EG7217/EG4217 Advanced Communications Module 2022-23 Coursework 3

Introduction

For this assessment, you are asked to design a cellular mobile telephone system for part of a  city centre and determine the best locations for the deployment of the base stations.  The       system you’ll build is simplified to make this task manageable: it carries only voice-calls and not data and lacks the advanced features that are found in 5G, but you will have to consider   propagation loss and fading, interference and traffic capacity.

The Matlab programme urban.m calculates the loss due to free space and diffraction in an      urban environment using the Walfisch-Ikegami model described in ITU P1411.  The software allows you to place base-stations on a city map, and then look at how they perform as a          cellular network.  You will each be given your own district of a city in which to plan your      network, represented as a map in Matlab.  The assignment has three tasks:

In task 1, you’ll do some simple exercises to get you used to the Matlab programme urban.m In task 2, you’ll create a theoretical plan for your network.

In task 3, you’ll implement your plan in urban.m and make any changes necessary to improve the network.

Tasks 2 and 3 should be written up as a formal report.

Task1:

The exercises in task 1 are for your understanding and there is no need to document them.      You should however, do them all, so that you can use the programme correctly in task 3.       Please make sure you fist have the university version of Matlab installed.  The programme     ‘urban.m’ can be found on the EG4217/7217 Blackboard site under Coursework.  Download it and place it in an empty directory on your university-provided Z:-drive or your own laptop. You’ll also need to download the city assigned to you.  This will be named after your login    name (e.g. ‘city_abc123.bldg if your name is Avinash Bilal Chaudhury).  Finally, download  the programme blocking.m, cost231WalIke.m and hexfill.m, and the file district00.bldg.

The software is run by simply typing “urban” into the Matlab command window.  It will      prompt you for the name of a building database and you should respond by typing                 “city_abc123” or whatever your city is named.  This building (.bldg) file can be viewed in    Matlab or in Textedit.  It consists of several buildings, each defined by a serial number, a     height and three or more points which define its shape in plan-view relative to the x and y    axes, which represent easterly and northerly directions.  When read in, the buildings file will display as a Matlab figure, showing a city map with streets of various widths, open areas (parks and squares) and buildings whose height is displayed by a number.  Along the lower   and left-hand edge, the x- and y-coordinates are shown in metres.  Another figure is also        produced, showing the building serial numbers.  You can zoom into these figures to see more detail.

Once the map data is read in, the user may add base-stations to the map using the “Add”       button in the lower-left of the figure and choosing where to locate your base-station by           clicking the mouse on some point on the map.  A new transmitter dialogue box will appear,   showing the x and y coordinates of the base-station, along with suggested values for the         height of antenna, transmitter power in dBm, horizontal and vertical beamwidth of the           antenna, azimuth (= angle in the horizontal plane with respect to north), downtilt with respect to the horizontal, frequency in MHz and channel number.  Try changing these and then press “OK” .  If any of these parameters are outside the allowed range, the dialogue box will return to allow you to enter another value.

Create three base-stations on the map and then press the “Save” button. Name the base-          stations file “mynetwork.base” and press “OK” . Now close the map window, type “close all” to remove all previous figures and restart the programme by typing “urban” .  Type in the         name of the building file again and it will bring up the city, but without base-stations.  Press    the “Load” button and find the base-station file that you made.  Check that the same three       base-stations appear on the map.

At this point, you may add other base-stations and save the file again to reassure yourself that you can save your network and edit it later.  You may also want to open the .base file in         Matlab or in a text editor, alter it manually and save it.  You’ll see all the same properties that were in the dialogue box.  In particular, the HBW parameter (horizontal beamwidth) will, by default be set to 360 degrees for the base-stations you created.  These base-stations would be in the centre of their cell and radiate in all horizontal directions.  If you want to have               sectorised cells, you’d change this to say, 90 degrees, but then would also have to make sure  that one BS is pointing north (Az = 0), another is pointing East (Az = 90) and so on.

