polardetective

Let’s expatiate on the concepts of hard decision and soft decision decoding.Consider a simple even parity encoder given below. Check out this ebook. How can the answer be improved?

Hey Guys, I want you to look at it this way, the decoder allocated after the de-modulator and the channel and it recieves the transmitted voltages over the system, ofcourse due to noise and other factors the values of these voltages are varied some are severely and some not. Hard decision almost goes after polarity like if your code is 1/3 repetition code( every bit becomes three bits ie. 0 becomes 000 and 1 becomes 111) and the 000 is sampled by -1,-1,-1 volts and the 111 bits fore +1,+1,+1 volts and sent over the channel, if the recieved voltage is -0.1,-0.1,1.5 then the decoder using Hard decision will take it as a 0 because the number of -ve voltages are greater than the positive. But what the soft decision decoder is that it sums them up so the overall voltage is +1.3 and that is more close to +3 volts of the 111 than the -3 volts of the 000. Videostudio Ultimate X5 Activation Code. AND Both uses Maximum Likelihood decision making, but in hard decision the decoder treats every bit ( of the three repeated bits) as an independant indetity without taking any info from the de-modulator about the other two bits, and thats not the case in Soft Decision ofcourse Soft decision is more developed and provide better performance but its also more cost. So its a debate and you have to choose between cost and performance.

Thanks for you time. Hard decision decoding takes a stream of bits say from the 'threshold detector' stage of a receiver, where each bit is considered definitely one or zero. Crack Lightroom Cc Mac Serial. For binary signaling, received pulses are sampled and the resulting voltages are compared with a single threshold.

If a voltage is greater than the threshold it is considered to be definitely a 'one' say regardless of how close it is to the threshold. If its less, its definitely zero. Crack Sarmsoft Resume Builder. Soft decision decoding requires a stream of 'soft bits' where we get not only the 1 or 0 decision but also an indication of how certain we are that the decision is correct. One way of implementing this would be to make the threshold detector generate instead of 0 or 1, say: 000 (definitely 0), 001 (probably 0), 010 (maybe 0), 011 (guess 0), 100 (guess 1), 101 (maybe 1), 110 (probably 1), 111(definitely 1).

We may call the last two bits 'confidence' bits. This is easy to do with eight voltage thresholds rather than one. This helps when we anticipate errors and have some 'forward error correction' coding built into the transmission. Define FEC precisely. Example: A receiver receives a bit stream consisting of sequences of 8 bit words which contain 7 information bits and one parity bit.