CN2687960Y - CDMA cellular communication initial pilot frequency acquisition system - Google Patents

Abstract

The utility model discloses a CDMA cellular communication initial pilot frequency acquisition system, the system of the cold starting initial acquisition is accomplished through a series of first stage search and corresponding second stage search, the first stage search adopts the coarse frequency and codephase value to search, and the second stage search adopts the accurate frequency and codephase value to search. The code phase acquired by successfully cold starting initial acquisition is memorized in a durable memory to be a default when needing the cold starting initial acquisition next time, if the testing is unsuccessful, the CDMA cellular communication initial pilot frequency acquisition system needs some frequency default to test. The second stage code phase searching window uses the searching result of the first stage as a center, the size of the searching window is just accommodated to the code phase drifting value acquired by the first stage search and the second stage search, next the CDMA cellular communication initial pilot frequency acquisition system searches the second stage window and checks whether two PN phase locations are in a same chip or not, the searching window is positioned at the middle of the PN phase (the strongest paths in the corresponding activating aggregation of the finally moment of the last time calling), and the frequency to be tested is a frequency stored in a volatile memory at the finally moment of the last time calling.

Description

The initial pilot tone of cdma cellular formula communication is obtained system

Technical field:

The utility model relates to the initial pilot tone of a kind of cdma cellular formula communication and obtains technology, is mainly used in wireless cellular communication.

Background technology:

CDMA1, the CDMA2000 and the WCDMA that are used for wireless cellular communication adopt code division multiple access (CDMA) technology.In these systems, each base station broadcast one pilot signal is so that the service area mobile subscriber terminal connects Traffic Channel.Pilot signal is not a data-modulated, in fact, it just carried the puppet relevant with certain base station make an uproar the sign indicating number (a PN code).In CDMA1 and CDMA 2000 standards, the PN code relevant with the base station is the time offset version of the primary key of whole clock synchronization system.Time migration is corresponding to the integer amount of digital block, and title more commonly used is the puppet code phase (PNcode phase) of making an uproar.

For and base station communication, mobile radio station must be known accurate frequency of the carrier wave of base station broadcast and pilot phase.More precisely, mobile radio station (terminal) must carry out with the make an uproar frequency and the sequential of sequence (PN sequence) of the puppet of base station synchronously.This processing procedure claims initially to obtain (initial acquisition).Two kinds of basic initial acquisition are arranged: open initialacquisition behind the mobile subscriber terminal power supply and be called cold start-up and initially obtain, the initial acquisition that communications status occurs is called mutual calling and obtains.In communication process, if mobile radio station is moved to an area that new system parameters is arranged, the latter will carry out, and recaptures a part and the mobile station communicate of getting as system.

A kind of initial acquisition method of suitable standard is to test with frequency in certain scope, for each frequency values, adopts the PN code phase of certain limit, tests one by one.If meet certain criteria, then think and obtain success with certain frequency and phase value measured signal strengths.

Precision, mobile radio station that the base station is used for producing the oscillator of radio-frequency carrier are used for producing the precision of the oscillator that is used for radiofrequency signal and the Doppler frequency scope that cellular system exists, and this three has determined the test quantity of frequency.At the cellular system that uses cellular band or person-to-person communication service (PCS) wave band, the precision of user terminal oscillator is the main factor that influences of frequency unreliability.Usually user terminal has automatic frequency control (AFC) mechanism, makes and enough close of original frequency with automatic adjustment target frequency.The initialization precision that requires is usually greater than insecure original frequency, so need a plurality of hypothesis frequencies of test.

The sequence very long (cdma1 is 2^15chips) because puppet is made an uproar, the tested code phase of the needs of each frequency correspondence is very huge.The time-dependent of initial acquisition is tested quantity in the time of hardware supports, might reach the degree that the mobile radio station operator is difficult to stand.Therefore, need intelligent search strategy to reduce the average time of initial acquisition.

Summary of the invention:

Purpose of design: the system of a kind of initial acquisition and suitable emulator are discussed, and they can greatly reduce, and cold start-up is obtained and mutual the calling search average time of obtaining.

Design: 1, the system of cold start-up initial acquisition finishes by a series of phase I search and corresponding second stage search, the phase I search adopts coarse frequency and code phase value to search for, and the second stage search adopts accurate frequency and code phase value to search for.Search system comprises the high/low conversion of radio frequency, search hardware, M control, memory and DAC digital to analog converter.

2, the system of cold start-up initial acquisition takes as follows: the code phase that successful cold start-up initialacquisition obtains is stored in permanent memory, when need cold start-up initial acquisition next time as default value, if test is unsuccessful, just need with some frequency default tests.

3, the search of cold start-up initial acquisition second stage:

A. second stage code phase search window is the center with the Search Results of phase I, and the size of search window should be just in time greatly to holding the code phase drift value that phase I search and second stage search obtain.

B. and then search for the second stage window, and check that two PN phase locations are whether in same chip.

4, the system of inter-call acquisition:

A. search window is positioned at the centre of PN phase (the strongest multipath in the activation set of preceding call last moment correspondence).

