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Base Station

Base station

Base stations (or BSc) are low-power multi-channel two-way radios which are in a fixed location. They are typically used by low-power single-channel, two-way radios such as mobile phones, portable phones and wireless routers. When you talk on such a mobile phone, you (and perhaps dozens of other people around you) are talking to a nearby base station. From that base station your phone call is connected into the regular land-line phone system by the mobile phone network. In the case of a portable phone, the connection is typically direct to a land line.

Emissions issues

Because mobile phones and their base stations are two-way radios, they produce radio-frequency (RF) radiation (that's how they communicate), and they expose people near them to RF radiation giving concerns about mobile phone radiation and health. However, because both the phones and the base stations are low power (short range), the RF radiation exposure levels from them are generally very low. The consensus of the scientific community, both in the US and internationally, is that the power from these mobile phone base station antennas is far too low to produce health hazards as long as people are kept away from direct access to the antennas. It is critical to be aware of the difference between antennas, the objects that produce RF radiation; and towers or masts, the structures that the antennas are placed on. It is the antennas that people need to keep their distance from, not the towers that hold the antennas. It is also important to be aware that there are many different designs of mobile phone base stations that vary widely in their power, their characteristics, and their potential for exposing people to RF radiation. It is well worth considering, however, that the current international exposure guidelines (INCIRP) are based largely on what is described as the thermal effects of base station emmissions. Some scientists have questioned whether there are non thermal effects from being exposed to low level RF frequencies such as are transmitted from mobile phone base stations. Such 'non-thermal' effects include how the actual frequencies interfere with the human brain and all other cells in the human body. Sources for consideration can be found at [www.emf-solutions.org.uk]

See also


- Base Transceiver Station
- Mobile phone
- Portable phone
- Mobile phone radiation and health Category:Wireless communications

Base station

Base stations (or BSc) are low-power multi-channel two-way radios which are in a fixed location. They are typically used by low-power single-channel, two-way radios such as mobile phones, portable phones and wireless routers. When you talk on such a mobile phone, you (and perhaps dozens of other people around you) are talking to a nearby base station. From that base station your phone call is connected into the regular land-line phone system by the mobile phone network. In the case of a portable phone, the connection is typically direct to a land line.

Emissions issues

Because mobile phones and their base stations are two-way radios, they produce radio-frequency (RF) radiation (that's how they communicate), and they expose people near them to RF radiation giving concerns about mobile phone radiation and health. However, because both the phones and the base stations are low power (short range), the RF radiation exposure levels from them are generally very low. The consensus of the scientific community, both in the US and internationally, is that the power from these mobile phone base station antennas is far too low to produce health hazards as long as people are kept away from direct access to the antennas. It is critical to be aware of the difference between antennas, the objects that produce RF radiation; and towers or masts, the structures that the antennas are placed on. It is the antennas that people need to keep their distance from, not the towers that hold the antennas. It is also important to be aware that there are many different designs of mobile phone base stations that vary widely in their power, their characteristics, and their potential for exposing people to RF radiation. It is well worth considering, however, that the current international exposure guidelines (INCIRP) are based largely on what is described as the thermal effects of base station emmissions. Some scientists have questioned whether there are non thermal effects from being exposed to low level RF frequencies such as are transmitted from mobile phone base stations. Such 'non-thermal' effects include how the actual frequencies interfere with the human brain and all other cells in the human body. Sources for consideration can be found at [www.emf-solutions.org.uk]

See also


- Base Transceiver Station
- Mobile phone
- Portable phone
- Mobile phone radiation and health Category:Wireless communications

Portable phone

A cordless telephone or portable telephone is a telephone with a wireless handset which communicates with a base station connected to a fixed telephone landline (POTS) via radio waves and can only be operated close to (typically less than 100 metres of) its base station, such as in and around the house. Unlike a standard telephone, a cordless telephone needs household mains electricity to power the base station. The cordless handset is powered by a battery which is recharged by the base station when the handset is connected to the base station when not in use. There are also some advanced cordless phone systems that can operate without power. In the event of a power outage, the phone will convert itself into a standard telephone that gets its power from the landline. However, in this mode, only a handset attached directly to the base could work. All wireless handsets would not function. Modern cordless telephone standards, like PHS and DECT, have blended the once clear-cut line between cordless and mobile telephones by supporting cell handover, various advanced features like data transfer and even, on a limited scale, international roaming. In these deployment models, base stations are maintained by a commercial mobile network operator and users subscribe to the service.

