ES2990195A1 - INTERNATIONAL ATOMIC TIME (TAI) AND COORDINATED UNIVERSAL TIME (UTC) INFORMATION TRANSMISSION SYSTEM WITHIN THE ONE PULSE PER SECOND (1PPS) SYNCHRONIZATION SIGNAL - Google Patents

Abstract

TAI and UTC information transmission system within the 1PPS synchronization signal that sends 60-bit information packets in the pulses transmitted throughout each minute of TAI, encoding each bit with a different pulse width. The width of the pulses is modified by altering the position of the edge that does not provide synchronization information. The content of the transmitted packets allows the beginning of each minute of TAI to be identified and the precise date and time at that instant to be known, both in TAI and UTC. With this system, the 1PPS synchronization signal is provided, without degrading its characteristics, with the necessary information so that the equipment that receives it can set their clocks to TAI and/or UTC time in a simple and fast way. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

ATOMIC TIME INFORMATION TRANSMISSION SYSTEM

INTERNATIONAL TIME (TAI) AND COORDINATED UNIVERSAL TIME (UTC) WITHIN THE ONE PULSE PER SECOND (1PPS) SYNCHRONIZATION SIGNAL

TECHNICAL SECTOR

The invention falls within the field of telecommunications and more specifically within the sector of generating reference signals for radio, television and telephone signal transmitting stations.

BACKGROUND OF THE INVENTION

The 1 PPS signal is a timing signal commonly used in telecommunications centres to synchronise equipment in frequency and phase with one of the atomic time scales. It is an electrical signal, usually in Transistor-Transitor Logic (TTL) levels, consisting of a pulse that repeats periodically every second. The phase and frequency information provided by this signal is obtained from one of the two edges of the transmitted pulses, usually the rising edge.

Sometimes, devices that are provided with the 1PPS signal have an internal clock with date and time information that they need to keep synchronized with it. From the 1PPS signal, it is possible to obtain the exact instant at which each second begins, set it on the clock and keep it in place accurately while the signal is available. However, to initialize the date and time of the clock, these devices have to use other mechanisms such as the Network Time Protocol (NTP).

There are multiple international standards for representing time information, such as date and time, based on the definition of a second in the International System of Units (SI). The pace at which all standards advance is the same because they are all linked to the time unit of the second, but there may be differences between them of an integer number of seconds.

The date and time maintained by the internal clocks of computers depend on the intended use. For most business and engineering applications, the recommended date and time is that provided by the Coordinated Universal Time (UTC) scale. The UTC scale is based on the rotation of the Earth and has the disadvantage of being discontinuous. The UTC scale seconds counter is reviewed and adjusted on the last day of June and December of each year to account for the effects of the Earth's rotation. The adjustment is made by introducing what are called leap seconds. These leap seconds are positive when they result in a minute of 61 seconds on the UTC scale (... - 23:59:59 -23:59:60 - 00:00:00 - ...) or negative when they result in a minute of 59 seconds on the UTC scale (...- 23:59:58 - 00:00:00 - ...).

In many telecommunications applications, the discontinuities that exist in the UTC scale are a problem and it is more convenient to use a date and time related to the International Atomic Time (TAI) scale, which is always continuous.

For a device to be able to use both TAI and UTC, it is sufficient to provide it with the necessary information to set the time using one of the two scales, the difference between the two and when this difference will change in advance.

The way to provide time information to the equipment is through what are called timestamps, which indicate the number of seconds and/or fractions of a second elapsed from a certain instant or epoch, which is the origin of the scale, until the moment in which the timestamp is generated. A very commonly used scale in telecommunications is the one defined in the Precise Time Protocol (PTP) IEEE Std 1588-2008. This is a TAI scale whose time origin, the PTP epoch, is defined on January 1, 197000:00:00 TAI.

1PPS signals are typically generated by equipment that has very precise oscillators that are synchronized to atomic time patterns by the Global Navigation Satellite System (GNSS) receiver modules they incorporate. These modules obtain the TAI and UTC information from the GNSS signal they receive and can provide it to the equipment on which they are mounted for use.

