A clock synchronization system and method for DECT call system

Abstract

The present invention provides a clock synchronization system and method for a DECT call system, wherein the first clock of a call master station is synchronized with the second clock of one or more remote control units, a first clock source is provided in the call master station, the first clock source is connected to a first clock generator, the first clock generator is connected to a first PHY chip, and the first PHY chip is connected to an extended Ethernet interface; the remote control unit includes a second PHY chip and a third PHY chip, the second PHY chip and the third PHY chip are respectively connected to the second clock generator; the remote control unit is also provided with a first interface and a second interface, the first interface is connected to the extended Ethernet interface and is also connected to the second PHY chip, the second interface is connected to the third PHY chip and is also connected to the first interface of another remote control unit, and they are linked in sequence to achieve clock synchronization between several remote control units and the call master station.

Description

Technical Field

[0001] The invention relates to the field of digital cordless telephone communication, in particular to a clock synchronization system and method for a DECT call system. Background Art

[0002] The Digital Enhanced Cordless Telecommunications (DECT) system is an enhanced digital cordless telephone standard developed by the European Telecommunications Standards Institute. It is an open, evolving digital communication standard mainly used for cordless telephone systems. It can provide high-quality voice and data services for high-density, small-scale communications. It is a framework for cordless communications. In a call system, clock synchronization can ensure that the time base of all devices is consistent, thereby avoiding communication errors and data loss caused by time differences, which helps to improve the overall performance and reliability of the communication system. At the same time, clock synchronization can reduce data conflicts and inconsistencies caused by time asynchrony, thereby improving the efficiency and accuracy of data transmission. Therefore, clock synchronization is particularly important in call systems that require high-speed, real-time transmission.

[0003] The common practice for achieving clock synchronization in the existing DECT call system is that the wireless transceiver unit of the call master station (BS) generates a high-precision square wave synchronization signal DECT SYNC, and uses a differential driver such as an RS485 isolation driver or transformer coupling to differentially transmit the analog square wave signal to the wireless transceiver unit of the remote control unit (RRU) to achieve clock synchronization of all wireless transceiver units between the RRU and the BS. This is a wired analog signal transmission method, which will cause the following problems: 1. The analog clock synchronization signal is affected by the cable length and the differential driver transceiver, resulting in a large delay, so that only a star connection is supported between the call master station (BS) and the remote control unit, which is extremely inconvenient for wiring on large-scale events; 2. The delay of the clock synchronization signal is affected by the line length, and delay compensation needs to be performed according to different line lengths, which increases the difficulty of use for users; therefore, a clock synchronization system and method for a DECT call system is urgently needed to solve the above problems. Summary of the invention

[0004] The present invention provides a solution to the technical problem in the prior art that the transmission delay of analog synchronous clock signals in cables is large, the delay of clock synchronization signals is affected by the line length, and compensation needs to be made according to different line lengths.

[0005] Specifically, the present invention provides a clock synchronization system for a DECT call system, wherein a first clock of a call master station (BS) is synchronized by a second clock of one or more remote control units (RRU1, ..., RRUN), a first clock source (TCXO1) is provided in the call master station (BS), the first clock source (TCXO1) is connected to a first clock generator, the first clock generator is connected to a first PHY chip, and the first PHY chip is connected to an extended Ethernet interface; the remote control unit (RRU1) includes a second PHY chip and a third PHY chip, the second PHY chip and the third PHY chip are respectively connected to the second clock generator; the remote control unit (RRU1) is also provided with a first interface and a second interface, the first interface is connected to the extended Ethernet interface and the second PHY chip, the second interface is connected to the third PHY chip, and the first interface of another remote control unit (RRU2) is connected, and the two interfaces are linked in sequence to achieve clock synchronization of a plurality of remote control units (RRU1, ..., RRUN) and the call master station (BS).

[0006] Preferably, the call master station (BS) is further provided with a first main control chip, the first main control chip is connected to the first PHY chip via a first RGMII port, the first main control chip is provided with a timer, and the timer is connected to a first clock generator.

