Dynamic Spectrum Access Decisions. George F. Elmasry

GHz for future considerations.

Notice that different countries have different ranges of spectrum allotted for the first trials of 5G. Table 6.1 gives an example of different spectrum allocations for below 6 GHz in different areas of the world. This trend of using different bands at different areas of the world is expected for all 5G bands as spectrum licensing agents such as the US FCC has plans for spectrum use for civil applications that are different from those of other countries.

Table 6.1 5G frequency bands allotted below the 6 GHz range.

Country	Range (GHz)
Europe	3.4–3.8
China	3.3–3.6 4.4–4.5 4.8–4.99
USA	3.1–3.55 3.7–4.2
Japan	3.6–4.2
Korea	3.4–3.7

This chapter will reference below 6 GHz access as “lower frequency” access (LTE or enhanced LTE). Lower frequency access plays an important role in 5G deployment and 5G DSM.

      Opportunistic spectrum use at the cell level is a core part of 5G dynamic spectrum management while points of presence of LTE are still part of 5G. Notice that 5G standardizations call for cells to be deployed dynamically, making dynamic spectrum access more challenging because mobility is not limited to the end user only. 5G will also operate in a wide range of frequencies, including the mm‐wave range, which comes with its own challenges in designing advanced receiver techniques. 5G gives access to as much licensed spectrum as possible in addition to as much opportunistic use spectrum as possible, making it an umbrella for many commercial wireless capabilities outside of cellular technology. The mix of licensed spectrum and unlicensed spectrum makes the 5G dynamic spectrum management problem space as challenging as that of military communications systems, which do not have the concept of a fixed tower and all nodes are mobile.

There are different types of 5G cells, as shown in Table 6.2, where each size has an intended deployment. The ranges depicted in Table 6.2 can be increased with better antenna technologies and are included in this table to help explain the concept of spatial modeling with dense deployment of 5G access points detailed later in this chapter. Notice that the number of users (end users) varies as it is dependent on many factors, such as proximity to the access point (which can decide the chip code), requested data rate, and propagation models. Notice also that 5G makes use of fiber cable ground infrastructure for connectivity of 5G points of presence (cells and towers) to the core network but also relies on using existing infrastructure such as LTE access points to achieve complete wireless coverage in areas where fiber infrastructure is not abundant.

Table 6.2 5G cell types.

Cell type	Intended commercial deployment	Number of users	Power (W)	Range
Femto	Residential and enterprise	4–8	0.2–1	Few tens of meters
Pico	Public areas (airports, malls, etc.)	64–128	1–5	Tens of meters
Macro	Urban	128–256	5–10	Few 100s of meters
Metro	Urban for additional coverage	>256	10–20	100s of meters

This chapter focuses on some of the 5G spectrum management techniques that are presented in research communities and standardization bodies. Note that 5G standardization gives a great deal of flexibility in dynamic spectrum management to the implementer, making the problem space of this area convoluted as there are different approaches to dynamic spectrum management and how it addresses challenges such as traffic allocation, network density, interoperability between the heterogeneous networks, and the use of orthogonal and nonorthogonal waveforms. The approach adopted in this chapter is to cover many DSM aspects without particularly diving into the details of building the cognitive algorithms that needs to be deployed in a service provider's network.

6.1 Basic Concepts of 5G

      This section focuses on basic concepts for 5G that are needed to understand DSM. The reader is encouraged to refer to 5G references for more details. 5G can be conceptualized through the possible deployment scenarios of the 5G cells. Let us consider the following three possible deployments:

      1 Standalone mm‐wave access. This deployment scenario is illustrated in Figure 6.1. One can think of dense urban deployments for this scenario where a high‐rise building would have most apartments using 5G cells connected to the core network through fiber links. This deployment scenario offers multiple access points to the end user and 5G calls for opportunistic serving of the end user where the cell that can offer the best service can be elected to serve the end user and hand over between cells can happen frequently.Opportunistic serving of an end user relies on DSM approaches. For example, the signal strength indicator from the different reachable cells can be used to decide which cell can be selected by the end‐user device as the access point. Other factors, such as the availability of services (a cell may have no more resources to allocate to a new end user), are also considered. Handover between cells also relies on signal strength and the calculation of self‐interference (SI) to decide which cell to switch to. This chapter elaborates more on how an end‐user device arbitrates between different access points.

      2 Nonstandalone mm‐wave access. With this deployment scenario, which is illustrated in Figure 6.2, the end user can get services through either a 5G cell or an LTE (or enhanced LTE) tower. Opportunistic serving is also used with this deployment scenario where the end user can connect through the cell or tower access point, selecting the access point that would offer the best services. The tower DSM algorithms may override the end user selection. One can conceptualize such a deployment scenario in suburbs where cell access relying on fiber cables to houses may exist offering high density mm‐wave access and high bandwidth reach to the core network through the fiber cables. This cell access does not cover all the areas, however, making the use of cellular towers using LTE or enhanced LTE necessary to create full wireless coverage.Notice in Figure 6.2 the difference between mm‐wave access depicted by the dotted small circles and the cellular tower access using the below 6 GHz range depicted by the gray circles and wider areas of coverage.

      3 The mm‐wave as an enabler. With this deployment scenario, which is illustrated in Figure 6.3, the mm‐wave is an enabler in the sense that the LTE or enhanced LTE