Do we need LTE scanners for scanning of LTE or are spectrum analyzers enough?

Edited by Zahid Ghadialy

Last Updated: 10/01/2011

QUESTION: Do we need LTE scanners for scanning of LTE or are spectrum analyzers enough?


John Morfit: the advantage of using purpose-built LTE scanners vs. using spectrum analyzers lies in the ability of the LTE scanners to recognize the LTE signals and to identify the physical cell ID (thus giving a good idea of which base station you are monitoring). Some LTE scanners go a bit further and decode the MIB and SIBs. SIB1 contains CellIdentity, a unique 28 bit identifier of the cell. In any case, the LTE scanners are able to detect the SCH and synchronize to each cell site, then measure the PSCH, SSCH, and RS. The detection and measurement of the LTE signals is done by correlation with all the possible modulation codes on each of the subcarriers for the signal in question. This means that the sensitivity of the LTE detection is much better than a simple power measurement as done by the spectrum analyzers. Since the LTE scanners are synchronized to the LTE signal, they measure the proper duration of the symbols and only the symbols used by each signal being measured. The spectrum analyzer is ignorant of the framing of the LTE downlink, is measuring asynchronously, and mixing together the various signals and channels into one big mashup. Therefore, the spectrum analyzer is inappropriate for determining the levels of LTE channels and signals needed in order to validate and optimize networks in the field.

Spectrum analyzers are best used to quickly search large swaths of spectrum to look for known and unknown signals, especially the unknown signals. Spectrum analyzers are very configurable and excel at allowing signals to be carefully studied in the frequency domain, and sometimes in the time domain. A high-level LTE signal should be identifiable by a knowledgeable engineer by the energy vs bandwidth, plus center frequency information. However, a blind search for LTE signals would be more difficult with a spectrum analyzer due to the variety of LTE bandwidths, some of which correspond roughly to CDMA or GSM/WCDMA signals, or even WiMAX signals.

LTE scanners typically include a “narrowband RSSI” measurement that measures the energy in a bandwidth usually set equal to the channel raster for the technology in question. For LTE, the channel raster is 100 kHz, so a NB RSSI measurement measures 100 kHz bandwidths, spaced 100 kHz apart. This sort of scan is very fast, and can be viewed as a bar chart for quickly checking a) LTE base station channel occupancy, and b) interfering signals. If either is found, then appropriate secondary scans may be created, either an LTE signal scan for a base station, or a spectrum analysis scan for an unknown interfering signal.

Source: Linkedin Discussion from 'LTE (Long Term Evolution) - 3GPP' group

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