A power and time efficient radio architecture for LDACS1 air-to-ground communication

L-band Digital Aeronautical Communication System (LDACS) is an emerging standard that aims at enhancing air traffic management by transitioning the traditional analog aeronautical communication systems to the superior and highly efficient digital domain. The standard places stringent requirements on the communication channels to allow them to coexist with critical L-band systems, requiring complex processing and filters in baseband. Approaches based on cognitive radio are also proposed since this allows tremendous increase in communication capacity and spectral efficiency. This requires high computational capability in airborne vehicles that can perform the complex filtering and masking, along with tasks associated with cognitive radio systems like spectrum sensing and baseband adaptation, while consuming very less power. This paper proposes a radio architecture based on new generation FPGAs that offers advanced capabilities like partial reconfiguration. The proposed architecture allows non-concurrent baseband modules to be dynamically loaded only when they are required, resulting in improved energy efficiency, without sacrificing performance. We evaluate the case of non-concurrent spectrum sensing logic and transmission filters on our cognitive radio platform based on Xilinx Zynq, and show that our approach results in 28.3% reduction in DSP utilisation leading to lower energy consumption at run-time

Design of low complexity variable digital filters and filter banks for software defined radio receivers

To seamlessly support the existing and upcoming wireless communication standards, the software defined radio (SDR) has been proposed as a solution. SDRs can process signals of different wireless communication standards by software reconfiguration of the same transceiver architecture, thereby reducing hardware resource utilization and associated costs. To perform multi-standard channelization, i.e., extraction of desired radio channels (frequency bands) from a wideband input signal, SDR receivers typically employ variable digital filters (VDFs) and filter banks that provide variable frequency responses by controlling a small set of parameters. VDFs and filter banks are also used in SDR based cognitive radios (CRs) to perform spectrum sensing (detection of presence/ absence of licensed user signals in a wideband input frequency range) for dynamic spectrum access, to achieve opportunistic and efficient usage of the radio frequency spectrum. Realizing such VDFs and filter banks which showcase the desired attributes of high frequency response flexibility and low implementation complexity is a challenging task. To address this challenge, new algorithms and various architectures for designing VDFs and filter banks have been proposed in this thesis. The first work presents design techniques to obtain variable frequency responses using the same set of prototype filter coefficients, along with the corresponding mathematical formulations. Two techniques are proposed – a modified coefficient decimation method (MCDM) and the improved coefficient decimation method (ICDM), the latter being a combination of the proposed MCDM and the conventional coefficient decimation method (CDM). Both the proposed techniques, i.e., MCDM and ICDM, involve selective usage of filter coefficients by performing operations such as replacing them by zeros and retaining/ discarding them appropriately to obtain variable frequency responses. The ICDM is categorized into ICDM-I and ICDM-II, each comprising of two distinct coefficient decimation operations. The ICDM provides discrete control over the bandwidths and center frequencies of the subbands in the obtained frequency responses. The second work presents the design of VDFs which can be used for channelization in SDR receivers. Three such VDFs, one each based on ICDM-I, ICDM-II and comprehensive ICDM are proposed and analysed. The comprehensive ICDM based VDF involves both ICDM-I and ICDM-II operations and features their constituent advantages while minimizing the effects of their individual limitations. The comprehensive ICDM based VDF can provide variable lowpass, highpass, bandpass, bandstop and multi-band frequency responses on-the-fly, by performing appropriate ICDM operations on the same set of prototype filter coefficients. Similar to the design of VDFs based on ICDM-I, ICDM-II and comprehensive ICDM, the third work presents design of filter banks based on these three techniques. While the ICDM-I based filter bank can only be used for uniform channelization, the ICDM-II and comprehensive ICDM based filter banks can be used in SDR receivers for uniform as well as non-uniform channelization of signals corresponding to multiple wireless communication standards. The fourth work presents the design of VDFs based on the combination of all pass transformation (APT) technique and the proposed ICDM. The proposed VDFs employ 1st order APT techniques along with the ICDM to provide variable lowpass, highpass, bandpass, bandstop frequency responses with unabridged control over the bandwidths and center frequencies of the constituent subbands. A spectrum sensing scheme employing VDFs based on the combination of APT and ICDM is proposed. Also, pipelined hardware implementation architectures for realizing high speed APT based VDFs are presented. These VDFs based on the combination of APT and ICDM can be used for realizing low complexity spectrum sensing schemes in SDR based CR receivers, wherein unabridged control over cutoff frequency is desired to obtain a fine sensing resolution over the entire Nyquist frequency range.DOCTOR OF PHILOSOPHY (SCE

An improved coefficient decimation based reconfigurable low complexity FIR channel filter for cognitive radios

Multi-standard channel adaptation is a critical function in cognitive radio handsets which involves the transmission/reception of individual frequency channels of multiple wireless communication standards at different intervals of time. This needs dynamically reconfigurable, low complexity and high speed digital channel filters. In this paper, we present a reconfigurable finite impulse response (FIR) channel filter design technique based on the combination of the conventional coefficient decimation method (CDM) and a modified CDM. Our method enhances the frequency response flexibility of the filter and doubles the center frequency resolution when compared to the conventional CDM. The proposed channel filter has a significantly lower multiplication complexity and achieves superior stopband and transition band characteristics when compared to the channel filters based on the conventional CDM. Design example shows that a 57.1% reduction in multiplication complexity is achieved if the proposed channel filter is designed instead of the conventional CDM based channel filter

A modified coefficient decimation method to realize low complexity FIR filters with enhanced frequency response flexibility and passband resolution

Low complexity, reconfigurable finite impulse response (FIR) filters using coefficient decimation method (CDM) has been recently proposed in literature. In this paper, we propose a modified coefficient decimation method (MCDM) which enhances the flexibility of CDM in obtaining FIR filters with varied passband locations. The resolution of the center frequency locations in the multi-band frequency responses obtained using MCDM is twice that of the conventional CDM. Further, the stopband attenuation of FIR filters realized using our MCDM is higher compared to the filters obtained using conventional CDM. Also, for the same prototype modal (original) filter, the number of distinct frequency band locations that can be obtained after coefficient decimation is greater for MCDM than CDM due to the increased center frequency resolution of the former method. The hardware realization architecture of MCDM is presented. The advantages of our method for realizing reconfigurable filter banks are also discussed

Design and realization of variable digital filters for software defined radio channelizers using improved coefficient decimation method

Variable digital filters (VDFs) are used in software defined radio handsets for extraction of individual radio channels corresponding to multiple wireless communication standards. In this paper, we propose a VDF based on the improved coefficient decimation method (ICDM). The proposed VDF provides variable lowpass, highpass, bandpass, bandstop and multi-band frequency responses on-the-fly, using the same set of prototype filter coefficients. We present non-pipelined as well as pipelined implementation architectures for the proposed VDF, along with FPGA implementation results for multiple VDF designs. Analysis of the implementation results shows that the pipelined implementations achieve average reductions of 27.66%, 49.17% and 25.59% in the number of occupied slices, dynamic power and energy consumption respectively, when compared with corresponding non-pipelined implementations. Also, the proposed pipelined implementation architecture provides high operating frequencies that are independent of the prototype filter order across different VDF designs. An average maximum frequency of 157.89 MHz is obtained