test specification document forSpread Spectrum Modemsubmitted to:Professor Joseph PiconeECE 4512: Senior Design IDepartment of Electrical and Computer EngineeringMississippi State UniversityMississippi State, Mississippi 39762April 28, 2000submitted by:Ian Smith, Shane Easterling, Daniel Ling, April MartinFaculty Advisor: Professor James FowlerDepartment of Electrical and Computer EngineeringMississippi State UniversityBox 9571Mississippi State, Mississippi 39762Tel: 662-325-3912, Fax:662-325-2298email: {ims1, pse1, tdl1, adm2}@ece.msstate.eduEXECUTIVE SUMMARYSpread spectrum is a technique which is used as a way to reduce the power density of radiotransmission. Spread spectrum waveforms can also be used to primarily improve performance inthe area of interference tolerance. This is done by spreading the signal over a wide band offrequencies. The signal is usually spread to at least 10 times the information rate or much higher.Under some conditions, the reduction of power density allows for greater spectrum sharingopportunities in comparison with using the traditional access. Traditional access consists of themethod of frequency-division multiple access (FDMA) or even time-division multiple access(TDMA). The receiving system must despread the spectrum signal just the opposite from how itwas originally spread and in exact synchronization. This gives us the added advantage of rejectionof interference or jamming and immunity from frequency-selective fading. Some modern cellularand other systems use a form of spread spectrum called code-division multiple access (CDMA)[10].Our approach to this problem will be a design that consists of mostly hardware and minimumsoftware to implement error checking. The circuit design will be divided into three phases. Thefirst phase will consist of the transmitter. The purpose of the tramsmitter is to generate the directsequence spread spectrum method and modulation. The second phase will consist of the receiver.The receiver is responsible for the demodulation and correlation of the received data. Our designwill be based on direct sequence design. This is where the information signal is modulated by thesignal that is spread and then the resulting wideband signal is transmitted. Upon reception, thewideband signal is demodulated using a scynchroninzed copy of the code signal and theinformation is recovered.[10] This is represented in the figure below.By using this method of spread spectrum we can obtain a data rate of 115 Kbps at full duplex.However, our project is geared more towards internal uses. Our project will be more suited foruse in schools and small business who are seeking a more cost effective way of inplementing theirLAN network. Our project will enable teachers and workers to use the internet in any room oftheir building whether a jack is available or not. This will allow users to save time by being ableto move their laptop to any room and not have to hook up to the wall. Users will only have toboot up and connect.1. INTRODUCTIONIn general, a spread spectrum system is one in which the transmitted signal is spread over a widefrequency band, much wider than that of the minimum bandwidth required to transmit theinformation being sent. Spread spectrum communications are not an efficient way of utilizingbandwidth when it is used by itself. However, it does become a more effective way whencombined with existing systems occupying the frequency. The spread spectrum signal being“spread” over a large bandwidth can coexist with narrowband signals and will only add a slightincrease in the noise floor that the narrwoband receivers see.In 1980, the FCC expressed a desire to extend spread spectrum communications outside of themilitary-only realm and allow radio amateurs to experiemnt with spread spectrumcommunications. The FCC in following Title 47, Section 303 of the Code of Federal Regulations(CFR) shall…(g) Study new rules for radio, provide for experimental uses of frequencies, and generallyencourage the larger and more effctive use of radio in the public interest…What this meant was that a new mode of communications was opening up for experimentationand exploration for radio amateurs.In 1980 AMRAD took the lead and forged the beginnings of amateur spread spectrumexperimentation. The results of their experimentation were documentated in the AMRADNewsletter, QEX, QST and compiled into a single book entitled “The ARRL Spread SpectrumSourcebook.” This book is a good guide and provides a historical perspective into the merging ofspread spectrum into amateur radio.There are many different uses and advantages to spread spectrum waveforms. Spread spectrumcommunications systems are useful for providing resistance to jamming. They also provide ameans for masking the transmitted signal from unwanted interceptors. Spread spectrumcommunications provide resistance to multipath, and a way for more than one user to use thesame time-frequency allocation. Finally, they also provide range measuring capability.Spread Spectrum Modem 1 of 18ECE 4512 April 17, 20002. TEST SPECIFICATIONTesting will be done to ensure the precision of the system. Circuit modeling will involve the use ofPSPICE, MATLAB and SYSTEMVIEW to simulate block diagrams of both the receiver andtransmitter. In addition, software testing will also be done for the error correction purpose.Finally, our device must adhere to FCC standard.By using the tests in Table 1, we will ensure that our project will function properly.Requirement CircuitModelingCalculation Class BEmissionReceiver *Transmitter *DirectSequence*Throughput *Range *Power *Cost *Table 1 Summary of tests being performed.2.1. CIRCUIT MODELINGThis test will be used to verify that the modem will operate according to DSSS specifications. Thetransmitter, receiver and indicators will be tested using SYSTEMVIEW and MATLAB. Thesetests will involve the use of block diagrams as indicated above. [Fig 4.1 and Fig 4.2] The resultsthat we obtained from SYSTEMVIEW and MATLAB will verify the power requirements fortransmitter and receiver. The circuit for indicators will be drawn in PSPICE. The cost will bebased on the overall circuit requirements.2.2. CalculationComputer software will be used to control the data that are sent and received between thetransmitter and receiver and also perform the calculation.From the simulation, we will show a certain probability of error for the receiver structure, usingthe SNR at the
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