WO1994014252A1

WO1994014252A1 - Rf communication system using waveguide disposed within modular furnishings

Info

Publication number: WO1994014252A1
Application number: PCT/US1993/010689
Authority: WO
Inventors: James E. Mitzlaff; Thomas A. Freeburg; Scott D. Munier
Original assignee: Motorola Inc.
Priority date: 1992-12-14
Filing date: 1993-11-08
Publication date: 1994-06-23
Also published as: MX9307880A

Abstract

A radio frequency (RF) signal transmission system (500) for overcoming radio interference within an in-building environment includes a plurality of waveguide segments (200) connected together to form an enclosed transmission medium. A plurality of transceiver devices (560) are coupled to the transmission medium for transmitting RF signals into and receiving RF signals from the transmission medium, thereby avoiding the deleterious effects of in-building radio interference. In accordance with one embodiment, the waveguide segments (200) are integrated into or disposed within modular wall panels (310).

Description

RF Communication System Using Waveguide Disposed Within Modular Furnishings

Field of the Invention

This invention relates generally to high data rate radio-frequency (RF) communication systems, and more particularly to a waveguide transmission system for use within an in-building environment.

Background of the Invention

Current in-building RF communication systems employ highly complex transceiver circuitry in order to overcome those signalling problems associated with high data rate communications. Such communications is often severely impaired as a result of radio interference such as, for example, co-channel, adjacent channel and multipath interference. Co-channel and adjacent channel

interference is caused by the reception of signals from a nearby source using the same or an adjacent frequency to the communication channel of concern. Multipath interference is caused when signals, subject to varying propagation delays, are received, offset in time, thereby creating an overlapping effect (intersymbol interference) which distorts the signal's intelligibility at the receiver.

Recent attempts to overcome such interference in high data rate communications systems (exceeding 2 Mega Bits Per Second (MBPS)) suggest employing either time domain equalization, spread spectrum technology, or some form of sectorized antenna selectivity. Systems employing time domain equalization attempt to identify the various differential path delays so that they may be subtracted out by the receiver. Commonly, a tapped delay line is employed to provide various delayed output signals which may be analyzed to identify the time delayed signal paths. The output signals of the tapped delay line are then selectively summed so that the identified time delay signal paths add to produce a composite signal representative of the original non- deflected signal.

Most in-building spread spectrum systems use a technique known as direct sequence, in which each data bit is broken up into a series of smaller fragments known as chips. The same chip pattern is used to represent each bit at both the transmitter and receiver, and this pattern is chosen to be as random as possible for a fixed length binary sequence. This allows the receiver to reverse the effects of of the chip-level fragmentation in the transmitter by correlating the received signal with the common chip pattern.

The key parameter in this type of system is the number of chips per bit, which is referred to as the spread ratio. The expansion in signal bandwidth produced by the chip-level processing is directly proportional to this spread ratio. This expanded bandwidth, in turn, creates a third wavelength scale, namely the chip

wavelength, which is simply the data wavelength divided by the spread ratio. This reduction in critical

wavelength is what makes it possible for a spread

spectrum system to isolate and resolve echoes before they combine to produce fading and/or intersymbol

interference. Systems employing antenna selectivity utilize a plurality of sectorized (directional) antennae at the receiver. Signals received on each antenna are evaluated for both signal strength and signal integrity. The antenna sector which boasts the highest signal strength and the least signal degradation due to multipath, co- channel and/or adjacent channel interference is selected.

Each above mentioned approach has the disadvantage that it requires substantial receiver circuitry and complexity in order to effectively operate within an environment characterized by substantial interference. The spread spectrum approach requires not only a pseudo random (PN) signal generator but also phase-locking circuitry at each receiver to phase lock the PN signal generated at the transmitting and receiving points.

Systems employing time domain equalization such as, for example maximum likelihood sequence estimation (MLSE), require delay lines circuitry or its equivalent in addition to substantial processing intelligence to effectively produce a representative composite signal.

The antenna selection approach requires enough processing intelligence to evaluate a plurality of possible

communication paths and select from the options that path least effected by radio interference. Such circuitry significantly adds to the transceiver's complexity, size and ultimately cost.

