Method and apparatus for multi-dimensional channel sounding and radio frequency propagation measurements
View Patent ↗Apparatus and methods facilitating a distributed approach to measuring the RF propagation characteristics of an indoor area or region are described. Such measurements are particularly useful during the installation and management of indoor wireless data communication networks, such as Wireless Local Area Networks (WLANs). A plurality of sounder units may be geographically distributed at arbitrary points in a two-dimensional area surrounding the indoor area or region whose RF propagation characteristics are to be measured. These sounder units are linked to a central controller, which functions to control all of the sounder units as well as to maintain a user interface that provides a user with a display of the measured propagation characteristics of the region. Each sounder unit is capable of independently injecting RF stimulus signals with some desired radiation pattern into the region being measured, as well as recording received signals from which the RF propagation characteristics may be calculated. The central controller co-ordinates the set of sounder units to ensure that they act as a logical whole, and also enables propagation measurements to be made over long periods of time in order to capture time-varying characteristics of the indoor environment.
1. A distributed radio frequency (RF) propagation measurement system for automatically characterizing RF properties of a predefined physical space, said system comprising:
a single central controller;
a plurality of sounder units controllable by said central controller, each sounder unit including,
antenna array means adjustable for directionally transmitting and receiving RF energy,
a channel sounder transmitter,
a channel sounder receiver, and
a processing means for calculating a plurality of power-delay profiles from RF energy received by said channel sounder receiver;
synchronization means for aligning frequency and phase of said channel sounder transmitters and said channel sounder receivers within said plurality of sounder units;
communication means for transferring data and commands between said central controller and said plurality of sounder units;
location determining means to measure position of said plurality of sounder units within said predetermined physical space;
software means for sequencing operation of said plurality of sounder units, adjusting directionality of said antenna array means and combining said plurality of power-delay profiles obtained from said plurality of sounder units in conjunction with said location determining means to obtain RF scattering and attenuation properties; and
control means for controlling said plurality of sounder units in accordance with said software means;
wherein said distributed RF propagation measurement system automatically obtains RF scattering and attenuation properties in at least two dimensions within said predefined physical space.
2. The system as claimed in claim 1 wherein said central controller is embodied in software executed by a host computer, said software for performing user interface functions along with communication and coordination of said plurality of sounder units forming said distributed channel sounder.
3. The system as claimed in claim 1 wherein said antenna array uses beamforming means to transmit and receive RF energy with distinct directional characteristics.
4. The system as claimed in claim 3 wherein said antenna array and beamforming means further include operational mechanisms for performing operations selected from the group consisting of phasing, gain control, power division, and power combining.
5. The system as claimed in claim 1 wherein said channel sounder transmitter generates RF stimulus signals that are transmitted into said predefined physical space.
6. The system as claimed in claim 5 wherein said channel sounder receiver processes RF signals received from within said predefined physical space and obtains said power-delay profiles indicative of RF propagation channel characteristics.
7. The system as claimed in claim 1 wherein said location determining means measures a precise three-dimensional coordinate of each of said plurality of sounder units relative to said central controller.
8. The system as claimed in claim 7 wherein said location determining means is configured for use with a Global Positioning System (GPS).
9. The system as claimed in claim 7 wherein said location determining means uses an independent location determining capability that employs pseudolites to provide accurate spatial references from which three-dimensional vectors are computable.
10. The system as claimed in claim 7 wherein said sounder units communicate said precise three-dimensional coordinates of each of said plurality of sounder units to said central controller.
11. The system as claimed in claim 1 wherein said communication means uses a dedicated Ultra High Frequency (UHF) radio data link to communicate with said central controller.
12. The system as claimed in claim 1 wherein said control means resides as software within an embedded controller, and controls and coordinates activities of said distributed channel sounder formed by said plurality of sounding units.
13. The system as claimed in claim 1 wherein said control means resides as software within a Central Processing Unit (CPU), and controls and coordinates activities of said distributed channel sounder formed by said plurality of sounding units.
14. The system as claimed in claim 1 wherein said channel sounder transmitter and said channel sounder receiver are formed by a sliding correlator function.
15. The system as claimed in claim 1 wherein said synchronization means includes clock synchronization signals derived from location determining signals utilized by said location determining means.
16. The system as claimed in claim 1 wherein said predefined physical space is a Wireless Local Area Network (WLAN).
17. The system as claimed in claim 1 wherein said predefined physical space is a Wireless Local Area Network (WLAN) and said distributed channel sounder performs RF propagation measurements in three dimensions.