W-CDMA reception with a DSP based software radio

With the increasing number of mobile-phone standards there is a demand for a software-based radio for use in base-stations that can adapt to many standards. This paper discusses how to implement a RAKE receiver in a high performance standard DSP that can search out the multiple paths and combine them to demodulate the received data. To perform a complete search for a mobile within a cell there will typically be 8000 potential radio delay paths of which only a small number (3-6) will actually contain any useful data. However as each path contains 5120 chips of data the correlation exercise necessary to find these paths is a very MIPS intensive task. The paper highlights a number of techniques based on rough data on the mobiles whereabouts from the initial random link and information on the relationship between the samples to perform an intelligent simplified search that will still find the paths. This allows a much smaller subset to be searched initially of 512 delay paths and 1536 chips making the task simple enough for a DSP based RAKE receiver implemented on a single TMS320C62xx with a 100 MHz-search engine and receive data using a 6-finger RAKE receiver at 58 MHz.