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DIGI COMMS
| Term | Definition |
|---|---|
| Digital | _________ systems are resistant to noise |
| Information Source | The source output may be either an analog signal or a digital signal. |
| Source Encoder | Efficiently converts an analog signal into a sequence of binary bits. |
| Compression, compaction | Source encoder performs data _________ (lossy), data __________ (lossless). |
| inherent redundancy, efficient use | Source encoder removes __________ information from the message signal, and is responsible for the ___________of the channel. |
| source codeword | Source encoder's resulting sequence of symbols is called _________ |
| Data encryption | Source encoder may also include _________ for privacy and/or authentication purposes. |
| 1. Sampling 2. Quantization 3. Source Coding | Source encoder is generally composed of three parts: |
| Sampling | Converts analog signals into a corresponding sequence of samples that are usually spaced uniformly in time |
| continuous, discrete | The output of sampling is _________ in amplitude and ________ in time |
| Quantization | The process of transforming the sample amplitude of a baseband signal into a discrete amplitude taken from a finite set of possible levels. |
| Discrete, discrete | The output of quantization is _________ in amplitude and ________ in time |
| Midtread and midrise | Two types of quantization? |
| Quantization | It maps amplitude levels that minimizes the number of bits and minimizes distortion. |
| 1. Uniform or non-uniform quantization 2. Scalar or vector quantization | Quantizers can be categorized as |
| Controlled, mitigate | Channel encoder adds ___________ redundancy to _________ channel effects |
| channel codeword | Channel encoder's resulting sequence of symbols is called _________ |
| Digital Modulator | Its primary purpose is to map the binary information sequence into signal waveforms |
| Binary Modulation | A type of modulator: Suppose that the coded information sequence is to be transmitted one bit at a time |
| M-ary Modulation | A type of modulator: The modulator may transmit b coded information bits at a time by using M distinct waveforms. |
| communication channel | The ___________ is the physical medium that is used to send the signal from the transmitter to the receiver. |
| guided, unguided | Channels could either be _________ (wired communications) or ___________ (wireless communications) |
| random | The transmitted signals of a communication channel are corrupted in a ___________ manner by a variety of mechanisms such as thermal noise, man-made noise, atmospheric noise, and many more |
| 1. Attenuation 2. Noise 3. Filtering 4. Fading 5. Time Variation | The effects of the communication channel include? (There are 5) |
| Attenuation | This is typically measured in decibels (dB) |
| inverse, square distance | Attenuation is described as decrease in power as ________ of ____________ |
| Noise | It is additive in nature that falls within the passband of the signal. A typical mathematical model to represent noise is the White Gaussian Noise (WGN). |
| Intersymbol interference | ______________ is a form of distortion of a signal in which one symbol interferes with subsequent symbols. |
| Fading | It is the variations of the channel strength over time and over frequency. |
| 1. Large-scale fading 2. Small-scale fading | Variations of Fading can be divided into two types |
| Large-scale fading | - due to path loss of signal as a function of distance and shadowing by large objects such as buildings and hills. |
| Small-scale fading | - due to the constructive and destructive interference of the multiple signal paths between the transmitter and receiver. |
| Time Variation | Time-varying channels cause signal fading |
| Digital Demodulator | processes the channel-corrupted transmitted waveform. |
| Digital Demodulator | translates the waveforms to a sequence of numbers that represent estimates of transmitted data symbols |
| Channel decoder | ______________ attempts to reconstruct the original information sequence from knowledge of the code used by the channel encoder and the redundancy contained in the received data. |
| Channel decoder | It performs error-detection and/or error-correction processes |
| Source decoder | It attempts to reconstruct the original signal from the source (decompression). |
| approximation | The output of the source decoder is an __________ to the original source output. |
| distortion | The difference of original and reconstructed signals is a measure of _________ of the digital communication system. |
| 1. Transmit Power 2. Channel Bandwidth | Communication systems are designed to provide efficient utilization of two primary communication resources: |
| Transmit Power | defined as the average power of the transmitted signal. |
| Channel bandwidth | The width of the passband channel. |
| Wireless channels (Power - limited channels) | where it is desirable to keep the transmitted power low to prolong battery life. |
| Satellite channels (Power - limited channels) | where the available power on board the satellite transponder is limited, which necessitates keeping the transmitted power on the downlink at a low level. |
| Telephone channels (Bandwidth-limited channels) | where, in a multi-user environment, the requirement is to minimize the frequency band allocated to the transmission of each voice signal. |
| Television channels (Bandwidth-limited channels) | where the available channel bandwidth is limited by regulatory agencies. |
| 1. Small 2. Small 3. Large 4. Low 5. Low | Feature of Good communication? 1._______ signal power (measured in W or dBm) 2. _______ bandwidth (measured in Hz) 3. _______ data rate (measured in bps) 4. _______ distortion (measured in SNR or BER) 5. _______ cost (complex systems with low cost) |
| Bandwidth efficiency | Data-rate VS Bandwidth is a metric used to quantify this trade off which is defined as the ratio of data rate to bandwidth (bps/Hz). |
| Bandwidth efficiency | Data-rate VS Bandwidth a measure of how efficiently a limited frequency spectrum is utilized |
| Nb = data rate/transmission BW UNIT: bps/Hz | Formula of BW efficiency |
| Energy efficiency | Fidelity VS Signal Power is a metric used to quantify this trade-off which is defined as the ratio of transmitted data to consumed energy (bits/Joule). |
| Energy-to-Noise ratio Ye = Eb/No | is useful when comparing the BER performance of different modulation schemes without taking bandwidth into account Formula? |
| 1. Power efficiency is more important, spectral efficiency should not be sacrificed so much 2. Power efficiency more important, Spectral efficiency is not that important 3 and 4. Spectral efficiency is more important. | Power VS Spectral Efficiency 1. Cellular transmission - ? 2. Sending data to a station in Mars - ? 3. Voice Communication (e.g. telephone systems) - ? 4. Data Communication (using telephone network) - ? |
| 1. Performance 2. Ruggedness 3. Reliability 4. Security 5. Efficiency 6. System Integration | Advantages of Digital Systems (Give 6) |
| Performance | (Advantages) it permits the use of regenerative repeaters which can eliminate degrading effects of channel noise and signal distortion. |
| Ruggedness | (Advantages) it can be designed to withstand the effects of channel noise and signal distortion. |
| Reliability | (Advantages) made possible by exploiting powerful error control coding techniques. |
| Security | (Advantages) it can be made highly secure by exploiting powerful encryption algorithms |
| Efficiency | (Advantages) more efficient in terms of tradeoff between bandwidth and SNR. |
| System Integration | (Advantages) it is possible to integrate digitized analog signals |
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