[0007] Preferably, the remote control unit (RRU) includes a second main control chip, the second PHY chip and the third PHY chip are respectively connected to the second main control chip, and the second main control chip is connected to the second clock generator.

[0008] Preferably, it is characterized in that the remote control unit (RRU1) further includes a second clock source (TCXO2) and a DECT wireless transceiver, the second clock generator includes a first PLL, a second PLL and a third PLL, the second clock source (TCXO2) is connected to the ref1 pin of the first PLL, the ref1 pin is respectively connected to the ref2 pin of the second PLL and the ref3 pin of the third PLL; the first PLL is connected to the second main control chip, the INA pin of the first PLL is connected to the OUTB pin of the second PLL, the second PLL is respectively connected to the second PHY chip and the third PHY chip, the second main control chip is connected to the INC pin of the third PLL, and the third PLL is connected to the DECT wireless transceiver.

[0009] A clock synchronization method for a DECT call system, which uses the above-mentioned clock synchronization system for a DECT call system, is specifically as follows:

[0010] First, the first clock source (TCXO1) is divided by the first time generator to generate a first reference clock to the first main control chip, and the first main control chip generates a PTP timestamp message; at the same time, the first clock source (TCXO1) is divided by the first time generator to generate a clock signal to the first PHY chip, and the first PHY chip generates a first SyncE synchronous Ethernet signal; the PTP timestamp message and the first SyncE synchronous Ethernet signal are both transmitted to the remote control unit (RRU1) through the extended Ethernet interface;

[0011] Then, the first SyncE synchronous Ethernet signal is input into the second PHY chip and enters the second clock generator, and the second clock generator loops back the clock signal to the third PHY chip, and the third PHY chip generates a second SyncE synchronous Ethernet signal and outputs it to another remote control unit (RRU2), and at the same time, the second clock generator outputs a second reference clock to the second main control chip;

[0012] The PTP timestamp message enters the second main control chip for phase modulation and then outputs a 1PPS_OUT signal to the second clock generator. The second clock generator refers to the 1PPS_OUT signal and then outputs a DECT SYNC signal to the DECT wireless transceiver, thereby realizing synchronization of the roaming clock of the DECT wireless transceiver of the remote control unit with the clock of the call master station (BS).

[0013] The beneficial effects of the present invention are as follows: compared with the prior art, the present invention provides a clock synchronization system for a DECT call system, wherein a first clock of a call master station (BS) is synchronized by a second clock of one or more remote control units (RRU1, ..., RRUN), the call master station (BS) is provided with a first clock source (TCXO1), the first clock source (TCXO1) is connected to a first clock generator, the first clock generator is connected to a first PHY chip, the first PHY chip is connected to an extended Ethernet interface; the remote control unit (RRU1) includes a second PHY chip and a third PHY chip, the second PHY chip and the third PHY chip are respectively connected to the second clock generator; the remote control unit (RRU1) RU1) is also provided with a first interface and a second interface, wherein the first interface is connected to the extended Ethernet interface and is also connected to the second PHY chip, the second interface is connected to the third PHY chip and is also connected to the first interface of another remote control unit (RRU2), and they are linked in sequence to achieve clock synchronization between several remote control units (RRU1, ..., RRUN) and the call master station (BS), the call master station and the remote control unit can be connected through a standard network cable for network communication, without the need to arrange a clock synchronization signal line separately, the wiring method is diversified, and daisy chain, star, and star daisy chain mixed modes are supported. When interface expansion is required, a standard PTP switch can be purchased, which is of great convenience for the construction and replacement of user equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of a daisy chain connection of the present invention;

[0015] Figure 2 This is a star connection schematic diagram of the present invention;

[0016] Figure 3 This is a schematic diagram of the daisy chain star-shaped hybrid connection of the present invention;

[0017] Figure 4 This is an internal schematic diagram of the main call station of the present invention;

[0018] Figure 5 is an internal schematic diagram of a remote control unit of the present invention;

[0019] Figure 6 A schematic diagram of the signal flow of the main call station of the present invention;

[0020] Figure 7 Schematic diagram of signal flow of the remote control unit of the present invention. DETAILED DESCRIPTION

[0021] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with the accompanying drawings.

