CSI Feedback-based CS for Underwater Acoustic Adaptive Modulation OFDM System with Channel Prediction

In this paper, we investigate the performance of adaptive modulation （AM） orthogonal frequency division multiplexing （OFDM） system in underwater acoustic （UWA） communications. The aim is to solve the problem of large feedback overhead for channel state information （CSI） in every subcarrier. A novel CSI feedback scheme is proposed based on the theory of compressed sensing （CS）. We propose a feedback from the receiver that only feedback the sparse channel parameters. Additionally, prediction of the channel state is proposed every several symbols to realize the AM in practice. We describe a linear channel prediction algorithm which is used in adaptive transmission. This system has been tested in the real underwater acoustic channel. The linear channel prediction makes the AM transmission techniques more feasible for acoustic channel communications. The simulation and experiment show that significant improvements can be obtained both in bit error rate （BER） and throughput in the AM scheme compared with the fixed Quadrature Phase Shift Keying （QPSK） modulation scheme. Moreover, the performance with standard CS outperforms the Discrete Cosine Transform （DCT） method.

Study of adaptive modulation and LDPC coding in multicarrier systems

An adaptive modulation （AM） algorithm is proposed and the application of the adapting algorithm together with low-density parity-check （LDPC） codes in multicarrier systems is investigated. The AM algorithm is based on minimizing the average bit error rate （BER） of systems, the combination of AM algorithm and LDPC codes with different code rates （half and three-fourths） are studied. The proposed AM algorithm with that of Fischer et al is compared. Simulation results show that the performance of the proposed AM algorithm is better than that of the Fischer＇s algorithm. The results also show that application of the proposed AM algorithm together with LDPC codes can greatly improve the performance of multicarrier systems. Results also show that the performance of the proposed algorithm is degraded with an increase in code rate when code length is the same.

Simultaneous wireless information and power transfer with fixed and adaptive modulation

Activating Wireless Power Transfer (WPT) in Radio-Frequency (RF) to provide on-demand energy supply to widely deployed Internet of Everything devices is a key to the next-generation energy self-sustainable 6G network. However, Simultaneous Wireless Information and Power Transfer (SWIPT) in the same RF bands is challenging. The majority of previous studies compared SWIPT performance to Gaussian signaling with an infinite alphabet, which is impossible to implement in any realistic communication system. In contrast, we study the SWIPT system in a well-known Nakagami-m wireless fading channel using practical modulation techniques with finite alphabet. The attainable rate-energy-reliability tradeoff and the corresponding rationale are revealed for fixed modulation schemes. Furthermore, an adaptive modulation-based transceiver is provided for further expanding the attainable rate-energy-reliability region based on various SWIPT performances of different modulation schemes. The modulation switching thresholds and transmit power allocation at the SWIPT transmitter and the power splitting ratios at the SWIPT receiver are jointly optimized to maximize the attainable spectrum efficiency of wireless information transfer while satisfying the WPT requirement and the instantaneous and average BER constraints. Numerical results demonstrate the SWIPT performance of various fixed modulation schemes in different fading conditions. The advantage of the adaptive modulation-based SWIPT transceiver is validated.

LSTM-Based Adaptive Modulation and Coding for Satellite-to-Ground Communications

Satellite communication develops rapidly due to its global coverage and is unrestricted to the ground environment. However, compared with the traditional ground TCP/IP network, a satellite-to-ground link has a more extensive round trip time(RTT) and a higher packet loss rate,which takes more time in error recovery and wastes precious channel resources. Forward error correction(FEC) is a coding method that can alleviate bit error and packet loss, but how to achieve high throughput in the dynamic network environment is still a significant challenge. Inspired by the deep learning technique, this paper proposes a signal-to-noise ratio(SNR) based adaptive coding modulation method. This method can maximize channel utilization while ensuring communication quality and is suitable for satellite-to-ground communication scenarios where the channel state changes rapidly. We predict the SNR using the long short-term memory(LSTM) network that considers the past channel status and real-time global weather. Finally, we use the optimal matching rate(OMR) to evaluate the pros and cons of each method quantitatively. Extensive simulation results demonstrate that our proposed LSTM-based method outperforms the state-of-the-art prediction algorithms significantly in mean absolute error(MAE). Moreover, it leads to the least spectrum waste.

