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ABSTRACT: In this paper, we propose an initial synchronization scheme for time and carrier frequency synchronization and cell identification in 802.16e OFDMA downlink. The proposed method does not require knowledge of actual transmitted preamble, but only utilizes the preamble structure and inverse Fourier transform properties to obtain time/frequency synchronization. Through simulations, we show that the proposed synchronization method is suitable in multipath as well as multicell environment. Although evaluated for IEEE 802.16e, the proposed method can also be used in other OFDM systems with similar signal properties.
Signals, Systems and Computers, 2006. ACSSC '06. Fortieth Asilomar Conference on; 12/2006
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ABSTRACT: In this article we provide a practical standardization related viewpoint on beamforming and MIMO technologies. In particular, we address the status in different industry-driven standardization for a (3GPP and IEEE 802) and discuss the rationale for possible adoption or use of such technologies in current or future wireless systems. We draw attention to some practical system-level and implementation aspects that need to be resolved before a successful application of beamforming or MIMO in real systems
IEEE Wireless Communications 09/2006; · 2.58 Impact Factor
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ABSTRACT: It is known that the achievable capacity of wireless communications increases when multiple transmitter and receiver antennas are used. A step towards achieving MIMO capacity was taken by the introduction of the layered space-time architecture, also known as BLAST (Bell Laboratories layered space-time code), which advocates a simple demultiplexing of the data stream instead of some specific encoding in space-time, and does not require instantaneous channel information at the transmitter. When such channel information is available at the transmitter, however, the capacity of the link is increased. The PARC (per antenna rate control) method is an example of a technique that utilizes channel information for rate control of two separately encoded packets. In the literature, it has been shown that eigenbeamforming and water-filling are essential for achieving the relevant MIMO capacity. In this paper, we introduce a variant of water-filling called SWF-MIMO (systematic water-filling) for the transmission of an encoded packet across a MIMO channel by a simple extension of the current cdma2000 packet data structure. In this concept, we use the well-known fact that the reliability of the systematic part of a turbo code is crucial during the iterative decoding of the coded packet. The paper provides a detailed description of the SWF-MIMO algorithm and provides simulation results to compare the performance of the scheme with other MIMO schemes such as coded VBLAST and PARC.
3G Mobile Communication Technologies, 2004. 3G 2004. Fifth IEE International Conference on; 02/2004
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ABSTRACT: In this paper, we propose an FFT-based linear equalization algorithm for the CDMA downlink. By approximating the correlation matrix with a circulant matrix, which is diagonalized by the DFT matrix, we are able to incorporate the efficient FFT operations and avoid the direct matrix inversion. Furthermore, we show that with the help of Kronecker algebra and the notion of dimension-wise and element-wise FFT, we are able to extend the FFT-based method to cases where multi-channel diversity, such as over-sampling or receive antenna array diversity, is present. Numerical simulations show that the FFT-based algorithm overlaps with the direct matrix inversion method for most of the low to medium SNR range and have a small loss at high SNR.
Signals, Systems and Computers, 2003. Conference Record of the Thirty-Seventh Asilomar Conference on; 12/2003
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ABSTRACT: In this paper, we propose a novel channel quality indicator (CQI) measure for the space-time jointly encoded MIMO-CDMA systems in frequency selective channels. The CQI proposed here is derived from a so-called per-Walsh code joint detection structure consisting of a front-end linear filter followed by joint symbol detection across all streams. The linear filter is designed to convert the multipath channel into a single-path channel to restore orthogonality of Walsh codes and to avoid joint sequence detection. We derive a class of filter that maximizes the so-called constrained mutual information, and show that the conventional LMMSE and MVDR equalizers belong to this class. Similar to the notion of generalized SNR (GSNR), this constrained mutual information provides us with a CQI measure describing the MIMO link quality. Such a CQI measure is essential in providing a simple one-dimensional mapping for both link adaptation and link-to-system mapping for jointly encoded MIMO-CDMA system.
Global Telecommunications Conference, 2004. GLOBECOM '04. IEEE;
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ABSTRACT: The evaluation of the performance of a cellular system using a simulation environment usually involves a link-to-system mapping based on a channel quality indication. The mapping is done using a set of link curves characterizing the link behavior, that are generated offline. In some cases, the static performance of a link is a sufficient indicator. But in high mobility, the block-fading assumption introduces inaccuracies in the link-to-system mapping. This paper proposes a dual-variable mapping technique that can be used in high-mobility conditions, using the mean and the variance of the SINR seen during a frame. Simulations show that, using this methodology, the mapping can be created independent of the velocity and the multipath profile of the channel. This mapping technique can also be used as a channel quality indication for link adaptation purposes.
Global Telecommunications Conference, 2004. GLOBECOM '04. IEEE;
