Design and implementation of digital filters with very high frequency response flexibility for multi-standard wireless communication receivers

• Main Author: Dhabu, Sumedh Somnath
• Other Authors: Vinod Achutavarrier Prasad
• Format: Theses and Dissertations
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Electronic systems::Signal processing; DRNTU::Engineering::Electrical and electronic engineering::Wireless communication systems
• Online Access: http://hdl.handle.net/10356/66077
• Institution: Nanyang Technological University

Variable digital filters and reconfigurable filter banks (the filters and filter banks whose frequency response can be changed on-the-fly, based on the desired specifications) find application in multi-standard wireless communication receivers for channelization and spectrum sensing. Realization of area- and power-efficient, dynamically reconfigurable digital filters and filter banks is a challenging task. This thesis proposes area-efficient variable digital filters and reconfigurable filter bank architecture suitable for multi-standard wireless communication receivers. Proposed reconfigurable architectures offer different trade-offs between filter complexity and frequency response flexibility. In the first work, a low complexity design technique, termed as ‘improved coefficient decimation-interpolation-masking (IDIM)’ technique, is proposed to design low complexity, highly flexible variable filter and reconfigurable filter bank. The IDIM technique provides only discrete (coarse) control over the cutoff frequency. In multi-standard wireless communication receivers, it is desirable to have very fine or continuous (unabridged) control over the cutoff frequency of the variable filter. Fractional delay structure based filters provide very fine control over the cutoff frequency, at the cost of higher complexity. In the second work, fractional delay structure based variable filter designs using a novel fractional delay element are proposed. When compared to the existing fractional delay structure based filter, the proposed fractional delay structure based filters provide wider cutoff frequency range along with variable lowpass, bandpass, and highpass filter responses. The fractional delay structure based filters provide very fine control over the cutoff frequency, but in disjoint ranges. Also, they possess linear-phase property only in the passband region. Frequency transformation based filters provide a continuous control and have linear phase; but have very limited cutoff frequency range. The proposed modified second-order frequency transformation based filter provides a continuous control over the cutoff frequency on much wider range without increasing the transition bandwidth. Further, by integrating the second-order frequency transformation and interpolation techniques, a variable filter, termed as interpolated second-order frequency transformations based filter (ISFT filter), is proposed which can provide variable lowpass responses with narrow transition bandwidth over the entire Nyquist band. This design of variable lowpass filter is then extended to a bandpass filter with continuous and independent control over both the cutoff frequencies. The proposed transposed Taylor structure reduces the complexity of this bandpass filter and makes it suitable for designing reconfigurable filter banks. Spectral parameter approximation (SPA) based filters provide a continuous control over the cutoff frequency and offer trade-off between area and group delay with the frequency transformation based filters. Therefore, it is of interest to design low complexity SPA based filters which can provide similar cutoff frequency range as the proposed ISFT filter. A new time-domain approach is proposed in this thesis to design the SPA filters with reduced filter complexity. This time-domain approach is shown to result in lower filter complexity compared to the conventional design approach. Finally, the interpolation and SPA techniques based filter (ISPA filter) is proposed, which overcomes all the limitations of all the existing SPA based filters. Similar to the ISFT filter, the ISPA filter can provide a continuous control over the cutoff frequency in the entire Nyquist band along with narrow transition bandwidth. The viability and area-efficiency are also verified by the FPGA implementations of these proposed variable filters and it is shown that the ISPA and ISFT filters offer trade-offs between area, group delay and operating speed.