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... In the following papers modulation scheme was kept constant, while code rate was varied with respect to channel conditions. Al-Askary (2006) [20], in his doctoral thesis, proposed adaptive coding scheme for OFDM systems using concatenated multi-level codes. In this proposed technique same modulation scheme was used for all the OFDM subcarriers during a transmission interval, while different code rates were used on different subcarriers. ...
Adaptive communication is one of the hottest areas of research for last two decades or so. This technique is recommended for many 3rd Generation (3G) and 4th Generation (4G) communication standards like WIFI (IEEE 802.11n/b/g) and WiMAX (IEEE 802.16/e) etc. These systems are mainly Orthogonal Frequency Division Multiplexing (OFDM) based communication systems. In OFDM systems there are several subcarriers that may exhibit different channel state information. In adaptive communication, the various transmission parameters like code rate, modulation scheme and power are adapted with respect to the channel state information at different subcarriers, so that the overall throughput of the system may be maximized while satisfying certain constraints like bit error rate and total transmit power, at the same time. In this paper, a comprehensive review of adaptive communication techniques along with their pros and cons and future directions is presented.
... In the literature survey, we have observed that the second step is most critical where parameters are intelligently adapted while remaining two steps are mostly assumed to be known in many contributions. Like Bockelmann et al. (2009) andAl-Askary (2006) proposed schemes for adaptive communication assuming that channel state information is known at transmitter and receiver both. Sastry et al. (2010) proposed a Fuzzy logic based scheme for channel estimation and adaptive modulation with an assumed synchronization. ...
... In most of the adaptive communication schemes for OFDM systems, those subcarriers are chosen to shut down where channel conditions are very poor. Once a subcarrier is chosen to shut down the resources like power are redistributed among rest of the subcarriers like in Faezah et al (2009), Al-Askary (2006. But as far as the proposed scheme is concerned transmission is even possible at a subcarrier with such a hostile scenario. ...
Dynamic allocation of the resources for optimum utilization and throughput maximization is one of the
most important fields of research nowadays. In this process the available resources are allocated in
such a way that they are maximally utilized to enhance the overall system throughput. In this chapter a
similar problem is approached which is found in Orthogonal Frequency Division Multiplexing (OFDM)
environment, in which the transmission parameters namely the code rate, modulation scheme and power
are adapted in such a way that overall system’s data rate is maximized with a constrained bit error
rate and transmit power. A Fuzzy Rule Base System (FRBS) is proposed for adapting the code rate and
modulation scheme while Genetic Algorithm (GA) and Differential Evolution (DE) algorithm are used
for adaptive power allocation. The proposed scheme is compared with other schemes in the literature
including the famous Water-filling technique which is considered as a benchmark in the adaptive loading
paradigm. Supremacy of the proposed technique is shown through computer simulations.
... Modified Iterative Decoding Algorithm (MIDA) was proposed by [14] and it is a revised version of Iterative decoding algorithm origionally proposed by [15] which is a suboptimum decoder. MIDA is a hard decision decoder.. ...
... Ojala et al. [14] proposed a local binary pattern (LBP) operator for calculating texture sensitivity that was based on the postulation that the texture has locally two paired aspects, strength and the pattern. The effectiveness has been proposed to be an operative descriptor in texture classification [15]. In experimental studies, LBP has became the strongest measure for texture analysis which can be comprehended as a universal methodology to the traditionally different statistical and physical models of texture analysis [16]. ...
In this paper, a novel technique for robust digital image watermarking is proposed using simple product codes (PC) and cubic product codes (CPC) respectively. Product codes are two dimentional matrix codes while CPC are three dimensional product codes where the constituent codes in each dimension are linear block codes. The structure of PC and CPC makes them suitable for the proposed scheme. The embedded watermark is vulnerable to various attacks on the image like compression, noise and geometric attacks namely translation rotation and scaling (TRS) etc. This could limit the performance of digital watermarking schemes. Our proposal is to encode the watermark with PC/CPC prior to embedding it into the image. This could easily be done because our watermark is also a three dimensional data (image/logo etc), so each dimension can easily be encoded with corresponding codes in PC/CPC. The modified iterative decoding algorithm (MIDA) is employed to decode the PC/CPC. Moreover, a Fuzzy Rule Based System (FRBS) is used to find the suitable regions in the host image where watermark can be embedded such that the imperceptibility of the host image should not be affected. The FRBS makes used of Human Visual System (HVS) parameters to obtain those regions. The scheme is tested against various attacks and compared with the well-known schemes in the literature. Moreover, role of PC is also compared with CPCs and results are demonstrated.
