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就802.20协议物理层目前采用的OFDM/OFDMA技术和Flash-OFDM技术进行比较。OFDMA是一种多载波调制技术,它的原理是无线通信信道划分为多个窄带子信道同时传送,在每个子信道上使用一个子载波进行调制。Flash-OFDM技术采用FDD双工方式,上下行链路是数百个子信道组成的宽带载波。传输数据时给每个用户分配子信道。每个子信道采用了自适应调制和先进的编码技术,其频谱利用宰比CDMA2000系统高3倍.Flash-OFDM在时间上以跳频方式使用OFDM的子载波,以实现信号扩频。它还有频率分集能力,减小了同一小区内的用户间干扰,同时具有OFDM和跳频扩频技术的优点,因而相邻节点可以使用相同频率的子载波。Flash-OFDM为解决小区间干扰,采用了功率控制,用户只发射能有效通信的功率。
The OFDM / OFDMA and Flash-OFDM technologies currently used in the 802.20 protocol physical layer are compared. OFDMA is a multi-carrier modulation technique. Its principle is that the wireless communication channel is divided into multiple narrow-band sub-channels for simultaneous transmission, and one sub-carrier is used for modulation on each sub-channel. Flash-OFDM technology uses FDD duplex mode, the downlink is composed of hundreds of sub-channel broadband carrier. Each user is assigned a sub-channel when transferring data. Each subchannel adopts adaptive modulation and advanced coding technology, and its spectrum is 3 times higher than that of Zambi CDMA2000 system.Flash-OFDM uses OFDM subcarriers in frequency hopping manner in time to realize signal spectrum spreading. It also has frequency diversity capabilities that reduce inter-user interference in the same cell and have the advantage of both OFDM and frequency-hopping spread spectrum techniques so that neighboring nodes can use subcarriers of the same frequency. Flash-OFDM to solve the inter-cell interference, the use of power control, the user can transmit only the power to communicate effectively.