A Noise Suppression aided Multi-Carrier$M$-ary Differential Chaos Shift Keying (NS-MC-MDCSK) system is proposed here where each information subcarrier transmits an$M$-ary information-bearing signal and the$M$-ary constellation symbols are constructed by orthogonal Walsh codes to improve the energy efficiency. Exploiting the redundant information available in the received signal, we propose a noise suppression algorithm to suppress channel noise in the reference and$M$-ary information-bearing signals. In the proposed algorithm, correlation coefficients detected between the received reference and information-bearing signals are fed back to suppress the noise corrupting the signal received. This method reduces the channel noise significantly and provides an outstanding Bit Error Rate (BER) performance. A performance analysis is performed for the NS-MC-MDCSK system over Additive White Gaussian Noise (AWGN) and multipath fading channels. Finally, the BER performance of the NS-MC-MDCSK system is compared to that of other chaotic communications systems. It is shown that the NS-MC-MDCSK system offers better BER performance than its competitors.

A new Differential Chaos Shift Keying modulation scheme exploiting Chaotic Shape-forming Filter and Sequence Mapping (CSF-SM-DCSK) is being proposed. The new CSF-SM-DCSK system employs a novel sequence mapping rule and includes a data correction module to achieve a good trade-off between the low Bit Error Rate (BER) performance and high transmission rate. It transmits two data streams simultaneously and preserves the simplicity and robustness of DCSK method. Channel one, transmitting a Low Priority Stream (LPS), generates the chaotic carrier by a Chaotic Shape-forming Filter (CSF) at the transmitter and applies a coherent Matched Filter (MF) at the receiver to recover the information. Channel two, transmitting a High Priority Stream (HPS), relies on conventional DCSK modulation, while the reference and information-bearing parts are transmitted simultaneously with orthogonal sine and cosine carriers. This double-stream solution eliminates the need for analog RF delay lines and doubles the data transmission rate. Before feeding the LPS data stream into the modulator, each LPS bit is encoded into a symbol sequence using sequence mapping. This approach, together with the coherent MF reception, equips the LPS channel with an extremely high robustness against channel noise and multipath propagation. To handle every possible redundancy in the received signal and to minimize the possibility of making wrong decisions, a data correction block is also introduced. Initially, a rough estimation of the received HPS DCSK bit is done at the receiver, then this estimation is used to remove the DCSK modulation from the received information-bearing signal. The three inputs of data correction blocks are: (i) the reference and (ii) the information-bearing parts of the received signal in their original form, and (iii) the received information-bearing signal where the DCSK modulation is removed. The data correction block improves the BER performance while the increased channel capacity, enabled by the double-stream approach, improves the spectral efficiency. Analytical expressions are derived to predict the BER performances in additive white Gaussian noise channel for both the LPS and HPS channels. Computer simulations are used to show that the system performance of the CSF-SM-DCSK modulation scheme proposed in this work is superior to that of the already published solutions. In addition to the computer simulations, the new chaos-based wireless communications system has been implemented on a wireless open-access research platform to experimentally demonstrate the feasibility and the superiority of CSF-SM-DCSK.

A new multicarrier M-ary orthogonal chaotic vector shift keying with index modulation (MC-MOCVSK-IM) is presented in this paper. In this design, information bits are conveyed not only by the multiple groups of M-ary information bearing signals, but also by the specific indices of the selected reference signals which depend on the incoming mapped bits. Benefiting from the favorable features of multicarrier modulation, M-ary modulation and index modulation, MC-MOCVSK-IM system is capable to offer higher energy efficiency and spectral efficiency at some expense of hardware complexity. In addition, the analytical bit error rate (BER) expressions of MC-MOCVSK-IM system are derived over additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels. The BER performance comparison between MC-MOCVSK-IM system and other non-coherent chaotic communication systems is carried out to highlight the superiority of MC-MOCVSK-IM system in terms of BER performance. Considering the dramatically increased demand for high-data-rate transmission and the harsh environment of future wireless communication, MC-MOCVSK-IM system shows strong robustness and offers competitive solutions for high-data-rate non-coherent chaotic communication systems.