... Therefore joint network and channel coding based on product code representation improves the error correcting capability and diversity gain as compared to separate network and channel decoding. Other decoding methods for decoding product codes as described in [57][58][59][60][61][62], can also be used for joint network and channel decoding. Clearly, the correction capability offered by channel and XOR-based network coding is limited by the performance of network coding scheme used. ...
... The base station receiver takes the packets received directly from the cooperating users and the packets received from the relay node to form a received version of the complete product code matrix. This received codeword can now be decoded using known decoding algorithm of product codes [57][58][59][60][61][62]. ...
... Besides optimum joint detection method, there are many other methods described in literature for decoding product codes. These methods are based on generalized minimum distance decoding, turbo decoding of concatenated codes and iterative decoding, as discussed in [57][58][59][60][61][62]. These detection methods have performance close to joint detection and offers less complexity. ...
... Multi-level codes are also quite practical in a sense that they have been used in many wireless standards nowadays especially in adaptive systems like WIFI (IEEE 802.11n) [7] and WiMAX (IEEE 802.16/e) [8]. Since their structural characteristics are very much compatible with OFDM systems, product codes are recommended for almost all 3 rd Generation (3G) and 4 th Generation (4G) systems including wireless local area networks (WLAN) and HYPERLAN standards [4]. ...
... In his PhD dissertation, Al-Askary [4] proposed an iterative decoding algorithm for Product codes. That algorithm was based upon List Decoders for rows are columns and designated as the Maximum Likelihood (ML) decoder of product codes [5]. ...
... The modified iterative algorithm (MIDA) was originally proposed for decoding of Product codes by Attaur-Rahman et al [6]. It is hard decoding algorithm that significantly reduces complexity of the basic iterative algorithm proposed by [4]. ...
In this paper, the Modified Iterative Decoding Algorithm (MIDA) is investigated for decoding Multi-level codes. Adaptive Orthogonal Frequency Division Multiplexing (AOFDM) system is used as system model for this experiment. MIDA is a hard decision decoder that was initially proposed for decoding of Product codes and later for Multi-level codes by same authors. As Multi-level codes are matrix codes we have found that they have structural compatibility with OFDM systems. In OFDM system each subchannel may have different
channel state information (CSI) which may be varying over the time. So a Multilevel code with suitable combination of constituent row codes can play a vital role in combating poor channel conditions on OFDM subchannels. A fuzzy rule based system (FRBS) is used for selection of suitable most Multilevel code and modulation symbol. Performance is shown by simulations.
... Jointly, these two codes make the bit error rate (BER) performance noteworthy. Alaskary [3] investigated the performance of product codes in an orthogonal frequency division multiplexing (OFDM) system during adaptive coding and modulation (ACM). He also proposed an iterative decoder whose complexity was less compared to the maximum likelihood (ML) decoder of product codes, while the complexity of ML decoder grows exponentially with the code size and number of iterations. ...
... Atta-ur-Rahman et al. [4] proposed a modified iterative decoding algorithm (MIDA) for the product codes originally motivated by [3]. This algorithm made use of the basic syndrome detection technique to identify the received code words as correct while remaining code words pass through the iterative decoder. ...
... A is a code whose each element of is a member of code 3 A . ...
In this paper a modified iterative decoding algorithm (MIDA) is proposed for decoding the Cubic Product Codes (CPC), also called three dimensional product block codes. It is a hard decision decoder that was initially proposed by the same authors for decoding simple product codes, where the decoding complexity of the basic iterative algorithm was significantly reduced with negligible performance degradation. Two versions of the proposed algorithm are investigated that are with and without complexity reduction. A complexity and performance trade-off is also highlighted. Bit error rate (BER) performance of the proposed algorithm over a Rayleigh flat fading channel, is demonstrated by the simulations.
... La codificación del canal en OFDM, se ha convertido en una parte inseparable de la mayoría de sus aplicaciones. Una alta cantidad de trabajos investigativos se han focalizado en el diseño del codificador, decodificador e interleaver (entrelazador) para la transmisión de información mediante OFDM a través de ambientes con desvanecimiento 12,13 Aquí se revisarán los códigos externos que serán empleados en el análisis del desempeño de OFDM sobre canales ruidosos y con desvanecimiento 20,21,23 . ...
