# Presentation: 028991

## LITERATURE SEARCH AND REVIEWof Radio Noise and its Impact onWireless Communications

**Prepared by:**
**Signal Enhancement Laboratory**
**Department of Electrical and Computer Engineering**
**Naval Postgraduate School**
**Monterey, California**

## PARTICIPANTS

**Professor Richard W. Adler, Project Leader**
**Professor Wilbur R. Vincent**
**Mr. George F. Munsch, Consultant**
**Dr.  David Middleton, Consultant**

**Notes:**
Mr. George Hagn, a long time noise research scientist, started this effort.  Shortly after the start of the library search work, Mr. Hagn had major bypass surgery and was unable to continue working on the program.  His part of the effort was divided between the listed participants.
Mr. Hagn did arrange to obtain help from Dr. David Middleton of New York City.  Dr. Middleton is considered to be the leading expert in modeling radio noise.  Dr. Middleton prepared the material in Section 1 of the report.  
The participants consider the work of Dr. Middleton is most significant, and his work has direct applications to Wireless radio problems.

## DEFINITION OF NOISE

**NOISE IS DEFINED AS ALL UNWANTED RADIO ENERGY AT THE INPUT TERMINALS OF A WIRELESS RECEIVER THAT DEGRADES THE RECEPTION OF A DESIRED SIGNAL.**

**THUS, NOISE INCLUDES UNWANTED AND INTERFERRING SIGNALS PLUS MAN-MADE RADIO NOISE.**

**Notes:**
In past years, the term “radio noise” was generally considered to be “man-made noise”.  Interference was used to describe the signal reception degradation due to other intended signals.  Mr. Hagn participated in these discussions and related his experience in establishing a new definition for “noise” which is currently under consideration by such organizations as the International Telecommunications Union and other individuals conducting noise research and noise measurements.  
We agreed that the variety  of signal formats and noise sources affecting the performance of Wireless Radios require a new definition for “noise”.   Thus the definition as stated is accepted.  

## LITERATURE SEARCH

-  **MORE THAN 100,000 DOCUMENTS REVIEWED.**
** ****ON-LINE LIBRARIES WERE ESSENTIAL.**
** ****ORGANIZATIONS WITH ON-LINE DOCUMENTS                WERE ALSO VALUABLE.**
** ****SOME DOCUMENTS WERE ONLY AVAILABLE FROM TRADITIONAL LIBRARIES.**

**Notes:**
More than 100,000 online abstracts were reviewed.  This required the use of a fast connection to the Internet.
In addition, several thousand documents were reviewed by visits to libraries.  We are grateful to Dr. Robert Hunsucker, the edition of Radio Science for allowing us to use his personal and extensive library of URSI documents.. 

## EXAMPLE OF DOCUMENT SEARCH PROCESS

**ON-LINE LIBRARY**

**END NOTE**

**WORD 97**

**ADOBE PDF**

**TEXT**

**Notes:**
The online library of the Institute of Electronic and Electrical Engineers (IEEE), IEEE Xplore, and the older INSPEC libraries were especially useful in gaining access to documents.  In many cases, the on-line material was copied and pasted into the EndNote program.  Off-line material was typed into EndNote.
The EndNote program provided a means to sort entries by categories.  Each entry was labeled with one seven categories.  In addition, EndNote sorted each category by author and then by publication data.  
The EndNote program provided a means to convert its files into Word 97 files.  After this conversion, text was added as needed.  The final file was then converted to Adobe PDF and the report was recorded on CDs for distribution.  

