Two Types of Error-Performance Degradation 1.2 2007/11/13 03:46:46 US/Central 2007/11/14 05:41:55.054 US/Central Ha Hong Ta tahongha@yahoo.com Tuan Do-Hong do-hong@hcmut.edu.vn Ha Hong Ta tahongha@yahoo.com Tuan Do-Hong do-hong@hcmut.edu.vn Degradation Error-Performance Error-performance degradation can be classifyed in two group. The first one is due to a decrease in received signal power or an increase in noise or inteference power, giving rise to a loss in signal-to-noise ratio EB/N0 size 12{E rSub { size 8{B} } /N rSub { size 8{0} } } {}. The second one is due to signal distortion such as ISI.

Bit error probability

Suppose that we need a communication system with a bit-error probability PB size 12{P rSub { size 8{B} } } {} versus Eb/N0 size 12{E rSub { size 8{b} } /N rSub { size 8{0} } } {} characteristic corresponding to the solid-line curve plotted in figure 1. Suppose that after the system is configured, the performance dose not follow the theoretical curve, but in facts follows the dashed line plot (1). A loss in Eb/N0 size 12{E rSub { size 8{b} } /N rSub { size 8{0} } } {} due to some signal losses or an increased level of noise or interference. This loss in EB/N0 size 12{E rSub { size 8{B} } /N rSub { size 8{0} } } {} is not so terrible when compared with possible effects of degradation caused by a distortion mechanism corresponding to the dashed line plot (2). Instead of suffering a simple loss in signal-to-noise ratio there is a degradation effect brought about by ISI. If there is no solution to this problem, there is no a mount of EB/N0 size 12{E rSub { size 8{B} } /N rSub { size 8{0} } } {} that will improve this problem. More EB/N0 size 12{E rSub { size 8{B} } /N rSub { size 8{0} } } {} can not help the ISI problem because a incresing in EB/N0 size 12{E rSub { size 8{B} } /N rSub { size 8{0} } } {} dose not make change in overlapped pulses.