Research On Polar Coding And Multi-layer OFDM Modulation In VLC Systems

Due to the scarcity of spectrum resources,it is generally believed that the traditional radio frequency(RF)communication will meet the spectrum crisis soon.Moreover,any single means of communication is difficult to establish a full-time,full coverage high-speed communication network.Therefore,the future network architecture must support the coexistence and cooperation of various wireless communication technologies.On the other hand,thanks to the rapid development of semiconductor technology,the advantages of light-emitting diode(LED)are increasingly prominent.At present,LED has been widely deployed in residential,office buildings,shopping malls and other indoor environments.Therefore,the visible light communication(VLC)based on LED will undoubtedly become an important supplement to the indoor access part of RF communication.Based on quadrature amplitude modulation(QAM)and orthogonal frequency division multiplexing(OFDM),the coverage and energy efficiency of VLC are studied in this paper as follow:1.A bit-interleaved polar-coded modulation(BIPCM)scheme combined with MIMO is proposed and experimentally demonstrated in an OFDM based VLC system.The sensitivity of the receiver is improved by BIPCM,the spectral efficiency of the system is improved by MIMO,and the interference between the light sources is eliminated by two-dimensional single carrier frequency domain equalization(SC-FDE).The experimental results show that the proposed scheme can achieve error free transmission of 2.18Gbps(1.09Gbps×2).Compared with 8-QAM without coding,the proposed scheme can obtain a signal-to-noise ratio gain of about 2.5dB at a bit error rate of 1×10^-4.2.An adaptive modulation scheme based layered asymmetrically clipped OFDM(LACO-OFDM)is proposed and experimentally demonstrated in the VLC system.Aided by the measured signal-to-noise ratio as channel state information,adaptive modulation can balance the bit-error ratio of subcarriers,and the inter-layer interference of LACO-OFDM is accordingly mitigated.In addition,we reuse the loading information of the first layer to suspend the feedback on subsequent layers.Therefore,the proposed scheme can effectively reduce the feedback delay of LACO-OFDM.Compared to the 16-QAM with same spectral efficiency,a 0.68dB signal-to-noise ratio improvement can be achieved by the proposed adaptive modulation scheme at BER of 3.8×10^-3.