## 2 Broadband System
### Worldwide Interoperability for Microwave Access (WiMAX)
Apart from being a wireless solution for direct-to-home digital TV/radio broadcasting services, Direct Broadcast Satellite (DBS) can also support two-way remote telephoning and high-speed Internet access to the subscribers. In DBS, geostationary satellites that are operating in the Ku band are usually employed. The downlink (DL) and UL frequencies are 12 GHz and 14 GHz, respectively. A typical DBS architecture can be PtP or PtMP topology, as depicted in Figure 7. A digitized video and data composite signal from the Earth station is relayed through broadcast from the satellite to the required subscribers' location [16]. The subscriber can send and receive data through a rooftop installed satellite dish [19]. \begin{table}
\begin{tabular}{l l l l l} \hline \hline  & **802.16** & **802.16-2004** & **802.16e-2005** & **Reference** \\ \hline Completed & December 2001 & June 2004 & December 2005 & [159; 183] \\ \hline Frequency band & 10–66 GHz & 2–11 GHz & 2–11 GHz for fixed; 2–6 GHz for mobile applications & [183; 184; 185; 186; 187; 188] \\ \hline MAC architecture & PtMP, mesh & PtMP, mesh & PtMP, mesh & [183; 185; 185] \\ \hline Application & LoS, fixed & NLOS, fixed & NLOS, fixed and mobile & [183; 184; 185; 186; 187; 188] \\ \hline Gross data rate & 32–134.4 Mbps & 1–75 Mbps & 1–75 Mbps & [183; 184; 185; 186; 187; 188] \\ \hline Modulation & QPSK, 16-QAM, 64-QAM & QPSK, 16 QAM, 64 QAM & QPSK, 16 QAM, 64 QAM & [183; 184; 186; 187; 188] \\ \hline Transmission scheme & SC only & SC, 256 OFDM or 2048 OFDM & SC, 256 OFDM with 128, 512, 1024, or 2048 subcarriers & [183; 185; 186] \\ \hline Multiplexing & Burst TDM/TDMA & Burst TDM/TDMA/OFDMA & Burst TDM/TDMA/OFDMA & [183; 186; 187] \\ \hline Cell radius & Over 10 km & 7–10 km & 2–5 km & [184; 185] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Basic data on IEEE 802.16 standards. Furthermore, typical achievable data rates are between 16 kbps and 155 Mbps [16]. Besides, it has been noted that there is a high similarity between satellite broadband and DSL broadband regarding the cost and performance. Moreover, although the fiber solution offers relatively superior performance, the required roll-out time and cost make its deployment unsuitable for an immediate solution. On the other hand, satellite solution's accessibilities are instant. This makes DBS a nice solution for areas without or with limited terrestrial or wireless broadband access [19]. However, about 250 ms delay could be experienced in this kind of network. The associated network delay is mainly due to the geostationary satellites that are located at about 22,300 km from the surface of the earth. Noted that in some broadband applications and services, the resulting latency is unacceptable for effective operation. This challenge can be alleviated with the aids of a network of satellites (around 700 per system) in the low Earth orbit (LEO) which are located at \(\sim\)1000 km from the earth's surface. Consequently, with LEO implementation, the signal propagation delay is comparatively lower. Subsequently, the latency can be reduced to about 50 ms. Note that the LEO implementation may demand an entirely different antenna constellation at the subscriber end. In addition, as DBS is based on the constrained RF spectrum, its capacity is limited by the available bandwidth [16; 19]. Based on the advantages of SDN, its integration with LEO satellite networks can offer more flexible network monitoring and management. Besides, it can considerably facilitate network expansion [50].