Maximin SNR beamforming strategies for two-way relay channels

In this letter, we consider beamforming strategies in amplified-and-forward (AF) two-way relay channels, where two terminals and the relay are equipped with multiple antennas. Our aim is to optimize the worse end-to-end signal-to-noise ratio of the two links so that the reliability of both terminals can be guaranteed. We show that the optimization problem can be recast as a generalized fractional programing and be solved by using the Dinkelbach-type procedure combined with semidefinite programming. Simulation results confirm the efficiency of the proposed strategies.

Power allocation strategies for distributed space-time codes in two-way relay networks

We study a two-way relay network (TWRN), where distributed space-time codes are constructed across multiple relay terminals in an amplify-and-forward mode. Each relay transmits a scaled linear combination of its received symbols and their conjugates,with the scaling factor chosen based on automatic gain control. We consider equal power allocation (EPA) across the relays, as well as the optimal power allocation (OPA) strategy given access to instantaneous channel state information (CSI). For EPA, we derive an upper bound on the pairwise-error-probability (PEP), from which we prove that full diversity is achieved in TWRNs. This result is in contrast to one-way relay networks, in which case a maximum diversity order of only unity can be obtained. When instantaneous CSI is available at the relays, we show that the OPA which minimizes the conditional PEP of the worse link can be cast as a generalized linear fractional program, which can be solved efficiently using the Dinkelback-type procedure.We also prove that, if the sum-power of the relay terminals is constrained, then the OPA will activate at most two relays.

Impact of I/Q imbalance on the performance of two-way CSI-assisted AF relaying

In this paper, we investigate half-duplex two-way dual-hop channel state information (CSI)-assisted amplify-and-forward (AF) relaying in the presence of in-phase and quadrature-phase (I/Q) imbalance. A compensation approach for the I/Q imbalance is proposed, which employs the received signals together with their conjugations to detect the desired signal. We also derive the average symbol error probability of the considered half-duplex two-way dual-hop CSI-assisted AF relaying networks with and without compensation for I/Q imbalance in Rayleigh fading channels. Numerical results are provided and show that the proposed compensation method mitigates the impact of I/Q imbalance to a certain extent.

Two-way communication costs and the boundaries of the firm

Casson and Wadeson (International Journal of the Economics of Business, 1998, 5, pp. 5-27) have modelled the dialogue, or conversation, which customers have with their suppliers in order to convey their requirements, while taking production implications into account. They showed that this has important implications for the positioning of the boundaries of the firm. Unfortunately, their model has the restriction that communication is only costly in the direction of customer to supplier. This paper extends their model by introducing two-way communication costs. It shows that the level of communication cost in the direction of supplier to customer is a key additional factor in determining the nature of the dialogue that takes place. It also shows that this has important additional implications for the positioning of the boundaries of the firm. Custom computer software development is used as an example of an application of the theory.

Two-way CSI-assisted AF relaying with HPA nonlinearity

In this paper, we investigate half-duplex two-way dual-hop channel state information (CSI)-assisted amplify-and-forward (AF) relaying in the presence of high-power amplifier (HPA) nonlinearity at relays. The expression for the end-to-end signal-to-noise ratio (SNR) is derived as per the modified system model by taking into account the interference caused by relaying scheme and HPA nonlinearity. The system performance of the considered relaying network is evaluated in terms of average symbol error probability (SEP) in Nakagami-$m$ fading channels, by making use of the moment-generating function (MGF) approach. Numerical results are provided and show the effects of several parameters, such as quadrature amplitude modulation (QAM) order, number of relays, HPA parameters, and Nakagami parameter, on performance.

Firms’ exporting and importing activities: is there a two-way relationship?

The literature on firm heterogeneity and trade has highlighted that most trading firms tend to engage in both importing and exporting activities. This paper provides some evidence that helps understanding to what extent this is the result of a two-way relationship. Using firm-level data for a group of 27 Eastern European and Central Asian countries from the World Bank Business Environment and Enterprise Performance Survey (BEEPS) over the period 2002–2008, we estimate a bivariate probit model of exporting and importing. After controlling for size (and other firm-level characteristics) we find that firms’ exporting activity does not increase the probability of importing, while the latter has a positive effect on foreign sales. This effect is mainly channeled through an increase in firm productivity and product innovation.