[0022] First, the English abbreviations that may be used in this application are explained:

[0023] DECT: Digital enhanced cordless telephone, an enhanced digital cordless telephone standard developed by the European Telecommunications Standards Institute (ETSI), is an open, evolving digital communication standard mainly used in cordless telephone systems. It can provide a framework for high-quality voice and data services for high-density, small-scale communications.

[0024] Time slot: In order to increase the number of users, the time is divided into N parts in the time division multiplexing system, and each time slice is allocated to N users for access. Each time slice is called a time slot.

[0025] Intercom: Internal wireless communication system, mainly used for internal communication needs between a group of people

[0026] BS: Base Station. All waistpacks need to be connected to the base station to complete voice calls.

[0027] RRU: Remote Radio Unit, (remote radio unit - usually translated as 'remote control unit'), separates the baseband signal unit and the transceiver unit (remote). That is, the baseband unit and the radio unit of the base station are separated, and the baseband signal is transmitted between the two (baseband signal unit and transceiver unit) (long distance) (using light or the Internet), so that the signal-to-noise ratio can reach the best state.

[0028] PU: Portable Unit, a communication device carried by internal communication users, which needs to be connected to the main communication station to complete voice transmission

[0029] TDMA: Time division multiple access Time division multiple access technology divides time into small parts and allocates them to different users

[0030] DAC: Digital-Analog convertor, used in receivers to convert received digital signals into voice, images, etc.

[0031] ADC: Analog-Digital converter, used in transceivers to convert analog signals such as voice and images into digital signals.

[0032] DECT SYNC: SYNC is the abbreviation of synchronization. DECT SYNC refers to the DECT synchronization signal, which is usually used for DECT wireless data frame synchronization. Since the DECT frame data cycle is 10ms, the DECT SYNC synchronization signal is usually 100Hz;

[0033] SyncE: Synchronous Ethernet, refers to a PHY chip that supports SyncE and receives serial data streams from upstream devices and extracts clock signals from them.

[0034] PTP: precision time protocol, a high-precision time synchronization protocol with sub-microsecond accuracy;

[0035] PPS: Pulse Per Second, pulse per second signal, outputs a pulse square wave in 1 second.

[0036] OC: Ordinary Clock. This clock node has only one PTP port in the same PTP domain to participate in time synchronization, and synchronizes time from the upstream clock node through this port.

[0037] BC: Boundary Clock, a clock node with multiple PTP ports in the same PTP domain that participate in time synchronization. It synchronizes time from the upstream clock node through one of its ports and publishes time to downstream clock nodes through the remaining ports.

[0038] TC: Transparent clock, compared with BC / OC, BC / OC needs to keep time synchronization with other clock nodes, while TC does not keep time synchronization with other clock nodes. TC has multiple PTP ports, but it only forwards PTP protocol messages between these ports and corrects the forwarding delay, and does not synchronize time through any port.

[0039] See also Figure 1-7The present invention provides a clock synchronization system for a DECT call system, comprising a call master station BS and several remote control units (RRU1, ..., RRUN). The call master station BS is provided with a first clock source TCXO1, the first clock source TCXO1 is connected to a first clock generator, the first clock generator is connected to a first PHY chip, and the first PHY chip is connected to an extended Ethernet interface; the remote control unit comprises a second PHY chip and a third PHY chip, the second PHY chip and the third PHY chip are respectively connected to the second clock generator; the remote control unit is also provided with a first interface and a second interface, the first interface is connected to the extended Ethernet interface and is also connected to the second PHY chip, the second interface is connected to the third PHY chip and is also connected to the first interface of another remote control unit, and the two interfaces are linked in sequence to realize clock synchronization of several remote control units and the call master station BS, the call master station BS and the remote control unit RRU can be connected to the network through a standard network cable for network communication, and there is no need to arrange a clock synchronization signal line separately.

