Conference Report: THE AUTOMATIC RADIO FREQUENCY TECHNIQUES GROUP CONFERENCE ON CHARACTERIZATION OF BROADBAND TELECOMMUNICATIONS COMPONENTS AND SYSTEMS Denver, CO June 13, 1997

or office, the “return-path” or “upstream” data requirements are growing rapidly in markets such as telecommuting and video conferences. To satisfy the demand, the major telecommunications players are rushing to establish high bandwidth, two-way digital networks for video, telephony, and Internet to homes and businesses. One major techn ology expected to play a key role as a future broadband telecommunications system is twoway digital transmissions over coaxial cable. An advantage of such systems is that much of the infrastructure is currently in place for analog cable television systems. The major upcoming competitors to coaxial systems are based on wireless transmission. What these have in common is radio frequency (RF) techn ology.Successful deployment relies on RF components and subsystems of exceptionally high performance. The Automatic Radio Frequency Techniques Group (ARFTG) annually sponsors two conferences on critical topics in RF techn ology, with a focus on measurement issues. For its 49th Conference, held in Denver, CO on June 13, 1997, ARFTG chose the theme “Characterization of Broadband Telecommunications Components and Systems” to address the critical RF technology issues of broadband communications, needs that have not been directly addressed by other microwave or radio frequency symposia. The conference, which was cosponsored by the Microwave Theory and Techniques (MTT) Society of the Institute of Electrical and Electronics Engineers (IEEE), featured 18 technical talks, 11 poster presentations, and a product exhibition. It proved to be popular, as the registration level of 205 broke the ARFTG record of 168. Attendees came at least 18 nations: Australia, Belgium, China, Finland, France, Germany, Italy, Japan, Korea, the Netherlands, Norway, Canada, Poland, Singapore, Sweden, Taiwan, the United Kingdom, and the United States. Dr. Roger Marks of NIST was the Conference Chair.


Oral Sessions
The Technical Sessions, under the direction of Conference Technical Program Chair Dr. Gary Alley of Lucent Technologies, included 18 talks and 11 poster presentations. The oral sessions were presented in the traditional ARFTG single-track format. The morning talks focused on coaxial systems and the afternoon on wireless.

Broadband Coaxial Systems
Over the past 7 years, community antenna television (CATV, or cable television) systems have been evolving from one-way transmission of NTSC (U.S. Standard) video signals using long cascades of coaxial amplifiers and directional couplers into bidirectional transmission of NTSC video and digital signals on Hybrid Fiber-Coaxial (HFC) distribution systems. The use of linear lightwave transmitters and receivers has resulted in improved performance for NTSC video transmission but has increased the degradation in digital performance due to laser clipping caused by peaks produced by the broadband multichannel NTSC video waveform. HFC systems being deployed today typically transmit signals from the headend to the home in the 50 MHz to 750 MHz portion of the spectrum while transmitting digital signals from the home to the headend in the 5 MHz to 40 MHz band. The downstream band from 50 MHz to 550 MHz is generally used for up to 83 NTSC video channels while the spectrum from 550 MHz to 750 MHz is reserved for a mixture of digital services including telephony, video telephony, compressed digital video, and Internet access. It has been known for many years that the performance of the upstream portion of these systems, at 5 MHz to 40 MHz, was limited by ingress into the coaxial portion of the system. The sources of this ingress include impulse noise due to lightning and power line currents, intermodulation noise due to the downstream signals in the 50 MHz to 750 MHz band, and coupling of RF broadcast signals into the cable system. The effect of these interfering signals on upstream digital transmission is the subject of current research.
The conference talks on broadband coaxial systems were: • RF Measurements for Broadband Networks, S.
Fluck (Hewlett-Packard Co., Santa Rosa, CA) The morning sessions led off with an invited keynote address by Syd Fluck of Hewlett-Packard. Fluck discussed the evolution of CATV systems from the 1960s through the present. The introduction of digital transmission on cable systems resulted in the need to charac-terize the digital performance of these systems in their commercial environment. Current test sets and methods required to accomplish this task were discussed. Williams discussed the test and maintenance needs of the reverse plant, as well as a set of nontraditional burst-mode tests. These tests used a high speed analogto-digital converter to capture test and data signals which were then analyzed using a personal computer located at the headend. Examples of data collected and analyzed using these techniques were presented. This paper presented methods for characterizing both ingress and impulse noise in the upstream portion of the system. These methods were independent of the modulation and access techniques used in the systems. Examples were presented using data collected in the field. Bianchi discussed the digital system performance of an operational HFC CATV system using measured data from both upstream and downstream 4 and 64 Quadrature Amplitude Modulation (QAM) modems. The resulting performance is found to vary with respect to time, to signal amplitude, and to direction of transmission. In the forward path, the effect of background impairments varies with time and signal power. In the return path, the effect of interferer-like impairments limits the system performance. Statistical bit-error-rate (BER) data were presented along with BER and signalto-noise (S /N ) data which show the variation in system performance with time. Steel presented a paper which discussed the need for characterization of cable network elements for use in digital cable networks. The paper focused on the characterization of nonlinear, frequency-dependent network elements by using a combination of filter blocks and nonlinear blocks. The 2nd and 3rd order distortion performance of CATV amplifiers was presented as an example of the technique. Alley discussed a technique for minimizing the peak-to-RMS values of the broadband multichannel NTSC video waveform while minimizing both the 2nd and 3rd order distortion products. This was accomplished by optimally controlling the phases of the NTSC video carriers. Both theoretical and experimental results were presented. This paper was selected to receive the conference's Best Paper Award.
• CATV Tap and Splitter Linearity Improvement for Broadband Information Networks, M. W. Goodwin (Lucent Technologies, N. Andover, MA) Goodwin presented an analysis of the source of the intermodulation distortion in HFC CATV systems produced by CATV taps and splitter/combiners, as well as a method for improving the linearity of these devices.

