Patent Application
20190059066
The present disclosure generally relates to time synchronization within a synchronization domain comprising one or a plurality of network nodes, and more specifically relates to time synchronization involving a wireless packet data network.
In a typical cellular system, also referred to as a wireless communications network, wireless terminals, also known as mobile stations or user equipments communicate via a Radio Access Network, RAN, to one or more core networks. The radio access network may comprise a plurality of access nodes or base stations that communicate with the wireless terminals or user equipments by means of radio signals and provide access to the core network.
The Third Generation Partnership Project, 3GPP, has established a plurality of generations of mobile communication standards. The Universal Mobile Telecommunications System, UMTS, is a third generation mobile communication system, which evolved from the Global System for Mobile Communications, GSM, to provide mobile communication services based on Wideband Code Division Multiple Access, WCDMA, access technology. Long-Term Evolution, LTE, often being referred to as fourth generation (4G), has been specified to increase the capacity and speed using orthogonal frequency division multiplexing, OFDM, in the downlink and Discrete Fourier Transform (DFT)-spread OFDM, also being referred to as single-carrier frequency-division multiple access (SC-FDMA) in the uplink.
With the ever increasing demands to increase the traffic volume and to reduce the latency, so-called fifth generation (5G) systems are currently been specified by 3GPP. Important aspects of 5G are to densify the network, and to use more spectrum. Additional available frequencies for next generation (5G) networks that are practically usable are located in very high frequency ranges (compared to the frequencies that have so far been used for wireless communication), such as 10 GHz and above.
Industry automation is also an expanding area, since tasks and complex processes are increasingly taken over by high-precision robots, automatized devices and factory cells. Many use cases require interworking of different devices and precise time synchronization of device actuation.
The required precise control in many cases can only be guaranteed if the latency between the controller unit (also being referred to as Programmable Logical Controller, PLC) and the field devices (also being referred to as IO devices or industry devices) is sufficiently low. In exemplary cases, the required end-to-end latency is in the range of 1-10 ms (e.g. for manufacturing cells), but in several extreme cases the required end-to-end latency may be less than 1 ms (e.g. for high-speed motion control).
Currently such low latency requirements of industry automation use cases are realized by wired technologies. Currently available wireless solutions, such as solutions called ISA100 wireless defined by the ISA100 Wireless Compliance Institute, WirelessHART defined by the HART Communication Foundation, or IEEE defined solution as IEEE 802.15.4 or IEEE-802.11 (also being referred to as WLAN), are not be able to provide the synchronized communication and the latency required for some use cases as described above. In the wired segment on the one hand some specific fieldbus technologies have been developed, while on the other hand industrial Ethernet-based solutions are also available. The most wide-spread and expanding Ethernet-based technology is the so-called PROFINET, which is an open, cross-vendor standard being standardized in IEC 61158, IEC 61784 for industry automation.
The PROFINET has following features and characteristics:
In case of RT (Real Time) class the latency between the controller and field device is in the 1-10 ms range and cyclic or a-cyclic communication can be used. In case of IRT (Isochronous Real Time) the delay is equal or less than 1 ms, together with 1 us jitter requirement. Most of the above mentioned industry applications may require IRT class-based communication, for others of them RT class may also be suitable.
RT-3 traffic class supports the Isochronous Real-time (IRT) communication, in which devices communicate to each other in a totally synchronized way, based on a pre-defined communication plan (organized in advance by a management/planning system). In RT-3 phase each of the devices has its own allocated time slice when it can send/receive a message. Devices are not permitted to communicate outside their own time-slice, the sent data will be dropped. This synchronous communication is compliant with the strongest latency and accuracy requirement, however to achieve the required accuracy very strict synchronization requirement should be fulfilled—no more than 1 us jitter can be tolerated. Nowadays, this extreme low latency and strict synchronization accuracy can only be achieved by using wired deployment and specific (ASIC-based) hardware support.
In RT-2 traffic class, with no time-slices, the Ethernet packet are handled according to their priority (by using IEEE 802.1Q), however the start of RT-2 part of the cycle is also strictly synchronized. For loose latency use cases RT-2 enables to use unsynchronized communication, where the frame prioritization is handled, but there is no strict synchronization requirement.
In RT-1 traffic class, no synchronization is required; the frames are forwarded according to their priority stored in the VLAN header.
Unsynchronized RT-2 and RT-1 communication can be realized by using standard industrial Ethernet components and in case of longer transmission cycles even by using wireless technologies (e.g. 802.11).
Beyond low latency, a strict time synchronization of industry devices may be additionally required.
In wired, industrial Ethernet-based industry automation solution, such as PROFINET, there is a robust synchronization solution, based PTCP enables to realize automation processes that need isochronous real-time communication.
