash, so the purer ALOHA of the network throughput of mode doubles.But for the OFDM cellular system of large-capacity user, the network throughput of pure time slot A LOHA technology when traffic carrying capacity is heavier still can't meet the demands.
Summary of the invention
Purpose of the present invention is in order to overcome the problems referred to above and the deficiency that prior art exists, accidental access method in a kind of OFDM ofdm system that provides, this method is a kind of based on time slot A LOHA technology, and at the accidental access method of the characteristics of ofdm system design.This accidental access method adopts the access thought at random of time domain-sign indicating number territory two dimension, 8 access slots of every frame design carry out the access at random of time slot A LOHA in the time domain, arrange to have 16 prefix codes to select at random in the sign indicating number territory for the user, its advantage is if having a plurality of users to arrive at same access slot, as long as these user-selected prefix code inequality or part inequalities are arranged, the base station end still can be correctly or correctly a certain user is wherein inserted by certain probability and to reply indication, and conflict can not occur.This design makes the access at random in the ofdm system can not be subjected to the restriction of time slot A LOHA theoretical throughput, and hour has bigger access throughput at offered load, and, also can guarantee that certain throughput makes it can rapid deterioration with the increase of offered load.
Technical scheme of the present invention is:
Accidental access method in the OFDM ofdm system comprises that handle the mobile terminal and the base station end is handled two parts, and the step that handle the mobile terminal is as follows:
1., after mobile-terminated access indication and given access service grade of receiving from the media access control MAC layer, from several available Access Preamble symbols, select one equiprobably at random with its interim ID of user as the access application, and then in given time slot scope, select an access slot in this time slot, to send the access application at random according to keeping out of the way probability, the mobile terminal begins to monitor descending access control message after finishing transmission;
2., if the mobile-terminated secondary response of negating from the base station end of receiving then report upper strata MAC and inform access failure.If do not receive response, then can in the moment of next frame, reselect time slot and prefix and initiate to insert application up to reaching maximum retransmission, if receive a sure secondary response, the mobile terminal will send user's collision detection message at next time slot, begin to monitor the message of descending access control indicating channel simultaneously, wait for from the secondary of base station end and confirming;
3., if the quadratic response that negate the base station is received in the mobile terminal, judge that then conflict has taken place needs to initiate again to insert application.If do not receive any response, then need to initiate again to insert.As if receiving sure second set response, then judgement does not have the conflict generation, sends the user subsequently and inserts message and report MAC layer access end;
The treatment step of base station end is as follows:
1., the base station constantly monitors the uplink random access slot, according to the method for coupling will insert application part and the sequence of this locality carry out relevant judge current have several Access Preambles to be used simultaneously to initiate to insert apply for;
2., do not insert application, then continuation supervision if detected.If detecting some access applications then estimates synchronously it at first respectively and adjusts, thereafter again according to etc. general principle therefrom one of picked at random it is carried out sure replying, and synchronization message is fed back to corresponding mobile terminal require it to compensate, other access application then all offers a negation and replys to same time slot, continues simultaneously to monitor that Random Access Channel waits for this user's collision detection message and other users' access application;
3., after the base station termination is received the collision detection message of mobile terminal, at first it is estimated synchronously and adjust, message part carried out CRC check thereafter, if find the CRC mistake, then judge and clash and send negative quadratic response it carries out retransmission process to this customer requirements, if CRC check is correct, think that then not having conflict takes place, send sure secondary acknowledge message, continue monitor uplink simultaneously and wait for that the user sends access message to the mobile terminal.
4., receive when the base station termination and at first it to be estimated synchronously after the access message of mobile terminal and adjust, extract user profile then and report the upper strata and finish this access procedure.