One partial solution was suggested by the American Telephone and Telegraph Company (AT&T) in the December 1977 issue of The Bell System Technical Journal, which describes the design of a long-haul millimeter waveguide transmission system capable of carrying two-way voice, data, or video communications. This system, better known as the WT4, employed 60 millimeter internal diameter waveguide as the transmission medium for a coast-to-coast long-distance communications service. Its basic structure comprised fusion-joined steel tube sections encased in a fushion-joined protective steel outer casing buried about 0.6 meters (2 ft) below the earth's surface. A block diagram of one fully equipped hop or span of this system is shown in FIG. 1.

Sixty-two transmitters which operate at different millimeter-wave carrier frequencies in one-half of the frequency spectrum carry east-west signals to 62

receivers at a next repeater station. Correspondingly, another set of 62 receivers and transmitters carry west- east signals in the opposite direction in the other half of the frequency spectrum. A multiplexer connects the 124 individual channels to the single waveguide

transmission medium. Depending on terrain, repeater spacing will vary from 50 to 60 kilometers, approximately every 30-40 miles. For additional information on this system, the interested reader may refer to The Bell

System Technical Journal, Vol.56, No.10, December 1977, pgs. 1825-2208.

Due to the sheer size and nature of the WT4 system, it will be appreciated by those skilled in the art, that its direct application for in-building communications would be quite impracticable. For these reasons, a communication system is needed which overcomes the above- mentioned shortcomings.

Summary of the Invention Briefly described, the present invention is an RF signal transmission medium and system for overcoming radio interference within an in-building environment. A plurality of waveguide segments are connected together and disposed within an in-building environment to form an enclosed transmission medium. Thereafter, a plurality of transceiver devices are coupled to the transmission medium for transmitting RF signals into and receiving RF signals from the enclosed transmission medium. In accordance with the preferred embodiment of the invention, the waveguide segments are disposed within or integrally fashioned into modular office furnishings.

Brief Description of the Drawings

FIG. 1 is a block diagram of a portion of a prior art waveguide transmission system;

FIG. 2 is a perspective view of a waveguide segment for use with the present invention;

FIG. 3 depicts the waveguide segment of FIG. 2 disposed within a wall panel;

FIG. 4 is a reference table which provides

information on rectangular waveguide data and fittings;

FIG. 5 illustrates an embodiment of a waveguide transmission system utilizing the wall panels of FIG. 3; and

FIG 6 is a block diagram of a transceiver as shown in FIG 5.

Detailed Description of the Preferred Embodiment

The present invention has application to RF communication systems deployed within in-building environments. Such in-building environments are

typically characterized by residential homes; commercial buildings, such as offices, warehouses, and factories; and public buildings such as schools, libraries, hospitals and municipal buildings. Current in-building wireless communication systems employ highly complex transceivers that utilize complicated signalling schemes or antenna selection techniques in order to combat problems associated with radio interference such as co- channel and adjacent channel interference, multipath interference and/or fading.

Implementation of a typical spread spectrum solution requires not only the adoption of pseudo random (PN) signal generators, but also phase lock loop

circuitry at the receiver. Systems which employ time domain equalization require delay line circuitry in addition to substantial processing intelligence in order to effectively recapture transmitted data. Antenna selection techniques require substantial processing intelligence and detection circuitry in order to

evaluate the quality of potential communications paths. Such circuitry significantly adds to the receiver's complexity, expense, size and ultimately cost. For these reasons, the present invention discloses a

communication system which overcomes the problems associated with radio interference without the inherent cost and complexity of the prior art.

In accordance with the present invention, RF communication signals are transmitted within an enclosed propagation medium comprised of a plurality of

detachable waveguide segments . A plurality of

transceiver devices are coupled to the propagation medium for transmitting RF signals into and receiving RF signals from the enclosure. Since the enclosed

propagation medium is isolated from a multipath

environment, radio transmissions within the enclosure are no longer susceptible to the deleterious effects of radio interference. In accordance with a preferred embodiment, the waveguide segments are integrally fashioned as a part of and disposed within modular office furnishings such as partitioning walls.

When assembled, the partitioning wall functions as both a data communications network and an office space organizer.

