CN1199377C - Method and device for searching user station in CDMA system - Google Patents

Abstract

The method involves associating each significant tap of a subscriber terminal with a virtual subscriber terminal, as long as sufficient system resources are available, if the terminal's channel pulse response has a number of significant taps. The virtual terminals have the same CDMA code as the real terminal. The virtual and real terminals are detected by a detector. The symbols of the virtual terminals are adaptively controlled.

Description

The method and apparatus of searching user station in cdma system

Technical field

The present invention relates to the method and apparatus of searching user station in cdma system, and be particularly related to the reduction of one group of time variable of the subscriber station of a mobile radio communications system, in this system in a radio honeycomb by means of multi-user's detector searching user station.

Background technology

In multi-user's detector in cdma system, these cdma systems for example with interference counteracting, abbreviation IC or comprehensive survey, abbreviation JD work, are surveyed each subscriber station no longer independently of one another, such as being such situation in present gsm system.By subscriber station these correlations when surveying each other, time dependent subscriber station, that is to say and for example in radio honeycomb, move and therefore cause that in addition the subscriber station of Doppler effect may disturb and influence the detection of other subscriber station.To this, time dependent subscriber station is by its time variable, that is to say with respect to the translational speed of base station or reflects moving of electromagnetic environment, is interfered when it is surveyed.

In the error rate, be abbreviated as under the situation of BER, show this interference with the form of the wrong lowest limit that can not reduce, it is called the error minimum below.In other words, pressing down low error rate BER in the situation of determined value also is impossible under the situation of the signal to noise ratio S/N of infinite height.Even iff a spot of subscriber station is time dependent, all users that must survey simultaneously also may suffer damage in a honeycomb.

This also is adapted to this situation especially, and promptly the small number of users station is in time and marked change in the environment that changes time, for example that is to say and moves in the honeycomb of mobile radio communications system with higher speed.In view of the capacity in the mobile wireless network zone with a small amount of (very) time dependent subscriber station, the interference of subscriber station is very disadvantageous in addition.

In the following explanation of this lay special stress on:

-in the honeycomb of mobile radio communications system, what generally find only is the subscriber station of minor variations in time.This is designed the expansion and the capacity of this network.The subscriber station of a marked change in time disturbs this structure consumingly owing to its interference that can not eliminate.

-the strict especially requirement of this error rate is suitable for LCD data service (low restriction data).Yet these professional environment that probably only are applied to a spot of time variation.If these business receive with normal language business, then this situation may appear, promptly significantly disturb and hinder these resistless especially business owing to the subscriber station of marked change in time.

Former, in the main research on the analog result basis, such as at A.Klein: " Multiuser Detection of CDMA signal-algorithm and their application in cellular mobile radio communication ", Germany Kaiserslautern university thesis for the doctorate, continue report VDI, 1996 the 10th, 423 phases, the 146-155 page or leaf, with at M.Nasshan: " the authenticity simulation and the emulation of information system ", example at the CDMA mobile radio communications system, Kaiserslautern university thesis for the doctorate, nineteen ninety-five 128-135 page or leaf tackles owing to the time changes the error minimum that causes with traditional method:

-by improving the raising that system bandwidth draws the multipath diversity, therefore reduced the irresistance of system to time variable.

-by introducing antenna diversity, that is to say by the independently condition of acceptance on antenna and set up diversity, draw the minimizing of system equally to the irresistance of time variable.

-select suitable chnnel coding, that is to say and utilize time diversity and coding benefit, draw minimizing equally to the irresistance of time variable.

These traditional methods have been avoided the essence of time variable, therefore directly do not overcome time variable.Therefore inoperative from the traditional measure of regular hour intensity of variation.

In addition, it is possible following the tracks of the channel of having assessed adaptedly.To this, it is necessary reevaluating impulse response from the data of having surveyed.If the basis of variable sending mode as this detection, then detector generally is expensive.Approaching that Cholesky decomposes under the situation of this external combined detection no longer is possible.

Summary of the invention

The present invention is based on this task, set up a method and a CDMA mobile radio communications system, time dependent therein user will be seldom disturbed.

Solved above-mentioned task by the following technical programs.