Broadband Wireless Systems
Broadband wireless access is emerging as an alternative method of providing a high capacity digital channel to and from the home. Multichannel Multipoint Distribution Systems (MMDS, or "wireless cable") have existed for some time, offering up to 33 analog video channels in the 2.150 GHz to 2.682 GHz band. The current direction with MMDS is the introduction of compressed digital video in an effort to increase the capacity of these systems and make them more competitive with cable and satellite video distribution systems. The FCC's allocation of over 1 GHz of bandwidth between 27.5 GHz and 31.3 GHz has stimulated interest in Local Multipoint Distribution Systems (LMDS). The bandwidth available is expected to provide high capacity two-way wireless services to the home. Wireless systems are physically easier to deploy than wired systems but still present significant challenges to the system provider. Issues such as co-channel adjacent-cell interference and multipath propagation with the resulting finite coherence bandwidth must be addressed. Yang presented a novel technique which has been developed to optimize power monotithic microwave integrated circuit (MMIC) performance by using onwafer pulsed power tests. The tests are used to determine the functionality of the device and allows the MMIC chip performance to be optimized through manual bias tuning at the module level.

Interactive Forum
The Conference included 11 poster papers in an Interactive Forum. While these papers addressed significant problems in ARFTG's traditional field of microwave measurements, most did not directly address the primary conference theme. These papers were:

Joint Session on Crosstalk
On Thursday, June 12, ARFTG cosponsored a session of the 1997 IEEE MTT-S International Microwave Symposium. The session, entitled "Crosstalk, Coupling, and Multiconductor Transmission Line Characterization," was organized and chaired by Dr. Dylan F. Williams of

Summary
Broadband telecommunications systems are undergoing rapid development and will soon begin to make a significant thrust into consumer and industry markets. Advances in radio frequency technology are critical to the cost and timing of this potential economic and sociological revolution.

Proceedings
The 49th ARFTG Conference Digest, which includes 36 papers in 251 pages, was distributed at the conference. Ordering information is available on the ARFTG web site or from the ARFTG Executive Secretary (+1-602-839-6933).

Future Conferences
The 51st ARFTG Conference will be held in Baltimore on Friday, June 12, 1998 in conjunction with the 1998 IEEE MTT-S International Microwave Symposium. The meeting topic is "Characterization of Spread Spectrum Components and Systems." In order to continue its focus on broadband telecommunications, ARFTG will cosponsor a Joint Session with the 1998 IEEE MTT-S International Microwave Symposium on the topic "Broadband Telecommunications Systems" during the week of June 8 in Baltimore. A second Joint Session will cover "Digital Interconnection Techniques and Characterization at GHz Frequencies." In addition to its odd-numbered conferences in the spring, ARFTG presents an even-numbered conference each fall during the week after Thanksgiving. The 50th ARFTG Conference, on "Measurement Techniques for Digital Wireless Applications," will take place on December 4-5, 1997 at the Benson Hotel in Portland, OR. ARFTG and NIST will also present their fourth annual Microwave Measurements Short Course on December 2-3.

More Information
More information on ARFTG and its conferences is available on the ARFTG Web Site at http:// www.arftg.org.