8960 in Wireless Device Design News
HSDPA RF Measurements for Designers
High speed downlink packet access (HSDPA) is being deployed widely in UMTS-based mobile systems to provide higher download speeds for data. HSDPA accomplishes its end using adaptive modulation and coding to continually reconfigure the downlink, optimizing data throughput for each user depending on the instantaneous quality of the link. The technology is complemented by high speed uplink packet access (HSUPA), which is expected to debut in networks later this year.
Although HSDPA is primarily a baseband or signaling extension to UMTS W-CDMA, several aspects of the technology affect the operation of user equipment (UE) and require specialized testing, specifically at the physical (RF) layer. To address the challenges introduced by HSDPA, a number of HSDPA-related tests were added to the UE conformance specification (3GPP TS34.121) in Releases 5, 6, and 7 of the 3GPP standards. These additions include important new transmitter tests, a receiver characteristics test, and an entirely new section of HSDPA performance requirement tests. New tests are added as the standards evolve.
The Agilent 8960, used in conjunction with W-CDMA/HSDPA (E6703D/T) lab applications, provides complete and up-to-date coverage of the UE conformance standards in a one-box tester that combines network emulation and mobile analysis. New enhancements to the lab applications make RF validation testing easier than ever with
- Preset Call Configurations for TS34.121 conformance tests
- The latest HSDPA phase discontinuity measurement
- 25% faster HSDPA transmitter measurements
This article looks more closely at the required HSDPA RF conformance measurements and the 8960 capabilities that enable UE designers to test faster with greater confidence in meeting conformance requirements.
How does HSDPA affect user equipment testing at the physical layer?
The changes introduced by HSDPA necessitate new physical layer tests for several reasons.
The uplink High Speed Dedicated Physical Control Channel (HS-DPCCH) increases the peak-to-average power ratio (PAR). Higher PAR-up to about 1 dB depending on beta factors-increases stress on the power amplifier, which impacts adjacent channel leakage ratio (ACLR), spectrum emissions mask (SEM), and error vector magnitude (EVM) performance. To enable the continued use of W-CDMA Release 99 power amplifiers with the higher PAR signal, the maximum HSDPA output power requirement is reduced. Thus new tests for ACLR, SEM, and EVM must be performed to ensure that UEs operate correctly at the reduced power with the higher PAR signal.
34.121 Preset Call Configurations in the 8960 lab applications allow designers to quickly and accurately set up these complex tests in the lab environment (see figure 1). These presets reduce the number of parameters that need to be set by up to 80%, leaving only a few settings that need to be adjusted to perform the measurement.
The uplink HS-DPCCH is transmitted in bursts and can be offset in time from the Dedicated Physical Control Channel (DPCCH). Some combinations of beta values can cause composite power steps of up to 7 dB when the HS-DPCCH is turned on and off. If the HS-DPCCH and DPCCH are not time-aligned, the 7 dB power step may occur during a DPCCH slot transmission, possibly introducing phase transients or other distortions and degrading the signal. New modulation accuracy requirements address this issue. Figure 2 shows example measurements testing EVM for HSDPA (5.13.1A) and the new Phase discontinuity requirement (5.13.1AA)
The 16QAM format in the downlink High Speed Physical Data Shared Channel (HS-PDSCH) has less margin for UE receiver impairments than does QPSK. Figure 3 illustrates this difference. With a smaller margin of error, 16QAM is more susceptible to distortion and noise that can result in symbol error. Thus a new block error ratio (BLER) requirement for 16QAM reception at the maximum input level has been added to the specifications.
One way to validate receiver performance is with the 8960's fast and flexible HSDPA BLER measurement. Figure 4 shows the receiver impact using FRC H-Set 1 in the presence of a high AWGN noise level.
In summary, certain HSDPA technology characteristics affect UE RF performance. As a result, 3GPP specifications have been updated to address new transmitter and receiver testing needs. The Agilent 8960 with W-CDMA/HSDPA lab applications provides a comprehensive and up-to-date test solution for RF designers.
Learn More and Stay in Touch:
- To view an online video demonstration of HSDPA 7.2 Mbps data throughput, view
- To see a description of the newest features that have been added to the 8960 go to www.agilent.com/find/8960news
- For more information about the 8960, visit www.agilent.com/find/8960
- For past issues of the "8960 in Wireless Device Design" News eNewsletter bookmark www.agilent.com/find/8960eNews
- To view our December HSUPA webcast, view
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