System Design Issues and Performance Evaluations for Adaptive Modulation in New Wireless Access Systems

The performance of adaptive modulation system over satellite channels under Gaussian distribution, Rayleigh distribution and Rice distribution is analyzed and investigated according to the channel environment of satellite communication. A suitable adaptive modulation algorithm is proposed for the statistical properties of satellite channels comparing to the existing fixed modulation performance. The optimization criterion of the setting of the modulation switching levels is to maintain the target bit error rate (BER). BER analysis is performed and spectrum efficiency for adaptive modulation system at different SNRs is analyzed. The closed-form formulas of BER performance and spectrum efficiency are derived. The performance analysis of throughput and transmission outage probability of the proposed adaptive modulation system is presented. Finally, the simulation results show that the adaptive modulation system can theoretically achieve high throughput performance, and low transmission outage probability under satellite channel conditions.

Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier transmission scheme. OFDM transmits data by using a large number of narrow bandwidth carriers. In an OFDM transmission system, each subcarrier is attenuated individually under the frequency-selective and fast fading channel if the same fixed transmission scheme is used for all OFDM subcarriers thus it results in highest attenuation and hence poor performance. The purpose of this paper is to introduce the adaptive modulation to get an understanding of the differences between fixed and adaptive modulations schemes. In this work adaptive modulation is implemented by dividing whole subcarriers into blocks of adjacent subcarriers. Based on calculated average instantaneous signal to noise (SNR) same modulation scheme is applied to all subcarriers of same block. Here average bit error rate (BER) performance of OFDM system under fixed modulation and adaptive modulation is observed. Average BER performance of these modulation techniques is observed with various inverse fast Fourier transform (IFFT) size and using simpler adaptive quadrature amplitude modulation (QAM) schemes. The simulation results show that BER performance of OFDM system using adaptive modulation is better than fixed modulation.

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.

A 2-bit adaptive sigma delta modulation system that inherently eliminates the idle tones present in conventional and other adaptive sigma delta systems is described. The system incorporates both memory and look-ahead instantaneous step-size estimations and, as shown by computer simulation results apart from eliminating the unwanted idle tones despite dithering, it offers improved SNR performance and extended dynamic range.

Throughput improvement of STS-based MC DS-CDMA system with adaptive modulation

One property, bandwidth uneven distributed with time slots (BUDTS) in the adaptive modulation wireless system destroys an implicit assumption of traditional traffic scheduling algorithm that the bandwidth is evenly distributed with time slots. Therefore, new scheme fit for such circumstance is needed. We propose a novel algorithm, named adaptive differentiated compensation fair queuing (ADCFQ), to provide basic QoS requirement and fair residual bandwidth sharing to all backlogged flows, as well as the compensation mechanism to the lagged flows due to burst channel error. Simulation shows that in ADCFQ, the effect of uneven bandwidth distribution is well considered.

In this paper, we propose and analyze an adaptive modulation system with optimal turbo coded V-BLAST (vertical-bell-lab layered space-time) technique that adopts the extrinsic information from MAP (maximum a posteriori) decoder with iterative decoding as a priori probability in two decoding procedures of V-BLAST scheme; the ordering and the slicing. The result indicates that the proposed systems achieve a better throughput performance than the conventional systems in the whole SNR range. In addition, the simulation result shows that the maximum throughput improvement in each MIMO scheme is respectively about 421 kbps, 545 kbps, and 880 kbps. It is suggested that the effect of the proposed decoding algorithm accordingly gets higher as the number of system antenna increases.

New analytical formulas for quantization noise of two widely known adaptive delta modulation (ADM) systems, continuously variable slope delta modulation (CVSD) and Jayant's firstorder constant factor delta modulation (CFDM), have been obtained. These formulas are derived based upon the previously obtained results for linear delta modulation (LDM) and adaptive differential pulse code modulation (ADPCM). To verify the results, computer simulation has been done using band-limited Gaussian signals. Close agreements between the formulas and the simulation results have been obtained in the wide range of the input signal level.