## LIBRARY SEARCH WAS DIVIDED INTO SECTIONSTO SIMPLIFY PRESENTATION OF RESULTS 

**  ****SELECTED BIBLIOGRAPHY AND REFERENCES ****(Dr. David Middleton)**
**  ****NOISE MEASUREMENTS**
**  ****NOISE PROPAGATION **
**  ****SPECTRUM PLANNING**
**  ****SYSTEM MODELS**
**  ****MEASUREMENT INSTRUMENTATION**
**  ****DISCUSSION**
-   **APPENDIX -- MEASUREMENTS AT 2.4 GHz**

**Notes:**
Section 1 was provided by Dr. David Middleton.  It summarizes the important work of Dr. Middleton and some of his close associates.  
Section 2 identifies documents found with measured data of direct interest to Wireless Radio systems.  No document was found that provides a good  up-to-date summary of noise, but a number were found with some information.  For example, the Institute of Telecommunications Sciences undertook an extensive measurement program starting in 1995, but that was prior to the widespread introduction of Wireless Radio devices into the ISM bands.
Section 3 lists the work of other noise model investigators.  It supplements Section 1.
Section 4 provides papers related to the propagation of noise from its source to a victim receiver.
Section  5 lists publications related to efficient spectrum planning.  Of special interest are a series of documents funded by the Radio Communications Agency of the United Kingdom that examine the implications of license-exempt use of bands.
Section 6 provides papers related to the impact of noise on signal detection processes.
Section 7 describes various approaches to noise measurement instrumentation.  

## Section 1---HIGHLIGHTS

**This section describes the work of Dr. David Middleton and his close associates.  It lists key documents related to noise models and some that relate to the detection of signals in the presence of noise.**

## Section 2--MEASUREMENTS 

**Notes:**
It became apparent very early in the program that the measurement of noise affecting a Wireless Radio receiver was a complex problem.  The view shows some of the sources of noise that appear at the input terminals of a 2.4 GHz Wireless Radio or a measurement system.  We used the 2.4 GHz band as an example since a large variety of devices and users now produce emissions in this band.  
The illustration describes the situation at the business location of one of the authors.  We are concerned that a variety of users are already using this band with no ground rules for the efficient use of the 100-MHz wide band.  
An excellent survey of signals and noise in several major urban areas was performed by the Institute for Telecommunications Sciences starting in 1995.  
But, this survey was conducted prior to the widespread introduction of wireless devices into the license-free bands.  As expected, this survey shows only minimal use of these bands.  No such comprehensive survey has since been conducted.  Thus we have little factual information about the present use of these bands.  

## Section 3--ADDITIONAL INFORMATION ABOUT NOISE MODELS

**WHILE ADDITIONAL INFORMATION WAS LOCATED, THE DOCUMENTS IN THIS SECTION SUPPLEMENT THOSE IN SECTION 1**
**A REFERENCE BY SPAULDING AND HAGN PROVIDE INFORMATION ABOUT THE HISTORY OF NOISE MODELS**

## Section 4--NOISE PROPAGATION

**PROPAGATION OF NOISE FROM ITS SOURCE TO A VICTIM IS A KEY FACTOR IN ANY MODEL DEALING WITH THE IMPACT OF NOISE ON SIGNAL RECEPTION.**
**A NUMBER OF DOCUMENTS WITH USEFUL INFORMATION ABOUT PROPAGATION WERE LOCATED.  **
**THIS INCLUDES A NUMBER OF PAPERS ON THE PROPOGATION OF SIGNALS AND NOISE IN AND AROUND BUILDINGS**.

## Section 5--SPECTRUM PLANNING

-  **ONLY MINIMAL INFORMATION IS AVAILABE FROM US SOURCES**
** ****SEVERAL EXCELLENT DOCUMENTS FOUND FROM UK SOURCES**
** ****THIS IS A HIGHLY NEGLECTED TOPIC IN THE US**

**Notes:**
The introductory page of this section identifies several important documents concerning the use of license-exempt spectrum.  These documents were funded by the Radio Communications Agency of the UK.  
A key aspect of the UK studies is that they were conducted by a combination of academic and industrial organizations.  Thus, a broad view of planning for the effective use of license-exempt bands was obtained.  
These documents provide an excellent basis for ongoing similar efforts in the UK, the US, and other countries that will encounter similar spectrum planning problems.
No similar studies have been funded in the US, yet we have a larger problem and should be the pioneers in the use of license-exempt bands.   It  would be logical and highly desirable for the FCC to fund and conduct similar studies directed toward the US problem. 

