The multitude of items an engineer needs to consider during the communication system design phase is becoming more and more complicated. Properly designed communication sites, particularly cellular and personal communications services cell sites, must meet rigid system design criteria to facilitate integration into the network.
The design criteria for site selection in cellular and PCS must take into account a number of items, including technical, financial, maintenance and regulatory compliance issues. Electromagnetic radiation compliance needs to be one of the design criteria in the cell site acquisition and design phase.
Electromagnetic radiation invokes a range of responses from the sublime to outright panic, both from the community at large and from wireless operators. Almost everyone who has been in the wireless telecommunications industry, primarily cellular, has been asked, “Is electromagnetic radiation safe?” The answer to the EMF safety question is yes, the electromagnetic energy emitted from our site is safe but there are a few conditions. The caveat to the electromagnetic radiation question is the part that tends to draw attention since a definitive yes or no is the real desired response.
Emotional issues
Most current operators tend to take a reactive role in dealing with the EMF topic. Specifically, the unwritten rule tends to be, “Do not discuss it and it might go away.” Unfortunately or fortunately, depending on your point of view, the issue is not going to disappear and will likely intensify with the PCS spectrum.
During site acquisition there are several steps to minimize the controversy associated with electromagnetic fields and installation. Currently, towers or monopoles tend to draw the most responses, however more structures in urban and suburban areas are being located on top of existing building structures. Placing sites away from schools and residential homes is one technique pursued to help build out networks and avoid controversy. However this solution leads to two primary problems, the first is system design compromises, since there is no real grid and no perfect site. The other issue ties to the emotional controversy, “Why are you avoiding these areas for building sites if it is safe?” Cell site locations often are chosen that will avoid controversy to help ensure they will be constructed within that year’s goals and objectives.
Everyone that has had the pleasure of participating in the site acquisition process can tell you there are several key items that constantly arise. After the lease negotiation phase, there is concern about aesthetics, property devaluation and electromagnetic radiation. The first two items probably are the easiest to address since they are the most tangible. However, electromagnetic radiation always will invoke an emotional response from the landlord, local residents, board members or some combination, since radiation often is associated with cancer.
Prequalifying a potential site is one of the most important aspects to help move the process along. Explaining to the landlord your intentions, prior to a transmitter test, is essential. Problems due to miscommunication with the landlord have at times prevented site construction after a large amount of capital dollars already have been expended.
The potential landlord might not have understood what was being proposed to him or the communication system employee did not mention there would be antennas at the location. Another example is the residents at a location raised concerns regarding the EMF issue and the landlord decided not to pursue having the wireless operator as a tenant. A third example is where the landlord understands what is going on but when residents raise concerns about EMF, the site is eliminated for political reasons by the operator.
A key item for prequalifying a site to be located on top of a building involves walking the roof top and determining where potential antennas would be placed prior to any transmitter test. Conducting a pretransmitter survey of the location can avoid having the antennas placed right above or right next to someone’s balcony, roof patio or window. When the design calls for a monopole or a tower construction, having some flexibility in placing the structure on the property also can assist the effort. Properly placing the antenna or tower does not simply meet the design conditions for the location, but also minimizes or eliminates any negative responses.
A more expeditious method for site acquisition involves collocating with another service provider on a tower, monopole or building. However, whether you are a sole occupant or one of many at a communication site, there are a few rules that pertain to electromagnetic fields. Intermodulation usually is the primary focus of the RF engineer in a collocation situation, instead of composite power density levels. Cellular system operators currently use Part 22 and PCS providers will use Part 24 of the CFR 47 rules for determining electromagnetic emission levels from their facilities. Both use C95.1 as the basic reference for determining the allowable electromagnetic field strength permitted. Cellular currently uses the C95.1-1982 specification while PCS will use C95.1-1991.
The C95.1-1991 specification has two basic sets of criteria used to determine if a communication facility meets the regulations for a controlled and uncontrolled environment. Controlled pertains to the workers for the communication company, usually its RF technicians. The uncontrolled specification pertains to everyone else, that is, the general public. Generally the maximum uncontrolled environment power density level allowed is about one-fifth that of the controlled environment. The C95.1-1982 however does not differentiate between a controlled and uncontrolled environment. Many cellular operators are following C95.1-1991 already, if for no other reason than public relations.
The C95.1 specification not only differs for controlled and uncontrolled but also with frequency. Currently, cellular base stations transmit between 869 MHZ and 894 MHz. The new PCS systems will operate between 1850 MHz and 1990 MHz.
The new PCS frequencies are in the microwave region. Usually most people in cellular stress that cellular is not microwave, depending on what definition is used. PCS will operate in the microwave region, creating a thorn in the process for site acceptances, regardless of the low transmit power and the rapid attenuation experienced at this frequency.
Generally, the particular company petitioning to get on the facility will point out that its emission levels are well within specification levels. However, when collocating, the total power from all the transmitters at that facility must be considered.
