WO2007041900A1

WO2007041900A1 - A mixed-path processing method in cdma system

Info

Publication number: WO2007041900A1
Application number: PCT/CN2005/001667
Authority: WO
Inventors: Jiewei Ding; Ling Li; Zhen Ren; Haiyan Xu
Original assignee: Zte Corporation
Priority date: 2005-10-11
Filing date: 2005-10-11
Publication date: 2007-04-19
Also published as: CN101167287B; CN101167287A

Abstract

The technical scheme of a mixed-path processing method in CDMA system is that: when two multi-paths are very close to each other, if the energy of each multi-path is equivalent, they should only slide in opposite direction or keep the current position; if the energy of one multi-path is evidently higher than the other, then the strong one can slide freely, and the weak one can only slide in a deviating direction apart from the strong path. On the basis of said above, a further rule is included in order to enhance the performance, i.e. when the weak multi-path is very close to the strong one and still slides to the strong one, then delete the weak path. If the present method is adopted, it can keep a stable multi-path updating when processing a closer multi-path updating, and can prevent multi-paths sliding to each other, and thus improve the demodulating performance.

Description

Code division multiple access system fat path processing method

Technical field

The present invention relates to the field of wireless communication technologies, and in particular, to a fat path processing method in multipath update of a code division multiple access (CDMA) wireless communication system. Background technique

CDMA is a multiple access method based on spread spectrum technology and has recently become a method of addition to existing Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA) methods. Another multiple access method applied to communication systems. Compared to existing methods, CDMA has many advantages, such as high spectrum utilization and simple planning. The systems currently using the CDMA method mainly include: narrowband CDMA (Interim Standard 95 (IS-95)) system, Wideband CDMA (WCDMA) system, CDMA2000 system, time division synchronous code division multiple access. (Time Division Synchronous Code Division Multiple Access, TD-SCDMA for short) system and Time Division-Code Division Multiple Access (TD-CDMA) system.

In a typical mobile communication environment, signals between a base station and a mobile station propagate along several paths between the receiver and the transmitter. This multipath propagation phenomenon is mainly caused by the reflection of signals on the surface of the object around the transmitter and receiver. Due to the propagation path Similarly, the propagation delay of the same signal arriving at the receiver along different paths is also different, resulting in multipath interference and signal fading.

A receiver used in a CDMA system is a multi-branch receiver in which each branch is substantially synchronized with the same propagation path delay. Each branch is a separate receiver component that functions to demodulate the desired received signal components and combine the different receiver component signals to improve received signal quality. This kind of receiver is also called Rake (hereinafter referred to as Rake) receiver, which can superimpose the energy of the same user's different delay paths according to certain rules, thereby improving the receiving performance. Each of these branches is also called finger, or demodulated multipath.

The synchronization of the local spreading code with the spreading code in the received signal is a prerequisite for normal communication in a CDMA system. If the spread code synchronization cannot be obtained, the original information cannot be correctly despread and the original information cannot be solved correctly. Multipath search is to detect the multipath signal propagation delay from the received signal, which can be called Path, or search for multipath. Based on these search multipaths, the local spreading code in the Rake receiver is adjusted to be synchronized with the spreading code of each multipath information in the received signal. Therefore, in a CDMA system, the Rake receiver updates the finger parameters of the Rake receiver based on the multipath result Path searched by the multipath search module. If the update process is unreasonable, the demodulation performance of the Rake receiver will be lost.

In addition, for more timely and accurate synchronization of the spreading code, the industry also generally adopts a multipath tracking method. The multipath tracking module compares the demodulated multipath position, slightly earlier than the demodulation multipath position, and slightly later than the demodulation multipath. The demodulation energy between the locations is used to estimate whether the true multipath should be earlier or later than the current demodulation multipath position, and the demodulation multipath position is adjusted based on the estimation result. Among them, the multipath tracking method is also called the early and late door tracking method.

