A novel design of an embedded cardiorespiratory monitoring system for wheelchair users is proposed. The entire system is composed of a sensor node, a smartphone, and a cloud server. The sensor node contains two parts of an ultra-wideband pulse radar and the data processing module; the former is used to obtain continuous vital-sign signals, and the latter processes the sampled signals to estimate the heart rate and the respiration rate, implemented in an embedded system to achieve a fully integrated radar system. The smartphone functions as the data bridge between the sensor node and the cloud server, which is responsible for sending emergent messages. Experiment results show that the proposed system could work reliably in static and dynamic cases of wheelchairs.

This letter proposed a novel design of the hybrid asymmetrically clipped optical orthogonal frequency division multiplexing (HACO-OFDM) system with cyclic shifted PAM-DMT signals called CSPAM-HACO-OFDM for visible light communication. The transmitted signal generated by the CSPAM-HACO-OFDM system combines the PAM-DMT signals with cyclic shift equivalents by using even subcarriers and the ACO-OFDM signals by using odd subcarriers. Peak-to-average power ratio (PAPR) reduction with remarkably low computational complexity is achieved, and side information is not required. A near-optimal side information detector, which has a similar detection error probability as the perfect-side information detector, is used at the receiver side. Simulation results demonstrate the effectiveness of the CSPAM-HACO-OFDM system in terms of PAPR reduction and average bit error rate.

This paper proposes an energy-efficient asymmetrically clipped direct-current (DC) biased optical orthogonal frequency division multiplexing (EEADO-OFDM) scheme, which replaces the fixed DC bias of DC biased optical OFDM (DCO-OFDM) branch with a adaptive DC bias for optical wireless communications. In the EEADO-OFDM, an adaptive DC bias is dynamically designed according to amplitude of DCO-OFDM signal samples to enhance the power efficiency. After superimposing the obtained DC bias on the original DCO-OFDM signal, the resultant DCO-OFDM signal is non-negative and further ensure that a non-negative EEADO-OFDM signal is produced by directly combining DCO-OFDM signal with the clipped asymmetrically clipped optical OFDM (ACO-OFDM) signal. In particular, the interference caused by the obtained DC bias is proved to fall on even subcarriers only, which implies that the interference can be modulated on the partial odd subcarriers of ACO-OFDM branch. Afterward, we could use conventional ACO-OFDM receiver to demodulate the adopted odd subcarriers for the detection of interference. Simulation results show that, under the equal optical power constraints, the proposed EEADO-OFDM achieves no error floors of bit error rate compared with the ADO-OFDM, thus indicating that the clipping noise is always negligible in EEADO-OFDM.

Compared to the direct current (DC) biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) schemes, the asymmetrically clipped DC biased optical OFDM (ADO-OFDM) has demonstrated a better balance between optical power efficiency and spectrum efficiency. However, both the traditional ADO-OFDM and ADO-OFDM with iteration receiver suffer from an error floor issue when a lower DC bias is allocated to the DCO-OFDM branch. In this paper, we propose an enhanced receiving technique for ADO-OFDM that introduces an adjacent symbol detection (ASD) scheme in the DCO-OFDM branch of ADO-OFDM, named as ASD-based ADO-OFDM (ASD-ADO-OFDM). Simulation results indicate that the proposed ASD-ADO-OFDM provides a lower bit error rate performance at lower DC bias and fewer computational complexity compared with traditional ADO-OFDM with iteration receiver.