Wavtrace Awarded PTM System Patent

The U.S. Patent and Trademark Office has awarded Wavtrace Inc. (Bellevue, WA) patent protection for the invention of adaptive time division duplex (TDD) point-to-multipoint (PTM) millimeter wave systems. The patent, number 6,016,313, filed Nov. 6, 1996, was awarded Jan. 18, 2000. Robert Foster, Wavtrace's founder and chief technology officer, filed for a series of patents related to adaptive TDD and other aspects of third generation point-to-multipoint systems. This patent is the first to be awarded. Foster's invention marked the launch of Wavtrace and a new generation of millimeter wave point-to-multipoint technology.

Adaptive TDD is the method of establishing a bi-directional communications link using a single channel, whereby any part of the channel up to its full capacity can be used in either the upstream or downstream direction in response to demand. TDD's adaptability when combined with other dynamically adjustable system parameters, such as variable information densities, link distances, and the sharing of bandwidth among remote units, allows for an efficient system design, providing 20 to 50% greater throughput than systems using older FDD technology (depending on level of asymmetry).

The patent is comprehensive and includes 86 claims covering not only the adaptive TDD airlink, which allows variable asymmetry, but also many other aspects of point-to-multipoint system design. These include the design of the hub, remote, antenna array, modem array, variable index QAM (quadrature amplitude modulation), and interface to the backbone network.

Evolution
Wavtrace's third generation adaptive TDD technology fulfills the vision that gave rise to the PTM industry: to maximize the savings inherent in sharing bandwidth resources among multiple remote sites.

• First generation PTM used frequency division duplexing (FDD) and frequency division multiple access (FDMA) that introduced the sharing of capacity among remotes by dividing bandwidth into slices. This allowed sharing of capacity downstream, but because each remote had its own dedicated slice of bandwidth on the upstream, it offered only a modest gain in spectral efficiency.
  
• Second generation PTM incorporated time division multiple access (TDMA) with FDD to introduce time sharing of both downstream and upstream capacity among remotes. This offered a significant improvement in spectral efficiency, yet still relied on FDD to establish separate and dedicated downstream and upstream links.
  
• Third generation PTM incorporates adaptive TDD and introduces the sharing of capacity between both upstream and downstream links. This approach offers the greatest improvement in spectral efficiency.

Edited by Ellen Jensen