PERFORMANCES OF ADAPTIVE MODULATION AND CODING IN SATELLITE MOBILE CHANNEL

Given that satellite mobile channel is a time-varying channel,Adaptive Modulation and Coding(AMC) was proposed to provide robust and spectrally efficient transmission over satellite mobile channel.Three different kinds of channel environment were considered in this paper:the urban area,the rural area,and the open space.Four combinations of modulation and coding were designed to meet reliable communication on time-varying channel,and spectral efficiency and system throughput of these three kinds of channel environment were simulated.Based on the simulation results,this paper analysed the results and compared the performances of AMC with non-AMC system in these three kinds of channel environment.At last,we come to the conclusions:a system with AMC can achieve higher spectral efficiency and better system throughput;and the spectral efficiency and system throughput of AMC system will be higher on better satellite mobile channel.

Adaptive Modulation and Coding Based on Fuzzy Logic Cognitive Engine

Adaptive modulation and coding( AMC) which depends on channel state information( CSI) can make the modulation and coding scheme( MCS) for the sender changed, and make the spectrum efficiency enhanced. The traditional method of AMC establishes a lookup table of MCSs at first,and then the sender chooses the proper MCS according to the CSI from feedback channel. However,this method is not suitable for frequency selective and fast fading channel. Thus, a method based on fuzzy logic cognitive engine is proposed in this paper. The type of channel is recognized by the fuzzy logic cognitive engine,then the MCSs are modified to suit for the channel type. The simulation results show that the proposed method is more suitable for frequency selective and fast fading channel. And it is more reliability under the condition of meeting the bit error rate( BER).

Cluster Modulation: A Generalized Modulation Scheme Leading to NOMA or Adaptive Modulation

The need for higher data rate and higher systems capacity leads to several solutions including higher constellation size, spatial multiplexing, adaptive modulation and Non-Orthogonal Multiple Access (NOMA). Adaptive Modulation makes use of the user’s location from his base station, such that, closer users get bigger constellation size and hence higher data rate. A similar idea of adaptive modulation that makes use of the user’s locations is the NOMA technique. Here the base station transmits composite signals each for a different user at a different distance from the base station. The transmitted signal is formed by summing different user’s constellations with different weights. The closer the users the less average power constellation is used. This will allow the closer user to the base station to distinguish his constellation and others constellation. The far user will only distinguish his constellation and other user’s data will appear as a small interference added to his signal. In this paper, it is shown that the Adaptive modulation and the NOMA are special cases of the more general Cluster Modulation technique. Therefore, a general frame can be set to design both modulation schemes and better understanding is achieved. This leads to designing a multi-level NOMA and/or flexible adaptive modulation with combined channel coding.

Research on Threshold Adjustment Algorithm in Adaptive Modulation and Coding

Adaptive Modulation and Coding （AMC） has gained a lot of attentions in the research of High Speed Downlink Packet Access （HSDPA）. The idea is to adapt the transmission to the fast changing channel conditions by the use of different Modulation and Coding Schemes （MCS）. This paper presents an adaptive AMC algorithm and introduces a theoretical analysis model in order to to investigate its throughput and Frame Error Rate （FER）. Subject to the given FER target, our numerical and link level simulation results both show that our algorithm outperforms other existing adaptive algorithms.

Cross-layer combining of power control and adaptive modulation with truncated ARQ for cognitive radios

To maximize throughput and to satisfy users＇ requirements in cognitive radios, a cross-layer optimization problem combining adaptive modulation and power control at the physical layer and truncated automatic repeat request at the medium access control layer is proposed. Simulation results show the combination of power control, adaptive modulation, and truncated automatic repeat request can regulate transmitter powers and increase the total throughput effectively.

