RU2855395C1 - Method for synchronising multiple high-frequency base stations in mobile broadband wireless access systems - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention relates to a method for synchronising base station signals in a wireless radio communication system, and can be used in LTE and 5G radio communication systems for synchronising signals of eNodeB or gNodeB base stations. The method includes primary synchronisation of base station signals and secondary synchronisation of base station signals, characterised in that during secondary synchronisation of base stations, frames of the forward channel from neighbouring base stations are received, the reception delay of frames relative to the nearest signal of the receiver base station is calculated, the calculated delay values of frame reception from each base station are transmitted to a time server located in the network core, corrective values of time intervals are calculated in the time server based on the delay values obtained from multiple base stations, the calculated corrective values of time intervals are transmitted from the time server to the corresponding base stations via a forward communication channel, the signal is corrected by the received corrective value of the time interval.

EFFECT: reduction of switching time and reduction of data loss when a mobile station moves between cells.

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Description

The invention relates to the field of radio engineering, in particular to a method for synchronizing signals of base stations in a wireless radio communication system, and can be used in LTE and 5G radio communication systems for synchronizing signals of eNodeB or gNodeB base stations.

Synchronicity of an LTE or 5G radio communication system refers to the synchronicity of the transmission of message frames from different base stations in the forward channel.

A high-frequency base station array refers to several eNodeB or gNodeB base stations interacting with each other within a single LTE and 5G radio network, with up to 20 stations. High-frequency base stations operate at frequencies defined by the relevant 3GPP LTE and 5G standards.

The closest to the claimed method is the method for synchronizing base stations in mobile communication networks WO 1999057826 “Method of synchronization of a base station network”, which is a prototype for the proposed technical solution, in which each base station is equipped with a measuring unit for receiving signals from neighboring base stations, time shifts are measured between the signals of the base stations, data on time shifts are transmitted to the central server, where correction time intervals are calculated [1].

The disadvantage of the above method is the impossibility of quickly automatically switching to other base stations when the mobile station moves.

Also known is the synchronization method RU 2438247 “Method for synchronizing base station nodes”, in which the signal of the GPS satellite system is used for the purposes of synchronizing base station signals [2].

The disadvantage of the above method is the need for each base station to have a device for receiving GPS satellite signals, which leads to an increase in the cost of the base station.

The technical problem is the need to develop a synchronization method that is free from the above-mentioned shortcomings and ensures fast automatic switching to other base stations when a mobile station moves from cell to cell without data loss and increases the accuracy of determining the location of the mobile station.

The technical result consists in reducing the switching time and decreasing data losses when moving a mobile station between cells.

Reduction of switching time and reduction of data loss when moving a mobile station between cells is ensured by synchronization of base stations of the communication system, which ensures fast and coordinated transmission of control and signaling messages and increased accuracy of determining the location of mobile users through the use of time-synchronized measurements of signal parameters from multiple base stations, which minimizes errors caused by desynchronization of signal sources.

The claimed method is carried out as follows.

Synchronization according to the claimed invention is carried out in two stages.

The first stage involves initial clock adjustments for all eNodeBs or gNodeBs. This can be accomplished in several ways. For example, at this stage, the base station time can be set to Moscow time via the internet, or synchronization can be accomplished by connecting to external time servers using NTP, PTP, and other protocols. Accuracy requirements at this stage are not high—up to 2 µs.

At the second stage, secondary, more precise synchronization is performed.

Secondary synchronization is performed in the forward link of an LTE or 5G radio system by determining the difference between the exact (expected) time of frame reception and its actual reception. This time determination is based on determining the angles of the complex representation of CRS or DMRS signals, proportional to the timing offset of the reference signals (Cell Reference Signals (CRS) in LTE and DeModulation Reference Signal (DMRS) in 5G). After determining the difference between the exact and actual frame reception times, the transmission delay of subsequent frames for each eNodeB or gNodeB is calculated. This delay is calculated by the LTE or 5G network core time server and transmitted to adjust the eNodeB or gNodeB clock in the forward link, monitored by each base station, in order to minimize the difference between the exact and actual frame reception times.

We will cover the synchronization method in more detail.

1. Perform an initial adjustment of the clocks of all eNodeBs or gNodeBs with an accuracy of 2 µs.

To do this, synchronize each eNodeB or gNodeB with the internet server. To do this, set the time zone to Europe/Moscow and synchronize the time using NTP (Network Time Protocol) as follows.

Sets the time zone by automatically creating a symbolic link to determine the current local time and will update the time zone if it exists.

Checking the time zone

2. Perform time synchronization using NTP.

To do this, install and run an NTP client. In most distributions, this is ntp or ntpdate.

Start the NTP service and check synchronization, including checking available NTP servers and the time offset value.

3. Receive forward channel reference signals (CRC for eNodeB base stations and DMRS for gNodeB base stations) of each base station from neighboring eNodeBs or gNodeBs at a specified frequency.

