DESC:TITLE: A METHOD FOR ACHIEVING PHASE SYNCHRONIZATION BETWEEN NODES IN A COMMUNICATION NETWORK

TECHNICAL FIELD
The present subject matter is related, in general to synchronization between nodes in a communication network, and more particularly, but not exclusively to a method and device for achieving accurate phase synchronization between nodes in a communication network.
BACKGROUND
Synchronization refers to the process of achieving and maintaining coordination among physically isolated clocks through the exchange of local time information. The synchronization is an important feature in any distributed network as it enables a system to generate a consistent view and perform coordinated actions between the network nodes. The network nodes can be a Data Terminal Equipment (DTE) or a Data Communication Equipment (DCE). The DTE may be a device including, but not limited to, personal computers (PCs), workstations, file servers, or print servers that, as a group, are all often referred to as end stations. The DCE may be an intermediate network device that receive and forward frames across the network. The DCE may be a standalone device including, but not limited to, repeater, network switch, and router, or communication interface unit such as interface card and modem. Depending on the required accuracy, special measures such as IEEE 1588 and Network Time Protocol (NTP) are considered to achieve synchronization between the network nodes. These protocols have in common that the synchronization is performed by a regular exchange of messages and use a local oscillator to maintain a continuous timescale between the messages. Apart from the stability of the oscillator, the quality of the timestamp taken at the transmission and reception of the synchronization messages is a limiting parameter for attaining accuracy. Using accurate time stamping, hardware in every network element allows calculating a time delay at each network element and enables the system to derive the total end-to-end delay.
The problem with the conventional synchronization protocols like IEEE 1588 and NTP is that, the IEEE 1588 and the NTP uses packets to send the timing information. The packets encounter jitter and latency in the network, which leads to large errors in the recovered time/phase and requires large convergence time.
One of the conventional methods as disclosed in US8259758 provides a network slave node based on Precision Time Protocol (PTP) and synchronization method. The network slave node sends a standard packet, which includes packet receiving time and/or a packet sending time to a local master node and the local master node calculates a time offset between each network slave node and the local master node and sends the time offset to the slave node. The slave node includes a packet detection unit, a hardware clock and a control unit. The packet detection unit detects whether the slave node receives or sends a synchronization protocol packet and records a synchronization protocol packet receiving time and a synchronization protocol packet sending time. The control unit coupled to the packet detection unit reads out the synchronization protocol packet receiving time and the synchronization protocol packet sending time and informs the local master node about the synchronization protocol packet receiving time and the synchronization protocol packet sending time. The control unit receives a time offset between the local master node and the slave node and a packet transmission delay time which are both calculated by the local master node. The control unit adjusts the hardware clock according to the time offset and the packet transmission delay time, so that the slave node and the local master node are time synchronized.

In the above conventional method of US8259758, accuracy of phase synchronization recovery is a function of the long term averaging and hence takes a long time to synchronize the slave node. Also, the method requires one or more components like packet detection unit and control unit to synchronize the slave node, which increase more number of components and so the power consumption. Thus, the solution offered by the conventional method is not economical.

Hence, there exists a need for a method to achieve accurate phase synchronization between the nodes in a communication network such that there is no requirement of averaging, accuracy is high and the slave node synchronizes at a faster rate.

SUMMARY
One or more shortcomings of the prior art are overcome and additional advantages are provided through the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.
Accordingly, the present disclosure relates to a method for achieving phase synchronization between nodes in a communication network. The method comprising receiving, by a first node configured in the communication network, one or more signals from one or more second nodes configured in the communication network. The first node receives the one or more signals through a physical link between the first node and the one or more second nodes. Upon receiving the one or more signals, the control unit configured in the first node detects change in at least one physical attribute of the one or more signals. The method further comprising identifying phase information in the one or more signals upon detecting change in the at least one physical attribute by the control unit. Thereafter, the control unit adjusts the phase of the first node upon identifying the phase information for achieving the phase synchronization.
Further, the present disclosure relates to a first node for achieving phase synchronization with one or more second nodes in a communication network. The first node comprises a transceiver and a control unit. The transceiver is configured to receive one or more signals from the one or more second nodes. The control unit is configured to detect a change in at least one physical attribute of the one or more signals, identify a phase information in the one or more signals based on the change in the at least one physical attribute and adjust phase of the first node upon identifying the phase information for achieving the phase synchronization.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, serve to explain the disclosed principles. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and with reference to the accompanying figures, in which:

