Traditionally, cellular deployments were based solely on achieving ubiquitous coverage with little consideration for capacity requirements. Since the only services offered were voice and the market was uncertain, this was a very reasonable approach. Moreover, the voice service offering is a low data rate application enabling traditional cellular networks to achieve wide outdoor and indoor coverage with a low data rate network (~10-15 kbps bandwidth depending on type of vocoder). As the customer base grew and more services offered, additional base stations were deployed and/or channels added to existing base stations to meet the growing capacity requirements. With Mobile WiMAX, however, operators will want to offer a wide range of broadband services with Quality-of-Service (QoS) support. To meet customer expectations for these types of services it will be necessary to predetermine capacity requirements and deploy accordingly at the outset. Careful deployment planning in anticipation of growing customer demands will ensure a quality user experience when the network is at its busiest.
Determining Capacity Requirements
Arriving at an accurate estimate of capacity requirements for new broadband services is not a simple exercise. One must anticipate how users will make use of the new services being offered and how often users will be actively engaged with the network. Data density, expressed as Mbps per km^2, is a convenient metric for describing capacity requirements. Determining the required data density for a specific demographic region is a multi-step process.The expected market penetration, or take-up rate, at maturity is dependent on a number of factors including the competitive situation and the services offered that distinguish one service provider from another. The service provider’s penetration may also vary within the metropolitan area since urban and dense urban residents will often have other broadband access alternatives from which to choose as compared to residents in suburban and rural areas.
Base Station Deployment Alternatives
Mobile WiMAX base station equipment will be available from many different vendors and, although all will be WiMAX compliant and meet performance and interoperability requirements, a great many different configurations will be available from which service providers can choose. The availability and timing of optional features also adds to the equipment variability. Additionally, there are different frequency bands that can be considered and varied amounts of spectrum availability within these bands. The spectrum choices will, in many cases, affect the frequency reuse factor and the channel bandwidths that can be employed in the access network.WiMAX solutions with beamforming will generally be architected quite differently from
SIMO and MIMO solutions. A typical SIMO or MIMO configuration will have power amplifiers mounted at the base of the tower to facilitate cooling and maintenance. The amplifiers in this case would have to be sized to compensate for cable losses, which can range from 2 to 4 dB depending on tower height and frequency. Beamforming solutions require good phase and amplitude control between transmitting elements and will often be architected with their power amplifiers integrated with the antenna elements in a tower-mounted array. The larger size and weight of these structures will also require more robust mounting. There is additional signal processing requirements for beamforming solutions with Adaptive Beamforming being the most computational intensive.
The selection of channel bandwidth and duplexing method can also have an economic impact on the varied WiMAX deployment alternatives. In addition the desired “worse case” UL rate will affect the UL link budget and therefore, impact the range and coverage of the base station.
Conventional cellular deployments used cell frequency reuse factors as high as seven (7) to mitigate intercellular co-channel interference (CCI). These deployments assured a minimal spatial separation of 5:1 between the interfering signal and the desired signal but required seven times as much spectrum. With technologies such as CDMA, introduced with 3G, and OFDMA, introduced with WiMAX, more aggressive reuse schemes can be employed to improve overall spectrum efficiency.
Number of Base Stations
The key metric for a quantified comparison will be the number of WiMAX base stations required to meet both capacity and coverage requirements in the varied demographic regions. The WiMAX base station is a key network element in connecting the core network to the enduser in that it determines the coverage of the network and defines the end-user experience. If too few base stations are deployed the coverage will not be ubiquitous and the end-user may experience drop outs or periods of poor performance due to weak signal levels as he moves throughout the coverage area. And since the base station investment will tend to be a dominant contributor to the total end-to-end network costs, deploying too many base stations can result in unnecessary start-up costs for the operator leading to a weaker business case.
Summing up
In the long term, the higher performance base stations with wideband channels provide a potentially more cost-effective deployment solution as measured by the number of required base stations. One might conclude that it would be worth waiting for antenna technologies such as beamforming and beamforming + MIMO and possibly even 20 MHz channels, before deploying a Mobile WiMAX network. This however, is not the case. In the early years , deployment can begin with range-limited base stations using (1x2) SIMO or (2x2) MIMO base station configurations to get ubiquitous coverage over the entire metropolitan area. These base stations can then be upgraded in the following years with beamforming and beamforming + MIMO as necessary to meet the capacity requirements in anticipation of a growing customer base. In most metropolitan area deployments this will only be necessary in the dense urban and urban areas.
