Non-fading Channels Research Articles

Spectrum sensing in cognitive radio networks: threshold optimization and analysis

Cognitive radio is a technology developed for the effective use of radio spectrum sources. The spectrum sensing function plays a key role in the performance of cognitive radio networks. In this study, a new threshold determination method based on online learning algorithm is proposed to increase the spectrum sensing performance of spectrum sensing methods and to minimize the total error probability. The online learning algorithm looks for the optimum decision threshold, which is the most important parameter to decide the presence or absence of the primary user, using historical detection data. Energy detection- and matched filter-based spectrum sensing methods are discussed in detail. The performance of the proposed algorithm was tested over non-fading and different fading channels for low signal-to-noise ratio regime with noise uncertainty. In the conclusion of the simulation studies, improvement in spectrum sensing performance according to optimal threshold selection was observed.

Energy efficiency maximization by optimal fusion rule in frequency-flat-fading environment

In cognitive radio networks, cooperative spectrum sensing improves the reliability of decision about the primary user channel condition. However, the challenge is to optimize the energy efficiency, as energy consumption is high with cooperative spectrum sensing due to multiple secondary users. In this paper, energy efficiency for cooperative spectrum sensing by optimal fusion rule is investigated and maximized by minimizing the number of secondary users. Here, decision fusion rule for the number of secondary users, is optimized and compared for the fading and non-fading environment. The energy efficiency is maximized and compared for frequency flat-fading channel with non-fading Additive White Gaussian Noise channel. The detection quality metrics as the measure of probability of detection and probability of false alarm, are also considered as constraints. The exhaustive numerical results achieved after simulation in MATLAB, illustrate that the energy efficiency is maximum for non-fading channel and k-out-of-N rule is the best among all fusion rules.

Improving the performance of underwater wireless optical communication links by channel coding.

We investigate the efficacy of error correcting codes in improving the performance of underwater wireless optical communication systems. For this purpose, the effectiveness of several coding schemes, i.e., the classical Reed-Solomon and a recent family of low-density parity check codes, is studied in the physical (PHY) and the upper layers assuming negligible water turbulence. The presented numerical results testify to the interest of using efficient codes both at the PHY and upper protocol layers, although we are concerned by a non-fading channel. Furthermore, we discuss the choice of coding schemes and the appropriate degree of data protection in the PHY and upper layers.

Nonparametric Blind Signal Detection Based on Logarithmic Moments in Very Impulsive Noise

The detection problem in impulsive noise modeled by the symmetric alpha stable SαS distribution is studied. The traditional detectors based on the second or higher order moments fail in SαS noise, and the method based on the fractional lower order moments (FLOMs) performs poorly when the noise distribution has small values of characteristic exponent. In this paper, a detector based on the logarithmic moments is investigated. The analytical expressions of the false alarm and detection probabilities are derived in nonfading channels as well as Rayleigh fading channels. The effect of noise uncertainty on the performance is discussed. Simulation results show that the logarithmic detector performs better than the FLOM and Cauchy detectors in very impulsive noise. In addition, the logarithmic detector is a nonparametric method and avoids estimating the parameter of the noise distribution, which makes the logarithmic detector easier to implement than the FLOM detector.

Performance Analysis of FFH/MFSK Using Division Combining Receiver in GPS System

In this paper, a new kind of nonlinear combining receiver of fast frequency hopping/multiple frequency shift keying (FFH/MFSK) modulation in GPS system is proposed. The performance of the receiver is analyzed in the effects of partial band noise jamming over additive white Gaussian noise channel and Ricean fading channel. The diversity of the system is performed using multiple hops per data bit. The non-central F distribution is found in the random variable of the division combining algorithm under the partial-band noise jamming in the additive white Gaussian noise channel. The mathematical results of the bit error ratio of the division combining system are achieved in both fading and non-fading channels. The numerical results are achieved by the simulation environment of the signal transmission while the signal to noise ratio was relatively small and the partial band noise jamming factor is relatively large. It was shown that the GPS system using division combining receiver has better performance under the strong partial band interference than the system without diversity and system with self-normalized combining receiver. This performance gain is because that the interference signal is scattered into several hops and partly diminished by the operation of division algorithm. As its simple structure to be implemented and anti-interference property, the proposed combining algorithm is useful for GPS signal transmission in the strong partial band noise jamming environment.