## Section 6--SYSTEM MODELS

-  **THE VARIETY OF MODULATION AND DETECTION SCHEMES USED IN WIRELESS RADIO PREVENTS THE USE OF SIMPLISTIC SYSTEM MODELS**
** ****A MASSIVE AMOUNT OF MATERIAL WAS IDENTIFIED DEALING WITH THE DETECTION OF SIGNALS IN THE PRESENSE OF NOISE**
** ****ONLY SELECTED DOCUMENTS ARE INCLUDED**

**Notes:**
This section will be of interest primarily to those modeling the performance of various wireless radio systems.  
Of interest is that a vast amount of material is available.  This is largely the result of the ability of individuals to formulate models for each type of modulation and each type of detection process.
All such models are limited in that useful descriptions of noise at the input terminals of wireless receivers is not available.  While assumptions about the properties of noise are used, these assumptions limit the application of each result to the limitations of the noise assumptions.

## Slide 13

**Notes:**
This view shows the components of a complete system model.

 The horizontal blocks in the middle of the view show a Wireless Radio
 The other blocks represent sources of noise that adversely affect reception of a desired signal.

 The center block has been modeled by a few individuals.  Three NPS theses and a few other individuals have deal with this aspect of modeling of a wireless system inside and outside structures.
 But no one has entered the noise blocks.

 Sub models exist that can be modified for use in all block, but they have not been assembled and used for a complete analysis.  This has been done at HF but not for Wireless Radios.

## Section 7--MEASUREMENT INSTRUMENTATION

-  **THERE IS NO LACK OF INSTRUMENATION**
** ****THREE APPROACHES ARE DESCRIBED**
** ****THE ITS APPROACH**
** ****THE SPECTRUM ANALYZER APPROACH**
** ****THE COMPUTER CONTROLLED RECEIVER APPROACH**

**Notes:**
 The measurement equipment used by the ITS exists and it can provide the inputs needed by the Middleton models.
 This is the most expensive approach, but it provides the most useful data.
 The spectrum analyzer approach is more flexible, smaller, and less costly.
But it requires preamplifiers, filters, and a control mechanism.
NPS employs this approach with manual control.
Others employ a similar approach with computer control.
 Both take advantage of the gaussian shaped IF of most spectrum analyzers to enable one to scale the amplitude of band-limited noise.
 The computer-controlled receiver approach is attractive because of available packages.  It can provide considerable information about the use of portions of the radio spectrum.
 One limitation is of concern--the shape of the bandwidth of all available receivers prevents scaling the amplitude of pulse and other wide-band emissions to other bandwidths.

## APPENDIXEXAMPLES OF EMISSIONS IN 2.4 GHz BAND

** ****SEVEN MEMORANDA SHOWING EXAMPLES**
** ****DATA OBTAINED AT ONLY ONE LOCATION**
** ****FIRST MEMO SHOWS EMISSIONS IN 2.4 GHz BAND**
** ****OTHERS SHOW TEMPORAL AND SPECTRAL STRUCTURE OF SOME OF THE EMISSIONS**

## Slide 16

**Notes:**
Bands Instrumentation used to collect data on emissions in 915 MHz and 2.4 GHz 
 Antenna at upper right.
 High dynamic range preamplifier on spectrum analyzer.  Peanut preamplifiers are not used since they overload and produce bum results contaminated with IM products.
 HP 8565A Spectrum Analyzer used as a scanning or fixed-tuned receiver.
 ELF Engineering time-history display used in real time.
 Tektronix camera used to record snapshots of data.
 Laptop computer with Paint-Shop Pro 7 used to format data and add scales.
 All data fully calibrated in frequency, time, and amplitude.
 All instrumentation mounted on a cart to move to any location.
 Identical instrumentation is installed in a small van.  
 Instrumentation provides real time views of the temporal and spectral properties of emissions in any part of the radio spectrum.  Both gross-scale and fine-scale data are obtained.

