Adaptive Code Modulation Research Articles

Error-Rate Analysis for Bit-Loaded Coded MIMO-OFDM

Bit-loaded orthogonal frequency-division multiplexing (OFDM) with convolutional coding is a powerful technique for transmission over quasi-static frequency-selective fading channels. Further enhancements in data rate are achieved by combining loaded OFDM with multiple-input-multiple-output (MIMO) transmission. Motivated by the lack of appropriate error-rate analysis techniques for this popular type of transmission system, in this paper, we develop a novel analytical method for bit-error-rate (BER) and frame-error-rate (FER) estimation of bit-loaded coded OFDM and MIMO-OFDM systems using singular value decomposition (SVD), operating over frequency-selective quasi-static channels with nonideal interleaving. Then, we introduce three different applications of the proposed analysis. First, we compare the performance of several OFDM bit-loading schemes and propose a hybrid loading scheme that selects the best loading for each channel realization from a number of candidates. Second, we introduce three adaptive interleaving schemes: 1) selecting the best interleaver from a number of predefined interleavers; 2) a novel adaptive bit-interleaving algorithm based on the pairwise error probability; and 3) a spatial interleaving scheme for MIMO-OFDM-SVD systems with separate information sources. Third, we introduce an adaptive coded-modulation algorithm by using our BER and FER estimation techniques.

Analysis and Design of Wireless Networked Control System Utilizing Adaptive Coded Modulation

摘要: 研究了利用自适应编码调制的无线网络控制系统的分析和设计, 自适应编码机制引入无线网络能够提高衰退信道的能量效率, 增加数据传输率. 进一步, 通过等价时延的概念来描述无线传输信道中的时变速率, 干扰和路由特性. 基于时变的网络条件给出了等价时延的上下界. 无线网络控制系统被建模为具有时变输入时延的离散系统. 通过新的时滞系统技术给出了该闭环无线网络控制系统可稳定化的充分条件. 最后, 数值算例表明了所提控制策略的有效性. 关键词: 无线网络控制系统 / 自适应编码调制 / 等价时延 / 离散系统 / 时变输入时滞 / 可稳定化

Simple closed-loop method to compensate interference asymmetry in time-division duplex MIMO-OFDM systems

In wireless communications systems with time-division duplex (TDD) deployment, channel reciprocity and symmetric interference between transmitter and receiver sides are two widely-adopted assumptions for the design of optimal adaptation transmission mode. However, in practice, there is an undesirable but non-negligible effect, namely the asymmetric interference, that makes the assumptions no longer valid. In this paper, a simple closed-loop feedback method of compensating interference asymmetry in TDD multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system is proposed. The system makes the estimated interference at transmit-side be able to track the instantaneous receive-side interference dynamically. The proposed method maintains constant frame error rate (FER) by adopting adaptive modulation coding (AMC) and power loading. The final simulations have verified the effectiveness of the new method.

Analysis and Design of Wireless Networked Control System Utilizing Adaptive Coded Modulation

In this paper, we explore the analysis and design of wireless networked control system (WNCS) utilizing adaptive coded modulation (ACM) schemes, which can improve the energy efficiency and increase data rate over a fading channel. To capture the characteristics of varying rate, interference, and routing in wireless transmission channel, we introduce the concept of equivalent delay (ED). Based on the time-varying network condition, the analytic lower and upper bounds of EDs are given. Whereafter, WNCS is modelled as a discrete-time system with time-varying input delay. Sufficient stabilization condition of the closed-loop WNCS is derived by making use of novel techniques of time-delay system. Finally, the numerical result shows the validity of our proposed control strategies.

Optimum Adaptive Modulation and Channel Coding Scheme for Frequency Domain Channel-Dependent Scheduling in OFDM Based Evolved UTRA Downlink

In the Evolved UTRA (UMTS Terrestrial Radio Access) downlink, Orthogonal Frequency Division Multiplexing (OFDM) based radio access was adopted because of its inherent immunity to multipath interference and flexible accommodation of different spectrum arrangements. This paper presents the optimum adaptive modulation and channel coding (AMC) scheme when resource blocks (RBs) is simultaneously assigned to the same user when frequency and time domain channel-dependent scheduling is assumed in the downlink OFDMA radio access with single-antenna transmission. We start by presenting selection methods for the modulation and coding scheme (MCS) employing mutual information both for RB-common and RB-dependent modulation schemes. Simulation results show that, irrespective of the application of power adaptation to RB-dependent modulation, the improvement in the achievable throughput of the RB-dependent modulation scheme compared to that for the RB-common modulation scheme is slight, i.e., 4 to 5%. In addition, the number of required control signaling bits in the RB-dependent modulation scheme becomes greater than that for the RB-common modulation scheme. Therefore, we conclude that the RB-common modulation and channel coding rate scheme is preferred, when multiple RBs of the same coded stream are assigned to one user in the case of single-antenna transmission.

