the project
Project Goals

Our objective is to design, analyze, prototype, and experimentally study the theoretical underpinnings for a wireless Internet that simultaneously achieves deployability, scalability, high-performance, and a cost-effective economic model. A core building block will be what we call wireless Transit Access Points (TAPs). By removing the requirement for each access point (AP) to have a wired connection to the Internet, we envision an architecture with a multihop mesh of fully wireless TAPs communicating among each other, multihop wireless mobile units (MUs), and the wired Internet (see Figure 1). Unfortunately, simply removing the wires of APs and treating the system as a large ad hoc network is not enough. One reason is capacity: if the scarce spectrum is used for packet forwarding as well as "access," the system capacity limits will dramatically degrade to the well-known scalability limits of ad hoc networks. Such a network would suffer from low throughput and high delay due to excessive contention and variable channel conditions.

Thus, to achieve high performance and scalability, wireless TAPs (which are non-mobile and non-battery- powered) form an interconnected mesh using MIMO such that the connections between all TAPs form a wireless "backbone" and enable a high degree of spatial reuse. Moreover, a wired TAP also has a connection to the wired Internet (TAPs B and E in Figure 1) that can have diverse capacity, ranging from 100s of kb/sec (DSL-range capacity) to 100s of Mb/sec (e.g., Ethernet, Gigabit Ethernet, and OC-X access links).

In this architecture, mobile users, such as G and H in Figure 1, will have their packets forwarded by other mobile users before reaching a TAP and then possibly forwarded through a number of wireless TAPs to the wired network; multihop forwarding through mobile users is important since the transmission range of all TAPs will not necessarily provide complete "coverage" to a region due to economic reasons, environmental obstructions, or lack of a suitable power source. Thus, the objective of the TAP architecture is to leverage the vast base and economics of existing IEEE 802.11 devices and provide a key building block for a scalable, deployable, high-rate wireless Internet.

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Transit Access Points (TAPs)
ECE Department, MS 380
Rice University
6100 Main Street
Houston, Texas 77005-1892