ADAPTIVE CODING TECHNIQUES TO IMPROVE BER IN OFDM SYSTEM

Adaptive modulation and diversity combining represent very important adaptive solutions for the future generations of communication systems. In order to improve the performance and the efficiency of wireless communication systems these two techniques have been recently used jointly in new schemes named joint adaptive modulation and diversity combining .The highest spectral efficiency with the lowest possible combining complexity, given the fading channel conditions and the required error rate performance. Increase the spectral efficiency with a slight increase in the average number of combined path for the low signal to noise ratio (SNR) range while maintaining compliance with the bit error rate (BER)

Transmission of compressed multimedia data over wireless channels using space-time OFDM with adaptive beamforming

The transmission of multimedia data over wireless channels poses significant constraints on the communication system bandwidth, energy, and latency. To overcome these bottlenecks to wireless multimedia communication, various channel coding and transmit diversity schemes have been proposed. In previous work, we have shown that space-time block-coding (STBC) with adaptive beamforming (STBC-OFDM-AB) is an effective technique for improving the error-rate performance and channel capacity of wireless multimedia systems utilizing OFDM. In this paper, we introduce a transmission system for multimedia communication employing STBC-OFDM with adaptive beamforming incorporating a perceptually-based image compression coder - which consists of a 2-D discrete wavelet transform (DWT), an adaptive quantizer (with thresholding) and variable-length entropy encoding. Initial simulation results based on the transmission of compressed images, showed that the performance improvement introduced by STBC-OFDM-AB can be readily observed, and compared to other transmission methods is better suited to wireless multimedia communication

Joint Adaptive Modulation-Coding and Cooperative ARQ for Wireless Relay Networks

This paper presents a cross-layer approach to jointly design adaptive modulation and coding (AMC) at the physical layer and cooperative truncated automatic repeat request (ARQ) protocol at the data link layer. We first derive an exact closed form expression for the spectral efficiency of the proposed joint AMC-cooperative ARQ scheme. Aiming at maximizing this system performance measure, we then optimize an AMC scheme which directly satisfies a prescribed packet loss rate constraint at the data-link layer. The results indicate that utilizing cooperative ARQ as a retransmission strategy, noticeably enhances the spectral efficiency compared with the system that employs AMC alone at the physical layer. Moreover, the proposed adaptive rate cooperative ARQ scheme outperforms the fixed rate counterpart when the transmission modes at the source and relay are chosen based on the channel statistics. This in turn quantifies the possible gain achieved by joint design of AMC and ARQ in wireless relay networks.Comment: 5 pages, 4 figures, To appear in the Proceedings of the 2008 IEEE International Symposium on Wireless Communication Systems (ISWCS), Rykevick, Island, Oct 200

Adaptive Modulation based MIMO-OFDM Receiver design for Underwater Acoustic Communication

Adaptive modulation (AM) technique may make more promote in the execution of wireless communication systems through adaptively conformity transmitter parameters to fading channels; therefore, it has been taken as one of the key physical techniques in underwater acoustic communication. This paper offers a general overview of the adaptive modulation scheme in wireless multiple-input multiple-output (MIMO) systems with Orthogonal Frequency Division Multiplexing (OFDM). Study a set of properties by which adaptive modulation systems are evaluated, and also, discuss modulation schemes, channel modeling and estimation in detail since it is utilized in most current system or solutions, as well survey some MIMO models which are included in adaptive modulation activities in order to enhance the data rate and throughput. In this work, the channel is estimated using Kalman filter. Kalman Filter (KF) is a well-known algorithm for estimation and prediction especially when data has a lot of noise. The EKF is also considered to be the de-facto standard. This paper will provide the idea of MIMO-OFDM receiver design using Adaptive modulation and channel estimation for underwater acoustic communication