Described Access Preamble and collision detection message all adopt the mode of two short symbols to come bearer messages.Access Preamble be to utilize the correlation of Cyclic Prefix to carry out symbol synchronously and frequency offset estimating and utilize the strong correlation of PN sequence in the Access Preamble to carry out fine symbol synchronization just synchronously, adopt two short symbols to carry Prefix message, with the correlation weighted average of two short symbols.Collision detection message be to utilize Cyclic Prefix and be inserted in the characteristic that inserts pilot tone in the message to carry out symbol synchronously and frequency offset estimating just synchronously, and carry out fine symbol synchronization by the mode of estimating channel impulse response, the collision detection message part also adopts the mode of two short symbols, with the correlation weighted average of two short symbols.What insert message part is to utilize the correlation of Cyclic Prefix and pilot frequency information characteristic to carry out the just synchronous and Frequency Estimation of symbol synchronously, and carry out fine symbol synchronization by the mode of channel impulse response, insert message part owing to adopt a plurality of OFDM symbol transmission, with the result of calculation weighted average of a plurality of symbols.
Related Access Preamble search is that the base station end judges whether to receive the process that inserts application according to certain strategy, and according to the difference of this strategy, the false dismissal probability and the empty inspection probability that insert application can change to some extent.Prefix search principle among the present invention is to reduce false dismissal probability to reach best access state on the basis that guarantees enough low void inspection probability as far as possible.Here the method that is adopted is according to dynamic threshold of peak-to-average force ratio feature calculation, judges whether receive the access application according to this thresholding.Peak-to-average force ratio is the signal maximum peak power and the ratio of average power signal value.
It is to utilize the information of mobile terminal collision detection part to extract that involved access interference detects, when different user owing to send same access application simultaneously by the base station affirmative acknowledgement after, the different collision detection message that they send can cause base station end CRC check mistake, thereby can utilize it to judge the situation of conflict.
Among the present invention in the designed access procedure mobile terminal at first send Access Preamble and sound out, obtain affirmative acknowledgement and send collision detection message later on again and carry out collision detection, obtain sure quadratic response and send the subscriber-related information of transmission of messages that inserts later on again.Wherein Access Preamble, collision detection message and access message are independently to transmit in time slot or the channel mutually, and the reception of the processing of access message and Access Preamble, collision detection message is relatively independent, and this design has improved access throughput and access efficiency to a certain extent.
The present invention not only can make the user insert ofdm system at any time fast, also can make the base station timing and frequency departure are controlled within the scope of system's permission for before user's distribute data channel.The present invention adopts the access thought at random of time domain-sign indicating number territory two dimension, 8 access slots of every frame design carry out the access at random of time slot A LOHA in the time domain, arrange to have 16 prefix codes to select at random in the sign indicating number territory for the user, its advantage is if having a plurality of users to arrive at same access slot, as long as these user-selected prefix code inequality or part inequalities are arranged, the base station end still can be correctly or correctly a certain user is wherein inserted by certain probability and to reply indication, and conflict can not occur.This design makes the access at random in the ofdm system can not be subjected to the restriction of time slot A LOHA theoretical throughput, and hour has bigger access throughput at offered load, and, also can guarantee that certain throughput makes it can rapid deterioration with the increase of offered load.Main feature of the present invention: 1. independently arrange access exploration, collision detection message and insert the time slot that message sends, make the multi-user Access Preamble, collision detection message and insert between the message separately independent process and be independent of each other; 2. the method for synchronous that adopt to be fit to ofdm system makes system also can effectively estimate and correct the timing of mobile terminal and frequency deviation when inserting handling; 3. adopt the CRC error detection to judge that the mode of conflict detects multi-user's access interference.The present invention is a kind of accidental access method of suitable ofdm system, simultaneously also is a kind of ofdm system to be carried out estimation approach at the beginning of timing and the frequency deviation.
Description of drawings
Fig. 1 is that realization of the present invention is always schemed.
Fig. 2 inserts the mobile terminal processing module at random.
Fig. 3 is an access base station end processing module at random.