Determining the total power density at a potential location is not easy since the degree of documentation from one facility to another varies greatly depending on the site manager. The alternative is to take a spectrum analyzer, or wideband power density probe and measure power density in the area around the facility. Conducting a field test is a viable method but determining composite power is difficult since simultaneous full loading of cellular, paging and two-way systems is not normal. The biggest disadvantage to using the physical testing methodology is the time and effort spent collecting data when an analytical method could suffice for more than 90 percent of the locations.
During the site acceptance phase, it is strongly advisable to keep the antennas away from a common access area in any residential buildings. Although this should be common sense, most of us can recall situations where this simple first step did not take place resulting in much after-the-fact work and damage control. A simple chart with distances and power levels should be used as an initial step in the process when conducting the initial site survey. Once the actual antenna locations are selected and after a structural review, the distance calculations should be checked ag
ain.
There are a variety of things that can be done to keep in compliance with the specification if the calculations or field measurements show the appropriate power level has been exceeded. One obvious method is to reduce the power, but this has a negative impact on the site’s coverage area. Another suggestion is to relocate the antennas so there is more vertical isolation, however this might lead to aesthetic problems, installation complications and cost increases for the facility. A third suggestion is to lower the maximum amount of channels available at the facility, but this would create a limited site in the system design.
A proactive approach
When the time comes to meet with the local board to request a variance, it is important to address the EMF issue right away. There are two primary schools of thought on the topic, proactive and reactive. Most cellular communication companies promote the reactive method for dealing with EMF. The method has its advantages. The philosophy is not to educate or notify the groups that will oppose the construction of the facility.
The other philosophy is to be proactive in the site acquisition phase, setting up an abutter meeting and sending out preliminary information about what the intentions are, with a brief drawing prior to the mandatory mailing. Both of these philosophies have met with success and failure on a site-by-site basis.
A proactive EMF campaign is the desired method with the amount of build-out activity that will take place with PCS. It is in everyone’s interest to educate the public about EMF and the benefits of cellular and PCS.
When presented at a planning board or zoning board meeting, the EMF issue often will not be raised. One commonly overlooked step during the process is the presenters tend to focus on the board and not the public. Specifically, if the public does not want to have the site, the board’s chance to approve it is low, even in the face of a costly appeal. It is suggested that a document on EMF be presented including all the topics that are normally asked. You can either craft your own or rely on the information the Cellular Telecommunications Industry Association and the Electromagnetic Energy Association have available to pass out. Either method will generate some immediate benefit in addressing the EMF issue up front and leave people with something in their hands.
One technique that has found merit in presentations to a planning or zoning board is to reference the proposed emission levels of the facility to the C95.1-1991 specification. This method avoids trying to equate the power level of one service to that of another, which is a common practice. Focusing on specification compliance reduces the number of questions that are not relevant to the topic at hand. Several data points are chosen with the aid of the real estate representative that the local board or residents might be interested in knowing.
It also is strongly suggested that EMF discussions be rehearsed in front of company management. The testimony or comments issued by the employees during this time are recorded and will be used when generating an appeal. Having a common set of answers for routinely asked questions will ensure a uniform response from the company. Therefore, when a subscriber or resident near a cell site calls the company to ask a question on EMF, the same response is provided by customer service, sales and the technical staff.
The most direct method of establishing a uniform response to EMF questions is to refer to an EMF Policy. A few companies have established or an electromagnetic or EMF Policy for their employees. Some have gone to the point of employing personal dosimeters on their technicians.
There should be a phased approach to handling people who call in to customer service or through corporate communications, requesting information about EMF. Standard information packages should be ready that contain the documents used for the planning and zoning board meetings with a standard cover letter attached. The second level of response involves a brief conversation with the resident, using standard answers and asking specific questions about their concerns. The next phase is to conduct a site visit to the location, using someone from customer service or corporate communications, along with engineering staff.
There are a variety of cost-effective mitigation solutions available for handling location specific problems besides those mentioned previously. The key to implementing any mitigation technique is ease of installation, minimizing complexity and cost.
Conclusion
All communication site designs need to incorporate a design criteria associated with electromagnetic compliance. Scenarios were presented with some recommended action items that could be taken. Electromagnetic compliance needs to be integrated into the site acquisition and design phase and the operation of the communication facilities. Establishing a composite power budget also is recommended when collocating with another service provider.
Uniform EMF guidelines are recommended for cellular and PCS carriers to follow. Establishing uniform EMF guidelines will facilitate handling this emotional issue with the public. By addressing the EMF issue in a proactive position at the beginning of the site acquisition process, the time to activation of the communication facility can be minimized. Lastly, compliance with the EMF emission levels referenced in C95.1-1982 and 1991 need to be adhered to in order to remain in compliance with the FCC license.
For further information on this topic, the following documents can be acquired or the organizations can be contacted for assistance: CFR 47, Government Printing Office, Washington D.C., at (202) 512-1800; C95.1-1991 specification can be acquired from IEEE (800) 678-IEEE; EMF INFOLINE (800) EMF-2383; EEA (202) 452-1070; CTIA (202) 785-0081; TWS (800) SERV-PCS.
Clint Smith is the director of TWS and is a registered professional engineer. He has more than 13 years of engineering and management experience, eight years directly in cellular communications. Prior to TWS, Smith was the director of engineering at Nynex Mobile Communications Inc.
