Adaptive reconfigurable V-BLAST type equalizer for cognitive MIMO-OFDM radios

Abstract

An adaptive channel shortening equalizer design for multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) radio receivers is considered in this presentation. The proposed receiver has desirable features for cognitive and software defined radio implementations. It consists of two sections: MIMO decision feedback equalizer (MIMO-DFE) and adaptive multiple Viterbi detection. In MIMO-DFE section, a complete modified Gram-Schmidt orthogonalization of multichannel input data is accomplished using sequential processing multichannel Givens lattice stages, so that a Vertical Bell Laboratories Layered Space Time (V-BLAST) type MIMO-DFE is realized at the front-end section of the channel shortening equalizer. Matrix operations, a major bottleneck for receiver operations, are accordingly avoided, and only scalar operations are used. A highly modular and regular radio receiver architecture that has a suitable structure for digital signal processing (DSP) chip and field programable gate array (FPGA) implementations, which are important for software defined radio realizations, is achieved. The MIMO-DFE section of the proposed receiver can also be reconfigured for spectrum sensing and positioning functions, which are important tasks for cognitive radio applications. In connection with adaptive multiple Viterbi detection section, a systolic array implementation for each channel is performed so that a receiver architecture with high computational concurrency is attained. The total computational complexity is given in terms of equalizer and desired response filter lengths, alphabet size, and number of antennas. The performance of the proposed receiver is presented for two-channel case by means of mean squared error (MSE) and probability of error evaluations, which are conducted for time-invariant and time-variant channel conditions, orthogonal and nonorthogonal transmissions, and two different modulation schemes.

Sequential convex combinations of multiple adaptive lattice filters in cognitive radio channel identification

“…Adaptive positioning, determining the coordinates of a cognitive radio in space, is a step towards realization of accurate location awareness in cognitive radios [18]. The author has recently proposed a receiver (equalizer) architecture for use in cognitive MIMO-OFDM radios that performs joint channel estimation and data detection, addresses the receiver complexity problems, and contributes to the flexibility, reconfigurability, and reprogrammability of receiver [19]. It was also shown in [20][21][22] that this receiver architecture can be configured for spectrum sensing as well as adaptive positioning function of cognitive radio virtually at no cost.…”

“…In order to capture the statistical variations in the CR environment, the combination of multiple lattice filters with different exponential weighting factors has been considered so as to bring together the convergence properties of fast filters that have small exponential weighting factors and steady-state MSD properties of slow filters that have large exponential weighting factors. Accordingly, the author envisions multiple adaptive lattice filters as channels of sequential processing multichannel lattice stages (SPMLSs) [19][20][21][22]50] and proposes to sequentially combine these multiple lattice filters in a CR channel identification task. In view of the aforementioned issues concerning convex vs. affine combinations, the focus is on convex combinations of multiple adaptive lattice filters.…”