Telecommunications – Transmitter and receiver at same station – With transmitter-receiver switching or interaction prevention
Reexamination Certificate
2000-12-18
2004-06-29
Vuong, Quochien B. (Department: 2685)
Telecommunications
Transmitter and receiver at same station
With transmitter-receiver switching or interaction prevention
C455S080000, C455S073000, C333S103000
Reexamination Certificate
active
06757523
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to economical collection and transmission of data via wireless data telemetry utilizing a plurality of transceivers, each preferably configured with single antenna.
2. Discussion of the Prior Art
Infrared and radio frequency (RF) data transmission methods are the principal wireless communication technologies described in the prior art. Infrared beam communications systems cannot operate over distances of more than a few feet and so are limited to applications such as bar code scanning and television (or other home appliance) remote control.
As a result, most of the prior art wireless data transmission products utilize standard RF technology, i.e., radios, the same technology used in vehicle dispatch and police communication systems. Standard RF products are relatively simple and inexpensive to build, but for operation FCC licenses may be required. RF transmissions are susceptible to interference from a growing number of sources and to interception by readily available eavesdropping equipment. The unreliable quality of standard RF transmissions makes the technology unsuitable for applications where all of the information transmitted must be accurate, complete, and secure.
In order to overcome the shortcomings of standard RF transmission methods, direct sequence spread spectrum (DSSS) was developed. DSSS radios divide or slice transmissions into small bits, thereby spreading energy from the bits simultaneously across a wide spectrum of radio frequencies. DSSS is a relatively unreliable transmission medium, however, because spreading the message across a wide spectrum greatly reduces the strength of the radio signal carrying the message on any one frequency. Since a DSSS receiver must simultaneously monitor the entire allotted spectrum, severe interference from a high energy RF source within the monitored spectrum can pose an insurmountable problem. DSSS performance also degrades quickly in shared-service environments having multiple radio systems operating simultaneously.
Frequency hopping spread spectrum (FHSS) technology was developed by the U.S. military to prevent interference with or interception of radio transmissions on the battle field and is employed by the military in situations where reliability and speed are critical. Standard RF and DSSS cannot match the reliability and security provided by frequency hopping. Instead of spreading (and therefore diluting) the signal carrying each bit across an allotted spectrum, as in DSSS, frequency hopping radios concentrate full power into a very narrow spectral width and randomly hop from one frequency to another in a sequence within a defined band, up to several hundred times per second. Each FHSS transmitter and receiver coordinate the hopping sequence by means of an algorithm exchanged and updated by both transmitter and receiver on every hop. Upon encountering interference on a particular frequency, the transmitter and receiver retain the affected data, randomly hop to another point in the spectrum and then continue the transmission. There should always be frequencies somewhere in the spectrum that are free of interference, since neither benign producers of interference or hostile jammers will likely interfere with all frequencies simultaneously and at high power radiation levels, and so the frequency hopping transmitter and receiver will find frequencies with no interference and complete the transmission. This ability to avoid interference enables FHSS radios to perform more reliably over longer ranges than standard RF or DSSS radios. In the prior art, frequency hopping FHSS communication systems have been used almost exclusively in the extremely expensive robust military or government communication systems.
Generally speaking, data telemetry is the transmission of short packets of information from equipment or sensors to a recorder or central control unit. The data packets are transferred as electric signals via wire, infrared or RF technologies and data is received at a central control unit such as a computer with software for automatically polling and controlling the remote devices. The control unit analyzes, aggregates, archives and distributes the collected data packets to other locations, as desired, via a local area network (LAN) and/or a wide area network (WAN). Wireless data telemetry provides several advantages over data telemetry on wired networks. First, wireless systems are easier and less expensive to install; second, maintenance costs are lower; third, operations can be reconfigured or relocated very quickly without consideration for rerunning wires, and fourth, wireless telemetry offers improved mobility during use.
The Federal Communications Commission (FCC) has designated three license-free bandwidth segments of the radio frequency spectrum and made them available for industrial, scientific and medical (ISM) use in the United States. These three segments are 900 MHZ, 2.4 GHz and 5.8 GHz. Anyone may operate a wireless network in a license-free band without site licenses or carrier fees and is subject only to a radiated power restriction (i.e., a maximum of one watt radiated power). The radio signals transmitted must be spread spectrum. Foreign national spectrum regulation organizations and international telecommunications bodies have also agreed to recognize a common license-free ISM frequency at 2.4 GHz, and so a defacto international standard for license-free ISM communications has emerged. The ISM band at 2.4 GHz provides more than twice the bandwidth capacity and is subject to far less congestion and interference than the ISM band at 900 MHZ. Several industrial nations do not permit a license-free ISM band at 900 MHZ and relatively few nations have a license-free ISM band at 5.8 Ghz, but the United States, Europe, Latin America and many Asian countries have adopted an ISM band at 2.4 GHz.
Not just any wireless telemetry system will do for many applications, however. The realities of the marketplace dictate that data telemetry cannot be the most expensive part of a system having commercial application. For example, if a retail point-of-sale cash register is to be configured with a wireless data telemetry radio; the radio cannot be more expensive than the cash register. In many commercial applications, buyers have fixed expectations for what things cost and new features, however useful, cannot substantially exceed those expectations. Thus, it would be best if the wireless data telemetry radio were free. In the interest of providing the most economical wireless data telemetry radio, a transceiver with a shared antenna for both transmit and receive segments is suggested, but how is the switching between transmit function and receive function to be accomplished? The off-the-shelf transmit/receive (T/R) switches are expensive, have a high parts count, and are often configured such that the components within the switch dissipate transmitter energy when in the receive state, adding heat and raising the energy required to operate the wireless data telemetry transceiver. Use of off-the-shelf T/R switch components, as is customary in the prior art, make it difficult to provide a wireless data telemetry radio that is small, light, resistant to interference from adjacent RF noise sources, and uses as little energy as possible.
What is needed, then, is an inexpensive, easy to use and robust data telemetry and communication system including an inexpensive and compact transceiver, preferably operating in the common license-free ISM frequency band, and providing reliable communications for a variety of users in commercial and industrial environments.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to overcome the above mentioned difficulties by providing an economical, compact wireless data telemetry transceiver is adapted to establish and maintain communication links in the license-free ISM frequency band at 2.4 GHz.
Another object of the present invention is to efficiently switch
Hamilton Brook Smith & Reynolds P.C.
Le Lana
Vuong Quochien B.
Zeus Wireless, Inc.
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