Once you’ve finished editing the .base file, start urban again and load the .base file to see      your changes on the map. Now press the “Out” button to choose the outputs produced by the programme. Untick all boxes apart from “Max Rx power for BS No. 0” and choose the root  filename and directory for output.  Press “OK” and then click the “Calc” button to show the  maximum power received at all points on the map.  By choosing a number other than zero,    say 3, you can also check the signal power provided to all places in the city by base-station

no. 3.

Press the “Out” button and untick all boxes except “Threshold” . Now press “Calc” to see     which locations that receive signal at a level above the threshold and which do not.  Press the “Out” button and set the threshold value to - 100dBm and press ”OK” .  Press “Calc” to run    the calculation.  You should see that the area covered by each base-station has increased.       You may also edit base-stations file and adjust the power (Pwr) of each base-station to          improve the coverage.

The current base-stations will be set to channel 0 by default. Add two or three more base-      stations with channel number set to 1 and select the Co-channel Interference (CCI) output.    Pressing the Calc button will now show in red the areas that receive one base-station clearly  above the others using that channel, and in blue, those which receive two or more different    signals using the same channel, but at similar power levels.  The latter are problematical, and measures must be taken to reduce the interference to the level in the requirement.  (E.g. reallocate channels or turn the power down on one base-station.)

Now, tick the remaining output boxes and run the calculation to identify what information each output provides. Note: one of the outputs is a text file.

Finally, to save effort, an extra programme, hexfill.m is provided to create several evenly-    spaced base-stations in a hexagonal layout.  To use this type “hexfill(0,400,'test1')” into the  Matlab command window:  This will create an array of base-stations of height 10 m and       400 m apart from their neighbours and save them in a file called test1.base.  This can then be loaded into urban in the same way as any other .base file.  The programme will make            adjustments to this array if some base-stations are placed illegally.  You must then press the  Save button to keep these corrections.  The base-stations will be set to channel 0, so you will need to reallocate these to your preferred re-use pattern manually in the text-editor.  To see   the cellular configuration most clearly, you should load the district00.bldg file, which has     hardly any buildings, but your final design should, of course be for your own .bldg file.

NB The programme restricts the base-station parameters as follows:

•   The x and y coordinates must be within the area shown on the map.

•   If the base-station is placed on top of a building, it’s height from the ground must be no more than the height of the building plus five metres.

•   If the base-station is placed in a street, the programme finds the nearest three             buildings to the base-station, and restricts its height to the highest of these buildings. These two rules represent the restriction found in most cities that you mustn’t “spoil the skyline” with antennas.

•    The transmit power cannot exceed 50 dBm for any base-station.

•   The horizontal beamwidth should be equal or greater than one degree for a directional antenna and 360 degrees for an omnidirectional antenna.

•    The azimuth should be any value from 0 up to 359 degrees.

•    The vertical beamwidth should be between 1 and sixty degrees.

•   The downtilt is the amount by which the antenna points below the horizontal and should be between - 10 and 30 degrees.  A negative value would make the antenna point above the horizontal.

•   The frequency should be between 300 and 5000 MHz.  It is set at 1800 MHz and      doesn’t need to be changed.  It is only used to determine propagation characteristics.

•   The channel number is limited in the software to the range 0-50,  but in practice, it should be limited to the number of cells per cluster chosen by the user.

•   Note, all base-stations should have the same ‘frequency’ as they’ll all be close to

1800 MHz, whereas if two base-stations have ‘channel’ then their frequencies /codes/ timeslots (depending on whether FDMA, CDMA or TDMA is used) are exactly the    same and they will therefore interfere with one another.  Base-stations using adjacent

channels (e.g. 4 and 5) are assumed not to interfere.

Task 2

Plan a theoretically viable network. This will be a paper-based study using the material          covered in the Advanced Communications lectures. Make a calculation of the parameters you need using Matlab functions cost231WalIke.m and blocking.m.  This enables you to plan an idealised configuration for the base stations without considering the details of the terrain.  All your values and reasoning should be explained, along with the necessary figures in the report.