[0040] See also Figure 1 In this embodiment, a daisy chain connection is adopted between the call master station BS and the remote control unit RRU. The call master station BS serves as a PTP clock source and is synchronized with the first interface of the remote control unit RRU1 through the 1588V2 standard protocol. The second interface of the remote control unit RRU1 is synchronized with the first interface in the Linux system through the phc2sys instruction. At the same time, a bridge relationship is established between the first interface and the second interface to realize the intercommunication of network data packets. Similarly, RRU2 is synchronized with RRU1, and RRU3 is synchronized with RRU2. Finally, each level of RRU realizes clock synchronization with the call master station BS.

[0041] See also Figure 2 In this embodiment, the call master station BS and the remote control RRU are connected in a star shape. When the call master station BS is connected to multiple remote control units RRU, if the number of physical ports is insufficient, a PTP switch can be connected as an extended Ethernet interface for expansion. Each network port of the switch is connected to a remote control unit RRU, forming a star shape. At this time, the call master station BS acts as the master clock source and acts as an OC; the PTP switch acts as a TC, the slave port of the switch is synchronized with the call master station BS, and the master clock port of the switch is connected to the RRU; all remote control units RRU are synchronized with the switch as slaves, and finally the clock synchronization of all RRUs and BS is achieved.

[0042] See also Figure 3In this embodiment, the call master station BS and the remote control unit RRU support a daisy chain star hybrid connection mode. The call master station BS is connected to the PTP switch for interface expansion. Each network port of the switch is connected to a remote control unit RRU, forming a star architecture. The first-level RRU is then daisy-chained to 2~3 RRUs, forming a hybrid connection mode. At this time, the BS serves as the main clock source and acts as the OC; the PTP switch acts as the TC, the switch slave port is synchronized with the call master station BS, the master port is connected to the first-level remote control unit RRU, the first-level remote control unit RRU serves as the BC, and then the RRU is cascaded downward, and finally all RRUs are synchronized with the BS.

[0043] See also Figure 4 and Figure 5 In this embodiment, a first main control chip is also provided in the call master station (BS), and the first main control chip is connected to the first PHY chip through the first RGMII port. The first main control chip is provided with a timer, and the timer is connected to the first clock generator. The timer is used as a PTP Master to send and receive timestamps to achieve frequency and phase adjustment between the RRU and the BS; the first PHY chip transmits Ethernet data packets and also outputs frequency signals as a clock source of SyncE; the remote control unit also includes a second main control chip, and the second PHY chip and the third PHY chip are respectively connected to the second RGMII port and the third RGMII port of the second main control chip, and the second main control chip is connected to the second clock generator. A 1588 timer is provided in the second main control chip, which is responsible for processing timestamp information and performing frequency and phase modulation according to the message transmitted from the call master station BS. The second PHY chip and the third PHY chip are set as a master-slave relationship in the system (the second PHY is the master and the third PHY is the slave), and are synchronized in the Linux system through phc2sys.