PTCP—similarly to IEEE 1588 standardized synchronization protocol, Precision Time Protocol (PTP)—uses time stamps for synchronizing devices' clocks in the network. The clocks are arranged in master-slave hierarchy. A two-way delay measurement procedure helps to calculate the delay (caused by processing time of intermediate devices, propagation delay, etc.) between a certain slave clock and the master clock. The delay measurement may be performed multiple times in order to minimize the jitter. PTP-based synchronization is able to provide about 1 us synchronization accuracy in a wired (Ethernet) industrial environment.
Differently to previous generations, the fifth generation mobile technology (5G) will be able to provide a much wider range of services compared to 4G technology. It will enable a fully connected society, which goes beyond just everything is connecting by wireless. A rich set of use cases will be supported from Mobile Broadband, machine-to-machine (M2M), Internet of Things (IoT), connected cars, homes, etc. through numerous Industrial services which needs extra low latency, extra high reliability, which cannot be handled by the current mobile system.
The expected performance of the new 5G radio interface and the new, flexible core network will be suspected to guarantee such low latency, which meets the strict requirements of the industry automation use cases. Consequently, 5G is being expected to provide a relevant wireless technology for deploying industry use case on a wireless platform. However, above-described synchronization cannot be readily applied to industry automation applying wireless communication.
It is thus an object to provide a synchronization method and means thereto that allow an employment in networks involving a wireless packet data network, though guaranteeing high synchronization accuracy.
According to embodiments, a method of synchronization communication is performed between a master clock and a slave clock, wherein the communication involves wireless network comprising a base station or eNB and a wireless terminal or UE, wherein the base station performs the following steps:
In an embodiment, a base station or eNB of a wireless network is disclosed being adapted for communicatively connecting a master clock to the wireless device or UE, wherein the base station may comprise:
In an embodiment, the method uses afore-mentioned Precision Transparent Clock Protocol, PTCP. The synchronization packet is then a PTCP packet that may comprise a time stamp indicative of the time of the master clock at the generation or transmission time at the master clock.
Afore-described embodiments solve the problem of unpredictable delays within the wireless network, e.g. caused by radio scheduling or radio framing that cannot be performed with a sufficient accuracy by applying the normal IEEE1588 delay measurement process.
This solution can provide synchronization to a plurality if industry devices connected to different base stations without requiring synchronization among the clocks of the base stations. The mobile system may have its own synchronization solution independent from the master clock.
In an embodiment, a method for performing a synchronization communication between master clock and slave clock is disclosed wherein the UE performs the following steps:
In an embodiment, a corresponding UE is disclosed comprising:
Present embodiments also concern computer programs comprising portions of software codes in order to implement the method as described above when operated by a respective processing unit of appropriate nodes, e.g. a wireless terminal or a base station of a radio access network. The computer program(s) can be stored on a computer readable medium. The computer-readable medium can be a permanent or rewritable memory within the wireless terminal or base station, or located externally. The respective computer program can be also transferred for example via a cable or a wireless link as a sequence of signals.
In the following, detailed embodiments of the present invention shall be described in order to give the skilled person a full and complete understanding. However, these embodiments are illustrative and not intended to be limiting.
The accompanying drawings illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.
An example synchronization (sub-) domain as depicted in
Returning to
The following description shall illustrate some embodiments of a clock synchronization involving a wireless network in more detail.
The master clock 100, as well as the IO device 130 may belong to a set of factory devices which applies afore-mentioned PTCP. The master clock 100 may constitute a so-called synchronization domain, which may comprise a plurality of industry devices, of which IO device 130 is shown by way of example; the industry devices (or some of them) may e.g. be connected via wired deployment (e.g. PROFINET).
In accordance to PTCP, in order to synchronize the IO device 130, the master clock 100 may transmit a PTCP frame over the eNB 110 and the UE 120 to the slave clock 130. The PCTP frame comprises information indicative of a time value (that may take into account a local delay time) of the master clock.
The eNB 110 may act as a PTCP node in the transmission link between the master clock 100 and the slave clock (IO device 130), e.g. as a so-called transparent clock. In such role, the eNB modifies the delay information such that it adds a delay that is due to internal delay or processing, and forwards such modified PCTP frame to be forwarded to the UE 120.
In order to determine the eNB internal delay time, the base station may comprise a set of synchronization functions, in the following also being referred to as synchronization assistant entity, SAE 1101. The SAE 1101 participates in the delay measurement between the master clock 100 and the slave clock of the IO device 130.
