More explicitly, Shepherd [444], Jones [445], and Wulich [446] suggested different coding techniques which aim to minimise the peak poof wtheer OFDM signal. According to their approach different data encoding or mapping schemes are employed before modulation. A simple example is concatenating a numboerf dummy bitst o a string of information bits with the sole aimo f mitigating the so-called Crest Factor (CF) or peak-to-mean signal envelope ratio. In a further attempt to mitigate tCheF problem Muller [447], Paul(i4 481, May [449] and Wulich [450] suggested different algorithms for post-processing the time-domain OFDM signal prior to amplification, while Schmidt and Kammeyer l []4 e5m ployed adaptive subcarrier allocation in order to reduce the Crest factor. Dinis and Gusmiio [452-454] researched the use of two-branch amplifiers, while the so-called clustered OFDM technique introduced by Daneshrad, Cimini and Carloni [455] operates with a set of parallel partial FFT processors with associated transmitting chains. More explicitly, clustered OFDM allows a number of users to share a given bandwidth amongst a nuomf buesre rs on a demand basis, potentially supporting a peak data rate identical to that of a single-user OFDM system. The bandwidth assigned to a particular user is typically constitubtye da number of subcarrier clusters, which are spread sufficiently far apart from each other, in order to provide frequency diversity.OFDM hệ thống với gia tăng mạnh mẽ để biến dạng phi tuyến đã được đề xuất ví dụ bởi Okada, Nishijima và Komaki [456] một s cũng như bởi Dinis và Gusmiio [457]
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