# Self-Optimizing Traffic Steering for 5G mmWave Heterogeneous Networks
## 2 Overview of mmWave HetNets
### Characteristics of 5G Networks and Devices
#### 2.1.3 Networks  
With the above available spectrum bands, there exist four kinds of networks, namely, the LTE network, LTE-licensed-assisted-access (LTE-LAA) (or LTE-U) network, WiFi network, and mmWave network. The main characteristics of these networks are summarized in Table 1 and elaborated upon in the following. * The LTE network is specifically designed to operate in the licensed spectrum under a centralized control of network protocols to prevent packet collision among subscribers. Therefore, LTE networks can provide stable transmission, reliable communication, and large signal coverage. However, the limitation of available licensed spectra is the major \begin{table}
\begin{tabular}{p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Candidate** & **Spectra** & **Merits** & **Demerits** & **Applications** \\ \hline LTE & Licensed & \begin{tabular}{c} Stable transmission, \\ reliable communication, \\ and large signal \\ coverage \\ \end{tabular} & Limited resources and low data rate & Voice communication, video conference, and location-based service \\ \hline WiFi & Sub-6 GHz unlicensed & Easy deployment, low cost, and quick access & \begin{tabular}{c} Large traffic congestion, \\ high dropping \\ probability, and unstable \\ QoS \\ \end{tabular} & Video and web browsing \\ \hline LTE-LAA & Licensed + sub-6 GHz & \begin{tabular}{c} Unified management, \\ megabit data rate, larger \\ coverage than WiFi, \\ butec QoS than WiFi, \\ lower cost than LTE, and \\ richer bandwidth than LTE \\ \end{tabular} & \begin{tabular}{c} Larger path loss than \\ LTE and harsher access \\ than WiFi \\ than WiFi \\ \end{tabular} & \begin{tabular}{c} New applications with \\ hundreds of megabits \\ per second data rate \\ requirement \\ \end{tabular} \\ \hline mmWave & Licensed + mmWave & \begin{tabular}{c} Affluent resources, \\ limited interference, \\ millisecond delay, and \\ gigabit data rate \\ \end{tabular} & \
\begin{tabular}{c} Small coverage, high \\ propagation loss, \\ sensitivity to blockage, \\ and complex hardware \\ \end{tabular} &
\begin{tabular}{c} New applications with \\ multi-Gbps data rate \\ requirement, such as \\ HDTV, UHDV, and \\ virtual reality \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of different networks. shortage of LTE networks. Hence, it can only support low data rate transmissions, e.g., voice communication, online conference, and location-based service. * The WiFi network utilizes the sub-6 GHz unlicensed band based on the carrier sense multiple access with collision avoidance (CSMA/CA) protocol that can reduce packet collision, such as the distributed contention-based IEEE 802.11-compliant standards. The main advantages of the WiFi network are its low cost, easy deployment, and quick/open user access. However, the quality-of-service (QoS) of WiFi users can be hardly guaranteed due to the distributive nature of WiFi protocols. Therefore, the WiFi network is mostly used for video, web browsing, and so on. * The LTE-LAA (or LTE-U) network allows users to access both licensed and sub-6 GHz unlicensed spectra under a unified LTE network infrastructure by carrier aggregation, which has already been defined in the 3 GPP Release 13 standard. Combined with the benefits from both licensed and unlicensed spectra, the LTE-LAA network can provide better link performance, higher data rate and larger coverage than the legacy WiFi network. Meanwhile, it has a lower cost and is more bandwidth-rich as compared with the LTE network. However, the coverage of the LTE-LAA network is generally smaller than that of the licensed LTE network due to the large channel path loss in the sub-6 GHz unlicensed band. Thus, LTE-LAA networks can support new applications with the data rate requirement of megabits per second. * The mmWave network is mainly focused on the 28 GHz band and other bands ranging from 30 GHz to 300 GHz, which can offer bandwidths up to 850 MHz in 28 GHz and even greater in other bands combined with further gains via directional beamforming.