Comparing single and multiple carrier schemes using channel coding Daniel L. Hatae, F´ abio C. Zottino, Marcio Eisencraft, Magno T. M. Silva, and Maria D. Miranda Mackenzie Presbyterian University S˜ ao Paulo, Brazil {daniel.hatae, magnotmsilva}@gmail.com, fzottino@yahoo.com, {marcioft, mdm}@mackenzie.br Abstract— Recently, a comparison between OFDM (Orthogonal Frequency Division Multiplex) and single carrier with fractionally DFE (Decision Feedback Equalizer) was presented in the absence of channel coding. In this paper, we extend this comparison, considering convolutional coding. Rice and Rayleigh channel models limited to six echoes are assumed in the simulations. Index Terms— OFDM, Decision Feedback Equal- izer, fractionally equalizers, channel coding. I. I NTRODUCTION T HE transmission and reception techniques are the main differences among the digital TV standards in each country. The ATSC (Advanced Television Systems Committee) is responsible for the American terrestrial digital TV standard, which considers a single-carrier transmission scheme [1]. The European and Japanese standards, known re- spectively as DVB-T (Digital Video Broadcasting - Terrestrial) and ISDB-T (Integrated Services Digital Broadcasting - Terrestrial), use a multiple-carrier transmission scheme, known as COFDM (Coded Orthogonal Frequency Division Multiplex) [2], [3]. One of the most suited reception techniques for single-carrier uses the Decision Feedback Equalizer (DFE). When compared to Linear Transversal Equal- izer (LTE), DFE presents a more favorable tradeoff between computational cost and efficient behavior for channels with severe intersymbol interference [4]. The superiority of DFE with respect to LTE also occurs in the fractionally space. The third and the fourth receiver generations of ATSC digital TV standard consider the fractionally DFE with double symbol transmission rate [5], [6]. Motivated by the recent Brazilian digital TV standard definition, a comparison between single carrier and OFDM, in the absence of channel cod- ing, was presented in [7]. In this case, single- carrier transmission scheme with the fractionally DFE presents equivalent or even better performance when compared to OFDM. Since channel coding provides better performance in both transmission techniques, we extend, in this paper, the comparison of [7], considering convolutional coding and the soft decision Viterbi algorithm decoding [8]. The paper is organized as follows. In Section II, the most important aspects of problem formulation, considering OFDM, single carrier using DFE, and channel coding are revisited. Simulation results and concluding remarks are presented respectively in sections III and IV. II. PROBLEM FORMULATION A. OFDM Systems The OFDM systems divide the available band- width into N subcarriers. A spectrally and com- putationally efficient method to put data on the sub-carriers uses the inverse Fast Fourier Transform (iFFT). The addition of cyclic prefix allows that the linear convolution with the channel can be considered as a circular convolution [9], [10]. In the receiver, inverse operations remove the cyclic prefix and convert the data from frequency to time domain. Channel Coding is important to spread the information over multiple subcarriers. This ensures frequency diversity and improves the OFDM perfor- mance [10]. A block diagram of a typical OFDM system is shown in Figure 1. In order to compensate the channel effect, channel estimation techniques must be considered, using pi- lot subcarrier information [11]. The most used meth- ods are the Least Squares (LS) and the Minimum Mean Square Error (MMSE) [9], [12]. After the channel estimation at the pilot subcarrier frequen- cies, an interpolation method is used to obtain the channel response at the other subcarrier frequencies.