WO2003007520A1

WO2003007520A1 - A method and system for fast synchronization of uplink and a receiver for base station's access channel

Info

Publication number: WO2003007520A1
Application number: PCT/CN2001/001173
Authority: WO
Inventors: Li Fang; Yuan Zhang; Rakesh Tamrakar
Original assignee: Linkair Communications, Inc.
Priority date: 2001-07-13
Filing date: 2001-07-13
Publication date: 2003-01-23
Also published as: CN1211966C; CN1452821A

Abstract

A method for fastly synchronizing uplink in the synchronization code division multiple access(SCDMA) communication system, wherein the method comprising the steps of: (1) a mobile station selects one idle access time slot from a plurality of access time slot into which a access channel including in uplink be divided, in accordance with a base station's transmitting information; (2) the mobile transmits access code at point of time in said idle access time slot; (3) the base station detects said access code, and determines a time delay adjustment information for said mobile station; (4) the base station transmits said time delay adjustment information to the mobile station; (5) the mobile station adjusts transmission time thereof in accordance with received said time delay adjustment information, thereby making subsequently transmitting information arrive at the base station at standard access time.

Description

Uplink fast synchronization method and system, and

TECHNICAL FIELD

The present invention relates to a wireless communication system, and more particularly, to a synchronous code division multiple access (CDMA) communication system.

In recent years, wireless communication has become one of the most active aspects in the communication field. Due to its unique advantages such as large capacity, soft capacity, soft handover, high voice quality and low transmit power, and strong anti-interference and confidentiality, It has stood out, developed rapidly, and has become the technology of choice for third-generation cellular systems.

CDMA is a modulation and multiple access technology based on spread-spectrum communications. In the CDMA communication system, the signals used by different users to transmit information are distinguished by their own different coding sequences. Since the CDMA system uses different code patterns to distinguish channels, these channels are both in the frequency and time domains. They overlap each other, or they all occupy the same frequency band and time. Therefore, the performance of a CDMA system depends to a large extent on the characteristics of the code pattern, that is, the degree of mutual interference between multiple channels is important for determining the channel capacity of a CDMA system. And characteristics will be an important factor.

Referring to FIG. 1, it shows a schematic diagram of a cellular mobile communication system. A hexagon is a cell, and wireless communication is performed between a base station and a mobile station in the cell. There is a base station and multiple cells in the cell. Mobile stations, each mobile station uses an independent channel, that is, a different spreading address code, and performs wireless communication with the base station at the same time. Generally defined as the downlink from the base station to the mobile station (downl ink), the mobile station to the base station is called the uplink (upl ink).

In CDMA systems, the channels are distinguished from each other by the different codes used, so the correlation between such codes is very important. That is, the independence between such channels if and only if assigned to The codes of the respective channels are not correlated with each other and are guaranteed. When receivers use a given signal to recover their associated signals, these receivers should not be affected by channels that use other encodings.

However, in a conventional CDMA system, such as the IS95 system, the spreading code used is generated by a pseudo-noise code sequence Walsh code having the smallest cross-correlation value and the largest auto-correlation value. Since IS95 The system is an asynchronous CDMA system. Its uplink channel, that is, the signals sent by all mobile stations to the base station are transmitted asynchronously, because the pseudo noise sequences from different mobile stations cannot be synchronized, and the pseudo noise code sequences of different mobile stations cannot be positive to each other. Therefore, spread-spectrum signals in the same frequency band and at the same time will form great interference with each other, that is, multiple-access interference. This interference not only greatly reduces the channel capacity, but also increases the complexity of power control.

In order to eliminate the multiple access interference of the asynchronous communication system described above, it is required to use a spreading code with zero cross correlation value, that is, an orthogonal code (not only orthogonal but also a zero correlation window!), And because orthogonal code sequences are between The orthogonality characteristic is established under the premise of complete synchronization of the code sequences, so complete synchronization between these code sequences is required. Therefore, in a synchronous CDMA system, synchronization of the uplink and the downlink is very important.

In the CDMA system, the synchronization of the downlink is easy to achieve, because all signals are sent from a single base station. However, the realization of the synchronization of the uplink is much more difficult. The distance between each mobile station and the base station is different. The signal delay is also different, and the mobile station does not know the distance between itself and the base station, and cannot adjust the time to send the signal, which causes the mobile station to send the signal to the base station out of synchronization. It becomes more difficult to establish.

