Special Issue on Signal Processing for Software Defined Radio Handsets

A software-defined radio (SDR) for ultrawideband (UWB) communication systems places several stringent requirements on the analog-to-digital converter (ADC). One alternative to using a single ADC is to sample the received signal with an array of lower speed ADCs that were driven by interleaved sampling clocks; however, mismatches among the ADCs will result in signal distortion. This paper makes three important contributions to overcoming this problem: 1) analytical quantification of the impact of ADC gain, offset, and timing mismatches on the performance of a time-interleaved sampling ADC array for UWB signals; 2) demonstration of the efficacy of using a pilot-based matched-filter architecture to mitigate the impact of timing mismatches in the presence of multipath; and 3) implementation of an 8-ADC time-interleaved UWB SDR testbed that operates at an effective sampling frequency of 6.4 GHz. In addition, our findings allow for the design specification of the number of pilots required to obtain a desired system performance. The simulation and measured performance results from this paper demonstrate that ADC mismatches can be controlled to within plusmn10%, yielding acceptable levels of distortion and bit-error-rate (BER) performance on the UWB SDR testbed. Both analytical and simulation results also demonstrate the efficacy of a pilot-based matched filter in mitigating the impact of timing mismatch errors, even in the presence of multipath.

Cyber is concerned with networks of systems in all their possible forms. Electronic warfare (EW) is focused on the many different uses of the electromagnetic spectrum (EMS). Given that many networks make use of the EMS (wireless networks), there is clearly large scope for collaboration between the cyber-warfare and EW communities. Unfortunately, such collaboration is complicated by the significant differences between these two realms. Software-defined radio (SDR) systems are based on interfaces between the EMS and computers and thus offer tremendous potential for encouraging cyber-EW collaboration. The concept of SDR is reviewed along with some hardware and software SDR systems. These are then used to propose a number of projects where SDR systems allow collaboration between the cyber and EW realms to achieve effects which neither realm could achieve alone.

We summarize the security necessary for software defined radio (SDR) systems, and propose a flexible structure for security systems on SDR. We introduce a new electronic commerce scheme for SDR that utilizes the ability of SDR to switch between different security algorithms for electronic commerce. We evaluate the performance of the cryptographic algorithms used in electronic commerce on various platforms including SDR systems, as basic research toward the implementation of SDR.

Since the initiation of the Joint Tactical Radio System (JTRS) program, the concept of software defined radio (SDR) has received considerable attention and significant progress has been made. While the raison d'etre of SDR is somewhat different for military and commercial applications, they share similar challenges in implementing a true SDR. A true SDR faces numerous hardware and software challenges, many of them still to be addressed by research. In the literature concerning SDR software architecture and requirements, the technology requirements tend to be sidelined. This is mainly because, in the JTRS program, the focus is on voice and low data rate applications; also, the frequency band is limited to UHF. On the other hand, the implementation cost is less of a concern for now. However, by the emergence of advance warfare technology where it is required to transport more bits per warrior to accommodate video and telemetry data, and also by introducing initiatives similar to the JTRS to other communication systems, the technology requirements of SDR have to be revisited. The paper focuses on the hardware technology aspect of SDR. The main technical objective of SDR is a versatile reconfigurable platform, which provides interoperability. The main blocks of a true SDR are: intelligent antenna; programmable RF modules; high-performance digital-to-analog (DAC) and analog-to-digital converters (ADC); digital signal processing (DSP) techniques/technology; interconnection technology.

This paper presents a low-cost Software-Defined Radio (SDR) Transceiver module simulated in LabVIEW, which supports the data transfer scheme using the ZigBee protocol. The proposed SDR transceiver has been entirely defined in software and provides a Graphical user interface environment built-in LabVIEW. The proposed system provides the flexibility o the users, where they can reconfigure any parameter according to the changing requirements. The modulated data can be sent in a secure way with the use of two Forward Error Correction (FEC) codes like the Convolution and Turbo Coding. The SDR module provides the capability to navigate over a wide frequency range providing programmable channel bandwidth and multi-modulation characteristics. Generic platform design for the SDR transceiver is proposed in this paper, where the users can analyze the transmitted data in real time for the ZigBee protocol. The proposed system provides rapid prototyping of the SDR system, especially for home-based applications. The developed SDR system is further put to test for flexibility by altering the different protocols and physical layer applications in real time. XBee-PRO test jig supporting ZigBee module has been used for testing the SDR system for real-time transmission and reception of binary data, text, and image.