The C-band frequency is used worldwide by fixed satellite services (FSS) operators to eliver TV transmissions, distancelearning, telemedicine, disaster recovery, meteorological and earth observation services, and also by certain military services. Today, there are approximately 160 geostationary satellites operating in the C-band frequency worldwide. In addition, two out of every three commercial satellites under construction will utilize C-band. The deployment of broadband wireless access (BWA) services, including WiMax, has been gaining momentum in several countries. BWA equipment, slated to operate within the 3.4-3.7 GHz ranges of the FSS extended C-band frequency, has been demonstrated to severely interfere with satellite communications operating within the C-band. Early Indications With several national administrations having designated portions of the C-band for terrestrial wireless applications, including BWA and future mobile services, massive interruptions of satellite services, radar and microwave links has occurred in those regions. Interference has also been reported in other parts of the world, including Australia, Bolivia, Fiji, Hong Kong, Indonesia, Pakistan, Kazakhstan, and Sub-Saharan Africa. Compatibility testing in areas where WiMax services are being implemented has clearly indicated the potential for significant threat to satellite services operating in Cband. A BWA field trial in Hong Kong, for example, inadvertently knocked off the TV-signal feeds to an estimated 300,000 households throughout Asia.
Airspan and Fujitsu were selected as mobile WiMAX equipment providers to UQ Communications, a mobile WiMAX operator in Japan. UQ Communications is jointly owned by KDDI, Intel, East Japan Railway Company, Kyocera, Daiwa Securities and the Bank of Tokyo-Mitsubishi.
Airspan products also include “self install” and professionally installed customer premise equipment.
KDDI, Japan’s number two cellular carrier, will receive one of two WiMax licenses to be awarded by the Japanese government.
The KDDI group, called Wireless Broadband Planning, and one led by rival carrier Willcom was recommended by Japan’s Ministry of Internal Affairs and Communications recently to win the licenses, reports Reuters.
Intel owns a 17.65 percent stake in KDDI’s Wireless Broadband Planning group. The stake is matched by East Japan Railway and Kyocera, and all three sit behind leading shareholder KDDI, which has a 32.26 percent stake.
The WiMax services will operate in the 2.5GHz band and will be capable of providing data service at up to 20Mbps to terminals travelling at up to 100 kilometers per hour, according to the Japanese government.
Japan’s cell phone carriers have been testing WiMax for some time. It will likely mean that cellphone leader NTT DoCoMo and third-ranked Softbank probably will have to lease networks from KDDI or Willcom if they are to offer competing services.
KDDI, Japan’s number two cellular carrier, had 29 million subscriptions to its CDMA2000 cell phone service at the end of November this year. Willcom, which uses the PHS (Personal Handyphone System) technology to offer a data-centric service, had 4.6 million subscriptions.
Mobile phone radiation and health concerns have been raised, especially following the enormous increase in the use of wireless mobile telephony throughout the world (as of August 2005, there were more than 2 billion users worldwide). This is because mobile phones use electromagnetic radiation in the microwave range. These concerns have induced a large body of research (both epidemiological and experimental, in non-human animals as well as in humans). Concerns about effects on health have also been raised regarding other digital wireless systems, such as data communication networks.
The World Health Organization has concluded that serious health effects (e.g. cancer) are very unlikely to be caused by cellular phones or their base stations, and expects to make recommendations about mobile phones in 2007–08.
However, some national radiation advisory authorities, including those of Austria, France, Germany and Sweden recommend to their citizens measures to minimize exposure. Examples of the recommendations are:
However, the use of "hands-free" was not recommended by the British Consumers' Association in a statement in November 2000.
Calculated specific absorbed radiation (SAR) distribution in an anatomical model of head next to a 125 mW dipole antenna. Peak SAR is 9.5 W/kg over 1 mg. (USAF/AFRL).Part of the radio waves emitted by a mobile telephone handset are absorbed by the human head. The radio waves emitted by a GSM handset, can have a peak power of 2 watts, and a US analogue phone had a maximum transmit power of 3.6 watts. Other digital mobile technologies, such as CDMA and TDMA, use lower output power, typically below 1 watt. The maximum power output from a mobile phone is regulated by the mobile phone standard it is following and by the regulatory agencies in each country. In most systems the cellphone and the base station check reception quality and signal strength and the power level is increased or decreased automatically, within a certain span, to accommodate for different situations such as inside or outside of buildings and vehicles.
The rate at which radiation is absorbed by the human body is measured by the Specific Absorption Rate (SAR), and its maximum levels for modern handsets have been set by governmental regulating agencies in many countries. In the USA, the FCC has set a SAR limit of 1.6 W/kg, averaged over a volume of 1 gram of tissue, for the head. In Europe, the limit is 2 W/kg, averaged over a volume of 10 grams of tissue. SAR values are heavily dependent on the size of the averaging volume. Without information about the averaging volume used comparisons between different measurements can not be made. Thus, the European 10-gram ratings should be compared among themselves, and the American 1-gram ratings should only be compared among themselves. SAR data for specific mobile phones, along with other useful information, can be found directly on manufacturers' websites, as well as on third party web sites.
