The accidental access method that a kind of TD-SCDMA system overloading covers frequently
Technical field
The present invention relates to a kind of mobile communication technology, relate in particular to the accidental access method that a kind of mobile communcations system overloading covers frequently.
Background technology
TD-SCDMA (Time Division-Synchronization Code Division MultipleAccess) is one of 3G (Third Generation) Moblie air interface technical specification of the formal issue of ITU, the TD-SCDMA system is the same with other mobile communication system, in order to satisfy the ever-increasing demand in mobile communication market, carrying out in same sectors/cells that overloading covers frequently will be the important means that the TD-SCDMA system increases power system capacity.
The Uu interface all carries out at a carrier frequency for operation, the configuration of Radio Resource at present, and a sub-district (Cell) also is only to have disposed an absolute frequency point number in the process that the Iub interface sub-district is set up; If overloading frequently, then each carrier frequency is taken as a logic district.For example, for the situation of three sectors, three carrier frequency, then thinking has 9 logic district, finishes independently operation at each sub-district, also is that 9 sub-districts send pilot tone and broadcast message separately.Like this, each carrier frequency of multi-carrier frequency system all must configuration one overlap complete common signal channel, and broadcast channel wherein (BCH), access channel (FACH) and grouped channels (PCH) all are omnidirectional channel.Then multiple carrier frequency base station when actual networking, not only transmitter power is required very high, and, under the situation of identical networking, between carrier frequency the interference of broadcast channel also very serious, the efficient of simultaneity factor is also very low.In Fig. 1, disclosed a kind of typical case, it is a cellular mobile communications networks that works in the frequent rate of overloading, if this network uses the 10MHz bandwidth, each base station is operated on 6 identical carrier frequency frequencies.If a terminal is in the sub-district intersection, it will face following particular problem:
1, Cell searching difficulty.In order to solve the initial cell search problem of TDD system under Cellular Networks, TD-SCDMA has designed unique frame structure, realizes Cell searching by downward guide time slot (DwPTS).Do not have business datum in this time slot, signal to noise ratio is very high.And in network shown in Figure 1, because neighbor cell all will be at this frequency emission DwPTS, sign indicating number is different, and the base station separation is more or less the same again from the position of terminal, and terminal receives the signal to noise ratio of this steering signal may be at-5dB, even poorer, and adjacent carrier frequency is all similar.Like this, will make very difficulty of initial ranging.
2, terminal is measured complicated.Because each carrier frequency is a sub-district, this terminal may measure contiguous 18 sub-districts among Fig. 1 similar identical signal level.In present standard, terminal is only measured 6 sub-districts the strongest, faces far away more than the sub-district of this quantity, and terminal may be absorbed in the measuring process complicated, that be difficult to differentiate fully.
3, switch difficulty.Above-mentioned measurement result is delivered to radio network controller (RNC), will cause the difficulty that is switched and determined, and will cause the handoff procedure that do not stop, and system loading is obviously increased.The also switching determination that may lead to errors reduces the service quality of system.
4, system effectiveness is low.A large amount of measurement results are delivered to RNC, and the handoff procedure that does not stop must will seriously reduce the efficient of system.
Summary of the invention
Technical problem to be solved by this invention provides a kind of TD-SCDMA system overloading coverage condition accidental access method down frequently, and Cell searching is stranded to solve, terminal is measured complicated, switching difficulty and the low problem of system effectiveness.
To achieve these goals, the invention provides a kind of TD-SCDMA system overloading and cover accidental access method frequently, comprise the steps:
By each cell/section at least one logic district for being made up of a plurality of carrier frequency is set; Make that a carrier frequency is as the pilot tone carrier frequency in each sub-district, the carrier frequency of other frequency is as minor carrier; This pilot tone carrier frequency sends descending DwPCH channel at the DwPTS time slot; The DwPTS time slot of this minor carrier is in blocked state, does not send descending DwPCH synchronizing channel.
This pilot tone carrier frequency is set uses identical scrambler and basic midamble sign indicating number with minor carrier; Common Control Channel P-CCPCH (Primary Common Control Physical Channel) is configured in the TSO of pilot tone carrier frequency, is used to carry the data from transmission channel BCH, and the system message that covers whole cell/section broadcasting is provided; Auxiliary Common Control Channel (S-CCPCH, Secondary Common Control Physical Channel) and the Page Indication Channel (PICH) of carrying transmission channel FACH and paging channel PCH also are configured in the pilot tone carrier frequency.
