## 2 Broadband System
### Mobile Network Evolution
It includes support for OFDM-based multi-antenna schemes, spatial multiplexing, and channel bandwidth up to 20 MHz. However, the UMB is not backward compatible with the earlier CDMA2000 standards [20; 21; 22; 22]. Besides, although the 3G mobile system can support up to 2 Mbps broadband data transmission, the associated capacity is inadequate to make the 3G system a key broadband technology market competitor. Consequently, mobile 3G has been offering complementary broadband services [16]. 4. 4G Mobile Systems: The 4G mobile communication is well-signified by the LTE technology. Compared with HSPA, LTE not only offers higher efficiency, but also further improves the mobile-broadband experience regarding the achievable end-user data throughputs. The offered improvement is a result of the implemented advanced schemes such as OFDM and multi-antenna technologies that present wider transmission bandwidths. In addition, 3G supports mobile communication in the unpaired spectrum, whereas LTE offers both time-division duplex and FDD operations. Therefore, within a common radio-access technology, LTE accommodates operation in both unpaired and paired spectra [21]. 5. 5G Mobile Systems: The 5G network is the mobile telecommunication system that was officially launched in 2020. Basically, it is envisaged to transform mobile networks and considerably improve the existing 4G/LTE network performance. Furthermore, it is expected to support many advanced radio technologies such as network slicing, to facilitate quick deployment of different services; Information-Centric Networking (ICN), for the reduction in network traffic; Software-Defined Networks (SDN), to ensure sufficient network flexibility; and Massive MIMO and millimeter-wave for enhancing the system capacity [218; 219]. Moreover, it is envisaged to deliver enhanced transmission rates with a minimum rate of 1 Gbps so as to offer an outstanding mobile experience through an eMBB. Similarly, it should offer end-to-end latency of about 1 ms or less to support ultra-reliable and low-latency (URLLC) applications. Apart from the performance improvement regarding substantial high data rates and low latency, massive connection density based on massive machine-type communications (mMTC), as well as other improvements, are anticipated. In this context, use cases such as mMTC, eMBB, and URLLC have been defined by the International Telecommunication Union (ITU) for the 5G networks [218]. Furthermore, the 5G system is a converged network in which wired and wireless systems are to exploit the same infrastructure [220]. In general, 5G is an integrated network that will cooperatively operate for efficient and seamless communication, resulting in a fiber-like user experience [19; 48; 208]. Note that as the 5G network deployment is in its early stage, different teething problems are envisaged. Besides, like its predecessor networks, 5G might not be able to stand the test of time in offering future system requirements regarding full connectivity. Therefore, research attention should be focusing on beyond 5G wireless communications [218]. 6. Network 2030 and Beyond: The low-frequency spectrum band is capable of long-distance propagation and consequently can support wide coverage. However, owing to its relatively narrow bandwidth, the achievable transmission rate is significantly low. Furthermore, due to the growing increase in traffic and the associated network requirements, the mm-wave band is recommended for the 5G. This band can offer bandwidths in the order of some gigahertz. However, with the current trend in the traffic increase, the mm-wave band may not be an efficient solution that can effectively meet the bandwidth requirements of the Network 2030 (6G and Beyond). In the light of this, the International Telecommunication Union (ITU) has established another ITU Focus Group for Network 2030. The Group aims to guide the global information and communications technology (ICT) community in the analysis of the network capability for the year 2030 and beyond.