TW201338489A - Base station synchronization for wireless communication systems - Google Patents

Abstract

The present invention is a system and method for time synchronizing a plurality of base stations in a wireless communication system. The system determines an estimate of a timing accuracy associated with each base station. When a base stations's timing accuracy is over a threshold, the system determines if there is a neighboring base station with a better timing accuracy. The base station over the threshold is adjusted in response to an estimated difference between that base station and the neighboring base station.

Description

Base station synchronization of Wuxian Communication System

The present invention is related to digital communication systems. In particular, the present invention relates to a system and method for synchronizing a plurality of base stations in a cellular communication system.

The disclosed third generation wireless protocol requires a method based on a simple but expensive procedure whereby the base stations are externally synchronized to an external power source of high accuracy.

The technique of supporting base station synchronization requires that a base station listen to synchronous transmissions from its neighbors, such as a synchronous channel (SCH) or a universal control physical channel (CCPCH), and engage in a program executed by a similar user equipment (UE) to synchronize. Another method requires each base station to send a special synchronization data set (Burst) from time to time to coordinate listening to one or more neighbors of the transmission. Another method allows the user device to measure the time difference of arrival (TDOA) of the transmissions from the two hives, respectively. These technologies use a highly prepared power source in each base station. These technologies are expensive and inconvenient because each base station has this power source.

Therefore, there is a need for a system and method that allows for fast, efficient, and less expensive synchronization between operating base stations without consuming additional physical resources.

The invention is a time synchronization complex base station in a wireless communication system System and method. The system determines a predicted value associated with one of the time accuracy of each of the base stations. When the time accuracy of a base station exceeds a critical value, the system determines whether a neighbor base station has an optimal time accuracy. The base station exceeding the threshold value is adjusted according to a predicted time difference between the base station and the neighbor base station.

Other objects and advantages of the system and method of the present invention will become apparent to those skilled in the <RTIgt;

The preferred embodiments of the present invention are described below with reference to the drawings, in which like elements are denoted by like reference numerals.

The first diagram introduces a simple wireless broadband code division multiple access (CDMA) or time division duplex (TDD) communication system 18. The system 18 includes a plurality of Node Bs 26, 32, 34, a plurality of wireless network controllers 36, 38, 40, a plurality of user devices 20, 22, 24 and a core network 46. A Node B 16 within the system 18 communicates with the User Equipment (UE) 20-24. The Node B 16 has a Single Site Controller (SC) coupled to a single base station 30 or a plurality of base stations 30 ₁ ... 30 _n . Each base station has a connected geographical area, that is, a honeycomb. Although the present invention only discloses base station synchronization, those skilled in the art may also utilize the present invention to perform cellular synchronization.

A group of Node Bs 26, 32, 34 are coupled to a Radio Network Controller (RNC) 36. The wireless network controllers 36...40 are also connected to the core network 46. For the sake of brevity, only a single Node B will be discussed below, but the present invention is applicable to a complex Node B.

According to a preferred embodiment, the radio network controller 36 maintains base station synchronization within and between the B nodes 26, 32, 34. Referring to the second figure, the wireless network controller 36 can request measurement from a base station 30 ₁ ... 30 _n or user equipment 20, 22, 24 through its message generating device 53; through its measurement receiving device 54 is used to receive measurements; its synchronization controller 55 is used to optimally update its state predictions based on the measurements; and management is stored in a group state of a covariance matrix 57. The storage states are used to synchronize and represent the time error of each base station relative to a reference value, the rate of change of each time error, and the transmission delay between base stations 30.

The wireless network controller 36 also manages a set of measurements stored in a database 59, including: the arrival time of a measured waveform (ie, a synchronized data set); measured by a user device 20 from two base stations The arrival time difference of the transmission; and the prediction of the state uncertainty and measurement uncertainty. The wireless network controller 36 uses advanced filtering techniques, such as Kalman filters, to predict parameters that define relative clock migration, and to refine parameters such as the exact range between a component and other components. The predicted time migration is used to infer the frequency mismatch between the base station frequency reference values and a reasonable check to ensure that occasional, inaccurate measurements do not destroy the process.

