Orthogonal Wavelet Division Multiplex: An Alternative to OFDM

Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation used in a variety of broadband systems, such as asymmetric digital subscriber lines, very-high-speed digital subscriber lines, digital video and audio broadcasting, and wide local area network standards. OFDM is a promising solution achieving high data rates in a mobile environment. In wireless communication systems, signal distortion and attenuation in transmission caused by multipath effects makes it necessary to obtain knowledge related to the channel impulse response using channel estimation to provide compensation. This study combined a back propagation neural network for the estimation of channel and compensation signals with a genetic algorithm to improve performance and the convergence rate. We compared bit error rates and the mean square error of the proposed neural network with that of the conventional neural network, the least square (LS) algorithm, and the minimum mean square error (MMSE) algorithm in existing OFDM channel environments. Our results demonstrate that the proposed algorithm outperforms the LS algorithm and is on par with the MMSE algorithm.

As an effective technique for combating multipath fading and for high-bit-rate transmission over wireless channels, orthogonal frequency division multiplexing (OFDM) is extensively used in modern digital television terrestrial broadcasting (DTTB) systems, such as the OFDM based Digital Video Broadcasting for Handheld (DVB-H) system, to support high performance bandwidth-efficient multimedia services. OFDM based DVB-H system is very sensitive to the nonlinear distortion at the transmitter and the carrier frequency offset at the receiver. The objective of this paper is to research and analyze the performance of the OFDM based DVB-H system in the presence of carrier frequency offset and nonlinear distortion under multipath fading channel. A closed form of symbol error probability is derived for the OFDM based DVB-H system in the presence of carrier frequency offset and nonlinear distortion under multipath fading channel. Theoretical results show closely matching with those obtained by simulations for the OFDM based DVB-H system in the presence of carrier frequency offset and nonlinear distortion under multipath fading channel.

System-on-a-chip (SoC) is now a trend in digital design because it gives a lot of advantages over discrete electronic based product such as higher speed, lower power consumption, smaller size, lower cost etc. Reconfigurable platforms such as FPGA, CPLD, and PLD are now being used for designing and implementing SoC due to their low cost, high capacity and tremendous speed. In this project single chip Orthogonal Frequency Division Multiplexing (OFDM) transmitter and receiver have been designed using Verilog HDL. OFDM is a multi carrier modulation technique used in the various digital communication systems like 3G GSM, WiMAX and LTE etc. The main advantage of this transmission technique is its robustness to channel fading in wireless communication environment. There are many applications of OFDM in communication such as digital audio broadcasting, Asynchronous Digital Subscriber Line (ADSL) and High bit-rate Digital Subscriber Line (HDSL) systems. In OFDM, two algorithms digital signal processing algorithm Fast Fourier transform (FFT) and Inverse Fast Fourier Transform (IFFT) are mainly involved. The 8-point IFFT/FFT Decimation-In-Frequency (DIF) with radix-2 algorithm has been analyzed and incorporated in the design. The design has been simulated on the FPGA platform with Altera's Quartus II simulator. Simulation results show that each of the modules of the proposed OFDM is working as desired. The test output achieved from the simulation result of the OFDM has been verified with that of the MATLAB output.

For digital terrestrial television broadcasting (DT-TB) systems, orthogonal frequency division multiplexing (OFDM) technique is considered to be an effective method to combat the frequency selective channel cause by multi-path effect. In the single frequency network (SFN) scenario, Alamouti space frequency block coding (SFBC) is introduced to provide spatial diversity gain and improve the link stability. However, both OFDM and Alamouti SFBC are sensitive to time-variant during mobile reception. In this paper, we propose a decision feedback equalization algorithm for inter-carrier interference (ICI) can-celation of the dual (PN) padded time domain synchronization OFDM (TDS-OFDM) DTTB system over doubly selective channel. Our algorithm is proven by numerical simulations which show bit error rate (BER) gain over mobile SFN channel and can be adopted in mobile high density television (HDTV) transmission systems.