Cross-Layer Adaptive Feedback Scheduling of Wireless Control Systems

There is a trend towards using wireless technologies in networked control systems. However, the adverse properties of the radio channels make it difficult to design and implement control systems in wireless environments. To attack the uncertainty in available communication resources in wireless control systems closed over WLAN, a cross-layer adaptive feedback scheduling (CLAFS) scheme is developed, which takes advantage of the co-design of control and wireless communications. By exploiting cross-layer design, CLAFS adjusts the sampling periods of control systems at the application layer based on information about deadline miss ratio and transmission rate from the physical layer. Within the framework of feedback scheduling, the control performance is maximized through controlling the deadline miss ratio. Key design parameters of the feedback scheduler are adapted to dynamic changes in the channel condition. An event-driven invocation mechanism for the feedback scheduler is also developed. Simulation results show that the proposed approach is efficient in dealing with channel capacity variations and noise interference, thus providing an enabling technology for control over WLAN.Comment: 17 pages, 12 figures; Open Access at http://www.mdpi.org/sensors/papers/s8074265.pd

Adaptive Channel Coding and Modulation Scheme Selection for Achieving High Throughput in Wireless Networks

Modern wireless communication demands reliable data communication at high throughput in severe channel conditions like narrowband interference, frequency selective fading due to multipath and attenuation of high frequencies. Traditional single carrier systems address this set of problems by the use of complex, computationally intensive equalization filters. The Orthogonal Frequency Division Multiplexing (OFDM) based system, as opposed to single-carrier systems, is considered to be the future of the wireless communication and is being used to achieve high data rate by overcoming severe channel conditions without the use of these complex filters.This paper discusses the problem of Adaptive Modulation scheme selection through an OFDM based system over parallel frequency selective fading channels. An adaptive coding scheme is proposed by using Generalized Concatenated Codes (GCC), which have simple structure and are designed in such a way that they are best suited for fading channels. GCC are based on binary cyclic codes. The criterion of the proposed research is to optimize the throughput of a wireless system. Depending on the quality of sub-channels an adaptive modulation selection scheme and code assigning method is proposed. The proposed research combats against channel impairments better than those used in conventional systems by exploiting individual sub-channel condition. Results show better performance in terms of higher throughput by minimizing the bit error rate

Adaptive Transmission Protocols for Wireless Communication Systems with Fountain Coding

We present low-complexity adaptive protocols for both unicast and multicast transmission in wireless communication systems that employ higher layer fountain codes. Our adaptive protocols respond to variations in channel conditions by adapting the modulation and channel coding of transmitted packets, and they provide efficient communication over wireless channels that experience fading, shadowing, and other time-varying propagation losses. The operation of our protocols is governed by simple receiver statistics that can be obtained during the demodulation of received packets. We present three adaptive protocols for fountain-coded unicast transmission, and compare the throughput performance of our protocols with that of fixed-rate systems, as well as hypothetical ideal protocols that are given perfect channel state information and use ideal fountain codes. We also present two adaptive protocols for fountain-coded multicast transmission. Our adaptive multicast transmission protocols operate with limited feedback from the destinations and provide scheduling to avoid collisions among the feedback messages. We compare the performance of our multicast protocols to systems with fixed modulation and coding, as well as hypothetical protocols that are given perfect channel state information. We demonstrate that our practical adaptive protocols for fountain-coded unicast and multicast transmission outperform fixed-rate coding schemes and provide throughput that is nearly as high as that achieved by hypothetical protocols that are given perfect channel state information

ERROR CORRECTION CODE-BASED EMBEDDING IN ADAPTIVE RATE WIRELESS COMMUNICATION SYSTEMS

In this dissertation, we investigated the methods for development of embedded channels within error correction mechanisms utilized to support adaptive rate communication systems. We developed an error correction code-based embedding scheme suitable for application in modern wireless data communication standards. We specifically implemented the scheme for both low-density parity check block codes and binary convolutional codes. While error correction code-based information hiding has been previously presented in literature, we sought to take advantage of the fact that these wireless systems have the ability to change their modulation and coding rates in response to changing channel conditions. We utilized this functionality to incorporate knowledge of the channel state into the scheme, which led to an increase in embedding capacity. We conducted extensive simulations to establish the performance of our embedding methodologies. Results from these simulations enabled the development of models to characterize the behavior of the embedded channels and identify sources of distortion in the underlying communication system. Finally, we developed expressions to define limitations on the capacity of these channels subject to a variety of constraints, including the selected modulation type and coding rate of the communication system, the current channel state, and the specific embedding implementation.Commander, United States NavyApproved for public release; distribution is unlimited