The wireless network controller 36 assigns a time quality to each of the base stations 30 ₁ ... 30 _n . This time quality is measured by the radio network controller 36 by selecting a base station as the time reference reference for all other base stations. All other base stations assign a variable time quality that is updated based on measurements and applied corrections. This time quality can be an integer (such as 0 to 10). Smaller quality values suggest better accuracy. Alternatively, this time quality can be a continuous (eg floating point) variable. Preferably, the reference base station (master base station) permanently assigns a time quality of zero. All other base stations are assigned changes and can be adjusted based on the reference base station. To introduce this time quality hierarchy design, the fourth diagram shows a master base station in which all slave base stations Slave 1, Slave 2, and Slave 3 are assigned time quality values based on the changes of the master base station. In one embodiment, the time quality of the slave base station Slave 2 is assigned a value that varies according to the slave base station Slave 1, and the slave base station Slave 3 is assigned a time quality value that varies according to the slave base station Slave 1.

The normal operating mode of the wireless network controller 36 updates a covariance matrix 57 based on the state stored in the wireless network controller database 59, which is updated every other predetermined time unit (eg, every 5 seconds). Clock or time determined by an operator). One of the components of the covariance matrix 57 is the predicted variation of the time error of each base station.

When the time error variation of a base station exceeds a predetermined threshold, the radio network controller 36 initiates a message to support the time error update of the base station. This update action can be achieved by one of three methods. The first is that the base station measures from a neighbor base station 30 ₁ , 30 ₂ ... 30 _n according to the indication.

Base station arrival time (BSTOA) of the data group; the second is that the neighbor base station 30 ₁ , 30 ₂ ... 30 _n with one of the better accuracy measures the arrival time of the base station transmitted by the target base station according to the indication; The third is that a user equipment 20 measures the base station arrival time of the synchronization data group of the base station and a neighbor base station 30 ₁ , 30 ₂ ... 30 _n .

In the first and second methods of using the base station to the base station arrival time of the base station, it is necessary to observe the arrival time of one base station transmission to another base station. Please refer to FIG Third, a base station 30 ₁ to transfer a predetermined time sends a known transmission pattern. The transmission pattern may be a synchronization data set from the synchronization data set generation device 62 in the base station 30 ₁ that penetrates an isolation device 64 before being transmitted via an antenna 70. The receiving base station 30 ₁ uses its measuring device 60 to detect the transmitted waveform, which will output a large value when the received signal matches the expected flag. If the receiving device and the transmitting device are in the same position and have an accurate synchronized clock, the output of the measuring device 60 will coincide with the transmitted waveform. However, the clock is not accurate and the transmission path delay will cause a time difference.

The transmission path delay is defined by equation (1).

R/c+x (l)

R/c is the distance between a transmitting unit and a receiving unit, R, divided by the speed of light, c. The x term compensates for device delays. When the base station is very far away, the transmission path delay is usually dominated by the R/c term. Radio waves travel at the speed of light, about 1 ft/ns or 3 x 108 m/s. The purpose of the base station synchronization is to align these base stations between 1-3 us. Therefore, this distance makes sense when the base station separation distance is on the order of 1/2 哩 (1 km) or more. However, for pico or micro honeycombs, the separation distance is tens of meters, which is meaningless compared to the measurement accuracy of the advantage, x.

Based on these considerations, it is important to obtain the separation distance when attempting to synchronize a base station that is far away (greater than 1 km). When attempting to synchronize base stations within a distance of 50 meters, the actual position does not matter. After the measurement of the arrival time of the base station to be executed, the known transmission distance stored in the wireless network controller database 59 is subtracted, and the difference between the two is regarded as the time between the base stations.

The third method measures the relative time difference of arrival (TDOA) of transmissions transmitted from two different base stations as observed by a user equipment. The user equipment is measured and Report the observed time difference of arrival (TDOA) from the transmission between the two base stations. The wireless network controller 36 sends a message to the user devices 20, 22, 24 to measure the time difference of arrival between the two base stations. Upon receiving the message, the user equipment 20, 22, 24 receives the transmission of the two base stations via its antenna 72 and isolation device 66, and uses the user equipment measurement receiving device 68 to measure the time difference of arrival and the amount. The test is transmitted to the base station to which it is connected.

If the location of the user equipment is known (ie, its range r1 and r2 to the two base stations are known) and both base station times are correct, the time difference of arrival is defined by equation (2).

(r1-r2)/c (2)

The measurement error from this value may be an indicator that the time reference is inaccurate. As is known to those skilled in the art, if the ranges r1 and r2 are small enough to be true in a pico-sized hive, the value does not need to be known. Observing the arrival time difference can be directly used as one of the transmission time differences.

