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  Communication SystemsIntroductory AssignmentDue date: 5pm, 18 August 2017

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Communication SystemsIntroductory AssignmentDue date: 5pm, 18 August 2017.Where to submit: the Faculty of EAIT (Hawken Building 50) assignment chute.Note: All assignments require a cover sheet (available fromhttps://student.eait.uq.edu.au/coversheets/)This assignment is 10% of your final mark for COMS4105/7410 and has 20 marks.Q1 Communication Channel Modelling (7 marks)Intelligent transporation systems (ITS) are being more present in our road infrastructure. Futurevehicles will have vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communicationlinks keeping the driver (and passengers) more informed about traffic conditions, and to ensuresafer, and ‘smarter’ use of the road.Communication occurs over a medium known as the channel. The channel here will be betweena vehicle on the road and some road-side infrastructure. The added complexity of thissystem is the non-static nature of the channel, and there will also be a Doppler effect. A diagramof this scenario is shown in Fig 1.RoadTxh RxFigure 1: Signal Model Diagram – V2I communication linkWe assume that the transmitter is fixed (0; h) and that the receiver is attached to the vehiclemoving along the road. For simplicity, analysis will be performed in a single plane. Reflectionswhich occur, operate like a ’mirror’, that is the angle of incidence and departure from the surfacemust be equal. Each time the signal reflects it is phase shifted by 180 degrees and attenuated.Due to the spreading of the signal, there is also a loss associated with distance.The spreading loss provides a multiplication by L = 1/D2, where D is the length of the path.The reflectivity of the road and vehicle is assumed to be 80% and 95% respectively. The Dopplerfrequency is the velocity of the vehicle in the direction of the signal path. Note that the signaltravels at the speed of light, c.Question 1.1 Multiple paths between Tx and Rx are superimposed at the receiver. Draw a diagramincluding each of these paths and write a formula for each of the path lengths. Allowthe receiver position (Rx, Ry) to be a variable, which means we can explore the changes thatoccur as we select different positions.HINT: each path length be in terms of T = (0; Ty), R = (Rx;Ry). ¦Question 1.2 Calculate the bounds for the various paths. That is, at what location will a reflectionno longer occur, and where will communication be no longer possible? ¦Question 1.3 Write the impulse response of the channel assuming the vehicle is 5 m from thetransmitter, and travelling at a speed of 100 km/h. Assume that the signal has a operatingfrequency of 5.8 GHz.HINT: h(t) = A(t ?? ) exp(j!t) is an impulse response of a (single path) channel which provides adelay of , a amplitude change of A, and a frequency shift of !. The propagation velocity is the speedof light. ¦Question 1.4 Using the provided signal data provided (See COMS dashboard), which has beensampled at 2 MS/s, plot the spectrum at the transmitter, and the receiver for the parametersspecified in the previous question. NOTE: this is a baseband equivalent signal on a carrier frequencyof 5.8 GHz. ¦Question 1.5 We can explore the effect of the channel on a simple modulated system in termsof the bit error rate (BER). To demonstrate this we will make use of a set of communicationsystem blocks. Use the provided NRZ encoder and decoder and the top level design to simulateBER. You will need to implement two types of channels: (a) an additive white gaussiannoise channel (AWGN) and (b) the channel which has the transfer function of the previousquestion in addition to AWGN.• Create the code necessary for each of the channels, and complete the top level design.• Plot a BER graph of the level of AWGN (x axis) vs the BER (y axis) for both channels byusing your top level design. SNR should be between 0 dB and 30 dB SNR. BER shouldbe between 10??6 to 100. Note that a large number of bits needs to be sent (over 1 million).• Briefly describe the plot itself. What is the maximum/minimum BER, where are theylocated, if the SNR was more extreme what BER would you predict (ie SNR = -100 dBand 100 dB)NOTE: For your BER graph, a noise power of 1 (the simple randn function), is for a symbol durationof one sample. If you oversample your signal, you should use the appropriate scaling amplitiude foryour noise power. Assume a bit rate of 100 MBit/sec. ¦Q2 Baseband Communication - Line Codes (7 Marks)In baseband communication systems there are a large number of line codes which are availableto the designer. The best choice depends on the requirements and limitations imposed. Such limitationsmay be in terms of the bandwidth available, the need for extensive timing information,the requirement to reduce the DC component (due to long line lengths).A line code which will we will call ‘MX1’ combines clock and data into one signal. In MX1encoding logic 0 is encoded as transisiton during a bit period, whereas a logic 1 has no transitionduring the bit period. Each bit ALWAYS has a transition at the start of the bit period. Thepossible representations are shown in Figure 2.Question 2.1 Sketch (or plot) MX1 representation of the binary bit sequence “0010”. ¦Question 2.2 Using the formulas provided in class, find the power spectral density of the encodingmethod assuming a sequence of equally likely 1s and 0s. ¦Figure 2: MX1 line code, Logic 0 and 1Question 2.3 Create a program which encodes a sequence of bits into MX1 encoding. Then findthe simulated power spectral density for a long sequence of bits (>1000). HINT: In order to seemultiple spectral nulls you will need to oversample the original time domain signal ¦Question 2.4 Comment on the bandwidth (with respect to the first spectral null), the availabletiming information, and the level of DC component in this signal. Use your results of thesimulation and theoretical result. ¦Q3 RTLSDR – Capturing signals from around us (6 Marks)We will be using the RTL2832 tuner stick to capture signals in over-the-air experiments. Thissmall exercise will prepare you for the practicals later in this course. Also, it will give you agreater understanding and appreciation of the signals being transmitted in the air around us.Follow the instructions in the course GitHub website (via COMS dashboard) to setup yourRTLSDR device. Also, further instructions are available for the basic usage of the device. One ofthe main commands you will be using is rtl_sdr:rtl_sdr dump.bin -s 2e6 -f 110.9e6 -n 1e6which will capture one million samples at 2 megasamples per second and a center frequencyof 110.9 MHz to a file called dump.bin.Question 3.1 The RTLSDR USB software-defined radio device with R820T supports frequenciesfrom 24 MHz to 1.7 GHz, and sampling rates of 250 kHz to almost 3 MHz. Using the device:• Identify three signals of interest which can be captured (their centre frequency and bandwidth).They can be:– an FM radio station– a DAB radio multiplex– something else• Capture one second each signal and plot the power spectral density. You should adjustthe sampling rate to as just cover the full bandwidth.HINT: Know the difference between carrier frequency and bandwidth. ¦Question 3.2 Based on the spectral density plots and your research, describe the• the carrier frequency and bandwidth of the signal,• the signal to noise ratio,• the signal’s purpose,• and comment on any interesting features of the PSD (eg BW efficiency).¦