According to a kind of method of in based on the mobile radio communications system of CDMA, surveying multiple user signals of the present invention, it is characterized in that,

If the channel impulse response of-one subscriber station has a plurality of significant Tap, distribute a virtual subscriber station then for each significant Tap, as long as there is enough system resource, identical CDMA code is used at these Virtual User stations, CDMA code such as this subscriber station

-with a subscriber station detector detecting visual and real.

The present invention also comprises the advantageous embodiment based on technique scheme.

At first illustrate according to solution of the present invention according to a joint detector.Then promoting on the detector in addition.

At first go up the basic operation principle of setting forth time variable at a linearity, relevant detector (for example force the grouping linear equalizer, be abbreviated as ZF-BLE) according to one zero.

ZF-BLE minimizes following tolerance:

${\widehat{\underset{\_}{d}}}_{\mathrm{ZF}-\mathrm{BLE}}=\arg \left(\underset{d\∈C^{\mathrm{KN}}}{\min }({\left(\underset{\‾}{\mathrm{eAd}}\right)}^{*T}{\underset{\‾}{R}}_n^{-1}(\underset{\‾}{e}-\underset{\‾}{\mathrm{Ad}})\right)$

In above-mentioned equation, so select data vector d, make from data vector dThe middle received signal of reproducing AdUnder the situation of considering the noise covariance function, pass through noise covariance matrix RAnd sytem matrix AExpress received signal with the meaning of tolerance like recently eTo this, the data of having assessed are complex values.In the paper of already mentioned A.Klein, obtain going through of above-mentioned equation, therefore here no longer it is inquired into.

If present time dependent user has a channel impulse response, it is based on a sampled value, this sampled value is called Tap below, in during a fixed delay, therefore whether detector, for example ZF-BLE can not be distinguished by data-modulated or by the time variable of a channel impulse response-Tap and cause this probe value.Detector is rotation and the correct data assessment of scale so, and is feasible consistent with the change of channel impulse response-Tap, or expresses in addition, up to above-mentioned tolerance minimum.The data of subscriber station do not change in addition.The error minimum value is limited in time dependent subscriber station in this case.

Because in its data assessment, reflect the time variable of time dependent subscriber station fully, so on the mark level, for example under the situation of considering modulation alphabet and/or channel code, implement the coupling of a Tap and follow the tracks of.Therefore can reduce the error minimum of time dependent subscriber station significantly.

In the back to back stage, the channel impulse response of time dependent subscriber station has a plurality of Tap, and these Tap are strong each other relevant.For example this may be caused by chip pulse shaping and/or emission and receiving filter.All static component of channel impulse response are called total chip shaped pulse from now on.Therefore time dependent subscriber station has the channel impulse response Tap of the time variation of a reality.Because these a plurality of Tap as a synchronous variation of Tap, therefore do not change on the performance of detector.These time dependent subscriber stations do not bear the error minimum value, and may follow the tracks of the error minimum value that reduces time dependent user by coupling.

A basic other performance of system is that if the channel impulse response of these time dependent subscriber stations (or a time dependent subscriber station) has the significant Tap more than, these Tap are uncorrelated mutually more or less.This is considered to convention.Because here time variable has the degree of freedom more than, thus detector can not be again distortion by time dependent subscriber station only minimize tolerance.In addition, make the tracking degradation of coupling equally, thus the time change have an error minimum value with constant subscriber station of time.Detector can not be understood, and the different piece of the channel impulse response of subscriber station may be in different situations.

Different piece for the channel impulse response that can understand a time dependent subscriber station, therefore so survey time dependent subscriber station according to the present invention, these subscriber stations comprise the subscriber station so-called virtual, that have each actual Tap that a plurality of times change, and these Tap use identical CDMA code.For this reason, that the channel impulse response of time dependent subscriber station is divided is a plurality of, comprise the only branch channel impulse response of an actual channel impulse response-Tap, these minutes channel impulse response distribute to a plurality of virtual subscriber stations then.Survey these virtual subscriber stations of time dependent subscriber station and other subscriber station, so-called real subscriber station together with a traditional detector then.Therefore, distribute the degree of freedom, distribute because the interference of time variable is possible only for time dependent subscriber station by means of this degree of freedom to detector.The error minimum value of subscriber station is minimized in addition, and can mate the mark of following the tracks of the Virtual User station again better.After following the tracks of the Virtual User station or during these signals can merge into the data-signal of time dependent subscriber station again.

