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In Orthogonal Frequency Division Multiplexing (OFDM) systems over fading channels, channel estimation is carried out by transmitting pilot symbols in different patterns. The process consists of two steps. First, the estimation of channel at pilot frequencies is done based on LS criteria. Then, this estimation is interpolated using linear interpolation, cubic interpolation, and spline interpolation...
OFDM (orthogonal frequency division multiplexing) can utilize one-tap equalization for multipath (frequency selective) fading and is widely used in many wireless systems today. However, according to the demand for high-mobility communication and the use of higher carrier frequency, the influence of time selectivity of fading is increasing. Therefore, an accurate channel estimation of time and frequency...
We present a fast converging scheme for estimating the coarse frequency offset in multi-band orthogonal frequency division multiplexing (MB-OFDM) based ultra-wideband (UWB) systems. Our estimator performs an averaging of initial estimate over multiple bands and shows an improved estimation of =3 times for band group 1 compared to our earlier proposed scheme. Cramer Rao lower bound (CRLB) on the estimation...
A 4??4 multi-input multi-output (MIMO) orthogonal frequency-division multiplexing (OFDM) modem with one-symbol-locked timing recovery, anti-I/Q mismatch frequency recovery, frequency-dependent I/Q mismatch estimation and adaptive equalization is implemented in 0.13-??m CMOS library. This chip occupies 4.6??4.6 mm2 and consumes 62.8 mW at 1.2 V.
In orthogonal frequency division multiplexing (OFDM) system, synchronization and channel estimation are two important issues under the wireless fading channel in broadband wireless communication. The timing and frequency offset will affect the accuracy of channel estimation. These issues are studied in this paper, and a frequency selective fading channel under the OFDM system model is set up. This...
In the DFT-spread-OFDM system, the traditional frequency estimation scheme can accurately estimate half of channel frequency responses (on the odd-indexed sub-carriers) and yet the other half (on the even-indexed sub-carriers) can only be made out of approximation or interpolation. It is because that the long block used for data-transmission is double length of short block used for channel estimation...
A modified deterministic structure based carrier frequency offset (CFO) estimation algorithm is presented for the interleaved orthogonal frequency division multiple access (OFDMA) uplink transmission. The presented algorithm combines the conventional deterministic structure algorithm with multiple access interference (MAI) cancellation method so that the estimation performance can be significantly...
Multiple antenna systems have been shown to provide significant performance improvements for network nodes; however, the vast majority of nodes in military networks will be limited to single channel devices due to mobility (size and power) and ease of use considerations. In this paper we apply a new joint synchronization-pilot sequence (JSPS) optimization design technique to multiple transmitter OFDM...
We consider the problem of pilot-aided accurate least squares (LS) channel estimation in the presence of carrier frequency offset (CFO). We first formulate the mean square error (MSE) of the LS channel estimator in the presence of CFO and then show how to select the pilot sequence (with element values constrained to plus or minus one) that minimizes the MSE. Our main conclusion is that, in the presence...
Carrier frequency offset estimation in MIMO systems is much more difficult than that in single antenna systems, especially in uplink transmission in a full-multiplexing transmission mode system. That is because in MIMO uplink transmission systems, different mobile nodes use different oscillators (even with different Doppler Shifts), each introducing one unique carrier frequency offset. In addition,...
This paper aims to improve the performance of estimation and compensation for both the transmitter and receiver radio impairments in the MIMO-OFDM (multiple-input, multiple-output orthogonal frequency-division multiplexing) systems. First, a joint least-squares estimation of channel and radio impairments is developed with a complete set of radio impairments being taken into consideration, including...
In this paper, we propose two robust frequency offset estimation methods for OFDM systems in single frequency network (SFN) with large delay spread. Conventional guard-interval-based (GIB) estimation method is very sensitive to intersymbol interference (ISI) caused by long and strong echoes of the SFN channel. In order to minimize ISI-dependent performance degradation, we first introduce a suboptimal...
The high-density deployment of access points (APs) and their serious mutual interference have made both frequency acquisition and data detection even more difficult in wireless local area network (WLAN). In light of this, this paper presents an antenna-array-assisted algorithm to solve above problems in a multiuser multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM)...
In this contribution we evaluate pilot-based carrier frequency offset (CFO) estimation and its correction in a filter bank based multicarrier (FBMC) system. We show that by applying certain pilots designed specifically for filter banks, the CFO can be accurately estimated. The performance evaluation is done in a hypothetical WiMAX scenario in which an FBMC system would substitute OFDM maintaining...
An uplink OFDMA systems is considered. Different users use different transmit antennas, thus, each user contributes a different carrier frequency offset (CFO) at the receiver. The multiple CFOs introduce intercarrier interference, thus impeding user separation and transmit signal recovery. A low complexity CFO estimation approach is proposed for estimating multiple CFOs. The proposed approach relies...
In this paper, a novel demodulation structure in high-frequency (HF) channel is introduced and studied. Frequency-offset estimation, fractionally spaced adaptive equalization and carrier recovery techniques are involved. Frequency-offset correction is carried out based on channel impulse response estimation. Fractionally spaced adaptive equalization and carrier recovery are combined with non-linear...
This paper addresses the problem of carrier frequency offset (CFO) estimation in orthogonal frequency division multiplexing (OFDM) systems using Bayesian method. Depending on the availability of the noise variance, two general CFO estimators are derived. Furthermore, the two general maximum a posteriori (MAP) estimators are developed into several special cases based on different degrees of prior information...
In this paper, we address the problem of frequency offset and channel gains estimation for correlated multi-input multi-output (MIMO) channels. The channel is assumed to be frequency-selective and block fading with both spatial and multipath correlations. A maximum-likelihood (ML) frequency offset (FO) estimator is proposed by using the Baysian approach and the mean and variance of the FO estimation...
Orthogonal frequency division multiplexing (OFDM) offers high data rates and robust performance in frequency selective channels by link adaptation utilizing information about the channel quality. A crucial parameter required for adaptive transmission is the signal-to-noise ratio (SNR). In this paper, we propose a novel SNR estimation algorithm for wireless OFDM systems based on the reuse of the synchronization...
In this paper, simultaneous channel estimation, carrier frequency offset (CFO) estimation, and data decision are considered for multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. It is shown that the expectation maximization (EM) approach is complementary to the Kalman filter (KF) approach where the latter provides poor CFO estimation but good channel estimation...
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