The availability of commercial Radio Frequency System on Chip (RFSoC) devices brings new possibilities for implementing Software Defined Radio (SDR) systems. Such systems are of increasing interest given the pace of innovation in wireless technology, and the pressure on RF spectrum resources, leading to a growing need to access the spectrum in more dynamic and innovative ways. In this paper, we present an SDR demonstration system based on the Xilinx RFSoC platform, which leverages the Python-based ‘PYNQ’ (Python Productivity for Zynq) software framework. In doing so, we highlight features that can be extremely useful for prototyping radio system design. Notably, our developed system features Python-based control of hardware processing blocks and Radio Frequency (RF) data converters, as well as direct visualisation of communications signals captured within the chip. The system architecture is reviewed, hardware and software components are discussed, functionality is demonstrated, and aspects of the system’s performance are evaluated. Finally, it is noted that this combined RFSoC + PYNQ approach is readily extensible for other SDR systems; we highlight our online shared resources, and invite other engineers to investigate and build upon our work.

Software-defined radio (SDR) is an emerging technology that offers various advantages over conventional radio designs. The SDR approach uses a common hardware platform, programmed by software modules and firmware, to support many communications standards and operating frequencies. The technology is being promoted by the US Department of Defense to replace tens of thousands of single-protocol, single-purpose radios with a common platform. Military and public safety organisations worldwide are also considering this technology to solve interoperability problems enabling, for example, police and firefighters to easily communicate in the field. In addition, the commercial wireless industry views SDR as a means of reducing development cost and time to market. To fully realize SDR’s promise of an all-encompassing communications device capable of transmitting and receiving over a very wide frequency range requires special attention to the radio frequency (RF) transceiver. Although it is relatively easy to use conventional electronics to build SDRs operating at up to 6GHz, it is increasingly difficult to do so at higher operating frequencies. It needs a hardware platform capable of operating up to about 60GHz to take full advantage of the SDR concept. Ideally, the SDR hardware platform has a continuouslytunable source to act as a local oscillator. It should be possible to modulate this source in any format, perform signal conditioning, and distribute the signal: either by wireless transmission or over an optical network. The prospect of using conventional electronics to develop a commercially-viable source with these properties is limited, so it may be necessary to find another approach. Optical technology can emulate many of the functions normally associated with RF reception and transmission. For example, it is possible to generate microwave signals optically over a very large frequency range—from MHz to THz—using heterodyne techniques such as optical injection locking, optical phaselocked loops, and nonlinear up-conversion. The electrical RF signal is generated by shining two optical inputs, separated by the desired microwave frequency, on to a square-law photodetector that acts as a mixer and generates their beat frequency. In general, when no phase or frequency control is applied, the phase noise of the microwave signal is approximately equal to the sum of the optical linewidths. The key to reducing this typicallyMHz linewidth down to values that are more practical for a communications system is to ensure that the phases of the optical signals are highly correlated. If they are, a very narrow RF linewidth can be achieved, even from large-linewidth optical sources. A carrier is of limited use in a communication system without some form of encoded information. A laser source can be modulated by inserting a baseband optical modulator in the optical path, or by other means. The modulation formats are varied and may act on the frequency, amplitude, or phase of the signal. In general, the bandwidth of the modulator/demodulator is dictated by the format of the protocol or the radio-spectrum channel allocation and is relatively modest, since the high-frequency carrier is already optically generated. This means that digital demodulation can be done directly by the computer, after optical down-conversion, to make it easier to interface with the SDR software. Both the receiver and transmitter need RF filtering for signal conditioning. Techniques for electrical filtering in the optical domain have been examined extensively, but the all-optical microwave filters proposed to date are primarily based on incoherent manipulation of optical carriers with only positive taps. This approach can only create low-pass filters. Many applications, including SDR systems, need bandpass and flat-top filters as well. To overcome this limitation, Yao et. al. recently reported a way to build an all-optical microwave bandpass filter with a simple structure.

It is expected that multiple radio access standards and systems will coexist in the same environment beyond 3G. The superior re-configurability and re-programmability of software-defined radio (SDR) had made itself become the most promising technology to realize such a flexible radio system. Several research projects have involved in the development of SDR systems, but their efforts mainly focus on hardware design. A software framework that allows users, manufactures or operators to insert, remove, update and configure protocols, applications and hardware modules is also an essential part of a SDR system. Unfortunately, current commercial operating systems (OS) lack of fully supports of SDR features. In this paper, the impacts of SDR on the OS and the extension of the OS for a SDR system are investigated. Moreover, the design and implementation of a software framework based on a commercial on-the-shelf (COTS) OS are also presented.

