One limiting issue in implementing high-speed wireless systems is the impairment associated with analog processing due to component imperfections. In uplink transmission of multiuser systems, a major source of such impairment is IQI introduced at multiple transmitters. In this paper, we deal with OFDMA and SC-FDMA which have received attention in recent years as physical layer protocol in WiMAX and 3GPP LTE, and analyze the effect of the transmitter (Tx) IQ imbalances on OFDMA and SC-FDMA receivers. To cope with the inter-user interference problem due to Tx IQ imbalances, we propose a widely linear receiver for OFDMA and SC-FDMA systems and also propose a novel subcarrier allocation scheme, which has high tolerance to such Tx IQ distortion.

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In this paper, we propose to adapt simultaneously the transmit power both in the spatial and frequency domains using a heuristic expression of the bit error rate (BER) for each subcarrier and transmit antenna. The proposed method consists of grouping a certain number of subcarriers and performing local power adaptation in each subcarrier group and transmit antenna. The subcarrier grouping is performed in such a way that equalizes the average channel condition of each subcarrier group. The grouping and the local power adaptation allow us to take advantage of the channel variations and to reduce the computational complexity of the proposed power distribution scheme. With the simplicity of the heuristic BER expression, we can obtain a closed form expression of the transmit power to be allocated. Simulation results show significant performance gain in term of BER compared to the equal power distribution.

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SUMMARYRecently, the marginalized particle filter (MPF) has been applied to blind symbol detection problems over selective fading channels. The MPF can ease the computational burden of the standard particle filter (PF) while offering better estimates compared with the standard PF. In this paper, we investigate the application of the blind MPF detector to more realistic situations where the systems suffer from analog imperfections which are non-linear signal distortion due to the inaccurate analog circuits in wireless devices. By reformulating the system model using the widely linear representation and employing the auxiliary variable resampling (AVR) technique for estimation of the imperfections, the blind MPF detector is successfully modified to cope with the analog imperfections. The effectiveness of the proposed MPF detector is demonstrated via computer simulations.