Sub-Terahertz communication is a key enabling technology to deliver ultra-high rates up to Terabit/s - one of 6G envisioned goals. However, hardware limitation and impairments set practical challenges in realizing real-world networks operating at such high frequency range. In this paper, based on simulation findings, we analyze the performance of different single- and multi-carrier transmission concepts in the sub-Terahertz range under hardware impairments and limitations, both from a today’s New Radio (NR) up-scaling perspective, and whether it is best to deviate from the straightforward up-scaling into a new design. We therefore focus on the following sub-Terahertz network determinants: the signal peak amplitude characteristics, the phase noise of the local oscillators and the quantization effect of the analog-to-digital-converter. Insights drawn from the analysis are considered to make proposals on the signaling concepts for a practical access network design in the sub-Terahertz range. We also demonstrate how further improvement can be harvested considering signal amplitude variation optimized constellation modulation.

In this work, we investigate the spectral efficiency (SE) of a system where the transmitter utilizes zero crossing modulation (ZXM), which was implemented by combining faster-than-Nyquist signaling with runlength-limited transmit sequences, and the receiver employs 1-bit quantization and temporal oversampling. The SE is evaluated numerically with respect to a fractional power containment bandwidth, which allows for a fractional amount of out-of-band emissions. In contrast to most existing works, the SE is evaluated for a practical transmitter and receiver implementation under a wideband line-of-sight channel model. The studied system achieves SEs above 3 bit/s/Hz, which corresponds to an increase of more than 50 % as compared to standard QPSK. Furthermore, the studied system outperforms a related system by Deng et al., which also employs 1-bit quantization and temporal oversampling, by approx. 15 dB at a SE of 3 bit/s/Hz.

An overview of the 5G New Radio (NR) physical downlink control channel (PDCCH) design of 3GPP Release 15 is presented and performance enhancements are proposed. A novel PDCCH hash function is shown to outperform the legacy hash function by about one order of magnitude in terms of inter-user blocking probability while maintaining the frequency-selective scheduling capability for downlink control information. Enhanced PDCCH candidate overbooking and mapping/dropping algorithms are investigated. Link level performance results of NR PDCCH with precoder cycling transmit diversity are presented for various aggregation levels and physical resource configuration options.

The fifth-generation (5G) cellular networks will face the challenge of integrating the traditional broadband services with the Internet of Things (IoT), which is characterized by sporadic uplink transmissions of small data packets. Indeed, the access procedure of the previous generation cellular network (4G) is not able to support IoT traffic efficiently, because it requires a large amount of signaling for the connection setup before the actual data transmission. In this context, we introduce two innovative radio access protocols for sporadic transmissions of small data packets, which are suitable for 5G networks, because they provide a resource-efficient packet delivery exploiting a connectionless approach. The core of this paper resides in the derivation of an analytical framework to evaluate the performance of all the aforementioned protocols. The final goal is the comparison between 4G and 5G radio access solutions employing both our analytical framework and computer simulations. The performance evaluation results show the benefits of the protocols envisioned for 5G in terms of signaling overhead and access latency.

Among the many proposals to meet the fifth generation (5G) data rate demands, current spectrum scarcity has motivated the use of millimeter-Wave (mmW) bands for cellular communication. It is well known that mmW communication involves many propagation challenges, which can be compensated through massive multi-antenna techniques. However, implementing fully digital precoding schemes with massive arrays entails huge complexity and costs, which have recently boosted the interest for hybrid beamforming solutions. Although hybrid schemes have shown good performance in simplified setups, their suitability for realistic cellular systems with many interfering base stations and users is still unclear. In this sense, this paper assesses the performance of hybrid beamforming in a dense urban cellular system with a realistic mmW channel model and shows that it can reach the performance of fully digital maximum ratio transmission under line of sight conditions and with a sufficient number of parallel radio-frequency chains. Another important result is that multi-user hybrid beamforming provides a substantial capacity increase with respect to its single-user (SU) counterpart. This finding complements the views on mmW communication usage, which has been so far mainly intended for SU communication to provide high beamforming gains.

