In my previous blog post, I covered a number of technologies related to the use of LTE in unlicensed spectrum. This blog post continues on that topic, with a focus on spectrum management systems.
Today, wireless spectrum below 6GHz is fully allocated to incumbents who, unsurprisingly, oppose any proposals to repurpose the spectrum to someone else. Thus, the traditional approach of repurposing spectrum for new cellular technologies is no longer sufficient in the case of 5G – novel ways to manage spectrum below 6GHz are needed. Two such technologies are LSA (Licensed Shared Access) and SAS (Spectrum Access System). LSA is a shared spectrum technology deployed in Europe, whereas SAS is its counterpart in the US.
SAS authorizes and manages use of spectrum for the Citizens Broadband Radio Service (CBRS), which is 150MHz of spectrum in the US in the 3550-3700MHz band that the FCC (Federal Communications Commission) opened up in 2015 for commercial use. CBRS enables almost anyone to use this spectrum while it is still being used by existing incumbents such as the military or satellite communication [QC-1].
CBRS defines three levels of priority when assigning shared spectrum [TSC]:
The 3.5GHz band does not penetrate indoors as much as lower frequencies. Thus, it is a good fit for small cells and their dense deployment model. As an example, organizations such as private enterprises, venues, and fixed operators could autonomously deploy high-quality in-building LTE networks e.g., following a floor-by-floor deployment model [FW].
The LSA system includes coordination of resource usage between incumbents and LSA licensees. Its main use case is the extension of cellular capacity below 6GHz in Europe. One major difference between SAS and LSA is that LSA is missing tier-3 (i.e., GAA). LSA enables an LTE network to be operated on licensed shared basis in the 2.3-2.4GHz frequency band between incumbents (tier-1) and Mobile Network Operators (MNOs; tier-2) [Intel]. Tier-1 is prioritized over tier-2, meaning that the MNO using the LSA band is required to vacate it for a given geographic area, frequency range, and period of time for which the incumbent is requiring access. The expectation is that MNOs will enter in multi-year (typically ten years or more) sharing agreements with the incumbents for the LSA band. The LSA band is typically combined with LTE in dedicated licensed spectrum through carrier aggregation mechanisms
Spectrum management in LSA relies on an LSA Repository, which is a centralized database providing information about the availability of the LSA spectrum to multiple MNO networks [Intel]. Incumbents need to provide a priori usage information to the database on the LSA band’s availability. Based on this information, the LTE system is either granted access or requested to vacate the concerned bands using control mechanisms of an LSA Controller located within the MNO network. The LSA Controllers and the LSA Repository interact through an ETSI (European Telecommunications Standards Institute) defined interface. In LSA, no sensing mechanisms are required for the identification of incumbent operation in the LSA band.
In contrast to LSA, SAS is designed to ensure coexistence with incumbents (e.g., the military using networks operated mainly close to US coastal areas) who are not able to provide a priori information to the central repository [Intel]. SAS can be operated throughout the US territory except within exclusion zones close to the coastal areas. In the second step of SAS, an Environmental Sensing Capability (ESC) component is added which allows operation even within the exclusion zones. ESC performs required sensing tasks to discover incumbent operation in the CBRS band. Spectrum access for tier-2 and tier-3 users is based on the sensing results. ESC will consist of networks of sensors that detect the presence of signals from incumbent systems in the CBRS band and communicate that information to one or more SAS repositories to facilitate protection of incumbent operations in the band [FW-2].
One of the companies that has filed SAS Administrator and ESC Operator applications with the FCC is Google [FW-2]. Google wrote in its application that it has been trialing a prototype SAS for almost two years. Google has also demonstrated its SAS prototype to industry and government. Google believes that 5G deployment will receive a boost from the CBRS band and that SAS will make the traditional model of MNOs spending billions of dollars to gain control of specific spectrum blocks no longer valid [RCR]. According to Preston Marshall, an engineering director for Alphabet Access at Google, “This [SAS] changes what spectrum ownership means. There is no owner”. Google believes that the killer application for the CBRS band will be the neutral host concept, which is an attractive model in places where it is not feasible for every operator to deploy their own radio systems independently, such as in enterprises or public venues like sports stadiums or shopping malls.