To achieve this, primary synchronization is performed using PSS (Primary Synchronization Signal) signals. PSS signals are used for time synchronization (TTI, slots, OFDM symbols) and determination of the physical cell identifier. The implementation of primary synchronization is described in 3GPP standard 38.211 [1].

For each eNodeB or gNodeB, CRC signals are received in accordance with [1] from no more than five base stations. CRS or DMRS signals in the resource grid are spaced in time and do not overlap [3].

Reception of CRC/DMRS reference signals is carried out by direct discrete Fourier transform [4].

4. Determine the sets of time delays { } reception of reference signals of the m -th base station relative to the time of reception of reference signals from the n -th base station, where k , m , n = 1… N.

When receiving individual symbols of an LTE and 5G frame, the adjacent CRS or DMRS have a difference , where k , m , n = 1… N , the angles of the complex representation of CRS or DMRS signals (reference signals) from neighboring stations are proportional to the time offset – delay. Given that the reception level of signals from the m -th and n -th base stations in the receiver of the k -th base station must be higher than the required value acceptable for communication with the k -th base station.

For each k -th base station, k = 1… N , where N is the number of base stations in the network, the time delay is determined reception of the reference signal of the m -th base station relative to the time of reception of the reference signal from the n -th base station. Here, as in determining the difference in angles , the reception level of signals from the m -th and n -th base stations in the receiver of the k -th base station must be higher than the required value acceptable for communication with the k -th base station. Delay is defined as follows

,

Where – central reception frequency.

5. The found values of the set of time delays { } received frames from neighboring base stations eNodeB or gNodeB are sent to the LTE or 5G network core time server to adjust the base station clocks.

The forwarding of frame reception delay values from neighboring network base stations to the LTE or 5G network core time server is carried out at least twice per second via the existing wired network connecting eNodeB/gNodeB base stations based on the Ethernet protocol described in IEEE standards of the 802.3 group [5, 6].

6. In the time server, the LTE or 5G network core calculates the time interval values by which the “clock” of each eNodeB or gNodeB must be shifted to synchronize them.

Based on the found values of the set of time delays { } the reception of reference signals from the m -th base station relative to the time of reception of reference signals from the n -th base station, where k , m , n = 1… N , constitute a system of target functions:

;

…………………..………………

;

…………………..………………

,

Where , i = 1… N – the values of time intervals by which it is necessary to shift the “clock” of each of the base stations of the LTE or 5G network for their synchronization;

m – the smaller number of the base station from which the signal is received;

n is the higher number of the base station from which the signal is received;

k is the number of the base station in which the difference in signal reception time from neighboring base stations is calculated;

N is the number of base stations in the LTE or 5G network.

This system is solved using the least squares method.

According to the least squares method [7], the solution of this system for each base station ( k , = 1… N ) is a system of differential equations:

;

;

……………………………………………………………………………..………………

= 0,

where k , m , n = 1… N.

After taking partial derivatives, we obtain a system of linear equations consisting of N equations with N unknowns. The solution to this system for the k -th base station, k = 1… N , is the set of values of time intervals , i = 1… N , by which it is necessary to shift the “clock” of each of the base stations of the LTE or 5G network for their synchronization.

7. The found values of time intervals are transmitted in the forward channel in each frame in pre-determined positions of the resource grid by all eNodeB or gNodeB.

8. Receive frames and select from specific positions in the resource grid the time interval values by which the clock of each base station of the LTE or 5G network must be shifted. Once these time interval values are known, the clock of each eNodeB or gNodeB is adjusted. , i = 1… N , for the i -th base station in order to minimize the difference between the exact and real time of frame reception and ensure synchronization.

Figure 1 shows an LTE or 5G network consisting of eNodeB or gNodeB base stations, an X2 interface connecting the base stations in accordance with an example of the present invention.

Figure 2 shows a connectivity matrix according to an example of the present invention.

Figure 3 shows a plurality of time delays in accordance with an example of the present invention.

The claimed invention is explained by an example.

Fig. 1 shows an LTE or 5G network consisting of eNodeB or gNodeB base stations and X2 interface links connecting these base stations. X2 in Fig. 1 represents a connection between adjacent base stations (eNodeB or gNodeB) intended for information exchange and subscriber mobility management between these stations.

It is assumed that the first stage has been completed, with the initial clock adjustment of all eNodeBs or gNodeBs performed with an accuracy of 2 μs. It is assumed that the connectivity of the network's base stations is defined by the following connectivity matrix, shown in Fig. 2, where "1" indicates the presence of radio communication between the base stations, and "0" indicates its absence.

In accordance with the connectivity matrix shown in Fig. 2, Fig. 3 shows a set of time delays in μs { } reception of reference signals of the m -th base station relative to the time of reception of reference signals from the n -th base station, where k , m , n = 1…7.