A universal portable software defined electronics platform developed to teach info-communications systems is proposed here. Because every application is implemented in software, the universal platform is suitable for the implementation and simulation of any kind of communications or measurement systems where the information is carried by band-pass signals. The software defined electronics platform needs only a laptop and two universal software radio peripheral devices, and it can be used everywhere without a laboratory infrastructure.

Energy usage and data rate of differential chaos shift keying (DCSK) are both inefficient since half of the symbol duration is used to transmit reference. To improve the energy efficiency and data rate, we propose a new chaos modulation scheme which combines DCSK with code index modulation (CIM) referred to as CIM-DCSK. In the proposed scheme, a short reference signal is transmitted first. Then P repeated reference signals, which serve as information-bearing signals, are simultaneously modulated by an information bit and a Walsh code with a specific index which is determined by an extra information symbol. The analytical bit error rate (BER) performance of the proposed scheme is derived and verified by simulations. Further, we improve the performance of the proposed system by applying noise-reduction and optimizing power coefficients on the reference and the information-bearing signals of CIM-DCSK. Simulation and analytical results show that these optimization methods significantly boost the BER performances of the proposed schemes. Finally, the BER performances of the proposed systems are compared with that of the conventional DCSK system and the short reference DCSK (SR-DCSK) system. Numerical results show that the proposed schemes outperform both DCSK and SR-DCSK.

Summary Multiple‐input multiple‐output (MIMO) systems have attracted considerable attention in wireless communications because they offer a significant increase in data throughput and link coverage without additional bandwidth requirement or increased transmit power. The price that has to be paid is the increased complexity of hardware components and algorithms. The sphere detector (SD) algorithm solves the problem of maximum likelihood (ML) detection for MIMO channels by significantly reducing the search space of possible solutions. The main drawback of the SD algorithm is in its sequential nature, consequently, running it on massively parallel architectures (MPAs) is very inefficient. In order to overcome the drawbacks of the SD algorithm, a new parallel sphere detector (PSD) algorithm is proposed. It implements a novel hybrid tree search method, where the algorithm parallelism is assured by the efficient combination of depth‐first search and breadth‐first search algorithms. A path metric‐based parallel sorting is employed at each intermediate stage. The PSD algorithm is able to adjust its memory requirements and extent of parallelism to fit a wide range of parallel architectures. Mapping details for MPAs are proposed by giving the details of thread dependent, highly parallel building blocks of the algorithm. Based on the building blocks proposed, a mapping to general‐purpose graphics processing unit is provided, and its performance is evaluated. In order to achieve high‐throughput, several levels of parallelism are introduced, and different scheduling strategies are considered. Copyright © 2015 John Wiley & Sons, Ltd.

Radio coverage is limited by two parameters: (i) energy per bit radiated by the transmitter and (ii) BER performance of the receiver. In Ultra-Wideband Impulse Radio (UWB IR) the former is limited by the FCC Regulations while the latter depends on the detection algorithm. The fact that prevents the use of UWB IR devices in real applications is the unacceptable short radio coverage. The pulse compression technique, that simultaneously increases the maximum attainable energy per bit and introduces a processing gain at the receiver is proposed here to overcome this problem. As a result of pulse compression, the coverage of the new UWB chirp IR devices is 6-times longer than that of the conventional UWB IR devices, i.e., the radio coverage is extended from less than 10 meters up to 40 meters.

Both the peak power and the average power of emission are limited in UWB systems in order to keep the interference caused in an already existing narrowband radio system low enough. It is frequently overlooked that these power limits have to be checked not over the transmitted UWB signal but at the output of a bandpass filter specified in the FCC regulations. A further constraint exists in the handheld cheap devices where the low supply voltage reduces even further the attainable energy available to carry one bit information. The bit energy determines the coverage, the larger the bit energy, the larger the coverage. Introducing a novel approach an exact link budget calculation is proposed here for UWB impulse radio. Since the NLOS coverage of impulse radio obtained from the link budget is less than 2 m, the implementation of WLAN systems is not feasible with UWB impulse radio devices. To increase the bit energy, the UWB carrier-based approach, where the duty cycle is considerably increased, is proposed here. More than 16-dB improvement in bit energy has been achieved by increasing the UWB carrier duration to 300 ns.

