Microwave Engineering Europe - November 2007 - (Page 17)

TESTING OFDMA 17 that the orthogonality and receiver signal strength is maintained across the whole band. If one side of the band has a drop in power level then this can seriously affect the performance of the whole system. The baseband of the processor system must be able to form these 1200 simultaneous channels with exact power levels, and then the RF up-conversion must maintain this level accuracy across it’s whole RF bandwidth and at all power levels. So this can be a demanding speciﬁcation for the system to reach. In addition, this of course requires that the measurement system has power accuracy that is ﬂat across the band to a signiﬁcantly greater level than the signal being measured to prevent the measurement instrument being the cause of some perceived errors. Figure 3 shows an example of measuring the RF spectral ﬂatness across the whole band, to see the variation in power level across all 1200 subcarriers individually. Our measurements of LTE waveforms are generally split into three domains: 1) — Measurement by sub-carrier or group of sub-carriers. When measuring by subcarrier we are looking at the individual performance at an RF channel level, and we will need to specify the individual channel (or group of channels) to be measured, form channel 0 to channel 1199. 2) — Measurement by OFDM symbol. When measuring by symbol, we will see the effect of the multiple RF subcarriers being used to see the composite performance at one individual time period. Each transmission may specify a number of sub-carriers to be used and the symbol performance is the sum of all of these subcarriers being used. 3) — Measurement by resource block. Here we will specify the exact combination of sub-carriers and OFDM symbols that correspond to the data being transmitted to the user. Hence, this is a composite of the above two measurements and shows the overall quality of the RF as it would affect the system throughput. Summary LTE introduces new ways of thinking for measurement of RF, in terms of sub-carriers and resource blocks, and the various combinations of sub-carrier, symbol and resource blocks that should be measured. We must correctly understand these to be able to evaluate the RF characteristics of a base-station. It is important that our measurement system is ﬂexible enough to be able to capture and process enough information to make all of these various combinations of measurements, and be simple to use so that results can be compared and contrasted to quickly locate and possible problems in the RF design. We have seen above, though some examples from the Anritsu MS2690A LTE measurement software, how the different RF measurements for an LTE base-station can be made. Company Information Figure 2: Measurement of EVM versus sub-carrier for all 1200 sub-carriers in LTE in the bottom trace. Figure 3: Measurement of the RF spectral ﬂatness across the whole band, to see the variation in power level across all 1200 sub-carriers individually. Anritsu www.anritsu.com Microwave Engineering ● November 2007 ● www.mwee.com 016_017_MWEE.indd 17 25/10/07 13:53:59 http://www.anritsu.com http://www.mwee.com

Table of Contents Feed for the Digital Edition of Microwave Engineering Europe - November 2007

Microwave Engineering Europe - November 2007 Contents News Comment Metamaterials: Metamaterials Tackle Communications Wavelengths Microwave Components — EM tools: Microwave Component Design Easier With New EM and EDA Tools Cover Feature: RF Testing for OFDMA in LTE Base-Stations Startup Eyes Battery-Free Wireless Sensor Nets High-speed ADC Technology Paves the Way for Software Defined Radios Planning a WiMAX network: Maximising the ROI by Using Advanced Optimisation Tools Transporting Video Over Wireless Networks Ultrawideband Under the Gun Specifying the Proper SAW Filter Products Product Feature: RF Test Solution Supports Emerging 4x4 MIMO as Well as Multiple Commercial Standards Calendar

Microwave Engineering Europe - November 2007

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