The SAE 1101 may comprise the following functions or functionality:
A further set of functions, in the following also being referred to as delay measurement assistant entity, DMAE 1201 may be implemented in the UE 120. The DMAE may cooperate with SAE 1101 to perform delay measurements between eNB 110 and UE 120. The DMAE may further be involved in delay measurements between UE 120 and IO device 130. The DMAE may provide a time offset information indicative of such delay between the UE 120 and the IO device 130, e.g. be used by the slave clock of the IO device 130. The IO device 130 may then added such delay to the other delay conveyed by the modified PTCP frame.
In unicast communications, the PTCP frame may be sent towards the IO device when a Physical Resource Block (PRB) is allocated for its serving UE. According to current LTE standards, the length of a PRB is 1 ms while in 5G radio a significantly smaller PRB is expected (e.g. several times of 10 us), and it may already perform the desired latency criteria, but not an accuracy desired for synchronization. In unicast, only a single UE communicates in a given time frame, so the IO devices which are connected to a common base station can get the synchronization information at different times (when their UEs are scheduled).
The following
In an embodiment, a delay measurement between the UE 120 and the IO device 130 may be performed by the IO device:
When the IO device 130 initiates a delay request message M01, the DMAE 1201 detects it and responds e.g. as a (virtual) master clock (e.g. according to a peer delay measurement procedure) by delay response message M02. By using this procedure the slave clock in the IO device 130 can determine a one way delay tIO_offset (e.g. as half the time between sending of delay request message M01 and reception of reception of response message M02). This value may be used as a time offset tIO_offset related to the IO device 130, e.g. to be added to a timestamp carried by the incoming PTCP packet.
Alternatively, the IO device 130 may be configured to add a pre-configured constant time offset to the PTCP provided time, corresponding to the downlink delay between the reception of the downlink PDUs in the UE and the industry device. (Such pre-configuration can also be implemented by a virtual master clock in the IO device). Especially in cases, wherein this value is small or negligible (e.g. if it is in the order of a few ns in case of a distance in the order of 1 m) it may not be necessary to perform a delay measurement between the UE and the IO device.
In an embodiment, the delay measurement between the SAE 1101 and the UE may be considered to consist of two parts: a first part is the propagation delay and a second part is the processing of PTCP PDU in the UE.
To calculate the delay, the SAE 1101 may initiate a delay measurement process to send out a delay test message M03 to be received by the DMAE 1201. Since in this measurement only the SAE and DMAE communicate with each other, not standardized (or proprietary) messages may be used.
Thereto the following steps may be performed by the DMEA:
The following steps may be performed by the SAE:
t
UE
_
offset=(treceive−tsent−twaiting)/2
If no synchronization support function is implemented in the UE (i.e. if no DMAE is implemented), the processing time may be approximated by a pre-configured constant as mentioned above; the propagation time between the eNB and the UE may be estimated in the eNB, e.g. by means of timing advance measurements.
In an embodiment, a delay measurement of a time delay between the eNB 110 and the master clock 100 is performed (that may be performed for each of a plurality of base stations associated to the synchronization sub domain). Thereto, a standard PTCP peer delay measurement may be performed. The eNB 110 may send a PTCP delay request message M05 towards the master clock 100. In response to the delay request message M05 the master clock 100 responds with a delay response message M06; based on this, the time delay between master clock and eNB may be determined. This delay value (teNB_offset) may be assumed to be as accurate as in a wired industry deployment, since local communication is assumed (limited hops between the master clock and the base station) and the PTCP packet is assigned by high priority.
In the following
At the master clock 100:
At the eNB 110:
t
variable
=t
scheduling
−t
arriving,
At the UE 120:
At the IO device 130:
Additionally, a packet processing time within the eNB may be determined or assumed indicative of how much time is to be used to prepare a radio PDU from the incoming PTCP frame; the packet processing time may be added to the scheduling time (and such to the internal delay time).
Further additionally, afore-discussed offset time values tUE_offset for the given UE and teNB_offset for the delay between master clock and eNB may be taken into account. In particular, the time information (or correction field) of the sync message may in conclusion be increased by the following time offset:
t
offset
=t
variable
+t
eNB
_
offset
+t
UE
_
offset
This time offset value compensates for the delay caused by the waiting for UE scheduling and considering the eNB—master clock and eNB—UE delay; further a measured or assumed processing time in the UE may be added to the time offset.
Accordingly, the new time information carried by the modified PCTP packet M12 recovered by slave clock of the IO device 130 will be:
T
M
=T
o
+t
offset,
wherein To is the original master time, i.e. the time being included in the PTCP frame by the master clock 100n and TM is the corrected time corrected by the SAE to being transmitted from the eNB to the UE.
