This process is assisted by activity status reporting from the ONUs, or implicitly by the observation of idle XGEM frames at the OLT side. Varvarigos, in Smart Cities and Homes, 2016 4.1 PANDA DBA structureĭBA is the process of allocating upstream transmission opportunities by the OLT to its connected ONUs. Also, the upper frequency will be constrained by the characteristics of the passive devices used, by the increasing loss of the cables, and by the practical limits on signal levels in the network, as discussed in Chapter 2.Ĭ.A. As a practical matter, however, these freedoms are restricted by regulations covering carriage of over-air broadcast signals (even after the cessation of analog broadcasting in February 2009), regulations about signal delivery to customer-owned devices, and the tuning range of deployed cable-supplied devices. Such networks have the advantage that the division between upstream and downstream bandwidth can be altered at will, as can the upper frequency limit. Since these are determined primarily by the amplification equipment, some operators are proposing the use of coaxial distribution networks small enough that they can be totally passive between the output of the fiber node and the user. The most basic parameter of any coaxial network is the forward and return bandwidth. The use of block conversion may force an operator to use a DFB return laser rather than a lower-cost F-P laser.ĭavid Large, James Farmer, in Broadband Cable Access Networks, 2009 RF Bandwidth This reduces the carrier-to-noise ratio available in the optical portion of the return path. However, since the one optical transmitter is loaded with more signals, the performance of that transmitter must increase, or the OMI must be reduced. A pilot tone is transmitted between the node and headend to allow phase locking.īlock conversion increases the bandwidth available per customer and reduces noise funneling without requiring more optical transmitters and receivers.

If this is required, then most commonly, the oscillators in the node will be phase locked to those in the headend, or vice versa. In some cases, it is necessary to provide very accurate frequency conversion in the node and headend, such that the frequency to which a signal is restored in the headend is very close to the frequency at which it existed before conversion at the node. Inversion is brought about by the practical need to use high-side local oscillators. The conversion back in the headend will reinvert the spectrum. The single conversion results in inversion of the spectra of the three converted bands so that what was the low end of the band becomes the high end of the converted band. For other applications, double conversion might be used if it is necessary to put many blocks close together, but the cost can be higher.

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