Taking the WCDMA system as an example, the resolution of multipath is about one chip (hereinafter referred to as Chip), corresponding to 78.125 meters in the air, that is to say, in the general urban environment, there are often multiple paths with similar distances. The channel environment of Case3 and Case4 is specified in the 3rd Generation Partnership Project (3GPP). There are four multipaths in this channel environment, and each multipath is separated by lchip. In the multipath search module, the four multipaths are mixed together, like a fat path, which is more difficult to distinguish. Like two or more such multipaths that are close together and interact with each other, this is referred to as a fat path phenomenon in this specification. In the actual wireless environment, the fat path phenomenon may also occur. If the multipath tracking method described above is used, and the fingers are free to slide independently, these multipaths can easily slide together. The results of the multipath search module are also likely to make these multipaths slip together. For Case3 or fat path, a certain restriction method is needed instead of sliding these multipaths together. This method can be called a fat path processing method.

So far, a lot of multipath search and multipath tracking methods have been proposed in the public data, and a few of them refer to the fat path processing method. For example, in the Chinese patent "Online Multipath Tracking Method for Wideband Code Division Multiple Access (WCDMA) System", the application number is 03116715, and the US Patent "Pattern Generation Circuit" with the publication number 20010010703, using the same A method of peak interference removal is mentioned in "pattern generation circuit, multi-path detection circuit employing the same and multi-path detection method". In the Chinese patent "Assignment and Redistribution of CDMA Second Fingers" with application number 01816460, a method of adjusting the time tracking loop speed is mentioned. In the Japanese Patent "CDMA Signaling Receiver"("CDMA Signaling RECEIVERS"), which discloses the amplitude and the phase angle, a method of distinguishing multipath is proposed, which is complicated to calculate. Summary of the invention

In view of the above, it is an object of the present invention to provide a compact and efficient CDMA system fat path processing method to solve the problem of close proximity multipath position adjustment.

The technical problem to be solved by the present invention is: a multipath position adjustment problem when the delay difference of each multipath in a multipath update in a CDMA system base station or a mobile station is small.

In order to solve the above technical problem, the technical solution adopted by the present invention is: when the two multipaths are close together, if the energy of the two multipaths is equal, the sliding can only be moved in the direction of the deviation or in the original position; If the energy of the multipath is obviously stronger than the other multipath, the strong path can slide freely, and the weak path can only slide away from the strong path. On the basis of the above, a rule can be added to further improve the performance, that is, when the weaker multipath is too close to the strong path and also slides in the direction of the strong diameter, the weak path is deleted.

To achieve the above object, a method for processing a fat path of a CDMA system of the present invention includes the following steps:

The multipath search module or the multipath tracking module steps up the phase slip request of the multipath Fingerl, and the phase of the multipath Fingerl is Offsetl, and the energy is Energyl; Step 2: Find the closest phase to the multipath Fingerl in the sliding direction. Multipath, if such a multipath Finger2 is found, record the energy of the multipath Finger2 as Energy2 and the phase as Offset2, and calculate the multipath phase difference variable: DeltaOffset=abs(Offsetl -Offset2), where abs() means absolute Value

If such a multipath is not found, the above multipath phase difference variable is assigned: DeltaOffset = INVALID_VALUE , where the INVALID_VALUE represents an invalid value, and the true multipath phase difference variable does not take this value; Step 3: It is determined whether the multipath phase difference variable DeltaOffset is not equal to the above INVALID_VALUE, and whether the multipath phase difference variable DeltaOffset is less than the threshold value OffsetTh; if the condition is not satisfied, step 5 is performed; otherwise, step 4 is performed; : Determine whether K*Energy2<Energyl, where K is a coefficient greater than 1; if the condition is not true, proceed to step 6; otherwise, perform step 5;

Step 5: Update the phase of the multipath Fingerl according to the request of step 1 above, and the current multipath update ends;

Step 6: Keep the phase of the multipath Fingerl unchanged, and the multipath update ends. The threshold value OffsetTh in the above step 3 does not exceed lchip.