Frequencies

In the United States, there are six frequency bands that have been allocated by the Federal Communications Commission for use by cordless telephones. These are:
- 1.7 MHz [http://electronics.howstuffworks.com/question320.htm]
- 27 MHz (allocated in 1980)
- 43–50 MHz (allocated in 1986) Modern telephones are all manufactured to use the following bands:
- 900 MHz (902–928 MHz) (allocated in 1990)
- 2.4 GHz (allocated in 1998)
- 5.8 GHz (allocated in 2003)

Performance

Communication companies usually advertise that higher frequency systems improve audio quality and range, though this is an oversimplification. Though higher frequencies can pass through some materials more easily, and the bands are less crowded, the primary factors that determine quality and range are signal strength and the method of modulation used. Plain old telephone service landlines are designed to transfer audio with a quality that is just enough for the parties to understand each other. Typical bandwidth is 3 kHz; only a fraction of the frequencies that humans can hear, but it is enough to make the voice intelligible. No phone can improve on this quality, as it is part of the phone system itself. Higher-quality phones can transfer this signal to the handset with less interference over a greater range, however. The system's operating range (regardless of frequency) depends on the strength of the signal, not the frequency. (For instance, FM radio stations are typically in the range of 70–120 MHz, yet they are able to provide city-wide coverage due to their high-power broadcasting antennas.) Most manufacturers claim a range of about 30 m (100 ft) for their 2.4 GHz and 5.8 GHz systems but, not surprisingly, most inexpensive models fall short of this claim. However, there are some clear advantages of moving into higher frequency. The 900 MHz and 2.4 GHz band are increasingly being used for a host of other devices including baby monitor, microwave oven, Bluetooth, wireless LAN — thus, it is likely that the signal from the base unit will interfere with signals broadcast by those devices. The 5.8 GHz band is less crowded, currently being used only for the less popular 802.11a wireless standard and military communication so it is more immune to interference. Also, higher frequencies are, in theory, less likely to be blocked by objects such as walls and other household objects.

Security

Many analog phones are easily picked up by radio scanners, allowing anyone within range to listen in on conversations (though this is illegal in many countries). Though many such analog models are still produced, modern digital technology is available to greatly reduce the risk of eavesdropping. Digital spread-spectrum, or DSS, typically uses frequency hopping to spread the audio signal (with a 3 kHz bandwidth) over a much wider range of frequencies in a pseudorandom way. Spreading the signal out over a wider bandwidth is a form of redundancy, and increases the signal-to-noise ratio, which means better range and less susceptibility to interference. Higher frequency bands provide more room for these wide-bandwidth signals. To an analog receiver like a scanner, a DSS signal sounds like bursts of noise. Only the base unit with the same pseudorandom number generator can receive the signal, and it chooses from one of thousands of such unique generators each time the handset is returned to the cradle. Additionally, the digital nature of the signal increases its tolerance to noise, and some even encrypt the digital signal for even more security.

See also


- Digital Enhanced Cordless Telecommunications (DECT) in Europe
- DCTS in North America
- Personal Handy-phone System (PHS) in Japan and China
- Mobile phone
- Radio frequency

External links


- [http://www.ofta.gov.hk/en/ad-comm/rsac/paper/rsac6-2002.pdf Review of Frequency Allocations for Cordless Telephones]
- [http://electronics.howstuffworks.com/cordless-telephone2.htm How Cordless Telephones Work]
- [http://electronics.howstuffworks.com/question326.htm Information about Digital Spread-Spectrum cordless phones]
- [http://www.affordablephones.net/HistoryCordless.htm Cordless Phone History] Category:Consumer electronics Category:Telephony

