CN1627674A - Interference cancellation method base on threshold of error probability in CDMA system - Google Patents

Abstract

The method includes following steps: (1) receiving demodulated output signal; (2) calculating two threshold values in use for making decision, this step includes following substeps: (a) determining prior probability value of symbol based on result information of previous modulation; (b) calculating two threshold values in use for making decision from prior probability value of symbol and threshold value of error probability; (3) determining whether modulated output signal is located between two threshold values in use for making decision; if yes, result of decision is invalid value not taking part in cancellation treatment, otherwise result of decision is a valid value of taking part in cancellation treatment. The method is more accurate, improves effect and performance of CDMA system.

Description

In the code division multiple access system based on the interference cancellation method of error probability thresholding

Technical field

The present invention relates to the interference cancellation method in the CDMA mobile communication systems, particularly in the code division multiple access system based on the interference cancellation method of error probability thresholding.

Background technology

3-G (Generation Three mobile communication system) is to satisfy international mobile communication (the International Mobile Telecommunication 2000 that International Telecommunications Union proposes, be called for short " IMT-2000 ")/following public land mobile (the Future Public Land Mobile Telephone Systems of system, abbreviation " FPLMTS ") third generation mobile communication system of standard, requirement has good network compatibility, can realize the roaming between a plurality of different systems in the global range, not only will be for the mobile subscriber provide speech and low-rate data business, and multimedia service widely will be provided.According to this standard, Wideband Code Division Multiple Access (WCDMA) (Wideband Code Division Multiple Access has been proposed at present in the world, be called for short " WCDMA "), code division multiple access (Code Division Multiple Access, be called for short " CDMA ") 2000, time division CDMA (Time Division Code Division Multiple Access, be called for short " TD-CDMA "), TD SDMA (Time Division Synchronous CodeDivision Multiple Access is called for short " TD-SCDMA ") 3-G (Generation Three mobile communication system) scheme.Though these schemes are very not identical, the whole world adopts CDMA technology to reach common understanding in 3-G (Generation Three mobile communication system).

CDMA mobile communication system has advantages such as high power capacity, high quality-of-service and good confidentiality.But also there are many shortcomings accordingly, disturb (Mutiple Access Interference is called for short " MAI ") such as multiple access.In the cdma communication system of reality, there is certain correlation between each subscriber signal, Here it is, and multiple access disturbs the root that exists.The MAI that is produced by the individual user is no doubt very little, and along with the increase of number of users or the increase of signal power, MAI just becomes main an interference of cdma communication system, has directly limited the raising of cdma system capacity, coverage and performance.

Multiuser detection (Multi-user Detection is called for short " MUD ") is the key technology that overcomes interference in the cdma system, is a kind of Enhanced Technology that improves cdma system capacity, coverage and performance.Traditional detection technique is carried out the spreading code matching treatment according to classical direct sequence spread spectrum theory respectively to each user's signal fully, thereby anti-MAI interference performance is relatively poor; Multiuser detection is on the basis of traditional detection technology, make full use of and cause all subscriber signal information that MAI disturbs that the signal of unique user is detected, thereby has good interference free performance, solved near-far problem, reduced the requirement of system to the power control precision, therefore can effectively utilize the uplink spectrum resource more, significantly improve power system capacity.

Verdu in 1986 proposes to add viterbi algorithm with matched filter and realizes Maximum likelihood sequence detection (Maxinum-Likelihood Sequence Detection, be called for short " MLS detection "), be applicable to the channel that is subjected to intersymbol interference (Inter Symbol Interference is called for short " ISI ") influence.But the complexity of viterbi algorithm remains the index power level of number of users, and promptly 2 ^k, and the MLS detector need know the amplitude and the phase place of received signal, this will obtain by estimating.MLS detects too complicated, impracticable, the suboptimum multiuser detection that everybody is easy to realize in searching.The suboptimum multiuser detection is divided into two classes, and promptly linear multi-user detects and non-linear Multiuser Detection.Decorrelation is carried out in the output of conventional detector for the former or other linear transformation is beneficial to receive judgement, comprises methods such as decorrelation detection, least mean-square error detection, subspace oblique projection detection and multinomial expansion detection; The latter is different from the former, comprise interference cancellation (Interference Cancellation, be called for short " IC ") detection method, the interference cancellation method is considered as useful signal with the signal of desired user, other users' signal is considered as interference signal, from received signal, eliminates other users' interference earlier, obtain the signal of desired user, signal to desired user detects then, thereby improves the performance of system.