Field Experiments on Real-Time 1-Gbps High-Speed Packet Transmission in MIMO-OFDM Broadband Packet Radio Access

This paper presents experimental results in real propagation channel environments of real-time 1-Gbps packet transmission using antenna-dependent adaptive modulation and channel coding (AMC) with 4-by-4 MIMO multiplexing in the downlink Orthogonal Frequency Division Multiplexing (OFDM) radio access. In the experiment, Maximum Likelihood Detection employing QR decomposition and the M-algorithm (QRM-MLD) with adaptive selection of the surviving symbol replica candidates (ASESS) is employed to achieve such a high data rate at a lower received signal-to-interference plus background noise power ratio (SINR). The field experiments, which are conducted at the average moving speed of 30km/h, show that real-time packet transmission of greater than 1Gbps in a 100-MHz channel bandwidth (i.e., 10bits/second/Hz) is achieved at the average received SINR of approximately 13.5dB using 16QAM modulation and turbo coding with the coding rate of 8/9. Furthermore, we show that the measured throughput of greater than 1Gbps is achieved at the probability of approximately 98% in a measurement course, where the maximum distance from the cell site was approximately 300m with the respective transmitter and receiver antenna separation of 1.5m and 40cm with the total transmission power of 10W. The results also clarify that the minimum required receiver antenna spacing is approximately 10cm (1.5 carrier wave length) to suppress the loss in the required received SINR at 1-Gbps throughput to within 1dB compared to that assuming the fading correlation between antennas of zero both under non-line-of-sight (NLOS) and line-of-sight (LOS) conditions.

Performance analysis of a rate-adaptive dual-branch switched diversity system

In this letter, a performance analysis of a dualbranch switched diversity system operating on statistically independent and identically distributed Nakagami-m flat-fading channels is presented. An adaptive coded modulation (ACM) scheme is employed to increase the spectral efficiency of the system. The ACM scheme consists of a set of multidimensional trellis codes originally designed for additive white Gaussian noise channels, where the codes are based on quadrature amplitude modulation (QAM) signal constellations of varying size. The performance is evaluated by assuming perfect channel knowledge at both transmitter and receiver and instantaneous feedback of channel state information, conveyed from the receiver to the transmitter on an error-free feedback channel. The optimal switching threshold of the switched diversity combiner, maximizing the average spectral efficiency, is identified for spatially uncorrelated antenna branches.

Analysis and Optimization of Adaptive Coded Modulation Systems in Spatially Correlated SIMO Rayleigh Fading Channels

This paper generalizes the performance analysis of an adaptive coded modulation system operating on a single-input-multiple-output (SIMO) channel in our recent paper to include spatial correlation between the receive branches. First, the prediction procedure originally developed for a system with spatially uncorrelated branches is used in a correlated branch system. Then, an optimal ldquospace-time predictorrdquo is derived based on the assumption that the spatiotemporal correlation function of the data in the receiver branches is represented as a product of the individual spatial and temporal correlation functions, respectively. The pilot symbol interval and the power allocation scheme between pilot and data symbols are optimized under an average power constraint, such that the throughput is maximized while keeping the bit error rate below a predefined level. Numerical examples are given for Rayleigh flat fading subchannels with Jakes correlation profile.

On the Performance of Broadband Mobile Internet Access System

In this paper, we evaluate the performance of OFDMA/TDD-based broadband mobile internet access system with the features of adaptive modulation & coding (AMC) and hybrid ARQ. We present a framework of system-level simulation and furthermore, intend to derive the insightful results towards understanding the performance of broadband mobile internet access system. The average system throughput as well as delay performance is evaluated for the different channel characteristics and system parameters, which allows for predicting the system capacity in the varying cellular network environment.

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.

