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Problem Statement
Wireless systems carrying voice, data or video, find themselves working in increasingly crowded, tightly allocated channel environments. In commercial applications, often modulation and coding techniques are specified but the systems must work in urban environments which are very apt to present receivers with severe multipath. In addition, as new networks emerge in support of increased demand for data and are assigned spectrum adjacent to legacy systems, demodulators are required to perform in increased adjacent channel interference with little or no change in Eb/No performance. Or, perhaps those same demodulators are presented an IF bandwidth occupied by waveforms not filtered according to specifications and transmitting at higher than expected power levels. In military applications, modulation and FEC design choices must be tested in channel environments that have to accurately reflect their operational situations. As those systems enter production, testing must be standardized against waveforms whose defining parameters may be classified beyond the clearance level of the factory floor technicians.
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X-COM Systems Products
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SigAnalyst Workstation
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Resources
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X-COM Systems Solutions for Wireless Communications
Problems involving interference and multipath performance are solved most quickly if the environment producing the undesired channel conditions can be reproduced in high fidelity and played back, in their entirely or in portions, as often as required. New designs also benefit by lab testing using simulated environments, the basis of which are derived from recordings of wide bandwidth segments of their full operational spectrum assignments. The X-COM Systems IQC-2110, WARP, CPG-2110 and 4CH-VSG2000 products provide unsurpassed capabilities to record wide bandwidth spectrum and replay it with no degradation in fidelity.
The IQC-2110 records digital I & Q data streams that are provided from industry leading signal analyzers. No signal degradation results from this recording and storage. The signal fidelity is exactly that produced by the superior RF front end, down converter and A/Ds of the signal analyzer. All amplitude and phase corrections applied by the signal analyzer are also applied in the recording. One need look no further than the specifications of the Agilent, Tektronix or Rohde & Schwarz signal analyzers that are directly plug compatible with the IQC-2110.
The IQC-2110 can record RF spans of up to 110 MHz. It samples the digital I&Q data streams from the signal analyzers at up to 150MS/s and can store data on RAID5 disk arrays up to 23 Tbytes in storage capacity. This translates to over 9 hours at this maximum sample rate. Lower spans and commensurately lower sample rates provides days worth of capacity. The "Step and Stare" feature of the X-COM IQC-2110 allows the operator to use the system as a scanning signal recorder by dwelling at a specified RF center frequency before tuning to a new span. Thus contiguous or non-contiguous segments of spectrum can be recorded for as little as 2 second increments. If wider RF segments are required without retuning, the X-COM WARP product line allows direct RF sampling and recording of bandwidths up to 6GHz. Even the resulting terabyte files can be easily offloaded for post-processing sing the IQC-2110's built-in mini SAS or eSATA ports.
Once there, the X-COM Spectro-X application is used to view (See Fig. 1), and then search for waveforms of interest. Of particular interest to the commercial wireless industry, Sepctro-X understands the training sequences of GSM, Edge, LTE and 802.11a/g and will find them with extremely high levels of confidence (See Fig. 2). Baseband processing software such as the Agilent 89600B vector signal analyzer application allows for complete demodulation and quantification of the error vector magnitudes of the captured waveforms. Spectro-X also allows for specific time segments of the capture file to be stored so searches can be narrowed in scope or an arbitrary waveform occurrence saved and used as a search mask. In this way, long durations of pulsed waveforms can be searched for the errant misshaped pulse from an interferer or malfunctioning transmitter. Multiple views of the captured spectral recording can be open at the same time allowing the operator frequency, time, phase, amplitude and persistence views simultaneously.
The X-COM software tool set also lets the user modify or create new sets of waveforms. The RF Editor application provides a user interface identical to music or video editing tools. Waveforms can be decimated, frequency shifted, filtered, interpolated and saved. In this manner a library of waveforms or waveform segments can be created and then precisely aligned and concatenated in the time domain. These new files are then available for playback.
The IQC Control software enables the user to recall files from storage and to be played through the X-COM Continuous Playback Generator (CPG). Looped or single file playback are set via a menu. The CPG-2110 outputs analog I & Q symbol streams which drive the baseband inputs of industry leading Vector Signal Generators. Alternatively, the user can drive the X-COM 4CH-VSG-2000 which accepts digital I&Q from stored files and provides up to four, independently sourced, simultaneous, phase coherent RF outputs from 50MHz to 2GHz and bandwidths to 150MHz. Either hardware configuration is extremely useful as it can replace a "golden radio" or production standard. Spectrum recordings can be encrypted and then played back in secure environments without fear of exposure of the waveform shape, pattern, power level or other defining parameters.
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