Description of drawings

Elaborate the present invention according to preferred embodiments and drawings below.

Fig. 1 a-1c pointed out two Virtual User stations impulse response determine and

Fig. 2 has pointed out the calibration between S/N degradation and error minimum value.

Embodiment

The present invention of the time dependent user be suitable for having two significant actual Tap is discussed below.

The method according to this invention has following process:

I) identification has the time dependent subscriber station of a plurality of significant actual Tap.

At first must discern time dependent user, and, if resource or same asset are surveyed in restriction, then must select this to indicate the subscriber station of bigger improvement.If the stock number of detector is enough not big, this and its are had significant actual Tap to be compared, perhaps must survey a subscriber station, that is to say that it is necessary comparing a spot of virtual subscriber station to this subscriber station distribution with corresponding its Tap with a small amount of Virtual User station.

Step I) understanding is judged relevant with following four steps:

The correlated performance of the channel impulse response of-analysis successive pulse groups;

-check candidate likely according to the trial-and-error method principle;

-definite uncoded error rate BER from the tolerance of channel encoder;

-analyze the deviation of the not coded data of undistorted value, wherein perhaps can consider channel code and S/N.

Under situation, can omit above-mentioned four steps about time dependent user's prior information.

II) channel impulse response of time dependent subscriber station is divided into the channel impulse response at Virtual User station.

Fig. 1 a pointed out the channel impulse response that a time changes, and Fig. 1 b has pointed out the distribution of two nonoverlapping Virtual User stations 1 and 2, and Fig. 1 c pointed out two overlapping Virtual User stations 1 and 2.

As what show from the example among Fig. 1 b-1c, the channel impulse response at Virtual User station can be defined as overlapping with nonoverlapping.The position of actual channel impulse response-Tap and intensity for example can be determined with the inverse filtering of the method for pattern recognition or the channel impulse response by having total chip shaped pulse (=with mid portion code channel impulse response be equivalent to total chip shaped pulse, the channel impulse response that mid portion is equivalent to assess).

III) by means of a suitable detector, for example JD or IC normally survey virtual and real subscriber station.

IV) follow the tracks of and perhaps make up simultaneously the signal at a time dependent user's Virtual User station.

Fig. 2 has pointed out for the relation of different system state between the error rate and signal to noise ratio.Curve A has been described this situation, does not occur time dependent subscriber station in honeycomb.The error minimum value does not appear.The situation of the subscriber station that curve B has been pointed out is time dependent, cause interference is not introduced the Virtual User station, that is to say and does not use the method according to this invention.The result is the higher error minimum value of of error rate BER, and it is constant for high S/N, and its error rate can not drop under the high initial value.The use curve C of the method according to this invention that is to say and used the Virtual User station to point out the time dependent situation that causes the subscriber station of interference.Must know clearly, though curve C provides an obvious lower error rate under the situation of high S/N ratio, that is to say that the error minimum value is obviously less, compare with curve B, curve C provides some worse results.

Set forth this method according to the example of two subscriber stations below.Each additional Virtual User station causes an additional S/N degradation.If for example under the TD-CDMA of reality suggestion, receive subscriber station worker with a channel impulse response Tap and subscriber station II for third generation mobile radio communications system with two channel impulse responses, then for example MMSE-BLE (compensation of lowest mean square differential set) for subscriber station II under the situation of the Tap of same intensity with for two subscriber stations during at static condition of acceptance under the situation in identical received power, provide the degradation of the additional S/N of 0.25db for this situation, promptly received subscriber station II with Virtual User station.If subscriber station II is marked change in time, then for two subscriber stations, can significantly reduce the error minimum value.If may not provide use enough virtual sounding channels for time dependent user, then then improve lower error minimum value again.In the JD detector, when with the expansion multiple big or small consistent the time generally may not survey a plurality of subscriber stations.If the number of actual channel impulse response Tap is higher than the number at Virtual User station, the reduction that then common the method according to this invention is also brought the error minimum value.

