Fcop Support For Gsm; Introduction - Motorola DSP56305 User Manual

12.1

INTRODUCTION

The Filter Co-Processor (FCOP) is a peripheral module designed as a general purpose
fully programmable complex FIR filter, with up to 21 complex taps.
It also has dedicated modes of operation optimized for cellular Global System for Mobile
Communications (GSM) base station applications, taking advantage of the special
GMSK modulation scheme used in GSM.
12.1.1

FCOP Support for GSM

The FCOP assists the DSP56300 core to perform channel equalization of one radio carrier
in a GSM base station, which involves both correlation and matched filtering. A matched
filter is commonly used in channel equalization to maximize the Signal-to-Noise Ratio
(SNR) at sampling time. In the base station receiver path (uplink), FCOP performs cross
correlation between the received training sequence and a known mid-amble sequence.
The result of this correlation is used to determine the impulse channel response, which is
then used to calculate the coefficients for match filtering on the received data symbols
(bits).
The FCOP simplifies computation of the cross correlation and match filter outputs fed
into the Maximum Likelihood Sequential Estimation (MLSE) process performed by the
Viterbi Co-Processor (VCOP). In GSM, while the MLSE algorithm uses the Ungerboeck
scheme, the match filter output can be represented by a sequence of ordered pairs (x, y)
such that x, y are real numbers.
The main features of FCOP supporting GSM are as follows:
• Special optimized mode (Mode 3) for performing cross correlation between the
received training sequence and a pre-defined mid-amble
• Special optimized mode (Mode 2) for performing matched filtering required for
channel equalization using the Ungerboeck scheme
• Internal data and coefficient memory banks supports GSM normal burst, as well
as GSM access burst.
MOTOROLA DSP56305 User's Manual
Filter Co-Processor
Introduction
12-3