Land line

A landline or main line is a telephone line which travels through a physical, land-based medium. This is distinguished from a mobile cellular line, where the medium used is the airwaves. Landlines usually cost less than cellular lines and are used when there is no need for mobility or cellular service is unavailable. A land line is also used to increase the security of communications, as it cannot be intercepted by a receiver without physical access to the line. This does not, however, mean that a telephone company will not send the call over the air on some point in the journey. In 2003, the CIA reported approximately 844 million main telephone lines worldwide. China had more than any other country, at 263 million, and the United States was second with 181.6 million. This compared with 158.7 million cellular telephones, a number which is expected to exceed the main line number within a few years. Category:Telephony



Mobile phone radiation and health

Mobile phone radiation and health concerns have been raised 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 waves in the microwave range. These concerns have induced a large body of research (both epidemiological and experimental, in 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 results, so far, have been controversial: the majority of epidemiological studies have not found any clear indication of short and medium term health hazards. On the other hand there is extensive literature (see "[http://www.iegmp.org.uk/documents/iegmp_5.pdf The Stewart Report]" for a survey) on so-called non-thermal effects of weak microwave radiation on biological tissue in animal models or in-vitro, including affecting the growth of certain tumors, cell death, increased permeability of the blood-brain barrier, DNA damage and others, which suggest the possibility of adverse health effects in humans.

Health hazards of handsets

DNA 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, for example, can have a power of up to 2 watts, and an analog phone in the USA (probably very few in use today) can have 3.6 watts, as in the old large mobile phone units installed in cars. Other digital mobile technologies, such as CDMA and TDMA, have today lower rates, under 1 watt. The average radiation rate of cellphones in some countries is regulated and it is mandatory to inform the consumers about it (usually printed in the battery compartment). In some systems the cellphone and the tower (radio base station) check reception quality and signal strength and the power level is increased or decreased automatically, within the above limits, such as inside buildings or vehicles, etc. 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 for most parts of the body.

Thermal effects

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 may occurr in the head surface, causing its temperature to increase by a fraction of a degree. The level of temperature increase is an order of magnitude less than that obtained during the exposure of head to direct sunlight. The brain's blood circulation easily disposes of excess heat by instantaneously increasing local blood flow. However, the cornea of the eye does not have this temperature regulation mechanism. Premature cataracts is known as an occupational disease of engineers who work on high power radio transmitters at similar frequencies. Cataracts have not been reported to occur in users of mobile telephones, even heavy users, however. It has been claimed that some parts of the human head are more sensitive to damage due to increases in temperature, particularly in anatomical structures with poor vasculature, such as nerve fibers. More recent results from a Swedish scientific team at the Karolinska Institute (Lonn, Ahlbom, Hall and Feychting) have suggested that continuous use of a mobile phone for a decade or longer can lead to a small increase in the probability of getting acoustic neuroma, a type of brain tumor. However, according to the study, the overall effect of mobile phone use is not associated with a statistically significant increase in overall tumor incidence. The increase was only noted in those who used phones for longer than 10 years. The study has also been criticized for possible problems in data analysis such as recall bias.

Non-thermal effects

In December 2004 a pan-European study showed compelling evidence of DNA damage of cells when exposed between 0.3 to 2 watts/kg. This overlaps with the level of radiation typically emitted by digital cell phones of around 0.2 to 1 watt/kg. 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. ([http://www.nature.com/news/2004/041220/full/041220-6.html]) The results of this study run contrary to many similar studies that were conducted before and showed no increase in DNA damage. ([http://www.radres.org/rare_151_05_0513.pdf]). The communications protocols used by mobile phones often result in low-frequency pulsing of the carrier signal. These low frequencies are similar to those that exist in the electrical oscillations of the human body, specifically the alpha and delta brain waves. Non-linear interactions could theoretically result when resonances are created when the brain is subjected to mobile phone radiation, in a manner similar to that observed when light strobing induces photosensitive epilepsy in susceptible individuals. No experimental results have indicated this theoretical possibility, however. These and other non-thermal effects are summarized in (Hyland, 2000).