•   Estimate the power loss exponent v in your city.  Use the cost231WalIke.m                  programme to plot loss as a function of log10(distance).  Use input parameters              (building heights, building separations etc.) which are typical of the map you’ve been given (though of course, these vary, so you cannot be exact).  Details of this empirical model can be found in the ITU-R document P1411.  This is the loss model used in      urban.m, so it should be relevant, but don’t worry about being exact about the              parameters.  From the gradient ofpower decay with log(d) in the plot, estimate the      loss exponent, v.  Remember that free-space propagation has a power exponent of       v =2, so you should get a value exceeding 2. Show the plot and the lines you used to    calculate the gradient in your report.

•   Consider at least 2 different numbers of Nc (cells/cluster) in your report.  For each,  calculate the S/I ratio (possibly including sectorisation), compare to the requirement and make a justified choice of Nc .

•   Calculate the number of channels available per cell.  Use this number, along with the required grade-of-service to estimate the offered traffic that can be sustained in a cell. This will require you to use the programme blocking.m.

•   From your behaviour and that of your acquaintances, estimate the typical telephone voice usage.  Remember that we’re considering only voice-calls in this exercise, as data is handled slightly differently.  From this, and the population density, calculate the maximum cell area that can be sustained without dropping calls.

•   Calculate the required distance between base-stations and state the disadvantages of  having them closer to, or further from one another.  This distance can now be put into hexfill.m.

Task 3

Use the software urban.m, the city map you are given individually to implement the network you designed in task 1.  Then make adjustments to the position, height, power, beamwidth, sectorisation, downtilt and direction of the base-stations until you are confident that you have a well-designed system that will satisfy the requirements of traffic, power and interference.

•   Each map has a 1.5 km x 1.5 km square in the middle, marked by a red line.  This is the area that will be assessed.  You may put base-stations outside this area if they    contribute to the network inside the area, or you may leave it empty.

•   Put a few base-stations on the map, run the calculation and look at the ‘std@150m’ values in the statistics file to find the typical standard deviation of fading. G that you can expect from the terrain.  This is measured at 150m from the base-station.

•   Using the requirements stated below and G, estimate the power margin.  If the      distance from the base-station to the cell edge is much more than 150 m, then you may want to add more margin.

•   From the cost231WalIke.m programme calculate the power loss at the edge of each cell, decide the transmit power to use.

•    State the trunking efficiency of your ideal network.

•   Load in the base-station file you created in hexfill.m, with your own value of spacing and run the calculation.  Save the .base file, once urban has corrected any illegally-     placed base-stations.  This is your first approximation and it should be shown in the    report with all its failings, to show how your final arrangement has improved upon it..

•   Now move or change the base-stations to conform to the requirements.  Put the          relevant outputs in your report as a benchmark to make it clear how the final network configuration has been improved by your adjustments.

•   An almost blank file district00.bldg, is also provided on the Bb site, so that you can  look at you ideal network on a featureless plane to check that it behaves as expected. There is no need to show this in your lab-book.

Constraints

You should try to make your finished network conform to the following constraints in as    many places as possible.  Marks will be awarded for evidence of having considered all the aspects mentioned below and more marks will be awarded for achieving them as closely as possible.

•    The network has an operating frequency of 1800 MHz. This parameter determines the physical propagation (diffraction etc.), is the same for each base-station and is entirely separate from the channel number. The channel number has no effect on the physical  propagation, and is present only to distinguish the blocks of channels used to define    the frequency reuse pattern. For a seven-cell network (Nc=7), the ‘channel’ parameter for each base-station should be a single number from 0 to 6. Different base-stations     may use different values of the ‘channel’ parameter in urban.m to represent the            different frequency blocks, but the frequency value used by all base-stations should be

1800 MHz.

•    Estimation of traffic: You have a license for up to 480 channels (e.g. for a 3-cell         cluster there would be 160 channels per cell, and the ‘channel’ parameter for each       base-station would be 0, representing channels 1- 160; 1 representing channels 161-     320; or 2 representing channels 321-480). The probability of a channel being                unavailable due to bandwidth contention should be no more than 2.0 %. This will        probably be the primary constraint in a metropolitan environment. You should assume that at peak time, there is an even distribution of ten thousand users of your network    in each square kilometre of the city. The Matlab programme, blocking.m is available  on the Bb site to allow you to use the Erlang B formula. You should aim to make all   the cells approximately equal in area to avoid overloading the larger ones with too       much traffic.  Traffic is not modelled by urban.m, so it is up to you to make sure the    cells are similar in area, as shown in the statistics file output.