In recent years, in the prior art, several technical solutions have been proposed for achieving uplink synchronization in a CDMA system. For example, Chinese patent 97118934 discloses a method for establishing and maintaining uplink synchronization in a synchronous CDMA system. The method is tedious. It uses a complicated frame structure and control instructions to solve the uplink synchronization establishment process, and it cannot quickly make multiple mobile stations simultaneously establish synchronization.

Therefore, a method for performing fast synchronization on the uplink is urgently needed in the prior art. Summary of the Invention

A first object of the present invention is to provide a method for quickly synchronizing an uplink in a synchronous code division multiple access communication system, so as to solve the above-mentioned problems and defects in the prior art.

A second object of the present invention is to provide a system for quickly synchronizing an uplink in a synchronous code division multiple access communication system.

A third object of the present invention is to provide a base station access channel receiver used in a synchronous code division multiple access communication system.

In order to achieve one of the foregoing objectives, the present invention provides a method for The method for performing uplink synchronization quickly includes the following steps:

(1) the mobile station selects an idle access slot from a plurality of access slots into which the access channel included in the uplink is divided according to the information sent by the base station;

(2) the mobile station sends an access code at a certain time within the idle access slot;

(3) The base station detects the access code, and determines delay adjustment information of the mobile station;

(4) the base station sends the delay adjustment information to the mobile station;

(5) The mobile station adjusts its transmission time according to the received delay adjustment information, so that the subsequently transmitted signals reach the base station at the standard access time.

To achieve the above-mentioned second object, the present invention provides a system for fast synchronization of an uplink in a synchronous code division multiple access communication system. The synchronous code division multiple access communication system includes at least one mobile station and at least one base station. ,

The rapid synchronization system is characterized by:

The at least one mobile station includes:

Means for selecting an idle access time microphone from a plurality of access time slots into which an access channel included in an uplink is divided according to information transmitted by a base station;

Means for sending an access code at a certain time in the idle access slot; the at least one base station includes:

Means for detecting the access code and determining delay adjustment information of the mobile station; means for sending the delay adjustment information to the mobile station; and

The at least one mobile station further includes:

To achieve the third object, the present invention provides a base station access channel receiver used in a synchronous code division multiple access communication system, which is characterized by including:

A demodulator for demodulating an access code signal sent by a mobile station included in an uplink access channel;

A low-pass filter for low-pass filtering the demodulated signal;

A matched filter, configured to perform a correlation operation between a low-pass filtered signal and a pre-stored access code sequence;

A maximum value search circuit, configured to determine an output signal of the matched filter according to a related parameter Threshold value

A limiter, configured to output a valid signal at the threshold value;

A sliding correlator, configured to calculate, according to the valid signal, a time elapsed when the access code arrives at the base station from the mobile station; and

An offset calculation module, configured to compare the elapsed time with a standard time, and calculate a time offset; and

Means for sending the time offset back to the mobile station,

According to the method or system for performing fast synchronization on an uplink in a synchronous code division multiple access communication system of the present invention, it is possible to quickly and simultaneously realize synchronous reception between uplink signals of multiple mobile stations, thereby reducing the number of channels between channels. Interference, increase the channel bulk density of the system, and because of the unique access code and special matched filter structure, the synchronization accuracy is high, the number of adjustments is small, and the uplink synchronization can be established quickly and efficiently. Easy to implement.

According to the base station access channel receiver of the present invention, in each different access time slot, the arrival time of the mobile station signal is calculated from the signal energy of each mobile station user, and it is compared with the standard time, and then the adjusted time The delay information is placed in the downlink and sent to the mobile station. After receiving the delay adjustment information of the base station, the mobile station adjusts its transmission time so that the signal reaching the base station finally meets the standard access time. Overview of the drawings

The above and other features and advantages of the present invention will be more apparent through the detailed description of the best embodiment of the present invention in conjunction with the accompanying drawings.

