DESIGN & IMPLEMENTATION OF DIGITAL DOWN CONVERTOR FOR WCDMA SYSTEMS

In this paper, we present Matlab implementation of a digital down convertor (DDC) for a single carrier WCDMA system. The implementation of DDC is simple and flexible due to use of FIR filters. In recent times ,mobile communications need not only high data rate but also a relatively fast mobility. To implement a WCDMA system,one must address a number of key issues in signal processing related to implementation. Aiming at multi-channel IF signal processing requirements, DDC is designed and overall function diagram is given. The test on function and performance of multi-stage digital down converter system was conducted. Efficient design of DDC can contribute in the overall efficient system implementation. The DDC is designed for digital signal processing applications and wireless communication systems along with capability of flexible digital filtering. Keywords—Digital up converter (DUC) , Finite Impulse Response filter(FIR) , Wide band Code Division Multiple Access (WCDMA), Cascaded Integrator and Comb filter (CIC) , Intermediate Frequency (IF) DDC are extensively used in the radio systems. They are more popular than their analogue counterparts because of small size, low power consumption and accurate performance. The DDC converts the signal at the output of analog to digital convertor (ADC), centered at the intermediate frequency (IF) , to complex baseband signal. In addition, DDC also decimates the baseband signal without affecting its spectral characteristics. The decimated signal , with a lower data rate, is easier to process on a low speed DSP processor. This paper discusses the DDC for the WCDMA system and implements them on the Matlab. WCDMA is a leading choice of data communication in the wireless industry nowadays and is selected as the air interface for the UMTS. WCDMA supports a higher data rate and is less susceptible to narrowband interferers and multipath fading. (1). This paper discusses an efficient implementation of three stage DDC design for WCDMA to increase productivity and performance.