SPECIAL FOCUS PAPER A REMOTE DIRECT SEQUENCE SPREAD SPECTRUM COMMUNICATIONS LAB UTILISING THE EMONA DATEX A Remote Direct Sequence Spread Spectrum Communications Lab Utilising the Emona DATEx http://dx.doi.org/10.3991/ijoe.v8iS4.2187 Helen Kyomugisha, Tom Kigezi, Cosmas Mwikirize, Roseline Akol, Doreen Orishaba, Michael Kyesswa Makerere University, Kampala- Uganda Abstract—Remote labs have become popular learning aids due to their versatility and considerable ease of utilisation as compared to their physical counterparts. At Makerere University, the remote labs are based on the standard Massachusetts Institute of Technology (MIT) iLabs Shared Architecture (ISA) - a scalable and generic platform. Pre- sented in this paper is such a lab, addressing the key practi- cal aspects of Direct Sequence Spread Spectrum (DSSS) communication. The lab is built on the National Instruments Educational Laboratory Virtual Instrumentation Suite (NI ELVIS) with the Emona Digital and Analog Telecommuni- cations Experimenter (DATEx) add-on board. It also incor- porates switching hardware. The lab facilitates real-time control of the equipment, with users able to set, manipulate and observe signal parameters in both the frequency and the time domains. Simulation and data Acquisition modes of the experiment are supported to provide a richer learning experience. Index Terms—Direct Sequence Spread Spectrum, Emona DATEx, Interactive iLabs Shared Architecture, LabVIEW I. INTRODUCTION Wireless communication is by any measure the fastest growing segment of the telecommunications industry [1]. Early development of wireless technologies was inhibited by several factors, including spectral capacity limits, propagation effects such as multipath, and the need for asynchronous access [2]. Even more critical today is the security aspect of wireless communications, a subject of growing concern for many individuals and organisations. An ingenious solution to these challenges was realised in adoption of spread spectrum communications. Spread- spectrum techniques are a means of signal transmission in which the signal occupies a bandwidth in excess of the minimum bandwidth necessary to send the information. The band spread is accomplished by means of a code which is independent of the data, and synchronized recep- tion with the code at the receiver is used for de-spreading and subsequent data recovery. Popular applications in- clude Code Division Multiple Access (CDMA) cellular- telephony networks, Global Positioning Systems, and Bluetooth [3]. Two main types of spread spectrum techniques exist; Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS). Specifically, DSSS multiplies the data being transmitted by a "noise" signal, typically a pseudorandom number (PN) sequence of 1 and −1 values, at a frequency much higher than that of the original signal. This consequentially makes DSSS signals noise-like, making them hard to detect, intercept or demodulate. Furthermore, they are harder to jam (interfere with) and because they are so wide, the signals are trans- mitted at a much lower spectral power density than nar- rowband signals [4]. Owing to the exceptional qualities and rapid adoption of spread spectrum, it is vital that students pursuing Elec- trical, Telecommunications and Computer Engineering disciplines get versed with this key technology, through experimentation. Makerere University (MAK) has adopted the scalable MIT iLabs Shared Architecture (ISA) as a platform for development and deployment of remote shared laboratories (iLabs). These have helped to mitigate challenges arising from the scarcity of laboratory equip- ment vis-à-vis the skyrocketing student numbers. iLabs have been used to support several courses in the curricula of the Bachelors of Science in Electrical, Telecommunica- tions and Computer Engineering Programmes over the past seven years.[5]-[7]. The iLabs at MAK utilise the National Instruments Educational Laboratory Virtual Instrumentation Suite (NI ELVIS) with a host of add-on boards, supported by the Laboratory Virtual Instrumentation Engineering Work- bench (LabVIEW) graphical programming language. One such board is the Emona Digital Analog Telecommunica- tions Experimenter (DATEx) which uses a block diagram model approach to implement a very wide range of tele- communications experiments [8]. Using its adders, multi- pliers, noise generators, sequence generators, amplifiers and a tuneable low-pass filer, the principles of DSSS communication can be demonstrated. The user interface to the DSSS lab is a LabVIEW Vir- tual Instrument (VI), on which interactive controls for the DATEx are exposed. Remote access to the VI is imple- mented within the interactive ISA [9]. II. IMPLEMENTATION A. Lab Equipment The principal hardware for the DSSS lab is the NI EL- VIS/Emona DATEx combination. To alternate different circuit configurations on the DATEx, the NI Signal Con- ditioning eXtensions for Instrumentation (SCXI) 1169 switch is integrated into the physical architecture. A portable data acquisition device, the NI myDAQ [10], is used to provide four extra oscilloscope channels, neces- sary for viewing the experiment data. The hardware is shown in Figure 1. iJOE – Volume 8, Special Issue 4: "REV2012/2", December 2012 5