Heritability estimation in early generations of two-way crosses in soybean

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Two-way regionalized classification of multivariate datasets and its application to the assessment of hydrodynamic dispersion

Zones of mixing between shallow groundwaters of different composition were unravelled by two-way regionalized classification, a technique based on correspondence analysis (CA), cluster analysis (ClA) and discriminant analysis (DA), aided by gridding, map-overlay and contouring tools. The shallow groundwaters are from a granitoid plutonite in the Funda o region (central Portugal). Correspondence analysis detected three natural clusters in the working dataset: 1, weathering; 2, domestic effluents; 3, fertilizers. Cluster analysis set an alternative distribution of the samples by the three clusters. Group memberships obtained by correspondence analysis and by cluster analysis were optimized by discriminant analysis, gridded memberships as follows: codes 1, 2 or 3 were used when classification by correspondence analysis and cluster analysis produced the same results; code 0 when the grid node was first assigned to cluster 1 and then to cluster 2 or vice versa (mixing between weathering and effluents); code 4 in the other cases (mixing between agriculture and the other influences). Code-3 areas were systematically surrounded by code-4 areas, an observation attributed to hydrodynamic dispersion. Accordingly, the extent of code-4 areas in two orthogonal directions was assumed proportional to the longitudinal and transverse dispersivities of local soils. The results (0.7-16.8 and 0.4-4.3 m, respectively) are acceptable at the macroscopic scale. The ratios between longitudinal and transverse dispersivities (1.2-11.1) are also in agreement with results obtained by other studies.

Two-Way Selection for Daily Gain and Feed Conversion in a Composite Rabbit Population

We conducted a two-way selection experiment in a composite rabbit population to investigate the responses to selection for postweaning ADG and feed conversion (FC). Two generations of crossing, followed by four generations of random pair matings, preceded three generations of selection. Selection was practiced within four lines: high-feed conversion (HFC), low-feed conversion (LFC), high gain (HG), and low gain (LG). Data on 1,446 rabbits from the random mating and selection generations were fitted to an animal model to estimate heritabilities of and the genetic correlation between ADG and FC. The two-trait model included rabbit and common litter random effects and line, generation, and sex fixed effects. Estimates of heritability of ADG and FC were .48 and .29, respectively, and the genetic correlation between them was -.82. Common litter environmental effects accounted for a proportion of .11 and . 13 of the phenotypic variation of the two traits, respectively. For ADG (in g/d) the regressions of mean breeding values on generation number during the selection period were 1.23 ± .12 (P < .01) in the HG line and -.86 ± .12 (P < .01) in the LG line; the regressions for FC (in g feed/g gain) were -.07 ± .01 (P < .01) in the HFC line and .03 ± .01 (P < .05) in the LFC line. Selection for ADG was effective in improving ADG and FC.

(Table 1) Two-way travel times and depths of picked internal reflection horizons (IRHs) of the NGRIP ice core

During the summer of 2003, a ground-penetrating radar survey around the North Greenland Icecore Project (NorthGRIP) deep ice-core drilling site (75°06' N, 42°20' W; 2957 m a.s.l.) was carried out using a shielded 250 MHz radar system. The drill site is located on an ice divide, roughly 300 km north-northwest of the summit of the Greenland ice sheet. More than 430 km of profiles were measured, covering a 10 km by 10 km area, with a grid centered on the drilling location, and eight profiles extending beyond this grid. Seven internal horizons within the upper 120 m of the ice sheet were continuously tracked, containing the last 400 years of accumulation history. Based on the age-depth and density-depth distribution of the deep core, the internal layers have been dated and the regional and temporal distribution of accumulation rate in the vicinity of NorthGRIP has been derived. The distribution of accumulation shows a relatively smoothly increasing trend from east to west from 145 kg/m**2/a to 200 kg/m**2/a over a distance of 50 km across the ice divide. The general trend is overlain by small-scale variations on the order of 2.5 kg/m**2/a/km, i.e. around 1.5% of the accumulation mean. The temporal variations of the seven periods defined by the seven tracked isochrones are on the order of +-4% of the mean of the last 400 years, i.e. at NorthGRIP ±7 kg/m**2/a. If the regional accumulation pattern has been stable for the last several thousand years during the Holocene, and ice flow has been comparable to today, advective effects along the particle trajectory upstream of NorthGRIP do not have a significant effect on the interpretation of climatically induced changes in accumulation rates derived from the deep ice core over the last 10 kyr.

Ages and two-way travel times of ODP Sites 180-1109, 180-1115 and 180-1118

Synthetic seismograms are constructed from check shot-corrected velocity and density measurements collected during Ocean Drilling Program (ODP) Leg 180 at Sites 1109, 1115, and 1118. The synthetic seismograms facilitate direct correlation of a coincident multichannel seismic (MCS) profile with borehole data collected at the three sites. The MCS data and the synthetic seismograms correlate very well, with most major reflectors successfully reproduced in the synthetics. Our results enable a direct calibration of the MCS data in terms of age, paleoenvironment, and subsidence history. Seismic reflectors are time correlative within stratigraphic resolution but are often observed to result from different lithologies across strike. Our results facilitate the extrapolation of the sedimentation history into an unsampled section of Site 1118 and enable a full correlation between the three sites using all the data collected during ODP Leg 180. This study forms the foundation for regionalizing the site data to the northern margin of the Woodlark Basin, where the transition from continental rifting to seafloor spreading is taking place.