Fig. 4 is the Access Preamble search module.
Embodiment
The present invention is further described below in conjunction with accompanying drawing.
Fig. 1 is the figure of access process at random that comprises that mobile terminal and base station end are handled.Ind is control information and the required information of subscriber-related access that access is at random initiated in the MAC indication, Res is that access module is reported the message of access situation to the MAC layer at random, Ari (i=1,2...n be user's number) be that Client-initiated inserts application, collision detection message and inserts message, Dld is the descending access control information that the base station end sends.
It is as follows to insert handling process at random:
1., the access indication that mobile terminal processing module 101 receives the MAC layer that inserts at random of user i initiates to insert at random, and will insert and apply for passing to the base station end, begins to monitor the control messages Dld of down link simultaneously.
2., access base station end processing section 102 constantly monitors Random Access Channel at random, when finding the application of access is arranged, at first carry out Synchronous Processing, select one of them satisfactory application it once to be replied again by descending control messages Dld, and negate to begin to monitor the collision detection message part in the Random Access Channel simultaneously to other applications.
3., when user i insert at random processing section, mobile terminal 101 find to contain among the D1d to this accesss application sure once reply after, promptly send this user's collision detection message constantly by Random Access Channel at the next one, continue monitoring Dld simultaneously.
4., after access base station end processing section 102 receives collision detection message at random, at first it is carried out Synchronous Processing, judge whether to clash by CRC check again.If clash, then send the secondary negating and confirm notice mobile terminal processing module access failure and make it carry out respective handling by Dld; If do not clash, then send sure secondary and confirm to notify the mobile terminal processing module not have conflict by Dld, the user who continues thereafter to monitor in the up channel inserts message.
5., after user i inserts processing section, mobile terminal 101 at random and receives sure second set response among the Dld, send and insert message part and report that also the MAC layer inserts success and finishes random access procedure; If receive negative second set response, then take corresponding retransmission process.
Fig. 2 is the implementation procedure that inserts the mobile terminal processing module at random.
Inserting the mobile terminal processing module at random handles according to flow process shown in the arrow.Now implementation procedure is described as follows:
1., after inserting the indication Ind message that mobile terminal control module 201 receives the MAC layer at random just indication insert application sending module 202 and send and insert application.
2., descending access control processing module 206 can monitor descending access control message and control module 201 is sent in its extraction according to the process that inserts at random.
3., receive after the message of descending access control processing module 206, carry out alignment processing according to the message content indication collision detection message transmission module 203 of a secondary response when control module 201.
4., receive after the message of descending access control processing module 206, insert message transmission module 204 according to the message content indication of quadratic response and carry out alignment processing when control module 201.
5., will report the MAC layer by Res after inserting message and inform and insert success and finish access procedure, after receiving the second set response of denying, then inform MAC layer access failure when 201 modules are sending.
6., entering upstream data from module 202,203 and 204 information becomes frame module 205 to carry out data map and forms uplink frame to send to the base station end.
Fig. 3 is the inside implementation procedure handled of access base station end at random.
The base station end is received after the access information from the mobile terminal, according to structure of time slot it is isolated Access Preamble, collision detection message and inserts message part, and flow to by arrow among the figure and to handle respectively.Now inner implementation procedure is described as follows:
1., insert the application processing procedure:
The access request for data at first enters Access Preamble synchronization module 301 and finishes regularly synchronous and Frequency Synchronization, enter Access Preamble match search module 302 and mate relevant search and obtain the Access Preamble sequence number used by the user, information such as the 302 Access Preamble sequence numbers that search and 301 timings of calculating, frequency deviation are passed to inserted application processing unit 303 thereafter.303 modules are then according to 302 and 301 information that provide, and one of them inserts application and makes an affirmation and reply with a kind of policy selection, and all the other give negative response.To give prefix sequence number and regularly corresponding and the frequency deviation information of affirmative acknowledgement simultaneously, be integrated in the access control message (API); Negative response is then carried out in unchecked access application in API.