Rate and Power Allocation for Discrete-Rate Link Adaptation

Link adaptation, in particular adaptive coded modulation (ACM), is a promising tool for bandwidth-efficient transmission in a fading environment. The main motivation behind employing ACM schemes is to improve the spectral efficiency of wireless communication systems. In this paper, using a finite number of capacity achieving component codes, we propose new transmission schemes employing constant power transmission, as well as discrete- and continuous-power adaptation, for slowly varying flat-fading channels. We show that the proposed transmission schemes can achieve throughputs close to the Shannon limits of flat-fading channels using only a small number of codes. Specifically, using a fully discrete scheme with just four codes, each associated with four power levels, we achieve a spectral efficiency within 1 dB of the continuous-rate continuous-power Shannon capacity. Furthermore, when restricted to a fixed number of codes, the introduction of power adaptation has significant gains with respect to average spectral efficiency and probability of no transmission compared to a constant power scheme.

Information Theoretic Foundations of Adaptive Coded Modulation

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In wireless/mobile communications, terminals adapt their rate and transmit power or, more in general, their coding and modulation scheme, depending on the time-varying channel conditions. This paper presents, in a tutorial form, the information theoretic framework underlying such “adaptive modulation” techniques. First, we review fading channel models, channel state information assumptions, and related capacity results. Then, we treat the case of input power constraint, where the optimal input distribution is Gaussian. Finally, we address the case of discrete modulations. In order to treat the latter, we make use of the recently developed method of “mercury-waterfilling,” based on the relationship between mutual information and minimum mean-square error (MMSE) estimation of the channel input from the channel output. While the traditional design of adaptive modulation schemes based on uncoded bit-error rate (BER) involves the optimization over a discrete set of signal constellations, when powerful (i.e., capacity approaching) coding schemes are used the corresponding adaptive coded modulation design becomes surprisingly simple. The regime of very powerful coding is justified by the use of modern coding schemes, such as turbo codes and low-density parity-check codes, able to perform close to channel capacity at very small BER. </para>

Impact of Spatial Correlation on Adaptive Coded Modulation Performance in Rayleigh Fading

A performance analysis of an adaptive coded modulation (ACM) scheme operating on identically distributed and spatially correlated Rayleigh flat-fading channels is presented. In particular, we study a single-input multiple-output system where spatial diversity is exploited at the receiver by using a maximum ratio combining scheme. The ACM scheme consists of a set of multidimensional trellis codes originally designed for additive white Gaussian noise channels, with codes being based on quadrature amplitude modulation signal constellations of varying size. Rate adaptation is achieved by providing the transmitter with channel state information as predicted by the receiver. Approximate closed-form expressions for the average bit error rate and the average spectral efficiency are derived, and numerical examples are given for the case of Jakes correlation profile and maximum a posteriori optimal predictor coefficients

Analyzing and Optimizing Adaptive Modulation Coding Jointly With ARQ for QoS-Guaranteed Traffic

A cross-layer design is developed for quality-of-service (QoS)-guaranteed traffic. The novel design jointly exploits the error-correcting capability of the truncated automatic repeat request (ARQ) protocol at the data link layer and the adaptation ability of the adaptive modulation and coding (AMC) scheme at the physical layer to optimize system performance for QoS-guaranteed traffic. The queuing behavior induced by both the truncated ARQ protocol and the AMC scheme is analyzed with an embedded Markov chain. Analytical expressions for performance metrics such as packet loss rate, throughput, and average packet delay are derived. Using these expressions, a constrained optimization problem is solved numerically to maximize the overall system throughput under the specified QoS constraints

Fine-Granularity Loading Schemes Using Adaptive Reed-Solomon Coding for xDSL-DMT Systems

While most existing loading algorithms for xDSL-DMT systems strive for the optimal energy distribution to maximize their rate, the amounts of bits loaded to subcarriers are constrained to be integers and the associated granularity losses can represent a significant percentage of the achievable data rate, especially in the presence of the peak-power constraint. To recover these losses, we propose a fine-granularity loading scheme using joint optimization of adaptive modulation and flexible coding parameters based on programmable Reed-Solomon (RS) codes and bit-error probability criterion. Illustrative examples of applications to VDSL-DMT systems indicate that the proposed scheme can offer a rate increase of about in most cases as compared to various existing integer-bit-loading algorithms. This improvement is in good agreement with the theoretical estimates developed to quantify the granularity loss.

Adaptive Coded Modulation With Receive Antenna Diversity and Imperfect Channel Knowledge at Receiver and Transmitter

Unifying and generalizing the works of Cai and Giannakis and Oien et al., the performance of an adaptive trellis-coded modulation system where receive antenna diversity is implemented by means of maximum ratio combining is analyzed and optimized. As in the work of Cai and Giannakis, the analysis is done in the presence of both estimation and prediction errors. Rayleigh fading on each subchannel is considered, with the estimation and prediction being performed independently on each subchannel. The system optimization process is done in such a way that the throughput is maximized under a bit-error-rate (BER) constraint. The numerical example employs a Jakes-fading spectrum and shows how the power should be distributed between pilot and data symbols and how often pilot symbols should be transmitted for maximum throughput under an instantaneous (with respect to the predicted channel) BER constraint.

