System for short range wireless data communication to...

Details System for short range wireless data communication to... System for short range wireless data communication to...

1998-07-17

2001-01-23

Horabik, Michael (Department: 2735)

Communications: electrical

Selective

Interrogation response

C370S229000, C340S010200, C340S010300

Reexamination Certificate

active

06177861

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to wireless communication systems and, more particularly, to a system for a wireless communication system that provides short range communications to inexpensive endpoints.
BACKGROUND OF THE INVENTION
It is desired to develop a system to support short range wireless data communication to inexpensive endpoints. Radio Frequency IDentification (RFID) systems are radio communication systems that communicate between a radio transceiver, called an Interrogator, and a number of inexpensive devices called Tags. RFID technology may be appropriate to consider in the development of such a system. In RFID systems, the Interrogator communicates to the Tags using modulated radio signals, and the Tags respond with modulated radio signals. Typically, communications from the Interrogator to the Tag utilize amplitude modulated radio signals, which are easily demodulated. For communications from the Tag to the Interrogator, Modulated BackScatter (MBS) is a commonly used technique. In MBS, the Interrogator transmits a Continuous-Wave (CW) radio signal to the Tag. The Tag then modulates the CW signal using MBS where the antenna is electrically switched, by the Tag's modulating signal, from being an absorber of RF radiation to being a reflector of RF radiation; thereby encoding data from the Tag onto the CW radio signal. The Interrogator demodulates the incoming modulated radio signal and decodes the Tag's data message. For Tag to Interrogator MBS communications, prior art maintains the use of Frequency Shift Keying (FSK) modulation and Phase Shift Keying (PSK) techniques for communications.
What is needed is a communications system that will allow short range wireless data communication to a number of inexpensive endpoints. As an example, consider the communication of sensor data within a space where a large amount of electronic equipment is present. Such a situation could occur within the control room of an industrial process, within a compartment of a naval vessel, within a manufacturing environment, within a military vehicle such as a tank, within the electronics on board an aircraft, etc. In such applications there may be as many as 1,000 sensors to be monitored. Present technology supports the use of sensors connected via wires to central communication points which can be very expensive to install. Current technology also supports the use of wireless Local Area Networks (WLANs) to interconnect the endpoints to a central communication point, however they are expensive.
Thus, there is a continuing need for an inexpensive wireless data network which will allow data communications to a large number of inexpensive devices, such as sensors.
SUMMARY OF THE INVENTION
In accordance with the present invention, a system provides short range wireless data communication from a central control point (e.g., interrogator) to inexpensive endpoints (e.g., tags). The endpoints utilize the technology of modulated backscatter for transmission from the tags to the interrogator. The system uses a new downlink protocol for data transmission from the interrogator to the tags and a new uplink protocol for data transmission from the tags to the interrogator. Both protocols use a backoff/retry algorithm to randomly retransmit any non-acknowledged messages. System capacity from the tags to the interrogator is further enhanced by the use of uplink subcarrier frequency division multiplexing.


REFERENCES:
patent: 5721733 (1998-02-01), Wang et al.
patent: 5896060 (1999-04-01), Ovard et al.
patent: 5929779 (1999-07-01), MacLellan et al.

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