Cross-Layer Design for Multiuser MIMO MRC Systems With Feedback Constraints

In this paper, we propose a throughput optimization scheme for relay protocols based on Adaptive Modulation and Coding (AMC). The performance of relay protocols with the AMC scheme and show that relay protocols with the AMC scheme are capable of providing better average throughput at a lower Signal to Noise Ratio (SNR) level as compared to the conventional scheme with no AMC. We perform 3GPP Long Term Evolution-Advanced (LTE-A) parameters based simulations to prove the performance comparison of adaptive Modulation and Coding Scheme (MCS) relay protocols with non-adaptive MCS relay protocols. The simulation results of the proposed system with adaptive MCS prove that among the Amplify-and-Forward (AF), Decode-and-Forward (DF) and De-Modulate-and-Forward (DMF), the DMF protocol performs best, at a lower SNR value and higher average throughput.

Long Term Evolution (LTE) network offers a high throughput with low latency that makes it the best choice for Evolved Multimedia Broadcast Multicast Service (E-MBMS). E-MBMS transmits data to all users simultaneously using the same channel and same Modulation and Coding Scheme (MCS) level. Each user experiences different channel condition, so an MCS level should be selected properly to satisfy all users. Typically, MCS level is selected on the basis of users' worst channel condition which results in wasting network resources. Since the E-MBMS performance directly depends on the selected MCS level, an efficient Adaptive Modulation and Coding (AMC) scheme is essentially needed. This paper introduces a new mechanism that uses the Standard Deviation (SD) of MCS level of E-MBMS user group operated on single cell mode to efficiently select its optimal MCS level. Simulation results show that the proposed mechanism increase the spectrum efficiency, throughput, and lower Packet Loss Ratio compared to the Worst User Channel Condition mechanism and Fixed Predefined MCS mechanism.

In this paper, a joint cross-layer design of adaptive modulation and coding (AMC) and cooperative automatic repeat request (C-ARQ) scheme is proposed for a secondary user in a shared-spectrum environment. First, based on the statistical descriptions of the channel, closed-form expressions of the average spectral efficiency (SE) and the average packet loss rate (PLR) are presented. Then, the cross-layer scheme is designed, with the aim of maximizing the average SE while maintaining the average PLR under a prescribed level. An optimization problem is formed, and a sub-optimal solution is found: the target packet error rates (PER) for the secondary system channels are obtained and the corresponding sub-optimal AMC rate adaptation policy is derived based on the target PERs. Finally, the average SE and the average PLR performance of the proposed scheme are presented.

A low-density parity-check (LDPC) coded adaptive modulation and coding (AMC) strategy is presented for orthogonal frequency division multiplexing (OFDM) systems. Since system performance is improved as the maximum iteration times for LDPC decoding increase, iteration times for decoding reflect channel quality. We first propose an AMC strategy to utilize the information of iteration times for decoding to adopt higher order modulation and coding schemes (MCS) than the conventional strategy, so as to improve system throughput. Since it may bring worse reliability, hybrid automatic repeat request (H-ARQ) is used in a second strategy. Simulation under typical urban channel is carried out, and the results show the proposed strategies can bring higher throughput, and the strategy with H- ARQ can improve throughput and guarantee reliable transmission simultaneously.

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 presents the performance of outer-loop control for adaptive modulation and coding (AMC) using mutual information (MI) based mapping between the block error rate (BLER) and received signal-to-interference plus noise power ratio (SINR) in the multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) downlink employing maximum likelihood detection (MLD). In AMC, we generate a mapping table between the BLER and MI per bit in advance, which is computed from the received SINR, assuming typical channel conditions including the path model and fading maximum Doppler frequency. Then, in the proposed outer-loop control, the measured MI per bit value for selecting the best modulation and coding scheme (MCS) is adjusted so that the measured BLER after turbo decoding satisfies the prescribed target value. Computer simulation results show that the outer-loop control achieves almost the same throughput as that with a mapping table assuming channel conditions identical to those for the actual measurement, while achieving nearly the identical target BLER. Moreover, we show that the best step size, which provides nearly the maximum throughput, differs according to the change in the maximum Doppler frequency in contrast to the relative feedback delay of the AMC loop. Nevertheless, it is insensitive to the target BLER value and frequency-selectivity of a channel model.

This paper presents a performance model of a wireless network with one-antenna transmitter scheduling information towards a set of terminals in a time-division fashion. Each terminal is enabled with a multiple-antenna maximum ratio combining (MRC) receiver. The objective of this model is to evaluate the performance of adaptive modulation and coding (AMC) in Rayleigh fading channels under two assumptions: 1) correlation between antennas, and 2) user scheduling based on maximum channel gain. The model is useful for cross-layer design purposes, as it provides a relatively low-complex representation of the physical-layer. Closed-form expressions are here derived of correct packet reception probabilities for different modulation and coding schemes (MCSs) with different values of block error rate (BLER) and spectral efficiency. Analytic expressions are derived with the help of the theory of order statistics, which allows for the study of the statistics of channel-aware scheduling. The results indicate that correlation does not always reduce performance. At low signal-to-noise ratio (SNR), correlation can improve performance rather than reducing it. By contrast, at high SNR, correlation is shown to always reduce the performance of the receiver. This low-SNR behavior is less evident as the number of antennas increases and more evident when the number of users included in the scheduling process increases.