"Electromagnetic hypersensitivity syndrome"

Many users of mobile handsets have reported feeling several unspecific symptoms during and after its use, such as 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) and disturbances of the digestive system. Some researchers, implying a causal relationship, have named this syndrome as a new diagnostic entity. The World Health Organization prefers to name it "idiopathic environmental intolerance", in order to avoid the implication of causation. This entity is quite controversial, because albeit identified in unmistaken terms by the patients who affirm to suffer from it, in some cases in such a radical way that they avoid using cellphones, it has not been recognized as a separate clinical entity by most medical researchers. Two recent literature reviews, however, one reviewing 13 published papers in 2003 and 2004, and another reviewing 31 papers published before 2004, have concluded that there is no scientific evidence for a causal relationship between the reported clusters of symptoms and exposure to microwave radiation used in cellphones, well below the safety standards. A workshop conducted by the WHO in Prague in 2004 also reached the same conclusions, viz., that 1) reported symptoms are very unspecific and could have other causes; 2) there is no causal association demonstrated between exposure and symptoms, 3) that patients who display those symptoms should be medically examined for alternative explanations and causes, including psychiatric/psychological ones (since they are typical manifestations of stress and other somatization/psychosomatic causes), and that the environment where they work or live should be assessed in order to discover other factors at work that could explain the symptoms; and 4) lowering the safety limits for handset radiation (SAR levels) will not affect the situation.

Health hazards of base stations

Another area of worry about effects on the population's health have been the radiation emitted by base stations (the antennas located inside geographical areas named cells which are part of the cellular network), because, in contrast to mobile handsets, it is emitted continuously. Due to the attenuation of power with the square of distance, however, field intensities are extremely low, even a few meters away from the base of the antenna. Any significant biological effects are thus improbable. If epidemiological evidence is accumulated to show some health risks as a result, base stations may be implicated in addition to handsets. So far, all evidence shown by methodologically correct studies have shown no discernible effects. As technology progresses and data demands have increased on the mobile network, the number of towers has increased sharply in many cities, and competing telco companies usually do not make an effort toward sharing towers. The latest trend is 3G towers, which work with higher bandwidths. The buildup of cell networks has sparked many health concerns and community outrage. Examples of such can be seen from headlines around the world; locals pulling down base station masts, or even, in some countries, physically attacking installation crews, communities lobbying against the rollout of cell networks, protest banners, demonstrations near hospitals, houses and local schools. Many measurements and experiments have shown, however, that transmitter power levels are relatively low - in modern 2G antennas, in the range of 20 to 100 watts. The ACA (Australian Communications Authority) and ARPANSA (Australian Radiation Protection and Nuclear Safety Agency) recently announced that the 3G towers actually cause less radiation than the already present 2G network. An average radiation power output of 3 watt is used. So-called micro-cell geometries inside cities have decreased the amount of irradiated power even further. A common misconception is that the propagation of more towers inevitably adds to a more strongly irradiated area. In fact, it can result in lower radiated powers since the distance between transmitter and receiver is lower. Base stations create interference patterns or regions where their signals add (in phase) or cancel (out of phase). Base stations which are too closely located can also interfere with each other's operation, leading to competition between cell phone companies for sites.

Occupational health hazards

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. Unfortunately, many times base stations are not turned off during maintenance, because that would affect the network, so people work near "live" antennas. In this way, excessive radiation levels may lead to adverse health effects, including severe acute burns or milder chronic alterations of the skin, and perhaps other non-thermal effects which have not yet been fully documented. Adequate individual protection equipment, short stays and turning off the equipment while nearer to them should suffice to prevent health hazards for the workers. 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 reduces cancer rates also occurred. [http://www.radres.org/rare_151_05_0513.pdf]

Safety standards and licensing

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 Committee 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. Telcos are required to obtain construction licenses, provide certification of antenna emission levels and assure compliance to ICNIRP standards and/or to other environmental legislation. Posterior alterations in the level of emission, number of active antennas or technology standards used in an installed antenna array might require new licensing procedures. Many governmental bodies also require that competing telcos try to achieve sharing of towers so as to decrease environmental and cosmetic impact. Regarding this issue, it is an influential factor of rejection of installation of new antennas and towers in communities. In some cases, camouflaging the towers like tree trunks and other visually more acceptable structures has been tried.

