The Benefits and Challenges of LTE in Unlicensed Spectrum

Using unlicensed spectrum can significantly reduce the cost of deploying LTE networks, with estimates suggesting that it can be up to 70% cheaper than traditional licensed spectrum.

The benefits of LTE in unlicensed spectrum are numerous, but they also come with some challenges. One of the main challenges is the risk of interference from other devices operating in the same frequency band.

LTE in unlicensed spectrum can achieve data rates of up to 150 Mbps, which is comparable to traditional licensed spectrum. This is made possible by the use of advanced techniques such as carrier aggregation and multiple-input multiple-output (MIMO) technology.

However, the unlicensed spectrum band is also home to many other devices, including Wi-Fi routers, cordless phones, and microwave ovens, which can cause interference and affect network performance.

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LTE in Unlicensed Spectrum is an approach to expand the capacity of 4G LTE networks by utilizing unlicensed spectrum, primarily the 5 GHz band used by 802.11a/ac WiFi equipment.

Qualcomm originally proposed LTE-U, which serves as an alternative to carrier-owned WiFi hotspots, enabling mobile operators to boost network coverage and capacity.

LTE-U was designed for quick launch in countries like the United States and China, where implementing the listen-before-talk (LBT) technique is not mandatory.

The LTE-U Forum was created by Verizon, along with Alcatel-Lucent, Ericsson, Qualcomm, and Samsung, to develop technical specifications for base stations and consumer devices passing LTE-U on the unlicensed 5 GHz band.

T-Mobile and Verizon Wireless have expressed interest in deploying LTE-U as early as 2016.

As of late January 2019, there were three LTE-U deployed/launched networks in three countries, with eight further operators investing in the technology through trials or pilots in seven countries.

LTE-U works by augmenting a carrier's LTE service by utilizing the unlicensed spectrum in the 5 GHz range.

Cellular carriers will continue to use LTE in the licensed bands they own for their anchor service but would augment that service with unlicensed 5 GHz spectrum via small cells.

Proponents of LTE-U argue that the use of LTE in unlicensed bands produces better spectrum efficiency than WiFi, leading to higher data rates and capacity.

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LTE-U deployments started as early as 2016, with T-Mobile and Verizon being among the first carriers to adopt the technology.

By 2017, the FCC had approved the use of LTE-U on base stations manufactured by Ericsson and Nokia, paving the way for wider adoption.

In February 2017, the FCC gave the green light for LTE-U on Ericsson and Nokia base stations.

T-Mobile successfully launched LTE-U in several cities across the US, including Bellevue, Washington, and Brooklyn, New York, by June 2019.

As of June 2017, T-Mobile had launched LTE-U in six cities.

The Global Mobile Suppliers Association reported that 32 operators were investing in LAA across 21 countries by January 2019, with this number increasing to 37 operators in 21 countries by July 2019.

Eight operators had announced LAA network launches in six countries, while 29 operators were trialling or deploying the technology in 18 countries.

Operators use LTE-U to complement licensed spectrum, offloading traffic to the 5 GHz band while maintaining control via licensed bands.

21 chipsets containing modems that support one or more of LTE-U, LAA, LWA, or CBRS have been identified by the GSA.

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LTE-U builds on LTE-Advanced's carrier aggregation technology, allowing user equipment to combine multiple frequency bands for increased bandwidth.

The licensed band serves as the primary cell for control signalling, while the unlicensed band serves as the secondary cell for data. This integration of licensed and unlicensed spectrum is a key feature of LTE-U.

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LTE-U was introduced in 3GPP Release 13. It builds on LTE-Advanced's carrier aggregation technology, which allows user equipment to combine multiple frequency bands for increased bandwidth.

The licensed band serves as the primary cell (PCell) for control signalling in LTE-U. This is the cell that handles critical control functions.

LTE-U integrates licensed and unlicensed spectrum, with the unlicensed band serving as the secondary cell (SCell) for data. This allows for increased data capacity.

Carrier aggregation is a key technology behind LTE-U, enabling user equipment to combine multiple frequency bands for increased bandwidth.

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To integrate LTE-U into your existing network, you'll need to consider the technical requirements.

LTE-U leverages the existing LTE core network for backhaul, security, and authentication, requiring no significant changes to the core infrastructure. This means you can easily add LTE-U to your network without having to overhaul your entire system.

Base station modifications are necessary to support unlicensed frequencies and implement LBT/CCA to comply with regulatory requirements. This involves updating your eNodeBs to work with the new frequencies and ensure they're following the rules.

To access the 5 GHz band, smartphones and other devices need LTE-U/LAA-compatible chipsets. This is a crucial step in ensuring seamless connectivity and avoiding any potential technical issues.

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Tracking technologies have come a long way, and it's essential to understand the basics.

GPS technology uses a network of satellites orbiting the Earth to provide location information, with an accuracy of up to 10 meters.

Many devices, including smartphones and cars, use GPS to navigate and track their location in real-time.

Cellular networks use cell towers to provide location information, with an accuracy of up to 100 meters.

Wi-Fi routers can also be used to track devices, with an accuracy of up to 10 meters.

