1F8LZF…8gsQ

初心

happy birthday 🎂🎉

Young jazz men with a new sense are gathering. At last they created a new genre itself. They are sick and tired of the conventional fixed style jazz. They're eager to play jazz more freely as they wish then... in 2071 in the universe...

The bounty hunters, who are gathering in the spaceship "BEBOP", will play freely without fear of risky things. They must create new dreams and films by breaking traditional styles. The work, which becomes a new genre itself, will be called...

Once upon a time, in New York City in 1941... at this club open to all comers to play, night after night, at a club named "Minston's Play House" in Harlem, they play jazz sessions competing with each other.

i wish more people would build things that won’t be finished in their lifetime

i wanna do more things without letters and words

https://twetch.app/t/0a312329671a219b28dd19ecfbd9e834a1959022ac278ae7fd38c0695187c1ac

https://twetch.app/t/039cc0e3e29db4c6e94f5315d937f7e61fcd73e055cc597604c81a56709fe19f

海賊王に俺はなる!

The name is an acronym of the Post Office Code Standardisation Advisory Group, the name of the group that developed the code under the chairmanship of the British Post Office that used to operate most telecommunications in Britain before privatization.

Then, compute (also over GF(2)):

s(x)
= p(x) * g(x)
= (x^20 + x^18 + x^17 + x^15 + x^14 + x^13 + x^11 + x^10 + x^9 + x^8 + x^6 + x^5 + x^4 + x^3 + x^2 + 1) * (x^10 + x^9 + x^8 + x^6 + x^5 + x^3 + 1)

To encode the 21-bit message {101101110111101111101}, we first represent it as a polynomial over GF(2):

p(x) = x^20 + x^18 + x^17 + x^15 + x^14 + x^13 + x^11 + x^10 + x^9 + x^8 + x^6 + x^5 + x^4 + x^3 + x^2 + 1

The codewords are either address or data, which is indicated by the first bit transmitted, bit 31. An address codeword contains 18 bits of address (bit 30 through to 13), and 2 function bits (12 & 11).

Before the development and adoption of the POCSAG code, pagers used one of several proprietary codes such as GOLAY.

Codewords are transmitted in batches that consist of a sync codeword, defined in the standard as 0x7CD215D8, followed by 16 payload codewords that are either address or data. Any unused codewords are filled with the idle value of 0x7A89C197.

The error-correcting code has a 6-bit Hamming distance: each 31-bit codeword differs from every other codeword in at least 6 bits. Consequently, the code can detect and correct up to 2 errors in a codeword.

for more information on POCSAG:

http://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.584-2-199711-I!!PDF-E.pdf

as you can see, this is considered a BCH code (31, 21) because our encoded messages are 31 bits {1100111010010111101011101110101} and our decoded messages are 21 bits {101101110111101111101}

The generating polynomial g(x) for the BCH (31, 21) code is:

x^10+ x^9+ x^8+ x^6+ x^5+ x^3+ 1

The modulation used is FSK with a ±4.5 kHz shift on the carrier. The high frequency represents a 0 and the low frequency a 1.

Each data codeword carries 20 bits of data (bits 30 through to 11).

here's an example of a BCH code

The ±4.5 kHz frequency shift is used along with a 25 kHz channel spacing, known as "wideband". Some jurisdictions require that all systems move to a "narrowband" configuration, using 12.5 kHz channels and ±2.5 kHz frequency shifts

= x^30 + x^29 + x^26 + x^25 + x^24 + x^22 + x^19 + x^17 + x^16 + x^15 + x^14 + x^12 + x^10 + x^9 + x^8 + x^6 + x^5 + x^4 + x^2 + 1

Thus, the transmitted codeword is {1100111010010111101011101110101}.

POCSAG is an asynchronous protocol used to transmit data to pagers.

Transmission use 32-bit blocks called codewords. Each codeword carries 21 bits of information (bits 31 through 11), 10 bits of error-correcting code (bits 10 through 1), and an even parity bit (bit 0). Bits 31 through 1 are a binary BCH code (31, 21).

The receiver can use these bits as coefficients in s(x) and, after error-correction to ensure a valid codeword, can recompute p(x) = s(x) / g(x)