d spectrum allocations of sufficient size to allow for thus also the detailed structure of the channel frequency very wideband transmission, especially at lower-fre- response, may vary rapidly in time. The rate of the quency bands. variations in the channel frequency response is related to The use of wider transmission and reception the channel Doppler spread, fD, defined as fD = v/c fc, bandwidths has an impact on the complexity of the where V is the speed of the mobile terminal, fc is the radio equipment, both at the base station and at the carrier frequency (e.g. 2 GHz), and C is the speed of light. mobile terminal. As an example, a wider transmis- Receiver-side equalization has for many years been sion bandwidth has a direct impact on the transmit- used to counteract signal corruption due to radio-channel ter and the receiver sampling rates, and thus frequency selectivity. Equalization has been shown to on the complexity and power consumption of provide satisfactory performance with reasonable com- digital-to-analog and analog-to-digital converters as plexity at least up to bandwidths corresponding to the well as front-end digital signal processing. RF com- WCDMA bandwidth of 5 MHz. However, if the trans- ponents are also, in general, more complicated to mission bandwidth is further increased up to, for ex- design and more expensive to produce, the wider the ample 20 MHz, which is the target for the 3GPP LTE, bandwidth they are to handle. the complexity of straightforward high-performance equalization starts to become a serious issue. One option The two issues above are mainly outside the scope of this is then to apply less optimal equalization, with a corre- book. However, a more specific technical issue related to sponding negative impact on the equalizer capability to wider-band transmission is the increased corruption of counteract the signal corruption due to radio-channel the transmitted signal due to time dispersion on the radio frequency selectivity and thus a corresponding negative channel. Time disp