In the recent few years, it is observed that in wireless communication there has been a rapid growth in terms of different communication standards/ technologies being used. Thus, to support different communication standards, flexible system should be used to convert the digital signal from one sample rate to another (up sampling or down sampling). The solution is the use of Software defined Radio (SDR), which is a reconfigurable radio communication system. Therefore the most critical and demanding element in the digital signal processing chain of an SDR is the Sample Rate Converter. At high sampling rate, the signals cannot be processed by using baseband signal processing unit. Instead of any unique air-interface, SDR simultaneously handles multiple air-interfaces of different wireless standards that require sample rates for baseband processing. Thus, in SDR, Sampling Rate Conversion (SRC) is an important functionality to provide synchronization between the ADC and baseband signal processor. This paper provides a review on various types of SRC circuits, where their design characteristics are analyzed and compared. The review is based on designing of Sample Rate converters on Field-Programmable Gate Array (FPGA) and Applications Specific Integrated Circuit (ASIC) platform. For FPGA based design, LUT, slices, FFT, and other hardware resource parameters are estimated to evaluate their performance. For ASIC, area, power and delay are considered for performance evaluation.

Fast Fourier Transform (FFT) is computationally an efficient algorithm that transforms a function in time domain to function in frequency domain. All 3G and 4G wireless technologies use OFDM and FFT is an integral block of transceiver loop. In this paper three FFT architectures are designed that fall within the Cooley-Tukey class of algorithms. These FFT designs are targeted for OFDM applications especially in future generations of Software Defined Radio (SDR) systems. The FFT is performed on 64-point complex valued input samples with 16-bit precision. Each core is optimized for a combination of area, power, and speed. The design is targeted for a partially reconfigurable FPGA platform such as Xilinx Virtex-4 or above. The FFT cores have been simulated in Model Sim and synthesized using Xilinx ISE software. The cores can be readily downloaded on to target FPGA board to check for run time configurability. The performance evaluation of these cores show that they run at clock frequency of about 80MHz.

New wireless communications standards do not replace old ones, instead the number of standards keeps on increasing and by now an abundance of standards exists. Moreover there is no reason to assume that this trend will ever stop. Therefore, the software-radio concept is emerging as a potential pragmatic solution: a software implementation of the user terminal able to dynamically adapt to the radio environment in which the terminal is located. For manufacturers this could result in shorter development time, cheaper production due to higher volumes. Furthermore software radio has advantages for consumers because it enables only software updates for new functionality without new hardware. Because of the analog nature of the air interface, a software radio will always have an analog front-end. In an ideal software radio, the analog-to-digital converter (ADC) and the digital-to-analog converter (DAC) are positioned directly after the antenna. Such an implementation is not feasible due to the power that such a device would consume and other physical limitations. It is therefore a challenge to design a system that preserves most properties of the ideal software radio while being realizable with current-day technology. Such a system is called a software-defined radio (SDR). A flexible, all-standard radio will consume more energy than a dedicated radio for a single standard. The first flexible radio could be an application where power consumption is less an issue; an example being a flexible radio in a notebook. This thesis presents such a radio with the focus on wireless LAN standards. These standards use phase modulation or OFDM in the $2.4$ GHz or $5$ GHz frequency band, so we decided in our project to combine a receiver of a phase modulation standard (Bluetooth) with an OFDM receiver (HiperLAN/2) first. In our view SDR is an implementation technology: the HiperLAN/2 hardware is that complex to the Bluetooth hardware that the Bluetooth receiver may be added to the HiperLAN/2 one at limited costs. In this thesis we describe how the physical layer of the OSI model of a phase-modulation receiver can be combined with an OFDM receiver at a functional level. The second goal of this research is to investigate whether this combined receiver can be implemented in software running on a General Purpose Processor (GPP) and estimate the costs of such an implementation with respect to power consumption and computational power requirements. For this reason, a testbed has been developed where all baseband physical layer functions have been successfully mapped on a Pentium 4 processor. This has been tested in combination with a CMOS-integrated wideband analog SDR front-end, containing a low noise amplifier, down-conversion mixers and filters. The testbed can be extended to other standards, because the only limitations in our testbed are the maximal channel bandwidth of $20$ MHz, the dynamic range of the wideband SDR analog front-end and the processing capabilities of the used PC. In 1999, Bose showed for second-generation mobile standards that it is possible to perform most baseband functions of the physical layer on a GPP processor. In his research, I/O was one of the main bottlenecks. In thesis we have identified that this is no longer true for current-day computers. Nowadays, an important bottleneck is the latency of the operating system, because wireless standards require fast response times. Major contributions of this thesis to the field of SDR research are extending the work of Bose for wireless LAN standards and developing a functional SDR receiver architecture that is capable of receiving standards that use OFDM or phase modulation.