One well-understood effect of microwave radiation is dielectric heating, in which any dielectric material (such as living tissue) is heated by rotations of polar molecules induced by the electromagnetic field. In the case of a person using a cell phone, most of the heating effect will occur at the surface of the head, causing its temperature to increase by a fraction of a degree. In this case, the level of temperature increase is an order of magnitude less than that obtained during the exposure of the head to direct sunlight. The brain's blood circulation is capable of disposing of excess heat by increasing local blood flow. However, the cornea of the eye does not have this temperature regulation mechanism. Premature cataracts have not been linked with cell phone use, possibly because of the lower power output of mobile phones.
It has been claimed that some parts of the human head are more sensitive to damage from increases in temperature, particularly in anatomical structures with poor vasculature, such as nerve fibers.
The communications protocols used by mobile phones often result in low-frequency pulsing of the carrier signal.
Some studies have claimed to show that mobile phone signals affect sleep patterns and possibly delay sleep onset during exposure. In another clinical study, carried out by Sweden's Karolinska Institute and Wayne State University in the US, the authors concluded their research suggested an association between RF exposure and adverse effects on sleep quality within certain sleep stages, though participants were unable to determine better than chance if they had been exposed to actual radiation or sham exposure. The UK National Health Service criticized the research because of the small sample size used, and because of the 53% of participants who reported sensitivity to mobile use, a proportion unlikely to be representative of the general population. The NHS also criticized the press for inaccurate reporting of the study.
Some researchers have argued that so-called "non-thermal effects" could be reinterpreted as a normal cellular response to an increase in temperature. The German biophysicist Roland Glaser, for example, has argued that there are several thermoreceptor molecules in cells, and that they activate a cascade of second and third messenger systems, gene expression mechanisms and production of heat shock proteins in order to defend the cell against metabolic cell stress caused by heat. The increases in temperature that cause these changes are too small to be detected by studies such as REFLEX, which base their whole argument on the apparent stability of thermal equilibrium in their cell cultures.
Swedish researchers from the University Lund, Salford, Brun, Perrson, Eberhardt and Malmgren, have studied the effects of microwave radiation on the rat brain. They found a leakage of albumin into brain via a permeated blood-brain barrier.
Research published in 2004 by a team at the University of Athens had a reduction in reproductive capacity in fruit flies exposed to 6 minutes of 900 MHz pulsed radiation for five days. Subsequent research, again conducted on fruit flies, was published in 2007, with the same exposure pattern but conducted at both 900 MHz and 1800 MHz, and had similar changes in reproductive capacity with no significant difference between the two frequencies. Following additional tests published in a third article, the authors stated they thought their research suggested the changes were “…due to degeneration of large numbers of egg chambers after DNA fragmentation of their constituent cells …”.
In December 2004, a pan-European study named REFLEX (Risk Evaluation of Potential Environmental Hazards from Low Energy Electromagnetic Field (EMF) Exposure Using Sensitive in vitro Methods), involving 12 collaborating laboratories in several countries showed some compelling evidence of DNA damage of cells in in-vitro cultures, when exposed between 0.3 to 2 watts/kg, whole-sample average. There were indications, but not rigorous evidence of other cell changes, including damage to chromosomes, alterations in the activity of certain genes and a boosted rate of cell division.
In 2006 a large Danish study about the connection between mobile phone use and cancer incidence was published. It followed over 420,000 Danish citizens over 20 years and showed no increased risk of cancer.The German Federal Office for Radiation Protection (BfS) consider this report as inconclusive.
In order to investigate the risk of cancer for the mobile phone user, a cooperative project between 13 countries has been launched called INTERPHONE. The idea is that cancers need time to develop so only studies over 10 years are of interest.
The following studies of long time exposure have been published:
Other studies on cancer and mobile phones are:
Some users of mobile handsets have reported feeling several unspecific symptoms during and after its use; ranging from burning and tingling sensations in the skin of the head and extremities, fatigue, sleep disturbances, dizziness, loss of mental attention, reaction times and memory retentiveness, headaches, malaise, tachycardia (heart palpitations), to disturbances of the digestive system all of which can be attributed to psychological stress (e.g. Placebo, Nocebo).
Another area of worry about effects on the population's health have been the radiation emitted by base stations (the antennas on the surface which communicate with the phones), because, in contrast to mobile handsets, it is emitted continuously and is more powerful at close quarters. On the other hand due to the attenuation of power with the square of distance, field intensities drop rapidly with distance away from the base of the antenna. Base station emissions must comply with ICNIRP guidelines of a maximum power density of 4.5 W/m² for 900 MHz and 9 W/m² for 1800 MHz.
These guidelines are set for short term heating, which is the only understood mechanism of electromagnetic fields on biological tissue. The ICNIRP guidelines are distrusted by some scientists, such as the BioInitiative group, who report that the existing standards for public safety are inadequate to protect public health.
