This paper introduces a reduced complexity approach to cyclostationarity detection of primary user signals in cognitive radio systems. The decision statistic is formulated by exploiting the variations of portions the sensed signal's spectral correlation density function estimate, due to either the presence or absence of the primary user signal. The presented detector has low computational complexity and has decision error performance which is superior to energy detection; these qualities make it suitable for energy-efficient cognitive radio terminals operating with limited power sources. The performance of this detection method is obtained by computer simulation and the computational complexity is evaluated.

In the context of UWB (ultra-wide band) impulse radio (IR) heterogeneous low data-rate networks, the need for coding/modulation schemes amenable of both coherent and noncoherent detection has emerged. The rationale is the potential coexistence of different classes of nodes, characterized by different complexity and performances. In such scenario, one of the main technical challenges is the design of efficient coding/modulation schemes incorporating forward error correction (FEC) and spreading capabilities, thus providing the necessary processing and coding gain, to guarantee robust communications. In this work, we introduce novel coding schemes exploiting the trellis structure of orthogonal convolutional codes for generating time-hopping sequences suitable for UWB-IR, while simultaneously mapping the information bits onto the transmitted waveforms. Namely, we present a new class of orthogonal convolutional modulation (OCM) schemes, highlighting the trade-offs in terms of coherent vs. non-coherent detection performance. Then we develop an adaptive OCM scheme (AOCM) for application to broadcast transmission in heterogeneous UWB-IR networks, illustrating advantages in terms of energy savings and potential drawbacks.

As the radio spectrum usage paradigm shifting from the traditional command and control allocation scheme to the open spectrum allocation scheme, wireless mesh networks meet new opportunities and challenges. The open spectrum allocation scheme has potential to provide those networks more capacity, and make them more flexible and reliable. However, the freedom brought by the new spectrum usage paradigm introduces spectrum management and network coordination challenges. In this paper, we study the network formation problem in cognitive radio based mesh networks. A cluster-based approach is proposed to form a mesh network in the context of cognitive radio scenario. Moreover, a topology management algorithm is developed to optimize the cluster configuration with regard to the network topology. The prominent feature of the proposed approach lies in the capability to adapt the cluster configuration to network and radio environment changes.

In the context of UWB (ultra-wideband) impulse radio, one of the challenges, for both high and low data-rate applications, is the design of an efficient coding/modulation scheme incorporating forward error correction (FEC) and spreading capabilities. In this paper, we introduce encoding strategies exploiting the trellis structure of orthogonal convolutional codes for generating time-hopping sequences suitable for UWB impulse radio and, at the same time, for mapping the information bits onto the transmitted waveforms. It is shown that this solution improves the Euclidean distance among transmitted signals, without decreasing the corresponding information rate.

Iterative decoding algorithms may be viewed as high-dimensional nonlinear dynamical systems, depending on a large number of parameters. In this work, we introduce a simplified description of several iterative decoding algorithms in terms of the a posteriori average entropy, and study them as a function of a single parameter that closely approximates the signal-to-noise ratio (SNR). Using this approach, we show that virtually all the iterative decoding schemes in use today exhibit similar qualitative dynamics. In particular, a whole range of phenomena known to occur in nonlinear systems, such as existence of multiple fixed points, oscillatory behavior, bifurcations, chaos, and transient chaos are found in iterative decoding algorithms. As an application, we develop an adaptive technique to control transient chaos in the turbo-decoding algorithm, leading to a substantial improvement in performance. We also propose a new stopping criterion for turbo codes that achieves the same performance with considerably fewer iterations.

Ultrawideband (UWB) impulse radio is an emerging technology suitable for high-rate tactical wireless communications. One of the crucial challenges for a connecting station remains the initial code acquisition, in a hostile propagation environment (e.g., urban combat). In this paper, we address the coarse acquisition of pseudonoise (PN) codes and propose algorithms for speeding up the acquisition process and/or reducing the complexity of the acquisition algorithm itself. Also, in the case of energy detection, we show that the front-end sampling rate may be reduced. An in-depth analysis, supported by simulations in the presence of multipath is presented, and the results discussed.

