Communications Engineering II

The lecture Communications Engineering II is a follow-up lecture of the Bachelor lecture Communications Engineering I. The main focus is on mobile radio channels whose characteristics do not fully correspond to the assumptions made in Communications Engineering I, so that new scenarios and methods are introduced. On this basis, already known topics are expanded and deepened, further statements are derived, and their use is discussed. In the exercise, the knowledge acquired in the lecture is applied in classical calculations or by implementing algorithms and systems in Python, thus illustrating the theoretical concepts and their application.

The first chapter on fundamentals contains the vector representation of signals using orthogonal basis functions, which is often important for theoretical derivation and the transition between the baseband and the bandpass range. The transmission characteristics for linear digital modulation methods are then introduced on the basis of this representation. Among other things, the signal spectrum for digital modulation is derived as a function of pulse shaping and the statistics of the transmit symbols, and the error probability is calculated. Another important point is the treatment of Nyquist conditions, which contain criteria for transmission without inter-symbol interference.

The analysis of the mobile radio channel using the coherence terms and the modeling of multipath propagation using the tapped delay line model are the key points in the next chapter. The power-delay profile and the Doppler power profile, which serve as a starting point for characterizing the coherence terms, are also discussed. Furthermore, the well-known fading models Rayleigh, Rice and Nakagami are explained.

Transmission in fading channels is significantly more error-prone than in AWGN channels due to random attenuation and phase rotation. After deriving the corresponding error probabilities and comparing them with the AWGN case, the use of diversity methods in communication systems is discussed. Possible combining methods are discussed and their performance is analyzed.

Synchronization in the receiver is necessary for coherent data transmission. Various methods for time, phase, and frequency synchronization are presented on the basis of estimation theory approaches. The maximum likelihood estimators are derived and their applicability and possible simplification are discussed before further approaches for possible synchronization methods are discussed.

The chapter on equalization is motivated by the mobile radio channel and the associated signal distortions. Hereby, the term equalization describes processing steps such that the receiver copes with the channel distortions and aims at reversing them as far as possible. In this context, zero forcing, MMSE equalization, and various linear FIR equalizers are discussed after considering the optimum receiver.

After completing the course, students will be able to understand communication systems for real mobile radio channels and will have learned methods to guarantee reliable message transmission in these systems as well as to analyze and evaluate the subsystems.