The interference cancellation multi-user test method is divided into again: successive interference cancellation (Serial InterferenceCancellation is called for short " SIC ") and parallel interference cancellation (Parallel Interference Cancellation is called for short " PIC ").SIC is made up of multistage, and one-level is adjudicated, reproduces, eliminated user's sequence signal, and to give the following MAI that alleviate at different levels, each user's operating sequence is to determine according to the descending order of signal power.With the first order is example, and its output is the strongest user's data judgement of signal and removes the later received signal of MAI that this user causes.Subsequently at different levels in like manner and for it.Last result is that the weak more benefit of signal is many more.SIC improves a lot than conventional detector on performance, and changes not quite on hardware, be easy to realize, but the SIC time-delay is bigger, need carry out the power ordering, and amount of calculation is bigger, and initialize signal is estimated sensitivity.PIC has multilevel hierarchy, and what be different from SIC is that the parallel MAI that estimates and remove that each user causes of its each grade disturbs, and carries out data decision then.Design philosophy and the SIC of PIC are basic identical, but because PIC is parallel processing, overcome the shortcoming of the big time-delay of SIC, and need not when situation changes, to resequence, it is little to have time-delay, the advantage that computational complexity is little has higher utility in various MUD, be the most possible at present method that realizes.

Interference cancellation method as mentioned above, after the restituted signal to any user carries out symbol judgement, all need be by the court verdict of this this symbol of user this subscriber signal of regenerating, and from received signal, eliminate this user's interference, promptly deduct this user's regenerated signal, thereby eliminate the influence that this subscriber signal detects other subscriber signals.

The method that the restituted signal to the user that present interference cancellation method adopts carries out symbol judgement has following several, as: hard decision method, this method are directly adjudicated according to the symbol of receiving terminal user's restituted signal; For another example: decision method and the soft decision method that in US Patent specification US5418814, propose based on fixed threshold; And for example: also have a kind of decision method at present, calculate two threshold values,, then do not participate in offseting processing if the court verdict value between these two threshold values, illustrates that the possibility that court verdict makes a mistake is bigger based on the error probability thresholding.

The purpose of these methods is: the increase of the noise power that the court verdict of minimizing mistake as far as possible causes.Decision method based on the error probability thresholding can make the error probability of judgement not participate in interference cancellation above the court verdict of given error probability, has only the very high court verdict of those judgement correct probabilities just to participate in interference cancellation.The prior probability of its conventional letter evenly distributes, and calculates and adjudicate according to the error probability thresholding.It is from the angle of error probability, reduces the increase of the noise power that mistaken verdict causes, and with respect to preceding two kinds of methods, performance is improved.

Above-mentioned method based on the error probability thresholding comprises following steps:

Multiple user signals behind the receiving demodulation;

Use based on the decision method of error probability thresholding each subscriber signal of regenerating respectively;

In described multiple user signals, described regeneration subscriber signal is offseted processing.

In actual applications, there is following problem in such scheme: because the prior probability and the uneven distribution of symbol in the actual conditions, cause the decision threshold that calculates reasonable inadequately, the method performance is not ideal enough, has influenced the raising of systematic function.

Cause the main cause of this situation to be, existing decision method based on the error probability thresholding has supposed that in advance the prior probability of symbol evenly distributes, and it is not estimated.

Summary of the invention

The technical problem to be solved in the present invention provides in a kind of code division multiple access system the interference cancellation method based on the error probability thresholding, feasible more accurate based on the decision method of error probability thresholding, thus the performance of interference cancellation method and the performance of code division multiple access system improved.

In order to solve the problems of the technologies described above, the invention provides in a kind of code division multiple access system based on the interference cancellation method of error probability thresholding, comprise following steps:

A receiving demodulation output signal;

B calculates two judgement threshold values;

C judges whether described demodulated output signal value is in two described judgements with between the threshold value, if putting court verdict is invalid value, does not participate in offseting processing, otherwise putting court verdict according to described demodulated output signal value distribution situation is corresponding effective value, and participates in offseting processing;

Described step B also further comprises following substep:

Determine this demodulated symbols prior probability value according to the demodulation result information before this demodulation;

Calculate two judgement threshold values according to described symbol prior probability value and given error probability threshold value.