RESUMEN / ABSTRACT Los sistemas de Multiplexación por División de Frecuencias Ortogonales (OFDM), por sus siglas en ingles, han ganado creciente interés debido a su robustez frente a la interferencia provocada por el multitrayecto y a su elevada eficiencia espectral. Cuando se trata de sistemas de altas velocidades de transmisión, empleando mecanismos de corrección FEC sobre canales de comunicación inalámbricos, los esquemas que implementan OFDM constituyen la mejor opción. En el presente trabajo se estudia y caracteriza mediante simulación el rendimiento de estos sistemas cuando se emplea como esquemas de codificación de canal las técnicas de Reed-Solomon y los códigos BCH. Las combinaciones de estos esquemas de codificación externos concatenados con métodos de codificación convolucional internos proporcionan rendimientos desde el punto de la taza de error de bit así como eficiencias energéticas verdaderamente excepcionales a bajos niveles de relaciones señal a ruido. La simulación se lleva a cabo con la ayuda de la herramienta Simulink de Matlab sobre canales de comunicaciones AWGN y canales con desvanecimiento plano y selectivo. En la simulación se hace uso del framework 802.16-2004 que trae incorporado el bloque de comunicaciones de Simulink. Como casos de estudios se incluyen la caracterización de variantes de codificación RS y BCH. Palabras claves: OFDM, Codificación de Canal, Reed-Solomon, BCH, Simulink/Matlab Orthogonal Frequency Division Multiplexing (OFDM) has gained increased interest due to its robustness against multi-path interference and high spectrum efficiency. OFDM is a suitable candidate for high data rate transmission with forward error correction (FEC) methods over wireless channels. In this paper, the system throughput of a working OFDM system is studied and characterized by means of simulation when using channel coding techniques like Reed Solomon and BCH. Combinations of these external coding schemes concatenated with internal convolutional coding provide exceptional error performance and energy efficiency at low signal-to-noise ratio. Simulation of estimated system bit error rate (BER) is performed with the help of Simulink/Matlab tools under the additive white Gaussian noise (AWGN), flat fading and selective fading channel approximation. Characterization of RS and BCH codes is shown as study cases.
... Wireless communication systems suffer from channel impairments such as reflection, diffraction, pathloss, shadowing and fading. The signal that is transmitted into the wireless environment arrives at the receiver along a number of distinct paths known as multipath [3]. Also, multipath effects result in the late arrival of the signals at the receiver and the channel being in deep fade, which leads to signal distortion and burst errors [4] [5]. ...
The quest for a reliable reception of the replica of a transmitted signal over wireless medium has become very important in the transmission and reception of information. In order to mitigate the effect of the degradation of the transmitted signal, error correction techniques are employed to reliably recover the erroneous bits inherent especially when the channel is in deep fading. In this paper, the performance of Reed Solomon (RS) and Bose-Chaudhuri-Hochquenghem (BCH) codes over correlated Rayleigh fading is presented. This work also investigated the effect of error correction code in the variation of the modulation order of the QAM. The simulation was carried out by encoding randomly generated data using both RS and BCH codes and then modulated by varying the modulation order of the quadrature amplitude modulation before transmitted over a correlated Rayleigh distributed channel. At the receiver, the received signal was demodulated and decoded. The bits in error received were detected and corrected to retrieve back the original transmitted signal. The system was evaluated in bit error rate and the result showed that BCH code performs better for higher modulation order.
... This idea was originally motivated by [9]. Al-Askary [10], proposed an adaptive coding and modulation technique for OFMD Hyperlan/2 standard, in which modulation was fixed while different codes rates were chosen for the subcarriers. ...
... In case of a tight BER requirement, relatively low code rate product code with a smaller constellation will be chosen by FRBS, which results in a poor throughput. In fig-9 proposed scheme is compared with the adaptive coding and modulation scheme proposed by Al-Askary in [10] in which the adaptation was based upon SNR based coding and modulation thresholds. As simulation results reveal, proposed scheme profoundly performs better than that of proposed by Al-Askary as well as HYPERLAN/2 standard. ...
Adaptive communication is becoming requirement of every communication system for effective utilization of available radio resources. In this approach the transmission parameters like code rate, modulation size and available power are dynamically chosen so that the overall system throughput is maximized while certain constraints like bit error rate are satisfied. In this paper a similar constrained optimization problem is solved by optimally choosing the said parameters with the help of Differential Evolution algorithm with a Fuzzy Rule Based System (DE-FRBS) in an OFDM environment, in this proposal the FRBS is used to adapt the code rate and the modulation scheme according to channel state information (CSI) and desired quality of service (QoS) while DE is employed to find the optimum power vector (OPV) to be transmitted over OFDM subcarriers. Product codes and Quadrature Amplitude Modulation (QAM) are used as coding and modulation schemes respectively. Product codes are considered much powerful in terms of error correction capability. Significance of the proposed scheme is shown by the simulations.
... La codificación del canal en OFDM, se ha convertido en una parte inseparable de la mayoría de sus aplicaciones. Una alta cantidad de trabajos investigativos se han focalizado en el diseño del codificador, decodificador e interleaver (entrelazador) para la transmisión de información mediante OFDM a través de ambientes con desvanecimiento 12,13 Aquí se revisarán los códigos externos que serán empleados en el análisis del desempeño de OFDM sobre canales ruidosos y con desvanecimiento 20,21,23 . ...