FIG. 1 is a schematic structural diagram of a cellular mobile communication system;

2 is a flowchart of a method for performing fast synchronization on an uplink in a synchronous code division multiple access communication system according to the present invention;

3 is a detailed flowchart of the base station detecting the access code and determining the delay adjustment information; FIG. 4 is the uplink from the mobile station to the base station applied in the present invention;

FIG. 5 shows a characteristic diagram after an access code passes a matched filter for storing the same access code;

Figure 6 shows the characteristic after the access code passes the matched filter used to store different access codes. Figure;

Fig. 7 is a schematic structural diagram of a base station access channel receiver used in a system for fast synchronization of uplinks in a synchronous code division multiple access communication system according to the present invention. Best practice of the invention:

The best embodiment of the present invention is described in detail below.

Fig. 2 is a flowchart of a method for fast synchronization of uplinks in a synchronous code division multiple access communication system according to the present invention.

After the mobile station is powered on, the mobile station user first receives the information sent by the base station from the downlink, performs frequency correction and frame synchronization and bit synchronization with the system, and obtains the information of the available access channel microphones. The mobile station step 201 According to the information about the available access channel time slots, an idle access time is selected from a plurality of access time slots into which the access channel included in the uplink is divided. Then, in step 202, the mobile station sends a fixed access code at a certain time within the selected idle time slot. The specific structure of the access channel will be described later with reference to FIG. 4.

Thereafter, in step 203, the base station detects the access code sent by the mobile station, and determines the delay adjustment information of the mobile station.

In step 204, the base station sends the delay adjustment information to the mobile station.

In step 205, the mobile station adjusts its transmission time according to the received delay adjustment information, so that the subsequently transmitted signals reach the base station at the standard access time.

Figure 3 A detailed flowchart of the station detecting the access code and determining the delay adjustment information. The process shown in FIG. 3 constitutes step 203 in FIG. 2.

As shown in FIG. 3, in step 2031, the received signal is demodulated, low-pass filtered, matched filtered, and correlated. In step 2032, a maximum value search circuit and related parameters are used to determine a threshold value of the signal. In step 2033, a valid signal is output by the limiter by comparing with the threshold value. In step 2034, a sliding correlator is used to calculate the time it takes for the access code to reach the base station from the mobile station. In step 2035, the elapsed time is compared with a standard time, and a time offset is calculated as the delay adjustment information.

FIG. 4 is a schematic structural diagram of an uplink incoming channel from a mobile station to a base station applied in the present invention. As shown in FIG. 4, the access channel is divided into M time slots. When a mobile station attempts to access, each mobile station is allocated a time slot to perform access, and finally the time when the user signal arrives at the base station is at this time. Gap In a standard position, the signals of each mobile station in the uplink reach the base station synchronously. In order to ensure that the mobile station accesses the standard position, the mobile station must send an N-bit codeword (occupies NT _C ) in a time slot. Since one time slot allocated to the access channel is KTc

Therefore, the starting position of the codeword sent by the mobile station ranges from 0 to (KN) Tc. T _c other than the N-bit transmission codeword is not transmitted signal.

In addition, the access code used in the present invention is a unique spreading code. The access code is composed of three parts. The length of the access code is N bits, so the first N / 3 bits are determined as sequence 1, and the last N / 3 The bit is sequence 2, the middle complements N / 3 bit 0, and the sequence 1 and sequence 2 have orthogonal complementary characteristics.

For users in a cell, a fixed set of access codes can be used for access, but different time slots can be selected.

Each time a mobile station accesses, it sends a fixed access code in one of the M slots allocated to the access channel (KT _C ). Because the user does not know his own signal when he starts to access Whether it is the standard position for access after arriving at the base station, so the transmission time (the transmission time of the first bit of the N-bit codeword) is set to a fixed value S.

Secondly, the base station access channel receiver calculates the deviation of the signal sent by the mobile station once in each time slot (KT _C ) unit. The access channel receiver of the base station calculates the arrival time of the mobile station signal by receiving the signal energy of each mobile station user in different access time slots, and compares it with the standard time to calculate the user signal arrival time and The gap between the standard access locations is then transmitted to the mobile station via the downlink to transmit the time delay adjustment information. Through the time delay adjustment information, the mobile station user's controller adjusts the user's next access codeword transmission time until The time when the user access signal arrives at the base station is standard time.

Figure 5 shows the characteristic diagram after the access code passes the matched filter for storing the same access code. It can be seen that the sub-peaks are all less than or equal to 0, and the main peak is large.

