CN1855765A - Primary upload synchronizing method in TDMA system - Google Patents

Abstract

The invention discloses an initial uplink synchronization method in a time division synchronous code division multiple access system. Each subframe in the system includes TSO, downlink pilot time slot DwPTS, uplink pilot time slot UpPTS, guard time slot GP and TS1 ～TS6, TS0～TS6 are service time slots, the method is: after the mobile station receives the downlink pilot signal sent by the base station in the downlink pilot time slot DwPTS in the predetermined subframe, it completes the downlink synchronization; the mobile station does not send In the subframe of the downlink pilot signal, a time point is selected within a period of time from the end of TS0 to the end of GP as the starting moment for sending the uplink pilot signal to the base station, thereby initiating the initial uplink synchronization process. Moreover, in the initial uplink synchronization process, the base station searches for a period of time from the end of TS0 to the beginning of TS1 to detect the uplink synchronization signal. This method can increase the radius of the cell, and further meet the requirements of long-distance user access.

Description

A Method of Initial Uplink Synchronization in Time Division Synchronous Code Division Multiple Access System

technical field

The invention relates to an uplink synchronization technology in a mobile communication system, in particular to an initial uplink synchronization method in a Time Division Synchronous Code Division Multiple Access (TD-SCDMA) system.

Background technique

The Time Division Synchronous Code Division Multiple Access (TD-SCDMA) system is based on Time Division Duplex (TDD) technology, which uses different time slots on the same frequency channel to receive and transmit data.

The physical channel of TD-SCDMA includes three-layer structure: the first layer is radio frame, the second layer is subframe, and the third layer is time slot. Specifically, the physical channel is composed of several wireless frames, one wireless frame is 10ms, and each wireless frame is divided into two consecutive 5ms subframes, and each subframe includes seven business time slots and three special time slots .

As shown in Figure 1, among the seven business time slots, the 0th time slot is fixedly allocated to the downlink, the first time slot is fixedly allocated to the uplink, and the rest of the time slots can be allocated arbitrarily between the uplink and downlink. The three special time slots in the hatched part are downlink pilot time slot (DwPTS), uplink pilot time slot (UpPTS), and guard time slot (GP). Among them, the DwPTS time slot is used to send the downlink synchronization code to complete the downlink synchronization; the UpPTS time slot is used to send the uplink synchronization code to complete the initial uplink synchronization. Among them, DwPTS includes 96 chips (chip), GP includes 96 chips, UpPTS includes 160 chips, and the width of each chip is 0.78125us.

When the user is in an idle state, it needs to maintain downlink synchronization and listen to broadcast information, and randomly select one of the available uplink synchronization codes for initial uplink synchronization. The initial uplink synchronization process in the TD-SCDMA system is as follows:

The base station sends the DwPTS to the mobile station, and the mobile station completes downlink synchronization according to the downlink synchronization code after obtaining the downlink synchronization code. The mobile station obtains the usable uplink synchronization code according to the corresponding relationship between the uplink synchronization code and the downlink synchronization code. The mobile station sends UpPTS to the base station. After the base station searches and detects the UpPTS sent by the mobile station, it estimates the uplink transmission time and transmission power adjustment information corresponding to the user. The base station notifies the mobile station of the transmission through the fast physical access channel (FPACH). Power and sending time adjustment information: After receiving the adjusted power and sending time sent by the base station, the mobile station adjusts the sending power and sending time, and the establishment of initial uplink synchronization is completed.

The above process is the basic uplink synchronization process in the prior art. In the actual application process, due to the uncertain distance between the mobile station and the base station, when the mobile station sends UpPTS to the base station, the radio wave propagation delay generated between the two may be different. Therefore, if the mobile station is to realize the initial uplink Synchronization, from the perspective of the base station, should make the start time point of the received uplink synchronization signal fall within the GP time period specified in the frame structure. If the start time of the signal is advanced to the DwPTS time period or delayed to the TS1 time period, the base station may not be able to detect the uplink synchronization signal due to the interference of other signals on DwPTS or TS1, resulting in initial uplink synchronization failure.

Therefore, when the mobile station sends the UpPTS, in order to meet the above time requirements, the mobile station must send the UpPTS in advance based on the time specified in the frame structure, so as to avoid that the signal arrives at the base station within the TS1 time of the base station. However, the mobile station can only advance the UpPTS to the end of the DwPTS at most, that is, 96 chips in advance, that is, the time of the GP length, so as to avoid that the signal arrives at the base station within the DwPTS time of the base station.

