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We propose a maximum a-posteriori (MAP) based blind algorithm for carrier frequency offset (CFO) and symbol timing offset (STO) estimation, for a convolutionally coded orthogonal frequency division multiplexing (COFDM) system, in an additive white Gaussian noise (AWGN) channel. We derive the MAP estimators mathematically. It is observed that though the MAP metric for CFO estimation gives a good performance...
Traditional OFDM based transmission system uses Cyclic Prefix (CP) in an OFDM symbol in order to maintain orthogonality of transmission. Present days' Ultra-Wideband (UWB) systems use Multi-Band OFDM (MB-OFDM) techniques for transmission in application like Wireless Personal Area Network (WPAN). UWB based systems are power limited by the regulation of FCC. CP introduces correlation in the transmitted...
In cooperative relay systems, relayed signals propagate through different channels and are received at the destination node with distinct timing and carrier frequency offsets (CFOs). This feature makes synchronization a rather challenging task as compared with centralized multiple-input multiple-output systems. Unlike conventional preamble designs with good correlation properties only in time domain...
TCH (Tomlinson, Cercas and Hughes) sequences have been studied for code-spreading and channel coding, but their true purpose is for synchronization and channel estimation. This is due to their property of being (virtually) orthogonal to all of their sequences obtained via circular shifts, and the use of the FFT (Fast Fourier Transform) for decoding. This property is extremely useful for time-offset...
This paper presents baseband receiver design for the third Generation Partnership Project (3GPP) Long Term Evolution (LTE) downlink systems under fast-fading channels. We aim to support 2×2 open-loop spatial multiplexing at high mobility up to 240 Km/hr with well-synchronized capability. The proposed receiver contains the functional blocks of mode detection, synchronization, channel tracking, inter-carrier...
This paper presents a low-complexity architecture compensating for carrier frequency offset (CFO) and IQ imbalance circuits in MIMO-OFDM receiver systems. A coordinate rotation digital computer based sinusoid iteration generator is also developed for CFO estimation and correction in wireless communication receivers. Besides the main effect from the multi-path, some non-ideal effects from imperfect...
Time domain synchronous orthogonal frequency division multiplex (TDS-OFDM) is an effective multi-carrier modulation scheme to improve spectrum efficiency. Conventional synchronization algorithm based on the time-domain differential correlation of the pseudo noise (PN) sequence may not work well in severe multipath fading channels. In this paper, a robust synchronization algorithm is proposed where...
In this paper, we propose an efficient scheme using a new single-symbol preamble structure for OFDM data-aided synchronization. The preamble symbol is constituted of two successive equal-duration sub-symbols, the second one of which is a differentially encoded version of the first one, using an adequately designed precoding sequence. This structure leads to almost perfect channel autocorrelation profile...
OFDM (Orthogonal Frequency Division Multiplexing) has been chosen as the air interface technique for LTE (Long Term Evolution) standard. Furthermore, CA (Carrier Aggregation) is defined by 3GPP (the 3rd Generation Partnership Project) to support wide-bandwidth transmission. However, OFDM system is sensitive to synchronization errors generated by multipath delay, Doppler shift and oscillator instability...
A low complexity time domain channel estimation technique for OFDM systems is proposed. It uses training symbols to estimate the channel impulse responses (CIR) via circular cross-correlation. A CIR search window technique is also proposed to optimise the accuracy of synchronisation and channel estimation. The output of the search window can also be used for the estimation of channel delay spread...
A crucial parameter required for adaptive transmission in orthogonal frequency division multiplexing (OFDM) systems is the signal-to-noise ratio (SNR). In this paper, certain modifications to previously proposed preamble-based SNR estimator for wireless OFDM systems are suggested in order to improve estimation performance. Proposed modifications, related to DFT interpolation, are based on the adaptive...
This paper addresses the effect of timing synchronization errors for two different multicarrier techniques CPOFDM and FBMC. Such errors degrade the performance of the reference receiver by causing multi user interference. This interference occurs when the signals from different transmitters arrive at a given receiver with arbitrary timing misalignments, leading to the destruction of orthogonality...
This paper presents a new blind symbol timing offset (STO) estimation scheme for wireless orthogonal frequency division multiplexing (OFDM) systems with constant modulus constellation. In the proposed scheme, the STO estimation is performed by minimizing the power difference between either adjacent or consecutive subcarriers, which basically depends on the assumptions made on the channel conditions...
A new method for frequency synchronization based upon Zero-Intermediate Frequency (zero-IF) receiver and characteristics of the received signal's power spectrum for MC-DS-CDMA-Uplink system is proposed in this paper. The variance for Carrier Frequency Offset (CFO) estimators of MC-DS-CDMA-Uplink is compared with that of an OFDM system to estimate the CFO. Our study and results show that the MC-DS-CDMA...
A self-cancellation scheme is proposed to cope with the sample frequency offset (SFO) problem in OFDM systems in the presence of a carrier frequency offset (CFO). Making use of the symmetry between the phase shifts caused by SFO and the subcarrier index, we put the same constellation symbol on symmetrical subcarriers, and combine the pairs at the receiver coherently. In this way, the SFO effects are...
Frequency synchronization plays a critical role in acquiring cooperative diversity for cooperative OFDM systems. However, the superposition of different carrier frequency offsets (CFOs) among each relay and destination makes the estimation difficult. In this paper, a novel multiple CFOs estimation algorithm is proposed. With this algorithm, the CFO corresponding to each relay can be accurately estimated...
In this paper, based on mutually orthogonal (MO) ZCZ polyphase sequence (PS) sets proposed by Ref. [11], a method for improving the family size of ZCZ sequences in each set mentioned above is presented. As compared with Ref. [11], the resulting ZCZ sequences in each set can arrive to their theoretical bound due to expansion of their family size, whereas the length and width of ZCZ of ZCZ sequences...
A novel timing offset estimation scheme for orthogonal frequency division multiplex (OFDM) systems is proposed in this paper, which can eliminate the ambiguity of the first arriving path estimation in multipath channels. The timing of the first arriving path is determined by detecting the first falling edge of the sliding window of the correlation result. A predefined threshold is adopted to validate...
In this paper, a simple and effective synchronization scheme for NC-OFDM systems is proposed. To keep the autocorrelation in the scenario of subcarriers deficiency, the preamble is consists of two identical pseudo-noise (PN) sequences instead of ZC sequences. Coarse timing estimation and fractional CFO(carrier frequency offset) estimation are completed according to the correlation between the received...
The OFDM technology can conquer the frequency selected fading and the inter-channel interference (ICI) effectively, so it is the core technology in the future mobile communications. The basic principle and some key technologies of OFDM are studied in this paper. Then we gave the OFDM block diagram and simulink model. Under the non-ideal synchronization circumstance, we studied the signal changes before...
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