# Study and Investigation on 5G Technology: A Systematic Review
## 5 Description of Novel 5G Features over 4G
### Small Cell  
Small cells are low-powered cellular radio access nodes which work in the range of 10 meters to a few kilometers. Small cells play a very important role in implementation of the 5G wireless network. Small cells are low power base stations which cover small areas. Small cells are quite similar with all the previous cells used in various wireless networks. However, these cells have some advantages like they can work with low power and they are also capable of working with high data rates. Small cells help in rollout of 5G network with ultra high speed and low latency communication. Small cells in the 5G network use some new technologies like MIMO, beamforming, and mmWave for high speed data transmission. The design of small cells hardware is very simple so its implementation is quite easier and faster. There are three types of small cell tower available in the market. Femtocells, picocells, and microcells [83]. As shown in the Table 12.  
MmWave is a very high band spectrum between 30 to 300 GHz. As it is a significantly less used spectrum, it provides very high-speed wireless communication. MmWave offers ultra-wide bandwidth for next-generation mobile networks. MmWave has lots of advantages, but it has some disadvantages, too, such as mmWave signals are very high-frequency signals, so they have more collision with obstacles in the air which cause the signals loses energy quickly. Buildings and trees also block MmWave signals, so these signals cover a shorter distance. To resolve these issues, multiple small cell stations are installed to cover the gap between end-user and base station [18]. Small cell covers a very shorter range, so the installation of a small cell depends on the population of a particular area. Generally, in a populated place, the distance between each small cell varies from 10 to 90 meters. In the survey [20], various authors implemented small cells with massive MIMO simultaneously. They also reviewed multiple technologies used in 5G like beamforming, small cell, massive MIMO, NOMA, device to device (D2D) communication. Various problems like interference management, spectral efficiency, resource management, energy efficiency, and backhauling are discussed. The author also gave a detailed presentation of all the issues occurring while implementing small cells with various 5G technologies. As shown in the Figure 7, mmWave has a higher range, so it can be easily blocked by the obstacles as shown in Figure 7. This is one of the key concerns of millimeter-wave signal transmission. To solve this issue,  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Approach** & **Energy Efficiency** & **Power Optimization** & **Latency** \\ \hline [PERSON] et al. [80] & Good & - & Average \\ [PERSON] and jha [16] & Good & Good & - \\ [PERSON] et al. [81] & - & Average & Average \\ [PERSON] et al. [82] & Average & - & Low \\ \hline \hline \end{tabular}
\end{table}
Table 11: Summary of Optimization Based Approaches in 5G Technology.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Types of** & **Coverage** & **Indoor** & **Transmit** & **Number** & **Backhaul** & **Cost** \\
**Small Cell** & **Radius** & **Outdoor** & **Power** & **of Users** & **Type** & **Medium** \\ \hline Femtocells & 30–165 ft & Indoor & 100 mW & 8–16 & Wired, fiber & Low \\  & 10–50 m & Indoor & 250 mW & 32–64 & Wired, fiber & Low \\ Picocells & 100–250 m & Outdoor & 24 dBm & 2000–500 mW & 200 & Wired, fiber, Microwave & Medium \\ Microcells & 1600–8000 ft & Outdoor & 2000–500 mW & 200 & Wired, fiber, Microwave & Medium \\  & 500–250 m & Outdoor & 32–37 dBm & & & \\ \hline \hline \end{tabular}
\end{table}
Table 12: Types of Small cells.  
the small cell can be placed at a short distance to transmit the signals easily, as shown in Figure 7b.