To achieve the above object, another CDMA system fat path processing method of the present invention includes the following steps:

Step 1: The multipath search module or the multipath tracking module lifts the phase slip request of the multipath Fingerl, and the phase of the multipath Fingerl is Offsetl, and the energy is Energyl; Step 2: Find the phase with the multipath Fingerl in the sliding direction. Close multipath, if such a multipath Finger2 is found, record the energy of the multipath Finger2 as Energy2 and phase 0ffset2, and calculate the multipath phase difference variable: DeltaOffset=abs(Offsetl -0ffset2), where abs() indicates Take the absolute value;

If such a multipath is not found, the above multipath phase difference variable is assigned: DeltaOffset = INVALID_VALUE, where INVALID_VALUE represents an invalid value, and the true multipath phase difference variable does not take this value;

Step 3: Determine whether the multipath phase difference variable DeltaOffset is not equal to INVALID_VALUE, and whether the multipath phase difference variable DeltaOffset is smaller than Threshold OffsetTh; If the condition is not met, go to step 6; otherwise, go to step 4; Step 4: Determine if K*Energy2<Energyl, where K is a coefficient greater than 1; if the condition is true, go to step 6; otherwise, perform step 5 ;

Step 5: Determine whether the multipath phase difference variable DeltaOffset is less than the threshold OffsetThDel, and Energy l<Energy2; If the condition is met, go to step 7; otherwise, go to step 8;

Step 6: Update the phase of the multipath Fingerl according to the request of step 1, and the current multipath update ends;

Step 7: Delete the multipath Fingerl, and the multipath update ends.

Step 8: Keep the phase of the multipath Fingerl fixed, and the multipath update ends. The threshold value OffsetTh in the above step 3 does not exceed lchip; and the above steps

The threshold in 5 is OffsetThDel, whose value is less than or equal to lchip.

By adopting the method of the invention, it is possible to maintain a relatively stable multipath update when dealing with relatively close multipath updates, and prevent multipath slipping to improve the demodulation performance.

The above and other objects, features and advantages of the present invention will become more <RTIgt; DRAWINGS

1 is a flow chart of a first embodiment of the method of the present invention.

2 is a flow chart of the second method of the method of the present invention.

Figure 3 is a graph showing the variation of the multipath phase by the conventional method.

4 is a diagram showing the variation of the demodulation multipath phase of the second method of the method of the present invention. Fig. 5 is a distribution diagram of demodulation energy by a conventional method.

6 is a distribution diagram of demodulation energy of the second method of the method of the present invention.

Figure 7 is a graph showing the variation of multipath energy over time in a conventional method.

FIG. 8 is a graph showing changes in multipath energy with time according to the second method of the method of the present invention. 9 is a comparison diagram of demodulation performance of the conventional method and the second method of the method of the present invention. detailed description

The invention will now be further described in detail with reference to the drawings and embodiments. The present invention can be easily implemented by those skilled in the art from the drawings.

When the multipath search module or multipath tracking module requires updating the phase of a multipath and the phase change amount is less than 1 chip, it can be called multipath phase slip. The conventional method is to directly update the multipath phase as requested by the multipath search module or the multipath tracking module. However, the method of the present invention makes three kinds of decisions according to different situations: updating, not updating or deleting the multipath according to the request.

1 is a flow chart of a first embodiment of the method of the present invention. As shown in Figure 1, it includes the following steps:

The processing block 101 corresponds to the first step of the first method of the method of the present invention. In this step, the multi-path search module or the multipath tracking module proposes a phase slip request for a multipath Fingerl, and the current phase of the multipath is assumed to be Offsetl, the energy is Ene _r gy2, the sliding request is to make the phase Offsetl of the multipath Fingerl move backward, that is, the phase Offsetl increases; the processing block 102 corresponds to the second step of the first method of the method of the present invention, the purpose of this step is to judge Whether there is multipath in the sliding direction of multipath Fingerl, if there is (called multipath Finger2, whose phase is Offset2, the energy is Energy2), calculates the difference between the phase Offset2 and the phase Offsetl; the specific method may be: finding the multipath closest to the phase of the multipath Fingerl in the sliding direction, and calculating the multipath phase if found The difference variable DetlaOffset = abs(Offsetl -Offset2), where abs() indicates the absolute value; if not found, the multipath phase difference variable DeltaOffset = INVALID_VALUE, where INVALID_VALUE is an invalid value, true It is impossible to take this value for multipath phase difference;

The determination block 103 corresponds to the third step of the first method of the method of the present invention, which determines whether the multipath phase difference variable DeltaOffset is not equal to INVALID_VALUE, and whether the multipath phase difference variable DeltaOffset is smaller than the threshold value OffsetTh, where the threshold is The value OffsetTh does not exceed lchip; if this condition is true, the fourth step is performed; if not, the fifth step of the first scheme (corresponding to the block 105) is performed, and the phase of the multipath Fingerl is updated as required by the first step;

The determining block 104 corresponds to the fourth step of the first method of the method of the present invention, which determines whether K*Energy2 is less than Energyl, where K is a coefficient not less than 1; if the condition is satisfied, the fifth step of the first scheme is executed (corresponding box) 105), update the phase of the multipath Fingerl according to the requirements of the first step; if the condition is not established, execute the sixth step of the first scheme (corresponding to the block 106), and keep the phase of the multipath Fingerl unchanged.