Besides neutral host scenarios, the CBRS band can be useful for enabling MNOs to offer Gigabit LTE speeds in more places thanks to the additional spectrum, for small cell deployments to extend coverage and capacity outdoors, and for creating private LTE networks for enterprises or industrial IoT.
Google is not stopping at the CBRS band – the company has urged the FCC to seriously consider applying the SAS framework to the 24GHz band as well [SE].
[FW] Google, Intel, Nokia and more partner to advance U.S. 3.5 GHz CBRS, http://www.fiercewireless.com/tech/google-intel-nokia-and-more-partner-to-advance-u-s-3-5-ghz-cbrs
[FW-2] Google, Federated Wireless, others apply to fill role of SAS, ESC for 3.5 GHz, http://www.fiercewireless.com/tech/google-federated-wireless-others-apply-to-fill-role-sas-esc-for-3-5-ghz
[Intel] Spectrum Sharing Technology | LSA and SAS White Paper, http://www.intel.com/content/www/us/en/wireless-network/spectrum-sharing-lsa-sas-paper.html
[QC-1] A new kind of spectrum for new opportunities, https://www.qualcomm.com/news/onq/2016/08/29/new-kind-spectrum-new-opportunities
[RCR] Google sees CBRS spectrum band as key for 5G, new model for industry, http://www.rcrwireless.com/20161117/carriers/google-sees-cbrs-spectrum-band-key-5g-new-model-industry-tag2
[SE] Google urges FCC to consider SAS model for 24 GHz band, http://www.spectrumeffect.com/google-urges-fcc-to-consider-sas-model-for-24-ghz-band.html
[TSC] What is CBRS Shared Spectrum for in-building small cell wireless? https://www.thinksmallcell.com/LTE/what-is-cbrs-shared-spectrum-for-in-building-small-cell-wireless.html
Today, wireless spectrum below 6GHz is fully allocated to incumbents who, unsurprisingly, oppose any proposals to repurpose the spectrum to someone else. Thus, the traditional approach of repurposing spectrum for new cellular technologies is no longer sufficient in the case of 5G – novel ways to manage spectrum below 6GHz are needed. Two such technologies are LSA (Licensed Shared Access) and SAS (Spectrum Access System). LSA is a shared spectrum technology deployed in Europe, whereas SAS is its counterpart in the US.
Spectrum Access System (SAS)
SAS authorizes and manages use of spectrum for the Citizens Broadband Radio Service (CBRS), which is 150MHz of spectrum in the US in the 3550-3700MHz band that the FCC (Federal Communications Commission) opened up in 2015 for commercial use. CBRS enables almost anyone to use this spectrum while it is still being used by existing incumbents such as the military or satellite communication [QC-1].
CBRS defines three levels of priority when assigning shared spectrum [TSC]:
- Tier-1: Incumbent users (e.g., the Department of Defence) have the highest priority.
- Tier-2: Priority Access Licenses (PAL), where an organization can pay for a fee to be assigned a 10MHz block for a limited geographic area for a three-year period, giving them priority over other users. A maximum of seven such blocks can be concurrently allocated within the same geographic area. Thus, max 70MHz of the available 150MHz can be assigned to priority users and the remaining 80MHz is left for others to use.
- Tier-3: General Authorized Access (GAA) for general usage. In this third tier, anyone can use the spectrum when it is not used by the higher layers.
The 3.5GHz band does not penetrate indoors as much as lower frequencies. Thus, it is a good fit for small cells and their dense deployment model. As an example, organizations such as private enterprises, venues, and fixed operators could autonomously deploy high-quality in-building LTE networks e.g., following a floor-by-floor deployment model [FW].
