Conditional crosstalk
The condition of the code-free crosstalk is as long as the strong restriction waveform h (t) of the baseband transmission system has the maximum value on the sample time of this symbol, and the code interval crosstalk can be eliminated on the sample time of the other symbols. . That is, if H (t) is sampled at time t = kts (here the delay T0 = 0 caused by the channel and the reception filter), it should be established:
The above formula (1) is called the time domain condition of the codeless crosstalk. That is, if the sampling value of H (t) is not zero in T = 0, there is no inter-code crosstalk in all other sampling points.
Design of transfer characteristics of uncoded crosstalk
1, ideal low pass characteristics
There are many kinds of Nyquist's first guidelines, a limit of limits are ideal low, namely
When h (t) is equal to the positive and negative KTS (k is not equal 0), there is a periodic zero point. When the time interval of the sequence of sequences is TS, these zero points are ingenious, as long as the receiving end is sampled at T = KTS time points. In order to achieve a codeless crosstalk.
Regrettably, although ideal low-pass transmission characteristics reach the limit transmission rate and ultimate frequency band utilization of the baseband system, this characteristic is physically unable to implement. Moreover, its impulse response h (t) is still unsuitable as a transport waveform.
2, cosine rolling characteristics
In order to solve the problem of ideal low-pass characteristics, the edge of the ideal low pass filter characteristics can be slowly decreased, which is referred to as a rollback. As long as H (w) is quite symmetrical in the center frequency of the rolling segment, it is inevitably satisfying the Nyquist First Guidelines to achieve uncamined crosstalk transmission. This design can also be regarded as the result of rollback from the center of Nyquist bandwidth as a center. The key parameters of the design are the roll-off factor.
The bandwidth of such a system is 2 times the ideal low-pass system.
Verify the condition of the codeless crosstalk
Using the MATLAB simulation, verify the condition of coded crosstalk, draw the correlation waveforms and eye graphs, and draw the error rate characteristic when noise
Fundamental
1, code interval crosstalk
The transmitted digital signal can cause mutual overlapping between adjacent digital signal waveforms, that is, the so-called code interval, due to the presence of intermodal crosstalk, it may cause errors when the decoding decision is decoded. In addition, the textbook gives the condition of the code-free crosstalk, that is, the first standard of Nyquist, deepened the understanding of the symbol crosstalk and the first standard of Nyquist.
2. Introduction to the eye
In order to measure the performance of the baseband transmission system, the method of receiving signal waveforms is typically observed with an oscilloscope to analyze the effects of inter-code crosstalk and noise, which is the eye diagram analysis method, as shown below.
When the signal distortion is small: the eye is the big eyes, single eyelids;
When the signal distortion is large: the eye is small eye, multi-eyed skin.
Simulation results and analysis
Program operation results:
1. Actual value curve before the boostrine baseband transmission system
2, eye map
3, error rate curve
The above four figures are classified by the sample point actual value curve prior to the boostroexoid transmission system, the actual value curve, the eye graph, and the bit error rate curve before the boots, and Fig. 5 shows the operation of the program operation. information. From the bit error rate curve, it can be found within a certain range, the smaller the signal-to-noise ratio, the smaller the error rate of the corresponding channel transmission. Read more
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