The air interface for millimeter wave (mmWave) communications must be designed by properly taking into account the specific characteristics of the wireless channel at higher frequencies. In this work, we start by considering a channel model recently proposed in the literature for mmWave communications in outdoor urban scenarios. First, on top of this channel model we implement a sectorized beamforming model necessary to compensate the large path-loss at mmWave range and study how channel statistics, namely, delay spread and angle spread, are influenced by employing different beamwidths. Subsequently, adopting this beamforming model in the mmWave channel, orthogonal frequency division multiplexing (OFDM) and single carrier frequency domain equalization (SC-FDE) systems are compared. Extensive link level simulations are performed by considering different beamwidths, line-of-sight (LOS) coverage and channel coding. Numerical results show that SC-FDE using minimum mean square error (MMSE) equalization performs close to OFDM in coded systems. However, SC-FDE might be beneficial in practice due to much lower peak to average power ratio (PAPR) than OFDM.

We consider the downlink of a multi-cell system where base stations and users are equipped with multiple antennas. Therein, a cluster of base stations employ joint transmission with linear zero-forcing beamforming based on compressed channel state information (CSI) feedback. For propagation we assume a realistic 3D channel model including antenna patterns. We discuss in detail a novel compression algorithm exploiting the spatial and frequency domain and also present a feedback data format. We evaluate the proposed compression algorithm in the presence of channel estimation error in terms of throughput and feedback rate and compare it with the perfect CSI case. The proposed algorithm and feedback scheme is shown to reduce the feedback rate to less than 1 % of uncompressed feedback and at the same time increasing the sum throughput significantly.

This paper discusses two approaches of reliability-based HARQ, adapting the packet size of a retransmission in a 3GPP Long Term Evolution (LTE) system. We focus on the adaptation of the retransmission size in terms of physical resources by using information 1) of the channel, namely the signal-to-noise ratio (SNR) or 2) reliability information from the decoder output, taking the overall transmission into account. Both approaches will be compared to the HARQ system used in LTE in terms of throughput performance. Link level simulations will be performed with single bit feedback and 2 bit multilevel ACK/NAK. This work takes realistic impairments such as channel estimation, signal-to-noise ratio (SNR) estimation and implementation of a Turbo en- and decoder into regard.

Base station cooperation is a promising technique for next generation cellular systems as it reduces intercell interference. In this paper, we investigate to what extent performance degradation due to the feedback delay can be compensated by advanced channel prediction. We present a new method based on a Doppler-delay model of the time-variant radio channel. In a first step, significant channel taps are extracted in the delay domain. In a second step, a high-resolution algorithm extracts the major Doppler frequency components for each channel tap. In this way, a shorter history of the channel is needed, as compared to the standard discrete Fourier transform (DFT) technique. Prediction is performed by imposing the estimated parameters into the channel model and extrapolating into future. Evaluation over the extended spatial channel model (SCME) shows that the channel mean square error can be reduced by roughly 10 dB for feedback delays between 5 and 10 ms, which translates into signal to interference ratio (SIR) gains between 5 and 15 dB, also depending on the number of jointly served terminals. Finally, it is shown that, even if the channel state information (CSI) feedback is quantized, almost the same performance can be achieved as if based on perfect channel knowledge.

In 2020, mobile and wireless traffic volume is expected to increase thousand-fold over 2010 figures. Moreover, an increase in the number of wirelessly-connected devices to counts in the tens of billions will have a profound impact on society. Massive machine communication, forming the basis for the Internet of Things, will make our everyday life more efficient, comfortable and safer, through a wide range of applications including traffic safety and medical services. The variety of applications and data traffic types will be significantly larger than today, and will result in more diverse requirements on services, devices and networks. METIS is set up by leading global players to prepare the migration towards tomorrow's multi-purpose global communication infrastructure, serving humans and things. The main objective of METIS is to lay the foundation for this future global mobile and wireless communications system, and to generate a global consensus here. In particular, METIS will provide new solutions which fit the needs beyond 2020.

