WO2003036835A1

WO2003036835A1 - A method of improve handover performance in synchronism code division multiple access mobile communication system

Info

Publication number: WO2003036835A1
Application number: PCT/CN2001/001457
Authority: WO
Inventors: Yanshan Shi
Original assignee: Linkair Communications, Inc.
Priority date: 2001-09-27
Filing date: 2001-09-27
Publication date: 2003-05-01
Also published as: CN1226839C; CN1475060A

Abstract

The present invention discloses an arrange method of synchronism time delay of base station signal transmitting or despreading for Code Division Multiple Access Radio Spread Spectrum Communication and Digital Mobile Communication System. The invention can conduct relative time delay to signal transmitted, making it possible for signals from the neighbor base station to reach the borderline of its neighbor cell within very short time difference, disregard of whether radius of the two cell are the same or not. It can also conduct relative time delay to signal despreading, making it possible for signals in bi-directional synchronous systems, transmitted from mobile station in boundary cell, to be in reverse synchronization with signals from multiple neighbor base station on certain conditions. The method adopts the innovation can make bi-directional synchronous systems to realize easily soft handover, and meanwhile not cause search range of code synchronization of the mobile station to increase as a result of difference in radius of the two neighbor cell.

Description

In synchronous code division multiple access mobile communication system

Method for improving switching performance

Technical field

The invention relates to the technical field of wireless spread spectrum communication and digital mobile communication, and in particular to a method for improving handover performance in a synchronous code division multiple access (CDMA) wireless communication system. Background of the invention

In the field of wireless communication, the direct sequence 'J rect Sequence Spread Spectrum (DS-SS) wireless communication system is developing more and more rapidly. A typical system of a direct sequence spread spectrum system (DS-SS) is a code division multiple access (CDMA) system. In recent years, due to the unique advantages of large capacity, soft capacity, high voice quality and low transmission power, as well as anti-interference and confidentiality, CDMA systems have led to the rapid development of code division multiple access (CDMA) technology and become the current mobile communication system. Mainstream technology.

CDMA is a modulation and multiple access technology based on spread-spectrum communications. In a CDMA communication system, signals used by different users to transmit information are not distinguished by different frequencies or time slots, but by different coding sequences. The receiver correlator can select a signal using a predetermined pattern among a plurality of CDMA signals. Other signals using different code patterns cannot be demodulated because they are different from the code patterns generated locally by the receiver.

Generally, in a CDMA system, both a base station transmitter and a mobile station transmitter use a spreading code to spread the digital information to spread the spectrum, and the receiving device uses a local spreading code to despread the spread spectrum signal to extract useful information. . Synchronization is to realize that the local spreading code and the received spreading code are completely consistent in structure, frequency, and phase. A CDMA system has carrier synchronization, bit synchronization, and frame synchronization in addition to general digital communication systems. Spreading code synchronization is unique to it. Therefore, the synchronization problem of a spread spectrum system is more complicated than that of a general digital communication system. Getting system synchronization is not in a CDMA system Missing, and very important.

In a code division multiple access (CDMA) type system, users in each communication are uniquely assigned a pseudo noise (PN) code sequence or an orthogonal code sequence. Multiple users share the same frequency band at the same time. Communicate with the system. A method for distinguishing channels by using a unique code sequence is to spread a digital information signal by using a pseudo-noise (PN) code or orthogonal code allocated by the unique code sequence to form a spread-spectrum signal.

The spread spectrum signals of multiple users in the system are superimposed and then transmitted after radio frequency (RF) modulation. Each pseudo noise (PN) code or orthogonal code can be distinguished based on its unique phase or unique bit sequence.

As an example of a code division multiple access (CDMA) system, the communication system specified by the TIA / EIA IS-95 standard uses two pseudo noise (PN) codes, and the transmission of all forward links of each base station is determined by a certain amount. The same common system pseudo-noise (PN) code with unique phase in the area is spread; and each channel in the forward link is spread by the unique Walsh pseudo-noise (PN) code.