FIG. 2 is a perspective view of a waveguide segment for use in accordance with the present invention. As shown, each waveguide segment 200 is substantially rectangular in shape and is formed to have a cavity 202. The waveguide segment 200 is also shown having an aperture 204. This feature permits an external device such as a transceiver to propagate signals into and receive signals from the waveguide segment 200. As is known in the art, an external transceiver may utilize microstrip to waveguide transitions, RF probe to

waveguide transitions, or aperture coupled transitions in order to to propagate signals into and receive signals from the waveguide segment 200.

FIG. 3 depicts the waveguide segment 200 disposed within an article of modular office furnishing. In accordance with the preferred embodiment, the waveguide segment 200 is shown disposed within a partitioning wall 310. Additional articles of modular office furnishing which may contain waveguide segments 200 include, without limitation, desks, tables and cabinets. Such articles of modular office furnishing, without waveguide segments 200, have in the past been available by

contacting organizations such as Hayworth at 1014 East Algonquin Road, Schaumburg, IL 60173, or Steelcase at P.O. BOX 1967 Grand Rapids, MI 49501. The fabrication of such articles typically employ well known sheet metal roll forming operations such as, for example, hot- rolling, cold-rolling, seam-rolling, bead-rolling, flange-rolling and contour rolling.

The waveguide segment 200 may also be formed utilizing any of the previously mentioned and well known sheet metal roll forming operations such as, hot- rolling, cold-rolling, seam-rolling, bead-rolling, flange-rolling and contour rolling. Since the

fabrication of partitioning walls 310 and the

construction of waveguide segment 200 can be

implemented via identical sheet metal rolling

operations, the processing steps required to construct waveguide segment 200 may be integrated into the steps for fabricating partitioning wall 310 with minimal additional time or expense. Since the above-mentioned fabrication methods for forming sheet metals into tubular and channel shapes are well known in the art, no additional discussion is required at this time. The interested reader may nonetheless refer to E.V. Crane, "Plastic Working of Metals and Power Press Operations" Wiley Press for additional discussion on the subject. In addition, waveguide segments 200 have in the past been available by contacting Microwave Developments Labs at 10 Michigan Drive, Natick, MA 01760.

As an alternative, waveguide segment 200 may be fashioned separately from the construction of partitioning walls 310 and then mounted within or upon partitioning walls 310 or internal building wall (not shown). In the alternative, such waveguide segments 200 may be disposed within open areas typically found above removable ceiling panels or in spaces typically found below removable floor panels .

In addition, waveguide segment 200 may be made from materials other than metals. For example, waveguide segment 200 may be constructed from plastic. Suggested compounds comprise amorphous thermoplastics, such as Polycarbonate, Polystyrene and Polyetherimide; and crystalline thermoplastics such as Polypropolyne, modified Polypheneylene and nylon.

According to a preferred embodiment, the wave guide segment 200 is made from Polycarbonate, utilizing any of the well known injection-molding and extrusion

techniques. Polycarbonate combines the relatively high temperature performance of 152°C with enough tensile strength in order to insure mechanical and environmental stability. In addition. Polycarbonate components are easily fixed together utilizing well known adhering, fusing and welding techniques. Moreover, Polycarbonate structures readily accept the application of thin metal layer deposits by any of the well known metal deposition techniques. Despite the selection of Polycarbonate, it will be appreciated that several other thermoplastics provide available alternatives, such as, for example: Polyamide, Polyamide-imide, Polyether-imide, Polyaryl- ether-ketone, Polyaryl Sulfone, and Liquid Crystal

Polymers. For a discussion on state of the art

injection molding and extrusion, the interested reader should refer to: Dubois, H. J., Pribble, W. I.,

"Plastics Mold Engineering Handbook, " 3rd Edition, Van Nostrund Reinhold Company, New York 1978.

The external dimensions of waveguide segment 200 will be determined, in part, by packaging. In

accordance with the present invention, each waveguide segment 200 is integrally fashioned and disposed within an office partitioning wall panel 310. Each panel 310 is typically 2 inches wide by 48-60 inches long. The external dimensions of waveguide segment 200 must therefore be tailored to fit within these confines.