Multi-carrier modulations have generated strong interest recently because of the challenging characteristics of important contemporary channels. While the idea of partitioning spectrally using orthogonal frequency division multiplexing (OFDM) was developed over thirty years ago, its implementation as a practical solution to a communications system problem is much more recent due to advances in digital signal processing and VLSI. Implementation has brought about a simultaneous increase in developing analysis that allow the performance characteristics of the approach to be understood in practical channels. Example channels where OFDM is being strongly considered are data communications over CATV channels and wireless applications such as digital terrestrial broadcasting. Widespread consideration of OFDM as a primary transport mechanism has occurred to date only for high speed data over the twisted pair channel. In this application, the technology is referred to as the Asymmetric Digital Subscriber Line (ADSL). Unlike that application, however, CATV and wireless systems represent RF channels. As such, one important characteristic of each is the phase jittery nature of low-cost, high frequency synthesized carriers. The research will present unique results indicating how these impairments degrade the OFDM system. The approach taken is to model the untracked jitter variation as a lowpass process, note the breakdown of traditional assumptions associated with single carrier modulations, and proceed with analytical solutions from this practical model. The single carrier solutions required are developed, including solutions for slow and rapid phase noise for standard and offset 16-QAM. Results for 64-QAM are also developed, and can be easily extended to any rectangular constellation, such as 256-QAM or 1024-QAM. A comparison of the various simplifying analysis assumptions is made to contrast with exact performance curves when phase noisy RF channels are encountered. A straightforward technique to improve link margin on phase-noise limited, slow jitter channels is presented. Finally, system design guidelines are developed for the difficult moderately varying jitter situation, critical for multi-carrier systems that rely on multiple subchannels of individually low symbol rate.

The discrete multitone (DMT) modulation/demodulation scheme is the standard transmission technique in the application of asymmetric digital subscriber lines (ADSL) and very-high-speed digital subsc...

European standardisation, a key institution for the functioning of the EU single market, functions at the crossroads of private rule-making and public policy. Recently, it has been subjected to fierce scrutiny by the European Commission and the European Court of Justice. Expressed concerns relate to the legal value of standards and the legitimacy of institutions creating them but have broader implications for European competitiveness, highlighting the strategic role of standards. By far much of this critique has been directed towards the European Telecommunications Standards Institute (ETSI), the EU’s crown jewel of technology standardisation. ETSI’s normative power manifests itself in policymaking, legislation and market processes, rendering it an interesting organisation to study as a proxy to understand the legitimacy and resilience of European standardisation. Against this backdrop, this introduction sets the theoretical and legal context for this Special Issue. Upon discussing the background and dynamic of European standardisation, it provides a theoretical framework for ‘crises' and ‘legitimacy’, tailoring it to the particular case of ETSI and the challenges it faces at the policy and judicial level. Lastly, it provides a critical reflection on the Research Articles in this Special Issue, linking them to the current discourses on legitimacy and resilience.

Digital video broadcasting-terrestrial (DVB-T) is an important multimedia technology capable of high data-rate transmission. Orthogonal frequency division multiplexing (OFDM) is the backbone technique in the current DVB-T systems adopted by Europe and Japan. However, the OFDM system is very sensitive to the intercarrier interference (ICI) induced by the Doppler frequency drift and the fading channels. A means to deal with the ICI problem is called the ICI self-cancellation or polynomial cancellation coding scheme. In this paper, we evaluate the effectiveness of the ICI self-cancellation coded DVB-T system compared with the existing DVB-T system using the convolutional coding for different fading channels.

The transmission of high-speed data over severely band-limited channels may be accomplished through the use of discrete multitone (DMT) modulation, a modulation technique that has been proposed for a number of new applications. While the performance of a DMT system has been analyzed by a number of authors, these analyses ignore the effect of timing jitter on system performance. Timing jitter becomes an increasingly important concern as higher data rates are supported and larger constellations are allowed on the DMT subchannels. Hence, in this paper, we assume that synchronization is maintained by using a digital phase-locked loop to track a pilot carrier, Given this model, we derive error rate expressions for an uncoded DMT system operating in the presence of timing jitter, and we derive an expression for the interchannel distortion that results from a varying timing offset across the DMT symbol. In addition, we investigate the performance of trellis-coded DMT modulation in the presence of timing jitter. Practical examples from the asymmetric digital subscriber line (ADSL) service are used to illustrate various results.

