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本文提出一种基于回波抵消技术的ISDN用户环传输系统,这个系统完全保证CCITT建议的I S D N基本接口,即在金属电缆上B+B+D。文中讨论了电缆衰减、串音、脉冲噪声等系统设计考虑,以及在逐次呼叫基础上进行馈电的系统要求,并提出了一个传输系统。所提出的系统利用了一种称为“变形双相码”的新线路码。利用这种码形及固定线路衰耗均衡和相干检波方法,将达到电路的简化。回波抵消器结合专门的适应算法之后,大大减少了收敛时间。实验结果表明了剩余回波和比特误码率可达到满意的性能。因为系统对模拟部分只需要简单的非自适应电路,所以系统适合用大规模集成电路来实现。
In this paper, an ISDN user-ring transmission system based on echo cancellation technology is proposed. This system fully guarantees the CCST recommended ISDN basic interface, that is, B + B + D on metal cables. In this paper, system design considerations such as cable attenuation, crosstalk and impulse noise are discussed, as well as system requirements for feeding on a call-by-call basis, and a transmission system is proposed. The proposed system makes use of a new line code called “distorted biphase code ”. Using this pattern and fixed line attenuation equalization and coherent detection method, will achieve the circuit simplification. Echo Cancellation combined with a special adaptive algorithm greatly reduces the convergence time. Experimental results show that the remaining echo and bit error rate can achieve satisfactory performance. Because the system only needs a simple non-adaptive circuit for the analog part, the system is suitable for large-scale integrated circuits.