Phase modulated time code WWVB

1 phase modulated time code

1.1 one-minute time frames
1.2 announcement bits

1.2.1 dst , leap second warning
1.2.2 dst schedule


1.3 message frames
1.4 six-minute time frames

phase modulated time code

the phase-modulated time code has been updated , not related amplitude-modulated time code. connection is transmitted in 60-second frames, , amplitude-modulated markers (when 20% of second transmitted @ full strength) not used essential time code information.

one-minute time frames

the time transmitted 26-bit minute of century 0 52595999 (or 52594559 in centuries 24 leap years). amplitude-modulated code, time transmitted in minute after instant identifies; clocks must increment display.

an additional 5 error correcting bits produce 31-bit hamming code can correct single-bit errors or detect double-bit errors (but not both).

another field encodes dst , leap-second announcement bits similar standard wwvb, , new 6-bit field provides advanced warning of scheduled dst changes.

the 60 bits transmitted each minute divided follows:

14 fixed sync bits (0, 0, 0, 1, 1, 1, 0, 1, 1, 0, 1, 0, 0, 0)
32 bits of time, comprising:

26-bit binary minute of century (0–52595999 36525 days per century)
5 ecc bits, making hamming(31,26) code
1 bit copy of least significant bit of minute


5 bits of dst status , leap pending, comprising:

2 bits of dst status, in amplitude modulated code
2 bits (3 possibilities) of leap second warning
1 odd parity bit (with 1 exception, see below)


6-bit dst rules code, comprising:

2 bits indicating time of next change (1/2/3 o clock, or never)
3 bits indicating date of change (which sunday)
1 odd parity bit (with 1 exception, see below)


1 bit of nist notice
2 reserved bits

a receiver knows time within few seconds can synchronize fixed synchronization pattern, when unable distinguish individual time code bits.

the full time code (with amplitude-modulated code reference) transmitted follows:

bits within fields numbered bit 0 least-significant bit; each field transmitted significant bit first.

the example shows time code transmitted on july 4, 2012 between 17:30 , 17:31 utc. bcd amplitude code shows time of 17:30, on day 186 of year.

the binary time code shows minute 0x064631a = 6578970 of century. dividing 1440 minutes per day, minute 1050 (= 17×60 + 30) of day 4568 of century. there 365×12 + 3 = 4383 days in 12 years before 2012, day 185 of year. day number begins @ 0 on january 1, rather 1 bcd time code, encodes same date.

announcement bits

the phase-modulated code contains additional announcement bits useful converting broadcast utc civil time.

in addition dst , leap second warning bits found in amplitude-modulated code, additional dst schedule field provides several months advance warning of daylight saving time rules.

a final bit, notice bit, indicates there announcement of interest wwvb users posted @ https://www.nist.gov/pml/div688/grp40/wwvb.cfm.

two reserved bits not defined, not guaranteed zero; note 1 of them transmitted 1 in example above.

the dut1 information (+0.4s) , leap year indicator bits (2012 leap year) in amplitude modulated code not included in phase modulated code; use of dut1 celestial navigation has been obsoleted satellite navigation.

dst , leap second warning

the phase-modulated time code contains daylight saving time announcement , leap second warning information equivalent amplitude-modulated code, combined 1 5-bit field error detection purposes.

there 2 dst announcement bits let receiver apply u.s. daylight saving time rules:

dst_on[0] set if dst in effect @ beginning of current utc day (00:00 utc).
dst_on[1] set if dst in effect @ end of current utc day (24:00 utc).

the 2 bits differ on days when daylight saving time changing (at 02:00 local time).

there 3 leap second warning possibilities (0, +1, or −1 seconds), making twelve possible values need encoded. eleven of these encoded 5-bit codes odd parity, providing single-bit error detection (a minimum hamming distance of 2 between 2 valid codes).

five of 16 possible odd-parity values (all differing in 1 bit 00011) not used, , even-parity value 00011 used encode common condition: dst in effect, no leap second pending. provides single-bit error correction (a minimum hamming distance of 3) whenever code transmitted.

the above example illustrates common case: dst in effect, , no leap second pending (the last leap second 4 days ago).

during leap second, bit 59 (a marker bit phase-modulated code of 0) transmitted again.

dst schedule

to extend few hours warning provided dst_on[1], 6-bit field encodes schedule next dst change. encoding intricate, provides 5 bits of information. 3 bits supply date of change, either 0 7 sundays after first sunday in march (when dst_on[1] = 0), or 4 sundays before 3 sundays after first sunday in november (when dst_on[1] = 1).

two more bits encode time of change: 1:00, 2:00, or 3:00 local time. fourth combination of these 2 bits encodes (using date-of-change bits) several special cases: dst @ other time, dst off, dst on, , 5 reserved codes.

as other warning field, of assigned 6-bit codes have odd parity, providing hamming distance of 2 each other. however, 6 of 32 odd-parity codes not used (all differing in 1 bit 011011), , even-parity code 011011 used encode common dst rule (2nd sunday in march, or 1st sunday in november) hamming distance of 3.

the 5 additional reserved codes assigned other even-parity code words hamming distance of 1 unlikely dst rule codes.

the example code of 011011 indicates dst change @ 02:00 on first sunday in november.

message frames

a small percentage of time code frames (typically less 10%) may replaced one-minute message frames, containing other information, such emergency broadcasts.

the details of such frames has not been finalized, begin alternate synchronization word (1101000111010, , 0 during second 59), , include 42 bits of non-time data in non-marker bits of time code. message frames still contain time[0] during second 19 , notice bit during second 49, receiver knows time within ±1 minute can synchronize them.

messages expected span multiple message frames.

six-minute time frames

for 6 minutes each half hour, 10–16 , 40–46 minutes past each hour, one-minute frames replaced special extended time frame. rather transmitting 35 bits of information in 1 minute, transmits 7 bits (time of day , dst status only) on 6 minutes, giving 30 times energy per transmitted bit, 14.8 db improvement in link budget compared standard one-minute time code.

the 360-bit code word consists of 3 parts:

a 127-bit sequence (generated 7-bit lfsr), rotated left variable amount encode value 0 123.
a 106-bit fixed bit sequence.
the 127-bit reverse of initial sequence. because reversed, rotated in opposite direction.

the information transmitted time within day (one of 48 half hours), plus current u.s. daylight saving time status, making 2×48 = 96 possible time codes.

an additional 2×14 = 28 time codes transmitted between 04:10 , 10:46 utc on days when daylight saving time changing, providing several hours warning of imminent dst change.