2., collision detection message processing procedure:
The collision message data are carried out timing synchronously and Frequency Synchronization by collision detection message synchronization module 304, are sent to 305 modules afterwards and carry out channel estimating and it is compensated.The data of finishing compensation are finished the processing such as descrambling, despreading, demodulation, decoding and CRC check of collision detection message again through collision detection module 306.According to the result of CRC check, produce corresponding secondary and confirm indication (CI).
Indication message API is replied in access and secondary acknowledge message CI will be sent to descending access control message processing module 310, carries out framing here and sends at descending access control indicating channel.
3., insert message processing procedure:
Insert message data and carry out the synchronous and Frequency Synchronization of timing, be sent to 308 modules afterwards and carry out channel estimating and it is compensated by inserting message synchronization module 307.Finish the data of compensation and finish the processing such as descrambling, despreading, demodulation, decoding and CRC check that insert message through inserting message processing module 309 again.Simultaneously access informations such as the user ID that receives, short message are submitted to the MAC layer by RES.
4., Synchronous Processing process:
Access Preamble synchronization module 301 is to utilize the correlation of Cyclic Prefix (CP) to carry out the synchronously thick and frequency offset estimating of symbol, and utilizes the strong correlation of PN sequence in the Access Preamble to carry out fine symbol synchronization.Since make when synchronous by CP of an OFDM symbol, the poor-performing of its opposing noise and multipath, so, adopt two short symbols to carry Prefix message in order to obtain good synchronization performance.Each short symbol carries out Synchronous Processing separately, after the correlation weighted average with two short symbols, can obtain the sign synchronization and the frequency offset estimation result of better effects if.
Collision detection message synchronization module 304 mainly is to utilize Cyclic Prefix and be inserted in the characteristic that inserts pilot tone in the message to carry out the synchronously thick and frequency offset estimating of symbol, and carry out fine symbol synchronization by the characteristics of channel impulse response, it is the same with Access Preamble, also adopts the mode of two short symbols to come bearer messages.
Insert message synchronization module 307 and mainly be to utilize Cyclic Prefix and be inserted in the characteristic that inserts pilot tone in the message and carry out the synchronously thick and frequency offset estimating of symbol, and carry out fine symbol synchronization by the characteristics of channel impulse response, it adopts a plurality of symbols to come bearer messages.
Fig. 4 is the inside implementation procedure of Access Preamble search module.
The Access Preamble data flow to by arrow among the figure and handle.Now implementation procedure is described as follows:
(1), the access request for data is sent to 16 relevant search modules 401 simultaneously and is done match search.401 modules are utilized local i, and (i=0,1...N) PN does that sliding is correlated with realizes match search.It is by after the correlation weighted average and normalization to two short symbols, compares with thresholding and judges whether to receive the access application that sequence number is i.
(2), the Search Results of a N search module is sent to merge cells 402, and the timing that produces with front synchronization module 301 and frequency deviation information combine and carry out for Access Preamble processing unit 303.
