Getting to Know the FFT
What is the FFT? FFT = Fast Fourier Transform. The FFT is a faster version of the Discrete
Fourier Transform (DFT). The FFT utilizes some clever algorithms to do the same thing as the
DTF, but in much less time.
1. 下列說法正確的是 （ ）
A. Java語言不區(qū)分大小寫
B. Java程序以類為基本單位
C. JVM為Java虛擬機JVM的英文縮寫
D. 運行Java程序需要先安裝JDK
2. 下列說法中錯誤的是 ( )
A. Java語言是編譯執(zhí)行的
B. Java中使用了多進程技術(shù)
C. Java的單行注視以//開頭
D. Java語言具有很高的安全性
3. 下面不屬于Java語言特點的一項是( )
A. 安全性
B. 分布式
C. 移植性
D. 編譯執(zhí)行
4. 下列語句中，正確的項是 ( )
A . int $e,a,b=10
B. char c,d=’a’
C. float e=0.0d
D. double c=0.0f
In this paper we revisit hybrid analog-digital precoding systems with emphasis on their modelling
and radio-frequency (RF) losses, to realistically evaluate their benefits in 5G system implementations.
For this, we decompose the analog beamforming networks (ABFN) as a bank of commonly used RF
components and formulate realistic model constraints based on their S-parameters. Specifically, we
concentrate on fully-connected ABFN (FC-ABFN) and Butler networks for implementing the discrete
Fourier transform (DFT) in the RF domain. The results presented in this paper reveal that the performance
and energy efficiency of hybrid precoding systems are severely affected, once practical factors are
considered in the overall design. In this context, we also show that Butler RF networks are capable of
providing better performances than FC-ABFN for systems with a large number of RF chains.
Before delving into the details of orthogonal frequency division multiplexing (OFDM), relevant
background material must be presented first. The purpose of this chapter is to provide the necessary
building blocks for the development of OFDM principles. Included in this chapter are reviews of stochastic
and random process, discrete-time signals and systems, and the Discrete Fourier Transform (DFT). Tooled
with the necessary mathematical foundation, we proceed with an overview of digital communication
systems and OFDM communication systems. We conclude the chapter with summaries of the OFDM
wireless LAN standards currently in existence and a high-level comparison of single carrier systems versus
OFDM.
