Subject: Noise Environment Sub-Committee - Initial Proposal

Author: Motorola

Date August 11, 1999

Task Definition

In response to FCC requests, the TAC formed three sub-committees covering various topics impacting radio spectrum policy. These topics were Software Radio, Ultra Wideband Radio and the Noise Environment.

The charter of the Noise Environment sub-committee was defined as follows.

Noise Environment Sub-Committee Charter

Assess and report to the Commission the current state of knowledge on electromagnetic noise levels and the effects of such noise on the reliability of existing and future communications systems. Identify, if possible, man made causes of electromagnetic noise that have or are likely to have harmful effects on wireless communications. Identify issues or causes of man made electromagnetic noise that justify FCC attention or action. Determine what types (if any) of electromagnetic noise create significant concerns and suggest technical approaches for obtaining sufficient information on the subject.

Scope

Our approach to addressing this charter was to first define the scope of this effort. We felt that potential noise from RF communication devices (Cell phones, two-way radios, microwave equipment, etc), other types of devices (e.g. computers, cars, power lines, industrial equipment) and natural phenomena (atmospheric noise, sun spots) should be included as possible sources.

We also felt it necessary to focus any efforts that dealt with noise from RF communications devices. The FCC and industry already work closely to identify limits of emissions for services in specific bands. . These efforts help ensure that different types of communications systems designed for a specific service (such as cellular) can co-exist in their defined band. We did not wish to duplicate these on-going efforts. However, we also felt that at times the issues of interference to different services in other bands are not as fully considered. As a result, we are proposing that the noise from RF communications devices only be investigated for frequencies outside the intended band of operation for a given service.. This makes a lot of sense for the licensed bands. What about the unlicensed bands however? Is there an issue about the noise environment in 902-928 MHz or the other ISM/Part 15 bands?

Interference from computers will fall into this category. Also, any intentional radiator that is licensed under part 15 and operating in the ISM bands should be check for out-of –band emission levels. As an example, we would not evaluate interference between different types of point to point microwave systems in the 6Ghz commercial band. However, we might evaluate how noise from these microwave systems would impact cellular systems in the 2GHz band.

Approach

It is desirable to understand the level of concern for noise environment within the communications industry and to identify key current and future issues. Therefore, a survey of key operators and manufacturers on noise issues they have identified and where they feel additional regulatory focus is required should be the first step.

Assuming that the noise environment is a significant issue, the broad approach proposed to address the items in the charter is to measure the characteristics of specific noise sources, define a model for each type of source and then identify their impact on communication systems through simulation. This approach was chosen since direct and detailed measurements of the noise environment and its impact are very difficult and of questionable value. This is due to a number of factors. The first factor is that the environment can vary significantly from one location to another and from one time to another. A direct measurement approach would force the choice of a set of ‘typical environments’ or the establishment of a massive measurement program. Even if this approach were taken, it would be difficult to identify the impact of a specific source of noise through direct measurement. The result of direct measurement is usually a composite noise level rather than the contribution of a specific source. In many cases, the accurate measurement of noise is also very difficult due to the low signal levels being measured. With direct measurement, desired signals or large signals that are close in frequency to the noise being measured often mask the noise level. Further, direct measurements of the noise environment do not allow easy exploration of the impact of different scenarios, or possible solutions to noise problems. Finally, unless there is a significant ongoing measurement program, this approach is not useful for predicting the future noise environment.

The items in the charter would be specifically addressed as follows.

Item 1: The state of knowledge of electromagnetic noise levels

This item should be assessed through a literature search as well as through additional information that private companies, public institutions, and government agencies might have gathered through internal research. A consultant familiar with noise measurement and the impact of noise on communication systems would be the best way to consolidate the information gathered. This search should attempt to identify specific noise sources, their frequency characteristics and their level of impact on the noise environment. Review of this material by members of the sub-committee or their appointees would ensure meaningful analysis of the gathered information.

Item 2: Man-made causes of noise affecting wireless communications

This item should be addressed by measurement of the major current or projected causes of man-made noise identified from the literature search and other inputs. Broadband models of the noise emitted by these sources should be developed. The level of noise as a function of distance from the source should also be determined.

Item 3: The effects of noise on current and future communications systems

The minimum distance (or minimum attenuation) from potential noise sources to several different types of communications systems should be determined. This information along with the noise models generated above should be used in a simulation to identify the impact of particular noise sources on the different types of communication systems. In situations where multiple noise sources need to be taken into account, a statistical analysis using Monte Carlo techniques should be done.

Item 4: Issues and causes of interference that justify FCC attention

This item can also be assessed via modeling and simulation as discussed above. The simulations in item 3 will identify sources that can cause issues. It is also expected that inputs from manufacturers and operators of communications systems (see item1) will identify FCC regulations with the potential to cause noise issues.

New noise models should be defined based on these FCC regulations and the impact of equipment emitting at the maximum level allowed by the regulations would be evaluated through simulation.