Increasing the Capacity of Cellular Network With Nested Deployed Cooperative Base Stations

This paper investigates the capacity of the cooperative cellular networks and proposes to use the 2-D nested deployment on the base stations. Further analysis of sum-rate capacity and spectrum efficiency shows that this approach provides significant improvement. The study leverages the traditional model of regarding the coverage of base stations as the hexagonal blocks and views each hexagon as a macro-cell. One of the theoretical contributions of this paper is to use the invariance in the difference co-array to cover the derive the entire set of the channel fading coefficients. Furthermore, this paper proves the validity of using the average sum-rate capacity to calculate the capacity of the networks in both Rayleigh fading and non-fading channels. We also use simulations to confirm the correctness of the proposed theories from another perspective. As a result, the proposed approach remarkably improves the capacity of the network with the same amount of base stations.

Approaching Optimal Centralized Scheduling With CSMA-Based Random Access Over Fading Channels

Carrier sense multiple access (CSMA) based distributed algorithms can attain the largest capacity region as the centralized Max-Weight policy does. Despite their capability of achieving throughput optimality, these algorithms can either incur large delay and have large complexity or only operate over nonfading channels. In this letter, by assuming arbitrary backoff time, we first propose a fully distributed randomized algorithm whose performance can be pushed to the performance of the centralized Max-Weight policy not only in terms of throughput but also in terms of delay for completely connected interference networks with fading channels. Then, inspired by the proposed algorithm, we introduce an implementable distributed algorithm for practical networks with a reservation scheme. We show that the proposed practical algorithm can still achieve the performance of the centralized Max-Weight policy.

Game Theoretic Distributed Power Control Algorithms for Uplink Wireless Data in Flat Fading Channels

<p>In this paper we present a game-theoretic power control algorithms for wireless data in CDMA cellular systems under two realistic channels: (a1) Fast flat fading channel and (a2) Slow flat fading channel. The fading coefficients under both (a1) and (a2) are studied for three appropriate small scale channel models that are used in the CDMA cellular systems: Rayleigh channel, Rician channel and Nakagami channel. This work is inspired by the results presented by [1] under nonfading channels. In other words, we study the impact of the realistic channel models on the findings in [1] through the followings: we evaluate the average utility function, the average number of bits received correctly at the receiver per one Joule expended, for each channel model. Then, using the average utility function we study the existence, uniqueness of Nash equilibrium (NE) if it exists, and the social desirability of NE in the Pareto sense. Results show that in a non-cooperative game (NPG) the best policy for all users in the cell is to target a fixed signal-to-interference and noise ratio (SINR) similar to what was shown in [1] for non-fading channel. The difference however is that the target SINR in fading channels is much higher than that in a non-fading channel. Also, for spreading gain less than or equal to 100, both NPG and non-cooperative power control game with pricing (NPGP) perform poorly, where all the terminals except the nearest one were not able to attain their corresponding minimum SINR even if sending at the maximum powers in their strategy spaces.</p>

Resource-efficient fusion over fading and non-fading reporting channels for cooperative spectrum sensing.

Recently, a novel resource-efficient technique for the reporting channel transmissions in cooperative spectrum sensing was proposed. In this technique, secondary users are allowed to simultaneously send their local decisions to the fusion center, saving time and frequency resources. Expressions for the probabilities of detection and false alarm for the unitary-gain AWGN reporting channels were derived, while simulation results were given for both the AWGN and Rayleigh fading channels. Here, we provide an expression that is applicable to AWGN channels with different real-valued gains and to time-varying real-valued gains. A simple suboptimum receiver is proposed for the general complex-valued fading and non-fading channels, with an improved performance in the low signal-to-noise ratio condition. Numerical results are shown for both the AWGN and Rayleigh fading reporting channels, demonstrating the accuracy of the derived expressions and the attractive performance of the proposed receiver.

