Wen Xiaozhi has been saying thatEditor | Xiaozhi has been sayingBefore reading this article, we sincerely invite you to click on 'Follow', which not only facilitates your discussion and sharing, but also brings you a different sense of participation. Thank you for your supportprefaceThe low terahertz band is a promising candidate for achieving data rates up to 1Tbit/s

Wen Xiaozhi has been saying that

Editor | Xiaozhi has been saying

Before reading this article, we sincerely invite you to click on 'Follow', which not only facilitates your discussion and sharing, but also brings you a different sense of participation. Thank you for your support

preface

The low terahertz band is a promising candidate for achieving data rates up to 1Tbit/s. To develop suitable communication systems, new simulation methods that take into account the specific circumstances of constantly evolving technologies are needed.

brief introduction

Due to the current generation of mobile radio not being able to meet the data rate and latency needs of certain users, research and marketing have driven the development of new communication systems. In recent years, advances in the development of electronic devices have made the terahertz band attractive and easy to use. The low terahertz frequency band, commonly referred to as the range from 0.1THz to 1THz, is a promising candidate for the next generation of wireless systems, providing large frequency bands with limited molecular absorption effects.

Terahertz communication has great potential in data rate, but it faces different propagation mechanisms, leading to a paradigm shift in the design and deployment of mobile communication systems. For various applications, such as wireless backhaul links, device to device communication, vehicle environments, wireless enhanced data centers, or wireless personal area network office environments.

In terahertz communication, high path loss is conducive to point-to-point applications using high gain directional antenna, which may also reduce interference through spatial filtering. Beam tracking is necessary for mobile users. Starting to explore new technologies for fixed P2P applications with known locations is an obvious approach.

The DC use case has great potential, and fixed P2P links can be well applied. By integrating wireless links at the frequency of terahertz, DC has experienced performance improvement, as flexibility and adaptability have reached new levels. Combined with beam switching, the network controller can automatically reconfigure the network and dynamically modify the layout of the data center.

In order to adapt to new channel conditions and meet the requirements of the checked application, it is necessary to develop new transmission technologies and protocols for the physical layer and higher layers. A new geometric correlated channel model that combines antenna characteristics and beamforming is needed to evaluate system design. In the context of terahertz communication, especially single carrier systems, which have been discussed to provide lower peak to average power ratios, this means that there are lower requirements for the development of challenging THz devices. Due to the use of cutting-edge hardware devices in communication systems in the low terahertz frequency band, which have been optimized to reach the limits of technically feasible solutions, the impact of device characteristics and the resulting RF damage on signal and data transmission is particularly interesting.

The waveform description of the time discrete signal as a modulation channel allows for physical interpretation and relationship with hardware devices, as well as the use of signal and system theory. Simulators directly promote the artistic level of realistic, hardware close simulation. Providing a complete dataset is to facilitate the use of real-world simulation data for fundamental research at higher levels.

Current research

Software simulation is essential for the development of new communication systems. High performance simulation tools reduce development costs and accelerate the design process. In order to generate realistic and meaningful simulation results, simulators and models must cover all relevant influencing factors. For low terahertz communication systems, it is necessary to support relevant modulation and coding schemes, channel models, waveform, and hardware related loss reduction.

The error rate analysis tool in the MATLAB communication toolbox provides three simulation modes. The theoretical mode provides BER as a function of signal-to-noise ratio, while the semi analytical mode considers different modulation schemes and waveforms, but is limited to AWGN channel implementation. The Monte Carlo mode is used as an interface for MATLAB or Simulink models and allows simulation of selected SNR ranges.

The MATLAB communication toolbox represents a wide range of signal processing functions, including standard waveform filters, MCS, as well as multi carrier systems, statistical channel models, and antenna systems. The complete simulation tool chain for PHY design is well documented, but it is a closed source code with an additional license. The user's understanding of the specific implementation of algorithms and applications is limited. The closed design of functions and modules may hinder methods from adapting to special custom use cases and applications. This channel is also limited to high-level random descriptions in the absence of specific application scenarios or specific subscriber interactions.

The commonly used and standardized LLS for the fifth generation communication system is the Vienna 5G link level simulator, which simulates new concepts in 5G communication systems and mainly focuses on multi carrier systems. The implementation of dual fading and spatial channel models for processing time discrete signals is detached from any deterministic environment and maintained at a general level of implementing random functions. For P2P links that provide low THz ranges of hundreds of Gbit/s in the future, system performance largely depends on the deployment environment, and single carrier systems will make a comeback.

The Aff3ct library handles efficient implementation of forward error correction algorithms in C++and provides a wide range of FEC code and various decoders. It can also run LLS to implement the entire digital communication chain. The simulator remains at the bit level and only implements digital channels without any waveform generation. The ability to analyze the impact of signal and waveform related effects on data transmission is limited.

The ns-3 extension TeraSim is a system level simulator used for network simulation. Data transmission is modeled at the packet level, and the successful reception of data packets is determined based on the received power. The simulator adapts to terahertz communication through its channel module, which considers path loss related to frequency and specifically considers molecular absorption throughout the entire terahertz frequency band. The implementation of the signal is limited to the consideration of power density spectrum. The influence of intersymbol interference or multipath propagation cannot be checked.

The currently available LLS cannot meet all the requirements for simulating multi gigabit P2P links at terahertz frequency. SiMoNe has been expanded through link level modules to fill this gap. Channel representation includes broadband channel models, processing of time discrete signals in equivalent low-pass regions, and RF loss reduction. Due to its integration into the SiMoNe framework, LLS benefits from the interface of propagation simulation through real-time ray channel prediction and system level functions, which allow easy access to real-world interference simulations.