When a method is selected, the appropriate message is transmitted to a base station 30 ₁ ... 30 _n or a user device 20, 22, 24. If the message is sent to a base station 30 ₂ , the base station is told to observe and measure that neighbor. If the message is sent to a user device 22, the user device is told to observe the base station and its own base station.

Returning to the second diagram, the wireless network controller 36 has stored a range between the base stations 30 ₁ ... 30 _n in its database 59. The wireless network controller 36 then checks to see if a neighbor base station 30 ₁ needs to be updated, which has a better time quality than the base station 30 ₂ . When such a neighbor base station 30 ₁ is found, a message is initiated to the neighbor base station to take a measurement from the "out of sync" base station 30 ₂ . Alternatively, the wireless network controller 36 can send a message to the "unsynchronized" base station 30 ₂ and ask it to retrieve one of the neighbor base stations 30 ₁ for measurement. The requested base station (the "non-synchronized" base station 30 ₂ ), for the purposes of this embodiment, then takes the measurement of the "in-sync" base station 30 ₁ and sends the measured value Return to the wireless network controller measurement device 54. The wireless network controller measuring device 54 forwards the measured value to the synchronization controller 55, which calculates the transmission time of the measurement by subtracting the transmission time R/c.

When the wireless network controller synchronization controller 55 calculates the transmission time, the value is compared to the value stored in the wireless network controller database 59. The wireless network controller synchronization controller 55 then calculates the Kalman filter gain and uses the difference between the calculated and predetermined arrival times and the general gain to update the state in the covariance matrix 57. If the difference is greater than a certain threshold, the radio network controller message generating means 53 then sends another message to the "non-synchronized" base station 30 ₁ to adjust its time reference and its reference frequency, thereby The network controller 36 is "synchronized" with other base stations 30 ₃ ... 30 _n under the control of the network controller 36.

The base station 30 ₂ performs the required adjustments and reports it to the wireless network controller measurement device 54. Information within the radio network controller 36 updates the library system, comprising: the subject base station's 30 ₂ time reference calibration, the time rate of change, which co-variance matrix update points (57 of the most importantly, having a RMS prediction time Error and migration error), and the update of its time quality. Please refer to the fourth figure. A base station (whose time base is corrected according to comparison with other base stations) must not assign a time quality equal to or better than its subordinate base station. This ordering ensures stability. The description is as follows. If one base station Slave 2 is to be corrected, the base station Slave 2 can only assign a value smaller than the time quality of its slave base station Slave 1. This ensures that the time quality of a base station does not synchronize with a subordinate base station of the same or lower level, which may eventually cause a cluster base station to migrate to "non-synchronous" to the master base station.

As previously described, another method of extracting measurements to adjust the "non-synchronized" base station 30 ₂ uses a user device 20, 22, 24. If the wireless network controller 36 selects this method, a message is sent to the user equipment 22 to measure the "asynchronous" base station 30 ₂ and the "synchronous" base station 30 ₁ synchronization data set. When the user device 22 retrieves the measurements, the measurements are sent to the wireless network controller 36 for processing. Similar to the above method, the measurement is compared with the known measurement stored in the wireless network controller database 59 and the covariance matrix 57 and sent to the "asynchronous" base station 302. .

5A and 5B are flow diagrams showing a system in accordance with the preferred embodiment. The wireless network controller 36 updates the covariance matrix 57 and the database 59 once every unit time (step 501). When the radio network controller 36 detects that the time error variation of a base station 30 ₃ ... 30 _n exceeds a predetermined threshold (step 502), the radio network controller 36 determines whether to use a base station to measure the base. The arrival time of the station or a user equipment is used to measure the time difference of arrival, thereby updating the time error variation of the "non-synchronous" base station (step 503). If the wireless network controller 36 determines to measure the base station arrival time, a message is transmitted to the neighbor base station of the "non-synchronized" base station to measure the base station arrival time, or the message is transmitted to The "non-synchronized" base station is configured to measure the arrival time of the neighbor base station (step 504). The appropriate base station then takes the necessary measurements (step 505) and transmits the measurements to the wireless network controller 36 (step 506). If the radio network controller 36 determines to measure the time difference of arrival, the radio network controller 36 transmits a message to a user equipment to measure the time difference of arrival between the two base stations (step 507a), one of which is "non- Synchronize "base station. The user equipment measures the time difference of arrival of each base station (step 507b) and transmits the difference between the measurements to the wireless network controller 36 (step 57c). When the wireless network controller 36 receives the appropriate measurements (step 508), the wireless network controller 36 compares the measurements to the values stored in the wireless network controller database 59 (step 509). . If the difference is greater than a certain threshold, the wireless network controller 36 transmits a message to the "unsynchronized" base station to adjust its time reference or its reference frequency based on the difference (step 510). The "asynchronous" base station performs the required adjustments (step 511) and reports it back to the wireless network controller 36 (step 512). The wireless network controller database 59 and the covariance matrix 57 are then updated to incorporate the new values (step 513).