For the above-mentioned public system pseudo noise (PN) code, for example, a PN code is 2 ¹⁵ chips in length, and neighboring base stations will generate PN codes with different phases according to different preset chip phases. This preset chip phase is called offset, and one of its functions is to distinguish the base station.

Other types of code division multiple access (CDMA) systems, such as the LAS-CDMA spread-spectrum communication system under development, each base station is assigned a unique LA code, and each channel is assigned a unique LS code. The LS code spreads the uplink or downlink signals. LA codes and LS codes are disclosed in two patents described below.

In a PCT international patent application with application number PCT / CN98 / 00151, inventor Li Daoben, and entitled "A Spread Spectrum Multiple Address Code Coding Technology", a coding method for spread spectrum multiple access codes is disclosed. This type of spreading code has good auto-correlation and cross-correlation characteristics. For simplicity, the following In the description of the invention, such a spreading code is simply referred to as a LA code. The LA code is composed of polarized basic pulses with a normalized amplitude and width of 1. The number of basic pulses is based on the number of users required, the number of pulse compression codes that can be used, and the number of available pulse compression codes. The actual factors such as the number of orthogonal pulse compression codes, the number of orthogonal frequencies that can be used, the system bandwidth, and the maximum signal transmission rate of the system are determined. The intervals of the basic pulses on the time coordinate are different and different. Equal and different pulse position and pulse polarity arrangement coding. Taking the above design, it provides a concise and fast design method for the spread spectrum address code for the spread spectrum technology and digital multiple access technology. The characteristics of this LA code are: first: the main peaks of the autocorrelation function are equal to the number of basic pulses, and also the number of orthogonal codewords in the code group; second: the subpeaks of the autocorrelation and crosscorrelation functions are only +1 Three possible values, -1 and 0. The LA code can be used to identify different cells.

A patent (PCT / CN00 / 00028) entitled "A Spread Spectrum Multiple Address Coding Method with Zero Correlation Window" mentions a CDMA scheme with zero correlation window. In this invention, a spread-spectrum multi-address code, which is abbreviated as LS code, is disclosed. By applying the method for generating the spread spectrum multi-address code (see the patent for details), the auto-correlation and cross-correlation functions of the newly generated spread spectrum multi-address code can form a "zero correlation window" near the origin, and the "zero correlation" In the window, the multiple access interference (MAI) and the inter-symbol interference (ISI) are zero. Therefore, the code division channel codes selected within a cell have unique correlation characteristics with each other. Correlation characteristics between channel codes Not only has complete orthogonality, but its offset-related characteristics are also fixed within a certain offset interval (0); therefore, the CDMA scheme is very suitable for wireless communication systems with multipath effects. .

Unlike IS-95, LAS-CDMA does not use continuous pilots to assist mobile stations to obtain synchronization. The synchronization auxiliary channels (which may be pilot channels, broadcast channels, or synchronization channels) and service data channels may be time-division structures and synchronized. The spreading code sequence of the auxiliary channel may be a set of LS codes. In the LAS-CDMA system, base stations are distinguished according to the uniqueness of the LA code, and The uniqueness distinguishing channel may distinguish the synchronization auxiliary channel of the base station according to the uniqueness of the synchronization auxiliary channel orthogonal code (such as LS code).

The common point in these types of systems is that if a mobile station wants to start communication with a base station, it must establish synchronization between the receiver and the wireless signal generated by the base station using a spreading code.

The synchronization of the spreading code is divided into two steps. One is capturing, that is, coarsely adjusting the frequency and phase of the local spreading code so that the phase difference between the local spreading code and the receiving spreading code is less than one symbol width Tc. For example, the artificial noise PN code sequence or orthogonal code sequence generated by the transmitting end and the receiving end is roughly aligned in time and accurate to a gap of ch ip. The second is tracking, which automatically adjusts the phase of the local spreading code. It is precisely synchronized with the frequency and phase of the received spreading code.