Bluetooth Low Energy (BLE) beacons can be used to track devices in close proximity, with an accuracy of up to 1 meter.

These technologies are often used together to provide a more accurate and comprehensive picture of a device's location.

LTE in unlicensed spectrum offers several benefits, particularly in dense urban areas where it can significantly increase network capacity. This is a major advantage, as it allows for more devices to be connected without a decrease in performance.

One of the key benefits of LTE-U is its ability to boost data rates over short distances, providing a seamless alternative to Wi-Fi without requiring users to switch networks. This is a huge convenience for people who need to stay connected on-the-go.

LTE-U also benefits from operator-managed quality of service (QoS), which means it's less prone to congestion and inconsistent performance. This is a major advantage over public Wi-Fi, which can be unpredictable at best.

Here are the key benefits of LTE-U:

The benefits of LTE-U are numerous and impressive. It significantly increases network capacity, particularly in dense urban areas or indoor environments.

LTE-U boosts data rates over short distances, offering a seamless alternative to Wi-Fi without requiring users to switch networks. This is especially useful in areas with high internet demand, such as shopping malls or public transportation hubs.

One of the key advantages of LTE-U is its consistent performance. Unlike public Wi-Fi, which can suffer from congestion, LTE-U benefits from operator-managed quality of service (QoS).

LTE-U also supports emerging applications like augmented reality, IoT, and real-time communications, which demand high throughput and low latency. This future-proofing capability makes LTE-U an attractive option for businesses and individuals alike.

Here are some of the key benefits of LTE-U at a glance:

WiFi calling can be a convenient option, but it has its limitations. Unlike WiFi calling, LTE-U uses the unlicensed 5 GHz band for all data traffic.

This means that with LTE-U, you don't have to worry about connecting to a separate WiFi network.

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The controversy surrounding LTE-U's use in unlicensed spectrum is a complex issue. In 2015, Google sent a 25-page protest to the Federal Communications Commission (FCC) arguing against LTE-U in highly technical detail.

Industry experts have questioned Google's conclusions, calling its study "utterly artificial and speculative" and "embarrassing". The Wi-Fi Alliance and National Cable & Telecommunications Association (NCTA) also voiced opposition to LTE-U approval, citing concerns that it would severely degrade performance of other Wi-Fi devices.

Qualcomm responded to the allegations in a detailed filing with the FCC, stating that its tests showed LTE-U coexists well with Wi-Fi when operating above or below Wi-Fi's Energy Detect level. The company's tests used actual LTE-U equipment, unlike Google's study which used signal generators.

The New York City Mayor's Office expressed concern over LTE-U interference with Wi-Fi in 2016, given the City's investment in Wi-Fi technology. Qualcomm criticized the Wi-Fi Alliance's co-existence test plan, saying it lacks technical merit and is biased against LTE-U.

Research from the University of Chicago in 2021 found a marked decrease in Wi-Fi performance when LAA was in active use.

The frequency and band used for LTE in unlicensed spectrum are crucial for its operation. The 5 GHz band is the primary focus for LTE-U due to its wide bandwidth availability.

Specific bands vary by region, but in general, the 5 GHz band is divided into two segments: 5150–5350 MHz and 5350–5925 MHz. The former is typically limited to 200 mW and restricted to indoor use in many countries.

Higher power levels, up to 1 W, are often permitted in the 5350–5925 MHz segment, with fewer restrictions. This allows for more robust operation in this band.

Regulatory requirements mandate coexistence mechanisms, such as Listen Before Talk (LBT) or Clear Channel Assessment (CCA), to ensure fair spectrum sharing. These mechanisms prevent LTE-U from monopolising the band, allowing other users like WiFi to operate effectively.

Here's a breakdown of the two segments of the 5 GHz band:

LTE-U systems can operate in different deployment modes to minimize interference with other devices.

One of the key deployment modes is Listen Before Talk (LBT), which ensures the channel is clear before transmitting.

This mode reduces interference with WiFi and other devices by checking the channel before sending data.

Channel Selection is another important deployment mode that allows LTE-U to operate on different 5 GHz channels than WiFi.

This minimizes interference in many cases, making it easier to deploy LTE-U systems.

Fairness Algorithms are also used to balance spectrum usage, ensuring WiFi maintains adequate throughput even when sharing the same channel.

In practice, operators often select less congested channels to further reduce interference.

Studies show that properly implemented LTE-U systems achieve effective coexistence, with WiFi throughput degradation limited to 10–20% in worst-case scenarios.

This makes LTE-U a viable option for deployment in unlicensed spectrum.

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LTE in unlicensed spectrum requires sophisticated tracking and monitoring systems to ensure seamless operation and minimize interference.

To achieve this, operators can utilize dedicated monitoring and control channels, such as the LTE Device Management (LDM) protocol, which allows for real-time monitoring and control of devices operating in unlicensed spectrum.

This protocol enables operators to track device performance, identify potential issues, and adjust settings as needed to maintain optimal network performance.

Operators can also use machine learning algorithms to analyze network data and predict potential issues before they occur, reducing the need for manual intervention.

By leveraging these tools and techniques, operators can ensure reliable and efficient LTE operation in unlicensed spectrum.

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