# Basic Coding Concepts Flashcards

1
Q

What is a code?

A

An error correcting code is a device that adds redundant information to a block of data symbols and uses this information to correct potential transmission errors.

2
Q

What happens if a code has a high and low rate?

A

A high rate adds only a small amount of redundant information

A low rate adds a large amount of redundant information

3
Q

The rate of a code is a measure of what?

A

The bandwidth effiency

4
Q

How do we get the hamming weight?

A

We get the nymber of non-zero symbols (number of ones)

5
Q

Give an example of how to get the hamming distance

A

u = (00100)
v = (10101)

d(min)=2

6
Q

Give the formula for detectable errors (BSC)

A

d = dmin - 1

7
Q

Give the formula for correctable errors (BSC)

A

e = [dmin - 1 / 2]

8
Q

What’s the disadvantage of BI-AWGN channels

A

Not good for good dmin

9
Q

What’s the goal of a decoder?

A

To maximises the a posteriori probability

10
Q

Channel Coding Theorem

A
11
Q

What’s entropy?

A

A measure of “unpredictability” of a random variable

12
Q

What’s the capacity of a channel?

A

The maximum amount of information (expressed in “information bits per channel use” that a channel can convey)

13
Q

Explain what the rate should be when finding the best possible code

A

When the rate is equal to the capacity

14
Q

What is the absolute communication limit for AWGN and what is it?

A
• The worst channel we can communicate over and it’s -1.59dB

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15
Q

Explain what the Hard-Decision BI-AWGN Channel does

A

It has a decision factor transforms the channel into a BSC channel

16
Q

What’s the difference between AWGN and BI-AWGN

A

We need an SNR of 2db larger when doing Hard BI-AWGN; we destroy information

17
Q

Why are linear codes practical codes?

A
1. Channel capacity can be achieved with linear codes
2. Linear codes are very easy to implement using simple digital circuits
3. Almost all implemented codes are linear codes
18
Q

How are errors corrected in a BSC

A

Using a syndrome table