Under The aUspIces of the Third Generation Partnership Project 2 (3GPP2), the CDMA2000 specification provides a path from Code Division Multiple Access (CDMA) One. It is evolving in two stages: 1x Evolution Data Only (1xEV-DO) and 1x Evolution Data and Voice (1xEVDV). Among the issues surrounding CDMA2000 is whether a multicarrier transceiver can be implemented and how to predict the necessary performance for major subsystems. In an application note titled, "Multicarrier CDMA2000 Feasibility," Analog Devices' Brad Brannon and Bill Schofield delve into both of these issues.
At the root of this 29-page document is a generalized block diagram. It shows the architecture of a flexible radio platform that can easily implement a wide variety of air interface standards. Among the variations for this architecture is high or low intermediate-frequency (IF) sampling as well as direct conversion for receive. In the transmit path, direct RF modulation is feasible for most applicationsas long as some amount of in-phase and quadrature (I/Q) balance is provided. For applications requiring higher performance without an I/Q balance network, an optimal choice is superheterodyne IF upconversion. Aside from these variations, the authors note that many assembly options will have a wide impact, such as system-level partitioning.
In the receive section, the note explains the conditions given by the standard as well as intermodulation performance. To meet signal-to-noise ratio (SNR) requirements for the analog-to-digital converter (ADC), for example, the authors recommend using the firm's own AD9446. Yet the note also provides some tips on how to reach the necessary operating quality with other converters. For example, the engineer can add an automaticgain- control (AGC) function that responds after the two-tone levels have been surpassed.
This document discusses options for the architecture of the transmit signal path, carrier and radio configurations, ways of increasing power-amplifier (PA) efficiency, and more. The section on emission limitations details spectral emissions, which can become interferers to adjacent carriers and cells and even the base-station receiver. The note closes with examinations of both superheterodyne single upconversion and direct conversion. Although the purpose of this work is to show the firm's own devices and their suitability for direct-conversion architectures, it also succeeds in providing an informative summary of the requirements that must be met in order to create a multicarrier transceiver for CDMA2000.
Analog Devices, Inc.
3 Technology Way
Norwood, Ma 02062
(781) 329-4700
Internet: www.analog.com.