In this correspondence, we introduce a simple one-dimensional (1-D) nonlinear map to describe the iterates of the bit-error rate (BER) of parallel-concatenated convolutional codes (PCCC) on the binary-input Gaussian channel. A lower bound on this map is derived based upon the weight enumerator of the constituent codes, thus enabling the characterization of the dynamics of the decoder in terms of fixed points, along with the associated stability analysis.

Interleaved convolutional time hopping (ICTH) is a recently proposed coding/modulation scheme for UWB impulse radio. ICTH is based upon a low-rate convolutional code, with optimized distance properties, combined with multilevel pulse-position modulation (PPM). In this context, bit-interleaved coded modulation (BICM) is used to decorrelate the bit errors and, more importantly, to obtain a flat spectrum. We present analytical bounds for the BER (bit-error-rate) performance of ICTH and an analysis of its spectral properties.

We treat the turbo decoding algorithm as a dynamical system parameterized by a single parameter that closely approximates the signal-to-noise ratio (SNR). A whole range of phenomena known to occur in nonlinear systems, like the existence of multiple fixed points, oscillatory behavior, bifurcations, chaos and transient chaos are found in the turbo decoding algorithm. As an application, we have developed a novel stopping criterion based on the average entropy of an information block and propose an adaptive strategy as a function of the SNR.

We propose a novel density evolution approach to analyze the iterative decoding algorithms of low-density parity-check (LDPC) codes and product codes, based on Gaussian densities. Namely, for these classes of codes we derive a one-dimensional (1D) map whose iterates directly represent the error probability both for the additive white Gaussian noise (AWGN) and the Rayleigh-fading channel. These simple models allow a qualitative analysis of the nonlinear dynamics of the decoding algorithm. As an application, we compute the decoding thresholds and show that they are consistent with the simulation results available in the literature.

In this paper we introduce a model of the iterative decoding of product codes. For each iteration, an approximation of the bit error rate (BER) at the output of the decoders is used to evaluate the density of the extrinsic information. The decoding thresholds obtained for the additive white Gaussian noise (AWGN) and the Rayleigh fading channel are consistent with the simulation results available in the literature.

Pseudo-chaotic time hopping (PCTH) is a recently proposed modulation scheme for UWB impulse radio. PCTH exploits concepts from symbolic dynamics to generate aperiodic spreading sequences. In this paper, we present a general analytical expression for the average BER (bit-error-rate) of a synchronous multi-access PCTH system, as a function of the cross-correlation between the users' signatures in an AWGN (additive white Gaussian noise) channel. Also, it is shown that with enough users an error floor in the BER can develop.

Pseudochaotic time hopping (PCTH) is a previously proposed encoding/modulation scheme for ultra-wideband (UWB) impulse radio. PCTH exploits concepts from symbolic dynamics to generate aperiodic spreading sequences, resulting in a noise-like spectrum. We present a multiple-access technique suitable for the PCTH scheme. In particular, we provide an analytical expression of the bit-error rate performance as a function of the number of users and validate it by simulation.

We propose an enhanced version of the DCSK (differential chaos shift keying) scheme where the chaotic carrier is exploited for conveying useful information. This is achieved by means of a pseudo-chaotic encoder which spreads the input sequence, approximating the dynamics of the Bernoulli shift. The information encoded in the chaotic carrier is retrieved by means of standard maximum-likelihood detection methods.

SISO (soft input soft output) algorithms are present in several decoding schemes, particularly in concatenated ones that admit an efficient iterative detection, e.g. turbo codes. These algorithms have been an interesting research subject, especially for the aspects related to complexity reduction. This paper presents the idea of partitioning the set of original states in a channel or a code, generating a scaled (or reduced) trellis. Merging two or more states produces a new super-state and a standard SISO algorithm can follow the system evolution in terms of the new description.

A robustness assessment for the results of a bifurcation analysis of the Colpitts oscillator is presented. It is shown, by means of SPICE simulations, that the bifurcation phenomena occurring in the oscillator are relatively independent of the particular choice of the transistor model. Furthermore, the simulation results exhibit good agreement with the theoretical predictions. It is also demonstrated, through circuit experiments, that the predicted behaviors can be reproduced experimentally in a robust way.