This paper suggests that the regulatory tool known as the Block Edge Mask (BEM), which is used to define the technical conditions governing a spectrum license, can be used as an instrument to jointly drive spectrum and energy efficiency in a network. The paper explores this concept and goes on to show how networks can generate waveforms which comply with the energy limits of the BEM and at the same time make best use of the spectral resources available to them. The focus of the paper is on orthogonal frequency division multiplexing (OFDM) waveforms. The spectrum- and energy-efficient BEM-compliant waveforms are generated using a process that optimally combines symbol shaping and subcarrier-power loading to create a waveform that minimizes the difference between the transmitted wave and BEM. Practical considerations relating to peak-to-average-power-ratio (PAPR) reduction and time and frequency synchronization issues are explored to ensure the BEM-compliant waveforms can be transmitted with minimal changes to the transceiver. It is envisaged that these techniques will be used by transmitters that change their frequency of operation and in doing so need to shape their transmitted waveforms to comply with the different BEMs governing the use of the different spectrum blocks they wish to access.

Digital pre-distortion (DPD) is an advanced digital signal-processing technique that mitigates the effects of power amplifier (PA) nonlinearity in wireless transmitters. DPD plays a key role in providing efficient radio digital front-end (DFE) solutions for 3G/4G basestations and beyond. Modern FPGAs are a promising target platform for the implementation of flexible wireless DFE solutions, including DPD. In this paper, we present a software programmable design flow that facilitates the implementation and integration of efficient DPD solutions on Xilinx's Zynq All Programmable SoC, combining industry-standard embedded processors and programmable logic fabric into one chip. In addition to software programmability, another key contribution of this design flow is the flexible partitioning of functionality among hardware and software components, depending on the complexity of the DPD parameter estimation algorithm in use. We have applied processor-specific optimizations to the software implementation and used the Vivado High-Level Synthesis (HLS) tool as the design tool for the programmable logic. Using this design flow, we integrated a complete DPD feedback path on the Zynq SoC that achieves up to 7x speed-up from hardware acceleration.

We explore the question of when learning improves the performance of opportunistic dynamic channel selection by characterizing the primary user (PU) activity using the concept of Lempel-Ziv complexity. We evaluate the effectiveness of a reinforcement learning algorithm by testing it with real spectrum occupancy data collected in the GSM, ISM, and DECT bands. Our results show that learning performance is highly correlated with the level of PU activity and the amount of structure in the use of spectrum. For low levels of PU activity and/or high complexity in its utilization of channels, reinforcement learning performs no better than simple random channel selection. We suggest that Lempel-Ziv complexity might be one of the features considered by a cognitive radio when deciding which channels to opportunistically explore.

In this paper, a channel precoding technique is proposed for M-ary continuous phase modulation (CPM) for multipath downlink channels. The proposed pre-equalizer, based on the approximation of CPM signals by complex exponential functions, applies modulo-arithmetic operations to ensure the stability as in Tomlinson-Harashima method. Spectrally efficient precoded signals are obtained with small envelope variations by employing a transmit antenna selection technique. Because the equalization functions are transferred to the base station, the complexity in the mobile terminals is reduced significantly. The simulation results depict the power spectral density of the transmitted signals and the bit-error rate. An upper bound on the error performance is computed and the relation between the number of transmit antennas and the spectral efficiency is derived.

This paper describes a method to mitigate interference when the cyclic prefix (CP) is totally removed for shaped orthogonal frequency division multiplexing (OFDM) signals. The CP is removed to increase system throughput while shaping is applied to increase the spectral efficiency. Samples in the shaping extension are used to restore part of the cyclicity information missing in the $i$th received symbol. Furthermore, optimally weighted samples of the $(i+1)$th symbol are used to restore the remaining part of the cyclicity information with some residual error. Simulation results show that the bit error rate (BER) can be very close to the optimal bound in certain scenarios, while the complexity added to the standard OFDM receiver is low.

This paper identifies important features a cognitive radio framework should provide, namely a virtual architecture for hardware abstraction, an adaptive run-time system for managing cognition, and high level design tools for cognitive radio development. We evaluate a range of existing frameworks with respect to these, and propose a novel FPGA-based framework that provides all these features. By abstracting away the details of hardware reconfiguration, radio designers can implement FPGA-based cognitive nodes much as they would do for a software implementation. We apply the proposed framework to the design and implementation of a receiver node that works in two modes: discovery, where it uses spectrum sensing to find a radio transmission, and communication, in which it receives and demodulates the said transmission. We show how the whole design process does not require any hardware experience on behalf of the radio designer.

