Although there are potentially many benefits from a wideband-code-division-multiple-access (WCDMA) multicarrier third-generation (3G) transceiver, questions remain about whether the implementation of such a transceiver is feasible. In "Multicarrier WCDMA Feasibility," Analog Devices (Norwood, MA) strives to answer this question. The 22-page application note also tries to determine the major subsystem performance of such a transceiver.
One general block diagram is used throughout this document. Its architecture represents a flexible radio platform, which can easily be used to implement different air standards like WCDMA, CDMA2000, and TD-SCDMA. The architecture can be varied with high or low intermediate-frequency (IF) sampling. The white paper gets its specifications from the requirements for wide-area BS as defined by 3GPP TS 25.104 v6.2.0, section 7. For receiver operating conditions, for example, the standard states that the required minimum sensitivity is -121 dBm within a 3.84-MHz bandwidth. The WCDMA test conditions specify -115 dBm/3.84 MHz. This condition is used to determine the inband blockers.
The standard provides two important subconditions for blocking. After they are discussed, the note points out that the band filter may anticipate some attenuation because the signals in the adjacent bands are the same as inband. Compared to the inband blockers, though, they are at the same level or below. As a result, little additional dynamic range should be required.
Taking the same in-depth, step-by-step approach, the application note moves on to discuss analog-to-digital signal-to-noise-ratio (SNR) requirements. It then covers SFDR and third-order intercept (IP3) requirements. More than one method of increasing power-amplifier efficiency is discussed. By allowing the amplifier to move closer toward saturation, for example, one can increase efficiency. At the same time, this approach will compensate for the resulting distortion. The two main approaches to power-amplifier linearization, analog feedforward and digital predistortion, are examined in detail.
This application note provides an extensive, in-depth view of WCDMA and its potential for a multicarrier approach. Every essential technical aspect is included and discussed in depth. In summary, this application note offers a breadth of information on this topic in terms of both the standard and the engineering that makes such technology function and improve.
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