The transmission of digital TV pictures has become important topic. For terrestrial broadcasting, a multi-carrier system consisting of a large number of orthogonal carriers (orthogonal frequency division multiplexing (OFDM)) has been proposed. In geographical areas where the cable TV (CATV) distribution system is already widely spread, the CATV distribution network is the main candidate for broadcasting digital TV signals. As the impulse response duration of the CATV transmission channel is much shorter than the delay spread of the terrestrial broadcast channel and the linear distortion is much smaller, it is not evident that OFDM is still the preferred modulation for a CATV environment. The authors have previously pointed out that a single-carrier (SC) QAM system with ideal decision-feedback equalization (DFE) is about 2 dB better than OFDM, when transmitting digital TV signals over the CATV network. The present paper investigates the performance of M/sup 2/-QAM and M-PAM VSB single-carrier (SC) systems. The authors compute the degradation in SNR (as compared to a non-distorting channel) when using either ideal decision feedback equalization (with adaptive filtering) or reduced-complexity feedback equalization (with fixed filtering). They show that the performance of the reduced-complexity equalizer is sensitive to a timing offset (both QAM and VSB) and a carrier offset (VSB only). This indicates that the reduced-complexity equalizer should be used in combination with a synchronizer that carefully controls the phase of the carrier generator (VSB) and sampling clock (VSB and QAM).

Software-Defined Radio (SDR) has become a great tool for fast prototyping and developing new devices for communications systems as well as for implementing flexible, multi-standards communication equipment. In the same pace, Digital Terrestrial Television Broadcasting (DTTB) has become ubiquitous throughout the world and is continuously in development. Integrated System Digital Broadcasting Terrestrial version B (ISDB-TB) uses Band Segmented Transmission — Orthogonal Frequency Division Multiplexing (BST-OFDM), and a powerful channel code and interleavers. In this article, a new implementation of ISDB-TB modulator with SDR is proposed to achieve real time transmission fully compliant with the ISDB-TB standards. Also the computational performance characteristics of each processing block is presented to compare the total CPU consumption used. The software was developed in the GNU Radio and is a valuable tool in research and educational fields of digital communication.

ADSL (Asymmetric Digital Subscriber Line) adopts modulation scheme called DMT (Discrete multi tone), a multi carrier system. The process of allocating bits into various sub-channels is called bit-loading. In this paper, a new bit-loading algorithm that reduces the power required to transmit data is proposed. Comparison on power cut back with other algorithms is presented. Also the implementation of the algorithm in the transmitter is discussed. A Matlab simulation model has been developed to simulate ADSL transmitter (with bit-loading), channel and receiver. The ADSL system with bit-loading algorithm is also implemented in hardware using TT's DSK6713 kit and comparison of software and hardware results are tabulated.

In Japan, the Digital Terrestrial Television Broadcasting (DTTB) system is expected to have mobile reception capability. It is well known that the effect of multipath interference in the fixed condition can be reduced by using the Orthogonal Frequency Division Multiplex (OFDM) method. However, the signal quality degrades seriously due to frequency selective fading and Doppler shifts of the mobile environment. This is because the orthogonality between the carriers has been lost due to this interference. In this paper, we discuss about multipath channel modeling for mobile reception with an OFDM. And we propose a symbol equalization method for coherent demodulation. We also show that the BER characteristics have been improved, and that mobile reception using the 16QAM OFDM system is possible.

Orthogonal frequency division multiplexing (OFDM) is one of the transmission techniques used for digital television (DTV) terrestrial broadcasting. A high quality channel estimator with a low training overhead is the key to the successful delivery of DTV services which require high spectrum efficiency and robustness to strong and dynamic ghosts. Robustness to multipath distortion is especially important in a single frequency emission environment. This paper presents an application of a filtered decision feedback channel estimator for OFDM-based DTV systems using high order QAM modulations. The implementation and the performance of the channel estimator are discussed. Computer simulations were conducted to evaluate the performance of the channel estimator. The channel estimation loss is about 1.2 dB from the ideal case where the channel is assumed to be known by the receiver. For a given multipath spread, the loss can be further reduced by increasing the FFT size. The FFT size is however subject to an upper limit imposed by the Doppler spread.

A computationally efficient optimal discrete bit allocation algorithm is proposed for medium and high target bit rate discrete multitone (DMT) transmissions. Unlike conventional greedy bit-loading algorithms, which compare the incremental transmission power of multicarriers bit-by-bit and allocate one bit at a time, the proposed algorithm is based on parallel bit-loading with reference to a virtual equal power assignment bit allocation. After maximum bit rate allocation, the algorithm achieves the target bit rate by two types of parallel bit- loading. If the target bit rate allocation is not optimal, bit swapping is performed to obtain the optimal solution. Simulation results using the standard asymmetric digital subscriber line (ADSL) test loops demonstrate the reduced computational load of the proposed algorithm compared to the existing optimal discrete bit allocation algorithm when the target rate is between 60% and 99% of the loop's maximum bit rate.