On the receiving side, when the mobile station's power switch is turned on, the PN code generator generates a PN code sequence that moves ch i p phase gradually from zero offset. The receiver will monitor the correlation between these PN code sequences and the PN code in the synchronization assistance signal sent by the base station in order to search for the PN offset used by the base station. Once the PN offset used by a base station is searched, the mobile station will receive the synchronization channel and obtain synchronization information. If communication is required at this time, the mobile station will select the base station with the strongest signal among all the searched base station signals to make an access attempt, and will maintain synchronization with the base station.

For the LAS-CDMA system, the following scheme is adopted. After the mobile station power switch is turned on, different orthogonal code sequences (such as LS codes) are generated by the orthogonal code generator, and they are moved within a certain time domain to monitor their relationship with the base station. Correlation between orthogonal codes (such as LS codes) used by the transmitted signal. Once the code sequence used by a base station signal is the same as the code sequence generated locally by the mobile station and aligned in time, the receiver will despread the synchronization information in the signal. If communication with the base station is required thereafter, the mobile station will also select the base station with the strongest signal among all the searched base station signals, and will maintain synchronization with the base station.

The length of time to obtain synchronization and the probability of correctly obtaining synchronization are the criteria for determining synchronization performance. Standard. Due to the importance of obtaining synchronization, in this field, many schemes for detecting and determining base station signals have been proposed and applied.

After the synchronization with a certain base station has been obtained, the mobile station must continue to monitor the signals of other base stations, so as to switch to other base stations when the signal strength of the serving base station is insufficient and the signals of other base stations are strong enough.

For some code division multiple access (CDMA) or time division multiple access (TDMA) systems, taking LAS-CDMA as an example, the mobile station knows from the current base station the orthogonal code (such as the LS code) used by the neighboring base station to synchronize the auxiliary channel, but Because the time difference between the time when the base station signal arrives at the mobile station and the current base station signal is uncertain, the mobile station should search for signals from neighboring base stations within a certain time or phase difference range. On the other hand, because the LAS-CDMA system requires two-way synchronization, the system is required to maintain synchronization on both the forward and reverse links, that is, the signals sent by mobile stations in different positions in the cell must reach the base station synchronously, and the signals of each code channel The arrival time difference cannot exceed a certain range (for LAS-CDMA systems, the range is the interference-free window width), otherwise the base station may not be able to correctly despread or be subject to greater interference. When the distance between the mobile station and two neighboring base stations is almost equal and the base stations are synchronized (the clocks of the base stations are generally synchronized), the signals sent by the mobile stations will reach the two base stations synchronously. At the same time, it is equivalent to meeting the requirement of reverse synchronization with two base stations at the same time, so that soft handover may be realized.

However, because the user distribution is not always uniform, the user distribution density in densely populated areas is greater than in sparsely populated areas. Therefore, the radius of the cells covered by each base station is not always equal. When two cells with different radii are adjacent, it will cause some problems for this type of system. Because at this time at the cell boundary, that is, the area where the handover should occur, the distance from the two base stations is different. In the handover area, the possible time difference between the signals of the two base stations arriving at the mobile station is greater than that at the cell boundary with the same radius. The possible time difference between signal arrivals is large; and the more the two cell radii differ, the larger the The greater the time difference range.

In the above case, only by increasing the search range of the mobile station can it be guaranteed that the mobile station can search for signals of neighboring base stations at the cell borders with different distances from the two base stations, which undoubtedly increases the search time. At the same time, if the mobile station in the handover state wants to receive signals from neighboring base stations in macro diversity, it is bound to increase the delay between each Finger in the RAKE receiver to realize the reception of signals from neighboring base stations.

For a system requiring reverse synchronization, at such a cell boundary, signals sent by a mobile station cannot reach two base stations simultaneously and synchronously, and can only guarantee reverse synchronization with one of the base stations, so it is difficult to implement soft handover. Object of the invention

The purpose of the present invention is to provide a new synchronization delay setting method for a synchronous code division multiple access (CDMA) wireless spread spectrum communication system, so as to solve and overcome the defects and shortcomings existing in the prior art solutions.