Adaptive modulation for SVD-based MIMO systems with outdated CSI

The performance of singular value decomposition （SVD）-based multiple-input multiple-output （MIMO） with adaptive modulation （AM） is dependent on the accuracy of the channel state information （CSI） at the transmitter and the receiver. However, for a time-varying channel, the CSI obtained at the transmitter or the receiver is incorrect owing to an inherent delay or error. A typical system employing SVD suffers degradation in capacity when outdated CSI is used to transmit data. This article first addresses the adaptive modulation MIMO system designed under perfect CSI assumption. Based on that, two scenarios of outdated CSI are investigated and analyzed. The effect of imperfect CSI on the system performance is focused on and a simple post processing SNR （pSNR） adjustment design is proposed on AM system in the two scenarios for reducing degradation in average spectral efficiency （ASE）. Simulation results show that these designs provide good performance in an adaptive way, and enable the adaptive MIMO system considerably more to be robust against CSI imperfection.

Performance of two-way amplify-and-forward relaying with adaptive modulation over Nakagami-m fading channels

This paper investigates the performance of a two-way amplify-and-forward （AF） relay system with adaptive modulation over independent and non-identical Nakagami-m fading channels. The tight closed-form cumulative distribution function （CDF） expression of the instantaneous end-to-end signal-to-noise ratio （SNR） is provided. Further, approximate closed-form expression for the average spectral efficiency of the two-way AF system with adaptive modulation is obtained. Then, a tight lower bound of outage probability is derived. Finally, we use numerical simulations to verify the tightness of our analytical results.

Feedback Stabilization over Wireless Network Using Adaptive Coded Modulation

In this paper,we apply adaptive coded modulation (ACM) schemes to a wireless networked control system (WNCS) to improve the energy efficiency and increase the data rate over a fading channel.To capture the characteristics of varying rate, interference,and routing in wireless transmission channels,the concepts of equivalent delay (ED) and networked condition index (NCI) are introduced.Also,the analytic lower and upper bounds of EDs are obtained.Furthermore,we model the WNCS as a multicontroller switched system (MSS) under consideration of EDs and loss index in the wireless transmission.Sufficient stability condition of the closed-loop WNCS and corresponding dynamic state feedback controllers are derived in terms of linear matrix inequality (LMI). Numerical results show the validity and advantage of our proposed control strategies.

Pragmatic Approach to Adaptive Turbo Coded Modulation

This paper presents a pragmatic adaptive scheme for TuCM over slowly fading channels. The adaptive scheme employs a single turbo coded modulator composed of a variable-rate turbo encoder and a variable-rate variable-power MQAM for all fading regions, so it has an acceptable complexity to implement. The optimal adaptive TuCM scheme is determined subject to various system constraints. Simulations have been performed to measure the performance of the scheme for different parameters. It is shown that adopting both the turbo coded modulator and the transmit power achieves a performance within 2.5 dB of the fading channel capacity.

A Joint Rate Control and AMC Algorithm for Adaptive Transmission Systems

The traditional communication system is effectively designed for the worst-case channel state and it can not use the spectral efficiently over the time-varying multipath channel. In order to improve the spectral efficiency and ensure robust and spectrally-efficient transmission over the time-varying multipath channel,a joint rate control and adaptive modulation and coding ( AMC) algorithm for adaptive transmission systems is proposed in this paper. Firstly,the proposed algorithm can formulate a modulation and coding scheme ( MCS) switching table according to the offline simulation results and the target bit error rate ( BER) . Then,the optimal MCS is selected in MCS switching table according to the channel state information ( CSI) and then passes to the transmitter and receiver to implement. So the adaptive system which always uses the optimal MCS to transmit signals uses the spectral efficiently. The simulation results validate the proposed algorithm and show that under the premise of meeting the target BER,the adaptive system performing the proposed algorithm has a higher average spectral efficiency ( ASE) than that of the non-adaptive system.