Wireless QoS for High-Speed CDMA Packet Cellular Systems--With Radio-Condition-Aware Admission Control and Resource Allocation Reflected Multistage Scheduling--

Supporting diversified rates for real-time communications will become possible and essential with the rapidly increasing transmission rates provided by the 4th generation (4G) mobile communication systems. In this paper, a novel wireless Quality of Service (QoS) scheme suitable for broadband CDMA packet cellular systems with adaptive modulation coding is proposed and its characteristics are described. The proposed QoS scheme comprises several control factors laid on the MAC and RRC layers, and can be harmonized with IP-QoS. Two important control factors are proposed: radio-condition-aware admission control and resource allocation reflected multistage scheduling. Computer simulations and testbed experiments indicate that by using the radio-condition-aware admission control, stable and guaranteed service can be provided to real-time users regardless of the interference and the variation in the location of the mobile station. Moreover, resource allocation reflected multistage scheduling maintains guaranteed rates for real-time users and provides high resource utilization efficiency for best-effort users. Consequently, by using the proposed wireless QoS scheme, it is possible to provide users with high quality and diversified real-time services, on a packet based radio network for enhanced 3G and beyond.

Efficient Compression Method for Cell Animation Video

Animation video is becoming very popular with the availability of low cost computing resources. The cell animation is a popular method, used for producing animation video. In order to efficiently encode these videos, conventional video codecs, such as AutoDesk Animation Pro FLC, Intel Indeo 5, and MPEG-4 can be used to achieve high compression. However, when cell animation videos are compressed at very low bit rate by these traditional codecs, objectionable artifacts, e.g., false color, blurred contours, and blocking artifact, are severely occurred. In this paper, we propose an efficient compression method for cell animation images. The proposed method employs hybrid coding scheme which includes intraframe and interframe coding modes. The intraframe mode consists of color quantization, adaptive differential pulse code modulation, forward classification, and Golomb-Rice coding. The interframe coding consists of block-based techniques and exploits the characteristics of motion. Simulation results show that the proposed method provides superior performance over AutoDesk Animation Pro FLC, MPEG-1, Intel Indeo 5, and MPEG-4 standards.

Maximum Likelihood Estimation of Trellis Encoder and Modulator Transition Utilizing HMM for Adaptive Channel Coding and Modulation Technique

In order to achieve adaptive channel coding and adaptive modulation, the main causes of degradation to system performance are the decoder selection error and modulator estimation error. The utilization of supplementary information, in an estimation system utilizing channel estimation results, blind modulation estimation, and blind encoder estimation using several decoders information and encoder transitions have been considered to overcome these two problems. There are however many issues in these methods, such as the channel estimation difference between transmitter and receiver, computational complexity and the assumption of perfect Channel State Information (CSI). Our proposal, on the other hand, decreases decoder and demodulator selection error using a Hidden-Markov Model (HMM). In order to estimate the switching patterns of the encoder and modulator, our proposed system selects the maximum likelihood encoder and modulator transition patterns using both encoder and modulator transition probability based on the HMM obtained by CSI and also Decoder and Demodulator Selection Error probabilities. Therefore, the decoder and demodulation results can be achieved efficiently without any restraint on the pattern of switching encoder and modulation.

Impact of Channel Prediction on Adaptive Coded Modulation Performance in Rayleigh Fading

Adaptive coded modulation (ACM) is a promising tool for increasing the spectral efficiency of time-varying mobile channels while maintaining a predictable bit-error rate (BER). An important restriction in systems with such a transmission scheme is that the transmitter needs to have accurate channel-state information (CSI). Earlier analysis of ACM systems usually assumes that the transmitter has perfect knowledge of the channel or that the CSI is accurate but outdated. In this paper, we investigate the effects of predicting the CSI using a linear fading-envelope predictor in order to enhance the performance of an ACM system. For the case in which multidimensional trellis codes are used on Rayleigh-fading channels, we obtain approximative closed-form expressions for BER and average spectral efficiency. Numerical examples are given for the case of Jakes correlation profile and maximum a posteriori-optimal predictor coefficients.