|
Blind carrier frequency offset estimation for constant modulus signaling based OFDM systems: algorithm, identifiability, and performance analysis
Wei-yang XU, Bo LU, Xing-bo HU, Zhi-liang HONG
Front. Inform. Technol. Electron. Eng., 2010, 11(1): 14-26.
https://doi.org/10.1631/jzus.C0910150
Carrier frequency offset (CFO) estimation is critical for orthogonal frequency-division multiplexing (OFDM) based transmissions. In this paper, we present a low-complexity, blind CFO estimator for OFDM systems with constant modulus (CM) signaling. Both single-input single-output (SISO) and multiple-input multiple-output (MIMO) systems are considered. Based on the assumption that the channel keeps constant during estimation, we prove that the CFO can be estimated uniquely and exactly through minimizing the power difference of received data on the same subcarriers between two consecutive OFDM symbols; thus, the identifiability problem is assured. Inspired by the sinusoid-like cost function, curve fitting is utilized to simplify our algorithm. Performance analysis reveals that the proposed estimator is asymptotically unbiased and the mean square error (MSE) exhibits no error floor. We show that this blind scheme can also be applied to a MIMO system. Numerical simulations show that the proposed estimator provides excellent performance compared with existing blind methods.
|
|
Congestion avoidance, detection and alleviation in wireless sensor networks
Wei-wei FANG, Ji-ming CHEN, Lei SHU, Tian-shu CHU, De-pei QIAN
Front. Inform. Technol. Electron. Eng., 2010, 11(1): 63-73.
https://doi.org/10.1631/jzus.C0910204
Congestion in wireless sensor networks (WSNs) not only causes severe information loss but also leads to excessive energy consumption. To address this problem, a novel scheme for congestion avoidance, detection and alleviation (CADA) in WSNs is proposed in this paper. By exploiting data characteristics, a small number of representative nodes are chosen from those in the event area as data sources, so that the source traffic can be suppressed proactively to avoid potential congestion. Once congestion occurs inevitably due to traffic mergence, it will be detected in a timely way by the hotspot node based on a combination of buffer occupancy and channel utilization. Congestion is then alleviated reactively by either dynamic traffic multiplexing or source rate regulation in accordance with the specific hotspot scenarios. Extensive simulation results under typical congestion scenarios are presented to illuminate the distinguished performance of the proposed scheme.
|
8 articles
|