A Study of Adaptive Modulation with OFDM In High Mobility Environment
Date Issued
2007
Date
2007
Author(s)
Chih-Hua, Hsu
DOI
zh-TW
Abstract
The fundamental technology of adaptive modulation is to advance data throughput。The principle is receiver adjusts modulation level for next transmission depend on channel condition，i.e. when the channel condition is appropriate，it use high modulation level； when the channel is unfavorable，it use low modulation level，For example QPSK or BPSK。
OFDM (Orthogonal Frequency Division Multiplexing) can improve data throughput in the limited bandwidth。It transmits orthogonal sub-carriers in the limited bandwidth。OFDM can resist multi-path，ISI etc.. If we combine adaptive modulation and OFDM technology，we can get higher data throughput than single technology.
Traditional adaptive modulation with OFDM have single transmission direction only and many assumptive conditions。For example，there is a perfect channel between transmitter and receiver。Another is modulation level in the modulated frame mustn't affect by channel，i.e. the receiver can demodulate the level of modulation accurately. However these assumptive conditions were not true in the real world。
We propose a new algorithm for adaptive modulation with OFDM。We calculate pilot's BER to adjust modulation level for next transmission，and decide which modulation level we use to demodulate it。
Other topic is to separate many blocks in a OFDM symbol。Each block has different modulation level then we can get maximum data throughput。
Subjects
可適性調變
調變位階
正交頻率多工
抵抗多重路徑
產出量
adaptive modulation
modulation level
OFDM
resist multi-path
throughput
Type
thesis