The error rate is an important measure of performance in digital communications system, since it gives an indication of the quality of the received information. This paper provides a tutorial overview of methods of error monitoring under four broad classifications, namely, test sequences, parameter measurements, violation detection, and pseudo-error monitoring. A brief discussion of several approaches towards performance monitoring and the definition of error rate parameters is also given. The various methods are described and compared; but, no one monitor is singled out as the "best" since the final choice depends largely on the specific requirements of a given application.

Error rate monitoring for digital communications

An eye-opening monitor (EOM) architecture that can capture a two-dimensional (2-D) map of the eye diagram of a high-speed data signal has been developed. Two single-quadrant phase rotators and one digital-to-analog converter (DAC) are used to generate rectangular masks with variable sizes and aspect ratios. Each mask is overlapped with the received eye diagram and the number of signal transitions inside the mask is recorded as error. The combination of rectangular masks with the same error creates error contours that overall provide a 2-D map of the eye. The authors have implemented a prototype circuit in 0.13-/spl mu/m standard CMOS technology that operates up to 12.5 Gb/s at 1.2-V supply. The EOM maps the input eye to a 2-D error diagram with up to 68-dB mask error dynamic range. The left and right halves of the eyes are monitored separately to capture horizontally asymmetric eyes. The chip consumes 330 mW and operates reliably with supply voltages as low as 1 V at 10 Gb/s. The authors also present a detailed analysis that verifies if the measurements are in good agreement with the expected results.

A 10-Gb/s two-dimensional eye-opening monitor in 0.13-/spl mu/m standard CMOS

A technique that has been verified experimentally to improve the synchronization efficiency of digital communication systems over present systems without sacrificing reliability is presented. This technique is called the spread-spectrum system pilot technique (SSPT). Incorporated into this technique are elements of tone-calibrated techniques (TCT) and spread-spectrum systems. In the SSPT system, the desired pilot tone is modulated by a pseudorandom binary sequence (PRBS) generator of finite duration and then linearly added to the source (customer) data that is actually being sent. At the receiver, the same finite PRBS sequence is used to decode the received signal. The system works because it provides an accurate version of the actual data carrier to be used in demodulation of the received signal. Based on the research presented, it is expected that this type of system will lead to better performance than currently used transparent-tone-in-band and other techniques used in multipath fading environments, which are especially problematic in mobile broadcast and communication applications. >

A spread-spectrum based synchronization technique for digital broadcast systems

An on-line channel monitor, for measuring E b /N O , measures the quality of a communication channel while the channel is in use. The channel monitor employs a soft-decision demodulator so as to compare analog signal levels of an AGC compensated signal in a demodulator with the desired signal level. Deviations, termed pseudo-errors, are counted and the number of counts integrated. The result is employed to drive a meter calibrated in terms of E b /N O .

On-line channel quality monitor for a communication channel

The error rate of a signal is monitored by sampling an input signal with a first clock and also with second and third clocks phase delayed in equal but opposite directions with respect to the first clock, and then logically combining the first through third sampled outputs in order to obtain an error signal.

Signal quality monitoring device

Pseudo-error detectors are devices which show great potential for the measurement of the bit error rate of an on-line digital communications link. They are implemented in the form of a second detector (in addition and in parallel to the traffic data bit detector) which is very perturbation-sensitive. They do not compromise the traffic handling capacity of the system. Four methods of generating the pseudo-error characteristic are described: i) shifted detection threshold; ii) intersymbol interference enhancement; iii) noise addition; iv) sampling phase offset. Practical considerations generally govern the choice of method. Experimental results of pseudo-error detector behavior in the presence of Gaussian noise show that stable characteristics can be achieved to estimate a wide range of bit error rate (BER's) in very modest time intervals. In addition, experimental results in a real complex environment consisting of a 1.544 Mbits/s T1 capacity digital link using QPSK modulation techniques, including both Gaussian and non-Gaussian perturbations, show pseudo-error detection to be reliable for the measurement of BER and for controlling channel switching.

K. Feher

Papers

On-Line Pseudo-Error Monitors for Digital Transmission Systems