Modulator demodulator

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  • In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted. This is done in a similar fashion to a musician modulating a tone (a periodic waveform) from a musical instrument by varying its volume, timing and pitch. The three key parameters of a periodic waveform are its amplitude ("volume"), its phase ("timing") and its frequency ("pitch").

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  • This book is intended for courses at least at Masters level to provide an introduction to the field of signal processing in telecommunications. The text therefore deals mainly with source coding, channel coding, modulation and demodulation. Adaptive channel equalisation, the signal processing aspects of adaptive antennas as well as multi-user detectors for CDMA are also included. Shorter sections on link budget, synchronising and cryptography are also included. Network aspects are not discussed and very little is given about wave propagation.

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  • Communication systems consist of an input device, transmitter, transmission medium, receiver and output device, as shown in Fig. 1.1. The input device may be a computer, sensor or oscillator, depending on the application of the system, while the output device could be a speaker or computer. Irrespective of whether a data communications or telecommunications system is used, these elements are necessary.

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  • Receiver structure Impact of AWGN and ISI on the transmitted signal. Optimum filter to maximize SNR. Matched filter receiver and Correlator receiver.Demodulation and sampling: Waveform recovery and preparing the receivedl signal for detection: Improving the signal power to the noise power (SNR) using matched filter Reducing ISI using equalizerl Sampling the recovered waveform. Detection: Estimate the transmitted symbol based on the received sample

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  • How decoding is performed for Convolutional codes? What is a Maximum likelihood decoder? What are soft decisions and hard decisions? How does the Viterbi algorithm work?The demodulator makes a firm or hard decision whether one or zero was transmitted and provides no other information for the decoder such as how reliable the decision is.

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  • Mã hóa kênh ( Channel coding ) Mã hóa khối (Block codes) + Mã lập (Repetition Code) + Hamming codes + Cyclic codes * Reed-Solomon codes Mã hóa chập (Convolutional codes) + Encode + Decode Sơ đồ khối hệ thống DCS Source encode Channel encode Pulse modulate Bandpass modulate Channel Format Digital modulation Digital demodulation Format Source decode Channel decode Detect Demod.

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  • Trải phổ là một kỹ thuật truyền thông được đặc trưng bởi băng thông rộng và công suất thấp. Truyền thông trải phổ sử dụng các kỹ thuật điều chế (modulation) khác nhau cho mạng WLAN và nó cũng có nhiều thuận lợi so với người tiền nhiệm của nó là truyền thông băng hẹp. Tín hiệu trải phổ trông giống như nhiễu, khó phát hiện và thậm chí khó để chặn đứng hay giải điều chế (demodulation) nếu không có các thiết bị thích hợp.

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  • Hệ thống thông tin và điều chế biên độ Không gian tín hiệu và hệ thống thông tin số Khái niệm hệ thống thông tin kênh h(t) x(t) điều chế y (t) yr (t) giải điều chế x (t) ˆ ◮ ◮ ◮ ◮ ◮ ◮ Máy phát - máy thu (điểm - điểm). Kênh h(t) (fading, Doppler, v.v.) và nhiễu Gauss n(t). Signal-to-Noise Ratio (SNR). Ghép tin x(t) vào sóng mang tại phía phát sao cho phù hợp với môi trường truyền dẫn (điều chế - modulation).

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  • Coding and Modulation The block diagram in Figure 6.1 describes a digital communication system. Similarly, data transfer between reader and transponder in an RFID system requires three main functional blocks. From the reader to the transponder — the direction of data transfer — these are: signal coding (signal processing) and the modulator (carrier circuit) in the reader (transmitter), the transmission medium (channel ), and the demodulator (carrier circuit) and signal decoding (signal processing) in the transponder (receiver)....

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  • The oscillator in communication and measurement systems, be they radio, coaxial cable, microwave, satellite, radar or optical fibre, defines the reference signal onto which modulation is coded and later demodulated. The flicker and phase noise in such oscillators are central in setting the ultimate systems performance limits of modern communications, radar and timing systems. These oscillators are therefore required to be of the highest quality for the particular application as they provide the reference for data modulation and demodulation. ...

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  • Tầng 1: modem, repeater, hub Tầng 2: NIC, bridge, switch Tầng 3: router, brouter Khác: access point, gatewayModem - 1• MODEM = MOdulate and DEModulateModem - 2• Chức năng:– Điều chế [Modulate]: chuyển đổi tín hiệu số (digital) trên máy tính thành tín hiệu tương tự (analog) trên điện thoại. – Giải điều chế [Demodulate]: chuyển đổi tín hiệu tín hiệu tương tự trên điện thoại thành tín hiệu số trên máy tính

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  • bandpass modulation: là quá trình biến tín hiệu dữ liệu thành dạng sóng sin có biên độ/pha/tần số hoặc các kết hợp thay đổi theo tín hiệu đó. Demodulation: tín hiệu nhận được sẽ được chuyển sang tín hiệu dải gốc, lọc và lấy mẫu, Các v n đ đ u thu gây ra b ấ ề ở ầ ởi: (Source of carrierphase mismatch at the receiver): – Sự trễ / trì hoãn (Propagation delay).

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  • FREQUENCY MODULATED RADIO TRANSMITTER In Chapter 2, the amplitude of a high-frequency (carrier) sinusoidal signal was varied in accordance with the waveform of an audio-frequency (modulating) signal to give an amplitude modulated (AM) wave which could be transmitted, received, and demodulated to recover the original audio frequency signal. In frequency modulated (FM) radio, the frequency of the carrier is varied about a fixed value in accordance with the amplitude of the audio frequency.

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  • Modulation and Demodulation Modulation is a technique of imposing information (analog or digital) contained in a lower frequency signal onto a higher frequency signal. The lower frequency is called the modulating signal, the higher frequency signal is called the carrier, and the output signal is called the modulated signal. The benefits of the modulation process are many, such as enabling communication systems to transmit many baseband channels simultaneously at different carrier frequencies without their interfering with each other....

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  • Chuyển nguồn thông tin (âm thanh) trong hệ thống số Cấu trúc bộ Format Lấy mẫu Lượng tử hóa Luật nén A và luật nén PCM Formatting và truyền tín hiệu dải gốc Digital info. Textual source info. Analog info. Format Sample Quantize Encode Pulse modulate Bit stream Pulse waveforms Transmit Channel Analog info. Demodulate/ Detect Receive Format cho tín hiệu analog Để chuyển từ dạng sóng analog tương thích trong hệ thống số ta phải qua 2 bước sau 1....

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  • Modulation and demodulation 5.1 MAXIMUM LIKELIHOOD ESTIMATION We start again with the ML principle defined in Section 3.1 of Chapter 3. After the signal despreading, vector of parameters θ to be estimated includes timing of the received symbols τ0 , phase of the received carrier θ0 , frequency offset of the received signal ν0 , amplitude of the signal A0 and data symbols an θ (τ0 , θ0 , ν0 , A0 , an ) After despreading, the narrowband signal can be represented as r(t) = s(t, θ ) + w(t) The likelihood becomes ˜ L(θ ) = C1 exp − C2...

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