Marco Cardenas-Juarez

Spectrum Sensing and Throughput Trade-off in Cognitive Radio under Outage Constraints over Nakagami Fading

The spectrum sensing duration and the secondary users achievable throughput trade-off is optimized under outage constraints in a cooperative cognitive radio network over Nakagami fading conditions. The optimum trade-off depends not only on the maximum outage probability allowed by the primary user and the number of cognitive users involved in the sensing but also on the fading operational conditions of the cognitive radio. The parameters of the Nakagami fading distribution can be adjusted to fit different fading environments. The fading parameter (also called shape parameter) of the Nakagami distribution affects the optimum sensing time, which increases when the fading conditions are worse than Rayleigh fading. For the energy detector, the expression for the probability of false alarm is obtained in terms of a new threshold, which is derived considering an outage constraint on the channel-dependent probability of detection. Then, the optimization problem is formulated. Simulation results quantify the effects of different fading parameters on the optimum spectrum sensing duration.

Locally optimum detection for spectrum sensing in cognitive radio

Spectrum sensing is a key feature in cognitive radio networks. We propose a locally optimum (LO) detector, which is known to be optimum at low SNR. This is desirable in cognitive radio since the primary users signal may exhibit a very low power at the cognitive users transmitter. We focus here on linear modulation in the presence of an unknown phase shift and additive white Gaussian noise. In the case of BPSK modulation, the sufficient statistic of the LO detector is shown to be the sum of the absolute second-order moment (i.e., energy) and second-order moment (pseudo-energy) estimates. For higher size constellation, it is proven that the energy detector is locally optimum. The paper also addresses the issue of noise power uncertainty, to which the energy detector is very sensitive. Although the proposed LO detector is shown to be less sensitive than the energy detector, its performance does deteriorate at high noise power mismatch values. To overcome this problem, we also propose a detector whose probability of false alarm is independent of the noise power. Simulation results show that the proposed detectors in the case of BPSK significantly outperform the energy detector. Further, the complexity of the proposed detectors is only slightly higher than that of the energy detector.

Spectrum Occupancy Measurements below 1 GHz in the City of San Luis Potosi, Mexico

The cognitive radio technology is a promising solution to solve the scarcity problem of electromagnetic spectrum caused by the increase in the demand of wireless communications. Throughout the world, several measurement campaigns have been conducted to determine the real occupancy of the spectrum. In several countries, including Mexico, these measurements have not been realized yet. In this paper, we present results of the spectral power and duty cycle of the first measurement campaign conducted in the city of San Luis Potosi and in Mexico. The frequencies of interest considered in this study lies within the range of 30 MHz to 910 MHz. In order to improve the system sensitivity, the measurements were made with a directional antenna considering the four cardinal points. The study measures the power spectrum for 7.5 hours on a weekday. The results clearly show the critical underutilization of the spectrum in our country since it show an average duty cycle of 12.5% in the above mentioned frequency range.

On spectrum occupancy measurements at 2.4 GHz ISM band for cognitive radio applications

The 2.4 GHz industrial, scientific and medical (ISM) band is a shared electromagnetic resource where many wireless communications technologies such as wireless local area networks, Bluetooth, ZigBee, cordless phones, amongst others, coexist. Due to the large amount of users of different technologies that might utilize the band at the same time and geographical region, it is reasonable to assume that the band is very busy all the time. In this paper, however, a spectrum measurement campaign is carried out to determine the actual spectrum occupancy of the ISM band in an environment with high density of users. Although many wireless technologies share this frequency band, results show its low spectrum utilization. Indeed, it is shown that the spectral occupation of the band ranges between 7% and 34% of a normal working day, and it is moderate even during busy hours. Therefore, the use of a more sophisticated approach is essential to exploit the unlicensed access to this band, for which cognitive radio is well suited. This is valid despite the fact that, formally speaking, there are no licensed (or primary) users in the ISM band. Nevertheless, ISM users could be treated as pseudo-primary. Thus, cognitive radio techniques can be implemented to improve the spectrum utilization.

Improved semi-blind spectrum sensing for cognitive radio with locally optimum detection

In cognitive radio, there might be some information about primary users’ signals available at secondary users’ receivers since communications systems usually employ training signals for channel estimation and synchronization purposes. This training information can be exploited along with data symbols to perform semi-blind detection of primary users’ signals. In the literature, it is considered that the locally optimal semi-blind detection metric is the linear combination of the energy detector (ED) and the matched filter, i.e. the hybrid detector. Locally optimum detection (LOD), known to be optimum in the low signal-to-noise ratio, is proposed here in the design of a weighted semi-blind locally optimum detector (WSBLOD) by focusing on linear modulation in presence of an unknown phase shift and additive white Gaussian noise. By using LOD, it is shown that for binary phase shift keying-modulated signals, the semi-blind detector test statistic consists not only in combining linearly the matched filter and the ED but also the pseudo-energy of the received signal. Then, the designed semi-blind detector is improved by optimising the weights of the matched filter, energy and pseudo-energy in the test statistic, which maximises the probability of detection. Simulation results show that the proposed WSBLOD outperforms the hybrid detector.