According to the synchronization delay setting method of the present invention, in a downlink, by setting the synchronization delay of a transmission signal between adjacent base stations, the boundary of the cell where the adjacent base station is located, regardless of whether the cell radius is Similarly, the handover area coincides with the search area where the mobile station acquires the base station signal. At the same time, when a mobile station in this area receives signals from adjacent base stations at the same time, the delay between each F i nger in the Rake receiver does not depend on the phase. The neighbour cell radius is different.

According to the synchronization delay setting method of the present invention, in the uplink, by setting the synchronization delay of despreading a received signal between adjacent base stations, the boundary of the cell where the adjacent base station is located, regardless of whether the cell radius is the same Mobile stations can maintain reverse synchronization with all neighboring base stations under certain conditions, so that the realizable area of soft handover is located exactly at the border of the cell, and in mobile communications that require reverse synchronization In the system, soft handover is implemented.

The present invention is implemented using the following technical solutions:

A method for setting a time delay for a base station to transmit a signal or despread a signal, so that the time difference between a signal sent by a neighboring base station and a certain point can be reached, and the time difference between arrivals at the cell boundary is small; The base station is reached during operation, so that the signals sent by the mobile stations at the cell borders arrive at the respective base stations when they are despread separately.

A synchronization delay setting method for a synchronous code division multiple access (CDMA) spread-spectrum communication system. In downlink, by setting the synchronization delay of a transmission signal between adjacent base stations, the cell in which the adjacent base station is located is set. At the boundary of the cell, regardless of whether the cell radius is the same, the handover area coincides with the search area where the mobile station acquires the base station signal, and when the mobile station in the area receives the signal from the adjacent base station at the same time, the delay between the receivers is not The radius of neighboring cells is different. Summary of the Invention

In order to achieve the objective of the present invention, the synchronization delay setting method provided by the present invention determines the transmission or despreading delay amount of each adjacent base station according to the difference in cell radius between each adjacent cell. Specifically, in In the downlink, adjust the transmission delay of the signals transmitted by each neighboring base station, the base stations in the large radius cell transmit the signal in advance, and the base stations in the small radius cell lag the transmission; in the uplink, adjust the despread signal of each neighboring base station. The delay amount is extended by the base stations of the large-radius cell, and the base stations of the small-radius cell are despread in advance. That is, the time when all mobile stations in the cell send uplink data is based on the transmission time of the mobile station at the cell boundary. The interval is different and the transmission is delayed accordingly. After the base station completes the deblocking, the base station reversely adjusts the corresponding despreading delay amount and then communicates with the higher-level network to restore the synchronization between the base station and the higher-level network. The beneficial effects of the invention

According to the new method for setting the synchronization delay of a base station according to the present invention, no matter whether the radius of a cell is the same at a border between neighboring cells, it can be ensured that the cell border is a realizable area for handover. Therefore, at the cell boundary, the mobile station obtains the synchronization search time of the neighboring base stations, and the time or phase delay between each Finger when the Rake receiver receives the signals of the neighboring base stations in diversity, not because of the distance between the mobile station and the neighboring base stations. In the two-way synchronization system, the mobile station at the boundary is kept in reverse synchronization with multiple base stations under certain conditions, thereby improving the code synchronization performance and possible soft handover in the two-way synchronization wireless system. Brief description of the drawings

The present invention is described in detail below with reference to the drawings.

Figure 1 shows the relationship between the area of the cell with the same radius (take 2 cells as an example), the area of small search range, and the two-way synchronous soft handover implementation area and the cell boundary.

Figure 2 shows the relationship between the small search area area and the two-way synchronous soft handover implementation area at the cell boundaries with different radii (take 2 cells as an example) and the cell boundary.

Figure 3 shows the relationship between the small search area area, the two-way synchronized soft handover implementation area, and the cell boundary at the cell boundaries with different radii (taking 2 cells as an example) according to the method of the present invention.

Figure 4 shows the relationship between the small search area area, the two-way synchronized soft handover implementation area and the cell boundary at the cell boundaries with different radii (taking 3 cells as an example) according to the method of the present invention.

