Decoupled compensation of IQ imbalance in MIMO OFDM systems

The direct-conversion architecture is an attractive front-end design for multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. These systems are typically small in size and provide a good flexibility to support growing number of wireless standards. However, direct-conversion based OFDM systems are generally very sensitive to front-end component imperfections. These imperfections are unavoidable especially when cheaper components are used in the manufacturing process and can lead to radio frequency (RF) impairments such as in-phase/quadrature-phase (IQ) imbalance. These RF impairments can result in a severe performance degradation. In this paper, we propose training based efficient compensation schemes for MIMO OFDM systems impaired with transmitter and receiver frequency selective IQ imbalance. The proposed schemes can decouple the compensation of the transmitter and receiver IQ imbalance from the compensation of the channel distortion. It is shown that the proposed schemes result in an overall lower training overhead and a lower computational requirement as compared to a joint estimation/compensation of IQ imbalance and the channel distortion.     

Joint Adaptive Compensation of Transmitter and Receiver IQ Imbalance Under Carrier Frequency Offset in OFDM-Based Systems

Zero-intermediate frequency (IF)-based orthogonal frequency division multiplexing (OFDM) transmitters and receivers are gaining a lot of interest because of their potential to enable low-cost terminals. However, such systems suffer from front-end impairments such as in-phase/quadrature-phase (IQ) imbalance which may have a huge impact on the performance. Moreover, since OFDM is very sensitive to a carrier frequency offset, this distortion needs to be taken into account in the derivation and analysis of any IQ imbalance estimation/compensation scheme. In this paper, the effect of both transmitter and receiver IQ imbalance under carrier frequency offset in an OFDM system is studied and an algorithm is developed to compensate for such distortions in the digital domain. The algorithm involved is a very efficient post-FFT adaptive equalization which is shown to lead to near ideal compensation.     

Image encryption based on modified Henon map using hybrid chaotic shift transform

Multimedia Tools and Applications - In this paper, a new two dimensional modified Henon map (2D-MHM) which is derived from Henon map is proposed. Its chaotic performance is analyzed through...     

Image encryption based on 5D hyperchaotic system using hybrid random matrix transform

Multidimensional Systems and Signal Processing - In recent years, chaotic systems are widely used in the secured transmission of images due to the inherent properties relevant to cryptography. In...