CN104270810A - A kind of LTE-A system uplink synchronization method - Google Patents

Abstract

The present invention discloses an uplink synchronization method of an LTE-A system, comprising steps: 1) eNodeB obtains TA according to a reference signal in an uplink signal, and generates a timing adjustment command according to the TA value; 2) eNodeB sends the timing adjustment command to UE, then the eNodeB timer starts counting; 3) UE obtains the timing adjustment command, and adjusts the UE uplink TA value N _TA,new according to the TA value, and then restarts the UE timer; 4) eNodeB obtains the new TA value, and according to the new The TA value generates a timing adjustment command, then restarts the eNodeB timer, repeats steps 2) to 3); 5) the eNodeB timer times out and does not generate a timing adjustment command, restarts the eNodeB timer, and repeats steps 2) to 3). The invention overcomes the defect that the base station misjudges that the uplink is out of sync because the base station has not sent a timing adjustment command for a long time when the uplink channel quality is good and the time deviation is small, and maintains normal communication between the base station and user equipment.

Description

A kind of LTE-A system uplink synchronization method

technical field

The invention belongs to the technical field of LTE-A (Long Term Evolution Advance mobile communication long-term evolution) system, and specifically refers to an uplink synchronization method of an LTE-A system.

Background technique

In mobile communication systems, synchronization is a very critical process. Through this process, the user terminal and the base station realize time-frequency synchronization on the downlink and uplink, and the UE (user equipment) can obtain more detailed information of the current cell and information of neighboring cells before it can monitor paging or initiate a call. eNodeB (the name of the base station in LTE) can correctly demodulate the information sent by the UE.

Since LTE/LTE-Advanced adopts multiple access multiplexing technology based on OFDM (Orthogonal Frequency Division Multiplexing), it is very sensitive to time offset. In order to maintain the orthogonality between UE uplink signals, it is necessary to It is necessary to ensure that the UE and the eNodeB are synchronized—that is, when the uplink signals of each UE arrive at the eNodeB, the reception clocks are consistent. If the signals sent by different UEs arrive at the eNodeB at different times, different SC-FDMA symbols will be aliased together in the time domain, which will cause serious ISI (inter-symbol interference) and ICI (inter-carrier interference) at the eNodeB receiving end. , causing the eNodeB to fail to correctly demodulate the data sent by the UE, resulting in failure of normal communication between the UE and the eNodeB.

Whether the UE timer timeAlignmentTimer is running normally is the basis for judging synchronization at the UE side. When the timer is in the working state, the UE is considered to be uplink synchronized, and if the timer is not started or expires, the UE is considered to be out of uplink synchronization. When the UE is in the synchronization state, the eNodeB maintains uplink synchronization by sending a timing adjustment command, and the UE timer timeAlignmentTimer will restart after receiving the timing adjustment command from the eNodeB side of the base station. However, when the uplink channel quality is very good and the time deviation is small, because the eNodeB has not sent a timing adjustment command for a long time, the UE timer will time out due to the long-term failure to receive the timing adjustment command, which will cause the UE to wrongly determine that the uplink has occurred in the case of synchronization. out of step.

Contents of the invention

The purpose of the present invention is to solve the problem that when the uplink channel quality is very good and the time deviation is very small, the UE side timer times out due to eNodeB not sending a timing adjustment command for a long time, and it is wrongly judged that there is an out-of-sync situation in the uplink. A method for uplink synchronization of an LTE-A system.

In order to achieve the above object, a kind of LTE-A system uplink synchronization method designed by the present invention is special in that the method includes the following steps:

1) The eNodeB obtains the TA value according to the measurement of the reference signal in the uplink signal, and generates a timing adjustment command according to the TA value;

2) The eNodeB sends the timing adjustment command to the UE through the MAC control element, and then the eNodeB timer on the eNodeB side starts timing;

3) The UE acquires a timing adjustment command, and adjusts the UE uplink TA value N _TA,new according to the TA value in the timing adjustment command, and then restarts the UE timer;

4) The eNodeB obtains a new TA value according to the measurement of the reference signal in the uplink signal, and generates a timing adjustment command according to the new TA value, then restarts the eNodeB timer, and repeats steps 2) to 3) ;

5) The eNodeB timer expires and the eNodeB does not generate a timing adjustment command, restart the eNodeB timer, and repeat steps 2) to 3);

The eNodeB is a base station, TA is an uplink timing advance, and UE is a user equipment.

