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cerns are addressed by data encryption and built-in VLAN support. Quite a few public network usage scenarios are discussed below [21].

3.7.2.1 Wireless service provider access network
WiMAX networks are used by Wireless Service Providers to offer connectivity to both housing (voice, data and video) and business (mainly voice and Internet) [26] clients, as shown in figure 3.7.

3.7.2.2 Rural connectivity
WiMAX networks are used by Service providers to bring service to underserved markets in rural areas and the suburban outer edges of cities, as shown in figure 3.8.

In many developing countries and underserved areas of developed countries, the delivery of rural connectivity is critical, where little or no infrastructure is available. Rural connectivity brings much-needed voice telephony and Internet service. Because of the extended coverage of WiMAX solution, it is a greatly more cost-effective solution as compared to wired technology in areas with lower population densities. WiMAX solutions can be installed rapidly, providing communication links to these underserved areas, providing a more safe environment, and helping to get better their local economies.

CHAPTER 4
QUALITY of SERVICE in IEEE 802.16  IEEE 802.16的服务质量

4.1 QUALITY of SERVICE (QoS)
QoS refers to the network's capability to offer improved service to elected network traffic over several technologies. The aim of QoS technologies is to prioritize (comprising committed bandwidth to manage jitter and delay) various real-time and interactive traffic, while ensuring that in doing so the other traffic doesn't stop working [25]. In licensed-exempt bands deployment is generally open to everyone, so they can be subject to QoS issues. However, there are progresses in the associated standards and technologies, that help alleviate harms with licensed-exempt bands, for example multi-path interference [14].

On the Internet and in other networks, the idea behind QoS is to calculate, enhance, and, to some degree, assure the transmission rates, error rates, and other characteristics in advance. QoS is of particular concern for the nonstop transmission of high-bandwidth. The wireless technology's capability to efficiently bring high value services for example voice and video is determined by Quality of Service. Latency, jitter, packet loss, load and throughput are the chief detractors to good QoS.

WiMAX presents lower delay across the wireless extent. There are many vendors having products with delay less than 10ms from BS to customer premises equipment and vice versa. Keeping that in mind, delay have to be calculated end-to-end. VoIP, for instance, is extremely vulnerable to delay. If delay go beyond 150ms for example, the conversation quality starts draging. At or beyond 200ms, conversation might be meaningless for several viewers.

The figure 4.1 shows that delay on the network's wireless section is smallest compared to that on network's wired section.

4.2 IEEE 802.16 QoS MECHANISMS at PHY LAYER
The 802.16 standard incorporates numerous QoS mechanisms at the PHY layer, for example Time Division Duplex (TDD), Frequency Division Duplex (FDD) and Orthogonal Frequency Division Multiplexing (OFDM). All can assist in providing QoS. TDD can dynamically distri本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。