[0044] Also, see Figure 5 and Figure 7The remote control unit also includes a second clock source TCXO2 and a DECT wireless transceiver. The second clock generator includes a first PLL, a second PLL and a third PLL. The second clock source (TCXO2) is connected to the ref1 pin of the first PLL, and the ref1 pin is respectively connected to the ref2 pin of the second PLL and the ref3 pin of the third PLL; the first PLL is connected to the second main control chip, the INA pin of the first PLL is connected to the OUTB pin of the second PLL, the second PLL is respectively connected to the second PHY chip and the third PHY chip, the second main control chip is connected to the INC pin of the third PLL, and the third PLL is connected to the DECT wireless transceiver; specifically From the perspective of FIG. 1 , the second clock generator has multiple phase-locked loops PLL. The synchronous Ethernet SyncE_OUT signal of the second PHY chip is used as the frequency source and input to the second PLL. The second PLL generates a SyncE_IN signal and gives it to the third PHY chip and transmits it to the next level. The second PLL simultaneously loops back the SyncE_OUT frequency to the first PLL, outputs a PTP timestamp reference clock with the same frequency as SyncE_OUT to the second main control chip, and the second main control chip performs frequency and phase modulation according to the timestamp information of the PTP message, outputs 1PPS_OUT to the third PLL, and the PLL locks the frequency error and phase of 1PPS_OUT, and outputs a DECT SYNC signal to the DECT wireless transceiver. The signal is in the same frequency and phase as TCXO1 of the call master station BS. In this embodiment, the SyncE+PTP dual mode of roaming clock synchronization of DECT internal call equipment is realized. The SyncE+PTP dual mode, in simple terms, uses the SyncE synchronization frequency accuracy to achieve frequency homology, and the PTP synchronization phase makes the phase offset within a reasonable error range.

[0045] In this embodiment, the second clock source TCXO2 has temperature compensation and time keeping function. For example, the frequency stability of TCXO for 30 minutes is <±0.5ppm. With a synchronization interval of 1 second, the phase drift is <±1us to meet the accuracy requirement of DECT SYNC signal. The network clock synchronization is interrupted, the SyncE_OUT signal and the PTP time synchronization message are interrupted, and the RRU cannot obtain the clock synchronization of the upper level. At this time, the local TCXO2 will be used as the clock reference source of the first PLL / second PLL / third PLL in the second clock generator. The first PLL outputs the PTP timestamp reference clock to the second main control chip, and the second PLL outputs the SyncE_IN signal to the third PHY chip for transmission to the next level. The third PLL outputs the DECT SYNC signal to the DECT wireless transceiver. DECTSYNC is synchronized with the local TCXO2 for a certain period of time (<30min). When the clock signal phase drift exceeds the DECT requirement of <1us, the time keeping will fail. At this time, the line must be checked to restore the network clock synchronization.

[0046] This application provides a clock synchronization method for a DECT call system. Figure 6 First, the first clock source (TCXO1) is divided by the first clock generator to generate a first reference clock to the first main control chip, and the first main control chip generates a PTP timestamp message; at the same time, the first clock source TCXO1 is divided by the first clock generator to generate a clock signal to the first PHY chip, and the first PHY chip generates a first SyncE synchronous Ethernet signal; the PTP timestamp message and the first SyncE synchronous Ethernet signal are both transmitted to the remote control unit through the extended Ethernet interface;

[0047] Then, the first SyncE synchronous Ethernet signal is input into the second PHY chip and enters the second clock generator, and the second clock generator loops back the clock signal to the third PHY chip, and the third PHY chip generates a second SyncE synchronous Ethernet signal and outputs it to another remote control unit. At the same time, the second clock generator outputs a second reference clock to the second main control chip;

[0048] The PTP timestamp message enters the second main control chip for frequency and phase modulation, and then outputs a 1PPS_OUT signal to the second clock generator. The second clock generator refers to the 1PPS_OUT signal and then outputs a DECT SYNC signal to the DECT wireless transceiver; the roaming clock of the DECT wireless transceiver of the remote control unit is synchronized with the clock of the call master station (BS). The second clock source TCXO2 has temperature compensation and time keeping function. For example, the frequency stability of TCXO for 30 minutes is <±0.5ppm, and the phase drift is <±1us with a synchronization interval of 1 second, which meets the accuracy requirements of the DECT SYNC signal.

[0049] Furthermore, when the second master control of the remote control unit generates the 1PPS_OUT signal, it also generates a PTP timestamp message to the second interface, and the second interface transmits the PTP timestamp message to the next-level remote control unit.

