0
\$\begingroup\$

In Chapter "general performance criteria" the standard states that these criteria, for receiver performance tests, are equivlent:

  • after demodulation, a data signal with a bit error ratio of 1% without correction
  • after demodulation, a message acceptance ratio of 80%

My questions are: What is a message and is it equivalent to a packet? If not, how does it relate to a packet?

I am asking this because there is a formula which converts BER to PER and I would like to know if I can use it but just exchange message with packet.

\$\endgroup\$
  • \$\begingroup\$ Please don't respond to answers as part of the question. Instead post a comment underneath the answer. \$\endgroup\$ – Lundin Jan 24 at 10:38
  • \$\begingroup\$ Yes, found it strange anyway doing that.. Lundin, do you still have my edit so I could paste it or must I write it again? :/ \$\endgroup\$ – stowoda Jan 24 at 10:53
  • \$\begingroup\$ Below your post, click where it says "edited x hours ago" to get the edit history. You can copy/paste from there and post as comment. \$\endgroup\$ – Lundin Jan 24 at 12:24
1
\$\begingroup\$

You are reading a withdrawn version of the standard (2.4.1?) and therefore you got the requirements all wrong.

These standards have been revised together with the RED directive. The current version is EN/ETSI 300 220-1 V3.1.1. Major revision!

EN/ETSI 300-200-1 V3.1.1, chapter 4.1

  • after demodulation, a raw data signal with a Bit Error Ratio of 10-3 without correction; or
  • after demodulation, a message success ratio equivalent to above Bit Error Ratio:

    (1-p)n where p is the probability of single bit error (10-3) and n the number of bits.

As you can see, the requirement is now 10 times tougher. But this is quite easy to read. Only 0.1% of your message transmissions are allowed to fail during test.

As an engineer you only need to know that the radio isn't allowed to fail, and that's about it. Have the firmware light a LED or preferably spit out an error message on some serial bus each time you encounter an error.

\$\endgroup\$
  • \$\begingroup\$ That's indeed much tougher. You need a very good sensitivity in order to meet there requirements.. \$\endgroup\$ – stowoda Jan 24 at 13:36
  • \$\begingroup\$ @stowoda Not really, but the average "Ali Baba" radio won't conform to RED directive/CE marking. Keep in mind that this is test criteria with ideal test conditions: no background noise, no unknown interference etc. \$\endgroup\$ – Lundin Jan 24 at 13:41
  • \$\begingroup\$ So for a 64bit message, only 3% of messages can get lost. Comparing to the older revision of the standard it was about 47%.. Yes I am aware that sensitivity is determined without any interferer. \$\endgroup\$ – stowoda Jan 24 at 13:58
  • \$\begingroup\$ @stowoda You can apparently chose the test criteria to whatever suits your application. But seriously, if you have a radio link set up in ideal condition, antennas and everything, you should not have any message loss or something is wrong. This isn't a hard or unreasonable requirement. \$\endgroup\$ – Lundin Jan 24 at 14:01
1
\$\begingroup\$

Packet and message can be the same meaning but of course, the number of bits per packet can vary.

  • e.g. one packet can carry 1518 bytes * 8 bits/byte as per IEEE 802.3 ethernet standard.

Packet Error Rate (PER) is defined as ratio of number of packets received in error to total number of transmitted packets.

The relationship between BER and PER for n bits per packet is;

\$PER(n)=1-(1-BER)^n\$

The words Message & Bits are not used in the OSI model, instead it depends on the procotol used for each layer and detection counting method, shown here;

OSI Model
Layer    

 7  Application Data    High-level APIs, including resource sharing, remote file access
 6  Presentation        Translation of data between a networking service and an application; including character encoding, data compression and encryption/decryption
 5  Session             Managing communication sessions, i.e. continuous exchange of information in the form of multiple back-and-forth transmissions between two nodes
 4  Transport           Segment, Datagram   Reliable transmission of data segments between points on a network, including segmentation, acknowledgement and multiplexing
 3  Network             Packet  Structuring and managing a multi-node network, including addressing, routing and traffic control
 2  Data link           Frame   Reliable transmission of data frames between two nodes connected by a physical layer
 1  Physical            Symbol

Since Forward Error Correction must be disabled, the lowest levels must be used with FEC disabled for the Data or Physical Layer whichever can be used without FEC.

Generally the quality of radio is determined by the threshold for fixed error rate near threshold and the slope of error rate vs SNR or Eb/No e.g. enter image description here

A higher threshold may occur with discriminator error or multi-path Fading cancellation or Rx noise or adjacent channel interference or poor LO rejection etc. or Inter-symbol-Interference (ISI) or filter Group Delay distortion etc

The slope depends on noise characteristics being random, spectral shape, repetition rate etc, modulation method with BW compression affected by Comm. Theory such as (Shannon-Hartley's Law.)

It becomes much more steep, above some threshold using FEC depending on overhead and method used.

It is possible to have a lower threshold at 1% error yet higher threshold at 0.1% or 1e-9 threshold BER due to this slope and above interference.

Anecdotal

Back in the 70's,80's I found worst-case & random data patterns to measure contributions of the BER curve due to my path margin budget for contributors like;

  • Group Delay distortion, comparator asymmetry, unequal delays and rise time, pre-compensation and channel periodic defects.
  • By isolating each root-cause contribution to BER using different patterns or by fault of noise, ripple or jitter injection, radiated impulse rejection, impedance control, shielding, one can optimize the design including the filter characteristics of Bandpass vs Bandstop.
  • But 1st you must define an error budget from all sources( ie. a design spec)

I learned this the hard way, as my SCADA controlled robot over by a long distance coax cable fell to the ground from an arc-welder's noise, far away during a major client presentation. This was followed by 3 layers of error detection, correction implemented the following week.

\$\endgroup\$
  • \$\begingroup\$ so what you say is, that a message consists of packets but not the other way? \$\endgroup\$ – stowoda Jan 24 at 12:05
  • \$\begingroup\$ Yes so it depends what / how the errors are measured. \$\endgroup\$ – Sunnyskyguy EE75 Jan 24 at 17:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.