As it has already been revealed, the OFDM systems are very sensitive to the CFO. CFO is one of the most important drawbacks of the OFDM wireless systems. CFO destroys the orthogonality relationship between the subcarrier and creates ICI in OFDM systems. ICI can create frequency mismatched between the transmitter and receiver; this frequency mismatch can lead to the severe performance degradation issue for OFDM wireless systems. However for having a reliable receiver the effect of the CFO must be estimated and compensated in receiver side. This paper reviews the reasons of the creating CFO and analyses its effects on the performance of the OFDM systems. The results clearly illustrate the effects of CFO.
Tunable semiconductor laser has various applications including Wavelength Division Multiplexing (WDM), Frequency Division Multiplexing (FDM), optical switching in Local Area Networks (LAN) and Chemical Sensing, or Spectroscopy. There are different approaches for tunable semiconductor lasers. Large wavelength tuning range is required for communication applications, such as WDM. Whereas a frequency modulation (FM) requires small but fast frequency shifts. Two-Segment laser is one of the methods to realize continuous optical tuning. The device consists of two coupled cavities having a series of well-defined modes. The modes are equally spaced within a cavity but the mode spacing between the two cavities is slightly different. Characterization results of such lasers are very important. In this paper we will present the characterization results of two segment InGaAs/InP distributed feed back (DFB) tunable lasers.
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