SummaryThis paper introduces the concept of spatial and media‐based modulated (SMBM) orthogonal frequency division multiplexing (OFDM) as a potential candidate for highly mobile next generation beyond 5G (B5G) wireless communications. The proposed SMBM‐OFDM technique utilizes not only the transmit antenna and channel state indices but also OFDM subcarriers to improve the system performance under high mobility. In addition, this study sheds light on challenging fast time‐varying channel estimation problem of MBM‐based systems by using the linear minimum mean square error (LMMSE) approach due to its optimality to investigate the achievable system performance with the aid of basis expansion modeling. The minimum lower bound on the channel estimation error (Bayesian Cramer–Rao bound) is derived theoretically and shown to be attainable by the considered LMMSE estimator. Moreover, symbol detection performance is provided for different modulation types and higher mobile velocities. Simulation results demonstrate that SMBM‐OFDM system under high mobility is able to provide around 12‐dB performance gains in terms of both channel estimation and symbol detection error compared to conventional spatial modulation (SM)‐OFDM systems without MBM. The presented framework is important due to addressing the high mobility support of SMBM‐OFDM systems for B5G wireless communications in terms of achievable channel estimation and data detection performance.

In this paper, we propose and analyze an Adaptive Modulation System with optimal Turbo Coded V-BLAST (Vertical-Bell-lab Layered Space-Time) technique that adopts the extrinsic information from MAP (Maximum A Posteriori) Decoder with Iterative Decoding as a priori probability in two decoding procedure of V-BLAST scheme; the ordering and the slicing. Also, comparing with the Adaptive Modulation System using conventional Turbo Coded V-BLAST technique that is simply combined V-BLAST scheme with Turbo Coding scheme, we observe how much throughput performance can be improved. In addition, we apply a STD (Selection Transmit Diversity) scheme to the systems for more performance improvement. The results show that the proposed system applying a STD scheme gains about 1.77 Mbps at 11 dB SNR (Signal to Noise Ratio) compared to the conventional system using 2 transmit and 2 receive antennas.

In this paper, the combination of orthogonal frequency-division multiplexed (OFDM), multi-input multi-output (MIMO) and adaptive modulation can effectively eliminate or resist various fading in wireless channels, thus it can improve the capacity of system and transmission quality. Depending on the optimal bit and power allocation strategy based on greedy algorithm, in this paper, the performance of adaptive bit and power allocation MIMO-OFDM system based on greedy algorithm is completely studied. And the performance comparison among greedy algorithm, Chow algorithm and average algorithm is represented. We also compare the performance of MIMO-OFDM system under different antennas numbers. It is shown that the bit error rate (BER) of MIMO-OFDM system based on greedy algorithm is better than that based on Chow algorithm and average algorithm. And the spectral efficiency of greedy algorithm is superior to that of Chow and average algorithm. Ultimately, we show that the performance of MIMO-OFDM system is also superior to that of OFDM system with single transmit antenna and receive antenna which is under the same scheme as the former.

We introduce an analytical method that uses a finite-state Markov chain (FSMC) as an error model, for estimating the performance of adaptive modulation systems (AMSs) combined with automatic repeat request (ARQ) schemes in correlated slow fading channels. For the throughput performance evaluation of wireless packet networks, conventionally, we have assumed independent block fading, which may also be suitable to represent fast fading channels. However, in slow fading channels, error rates of consecutive packets are highly correlated and we cannot simply assume independent error structure in performance evaluations. We propose a multistate Markov error structure for AMS in correlated fading channels, which is also described by a finite-state Markov chain (FSMC) and we also present throughput-estimation methods for AMS combined with ARQ, using the proposed Markov error structure.

In this paper, we mainly study the performance of adaptive M-QAM in transmit antenna selection (TAS) with the Alamouti scheme. We first derive expressions for the statistics of the receiver SNR in TAS with Alamouti scheme. Then we provide the closed-form expressions for the average spectral efficiency and average BER of TAS with the Alamouti scheme employing adaptive M-QAM. Our analytical results indict that in the adaptive modulation system, TAS with the Alamouti scheme can obtain higher spectral efficiency compared with OSTBC without antenna selection.

A simple treatment is provided of the analysis of an adaptive delta modulation system for evaluating the performance of the system in terms of complexity, signalto- noise ratio and dynamic range. The analysis assumes a simple adaptation algorithm and a normal density function input signal with flat spectrum.A brief description of the implementation of the system is given and finally the experimental results are compared with the theoretical results.

We present a 100GHz millimeter-wave communication enabled by a photonics-assisted intensity modulation and direct detection system. The frequency-resolved discrete multi-tone (DMT) modulation is used to adapt the nonlinear response of the system and increase the rate of transmission compared to conventional pulse amplitude modulation. By loading different number of bits to the subcarriers based on the channel frequency response, 20 Gbps DMT signals is transmitted over 0.25 m free space distance, and the measured bit error rate (BER) is below the 7% FEC threshold without any equalization. This work is expected to provide a cost-effective solution to achieve high-speed millimeter-wave transmission for future beyond 5G and 6G mobile communications.