A preferred embodiment is a system and method stored in each wireless network controller 36. In the prior art, a Control Radio Network Controller (C-RNC) communicates directly with its base station and a Servo Radio Network Controller (S-RNC) communicates directly with its user equipment. In the case where the neighbor base station is controlled by a different radio network controller (RNC), it may be necessary to increase the communication between the control radio network controller and the servo radio network controller to control the neighbor base station and the user equipment. .

Another embodiment requires that each pair of base stations can listen to each other to shift their frequency closer to another base station. The relative amount of adjustment is defined by a unique set of weights that are assigned to each base station and stored in the wireless network controller database 59. The process of adjusting each base station is the same as that described in the preferred embodiment except for the "non-synchronous" base. Both the station and the "synchronous" base station need to be adjusted according to the weight assigned to each base station. With different weights, we can achieve centripetal degrees of varying degrees (from complete center to complete dispersion).

The preferred embodiment of the present invention enables a radio network controller 36 to transmit a time correction and/or frequency correction to a base station 30 ₃ ... 30 _n . The master base station is responsible for ensuring that each base station has a time reference value subordinate to the master base station, which accurately falls within a specified limit. The radio network controller 36, in its algorithm and correction, assumes that a negligible error exists between the master base station and its base station, and therefore assumes that all base stations have the same time reference value.

Therefore, the wireless network controller 36 does not attempt to predict an individual time error between the master base station and its base station, and the master base station must reduce or compensate the time between the master base station and other base stations. The error is because the link to the wireless network controller 36 does not perform a correction. This embodiment discloses a complete interface between a wireless network controller 36 and a master base station. This full interface allows the master base station to apply its solution to accommodate subordinate synchronization of the pico hive.

In another embodiment, each base station has an independent time and frequency reference value that enables a radio network controller 36 to transmit time correction and/or frequency correction to each base station. The radio network controller 36 predicts the state of each base time and frequency error in its algorithm and correction.

Therefore, the wireless network controller 36 attempts to predict individual time errors between the base stations and the master base station. The measurement associated with one base station does not help predict the status of another base station. Therefore, the base station manufacturer only needs to be in time for the base station. Inter-migration provides an error in loose boundaries, and each base station must have an acceptable connectivity when transmitting over the air to another base station (same or different base stations).

This embodiment facilitates the large honeycomb area with a relatively long distance between the base stations. However, its ability to correct a base station (which is subordinate to the time reference of the same master base station) is limited by the measurement associated with a base station (which is dependent on a time reference value of a master base station). .

Each base station in this embodiment uses an independent time reference value, but the master base station provides a frequency reference value. A radio network controller 36 transmits time corrections and/or single frequency corrections for each base station to a master base station. The wireless network controller 36 ensures that the clock frequency of each base station is subordinate to the clock of the master base station. The wireless network controller 36, in its algorithm and correction, assumes that a negligible migration error exists between the master base station and its assigned base station, and predicts an offset that is considered constant. .

Therefore, the radio network controller 36 predicts an individual time error between the master base station and its base station, and the base station's common frequency shift compared to the master base station.

The features of this embodiment are similar to those of the previous embodiment, wherein a base station that is farther from the master base station is advantageous. This embodiment provides a mechanism to remove long distances from time to time. Using the assumption that the time offsets are stable, this embodiment uses one of the base stations (whose frequencies are subordinate to the master base station) to measure all of the base stations (which are subordinate to The mobility of the master base station).