Multiantenna Spectrum Sensing in the Presence of Multiple Primary Users over Fading and Nonfading Channels

The basis of this paper is Wei and Tirkkonen, 2012, in which expressions for the key performance metrics of the sphericity test applied to the multiantenna cooperative spectrum sensing of multiple primary transmitters in cognitive radio networks over nonfading channels are provided. The false alarm and the detection probabilities were derived in Wei and Tirkkonen, 2012, based on approximations obtained by matching the moments of the test statistics to the Beta distribution. In this paper we show that the model adopted in Wei and Tirkkonen, 2012, does not apply directly to fading channels, yet being considerably inaccurate for some system parameters and channel conditions. Nevertheless, we show that the original expressions from Wei and Tirkkonen, 2012, can be simply and accurately applied to a modified model that considers fixed or time-varying channels with any fading statistic. We also analyze the performance of the sphericity test and other competing detectors with a varying number of primary transmitters, considering different situations in terms of the channel gains and channel dynamics. Based on our results, we correct several interpretations from Wei and Tirkkonen, 2012, in what concerns the performance of the detectors, both over a fixed-gain additive white Gaussian noise channel and over a time-varying Rayleigh fading channel.

Performance of $p$-Norm Detector in AWGN, Fading, and Diversity Reception

Performance analysis of the p-norm detector to date has been limited to ad hoc approximations, nonfading channels, and Rayleigh fading. To overcome these limitations, we develop several analytical/numerical solutions for detection probability P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> and false alarm probability P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> , which are necessary to specify the receiver operating characteristic (ROC) curves of the p-norm detector. First, for nonfading channels (additive white Gaussian noise (AWGN) only), the moment-generating function (mgf) of the decision variable is derived in two forms: 1) closed form for even integer p and 2) series form for arbitrary p. To evaluate P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> and P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> , a numerical method utilizing the Talbot inversion is developed for case 1, and an infinite series expansion with convergence acceleration based on the e-algorithm is derived for case 2. As an alternative to mgf-based analysis, a Laguerre polynomial series is also used to derive new P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> and P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> approximations. Second, series-form mgf-based P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> expressions are derived for κ-μ and α-μ fading channels. Third, for antenna diversity reception, new p-law combining (pLC) and p-law selection (pLS) schemes are proposed. The performance of these combiners with the p-norm detector is derived for Nakagami-m fading and is compared with that of the classical maximal ratio combining (MRC) and selection combining (SC). Interestingly, both pLC and pLS perform similarly to SC at low signal-to-noise ratio (SNR) but outperform it at relatively high SNR, with pLC performing closer to the optimal MRC. Numerical results are presented to verify the derived results and to provide further insights.

Energy-Efficient Power Allocation Over Nakagami- &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$m$&lt;/tex-math&gt;&lt;/inline-formula&gt; Fading Channels Under Delay-Outage Constraints

This paper presents an energy-efficient power allocation strategy for Nakagami-m flat-fading channels with a delay-outage probability constraint. The operating input transmit power value is limited to P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> . The energy efficiency (EE), expressed in units of b/J/Hz, is represented as the ratio of the effective capacity to the sum of transmission power (P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> ) and circuit power (P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ). Since the EE-maximization objective function is quasi-concave, a unique global maximum exists. By using fractional programming, we develop an EE-optimal power allocation strategy that consists of two steps: 1) obtaining the power level P̅ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">un</sub> , at which the maximum EE can be achieved, and 2) distributing the power optimally based on the minimum of P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> and P̅ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">un</sub> . We prove that while P̅ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">un</sub> monotonically increases with P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , the maximum achievable EE is a monotonically decreasing function of P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> . The analysis further allows us to derive the EE of three important cases: non-fading channels, extremely stringent delay-limited systems, and systems with no delay constraints. Simulation results confirm analytical derivations and further show the effects of the circuit power, fading duration, and fading severeness on the achievable EE and effective capacity of a delay-limited fading channel.

