Agilent Measurement Journal - Issue 4 - 2008 - (Page 47)

W Wireless communication systems use scarce radio spectrum efﬁciently by applying sophisticated mathematical coding algorithms, agreed by speciﬁcation standards bodies such as the Third-Generation Partnership Project (3GPP) and implemented in silicon by device and equipment manufacturers. Component and system performance is speciﬁed using parameters such as error vector magnitude (EVM), which quantiﬁes the relative root mean square (RMS) error in the signal. To ensure acceptable operation of wireless systems, EVM is measured with dedicated test instrumentation during design, manufacturing, installation and maintenance. Parametric measures are simple and useful, and they can answer yes/no questions — but can’t explain why a problem exists. What’s more, ﬁnding the root problem is made more difﬁcult if two measurement instruments disagree. RF waveform metrology is important in aerospace/defense, instrumentation and telecommunications applications because it helps answer why. Modeling and simulation provide accurate predictions of what should happen but eventually real measurements of actual devices are required. As such, waveform metrology is valuable for developing new designs, diagnosing problems and verifying implementations. Traceability of waveform measurements provides a common reference and supports the ISO 17025 standard for testing and calibration. DTCH DTCH data bits DCCH data bits DCCH 60 kbps I SF = 64 3840 kcps Data OVSF generator Control OVSF generator DPCCH 3840 kcps Data bits 15 kbps Pilot, power control, and TFCI Gain 0 dB Gain –6 dB 3840 kcps Add CRC and tail bits Add CRC and tail bits 1/3 rate This article provides an overview of joint research conducted by Agilent and the National Physical Laboratory (NPL) of the United Kingdom. The NPL’s industry-focused “waveform metrology for wireless communications” project is scheduled to run until 2009.1 Its aim is to provide traceability for W-CDMA and other formats such as WiMAX™ and ultra-wideband (UWB). Overview of W-CDMA 3GPP W-CDMA was leveraged from the W-CDMA system developed in Japan and Europe. The 3GPP version is viewed as the next-generation replacement for PDC (Japan) and GSM (worldwide) and is designed to have a higher data rate than 2G systems — up to 2 Mbps for W-CDMA versus 14.4 kbps for GSM. W-CDMA allows several users to efﬁciently share the same RF carrier by assigning unique codes to each user and dynamically adjusting data rates and link budgets to balance the cumulative demand from all active users. Figure 1 shows the mapping of W-CDMA logical channels (dedicated to control and trafﬁc) to the W-CDMA physical channel (dedicated to physical data/control) of an uplink signal. 3GPP deﬁnes a logical channel as an information stream dedicated to the transfer of a speciﬁc type of information over the radio interface. It also deﬁnes a physical channel having speciﬁc carrier frequency, scrambling code, channelization code and relative phase.2 CCTrCH conv. coder 1/3 rate conv. coder First interleaver First interleaver Frame segment Segment and match Rate matching Rate matching TrCH MUX CCTrCH Second interleaver 60 kbps DPDCH Data bits I scramble code + OVSF 2 generator 225 Scramble code generator Decimate by 2 Q 3840 kcps I scramble code 1,–1 Q – ∑ I Complex scrambling SF = 256 Q + + ∑ Q Figure 1. Uplink data-channel air interface Agilent Measurement Journal 47

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 4 - 2008

Agilent Measurement Journal - Issue 4 - 2008 Delivering Confidence through Compliance with Standards Contents Emerging Innovations Trying Early Device Implementations at the IEEE 1588 PlugFest Achieving Greater Confidence in Measurement Accuracy through Consistency in Calibration Services Overcoming the Challenges of RFID Component Testing 3GPP LTE: Introducing Single- Carrier FDMA Ensuring Reliable Operation and Performance in Converged IP Networks Testing Storage Area Networks and Devices at 8.5-Gb/s Fibre Channel Rates Choosing an Appropriate Calibration Method for Vector Network Analysis Making Traceable EVM Measurements with Digital Oscilloscopes Exploring Terahertz Measurement, Imaging and Spectroscopy: The Electromagnetic Spectrum’s Final Frontier Interpreting Quoted Specifications when Selecting Digitizers

Agilent Measurement Journal - Issue 4 - 2008

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