Algorithms for Communications Systems and their Applications, 2nd Edition

Chapter 19High‐speed communications over twisted‐pair cables

In this chapter, we describe the design of two high‐speed data transmission systems over unshielded twisted‐pair (UTP) cables [1, 2].

19.1 Quaternary partial response class‐IV system

Figure 19.1 shows the block diagram of a transceiver for a quaternary partial response class‐IV (QPR‐IV), or quaternary modified duobinary (see Appendix 7.C), system for data transmission at 125 Mbit/s over UTP cables [1]. In the transmitter, information bits are first scrambled and then input to a 2B1Q differential encoder that yields output symbols belonging to the quaternary alphabet (see Example 16.1.1 on page 793); differential encoding makes the transmission of information insensitive to the polarity of the received signals. Signal shaping into partial response class‐IV (PR‐IV) form is accomplished by the cascade of the following elements: the digital‐to‐analog converter (DAC), the analog transmit filter (ATF), the cable, the analog receive filter (ARF) with automatic gain control (AGC), the analog‐to‐digital converter (ADC), and, in the digital domain, the fixed decorrelation filter (DCF) and the adaptive equalizer. After equalization, the sequence of transmitted quaternary symbols is detected by a Viterbi algorithm. Since the Viterbi algorithm introduces a delay in the detection of the transmitted sequence, as an alternative ...