FIG. 5 is a schematic diagram of setting a synchronization delay for transmitting or despreading a base station according to the method of the present invention (taking 4 cells as an example). Mode of Carrying Out the Invention It can be known from the prior art that if two neighboring base stations transmit signals at the same time, the signals will reach the area with a smaller time difference from the two base stations with a smaller time difference. At this time, the mobile station can search for signals of adjacent base stations and implement handover within a small uncertainty range. This search range is referred to as a signal search area for handover in the present invention, and corresponds to the handover implementation area. . In the present invention, the search range in which the mobile station can search for signals of adjacent base stations within a small range is referred to as a small search range, and the area corresponding to the range is called a small search range area.

Referring to FIG. 1, there are two cells with the same radius, and the radii are respectively set to 1 ₂ , and

The base stations are set to 8! And B _{2 respectively} ; the distance between the two base stations is set to D ₁₂ ; a mobile station M is set somewhere between the two base stations and the distances to the base stations ^ and B ₂ are ^ and r ₂ respectively. If the clocks of the two base stations are synchronized, that is, the two base stations start to send their respective frame signals at the same time, then near the center line M (that is, the vertical line and the boundary line) that is equal to the two base stations, (the vicinity of this center line M is simultaneously It is also the boundary of the cell.) The time difference between the frame header signals sent by the two base stations near the center line is small. At this time, a mobile station located near the center line M can capture signals of neighboring base stations with a small search range. Similarly, if two base stations despread the received signal at the same time, the signals transmitted by the mobile station near the center line M with the same distance from the two base stations will reach the two base stations at almost the same time. Therefore, under certain conditions, the mobile station can achieve Reverse synchronization of two base stations. In this case, the small-area search area, the handover implementation area, and the cell boundary overlap. E is a small-area search area, and a central area and a soft handover realizable area in each synchronization system. S is a boundary area and a switching area.

However, if the radii of the two adjacent cells are different, that is, the distance between the cell boundary and the two base stations is different, the time difference between the signals transmitted by the two base stations at the boundary will inevitably become larger. Therefore, the mobile station must increase the search range to capture the signals of neighboring base stations, which is equivalent to expanding the implementation area of the handover and covering the cell boundary.

Referring to FIG. 2, if R, <R ₂ , that is, when the cell radius is different, at the boundary of two cells The distance between the mobile station and the base stations B! And B ₂ is different, then the time difference between the downlink signals of the two base stations arriving at the boundary will become larger. As can be seen from FIG. 2, the small-area search area and the two-way synchronization system The area E for soft handover has deviated from the cell boundary S. At this time, the mobile station at the boundary may need to increase the search range to capture neighboring base stations. When receiving macro-diversity signals from multiple base stations, each Finger in the Rake receiver The time or phase delay between them is also increased; if the base stations despread at the same time, the signals transmitted by these mobile stations cannot arrive at the same time when the two base stations despread, and it is difficult to achieve reverse synchronization with multiple base stations in a two-way synchronization system.

If the multipath factor is ignored, the time difference between the signal sent by 8 _{2 and} the signal of base station 8 arrives late is

t = l ^ Z∑i (1) l c

The time when the signal transmitted by the mobile station arrives at the base station B ₂ relative to the base station is _2, where c is the speed of light, the unit is meter / second, the unit of rnr ₂ is meter, and the unit of t _i2 and _tu is second.

From (1) and (2), it can be seen that the time difference between the signals sent by two neighboring base stations at the same time and the time difference between the signals transmitted by the mobile station at the point and the two base stations are the same. The distance to the two base stations is poor. Since the trajectories of the points with the same distance difference between the two fixed points are hyperbolic. Therefore, any time difference t ₁₂ or ^ will correspond to a set of hyperbola between two base stations. When t ₁₂ ≧ Q or, ₂ > 0, it corresponds to a curve near the base station ^; When t ₁₂ <G or ₁₂ <0, it corresponds to a curve near the base station B ₂ . When t ₁₂ = 0 or more, it corresponds to the center line where the two base stations are connected. Because the wireless signal is in units of ch i ρ, in the current system, each ch ip runs at a speed equivalent to about 244 meters. Each of the above curves corresponds to a zone band of about 244 meters wide. A width will vary depending on the chip rate. Since <1 ₂ , the boundary between the two cells should be close to the base station and because the coverage areas of the two base stations overlap, it is defined on the connection between the two base stations. The distance between the boundary between the two cells and the base station is