2 is a flow chart of the second method of the method of the present invention. The processing blocks 201, 202 and the decision blocks 203, 204 are the same as the processing blocks 101, 102 and the decision frames 103, 104 in Fig. 1, respectively, and are not repeated here.

The determining block 205 corresponds to the fifth step of the second method of the method of the present invention, and the judging multipath phase Bit difference variable DeltaOffset is smaller than a threshold OffsetthDel, and Energy 1 is smaller than En _erg _y2; If the condition is satisfied is executed program step II, VII (corresponding to block 207), remove multipath Fingerl; If the condition is not established on the second solution is performed In eight steps (corresponding to block 208), the phase of the multipath Finger is kept stationary. Adding the option to delete multipath can make the multipath adjustment method more flexible, and can handle the case where two multipaths slide to one position.

Figure 3 is a graph showing the variation of the multipath phase of the conventional method, which is the test result of the dual antenna reception in the case of C _aS e3. As shown in Fig. 3, the horizontal axis is the time axis and its unit is 10 ms; the vertical axis is the multipath delay phase Offset, and its unit is l/8 chip. The four horizontal lines in Figure 3 are the four true multipaths in the Case3 wireless environment defined in the protocol. The average energy of the first true multipath 1 in Case3 is the strongest, and the average energy of the second true multipath 2 is For the first half of the real multipath 1, the average energy of the third true multipath 3 is half of the second true multipath 2, and the average energy of the fourth true multipath 4 is the third true multipath 3 Half of the four multipaths have the same phase, but there is fading, that is, the energy changes with time. The curves in Fig. 3 are the curves of the phase of the demodulation multipath of each real multipath with time. The phase changes of these demodulation multipaths are controlled by the multipath search module or the multipath tracking module. As can be seen from Fig. 3, in addition to the fact that the true multipath 1 with the strongest average energy remains demodulated more stably, the demodulation multipath at the other three true multipath positions often slides toward the true multipath 1 and demodulates. Multipath cannot be maintained on the correct true multipath phase.

4 is a diagram showing the variation of the demodulation multipath phase of the second method of the method of the present invention. The test conditions are the same as those of the test conditions in Fig. 3. As can be seen from Fig. 4, each of the demodulated multipaths can be stably maintained at the phase positions of the four true multipaths, and is not as shown in Fig. 3. Total It is sliding in the direction of the strongest diameter.

Figure 5 is a distribution diagram of demodulation energy by a conventional method. The test conditions are the same as those in Figure 3, as shown in Figure 5. From the demodulation energy distribution, it can be seen that there are three more obvious multipaths, the energy of the fourth multipath is small, and each multipath There is also some energy between them.

6 is a distribution diagram of demodulation energy of the second method of the method of the present invention. The test conditions are the same as those in Fig. 5. As shown in Fig. 6, from the demodulation energy distribution, there are obvious four multipaths, and the separation between the four multipaths is clear, unlike the four multipaths as shown in Fig. 5. The energy is rather vague. It can also be seen from this figure that the method of the present invention can efficiently collect the energy of multipath. Fig. 7 is a graph showing the variation of multipath energy with time in the conventional method. The test conditions are the same as in Fig. 3, as shown in Fig. 7, it is difficult to distinguish several multipaths from this figure.

FIG. 8 is a graph showing changes in multipath energy with time according to the second method of the method of the present invention. The test conditions are the same as those in Figure 7, as shown in Figure 8. From this figure, it can be clearly seen that there are four multipaths, which is also the four multipaths in Case3.

