Design of nonlinear phase prototype filter based on coefficients symmetry for UFMC communication system.

One of the candidates for short burst communication is universal filtering multicarrier (UFMC), which applies filters in each sub-band to reduce intercarrier interference. Compared with the linear phase FIR filter (LPFF), prototyping a nonlinear phase FIR filter (NLPFF) as the UFMC filter can benefit system performance by improving the filter magnitude response. However, the benefit, namely the tradeoff between phase response and better magnitude, is limited in previous NLPFF designs. Aiming at this problem, this paper has done the following works. First, we propose a new measure called sum of symmetric coefficient differences (SSCD) to represent the phase deviation. Furthermore, we propose a constrained least squares design for NLPFF, where constraints are imposed on the SSCD and squared magnitude. The design can be effectively realized under the second-order cone programming (SOCP) framework. Due to the significantly reduced constraint size and enhanced performance tradeoff area, the proposed SOCP-SSCD approach is the most competitive in effectiveness and efficiency. We have demonstrated this advantage by comparing with previous NLPFF methods. Consequently, by applying this method to design NLPFF as a prototype filter in the UFMC system, we have achieved better power spectral density, symbol error rate (SER), and demodulated constellation than previous prototype filters. For the SER indicator, Fig. 6(a) indicates an SNR gain of 1.2dB@{SER=0.001} between the designed NLPFFs and the previous prototype filters.