Research On Several Key Techniques Of Optical MB-OFDM Ultra-wideband Communications

Ultra wideband?UWB?technology has been attracting great interest in broadband wireless communications and wireless local area networks.Due to the constrained power spectral density of a multiband orthogonal frequency-division multiplexing ultra-wideband?MB-OFDM UWB?signal regulated by the Federal Communications Commission?FCC?,the typical transmission distance for MB-OFDM UWB is a few meters to ten meters.To extend the area of coverage,a technique,called radio over fiber?RoF?,is thus proposed to distribute MB-OFDM UWB signals over fiber.In this way,MB-OFDM UWB-over-fiber system combines the high speed and wide spectrum features of UWB with the low loss and long transmission distance of optical access technology.In this paper,the generation,pre-coding modulation scheme and transmission performance of MB-OFDM UWB millimeter wave signals over fiber system are studied.The innovations of the work in the paper are as follows:1.The generation of optical MB-OFDM UWB signal is proposed.The simulation and experiment results show that the generated MB-OFDM UWB signal have comply with the FCC spectral requirements.The MB-OFDM UWB over fiber system with direct detection is experimentally demonstrated.Different subcarrier modulation formats?QPSK and 16QAM?is investigated in the MB-OFDM UWB over fiber system.2.A pre-coding scheme based on low-density parity-check?LDPC?in the MB-OFDM UWBoF system is investigated.To avoid inter-symbol interference?ISI?or inter-channel interference?ICI?,a symbol synchronization and pilot-aided channel estimation scheme is implemented on the LDPC-coded MB-OFDM UWBoF system.The experimental results show,after 100km single-mode fiber?SMF?transmission,at the bit error rate of1?10^-3,the receiver sensitivities have been improved about 4.5,3.8,2.9dB for 62.5%,75%and 87.5%rate codes,respectively.The experiment results show that short block length LDPC is effective for MB-OFDM UWBoF system.3.A full-duplex MB-OFDM UWBoF system based on fiber Bragg grating?FBG?filter is proposed.The 60GHz optical millimeter wave is generated based on optical remote heterodyning.The 60GHz MB-OFDM UWB signal is then implemented for down-link wireless services.And an optical carrier without modulation data can be extracted by using an FBG for up-link MB-OFDM UWB signal transmission.By employing the scheme without laser in the base station for up-link connection,simplicity and cost efficiency of the base station is achieved.By measured the BER performance for both the downstream and upstream data,at a BER of1?10^-4,after transmission over 50km SSMF,the power penalties are 0.5dB for 4QAM-downlink and0.7dB for 16QAM-downlink,respectively.Meanwhile,the power penalties are 0.7dB for 4QAM-uplink and 1.0-dB for 16QAM-uplink,respectively.