Optimization of Adaptive Communication Systems with Feedback Channels

This paper presents capacity limits of novel position aware adaptive cellular communication systems exploiting channel state information (CSI) at the transmitter (CSIT). The position aware adaptive communication systems are benchmarked against state-of-the-art adaptive modulation and coding (AMC) systems that use only feedback or predict CSIT in addition to the feedback CSI. We analyze the position aware adaptive communication systems both with perfect and imperfect position information. Numerical results demonstrate that position aware adaptive systems operate close to the channel capacity over a large range of feedback delays and channel variability with perfect position information. Further, position aware adaptive communication systems can outperform state-of-the-art AMC systems for Gaussian distributed position errors with standard deviations smaller than 2.5 m by more than 0.6 bits/s/Hz.

This paper evaluates at the various modulation and coding techniques suitable for adaptive data communication system. The techniques evaluated are applicable to HF spectrum. Examples of modulation and coding scheme that are evaluated include PACTOR I, PACTOR II, PACTOR III, GTOR and STANAG 4285. Analysis of system performance is made in the presence of AWGN with future extension for multipath fading conditions. Comparison will be made based on the bit-error rate (BER), packet-error rate (PER) and the throughput. In addition, the effective data rate for all the schemes is compared with the Shannon capacity limit to ensure the optimal utilization of the given channel bandwidth. The modulation and coding scheme that meets all of the above requirements will be used for future adaptive data communication system.

The paper considers the implementation of adaptive video communication systems. The analysis of the current state of models of color perception is presented on the basis of which conclusions are drawn and further ways of solving problems of correct color representation in adaptive systems are proposed. The results of using the mesopic and scotopic vision apparatus in the framework of one color perception model are presented. Recommendations for further modernization of the color perception model, as well as expansion of the functionality of adaptive video communication systems are given.

An adaptive rate communication system based on the new DECT standard is evaluated. One of the three modulated signals, namely /spl pi//2-D2PSK, /spl pi//4-D4PSK and /spl pi//8-D8PSK, is chosen for transmission, according to the channel conditions estimated by the Euclidean distance between the received and detected signals. The simulations show that the adaptive rate DECT system tracks a slowly varying fading channel with Rayleigh distribution in the case of low mobile unit speed. The achieved data throughput is up to three times higher in comparison to the fixed rate DECT communication system. It is shown also that in the presence of cochannel interference, the Euclidean distance switching approach is superior to the RSSI approach.

Covert channels are secret communication paths, which existance is not expected in the original system design. Covert channels can be used as legimate tools of censorship resistance, anonimity and privacy preservation to address issues with rdquonationalrdquo firewalls, citizen profiling and other rdquounethicalrdquo uses of Information Technology. Current steganographic methods that implement covert channels within network traffic, are highly dependent on particular media data or network protocol to hide data. In this paper we investigate the methods and an algorithm for implementing adaptive covert communication system that works on real-world Internet, capable of using multiple application-level protocols as its communication media and can be implemented as network application, therefore requires no system modifications of communicating nodes. The key difference from previous solutions is the use of adaptive redundant mechanism, which allows real-time underlying protocol switching and adaptation to the dynamic network configuration changes. Further, covert channels can be extended with P2P architecture in order to improve channel ressistance.

A new approach to drift compensation in adaptive feedback communication systems is presented in the paper. The proposed approach is based on application of the extended multidimensional algorithm that estimates simultaneously the value of a transmitted sample and the value of an unknown drift rate. The knowledge of a drift rate enables compensation of drifts and improves transmission efficiency of systems suffering problems with drifts.

With the gradual improvement of the future wireless communication technology, the demand for high information capacity and reliable links in communication systems is also ever-increasing. Programmable topological plasmonic metasurfaces, consisting of artificially engineered structures with robust propagation pathways control, have emerged as a revolutionary technology for stable microwave and on-chip communication systems. Programmable topological plasmonic metasurfaces offer unprecedented flexibility and adaptability in managing multiple communication channels as the propagation paths can be easily reconfigured to meet specific communication requirements. Here, we have experimentally demonstrated the ability to dynamically manipulate electromagnetic waves along eight distinct topological pathways for a multichannel direct communication system. The simulation results of topological plasmonic metasurfaces with different coding schemes have showcased their excellent performance in multichannel wavefront control. Experimental results have consistently aligned with the simulation findings, validating the effectiveness of multichannel topological routes. Furthermore, an eight-channel direct communication system based on a programmable topological plasmonic metasurface is designed and implemented to transmit different information. The proposed multichannel communication system based on a programmable topological plasmonic metasurface opens up new possibilities for high-capacity, efficient, and adaptive communication systems, which hold great potential in transformative applications in areas such as 6G, Internet of Things, and beyond.

In this work, we propose a Visible Light Communication (VLC) system dynamically adapting, through a decision-making process based on a simple fuzzy-logic, the transmitting color selection to the external environmental conditions. Transmitted Signals are opportunistically treated through softwarization approaches by using basic hardware (i.e. Arduino boards and inexpensive LEDs in the transmitting stage) in order to implement an effective, end-to-end, adaptive communication system. In particular, we will show that, if a low environmental noise is added, the system keeps to be well-performing in terms of Bit Error Rate (BER) also at higher distances (up to 8–9 m) using a warm white front-end, while, if high external interfering lights are present in the environment, a low power red front end is dynamically fed for maintaining a good-level communication (with low Bit Error Rate).

