Dual Branch Research Articles

Linear Diversity Combining on Nakagami-0.5 Fading Channels

The Nakagami-0.5 distribution is an important special case of the Nakagami distribution as it represents a worst case fading scenario. This scenario is of particular significance for wireless applications with high quality of service requirements. The bit error probability (BEP) performances of three basic diversity combining schemes in Nakagami-0.5 fading are considered. It is shown that the error rate performances of dual branch equal gain and selection combining (SC) diversity are identical regardless of modulation format. It is also shown that L-branch maximal ratio combining diversity in Nakagami-0.5 fading has the same BEP performance as single branch reception in Nakagami-L/2 fading with L times the transmission power of each branch. A useful upper bound for the BEP of L-branch SC diversity in Nakagami-0.5 fading is also derived. The performance degradation for the worst case Nakagami-0.5 fading relative to Rayleigh fading can be as much as 24.6 dB for a dual-diversity receiver at target BEP of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> . The additional resources required to restore a specified performance level, as increased channel signal-to-noise ratio and as number of additional diversity branches, are quantified. It is concluded that worst case Nakagami channels can result in dramatically poorer performance than Rayleigh channels, making proper system design and evaluation essential to achieve a required transmission quality.

Influence of imperfect cophasing on performance of EGC receiver of BPSK and QPSK signals transmitted over Weibull fading channel

This paper presents an analysis of maximum ratio combining (MRC) receiver of quaternary phase-shift keying (QPSK) signals transmitted over a Weibull fading channel. We determine the influence of imperfect cophasing and branches unbalance on bit error rate dependence on average signal-to-noise ratio. The performance dependence on diversity order and fading severity is also observed. Keywords — Cophasing, Diversity systems, Error probability, Fading. I. INTRODUCTION N order to reduce the influence of multipath fading on signal detection, it is possible to use spatially separated receiver antennas at the reception and to combine the signals from different branches of the receiver in a certain manner. The optimal combining technique is maximum ratio combining (MRC). This combining technique involves cophasing of the useful signal in all branches, multiplication of the received signal in each branch by the estimated envelope of that particular signal and summing of the received signals from all antennas (1). By cophasing, all the random phase fluctuations of the signal that emerged during the transmission are eliminated. For this process it is necessary to estimate the phase of the received signal. This phase estimation can be performed from the modulated or unmodulated received signal carrier. In previous papers concerning this matter the assumptions of the ideal phase estimation of the incoming signal were mainly used (2), (3). Only in (4) and (5) the influence of the imperfect phase estimation was examined and that was in the case of the equal gain combining (EGC) in the receiver. In paper (4), the influence of the phase error on the error probability in the case of digital binary (BPSK) and quaternary phase-shift keying (QPSK) signal detection was observed. This error probability was calculated applying the Gram-Charlier expansion. The analysis is performed under the assumption of the uncorrelated Rayleigh fading at receiving antennas. In paper (5) closed-form expressions for outage probability and error probability during the BPSK and QPSK signal detection over the Nakagami-m fading channel were obtained. Dual branch EGC technique was applied. In both papers the analysis of the system was done under the assumption that the branches of the receiver are balanced. However, as it is well-known (6), it is very rare to meet in practice the identical propagation paths in each branch. Also, the electrical components in different branches of the receiver are not ideal. Thus, it is also of interest to consider the influence of the branch unbalance in the receiver on system performances. In this paper an analysis of QPSK signal reception is presented. The signal is transmitted over the Weibull fading channel and MRC technique is applied in the receiver, while the receiving branches are assumed unbalanced. The phase estimation is performed from the unmodulated carrier and is not ideal. The difference between the phase of the incoming signal and the estimated phase for that signal is a statistical process and it follows the Tikhonov distribution (4), (5), (7). It is shown in which measure the imperfect phase estimation affects the bit-error rate (BER).

Planar Inverted-L Antenna for Octa-Band Operations of Smart Handsets

This paper applies inverted-L antenna (ILA) to design a smart handset antenna in accordance with octa-band operations, as GSM 850 (824–894 MHz), GSM 900 (880–960 MHz), GSM 1800/1900, DCS 1800 (1710–1880 MHz), PCS 1900 (1850–1990 MHz), UMTS (1920–2170 MHz), IEEE 802.11b WLAN (2400–2484 MHz) and LTE (1700 MHz/2300 MHz/2600 MHz) band operations for S 11 ≦ −10 dB. The entire antenna is 70 mm × 24 mm with one-quarter wavelength design of hub. With the inter-coupling between dual branch circuit radiation and multiple branch circuit radiation, the wideband for GSM 1800/1900, DCS, PCS, UMTS, IEEE 802.11b WLAN and LTE 1700/2300/2600 is generated. When integrating with mobiles, the designed ground plane area is also taken into consideration. In this case, the ground plane area can be increased in accordance to the system motherboard. The enlarged antenna size therefore becomes 9 mm × 42 mm that the ground plane area does not affect the bandwidth and can enhance the impedance matching. Consequently, the mobile antenna can not only reduce or increase the size to match up the products, but also be designed for tablet computers because it covers octa-band operations of smart handsets.