Wherein, described two judgements are formulated as with threshold value

$T_1=-\frac{{\mathrm{\σ}}_{m,k}^2}{2A(m,k)}[\ln (\frac{1}{T}-1)-\ln \frac{P_{-1}}{P_1}]$

$T_2=\frac{{\mathrm{\σ}}_{m,k}^2}{2A(m,k)}\left[\ln (\frac{1}{T}-1)+\ln \frac{P_{-1}}{P_1}\right]$

Wherein, T ₁Being threshold value one, whether be invalid then get 0 value, perhaps effectively then get-1 value if being used to adjudicate symbol; T ₂Being threshold value two, whether be invalid then get 0 value, perhaps effectively then get+1 value if being used to adjudicate symbol; σ _{M, k} ²Variance for noise in the signal after the demodulation; A (m, during k) for m symbol of transmission, the distortion factor that channel fading causes described symbol; T is described given error probability threshold value; P ₁, P _-1Be respectively the prior probability value that this promptly separates the described symbol value of timing+1 ,-1 for the k time; Ln () takes from right logarithm operation.

The method of described definite symbol prior probability value is: get the symbol posterior probability values that this demodulated symbols prior probability value equals a preceding demodulation result, and described symbol posterior probability values is calculated gained by supposing that a preceding demodulated symbols prior probability evenly distributes, and the natural logrithm value of separating the ratio of the described symbol prior probability of timing value for the k time is formulated as:

Wherein, P ₁, P _-1Be respectively the prior probability value that this promptly separates the described symbol value of timing+1 ,-1 for the k time, (m is the property the taken advantage of distortion factor of channel in the k-1 demodulation of m symbol k-1) to A, and (m k-1) is the k-1 demodulated output signal value of m symbol, σ to Y _{M, k-1}Be the variance of noise in the signal after the k-1 demodulation of m symbol, right logarithm operation is taken from ln () expression.

The method of described definite symbol prior probability value is taken as the ratio of the symbol posterior probability values of a preceding demodulation result for the ratio of the required symbol prior probability of this demodulation value, and described posterior probability values is formulated as by iterative computation gained repeatedly:

P wherein ₁, P _-1Be respectively the prior probability value that this promptly separates the described symbol value of timing+1 ,-1 for the k time, (m is the property the taken advantage of distortion factor of channel in the k-1 demodulation of m symbol k-1) to A, and (m k-1) is the k-1 demodulated output signal value of m symbol, σ to Y _{M, k-1}Be the variance of noise in the signal after the k-1 demodulation of m symbol, right logarithm operation is taken from ln () expression, and ∑ is represented summation operation.

By relatively finding, technical scheme difference with the prior art of the present invention is, on interference cancellation method basis based on the error probability thresholding, the present invention determines this demodulated symbols prior probability according to the demodulation result information before this demodulation in the demodulation repeatedly, such as according to the second order iteration or a more preceding demodulated symbols posterior probability values of high-order iteration gained come this demodulated symbols prior probability value of approximate evaluation, and carry out decision threshold according to the prior probability value and calculate, be used for symbol judgement.

Difference on this technical scheme, brought comparatively significantly beneficial effect, promptly by accurate estimation to the symbol prior probability, improve and adjudicate with the accuracy of threshold value and the reliability of decision method, further improve the validity of interference cancellation method, thereby improved the performance of whole CDMA mobile communication systems.

Description of drawings

Fig. 1 is the decision method flow chart of interference cancellation method according to an embodiment of the invention.

Embodiment

For making the purpose, technical solutions and advantages of the present invention clearer, the present invention is described in further detail below in conjunction with accompanying drawing.

The decision method based on the error probability thresholding of one embodiment of the present of invention is described earlier.

From certain user's of receiving terminal demodulation output signal with Y (m represents it is that the corresponding demodulation of m symbol is exported for m, k) expression, and k represents it is the output result of the k time demodulation, then Y (m k) can be expressed from the next:

Formula one Y (m, k)=A (m, k) a (m)+n (m, k)

Wherein, a (m) is this user's a m symbol, and value is+1 or-1; A (m k) is the property the taken advantage of distortion factor that channel fading causes symbol, and A (m, k)＞0; N (m k) is additive white Gaussian noise, obey the N that distributes just very much (0, σ _{M, k} ²), average is 0, σ _{M, k} ²Be variance.

