Channel Aggregation Technique Based On Code Division Multiplexing For Mobile Fronthaul

In the last few decades,thanks to the rapid development of the communication technology,the capability of network accessing substantially enhanced,leading to the emergence of novel businesses and applications,including machine-to-machine communication,cloud computing,virtual reality,and self-driving.All of these services and applications stimulate the demand of end-user network access.Fiber optical communication has the inherent advantages of large transmission capacity and low transmission loss,making it indispensable infrastructure in modern telecommunication system.The mobile fronthaul connecting the baseband unit(BBU)and radio remote units(RRUs)with standard single mode fiber(SSMF)plays a vital role in the radio access network even for the upcoming 5G.The mobile fronthaul based on the analog signal transmission has the features of high frequency efficiency and low cost,thus it is attractive for building up an effective fronthaul system.Meanwhile,the analog fronthaul suffers high nonlinearity induced transmission impairment.In this thesis,both numerical simulation and experimental verification have been implemented in order to solve the problem of high peak-to-average power ratio(PAPR)occurred during the channel aggregation operation.The main research outcomes can be summarized as follows,(1)We investigate the channel aggregation technique for the analog mobile fronthaul,and carry out numerical performance comparison between two aggregation schemes including the frequency division multiplexing(FDM)and the code division multiplexing(CDM).By taking 48 Long Term Evolution(LTE)signals into account,we systematically investigate the key parameters of channel aggregation technique,including the spectrum efficiency,the calculation complexity of algorithm,and corresponding fronthaul transmission performance.(2)We find that the PAPR characteristic when large amount channels are aggregated.Essentially,LTE signal is a specific orthogonal frequency division multiplexing(OFDM),multicarrier modulation.When they are aggregated,the PAPR of aggregated signal becomes even severe.Since many optoelectronic devices have a linear operation range during the electronic-to-photonic conversion,the clipping noise happens,leading to very poor performance of fronthaul transmission.(3)We propose an effective scheme to mitigate the PAPR arising in the CDM aggregation system,by using the reserved code sequence to generate peak-cancellation signal.After optimizing the simulation parameters,we complete the experiment to verify the improvement for the mobile fronthaul system.The PAPR of aggregation signal,which is formed of 48×20 MHz LTE signals,is reduced.Owing to the reduction of PAPR,the larger optical modulation index(OMI)can be supported,leading to higher optical signal-to-noise ratio(OSNR).In experiment,receiver sensitivity is improved by 4dB under the condition of 10 km fiber transmission.