General instructions

LI Communication Systems (13812) & LH Communication Systems for Aerospace A (33289) are practical modules. All of the assessments are via coursework, and the final assessment includes a number of design tasks. This draws on material taught throughout the module, with a particular emphasis on any material not covered in the first two labs. When working on this assessment, make sure that you refer back to the lectures. You will also need to have done the MATLAB on ramp. This can be found at:https://uk.mathworks.com/learn/tutorials/matlab-

onramp.html?s_tid=tah_po_mlonramp

Some, but not all, questions say ‘write a routine in MATLAB’ . In these cases, you should create a .m  file, which can be run by any user who opens the file in MATLAB and clicks ‘run’ . An example of such a file is fib.m, which has been loaded onto Canvas as an example. fib.m includes clear, concise comments. Anything that can be changed by the user is clearly marked. You should work to the same standards.

Unless a question specifically requires you to use MATLAB, it is up to you whether or not you use MATLAB when answering that question.

This assignment is worth 50 % of the module.

Support for this assignment

Please make sure that you read through the assignment before the end of term 1 and ask any questions that you need in order to get started on this assignment.

Alan Wood ran a lab on Tuesday 29th  November between 2pm and 5pm in room G27 of the School of Engineering building, which supported question 1 of this assignment. Alan Wood will also run a drop in session on Monday 12th  December between 13:30 and 14:30 in room 226 of the School of Engineering where you are welcome to ask any questions related to questions 1 and 2 of this assignment.

Yi Wang will be delivering the lectures for Communication Systems between 11am and 12noon in LT1 of the Law School on Monday 5th  December and Monday 12th  December. You are welcome to ask any questions related to questions 3 and 4 of this assignment during these sessions.

Alan Wood and Yi Wang are both very happy to answer questions via email, and their emails are a.wood.1@bham.ac.ukandY.Wang.1@bham.ac.uk. Please the university is closed between 17th December 2022 and 4th January 2023. Staff do not check emails during this interval. You are welcome to send emails during this time, and we will respond when we return to work in January.

Submission of work

You will submit a single word document on Canvas which contains your work for this assessment, plus MATLAB (.m) files where these are needed. You may spend as much time as you like on this, provided that your work is submitted on Canvas by 11:00 on Tuesday 10th January 2023.

There is no limit as to how much, or how little, you should write. However, as a guide, students who have submitted approximately two pages per question in previous years tend to have covered the material in the right amount of detail. This guide of two pages per question includes any plots or equations which are needed to answer the question.

Asking for help

Please do ask for help. All questions are welcome. As this is a substantial assessment, there is a limit to the amount of help which we can provide. You are welcome to ask any question, any time. There might be some questions which we cannot answer, as they are an integral part of the assessment, but you are welcome to ask.

Question 1

A binary signal is transmitted along a twisted pair of copper wires, with a potential difference of -1 V representing binary 0 and a potential difference of +1 V representing binary 1.

This signal is affected by thermal noise, which can be assumed to follow a Gaussian distribution. You can assume that the noise level is not a function of frequency. Create a routine in MATLAB which models this system and where the user can vary the signal power, bandwidth and temperature.

Produce a plot which shows the maximum possible information rate as a function of temperature:

•    At a fixed bandwidth

•    If the bandwidth is trebled

•    If the bandwidth is reduced to a third of the original value

Produce a plot which shows the probability of a bit error as a function of temperature:

•    At a fixed bandwidth

•    If the bandwidth is trebled

•    If the bandwidth is reduced to a third of the original value

You should make a recommendation for the operating characteristics (signal power, bandwidth and temperature) of the system. Please note that there is no right or wrong answer for this part of the   question – I am interested in your reasoning, not the precise numerical value.