We propose a hybrid Analog to Digital Converter (ADC) combined with the first-stage as a first-order feedforward incremental (FF I-) ADC and the second-stage as a SAR (Successive Approximation Register) ADC as high-precision and high-speed ADCs. As a result of simulation, the proposed hybrid ADC correctly converts data even if capacitance in FF path of the first-order I-ADC has 10% error.

Efficient and effective broadband wireless technologies are required to support the foreseeable need to process and exchange large amounts of data. In this Special Issue of the Springer Journal of Signal Processing Systems various disciplines of such efficiency and effectiveness in the context of Software-Defined Radio (SDR) technologies are discussed. At first, a selection of articles focuses on “spectral efficiency”. Since frequency spectrum is known to be scarce and limited, it becomes a resource of increasing value whose utilization must be handled with care. The rapidly growing demand for higher data throughputs in wireless communication does not allow inefficient use of spectrum anymore. Two promising approaches to tackle the “spectral efficiency” issue are Cognitive Radio (CR) and Dynamic Spectrum Access (DSA). A Cognitive Radio is capable of learning and adapting to its transmission environment. Taking e.g. spectrum sensing results into account, the decisions for accessing the scarce frequency spectrum in the most flexible and effective manner are made. CRs are typically based on SDR technology. Thus, the first set of articles puts emphasis on topics in the areas of Cognitive Radio, Cognitive Radio Networks, and Spectrum Sensing. The second selection of articles addresses the problems of “energy efficiency” and “implementation efficiency”. Especially in wireless communications these types of efficiencies are highly important to increase battery time of modern SDRbased platforms. The architectures of such SDRs are typically based on heterogeneous multi-processor hardware platforms hosting General Purpose Processors (GPP), Digital Signal Processors (DSP), Field Programmable Gate Arrays (FPGA) and sometimes even more specific processing elements. Each type of processor has a specific advantage in one or the other performance criterion like energy consumption, flexibility, processing time, throughput, waveform portability, components reusability etc. Whenever a new waveform shall be implemented on an SDR, the system designer has to take the decision for the best possible trade-off between all of these, partly conflicting, criteria under the given circumstances. For instance, the portability of waveform components can be improved by fulfilling the constraints of the Software Communications Architecture (SCA) specification and by using common Application Programming Interfaces (API). Thus, the second set of articles puts particular emphasis on topics in the areas of SDR and SCA Implementations.

Abstract. An ultra-wideband (UWB) software defined radio (SDR) implementation is presented. The developed impulse radio (IR) transceiver employs first order bandpass (BP) sampling at a conversion frequency which is four times the channel bandwidth. The subsampling architecture directly provides the RF signal avoiding any non-ideal mixer stages and reduces the requirements of digital signal processing implemented in a field programmable gate array (FPGA). The transmitter consists basically of a multi-Nyquist digital to analog converter (DAC), whereas the implemented matched filter (MF) receiver prototype employs a standard digitizing oscilloscope. This design can be adaptively reconfigured in terms of modulation, data rate, and channel equalization. The reconfigurable design is used for an extensive performance analysis of the quadrature phase shift keying (QPSK) modulation scheme investigating the influence of different antennas, amplifiers, narrowband interferers as well as different equalizer lengths. Even for distances up to 7 m in a multipath environment robust communication was achieved.

The Software-Defined Radio (SDR) concept was originally developed by the combined efforts of various research groups in the private and government organizations of the United States (US) in 1970s–1980s. The important ones to mention are the US Department of Defense Laboratory and a team at the Garland, Texas Division of E-Systems Inc. In 1991, Joe Mitola independently reinvented the term ‘Software Radio’ (SR) in cooperation with E-Systems as a plan to build a true software-based GSM transceiver (Mitola, Telesystems Conference, 1992). The SR platform essentially processes almost all the transceiver algorithms as software for a processor. This includes nearly all layers of transmission. However, an optimal implementation of physical layer is always challenging due to an enormous amount of mathematical computation. Over the period of time, many developmental changes occurred and an interesting feature of cognition was added to existing SDR platforms, thereby inventing the term ‘Cognitive Radio’. The main idea was to reduce over-sampling by the analog to digital converter, reduce on-chip processing and to target only the spectrum of interest. This book also touches the CR feature in the large SDR field in some of its selected chapters. Since, the very first few articles of J. Mitola, there has a been a tremendous amount of research work conducted in industry and academia. The evolution in SDRs is continuous with time and provides a number of excellent opportunities to researcher for exploration and to come up with their findings. The present day SDR implementations are such that the designers are focused mostly on the design of hardware and software, their interfacing and optimizations for varying architectural choices. It includes multiple cases of application-specific general-purpose acceleration platforms that are scalable, homogeneous and heterogeneous in nature while providing multiple programmable cores on a single chip computing system.