Bit Arrangement

Thread Starter

SD23

Joined Oct 10, 2020
3
Hi There,

I am new to EEE, so please excuse my lack of communication in expressing the question.

I would like to know, how bits are arranged in circuits. for example in this document [pg. 10-12] (https://www.icao.int/SAM/eDocuments/ADSB Guide Vs1.2 English.pdf) it is stated that there are 2 blocks one is 56 bit data block and the other a 112 bit data block.

My question is that how does this work? if i were to add more bits lets say another 56 bits, how can i do that or if it is not possible due to hardware limitations, are there any other alternatives?

The document is part of ADS-B implementation in case if it is helpful.

Thank you.
 

Papabravo

Joined Feb 24, 2006
16,158
It means that an aircraft can send data in either of two fixed formats. It does this by a process called parallel to serial conversion. the data is loaded into a shift register 8 bits at a time and clocked into the transmitter where it is encoded for transmission and sent into the the ether. On the receiving side the RF signal is received, decoded, and run through a serial to parallel shift register and then stored in memory 8 bits at a time. The the formats are fixed and your only option is to choose one or the other and repeat the process,

Why do you ask? Did you have something else in mind?
 

Thread Starter

SD23

Joined Oct 10, 2020
3
It means that an aircraft can send data in either of two fixed formats. It does this by a process called parallel to serial conversion. the data is loaded into a shift register 8 bits at a time and clocked into the transmitter where it is encoded for transmission and sent into the the ether. On the receiving side the RF signal is received, decoded, and run through a serial to parallel shift register and then stored in memory 8 bits at a time. The the formats are fixed and your only option is to choose one or the other and repeat the process,

Why do you ask? Did you have something else in mind?
Thanks papabravo for the reply.

I am a computer science student and was wondering how i can implement data encryption to ADS-B, as a matter of fact found out that no matter which algorithm i choose i wont be able to fit in any additional bits. The only way is to modify the hardware which is costly. There have been many proposed solutions like HMACS or removing the parity but with limited results.

Furthermore i am trying to study more about how this whole thing works and figure out someway that i can do this.

It will be a great help if you could suggest me a textbook or additional materials where i can learn more, since i realized i need to have some degree of understanding in electronics.

Cheers.
 

Papabravo

Joined Feb 24, 2006
16,158
Thanks papabravo for the reply.

I am a computer science student and was wondering how i can implement data encryption to ADS-B, as a matter of fact found out that no matter which algorithm i choose i wont be able to fit in any additional bits. The only way is to modify the hardware which is costly. There have been many proposed solutions like HMACS or removing the parity but with limited results.

Furthermore i am trying to study more about how this whole thing works and figure out someway that i can do this.

It will be a great help if you could suggest me a textbook or additional materials where i can learn more, since i realized i need to have some degree of understanding in electronics.

Cheers.
There are at least two approaches you could take
  1. You could encapsulate the ADS-B information in a larger frame
  2. You could scramble the existing fixed format bits using a CRC polynomial
 

Thread Starter

SD23

Joined Oct 10, 2020
3
There are at least two approaches you could take
  1. You could encapsulate the ADS-B information in a larger frame
  2. You could scramble the existing fixed format bits using a CRC polynomial
I can try scrapping parity and include a smaller algorithm since it has integrity checks in it. Cheers.
 
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