ELEC 5510 Satellite Communication Systems Group Project 2016 Overview In this project, you will learn how to plan, implement, analyse and simulate satellite communication systems in compliance with the digital video broadcasting – satellite (DVB-S & DVB-S2) standards. Based on that you will then compare the two standards and make a recommendation on which one should be used for a specified application. The project consists of seven parts. Part I involves link budget calculations, where signal-to-noise ratios (SNRs) are determined to satisfy a certain performance requirement. Part II involves baseband simulations and performance analysis of the DVB-S standard. Part III involves baseband simulations and performance analysis of the DVB-S2 standard. In Part VI, you are required to provide a recommendation on which communication system (DVB-S or DVB-S2) should be used, based on your findings in this project, as well as the techniques presented in the lectures. Parts IV and V are optional and aim 1) to develop an adaptive modulation coding scheme at the satellite transponder, proposed in DVB-S2, to adapt the transmission parameters to the reception conditions of terminals, e.g., switching to a lower code rate during fading; 2) to develop diversity and combining techniques by employing multiple antennas at the receiver at the customer premises to improve DVB-S transmission. Part VII is a project presentation highlighting your results obtained in the other parts. This project involves teamwork. You need to form groups of 4 members each. All groups must complete Parts I, II, III and VII. Parts IV, V and VI are optional. Note that the overall mark for the compulsory parts is 100%, while the optional parts are worth additional 30%. The project carriers 39% of the overall unit of study assessment mark. The percentage mark allocation is shown for each part. DVB-S Standard The digital video broadcasting-satellite (DVB-S) [1] is the physical layer standard for satellite television broadcast and data services. It specifies the framing structure, forward error correcting (FEC) coding and modulation schemes, and it is currently the most widely used standard for direct broadcast satellite (DBS) services all over the world. While the DVB-S standard only specifies the physical layer, the overlaid transport stream is mandated as MPEG-2, known as MPEG transport stream (MPEG-TS). Fig. 1 shows a block diagram of a DVB-S baseband transmitter, according to the DVB-S standard. A DVB-S baseband transmitter consists of four blocks: the outer Reed Solomon encoder; convolutional interleaver, inner convolutional encoder and QPSK modulator. Fig. 1. Block diagram of DVB-S modulator transmitter and receiver RS decoder Convolutional Decoder Convolutional DeInterleaver Demodulator RS (204,188) Encoder Convolutional Enoder Convolutional Interleaver QPSK Modulator Wireless ChannelOuter Reed-Solomon encoder: Each randomised MPEG packet is encoded by a (204,188) Reed-Solomon (RS) code, which is a shortened code of the original (255,239) RS code with an error correcting capability of t=8. Each 188-byte packet is encoded into a 204-byte RS codeword, where the byte length is 8 binary symbols. Convolutional interleaver: The RS coded packets of 204 bytes are interleaved by a convolutional interleaver with depth I=12 and a shift register length of 17. The 1st depth of output bytes of the convolutional interleaver experience a zero delay and thus preserve the periodicity of 204 bytes at the receiver. The time interleaving provides a mechanism to spread a burst error across multiple RS codewords and hence enhance the error correcting capability of the concatenated FECs. Inner convolutional encoder: The interleaved bytes are first converted to a binary stream according to the most significant bits (MSB) first principle and then encoded by the inner encoder. Punctured convolutional codes based on a rate-1/2 mother code are used as the inner code. The mother code has a memory order of 6 and generator sequence (171, 133)OCT. In order to cater for different service requirements, five levels of puncturing are specified resulting in code rates of 1/2, 2/3, 3/4, 5/6 and 7/8. Note that the convolutional encoder operates in a continuous mode, and thus the trellis is never terminated. This also implies that the Viterbi decoder in the receiver should also run in a continuous mode with an appropriate decision depth. QPSK modulator: The convolutional encoded binary stream is QPSK modulated with Gray mapping and transmitted over the wireless channel. DVB-S2 Standard The DVB-S2 standard defines a second generation modulation and channel coding system for satellite communications. It is a flexible standard, covering a variety of satellite applications with the following properties: • a flexible input stream adapter, suitable for operation with single and multiple input streams of various formats (packetised