Hamilton W. Arnold

Architecture and implementation of an efficient and robust TDMA frame structure for digital portable communications

The architecture and implementation of a TDMA (time-division multiple access) digital portable communication system using short bursts are considered. The authors describe an efficient and robust TDMA frame structure that requires very low overhead for burst demodulation and synchronization while being robust against both fading and carrier frequency offset. Based on this frame structure, an experimental radio link was implemented, using a hardware architecture that is suitable for digital signal processing and VLSI implementation. Performance results are presented.<<ETX>>

28 GHz local multipoint distribution service (LMDS): strengths and challenges

Local Multipoint Distribution Service (LMDS) is a terrestrial point-to-multipoint radio service providing wireless broadband access to fixed networks. LMDS could be used to provide wireless access to services ranging from one-way video distribution and telephony to fully-interactive switched broadband multimedia applications. Multiple hub transmitters that communicate via point-to-multipoint radio links with subscribers at fixed locations throughout the service area are placed in a cellular-like layout. LMDS systems attempt to completely reuse the frequency band in each cell through the use of highly directional subscriber antennas and polarization reuse in adjacent cells. Proposed LMDS system architectures differ in terms of cell size, modulation, and hub antenna type. This paper describes the potential service offerings and technical characteristics of LMDS systems. Publicly available system design information was gathered from the FCC Negotiated Rulemaking Committee (NRMC) on co-frequency sharing in the 28 GHz band between LMDS and satellite services. This paper also describes some of the challenges that face LMDS such as a “fragile” propagation environment. The results of a propagation measurement campaign at 28 GHz in Brighton Beach, Brooklyn, to investigate the performance of Local Multipoint Distribution Service (LMDS) indicate that building blockage is a major limitation on the ability to cover a particular location. Strong signals were only received at locations where a line-of-sight path was available between the transmitter and receiver.

Interference, sensitivity and capacity calculations for measurement-based wireless access spectrum sharing

Interference caused by multiple uncoordinated low-power wireless access system transmitters to fixed point-to-point microwave receivers is analyzed. The analysis shows that the density of wireless access system users that can share spectrum with a point-to-point microwave system depends critically on the propagation relation, the threshold of detecting energy from point-to-point transmitters, and the allowable interference into point-to-point receivers. It is found that for reasonable assumptions of point-to-point link, wireless access system, and propagation parameters, a wireless access system employing measurement-based interference avoidance must detect energy of point-to-point transmissions far below the thermal noise floor of the wireless access system receivers which would increase their complexity. The implications to local exchange networks of wireless system alternatives that could provide access to those networks are addressed.

A beacon detection method for sharing spectrum between wireless access systems and fixed microwave systems

A measurement-based frequency sharing technique using an alternative to detecting power from existing point-to-point microwave transmitters is proposed. In this technique, continuous wave (CW) beacon signals are transmitted through every point-to-point microwave receiver antenna system. Each beacon protects its corresponding microwave receiver by identifying the frequency of the point-to-point receiver. Appropriately designed beacon signals can be adequately detected with simple receivers. This technique allows a higher density of simultaneous uncoordinated wireless access system transmissions, without causing interference to point-to-point receivers, than could be achieved using path loss models to design geographic exclusion zones or by detecting energy from point-to-point transmitters.