Another embodiment enables the wireless network controller 36 to provide predictions for the master base station to support base station synchronization with the master base station. A radio network controller 36 transmits time correction and/or frequency correction of each connected base station to its master base station. The master base station ensures that its associated base station has a time reference value subordinate to the master base station, which falls within a specified limit. The master base station can be elected to use the base station's unique predictions for the base station synchronization. The radio network controller 36, in its algorithm and correction, generates an optimal prediction of one of the time and frequency errors between the master base station and its base station. In performing state prediction, the wireless network controller 36 weights the relative trust between the measurements and the base station error uncertainty.

Therefore, the wireless network controller 36 attempts to predict an individual time error between the master base station and its base station, and the master base station reduces and/or compensates the master base station and each base station (its Time error dependent on its time reference value, or assistance from the wireless network controller 36.

While the invention has been described in its preferred embodiments, the scope of the invention is defined by the following claims.

16, 26, 32, 34‧‧‧ Node B

18‧‧‧Communication system

20, 22, 24‧‧‧ User equipment

30, 30 ₁ ... 30 _n ‧‧‧ base station

36, 38, 40‧‧‧ Wireless Network Controller

46‧‧‧core network

54‧‧‧Measurement receiving device

55‧‧‧Synchronous controller

57‧‧‧Covariance matrix

59‧‧‧Database

60‧‧‧Measurement device

62‧‧‧Synchronous data set generation device

64‧‧‧Isolation device

70‧‧‧Antenna

The first figure is a block diagram of a communication system.

The second figure is a block diagram of a Radio Network Controller (RNC) made in accordance with a preferred embodiment of the present invention.

The third figure is a block diagram of a base station and user equipment in accordance with a preferred embodiment of the present invention.

The fourth figure is an introduction to the hierarchical time quality design produced in accordance with a preferred embodiment of the present invention.

5A and 5B are flow diagrams of a system made in accordance with a preferred embodiment of the present invention.

26, 32, 34‧‧‧ Node B

18‧‧‧Communication system

20, 22, 24‧‧‧ User equipment

30, 30 _1...n ‧‧‧ base station

36, 38, 40‧‧‧ Wireless Network Controller

46‧‧‧core network

Claims (7)

The apparatus for time synchronization of a plurality of base stations in a wireless communication system includes: transmitting a synchronized burst from at least one hosted hive, wherein the master hive has a better comparison than other hives a time synchronization quality; measuring, for at least one cell other than the master cell, a synchronization burst from at least the master cell and indicating to a radio network controller (RNC) a timing associated with the synchronization burst; And transmitting, by the RNC, a timing adjustment to the at least one hive other than the master hive. For example, the method described in claim 1 further includes: updating a covariance matrix database. The method of claim 1, wherein the measuring further comprises: transmitting a request for a base station arrival time (BSTOA) value to a hive other than the master hive; and transmitting the BSTOA value. The method of claim 1, wherein the measuring further comprises: transmitting a request for a base station arrival time (BSTOA) value to at least one of the plurality of user equipments (UEs) to Measuring the at least one honeycomb in addition to the master honeycomb; and transmitting the BSTOA value. A base station comprising: a circuit configured to transmit a synchronized burst from at least one master beacon, wherein, in the case where the base station is in the master honeycomb, the master honeycomb has a better comparison than the other honeycombs a time synchronization quality; configured to measure a synchronized burst from at least the master beehive for at least one of the bees other than the master honeycomb and the case where the base station is in the hive other than the master honeycomb Dedicating, to a radio network controller (RNC), a timing circuit associated with the synchronization burst; and configured to use the base station in the hive other than the master beacon The RNC receives a timing adjustment circuit for the at least one hive other than the master beehive. The base station of claim 5, further comprising: configured to send a request for a base station arrival time (BSTOA) value to the base station if the base station is in the master control cell a circuit in addition to a hive outside the hosted beehive; and circuitry configured to transmit the BSTOA value if the base station is in the hive other than the master hive. An integrated circuit (IC) comprising: circuitry configured to output a synchronized burst from at least one master cell, wherein, in the case where the base station is in the master cell, compared to the other a honeycomb, the master honeycomb having a preferred time synchronization quality; configured to measure at least one of the honeycombs other than the master honeycomb Retrieving a synchronization burst of the master cell and indicating to the radio network controller (RNC) a timing associated with the synchronization burst if the base station is in the cell other than the master cell And circuitry configured to receive, from the RNC, a timing adjustment of the at least one hive other than the master beacon, in the case where the base station is in the hive other than the master beehive.