Claims (8)
1, the accidental access method in the OFDM ofdm system comprises that handle the mobile terminal and the base station end is handled two parts, and the step that handle the mobile terminal is as follows:
1., under given access service grade, from several available Access Preamble symbols, select an Access Preamble symbol equiprobably at random, with its interim ID of user as the access application, and then in given time slot, select an access slot at random, and determine whether sending the access application at selected time slot according to keeping out of the way probability;
2., after having sent the access application, if the negative response of receiving the base station end, then access failure is reported upper strata MAC, if do not receive response, then can reselect time slot and prefix sign and initiate to insert application up to reaching maximum retransmission at next frame, if receive positive response, will send user's collision detection message part at next access message time slot, and monitor that descending access control message enters the state of waiting for that secondary is confirmed simultaneously;
3., wait for the secondary acknowledge message of base station, if receive the negative response of base station, judge that then conflict has taken place needs to initiate again to insert application, if do not receive any response, then initiate again to insert,, judge that then not having conflict takes place if receive sure second set response, send the user subsequently and insert message and report the upper strata and insert successfully, access procedure finishes;
The treatment step of base station end is as follows:
1., random access time slot in the base station monitoring uplink frame, according to the method for coupling will insert application part and the sequence of this locality carry out relevant judge current have several Access Preambles to be used simultaneously to initiate to insert apply for;
2., do not insert application if detected, then continue to monitor, if detecting some access applications then estimates synchronously it at first respectively and adjusts, thereafter again according to etc. general principle therefrom one of picked at random it carried out sure replying and synchronization message is fed back to the mobile terminal require it to compensate, other application then all offers a negation to same time slot, continues simultaneously to monitor that Random Access Channel waits for this user's collision detection message;
3., after base station end transmission access control is replied a certain access application, continue to monitor the uplink frame random access time slot, after receiving the collision detection message of being affirmed the mobile terminal, at first it is estimated synchronously and adjust, message part carried out CRC check thereafter, if find the CRC mistake, then judge conflict or failure, it carries out retransmission process to this customer requirements to send the quadratic response negating, if CRC check is correct, think that then not having conflict takes place, and sends sure secondary acknowledge message simultaneously to the mobile terminal.
2, accidental access method according to claim 1 is characterized in that Access Preamble and collision detection message part all adopt the mode of two short symbols to come bearer messages.
3, accidental access method according to claim 2, it is characterized in that Access Preamble is to utilize the correlation of cyclic prefix CP to carry out symbol synchronously and frequency offset estimating and utilize the strong correlation of PN sequence in the Access Preamble to carry out fine symbol synchronization just synchronously, adopt two short symbols to carry Prefix message, with the correlation weighted average of two short symbols.
4, accidental access method according to claim 2, it is characterized in that the collision detection message synchronization is to utilize Cyclic Prefix and be inserted in the characteristic that inserts pilot tone in the message to carry out symbol synchronously and frequency offset estimating just, and carry out fine symbol synchronization by the mode of estimating channel impulse response, insert the mode that message part also adopts two short symbols, with the correlation weighted average of two short symbols.
5, accidental access method according to claim 2, it is characterized in that inserting message synchronization and be utilizing Cyclic Prefix and being inserted in the characteristic that inserts pilot tone in the message and carry out symbol synchronously and frequency offset estimating just, and carry out fine symbol synchronization by the mode of estimating channel impulse response, insert the mode that message part also adopts a plurality of OFDM symbols, with the result of calculation weighted average of a plurality of symbols.
6, accidental access method according to claim 1, it is characterized in that inserting the method that application adopts is according to dynamic threshold of peak-to-average force ratio feature calculation, satisfy threshold requirement and just judge and receive and insert application, peak-to-average force ratio is the signal maximum peak power and the ratio of average power signal value.
7, accidental access method according to claim 1, it is characterized in that the access interference detection utilizes CRC check to extract, if different users is simultaneously by positive response, their collision detection message of sending can partly cause overlappingly at CRC so, can utilize it to judge the situation of conflict thereby cause the verification of CRC part to make mistakes.
8, accidental access method according to claim 1, it is characterized in that Access Preamble, collision detection message and inserting message is independently to transmit in time slot or the channel mutually, and the reception of the processing of access message and Access Preamble is relatively independent.
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| CN108900459A (en) * | 2018-05-25 | 2018-11-27 | 西南电子技术研究所（中国电子科技集团公司第十研究所） | GFDM/CDMA mixing multiple access radio switch-in method |
| CN115862352B (en) * | 2022-11-24 | 2024-02-27 | 浙江欧菲克斯交通科技有限公司 | Calculation method, system, medium and equipment for solving parallel code sending conflict by random number |
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