Lawsuits

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 [http://infoventures.com/emf/legal/lt-il001.html]. So far, most of these lawsuits have been dismissed by the courts, on lack of scientific evidence of such a causal relationship, and this has been reducing the motivation of tort lawyers eager to invest in a new health injury lawsuits fad.

Vested interests in scientific research

Some commentators who are militants against the widespread use of mobile telephony have alleged that the mobile phone industry has pressured research institutions to reduce funding for independent investigation of possible health effects, interfered with publicity of research results suggesting health concerns, and attacked the credibility and integrity of such research and researchers. No hard evidence has been provided for this allegations, however. In fact, it seems to be the opposite: the Mobile Manufacturers Forum (MMF), for instance, applies every year several million dollars for funding independent research on the subject. The money is provided with no strings attached by the biggest manufactureres, such as Motorola, Nokia, Samsung, etc. The MMF is a not-for-profit organization based in Brussels, Belgium. Only research which adheres to the highest methodological standards are funded. Results are required to be published in the best peer-reviewed journals and scientific conferences. The World Health Organization International EMF Project maintains a public database of research studies which can be consulted on-line [http://www10.who.int/peh-emf/emfstudies/studychart_criteria.cfm]. Abstracts of studies are published as well as the complete reference. There are ca. 450 studies in the database related to mobile telephony EMF and health.

Precautionary Principle

Although scientific evidence for health hazards of low level cellphone radiation is weak, the World Health Organization has recommended that the precautionary principle could be voluntarily adopted in this case (see [http://www.who.int/docstore/peh-emf/publications/facts_press/EMF-Precaution.htm WHO Electromagnetic Fields and Public Health Cautionary Policies]). 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 economical 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.

See also


- Electromagnetic radiation hazard
- Wireless electronic devices and health
- Specific absorption rate
- Radiation biology

References


- Repacholi, M.H. Health risks from the use of mobile phones. Toxicology Letters, 2000. available at [http://scholar.google.com/url?sa=U&q=http://users.ntua.gr/mmakro/healthrisk-mobile.pdf] (PDF Format)
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- Seitz, H, Stinner, D, Eikmann, Th, Herr, C, Roosli, M. Electromagnetic hypersensitivity (EHS) and subjective health complaints associated with electromagnetic fields of mobile phone communication -- a literature review published between 2000 and 2004. Science of the Total Environment, June 20 [e-publication ahead of print], 2005, available at http://www.sciencedirect.com].
- Rubin, GJ, Das Munchi, J, Wessely, S. Electromagnetic hypersensitivity: a systematic review of provocation studies. Psychosom Med. Mar-Apr; 67(2): 224-32. 2005, available at [http://www.psychosomaticmedicine.org].
- [http://www.who.int/pehemf/meetings/hypersens_summary_oct04.pdf WHO Workshop on Electromagnetic Hypersensitivy], Prague 2004.