In accordance with the set of time delays presented in Fig. 3, we obtain the following system of differential equations.

;

;

……………………………………………………………………..

= 0.

After taking partial derivatives, the following system of linear equations is obtained.

;

;

;

;

;

;

;

Let us present similar terms

;

;

;

;

;

;

.

The solution to this system of equations is the following values , i = 1…7, by which it is necessary to shift the “clock” of each of the base stations of the LTE or 5G network for their synchronization:

; ; ; ; ; ; .

Bibliography

1. International application WO 1999057826 for the invention “Method for synchronizing a network of base stations”, published 11.11.1999.

2. Patent RU 2438247 for the invention “Method for synchronizing base station nodes”, Russian Federation, published 12/27/2011.

3. GPP TS 38.211 V17.3.0 (2022-09). ^3rd Generation Partnership Project. Technical Specification Group Radio Access Network. NR. Physical channels and modulation (Release 17).

4. Sergienko A.B. Digital signal processing. - 2nd. - St. Petersburg: Piter, 2006. - P. 751. - ISBN 5-469-00816-9.

5. IEEE 802.3u-1995. doi: 10.1109/IEEESTD. 1995.7974916. ISBN 978-0-7381-0276-4.

6. H. Frazier (2002) [1998]. “The 802.3z Gigabit Ethernet Standard.” IEEE Network. 12(3). IEEE: 6-7. doi: 10.1109/65.690946.

7. Linnik Yu.V. The method of least squares and the basics of the mathematical-statistical theory of observation processing. – 2nd ed. – Moscow, 1962.

Claims (21)

1. A method for synchronizing a plurality of high-frequency base stations in a mobile communications network, including primary synchronization of signals of base stations eNodeB and/or gNodeB and secondary synchronization of signals of base stations eNodeB and/or gNodeB, characterized in that during secondary synchronization of base stations eNodeB and/or gNodeB the following is performed: 1) reception of signals from base stations eNodeB and/or gNodeB of the direct channel from neighboring base stations eNodeB and/or gNodeB, 2) determination of a set of time delays receiving signals from base stations eNodeB and/or gNodeB relative to the nearest reference signal Cell Reference Signals (CRS) and/or DeModulation Reference Signal (DMRS) of a neighboring base station eNodeB and/or gNodeB by direct discrete Fourier transform, wherein for each base station eNodeB and/or gNodeB, the delay in receiving signals from base stations eNodeB and/or gNodeB is determined relative to the time of receiving the signal from base stations eNodeB and/or gNodeB according to the formula Where - the delay in the time of reception of the reference signal CRS and/or DMRS from the base station eNodeB and/or gNodeB relative to the time of reception of the reference signal CRS and/or DMRS from the neighboring base station eNodeB and/or gNodeB, measured by the base station eNodeB and/or gNodeB performing the measurement; wherein k, m, n = 1…N, N is the number of base stations in the network; - the difference in the presentation angles of the reference signals CRS and/or DMRS received from the neighboring base stations eNodeB and/or gNodeB, measured by the base station eNodeB and/or gNodeB performing the measurement; - the circular frequency at which the eNodeB and/or gNodeB base station conducting the measurement operates; - the central reception frequency at which the eNodeB and/or gNodeB base station conducting the measurement operates; 3) transmission of calculated values of signal reception delays base stations eNodeB and/or gNodeB from each base station eNodeB and/or gNodeB to the time server located in the network core, 4) calculating the correction values of time intervals in the time server based on the values of signal reception delays received from multiple base stations eNodeB and/or gNodeB base stations eNodeB and/or gNodeB by solving the system of objective functions using the least squares method: Where - the measured delay in receiving signals from base stations eNodeB and/or gNodeB relative to the time of receiving the reference signal CRS and/or DMRS from the neighboring base station eNodeB and/or gNodeB; - the value of the correction value that must be applied to the eNodeB and/or gNodeB base station; - the value of the correction value that must be applied to the neighboring eNodeB and/or gNodeB base station; where m is the smaller number of the base station from which the signal is received; n is the larger number of the base station from which the signal is received; k is the number of the base station in which the difference in signal reception time from neighboring base stations is calculated; N is the number of base stations in the LTE or 5G network. 5) transmission of the calculated correction values of time intervals from the time server to the corresponding base stations eNodeB and/or gNodeB via a direct communication channel, 6) adjusting the signal of the base station eNodeB and/or gNodeB to the received correction value of the time interval. 2. The method according to paragraph 1, characterized in that synchronization is performed in two stages, wherein in the first stage the primary synchronization of the clock signals of all base stations eNodeB and/or gNodeB is performed with an accuracy of no more than 2 microseconds by connecting to external time servers. 3. The method according to paragraph 1, characterized in that the reception of signals from base stations eNodeB and/or gNodeB of the direct channel from neighboring base stations eNodeB and/or gNodeB is carried out from no more than five neighboring stations.