Upon reception of the modified PCTP packet M12, the UE will send the modified PTCP packet M12 to the IO device (slave clock) by forwarding the modified PCTP packet M12. The IO device may add afore-determined offset time tIO_offset such that the accurate time information in the IO device TM′ can be calculated as:
T
M′
=T
M
+t
IO
_
offset
PTCP packets may use dedicated bearers with a specific QCI value; thus the eNB may make a pre-allocation of the scheduling time of the PTCP frames. (Alternatively, instead of using dedicated bearers only for PTCP packets, it is possible to identify those packets by DPI as well.) This is well feasible as the amount of such packets is rather small. The knowledge of the pre-allocated time schedule for PTCP frames facilitates for the eNB to know when the given PTCP frame will be scheduled, even before the eNB may perform segmentation and encryption of the PTCP packet.
According to embodiments, the eNB acts as a so-called transparent clock. Alternatively, the eNB may act as a so-called boundary clock. In principle, both approaches are similar in that the SAE (and the DMAE) are able to properly process the PTCP packets.
In case of the transparent clock implementation the SAE may modify the existing PTCP packet. Since PTCP is carried over UDP/IP, in this case the checksum of the UDP packet may be re-calculated according to the modified data to keep the integrity of the packet.
In case of the boundary clock approach, a corresponding functionality may be implemented as part of the SAE such that a new PTCP packet may be generated by the boundary clock with the correct time value.
Usually more than one IO devices are handled by the base station. In this case the SAE's responsibility may be to handle the synchronization of all devices. When a new PTCP packet arrives, SAE detects and catches it as described above and logs the new arrival time tarriving.
In an embodiment, a hybrid automatic repeat request (HARQ) based retransmission is taken into account. This may be handled in one of the following ways:
In the following, an embodiment for a delay measurement in case of synchronization via broadcast or multicast will be considered:
The delay measurement between the IO device 130 and the UE 120, as well as the delay measurement between the eNB 110 and the master clock 100 may be similar to the unicast case examples described above.
The delay measurement between the eNB and the UEs may be performed on a per UE basis, in a way similarly as in the above-described unicast example. However, since the PTCP message is broadcasted, the individual delay tUE_offset between the eNB and a given UE cannot be determined at the eNB. Therefore instead of the individual delay tUE_offset the base station may us an estimated, approximated or averaged delay value of a plurality of individual delay values (tAver_UE_offset) to be used to modify the time information in the PTCP packet.
Compared to the unicast synchronization, such method may cause some inaccuracy in the synchronization, wherein the inaccuracy is proportional to the variance of the individual delay values tUE_offset between the base station and the UE. The variance may arise from the different distances between the UEs and the base station. However this difference may be limited, since most industrial (factory) deployments are done on a geographically limited area. In such case significant differences are not expected in the UE−eNB distances for UEs that are connected to the same eNB.
Another factor, which may cause some variance, may be a processing time difference among UEs, but in industry automation, UEs having an improved performance may be applied, that keep the processing time differences below defined limits.
As discussed, if synchronization is performed via broadcast way, a synchronization inaccuracy may be higher than a synchronization inaccuracy performed via unicast; so synchronization via unicast may be preferred over synchronization via broadcast in use cases that require very strict synchronization accuracy (e.g. 1 us).
In the following
A modified eNB operable for synchronization by means of broadcasting may have the following functions:
If there is time to process the PTCP packet before the next broadcast period, the SAE may modify the time information of the PTCP packet, or may generate a new PTCP packet (similar to above-described unicast case embodiment);
otherwise the next broadcast period may be used to transmit the synchronization information towards the UEs.
In the example of
At the master clock 100:
At the eNB 110′:
At the UE 120:
At the IO device 130:
PCTP packet M22, and
The modified SAE may further comprise function to perform the following measurements:
The modified SAE thus may perform a time information correction in the PTCP packet to add toffset according to the following calculation:
t
offset
=t
broadcast
−t
arriving
+t
eNB
_
offset
+t
Aver
_
UE
_
offset.
In a case where a next broadcast period is coming and no new PTCP packet has arrived at the base station, one of the two following options may be performed:
It is to be noted that in case of broadcasting, there is no retransmission; thus the above-mentioned HARQ problem does not need to be handled.
As shown in
As shown in
Further, the example base station or eNB 110, 110′ may comprise:
Further, the example base station or eNB 110, 110′ may comprise:
As shown in
As shown in
(M12, M22) is to be forwarded, and
The detection module 1106 may be adapted to detect if the synchronization packet M12, M22 is associated to a re-transmission, and in the affirmative, to initiate dropping the synchronization packet M12, M22 so that it is not forwarded to the slave clock 130.
The UE 120 may further comprise:
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/053770 | 2/23/2016 | WO | 00 |