Technical concepts

The development of SiMoNe began in 2014 as a tool for system level simulation of mobile wireless networks. Since then, it has developed into a simulation suite for real propagation and system level modeling of wireless communication systems.

For LLS, focusing on the signal processing of a link rather than the behavior of the network poses different requirements for component development. Due to the large bandwidth and high data rate envisioned for THz communication, strict runtime requirements are imposed on LLS.

With the rapid development of terahertz communication technology, simulators must have adaptability and flexibility to respond to new concepts, hardware, and simulation technologies. The modular combination of simulators allows for this. The functions should be bundled in interchangeable and connectable modules. Programming language, as an object-oriented language, provides concepts such as abstract classes and inheritance. By using parent classes to provide common functionality for different subclasses, code duplication can be reduced while allowing for interchangeability.

The mobile network simulator includes a framework for analyzing 3D scenes using ray optics methods. It can be used to predict the delay and amplitude of different communication paths, while considering the positions and directions of the transmitter and receiver. By implementing the interface of this framework, ray optics methods can be used in LLS to export realistic 3D scene channel information. It allows for simulating various scenarios and comparing measurement results with simulations, or drawing conclusions from scenarios where measurements may not be accessible.

SiMoNe is used in multiple research projects and collaborates with other research partners. It is crucial to have appropriate interfaces for collaboration and simulation data exchange with third parties. This framework provides import and export functions in. mat and. csv formats. Although MATLAB is a mature tool,. csv files are usually used to exchange data and allow high interoperability and universal use in many different programs and environments. By keeping in mind the need for interoperability, we can ensure that research conducted using SiMoNe can be shared with the research community and have a valuable impact.

PHY Layer Model and Simulator Implementation

The so-called link level coordinator serves as a control instance for simulation. It holds all configuration parameters and provides them to the actual transmission chain block. The coordinator controls block iteration until a statistically significant number of transmission bits are reached in the sink block. Every time the coordinator calls a block, the bit source block creates a configurable number of pseudo random bits. The created bits are provided as the status of the following encoder blocks.

Channel encoding for terahertz communication is a challenging task, as high data rates imply the need for efficient encoding and decoding of transmitted symbols. The IEEE standard 802.15.3d foresees advanced codecs that allow for efficient hardware implementation. The Aff3ct encoding library is a highly optimized C++library that can quickly implement various encoding schemes. Its encoding and decoding functions have been integrated into LLS to benefit from its efficient channel encoding.

Due to the fact that LLS is written in the C # programming language and the Aff3ct encoding library uses native C++, these two software projects cannot be directly compatible. Added a wrapper library using pointer programming techniques to handle and convert calls between two software. By using this wrapper, Hamming, RS, and LDPC codes are provided. Hamming and RS code can be configured using internal library parameters, while the custom generator and verification matrix of LDPC code are created according to standards and imported into the integrated Aff3ct library. Encoding bitb[k]Provided as the state of the modulator block.

Top of Rack Link Analysis in Data Center Scenarios

An efficient data center network is a necessary condition to meet the challenges of this century, requiring ultra-low latency, reliability, and flexibility. The additional wireless link will enable fast reconfigurability, improving the performance and efficiency of the DC. The ToR area is a promising area for inter rack connections, and it is highly likely to achieve line of sight connections. In a real-world DC model, a ray tracing based channel model is used to evaluate the performance of a single ToR link through link level simulation.

The DCs under investigation are organized by row. The plastic curtains above each row of cabinets are a characteristic of this DC, which divides it into hot and cold zones to ensure efficient and energy-saving airflow for cooling. TX and RX are located on the same line in the middle of the DC. TX and RX are initially placed at a distanced=On adjacent racks of 0.69m, then add another rack untild

Compared to higher-order modulation such as 16QAM, which provides smaller bandwidth at the same data rate, a combination of lower modulation orders and higher bandwidth is more robust. This observation supports a method of terahertz communication to utilize the large available bandwidth of terahertz frequency and low order modulation schemes.

RF reduction has a significant impact on data transmission and will shorten the maximum transmission distance. The amplitude is strongly influenced by the TF of PA and LNA, making it impossible to use QAM for data transmission. The interaction between pulse type and RF damage that leads to different BERs. This emphasizes the absolute need to consider radio frequency characteristics in order to reliably predict the PHY performance of low terahertz communication systems.

conclusion

The modular link level simulator uses high bandwidth and single carrier modulation as defined in IEEE standard 802.15.3d. Modeling precise transmission pulses and channels, antenna characteristics, and actual thermal noise of RX can achieve close modeling and simulation of hardware characteristics. The time discrete model provides the possibility of incorporating hardware characteristics and RF damage, which has a significant impact on the development of cutting-edge hardware for simulating low terahertz frequency bands. The simulator has been compared with state-of-the-art technology to demonstrate the necessity of novel simulation methods and the benefits of integrating the overall simulation suite of propagation, link level and system level simulations.

To demonstrate its operability, the simulator has been validated through AWGN simulation and comparison with MATLAB tools. The application in the ToR scenario of wireless enhanced DC demonstrates the general system performance of a single link with state-of-the-art hardware parameters.

reference:

Hagenauer, J., Offer, E., and Papke, L. (1996). Iterative decoding of binary block and convolutional code. IEEE Transactions on Information Theory, 42 (2), 429-445.

4. Moro Megar, D., Cojocari, O., Oprea, I., Hoefle, H., and Rickes, M. (2018). 275-305GHz transceiver based on high-power split Schottky diodes for FMCW radar. The 29th IEEE International Symposium on Space Terahertz Technology (ISSTT2018, pp. 233-235).

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