Here, the n of normal distribution (m, probability density function k) is:

Formula two $f\left(x\right)=\frac{1}{\sqrt{2\mathrm{\π}}{\mathrm{\σ}}_{m,k}}\exp (-\frac{x^2}{2{\mathrm{\σ}}_{m,k}^2})$

Wherein, f is the probability density value, and x is the value variable, and exp () represents the exponent arithmetic of natural constant e.

Formula one can physical interpretation be: arrive receiving terminal when symbol a (m) sends through channel from transmitting terminal, channel makes this symbol produce the property the taken advantage of distortion (first) of channel fading and the additivity distortion (second) of white Gaussian noise.This is a public channel model.

The demodulation first time of subscriber signal is that baseband signal is carried out demodulation, and each demodulation after this all is to carry out after the interference cancellation of a preceding demodulation is handled, and also promptly the later baseband signal of a preceding interference cancellation is carried out demodulation.

In one embodiment of the invention, earlier hypothesis is expressed as P{a (m)=1}=P in receiving terminal symbol a (m) value respectively for+1 and-1 prior probability ₁, P{a (m)=-1}=P _-1, wherein P{} represents the probable value that situation takes place in the bracket.

The present invention adopts the demodulation result information before this demodulation to calculate the prior probability P of the symbol value that this demodulation will use ₁, P _-1In a preferred embodiment of the present invention, adopt the symbol posterior probability values that calculates according to a preceding demodulation result, determine to calculate in this demodulation the required symbol prior probability value of decision threshold, i.e. P ₁, P _-1This paper will specifically set forth the method for compute sign prior probability value again after describing the computational methods of decision threshold.

When the k time demodulated output signal Y (m, k) through the consequential signal behind the hard decision be d (m, k), then d (m k) is expressed as:

Formula three

Because the distortion of channel, obviously hard decision can produce mistake, and the mistake here is meant court verdict d (m, k) situation about not conforming to former symbol a (m).According to probability theory, under known hard decision result's situation, can extrapolate hard decision and wrong probability expression occur, reasoning process is as follows, and error probability is expressed as Pe:

When court verdict d (m, k)=-1, promptly Y (m, k)＜0 o'clock, error probability is:

$\mathrm{Pe}(m,k)=P\{a\left(m\right)=+1|d(m,k)=-1\}$

$=P\{a\left(m\right)=+1|Y(m,k)<0\}$

$=\frac{P\{a\left(m\right)=+1,Y(m,k)<0\}}{P\{Y(m,k)<0\}}$

$=\frac{P\{a\left(m\right)=+1,Y(m,k)<0\}}{P\{a\left(m\right)=-1,Y(m,k)<0\}+P\{a\left(m\right)=+1,Y(m,k)<0\}}$

$\frac{P_1{f}_1\left(Y(m,k)\right)}{{\{P}_1{f}_1\left(Y(m,k)\right)+P_{-1}{f}_{-1}\left(Y(m,k)\right)}$

When court verdict d (m, k)=+ 1, promptly Y (m, k) 〉=0 o'clock, error probability is:

$\mathrm{Pe}(m,k)=P\{a\left(m\right)=-1|d(m,k)=+1\}$

$=P\{a\left(m\right)=-1|Y(m,k)\&GreaterEqual;0\}$

$=\frac{P\{a\left(m\right)=-1,Y(m,k)\&GreaterEqual;0\}}{P\{Y(m,k)\&GreaterEqual;0\}}$

$=\frac{P\{a\left(m\right)=-1,Y(m,k)\&GreaterEqual;0\}}{P\{a\left(m\right)=+1,Y(m,k)\&GreaterEqual;0\}+P\{a\left(m\right)=-1,Y(m,k)\&GreaterEqual;0\}}$

$\frac{P_{-1}{f}_{-1}\left(Y(m,k)\right)}{{\{P}_1{f}_1\left(Y(m,k)\right)+P_{-1}{f}_{-1}\left(Y(m,k)\right)}$

(m, k) probability distribution of value can obtain the expression formula with every probability in the following formula, wherein function f according to Y ₁(y) and f _-1(y) expression formula is shown by formula five, formula six, so error probability Pe (m, k) can unify to be expressed as:

