Energy efficiency optimization of one-way and two-way DF relaying considering circuit power

In this paper, the energy efficiency (EE) of a decode and forward (DF) relay system is studied, where two sources communicate through a half-duplex relay node in one-way and two-way relaying strategies. Both the circuitry power and the transmission power of all nodes are taken into consideration. In addition, three different coding schemes for two-way DF relaying strategy with two phases and two-way DF relaying with three phases are considered. The aim is to maximize the EE of the system for a constant spectral efficiency (SE). For this purpose, the transmission time and the transmission power of each node are optimized. Simulations are used to compare the EE–SE curve of different DF strategies with one-way and two-way amplify and forward (AF) strategies and direct transmission (DT), to find the best energy efficient strategy in different SE conditions. Analytical and simulation results demonstrate that in low SE conditions, DF relaying strategies are more energy efficient compared to that of AF strategies and DT. However, in high SE conditions, the EE of two-way AF relaying and DT strategy outperform some of the DF relaying strategies. In simulations, the impact of different circuitry power and different channel conditions on the EE–SE curves are also investigated.     

An evolutionary game theory–based security model in vehicular ad hoc networks

The word population is growing on a daily basis; consequently, the growth of commute and transport, developing efficient and intelligent transportation systems (ITS), has become one of the most popular requirements and the most significant attempts in modern urban areas containing large population. A key component of intelligent transportation systems is a vehicular ad hoc network. Devising internet‐based practical programs such as awareness of climatic conditions, geographical location, practical programs like on‐line payment services in the vehicular ad hoc network has led to safer driving, prevention of deadly accidents, transportation improvement, more welfare and convenience for passengers, and even offering more commercial opportunities. The special features of vehicular ad hoc network, such as intense activity, constantly‐changing topology, the vehicles' high speed, etc, will lead to challenges in gaining security. Therefore, providing vehicular ad hoc networks with security is of extreme importance in terms of users' anonymity, identification, and data privacy. In this paper, a security model is presented using a method based on evolutionary games. This method, in every vehicle, is applied as a node in the network while interacting with other vehicles; it aims at distinguishing some common attacks and defending against attackers. In this method, defending (honest) vehicles and attacking vehicles take part in an asymmetrical game; each vehicle aims at gaining the most utility and achieving its goals. The proposed method is simulated using various scenarios. The simulation results reveal that the proposed method is efficient and it reaches equilibrium and convergence at the end of the game in each scenario.     

Multiple-antenna capacity in correlated Rayleigh fading with channel covariance information

We analyze a mobile multiple input multiple output wireless link with M transmit and N receive antennas operating in a spatially correlated Rayleigh flat fading environment. Only the correlations between the channel coefficients are assumed to be known at the transmitter and the receiver. The channel coefficients are correlated in space and uncorrelated in time from one coherence interval to another. These coefficients remain constant for a coherence interval of T symbol periods after which they change to another independent realization according to the spatial correlation model. For this system we characterize the structure of the input signal that achieves capacity. The capacity achieving transmit signal is expressed as the product of an isotropically distributed unitary matrix, an independent nonnegative diagonal matrix and a unitary matrix whose columns are the eigenvectors of the transmit fade covariance matrix. For the case where the number of transmit antennas M is larger than the channel coherence interval T, we show that the channel capacity is independent of the smallest M-T eigenvalues of the transmit fade covariance matrix. In contrast to the previously reported results for the spatially white fading model where adding more transmit antennas beyond the coherence interval length (M>T) does not increase capacity, we find that additional transmit antennas always increase capacity as long as their channel fading coefficients are spatially correlated with the other antennas. We show that for fast hopping or fast fading systems (T=1) with only channel covariance information available to the transmitter and receiver, transmit fade correlations are beneficial. Mathematically, we prove this by showing that capacity is a Schur-convex function of the vector of eigenvalues of the transmit fade correlation matrix. We also show that the maximum possible capacity gain due to transmitter fade correlations is 10logM dB.     