or continuous); • a powerful forward error correction (FEC) system based on LDPC (Low-Density Parity Check) codes concatenated with BCH codes, allowing Quasi-Error-Free operation at about 0.7 dB to 1 dB from the Shannon limit, AWGN channel, depending on the code rates. • a wide range of code rates (from 1/4 up to 9/10); 4 constellations, ranging in spectrum efficiency from 2 bit/s/Hz to 5 bit/s/Hz, optimised for operation over non-linear transponders. • Adaptive Coding and Modulation (ACM) functionality, optimising channel coding and modulation on a frame-by-frame basis. The block diagram of a DVB –S2 system is shown in Fig. 2.BCH Decoder DeInterleaver LDPC Decoder QPSK/8PSK Demodulator BCH Encoder Block Interleaver LDPC Encoder QPSK/8PSK Modulator Wireless Channel Fig. 2. Block diagram of DVB-S2 modulator transmitter Outer BCH Encoder: A t-error correcting BCH (Nbch, Kbch) code is applied to each input data stream of length Kbch to generate an error protected packet. The BCH code parameters for nldpc = 64800 are given in Table 1. The generator polynomial of the t error correcting BCH encoder is obtained by multiplying the first t polynomials in Table 2 for nldpc = 64 800. Table 1. Channel code parameters in DVB-S2 standard Table 2. BCH primitive polynomials in DVB-S2 standard Inner LDPC Encoder: A function to simulate a standard LDPC code with variable code rates is available in MATLAB. Please use the standard functions in MATLAB and adjust the parameters, whenever required, according to Table 1. Bit Interleaver (for 8PSK, 16APSK and 32APSK only): For 8PSK, 16APSK, and 32APSK modulation formats, the outputs of the LDPC encoder are bit interleaved using a block interleaver. Data is serially written into the interleaver column-wise, and serially read out row-wise. This is specified in Table 8 [2]. Modulator: In DVB-S2 4 the following different modulations are used: QPSK, 8PSK, 16 APSK, and 32 APSK. In this project you only need to run simulations for QPSK and 8PSK with Gray mapping. The code rates which are used for each modulation are provided in Table 3.Table 3. Modulation and code rates in DVB-S2 standard Modulation LDPC code rates QPSK 1/4, 1/3,2/5,1/2,3/5,2/3,3/4,4/5,5/6,8/9,9/10 8PSK 3/5,2/3,3/4,4/5,5/6,8/9,9/10 The Application Scenario We consider a DVB-S/S2 receiver system operating in the C Band. Although the DVB-S/S2 standard was designed for the Ku band, a lot of C band broadcast services use DVB- S/S2 for global/zone coverage. The receiver system is illustrated in Fig. 3. Fig. 3. DBS receiver system A parabolic antenna (dish) is used outdoor to receive the satellite signal. A low noise block (LNB), usually fixed onto the dish, amplifies and down converts the satellite signal from radio frequency (RF) 3.7-4.2 GHz to intermediate frequency (IF) 950-1450 MHz. The IF signal is then carried by a coaxial cable to an indoor set-top box, which demodulates and decodes the signal into a format that a normal TV can display. This project involves calculation of receiver SNRs, simulation of the error control coding schemes and comparing DVB-S and DVB-S2 technologies for this particular application. Part I – Link Budget Calculation (25%) The emphasis of this part is to learn how to plan link parameters and budget the losses due to environment or imperfect system components. Assume that the satellite transponder of interest is transmitting in the C-Band using a global beam. Its footprint is shown in Fig. 4. Fig. 4. Satellite footprint LNB Set-Top Box TV CableThe receiver is located in Sydney and the link parameters are listed below. Distance from the receiver to the satellite: 38500 km Location of the receiver: latitude 33.9S, longitude 151.2E Elevation of the receive antenna: 36.6 Dish diameter D: 1.5 m Transponder carrier frequency fc: 3960 MHz Polarisation: horizontal Symbol rate rs: 3.57 M symbols/sec FEC code rate for DVB-S: 1/2, 3/4, and 5/6. FEC code rates for DVB-S2 with QPSK: 1/4, 1/2, 5/6, 8/9. Receive antenna aperture efficiency η: 0.55 Antenna noise temperature: 40 K Receiver noise temperature: 75.9 K Ambient temperature: 280 K Miscellaneous losses (e.g. receive antenna pointing loss, impedance mismatch loss): 2 dB Based on the above parameters, please carry out the following calculations. Please clearly state any assumptions you make during the calculation. Clear sky condition Under a clear sky condition, calculate 1) The system noise temperature Ts, including the antenna and the receiver, consisting of LNB, cable and set-top box noises. 2) The receive antenna gain Gr, and hence the receiver figure of merit, the G/T ratio. 3) The C/N0 ratio. 