Combination by curve B and C can obtain other optimization, this in Fig. 2 with thick line B+C explanation.In other words, this is judged whether used the Virtual User station, the action of being expected is dependently made at these Virtual User stations.

Generally speaking, can determine that have significant difference in the environment of a plurality of Tap if having in the time variable of subscriber station and/or at channel impulse response, it is extra high then improving by the method according to this invention.In addition, this is useful, is the Virtual User station and has distributed invalid resource, that is to say not busy channel.Therefore do not increase expense and just can realize the improvement surveyed.

Under the situation of the number that pre-determines the channel that to survey simultaneously, though reduced the number of the subscriber station that can survey simultaneously by using the Virtual User station, under the situation of not distributing the Virtual User station, it is impossible surveying under the situation of time dependent subscriber station when providing the quality of reception, such as the curve that provides from high error minimum value among Fig. 2.In addition, capacity is not lost by system, because originally must operate as normal under situation about taking fully, because because vacant channels and may not distribute the Virtual User station.

In using the detector of IC, time variable may be damaged the detection of the subscriber station of the powerful reception of power after receiving, and the reduction of the transmission mode that changes with a time may damage the detection of more weak subscriber station.If in IC, survey time dependent subscriber station by means of the Virtual User station, follow the tracks of and therefore make up the Virtual User station, and then under the situation of considering the tracking subscriber station, reduced interference, then also realized the reduction of error minimum value here, otherwise must the expensive detector of design.

RAKE receiver has illustrated the limiting case of using.Do not disturb though here eliminate, survey each finger-type contact respectively, it also is appreciated that actual channel impulse response Tap.Here receive under the situation of subscriber station at strong cohesiveness, by each tracking and then or be combined as a unique received signal simultaneously and can obtain improvement on finger-type contact, because each finger-type contact of RAKE receiver can be understood as the Virtual User station for time dependent subscriber station.

Claims (12)

1. a method of surveying multiple user signals in based on the mobile radio communications system of CDMA is characterized in that,

If the channel impulse response of-one subscriber station has a plurality of significant Tap, distribute a virtual subscriber station then for each significant Tap, as long as there is enough system resource, identical CDMA code is used at these Virtual User stations, CDMA code such as this subscriber station

-with a subscriber station detector detecting visual and real.

2. in accordance with the method for claim 1, it is characterized in that coupling is followed the tracks of the mark at Virtual User station.

3. in accordance with the method for claim 2, it is characterized in that, during following the tracks of or afterwards, it is the data-signal at a real user station that treated multiple user signals reconsolidates.

4. according to one of them described method of claim 1 to 3, it is characterized in that, before the significant Tap according to the relative users station implements the distribution at Virtual User station, by surveying the subscriber station of discerning and determining to have the time variation of a plurality of significant Tap.

5. in accordance with the method for claim 4, it is characterized in that, under the situation of restriction resource, that is to say the sum of the subscriber station that restriction allows, select its detection of indication that maximum Virtual User station of improving is arranged.

6. in accordance with the method for claim 5, it is characterized in that, by

The correlation properties of the channel impulse response of-analysis successive pulse groups, and/or

The subscriber station of a plurality of indications of-detection, and/or

-definite uncoded error rate from the tolerance of channel encoder,

Realization is by distributing to significant Tap the detection and the judgement at Virtual User station.

7. according to one of them described method of claim 1 to 3, it is characterized in that,

Position and the intensity of effective channel impulse response-Tap is determined in the inverse filtering of the channel impulse response by having total chip shaped pulse.

8. according to one of them described method of claim 1 to 3, it is characterized in that, for subscriber station detecting visual and real is inferred system resource from whole resources banks of detector.

9. according to one of them described method of claim 1 to 3, it is characterized in that, use a JD detector.

10. according to one of them described method of claim 1 to 3, it is characterized in that, use an IC detector.

11. one of them the described method according to claim 1 to 3 is characterized in that, uses a RAKE receiver.

12., wherein used according to the described method of claim 1 to 11 based on mobile radio communications system CDMA, that have at least one base station and at least one mobile radio station.

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