Then the distance between this point and the base station B ₂ is

R, + R, one A,

R--

2 Let mobile station ^ be located exactly at this point. At this time, t ₁₂ and tn are

R, + R, — D R, + R-,-D

R R, R —R,

2

(3)

R-R,

Two

c

The purpose of the present invention is to make the frame header signals sent by two base stations reach M at the same time. When the distance between the point and the two base stations is different, in order to achieve these objectives, the method proposed by the present invention is: On the downlink, the distance is long. The frame header signal of the base station is sent first, and the frame header signal of the near base station is sent later; in the uplink, the despread signal timing of the far base station is required to lag, and the despread signal timing of the near base station is advanced. The effect is This is achieved by setting the standard transmission position of the mobile station in the cell by the base station, that is, setting the standard transmission position to the boundary of the cell, so that the mobile station with a small distance from the base station delays the transmission of uplink data accordingly, so that its signal and the movement at the boundary The signals transmitted by the stations arrive at the base station of the cell synchronously. Because the radius of each cell is different, the boundary distance is different from the distance between adjacent base stations, thereby causing a delay between the despreading times of the uplink data by the adjacent base stations. Thus, the distance should be the base station B ₂ with respect to the base station B, t ₁₂ seconds ahead of the transmission signal, i.e., B ₂ with respect to the transmission delay amount d _[2 to R ― R,, d _n = -tn =-~~ ¹ (4) c

Similarly, if M, the transmitted signals reach 8 ₂ and the time difference is ₁₂ , respectively, the base station B ₂ that is far away should correspond to the base station B with a delay of ₂ seconds to despread the signal. Then the despreading delay of B ₂ relative to the received signal is

R —R,

d t = (5)

12

c

Then,

dyi-a d

(6) From this, it can be concluded that when there is a certain transmission delay in the signal frame header sent between the base station of the large radius cell and the base station of the small radius cell, and the amount of transmission delay is the radius of the large radius cell and the small radius cell. The difference between the radius and the quotient of the speed of light is the opposite, and the signals sent by the two base stations will arrive at the cell boundary with a small time difference. Similarly, when the base station of the large radius cell and the base station of the small radius cell resolve the received signal There is a certain despreading delay at the time of the expansion, and the amount of the despreading delay is the quotient of the difference between the radius of the large radius cell and the radius of the small radius cell and the speed of light. The same frame signal transmitted by the station.

Referring to FIG. 3, FIG. 3 is a schematic diagram adjusted by the foregoing method. After the adjustment, the small-area search area, the cell boundary, and the handover area overlap at the boundary of two cells with different radii.

Referring to Figure 4, when the number of base stations involved in a long time, for example three base station, the cell radii Ri, Rj and R _k, respectively, the base station B Bj and B _k; method defined boundary between each two of the cell The text is the same. According to the previous conclusions, the transmission delays d _i 4 d _jk , d, d _ki , and 4 between and B ″, B ″ and, 8 _1: and are respectively d .. = -d .. = ”L (7 )

U U c

d) _k = -d _jk = ^-^ (8) d _ki = ~ d _ki = (9)

C Can be calculated,

d ^ d _{jk +} d _ki =-^ ~ '一''~~ ^J ~~ 0 (10) cccdy + d _jk + d _ki =''—— + ———— ^J- + -—— ^L = 0 (11 ) ccc

From formulas (10) and (11), it can be inferred that, no matter the transmission delay or despreading delay, if two base stations (for example, and _Bk ) and another base station (for example, Bj) respectively satisfy formula (7) and formula (8) ), Then the delay between the two base stations will satisfy formula (9). The adjusted effect is shown in the figure. In three small areas with different radii, the small-area search area, boundary, and switching area overlap.

