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Erschienen in:
2019 | OriginalPaper | Buchkapitel
3. Characterization of the Noise at the Receiver
verfasst von : Joachim Speidel
Erschienen in: Introduction to Digital Communications
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Abstract
Before we are going to discuss various detection algorithms for the receiver output signal q(k), we have to characterize the noise \(n_{C}(t)\) in Fig. 1.1. The main sources of noise are the resistors and the electronic components such as transistors or the photodiode in an optical receiver. In a wireless system, the receive antenna collects noise coming from the channel. In most cases, the first stage of a receiver is composed of an amplifier associated with a bandpass filter to limit the noise spectrum to the passband of the transmit signal, which is given by the channel transfer function in (1.19). The resulting real-valued noise \(n_{C}(t)\) is demodulated and lowpass filtered with \(\sqrt{2}G_{R}(f)\) yielding the complex-valued noise \(n_{R}(t)\) with a lowpass spectrum. The noise sequence n(k) results after sampling and is depicted in the discrete-time equivalent baseband system in Fig. 1.5b. In the following, we analyze the noise at the receiver step by step. For the basics on stochastic processes we refer to the Appendix A