NV-1602S 16 Ports VDSL2 Managed IP DSLAM with Redundant Power USER S MANUAL Ver.A2
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On the other hand, UPBO reduces the transmit power of short loops and thus degrades their performance as well.
The UPBO technique should ta e in account both issues.
Downstream Power Back-Off (DPBO):
The development of Triple Play services requires higher bandwidth. Higher
bandwidth and substantial performance gain can be reached by deploying DSLAM-s in a remote side cabinet near to the
customer premises. There is no problem at clean networ s where all the customers are connected to the same local
cabinet.
Trellis coding : The name trellis was coined because a state diagram of the technique, when drawn on paper closely
resembles the trellis lattice used in rose gardens. The scheme is basically a convolutional code of rates (r,r+1).
Ungerboec 's unique contribution is to apply the parity chec on a per symbol basis instead of the older technique of
applying it to the bit stream then modulating the bits. The ey idea he termed Mapping by Set Partitions. This idea was to
group the symbols in a tree li e fashion then separate them into two limbs of equal size. At each limb of the tree, the
symbols were further apart. Although in multi-dimensions, it is hard to visualize, a simple one dimension example illustrates
the basic procedure. Suppose the symbols are located at [1, 2, 3, 4, ...]. Then ta e all odd symbols and place them in one
group, and the even symbols in the second group. This is not quite accurate because Ungerboec was loo ing at the two
dimensional problem, but the principle is the same, ta e every other one for each group and repeat the procedure for each
tree limb. He next described a method of assigning the encoded bit stream onto the symbols in a very systematic procedure.
Once this procedure was fully described, his next step was to program the algorithms into a computer and let the computer
search for the best codes. The results were astonishing. Even the most simple code (4 state) produced error rates nearly
1,000 times lower than an equivalent uncoded system. For two years Ungerboec ept these results private and only
conveyed them to close colleagues. Finally, in 1982, Ungerboec published a paper describing the principles of trellis
modulation.
