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5G Networks

Although the 5G frequency range varies by the commercial carrier, there are generally three frequency ranges (called the multi-layer spectrum), which are as follows:

1. Coverage and capacity—C-band, 2–6 GHz
2. High-bandwidth areas—Super Data Layer, over 6 GHz (e.g., 24–29 GHz and 37–43 GHz)
3. Indoor and broader coverage areas—Coverage Area, below 2 GHz (like 700 MHz)

For discussion, three frequencies are chosen for comparison:

1. 1850 MHz—high end of Rifleman Radio range
2. 6 GHz—high-end of C-band
3. 27GHz—close to mid-band Super Data Layer

The Coverage Area is excluded since the Rifleman radio frequencies overlap.

Starting with the 5W Rifleman Radio assuming 2km range at 1850 MHz (which may be an optimistic range), you could cover most of a 100 km² area with about 16 radios. There would be some dead spots, but this is just a cookie-cutter estimate. This discussion assumes a flat Earth and no path loss due to foliage, buildings, or environmental effects. It also ignores the additional power required to transmit at higher data rates. An

increase in data rate of 10 times requires 10 times the power with greater power losses. This factor was omitted to illustrate the effects of communication frequency on range. The calculations were all made assuming isotropic-antenna at transmit and receive radios (directional-antenna could perform better).

The required radio transmission powers per radio frequency to achieve a 2 km range in ideal conditions are the following:

1. 5W at 1850 MHz
2. 53W at 6 GHz
3. 1065 at 27 GHz

For comparison, based on a radio transmission power of 5W, the following are the achievable ranges in ideal conditions:

1. 2 km at1850 MHz
2. 616 m at 6 GHz
3. 137 m at 27 GHz

It’s challenging to get range as the frequency increases at a fixed power of 5W. To cover the 100 km² area would require 289 5W radios operating at 6 GHz or 5,184 radios at 27 GHz, making the higher frequencies unsupportable. These numbers are excessive.

Looking at this in terms of transmission power at a fixed range, the radio transmission powers per frequency required to achieve 1 km range are

1. 1850 MHz at 1.3W
2. 6 GHz at 14W
3. 27 GHz at 266W

and at 500 m they are

1. 1850 MHz at 0.4W
2. 6 GHz at 4W
3. 27 GHz at 67W

For coverage of 100 km², if the range of each radio were reduced to 1 km in an attempt to balance the number of required relay nodes with the power transmission requirements, you would need about 80 radios to cover the area. That’s a reasonably low number that could be accomplished using a combination of unmanned aerial vehicles (UAVs), robotic, and combat vehicle-based relay systems.

Based on physics, it doesn’t seem likely that the highest frequencies will reach 2 km unless the transmission power is much higher than 5W. Most base stations have ranges of about 500 m with mixed results. That range was achieved with MIMO (multiple-input, multiple-output) antenna arrays and “beam-forming” techniques and is highly susceptible to loss of connectivity.

UAV platforms provide the best opportunity for high bandwidth coverage on the battlefield. Lift and loitering capabilities of current UAVs could carry repeaters and steerable antenna arrays to a vantage point at which coverage could be provided to areas of need. Platforms equipped with multiple repeaters may sacrifice coverage area for higher data rates by ganging up repeaters on different channels. It’s conceivable the repeaters on these platforms could be reconfigurable in flight to provide higher data rates, greater coverage area, or redundancy required to meet mission needs. Further research is necessary to determine the optimal number and configuration of UAVs.

Large combat platforms could be augmented with expendable platforms to provide rapidly available high bandwidth hot spots. These expendable UAVs could potentially cover an area of a few hundred square meters serving squad operations. These smaller lightweight UAVs, potentially 3D printed close to the point of need, would carry lower power repeaters operating at the higher operating frequencies with higher bandwidth.

Ground-based robotic platforms are potential candidates for carrying repeaters and the high-speed processing of data. Like the UAV platforms, they can be deployed in a variety of sizes. The most significant impediment to their success in a given situation is the relatively low antenna height, where environmental effects are more likely to limit coverage area. The primary benefit is that once positioned, energy is not required to maintain their location, as is the case with the UAV.

New component devices in the high-frequency ranges (30-50 GHz) are becoming easier to source and are dropping in price as more products are being developed. Where previously cost-prohibitive, these devices can now reasonably be used to develop Army-specific radiofrequency equipment. While custom ASIC (application-specific integrated circuit) devices may improve radio energy utilization, they can be costly and not necessarily of high value considering ultra-compact device size is rarely high on the priority list.

The key enabling aspects of 5G for the battlefield are high bandwidth and low latency. These are the key drivers for advanced capabilities for the Soldier. However, some obstacles presented by current commercial and consumer-driven developments are significant, possibly preventing immediate adoption by the Army, such as limited range and security. Of

course, the limited range may also be seen as a benefit by creating a lower probability of detection by the adversary. However, the radio range can be improved through the use of UAVs and mobile ground platforms with higher power and greater area coverage.

These obstacles should not detract from the Army’s pursuit of 5G battlefield systems; instead, they should guide the research and acquisition decisions to most efficiently advance the state of the art so that they can be more easily adopted. For instance, 5G does not employ frequency hopping to improve security. The Army should conduct research into methods to accomplish this potentially important security feature. As with planned provider rollouts, 5G should not be seen as a single solution but should be coupled with existing well-known 3G, 4G, and 4G LTE architectures for resilience and speed of deployment. Research should explore the application of these capabilities to existing combat scenarios, while also developing the resources to include 5G capabilities.