CN1731887A - CDMA system random access threshold multi-path selection method - Google Patents

Abstract

The invention discloses a random access threshold multipath selection method of a code division multiple access system in the field of mobile communication, comprising: 1. processing an input signal; 2. the energy of each multipath of each signature and the primary threshold T1 comparison; 3. The energy of the strongest path in the result of step 2 and the secondary threshold T2; if the energy of the strongest path is greater than T2, the signature is considered valid and further multi-path management is performed; if the energy of the strongest path If it is not greater than T2, then the signature is considered invalid and the demodulation is abandoned; 4. The demodulation unit demodulates the message part of random access; The demodulation error rate dynamically adjusts the preamble detection threshold. The present invention overcomes the disadvantages of difficult threshold selection, too many false alarms, and demodulation unit blockage in the single threshold method in the prior art, and can ensure that there are enough multipaths for message demodulation after effective signature detection. A random access multipath selection method that can ensure low enough false alarms and prevent blocking phenomena.

Description

Random Access Threshold Multipath Selection Method for Code Division Multiple Access System

technical field

The invention relates to a mobile communication system, in particular to a random access (RandomAccess) multipath selection method of a code division multiple access system.

Background technique

With the rapid development of mobile communication, people have higher and higher requirements for the quality of mobile communication and the types of services it provides. The proposal and development of the third generation of mobile communication is exactly in line with this demand of people, so it has attracted much attention. . Wideband Code Division Multiple Access (WCDMA, Wide CDMA) is a Radio Transmission Technology (RTT) solution proposed by the ^3rd Generation Partnership Project (3GPP), which not only provides high-quality Voice services, and can provide multimedia services similar to fixed networks.

In the wideband code division multiple access (WCDMA) system, random access is a very important part of the system, and it is the user equipment (User Equipment, UE, terminal equipment in the WCDMA system) that establishes a dedicated The premise and foundation of the channel, so the performance of the random access part is very important. At present, the random access multipath selection method commonly used is mainly selected through a single threshold (as shown in FIG. 1 ), and all multipaths with energy greater than T2 will be sent to the multipath management module. This method is relatively simple to implement, but in fact it is very difficult to choose the threshold value T2: if T2 is too high, the detected multipath will be very few, so the demodulation performance of the message (the message part of random access) will be greatly reduced ; If T2 is too low, the false alarm may be too high again, and the false alarm will also occupy the message demodulation unit, and may cause blocking in severe cases, because the resources of the demodulation unit are very limited, so that the effective signature has to be to the demodulation unit.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings such as difficulty in threshold selection, too many false alarms, and blockage of demodulation units in the single threshold method existing in the prior art, in order to propose a method that can ensure that when the preamble (the leading part of random access) is effective After the signature (Signature, the sigature information carried in the preamble) is detected, there are enough multipaths for demodulation of the message, and the random access multipath selection method can ensure that the false alarm is low enough to prevent the occurrence of congestion.

In order to achieve the above object, the present invention proposes a random access threshold multipath selection method for a code division multiple access system, which is characterized in that, comprising the following steps:

Step 1: Descrambling, frequency offset, signature, and correlation integration are performed on the input signal to obtain the power delay profile (Power Delay Profile, PDP) of different signatures of the preamble.

The second step: the energy of each multipath of each signature is compared with T1 (primary threshold, the threshold is used twice in this method, this threshold is used first, called the primary threshold), and the multipath greater than T1 is considered useful multipath, and record all useful multipaths.

The third step: compare the energy of the strongest path in the result of the second step with T2 (the second threshold, where T1<T2). If the strongest path energy is greater than T2, the signature is considered valid, and all useful multipaths obtained in the second step are sent to multipath management, and the multipaths obtained after multipath management are used for message (the message part of random access) ) demodulation; if the strongest path energy is not greater than T2, the signature is considered invalid, and the message (the message part of the random access) corresponding to the signature is not demodulated.

The fourth step is to perform further multipath management on all useful multipaths input in the third step. The main processing is that when the phase distance between two adjacent multipaths is less than 1chip (chip, the multipath of the code division multiple access system phase unit), to remove paths with smaller energy. After multipath management, the multipath phase spacing will be no less than 1 chip (chip, the multipath phase unit of CDMA system), and the multipath distribution after multipath management processing will be sent to message (the message part of random access) ) demodulation unit, the demodulation unit will demodulate message (the message part of random access) according to the multipath distribution generated in this step.

