FULL PAPER International Journal of Recent Trends in Engineering, Vol 2, No. 5, November 2009 80 DHT Based 4 QAM OFDM Baseband System and Channel Estimation Vijay Kumar Ganapati Panda Prasant Kumar Sahu Department of E. E. School of Electrical Sciences School of Electrical Sciences . I.I. T. Madras, Chennai I. I. T. Bhubaneswar, Orissa I. I. T. Bhubaneswar, Orissa Email: nitrkl.vijay@gmail.com Email: ganapati.panda@gmail.com Email: prof.prasant@gmail.com Abstract - This paper presents the simulation of 4 Quadrature Amplitude Modulation (QAM) orthogonal frequency division multiplexing (OFDM) baseband system and channel estimation which uses inverse discrete Hartley transform (IDHT) and discrete Hartley transform (DHT). As the calculation of DHT and IDHT involves real operations hence the computational complexities are less as compared to DFT and IDFT. Moreover as IDHT is same as DHT hence we can use same hardware for both, while the DFT and IDFT require separate hardware to implement. As compared to DFT based OFDM system, the simulated DHT based OFDM system achieves approximately the same transmission performance with less computational complexity and hardware requirements. Index Terms - Channel estimation, DHT, DFT, QAM, OFDM I INTRODUCTION Frequency division multiplexing (FDM) is used to transmit multiple signals simultaneously over a wired or a wireless system. Each signal is limited by a specific frequency band, and is modulated by a data stream. Orthogonal Frequency Division Multiplexing (OFDM) [7, 8] is a special case of this, where the data is distributed over a large number of carriers that are ‘orthogonal’ to each other. OFDM is spectrally efficient compared to the conventional FDM system, since it does not need any guard bands between adjacent channels. This orthogonality property is the heart of OFDM, since the interference due to other carriers is prevented, when the receiver demodulates a particular carrier. The OFDM system avoids the tracking of a time varying channel by the use of differential phase shift keying (DPSK) in. However this will limit the number of bits per symbol and results in 3 db loss in signal-to-noise ratio (SNR) [2]. If the receiver contains a channel estimator, multipath signaling scheme can be used. OFDM system offers high bit rate transmission over a frequency fading channel due to use of spectrally efficient quadrature amplitude modulation (QAM). Because of high efficiency with no inter-symbol-interference (ISI), OFDM has been standardized or extensively investigated for various applications like digital radio applications and wireless communications [1]. Implementation of the DFT based OFDM system requires the complex calculation of a long length IDFT and DFT on the transmitter and receiver side of the OFDM system. Such a long length IDFT and DFT calculation requires a huge number of complex multiplications and additions. In this paper we simulated a discrete Hartley transform (DHT) [10] based OFDM system which uses IDHT and DHT on the transmitter and receiver side. DHT is purely real transform. The calculation of DHT involves only real multiplications and additions and it is having identical inverse. Here, we present a comparative analysis of DFT and DHT based OFDM system. The objective is to examine the computational complexities and bit error rate (BER) performance after channel estimation of DHT and DFT based OFDM system [12]. The rest of the work is organized as follows. In Section II DHT based OFDM system model is described. Section III includes the channel estimation algorithms. Section IV contains performance evaluation results obtained by means of simulations. This is followed by conclusions in Section V. The similar type of work might have been done by someone else too but the methodology adapted in this paper is totally new up to best of our knowledge and data available to us. II DHT BASED OFDM SYSTEM MODEL The OFDM system is modeled employing the following assumptions. 1) Accurate time & frequency synchronization at the receiver. 2) The channel impulse response length (L t ) is smaller than the cyclic prefix (CP) length of the OFDM symbol in order to avoid inter-block interference & preserve orthogonality of the OFDM symbol. We will consider the system shown in Fig. 1, where k x are the transmitted symbols, ) (t g is the channel impulse © 2009 ACADEMY PUBLISHER