Can dispose forward physical access channel (F-PACH) and Random Access Channel (P-RACH, Physical Random Access Channel) on this pilot tone carrier frequency and the minor carrier.For a multi-carrier district that N carrier wave arranged, can dispose m UpPTS carrier wave, 1<=m<=N, according to the system configuration requirement, configuration UpPTS channel, the UpPTS of pilot tone carrier frequency and minor carrier may be used to insert at random.UE can insert at the UpPCH of pilot tone carrier frequency channel, also can insert at the UpPCH of minor carrier channel.
The pilot tone carrier frequency uses identical uplink synchronous code SYNC-UL with minor carrier.Because the frequency of pilot tone and minor carrier is different, use identical SYNC-UL sign indicating number not have big phase mutual interference on the different frequent points.This overloading is access way at random frequently, the collision and the generation of blocking in the time of can reducing the multi-user and insert.
The different carrier frequency of each logic district/sector can be provided with different access priorities.Access priority is broadcasted in the system message of BCH channel.UE selects the UpPCH channel of the high carrier frequency of priority to insert according to system message at random.Reduce the access priority that inserts the serious carrier frequency of collision, improve the priority that inserts collision carrier frequency seldom, can play the effect that inserts the load sharing scheduling.
Selecting the UpPCH channel access of the high carrier frequency of priority at random is from available access carrier, select a carrier frequency to insert at random, it is relevant with access priority that used random function must satisfy the selected probability of the selection of each permission, the carrier frequency that access priority is high, and selected probability is big; The carrier frequency that access priority is low, selected probability is little.
In the very big wide coverage cell of radius of society, UE potential range base station is far.Need to improve Timing Advance TA, guarantee same time slot, the upward signal of different UEs arrives Node B (NodeB) synchronously.In system message, improve the access priority of minor carrier.Because the DwPTS time slot of minor carrier does not send data, UE can choose than pilot tone carrier frequency and insert bigger Timing Advance TA (Time Advance), needn't worry to collide with DwPCH.Like this, help the restriction of break through lead TA, increase the covering radius of sub-district.
Accidental access method under this TD-SCDMA system overloading frequency coverage condition that the present invention adopts, UE can be according to priority, and connecting system on pilot tone carrier frequency or minor carrier reduces the generation of colliding and blocking when the multi-user inserts.Being provided with of access priority can be shared inserting load, further reduces the generation of colliding.The sub-district that covering radius is very big, UE is at the minor carrier access network in guiding, helps the restriction of break through lead TA, increases the covering radius of sub-district.
Below in conjunction with accompanying drawing specific embodiments of the present invention is further described.
Description of drawings
Fig. 1 is that TD-SCDMA system overloading covers schematic diagram frequently
Fig. 2 is the physical frame formats of Cell_A multi-carrier frequency cell
Fig. 3 is the cell channel configuration
Fig. 4 is the flow chart of Cell searching and random access procedure
Embodiment
In Fig. 1, disclosed a kind of TD-SCDMA system overloading coverage condition frequently, UE is positioned at the covering intersection of 4 multi-carrier frequency cell Cell_A, Cell_B, Cell_C and Cell_D, and there are 6 carrier waves each sub-district.F3 is as the pilot tone frequency among sub-district Cell_A, Cell_B and the Cell_C, and minor carrier is f1, f2, f4, f5 and f6.F6 is as the pilot tone frequency among the Cell_D of sub-district, and minor carrier is f1, f2, f3, f4 and f5.
In Fig. 2, disclosed the physical frame structure of sub-district Cell_A multi-carrier frequency cell, be example with sub-district Cell_A, sub-district Cell_A is 6 carrier cells, and the pilot tone carrier frequency is f3, and the DwPTS time slot of f3 carrier frequency sends downlink frequency pilot code SYNC-DL.Other frequency f1, f2, f4, f5, f6 are " minor carriers ", and the DwPTS time slot of these carrier frequency is in obturation (Id1e) state, does not send any data, does not send descending DwPCH synchronizing channel.
The sign indicating number resource of TD-SCDMA is divided into 32 code characters.Neighbor cell uses different code characters.For example: Cell_A disposes code character 1.The DwPTS time slot of the f3 carrier frequency of sub-district Cell_A, the downlink frequency pilot code of transmission are selected from code character 1, i.e. SYNC-DL0.In the same sub-district, use identical scrambler and elemental user training sequence code (midamble sign indicating number).Such as, the scrambler of Cell_A and basic midamble choose from code character 1: scrambler Scrambling code1 and Midamble1.