Cavity 202 cross section dimensions are of greater concern, for they will influence the frequency of operation within a waveguide segment 200. Under well established guidelines provided by the International Electrotechnical Commission (IEC) located at 1 Rue de Varemb Geneva, Switzerland and the Electronic Industries Association (EIA) located at 2001 Eye Street, Northwest Washington, D.C. 20006, waveguide internal dimensions can be selected in order to promote propagation of desired signals within the waveguide, without causing the unwanted occurrence of moding (multipath

interference).

FIG. 4 is a reference table which provides

information on rectangular waveguide data and fittings in accordance with IEC and EIA standards. A similar table may be found by referring to "Reference Data for Radio Engineers", Section 25, Howard W. Sams & Co Inc., Indianapolis 1982.

In accordance with the preferred embodiment, 18-19 GHZ is the desired frequency of operation. With

reference to FIG. 4, the cavity 202 cross section internal dimensions are preferably 0.17 inches high and 0.42 inches across in order to provide single mode transmission for frequencies within this range. As will be appreciated, however, waveguide segments having cavity cross sectional dimensions larger than those preferably required may nonetheless be used. In such instances it may be necessary to employ some form of mode filtering in order to suppress the generation of undesired modes within the oversized waveguide. Of course, other frequencies of operation and waveguide dimensions may be selected from the table of values provided in FIG. 4 without departing from the spirit of the present invention.

FIG. 5 illustrates an embodiment of a waveguide transmission system in accordance with the present invention. In accordance with this embodiment, a plurality of wall segments 310 having integrally fashioned waveguide segments 200 are connected together to provide office organization, while simultaneously creating an enclosed transmission medium which operates as a communications network. The individual wall panels 310 are connected together via mechanical couplers such as straight through coupler 510, flanges 520, four way couplers 530, right angle couplers 540 and T couplers 550. These couplers operate to connect the waveguide segments 200 and wall panels 310 using either mechanical or adhesive coupling. As will be appreciated, these couplers may be constructed from sheet metal or plastic in accordance with known sheet metal roll forming operations or plastic injection molding and extrusion procedures as set forth above.

In accordance with the preferred embodiment, mechanical coupling is employed to connect the various wall panels together to create a transmission path. In this effort, couplers 510-550 are fashioned to have dimensions slightly larger than those of the waveguide segments 200 such that a coupler will physically overlap an exposed portion of waveguide segment 200. Overlapped coupling like that anticipated by the preferred

embodiment enjoys the advantages provided by ease of fabrication and assembly, as well as the performance enhancements provided by reduced signal leakage and minimal insertion loss at the coupling intersections.

It will be further appreciated that in the

alternative, couplers 510-550 may be dimensioned such that they can be physically inserted into or overlapped by the waveguide segments 200.

While the preferred method of coupling waveguide segments 200 together employs mechanical coupling, it will be appreciated by those skilled in the art that other forms of coupling can and may be used without departing from the spirit of the present invention.

These include, without limitation, fusing, adhering and/or welding operations such as, for example,

epoxy/resin adhesion, vibration welding, ultrasonic welding and solvent induced adhesion. Disposed at ends of the waveguide structure and connected to waveguide segments 200 are end caps 503. In conjunction with the interconnected waveguide

structure, end caps 503 operate to provide an enclosed transmission medium or communications network, disposed within the modular wall structure. Each end cap 503 includes or comprises RF absorbing material 505. The use of RF absorbing material 505 operates to minimize the reflection of RF energy within the communications network while preventing leakage of RF energy outside of the communications network.

Positioned at various points along the

communications network, as defined by the enclosed transmission medium, are transceiver devices 560. Each transceiver device 560 is connected to a partitioning wall panel 310 and coupled to the communications network via an aperture 204 in waveguide segment 200. The transceivers 560 operate to transmit signals into and receive signals from the enclosed communication network. As such, transceiver 560 are coupled to the

communications network, as defined by the enclosed waveguide structure, utilizing microstrip to waveguide transitions, RF probe to waveguide transitions or aperture coupled transitions.