Preferably, the configuration period of the eNodeB timer is shorter than the configuration period of the UE timer. Considering that the UE may not be able to successfully demodulate the TA sent by the eNodeB at one time, retransmission may be required, so the period difference between the two timers must exceed a certain threshold. The configuration period of the eNodeB timer is 450ms-10000ms. If the configuration period is too small, it will increase the overhead of the system and occupy the frequency band resources of the system. If the configuration period is too large, the sensitivity of the system will decrease, which will lead to the decline of system performance.

Preferably, an initial synchronization stage is also included before the step 1), and the specific steps include:

0.1) The eNodeB obtains the time position of the downlink synchronization signal according to the measurement of the reference signal in the uplink signal, calculates the frame boundary of the received downlink signal, and uses the frame boundary as the downlink synchronization timing;

0.2) The UE uses downlink synchronization timing as an uplink signal transmission frame boundary, and transmits a random access preamble sequence at the boundary time;

0.3) After receiving the random access preamble, the eNodeB measures the difference between the timing of the random access preamble and the frame boundary of the downlink signal, thereby obtaining an initial TA value, and generates a timing adjustment command according to the initial TA value;

0.4) The eNodeB sends the timing adjustment command to the UE through a random access response message;

0.5) The UE adjusts the timing ahead of time for the uplink signal transmission time boundary according to the initial TA value in the timing adjustment command, so as to realize uplink synchronization.

Preferably, in the step 1), the specific steps for the eNodeB to obtain the TA value according to the measurement of the reference signal in the uplink signal are:

1.1) The physical layer of the eNodeB calculates the time offset value according to the reference signal in the uplink signal And report to the MAC layer of the eNodeB, the MAC layer of the eNodeB calculates the TA value,

Where TA is a 6-bit uplink timing advance, TA=0,1,2,...,63, is the time offset.

Preferably, in the step 3), the UE obtains the timing adjustment command, and adjusts the UE uplink TA value N _TA,new according to the TA value in the timing adjustment command. The specific steps include:

3.1) The UE acquires a timing adjustment command, and adds the received current TA value to the previously adjusted UE uplink TA value N _TA,old to obtain an adjusted UE uplink TA value N _TA,new , namely:

N _TA,new =N _TA,old +(TA-31)×16

Where: N _TA,new is the UE uplink TA value of the nth TTI (transmission time interval), N _TA,old is the UE uplink TA value of the n-1th TTI.

The principle of the present invention is: when the UE is in the synchronization state, the eNodeB maintains uplink synchronization by sending a timing adjustment command, but when the quality of the uplink channel is good and the time deviation is small, the eNodeB does not send a timing adjustment command for a long time, and the UE timer In the case of uplink synchronization, it will be misjudged and out-of-synchronization will occur. The present invention adds an eNodeB timer on the eNodeB side, corresponding to the UE timer. The UE timer and the eNodeB timer are started almost at the same time, but the configuration period of the eNodeB timer is shorter than that of the UE timer. In this way, after the eNodeB timer expires, the eNodeB side will send a timing adjustment command to the UE to restart the UE timer, so as to ensure that the UE timer will not time out due to not receiving the timing adjustment command for a long time in the case of synchronization, and ensure that the UE is in sync status.

The present invention has the advantages of: overcoming the defect in the prior art that the base station has not sent a timing adjustment command for a long time when the uplink channel quality is very good and the time offset is very small, which leads to the timeout of the UE side timer and wrongly judges that there is an out-of-sync situation in the uplink , the technical solution of adding a timer on the base station side, and its configuration period is shorter than the UE timer, avoids misjudgment and out-of-synchronization, and maintains normal communication between the base station and the user equipment.

Description of drawings

Figure 1 The overall block diagram of the system processing timing adjustment commands.

Figure 2 eNodeB synchronization-related processing flow chart.

