RF Wireless Systems Simulation And Analysis Computer Science Essay

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Radio signals are converted first to an intermediate frequency (IF), before being converted higher to the radio frequency (RF). This is helpful with filters being easier to build with a given frequency response when the filter has a fixed centre frequency than are filters that have a variable centre frequency. The centre frequency is halfway between the filter's upper and lower cut-off frequencies and a cut-off frequency is where the frequency outputs a frequency component with half the power that it contained at the filter input. As well as at the Intermediate Frequency, there will be a filter at the higher RF, which is the final transmitter centre frequency. The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called heterodyning, resulting in a signal at the difference.

Intermediate Frequency (IF) is a frequency in which a carrier frequency is shifted as an intermediate step in transmission or reception. But the main reason for using an intermediate frequency is to improve frequency selectivity. In communication circuits, a very common task is to separate out or extract signals or components of a signal that are close together in frequency. This is called filtering. With all known filtering techniques the filter's bandwidth increases proportionately with the frequency. So a narrower bandwidth and more selectivity can be achieved by converting the signal to a lower IF and performing the filtering at that frequency.

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Perhaps the most commonly used intermediate frequencies are around 455 kHz for AM receivers and 10.7 MHz for FM receivers. However, the intermediate frequency can range from 10-100 MHz's Intermediate frequency (IF) are generated by mixing the RF and LO frequency together to create a lower frequency called IF. Intermediate frequency tends to be lower frequency range compared to the transmitted RF frequency. However, the choices for the IF are most depending on the available components such as mixer, filters, amplifiers and others that can operate at lower frequency. There are other factors involved in deciding the IF frequency, because lower IF is susceptible to noise and higher IF can cause clock jitters. The advantage of the intermediate frequency is for selectivity and static rejection.

A Line-of-Sight microwave link uses highly directional transmitter and receiver antennas to communicate via a narrowly focused radio beam. The transmission path of a line-of-sight microwave link can be established between two land-based antennas, between a land-based antenna and a satellite-based antenna, or between two satellite antennas. Line-of-sight microwave links are used for military communications, studio feeds for broadcast and cable television. The maximum range of land-based line-of-sight systems is limited by the curvature of the Earth. Line-of-sight microwave links are subject to severe fading, owing to refraction of the transmitted beam along the propagation path. Under normal conditions the refractive index of the atmosphere decreases with increasing altitude.

OBJECTIVES

Create a system project for an RF system using behavioural models( filters, amplifiers, mixers).

Use an RF source, LO with phase noise, and a noise controller.

Perform a Harmonic Balance Simulation.

Analysis the system spectra.

Perform system budget analysis.

Analyse the affect of the Line-of-Sight parameters on the system performance.

PART 1 Construct the Transmitter System

ADS software is used to develop the RF wireless transceiver system with all the blocks using the given specification and values.

C:\Users\Rohan\Desktop\microwave\system.JPG

Figure Radio Frequency Transmitter System

PART 2

At the transmitter section the 300 MHz baseband signal needs to be up-converted by mixer b1_MIX1 to an RF frequency of 19.5 GHz before transmission via the Line-of-Sight link, as shown in the figure above. The received signal is filtered and amplified before it is down-converted in two stages using mixers b7_MIX2 and b9_1_MIX2. Determine the frequency of the three oscillators (LOfreq1, LOfreq2 and LOfreq 3) and the centre frequency of the four band pass filter (IFfreq 1, IFfreq 2 and RFfreq) to implement the design.

For simulating the transmitter section, we have used the VAR (variable) function in ADS to change the values of the specific variables, we have labelled in the system. The values are shown below:

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LOfreq 1 = 19.2 GHz

LOfreq 2 = RFfreq - IF freq1 = 19.5 GHz - 1.5 GHz = 18 GHz

LOfreq 3 = 1.2 GHz

IFfreq 1 = 1.5 GHz

IFfreq 2 = 300 MHz

RFfreq = 19.5 GHz (given)

freqBase = 300 MHz (given)

BasePower = -2

C:\Users\Rohan\Desktop\microwave\part 2.JPG

Figure VAR function

PART 3

Simulation tools are used for the simulation of RF wireless system. They are used in schematic window such as AC gear, Budget power gain, Budget noise figure, Budget noise figure degradation and Budget incident power. These tools are used for power budget simulation.

For Harmonic Balance simulation, Harmonic Balance simulator is needed and OPTIONS tools are used for giving warnings during simulation and topology check.

C:\Users\Rohan\Desktop\microwave\part3.JPG

Figure Simulation Tools

PART 4 Simulation of Spectra

For Spectrum simulation, we need Harmonic Balance simulator HB1 for investigating the performance of the system output spectrum. We also need to deactivate the following simulation tools as described in the figure:

C:\Users\Rohan\Desktop\microwave\part4.JPG

Harmonic balance is a frequency-domain analysis technique for simulating nonlinear circuits and systems. Harmonic balance simulation calculates the magnitude and phase of voltages or currents in a potentially nonlinear circuit.