4) For a DVB-S system, find the Eb/N0 ratio, where Eb refers to the information bits before the RS decoder. Comparing your calculated ratio to the required Eb/N0 in the DVB-S standard Table 3 [1], shown in Table 4 below, find the SNR margin. Is the reception quality acceptable? Which code rate should be selected for transmission and why? Table 4. Eb/N0 ratio requirement excluding outer codes [1] 5) For a DVB-S2 system, find the Eb/N0 ratio, where Eb refers to the information bits before the BCH decoder. Comparing your calculated ratio to the required Eb/N0 in the DVB-S2 standard Table 13 [2], is shown in Table 5 below, find the SNR margin. Is the reception quality acceptable? Which code rate should be selected for transmission and why?Table 5. Eb/N0 ratio requirement excluding outer codes [2] 6) Calculate Es/N0 ratio, where Es refers to the energy per QPSK symbol before the RS decoder. Raining condition Assume that for 0.01% of the time in the region where the receiver is located, the rain rate is R=36.8 mm/h. The parameters for the CCIR rain attenuation method are listed below for the C band. a=0.0007, b=1.13, r=0.33. 1) Calculate the rain attenuation. 2) Assuming the rain attenuation is entirely absorptive, calculate the equivalent noise temperature caused by the rain attenuation Train. 3) Calculate the SNR margin for both the DVB-S and DVB-S2 under the raining condition and comment on which code rate performs best. 4) Assume that the transponder is operating in the Ku band with the following parameters: Carrier frequency fc=12706.5 MHz EIRP=50 dBW Dish diameter D = 0.9 m Symbol rate rs=22.5 M symbols/sec CCIR rain attenuation parameters: a=0.05, b=1.28, r=0.33 All other parameters not mentioned here are not changed relative to the C-band transmission specified in Part I. Calculate the SNR margins under clear sky and raining condition for the code rates considered for both DVB-S and DVB-S2, respectively. Is the reception quality acceptable in each condition? Which code rates for DVB standards should be selected for transmissions and why?Part II – Simulation of Channel Coding in DVB-S (30%) The emphasis of this part is to learn how build a simple simulation model to analyse the performance of satellite communication systems. The inner code in the DVB-S standard is a convolutional code with a memory order, m=6 (e.g., constraint length K=7) and generator sequence (171, 133)OCT. Five levels of puncturing, as shown in Table 2 of the DVB-S standard [1], provide different code rates for different service requirements. This is shown in Table 6 below. Table 6. Puncturing codes in the DVB-S standard [1] In this part, you will simulate the bit-error-rate (BER) of the convolutional code with QPSK modulation in additive white Gaussian noise (AWGN) channels unless stated otherwise. You only need to do a baseband simulation without simulating the actual carrier modulation and demodulation, but a simple bit-to-constellation mapping. For the simulations you will use binary random sequences with the length of 188 bytes, defined as an input frame transmission. To obtain an acceptable accuracy, the simulations for each BER will need to be run until you obtain at least 100 bit errors, for each Eb/N0. You also need to explain clearly all your assumptions as well as indicate all input and the output parameters used in your MATLAB functions. 1) Simulate and plot the BER versus Eb/N0 curves for three levels of puncturing (1/2, 2/3 and 5/6), with QPSK modulation. For comparison purposes, please also plot the uncoded QPSK BER curve in the same figure. You will need to determine the appropriate Eb/N0 range such that each curve spans a BER range at least from 10-5 to 10-2. Please note that the horizontal axis should be Eb/N0 with unit of dB, while the vertical axis should be the BER with log scale. [Using the MATLAB function semilogy(ber,snr,…);] 2) From the above curves, please comment on whether increasing the puncturing rates increases or decreases the BER and why? 3) Repeat Question 1 when the standard RS(188,204) outer code is used before the convolutional code. Please explain how the outer coding affects the overall BER performance. 4) For each simulated code rate, find the minimum Eb/N0 requirement that meet BER=210-4. Please comment on whether increasing the code rates increases or decreases the minimum Eb/N0 requirement and why? 5) In Table 4 above, the minimum Eb/N0 requirements for different inner codes are listed. Compare them with your results. Are they consistent? If not, please explain the impact of using the RS encoder. 6) From the minimum Eb/N0 requirements obtained from your curves in Question 1, find out the coding gains at BER=210-4 for the inner codes only with the code rates of 1/2, 2/3 and 5/6 by comparing them with the BER simulation for an uncoded QPSK. Compare these coding gains with the asymptotic coding gains calculated from the free distance dfree and comment. Note that you can find the dfree values from Table 6 above or Table 2 of the DVB-S standard [1] or the lecture material on DVB-S.7) Simulate the convolutional codes with QPSK and code rates of 1/2, 2/3 and 5/6 in a Rayleigh fading channel that changes every input frame transmission and plot their BER versus Eb/N0 curves. Compare it with the AWGN channel results and comment. Part III – Simulation of Channel Coding in DVB-S2 (30%) The emphasis of this part is to learn how to build a simple simulation model to analyse the performance of DVB-S2 satellite communication systems. The inner code in the DVB-S2 standard is an LDPC code with the codeword length of 64800. 