Fig.1a illustrates an exemplary system for achieving accurate phase synchronization between nodes in a communication network in accordance with some embodiments of the present disclosure;
Fig.1b illustrates block diagram of a node in accordance with some embodiments of the present disclosure;
Fig.2 illustrates an exemplary method for achieving accurate phase synchronization between nodes in the communication network in accordance with some embodiments of the present disclosure;
Fig.3 shows timing diagram illustrating method of transmitting phase information between the nodes in accordance with some embodiments of the present disclosure; and
Fig.4 shows flowchart illustrating method for achieving accurate phase synchronization between nodes in the communication network in accordance with some embodiments of the present disclosure.
It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.

DETAILED DESCRIPTION
In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure.
The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises…a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.
Accordingly, the present disclosure relates to a method for achieving phase synchronization between nodes in a communication network. The first node configured in the communication network receives one or more signals from one or more second nodes configured in the communication network. The first node receives the one or more signals through a physical link between the first node and the one or more second nodes. Upon receiving the one or more signals, the control unit configured in the first node detects change in at least one physical attribute of the one or more signals. The physical attribute is at least one of modulation mechanism and encoding mechanism. In an embodiment, the change in physical attribute may be shift in carrier frequency. Upon detecting the change in the physical attribute, the control unit identifies the phase information in the one or more signals. Thereafter, the control unit adjusts the phase of the first node upon identifying the phase information for achieving the phase synchronization with the one or more second nodes.
Fig.1a illustrates an exemplary system for achieving accurate phase synchronization between nodes in a communication network in accordance with some embodiments of the present disclosure.
The system 101 comprises plurality of nodes, node 1 1031 to node N 103n (collectively referred as 103) connected over a communication network 105 through plurality of communication channels. The communication channels is at least one of twisted pair cables, optical fibre channel or any other suitable type or combination of wired line channels. The nodes 103 can be a Data Terminal Equipment (DTE) or a Data Communication Equipment (DCE). The DTE are devices that are either the source or the destination of data frames. The DTEs are typically devices including, but are not limited to, PCs, workstations, file servers, or print servers that, as a group, are all often referred to as end stations. DCE are intermediate network devices that receive and forward frames across the network. DCEs may be either standalone devices including, but are not limited to, repeaters, network switches, and routers, or communications interface units such as interface cards and modems. Each node 103 in the communication network 105 comprises an encoder, a decoder, a transceiver and a control unit as shown in Fig.1b. The transceiver is configured to transmit one or more signals to one or more other nodes and receive one or more signals from one or more other nodes in the communication network 105. The control unit is configured to achieve phase synchronization with the one or more nodes in the communication network 105 during phase synchronization period. The encoder is configured to encode the data being transmitted from the node to one or more other nodes in the communication network 105. The decoder is configured to decode the data received from the one or more other nodes in the communication network 105.
Fig.2 illustrates an exemplary method for achieving accurate phase synchronization between nodes of the communication network in accordance with some embodiments of the present disclosure. As an example, node 1 1031 is a master node and node 2 1032 is a slave node. For simplicity, the intermediate nodes and the downstream nodes are not shown. The control unit configured in the master node changes physical attribute of the one or more signals. In an embodiment, the master node changes physical attribute of the one or more signals in order to indicate phase information. The physical attribute is at least one of encoding mechanism and modulation mechanism. The change in physical attribute may also be shift in carrier frequency.
The master node changes the physical attribute of the one or more signals during phase synchronization period and during rest of the period the master node performs encoding of the data using 8B10B encoder/decoder or any other encoder/decoder. In 8B10B encoding, 8 bits of data are transmitted as a 10-bit entity referred as character. The low 5 bit of data is encoded into a 6-bit group (the 5b/6b portion) and the top 3 bits are encoded into a 4-bit group (the 3b/4b portion). These code groups are concatenated together to form the 10-bit character which is transmitted on the communication link.
In an exemplary embodiment, changing the encoding mechanism comprises sending one or more wrong disparity codes to a slave node. A disparity code is a line code in which at least one of the data character is represented by two code of opposite disparity that are used in sequence so as to minimize the total disparity of a longer sequence of digits. A particular code of any line code can have one of no disparity i.e. the average weight of the code is zero, negative disparity i.e. the average weight of the code is negative, and positive disparity i.e. the average weight of the code is positive.