B. wanting tested frequency is the preceding call last moment to be kept at the frequency in the volatile memory.

Description of drawings:

Fig. 1 is a searcher system chart.

Fig. 2 produces a hypothesis frequency values block diagram.

Fig. 3 is that flow chart is initially obtained in cold start-up.

Fig. 4 is the energy test block diagram.

Fig. 5 is the first valency section search routine figure.

Fig. 6 is the second valency section search routine figure.

Fig. 7 is that mutual the calling obtained flow chart.

The tool present embodiment:

The search system of mobile radio station recipient is carried out the task of initial acquisition.Fig. 1 has showed each parts of mobile radio station recipient that comprise search system.Recipient uses a strip antenna to accept signal of communication at least, and signal of communication is sent to a Rx circuit (simulation recipient), and they are by frequency reducing, amplification and digitlization there.If want frequency reducing, Rx circuit must produce a fractional radio frequency's signal with input signal carrier frequency same frequency.Local oscillator provides a sequential benchmark to produce to be used for the radiofrequency signal of frequency reducing.The oscillator that mobile phone uses is VTCXO (a voltage-controlled temperature compensating crystal oscillator), and its output frequency changes along with the variation of input voltage.Although VTCXO has very strong opposing temperature effect ability, but still exist because of variation of temperature occurrence frequency drift situation, per 1,000,000 the insides have several changes.

In analogue system shown in Figure 1, initial the obtaining of microcontroller (MController) tissue, and the input voltage of responsible control VTCXO.It produces corresponding analog control voltage by writing digital controlled signal to DAC (digital to analog converter).The DAC that a lot of types are arranged now, just few here the discussion.Discuss for convenience, we have showed a DAC that can be used in frequency control system at Fig. 2, and it comprises a PDM (pulse strength modulator), next is low-pass filter (low pass filter).By the DAC/Interface equipment that Fig. 2 shows, the output frequency of the corresponding VTCXO of the value of a digital AFC PDM.Simulation recipient shown in Figure 1 (Rx circuit) uses the output of VTCXO to produce a fractional radio frequency.Like this, in initial acquisition process, by producing an AFC PDM value, microcontroller just produces a frequency.

Fig. 3 has showed cold start-up initial acquisition process by a flow chart.Last step after successfully obtaining is, there is permanent memory in AFC PDM value (producing that corresponding AFC PDM value of successful precise frequency value), and Valid_PDM Status Flag (also existing in the permanent memory) is set.The cold start-up acquisition algorithm is checked this mark at the very start, if mark is not set up, the frequency span is divided into i coarse frequency values and tests this i default.Give one example, if get 3 coarse frequency values tests in the whole frequency span, then this i will tested AFC PDM value be exactly NOMINAL, NOMINAL-DELTA, NOMINAL+DELTA, what particularly point out is, NOMINAL is the median of frequency span, is most possible correct value in 3 default values.Because in case coarse hypothesis frequency successfully pass through test, search procedure just enters into second stage from the phase I, so most possibly be that correct value is first detected.On the other hand, if the Valid_PDM Status Flag is set up, show that then permanent memory storing an effective AFC PDM value, this storing value will be tested by first, and the number of times of test reaches J time at most.If this storing value final test is unsuccessful, the Valid_PDM Status Flag will be eliminated, and i mentioned above hypothesis frequency values will be tested.Because the unlikely significant change of the characteristic of VTCXO so this storing value is tested the meeting success for the first time under most situation, has been saved the time of testing those coarse frequency values that set up and spending greatly.Test all roughness value and once constitute once test, same, test that storing value and also constitute once test J time.Obtain failure behind K the test crash.Processing procedure after the failure is that system is relevant, and this paper is not discussed.

Search has for the first time covered all possible time migration.In other words, be whole PN codephases span.The quantity of PN code phases is very huge, like this need be by the difference of adjacent default is searched for to widen under the successful possibility situation and reduced to want tested default quantity can not reducing the phase I as far as possible.One have digital searcher hardware analogue system, the increment size of code phase (code phases) test is  chip.The default quantity that second stage search will be checked still less, the increment of code phases is better.

For the PN phase of each hypothesis, energy test is to finish by circuit diagram shown in Figure 4.Digitized I and Q channel data can come quadrature with some famous technology.If the signal code phase and the local PN code of input are approaching, then the energy measurement instrument will show a big value, otherwise just can not.Fig. 5 show be the flow chart of phase I search, each hypothesis code phase is tested, the maximum that exhaustive search obtains again with the phase I threshold.Whether successful standard is that this maximum energy value is greater than some predetermined phase I threshold values in the phase I search.The size of threshold value can be determined by mathematical analysis or experiment.Obviously this frequency is not very accurate, and what be used among Fig. 4 continuously that the value of several N of summation will try one's best is little.The N size of IS-95 system is 64.In order to obtain the measured value of energy, summing value L is that discontinuous adding up by as shown in the figure obtains continuously.The size of L has influenced the precision of energy measure, and when L is big more, the average result of energy measure is just good more, but the time of the PN phase of test hypothesis is and being in proportion of L.