However, if the cell radius is too large, even if the mobile station sends the UpPTS signal ahead of the GP time, the UpPTS may still fall within the TS1 time period of the base station due to propagation delay when it arrives at the base station. That is to say, the coverage radius of the cell is constrained by GP,

The cell radius is: the number of chips that can be sent in advance x the speed of light/(chip rate x 2)

Then, since the number of chips that can be sent in advance is 96, the speed of light is 30×10 ⁴ Km/s, and the chip rate is 1.28M/S, the cell radius is calculated to be 11.25KM. That is to say, when the GP is 96 chips, the maximum cell coverage radius is 11.25 kilometers.

Moreover, after the N-frequency point system is introduced, even if the terminal sends Up-PTS at a frequency point that does not send DwPTS, since the base station transmits DwPTS, there is energy leakage to other frequency points, and the attenuation of this energy is often smaller than the path loss, so The terminal still can only send the UP-PTS after receiving the DwPTS, so as to prevent the uplink synchronization signal received by the base station from being interfered by the out-of-band leakage of the downlink pilot signal.

To sum up, the current single/multi-frequency TD-SCDMA cell radius bottleneck is 11.25Km. However, since TD-SCDMA works in the 2GHz frequency band in 3GPP, the coverage radius of 11.25km can meet the general networking requirements. However, if TD-SCDMA technology is applied in a lower frequency band, such as 400MHz trunking communication system, it may require a larger coverage radius, such as 20 kilometers, in some rural areas. However, the existing technology limits the radius of the cell to not exceed 11.25KM. If this limit is exceeded, the base station will not be able to detect the uplink synchronization signal, and the terminal will not be able to access the network.

Contents of the invention

In view of this, the purpose of the present invention is to provide an initial uplink synchronization method in a TD-SCDMA system, which can increase the radius of a cell, and further meet the access requirements of a long-distance mobile station.

In order to achieve the above object, the present invention provides an initial uplink synchronization method in the TD-SCDMA system, each subframe in the TD-SCDMA system includes TS0, downlink pilot time slot DwPTS, uplink pilot time slot UpPTS, guard time Slot GP and TS1~TS6, TS0~TS6 are business time slots, the method is implemented as follows:

a. The mobile station completes downlink synchronization according to the downlink pilot signal sent by the base station through the downlink pilot time slot DwPTS in the predetermined subframe;

b. In the subframe where the base station does not send the downlink pilot signal, the mobile station selects a time point within a period of time from the end of the time slot TS0 to the end of the GP as the starting moment for sending the uplink pilot signal to the base station, and initiates the initial Uplink synchronization, complete the initial uplink synchronization.

In step b, during the initial uplink synchronization process of the mobile station, the base station searches for a period of time from the end of TS0 to the beginning of TS1 to detect an uplink synchronization signal.

Initial uplink synchronization is initiated in step b, and the steps for completing the initial uplink synchronization include:

b1. The base station searches the window within the period of time, and estimates the uplink transmission time and transmission power adjustment information corresponding to the user according to the searched uplink synchronization signal;

b2. The base station notifies the mobile station of the transmission power and transmission time adjustment information;

b3. After receiving the adjusted power and sending time sent by the base station, the mobile station adjusts the sending power and sending time, and the initial uplink synchronization is completed.

In step b2, the base station notifies the mobile station of the transmission power and transmission time adjustment information through the fast physical access channel FPACH.

The predetermined subframe in step a is set periodically.

The period described in step a is fixed or irregular time intervals.

The method of the present invention transmits the uplink and downlink pilot signals at intervals in the TD-SCDMA system, and the window for the base station to detect the UP-PTS starts after TS0 and continues until before TS1 starts, so the radius of the cell can be increased to further satisfy Requirements for remote user access. And it can be calculated that since the uplink synchronization signal can be sent 96 chips ahead of time, the radius of the cell can be expanded to 22.5km. Failed to complete the initial uplink synchronization due to the impact.

Description of drawings

Fig. 1 is the subframe structure of TD-SCDMA system;

FIG. 2 is a schematic flow diagram of the present invention for realizing initial uplink synchronization;

FIG. 3 is a schematic diagram of the time for sending the uplink pilot signal and the time for the base station to detect the uplink pilot time slot according to the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings.

The present invention adopts the same frame structure as shown in FIG. 1 . It should be emphasized that: for the DwPTS in the present invention, a specific subframe is used to send downlink pilot signals, while in non-specific subframes, this time slot can be used to provide mobile stations to send uplink pilot signals. That is to say, the base station can send the downlink pilot signal in the time slot in the predetermined subframe, and the mobile station can use the time slot to send the uplink pilot signal in the subframe in which the base station does not send the downlink pilot signal.

