Figure 2.14(b) it can be observed that the eye diagram becomes "closed" because of jitter or variations in time of the binary pattern. This "closure" is observed in the lateral sides of the eye diagram and results in nonoptimum sampling times. Furthermore, the slower the rising and falling edges of the pulses, the more closed the eye will be, which can result in more errors at the receiver. Signal-to-Noise Ratio The energy per bit-to-noise power spectral density ratio is a normalized measure of the SNR. The energy per bit of a binary digital data transmitted at a bitrate, R, is equal to the signal power, Sp, times the bit transmission, Tb. No refers to the power spectral density of the noise measured at the detector input. Then, Transmission Performance (2.18) No No The noise can be calculated as No = kT, where k is the Boltzmann's constant (1.380650 X 10-23 J/K) and T is the receiving-system noise temperature. Equation 2.18 can be related to SNR by considering the noise, N, in a signal with bandwidth, B, being equal to N = NoB. Thus, (2.19) Eb/No is used as a measurement to compare the bit error rate performance of different digital modulation schemes without taking bandwidth into account. Eb/No is useful in the design of a transmission link because, knowing this parameter, the corresponding BER can be approximated and the parameters in the formula can be obtained. It is important to mention that the higher the bitrate, the higher the signal power must be to obtain the same Eb/No. Error Ratio In general terms, error ratio is the number of symbols, codes, or characters incorrectly received in a transmission system compared to the total number of symbols, codes, or char- acters received. If a binary system is used, the bit error ratio denotes the number of bits received in error divided by the total number of bits sent in a specified time interval. The BER is affected by the rate of data transmission and the sensitivity of the system to the signal (by "sensitivity" is understood the minimum power accepted by the r