11 different code rates, as shown in Table 3, provide different service requirements. In this part, you will simulate the bit-error-rate (BER) of BCH code, LDPC code with QPSK and 8PSK modulations in additive white Gaussian noise (AWGN) channels, unless stated otherwise. You only need to do a baseband simulation without simulating the actual carrier modulation and demodulation, but a simple bit-to-constellation mapping. For the simulations you can use binary random sequences with the length of Kbch that has been specified in Table 1, defined as an input frame. Note that for each code rate, denoted by LDPC code in Table 1, the length of sequences is different. To obtain an acceptable accuracy, the simulations for each BER will need to be run until you obtain at least 100 bit errors, for each Eb/N0. You also need to explain clearly all your assumptions as well as to indicate all input and the output parameters used in your MATLAB functions. 1) Simulate and plot the BER versus Eb/N0 curves for the LDPC code rates and modulations, according to the table below: Modulation LDPC code rates QPSK 2/5 and 9/10 8PSK 2/3 and 8/9 For comparison purposes, please also plot the uncoded QPSK and 8PSK BER curve in the same figure. You will need to determine the appropriate Eb/N0 range such that each curve spans a BER range at least from 10-4 to 10-2. Please note that the horizontal axis should be Eb/N0 with unit of dB, while the vertical axis should be the BER with log scale. [Using the MATLAB function semilogy(ber,snr,…);] 2) Repeat Question 1 when the standard BCH outer code is used before the LDPC code. Please explain how the outer coding affects the overall BER performance. 3) Repeat Question 1 when a block interleaver is used after the LDPC code. Please explain how the interleaver affects the overall BER performance. Please note that in this part you only need to consider 8PSK, as the interleaver is not used with QPSK in the DVB-S2 standard. The bit interleaver structure for different modulation in DVB-S2 standard is specified in Table 8 of reference [2]. 4) For each of the above curves, find the minimum Eb/N0 requirement to meet BER=210-4. Please comment on whether the BCH outer code increases or decreases the minimum Eb/N0 requirement and why? 5) In Table 5 of this document (i.e., Table 13 of the DVB-S2 standard specification [2]), the minimum Es /N0 requirements for different codes are listed. Compare them with your results. Are they consistent? If not, why? 6) From the minimum Eb/N0 requirements obtained from your curves, find out the coding gains at BER=210-4 for the code rates listed in Question 1 by comparing them with uncoded QPSK and 8PSK. 7) Simulate LDPC codes with QPSK and 8PSK modulations in a Rayleigh fading channel based on the table given in Question 1, Part III, and plot the BER versus Eb/N0 curve. Assume the channel changes every input frame transmissions. Compare it with the AWGN channel results and comment.Part IV – Adaptive Coding and Modulation (ACM) at Satellite Transponder (10%) The emphasis of this part is to learn how to use adaptive modulation coding features in DVB-S2. Adaptive coding and modulation (ACM) is used to adjust transmission parameters to the reception conditions of terminals, e.g., switching to a lower code rate during fading. 1. Design an ACM technique for the DVB-S2 transmission by adding a MATLAB function to the simulator developed in Part III, selecting the modulation and code rates adaptively according to the LDPC rate table given in Part III Question 1. You will need to explain clearly the input and the output parameters used in your MATLAB functions. 2. Simulate its performance under the Rayleigh channel given in Part III Question 7 and compare its performance in terms of data bit-rate and bit-error-rate to the results in Part III. You need to explain clearly 1) the assumptions that you make, 2) what information the transponder uses to decide which modulation and code rates in Table 3 are used for transmissions and 3) how the transponder obtains that information. 