In this paper, a doubly-iterative linear receiver, equipped with a soft-information aided frequency domain minimum mean-squared error (MMSE) equalizer, is proposed for the combined equalization and decoding of coded continuous phase modulation (CPM) signals over long multipath fading channels. In the proposed receiver architecture, the front-end frequency domain equalizer (FDE) is followed by the soft-input, softoutput (SISO) CPM demodulator and channel decoder modules. The receiver employs double turbo processing by performing back-end demodulation/decoding iterations per each equalization iteration to improve the a priori information for the front-end FDE. As presented by the computational complexity analysis and simulations, this process provides not only a significant reduction in the overall computational complexity, but also a performance improvement over the previously proposed iterative and noniterative MMSE receivers.

In this letter, an orthogonal space-time (ST) block coding (STBC) technique for continuous phase modulation (CPM) is proposed and combined with a frequencydomain equalizer (FDE) to obtain high performance gains over frequency-selective channels. The new method maintains the constant envelope and phase continuity of the CPM waveforms perfectly by using appropriate tail symbols during the addition of cyclic prefix and interblock transitions and, therefore, has no negative impact on the spectral efficiency. Because the STcoded CPM blocks remain orthogonal, FDE is applied as in the case of single antenna transmissions without any increase in the computational load. Simulations corroborate the performance improvement offered by STBC while also preserving the desired bandwidth efficiency of CPM.

In this paper, a doubly iterative receiver is proposed for joint turbo equalization, demodulation, and decoding of coded binary continuous-phase modulation (CPM) in multipath fading channels. The proposed receiver consists of three soft-input soft-output (SISO) blocks: a front-end soft-information-aided minimum mean square error (MMSE) equalizer followed by a CPM demodulator and a back-end channel decoder. The MMSE equalizer, combined with an a priori soft-interference canceler (SIC) and an a posteriori probability mapper, forms a SISO processor suitable for iterative processing that considers discrete-time CPM symbols which belong to a finite alphabet. The SISO CPM demodulator and the SISO channel decoder are both implemented by the a posteriori probability algorithm. The proposed doubly iterative receiver has a central demodulator coupled with both the front-end equalizer and the back-end channel decoder. A few back-end demodulation/decoding iterations are performed for each equalization iteration so as to improve the a priori information for the equalizer. As presented in the extrinsic information transfer (EXIT) chart analysis and simulation results for different multipath fading channels, this provides not only faster convergence to low bit error rates, but also lower computational complexity.

In this paper, a doubly-iterative receiver with a soft-information-aided frequency-domain minimum mean square error (MMSE) equalizer is proposed for coded continuous phase modulation (CPM). Equalization in the frequency-domain provides low computational complexity in long multipath fading channel responses. The front-end equalizer is followed by the soft- input soft-output (SISO) CPM and channel decoders at the back- end. The receiver exploits double turbo processing by employing back-end demodulation/decoding iterations per each equalization iteration to improve the a priori information for the front-end equalizer. Such processing results in high bit-error rate (BER) performance with less number of equalization iterations, as also shown in the simulation results.

In this paper, the convergence behavior of a doubly-iterative receiver, proposed for joint turbo equalization, modulation and decoding of coded binary continuous-phase modulation (CPM), is analyzed by using extrinsic information transfer (EXIT) charts. The doubly-iterative receiver consists of a central soft-input soft-output (SISO) CPM demodulator coupled with a front-end soft information aided minimum mean square error (MMSE) equalizer and a back-end SISO channel decoder. The EXIT chart analysis shows that performing a few back-end demodulation/decoding iterations per each equalization iteration improves the a priori information for the front-end equalizer, and provides faster convergence to low bit-error rates (BERs) with less computational complexity, as also illustrated in the BER simulations.

Wireless multiple-access protocols using retransmission diversity resolve packet collisions through source separation techniques. Retransmissions are applied to achieve the necessary diversity level to determine the collision multiplicity blindly, whose proper detection is essential for good resolution performance. The so-called network-assisted diversity multiple access (NDMA) employs the rank test (RT) method for blind multiplicity detection, but static channel parameters throughout the retransmissions and the tight control of the transmitter phase are required. In this paper, a superior blind collision multiplicity-detection technique is introduced by combining the minimum description length criterion and a variation of the RT method. Collision resolution is accomplished through independent component analysis (ICA). Unlike blind NDMA,the new protocol, named ICA-NDMA, works in quasi-static fading channels, and does not need any phase control. Extensive performance analyses corroborate the performance advantages offered by ICA-NDMA.

Network-assisted diversity multiple access (NDMA) is a novel algorithm that resolves packet collisions deterministically by means of source separation techniques. The blind version of NDMA (B-NDMA) relies on the presence of a fading process that induces constant channel parameters over long slot times, as well as, the transmitter-receiver phase synchronization. In this paper, independent component analysis (ICA) is integrated into NDMA to provide blind collision resolution with high throughput/delay performance in a fast-fading channel environment and without phase control.