Formula four

Formula five $f_1\left(y\right)=\frac{1}{\sqrt{2\mathrm{\&pi;}}{\mathrm{\&sigma;}}_{m,k}}\exp (-\frac{{(y-A(m,k))}^2}{2{\mathrm{\&sigma;}}_{m,k}^2})$

Formula six $f_2\left(y\right)=\frac{1}{\sqrt{2\mathrm{\&pi;}}{\mathrm{\&sigma;}}_{m,k}}\exp (-\frac{{(y+A(m,k))}^2}{2{\mathrm{\&sigma;}}_{m,k}^2})$

According to formula four calculate gained hard decision results error probability Pe (m, k), a given error probability threshold T, T value 0＜T＜1, and agreement, when Pe (m, k)＞T, this moment, error probability was big and court verdict does not participate in offseting processing; (m, k)≤T, this moment, court verdict participated in offseting processing as Pe.

(m k), can calculate with respect to Y (m, two judgement threshold T up and down k) according to formula four for given T value and demodulated output signal Y ₁, T ₂, be expressed as:

Formula seven $T_1=-\frac{{\mathrm{\&sigma;}}_{m,k}^2}{2A(m,k)}[\ln (\frac{1}{T}-1)-\ln \frac{P_{-1}}{P_1}]$

Formula eight $T_2=-\frac{{\mathrm{\&sigma;}}_{m,k}^2}{2A(m,k)}[\ln (\frac{1}{T}-1)+\ln \frac{P_{-1}}{P_1}]$

Wherein ln () is for taking from right logarithm operation.

When threshold value is used in the judgement of this demodulation of calculating in formula seven, the formula eight, also need to know prior probability P ₁, P _-1Value, as previously mentioned, in a preferred embodiment of the present invention, with the preceding symbol posterior probability P that once is the k-1 time demodulation result ₁' (k-1), P _-1' (k-1) value replaces this i.e. required prior probability P of the k time demodulation ₁, P _-1Value.Here use P ' ₁, P ' _-1The expression posterior probability is used P ₁, P _-1The expression prior probability.

According to top derivation, the symbol posterior probability P of the k-1 time demodulation result ₁' (k-1), P _-1' (k-1) value representation is:

Formula nine ${P^{\&prime;}}_1(k-1)=\frac{P_1^0{f}_1\left(Y(m,k-1)\right)}{P_1^0{f}_1\left(Y(m,k-1)\right)+P_{-1}^0{f}_{-1}\left(Y(m,k-1)\right)}$

Formula ten ${P^{\&prime;}}_{-1}(k-1)=\frac{P_{-1}^0{f}_{-1}\left(Y(m,k-1)\right)}{P_1^0{f}_1\left(Y(m,k-1)\right)+P_{-1}^0{f}_{-1}\left(Y(m,k-1)\right)}$

P wherein ₁ ⁰, P _-1 ⁰The symbol prior probability that sets when being illustrated in the posterior probability of calculating the k-1 time demodulation is different from P ₁, P _-1, also being different from the k-1 time and separating the symbol prior probability that adopts when timing promptly calculates the k-1 time judgement with threshold value, both existence are the approximate relation of same order not.

In a preferred embodiment of the present invention, put the required prior probability P of the k time demodulation ₁, P _-1Value is the symbol posterior probability P of the k-1 time demodulation result ₁' (k-1), P _-1' (k-1) be worth, can obtain according to formula nine, formula ten:

Formula 11 $\ln \frac{P_{-1}}{P_1}=\ln \frac{{P_{-1}}^{\&prime;}(k-1)}{{P^{\&prime;}}_1(k-1)}\ln \frac{P_{-1}^0}{P_1^0}+\ln \frac{f_{-1}\left(Y(m,k-1)\right)}{f_1\left(Y(m,k-1)\right)}$

P wherein ₁ ⁰, P _-1 ⁰Definite method of value can be weighed processing according to the required precision and the implementation complexity limit of practical situations.

