EV and HSPA does, however, mean that we will have a combination of CDMA and OFDM in at least two mainstream wide-area cellular standards, sometimes generically described as 'Super 3G'. It is therefore useful to have an understanding of how a combination of CDMA and OFDM will work in terms of signal processing task partitioning. Table 3.8 shows the transforms, or rather inverse transforms used in the transmit path of a hybrid CDMA/OFDM transceiver. The job of the inverse FFT in source coding is to take the composite time-domain waveform from the quantised voice, audio, image and video samples and to transform them to the frequency domain. The transform makes it easier to separate out the entropy (information) and redundancy in the source signal. The bandwidth of the signal is compressed. We cover this process in more detail in Chapter 9. The bit streams representing the voice, audio, image or video samples are then channel coded using convolution and block encoding. This expands the occupied bandwidth but increases the distance between the information bits (-1s and +1s). This is an inverse Hadamard transform. The bit stream is then 'covered' with a spreading code and scrambling code. This is another inverse Hadamard transform. This further expands the occupied bandwidth. The bit stream is then transformed again using an IFFT to distribute the data stream across discrete frequency subcarriers. Note that the IFFT is imposing a set of time-domain waveforms on a series of frequency subcarriers (lots of sine/cosine calculations). The number of points used in the I FFT/FFT and the characterisation of the IFFT/FFT determines the number of Table 3.8 FHT/ FFT task partitioning in future radio systems Transmit path Source coding Channel coding Channel Multiplexing, Frequency multiplexing Orthogonal spreading codes orthogonal frequency and scrambling codes division multiple access Voice, audio, Convolution and image, video block coding Inverse FFT Inverse FHT Inverse FHT Inverse FFT Interrelationship of the Physical Layer wi