In the fifth step, the demodulation of the message (message part of random access) corresponding to the invalid signature is abandoned.

In the sixth step, the demodulation unit will demodulate the message (the message part of the random access) according to the multipath distribution generated in the fourth step.

In the seventh step, according to the result of demodulation in the sixth step, the number of message demodulation errors is counted within a certain period of time, that is, the message demodulation error rate is counted.

The eighth step is to dynamically adjust the preamble detection threshold according to the message demodulation error rate. If the error rate increases, appropriately increase the preamble detection threshold; if the error rate decreases, appropriately decrease the preamble detection threshold. Of course, threshold adjustment should have an upper and lower limit to prevent the feedback loop from diverging, because too high or too low a threshold is detrimental to system performance.

Compared with the prior art, the random access multipath selection method described in the present invention not only utilizes more multipaths to demodulate message parts for effective signatures, improves message demodulation performance, but also ensures low false alarms, preventing The emergence of blocking phenomenon, and at the same time make the random access subsystem work in the best state through the method of dynamic threshold. By adopting the random access multipath selection method described in the present invention, both the simulation result and the actual system test show that the random access performance is obviously improved compared with the prior art random access performance.

Description of drawings

Fig. 1 is a flowchart of a random access multipath selection method in the prior art.

Fig. 2 is a flow chart of the random access threshold multipath selection method of the CDMA system according to the present invention.

Detailed ways

The implementation of the technical solution will be further described in detail below in conjunction with the accompanying drawings. According to these drawings, those skilled in the art can easily realize the present invention.

The present invention mainly proposes a random access multipath selection method for wideband code division multiple access (WCDMA) systems, and a method for sampling the secondary threshold, which not only ensures that there are sufficient multipaths when the message is demodulated, but also ensures The false alarm probability is low enough to improve the random access performance of the communication system.

FIG. 1 is a flowchart of a random access multipath selection method adopted in the prior art in a Wideband Code Division Multiple Access (WCDMA) system.

This logic flow diagram starts at step 101 and ends at step 105 .

Step 101, PDE (Preamble Dection Engine, preamble detection engine), descrambling the input signal (multiplied with the scrambling code), de-frequency offset (multiplied with the frequency offset value), de-signature (related to different signatures) Multiplication), coherent integration (coherent integration according to a given length), so that the power delay distribution (Power Delay Profile, PDP) of 16 signatures is obtained, that is, the energy of all multipaths of each signature is obtained.

Step 102, for each signature, compare the energy of each multipath with T2 (primary threshold), record the energy greater than T2 as useful multipath, and discard the multipath with energy less than T2.

Step 103, from the result of step 102, it can be known whether the energy of the strongest path of the signature is greater than T2, if the energy of the strongest path is not greater than T2, then the signature is an invalid signature, and no AI (Access Indication, access) is sent to the signature. indication), that is, the message (the message part of the random access) corresponding to the signature is not demodulated, that is, enter step 104 . If the energy of the strongest path is greater than T2, it means that the signature is a valid signature, and AI (Access Indication) is sent to the signature, that is, the message (the message part of random access) corresponding to the signature is demodulated, that is, Go to step 105 and step 106.

Step 104, according to the discrimination result of step 103, if it is an invalid signature, then enter this step, promptly discard this signature, do not send AI (Access Indication, access indication) to this signature, namely do not send the message (random access instruction) corresponding to this signature message part) demodulation.

Step 105, according to the judgment result of step 103, if it is a valid signature, enter this step, and perform further multipath management on all useful multipaths recorded in step 102, the main processing is, when the phase distance between two adjacent multipaths Less than 1chip (chip, the multipath phase unit of the code division multiple access system), the path with smaller energy is eliminated. After multipath management, the multipath phase spacing will be no less than 1 chip (chip, the multipath phase unit of CDMA system), and the multipath distribution after multipath management processing will be sent to message (the message part of random access) ) demodulation unit, the demodulation unit will demodulate message (the message part of random access) according to the multipath distribution generated in this step.

Fig. 2 is a flow chart of the random access multipath selection method described in the present invention.

This logic flow diagram starts at step 201 and ends at step 208 .

Step 201, PDE (Preamble Dection Engine, preamble detection engine), descrambling the input signal (multiplied with the scrambling code), de-frequency offset (multiplied with the frequency offset value), de-signature (related to different signatures) Multiplication), coherent integration (coherent integration according to a given length), so that the power delay distribution (Power Delay Profile, PDP) of 16 signatures is obtained, that is, the energy of all multipaths of each signature is obtained.