In the disparity code, every code that averages to a negative level (negative disparity) is paired with some other code that averages to a positive level. In an embodiment, the transceiver of the master node keeps track of a running disparity. The running disparity (RD) for a character is the difference between the number of 1 bit and 0 bits in said character. If there are more number of 1’s than 0’s in the RD of the character, then the RD is defined as positive. If there are fewer 1’s than 0’s, the RD is defined as negative. If the number of 1’s and 0’s in the RD are equal, the RD is defined as neutral or zero. If the RD does not represent the character, then the RD is wrong disparity code. The transceiver configured in the slave node decodes the data bits as transmitted by the master node. When the wrong disparity code is transmitted, the transceiver of the slave node identifies that the code is related to phase information.
The control unit configured in the master node changes the physical attribute to indicate transmission of the phase information to the slave node. Upon receiving the one or more signals by the slave node, the control unit identifies the change in the physical attribute of the one or more signals. Upon identifying the change in the physical attribute of the one or more signals, the control unit detects the phase information in the one or more signals. Thereafter, the control unit adjusts the phase of the slave and thereby achieves phase synchronization with the master node. After synchronizing, the control unit slave node decodes the actual data sent from the master node. In an embodiment, the master node generates the pulse indicating phase information on every second boundary, which is equivalent to One Pulse Per second (1PPS) signal. In an embodiment, the transceiver configured in node 1 1031 transmits the phase synchronization pulse (Phase_Sync_Pulse) to the slave node 1032 as shown in Fig.2.
Fig.3 shows a timing diagram illustrating a method of transmitting phase information between the nodes, in accordance with some embodiments of the present disclosure. A reference clock is used for synchronization of the communication network 105. The Phase_Sync_Pulse is a pulse indicating the phase information. The Phase_Sync_Pulse is the reference pulse indicating the time boundary for sending the phase information in the communication network. The transceiver configured in the master node transmits the Phase_Sync_Pulse on every second boundary signal. The master node transmits the data when the Phase_Sync_Pulse is in low state with normal encoding of the data, which is indicated by the un-filled area in the master_transmit signal. When the Phase_Sync_Pulse changes from low state to high state, the control unit configured in the master node performs special encoding of the signal by changing a predefined physical attribute indicated by shaded region in the master_transmit signal. By performing the change in the predefined physical attribute, the master node provides an indication to the slave node about the transmission of phase information. The slave node receives the signal after some delay shown as link delay in the slave_received signal. Upon identifying the changed physical attribute in the received signal, the control unit of the slave node recovers the pulse as shown in the Slave_Recovered_Pulse. The Slave_Recovered_Pulse is delayed as compared to the actual reference Phase_Sync_Pulse due to the link delay. The control unit of the slave node adjusts the pulse as indicated in the slave_recovered_pulse_adjusted by compensating with the link delay to recover the accurate phase information. In an embodiment, the link delay is calculated using conventional/ known techniques or it is configured statically.
In an embodiment, consider an example of an optical Gigabit Ethernet link between node 1 1031 and node 2 1032. The node 1 1031 uses 8B10B encoding technique for encoding the data, where 8 bits or each byte is encoded into 10 bits i.e. 8 ns. During the synchronization period, node 1 1031 implements special encoding mechanism to transmit the phase information i.e the transceiver configured in node 1 1031 uses a wrong disparity code to indicate the synchronization pulse to node 2 1032. Node 2 1032 identifies the synchronization pulse upon receiving the wrong disparity code. In an embodiment, the latency on the Gigabit Ethernet link can be statically configured so that the latency can be compensated by the node 2 1032.
Considering a sampling error, the transmitter transmits data with an accuracy of +/-1 byte interval i.e. +/- 8ns. Total uncertainty due to the sampling error at the receiver is 16 ns. Since, an optical link is used the delay can be very accurately measured. If the delay measurement accuracy is 4 ns, the overall uncertainty at the receiver is only 20 ns. So, the slave recovered pulse after adjustment can be offset at the most by 20 ns compared to the reference phase.
Fig.4 shows flow-chart illustrating method for achieving accurate phase synchronization between nodes of a communication network in accordance with an embodiment of the present disclosure. At step 401, the master node 1031 receives phase synchronization pulse (phase_sync_pulse). When the Phase-sync_pulse is in high state i.e the master node 1032 transmits the phase information to the slave node 1032. The master node 1031 changes the predefined physical attribute and transmits the phase_sync_pulse to the slave node 1032 at step 403. When the phase_sync_pulse is in low state the master node 1031 transmits the encoded data at step 405. When the slave node 1032 identifies the change in the physical attribute, it recovers the phase_sync_pulse at step 407. The slave node 1032 recovers the phase_sync_pulse after some delay referred as link delay. At step 409, the slave node 1032 adjusts the received pulse by compensating it with the delay time to recover the accurate phase information, thereby achieving accurate phase synchronization between nodes 103 of a communication network 105.
Referral Numerals:
Reference Number Description
101 Communication System
103 Node
105 Communication network

Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based here on. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
,CLAIMS:We claim:
1. A method for achieving phase synchronization between nodes in a communication network, the method comprising:
receiving, by a first node configured in the communication network, one or more signals from one or more second nodes configured in the communication network, wherein the one or more signals are received through a physical link between the first node and the one or more second nodes;
detecting, by a control unit configured in the first node, change in at least one physical attribute of the one or more signals;
identifying, by the control unit, phase information in the one or more signals based on the change in the at least one physical attribute; and
adjusting, by the control unit, phase of the first node upon identifying the phase information for achieving the phase synchronization.

2. The method as claimed in claim 1, wherein the adjusting the phase of the first node comprising:
identifying a transmission time of the one or more signals from the one or more second nodes;
identifying a reception time of the one or more signals by the first node;
computing a delay time in receiving the one or more signals by the first node based on the transmission time and the reception time; and
computing a phase value based on the delay time.

3. The method as claimed in claim 1, wherein the at least one physical attribute is modulation mechanism of the one or more signals.

4. The method as claimed in claim 1, wherein the at least one physical attribute is line encoding mechanism of the one or more signals.

5. The method as claimed in claim 1, wherein the change in at least one physical attribute is shift in carrier frequency of the one or more signals.
6. A first node for achieving phase synchronization with one or more second nodes in a communication network, the first node comprising:
a transceiver configured to receive one or more signals from the one or more second nodes;
a control unit configured to:
detect a change in at least one physical attribute of the one or more signals;
identify a phase information in the one or more signals based on the change in the at least one physical attribute; and
adjust phase of the first node upon identifying the phase information for achieving the phase synchronization

7. The first node as claimed in claim 6, wherein the control unit is further configured to:
identify a transmission time of the one or more signals from the one or more second nodes;
identify a reception time of the one or more signals by the first node;
compute a delay time in receiving the one or more signals by the first node based on the transmission time and the reception time; and
compute a phase value based on the delay time.

8. The first node as claimed in claim 6, wherein the at least one physical attribute is modulation mechanism of the one or more signals.

9. The first node as claimed in claim 6, wherein the at least one physical attribute is line encoding mechanism of the one or more signals.

10. The first node as claimed in claim 6, wherein the change in at least one physical attribute is shift in carrier frequency of the one or more signals.