The effect of filters in mobile radio systems

Abstract

The design and verification of today’s complex digital communications systems present a multitude of interesting challenges. A particularly difficult problem is the impairments caused by RF components such as filters and amplifiers included in the signal path as well as interfering signals that pass through the RF link. Linear devices such as filters typically add phase distortion and group delay to the signal, and nonlinear components such as amplifiers cause intermodulation (IM) products that generate additional harmonics.

A BER of 10-5 is typical for a satisfactory audio signal quality. BER is investigated using different filter types and the effect of amplifier distortion on RF front ends for third-generation (3G) mobile radio systems such as wideband code division multiple access universal mobile telecommunications systems (WCDMA-UMTS).

For WCDMA base stations, a single filter can be used for each channel. Designers typically use Chebychev or Cauer-Chebychev filters in the received path for protection against out-of-band signals.1,2 However, the poor group delay characteristic of these filters can degrade the desired waveforms and result in a higher BER.