Figure 3 is a flow chart of timing adjustment command processing on the UE side.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

The LTE-A system synchronization process is mainly divided into two parts: downlink synchronization and uplink synchronization. The downlink synchronization is mainly that the UE identifies the cell ID through the cell search process and obtains the downlink synchronization of the cell, and can read the cell broadcast information. This process is used both when the UE initially accesses a cell and when it is handed over between cells. Uplink synchronization is mainly that the eNodeB sends timing adjustment commands to instruct different UEs to adopt different TA (uplink time advance) to realize that the uplink data of each UE basically arrives at the eNodeB at the same time, and eliminates ISI (inter-symbol interference) and ICI (inter-subcarrier interference). Interference), as shown in Figure 1. After the downlink synchronization is established, the UE can successfully receive the downlink data, and the next step is the uplink synchronization process.

Uplink synchronization is mainly divided into two stages: initial synchronization and synchronization maintenance, which are respectively completed in PRACH (Physical Random Access Channel), PUSCH (Physical Uplink Shared Channel) and SRS (Sounding Reference Signal).

The process of the initial synchronization phase includes the following steps:

0.1) The eNodeB obtains the time position of the downlink synchronization signal based on the measurement of the reference signal in the uplink signal, calculates the frame boundary of the received downlink signal, and uses the frame boundary as the downlink synchronization timing.

0.2) The UE uses the downlink synchronization timing as the frame boundary for uplink signal transmission, and transmits a random access preamble (RACH Preamble) at the boundary time.

0.3) After receiving the random access preamble, the eNodeB measures the difference between the timing of the random access preamble and the frame boundary of the downlink signal, thereby obtaining the initial TA value, and generates a timing adjustment command (Timing Advance Command) according to the initial TA value .

0.4) The eNodeB sends the timing adjustment command to the UE through a random access response message.

0.5) The UE adjusts the timing of the uplink signal transmission time boundary in advance according to the initial TA value in the timing adjustment command, that is, adjusts in advance according to the initial TA value on the basis of the original transmission boundary, so that the propagation delay of the uplink and downlink can be offset, so that the uplink The moment when the signal arrives at the eNodeB side is aligned with the frame boundary of the downlink signal of the eNodeB, thereby achieving uplink synchronization. This initial TA value is used as the initial TA for the UE's uplink synchronization, and it is added to the initial TA value when the small-scale TA is subsequently received.

After the UE successfully completes the random access, the UE establishes a connection with the eNodeB.

The process of the synchronization hold phase includes the following steps:

1) The eNodeB obtains a 6-bit small-scale TA value based on the measurement of the reference signal in the uplink signal, and generates a timing adjustment command according to the TA value, as shown in Figure 2;

1.1) The physical layer of eNodeB is calculated according to the reference signal in the uplink signal (time offset value), and report to the MAC layer of the eNodeB, and the MAC layer of the eNodeB calculates the TA value,

Where TA is a 6-bit uplink timing advance, and the value range of TA is [0, 63], is the time offset.

2) The eNodeB sends the timing adjustment command to the UE through the MAC control element, and then the eNodeB timer on the eNodeB side starts timing.

The eNodeB timer on the eNodeB side corresponds to the UE timer. Considering that the UE may not be able to successfully demodulate the TA sent by the eNodeB at one time, retransmission may be required, and the period difference between the two timers must exceed a certain threshold. The periodic configuration of the eNodeB timer is obtained by subtracting the corresponding threshold from the UE timer, and the configuration range is 450ms-10000ms. Through various experiments and attempts, the relationship between the configuration period of the eNodeB timer and the configuration period of the UE timer in this solution is summarized as shown in Table 1 under the condition of ensuring the optimal system performance.

Table 1 eNodeB timer period configuration table

3) The UE obtains the timing adjustment command, and adjusts the UE uplink TA value N _TA,new according to the TA value in the timing adjustment command, and then restarts the UE timer, as shown in FIG. 3 ;

3.1) The UE obtains the timing adjustment command, and adds the received current TA value to the previously adjusted UE uplink TA value N _TA,old to obtain the adjusted UE uplink TA value N _TA,new , namely:

N _TA,new =N _TA,old +(TA-31)×16

Among them: N _TA,new is the UE uplink TA value of the nth TTI (transmission time interval), N _TA,old is the UE uplink TA value of the n-1th TTI, and the value range of TA is [0, 63] .