Your submission should include:

•    A detailed description of your work, including any plots which are needed to clearly explain your work

•    A single .m file which can be run in MATLAB which contains your routine. This .m file should contain any comments which the user needs to be able to easily run this file and reproduce your results

Question 2

A communication system represents symbols as a series of four binary numbers. These are transmitted from a sender to a receiver via a communication channel. Write a short essay which:

a)    Explains how noise in the communication channel can result in errors in the received code

b)   Explains how a Hamming (7,4) block code can be used to correct single errors in the signal

c)    Shows an example of this correction in practice

d)   Discusses a limitation of this method and suggests how this limitation could be addressed

Your essay must not be longer than two pages including any tables or diagrams that you wish to include. The font size for your text must be 11 pt or greater (this does not apply to any text on diagrams). You should ensure that your essay is both clear and concise. You are advised that it is possible to write an essay which obtains the highest grades in a single page (but you do not have to make your essay that short).

Hamming block codes were discussed in lecture 5, so you may want to look back at these notes and  examples on Canvas. However, for part c, you must not use one of the examples from the lectures. If you use any of the following series of binary digits for part c, then you will not get any marks for this part of the question:

1 0 0 1 0 1 0

1 0 1 1 0 1 1

1 0 0 1 0 1 1

Question 3

This exercise is a “link budget” analysis of a simple wireless communication system. Assume a base station transmits a power of 40W into a feeder cable with a loss of 10 dB. The transmitting frequency is 1.8 GHz. The mobile receiver had an antenna gain of 2.15 dBi and a feeder loss of 2 dB.

The mobile receiver has a noise power level of -114 dBm. The required signal-to-noise ratio is at least 10 dB.

The mobile receiver antenna is at a height of hm = 1.5 m. The base station antenna is at a height of hb = 20 m. Assume the distance-dependent path loss is determined by the two-ray ground reflection model. The system needs to allow a “fade margin” of 15 dB.

Note that we did not talk about “Fade margin” in the lecture. Find out what it is and make sure to take the fade margin into account in your link budget analysis.

a)   Convert the transmitting power from Watt to dBm.                [3 marks]

b)   What is the required minimum power received at the mobile receiver? Express this power in dBm.        [2 marks]

c)    For the base station to cover a range of 17.5 km, what is the required transmitting  antenna gain? Express the antenna gain in dBi.                 [15 marks]

d)   Among the dipole, horn and patch antennas discussed in the lecture, which one can achieve the gain obtained in c)? Justify your choice of the antenna. Use the Matlab   codes provided to design one antenna. A diagram of the design with dimensions and appropriate labelling must be provided. There is no unique answer. You are not expected to understand antennas in any detail, but it is useful to develop an appreciation of how the dimensions affect the gain.              [10 marks]

Your submission should include:

•    A detailed description of your workout, including any calculations. There is no requirement to use MATLAB. But if you do, any calculations should also be fully explained in the word document. Make sure to use the units carefully and correctly.

Question 4

You will design a Chebyshev filter for a Ku band satellite receiver operating over the bandwidth of 12.75 – 13.00 GHz. The filter should reject an interference signal at 13.25 GHz by 50 dB. The permitted in-band ripple is 0.5 dB. (Note that in practice this is typically 0.04 dB or even lower). The source and load impedances are 50 W. You should use minimum number of orders (or sections) for the filter.

Your submission should include:

•    A detailed workout of the design including your calculations. You can use the provided Excel  spread sheet (“BPF Element Calculator.xlsx”) to help with the design. All calculations must be fully explained.            [15 marks]

•    A figure of the filter response of your design, plotted using the MATLAB routine provided in the lecture. Set the frequency range from 12.3 GHz to 13.5 GHz at a step of 5 MHz. Marks will be awarded to the design process, not just to the correct final answers.          [5 marks]

Mark scheme

The questions are weighted as follows:

•    Question 1: 30%

•    Question 2: 20%

•    Question 3: 30%

•    Question 4: 20%

Questions 1 and 2 are practical-based questions. In common with the assessment of the labs earlier in the term, these are marked according to a number of strands, which indicate how well you have  performed in each of a number of categories (please see the following pages). Your overall mark for each question reflects the overall standard that you have achieved and is not the weighted average of the strands.

Questions 3 and 4 are theoretically-based questions and are marked on a numerical mark scheme. The number of marks available for each question are shown next to each question.

This assessment is worth 50% of the module