Licensed vs. unlicensed spectrum: Implications for network design.

Licensed spectrum is a part of the electromagnetic spectrum assigned exclusively to mobile network operators (MNOs) for independent usage. Individual companies pay a licensing fee for the exclusive right to transmit on an assigned frequency within a certain geographical area so that nothing interferes with transmissions. Licenses can be obtained from the Federal Communication Commission (FCC).

Unlicensed spectrum is a part of electromagnetic spectrum that can be assigned to or shared with anyone for non-exclusive usage, and it is subject to some regulatory constraints. Users do not have to get permission from FCC to use unlicensed spectrum. 

Reasons why spectrum licensing is needed

The amount of data is increasing on a daily basis and devices are becoming increasingly interconnected in an internet of things (IoT). These devices communicate with each other over wireless network via radio waves, a type of electromagnetic radiation which transmits data from one location to another. Radio waves are measured via wavelength and frequency. All wireless technologies use radio waves to transmit and receive information, so frequency band is needed in order for different technologies to use airwaves at the same time. But the electromagnetic spectrum is limited and too much activities on any one frequency band would cause massive amount of interference. Therefore, spectrum licensing is needed to ensure that mobile network operators and users do not interfere with one another.

Licensed spectrum 

Advantages

1. Reduced congestion: licensed spectrum belongs to one user and incase of any interference the user has the right to involve the authorities in removing the interfering party or parties from the licensed area.

2. Enhanced performance: due to lack of congestion, licensed spectrum outperforms unlicensed spectrum with the ability to transmit data ten times faster and with increased transmission time.

3. Increased efficiency: mobile network operations can be more flexible in the deployment of cellular networks to manage interference. The base stations that are transmitting signals to devices can be spaced apart, which optimizes network costs and as a result, makes service more affordable.

4. Increased security: since access is private, licensed spectrum decreases the risk of unauthorized access, control and manipulation of information. 

Disadvantages.

1. High equipment cost: licensed spectrum equipment is oftentimes far more expensive than unlicensed spectrum equipment.

2. License cost: purchasing a license can be expensive, especially if your network is large and requires extensive use of licensed spectrum. In addition, maintaining these licenses requires the use of FCC attorneys which can get very expensive.

Unlicensed spectrum. 

Advantages

1. Lower cost: there are no fees associated with using unlicensed spectrum.

2. Accessible and affordable equipment: equipment for popular unlicensed spectrum bands is widely available at a reasonable price.

3. Useful knowledge: due to its widespread use, there is a lot of practical information to be found on the properties of unlicensed spectrum.

Disadvantages

1. Higher congestion: some frequency bands are heavily utilized and as a result, they may be completely useless to mobile network operators. This especially true for the 2.4 GHz spectrum band, which is commonly used for personal and business reasons. But there are number of tools to enable unlicensed spectrum work in crowned areas.

2. Regulatory limits: Many frequency bands operate under regulatory limits on effective radiated power. It is crucial that users are aware of and comply with the regulations for their region.

3. Reduced security: Since access is public, unlicensed spectrum increases the risk of unauthorized access, control and manipulation of information.

Spectrum Licensing and 5G Use Cases.

Within the world of 5G, licensed spectrum is essential for long-term, reliable service-including network and spectrum access. Licensed spectrum provides a wide coverage, exclusive access, faster performance and supports high usage. This helps support 5G by enabling low-latency connectivity, security and increased data transfer rates. Within a military environment, this can help to enhance JADC2 and C6ISR applications. For example, say that servers within a command center on a submarine and inside an unmanned ground vehicle need to communicate with each other in a matter of seconds.

Licensed spectrum spans across these multiple domains to quickly send large amounts of actionable intelligence to and from these servers in real-time; additionally, since access to this type of spectrum is private, this reduces the risk of unauthorized personnel infiltrating a server to compromise its operations or delete/manipulate mission-critical data. 

Unlicensed spectrum, however, can also play a role in strengthening 5G. Shared/unlicensed spectrum access allows for more efficient spectrum usage, higher capacity and new deployments, extending the benefits of 5G to users who do not have access to licensed spectrum.

Managing interference between adjacent users in an unlicensed spectrum, can be done using the following strategies;

1. Reducing transmitting power: Radio waves will die quickly before it collides with adjacent.

2. Use higher frequency bands: radio waves travelling at higher frequency bands die much faster (at an exponential rate) compared with those travelling at lower frequency bands.

3. Use frequency hopping: Transmitting equipment are empowered with intelligence to select a specific block of spectrum (out of a large number) which is relatively interference free than others. This ends up wasting a lot of spectrums, as only a fraction of the total assigned is used at a time.

Unlicensed spectrum bands are at higher frequencies because:

1. Higher frequency bands help in managing interference between adjacent users, as the radio waves travelling in it die out much faster compared to other bans at lower frequencies.

2. Higher frequency bands have a large amount of spectrum compared to lower bands. Hence, using techniques like frequency hopping is easy compared to lower bands which have a significantly lower amount of spectrum.