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以下文字出于jssc05的troy beukema的文章,用于将ffe与dfe进行比较时的描述,这里他提到dfe的一个缺点,但我不理解为什么dfe只能对一小段时间内的isi进行补偿,意思是dfe不能使用太多tap吗?为什么ffe就不受限制呢?
a problem with dfe is that it can only compensate a fixed time span of isi. in contrast, an ffe can compensate isi arising from transmission line loss(i.e., unipolar post cursor impulse response) over a very wide time span since the ffe filter response, unlike the dfe filter response, is convolved with the impulse response of the channel.
therefore, in a very low bandwidth transmission line channel, significant unipolar post cursor isi may fall outside of the time span covered by the dfe and some level of pre-emphasis using ffe becomes required to lower the isi magnitude past the time span covered by the dfe feedback loops. |