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 access is already present and 5G cells can be added incrementally to the area. This scenario can be conceptualized at the start of early deployment of 5G in a given suburbs area as well as in rural areas where coverage can be sparse and fiber cables connectivity availability is limited. 5G cells can be added gradually to the area as user demand increases.One important aspect of this deployment scenario is the mm‐wave backhaul links where 5G cells can be deployed without the need for fiber cable connectivity. A 5G cell dropped anywhere can connect to the tower through a high capacity mm‐wave point‐to‐point wireless link. This ability to just deploy a 5G cell in a busy area that will find the closest tower and establish a mm‐wave point‐to‐point wireless link to the tower to flexibly offer 5G services is an important aspect of DSM. The concept of a self‐organized network (SON) is a core 5G capability.
Figure 6.1 Standalone mm‐wave 5G access.
Figure 6.2 Nonstandalone mm‐wave 5G access.
Figure 6.3 5G access with the mm‐wave as an enabler.
So far, this section has showed that 5G can use the following two features that are related to DSM:
Opportunistic serving with which an end user can find the best suitable access point to use and frequent handover to a different access point at any time using metrics such as signal strength.
5G as an enabler where a 5G cell can be deployed in an area without needing fiber cable connectivity and the cell establishes a wireless mm‐wave point‐to‐point link to the closest tower as part of the 5G SON. This mm‐wave link should impact dynamic DSM decisions as explained later in this chapter.
Part 1 of this book alluded to military communications systems approaches to DSA with MANET nodes, which include:
1 using directional antennas
2 using adaptive power control.
3 spectrum allocation of planned spectrum and opportunistic use of unlicensed spectrum
4 the continual change of spectrum allocation due to mobility.
5G has similar concepts that influence DSM. For example, 5G considers full duplex (FD) wireless communication which enables the radio to directionally transmit and receive on the same frequency band simultaneously.3 FD is considered because of the many advantages it brings, such as increasing transmission capacity and reducing end‐to‐end feedback delays while performing concurrent sensing.4 FD implementation comes with many challenges, however, such as the need to mitigate SI. 5G implementers use different SI cancellation techniques such as analog and digital antenna cancellation. The rest of this chapter will present 5G‐related DSA techniques, such as SI mitigation, in separate sections.
6.2 Spatial Modeling and the Impact of 5G Dense Cell Deployment
Commercial cellular technologies before 5G depended critically on spatial configuration and the separation of downlink (DL) and uplink (UL) frequencies. Frequency allocation to base stations ensured that interference from other base stations is minimal. In spread spectrum systems such as 3G and LTE, the base station assigns different spreading codes to the different end users to mitigate interference on the UL. Mobile end users can hand over from one base station to another while switching to a different frequency and after obtaining a different spreading code from the new base station. Figure 6.4 shows an oversimplified frequency planning illustration for a pre‐5G cell tower deployment where seven frequency bands can be reused spatially to create full spectrum coverage. Factors such as terrain and weather can change this plan and cellular providers rely on comprehensive testing of the cellular infrastructure performance to change the frequency allocation of such a simple plan where areas that have more dense end users can use more base stations with more frequency bands to add capacity where demand is higher.5