Step 202, for each signature, compare the energy of each multipath with T1 (primary threshold), record the energy greater than T1 as useful multipath, and discard the multipath with energy less than T1.

Step 203, for each signature, judge whether the signature is a valid signature according to the useful multipath recorded in step 202, if the strongest path energy is not greater than T2 (secondary threshold, T1<T2), then the signature is an invalid signature, Do not send AI (Access Indication, access indication) to the signature, that is, do not demodulate the message (the message part of random access) corresponding to the signature, that is, go to step 204. If the energy of the strongest path is greater than T2, it means that the signature is a valid signature, and AI (Access Indication) is sent to the signature, that is, the message (the message part of random access) corresponding to the signature is demodulated, that is, Go to step 205.

Step 204, according to the discrimination result of step 203, if it is an invalid signature, then enter this step, promptly abandon this signature, do not send AI (Access Indication, access indication) to this signature, namely do not send the message (random access instruction) corresponding to this signature message part) demodulation.

Step 205, according to the judgment result of step 203, if it is a valid signature, enter this step, and perform further multipath management on all useful multipaths recorded in step 202, the main processing is, when the phase distance between two adjacent multipaths Less than 1chip (chip, the multipath phase unit of the code division multiple access system), the path with smaller energy is eliminated. After multipath management, the multipath phase spacing will be no less than 1 chip (chip, the multipath phase unit of CDMA system), and the multipath distribution after multipath management processing will be sent to message (the message part of random access) ) demodulation unit, the demodulation unit will demodulate message (the message part of random access) according to the multipath distribution generated in this step.

In step 206, the message part is demodulated according to the multipath distribution obtained by the multipath management in step 205.

In step 207, according to the result of demodulation in step 206, the error rate of message demodulation (the total number of errors in a certain period of time) is counted.

Step 208, dynamically adjust the preamble detection threshold according to the message demodulation error rate. If the error rate increases, appropriately increase the preamble detection threshold; if the error rate decreases, appropriately decrease the preamble detection threshold. Of course, threshold adjustment should have an upper and lower limit to prevent the feedback loop from diverging, because too high or too low a threshold is detrimental to system performance.

Claims (6)

1, a kind of code division multiple access system random access threshold multipath selection method, is characterized in that, comprises the following steps: Step 1: Descrambling, frequency offset, signature, and correlation integration are performed on the input signal to obtain the power delay distribution of different signatures of the preamble; The second step: the energy of each multipath of each signature is compared with a threshold T1 once, and the multipath greater than T1 is considered as a useful multipath, and all useful multipaths are recorded; Step 3: Compare the energy of the strongest path in the result of the second step with the secondary threshold T2; if the energy of the strongest path is greater than T2, the signature is considered valid; if the energy of the strongest path is not greater than T2, the signature is considered Invalid, go to step 5; The fourth step is to perform further multipath management on all the useful multipaths input in the third step; The fifth step is to abandon the demodulation of the message part corresponding to the random access of the invalid signature; In the sixth step, the demodulation unit will demodulate the random access message part according to the multipath distribution generated in the fourth step; The seventh step is to count the number of message demodulation errors within a certain period of time according to the result of demodulation in the sixth step, that is, to count the message demodulation error rate; The eighth step is to dynamically adjust the preamble detection threshold according to the message demodulation error rate. 2. The CDMA system random access threshold multipath selection method as claimed in claim 1, wherein the processing contents described in the first step include descrambling, de-frequency offset, de-signature, correlation integration and other processes . 3. The CDMA system random access threshold multipath selection method according to claim 1, wherein the relationship between the primary threshold T1 and the secondary threshold T2 described in the second step is: T1<T2 . 4, CDMA system random access threshold multipath selection method as claimed in claim 1, is characterized in that, the main processing described in the 4th step is: When the phase distance between two adjacent multipaths is less than 1 chip, the path with less energy is eliminated; The multipath distribution processed by the multipath management is sent to the random access message part demodulation unit, and the demodulation unit will demodulate the random access message part according to the multipath distribution generated in this step. 5. The method for selecting random access threshold multipaths in a code division multiple access system according to claim 4, wherein the multipath phase interval after multipath management is not less than 1 chip. 6. The CDMA system random access threshold multipath selection method as claimed in claim 1, wherein in the eighth step, if the error rate increases, then appropriately increase the preamble detection threshold; if the error rate decreases, Then appropriately reduce the preamble detection threshold.

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