ABSTRACT
In this paper, we propose and demonstrate a 0.5-bit/s/Hz fine-grained adaptive orthogonal frequency division multiplexing (OFDM) modulation scheme for bandlimited underwater visible light communication (UVLC) systems. Particularly, integer spectral efficiency is obtained by conventional OFDM with quadrature amplitude modulation (QAM) constellations, while fractional spectral efficiency is obtained by two newly proposed dual-frame OFDM designs. More specifically, OFDM with dual-frame binary phase-shift keying (DF-BPSK) is designed to achieve a spectral efficiency of 0.5 bit/s/Hz, while OFDM with dual-frame dual-mode index modulation (DF-DMIM) is designed to realize the spectral efficiencies of 0.5+n bits/s/Hz with n being a positive integer (i.e., n = 1, 2, ). The feasibility and superiority of the proposed 0.5-bit/s/Hz fine-grained adaptive OFDM modulation scheme in bandlimited UVLC systems are successfully verified by simulations and proof-of-concept experiments. Experimental results demonstrate that a significant achievable rate gain of 18.6 Mbps can be achieved by the proposed 0.5-bit/s/Hz fine-grained adaptive OFDM modulation in comparison to the traditional 1-bit/s/Hz granularity adaptive OFDM scheme, which corresponds to a rate improvement of 22.1%.
ABSTRACT
In this paper, we for the first time propose a novel partitioning-based constellation design approach for discrete Fourier transform-spread-orthogonal frequency division multiplexing modulation with dual-mode index modulation (DFT-S-OFDM-DM) in visible light communication (VLC) systems. Specifically, two partitioning-based constellation designs, i.e., block-based constellation partitioning and interleaving-based constellation partitioning, are proposed to generate two distinguishable constellation sets for DFT-S-OFDM-DM in VLC, by considering four 8-ary constellations including 8-ary quadrature amplitude modulation (8-QAM), 8-ary phase-shift keying (8-PSK), circular (4,4)-QAM, and circular (7,1)-QAM. The superiority of DFT-S-OFDM-DM using circular (7,1)-QAM constellation with interleaving-based constellation partitioning over other benchmark schemes has been successfully verified by both simulation and experimental results. It is shown by the experimental results that a significant distance extension of 44.6% is obtained by DFT-S-OFDM-DM using circular (7,1)-QAM constellation with interleaving-based constellation partitioning in comparison to DFT-S-OFDM with index modulation achieving the same spectral efficiency of 2.5 bits/s/Hz. It is also demonstrated that the proposed constellation design schemes are also generally applicable to the constellation with an arbitrary shape and an arbitrary size.
ABSTRACT
In this paper, we for the first time propose and investigate a novel discrete Fourier transform-spread-orthogonal frequency division multiplexing with quadrature index modulation (DFT-S-OFDM-QIM) scheme for practical visible light communication (VLC) systems. By performing subcarrier index modulation on both the in-phase and quadrature components of each subcarrier, OFDM-QIM achieves a higher spectral efficiency than conventional OFDM with index modulation (OFDM-IM). Moreover, the peak-to-average power ratio (PAPR) of OFDM-QIM can be substantially reduced by applying DFT spreading, and hence DFT-S-OFDM-QIM exhibits high tolerance against light-emitting diode (LED) nonlinearity. The superiority of the proposed DFT-S-OFDM-QIM scheme over other benchmark schemes has been successfully verified by both simulation and experimental results.
ABSTRACT
UNLABELLED: Aims: To evaluate the feasibility and safety of Laparoscopic transcystic duct common bile duct exploration(LTCBDE) in elderly patients. METHODOLOGY: Between Jan 2010 and Dec 2011, 308 elderly patients (age 65 years) with CBD stones underwent surgery. 165 were initially treated with LTCBDE, 143 patients underwent open choledocholithotomy surgery. Two groups were compared with operative duration, incidence of postoperative complication, and the average days of in hospital. RESULTS: The LTCBDE was performed successfully in 157 of 165 patients 95.15%. 3 cases were converted to laparotomy and the other 5 were changed to laparoscopic choledocholithotomy and T-tube drainage. All he elderly patients receiving LTCBDE were dealt with primary closure of cystic duct. There were no severe complications such as bleeding and residual stones.The average duration of surgery was 102 ± 35 min and the mean blood loss 43 ± 20 ml. The postoperative hospital day was 3 ± 0.5 days. 143 patients underwent open choledocholithotomy surgery. There were 2 (1.4%) cases abdominal wall incision infection, 5 (3.5%) cases pulmonary infection, 2 (1.4%) bile leakage, and 1 (0.7%) local bile leakage for part T-tube pulled out postoperation. The operation duration was about 120 ± 30 minutes, and postoperative hospital day 7 ± 1.5 days CONCLUSIONS: Elective LTCBDE to treat CBD stones in elderly patients is safe and effective.