Beamforming problem is studied in wireless networks where both transmitters and receivers have linear adaptive antenna arrays. Algorithms are proposed that find antenna array weight vectors at both transmitters and receivers as well as the transmitter powers with one of the following two objectives: 1) to maximize the minimum signal-to-interference-and-noise ratio (SINR) over all receivers and 2) to minimize the sum of the total transmitted power satisfying the SINR requirements at all links. Numerical study is performed to compare the network capacity and the power consumption among systems having different number of antenna array elements in a code division multiple access network. Index Terms-Adaptive antenna arrays, adaptive beamforming, joint transmit and receive beamforming, power control.

Articles you may be interested inImproving the binding efficiency of quartz crystal microbalance biosensors by applying the electrothermal effect Biomicrofluidics 8, 054116 (2014); 10.1063/1.4898633 Effects of charge screening and surface properties on signal transduction in field effect nanowire biosensorsSimulation on binding efficiency of immunoassay for a biosensor with applying electrothermal effect J. Appl. Phys.

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The working principle of immunoassays is based on the specific binding reaction of an analyte-ligand protein pair in physiological environments. However, for a diffusion-limited protein, the diffusion boundary layer of the analyte on the reaction surface of a biosensor would hinder the binding reaction from association and dissociation. The formation of such association and dissociation layers thus limits the response time and the overall performance of a biosensor. In this work we have performed a two-dimensional full time scale finite element simulation on the binding reaction kinetics of two commonly used proteins, C-reactive protein ͑CRP͒ and immunoglobulin G ͑IgG͒. By applying a nonuniform ac electric field to the flow microchannel of the biosensor, the electrothermal force can be generated to induce a pair of vortices to stir the flow field. With the aid of the vortices and a suitable choice of the location of the biosensor, the fluids flowing over the reacting surface can be accelerated fast enough to depress efficiently the growth of the diffusion boundary layer on the reaction surface, and enhance the association or dissociation of analyte-ligand complex. The interference patterns of the flow field due to the existence of the sensor at different locations of the microchannel could cause different degrees of enhancement to the association and the dissociation. By changing the location of the sensor the largest enhancement is found at the position near the negative electrode. For the configuration of the microchannel we studied, the initial slope of the curve of the analyte-ligand complex versus time can be raised up to 5.17 for CRP and 1.93 for IgG in association, and 3.74 for CRP and 1.28 for IgG in dissociation, respectively, under the applied ac field 15 V rms peak-to-peak and operating frequency 100 kHz. At this optimal sensor location, we also studied the effect of various settings of temperature boundary conditions on the top and bottom walls, including the two limiting cases, namely, constant temperature and thermal insulation on both walls. We show that varying the temperature boundary conditions can cause an essential effect on the enhancement of the binding reaction and can be employed to find an optimal binding enhancement. Utilizing these simulation results, an improved design incorporating a pair of electrodes and a neck region near the reaction surface is demonstrated. The sensor is fixed to locate at the middle of the bottom side. With the existence of the stirring flow field, the association rate of the 30 m neck is 2.73 times faster than that of the original channel with no neck.

Specific binding reaction is a natural characteristic that is applied to design biosensors. This work simulates the binding reaction kinetics of two commonly used proteins, C-reactive protein and immunoglobulin G, in a reaction chamber ͑microchannel͒ of a biosensor. For a diffusion-limited protein, the diffusion boundary layer on the reaction surface of the biosensor would hinder the binding reaction from association and dissociation. Several crucial factors, which influence the binding reaction curves in the simulation, are discussed, including the concentration of analyte, the inlet flow velocity, the channel height, and the length of the reaction surface. A higher channel causes the diffusive transport of the analyte to take longer time to reach the reaction surface, which in turn decreases the reaction rate of the protein pairs. The length of the reaction surface plays an important role in the formation of the boundary layer. For longer reaction surface, it takes more time to allow diffusion to overcome the larger zone of the diffusion boundary layer, resulting in a slower binding rate and a longer time to reach saturation. The presented data of simulation are useful in designing the biosensors.

Long-term RBC transfusions can induce PLT alloimmunization, both to HLA antigens and to PLT-specific antigens. The residual PLTs and white blood cells in RBC components could be the sources of immunization. In our thalassemia patients, HLA antibodies likely sustain longer than PLT-specific antibodies.

Biochemical applications of microchips often require a rapid mixing of different fluid samples. At the microscale level, fluid flow is usually a highly ordered laminar flow and diffusion is the primary mechanism for mixing owing to the lack of disturbances, yielding inefficiency for practical biochemical analysis. In this work, we design a prototype active micromixer by employing the electrothermal effect. We apply to the flow microchannel a non-uniform AC electric field, which can generate an electrothermal force on the fluid flow and induce vortex pairs for enhancing mixing efficiency. The performance of this active micromixer is studied and compared, under the same mixing quality, with that of a conventional passive micromixer of the same size with obstacles in the flow channel by three-dimensional finite element simulations. The numerical results show that the pressure drop between the inlet and the outlet for the active micromixer is much less than (only 3000th) that for the passive micro-mixer with the same mixing quality. To obtain an optimal mixing quality, we have systematically studied the mixing quality by varying the geometrical arrangements of the electrodes. An almost complete mixing can be obtained using a specific design. Moreover, the temperature increases around the electrodes are lower than 3 K, which does not adversely affect the biochemical analysis. It is suggested that the prototype active micromixer designed is promising and effective and useful for biochemical analysis.

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