In one embodiment of the invention, consider that implementation complexity can not be too high, with P ₁ ⁰, P _-1 ⁰Directly be approximately equally distributed prior probability value, i.e. P ₁ ⁰=P _-1 ⁰=0.5, can obtain the precision of second order iterative approximation like this, so substitution formula 11 can obtain following formula, wherein the prior probability of demodulation is for the first time got even distribution automatically:

Formula 12 $\ln \frac{P_{-1}}{P_1}=\ln \frac{f_{-1}\left(Y(m,k-1)\right)}{f_1\left(Y(m,k-1)\right)}=-\frac{2A(m,k-1)Y(m,k-1)}{{\mathrm{\&sigma;}}_{m,k-1}^2}$ (when k=1, its value is 0)

In another embodiment of the present invention, consider required precision earlier, so with P ₁ ⁰, P _-1 ⁰Be taken as the posterior probability values of the k-2 time demodulation, can obtain the precision of k rank iterative approximation like this, so substitution formula 11 can obtain following formula, wherein the prior probability of demodulation is for the first time got even distribution automatically:

$\ln \frac{P_{-1}}{P_1}=\ln \frac{{P_{-1}}^{\&prime;}(k-2)}{{P^{\&prime;}}_1(k-2)}+\ln \frac{f_{-1}\left(Y(m,k-1)\right)}{f_1\left(Y(m,k-1)\right)}$

Formula 13 $=\underset{k^{\&prime;}=2}{\overset{k}{\mathrm{\&Sigma;}}}\ln \frac{f\left(Y(m,k^{\&prime;}-1)\right)}{f\left(Y(m,k^{\&prime;}-1)\right)}$

$=\underset{k^{\&prime;}=2}{\overset{k}{\mathrm{\&Sigma;}}}\frac{2A(m,k^{\&prime;}-1)Y(m,k^{\&prime;}-1)}{{\mathrm{\&sigma;}}_{m,k^{\&prime;}-1}^2}$ (when k=1, its value is 0)

σ in last two formulas _{M, k-1}Represent to separate the mean square deviation of timing channel additive Gaussian noise the k-1 time of m symbol.

Those of ordinary skill in the art are appreciated that, definite method of described prior probability can be according to practical situations, disclose in essence in the present invention, suitably revise, can increase an adjustable correction factor or increase a constant etc. such as formula 12, formula 12, and not influence the spirit and scope of the invention.

Formula 12 or formula 13 substitution formulas seven and formula eight can be calculated two judgements with probability threshold value T ₁, T ₂

So, described judgment condition equivalence be converted to Y (m, k) the judgement relation of value, and with d ' (m, k) represent final judging result:

Formula 14

Those of ordinary skill in the art are appreciated that in the described decision method that the mathematic sign of addressing and the form of mathematical formulae can change according to the judgement principle, and do not influence the spirit and scope of the invention.

Below according to this decision method, and with reference to Fig. 1, the step of the decision method of the k time demodulation of the interference cancellation method of corresponding certain subscriber signal of detailed description.

As shown in Figure 1, at first enter step 101, receive this demodulated output signal Y (m, k).The expression formula of described demodulated output signal is a formula one.

Then enter step 102, determine this demodulated symbols prior probability value according to the demodulation result information before this demodulation, computational methods see that the difference front of the computational methods that formula 12 or formula 13, two formulas are represented addresses; When calculating the prior probability value here, need use a preceding demodulation result parameter, suppose that then prior probability evenly distributes in the time of for the first time.

Then enter step 103, calculate the judgement threshold T according to described symbol prior probability value and given error probability threshold T ₁, T ₂The computational methods of described threshold value are seen formula seven, formula eight, and the error probability threshold T here can be set in advance according to actual conditions, also can adjust at any time according to the channel quality.

Then enter step 104, judge (whether m k) satisfies and concern T Y ₁＜Y (m, k)＜T ₂, if, the error probability height is described, then enter step 105, otherwise, enter step 106.(m, when k) being in up and down between two thresholdings, the court verdict error probability is higher, does not participate in offseting as Y in explanation by inference.

In step 105, put court verdict d (m, k)=0.Expression is not participated in and is offseted processing, finishes the interference cancellation of this subscriber signal and handles.

In step 106, court verdict d (m, k)=+ 1 (when Y (m, k) 〉=T ₂) or-1 (when Y (m, k)≤T ₁), and offset processing accordingly, then finish the interference cancellation of this subscriber signal and handle.The described method of processing that offsets is because of different interference cancellation method differences.