The compromise that the phase I L of emulation IS-95 system adopts is 8.To obtain energy value from codephase experimental provision output valve shown in Figure 4, need be divided into the result (N^2) L and standardize it.Yet more economical calculating should comprise the success and the failure threshold value of phase I search.Search for some frequency channels if desired, search will be searched for each channel in the phase I.Shown in the chart all is to have only channel needs searched.For those familiar with the art, it is easily that method discussed here is used for the multichannel search.

If the phase I searches for successfully, suppose that the composite value of PN phase and hypothesis frequency is stored, and the median of PN phase and frequency is offered second stage search shown in Figure 6.The division meeting of second stage search PN phase and frequency is thinner.These precise frequency values are cut apart by a certain number value, and this quantitative value is less than the deflation scope of AFC control system (initial acquisition calls it at last).In certain analogue system, the precise frequency of supposing is the frequency values as a result of phase I search, greater than the frequency of end value 3kHZ with less than the frequency of end value 3kHZ.It is 1/4chip that the hypothesis PN phase of second stage divides increment, and scope is to cover a little search window, the size of window enough cover any between phase I search and second stage are searched for during this period of time in the drift of code phase.The drift of Code phase is that generator does not also have frequency modulation because puppet is made an uproar.Please see that U.S. Patent number is 6,249,539 document how to be calculated the particulars of code phase drift.Loop test is carried out in the second stage search of a corresponding PN window of hypothesis frequency, compares the phase position of ceiling capacity correspondence in twice search.The effective prerequisite in maximum energy value and position is that these two positions must be in same chip.This step has reduced the time that another time search second stage search window is spent greatly.In the phase I, except N and L greater than the second stage search those defaults, each default is the instrument test by Fig. 4 all.The N of analogue system and L be value 64 and 64 respectively.Second stage success/failure threshold value also must corresponding setting.The microcontroller of Fig. 1 comes code search hardware with suitable N and L, and it realizes Fig. 3,5,6 and 7 functions that require.

Fig. 7 has showed the flow chart of inter-call acquisition, and we claim that also it is to obtain the phase III.Last what call out, current AFC PDM value is stored in volatile memory.Because this value is often corresponding to heat call, rather than that value of the last storage of cold start-up initial acquisition, so these two values are kept at different places.Keep this difference to help to reduce the needs of temperature-compensating, but be not the needs of eliminating temperature-compensating.Because of the mobile phone variation of temperature,, whenever several secondary frequencies also can occur 1,000,000 times and drift about even temperature compensated oscillator is arranged.

Search window is positioned in the middle of the PN phase position (the strongest multipath in the activation set of preceding call last moment correspondence).Per call last, microcontroller need be the PN location storage at volatile memory.In the second stage search, because the width of search window (being 32chips in the analogue system) can be very little, the difference of two hypothesis code phase can also just can reach very little.Because between calling out, the VTCXO drift is very little, and frequency can reach very high precision.In commercial cdma network, the base station is very strict for the tolerance of frequency.Like this, the value N that the phase III is used for coherent integration is bigger than the analog value of cold start-up initial acquisition, gets 128 in analogue system.A bigger N means and obtains the same littler L of energy measurement precision needs.In phase III analogue system L value 16.If the maximum energy value of finding in the phase III is bigger than the phase III threshold value, then inter-call acquisition success, local PN phase just is taken as the phase place corresponding to ceiling capacity.If the maximum energy value that three stages were found is less than the phase III threshold value, then inter-callacquisition fails, and system is cold start-up initial acquisition according to a conventional method.

What need understand is: above-mentioned embodiment is just to explanation of the present invention, rather than limitation of the present invention, and any innovation and creation that do not exceed connotation of the present invention all fall within the scope of protection of the present invention.

Claims (5)

1, the initial pilot tone of cdma cellular formula communication is obtained system, it is characterized in that: 1. cold start-up initialacquisition adopts coarse frequency and code phase value to search for by the phase I search, and the second stage search adopts accurate frequency and code phase value to search for.

2, the initial pilot tone of cdma cellular formula according to claim 1 communication is obtained system, it is characterized in that: the code phase that successful cold start-up initial acquisition obtains is stored in permanent memory, when need cold start-up initial acquisition next time as default value, if test is unsuccessful, just need with some frequency default tests.

3, the initial pilot tone of cdma cellular formula according to claim 1 communication is obtained system, it is characterized in that: the method for cold start-up initial acquisition second stage search:

A. second stage code phase search window is the center with the Search Results of phase I, and the size of search window should be just in time greatly to holding the code phase drift value that phase I search and second stage search obtain;

B. and then search for the second stage window, and check that two PN phase locations are whether in same chip.

4, the initial pilot tone of cdma cellular formula according to claim 1 communication is obtained system, it is characterized in that: the system of inter-call acquisition:

A. search window is positioned at the centre of PN phase (the strongest multipath in the activation set of preceding call last moment correspondence);

B. wanting tested frequency is the preceding call last moment to be kept at the frequency in the volatile memory.

5, the initial pilot tone of cdma cellular formula according to claim 1 communication is obtained system, it is characterized in that: search system comprises the high/low conversion of radio frequency, search hardware, M control, memory and DAC digital to analog converter.

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