Appendix H
Hopset Construction
H-1. Introduction
A hopset is a list of frequencies the spectrum manager authorizes a particular unit to use. A list of discrete frequencies or ranges and groups of frequencies specify the hopset.
Many frequency hopping (FH) or frequency agile equipment is either fielded or under development. While not all of these are communications equipment, the factors in constructing hopsets are basically the same.
An FH or agile transmitter changes frequency within a given frequency band in either a random, pseudorandom, or fixed order. Generally, this is done as ECCM, but, in some cases, is done when the equipment senses interference on a specific frequency. The number of frequencies used within the given frequency band can range from a dozen to several thousand. Normally, the more frequencies available in the required frequency band for inclusions in the hopset, the more effectively the equipment functions.
H-2. Construction Process
For this discussion, assume a corpswide hopset is being constructed for SINCGARS. The corps G6 is the frequency assignment authority for the band being used.
The entire construction process is actually one of subtraction. The frequency resource needed by the FH or agile transmitter is normally shared with other equipment, such as between SINCGARS and MSE, and radio access units (RAUs) and mobile subscriber radiotelephone terminals (MSRTs). The spectrum manager must consider the impact of the hopper on nonhopping assignments. Possible interference to existing users must be evaluated, and if the interference is determined to be unacceptable, those frequencies must be deleted from the frequency resource. The spectrum manager must also delete all assignments that have been designated by corps, higher headquarters, or civil authorities as restricted from the frequency resource.
To develop a truly corpswide hopset, the spectrum manager must consider all restrictions on frequency use imposed by divisions within their areas of operation. It may be that all of these frequencies were considered during the process discussed above.
Any frequency restrictions that apply to corps boundary areas must be considered and coordinated with the adjacent corps. Frequencies restricted in the boundary areas may be deleted from the frequency resource.
Using FH or agile transmitter in an aircraft can impose additional restrictions. Not only does the process discussed above apply, but also due to the increase in the radio horizon, additional consideration with adjacent corps will have to be made. This could lead to more frequencies being deleted from the frequency resource. This results in a much smaller hopset.
The spectrum manager starts the planning process by compiling all the frequency requirements from the subordinate units. He combines the subordinate unit requirements with those of his echelon.
The spectrum manager assigns frequencies based on the following criteria:
- Network priority.
- Equipment in use.
- Equipment separation.
- Retransmission requirements.
- Frequency use restrictions.
The spectrum manager assigns the maximum number of frequencies available in the area of operation and spreads the frequencies in the hopsets across the widest possible band to optimize ECCM capabilities. Spreading the frequencies across the frequency band is more important than increasing the total number of frequencies available. Fifty frequencies spread from 30 to 88 MHz are more effective than 100 frequencies from 35 to 40 MHz. Chances are very slight that an enemy jammer can cover the entire 58 MHz range or even a small portion of it with enough power to disrupt communications; however, a jammer could barrage jam the entire 5 MHz range.
The spectrum manager, with the signal planning element, uses the BECs computer to assign frequencies to hopsets. The computer mathematically manipulates the frequencies based on the restrictions the spectrum manager enters into the data base. The computer develops hopsets by correlating the restrictions with available resources.
Hopsets should maximize use of frequencies separate from any collocated networks. This requires knowledge of network structures and which nets are collocated. The spectrum manager must work closely with G3/S3 to minimize the effects on collocated networks.
To minimize possible interference between SINCGARS and MSRTs/RAUs, SINCGARS can be programmed to lock out certain frequencies from the hopset. Neither BECS nor the MSE SCC can engineer frequency use for both systems at the same time. The spectrum manager must plan the MSRT/RAU frequencies (up to 96 pairs) with the SCC (assigns MSRT/RAU frequencies) and enter them into the BECS computer as lockout sets. Frequency interference between the radio systems is minimized, particularly the cosite systems.
H-3. Considerations
Corps and division level communications are currently upgrading to MSE and fielding SINCGARS as a combat net radio. Both systems use the same frequency band and mutual interference has been noted.
Covehicular interference is the worst. Currently, there is no technical solution and no planned fix until MSE and SINCGARS are totally fielded. The area most affected by this interference is the brigade area. Users in this area need to be aware of the potential problem and given the operational work-arounds to overcome the interference.
There are three methods/work-arounds that help overcome the interference problem. No one method eliminates all interference. The three methods are--
- Time-sharing. The best answer to the vehicle problem is prioritize the device needed by the mission, situation, and echelon.
- Spectrum-sharing. Lock out MSRT/RAU frequencies on SINCGARS in the FH mode or delete from frequency resource for SINCGARS in the SINGLE-CHANNEL mode.
- Antenna separation. The best alternative available for the fried locations but is not possible for mobile users.
Common sense remains the best defense to resolve this interference. Standard communications principles and signal doctrine should be followed.
- Use lowest power possible to maintain combat net radio nets.
- Keep transmissions short for combat net radio and MSRT calls.
- Keep vehicles using communications systems separated during convoy and during halts.
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