A 2002 survey study by Santini et al. in France found a variety of self-reported symptoms for people who reported that they were living within 300 metres (984 ft) of GSM cell towers in rural areas, or within 100 m (328 ft) of base stations in urban areas. Fatigue, headache, sleep disruption and loss of memory were among the symptoms reported. Similar results have been obtained with GSM cell towers in Spain, Egypt, Poland and Austria. It is, however, important to note that these surveys do not show statistically significant clustering or causality and those complaining of adverse symptoms may be displaying the nocebo effect, unless this is controlled in the study.
However, a study conducted at the University of Essex concluded that mobile phone masts were unlikely to be causing these short term effects in a group of volunteers who complained of such symptoms. The study has been criticised as being skewed due to drop-outs of test subjects, although electrical sensitivity lobby groups have praised the study as a whole, and these criticisms were answered by the authors.
As technology progresses and data demands have increased on the mobile network, towns and cities have seen the number of towers increase sharply, including 3G towers which work with larger bandwidths. Many measurements and experiments have shown that transmitter power levels are relatively low - in modern 2G antennas, in the range of 20 to 100 W, with the 3G towers causing less radiation than the already present 2G network. An average radiation power output of 3 W is used. The use of 'micro-cell geometries' (large numbers of transmitters in an area but with each individual transmitter running very low power) inside cities has decreased the amount of radiated power even further. The radiation exposure from these antennas, while generally low level, is continuous.
Telecommunication workers who spend time at a short distance from the active equipment, for the purposes of testing, maintenance, installation, etc. may be at risk of much greater exposure than the general population. Many times base stations are not turned off during maintenance, because that would affect the network, so people work near "live" antennas.
A variety of studies over the past 50 years have been done on workers exposed to high RF radiation levels; studies including radar laboratory workers, military radar workers, electrical workers, amateur radio operators. Most of these studies found no increase in cancer rates over the general population or a control group. Many positive results could have been attributed to other work environment conditions, and many negative results of reduced cancer rates also occurred.
In order to protect the population living around base stations and users of mobile handsets, governments and regulatory bodies adopt safety standards, which translate to limits on exposure levels below a certain value. There are many proposed national and international standards, but that of the International Commission for Non-Ionizing Radiation Protection (ICNIRP) is the most respected one, and has been adopted so far by more than 80 countries. For radio stations, ICNIRP proposes two safety levels: one for occupational exposure, another one for the general population. Currently there are efforts underway to harmonise the different standards in existence.
Radio base licensing procedures have been established in the majority of urban spaces regulated either at municipal/county, provincial/state or national level. Mobile telephone service providers are, in many regions, required to obtain construction licenses, provide certification of antenna emission levels and assure compliance to ICNIRP standards and/or to other environmental legislation.
Many governmental bodies also require that competing telecommunication companies try to achieve sharing of towers so as to decrease environmental and cosmetic impact. This issue is an influential factor of rejection of installation of new antennas and towers in communities. The safety standards in the U.S. are set by the Federal Communications Commission (FCC). The FCC has based its standards primarily on those standards established by the Institute of Electronics and Electrical Engineering (IEEE), specifically Subcommittee 4 of the "International Committee on Electromagnetic Safety".
Camouflaging towers to look like tree trunks and other more visually acceptable structures has been tried so that the usually unaesthetic towers fit better into their surrounding environment.
In the USA, a small number of personal injury lawsuits have been filed by individuals against cellphone manufacturers, such as Motorola, NEC, Siemens and Nokia, on the basis of allegations of causation of brain cancer and death.[39] Many of these cases have been decided in a federal court[citation needed], where it is required that expert testimony relating to science must be first evaluated by a judge, in a Daubert hearing, to be relevant and valid before it is admissible as evidence.
In 2000, the World Health Organization (WHO) recommended that the precautionary principle could be voluntarily adopted in this case. It follows the recommendations of the European Community for environmental risks. According to the WHO, the "precautionary principle" is "a risk management policy applied in circumstances with a high degree of scientific uncertainty, reflecting the need to take action for a potentially serious risk without awaiting the results of scientific research." Other less stringent recommended approaches are prudent avoidance principle and ALARA (As Low as Reasonably Achievable). Although all of these are problematic in application, due to the widespread use and economic importance of wireless telecommunication systems in modern civilization, there is an increased popularity of such measures in the general public. They involve recommendations such as the minimization of cellphone usage, the limitation of use by at-risk population (such as children), the adoption of cellphones and microcells with ALARA levels of radiation, the wider use of hands-off and earphone technologies such as Bluetooth headsets, the adoption of maximal standards of exposure, RF field intensity and distance of base stations antennas from human habitations, and so forth.
