The cellular community is quickly becoming familiar with the name “Cel-Fi by Nextivity”. Within the last few years, Nextivity has established itself as a “Best-in-Class” smart booster for Cellular applications and also in the Hybrid-DAS space for Middleprise (50K-500K square foot) signal boosting applications.

While the Cel-Fi Intelliboost technology and components are what set Nextivity apart from the competition, an often overlooked component to the system design is the antennas.

RSRP is the generally recognized term for signal strength regarding LTE networks. For standard cellular gateways and routers, an RSRP reading of -120 dBm or lower is generally below the threshold for maintaining a reliable cellular connection. RSRQ is another term that is used to describe the quality of the signal reception and has value. However, for Cel-Fi boosting solutions, the term we are most interested in is Signal to Noise Ratio or SINR. SINR represents the clarity at which the signal of interest from the cellular tower can be received without interference from other radiators in the area transmitting on the same frequency band.

The donor antenna selected to provide the donor signal to the Cel-Fi amplifier can have a large impact on the SINR of the received signal. This is because the antenna radiation pattern determines what signals in the vicinity of the booster will be received. For example, using an Omni-directional antenna as a donor antenna will receive signals in all directions from the antenna, receiving both desired cellular signals from the desired carrier’s closest tower and also undesired cellular signals from other carriers operating on the same frequency bands.

Allowing both wanted and unwanted signals into the booster degrades the SINR value for the desired signals and can degrade the performance of the booster. In contrast, using a directional antenna, such as the Cel-Fi LPDA-R antenna with up to 14 dB of gain (pointed directly at the desired carrier’s closest tower) allows the desired signals to be received and significantly attenuates signals from other towers that are more than 45 degrees away from the desired tower.

In rural settings where there is not an overabundance of cell towers, this can be less of a necessity as the number of effective noise generators on the band of interest may be minimal. But in an urban setting where the density of cell towers can be greatly increased, using a high gain/directional antenna as a donor may be necessary to achieve a reasonable SINR value in the Cel-Fi smart booster to create the best result.

The antenna choice on the server-side of the boosting solution is also important but for different reasons. The server antennas are chosen depending on where they are mounted in the coverage area. An omnidirectional antenna may be used in an area where the antenna can be located in the center of the area to be boosted, whereas a directional panel antenna may be used when the antenna is mounted on one side or wall of the area to be boosted. The goal with the server antenna selection is to efficiently distribute the boosted power in the areas where it is needed. RF splitters and directional couplers are often used to strategically distribute the boosted signal to several server antennas.

Please contact GetWireless for additional detail regarding recommended antennas for specific Cel-Fi boosting applications.

Author: Craig Linder, Sr. Director of Product Management