th Other Layers of the OSI Model subcarriers and their spacing and is the basis of the 'scaleable bandwidth' delivered in an LTE system In the receiver, the OFDM demultiplex (an FFT), recovers the wanted symbol energy from the discrete frequency subcarriers. The benefit here is that the symbol rate per subcarrier will be divided down by the number of subcarriers. The more subcarriers, the slower the symbol rate. This reduces intersymbol interference and makes the next stage of the process easier. If this is a combined OFDM/CDMA system, this next stage involves the combining of the symbol stream (assuming this is a diversity or MIMO system) and the despreading and descrambling of the signal using an FHT. The result should be some useful diversity gain (cour- tesy of the multiple receive paths), some spreading gain (courtesy of the spreading/despreading codes) and additional selectivity (courtesy of the scrambling codes). This should make the next stage of the process easier, This next stage is channel decoding, usually or often implemented as a turbo coder (two convolution encode/decode paths running in parallel). The FHT produces some additional 'distance' that translates into coding gain. And finally, the bit stream now finally recovered from the symbol stream is delivered to the source decoder where an FFT is applied (frequency-domain to time-domain transform) to recover or rather reconstruct or synthesise the original analogue waveform. 3.4 Summary We have studied the properties of the Hadamard transform and its practical application in present CDMA cellular systems and early generation WiFi systems. We have showed how the IFHT/FHT is used in the code division multiplex/demultiplex and in channel encod- ing/decoding to deliver 'distance' which can be translated into coverage and capacity gain. We have reviewed how the IFFT/FFT is used to add in an OFDM multiplex to slow down the channel symbol rate as a (potentially) power-efficient mechanism for accommodating higher user data rates. Note that all these proces