In practical applications, the following manner can be used to specifically calculate the delay amount that each base station should adopt.

Among all the n neighboring base stations involved, one of the cells is arbitrarily selected as a standard cell, and the base station is set to B _Q and the radius is R. , The base station with the cell radius Ri and the base station B with the cell radius; the transmission delays d _iQ , d _jQ, and the despreading delays Ao relative to the base station B _Q are respectively set to d _a = -d _l0 = ^^ (12)

Then the delay between the base stations ^ and ^ satisfies

. R, .a /?,.

d _ri = -d = -i-

^{1 1} (14) Therefore, among the n base stations, if the delay of one of the base stations and the other n-1 base stations satisfy the formula (12), then the delay between the two base stations of the n-1 base stations must satisfy the formula ( 14). Refer to FIG. 5 for the delay value setting of each base station. At this time, the handover small area search area and implementation area are exactly at the borders of all the cells.

It can be deduced that the radius of any cell is taken as the standard radius, and the time when the base station transmits or despreads the signal is the standard transmission and standard despread time, respectively. When the transmission times of all other base stations are relative to The standard transmission time delay is the transmission delay calculated by dividing the difference between the cell radius and the standard radius by the inverse of the quotient of the speed of light; and the despread time of the base station is delayed by the difference between the cell radius and the standard radius divided by the standard despread time When the despreading delay calculated by the quotient of the speed of light, the handover realization area, the small-area search area, and the cell boundary can coincide at the cell boundary at all cell boundaries, that is, the result that all cell boundaries are exactly the area where the handover is performed .

Code division multiple access (CDMA) systems have the characteristics of soft capacity. Therefore, in actual operation, the range covered by a base station signal may change with different system loads. Therefore, the equivalent cell radius is dynamically changed. Therefore, the amount of signal transmission or despreading delay between base stations can also be dynamically changed.

Because each base station transmits signals and despread signals at different times according to the coverage radius of the corresponding cell, when each base station communicates with its superior network equipment, such as a switch, the delay amount must be adjusted back accordingly to meet the base station location. Requirements for synchronization in communication network systems.

In order to synchronize with the switch, the base station should adjust the communication delay with the switch according to the inverse of the despread delay. Let the despreading delay of the base station Bi be relative to the standard base station 8. Yes. While B. The moment when the despread data is formed is e. Send to the switch at time e _D + T, where T is the delay between sending data and forming data. Then the data formation time of the base station B _; is e. +. In order to send data to the switch at time e _Q + T to synchronize with the base station B _Q , the data transmission and formation delay of the base station should be 4), that is, the delay amount equivalent to B _Q is −. .

More specifically, for a two-way synchronization system, such as a LAS-CDMA system, each mobile station in the cell is required to transmit signals to the base station synchronously regardless of the distance from the base station, that is, reverse synchronization is required. If the base station simultaneously performs despreading of the received signal, it is also possible that only signals sent by mobile stations in areas with a small distance difference from neighboring base stations can reach these simultaneously when despreading is performed by multiple base stations. The base station implements reverse synchronization with multiple base stations, and when adjacent base stations use the same LA code, soft handover can be achieved. However, at cell boundaries with different radii, the mobile station cannot meet the requirement of reverse synchronization with multiple base stations simultaneously.

In order to make the cell boundary reverse synchronization with multiple base stations using the same LA code at the cell boundary, regardless of whether the cell boundary is the same, the time of despreading of the base station of the large radius cell should be delayed, while that of the base station of the small radius cell The timing of despreading is advanced, so that when the signals of the mobile station are despread separately at each base station, they just reach the base station, which is equivalent to setting the standard transmission position of the cell mobile station to the boundary of the cell, and the The implementation area just covers the cell boundary. In this way, it becomes possible for the two-way synchronization system to implement soft handover at cell boundaries with different radii.