Moreover, the transmission period of the Dw-PTS downlink pilot signal can be set, for example, the downlink pilot signal is transmitted every N frames, where N can be an integer greater than 1. Of course, the transmission period can be a fixed value, for example, if the transmission period is 2, then the downlink synchronization signal is sent every other frame, or it can be a series of preset values, such as the interval between the first and second transmission is 3 subframes, the second and third transmissions are separated by 4 subframes, etc.

As shown in Figure 3, the mobile station can use the subframe that does not transmit the downlink pilot signal to use the downlink time slot to transmit the uplink pilot signal, then the time period for sending the uplink pilot signal is between the beginning of the DwPTS and the end of the GP, that is, That is, the earliest is when the DwPTS starts, and the latest is when the GP ends; the base station's search and detection window for the UP-PTS should start from the end of TS0 and last until before the start of TS1.

In this way, the mobile station transmits UpPTS in the subframe that does not transmit DwPTS, and the start time of transmitting UpPTS can be extended forward by 96 Chips to occupy the position of the original DwPTS, so it can be calculated by using the above formula of cell radius The cell radius is 22.5KM.

Based on this, referring to Fig. 2, the initial uplink synchronization process of the present invention is as follows:

Step 201: the base station sends a DwPTS to the mobile station in a predetermined subframe, and the mobile station completes downlink synchronization according to the downlink synchronization code after obtaining the downlink synchronization code.

Step 202: The mobile station obtains the uplink synchronization code that can be used according to the correspondence between the uplink and downlink synchronization codes, and in the subframe where the base station does not send DwPTS, the mobile station performs a period of time from the end of TS0 to the end of GP In , select a time point as the starting time point for sending the UpPTS to the base station, and send the uplink pilot sequence.

Step 203: After searching for the UpPTS sent by the mobile station, the base station estimates the uplink transmission time and transmission power adjustment information corresponding to the user, and notifies the mobile station of the transmission power and transmission time adjustment information through the Fast Physical Access Channel (FPACH). Moreover, in the subframe in which the base station does not transmit the DwPTS, the search window of the base station starts at the end of TS0 and lasts until before the start of TS1.

Of course, in the subframe in which the base station sends the DwPTS, the mobile station can also send the uplink synchronization signal within the time period in the prior art, and at this time, the search and detection window of the base station can remain unchanged.

Step 204: The mobile station adjusts the transmission power and transmission time after receiving the power and transmission time that need to be adjusted from the base station. The establishment of the initial uplink synchronization is completed.

In a word, the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention.

Claims (6)

1, a kind of initial uplink method for synchronous in TDS-CDMA system; each subframe comprises TS0, descending pilot frequency time slot DwPTS in this system; uplink pilot time slot UpPTS, protection time slot GP and TS1～TS6; TS0～TS6 is a business time-slot; it is characterized in that this method may further comprise the steps:

A. travelling carriage is finished down-going synchronous according to the down-bound pilot frequency signal that the base station sends by descending pilot frequency time slot DwPTS in predetermined subframe;

B. travelling carriage does not send in the subframe of down-bound pilot frequency signal in the base station, finish to a period of time that GP finishes, to choose a time point at time slot TS0, as the initial moment that sends uplink pilot signal to the base station, the initiation initial uplink is synchronous, and it is synchronous to finish initial uplink.

2. initial uplink method for synchronous according to claim 1 is characterized in that: in step b, in the travelling carriage initial uplink synchronizing process, the base station was searched in a period of time that described TS0 finishes to begin to TS1, detected uplink synchronizing signals.

3, method according to claim 2 is characterized in that, the initiation initial uplink is synchronous among the step b, finishes the synchronous step of initial uplink and comprises:

B1, base station search window in described a period of time, and estimate the up transmitting time of this user's correspondence and the adjustment information of transmitting power according to the uplink synchronizing signals that searches;

The transmitting power and the transmitting time adjustment information of b2, base station notice travelling carriage;

B3, travelling carriage are adjusted transmitted power and transmitting time after receiving the power and transmitting time of the needs adjustment that the base station sends, and initial uplink is finished synchronously.

4, method according to claim 3 is characterized in that, the base station is by the transmitting power and the transmitting time adjustment information of physical access channel FPACH notice travelling carriage among the step b2.

5, method according to claim 1 is characterized in that, predetermined subframe described in the step a is to set in the cycle.

6, method according to claim 5 is characterized in that, the cycle described in the step a is fixed, or the random time interval.

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