Thi Tiếng Anh Chuyên Ngành · Tổng: 100 điểm · 90 phút
Tình huống: Bạn là chuyên gia thông tin đánh giá hệ thống vệ tinh và thông tin quang, đề xuất giải pháp kỹ thuật nâng cấp hạ tầng viễn thông hải quân.
40 điểm · 40 phút
Optical fibre technology has fundamentally transformed the capacity and reliability of long-distance telecommunications. Unlike copper-based systems that transmit electrical signals, optical fibres carry data as pulses of light through strands of glass or plastic as thin as a human hair. The core of the fibre is surrounded by a cladding material with a lower refractive index, creating the phenomenon of total internal reflection that confines the light signal within the core over distances of many kilometres.
The capacity of optical fibre systems is measured in terms of bandwidth — the range of frequencies the medium can support. Through a technique known as Wavelength Division Multiplexing (WDM), multiple data streams can be transmitted simultaneously on different wavelengths of light within a single fibre. Dense WDM (DWDM) systems can support over one hundred channels per fibre pair, each carrying data at rates of 10 to 100 Gbps, making them the preferred choice for submarine cable networks and national backbone infrastructure.
Optical amplifiers, particularly Erbium-Doped Fibre Amplifiers (EDFAs), have been a critical enabling technology. Before their development in the 1980s, optical signals required conversion to electrical form for regeneration every 80 to 100 kilometres. EDFAs amplify the optical signal directly without this conversion, dramatically reducing costs and supporting the ultra-long-haul transmission routes that connect continents via undersea cables.
Despite these advantages, optical fibre systems are not without limitations. The fibres are physically fragile and susceptible to damage from bending beyond a minimum radius. Signal dispersion — the spreading of light pulses over long distances — must be managed using dispersion compensation techniques. Furthermore, the installation of new submarine cables requires specialised vessels and significant financial investment, making upgrades to undersea infrastructure a long-term planning exercise.
Xác định mỗi câu là TRUE, FALSE hoặc NOT GIVEN theo Văn bản 1.
Chọn đáp án đúng nhất dựa trên Văn bản 1.
Chọn từ thích hợp từ ô từ. Mỗi từ chỉ dùng một lần.
Điền thông tin còn thiếu dựa trên Văn bản 1. Tối đa 3 từ/số.
| Thuật ngữ | Mô tả / Chức năng |
|---|---|
| Cladding | |
| DWDM | |
| EDFA | |
| Signal dispersion |
A. Orbital Classes and Their Trade-offs
Communication satellites are classified primarily according to their orbital altitude. Geostationary Earth Orbit (GEO) satellites operate at approximately 35,786 kilometres above the equator, where their orbital period matches the Earth's rotation, making them appear stationary to ground-based antennas. This characteristic enables reliable coverage of large geographic areas with fixed dish installations, but introduces a one-way signal propagation delay of approximately 240 milliseconds — a latency that is imperceptible in broadcast applications but problematic for real-time interactive communication.
B. LEO Constellations: A New Paradigm
Low Earth Orbit (LEO) satellites operate between 500 and 2,000 kilometres altitude, producing propagation delays of only 20 to 40 milliseconds — comparable to terrestrial broadband. Because individual LEO satellites cover only a small footprint, global coverage requires large constellations of hundreds or thousands of satellites operating in coordinated orbits. SpaceX's Starlink programme had deployed over 5,000 satellites by 2024, delivering broadband services with speeds exceeding 200 Mbps to remote and maritime users.
C. Military and Naval Applications
Satellite communications are indispensable in naval operations where ships operate beyond the range of shore-based radio stations. Very Small Aperture Terminal (VSAT) systems, with antenna diameters typically between 0.6 and 2.4 metres, can be installed aboard vessels to provide voice, data, and video connectivity. In tactical military environments, satellites must also meet stringent anti-jamming and low-probability-of-intercept requirements to ensure communications survivability in contested electromagnetic environments.
D. The Convergence of Satellite and Terrestrial Networks
Modern telecommunications architecture increasingly integrates satellite and terrestrial infrastructure. High-throughput satellites (HTS) employ spot-beam technology to concentrate capacity on high-demand areas, achieving spectral efficiencies comparable to terrestrial networks. When combined with fibre backbone infrastructure, hybrid satellite-terrestrial architectures can provide seamless connectivity even in the most remote maritime environments, ensuring that naval forces maintain communication superiority regardless of location.
Chọn tiêu đề phù hợp nhất cho mỗi đoạn (A–D). Có 2 tiêu đề dư.
Câu hỏi suy luận — đáp án không nằm trực tiếp trong văn bản.
Trả lời bằng 1–2 câu hoàn chỉnh, dùng ngôn ngữ của bạn.
30 điểm · 25 phút
Chọn từ đúng nhất.
Dùng dạng đúng của từ trong ngoặc.
Mỗi câu có một lỗi. Gõ dạng đúng vào ô bên phải.
Dùng từ khóa để viết lại câu. Không đổi từ khóa. Dùng 2–5 từ bao gồm từ khóa.
30 điểm · 25 phút · GV chấm theo rubric
📋 Rubric: Task Achievement · Coherence · Vocabulary · Grammar (mỗi tiêu chí 2.5đ)
📋 Rubric: Task Achievement · Coherence · Vocabulary · Grammar (mỗi tiêu chí 2.5đ)
📋 Rubric: Task Achievement · Coherence · Vocabulary · Grammar (mỗi tiêu chí 2.5đ)