Spectra of Baseband

C:\Users\Rohan\Desktop\microwave\baseband.JPG

Spectra of mixer1

C:\Users\Rohan\Desktop\microwave\mixer1.JPG

Spectra of filter1

C:\Users\Rohan\Desktop\microwave\filter1.JPG

Spectra of amp1

C:\Users\Rohan\Desktop\microwave\amp1.JPG

Spectra of link

C:\Users\Rohan\Desktop\microwave\link.JPG

Spectra of filter2

C:\Users\Rohan\Desktop\microwave\filter2.JPG

Spectra of amp2

C:\Users\Rohan\Desktop\microwave\amp2.JPG

Spectra of mixer2

C:\Users\Rohan\Desktop\microwave\mixer2.JPG

Spectra of filter3

C:\Users\Rohan\Desktop\microwave\filter3.JPG

Spectra of amp3

C:\Users\Rohan\Desktop\microwave\amp3.JPG

Spectra of mixer3

C:\Users\Rohan\Desktop\microwave\mixer3.JPG

Spectra of IFout

C:\Users\Rohan\Desktop\microwave\IFout.JPG

Determine the affect of received power IF out as a function of link distance Path length. Measure IF out power at different Path lengths and plot a graph of the data. Use the following Path lengths = 0.5 km, 1 km, 1.5 km, 2 km and 2.5 km. Comment on your result.

IFout for path length 0.5 km

C:\Users\Rohan\Desktop\microwave\IFout 0.5.JPG

IFout for path length 1 km

C:\Users\Rohan\Desktop\microwave\IFout.JPG

IFout for path length 1.5 km

C:\Users\Rohan\Desktop\microwave\IFout 1.5.JPG

IFout for path length 2 km

C:\Users\Rohan\Desktop\microwave\IFout 2 km.JPG

IFout for path length 2.5 km

C:\Users\Rohan\Desktop\microwave\IFout 2.5 km.JPG

When we increase the link path length from 0.5 km to 2.5 km, the received power IFout decreases. Here TXgain =30 dB. At 0.5 km, it is 20.088 dBm and at 2.5 km, it is 8.679 dBm.

Determine the affect of received power IF out as a function of link transmitter antenna gain TX gain. Investigate the following TX gains: 10 dB, 20 dB, 30 dB and 40 dB. Comment on your result.

For 10 dB:

C:\Users\Rohan\Desktop\microwave\Ifout 10 db.JPG

For 20 dB:

C:\Users\Rohan\Desktop\microwave\IFout 20 db.JPG

For 30 dB:

C:\Users\Rohan\Desktop\microwave\IFout 30 db.JPG

For 40 dB:

C:\Users\Rohan\Desktop\microwave\IFout 40 db.JPG

When we increase the link transmitter antenna TXgain from 10 dB to 40 dB, the IF output increases. We keep the link distance path length as 1 km.

PART 5 RF System Budget Analysis

For simulation of RF system Budget Analysis, we need to deactivate the Harmonic Balance tool and active AC and budget icons like BudGain, BudNF, BudNFdeg and BudPwrlnc.

C:\Users\Rohan\Desktop\microwave\part5.JPG

Figure AC and budget Simulation tools

our_bgain

The following table and equation is shown below:

C:\Users\Rohan\Desktop\microwave\our bgain.JPG

Using the trace expression as our_bgain[0::x,0], the gain budget graph is displayed below:

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C:\Users\Rohan\Desktop\microwave\bgain.JPG

our_bpwri

The following table and equation is shown below:

C:\Users\Rohan\Desktop\microwave\our bpwri.JPG

Using the trace expression as our_bpwri[0::x,0], the gain budget graph is displayed below:

C:\Users\Rohan\Desktop\microwave\bpwri.JPG

our_bnf

The following table and equation is shown below:

C:\Users\Rohan\Desktop\microwave\our bnf.JPG

Using the trace expression as our_bpwri[0::x,0], the gain budget graph is displayed below:

C:\Users\Rohan\Desktop\microwave\bnf.JPG

The table calculates the value of components i.e. mixers, amplifiers, band pass filters and oscillators according to bgain, bpwri and bnf. According to these values, a gain budget graph is plotted with the components on X axis and the equation on the Y axis.

Comparing, in the bgain graph, it is constant and then at link1 it decreases, for sometimes it remains constant and again increases at amp3.

In the bpwri graph, there is a sudden decrease and increase at mix1 giving it a steep slope response, then remains constant till amp3 and then similarly there are number of steep responses of high and low.

In the bnf graph, it increases from amp 1, then remains constant for some time and then again increases at amp 3 and stays constant.

CONCLUSIONS

Thus, we conclude that RF wireless system can be analysed and simulated using Agilent Advanced design system (ADS) software. Using the Harmonic Balance Simulator HB1, we have simulated the RF system and measured the received power and power at different sections of the circuit. Using the Budget simulating tools, we have measured the value of components according to the equations. We have used the marker to obtain the exact information (value) of the power. We have also analysed the Line-of-Sight antenna link on the system performance. Thus, we conclude that overall the RF wireless system can be used in many applications such as military wireless application, transportation, RF power and signal interface and many more.