Design of a 12-bit high-speed CMOS D/A converter using a new 3D digital decoder structure useful for wireless transmitter applications

In this paper a 12-bit Nyquist current-steering digital-to-analog converter (DAC) is implemented using TSMC 0.35 μm standard CMOS process technology. The proposed DAC is an essential part in baseband section of wireless transmitter circuits. Using oversampling ratio (OSR) for it leads to avoid use of an active analog reconstruction filter. The optimum segmentation (75%) has been used to get the best DNL and reduce glitch energy. This segmentation ratio guarantees the monotonicity. Higher performance is achieved using a new 3D thermometer decoding method which reduces the area, power consumption and the number of control signals of the digital section. Using two digital channels in parallel, helps reach 1 GHz sampling frequency. Simulations indicate that the DAC has an accuracy better than 10.7-bit for upcoming higher data rate standards (IEEE 802.16 and 802.11n), and a spurious-free-dynamic-range (SFDR) higher than 64 dB in whole Nyquist frequency band. The post layout four corner Monte-Carlo simulated INL is better than 0.74 LSB while simulated DNL is better than 0.49 LSB. The analog voltage supply is 3.3 V while the digital part of the chip operates with only 2.4 V. Total power consumption in Nyquist rate measurement is 144.9 mW. Active area of chip is 1.37 mm².     

Modulation and Detection for Simple Receivers in Rapidly Time-Varying Channels

We investigate the performance degradation of basic modulation schemes in a rapidly time-varying channel using a first-order autoregressive channel model. Various performance metrics are used to indicate the relative advantages of each modulation scheme. We find that noncoherent frequency-shift keying (FSK) is suitable for operating at very high mobility and high signal-to-noise ratio, ideal for some military applications. We then propose a partially coherent detector for FSK and differential phase-shift keying that exploits partial channel knowledge to enable the receiver to operate effectively in both fast and slow fading. The maximum-likelihood rule obtained for the partially coherent FSK turns out to be a linear combination of coherent and noncoherent detection rules. Results demonstrate that significant performance improvement can be achieved over the best of coherent and noncoherent FSK detection. The detector is robust to estimation errors present in the channel statistics. We also propose a few adaptive schemes that employ various combinations of modulation schemes to increase the robustness of the system in fast fading     

Antioxidant Capacity and Phenolic Content of the Aqueous Extract of Commonly Consumed Cucurbits

The antioxidant capacity of commonly consumed cucurbits vegetable was determined by the DPPH, FRAP, Fe³⁺ reducing power, and hydrogen peroxide scavenging assay. The aqueous extract of Luffa cylindrica showed the highest value of phenolic content and antioxidant capacity based on FRAP, Fe³⁺ reducing power, and hydrogen peroxide scavenging assay. However, Laginaria siceraria extract showed the highest flavonoid and DPPH scavenging activities among all three cucurbits used in this study. Phenolic content in aqueous extracts of Luffa cylindrica and Laginaria siceraria was almost equal. Cucurbita maxima exhibited the lowest phenolic, flavonoid content, and exhibited the lowest power of antioxidant scavenging. The antioxidant capacity of cucurbits was significantly correlated (P < 0.05) with the phenolic content of their extracts. The antioxidant capacity of Luffa cylindrica and Laginaria siceraria have also shown a significant correlation (P < 0.05).     

Production of propionic acid in a fermented dairy beverage

A dairy beverage containing propionic acid was produced using the adjunct starter cultures with Lactobacillus acidophilus and Propionibacterium freudenreichii ssp. shermanii. The impacts of temperature (30, 35 and 40 °C) and inoculation ratio (1:2, 1:4 and 1:8) on propionic acid production and viability of micro‐organisms were studied. The incubation temperature had a significant adverse (P < 0.05) effect on the viability of P. freudenreichii and propionic acid production. Maximum amount of produced propionic acid (in 1:4–30 °C treatment) was 0.77%w/w. P. freudenreichii and L. acidophilus counts remained high (9 × 10⁶ and 1.5 × 10⁶ cfu/mL, respectively) after cold storage.