4) The eNodeB obtains a new TA value according to the measurement of the reference signal in the uplink signal, and generates a timing adjustment command according to the new TA value, then restarts the eNodeB timer, and repeats steps 2) to 3);

5) The eNodeB timer expires and the eNodeB does not generate a timing adjustment command, restart the eNodeB timer, and repeat steps 2) to 3).

The content not described in detail in this specification belongs to the prior art known to those skilled in the art.

Claims (6)

1. an LTE-A system uplink synchronization method, characterized in that: the method comprises the steps: 1) The eNodeB obtains the TA value according to the measurement of the reference signal in the uplink signal, and generates a timing adjustment command according to the TA value; 2) The eNodeB sends the timing adjustment command to the UE through the MAC control element, and then the eNodeB timer on the eNodeB side starts timing; 3) The UE acquires a timing adjustment command, and adjusts the UE uplink TA value N _TA,new according to the TA value in the timing adjustment command, and then restarts the UE timer; 4) The eNodeB obtains a new TA value according to the measurement of the reference signal in the uplink signal, and generates a timing adjustment command according to the new TA value, then restarts the eNodeB timer, and repeats steps 2) to 3) ; 5) The eNodeB timer expires and the eNodeB does not generate a timing adjustment command, restart the eNodeB timer, and repeat steps 2) to 3); The eNodeB is a base station, TA is an uplink timing advance, and UE is a user equipment. 2. The method for uplink synchronization of an LTE-A system according to claim 1, characterized in that: the configuration period of the eNodeB timer is greater than the configuration period of the UE timer. 3. The method for uplink synchronization of an LTE-A system according to claim 2, characterized in that: the configuration period of the eNodeB timer is 450ms-10000ms. 4. a kind of LTE-A system uplink synchronization method according to claim 1, is characterized in that: also comprise initial synchronization stage before described step 1), concrete steps comprise: 0.1) The eNodeB obtains the time position of the downlink synchronization signal according to the measurement of the reference signal in the uplink signal, calculates the frame boundary of the received downlink signal, and uses the frame boundary as the downlink synchronization timing; 0.2) The UE uses downlink synchronization timing as an uplink signal transmission frame boundary, and transmits a random access preamble sequence at the boundary time; 0.3) After receiving the random access preamble, the eNodeB measures the difference between the timing of the random access preamble and the frame boundary of the downlink signal, thereby obtaining an initial TA value, and generates a timing adjustment command according to the initial TA value; 0.4) The eNodeB sends the timing adjustment command to the UE through a random access response message; 0.5) The UE adjusts the timing ahead of time for the uplink signal transmission time boundary according to the initial TA value in the timing adjustment command, so as to realize uplink synchronization. 5. A kind of LTE-A system uplink synchronization method according to claim 1, is characterized in that: in described step 1), the concrete steps that eNodeB obtains TA value according to the measurement of the reference signal in the uplink signal are: 1.1) The physical layer of the eNodeB calculates the time offset value according to the reference signal in the uplink signal , and report to the MAC layer of the eNodeB, and the MAC layer of the eNodeB calculates the TA value, Where TA is a 6-bit uplink timing advance, TA=0,1,2,...63, is the time offset. 6. A kind of LTE-A system uplink synchronization method according to claim 1, is characterized in that: in described step 3), UE obtains timing adjustment order, and adjusts UE uplink TA value N according to the TA value in the timing adjustment order _{TA, the specific steps of new} include: 3.1) The UE acquires a timing adjustment command, and adds the received current TA value to the previously adjusted UE uplink TA value N _TA,old to obtain an adjusted UE uplink TA value N _TA,new , namely: N _TA,new =N _TA,old +(TA-31)×16 Where: N _TA,new is the UE uplink TA value of the nth TTI (transmission time interval), N _TA,old is the UE uplink TA value of the n-1th TTI.