Wherein, in the time of demodulation for the first time, promptly during k=1, the symbol prior probability is taken as even distribution, illustrates in formula 12, formula 13.

The step of described decision method goes for the interference cancellation method of various different structures, and as successive interference cancellation method, parallel interference cancellation method etc., and corresponding other steps that are included in the interference cancellation method are identical with the technical scheme of present usefulness.

In the step of described interference cancellation method, the used processing method that offsets can be used the feasible program that exists in the existing technology with mechanism.

Though by reference some preferred embodiment of the present invention, the present invention is illustrated and describes, but those of ordinary skill in the art should be understood that, can do various changes to it in the form and details, and the spirit and scope of the present invention that do not depart from appended claims and limited.

Claims (4)

1. In the code division multiple access system based on the interference cancellation method of error probability thresholding, comprise following steps:

   A receiving demodulation output signal;

   B calculates two judgement threshold values;

   C judges whether described demodulated output signal value is in two described judgements with between the threshold value, if putting court verdict is invalid value, does not participate in offseting processing, otherwise putting court verdict according to described demodulated output signal value distribution situation is corresponding effective value, and participates in offseting processing;

   It is characterized in that described step B comprises following substep:

   Determine this demodulated symbols prior probability value according to the demodulation result information before this demodulation;

   Calculate two judgement threshold values according to described symbol prior probability value and given error probability threshold value.
2. 2. based on the interference cancellation method of error probability thresholding, it is characterized in that in the code division multiple access system according to claim 1 that described two judgements are formulated as with threshold value

   $T_1=-\frac{{\mathrm{\&sigma;}}_{m,k}^2}{2A(m,k)}[\ln (\frac{1}{T}-1)-\ln \frac{P_{-1}}{P_1}]$

   $T_2=\frac{{\mathrm{\&sigma;}}_{m,k}^2}{2A(m,k)}[\ln (\frac{1}{T}-1)+\ln \frac{P_{-1}}{P_1}]$

   Wherein, T ₁Being threshold value one, whether be invalid then get 0 value, perhaps effectively then get-1 value if being used to adjudicate symbol; T ₂Being threshold value two, whether be invalid then get 0 value, perhaps effectively then get+1 value if being used to adjudicate symbol; σ _{M, k} ²Variance for noise in the signal after the demodulation; A (m, during k) for m symbol of transmission, the distortion factor that channel fading causes described symbol; T is described given error probability threshold value; P ₁, P _-1Be respectively the prior probability value that this promptly separates the described symbol value of timing+1 ,-1 for the k time; Ln () takes from right logarithm operation.
3. 3. in the code division multiple access system according to claim 2 based on the interference cancellation method of error probability thresholding, it is characterized in that, the method of described definite symbol prior probability value is: get the symbol posterior probability values that this demodulated symbols prior probability value equals a preceding demodulation result, and described symbol posterior probability values is calculated gained by supposing that a preceding demodulated symbols prior probability evenly distributes, and the natural logrithm value of separating the ratio of the described symbol prior probability of timing value for the k time is formulated as:

   Wherein, P ₁, P _-1Be respectively the prior probability value that this promptly separates the described symbol value of timing+1 ,-1 for the k time, (m is the property the taken advantage of distortion factor of channel in the k-1 demodulation of m symbol k-1) to A, and (m k-1) is the k-1 demodulated output signal value of m symbol, σ to Y _{M, k-1}Be the variance of noise in the signal after the k-1 demodulation of m symbol, right logarithm operation is taken from ln () expression.
4. 3. in the code division multiple access system according to claim 2 based on the interference cancellation method of error probability thresholding, it is characterized in that, the method of described definite symbol prior probability value is taken as the ratio of the symbol posterior probability values of a preceding demodulation result for the ratio of the required symbol prior probability of this demodulation value, and described posterior probability values is passed through repeatedly iterative computation gained, is formulated as:

   P wherein ₁, P _-1Be respectively the prior probability value that this promptly separates the described symbol value of timing+1 ,-1 for the k time, (m is the property the taken advantage of distortion factor of channel in the k-1 demodulation of m symbol k-1) to A, and (m k-1) is the k-1 demodulated output signal value of m symbol, σ to Y _{M, k-1}Be the variance of noise in the signal after the k-1 demodulation of m symbol, right logarithm operation is taken from ln () expression, and ∑ is represented summation operation.

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