This paper discusses retransmission approaches to improve the throughput performance of Hybrid-ARQ (HARQ) schemes in a point-to-point single user 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) uplink system. One goal of communication systems is to achieve a reliable transmission with a throughput performance as close as possible to channel capacity. For that, reducing the channel utilization will improve the throughput performance. Instead of sending two retransmission packets for two HARQ processes of one users, a previously published HARQ scheme uses the XOR combining of these packets to get only one retransmission packet with the same size. Similar to this idea, a new varied scheme performs XOR combining of parts of one conventional full retransmission to generate a smaller retransmission packet. Both approaches will reduce the channel utilization. They will be compared with a HARQ system in LTE uplink using a full size retransmission and a half size retransmission. The main focus of this work is the throughput performance evaluation of these schemes in an LTE link-level simulator.

In cellular networks coordination among base stations (BSs) has been recognized as an important solution to handle inter-cell interference and increase spectral efficiency. In frequency division duplex systems one of the main issue that sensibly degrades the performance of coordinated multipoint (CoMP) transmission techniques is the imperfect channel state information (CSI) due to the limited bandwidth available for the feedback transmission. In this paper we focus on a CoMP scenario with data and CSI sharing among the BSs and we consider a feedback transmission scheme where each user equipment (UE) quantizes the different channels by using codebooks designed for a single-cell scenario. Due to the different propagation characteristics of the channels between a UE and each BS and by considering a constraint on the number of available feedback bits, we propose two practical algorithms depending on the large-scale fading to a) select the subset of BSs from whom the UE prefers to be served and b) optimize the number of feedback bits allocated to each channel. The developed techniques allow a UE to send more feedback bits to the BSs with a stronger signal and numerical results show the merits of the proposed approach.

In this paper, a novel HARQ transmission scheme based on network coding is proposed for wireless unicast scenarios. Instead of retransmitting erroneous packets individually, a network coded packet constructed by the XOR of two erroneous packets is transmitted similar to network coding. In order to fully exploit the network coded packet in combination with the previously received erroneous packets, soft combining methods with respect to Chase Combing (CC) and Incremental Redundancy (IR) are developed. The expected throughput gain of 33% for one retransmission for the proposed solution compared to common HARQ transmission is confirmed by LTE link-level simulations.

MOTIVATION: Animals build their bodies by altering the fates of cells. The way in which they do so is reflected in the topology of cell lineages and the fates of terminal cells. Cell lineages should, therefore, contain information about the molecular events that determined them. Here we introduce new tools for visualizing, manipulating, and extracting the information contained in cell lineages. Our tools enable us to analyze very large cell lineages, where previously analyses have only been carried out on cell lineages no larger than a few dozen cells. RESULTS: Ales (A Lineage Evaluation System) allows the display, evaluation and comparison of cell lineages with the aim of identifying molecular and cellular events underlying development. Ales introduces a series of algorithms that locate putative developmental events. The distribution of these predicted events can then be compared to gene expression patterns or other cellular characteristics. In addition, artificial lineages can be generated, or existing lineages modified, according to a range of models, in order to test hypotheses about lineage evolution. AVAILABILITY: The program can run on any operating system with a compliant Java 2 environment. Ales is free for academic use and can be downloaded from http://mbi.dkfz-heidelberg.de/mbi/research/cellsim/ales.

We investigate various array combining algorithms considering the special requirements of the UTRA/FDD uplink. After formulating the algorithms, we assess their performance in a modified vehicular B channel that is spatially inhomogeneous. The bit error ratios in different situations are presented together with some considerations about the computational complexity of the used methods. From bit error performance and required effort, we conclude that the minimum mean squared error (MMSE) algorithm with reduced complexity is the most suitable method for a real operating system.

We present an enumerative technique for encoding and decoding DC-free runlength-limited sequences. This technique enables the encoding and decoding of sequences approaching the maxentropic performance bounds very closely in terms of the code rate and low-frequency suppression capability. Use of finite-precision floating-point notation to express the weight coefficients results in channel encoders and decoders of moderate complexity. For channel constraints of practical interest, the hardware required for implementing such a quasi-maxentropic coding scheme consists mainly of a ROM of at most 5 kB.