Recently, multiple-input multiple-output (MIMO) technologies are adopted to wireless communication systems for high-speed, large capacity and high reliability communications. However, there can be variations of communication quality and throughput performance, because MIMO technologies depend on propagation channel environments, where communication property widely changes. An optimal wireless communication systems design which adaptively changes transmission systems depending on channel propagation is effective to realize stable wireless communications therefore, it is important that a transceiver knows propagation environment accurately. In this paper, we propose a new discrimination method for MIMO propagation scenarios by using channel state information (CSI), where azimuth spread (AS) and K-Factor estimation are considered. In addition, we evaluate discrimination performance by simulation, and then we get a discrimination result of high accuracy.

Millimeter-wave switches are essential for reconfigurable and adaptive communication systems, yet current solutions often face trade-offs between performance, scalability, and cost. Here we present a scalable, high performance and cost-effective approach to develop reconfigurable millimeter-wave substrate integrated waveguide (SIW) devices by integrating vanadium dioxide (VO₂) thin films with printed circuit board (PCB) technologies. The integration technique involves depositing VO₂ films on thin, flexible polymer substrates, which are then transferred and affixed to PCB circuits. The VO₂ is thermally activated and selectively doped to reduce power consumption depending on applications. Using experimental prototypes, we demonstrate several reconfigurable devices operating in the millimeter-wave band, including series and parallel switches and a reconfigurable hybrid coupler that transforms into dual through-line SIWs. Electromagnetic simulations and measurements validate the approach, revealing low insertion loss, good isolation, and broadband operation. This method simplifies fabrication and supports large-area integration, offering a practical route to scalable, low-cost, reconfigurable millimeter-wave components.

With the development of the underwater acoustic (UWA) adaptive communication system, energy-efficient transmission has become a critical topic in underwater acoustic (UWA) communications. Due to the unique characteristics of the underwater environment, the transmitter node will almost always have outdated channel state information (CSI), which results in low energy efficiency. In this paper, we take full advantage of bidirectional links and propose an adaptive modulation and coding (AMC) scheme that aims to maximize the long-term energy efficiency of a single link by jointly scheduling the coding rate, modulation order, and transmission power. Considering the complexity characteristics of UWA channels, we proposed a bit error ratio (BER) estimation method based on deep neural networks (DNN). The proposed network could realize channel estimation, feature extraction, and BER estimation by using a fixed pilot of the feedback link. Then, we design a channel classification method based on the estimated BERs of the modulation and coding scheme (MCS) and further model the UWA channels as a finite-state Markov chain (FSMC) with an unknown transition probability. Thus, we formulate the AMC problem as a Markov Decision Process (MDP) and solve it through a reinforcement learning framework. Considering the large state-action pairs, a double deep Q-network (DDQN) based scheme is proposed. Simulation results demonstrate that the proposed AMC scheme outperforms the fixed MCS with a perfect channel information state, and achieves near-optimal energy efficiency.

This paper introduces a communication system model with renewable power supply. As we assumed a battery-free microgrid system with conventional power as a backup power supply, we propose a method of power state and data transmission scheduling for delay-tolerant communication networks, which reduces conventional power consumption by operating adaptively to changes in renewable power. We found through computer simulations that the proposed method efficiently reduced conventional power consumption.

The paper presents an overview of design methodology and results of experiments with a Prototype of highly efficient optimal adaptive feedback communication systems (AFCS), transmitting low frequency analog signals without coding. The paper emphasizes the role of the forward transmitter saturation as the factor that blocked implementation of theoretical results of pioneer (1960-1970s) and later research on FCS. Deepened analysis of the role of statistical fitting condition in adequate formulation and solution of AFCS optimization task is given. Solution of the task – optimal transmission/reception algorithms is presented in the form useful for elaboration of the hardware/software Prototype. A notable particularity of the Prototype is absence of the encoding/decoding units, whose functions are realized by the adaptive pulse amplitude modulator (PAM) of the forward transmitter (FT) and estimating/controlling algorithm in the receiver of base station (BS). Experiments confirm that the Prototype transmits signals from FT to BS “perfectly”: with the bit rate equal to the capacity of the system, and with limit energy [J/bit] and spectral [bps/Hz] efficiency. Another, not less important and confirmed experimentally, particularity of AFCS is its capability to adjust parameters of FT and BS to the characteristics of scenario of application and maintain the ideal regime of transmission including spectralenergy efficiency. AFCS adjustment can be made using BS estimates of mean square error (MSE). The concluding part of the paper contains discussion of the presented results, stressing capability of AFCS to solve problems appearing in development of dense wireless networks.

The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -user cyclic Z-interference channel models a situation in which the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> th transmitter causes interference only to the ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> -1)th receiver in a cyclic manner, e.g., the first transmitter causes interference only to the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> th receiver. The impact of noiseless feedback on the capacity of this channel is studied by focusing on the Gaussian cyclic Z-interference channel. To this end, the symmetric feedback capacity of the linear shift deterministic cyclic Z-interference channel is completely characterized for all interference regimes. Using insights from the linear deterministic channel model, the symmetric feedback capacity of the Gaussian cyclic Z-interference channel is characterized up to within a constant number of bits. As a byproduct of the constant gap result, the symmetric generalized degrees of freedom with feedback for the Gaussian cyclic Z-interference channel are also characterized. These results highlight that the symmetric feedback capacities for both linear and Gaussian channel models are in general functions of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> , the number of users. Furthermore, the capacity gain obtained due to feedback decreases as <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> increases.

In this paper, we study the problem of stabilizability of LTI systems over both the forward (from the controller to the plant) and feedback (from the sensor to the controller) channel. We adopt the additive white noise (AWN) channel with a prescribed power constraint as our channel model. For first order systems, we derive explicitly the necessary and sufficient conditions for stabilizability and show the tradeoff between the minimum signal-to-noise ratio (SNR) required for the forward and feedback channel. We also show explicitly that the use of two-parameter controller in this problem assumes better performance.