A spectrum shaping technique to control spectrum emission of UTRA LTE user equipment

For the UTRA long term evolution (LTE), the transmit signal spectrum must comply with stringent spectrum emission mask requirements because of very low guard band size for high spectral efficiency. Compared to e.g. WCDMA, the requirements are tightened, which calls for efficient user equipment (UE) transmitter design, to balance the tradeoff among performance and hardware complexity. In this paper a spectrum shaping technique suitable for LTE user equipment is proposed and evaluated. The key component of this technique is an inverse Chebyshev digital IIR filter which has maximally flat in the passband and sharp transition from passband to stopband. We compare this technique with the well-known time windowing method which offers low implementation complexity. We study the two techniques impact on both error vector magnitude (EVM) and spectrum emission for two different LTE system bandwidths and for various bandwidth allocations for the user. Results show that for wideband setting (10 MHz) both techniques are able to produce acceptable EVM values less than 0.2%. However, for narrowband setting (1.4 MHz), only digital filtering performs sufficiently well since the time windowing method fails when the window overlap size is greater than the cyclic prefix length.