Item 5: Types of noise causing concern and approaches for gaining sufficient information on them

This item can be addressed through item 4 and verification of the models and simulation through measurements. Although the simulations should give representative values for the noise due to particular sources, it is desirable to verify the impact of the major sources through measurement.

Status

After reviewing and contacting various potential research organizations, IITRI has been requested and has provided a proposal for the literature search. We are working with them to further refine their proposal.

A proposal for a first phase evaluation of the noise environment has also been defined (see below). IITRI has responded with a plan for this phase as well. We are working with IITRI to further refine this proposal and will obtain a cost estimate within the next 2 weeks on this phase as well.

Proposal

The following is a proposal for a first phase of measurements of the noise environment.

Noise Sources

The first step taken in developing this proposal was to identify possible sources of noise. These sources are listed below.

1. Aircraft

2. Automotive electronics

3. Automotive ignition systems

4. Cell phones

5. Cellular base stations

6. Commercial and military satellites

7. Computers

8. Construction equipment

9. Heating, ventilating and air conditioning

10. Heavy industry and power generation facilities

11. High frequency cable systems

12. Home electronics

13. Natural sources (sun spots etc)

14. Radar

15. Railways, trolleys, electric buses

16. Repeaters

17. TV transmitters

18. Two way radios

19. Ultra wideband radios

The literature search and other inputs would be used to prioritize these sources in terms of level of impact on the noise environment and the most significant would be chosen for further investigation

Evaluation of the Impact of Noise Sources

Noise sources generally impact wireless communication systems by increasing the noise in the receiver. This reduces the range of the system. Two types of interference cases are relatively common; base station and subscriber interference. A base station case is shown below.

Interferer Desired

In this case, an interferer that is close to a base station has enough noise in the base stations receive band that it effectively increases the noise floor of the base station receiver. This reduces the ability of other subscriber units to communicate with the base station and thus reduces the range of the system. Since the base station antenna is usually mounted on a tower or building, interferers are limited in how close they can get to the antenna, so there is a significant minimum path loss.

The second type of interference is subscriber interference as shown below.

Interferer Desired

Although the mechanism for range reduction is the same (increase in the subscriber’s receiver noise floor), there is a significant difference in the minimum path loss since a subscriber unit can be very close to the interferer.

Although all radio systems do not have exactly these configurations, the interference mechanism is still the loss of range due to a noise floor rise and the key parameters are the interferers noise power spectral density and the minimum path loss.

From this example, two types of information are necessary: 1) the noise generated by the interferers and 2) the minimum path loss between the noise source and the receiver that is receiving the interference.

Measurement Details & Analysis

In order to adequately characterize noise sources and their impact on current and future communication systems, measurements of noise sources and communications systems will be necessary. The measurements of noise sources will allow the development of broadband noise models of significant sources of noise. The measurement of communication systems will consist of measurements of the propagation loss as a function of the distance to particular types of receiving systems. These measurements will then be combined in a simulator that calculates the noise floor rise as a function of the distance to the interferer. Worst case noise floor rise can be obtained by identifying and simulating worst case placements of one or more interferers.

Noise Source Measurements

As a first step, the most significant sources of noise should be measured. We propose measuring the 4-5 most significant sources. These sources should be determined based on the results of the literature search and other inputs.

Spectral characteristics of the emission from each noise source should be captured and characterized (discrete spectra and their levels and the noise spectra shape).

Noise field strength in a 1Hz bandwidth as a function of distance from the source should be measured at bands of interest (typically from 400MHz to 60Ghz).

Units from several manufacturers should be characterized to account for manufacturer variations.

Communication Systems Measurements

Various systems that might be interfered with should be measured to determine the loss versus the distance to potential interferers.

Some specific systems and frequency bands that should be considered as having potential to be interfered with are as follows.

1. Current & future cellular and land mobile systems (e.g. @ 700, 800MHz, 2 &

3.5GHz)

2. Navigational satellite systems (approximately 1600 MHz, and other

known future satellite bands).

3. Fixed point to point and point to multipoint microwave systems

(microwave bands including 2.5, 5.5, 30, and 60 GHz should be measured).

4. Wireless LAN -current and proposed bands

Analysis

Given the transmitted noise, the path loss versus distance to the interferer and the placement of specific noise sources, the maximum expected noise floor degradation for specific communication systems due to noise sources at those distances can be calculated. For situations where it is expected that multiple non-continuous interferers could be significant, a Monte Carlo simulation of a distribution of interferers should be done.

The noise floor impact on the above systems should also be analyzed assuming the interferers are radiating at a level equal to the FCC limit on radiation from the interfering source assuming a single interferer and also assuming a worst case distribution for multiple interferers. These measurements should help assess the ability of current FCC rules to protect various types of communication systems.

Additional Efforts

After the initial measurements and analyses are completed, additional potential noise contributors would be measured and analyzed to capture a broader range of potential noise sources.

A verification of the models and simulation results through measurement of a worst case situation may be desirable in specific cases where further regulation may be desirable.

The basic information and approach used in this assessment of the noise environment would also be available for analyses of other situations as other noise issues arise.