Claims

Claim

1. A method for setting a delay time for a base station to transmit a signal or despread a signal, which is characterized in that the time difference between signals sent by neighboring base stations to a certain point and the time difference at the cell boundary is small; or the mobile station sends The signals arrive at the base station just when the base station is operating, so that the signals sent by the mobile stations at the cell boundary arrive at the base stations when they are despread separately.

2. The method for setting a delay of a base station transmitting or despreading a signal according to claim 1, wherein the time delay amount of the base station transmitting or despreading is selected according to the radius of the corresponding cell of each base station.

3. The method for setting a delay of a base station transmitting a signal or despreading a signal according to claim 1, 2, characterized in that a channel sent by an adjacent base station reaches a cell boundary with a small time difference, or moves the cell boundary The channel sent by the station arrives at the base station just when the neighboring base stations start despreading, regardless of whether the boundary and the distance between the neighboring base stations are the same.

4. The method for setting a delay of a base station transmitting a signal or despreading a signal according to claim 1, 2 or 3, characterized in that the mobile station located in a certain area satisfies the requirements of reverse synchronization with multiple base stations simultaneously.

5. The method for setting a delay of a base station transmitting a signal or despreading a signal according to claim 1, 2 or 3, characterized in that reverse adjustment is made according to the set delay amount to make the station adapt to the synchronization requirements of the communication network.

6. A synchronous delay setting method for a synchronous code division multiple access (CDMA) spread-spectrum communication system, characterized in that, in a downlink, by setting a synchronous delay of a transmission signal between adjacent base stations, At the border of the cell where the adjacent base stations are located, no matter whether the cell radius is the same, the handover area coincides with the search area where the mobile station acquires the base station signal, or the mobile stations in this area can receive the signal at the same time. When receiving signals from adjacent base stations, the delay between each receiver does not increase due to the difference in the radius of the adjacent cells. In the uplink, by setting the synchronization delay of the despreading of the received signal between adjacent base stations, the mobile station can remain at all borders at the border of the cell where the adjacent base station is located, regardless of whether the cell radius is the same. The reverse synchronization of the base station enables the soft handover to be located exactly at the cell boundary.

7. A synchronization delay setting method for a synchronous code division multiple access (CDMA) spread spectrum communication system, characterized in that, according to a difference in cell radius between adjacent cells, transmission or despreading of each adjacent base station is determined. The amount of delay, in the downlink, adjusts the amount of transmission delay of the signals transmitted by adjacent base stations, the base stations of large radius cells transmit signals in advance, and the base stations of small radius cells lag behind in transmitting signals; in the uplink, each adjacent base station is adjusted The amount of despreading delay of the despreading signal is delayed by the base stations of the large radius cell, and the base stations of the small radius cell are despread in advance.

8. The method for setting a synchronization delay of a synchronous code division multiple access spread spectrum communication system according to claim 7, characterized in that, in the uplink, the time at which all mobile stations in a cell transmit uplink data is a cell boundary mobile station The transmission time is prevailing, and the transmission is respectively delayed according to the distance between itself and the current base station.

9. The synchronization delay setting method for a synchronous code division multiple access spread spectrum communication system according to claim 8, wherein after the base station completes the despreading, the base station reversely adjusts the corresponding despreading delay amount, and then communicates with the superior. Network communication to restore synchronization between the base station and a superior network.

10. The method for setting a synchronization delay of a synchronous code division multiple access spread spectrum communication system according to claim 6, characterized in that, in a downlink, a frame header signal of a base station with a long distance is transmitted first, and a base station with a short distance is transmitted The frame despread signal is sent after the frame header signal is delayed; the despread signal time of the base station with the longest distance in the uplink is delayed, and the despread signal of the base station with the short distance is advanced in time.

11. The method for setting a synchronization delay of a synchronous code division multiple access spread spectrum communication system according to claim 10, characterized in that, in the uplink, the base station despreading is performed according to the base station setting standard of the mobile station in the cell. Depending on the quasi-transmission position, the standard transmission position is set to the boundary of the cell, so that the mobile station with a small distance from the base station delays transmitting uplink data accordingly, so that its signal reaches the base station of the cell in synchronization with the signal transmitted by the mobile station at the boundary. .