| As the popularization of the smartphone,tablet personal computer and high-difinition television,an explosive growth of the transmission bandwidth and the high-quality user experience are required.However,these requirements are restricted by two main factors of the complicated wireless environment and the limited wireless spectrum sources.And using optoelectronic devices of higher bandwidth to improve the transmission capacity is uneconomical.Therefore,the combinations of advanced modulation formats and digital signal processing?DSP?algorithms are paid more attention.Among them,aspects of Carrierless amplitude phase modulation?CAP?and Orthogonal frequency division multiplexing?OFDM?technology with high spectral efficiency?SE?have been investigated broadly.In this paper,multiband CAP signal and OFDM signal with effective DSP algorithms are studied for visible light communication?VLC?system.And the transmission performances are analyzed.The innovations of the work in the paper are as follows:1.A multiband carrierless amplitude and phase modulation format based on low-density parity-check?LDPC?and adaptive modulation is proposed and experimentally demonstrated in visible laser light communication?VLLC?system.In order to achieve high-speed indoor VLLC system,LDPC code and adaptive modulation are investigated,and the relationship of spectral efficiency?SE?and size of subcarrier is analyzed.In the experiment,a blue laser diode with a total bandwidth of 862.5MHz is used.And the transmission distance can reach 5m by a reflector.Experiment results show that the optimal trade-off between SE and BER performance is employing 64/64/64/16 quadrature amplitude modulation?QAM?format based on LDPC and adaptive modulation for 4-CAP system,with SE?net bit rate?of 3.56b/s/Hz?3.08 Gb/s??In the case without LDPC code and adaptive modulation,only16-QAM can be achieved in 1-CAP system with a SE?net bit rate?of 2.98 b/s/Hz?2.57 Gb/s?.2.Based on minimum mean square error?MMSE?channel estimation algorithm and discrete fourier transmission?DFT?,a novel pilot pattern channel estimation algorithm is proposed and simulated to verify its BER performances in 2×2multiple-input and multiple-output?MIMO?OFDM VLC system.Compared with traditional channel estimation algorithm based on the space-time block code?STBC?,it not only reduces the computational complexity coming from STBC,but also remarkably improve BER performance.Under the condition of employing 32-QAM and hard decision forward error correction?HD-FEC?BER limit of 3.8×10-3,signal to noise ratio?SNR?of system obtains a gain of 3 dB.3.A combination of subcarrier mapping and bit-Interleaved coded modulation and Polar Code?BICM-Polar?is proposed and simulated in the MIMO-OFDM VLC system.In simulation,system BER performances of BICM-Polar,Polar code,LDPC code and none code have been compared.Moreover,the BER performances in case of increasing number of receiving antennas are investigated.Simulation results show that,as a code approaching the Shannon capacity and due to the character of channel polarization,Polar code with effective decoding algorithm can achieve better error correction performance than LDPC code.In 2×2 MIMO-OFDM VLC system with128-QAM,the minimum SNR requirement of achieving error-free transmission is 12dB.Furthermore,matrix gains of channel equalization coming from reception diversity further improve the BER performances.Compared with 2×2 MIMO-OFDM VLC system,2×4 MIMO-OFDM VLC system obtains a SNR gain of 2dB. |
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