9 is a comparison diagram of demodulation performance of the conventional method and the second method of the method of the present invention. As shown in Fig. 9, the abscissa is the ratio Eb/N0 of the signal energy to the noise power spectral density, in dB, and the ordinate is the block error rate BLER. Under the same Eb/NO condition, the smaller the block error rate BLER, the better the communication quality. Under the same block error rate BLER condition, the smaller the required Eb/NO is, the better. Curve 1 in Fig. 9 is a demodulation performance curve of the conventional method, and curve 2 is a demodulation performance curve of the second method of the method of the present invention. As can be seen from the figure, when the block error rate BLER is the same, the Eb/NO required by the method of the present invention is about ldB smaller than the conventional method, which is a very considerable performance gain. Furthermore, testing the method of the present invention in a wireless environment such as a Case4 mobile channel is also significantly superior to conventional methods.

It can be seen from the above analysis that according to the method of the present invention, the fat path can be well handled, the system performance is improved, and the method of the present invention is simple to implement.

The above is a detailed description of the working principle of the present invention, but this is merely a visual example for the purpose of understanding, and should not be construed as limiting the scope of the invention. Also, various possible modifications or substitutions may be made in accordance with the description of the technical solutions of the present invention and the preferred embodiments thereof, and all such changes or substitutions are intended to fall within the scope of the appended claims.

Claims

Rights request

A fat path processing method for a code division multiple access system, comprising the steps of _: step 1: multipath search module or multipath tracking module lifting a phase slip request of multipath Fingerl, and recording a phase of multipath Fingerl Offsetl, the energy is Energyl; Step 2: Find the multipath closest to the phase of the multipath Fingerl in the sliding direction. If such a multipath Finger2 is found, record the energy of the multipath Finger2 as Energy2 and the phase is Offset2, and Calculate the multipath phase difference variable: DeltaOffset = abs(Offsetl -Offset2) _;

If such a multipath is not found, assign the above multipath phase difference variable: DeltaOffset = INVALID_VALUE , where INVALID_VALUE represents an invalid value;

Step 3: determining whether the multipath phase difference variable DeltaOffset is not equal to the above INVALID_VALUE, and whether the multipath phase difference variable DeltaOffset is less than the threshold value OffsetTh; if the condition is not satisfied, step 5 is performed; otherwise, step 4 is performed;

Step 4: Determine whether K*Energy2<Energyl, where K is a coefficient greater than 1; if the condition is not true, proceed to step 6; otherwise, perform step 5;

Step 6: Keep the phase of the multipath Fingerl unchanged, and the multipath update ends.

2. The method of claim 1 wherein the gate in step 3 above The limit OffsetTh does not exceed 1 chip.

A method for processing a fat path of a code division multiple access system, comprising the steps of: Step 1: multipath search module or multipath tracking module lifting a phase slip request of multipath Fingerl, and recording a phase of multipath Fingerl Offsetl, the energy is Energyl; Step 2: Find the multipath closest to the phase of the multipath Fingerl in the sliding direction. If such a multipath Finger2 is found, record the energy of the multipath Finger2 as Energy2 and the phase is Offset2, and Calculate the multipath phase difference variable: DeltaOffset= abs(Offsetl -Offset2) _;

If such a multipath is not found, the above multipath phase difference variable is assigned a value - DeltaOffset = INVALID - VALUE, where the INVALID - VALUE represents an invalid value;

Step 3: It is determined whether the multipath phase difference variable DeltaOffset is not equal to INVALID_VALUE, and whether the multipath phase difference variable DeltaOffset is less than the threshold value OffsetTh; if the condition is not satisfied, step 6 is performed; otherwise, step 4 is performed; Determine whether K*Energy2<Energyl, where K is a coefficient greater than 1; if the condition is met, go to step 6; otherwise, go to step 5;

Step 5: Determine whether the multipath phase difference variable DeltaOffset is less than the threshold OffsetThDel, and Energy Energy 2; if the condition is met, perform step 7; otherwise, perform step 8;

Step 7: Delete the multipath Fingerl, and the multipath update ends. Step 8: Keep the phase of the multipath Fingerl unchanged, and the multipath update ends.

4. The method of claim 3 wherein

The threshold value OffsetTh in the above step 3 does not exceed 1 chip;

The threshold OffsetThDd in the above step 5 has a value less than or equal to 1 chip.