Performance of Dual Branch SSC Receiver in Correlated α-μ Fading Channels

In this paper, the performance analysis of dual branch switch and stay combining (SSC) receivers operating over correlated and identically distributed (i.d.) ?-μ fading channels is presented. Assuming this diversity technique, infinite series expressions with fast converging properties are derived for the probability density function (pdf), cumulative distribution function (cdf) and the moments of the output envelope. The proposed analysis is used for evaluating the important performance criteria, such as the outage probability, the mean square output envelope, the amount of fading and the average bit error probability (ABEP). The effects of fading severity, branch correlation and optimum choice of switching threshold are considered and numerically presented. Monte Carlo simulations confirm the validity and accuracy of the derived analytical expressions.

On the Effect of Correlation on the Performance of Dual Diversity Receivers in Lognormal Fading

The bivariate lognormal distribution has been extensively utilized for modeling the fading gains of dual branch diversity receivers in both indoor and outdoor communication systems. The contribution of this letter is twofold: firstly, a general expression for the average bit-error probability (BEP) of diversity combining with two correlated lognormal fading branches is presented, based on a Gauss-Hermite sum approximation to the moment generating function. Secondly, using the proposed expression, it is shown that correlation can be viewed as an increase in the standard deviations of an equivalent diversity system with uncorrelated lognormal fading gains.

Cochannel interference effect on BEP performance of SSC receiver in correlated Rician fading

Abstract We study the performance of dual branch switch and stay combining (SSC) diversity receivers operating over correlated Rician fading channels, in the presence of correlated Rayleigh distributed cochannel interference (CCI). Fast convergent infinite series representations for both the joint probability density function (PDF) of the SSC input signal-to-interference ratios (SIRs) and the PDF of the SSC output SIR are derived. The last one is applied to semi-analytically study the average bit error probability (ABEP) of differential binary phase shift keying (DBPSK). Furthermore, the optimum switching threshold in the sense of minimum ABEP is obtained numerically and the effects of fading severity and branch correlation on both ABEP and optimum switching threshold are investigated. Numerical and simulation results are presented to support the mathematical analysis.

A compact dual band branch line coupler with arbitrary power division ratio

This article presents a compact dual-band (DB) branch line coupler (BLC) with different power division ratio at arbitrary two frequency bands. In this article, we add a technique to satisfy transmission lines of conventional BLC with different impedance at two bands, while they are transformed to π-type equivalent circuits. The design equations for DB BLC with different coupling coefficients at two bands are given. Furthermore, folded shape of shunt lines make about 77% circuit dimension comparing to conventional single-band BLC. A DB BLC operating different power division ratio at 0.9 and 2.0 GHz is demonstrated in excellent agreement with both circuit simulation and experimental results. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1476–1480, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25258

Switching rates of two-branch selection diversity in correlated Doppler fading

The switching rate of a correlated dual branch selection diversity combiner in Rayleigh and Rician fading is derived in noise-free conditions. Balanced and unbalanced branches are considered. Numerical results are presented for a space-diversity system with horizontally spaced omnidirectional antennas at a mobile station.

Switching rates of dual selection diversity in noisy fading channels

The effect of noise on the switching rate of a dual branch selection diversity combiner in noisy fading channels is examined. A closed-form solution is derived for independent and identically distributed (i.i.d.) and independent and nonidentically distributed (i.n.d.) fading channels. The switching rate in noisy fading channels is compared to that in noise-free conditions.

Switching rates of two-branch selection diversity in κ-μ and α-μ distributed fadings

An analytical expression for the switching rate of a dual branch selection diversity combiner in kappa-mu and alpha-mu distributed fadings is derived. Independent and identically distributed (i.i.d.) kappa-mu as well as alpha-mu fading channels are considered. The switching rates for dual i.i.d. Rayleigh, Rician and Nakagami-m fading channels are special cases of the switching rate for dual i.i.d. kappa-mu fading channels. Similarly, the general switching rates for dual alpha-mu fading channels also include special cases such as Rayleigh, Nakagami-m, and Weibull fading channels.