MCS Selection Criteria Based on Performance Simulation for HSDPA

An adaptive modulation and coding (AMC) scheme integrated with multi-code transmission for high speed downlink packet access is presented and some modulation and coding scheme (MCS) selection criteria are proposed to maximize single user data rates. Based on link-level performance analysis, the MCS selection criteria are proposed with the constraints of QoS requirement, modulation level, channel coding rate and the number of available channelization codes. By allowing multiple transmission parameters changing, these criteria make the scheme more flexible to time-varying mobile channel with comparatively low complexity through a look-up table method. The AMC scheme is sensitive to the changes of channel condition and can save the channelization codes in an applicable way by applying these criteria.

A Low Complexity Algorithm for Subcarrier-and-Bit Allocation in OFDMA-Based LTE Systems

In this paper, we propose optimum and sub-optimum resource allocation and opportunistic scheduling solutions for orthogonal frequency division multiple access （OFDMA）-based multicellular systems. The applicability, complexity, and performance of the proposed algorithms are analyzed and numerically evaluated. In the initial setup, the fractional frequency reuse （FFR） technique for inter-cell interference cancellation is applied to classify the users into two groups, namely interior and exterior users. Adaptive modulation is then employed according to the channel state information （CSI） of each user to meet the symbol error rate （SER） requirement. There then, we develop subcarrier-and-bit allocation method, which maximizes the total system throughput subject to the constraints that each user has a minimum data rate requirement. The algorithm to achieve the optimum solution requires high computational complexity which hinders it from practicability. Toward this suboptimum method with the reduced to the order of O（NIO, the total number of subcarriers end, we complexity propose a extensively where N and K denote and users, respectively. Numerical results show that the proposed algorithm approaches the optimum solution, yet it enjoys the features of simplicity, dynamic cell configuration, adaptive subearrier-and-bit allocation, and spectral efficiency.

AQAM under high time delay spread conditions

An analysis process is described for adaptive quadrature amplitude modulation(AQAM)of constant-power constant-symbol-rate over frequency-selective Rayleigh fading channels with inter symbol interference(ISI)and Gaussian noise.The delay spread resistance of the AQAM scheme is put forward by studying its average throughput and average bit-error-rate(BER),both of which can be expressed as functions of two variables,the ratio of root mean square(RMS)delay spread to symbol period and the ratio of average symbol energy to noise.Average throughput reacts regularly to the latter,whereas it does not react to the former.The AQAM scheme is highly superior in the delay spread resistance in comparison with the fixed modulation modes.Gains of the AQAM scheme over the fixed modes become more significant as the delay spread becomes severer or the average throughput decreases.

Adaptive power loading with BER-constraint for OFDM systems

A novel adaptive power loading algorithm with the constraint of target overall bit error rate （BER） for orthogonal frequency division multiplexing （OFDM） systems is proposed in this article. The proposed algorithm aims to minimize the required transmit power with fixed data rate and uniform （nonadaptive） bit allocation, while guaranteeing the target overall BER. The power loading is based on the unequal-BER （UBER） strategy that allows unequal mean BERs on different subcarriers. The closed-form expressions for optimal BER and power distributions are derived in this article. Simulation results indicate the superiority of the proposed algorithm in terms of BER performance and algorithmic complexity.

A cross-layer adaptive transmission scheme over correlated fading channels

Conventional adaptive transmission schemes perform poorly in wireless correlated slow-fading channels.A cross-layer adaptive transmission scheme combined with selective repeat automatic repeat request(SR-ARQ)is proposed.We apply a multi-state Markov system model for analyzing the performance of systems and optimizing the selection of modulation levels and packet sizes in correlated fading channels,which is also described by a finite-state Markov chain.A general closed-form expression of the average throughput for our suggested scheme is presented.Numerical results show that our adaptive scheme combined with SR-ARQ can obtain good performance in correlated fading channels.