In high mobility scenarios, cell selection in preparation for handover is a non-trivial task. Particularly a user equipment (UE) installed on board a passenger aircraft faces a high handover frequency and strong interference from a terrestrial radio access network (RAN) due to the high velocities and altitude of the aircraft. Conventional reference signal received power (RSRP) measurements do not reflect the potential for interference mitigation in the aeronautical regime. Therefore, we incorporate beamforming into conditional handovers such that signal to interference power ratio (SIR) measurements are used for the cell selection in order to find a serving base station which provides the best SIR after beamforming. Link budget simulations to evaluate the proposed method are performed using real passenger aircraft flight trajectories and real world base station deployment data. The proposed method improves the link availability by 32 percentage points compared to the conventional handover procedure while decreasing the average handover interval by up to 0.6 s at the high UE velocities. We also show that a handover candidate filtering rule based on the direction of flight offers a trade-off by increasing the average handover interval by up to 2.3 s at the cost of availability.

This feasibility study deals with Air to Ground (ATG) communications between a 5G type Terrestrial Mobile Communication Network (TMCN) and an User Equipment (UE) installed onboard a passenger aircraft in approach to an airport. The network model is based on real gNodeB (gNB) deployment data and optimized for serving terrestrial UEs. The evaluation concerns a scenario in which the passenger aircraft is supported by a remote operator via an ATG link to assist its safe landing. To mitigate the interference expected to arise in ATG communications, the aircraft is assumed to be equipped with an Active Electronically Scanned Array (AESA). The simulation results discussed in this paper address the Signal to Interference power Ratio (SIR), link availability, and handover process during ATG communications along representative approach trajectories for different AESA configurations and levels of support by the TMCN. It is shown that SIR above 30 dB and link availability upto 97.7% can be achieved by using an 8 x 8 AESA at the aircraft when the network provides support in the form of dedicated radio resources. It is observed that the frequency of handovers increases with improving link quality.

Next-generation satellite communication systems require high spectral efficiency to meet future data rate requirements. Faster-than-Nyquist signaling offers improvement potential by exploiting excess bandwidth of the transmit pulses at the price of inter-symbol interference. This paper studies sophisticated receiver structures that lead to linear discrete minimum phase models with uncorrelated noise. They enable equalization of inter-symbol interference with feasible complexity in trellis-based decoders. Another challenge is nonlinear distortion in the transmit signal caused by the satellite’s high power amplifier. The distortions are accounted for using a linearized Volterra filter model. Finally, a comparison to conventional methods shows that the new approach yields considerable performance gains.

In today's chip-to-chip communication over multi-drop bus (MDB) interfaces, the trend of high-speed transmission has led to ever growing bandwidth requirements. An MDB channel is frequency-selective with deep notches at low frequencies, namely fnotch, which result from strong reflections at an MDB interface. In conventional chip-to-chip communication systems, the signal power is concentrated in the main lobe of the power spectral density (PSD), i.e., within |f|sNRZ, where fsNRZ= 1/T, is defined as the signal bandwidth. Limited by the complexity on the analog equalizer, fsNRZnotchshould hold to avoid strong distortions of the transmit signal. To cope with this problem, conventional signal processing methods, such as digital equalization and error control coding, are undesired in this application scenario due to extremely tight power and latency constraints. A spectrum shaping scheme named framed repetition code was proposed for the MDB channel of a single strong reflection. It aims at matching the signal spectrum to the channel magnitude response |H(f)|. However, a solution for multi-reflection channels, which is more often encountered in MDB interfaces, has not yet been investigated. This paper proposes a novel code construction algorithm for multi-reflection MDB channels. The algorithm is designed based on the root mean square delay spread. Using the constructed framed repetition codes, the degradation due to the channel filtering is reduced significantly. Simulations reveal a good performance. The data rate in multi-reflection MDB channels is increased by a factor of 2.6 without using any equalization compared to the conventional non-return-to-zero (NRZ) transmission scheme.

This paper presents a cross-layer concept with respect to a joint design of beamforming and scheduling in a cellular MIMO-OFDM-based network. Conventionally, the beamforming and scheduling processes are designed more or less independently of each other. In contrast, this paper describes a combined approach of the scheduling and beamforming procedure, with the aim to maximize the capacity and fulfill the QoS requirements for all users within the network. For the example of delay constraints, it is shown how a joint system design is beneficial to serve users with "urgent" data packets. This is accomplished by giving the scheduling unit a control over the beams to be applied, thus favorable radio channel conditions can be temporarily generated for specific users such that the associated packets are delivered in time.

In this paper, a system concept is proposed and investigated for the downlink of a cellular network which combines a self-organised beamforming approach with an opportunistic scheduling concept. In the considered OFDM-based system, different beams or grids of beams are formed in time and frequency and the available space-time-frequency resources are allocated by intelligent scheduling algorithms to those mobile terminals with high instantaneous signal-to-interference-and-noise ratios (SINRs). Analysing the impact of various design criteria, such as the type of beamforming, scheduling concepts and frequency reuse factors, the performance in the cellular network regarding throughput and fairness is assessed

The objective of the presented work is the design of flexible data link control (DLC) protocols with the focus on scheduling policies, which combine the information of the time variant radio channel (described by the channel transfer function) and the incoming data streams from real time video applications with variable data rates. The goal is to fulfil the quality of service (QoS) requirements in terms of data rate, reliability and delay for all wireless terminals and to improve the average system throughput. Fairness between the wireless terminals (WTs) is also a very important aspect of scheduling.

The OFDM transmission technique has the inherent flexibility to adapt the modulation scheme on each subcarrier according to the reception quality, i.e. the signal-to-noise ratio (SNR) on a subcarrier. The allocation of bits to subcarriers is performed by so-called loading algorithms. In this paper, a new and rather simple loading algorithm is introduced which shows comparable performance and lower computational complexity compared to the well-known algorithm of Chow et al. (1995). In the proposed algorithm, subcarriers are clustered in blocks, which are allocated the same modulation scheme. This way, the signalling overhead can be reduced in comparison with standard subcarrier bit loading algorithms.

Future multimedia services will require the transmission of very high data rates over broad-band radio channels. In order to provide these services to mobile users, an appropriate transmission technique has to cope with frequency-selective and time-variant radio channels. The computation complexity for an equalizer increases in a frequency-selective radio channel for high data rate applications. Furthermore, the overhead for channel estimation procedures increases in time-variant channels. To overcome these drawbacks orthogonal frequency division multiplexing (OFDM) has been considered for broadband applications in many publications. The objective of this paper is to describe the large potential, the flexibility and adaptivity of the OFDM transmission technique in frequency-selective and time variant radio channels. Several technical aspects of OFDM transmission systems are discussed, especially the topics of differential modulation for which we compare different demodulation methods and channel coding with soft decision decoding. For higher level differential modulation, multilevel coding is taken into consideration.