[0050] The advantages of the present invention are:

[0051] 1) The call master station BS and the remote control unit RRU can communicate through the network through a standard network cable connection, without the need to arrange a separate clock synchronization signal line. The wiring method is diversified and supports daisy chain, star, and star daisy chain mixed modes;

[0052] 2) When interface expansion is required, you can simply purchase a standard PTP switch, which is extremely convenient for user equipment construction and replacement;

[0053] 3) When the network quality degrades and synchronization fails or the network is interrupted, the system has the ability to maintain clock synchronization within 30 minutes, so that the roaming synchronization of several remote control units RRU1, RRU2...RRUN is not affected;

[0054] 4) The DECT SYNC synchronization signal meets the roaming clock synchronization accuracy requirements of the wireless transceiver.

[0055] The above disclosures are only several specific embodiments of the present invention, but the present invention is not limited thereto, and any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A clock synchronization system for a DECT call system, wherein: The first clock of the call master station (BS) is synchronized by the second clock of one or more remote control units (RRU1, ..., RRUN), characterized in that the call master station (BS) is provided with a first clock source (TCXO1), the first clock source (TCXO1) is connected to a first clock generator, the first clock generator is connected to a first PHY chip, and the first PHY chip is connected to an extended Ethernet interface; the remote control unit includes a second PHY chip and a third PHY chip, the second PHY chip and the third PHY chip are respectively connected to the second clock generator; the remote control unit is also provided with a first interface and a second interface, the first interface is connected to the extended Ethernet interface and the second PHY chip, the second interface is connected to the third PHY chip, and the first interface of another remote control unit is connected, and the two interfaces are linked in sequence to achieve clock synchronization of several remote control units with the call master station (BS); The call master station (BS) is also provided with a first main control chip, which is connected to the first PHY chip through a first RGMII port. The first main control chip is provided with a timer, which is connected to a first clock generator. The remote control unit includes a second main control chip, the second PHY chip and the third PHY chip are respectively connected to the second main control chip, and the second main control chip is connected to the second clock generator. The remote control unit also includes a second clock source (TCXO2) and a DECT wireless transceiver. The second clock generator includes a first PLL, a second PLL and a third PLL. The second clock source (TCXO2) is connected to the ref1 pin of the first PLL, and the ref1 pin is respectively connected to the ref2 pin of the second PLL and the ref3 pin of the third PLL. The first PLL is connected to the second main control chip, the INA pin of the first PLL is connected to the OUTB pin of the second PLL, the second PLL is respectively connected to the second PHY chip and the third PHY chip, the second main control chip is connected to the INC pin of the third PLL, and the third PLL is connected to the DECT wireless transceiver.

2. A clock synchronization method for a DECT call system, characterized in that: It adopts a clock synchronization system for a DECT call system as described in claim 1, which is specifically as follows: First, the first clock source (TCXO1) is divided by the first clock generator to generate a first reference clock to the first main control chip, and the first main control chip generates a PTP timestamp message; at the same time, the first clock source (TCXO1) is divided by the first clock generator to generate a clock signal to be transmitted to the first PHY chip, and the first PHY chip generates a first SyncE synchronous Ethernet signal; the PTP timestamp message and the first SyncE synchronous Ethernet signal are both transmitted to the remote control unit through the extended Ethernet interface; Then, the first SyncE synchronous Ethernet signal is input into the second PHY chip and enters the second clock generator, and the second clock generator loops back the clock signal to the third PHY chip, and the third PHY chip generates a second SyncE synchronous Ethernet signal and outputs it to another remote control unit. At the same time, the second clock generator outputs a second reference clock to the second main control chip; The PTP timestamp message enters the second main control chip for phase modulation and then outputs a 1PPS_OUT signal to the second clock generator. The second clock generator refers to the 1PPS_OUT signal and then outputs a DECT SYNC signal to the DECT wireless transceiver, thereby realizing synchronization of the roaming clock of the DECT wireless transceiver of the remote control unit with the clock of the call master station (BS).

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