Pulse or digital communications – Receivers – Angle modulation
Reexamination Certificate
1999-11-03
2001-08-14
Pham, Chi (Department: 2631)
Pulse or digital communications
Receivers
Angle modulation
C375S226000, C375S371000
Reexamination Certificate
active
06275544
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This disclosure pertains generally to devices and methods for recovering RF signals. More particularly, there is disclosed herein a base band spread spectrum receiver apparatus and method for use with wireless networked transceiver node devices for isochronous data communication.
2. Description of the Background Art
Wireless communication increasingly relies on transmission of data in digital formats. Typically, a data stream is modulated onto a carrier frequency, and the modulated carrier signal is transmitted over a communications channel to a receiver or receivers. Modulation techniques generally utilize phase information of the carrier frequency. Receivers for such transmission generally include a “front end” for filtering and amplifying the carrier signal, one or more mixer circuits for converting the carrier frequency to an intermediate frequency or IF, one or more IF stages where most of the receiver gain and selectivity takes place, and detection or demodulation circuitry for recovering information from the signal. Where data is received in a synchronous digital format, a clocking system such as a phase lock loop circuit is also included with the receiver.
Wireless network systems have been implemented using such receivers. These systems generally utilize some form of continuous wave communication typically based on frequency hopping spread spectrum. The use such of conventional narrow band modulated carriers for wireless network communication has some important disadvantages. Particularly, in multipath environments such as inside rooms and buildings, data communication degrades because of multipath propagation or fading and can result in poor signal reception. Further, the rapidly increasing use of wireless consumer products has “crowded the airwaves” and will result in increasing interference with reception of data via modulated narrow band carriers. Still further, rely on use of relatively expensive components such as high-Q filters, precise local high-frequency oscillators, and power amplifiers.
One approach to avoiding the aforementioned problems would be through use of base band spread spectrum communication systems for data communication. In such a system, information may be transmitted in short pulses, modulated by relatively simple keying techniques, with power spread across a relatively large frequency band. With the signal spectrum spread across a large band width, frequency selective fading and other disadvantages of narrow band communication can be avoided. Base band technology has previously been used effectively in radar applications, wherein a single short impulse is directed to a target. The short impulse, spread across a large bandwidth, has significantly reduced spectral power density and thus has reduced probability of detection and interference. The transmission of digital data in the form of short pulses over a spread spectrum would avoid the aforementioned problems associated with narrow band data communication. Suitable, cost-effective receiver architectures for receiving such data transmissions, however, have heretofore been unavailable.
Accordingly, there is a need for a base band spread spectrum receiver system and method which can receive data in the form of short, spread spectrum pulses, which can be used with a network of transceiver node devices, which is not susceptible to multipath fading or interference with narrow band communication systems, which can be used for indoor applications, and which is relatively simple and inexpensive to implement. The present invention satisfies these needs, as well as others, and generally overcomes the deficiencies found in the background art.
An object of the invention is to provide a base band receiver apparatus and method which efficiently receives data in the form of ultra-short, spread spectrum pulses.
Another object of the invention is to provide a base band receiver apparatus and method which is not susceptible to multipath fading or interference from narrow band communication devices.
Another object of the invention is to provide a base band receiver apparatus and method which converts RF pulses directly to data without intermediate frequency staging.
Another object of the invention is to provide a base band receiver apparatus and method which is simple and inexpensive to implement.
Another object of the invention is to provide a base band receiver apparatus and method for use in a wireless network comprising multiple transceiver node devices.
Another object of the invention is to provide a base band receiver apparatus and method which allows synchronization to a master clock of a remote master transceiver device in a multiple transceiver device network.
Another object of the invention is to provide a base band receiver apparatus and method which allows determination of phase offset corrections, based on timing information recovered from a master clock, for processing signals received from non-master transceiver devices.
Another object of the invention is to provide a base band receiver system and method which can be used for indoor applications.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing the preferred embodiment of the invention without placing limitations thereon.
SUMMARY OF THE INVENTION
Disclosed herein is a base band receiver system and method that receives and demodulates data transmitted, without a carrier frequency, as series of ultra-short, spread spectrum modulated electromagnetic pulses. The electromagnetic pulses each comprise a digital signal representative of a transmitted value. The receiver system advantageously converts the ultra-short, spread spectrum pulses directly to data without going through intermediate frequency (IF) staging. The elimination of IF staging allows reduced cost and easier fabrication of the receiver as a single chip device.
The receiver apparatus and method is generally utilized in connection with a network of transceiver node devices, one of which acts as a “master” transceiver. The other transceivers are structured and configured as “slave” transceiver devices, each of which includes a receiver apparatus in accordance with the present invention. Data is transmitted in the form of short base band spread spectrum radio frequency (RF) pulses. The master transceiver maintains a master clock which runs at a multiple of the data transmission bit rate. The slave transceivers have local clocks which also run at a multiple of the data transmission bit rate, and which are synchronized to the master clock. The master transceiver manages data transmissions between the slave node devices of the networked system.
Data transmission between the several transceiver node devices is preferably carried out via a Medium Access Control protocol utilizing a Time Division Multiple Access (TDMA) frame definition. Under the TDMA architecture, the data transmitted as short RF pulses is divided into discrete data “frames”, with the data frames being further subdivided into “slots”. Framing control by the master transceiver device generates and maintains time frame information through use of “Start-Of-Frame” (SOF) symbols, which are used by the slave transceivers to identify the frames in the incoming data stream.
The TDMA frame definition preferably comprises a master slot, a command slot, and a plurality of data slots. At least once per frame, the master transceiver generates a Master Sync Code which is used by the receiver apparatus in the slave transceivers for clock recovery. The Master Sync Code is preferably in the form of a unique bit pattern, located at the beginning or leading edge of the master slot, which identifies the master transceiver as the source of the transmission. The command slot is used for sending, requesting and authorizing commands between the networked master and slave transceiver devices. The master transceiver uses the command slots for ascertaining which sla
Aiello Roberto
Sparrell Carlton J.
Bayard Emmanuel
Fantasma Network, Inc.
Pham Chi
Sierra Patent Group Ltd.
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