Section 9.6. Summary


9.6. Summary

While the fundamental principles of networking are the same regardless of the underlying physical layer, UWB has unique characteristics that influence how protocols and a UWB system are designed. A UWB network can be represented by a five-layer model, compatible with the TCP/IP suite, that includes a UWB physical layer, associated data link layer, network layer, transport layer, and application layer. Each layer provides services to the layer directly above it and uses services provided by the layer beneath it. The unique characteristics of the UWB physical layer have the greatest influence on the design of the data link layer. The characteristics of the physical layer and the design of the associated data link layer may also influence the design of the network layer, transport layer, and even application layer, especially if a design is to achieve optimal performance.

A hybrid TDMA/CDMA medium access scheme has good properties for a UWB network because of its flexibility that allows, for example, differentiated services and channel allocations to minimize interference.

A hierarchical topology, rather than a flat topology, has significant benefits for a UWB network. A hierarchical topology supports a hybrid architecture where a selected node in a cluster, called a cluster head, can coordinate the assignment of spreading codes, power control, and other local functions, while also participating in a longer range, multiple hop, backbone network. The Bluetooth scatternet model uses such a hierarchical topology and serves as a good model for UWB multiple hop networks. In a scatternet, clusters are interconnected by cluster heads and gateway nodes. A number of scatternet formation protocols have been proposed.

There are a variety of different routing protocols for multiple hop ad hoc networks. Because no single routing protocol is the best for all types of networks, different routing protocols may be used for different situations.

Beyond scatternet formation and routing, there are additional network-related issues in a UWB network. In particular, there are several mechanisms to improve TCP performance over wireless links, including hiding packet losses from TCP, splitting an end-to-end TCP connection into two separate connections, and using explicit loss notifications. All three schemes have their advantages and disadvantages, and none of them have been implemented on a large scale. Quality of service and QoS management are also potential issues in a UWB network. In general, network protocols need to be able to adapt based on data traffic characteristics, QoS constraints, and link impairments.

Because UWB networking is such a new technology, many advances will be made that improve network-level and application-level performance. Of particular interest to researchers is the information that is potentially available in a UWB network that is not available in a traditional wireless network. Nodes in a UWB system can share an extremely accurate understanding of time with their peers and can determine the distance to neighboring nodes. Nodes located in one network can also cooperatively determine the location of other nodes in the same network [47]. This information can potentially be used to fundamentally alter the way that networks allocate channel resources and route packets, thus leading to novel network architectures and protocols that fully exploit the capabilities of UWB.



    An Introduction to Ultra Wideband Communication Systems
    An Introduction to Ultra Wideband Communication Systems
    ISBN: 0131481037
    EAN: 2147483647
    Year: 2005
    Pages: 110

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