External links


- [http://www.who.int/peh-emf/en/ WHO International EMF Program]
  - [http://www.who.int/mediacentre/factsheets/fs193/en/ Electromagnetic fields and public health: Mobile telephones and their base stations]. WHO Fact Sheet 193. June 2000.
- [http://www.mmfai.org/ MMF Mobile Manufacturers Forum]
- [http://www.icnirp.org/ International Commission on Non-Ionizing Radiation Protection (ICNIRP)]
- [http://www.iegmp.org.uk/ Independent Expert Group on Mobile Phones (IEGMP), UK]
  - [http://www.iegmp.org.uk/report/text.htm Mobile Phones and Health] ("Stewart Report", 2000)
- [http://www.cellphonesafetyguide.com/ Cell Phone Safety]
- [http://infoventures.com/emf/ A Biomedical Science and Engineering Clearinghouse on Electric and Magnetic Fields]. EMF-Link.
  - [http://infoventures.com/emf/top/cellular.html Cellular phones/towers and public health]
- [http://news.bbc.co.uk/1/hi/health/3742120.stm The Karolinska study]
- [http://www.radres.org/rare_151_05_0513.pdf Review of studies of Cell phone radiation and cancer (PDF)]
- [http://www.wave-guide.org/library/studies.html Reported Biological Effects From Radiofrequency Non-Ionizing Radiation]. WaveGuide.Org
- [http://www.nlm.nih.gov/medlineplus/ency/article/007151.htm Cell phones - do they cause cancer?] (NIH)
- [http://www.fda.gov/cellphones/ FDA Cell Phone Facts]
- [http://www.fcc.gov/oet/rfsafety/Welcome.html FCC Radio Frequency Safety]
- [http://www.evaluationengineering.com/archive/articles/0203emc.htm Happiness Is a Low-SAR Cell Phone] (Evaluation Engineering, February 2003)
- [http://www.mcw.edu/gcrc/cop/cell-phone-health-FAQ/toc.html Cell Phone Base Antennas and Human Health FAQ] (John Moulder, Medical College of Wisconsin)
- [http://www.opha.on.ca/ppres/2003-02_pp.pdf Health Risks of Cellular Telephones: The Myth and the Reality] (Ontario Public Health Association position paper, 2003)
- [http://www.wow-com.com/consumer/issues/health/articles.cfm?ID=126&SearchSection=&SearchCriteria=radiation Guide to Wireless Industry Health Questions]
- [http://www.fda.gov/cellphones/ctia-research-plan.html FDA/CTIA Research Agreement]
- [http://www.gao.gov/new.items/d01545.pdf GAO Report: Research and Regulatory Efforts on Mobile Phone Health Issues] - PDF
- [http://www.isracast.com/tech_news/250705_tech.htm How cell phone radiation can cause visual damage] - an online article
- [http://www.spectrum.ieee.org/oct05/1866 Sins Of Transmission? Vatican Radio's high-power antennas stand accused of causing cancer]. Article by Alexander Hellemans, IEEE Spectrum On-Line, Oct. 2005. Category:Public health Category:Radiobiology

Base Transceiver Station

The Base Station Subsystem (BSS) is the section of a GSM network which is responsible for handling traffic between a mobile phone and the Network Switching Subsystem. The BSS carries out transcoding of speech channels, allocation of radio channels to mobile phones, paging and many other tasks related to the radio network.

Base Transceiver Station

paging The Base Transceiver Station, or BTS, contains the equipment for transmitting and receiving of radio signals (transcievers), antennas, and equipment for encrypting and decrypting communication between the Base Station Controller. Typically a BTS for anything other than a picocell will have several different transceivers (TRXs) which allow it to serve several different frequencies or even several different cells (in the case of sectorised base station). Even having taken in consideration GSM is a standard the functions of a BTS varies from vendor to vendor. There are vendors in which the BTS is a plain tranceiver which receives an information from the MU through the Um and then converts it to a PCM based interface, the Abis, and sends it towards the BSC. There are vendors which build their BTSs so the information is preprocessed, target cell lists are generated and even intracell HO can be fully handled, the advantage in this case is low load on the expensive Abis interface. The BTSs are equipped with radios that are able to modulate the layer 1 of interface Um, for GSM 2G+ it is GMSK while for EDGE enabled networks it is 8PSK. Antenna combiners are implemented to use the same antenna for several TRXs (carriers), the more TRXs are combined the greater the combiner lose will be. Up to 8:1 combiners are found in micro and pico cells only.

Sectorisation

By using directional antennae on a base station, each pointing in different directions, it is possible to sectorise the base station so that several different cells are served from the same location. This increases the traffic capacity of the base station (each frequency can carry eight voice channels) whilst not greatly increasing the interference caused to neighboring cells (in any given direction, only a small number of frequencies are being broadcast).

Base Station Controller

The Base Station Controller (BSC) provides, clasicaly, the intelligence behind the BTSs. Typically a BSC has 10s or even 100s of BTSs under its control. The BSC handles allocation of radio channels, receives measurements from the mobile phones, controls handovers from BTS to BTS (except in the case of an inter-MSC handover in which case control is in part the responsibility of the Anchor MSC). A key function of the BSC is to act as a concentrator where many different low capacity connections to BTSs (with relatively low utilisation) become reduced to a smaller number of connections towards the Mobile Switching Center (MSC) (with a high level of utilisation). Overall, this means that networks are often structured to have many BSCs distributed into regions near their BTSs which are then connected to large centralised MSC sites. The BSC is undoubtly the most robust element in the BSS subsystem as it is not only a BTS controller but, for some vendors, a full switching center as well as a SS7 node with conection to the MSC and SGSN, it also provides all the requiered data to the network management subsystem as well as to the performance measuring centers. The data bases for all the sites, including information as carrier frequency, Hopping lists, power reduction levels, receiving levels for cell border calculation, are stored in the BSC, this data is obtained directly from radio planning engineering which involves modeling of the signal propagation as well as traffic projections.