It would be desirable to be able to use the 1PPS signal generated by the equipment mentioned in the previous paragraph to easily set the time of the clocks of the equipment that receives it without degrading the precision of the frequency and phase information provided by the 1PPS signal.

.EXPLAINATION OF THE INVENTION

The object of this invention is a system that allows the 1PPS signal to be provided with the time information necessary to initialize and maintain the date and time of the clocks of the equipment that receives it with TAI and/or UTC without having to resort to any other mechanism.

The transmission system of the invention uses each pulse of the 1PPS signal to transmit a bit of information encoded in the pulse width. A narrow pulse of duration T0 is used to represent a logical '0' and a wide pulse of duration T1 to represent a logical '1'. The pulse width is modified by altering the position of the edge that does not provide phase and frequency information, normally the falling edge, so as not to degrade the signal characteristics.

The TAI minute pulses are used to transmit 60-bit packets generated just before the minute begins, containing the information needed to identify the start of the TAI minute and to know the exact date and time, both in TAI at the start of the next TAI minute and in UTC at the start of the next UTC minute. This packet cadence ensures that within two minutes of receiving the 1PPS signal, the information needed to reset the clocks is available.

The 1PPS signal as it was conceived allows for the precise adjustment of the frequency and the instant at which each second begins on a clock. The information transmission system described in this invention provides the 1PPS synchronization signal with the necessary information so that the equipment that receives it can set their clocks to the TAI and/or UTC in a simple and fast way. This system does not degrade the characteristics of the 1PPS signal and is compatible with the distribution equipment that is normally used for this type of signal, both those that use linear amplifiers and those that allow the waveform to be regenerated.

BRIEF DESCRIPTION OF THE DRAWINGS

To complement the description being made and in order to help better understand the characteristics of the invention, a set of drawings is included as an integral part of said description, in which the following has been represented for illustrative and non-limiting purposes:

Figure 1 shows a time diagram showing pulse width modulation and packet alignment with the TAI. The packet structure in the preferred embodiment of the invention is also shown.

PREFERRED EMBODIMENT OF THE INVENTION

In its preferred embodiment, the 60-bit packets transmitted in each TAI minute are divided into six 10-bit blocks (see Figure 1).

The first block is a sequence of 10 consecutive ones that coincides with the beginning of each minute of TAI and signals the beginning of the packet. To ensure that this sequence cannot be repeated throughout the message, the first two bits of the second to sixth blocks are always set to zero, leaving 8 bits of useful information in each block.

The second to fifth blocks are used to transmit a timestamp (TS_PTPi in Figure 1) with the atomic time information encoded in a 32-bit unsigned integer. The timestamp value used represents the number of seconds elapsed from the beginning of the PTP epoch to the instant at which the current TAI minute began. The 32 bits of this number are transmitted in the 8 payload bits of each of the four blocks starting with the most significant bit. That is, in block 1 after the two zero bits, bits 31 to 24 of the timestamp are transmitted, in block 2 after the two zero bits, bits 23 to 16 are transmitted, and so on.

The sixth block is used to transmit an 8-bit unsigned integer containing information on the number of leap seconds (LS_UTCi in Figure 1) between the TAI scale and the UTC scale at the beginning of the next UTC minute. The 8 bits of this number are transmitted after the two zero bits in the block starting with bit number 7.

The time information transmission system presented is suitable for industrial application within the television signal broadcasting sector, in particular for single-frequency network broadcasts of DVB-T2 signals. In these environments, the transmitting equipment has a 1PPS signal input to synchronize and also needs to have TAI to generate the signal that they transmit in phase with those transmitted by the rest of the transmitters in the network.

Claims (2)

1. Time information transmission system within the 1PPS synchronization signal characterized by: • Use each pulse of the 1PPS signal to transmit one bit of information by pulse width modulation. • Use the 60 bits transmitted throughout each minute of TAI using the above modulation to send information packets that allow: a) Identify the beginning of the TAI minutes. b) Know the exact date and time on the TAI scale at the beginning of the next TAI minute. 2. Time information transmission system according to claim 1 that incorporates within the packets that are sent the information necessary to know the exact date and time in the UTC scale at the beginning of the next UTC minute.