Multi-channel power allocation based on market competitive equilibrium in cognitive radio networks

Cognitive radios such as intelligent phones and Bluetooth devices have been considered essential goods in next-generation communication systems. Such devices will have to share the same frequency band owing to the limited bandwidth resource. To improve spectrum efficiency, we formulate multi-channel power allocation as a market competitive equilibrium (CE) problem, and prove that its solution exists and is unique under the condition of weak interference. We then propose two distributed power allocation algorithms achieving CE, namely the fast convergent power allocation algorithm (FCPAA) and the social-fairness-aware FCPAA (SFAF). Theoretical analysis and simulation results demonstrate that the proposed algorithms lead to better system performance in terms of the guaranteed interference temperature constraint using the price mechanism instead of a strategy based on the Nash equilibrium. Moreover, it is shown that the FCPAA maximizes total utility, and converges more quickly than the method addressed in prior research with the help of improved round-robin rules. However, the FCPAA cannot ensure the same social fairness among secondary users as the SFAF scheme in both the non-fading channel and Rayleigh fading channel; the SFAF balances the individual utility by adjusting each user’s budget at the expense of a small quantity of system total throughput.

Random Access Compressed Sensing over Fading and Noisy Communication Channels

Random Access Compressed Sensing (RACS) is an efficient method for data gathering from a network of distributed sensors with limited resources. RACS relies on integrating random sensing with the communication architecture, and achieves overall efficiency in terms of the energy per bit of information successfully delivered. To address realistic deployment conditions, we consider data gathering over a fading and noisy communication channel. We provide a framework for system design under various fading conditions, and quantify the bandwidth and energy requirements of RACS in fading. We show that for most practical values of the signal to noise ratio, energy utilization is higher in a fading channel than it is in a non-fading channel, while the minimum required bandwidth is lower. Finally, we demonstrate the savings in the overall energy and the bandwidth requirements of RACS compared to a conventional TDMA scheme. We show that considerable gains in energy -on the order of 10 dB- are achievable, as well as a reduction in the required bandwidth, e.g., 2.5-fold decrease in the bandwidth for a network of 4000 nodes.

The Effect of Correlated Observations on the Performance of Distributed Estimation

Estimating unknown signal in Wireless Sensor Networks (WSNs) requires sensor nodes to transmit their observations of the signal over a multiple access channel to a Fusion Center (FC). The FC uses the received observations, which is corrupted by observation noise and both channel fading and noise, to find the minimum Mean Square Error (MSE) estimate of the signal. In this paper, we investigate the effect of the source-node correlation (the correlation between sensor node observations and the source signal) and the inter-node correlation (the correlation between sensor node observations) on the performance of the Linear Minimum Mean Square Error (LMMSE) estimator for three correlation models in the presence of channel fading. First, we investigate the asymptotic behavior of the achieved distortion (i.e., MSE) resulting from both the observation and channel noise in a non-fading channel. Then, the effect of channel fading is considered and the corresponding distortion outage probability, the probability that the distortion exceeds a certain value, is found. By representing the distortion as a ratio of indefinite quadratic forms, a closed-form expression is derived for the outage probability that shows its dependency on the correlation. Finally, the new representation of the outage probability allows us to propose an iterative solution for the power allocation problem to minimize the outage probability under total and individual power constraints. Numerical simulations are provided to verify our analytic results.

Impact of fading channel on decision fusion in wireless sensor networks

Wireless channel of monitoring the outdoor environment is very complex,and gets impacted by many factors such as multipath fading and noise,which deteriorates awfully the quality of signal reception.Further research on fading channel is helpful for receiving better signal and improving system performance.The factors of impacting fading channel were analyzed in detail,and the transmitting performance with fading channel was researched.The impact of fading channel on the probability of system detection was simulated,and the multi-bit local decisions in decision fusion with fading channel were researched.The simulation results suggest that the probability of system detection is lower compared to non-fading channel,and the sensor transmitting a bit decision is optimal.