Characterization and modeling of on-body spatial diversity within indoor environments at 868 MHz

For the first time in the open literature we present a full characterization of the performance of receiver diversity for the on-body channels found in body area networks. The study involved three commonly encountered diversity combining schemes: selection combination (SC), maximal ratio combining (MRC) and equal gain combining (EGC). Measurements were conducted for both stationary and mobile user scenarios in an anechoic chamber and open office area environment. Achievable diversity gain for various on-body dual branch diversity receivers, consisting of horizontal and vertical spatially separated antennas, was found to be dependent upon transmitter-receive array separation, user state and level of multipath contribution from the local environment. The maximum diversity gain (6.4 dB) was observed for a horizontal two branch MRC combiner while the transmitter and receiver were on opposite sides of the body, and the user was mobile in the open office area. A novel statistical characterization of the fading experienced in on-body diversity channels is also performed using purposely derived first and second order diversity statistics for combiners operating in Nakagami fading.

Enabling dual branch switched diversity in compact wireless devices

Dual branch switched diversity in compact wireless devices is considered. A simple technique for protecting a compact device from diversity loss incurred by antennas proximity is proposed. The technique is based on implementing the Karhunen-Loeve transform prior to down-conversion to baseband. The implementation reduces to constant and straightforward summation and subtraction of the two antennas RF outputs, and there is no need for channel estimation or additional operational complexity. It is shown that the proposed implementation protects the system from diversity loss by reducing outage probabilities, increasing the average SNR, and drastically lowering the mean switching rate. Implementation of the Karhunen-Loeve transform is achieved using a single RF combiner component located prior to the RF switch.

The Shiftable Complex Directional Pyramid—Part II: Implementation and Applications

In Part I ["The shiftable complex directional pyramid-Part I: Theoretical Aspects," IEEE TRANSACTIONS on Signal Processing, vol. 56, no. 10, October 2008], we proposed a novel image decomposition called the shiftable complex directional pyramid. The shiftable, multiresolution and multidirectional image decomposition is constructed by the pyramidal dual-tree directional filter bank (PDTDFB). In this Part II, we consider the design and implementation issues of the PDTDFB and its applications in image processing. The PDTDFB is composed of a multiresolution filter bank (FB) and a pair of directional filter banks (DFB); the design of each FB is considered separately. The binary tree structure of the DFB is modified to minimize the phase delay factor in order to reduce the border artifact in case symmetric extension is used. The filters presented in this paper are designed in frequency domain, and approximated by finite-impulse-response (FIR) filters. Numerical experiments show that the filters from the dual branches approximate the Hilbert transform of those from the primal ones, and the resulting PDTDFB yields acceptable shiftability. The shiftable pyramid decomposition is then tested in image processing applications, including image denoising, texture retrieval and seismic image migration.

Steady thermal regimes of a parallel-plane packed bed reactor with an organized structure

Abstract The steady conduction regime of exothermic chemical reactions in a packed bed reactor is investigated analytically. A plane-parallel stratification of the reactive granular material is assumed which modulates the rate of the local volumetric heat generation in the reactor. The approach is based on an exactly solvable nonlinear mathematical model which involves two experimentally accessible control parameters, the intensity parameter λ > 0 and stratification parameter s ≥ 0, respectively. In terms of these parameters, the existence domain of the steady temperature solutions and the occurrence of hot spots are discussed. For a given value of the stratification parameter, an upper bound λ max ( s ) of the intensity parameter has been found, such that above of this maximum value of λ the reactor becomes thermally uncontrollable. Below λ max ( s ), unique as well as dual solutions exist. The former ones describe high temperature steady states of the reactor, while the dual solution branches are associated with low and high temperature reaction regimes, respectively. The features of the corresponding temperature distributions are examined in detail.

Voter models with heterozygosity selection

This paper studies variations of the usual voter model that favor types that are locally less common. Such models are dual to certain systems of branching annihilating random walks that are parity preserving. For both the voter models and their dual branching annihilating systems we determine all homogeneous invariant laws, and we study convergence to these laws started from other initial laws.

On the Correlated $K$-Distribution With Arbitrary Fading Parameters

The correlated bivariate K-distribution with arbitrary and not necessarily identical parameters is introduced and analyzed. Novel infinite series expressions for the joint probability density function and moments are derived for the general case where the associated bivariate distributions, i.e., Rayleigh and gamma, are both arbitrary correlated. These expressions generalize previously known analytical results obtained for identical parameter cases. Furthermore, considering independent gamma distributions, the cumulative distribution and characteristic functions are analytically obtained. Although the derived expressions can be used in a wide range of applications, this letter focuses on the performance analysis of dual branch diversity receivers. Specifically, the outage performance of dual selection diversity receivers operating over correlated K fading/shadowing channels is analytically evaluated. Moreover, for low normalized outage threshold values, closed-form expressions are obtained.