Each cell/section pilot tone carrier frequency and minor carrier are chosen identical ascending pilot frequency sign indicating number.For example Cell_A chooses 8 ascending pilot frequency sign indicating number SYNC-UPO...7 from code character 1.
In Fig. 3, further disclosed the cell channel configuration, the Common Control Channel P-CCPCH of sub-district is configured in the TSO of pilot tone carrier frequency.S-CCPCH is configured on the pilot tone carrier frequency, is used to carry the data from transmission channel FACH and PCH.S-CCPCH can be configured in any descending time slot, also can with the P-CCPCH time division multiplexing at TSO.P-CCPCH broadcasts the frequency and the configuration of this other carrier frequency of sub-district, the pilot tone frequency of neighbor cell, the access priority of this each carrier frequency of sub-district.Each carrier frequency all disposes FPACH and PRACH, and UE can insert on the pilot tone carrier frequency, also can insert on other minor carrier.
In Fig. 4, disclosed Cell searching of the present invention and random access procedure, the process of mobile terminal device (UE) Cell searching and access network is as follows:
Step S100, search for pilots frequency and DwPTS position in each carrier frequency in the TDD frequency range.After the UE start, at first measure the broadband power of each carrier frequency in the TDD frequency range.The broadband power that records is sorted according to power, begin to search for DwPTS from the strongest frequency then.Respectively there is a zero energy district at DwPTS time slot two ends, and every frame all sends with constant power.According to the feature of DwPTS, can tentatively determine its position.
Step S110 is at DwPTS time slot search descending synchronous code SYNC-DL.Preliminary position has been arranged, determined the SYNC-DL sign indicating number of sub-district use and the accurate position of time slot according to the principle of matched filtering again.Determine the SYNC-DL sign indicating number of sub-district, also just determined the code character of sub-district.
Step S120 determines elemental user training sequence code and the scrambler (ScreamblingCode) that use the sub-district.Definite the 1st or the 2nd channel code of Midamble sign indicating number based on pilot tone frequency TSO, very strong because these two code channels are launched usually, cover whole cell/section.Use 4 Midamble sign indicating numbers of place, sub-district code character successively, the impulse response of calculating channel, the maximum are the Midamble sign indicating number that use the sub-district.Scrambler and Midamble sign indicating number have fixing corresponding relation, have determined that the Midamble sign indicating number also just determined scrambler Scrambling.All carrier frequency of each cell/section all use identical basic Midamble sign indicating number and scrambler.Step S130 judges that whether the Midamble code searching is successful, if success then continues, if fail, then returns execution in step S100.
Step S140 sets up the synchronous and reading system broadcast of basic Common Control Channel (P-CCPCH).UE is at the TSO of pilot tone frequency time slot, the 1st or the 2nd channel, and P-CCPCH channel synchronously, and read the system message of broadcasting on the P-CCPCH channel.Under the situation that multicarrier covers, the frequency and the time slot configuration information (for example whether TSO expands) of broadcasting current area minor carrier in the system message, the pilot tone frequency of neighbor cell, pilot code, basic Midamble and scrambling code information.The access priority of broadcasting minor carrier in the system message.
Step S150, the pilot tone that selection inserts according to system message.UE can be at the pilot tone carrier frequency, also can be at the minor carrier access network.According to system broadcast message, UE preferentially sends uplink synchronous code SYNC-UL at the UpPTS time slot of the high carrier frequency of priority.Can reduce like this and insert collision and carry out the load sharing between a plurality of carrier frequency in the sub-district.
Step S160, after Node B (NodeB) is received uplink synchronous code SYNC-UL, with the FPACH channel of the same carrier frequency of UpPTS time slot on, send downstream message, adjust uplink synchronous and the initial power of UE.
After step S170, UE receive the FPACH channel massage, adjust uplink synchronous and initial power; On the PRACH of same carrier frequency channel, send RRC connection request message.
Step S180, NodeB send the RRC connection and set up message to UE on the FACH channel, assigned with dedicated channel is given UE.The dedicated channel of distributing is limited on the carrier frequency of UE access.The FACH channel configuration is on the pilot tone carrier frequency.
Step S190, UE send the RRC connection setup complete message on the dedicated channel of distributing.
Step S199, random access procedure finishes.
Foregoing only is an optimum implementation of the present invention, and it is not to be used for limiting the specific embodiment of the present invention, and all modification and changes of carrying out according to the main inventive concept of this method all should belong to the desired protection range of claims of the present invention.