This paper presents the effect of joint modulation and coding scheme (MCS) selection on a turbo soft interference canceller (SIC) for OFDM-MIMO multiplexing using adaptive modulation and coding (AMC). We use a turbo SIC to detect signals by performing iterative interference cancellation using soft-symbol estimates based on the a posteriori log-likelihood ratio (LLR) at the Max-Log-MAP decoder output and linear minimum mean-square error (LMMSE)-based signal detection. Joint MCS section selects the best MCS combinations of all transmission streams so that the total throughput is maximized considering the residual interference from other streams for the turbo SIC. Computer simulations show that the joint MCS selection mitigates the decrease in throughput due to the large difference in the peak data rate between consecutive MCSs compared to independent MCS selection. Hence, we show that by using joint MCS selection, the total throughput with the number of MCSs of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MCS</sub> = 8 becomes almost identical to that for N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MCS</sub> = 12 for 4-by-4 MIMO multiplexing using the turbo SIC.

We address the application of adaptive modulation and coding (AMC) for third-generation (3G) wireless systems. We propose a new method for selecting the appropriate modulation and coding scheme (MCS) according to the estimated channel condition. We take a statistical decision making approach to maximize the average throughput while maintaining an acceptable frame error rate (FER). We use a first-order finite-state Markov model to represent the average channel signal-to-noise ratio (SNR) in subsequent frames. The MCS is selected in each state of this Markov model (among the choices proposed in the 3G standards) to maximize the statistical average of the throughput in that state. Using this decision-making approach, we also propose a simplified Markov model with fewer parameters, which is suitable in systems where changes in the fading characteristics need to be accounted for in an adaptive fashion. Numerical results are presented showing that both of our models substantially outperform the conventional techniques that use threshold-based decision making.

Based on imperfect channel state information (CSI) and relay selection, a cross-layer optimization scheme is developed for cooperative MIMO system, and the corresponding system performance is investigated in Rayleigh fading channel. By the theoretical analysis and mathematical manipulation, the average spectral efficiency (SE), packet error rate (PER) and packet loss rate (PLR) are derived. As a result, closed-form expressions of the average SE, PER and PLR are obtained, respectively. According to these, a cross-layer design (CLD) scheme subject to the average PER constraints is proposed to avoid the SE performance loss caused by the conventional instantaneous PER constraints. The scheme optimizes the adaptive thresholds by maximizing the average SE of the system, and an iteration method joint the Lagrange multiplier and Newton methods is presented to solve the above optimization problem. Simulation results verify the validity of the theoretical analysis. The results show that the proposed CLD scheme can improve the SE while target PLR is maintained. The CLD scheme under average PER constraints has higher SE than the conventional CLD scheme under instantaneous PER constraints.

In this paper, we combine adaptive modulation and coding (AMC) with multiple input multiple output (MIMO) VBLAST multiplexing to improve the throughput performance of AMC in next generation mobile communication systems. In addition, we propose a system that adopts selection transmit diversity (STD) in the combined AMC-MIMO VBLAST system. The received signal-to-noise ratio (SNR) is improved by adopting STD techniques and an improved SNR increases a probability of selecting modulation and coding scheme (MCS) level that supports higher data rate. From the simulation results, the investigated MIMO-STD VBLAST system provides a throughput gain of 1Mbps compared with simply combined AMC-MIMO VBLAST system when the required SNR is 15dB. Also, the higher throughput is achieved by AMC-TD schemes and AMC-STTD scheme provides about 250kbps increase in throughput. And AMC-STD with 2 transmit antennas achieves about 420 kbps throughput improvement over the conventional AMC at 9dB SNR.

GOFDM (generalized OFDM) has been proposed as a tradeoff solution between cyclic prefix single carrier (CP-SC) and OFDM system that can alleviate the peak to average power ratio (PAPR) problem of OFDM. In this paper, a novel estimation method for the estimation of the received SNR of GOFDM signal that is required in the adaptive modulation and coding (AMC) is presented. The simulation results of the estimated SNR show excellent correlation with the analytical results. Furthermore, the received SNRs of the GOFDM exhibit repetition of as set values that can be clustered for modulation and coding scheme (MCS) allocation in group-based AMC. The paper also presents various performances of the proposed GOFDM with AMC and compares them with the corresponding performance of OFDM and CP-SC under same operating conditions.

An important aspect of wireless networks is the dynamic behavior, cross-layer design is the central technique to cope with and utilize this behavior. In this paper, we present the cross-layer design for adaptive modulation and coding (AMC) with HARQ. For each of two widely used HARQ techniques-chase combining and incremental redundancy, the close-form functions of average retransmission time, average delay and average throughput are derived for a specific modulation and coding scheme (MCS). Based on the derived functions, a novel MCS selection method is proposed. Meanwhile, we give the analysis of how many retransmission is needed.

Research on Threshold Adjustment Algorithm in Adaptive Modulation and Coding

In this paper, we propose a cross-layer design which combines adaptive modulation and coding (AMC) at the physical layer with a hybrid automatic repeat request (HARQ) protocol at the data link layer to minimize the packet error rate (PER) and maximize the spectral efficiency. By using Markov model to predict the channel condition of next frame according to the second order statistics characteristics of the former frame, we calculate the conditional probability density function and joint probability density function of signal to noise ratio (SNR). Further, we derive the packet error rate and average spectral efficiency in closed-form for transmission over Nakagami-m fading channels. Numerical results show that the proposed scheme can obtain lower PER and higher spectral efficiency c ompared with traditional HARQ protocol s. The cross-layer design scheme combing type-III HARQ with AMC can achieve the highest spectral efficiency and the lowest PER than type-I HARQ and type-II HARQ.