英語翻譯
u
Abstract-This paper analyzes the benefits of using a decision feedback equalizer (DFE) in the indoor radio environment and examines the results of performance predictions for different channel modelings.It is found that a QPSK/DFE modem with second-order diversity can operate at a data rate which is an order of magnitude higher than a QPSK modem without equalization.A given set of measured profiles of the channel impulse response is interpreted using continuous and discrete channel models.The continuous channel model is represented by the delay power spectrum and the discrete channel model by the envelope delay power spectrum and the arrival rate of the paths.The sensitivity of the performance to the shape of the delay power spectrum,the shape of the envelope delay power spectrum,and the arrival rate of the paths is analyzed.
INTRODUCTION
TH IS paper investigates high speed (wideband) data transmission over the indoor radio channel using adaptive equalization and compares the results to those obtained over an unequalized channel.The existing performance predictions for various communication techniques are either based on a continuous or a discrete channel model.This paper compares performance predictions for both channel models and justifies the differences.To avoid expensive installation and relocation costs and to provide portability to various pieces of equipment,the concept of wireless indoor communication networks suggests itself as a replacement for wired data communication networks.Recently,both infrared and radio frequency communications have been examined for this purpose [l],[2].Research in radio frequency communications is concentrated on channel measurements [3],[4]and transmission problems both for spread spectrum [5],[6] and standard modulation techniques [7].Communication network applications demand very high data rates,but the data rate in indoor channels is bounded due to multipath and fading [7],[SI.To improve the data rate,performance enhancement techniques such as external
diversity,coding,and spread spectrum have been
studied [5]-[7].Another method of improving the data
rate is to use adaptive equalization.The advantage of
adaptive equalization over coding and spread spectrum is
that a modem with adaptive equalization provides high
data rates without any loss in bandwidth efficiency.The
decision feedback equalizer (DFE) has been shown to improve
the performance of digital communication systems
over various fading multipath channels such as troposcatter
[9],HF [lo],and microwave line-of-sight [ 111,[ 121.
This paper shows that the use of an adaptive DFE in the
receiver in indoor channels can result in high-speed transmission
in which the bandwidth of the transmitted signal
is about the same as the coherent bandwidth of the channel.
This data rate is an order of magnitude higher than
similar systems with no equalizer.
The existing performance predictions for narrowband