The frequency-selective channel-estimation problem in multi-input-multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems is investigated from the perspective of compressed sensing (CS). By minimizing the mutual coherence of the measurement matrix in CS theory, two pilot allocation methods for the CS-based channel estimation in MIMO-OFDM systems are proposed. Simulation results show that using the pilot patterns designed by the two proposed methods gives a much better performance than using other pilot patterns in terms of the mean square error of the channel estimate as well as the bit error rate of the system. Moreover, the optimal pilot patterns obtained by the proposed second method based on genetic algorithm and shift mechanism could offer a larger performance gain than those by the first method based on minimizing the largest element in the mutual coherence set possessed by pilot patterns for all multiple antenna ports.Index Terms-Channel estimation, compressed sensing (CS), multi-input-multi-output orthogonal frequency division multiplexing (MIMO-OFDM), mutual coherence, pilot allocation.

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This paper addresses the sparse channel estimation problem in multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems from the perspective of distributed compressed sensing (DCS). It is focused on deterministic pilot allocation of MIMO-OFDM systems to improve the performance of DCS-based channel estimation. By transforming the problem of DCS-based channel estimation to a problem of reconstructing block-sparse signals, a class of mutual coherence-related criteria is first proposed for optimizing pilot locations. By employing the proposed criteria, a genetic algorithm-based method of optimizing the pilot locations is then presented. Simulation results show that the DCS-based MIMO channel estimation with optimized pilot locations can improve the spectrum efficiency by nearly 36% and the bit error rate (BER) performance by 1.5dB, as compared with the least square (LS) channel estimation with equidistant pilot locations. Moreover, the DCS-based MIMO channel estimation yields a 4.7% improvement in spectrum efficiency under the same BER performance over the CS-based channel estimation. Index Terms-MIMO-OFDM, channel estimation, distributed compressed sensing, mutual coherence, block-sparse signals, pilot allocation.

The frequency selective channel estimation problem in orthogonal frequency division multiplexing (OFDM) systems is investigated from the perspective of compressed sensing (CS). By minimizing the mutual coherence or the modified mutual coherence of the measurement matrix in CS theory, two criteria for optimizing the pilot pattern for CS-based channel estimation are proposed. Simulation results show that using the pilot pattern designed by either of the two criteria gives a much better performance than using other pilot patterns in terms of the mean-squared error of the channel estimate as well as the bit error rate of the system. Moreover, the optimal pilot pattern designed by minimizing the modified mutual coherence offers a larger performance gain than that obtained by minimizing the mutual coherence.

Background Destruction of the intestinal mucosal barrier and visceral hypersensitivity are main pathogenesis of irritable bowel syndrome (IBS). The study aimed to establish a rat model of visceral hypersensitivity and explore mechanisms involved the changes of the intestinal barrier protein expression and intestinal flora. Methods A rat model of visceral hypersensitivity was established and evaluated using abdominal withdrawal reflex (AWR) scores, colonic paracellular permeability, and gastrointestinal motility. The expression of tight junction proteins, aquaporin proteins (AQPs), phosphorylated ERK, and proteinase‐activated receptor‐2 (PAR‐2) was determined. The intestinal microflora was evaluated by high‐throughput sequencing of the 16S rRNA gene. Key results In model rats, AWR score and fecal water content were significantly increased, gastrointestinal motilities were disorder and characterized by an inhibition of gastric motility and an enhancement of small intestinal and colonic movement. The expressions of colonic occludin, ZO‐1, AQP3, and AQP8 were decreased but claudin‐2 and claudin‐4 were markedly increased. Imbalance of intestinal flora appeared and showed an obvious decrease of Lactobacillus and an increase of Clostridiales_bacterium. Additionally, the total serine protease activity in feces, the expressions of PAR2 and phosphorylated ERK in the colon tissues were increased significantly. Conclusion and inferences The model rats of visceral hypersensitivity possess the decreased expression of occludin, ZO‐1, AQP3, AQP8, and the increased expression of claudin‐2 and claudin‐4, meanwhile develop an imbalance of intestinal flora which probably increase serine protease activity, thereby activating the PAR2/ERK signaling and causing the intestinal barrier disorder.