New approach seeks to optimize DTV spectrum allotment
Aug 5, 2010 9:48 AM, By Phil Kurz
Editor’s note: This article is the second in a multipart series of reports examining proposals to recoup spectrum discussed in the FCC’s "Spectrum analysis: Options for Broadcast Spectrum OBI Technical Paper No. 3." The first article is available on the Broadcast Engineering website.
Imagine the multiple, competing considerations and priorities the Federal Communications Commission must weigh when it advances its goal of clearing 120MHz of DTV spectrum for future wireless broadband Internet use.
Short of looking at the impact of various approaches on a station-by-station basis, how could it possibly evaluate different alternatives and all of their ramifications on the ability of over-the-air TV viewers to continue receiving their favorite DTV channels?
The agency's OBI (Omnibus Broadband Initiative) Technical Paper No. 3, published in June, sheds light on a likely approach. The document, which offers a menu of possible steps to recouping TV spectrum as envisioned by the agency in its National Broadband Plan, lays out a new method called the Allotment Optimization Model (AOM), that could serve as "a useful tool to inform decisions in the upcoming rulemaking proceeding regarding reallocation of spectrum from broadcast TV bands," the paper said.
An alternative to the simulated annealing approach used by the commission "to inform" the process of establishing the initial DTV Table of Allotments used by stations for their digital simulcast channels during the transition for analog to digital broadcasting, AOM is still "a developmental alpha version." However, when completed, the AOM computer algorithm is intended to let the agency input various constraints on the optimization process and identify the "best solutions" for optimizing spectrum use, it said. For instance, it could be used to identify "the minimum number of channels" that could be recovered through channel sharing and repacking based upon specific constraints.
With that information, the FCC could set up an incentive auction and establish a Table of Allotments "in an attempt to achieve the desired objective," the paper said. The AOM model also could be used to show a specific solution is impossible, thus giving the agency the option of re-evaluating its constraints and lowering its objective.
In effect, the new AOM approach has the potential to let the FCC weigh the likely costs and benefits of various approaches to shrinking the amount of spectrum allocated to DTV transmission, such as repacking channel assignments. "The new AOM could facilitate such analysis," the paper said.
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An appendix to the OBI paper examines the technical details of optimization model formulation. The AOM model discussed in the appendix can be solved for five different objectives, including:
- Maximizing how many channels are cleared at the top of the UHF and bottom of the VHF band, if VHF clearing is desired;
- Minimizing how many stations must be moved to a different tower;
- Minimizing how many stations share channels;
- Minimizing channel sharing where each station is weighted by DMA station count;
- Minimizing station channel reassignments and relocations.
In its initial iteration, the model ignores "the impact on the viewers (OTA households) due to station reassignment, relocation, channel sharing or relaxation of the interference constraints," the document said. A subsequent enhancement to the model "will consider these cost/benefit tradeoffs due to co-location or relaxation of interference restrictions," it added.
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