Recursive Detection of M-Ary Signals over Fast Varying Mobile Communication Channel

Mobile radio is characterized by a fast time varying channel. Conventional detectors which designed optimal for non-fading channel exhibit a limited performance in fast time varying channel. In this paper a recursive detector for M-ary signals over fast time varying mobile communication channel is introduced. The proposed detector continuously estimates the channel directly within the metric calculation of the log-likelihood function in a recursive manner. The estimation of the channel is performed by the covariance form of the recursive least square approach. The performance of the detector is evaluated in terms of the misdetection probability. The effects of timing and phase offsets on the performance of detector are examined by simulation. Simulation results show that the proposed detector can accommodate the fast time varying channel with adequate performance.

Error ratio model for synchronised‐OOK IR‐UWB receivers in AWGN channels

Synchronised On/Off keying (S-OOK) is a pulse modulation format where timing synchronisation pulses are embedded with each bit in the data stream resulting in a 1.5 pulse/bit format, but allowing for synchronisation and demodulation with a single block. In this reported work, the error ratio for S-OOK symbols received in a non-fading AWGN channel is analysed and a mathematical model aware of the physical parameters of a CMOS integrated prototype is introduced. Using this model, the S-OOK RX sensitivity is shown to be close to that of a high-threshold OOK RX for similar error-ratios but assuming perfect synchronisation.

On the Ergodic Achievable Rates of Spectrum Sharing Networks with Finite Backlogged Primary Users and an Interference Indicator Signal

Spectrum sharing networks are communication setups in which unlicensed secondary users (SUs) are permitted to work within the spectrum resources of licensed primary users (PUs). This paper aims to study the ergodic achievable rates of spectrum sharing networks with finite backlogged primary user and an interference indicator signal. Here, in contrast to the standard interference-avoiding schemes, the secondary user activity is not restricted within the primary user inactive periods. Considering both fading and nonfading channels, the unlicensed user ergodic achievable rate is obtained for different unlicensed user transmission power and licensed user received interference power or signal-to-interference-and-noise (SINR) constraints. In the case of fading channels, the results are obtained for both short- and long-term primary user quality-of-service requirements. Further, the results are generalized to the case of multiple interfering users. In terms of unlicensed user ergodic achievable rate, analytical results indicate that while the standard interference-avoiding approach is the optimal transmission scheme at low secondary user or high primary user transmission powers, higher rates can be achieved via simultaneous transmission at high secondary user SINRs. Moreover, numerical results show that, using an interference indicator signal, there is considerable potential for data transmission of unlicensed users under different licensed users quality-of-service requirements.

Adapting contention-based forwarding to urban vehicular topologies for active safety applications

Contention-based forwarding (CBF) is a broadcasting technique used to disseminate emergency messages for traffic safety applications in intelligent transportation systems. Its design hypotheses have however been based on three major assumptions: uniform vehicular topology, nonfading channels and homogeneous communication capabilities. Realistic vehicular urban topologies do not comply with any of them, making CBF select relays, which may not exist, may not be reached or may not be optimal due to heterogeneous transmit capabilities. In this paper, we propose to adapt CBF to such challenging environment by first employing two different mechanisms as a function of the topology and second by considering the dissemination capabilities of the relays, allowing for example road-side units or tall vehicles to preferably act as relays when necessary. Our protocol, called Bi-Zone Broadcast, is evaluated in a realistic urban environment and showed to provide around 46 % improvement in dissemination delay and 40 % reduction in overhead compared to plain CBF or flooding. We finally shed light to other aspects of CBF that remain unsolved and should be addressed in future work to further improve the reliability of dissemination protocols for traffic safety protocols.