3D Anatomical Variations of Hepatic Vasculature and Bile Duct for Right Lateral Sector of Liver with Special Reference to Transplantation

To achieve a safer living related liver transplantation (LRLT) using the right lateral sector, anatomical variations of the portal vein, hepatic artery and bile duct for the right lateral sector and their three dimentional (3D) relationship were assessed by integrated 3D-CT images. 52 patients who underwent contrast enhanced multi-detector row CT (MD-CT) and MD-CT cholangiography were enrolled. Data from contrast enhanced MD-CT were used to reconstruct the 3D images of the hepatic artery and portal vein. 3D images reconstructed from MD-CT data of the hepatic artery, portal vein and bile duct were integrated into a single image. The dual branching of the right lateral portal vein was observed in 22 (42.3%) patients. Three (5.8%) had dual right lateral ducts and 14 (26.9%) had dual right lateral arteries. Among them, "south-turning" artery and "north-turning" bile duct was observed in 22 (42.3%). "South-turning" artery and "south-turning" bile duct were 3 (5.8%). "North-turning" artery and "north-turning" bile duct were 2 (7.4%). Only 27 (51.9%) had single portal vein, bile duct and artery for the right lateral sector, those were preferable as candidates for right lateral sector graft transplantation. 3D anatomical variations of portal vein, artery and bile duct for the right lateral sector were complexed, and only half of the donor candidates had preferable hepatic structures for right lateral sector graft transplantation. Understanding of the 3D hepatic structures by 3D-CT may contribute to a better definition of anatomical contraindications for LRLT which may further results in more safe and widely applied right lateral sector graft LRLT.

Average LCR and AFD for SC Diversity Over Correlated Weibull Fading Channels

The analytic methods of average LCR (Level Crossing Rate) and AFD (Average Fading Duration) are applied in the analysis for the SC (Selection Combining) diversity, which works over the correlated Weibull statistics channel. The dual branch SC diversity was used to prove the accuracy of the derived theoretical formula in this paper. We adopt different probability density functions (pdf) and cumulate distribution functions (CDF) to show the Moreover, the numerical results obtained from computer are verified to the published researches.

A Self-Biased Receiver System Using the Active Integrated Antenna

A simple self-biased receiver system with a dual branch architecture consisting of a low-power consumption receiver and a rectenna is introduced. The system is efficiently integrated with a dual-fed circular sector antenna with harmonic rejection characteristics without a BPF. The receiver portion is designed by utilizing a low-noise amplifier (LNA) with low power consumption and a self-heterodyne mixer, while the rectenna achieves high conversion efficiency up to 80%, thanks to the harmonic rejection of the circular sector antenna. The rectified DC power from the rectenna is applied for a bias of the receiver without any external bias. Simultaneously, an ASK digital signal demodulation without an extra power supply are implemented successfully.

Rational War and Constitutional Design

Contemporary accounts of the allocation of war powers authority often focus on textual or historical debates as to whether the President or Congress holds the power to initiate military hostilities. In this Essay, we move beyond such debates and instead pursue a purely functional or comparative institutional analysis of the relationship between Congress and the President on war powers. More specifically, we focus on the following question: Which war powers system would best enhance the effectiveness of the United States in making decisions on war and peace? Our answer draws on one of the few facts considered to be close to an empirical truth in international relations: democracies do not tend to go to war with each other. First, we articulate and evaluate the various arguments that underpin the democratic peace literature and analyze their relationship to the United States constitutional structure of war powers. Second, we distinguish between two types of constitutional processes that would be most necessary for successfully combating different regimes. We argue that if the United States were involved in a dispute with another democracy, the President ought to involve Congress because a dual branch process would help facilitate a peaceful resolution to the dispute by allowing the United States to signal more effectively its intentions. If, however, the United States were involved in a dispute with a non-democracy or a terrorist organization, a unilateral presidential approach might make much more sense because a non-democratic regime or terrorist organization is unlikely to appreciate the value of congressional participation. Finally, we conclude with the observation that in the war powers debate, only an approach that gives the President the complete flexibility to seek congressional participation would permit the United States to adapt its domestic decision making structure to the exogenous demands of the international system.