hjr-Communication principle (c): Analog signal Digital carrier code

The above section says analog signal analog carrier modulation, this section says the following analog signal digital carrier code. Digital transmission of analog signals

The analog signal is sampled-quantified-encoded into a digital signal into the channel transmission

Sampling: processing a continuous signal over time into discrete signals in time

It should be noted that the Neiguist sampling theorem, that is, the sampling frequency is not less than the original signal frequency bandwidth of twice times

Bandwidth: The frequency range in which the signal contains a variety of different frequency components

The next step is quantifying

Quantization: discrete signal processing on time, so that it is also discrete in amplitude, divided into uniform quantization and non-uniform quantization

is to divide the amplitude into a number of small segments, each section of the upper point represents the value of this paragraph, to see the current time value in which paragraph, the value of his classification in that segment value

The difference between its value and the value of this segment is called the quantization error .

So on the time-amplitude curve, sampling and quantifying one is discrete on the x-axis, and one is on the y-axis discrete

Encoding: Transforms the amplitude of the quantized signal into corresponding binary digital signal code group process

The following is a more common 13 percent-wire A-law characteristic code

For example, the sampling value normalization (the difference between a large number of units into 0 to 1 or 1 to +1 decimal, to eliminate the unit effect, simply reflect the relationship between the values) to +-1

Divided into 4,096 quantization units, if the sampling value is +1270, with 8-bit C1C2C3C4C5C6C7C8 coded representation

First of all, C1 to C8 to be divided into 3 parts.

C1: Polarity code-because the sampling value is +1270, so the code is 1, negative code 0

C2C3C4: Paragraph code-0 to 2 of 4 power is 000,2 4 power to 5 power is 001,2 5 power is 010

That is, to the power of N (after the face value), (n-4) with 8421 encoding, and so on 1270 in the 2 10 power to 2 power 11, take 11 power (11-4) =7,7 1248 Code 111

C5C6C7C8: The code in the paragraph, the 2 of the 10 power and 11 of the power of the second is 1024-2048

It is subdivided into 2 of the 4 power is 16 parts, that is, each 64, then 1270 is between 3 and 4, take the preceding 3, and then 8421 to encode, 0011

So the final code is 11110011 and you can see

It 's a positive negative. Determine polarity code

2 0 power to 4 power to determine the code in the segment

2 4 power to 12 power to determine the paragraph code

all of them are encoded in 8421 .
Here are a few noun PAM (pulse amplitude modulation), PDM (pulse density modulation), ppm (pulse position modulation), PWM (pulse width modulation) PWM motor, such as the speed is often used, ppm do four axes, the remote control is used is the PPM
Here are two concepts:
Time Division Multiplexing : simply saying that different data is sent at different times. For example, in the first period of time to send a user's data, the second time to send B user data, in the third period of time to send the C user's data, and so on. For example, network transmission, at any time the line can only transmit a packet, different users of the packet is a tick transfer. Single channel radio communication, is also a relatively simple application, at the same time only one person to speak, different people must speak in turn.

Frequency Division Multiplexing : At the same time, the same line, different signals using different basic frequency transmission simultaneously, because the base frequency is different so that each other does not interfere, the terminal equipment through the selection of frequency to the signal of their own base frequency filter out. For example, in multichannel radios, data is sent simultaneously at different frequencies. In cable TV, different channels are transmitted using different basic frequencies.