Reducing Spectrum Handoffs and Energy Switching Consumption of MADM-Based Decisions in Cognitive Radio Networks

In a cognitive radio network (CRN), the number of spectrum handoffs increases energy consumption of cognitive (or secondary) users due to the channel switching process. This might limit the operation of the CRN, especially in scenarios where secondary users terminals are battery-powered. Thus, reducing the number of times a cognitive user involved in a transmission switch to different spectrum holes is required to increase battery life-time. In this regard, available spectrum holes possess different attributes (e.g., bandwidth) that can be exploited to satisfy specific secondary users requirements (i.e., connection profile) for data transmission while saving energy. Here, three multiple attribute decision-making (MADM) algorithms for the spectrum decision functionality are evaluated using real spectrum measurements of TV bands. This is performed by proposing six decision parameters, which are extracted from the spectrum data to characterize its suitability. Then, these are used as inputs of the MADM algorithms to select the most suitable spectrum hole for a cognitive user. Thus, an enhanced MADM-based decision process is proposed to reduce the number of handoffs considering energy consumption due to channel switching (ECCS). Results quantify savings from 30% to 90% in ECCS and spectrum handoffs reductions from 47% to 90%.

Performance of MADM algorithms with real spectrum measurements for spectrum decision in cognitive radio networks

Spectrum decision is an important functionality of a cognitive radio terminal, which allows the selection of the appropriate frequency band from the available underutilized spectrum. Spectrum decision conducts itself in accordance to the communication requirements of the secondary (or cognitive) users in the forthcoming Cognitive Radio Networks (CRNs). Selecting the best spectrum for a given transmission involves making preference decisions over the set of available alternatives of frequency bands, which are indeed characterized by different attributes. Therefore, spectrum decision can be modeled as a multiple attribute decision making (MADM) problem. In this paper, we evaluate the performance of MADM decision algorithms such as Simple Additive Weighting (SAW), Technique for Order Preferences by Similarity to Ideal Solution (TOPSIS) and the Compromise Ranking Method VIKOR for spectrum decision. The study, however, is conducted using real spectrum occupancy measurements to evaluate the performance of the aforementioned algorithms in a practical scenario. Some important attributes of underutilized spectrum are proposed for consideration in the decisions. Results show that SAW algorithm performs well for the preferred spectrum attributes in the selected scenarios, while offering a good performance also in other parameters.

A Multiple Beamforming Network for Unequally Spaced Linear Array Based on CORPS

This paper proposes an alternative and innovative way to design a simpler beamforming network (BFN) based on balancing alternated power combiners and dividers, to feed a nonuniformly spaced linear array with Gaussian amplitude and coherent (in-phase) signals. Thus, a two-beam design configuration of the feeding network for a nonuniform array with beam steering capability is proposed and analyzed. The nonuniform aperture and the complex inputs of the feeding network are optimized by means of a differential evolution algorithm. In addition, a comparative analysis between a uniform and nonuniform linear array with the proposed feeding network is performed. Simulation results show the advantages and effectiveness of the proposed feeding network exploiting the nonuniformity of the antenna elements, in terms of side lobe level and directivity. Furthermore, research results show an inherent reduction in hardware complexity of the network.

Adding quality in the user requirements specification: A first approach

Users need trusting in data managed by software applications that are part of Information Systems (IS), which supposes that organizations should assuring adequate levels of quality in data that are managed in their IS. Therefore, the fact that an IS can manage data with an adequate level of quality should be a basic requirement for all organizations. In order to reach this basic requirement some aspects and elements related with data quality (DQ) should be taken in account from the earliest stages of development of software applications, i.e. “data quality by design”. Since DQ is considered a multidimensional and largely context-dependent concept, managing all specific requirements is a complex task. The main goal of this paper is to introduce a specific methodology, which is aimed to identifying and eliciting DQ requirements coming from different viewpoints of users. These specific requirements will be used as normal requirements (both functional and non-functional) during the development of IS awareness of data quality.

A corrected model for non-contact-type RF MEMS switches

This paper presents a corrected electric model for a novel non-contact-type radio-frequency (RF) microelectromechanical systems switch for high frequency applications (f > 24 GHz). This type of switches were proposed in the ref. [1], however in the electric model it is necessary considerer two resistors to have excellent agreement between simulation and experiment results. The proposed switch is a capacitive shunt type operated by the change of capacitance between the signal line and ground lines, the switch consists of a coplanar waveguide line and variable capacitors OFF to the ON state and 200 ps in the ON to the OFF state. The simulation results show a good agreement with our proposed electric circuit of the designed switch and experimental results.