•    Bear in mind that a modern cellular network may transfer the load from one base-      station to an adjacent one, if the former gets overwhelmed. Of course, this is subject  to the physical constraint that the signal of the adjacent base-station is strong enough, and this is why the ‘Number of BSs received’ output is included in the software.        There is no reason why cells need to be the same shape, however, and it may be         convenient to make some round, and some long and thin to cover main streets.

•    You should assume that the ambient radio noise level is Pnoise = - 100 dBm (this           includes thermal and man-made radio noise, but excludes the interference from other cells in your network). You should use an appropriate margin in your system to          ensure that fading is not a problem for more than three percent of the locations. When looking at the coverage in urban.m, you should use Pnoise + your calculated value of    margin as the threshold level for successful signal transmission.

•    The minimum signal-to-interferer ratio that can be sustained by base-stations and        mobile stations is 15 dB. This means that the wanted signal is 15dB stronger than        other signals using the same channel.  Your customers in areas on the map where the  co-channel interference is less than this will experience poor quality voice on their      phones. If you need to, you can zoom in on these areas of the map and you can use the command ‘caxis([0,20])’ for example, to highlight the values of CCI between 0 and

20 dB.

•     The height of mobile units is 1.5m. This is implemented in the software.

•     You should attempt to minimise the base station power (for economic and environmental reasons).

•    The statistics file contains a compactness factor for each cell.  This will be large (e.g. 0.3) if the cell is a clearly defined polygon and low (<0.01) if the cell is spread out     with many branches or separate enclaves.  This factor is only measured within the     area of interest (250- 1750m), so don’t worry if cells are messy outside this area.

•    The stats file also contains a messiness index for the whole network which is obtained by taking a randomly placed straight line across the area of interest (250- 1750m) and  counting how many cell boundaries are encountered, compared to a network with        perfectly compact cells.  A value of 5 is bad, while 2 is good.

Problems

Sometimes, there may be an error in the buildings file.  If an error message reports that one of the building in the city is problematic, then please do the following:

•    Use the zoom-in button (top right of the figure window) to look at the shape of the problematical building in the figure entitled ‘Building Numbers’ .

•     Open the .bldg file in Matlab or in a text editor and scroll down to the building in question.

•    Edit the x and y points that define the building’s vertices until they make a convex   polygon.  If you remove a point completely, then you shoud also change the number npointss allocated to that building.

•     Save the .bldg file using Matlab or the text editor.

•     Save the base-stations (.base) file using the ‘Save’ button on the urban GUI.

•     Restart urban and use the ‘Load’ button to reload the base-stations.

•    If the problem persists, please email me (drs13@le.ac.uk) enclosing the .bldg and .base files.

Final Report and assessment

This coursework will be assessed as a formal report that you will upload by 12.00 noon on     Friday 2nd December 2022 to the Advanced Communications Blackboard site. Ideally this    would be in pdf format, though Microsoft Word is also acceptable. Marks will be awarded for  the clarity of the report, basic report skills such as whether the figures are numbered, captioned and referred to in the text,  demonstration of logical reasoning and whether you have done all   the tasks,.  Although headings may differ, the quality aspects defined in the Departmental         Writing Handbook should be adhered to. More advice is available at Academic Skill Online

The report should include:

•     A brief introduction that includes the background to and purpose of the work.

•    A theory section, showing your calculations in task 2, before you use urban.m. This  may include a map with the intended frequency reuse pattern, values of cell area, Nc, S/I etc.