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Antenna grouping algorithms are hybrids of transmit beamforming and spatial multiplexing. With antenna grouping, we can achieve combining gain through transmit beamforming, and high spectral efficiency through spatial multiplexing. In an independent identically distributed channel, the antenna grouping method has better bit error rate (BER) performance than the beamforming method. However, if the channel is correlated, then the BER performance of antenna grouping degrades. In that case, it is better to use beamforming instead of antenna grouping. In this article, we investigate the mode selection algorithms which select between the antenna grouping and the beamforming modes. By selecting a suitable mode for a given channel, we can achieve more robustness of the system performance. We introduce several mode selection criteria as well as a low complexity criterion which is derived from a low complexity antenna grouping algorithm. Simulation results show that the proposed mode selection algorithm performs better than the antenna grouping and the beamforming modes in various channel conditions.

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In this paper, chirp spread spectrum (CSS) based modulation schemes for capsule endoscopy applications are proposed. The On-Off-Keying (OOK) technique has been conventionally used for the capsule endoscopy applications, but it is known to be susceptible to narrow-band interference such as TV signals. In order to enhance robustness to interferences, we propose two CSS based modulation schemes which are chirp spread spectrum differential binary phase shift keying (CSS-DBPSK) and chirp spread spectrum on-off keying (CSS-OOK). The CSS-DBPSK scheme performs better than the CSS-OOK scheme in terms of BER, but it has high implementation complexity due to the strict synchronization requirement. On the other hand, the CSS-OOK scheme has both low receiver complexity and comparable BER performance. A key contribution of this paper is to use a low complexity chirp spread spectrum technique for interference mitigation in capsule endoscopy. A human body channel model is used in the simulations. Simulation results show that the BER performance of the CSS-OOK modulation is in between the CSS-DBPSK and the OOK schemes. We will show that the CSS-OOK modulation is a practical solution that achieves good compromise between the interference robustness and the receiver complexity.

Multilevel cell flash memory devices are galUlUg popularity because it can increase the memory capacity by storing two or more bits to a single cell. However, when the number of levels of a cell increases, the inter-cell interference which shifts cell (threshold) voltage becomes more critical. Thereare two approaches to alleviate the errors caused by the voltage shift.One is the error correcting codes, and the other is the signal processing methods. We focus on signal processing methods to reduce the cell to cell interference which causes the voltage shift, and propose algorithms which reduce the voltage shift effects by cIassfying and compensating erratic cells. The simulation resultsshow that the proposed algorithms are effective for interference reduction.