Figure 6 shows the characteristic diagram after the access code passes the matched filter for storing different access codes. It can be seen that its cross-correlation peak is very small compared to the main peak of the autocorrelation.

By describing the method of the present invention in conjunction with FIG. 2 and FIG. 3, those skilled in the art can easily conceive that the system of the present invention for fast synchronization of uplink in a synchronous code division multiple access communication system is provided with The following features.

At least one mobile station included in a synchronous code division multiple access communication system includes:

It is used to divide a plurality of access channels included in an uplink based on information transmitted from a base station. A device for selecting an idle access slot in the access slot;

Means for sending an access code at a certain time in the idle access slot;

At least one base station included in a synchronous code division multiple access communication system includes:

A device for detecting an access code and determining delay adjustment information of a mobile station;

Means for sending the delay adjustment information to the mobile station; and

The at least one mobile station further includes: means for reaching the base station at a standard access time.

More specifically, the foregoing apparatus for detecting the access code and determining delay adjustment information of a mobile station includes:

A demodulator for demodulating a received signal;

A low-pass filter for low-pass filtering the demodulated signal;

A maximum value search circuit, configured to determine a threshold value of an output signal of a matched filter according to related parameters;

The limiter outputs a valid signal according to a threshold value;

A sliding correlator for calculating the elapsed time from the mobile station to the base station according to the effective signal; and

The offset calculation module is configured to compare the elapsed time with the standard time, and calculate a time offset, where the time offset is delay adjustment information.

The above-mentioned components included in the base station may be set in a base station access channel receiver.

Figure 7 is a schematic diagram showing the structure of such an access channel, the access channel receiver is used for fast synchronization of the uplink of the synchronous code division multiple access communication system.

As shown in FIG. 7, reference numeral 601 represents a demodulator, 604 represents a low-pass filter, 607 represents a matched filter, 608 represents a limiter, 609 represents a maximum search circuit, 610 represents a sliding correlator, and 611 represents a time offset. Calculation module.

Assuming that the real part of the codeword sent by the user is x (t) and the imaginary part is y (/), the modulated signal is:

C (i) = x (cos (iy _c /) + _y (t) sin (6) If the influence of noise is not considered, the signal received by the base station is:

C (t) = j (t) cos (<y _c t) + ^ (/) sin (<y _c t)

After the access signal from the mobile station passes the demodulator 601, the I signal 602 is:

I (t) = C (t) x cos (iy _c = [; (t) cos (iy _c t) + y (t) sin (iy _c t)] x cos (iy _c t)

= x (t)

x (t) c. s (2 (y _c t) + y (t) sin (2iy _c t) passes the low-pass filter 604 to filter out the high-frequency signals. The 605 signal is: / (0 = ^ (0 Similarly, the connection from the mobile station The Q signal 603 of the incoming signal after the demodulator 601 is:

Q (t) = C (t) χ s {} _c t) = [(/) cos ((¾J _c /) + yt) sin (iy _c t)] χ sin (<w _c t)

= x (t) sin (2ty

After passing the low-pass filter 604, the high-frequency signal is filtered. The signal 606 is: 2 (0 = ^) The two signals after the low-pass filter are sent to a special matched filter 607. The filter stores the access code. Sequence, the output of the matched filter cancels all positive sub-peaks of the codeword autocorrelation, so that the sub-peaks of the autocorrelation are zero or negative. The large value search module 609 finds the largest value from the output signal of the matched filter 607, and uses the product of the value and a parameter as the threshold value of the limiter 608 at the back. In this way, after passing through the limiter 608, all the input energy values that are greater than the threshold value are output as they are, and the amount less than this threshold value is filtered out and the output is 0, which effectively reduces the autocorrelation secondary peaks, The effect of cross-correlation peaks and noise on calculating the position of the main peak.

The output signal of the limiter 608 is sent to the next-stage sliding correlator (length L) 610. The purpose is to find the position of the largest L adjacent values from the 2K values. That is, to find the last one from the 2K values. The position of the maximum value (if there are two or more equal maximum values in the 2K value, the last position is taken), that is, the time when the user arrives at the base station.

The calculated time when the user signal arrives at the base station is compared with the standard position, the offset is calculated in the time offset calculation module 611, and a delay control command DCC (Delay Control Command) command is generated.

