Cable Modem Sweep

Option for New DSP Family

The CM Sweep feature (patent pending) for the New DSP family of field analyzers allows the cable modem to launch bonded upstream carriers back to the CMTS for use as in-band sweep points. This gives the operator the ability to finally sweep inside their upstream modem channels and look for potential gain and tilt issues that otherwise may be hiding.

Cable Modem Sweep

In the past operators have always relied on out-of-band sweep carriers injected within their upstream for sweeping the return band. Until now, performing in-band sweep would require injecting sweep carriers into the channels where your modems are present, but that would incapacitate any active modems trying to reach the headend. As upstream bandwidth continues to fill, operators are now reducing the number of upstream sweep carriers, which severely affects the resolution of their return sweep frequency response.

So, how does the operator properly sweep the upstream, especially if there is no room to insert their sweep carriers? Trilithic’s answer to this question is our Cable Modem (CM) Sweep with Modem Quality of Service (MQS) measurements designed so technicians can quickly and easily assess the quality of your upstream channels. The CM Sweep feature allows the cable modem to launch bonded upstream carriers back to the CMTS for use as in-band sweep points. This gives the operator the ability to finally sweep inside their upstream modem channels and look for potential gain and tilt issues that otherwise may be hiding.

In short, this style of sweep transmission also looks at a new metric called Modem Quality of Service (MQS), which allows the operator to see the quality of both each individual upstream channel and all upstream carriers. The higher that the MQS score is indicates that the equalizer is working harder due to upstream impairments in the path of the cable modem. A value of less than 1 dB for your MQS score is considered excellent, while more severe impairments could lead to scores as high as 6 dB.

Figure 1 shows an example of a raw CM sweep trace that allows the operator to identify impairments before the reference measurement has been applied. By using CM Sweep in this manner, it allows technicians to see the modem transmit levels across the upstream bandwidth. But more importantly, this gives technicians the ability to see potential impairments within the upstream before a reference measurement is applied. This allows technicians to fix these impairments and then save a reference at the node. The technician can then bring up this reference for comparison to any point in the system, such as the next active amplifier.

Figure 2 shows an example of the CM Sweep trace once a reference is applied, which provides technicians with the ability to see the gain and tilt across the band based on the marker settings. Using a reference also allows the user to see their individual channel MQS scores and the overall MQS score of all of the cable modem channels in the upstream. At a quick glance, the technician is able to see the overall health of the upstream channels, which tell the operator how all the upstream channels are performing, so decisions can be made to either save the reference and move on, or look deeper into the individual carriers.

 

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