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Sender, Source & Channel Coding, Channel, Receiver in wireless communication - step by step



Mechanism of wireless communication - step by step:

Example: 

 

 Original Analog Message signal

 
 
 Sampled Message Signal (Digitalized Signal)
 
 
Quantized Message Signal (Mapped to Finite Signal Levels)


Encoded Signal (after Source Coding)

 
 
 
Then we perform channel coding to enable error correction during transmission. Then, we apply modulation and transmit the signal through a wireless medium. After receiving the signal, we first demodulate it, then apply channel decoding followed by source decoding, and finally retrieve the original message signal. 
In our case, the source message signal is analog, not digital. However, the process discussed here is applicable to Pulse Code Modulation (PCM) signal. For analog signal transmission, we simply modulate the signal with a higher frequency and then transmit it. On the receiver side, we apply the demodulation process to the received signal and retrieve the original analog message signal. 
 
 
 
 
 





Modern Wireless Communication Process:

 


 

Fig: Process of wireless communication

 

In the above figures, a typical wireless communication system is illustrated. The original message signal—such as digitized computer data (a bit stream of 0s and 1s)—is first sampled and then quantized. After quantization, the signal undergoes source coding, where it is efficiently encoded into binary form. To transmit this signal over a wireless medium, the binary bits are modulated using an appropriate modulation scheme.

At the receiver end, the signal is first demodulated, followed by source decoding and any additional processing needed to reconstruct the original message signal (e.g., audio). Channel coding, which is typically applied after source coding, enables error detection and correction to combat impairments like attenuation and multi-path fading introduced during transmission.

 

Wireless communication is a method of communication in which the transmitter and receiver communicate over the air or free space. Between the transmitter and the receiver, there is no wiring for wireless communication. The communication path, which is air or free space in this case, is referred to as a channel. The electrical signal is converted by the transmitter as '0' and '1'. The electric signal then transmits via the channel (air or free space) after a successful modulation procedure. The signal is then received by the receiver. It is practically difficult to recover the same signal that the transmitter sends. Due to attenuation or distortion, the signal becomes corrupted while travelling across the channel. A wireless communication system's fundamentals are as follows.

The following is a list of the various elements involved in the wireless communication process

1.Sender
2.Message
3.Encoding (source & channel coding)
4.Channel
5.Receiver
6.Decoding
7.Acknowlegement / Feedback


Sender:


Here, in communication process sender is who sends messages, files, audio, etc. to indented receiver. Here, sender send his message from smartphones, PCs, etc. using specific application.


Digitization of Message Signal in Communication Process (sampling + quantization):

In general, message signal's source is analogue in nature. Now, the analogue signal is turned into a digital signal (or, the original analogue signal is changed into '0' or'1' bits) by sampling and then quantization). Quantization helps to map the signal into finite levels. We convert analog signals to digital signals using the analog to digital converter (ADC).

There are also some exceptional cases where the source signal is not analog. The acquired images by radar, for example, are not analog signals because the image is a digital signal. After that, we process it and deliver it to the receivers on earth.


Source coding / encoding:


We are aware that the original message file is huge in size. Imagine how much memory is required to store a one-hour voice recording. It's likely that a few GB of memory is required. When we convert it to digital by just sampling at the very beginning of transmission procedure, it still requires a large number of memories to store. On the other hand, we always prefer to transmit a compressed signal over an uncompressed huge file if possible. So, we compress it. We use coding, also known as source coding, to compress the digitalized message signal. Source coding can reduce the size of a message signal. The message signal could be text, audio, or voice, for example. Text, voice, and audio messages can all benefit from source coding. For sending, original message without compressing it, it will take longer and result in more bit errors due to the larger file size. Popular examples of source coding are Huffman coding, LZW coding, etc.


Channel Coding:


After source coding, channel coding allows us to code the compressed message signal with various types of coding, such as forward error correcting (FEC) coding, so that we can recover the required message signal at the receiver terminal even if some bits are lost or distorted. Another illustration is the use of the CRC or cyclic coding technique in OFDM 4G-LTE communication to retrieve the original signal or measure the channel's status.


 

Simulation Results:

1. Suppose we are sending a text message signal 'Wireless'
 

2. Source Encoding (Huffman)

Original message: Wireless

Encoded bits: 10010111000111000101

3. Channel Encoding (Hamming 7,4)

Blocks:

1001001
0111001
0001111
1100011
0101010

 4. Then ASK Modulation

5. After Demodulation,

Recovered bits: 10010010111001000111111000110101010 

 

6. Channel Decoding (Hamming Decode)

Decoded bits: 10010111000111000101

 

7. Source Decoding (Huffman Decode)

Final Decoded Message: Wireless


Explore This Simulation

Explore Signal Processing Simulations

# Wireless channel are more prone to bit error than wired channels

Digital communication and its application and pictures


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