3. Compare it with your answers for Part III Question 7 and comment on the performance of ACM as compared to a non-adaptive system in Part III. 4. Comment on whether ACM improves the system performance and what are the challenges in employing ACM in a real system. Part V – Space/Antenna Diversity at Customer Premises (10%) The emphasis of this part is to learn how to use diversity to improve DVB-S. Note that the DVB-S standard does not have "adaptive" features as the DVB-S2 one and thus the improvement needs to be done at the receiver side at the customer premises. The diversity techniques are used to reduce the effect of fading. The diversity techniques require a number of independent signals, carrying the same/related information. In this section, you will implement space diversity (SD) techniques to the complete DVB-S systems described in Fig. 1 where you assume that there are two receive antennas with antenna separation higher than one half of the carrier wave length in order to get independent fades. You can assume that you have two receive antennas at the DVB-S receivers. 1. Design a SD technique with a maximum ratio combining (SD-MRC) for the DVB-S transmission by adding a MATLAB function to the simulator developed in Part III, performing SD-MRC. You will need to explain clearly the input and the output parameters used in your MATLAB functions. 2. By using your simulator, developed in Part II, simulate the BER performance of SD-MRC under a Rayleigh channel given in Part II Question 7 and compare its BER performance to the results in Part II. Comment on the performance improvements/degradation that are obtained. You need to explain clearly 1) the assumptions that you make, 2) what information the receiver uses to do SD-MRC and 3) how the receiver obtains that information. A minimum two puncturing rates of 1/2 and 7/8 must be simulated. 3. Compare it with your answers for Part II Question 7 and comment on the performance of SD-MRC as compared to a system with no diversity in Part II. 4. Comment on whether SD-MRC improves the system performance and what the challenges are in employing SD-MRC in a real system.Part VI – Technical Recommendations (10%) The emphasis of this part is to learn how to construct quantitative arguments based on mathematical facts and analysis. In this section, you will assume that University of Sydney plans to deploy a satellite mobile communication network for its staff with a minimum receiver BER=10-4 for data transmission. Your task is to select the technology (DVB-S or DVB-S2) that gives the best performance for the same satellite transponder bandwidth and signal power strength. You can assume that the Rayleigh fading channel is a good representation of the wireless channel and it changes every 2msec. Write a quantitative recommendation on whether DVB-S or DVB-S2 should be employed. The recommendations must be based on BER simulations of DVB-S and DVB-S2 systems, shown in Figs. 1 and 2 for the given channel requirement, the finding in Parts II and III, the lecture materials as well as optional Parts IV and V if you do them. The recommendations should contain quantitative comparisons of the transmission data rates and the BERs between the two technologies. Note that this is an open ended question and thus you will need to back up your reasoning quantitatively by using analysis and simulations. You are free to choose the system configurations however you will need to make sure that DVB-S and DVB-S2 are compared fairly. You will need to explain clearly the assumptions that you make in deriving these numbers and your recommendations. Part VII – Presentation on your Project (15%) In the last week of the semester, each group has to do a presentation on their project. Each group will be given 9 minutes for their presentation and 3 minutes for questions time. Each group should select one representative to do the presentation. The time for presentation is strict due to the large class and your presentation will be stopped if your allocated time slot is used up. Please rehearsal and be wellprepared before the presentation. References [1] Digital Video Broadcasting (DVB): Framing structure, channel coding and modulation for 11/12 GHz satellite services. Available Online: http://www.etsi.org/deliver/etsi_en/300400_300499/300421/01.01.02_60/en_300421v010102p.pdf [2] Digital Video Broadcasting (DVB); Second generation framing structure, channel coding and modulation systems for Broadcasting, Interactive Services, News Gathering and other broadband satellite applications (DVB-S2). Available Online: http://www.etsi.org/deliver/etsi_en/302300_302399/302307/01.02.01_60/en_302307v010201p.pdf When to Start You are advised to start working on your project as early as possible. Please note that you should NOT wait until all the relevant material has been being covered in the lectures. Otherwise, you might not have enough time to finish your project. You should reserve enough time for debugging and documentation.Early start is particularly important for those groups who want to try the bonus tasks, since the relevant knowledge will not be covered enough in the lectures or not at all. A successful completion of this part requires significant amount of efforts in self-study, research, programming, debugging and team works. Project Report A report has to be included in the project