Designing And Performance Research On The Multiuser Reverse Link Of Infrared Communications

In the age of information, people have a higher requirement of data communication rate and green com-munication, traditional radio wireless communication system employed widely at present faces with the signif-icant shortage of the available spectrum resources and the effect of electromagnetic radiation on the physical body, thus more and more people have diverted their attentions to seeking an environmental friendless com-munication mode which has a wider spectrum. Optical wireless communications(OWC) based on infrared light(or visible light) media have been one of the focus research area in recent year for plenty of advantages, such as rich spectrum resources, no requirement for license, better security performance and environmental friendless,etc. With respect to OWC, this thesis mainly focus on the research of key technologies of indoor Infrared communications(IRC) and the design of transceiver in IRC system.Firstly, the thesis makes an systematic overview of IRC system. The thesis gives some introductions related to infrared light emitting diodes(LED) characteristics and light source radiation model as well as eye safety. Then the features of PIN photodiode and APD photodiode is minutely compared as well as their advantages and disadvantages. Furthermore, the thesis discusses the infrared channel model and noise model, and shows the channel impulse response and amplitude frequency response measured actually in the designed circuits.Additionally, some point-to-point(p2p) communication techniques employed in infrared CDMA system are mainly studied. After presenting the common communication process of the p2p infrared CDMA sys-tem and a kind of feasible physical frame structure, the thesis introduces two well used channel estimation algorithms known as MMSE estimation and LS estimation and several kinds of time domain equalization technology which used to suppress the inter symbol interference(ISI). The performance simulation can be seen, in terms of channel estimation, the performance of LS estimation is inferior to MMSE estimation due to former is sensitive to noise, in another aspect on equalization, fractional spaced equalizer(FSE) obtains an superior performance than the symbol interval equalization such as LMMSE and ZF, what’s more, FSE is not insensitive to timing deviation compared with the two latter. At last, the influences of PAM modulation order, code channel number, spread frequency ratio and channel coding on system performance are investigated in detail.Furthermore, the thesis discusses some multi-access communication techniques used in infrared CDMA system, we present the concrete reasons causing the multiple access interference(MAI) by theoretical deriva-tion, meanwhile a pilot interference cancellation channel estimation algorithm is proposed for estimating the channels while interference between pilots exists in multi-access scenario, the results of the algorithm sim-ulation confirm that the channel estimation performance under multi-access can approaches the estimation accuracy under single-access. Lastly, the thesis mainly discusses several classic multi-user detection(MUD) technologies, and particularly carries out a series of numerical simulations on interference cancellation de-tector, simulation results show that interference cancellation detector can substantially mitigate the MAI, on top of that, Soft parallel interference cancellation(PIC) detector based on iterative structure obtains a more excellent performance than corresponding hard PIC detector.Finally, the thesis describes the hardware design method of infrared wireless communication system. On the basis of presenting the overview of indoor IRC hardware system, specific design ideas of analog transceiver are given, then we utilize the actual circuits to measure some important performance parameters, for example, we know the 3-dB bandwidth of infrared channel can be approximately expanded to 60 MHz from practical measurement. Additionally, in order to suppress ISI in IRC system, the thesis performs a series of digital hardware simulations on post-equalizer and confirms corresponding digital hardware design scheme, which provides a directing function for the follow-up realization of digital post-equalizer.