The matlab function fskdemo.m models simple transmission of a frequency shift ke
ID: 2292113 • Letter: T
Question
The matlab function fskdemo.m models simple transmission of a frequency shift keying signal. The input parameters include the number of frequencies M. Modulation is with simple rectangular pulses (i.e., no pulse shaping or filtering. Note that a transmission rate of one symbol per second is assumed for convenience. Also note that this is baseband fsk, with no carrier modulation. The entire baseband signal is typically up-converted to a carrier frequency, but we leave that step out of this demo for clarity. The following plots are produced: Figure 1. – a time plot of the transmitted signal for 10 symbols Figure 2. – the PSD of the transmitted signal Do the following: Study the code and read the help files for the functions used. Note that we are using built-in MATLAB functions from the comm toolbox, so you may not have them in a student version. They are available on the OHIO vitrtual desktop. Set the code to modulate 4-fsk. Turn in the two plots produced, and discuss your observations on the time signal and the PSD of this signal. Now set the code to modulate 16-psk. Turn in the plots along with a discussion of your observations. For both plots, list the specific frequencies used to modulate the data symbols, and discuss the differences of the two signals and spectra.
Explanation / Answer
Description
The M-FSK Modulator Baseband block modulates mistreatment the M-ary frequency shift keying methodology. The output may be a baseband illustration of the modulated signal. For info concerning the info sorts every block port supports, see Supported knowledge sorts.
To prevent aliasing from occurring within the signaling, set the oftenness bigger than the merchandise of M and also the Frequency separation parameter. oftenness is Samples per image divided by the input image amount (in seconds).
Integer-Valued Signals and Binary-Valued Signals
The input and output signals for this block square measure discrete-time signals.
When you set the Input sort parameter to whole number, the block accepts whole number values between zero and M-1. M represents the M-ary variety block parameter.
When you set the Input sort parameter to Bit, the block accepts binary-valued inputs that represent integers. The block collects binary-valued signals into teams of K = log2(M) bits
where
K represents the amount of bits per image.
The input vector length should be AN whole number multiple of K. during this configuration, the block accepts cluster|a gaggle|a bunch} of K bits and maps that group onto a logo at the block output. The block outputs one modulated image, oversampled by the Samples per image parameter price, for every cluster of K bits.
The image set ordering parameter indicates however the block maps a gaggle of K input bits to a corresponding image. after you set the parameter to Binary, the block maps [u(1) u(2) ... u(K)] to the whole number
K
?
i=1
u(i)2
K?i
and assumes that this whole number is that the input price. u(1) is that the most important bit.
If you set M = eight, image set ordering to Binary, and also the binary input word is [1 one 0], the block converts [1 one 0] to the whole number half-dozen. The block produces constant output once the input is half-dozen and also the Input sort parameter is whole number.
When you set image set ordering to grey, the block uses a Gray-coded arrangement and assigns binary inputs to points of a predefined Gray-coded signal constellation. The predefined M-ary Gray-coded signal constellation assigns the binary illustration
M = 8; P = [0:M-1]';
de2bi(bitxor(P,floor(P/2)), log2(M),'left-msb')
to the Pth whole number.
The following tables show the standard Binary to grey mapping for M = eight.
Binary to grey Mapping for Bits
Binary Code Gray Code
000 000
001 001
010 011
011 010
100 110
101 111
110 101
111 100
Binary to grey Mapping for Integers
Binary Code Gray Code
0 0
1 1
2 3
3 2
4 6
5 7
6 5
7 4
Single-Rate process
In single-rate process mode, the input and output signals have constant port sample time. The block implicitly implements the speed amendment by creating a size amendment at the output in comparison to the input. during this mode, the input to the block is multiple symbols.
When you set Input sort to whole number, the input is a column vector, the length of that is that the variety of input symbols.
When you set Input sort to Bit, the input breadth should be AN whole number multiple of K, the amount of bits per image.
The output breadth equals the merchandise of the amount of input images and also the Samples per image parameter price.
Multirate process
In multirate process mode, the input and output signals have totally different port sample times. during this mode, the input to the block should be one image.
When you set Input sort to whole number, the input should be a scalar.
When you set Input sort to Bit, the input breadth should equal the amount of bits per image.
The output sample time equals the image amount divided by the Samples per image parameter price.
To run the M-FSK Modulator block in multirate mode, clear the Treat every distinct rate as a separate task checkbox (in Simulation > Configuration Parameters > Solver).
Parameters
M-ary variety
The number of frequencies within the modulated signal.
Input type
Indicates whether or not the input consists of integers or teams of bits. If you set this parameter to Bit, then the M-ary variety parameter should be 2K for a few positive whole number K.
Symbol set ordering
Determines however the block maps every cluster of input bits to a corresponding whole number.
Frequency separation (Hz)
The distance between consecutive frequencies within the modulated signal.
Phase continuity
Determines whether or not the modulated signal changes phases in a very continuous or discontinuous approach.
If you set the section continuity parameter to Continuous, then the modulated signal maintains its section even once it changes its frequency. If you set the section continuity parameter to Discontinuous, then the modulated signal contains parts of M sinusoids of various frequencies. Thus, a amendment within the input price typically causes a amendment within the section of the modulated signal.
Samples per symbol
The number of output samples that the block produces for every whole number or binary word within the input.
Rate choices
Select the speed process possibility for the block.
Enforce single-rate process — after you choose this feature, the input and output signals have constant port sample time. The block implements the speed amendment by creating a size amendment at the output in comparison to the input. The output breadth equals the merchandise of the amount of images and also the Samples per symbol parameter price.
Allow multirate process — after you choose this feature, the input and output signals have totally different port sample times. The output sample time equals the image amount divided by the Samples per image parameter price.
Output knowledge sort
You can specify the output variety of the block as either a double or one. By default, the block sets this price to double.
Supported knowledge sorts
Port Supported knowledge sorts
Input
Double-precision floating purpose
Boolean (bit input mode only)
8-, 16-, and 32-bit signed integers (integer input mode only)
8-, 16-, and 32-bit unsigned integers (integer input mode only)
Output
Double-precision floating purpose
Single-precision floating purpose
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