Unlicensed Spectrum

Wi-Fi, an unlicensed wireless technology, has experienced huge success due to high throughput rates, ease of use for consumers, extensive deployment by businesses, widespread availability in public places, and large amounts of available spectrum.

For mobile operators, Wi-Fi can offload data traffic, relieving some stress from capacity demands. To make offload work more effectively, the industry is working to more tightly bind Wi-Fi functionality with cellular operation, as discussed below in more detail under “Wi-Fi Integration and Data Offload.”

Wi-Fi uses spectrum efficiently because its small coverage areas result in high-frequency reuse and high data density (bps per square meter). Less efficient are white-space unlicensed networks, sometimes called “super Wi-Fi,” that have large coverage areas, because the throughput per square meter is much lower. While white-space networks may be a practical broadband solution in rural or undeveloped areas, they face significant challenges in urban areas that already have mobile and fixed broadband available.34 See the section on “White Space Networks” in the appendix for further details.

Advocates argue that unlicensed spectrum unleashes innovation and that government should allocate greater amounts of unlicensed spectrum. Although Wi-Fi has been successful, the core elements that make unlicensed spectrum extremely successful are also the source of inherent disadvantages: local coverage and its unlicensed status. Local coverage enables high data density and high frequency reuse but makes widespread continuous coverage almost impossible. Similarly, unlicensed operation facilitates deployment by millions of entities but results in overlapping coverage and interference.

Wi-Fi cannot replace networks built using licensed spectrum. The two are complementary and helpful to each other, as summarized in Table 1

Table 1: Pros and Cons of Unlicensed and Licensed Spectrum

Unlicensed Pros	Unlicensed Cons	Licensed Pros	Licensed Cons
Easy and quick to deploy	Potential of other entities using same frequencies	Huge coverage areas	Expensive infrastructure
Low-cost hardware	Difficult to impossible to provide wide-scale coverage	Able to manage quality of service	Each operator has access to only a small amount of spectrum

Some operators, such as Republic Wireless, offer a “Wi-Fi first” capability under which devices always attempt to use a Wi-Fi connection and fall back to a cellular connection only if no Wi-Fi is available. Such cellular backup is essential because Wi-Fi, due to low- power operation in many bands, is inherently unsuited for providing continuous coverage. The sharp drop-off in signal strength makes coverage gaps over large areas inevitable, especially outdoors.

Figure 1: Propagation Losses of Cellular vs. Wi-Fi

A capability being discussed for Release 13 is LTE operating in unlicensed bands. Carrier aggregation would combine a licensed carrier with an unlicensed 20 MHz carrier in the 5 GHz band as a supplemental channel. LTE uses channels differently than Wi-Fi, so engineers are evaluating how LTE could be a fair neighbor in unlicensed bands and how it could meet varying regulatory requirements for unlicensed bands in different parts of the world.

LTE operating in unlicensed bands could eliminate handoffs to Wi-Fi, possibly creating a more seamless user experience. Under heavy load, LTE is spectrally more efficient than Wi-Fi, since it uses more sophisticated over-the-air scheduling algorithms.

A capability being discussed for Release 13 is LTE operating in unlicensed bands. Carrier aggregation would combine a licensed carrier with an unlicensed 20 MHz carrier in the 5 GHz band as a supplemental 

Harmonization | 5G Bands

Spectrum harmonization delivers many benefits, including higher economies of scale, better battery life, improved roaming, and reduced interference along borders.

As regulators make more spectrum available, it is important that they follow guidelines such as those espoused by 4G Americas

1.       Configure licenses with wider bandwidths.

2.       Group like services together.

3.       Be mindful of global technology standards.

4.   Pursue harmonized/contiguous spectrum allocations.

5.       Exhaust exclusive use options before pursuing shared use.

6.       Because not all spectrum is fungible, align allocation with demand.

Emerging technologies such as LTE benefit from wider radio channels. These wider channels are not only spectrally more efficient, they also offer greater capacity. Figure 1 shows increasing LTE spectral efficiency obtained with wider radio channels, with 20 MHz on the downlink and 20 MHz (20+20 MHz) on the uplink showing the most efficient configuration.

Figure 1: LTE Spectral Efficiency as Function of Radio Channel Size

Of some concern in this regard is that spectrum for LTE is becoming available in different frequency bands in different countries. Roaming in many cases is based on GSM or HSPA on common regional or global bands.

The organization tasked with global spectrum harmonization, the International Telecommunication Union, periodically holds World Radiocommunications Conferences (WRC).

Harmonization occurs at multiple levels:

q  Allocation of radio frequencies to a mobile service in the ITU frequency allocation table.

q  Establishment of global or regional frequency arrangements, including channel blocks and specific duplexing modes.

q  Development of detailed technical specifications and standards, including system performance, RF performance, and coexistence with other systems in neighboring bands.

q  Assignment for frequency blocks with associated technical conditions and specifications to appropriate operators and service providers.31

Figure 2 shows the harmonization process.

Figure 2: Spectrum Harmonization

5G Bands

As radio technology progresses, it can handle higher frequencies, and it occupies greater bandwidth. 1G systems used 30 kHz radio carriers, 2G in GSM uses 200 kHz carriers, 3G in UMTS uses 5 MHz carriers, and 4G in LTE uses carriers of up to 100 MHz through carrier aggregation.

Although 5G research and development is in its infancy, to achieve the 10 Gbps or higher throughput rates envisioned for 5G will require radio carriers of at least 1 GHz, bandwidths available only at frequencies above 5 GHz. Researchers globally are studying high-frequency spectrum options. For example, the 5G organization Mobile and wireless communications Enablers for the Twenty-twenty Information Society (METIS) has published a report on spectrum needs that evaluates the following frequency bands:

q  380 to 5925 MHz (current systems)

q 5.925 MHz to 40.5 GHz

q  40.5 GHz to 95 GHz

q  95 GHz to 275 GHz (representing the upper limits of mmWave bands)

Higher frequencies are well suited for ultra-dense small-cell deployments, but longer propagation is also possible using antenna arrays and beamforming. For example, Samsung has demonstrated 2 km line-of-sight transmission at 28 GHz.