The delay control instruction (or delay adjustment information) is transmitted to the mobile station in the downlink. After receiving the information of the base station, the mobile station user adjusts its transmission time so that the signal reaching the base station finally meets the standard access time. When the deviation between the value output from the sliding correlator and the standard position is within the allowable range, it indicates that the access is successful. If a "1" signal is successfully output, DCC will output a special command to inform the user that the access is successful; if not, a "0" signal will be output, and DCC will be a command.

If the calculated maximum energy window position of the user access signal of the mobile station exceeds the adjustable range, it indicates that the adjustment has failed. In this case, the base station wants to send a special DCC command to the user in the downlink, and the user sends the access pulse again. Access.

The above description can clearly show that because the access channel is used in the uplink and the access channel is divided into different time slots, more mobile stations can access the system at the same time, and the rapid establishment of the uplink is guaranteed. The combination of access code and matched filter is used to ensure the accuracy of calculating the delay deviation of the signal sent by the mobile station and speed up the uplink synchronization establishment process.

Although the best embodiment of the present invention has been described in detail above with reference to the accompanying drawings, for those skilled in the art, various modifications and changes can be made without departing from the scope and essence of the present invention. Accordingly, the scope of the invention is limited only by the claims.

Claims

Rights request

1. A method for performing fast synchronization on an uplink in a synchronous code division multiple access communication system, comprising the following steps:

(1) the mobile station selects an idle access slot from a plurality of access microphones into which an access channel included in the uplink is divided according to the information sent by the base station;

2. The method according to claim 1, wherein the step (3) comprises the following steps performed on a base station:

Perform demodulation, low-pass filtering, matched filtering, and correlation operations on the received signal, and then output the signal;

Determining a threshold value of the signal using a maximum value search circuit and correlation;

By comparing with the threshold value, the limiter outputs a valid signal;

Compare the elapsed time with the standard time, calculate a time offset, and the time offset is the delay adjustment information.

3. The method according to claim 2, characterized in that in the step (2), the access code is sent at a fixed time in the idle access slot.

4. The method according to claim 2, wherein the step of performing matched filtering on the received signal comprises: correlating the received signal with an access code sequence stored in a matched filter in advance. Operational steps.

5. The method according to any one of claims 1 to 4, characterized in that: the access code is an N-bit spreading code, wherein the first N / 3 bits are sequence 1 and the last N / 3 bits are sequence 2. The middle N / 3 bit is 0, and the sequence 1 and sequence 2 have orthogonal complementary characteristics.

6. A system for fast synchronization of uplink in a synchronous code division multiple access communication system, so The synchronous code division multiple access communication system includes at least one mobile station and at least one base station,

The rapid synchronization system is characterized by:

The at least one mobile station includes:

Means for sending an access code at a certain time in the microphone during idle access;

The at least one base station includes:

A device for detecting the access code and determining the delay adjustment information of the mobile station;

Means for sending said delay adjustment information to a mobile station; and

7. The system according to claim 6, wherein the means for detecting the access code and determining delay adjustment information of a mobile station comprises:

A demodulator for demodulating a received signal;

A low-pass filter for low-pass filtering the demodulated signal;

A maximum value search circuit, configured to determine a threshold value of an output signal of the matched filter according to a related parameter;

The limiter outputs an effective signal according to the threshold value;

A sliding correlator, configured to calculate, according to the valid signal, a time that the access code passes from the mobile station to the base station; and

An offset calculation module, configured to compare the elapsed time with a standard time, and calculate a time offset, where the time offset is the delay adjustment information.

The system according to claim 7, characterized in that the means for sending an access code at a certain time in the idle access microphone sends the access code at a fixed time,

9. M The system according to any one of claims 6 to 8, characterized in that the access code is an N-bit spreading code, wherein the first N / 3 bits are sequence 1 and the last N / 3 bits are sequence 2. The middle N / 3 bit is 0, and the sequence 1 and sequence 2 have orthogonal complementary characteristics.

10. A base station access channel receiver used in a synchronous code division multiple access communication system, comprising:

A low-pass filter for low-pass filtering the demodulated signal;

A limiter, configured to output a valid signal according to the threshold value;

Means for sending the time offset back to the mobile station.