语音增强设备与GSM网络质量

首先回顾了目前用于测量GSM网络中语音质量的多种方法．并介绍了一种新方法。该方法根据ITU-TG．107中的建议．为实际提供的语音质量以及用户感受提供了解决方案。接着讨论了增强语音质量的传统方法，并描述了基于网络的VED的具体功能。最后介绍并讨论了最近进行的实验以及基于ITU-TG．107条款所做的客观语音质量测量结果。这些实验和测量的对象是在几个部署先进VED的无线网络中发生的大量实际通话．将客观测量结果与实验室收听测试得出的结果进行对比．从而估算出典型网络条件下采用VED对语音质量的改善效果。     

Non white Gaussian multiple access channels with feedback

Although feedback does not increase the capacity of an additive white noise Gaussian channel, it enables prediction of the noise for non-white additive Gaussian noise channels and results in an improvement of capacity, but at most by a factor of 2 (Pinsker, Ebert, Pombra, and Cover). Although the capacity of white noise channels cannot be increased by feedback, multiple access white noise channels have a capacity increase due to the cooperation induced by feedback. Thomas has shown that the total capacity (sum of the rates of all the senders) of an m-user Gaussian white noise multiple access channel with feedback is less than twice the total capacity without feedback. The present authors show that this factor of 2 bound holds even when cooperation and prediction are combined, by proving that feedback increases the total capacity of an m-user multiple access channel with non-white additive Gaussian noise by at most a factor of 2     

Gaussian feedback capacity

The capacity of time-varying additive Gaussian noise channels with feedback is characterized. Toward this end, an asymptotic equipartition theorem for nonstationary Gaussian processes is proved. Then, with the aid of certain matrix inequalities, it is proved that the feedback capacity C_FB in bits per transmission and the nonfeedback capacity C satisfy C⩽C_FB ⩽2C and C⩽C_FB⩽ C+1/2