## Slide 17

**Notes:**
Example 1 
Shows an example of emissions in the 2.4 GHz band at a home office in Davis, CA
 Signal across the entire band is from FHSS portable phone.
 Strong signal near left edge of band is from SS portable phone,
 Lower level signal near left edge is narrow-band FHSS from an area coverage portable telephone.
 Signal slightly above center of band is unidentified pulse emission.

 Note the entire band has high-level signals except for two narrow spots not used by FFSS portable phone.
 Any new user at this location will encounter interference.
 Emissions change with time.
 Table at the bottom of the view provides measurement and location parameters.
 All data is fully calibrated in frequency, time, and amplitude.

## Slide 18

**Notes:**
 Example 2
 Another FHSS signal appears to add to the signal population.
 This signal appears erratically many times each day for long periods.
 It appears to be from a nearby portable phone with a different FH format than the other two FH signals.

## Slide 19

**Notes:**
 Example 3
 Microwave oven emissions were added to the band at erratic times.
 This oven was 30 feet from the victim antenna.
 Additional lower-level microwave oven emissions appeared frequently.

## Slide 20

**Notes:**
 Example of the gross spectral structure of microwave oven noise
 Note the strong spectral peak near the upper end of the band.
 Additional lower level spectral peaks are shown.
 Some spectral components are outside the ISM band.
 Spectral and temporal structures are both somewhat erratic.
 Noise comes in bursts synchronized with the power-line frequency.
 See ITS report for detailed measurements of spectral shape of many microwave ovens.
 Latest versions of microwave ovens using switching power supplies have not been examined.  This needs to be done to a few examples.  We have no information as yet about the structure of the emissions of these new ovens.

## Slide 21

**Notes:**
 Last Example
 Spectrum analyzer scan process was synchronized to power-line frequency.
 Spectrum analyzer set on zero frequency span so it is a fixed-tuned receiver.
 Analyzer output scanned with time-history oscilloscope.
 Top view shows microwave oven noise at 2450 MHz along with FHSS emissions from portable phone
 Bottom view shows microwave oven noise at 2420 MHz and FHSS emissions from a portable phone.

 Note that the FHSS signals appear at and near nulls in microwave oven noise.
 This FHSS portable phone experienced only minimal interference from microwave oven noise.
 The designers of this particular phone understood the temporal structure of microwave oven noise and inserted their hops between bursts of microwave oven noise.
 But the temporal structure of microwave oven noise severely limits the number of such emissions that can be added without encountering severe interference.

## SUMMARY COMMENTS

**1.  The concept of unlicensed bands for Wireless Radio is a highly popular and widely accepted type of radio service.  **
**2.  But, Wireless Radio is becoming an undefined monster that needs definition.  **
**3.  We find multiple kinds of users in the unlicensed bands that appear to be incompatible.  But we cannot find any useful US studies that examine the situation.**
**4.  The Radio Communications Agency in the UK has undertaken a series of excellent investigations into Wireless Radio.  We cannot find any equivalent work in the US.**

## SUMMARY COMMENTS CONTINUED

**5.  Only minimal data is available defining the growth and present use of the unlicensed bands. There is a vast difference between 1995 ITS data and the data in the appendix.**
**6.  We have the impression that Wireless Radios are clustered and not evenly distributed in location.  Thus, interference will be a clustered type of problem.**
**7.   Small amount of data available strongly suggests that interference is already a problem and it will only grow. **
**8.  The presence of multiple kinds of users in the unlicensed bands result in a confusing situation.  The mix of point-to-point data, video, portable telephone, wireless data, etc all add up to a highly confusing spectrum-use situation.**

## Slide 24

**Notes:**
 Wireless Radio at a small remote café in northern California 

 Only the big Harleys are missing in this view.
 Wireless Radio (a video link) is used to monitor the establishment during closed hours.
 It provides an inexpensive and highly effective way to detect and foil burglars and monitor unwanted nighttime activity in the parking lot.
 Wireless Radio is highly cost effective for this remote facility.