Transcoder

Although the Transcodification(compressing/decompressing) function is standard defined as a BSC function, there are several vendors which have implemented the solution in a stand alone rack using a propietary interface. This subsystem is also referred to as the TRAU (Transcoder and Rate Adaptation Unit). The transcoding function converts the voice channel coding between the GSM (Regular Pulse Excited-Linear Predictive a.k.a RPE-LPC) coder and the CCITT standard PCM (G.711 A-law or u-law). Since the PCM coding is 64 kbit/s and the GSM coding is 13 kbit/s, this also involves a rate adaption function to compress voice channels from the 64 kbit/s PCM standard to the 13 kbit/s rate used on the air interface. Some networks use 32 kbit/s ADPCM on the terrestrial side of the network instead of 64 kbit/s PCM and the TRAU converts accordingly. However, at least in Siemens' and Nokia's architecture, this is an identifiable separate system which will normally be co-located with the MSC. In some of Ericsson's systems it is integrated to the MSC rather than the BSC. The reason for these designs is that if the compression of voice channels is done at the site of the MSC, transmission costs can be reduced.

Packet Control Unit

The Packet Control Unit (PCU) is a late addition to the GSM standard. It performs some of the processing tasks of the BSC, but for packet data. The allocation of channels between voice and data is controlled by the base station, but once a channel is allocated to the PCU, the PCU takes full control over that channel. The PCU can be built into the base station, built into the BSC or even, in some proposed architectures, it can be at the SGSN site.

BSS Interfaces


- Um - The air interface between the MS (Mobile Station) and the BSC. This interface uses LAPD protocol, which is used to conduct Handover, Authentication, Authorization, Location Update and so on.
- Abis - The interface between the Base Tranciever Station and Base Station Controller. Generally consists of DS-1 or ES-1 circuits.
- A - The interface between the BSC and Mobile Switching Center it is used for carrying the BSSAP user part of the SS7 stack. Although there are usually transcoding units between BSC and MSC, the comunication takes place between these two ending points and the transcoder unit doesn't touch the SS7 information only the voice and CS data are compressed.
- The interface between the Base Station Controller and Transcoder. It is a proprietary interface whose name depends on the vendor, it carries out the A interface information from the BSC leaving it untouched. Category:GSM Standard

Portable phone

A cordless telephone or portable telephone is a telephone with a wireless handset which communicates with a base station connected to a fixed telephone landline (POTS) via radio waves and can only be operated close to (typically less than 100 metres of) its base station, such as in and around the house. Unlike a standard telephone, a cordless telephone needs household mains electricity to power the base station. The cordless handset is powered by a battery which is recharged by the base station when the handset is connected to the base station when not in use. There are also some advanced cordless phone systems that can operate without power. In the event of a power outage, the phone will convert itself into a standard telephone that gets its power from the landline. However, in this mode, only a handset attached directly to the base could work. All wireless handsets would not function. Modern cordless telephone standards, like PHS and DECT, have blended the once clear-cut line between cordless and mobile telephones by supporting cell handover, various advanced features like data transfer and even, on a limited scale, international roaming. In these deployment models, base stations are maintained by a commercial mobile network operator and users subscribe to the service.