Licensed Shared Access (LSA)
The LSA system includes coordination of resource usage between incumbents and LSA licensees. Its main use case is the extension of cellular capacity below 6GHz in Europe. One major difference between SAS and LSA is that LSA is missing tier-3 (i.e., GAA). LSA enables an LTE network to be operated on licensed shared basis in the 2.3-2.4GHz frequency band between incumbents (tier-1) and Mobile Network Operators (MNOs; tier-2) [Intel]. Tier-1 is prioritized over tier-2, meaning that the MNO using the LSA band is required to vacate it for a given geographic area, frequency range, and period of time for which the incumbent is requiring access. The expectation is that MNOs will enter in multi-year (typically ten years or more) sharing agreements with the incumbents for the LSA band. The LSA band is typically combined with LTE in dedicated licensed spectrum through carrier aggregation mechanisms
Spectrum management in LSA relies on an LSA Repository, which is a centralized database providing information about the availability of the LSA spectrum to multiple MNO networks [Intel]. Incumbents need to provide a priori usage information to the database on the LSA band’s availability. Based on this information, the LTE system is either granted access or requested to vacate the concerned bands using control mechanisms of an LSA Controller located within the MNO network. The LSA Controllers and the LSA Repository interact through an ETSI (European Telecommunications Standards Institute) defined interface. In LSA, no sensing mechanisms are required for the identification of incumbent operation in the LSA band.
And back to SAS
In contrast to LSA, SAS is designed to ensure coexistence with incumbents (e.g., the military using networks operated mainly close to US coastal areas) who are not able to provide a priori information to the central repository [Intel]. SAS can be operated throughout the US territory except within exclusion zones close to the coastal areas. In the second step of SAS, an Environmental Sensing Capability (ESC) component is added which allows operation even within the exclusion zones. ESC performs required sensing tasks to discover incumbent operation in the CBRS band. Spectrum access for tier-2 and tier-3 users is based on the sensing results. ESC will consist of networks of sensors that detect the presence of signals from incumbent systems in the CBRS band and communicate that information to one or more SAS repositories to facilitate protection of incumbent operations in the band [FW-2].
One of the companies that has filed SAS Administrator and ESC Operator applications with the FCC is Google [FW-2]. Google wrote in its application that it has been trialing a prototype SAS for almost two years. Google has also demonstrated its SAS prototype to industry and government. Google believes that 5G deployment will receive a boost from the CBRS band and that SAS will make the traditional model of MNOs spending billions of dollars to gain control of specific spectrum blocks no longer valid [RCR]. According to Preston Marshall, an engineering director for Alphabet Access at Google, “This [SAS] changes what spectrum ownership means. There is no owner”. Google believes that the killer application for the CBRS band will be the neutral host concept, which is an attractive model in places where it is not feasible for every operator to deploy their own radio systems independently, such as in enterprises or public venues like sports stadiums or shopping malls.
Besides neutral host scenarios, the CBRS band can be useful for enabling MNOs to offer Gigabit LTE speeds in more places thanks to the additional spectrum, for small cell deployments to extend coverage and capacity outdoors, and for creating private LTE networks for enterprises or industrial IoT.
Google is not stopping at the CBRS band – the company has urged the FCC to seriously consider applying the SAS framework to the 24GHz band as well [SE].
References
[FW] Google, Intel, Nokia and more partner to advance U.S. 3.5 GHz CBRS, http://www.fiercewireless.com/tech/google-intel-nokia-and-more-partner-to-advance-u-s-3-5-ghz-cbrs
[FW-2] Google, Federated Wireless, others apply to fill role of SAS, ESC for 3.5 GHz, http://www.fiercewireless.com/tech/google-federated-wireless-others-apply-to-fill-role-sas-esc-for-3-5-ghz
[Intel] Spectrum Sharing Technology | LSA and SAS White Paper, http://www.intel.com/content/www/us/en/wireless-network/spectrum-sharing-lsa-sas-paper.html
[QC-1] A new kind of spectrum for new opportunities, https://www.qualcomm.com/news/onq/2016/08/29/new-kind-spectrum-new-opportunities
[RCR] Google sees CBRS spectrum band as key for 5G, new model for industry, http://www.rcrwireless.com/20161117/carriers/google-sees-cbrs-spectrum-band-key-5g-new-model-industry-tag2
[SE] Google urges FCC to consider SAS model for 24 GHz band, http://www.spectrumeffect.com/google-urges-fcc-to-consider-sas-model-for-24-ghz-band.html
[TSC] What is CBRS Shared Spectrum for in-building small cell wireless? https://www.thinksmallcell.com/LTE/what-is-cbrs-shared-spectrum-for-in-building-small-cell-wireless.html
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