To satisfy the huge demand for unlicensed handheld wireless networking devices, the Federal Communications Commission (FCC, USA) made the application of ultra-wideband (UWB) technology possible in 2002. Since then an IEEE standard has already been approved for the physical layer of the UWB impulse radio networking devices. Because of the ultra-wideband property the design and implementation of UWB circuits and systems set up an enormous challenge for the circuit designers. Unfortunately, an exact specification has not yet been derived for the circuit designers. Starting from the FCC Regulations and the IEEE UWB standard this contribution derives the required specifications for the blocks of UWB transceivers. It shows that if CMOS technology is used then the coverage of UWB impulse radio is limited by the low supply voltage. To overcome this limit more than one UWB carrier pulse is used to keep transmitted energy per bit high enough but to reduce the required voltage swing below the supply voltage. The optimum value of delay to be set between the successive UWB pulses is also determined.

Since the coherent receivers are not feasible to implement low-cost ultra-wideband (UWB) impulse radio (IR) devices featuring extremely low power consumption, energy detector-based (ED-based) noncoherent receivers are more and more frequently chosen. The Pulse Polarity Modulation (PPM) scheme with a threshold compensated receiver is a promising candidate for the implementation of cheap and robust UWB IR devices. Unfortunately, the field tests and computer simulations have shown the well known fact that the noise performance of noncoherent demodulators is much behind that of their coherent counterparts. The poor noise performance results in a such a bad receiver sensitivity that prevents the use of noncoherent receivers in the majority of real applications. This contribution shows how the noise performance of noncoherent threshold compensated PPM receiver can be improved considerably by disabling the receiver outside of the UWB pulse where only channel noise and interference is observed. The novel receiver configuration, referred to as gated threshold compensated noncoherent PPM receiver offers an 8-dB improvement in receiver sensitivity.

Transmitted reference (TR) modulation scheme and the autocorrelation receiver offer a simple and robust transceiver configuration for ultra-wideband (UWB) communications. Unfortunately, the TR UWB system has a poor noise performance. The paper shows that the noise performance of a TR autocorrelation system can be improved considerably by placing a noise filter before the autocorrelation detector. The optimum frequency response of required noise filter is derived.

This paper provides a review of the principles of chaotic digital communications using correlator receivers. Modulation schemes using one and two chaotic basis functions, as well as coherent and noncoherent correlation receivers, are discussed. The performance of differential chaos shift keying (DCSK) in multipath channels is characterized. Results are presented for DCSK with multiuser capability and multiple bits per symbol.

In addition to the stable fixed point which should be achieved under steady-state conditions, the sampling phase-locked loop (SPLL) implemented with a loop filter has another stable attractor in which an unwanted periodic solution, called false lock, develops in the loop. After the acquisition process, the SPLL either reaches the desired fixed point or gets into false lock, depending on the initial conditions. In every implemented circuit, the development of false lock has to be prevented. Although the false lock problem was reported earlier, an exact model to describe the behavior of SPLL in false lock has not yet been published. This paper propose a phenomenological model to explain why the false lock can develop and to describe the operation of SPLL in false lock.

Double sampling phase-locked loop (2-SPLL) is used in frequency synthesis. The unique feature of single sampling PLL is that its phase detector (PD) has a very low unwanted periodic output in steady state. In 2-SPLL, a second sample and hold circuit (S&H) is connected in cascade to suppress further the unwanted periodic PD output. However, the absence of a proper baseband model and design equations prevent the exploitation of all benefits of 2-SPLL. This paper develops a nonlinear baseband model for the 2-SPLL. Then based on the linearized baseband model, analysis is performed in the frequency domain and the frequency responses required to determine the spectrum of the output signal as a function of reference and VCO noise and modulation inputs are developed. Finally, the theoretical results are verified by measurements.

In Frequency-Modulated Differential Chaos Shift Keying (FM DCSK) modulation scheme, the digital information to be transmitted is mapped to an inherently wide-band chaotic signal rather than to a sinusoidal carrier. In this sense, the FM-DCSK system offers a new solution to spread spectrum communications. The FM-DCSK can be used in every application where multipath propagation rather than thermal noise limits the overall system performance. Because there is no need for synchronization at the FM-DCSK demodulator, this modulation scheme is very robust against channel disturbances and distortion. This paper evaluates the multipath performance of the FM-DCSK system in WLAN application by computer simulation.