Low power peak detector

Details Low power peak detector Low power peak detector

2000-05-05

2003-03-18

Callahan, Timothy P. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific signal discriminating without subsequent control

By amplitude

C327S073000, C327S095000

Reexamination Certificate

active

06535027

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally telecommunications transmissions systems and more particularly to a peak detector for T
1
span equipment.
2. Description of Related Art
Many telecommunication transmission systems include a central office (CO) that may transmit useful data, or “payload,” signals over transmission lines to equipment on customer premises. Typically, digital payload signals are sent over the transmission lines through an office repeater a series of regenerative repeaters, to a network interface unit (NIU), and in turn to customer premises equipment (CPE). Similarly, payload is carried from the CPE to the NIU and in turn to the CO.
The NIU typically sits at the point of demarcation between the telephone operating company's side of the telephone line and the customer's side of the telephone line. In general, the NIU is electrically transparent to payload signals. However, the NIU can be used for special maintenance functions such as loopback and performance monitoring.
The Bell telephone system in the United States, for instance, has widely utilized a digital time-domain multiplexing pulse code modulation system known as the T
1
transmission system. Each T
1
transmission system carries 24 8-KB/second voice or data channels on two pairs of exchange grade cables. One pair of cables provides communication in each direction. T
1
transmission systems are used in multiples “N”, thus providing N×24 channels on N×2 cable pairs.
FIG. 1
illustrates in general the arrangement of a telecommunications transmission system
100
including an NIU. As shown in
FIG. 1
, system
100
includes a central office
120
, an NIU
140
and a CPE
160
. A first pair of tip and ring cables
180
,
220
carries signals from the central office to the customer premises and is referred to as the receive or “RCV” line. A second pair of tip and ring cables
240
,
260
carries signals from the customer premises to the central office and is referred to as the transmit or “XMT” line.
Thus, in regular operation, an NIU may receive signals from the network via a “RCV IN” line
280
and may then pass those signals via a “RCV OUT” line to the CPE
300
. Similarly, the NIU may receive signals from the CPE via an “XMT IN” line
320
and may then pass those signals via an “XMT OUT”
340
line to the central office. Of course, these designations are made only for convenience and may change depending on the perspective of an observer.
In the T
1
system, the data to be transmitted over the lines, such as speech, is sampled at a rate of 8,000 hertz, and the amplitude of each sample is measured. The amplitude of each sample is compared to a scale of discrete values and assigned a numeric value. Each discrete value is then encoded into binary form. Representative binary pulses appear on the transmission lines. The binary form of each sample pulse consists of a combination of seven pulses, or bits. An eighth bit is periodically added to allow for signaling.
A coding system is typically used to convert the analog signal to a digital signal. The system guarantees some desired properties of the signal, regardless of the pattern to be transmitted. The most prevalent code in the United States is bipolar coding with an all zero limitation (also called Alternative Mark Inversion or “AMI”). With bipolar coding, alternating ones (high bits) are transmitted as alternating positive and negative pulses, so as to assure a direct current balance and avoid base line wander. Further, an average density of one pulse in eight slots, with a maximum of fifteen zeros between “ones,” is required. This is readily obtained in voice-band coding, however, by simply not utilizing an all zero word. Contrasted with bipolar coding is unipolar coding, in which every occurrence of a high bit is seen as a positive pulse.
In many telecommunication systems, data may be transmitted sequentially in discrete groups of bits called “frames.” In the T
1
system, for instance, each of the 24 channels in the T
1
system is sampled within a 125 microsecond period (equivalent to {fraction (1/8000)}) of a second, constituting one frame. A synchronizing bit, or “frame bit,” is added to each frame to serve as a flag, enabling line elements to distinguish each frame from the preceding frame or from noise on the line. Since there are 8 bits per channel and there are 24 channels and one frame bit at the end of each frame, the total number of “bits” needed per frame is 193. Thus, the resulting line bit rate for T
1
systems is 1.544 million bits per second.
Signals that violate either the coding rules or the framing rules established in a particular system are detected as errors. Thus, for example, under a bipolar coding scheme, two positive pulses should never occur in sequence. To the extent such pulses do occur adjacent to each other, such a signal may be noted as a bipolar coding violation. Similarly, a digital signal that violates framing rules (such as framing bit requirements) established in a given system is detected as a “frame error.” In a given encoding protocol, a sufficient number of frame errors may be detected as a frame loss.
In telecommunications transmission systems, it is occasionally necessary to monitor the performance characteristics of a particular transmission line. By monitoring transmission line performance, service providers can proactively respond to facility performance degradation and can therefore improve the telecommunications circuit.
Being positioned at the point of demarcation between the network and CPE, an NIU can be conveniently configured to assist with performance monitoring in several ways. For example, an NIU can be arranged to provide a “maintenance loopback” function, in which the NIU shunts back incoming signals to the direction from which they came. Loopback can be used to test the continuity and performance of the transmission system up to and including the NIU, either from the network (CO) side or the customer (CPE) side, by allowing a remotely positioned test set to determine whether a signal sent to the NIU returns unaltered.
To establish loopback on the network side, for instance, the central office may send a “loopup” command to an NIU, instructing the NIU to enter loopback. In that event, the NIU would internally switch the signals that it receives from the network (on the RCV IN line) onto the line that transmits to the network (the XMT OUT line), so as to shunt signals from the central office back to the central office. In this state, if the same test signal that is sent down the transmission line from the central office to the NIU for a substantial period of time is received back by central office, then the central office can be substantially assured that the two way transmission system between the central office and the NIU is functioning properly. Alternatively, if the same signal applied to the transmit line does not return along the receive line, then the central office can determine that an error or malfunction has occurred at a point along that T
1
line.
When an NIU enters network loopback, the transmission of signals along the receive line from the central office to the CPE is interrupted. Consequently, during that period, an NIU will typically generate and apply to the RCV OUT line an alarm indication signal (AIS) (e.g., a continuous sequence of all 1's), indicating a loss of the network signal.
In addition to performing loopback, an NIU can serve other performance monitoring functions as well. For example, an NIU can monitor the signals being transmitted between the central office and CPE in order to identify the presence of transmission errors such as bipolar violations or out of frame conditions. The NIU may maintain a record of these errors for later reporting to a service technician or test system.
As another example, an NIU may be arranged to monitor the signals being transmitted along the transmission line in order to identify and respond to predefined control codes. These control codes may represent

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