Novel Estimation of MISO-OFDM System Using CDD

نویسنده

  • R Jeyanthi
چکیده

In Orthogonal Frequency Division Multiplexing (OFDM) systems, the cyclic-delay diversity (CDD)Scheme is a low-complexity means of increasing transmit diversity. Because it requires only one inverse discrete Fourier transform (IDFT) operation at the transmitter. The mean square error (MSE) of both the least square (LS) channel estimate and the minimum mean square error (MMSE) channel estimate are applied in the design of optimum pilot sequence for CDD MISO -OFDM system to enhance channel estimation performance. The simulation results confirm that the proposed pilot design minimizes the MSE of both the LS and the MMSE channel estimates in MISO-OFDM system and compared with the theoretical values. KEYWORDS—OFDM, pilot sequence, cyclic delay diversity (CDD), channel estimation. I.INTRODUCTION Orthogonal frequency division multiplexing (OFDM) is one of the most attractive transmission schemes for digital communications. It enables the frequency diversity by multi-path channels to be exploited by interleaving across sub-carriers and applying forward error correction (FEC) schemes. As a result, they provide an efficient means of improving the performance of multiple-input multiple-output (MIMO) networks. In general, the spatial diversity achieved by the multiple antennas in OFDM systems is exploited using either space-time block coding (STBC)[2,3] or cyclic-delay diversity (CDD) schemes[4-6]. CDD-OFDM increases the transmission diversity, in which the multiple-input single-output (MISO) channel is transformed into an equivalent singleinput single-output (SISO) channel with increased frequency selectivity. In other words, CDD-OFDM converts spatial diversity into frequency diversity[5-7]. Unlike the convolution inter-leaver with block delay, CDD scheme does not induce any rate loss. Compared to STBC-OFDM[8], CDD-OFDM has the advantage that only one inverse discrete Fourier transform (IDFT) operation is required at the transmitter. Furthermore, no additional decoders are required at the receiver end. Previous studies have reported that the pilots in SISOOFDM and MIMO-OFDM systems should be equally powered and equally spaced. Pilots transmitted from different antennas in MIMO-OFDM systems should be phase orthogonal to minimize the mean square error of the channel estimate. To achieve a phase orthogonal condition, pilot transmitted from different antenna must have different values in frequency domain. As a result, it needs IDFT Operation to generate pilot sequence for each transmitter, where is the number of transmitting antenna. In CDD OFDM system, only one IDFT operation is required at transmitter, regardless of the number of transmit antennas. As the transmitter architectures of traditional MIMO-OFDM and CDDOFDM systems differ, the pilot sequences in MIMOOFDM systems are inapplicable to CDD-OFDM systems. The equally spaced pilot[9-13] sequence was used to estimate the equivalent SISO channel but this scheme requires a large number of pilots. In [8] the authors presented a pilot-aided method to estimate the NT channels individually for CDD-OFDM systems, in which the MSE of the channel estimate was minimized under Novel estimation of MISO-OFDM system using CDD M.R. Thansekhar and N. Balaji (Eds.): ICIET’14 1640 the assumption that the channel remained static over NT consecutive OFDM symbols, this restricts its application. In this work, a pilot design for CDD OFDM system is implemented. There are two main contributions. First the pilot design criteria which minimize the MSE of both the least square (LS) channel estimate and the minimum mean square error (MMSE) channel estimate in CDD-OFDM systems are implemented. Second the simulated results are compared with theoretical results. The proposed design methodology enables the status of the channel to be estimated using one OFDM symbol. The organization of this paper is as follows. Section II describes the system model. Section III explains the LS and MMSE channel estimation methods in MISO-OFDM systems, it also presents the optimal pilot design procedure. Section IV demonstrates the illustration of the pilot design procedure. Section V confirms the optimality of the proposed pilot design methodology by performing simulation experiments. Section VI provides some concluding remarks.

برای دانلود رایگان متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

A Robust Frequency Offset Estimation Scheme for OFDM System with Cyclic Delay Diversity

Cyclic delay diversity (CDD) is a simple technique to intentionally increase frequency selectivity of channels for orthogonal frequency division multiplexing (OFDM).This paper proposes a residual carrier frequency offset (RFO) estimation scheme for OFDMbased broadcasting system using CDD. In order to improve the RFO estimation, this paper addresses a decision scheme of the amount of cyclic dela...

متن کامل

Channel Correlation Properties in OFDM by using Time-Varying Cyclic Delay Diversity

This paper analyzes the influence of time-varying cyclic delay diversity (TV-CDD) on the channel fading correlation properties in orthogonal frequency division multiplexing (OFDM) based systems. The underlying transmit diversity technique CDD only increases the frequency diversity at the receiver. In contrast, TV-CDD introduces additionally time diversity which can be exploited without the need...

متن کامل

Equalization and Channel Estimation for Cellular MIMO-OFDM

In this paper, the efficient channel estimation and equalization techniques for a high-rate multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) system is implemented. In particular the article presents the implementation of MLD along with Alamauti receiver technique for implementation of MIMOOFDM. Finally, we evaluate the BLER and BER for the proposed schemes by comp...

متن کامل

Carrier frequency offset estimation method for 2 × 1 MISO TDS-OFDM systems

In time-domain synchronous (TDS)-orthogonal frequency division multiplexing (OFDM) systems, a pseudo noise (PN) sequence is inserted instead of the cyclic prefix. The PN sequence is used not only as a guard interval but also as a training sequence for channel estimation and synchronization in the time domain. Recently, research studies on 2 × 1 multi input-single output (MISO) TDS-OFDM systems ...

متن کامل

Cooperative Coding Using Cyclic Delay Diversity for OFDM Systems

This paper proposes cooperative coding using cyclic delay diversity (CDD) for OFDM systems. The cooperative diversity is combined with channel coding while CDD is applied to the cooperative transmission of the multiple relays to improve the beneficial effects of the cooperating relays. Analyses of frame error probability (FEP) and the average channel power of the proposed scheme are shown. Simu...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 2015