submission. The report should contain no more than 25 pages including references with 10pt font at minimum. You must also indicate the contributions for each member of the group clearly in the report as a percentage in the first page. Please think carefully about these percentages as the individual marks of the project will contain a component based on the contribution as indicated by the group. Generally, a report should have the following sections and must answer the questions asked: 1) Introduction & background: gives an overview of your project; 2) Part I: answers the questions about calculations of the performance etc.; 3) Part II: describes the simulation system setup and design, presents the simulation results and comments and answer the questions. 4) Part III: describes the simulation system setup and design, presents the simulation results and comments and answer the questions. 5) Part IV and V: describe your ideas in a mathematical form and/or flow charts and give explanations of your ideas and answers to the question asked. 6) Part VI: presents detailed explanations covering justifications of your recommendations. 7) Conclusion: describes your views of this project, the key findings and difficulties, how the project fared in meeting the requirements, etc. 8) References: lists all references here. What to Hand In By the due date, you need to hand in the following materials: 1) Cover sheet filled and signed by EACH member in your group; 2) Project report (hard copy); 3) A CD/DVD-ROM containing all your design/program files (well-commented m files and others), the produced sample files for each level you have attempted and the electronic version of your report. Please clearly label it with your group number. Alternatively a USB flash memory stick submission is acceptable, but please do not bomb our computer with virus; 4) A note about how your program can be run: the platform (MATLAB version number, operating system, PC hardware configuration), how to launch each program, the parameters to be set (if applicable), etc. You MUST also indicate how long it took you to run each program. You need to submit in person to your tutor Mr. Zhanwei Hou (email: [email protected], office: Room 720, Electrical Engineering Building, J03). Important Dates Group Registration: 6 September 2016 5:00pm (by email to your tutor Ms. Yuhong (Julie) Liu (email: [email protected])) Project Submission: 21 October 2016 12:00pm Project Presentation: 25 October 2016 6:00pm-9:00pmProgramming Language The MATLAB programming language and its Communications System toolbox are to be used for this project. MATLAB provides a variety of off-the-shelf modules in communications and signal processing, which will greatly facilitate the implementation of the software based satellite receiver. In this project, you can use ANY functions/modules provided by MATLAB Toolboxes. Please differentiate MATLAB from MATLAB Simulink. MATLAB Simulink, Simulink Blocksets and third party MATLAB modules are NOT allowed for this project. If you are not familiar with MATLAB, there is a tutorial on MathWorks' website, http://www.mathworks.com/academia/student_center/tutorials/launchpad.html, which could help you develop the general skill in MATLAB programming. The information on the Communications System toolbox as well as examples can be found at http://www.mathworks.com.au/help/comm/ or MATLAB documentations within the software. We also run a MATLAB tutorial to get you prepared. MATLAB is a widely used high-level language and interactive environment in engineering simulation and modelling. With its abundant functions, modules and toolboxes, you can develop your software systems in a quicker and more efficient way than with traditional programming language such as C/C++ and Fortran. Being proficient in MATLAB will be a great advantage for your future career. About Plagiarism On the Internet or from other resources, you might obtain documentations or program codes, which are similar or can be modified to be used in your project. The direct copy from these codes/resources is strictly prohibited. However, learning from reading others' designs/codes is not a bad thing. Please include a reference list in your report/documentation in that case. When you hand in your completed project, a detailed report/documentation has to accompany the program codes. Meanwhile, the program codes your submitted need to be well commented. The quality of your report/documentations is one of the biggest factors that determine your mark for the project. The project presentation is another. If there is any suspicion of plagiarism, your group might need to attend an interview with the lecturer. If the plagiarism is confirmed, your group will get a zero mark for the project and a further heavy penalty might be imposed. Please refer to the University's policy on plagiarism http://www.usyd.edu.au/ab/policies/Academic_Honesty_Cwk.pdf