FIG. 6 is a block diagram representation of the transceiver as shown in FIG 5. As depicted, the

transceiver 560 includes a receive transition 602, diode detector 604, limiting amplifier 606, data squelch 608, transceiver controller 610, pulse modulator 612,

microwave oscillator 614 and transmit transition 616. The controller 610 is shown connected via bus 618 to a user device such as, for example, a personal computer (PC), a telephone or any other peripheral device desirous of communicating within the network defined by the interconnected waveguide segments 200. The transceiver controller 610 controls transmit and receive operations such as biphase encoding/decoding, synchronization and network protocol support. Such a controller has in the past been available under part number Am79C960 by contacting Advanced Micro Devices Inc. at 901 Thompson Place, Sunnyvale, CA 94088.

In the transmit mode (Tx), controller 610 receives a signal for transmission from a user device. This signal is biphase encoded by controller 610 and passed to pulse modulator 612 as a digital input signal. Pulse modulator 612 supplies power to microwave oscillator 614 when the data input signal from controller 610 is at a logic high status level and removes power to microwave oscillator 614 when the data input signal from controller 610 has a logic low status level, thereby producing a biphase encoded, pulsed microwave signal which is coupled into the waveguide segment 200 and propagated from transmit transition 616 to all of the other transceivers connected to the network.

In the receive mode (Rx), a transmitted signal is sensed by receive transition 602 and detected by diode detector 604 which produces a low level pulse waveform in response thereto. This waveform is amplified and clipped by limiting amplifier 606, thereby converting it back into a biphase encoded data signal. The limiting

amplifier also produces an output voltage labeled RSSI (received signal strength indication) which is

proportional to the logarithm of the average signal level appearing at the input to limiting amplifier 606. Data squelch 608 compares RSSI to a predetermined threshold and gates biphase encoded data signals to the controller 610 in response to a determination that a signal is actually present as determined by the comparison.

This process prevents the controller 610 from being

"falsed" or overwhelmed by noisy outputs from limiting amplifier 606, especially when no actual data signals are present.

Upon receipt of a data signal from data squelch 608, controller 610 biphase decodes the signal and passes it over bus 618 to the appropriate user device. While not shown, there are other user device interfaces controller 610 may communicate over. For example, controller 610 may be configured in order to transmit and receive signals via a twisted pair port such as 10 BASE-T as is known in the art.

What is claimed is:

Claims

1. A wireless transmission medium for overcoming radio interference within an in-building environment

comprising: a plurality of waveguide segments disposed within modular furnishings; couplers for connecting the waveguide segments together to form a transmission path; and end caps, having RF absorbing material, connected to the waveguide segments disposed at ends of the transmission path to form an enclosed transmission medium.

2. The wireless transmission medium of claim 1 wherein the couplers connect the waveguide segments together by mechanical coupling or adhesive coupling.

3. The wireless transmission medium of claim 1 wherein the couplers connect the waveguide segments together by overlapping a portion of a waveguide segment.

4. The wireless transmission medium of claim 1 wherein the couplers connect the waveguide segments together by being overlapped by a portion of a waveguide segment.

5. The wireless transmission medium of claim 1 further comprising a plurality of transceiver devices coupled to the transmission path for transmitting RF signals into and receiving RF signals from the transmission medium.

6. The wireless transmission medium of claim 5 wherein the transceiver devices are coupled to the the

transmission path via transitions selected from the group consisting of:

microstrip to waveguide transitions;

RF probe to waveguide transitions; and

aperture coupled transitions.

7. The wireless transmission medium of claim 1 wherein said modular furnishings comprise:

partitioning walls; desks; tables; and cabinets.

8. A wireless signal transmission system for

overcoming radio interference within an office

environment comprising: a plurality of waveguide segments disposed within modular walls; couplers for connecting the waveguide segments together to form a transmission path and to provide office organization; end caps, having RF absorbing material, connected to the waveguide segments disposed at ends of the transmission path to form an enclosed transmission medium; and a plurality of transceiver devices coupled to the transmission path for transmitting RF signals into and receiving RF signals from the enclosed transmission medium.

9. The system of claim 8 wherein the waveguide

segments comprise:

hollow metal pipe or tube; and

polymeric tubing having a cavity, the cavity layered with a conductive material.

10. The system according to claim 8 wherein the

couplers are selected from the group of devices

consisting of:

straight through couplers; flanges; four way couplers; right angle couplers; and T couplers.