OFDM (Orthogonal Frequency Division Multiplexing) is a special kind of multi-carrier digital modulation technique. Each OFDM subcarrier exists orthogonality and great use of spectrum resources. To a certain extent, the problem of shortage of spectrum resources will be eased in the future. OFDM has a good ability to resist inter symbol interference and fight against frequency selective fading, and be able to adapt to the future wireless high-speed data transmission without distortion. Each channel modulation and demodulation with FFT and IFFT is easy to implement and meet the need of the business in the wireless communication system. The paper introduces the basic principle of OFDM technology, describes the advantages of OFDM and the defects needed to be overcome. Moreover, we analyzes the characteristics of 4G technology and discusses the application of OFDM in 4G mobile network.
Cathode samples of titanium-based nanodiamond field emission were prepared by electrophoresis dispersed solutions in different formulas. Observe the surface and structure of the coating by using metaloscope, microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD); Test the field emission characteristic after annealing; Analyze the relation between the samples’ light photos and the uniformity of coating; Discuss the mechanism of the improved field emission characteristic after annealing. Under the same conditions the surface uniformity of diamond coating prepared by isobutyl alcohol is best,it is the minimum threshold electric field emission, 5.5 V/μm, the current density can reach to 85μA/cm2 at the field of 15V/μm. Field emission characteristic and luminescence could be best after annealing.
A cathode process of nanodiamond field emission display based on diode structure by electrophoretic deposition has been explored. In this process, a certain proportion of nanodiamond electrophoresis liquid has been developed, the nanodiamond field emission cathode has been deposited on the polished metal titanium substrate by electrophoresis. The surface appearance and microstructures of the coating has been observed by scanning electron microscopy and Raman spectroscopy and the field emission properties of the prepared cathode coating has been tested. The experimental results show, the diamond-coated surface which has been deposited on titanium substrate is thin and uniform. Compared with the cathode prepared by the spin coating process, it has more field emission current density and better field emission current uniformity and stability. With a simple, low cost and large-area production and other advantages, it can be widely used in flat panel displays.
The test of nano-diamond cathode field emission characteristics was conducted by changing the vacuum, the influence of vacuum change on nano-diamond field emission characteristics was also explored. It was found that under the condition of low vacuum, nano-diamond field emission turn-on field is relatively high, as the vacuum increases, turn-on field decreases gradually, and current density increases. When system vacuum reaches to above 10-4Pa level, turn-on field becomes stable, the stable value is 4.5 V/μm; and current density also becomes stable, the stable value is 117 μA/cm2; the luminescence effect of anode which is 200μm distant from the cathode in the vacuum chamber also becomes stable. Results show that 10-4Pa is system vacuum limit parameter of stable working of field emission display, the experiment provides a basis to the design and manufacture of nano-diamond field emission display.
Carbon nanotube field emission display (CNT-FED) is one of the most significant subjects due to its unique qualities and perfect performance. But there are still some problems in FED, for example, the modulation of each pixel unit of field emission display device is discrete, and the traditional voltage pulse-width modulation driving mode cannot solve luminance non-uniformity and non-linearity of FED. So a novel driving circuit based on cathode current source is proposed. The current driving circuit can be fabricated on Si substrate in advance, and then carbon nanotube is grown at room temperature, carbon nanotube and constant current source circuits are integrated on the same Si substrate. Current source circuit and cathode emission part are integrated together, which not only can solve the FED luminance problem, but also can meet FED thin design.
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