Xem 1-20 trên 50 kết quả Frequency bands
  • Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Research Article Demosaicking Based on Optimization and Projection in Different Frequency Bands

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  • Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Research Article Flexible Frequency-Band Reallocation Networks Using Variable Oversampled Complex-Modulated Filter Banks

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  • Handbook covers the latest advances in satellite technology and applications. Features new chapters on mobile digital audio radio and VSAT networks. For satellite communications professionals and network architects. Includes index and references. Let 's see with us.

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  • Nowadays, when we speak of GSM, we usually mean ªoriginalº GSM ± also known as GSM900 since 900 MHz was the original frequency band. To provide additional capacity and enable higher subscriber densities, two other systems were added later: GSM1800 (also DCS1800) and GSM1900 (also PCS 900).

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  • FILTER DESIGN A circuit designer frequently requires ®lters to extract the desired frequency spectrum from a wide variety of electrical signals. If a circuit passes all signals from dc through a frequency oc but stops the rest of the spectrum, then it is known as a low-pass ®lter. The frequency oc is called its cutoff frequency. Conversely, a high-pass ®lter stops all signals up to oc and passes those at higher frequencies. If a circuit passes only a ®nite frequency band that does not include zero (dc) and in®nite frequency, then it is called a band-pass ®lter.

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  • In keeping with the objectives of the previous editions, the third edition is intended to provide broad coverage of satellite communications systems, while maintaining sufficient depth to lay the foundations for more advanced studies. Mathematics is used as a tool to illustrate physical situations and obtain quantitative results, but lengthy mathematical derivations are avoided. Numerical problems and examples can be worked out using a good calculator or any of the excellent mathematical computer packages readily available.

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  • IMPEDANCE TRANSFORMERS In the preceding chapter, several techniques were considered to match a given load impedance at a ®xed frequency. These techniques included transmission line stubs as well as lumped elements. Note that lumped-element circuits may not be practical at higher frequencies. Further, it may be necessary in certain cases to keep the re¯ection coef®cient below a speci®ed value over a given frequency band. This chapter presents transmission line impedance transformers that can meet such requirements....

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  • What is a filter? A filter is a device that passes electric signals at certain frequencies or frequency ranges while preventing the passage of others. — Webster. Filter circuits are used in a wide variety of applications. In the field of telecommunication, band-pass filters are used in the audio frequency range (0 kHz to 20 kHz) for modems and speech processing. High-frequency band-pass filters (several hundred MHz) are used for channel selection in telephone central offices.

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  • TWO-PORT NETWORKS Electronic circuits are frequently needed for processing a given electrical signal to extract the desired information or characteristics. This includes boosting the strength of a weak signal or ®ltering out certain frequency bands and so forth. Most of these circuits can be modeled as a black box that contains a linear network comprising resistors, inductors, capacitors, and dependent sources. Thus, it may include electronic devices but not the independent sources. Further, it has four terminals, two for input and the other two for output of the signal....

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  • Who Needs 4G? What is 4G? Social Background and Future Trends There has been an evolutionary change in mobile communication systems every decade. The increase in the number of subscribers and transmission data rates leads to a shift to higher frequency bands where wider bandwidth is available. There are two directions for future trends in mobile communications.

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  • Systems designed to receive spatially propagating signals often encounter the presence of interference signals. If the desiredsignal andinterferers occupy the same temporal frequency band, thentemporal filtering cannot be usedto separate signal frominterference.

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  • The wide proliferation of wireless communications unavoidably leads to the scarcity of frequency spectra. On one hand, wireless users become increasingly difficult to find available frequency bands for communications. On the other hand, many preallocated frequency bands are ironically under-utilized and thus the resources there are simply wasted. This situation leads to the introduction of cognitive radio, which was proposed in the last decade to address this dilemma.

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  • The GSM Recommendation The early 1980s were marked by the development of a number of national and incompatible radio networks in Europe; see Table 1.2 and Figure 1.3. The seven different mobile radio networks made the prospect of the mobile telephone unattractive to many potential customers because of high tariffs and equipment costs. For this reason, at its general meeting in Vienna in June 1982, CEPT (see Appendix B.2.2) decided to develop and standardize a Pan-European cellular mobile radio network.

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  • Globalisation GSM is now in more countries than McDonalds. Mike Short, Chairman MoU Association 1995±1996 GSM was initially designed as a pan-European mobile communication network, but shortly after the successful start of the ®rst commercial networks in Europe, GSM systems were also deployed on other continents (e.g. in Australia, Hong Kong, and New Zealand). In the meantime, 373 networks in 142 countries are in operation (see Section 1.3).

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  • COVERAGE VERSUS CAPACITY Paraphrasing the late Tip O’Neill: “All coverage is local.” With 12–14-in. full wavelengths it is quite possible to encounter an ARDIS, BSWD, CDPD, or circuit switched cellular dead spot simply by walking to another position in a room. This annoying fact does not mean that all carriers operating near the same frequency band offer essentially the same coverage choices. Design trade-offs are made between area coverage and its close cousin, building penetration, versus subscriber capacity. ...

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  • RECENTLY, the interest in ultra-wideband (UWB) system for wireless personal area network (WPAN) application has increased significantly, though the international standard has yet to be finalized. The allocated frequency band of the UWB system is 3.1–10.6 GHz (low-frequency band: 3.1–5 GHz; highfrequency band: 6–10.6 GHz). Two recent major proposals [1], [2] for the IEEE 802.15.3a propose that data rates of up to 400–480 Mb/s can be obtained...

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  • Systems designed to receive spatially propagating signals often encounter the presence of interference signals. If the desiredsignal andinterferers occupy the same temporal frequency band, thentemporal filtering cannot be usedto separate signal frominterference. However, desiredandinterfering signals often originate fromdifferent spatial locations. This spatial separation can be exploited to separate signal frominterference using a spatial filter at the receiver.

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  • ADC expands the industry-leading FlexWave WMX WiMAX product family with the introduction of an economical series of base station radios operating in the 5.4 GHz and 5.8 GHz bands. WMX is the first system offering Dynamic Frequency Selection (DFS) compliant with US and ETSI standards and operating within the WiMAX profile. Subscribers enjoy the benefits of enhanced link-reliability even under interference conditions. Service providers and network operators can generate aggressive return of investment (RoI) from the use of license-exempt 5 GHz frequency band....

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  • A planar antenna with a broadband feeding structure is presented and analyzed for ultrawideband applications. The proposed antenna consists of a suspended radiator fed by an n-shape microstrip feed. Study shows that this antenna achieves an impedance bandwidth from 3.1–5.1 GHz (48%) for a reflection of coefficient and an average gain of 7.7 dBi. Stable boresight radiation patterns are achieved across the entire operating frequency band, by suppressing the high order mode resonances. This design exhibits good mechanical tolerance and manufacturability....

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  • QUY CHUẨN KỸ THUẬT QUỐC GIA QCVN 53 : 2011/BTTTT VỀ THIẾT BỊ VI BA SỐ SDH ĐIỂM - ĐIỂM DẢI TẦN TỚI 15 GHZ National technical regulation on Point-to-point SDH radio equipments operating in the frequency bands up to15 GHz Lời nói đầu QCVN 53 : 2011/BTTTT được xây dựng trên cơ sở soát xét, chuyển đổi Tiêu chuẩn Ngành TCN 68-234 : 2006 “Thiết bị Viba số SDH điểm - điểm dải tần tới 15 GHz - Yêu cầu kỹ thuật” ban hành theo Quyết định số 27/2006/QĐ-BBCVT ngày 25/7/2006 của Bộ trưởng Bộ Bưu chín...

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