## 2 Broadband System
### Worldwide Interoperability for Microwave Access (WiMAX)  
Another broadband wireless technology that is designed to offer Wi-Fi-type connectivity is WiMAX. It is a PtMP last-mile broadband wireless access scheme that offers standard-based solutions for portable, fixed, and mobile devices at a relatively wider range [16,182]. Furthermore, WiMAX can be based on LoS or NLOS wireless signal propa  
\begin{table}
\begin{tabular}{l l l l l l l l l l l l l} \hline \hline
**Standard** & **802.11** & **802.11a** & **802.11b** & **802.11c** & **802.11a** & **802.11c** & **802.11 ad** & **802.11 ad** & **802.11a** & **802.11a** & **802.11a** & **802.11c** & **Reference** \\ \hline \hline Advanced & 1997 & 1999 & 2003 & 2009 & 2013 & 2012 & 2014 & 2016 & 2019* & 2015* & 2017* & 2018* & 2018* & 2018* & 2018* & 2018* & 2018* & 2018* & 2018* \\ \hline Frequency & 2.4 & 5 & 2.4 & 2.4 & 2.4 & 5 & 60 & 2.4/5 & 2.4/5 & 2.4/5 & 40 & 2.5/5 & 40 & [8,112,173,174,175] \\ Input (GHz) & 2085 & PEBS & OFDM & DSSR & OFDM & OFDM & OFDM & SC/OFDM & OFDM & OFDM & SC/OFDM & [73,174,177] \\ \hline \hline Range (m) b  & 20 & 35 & 35 & 38 & 70 & 35 & 3.3 & 1000 & 1000 & 30048 & 10 & [73,174,177] \\ \hline Advanced & N/A & N/A & N/A & N/A & N/A & N/A & MIMO, & & & & & & & \\ numme & & & & & & & & & & & & & \\ subframe & & & & & & & & & & & & & \\ subframe & & & & & & & & & & & & & \\ \hline Bandwidth & 20 & 20 & 20 & 20 & 20 & 20,40 & 20,40 & 2010 & 6-6 & 1-16 & 20-160 & 8000 & [73,175,177,173,186] \\ (Oh) & & & & & & & & & & & & & & \\ \hline Data rate & 2 & 54 & 11 & 54 & 600 & 6003 & 675 & 5688 & 347 & 10,530 & 20,000 & [8,112,173,186] \\ (Oh)  & 20 & 35 & 35 & 38 & 70 & 35 & 3.3 & 1000 & 1000 & 3048 & 10 & [73,174,177] \\ \hline \hline Advanced & N/A & N/A & N/A & N/A & N/A & N/A & MIMO, & & & & & & & \\ subframe & & & & & & & & & & & & & & \\ subframe &gation, which enables it to operate both in PtP and PtMP configurations, respectively. Due to its ability to support a large coverage area, as well as capability to provide competitive and consistent broadband service, the NLOS systems are usually deployed by the operators for delivering large-scale broadband services [16]. Note that WiMAX products and specifications are based on the IEEE 802.16 group wireless metropolitan area networking standards with well-defined air interface protocols. Furthermore, note that its preliminary specifications and products focused on fixed-broadband solutions. However, they have been amended to support mobile services, majorly to enhance the use cases and market prospects [16; 182]. Consequently, wireless broadband services such as nomadic, fixed, and mobile have been provided based on NLOS communication [16]. In addition, WiMAX has been attracting considerable attention as a promising next-generation wireless broadband technology that can be employed not only for backhauling Wi-Fi hotspots but also deployed for metro access coverage [132]. Furthermore, Mobile WiMAX has been recognized as an IMT2000 technology as well as an attractive candidate for IMT-advanced. Advanced schemes such as multi-antenna system and orthogonal frequency division multiple access (OFDMA) technology are employed in the mobile WiMAX air interface [182]. Table 5 presents basic data on IEEE 802.16 standards. Typically, for portable and fixed access applications within 3 to 9 km cell radius deployment, WiMAX systems intend to offer up to 75 Mbps capacity per channel, while for mobile network deployments up to 15 Mbps capacity is envisaged within up to 3 km cell radius. Nevertheless, the existing realistic bandwidth capabilities are relatively lower. Furthermore, being a shared bandwidth technology, the eventual bandwidth offered to the subscriber could be lesser than the channel capacity. Besides, the achievable bandwidth depends on the number of subscriber per-channel contention ratio [16; 182]. Consequently, due to the relative bandwidth limitation, WiMAX might not be able to support ubiquitous high-data-rate broadband services for the envisaged massive devices [16; 182].