Frequencies

In the United States, there are six frequency bands that have been allocated by the Federal Communications Commission for use by cordless telephones. These are:
- 1.7 MHz [http://electronics.howstuffworks.com/question320.htm]
- 27 MHz (allocated in 1980)
- 43–50 MHz (allocated in 1986) Modern telephones are all manufactured to use the following bands:
- 900 MHz (902–928 MHz) (allocated in 1990)
- 2.4 GHz (allocated in 1998)
- 5.8 GHz (allocated in 2003)

Performance

Communication companies usually advertise that higher frequency systems improve audio quality and range, though this is an oversimplification. Though higher frequencies can pass through some materials more easily, and the bands are less crowded, the primary factors that determine quality and range are signal strength and the method of modulation used. Plain old telephone service landlines are designed to transfer audio with a quality that is just enough for the parties to understand each other. Typical bandwidth is 3 kHz; only a fraction of the frequencies that humans can hear, but it is enough to make the voice intelligible. No phone can improve on this quality, as it is part of the phone system itself. Higher-quality phones can transfer this signal to the handset with less interference over a greater range, however. The system's operating range (regardless of frequency) depends on the strength of the signal, not the frequency. (For instance, FM radio stations are typically in the range of 70–120 MHz, yet they are able to provide city-wide coverage due to their high-power broadcasting antennas.) Most manufacturers claim a range of about 30 m (100 ft) for their 2.4 GHz and 5.8 GHz systems but, not surprisingly, most inexpensive models fall short of this claim. However, there are some clear advantages of moving into higher frequency. The 900 MHz and 2.4 GHz band are increasingly being used for a host of other devices including baby monitor, microwave oven, Bluetooth, wireless LAN — thus, it is likely that the signal from the base unit will interfere with signals broadcast by those devices. The 5.8 GHz band is less crowded, currently being used only for the less popular 802.11a wireless standard and military communication so it is more immune to interference. Also, higher frequencies are, in theory, less likely to be blocked by objects such as walls and other household objects.

Security

Many analog phones are easily picked up by radio scanners, allowing anyone within range to listen in on conversations (though this is illegal in many countries). Though many such analog models are still produced, modern digital technology is available to greatly reduce the risk of eavesdropping. Digital spread-spectrum, or DSS, typically uses frequency hopping to spread the audio signal (with a 3 kHz bandwidth) over a much wider range of frequencies in a pseudorandom way. Spreading the signal out over a wider bandwidth is a form of redundancy, and increases the signal-to-noise ratio, which means better range and less susceptibility to interference. Higher frequency bands provide more room for these wide-bandwidth signals. To an analog receiver like a scanner, a DSS signal sounds like bursts of noise. Only the base unit with the same pseudorandom number generator can receive the signal, and it chooses from one of thousands of such unique generators each time the handset is returned to the cradle. Additionally, the digital nature of the signal increases its tolerance to noise, and some even encrypt the digital signal for even more security.

See also


- Digital Enhanced Cordless Telecommunications (DECT) in Europe
- DCTS in North America
- Personal Handy-phone System (PHS) in Japan and China
- Mobile phone
- Radio frequency

External links


- [http://www.ofta.gov.hk/en/ad-comm/rsac/paper/rsac6-2002.pdf Review of Frequency Allocations for Cordless Telephones]
- [http://electronics.howstuffworks.com/cordless-telephone2.htm How Cordless Telephones Work]
- [http://electronics.howstuffworks.com/question326.htm Information about Digital Spread-Spectrum cordless phones]
- [http://www.affordablephones.net/HistoryCordless.htm Cordless Phone History] Category:Consumer electronics Category:Telephony

Category:Wireless communications

This category is for anything pertaining to the use of radio waves in telecommunications. The use of radio waves in broadcasting is covered under sub-category radio. Category:Telecommunications

List of Colditz Castle staff

:This article has been spun off from Colditz Castle; please see that article for more information on the camp itself.

German staff at Colditz

These are the named members of the German staff from 1939 to 1945 at Colditz castle, as well as two from the related Schützenhaus, and one from the totally separate SS concentration camp.

Sources:


- Michael Booker, Collecting Colditz and Its Secrets, pp. 22-37, 46, 141-142, 157.
- Eric J. Narveson, Prison Citadel, pp. 22-38.
- Patrick Reid, Colditz: The Full Story, pp. 124, 259-263, 325-326.
- Georg Martin Schädlich, Tales from Colditz Castle, pp. 4-6, 16, 18-76, 91-101.

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