Performance criteria

In Chap. 11, the signaling or message-stream format, including the different types of bit syncs and word syncs, was discussed. In this chapter, the methods for analyzing the word-error rate of a message are discussed. The word-error rate is a major parameter for measuring the quality of signaling performance and can also be used for comparing the performance of different systems. The word-error rate is, to a large degree, dependent upon the bit-error rate; and the bit-error rate is directly affected by the signaling rate, which is determined by the channel capacity, as shown in Eq. (11.1). In a typical mobile-radio case, the curve for predicting the received power in dBm versus distance can easily be plotted, as was illustrated in Fig. 3.13 of Chap. 3. Given a transmission path of 8 mi, the average receiving power at this distance, as shown in Fig. 3.13, is -96.5 dBm. If a noise level of -121 dBm is assumed, based on a bandwidth of 30 kHz and a front-end noise of 8 dB, then, by applying Eq. (11.1), ^[*] the following is obtained:

(13.1)

where C is defined as the theoretical maximum rate at which the channel can be expected to supply reliable information to the terminal sub- scriber at the receiving destination. In actual practice, this rate cannot be achieved. In order to obtain an increase in reliability, it is necessary to lower the bit rate. In addition, for bit rates of...