The lack of this feature motivates the work presented in this chapter. Furthermore, in order to validate and evaluate the designed solution, a set of QoS oriented scenarios have been simulated in Network Simulator NS-2 [xlink-NIST], demonstrating that the designed model is able to efficiently differentiate users in a competitive environment, differentiating between the traffic classes defined for WiMAX, mainly in throughput and delay metrics.
The reminder of this chapter is organized as follows. Section 4 describes the proposed QoS model, including the packet classification mechanism and the scheduler, whereas Section 5 discusses the obtained simulation results for several scenarios. Finally, Section 6 concludes the chapter. Ubiquitous broadband Internet access is an important requirement to satisfy user demands and support a new set of real time services and applications. IEEE Therefore, all tasks are based on a connection, uniquely identified by a bit Connection Identifier CID , and no packets are allowed to traverse the wireless link without a specific connection allocated.
Five scheduling services are defined to meet the QoS needs of the data flows carried over the air link:. The service offers fixed size unsolicited data grants transmission opportunities on a periodic basis.
Unicast grants are provided to the MSs in an unsolicited manner, like in UGS, and therefore the latency of a bandwidth request message is saved. The service offers unicast polls on a periodic basis but uses more space intervals then rtPS.
This ensures that the flow receives request opportunities even during network congestion;. Best Effort BE : designed for traffic where no throughput or delay guarantees are provided. A set of convergence sublayers are defined to map the upper layer packets into the Both point-to-multipoint PMP and mesh modes of operation are supported by the standard, despite the mesh mode of operation is optional.
Finally, to satisfy the contracted services, transport connections are allocated for data packets. With respect to the IEEE Figure 1 illustrates the IEEE The interface between the The Each connection has a specific service flow associated providing the necessary QoS requirements for that packet.
If no classifier is found for a specific packet, a specific action must be taken. Since the classifier implementation is vendor dependent, the chosen decision depends on the algorithm implemented by the vendor — the packet can be discarded, sent on a default connection, or a new connection can be established for it, if enough resources are available.
Two main types of CSs are defined within the standard for mapping services to and from the It receives classified packets arriving from the CS and is responsible for a set of functions, such as addressing, construction and transmission of the MAC PDUs, scheduling, bandwidth allocation, request mechanisms, contention resolution, among others.
Finally, the PS is the third and last sublayer from the MAC layer and provides authentication, data encryption and security mechanisms. Since the IEEE Using this model, multiple implementation options for a given functional entity are allowed, maintaining interoperability across them through the RPs.
Additionally, it also performs relay functions to the CSN in order to establish IP connectivity and authentication mechanisms. The xlink IEEE Nevertheless, the overall architecture is set on top of a basic subset of IEEE However, information coding is yet missing and hence the module does not support any Adaptive Modulation and Coding AMC scheme.
The TDD duplexing technique is illustrated in Figure 3 , presenting both downlink and uplink subframes decomposition. Following the FCH, starts the downlink data bursts section. At the end of the frame, the Transmit Transition Gap TTG is used to separate the downlink and the following uplink bursts.
In the beginning of the uplink subframe there are two contention slots. Given these parameters, the module is able to compute the OFDM symbol duration, packet transmission time per modulation, maximum packet size per modulation and the number of OFDM symbols.
As the implemented architecture is an extension of the NS-2 wireless networking sub-module, the standard NS-2 channel models and transmission power levels can be set accordingly to the NS-2 standard tools [xlink]. Although the module can be easily extended, the Packet CS is essentially a classifier, supporting the IP destination address as the classifier parameter. The connection oriented nature of IEEE As the IEEE With respect to mobility, channel scanning, communication parameters negotiation, initial ranging and registration, the provided implementation adheres largely to IEEE Periodic ranging used to adjust coding and modulation is left out for now.
Finally, the most crucial missing feature, which motivates this work, is the lack of a complete The software has been prepared for future QoS integration but it was not implemented.
Despite scheduling services, service flows and a basic bandwidth request mechanism for BE Best Effort traffic is available, the current scheduler implements a simple Round-Robin discipline for the scheduler. As defined in the The creation of these new connections required the addition of new CID ranges, providing each peer node a unique CID for these types of traffic. These modifications were performed in the existing DestClassifier class.
To improve the packet classification mechanism, the QoSClassifier class was implemented, also as a subclass of the SDUClassifier class. Classifier Class Diagram. The most important method to implement the classification is the classify method, called for all packets, which finds the appropriate PeerNode based on the destination address and QoS requirements.
