滚降系数对自适应QAM的抗时延扩展性能和频谱效率的影响

在多径衰落信道中研究了自适应正交幅度调制(AQAM)的抗时延扩展性能和频谱效率,系统的接收-发送合成滤波器具有升余弦频谱.在平均误比特率受限的情况下,分析了平均bits-per-symbol和平均误比特率与归一化rms时延扩展(rms时延扩展与符号周期之比)的关系.计算结果显示:当滚降系数增大时,AQAM所能应对的最大归一化rms时延扩展也随之增大,由此证明AQAM的抗时延扩展性能随滚降系数的增大而改善.平均频谱效率可视为3个参数的函数,即滚降系数、归一化rms时延扩展及发送信号能量与噪声之比.分析结果表明,当滚降系数增大时,平均频谱效率的变化是不确定的,具体情况取决于另外2个参数.

Effects of rolloff factor on resistance to time delay spread and spectral efficiency of adaptive QAM

The resistance to time delay spread and spectral efficiency of adaptive quadrature amplitude modulation(AQAM) are investigated over multipath fading channels.The joint frequency response of the transmitting and receiving filters has the raised-cosine spectrum.The effects of normalized rms delay spread(ratio of rms delay spread to symbol period) on the average bits-per-symbol and average BER are analyzed under the average BER constraint.Data results show that AQAM can tolerate greater normalized rms delay spread when the rolloff factor increases,which affirms the notion that delay spread immunity improves with the rolloff factor rising.The average spectral efficiency is studied as a function of the rolloff factor,normalized rms delay spread,and signal-to-noise ratio.It is observed that when the rolloff factor increases,reaction of the average spectral efficiency is indefinite and depends on the other two parameters.