Thereafter, based on the packet type, the packet is sent to the appropriate connection queue on the scheduler, as illustrated in Figure 5.
Packet Classifier Diagram. For each one of these service classes, a range of transport CIDs for the data connections was given. Apart from this association, modifications throughout the different functions that make use of the service classes were made. In this case, a new type of connection is distinguished according to its type and respective CID.
Scheduler Class Diagram. This section is devoted to the results and performance evaluation of the implemented QoS model. In order to evaluate the modifications to the existing NIST model, several simulation scenarios were implemented to test QoS using distinct network topologies. The obtained results use performance metrics, such as packet loss, latency, jitter and bandwidth usage, and also make use of differentiated traffic sources for each service class. The tested network topologies consider differentiated traffic going in the uplink direction from different hosts.
The fixed line of sight LOS operation claims to provide a range of 35 miles with data rates up to 70 Mbps, and the non line of sight NLOS claims to provide a typical range of several miles with data rates of 2 to 63 Mbps depending on available bandwidths. Today, both applications of WiMAX technology are standardized, implemented in integrated circuit chipsets, and about to be deployed in the commercial market 6. Because this technology was developed for commercial licensed applications, the quality of service feature was well established, thus, it can support differentiated service levels.
The WiMAX Forum, serving as the industry lead, is developing specifications for conformance, interoperability and certification set of profiles that leverage the standards-based technical specifications defined by the standards bodies. However, it will face competition in the near future with nascent advanced broadband wireless technologies such as the 3G-LTE Long Term Evolution technologies currently under development.
Both have considerable promise for serving the public safety community with broadband capabilities. Currently, mobile WiMAX can be implemented in three spectrum bands 2. However, the technology is applicable in other bands as well remember - a standard looking for some spectrum? For example, it can be applied even in some unlicensed and public safety bands such as 2. Due to such wide operational spectrum bands, the WiMAX Forum is developing feature sets - or profiles - to meet worldwide interoperability within each profile.
Additional work to extend WiMAX into other spectrum bands such as 4. Also, a profile for the newly available MHz spectrum is expected soon. It uses various channel bandwidths of 1. It supports duplexing schemes of TDD Time Divisional Duplex where the uplink and downlink transmissions occur at different times and share the same frequencies, which has considerable throughput advantages by way of allocating flexible bandwidths for downlink and uplink.
The mobile version of FDD Frequency Divisional Duplex where the uplink and downlink channels are located on separate frequencies is planned to be added in a later version of the mobile WiMAX profile to support local regulations that do not allow the TDD scheme. The range of coverage is up to 30 miles with the downstream peak data rates up to 46 Mbps and upstream rates up to 7. The access protocol supports multimedia applications on a single integrated platform with the provision of quality of service mechanism to enable differentiated services among multiple users.
Overall, mobile WiMAX technology is one of the emerging broadband access technologies that delivers higher speed data applications covering wider areas and has evolved beyond initial fixed wireless access for residential and enterprise applications.
Public safety communication systems can leverage various WiMAX operational capabilities to benefit meeting PS fundamental requirements involving interoperability, reliability, ubiquity, flexibility, and security. In particular, WiMAX technology has some advantages for public safety use that are summarized below:. With this look at WiMAX - a next generation fixed and mobile technology - we have moved a bit away from our initial premise, which was public safety interoperability.
In our next note, we'll come back to this basic theme by considering the current interoperability channel allocations that exist by FCC designation. In conclusion, I'd like to extend my sincere thanks to my colleague, Yoon Chang, for his assistance with this article. With the aim of enhancing the user experience for wireless portable, mobile, and home entertainment devices, the Wi-Fi Alliance's testing and certification programs help ensure the interoperability of WLAN products based on the IEEE It is also frequently referred to as "fixed WiMAX" since it has no support for mobility.
It introduced support for mobility, amongst other things and is therefore also frequently called 'mobile WiMAX'". The following table summarizes some of the key attributes of the WiMAX technology standard. In particular, WiMAX technology has some advantages for public safety use that are summarized below: Extended range over existing Wi-Fi systems. Applicability to dedicated public safety spectrum that is not shared with the public at large.
Fixed and Mobile standards-based technologies consistent with potentially similar commercial mobile cellular systems developments. Higher data rates support full range of applications including voice, data, and video.
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