Code-division multiple access ( CDMA ) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access , where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies (see bandwidth ). To permit this without undue interference between the users, CDMA employs spread spectrum technology and a special coding scheme (where each transmitter is assigned a code).
72-557: Internet in Estonia has one of the highest penetration rates in the world. In the first quarter of 2010, 75% out of 1.34 million people in the country used the Internet according to Statistics Estonia . In 2017, according to the World Bank came 13th in the world by the percentage of population using the Internet, with 88.1% people using it. The 2022 Digital Economy and Society Index (DESI) by
144-575: A channel or medium access technology, like ALOHA for example or as a permanent pilot/signalling channel to allow users to synchronize their local oscillators to a common system frequency, thereby also estimating the channel parameters permanently. In these schemes, the message is modulated on a longer spreading sequence, consisting of several chips (0es and 1es). Due to their very advantageous auto- and crosscorrelation characteristics, these spreading sequences have also been used for radar applications for many decades, where they are called Barker codes (with
216-425: A code orthogonal to the others' codes to modulate their signal. An example of 4 mutually orthogonal digital signals is shown in the figure below. Orthogonal codes have a cross-correlation equal to zero; in other words, they do not interfere with each other. In the case of IS-95, 64-bit Walsh codes are used to encode the signal to separate different users. Since each of the 64 Walsh codes is orthogonal to all other,
288-452: A complete orthonormal set. The data signal is also binary and the time multiplication is achieved with a simple XOR function. This is usually a Gilbert cell mixer in the circuitry. Synchronous CDMA exploits mathematical properties of orthogonality between vectors representing the data strings. For example, the binary string 1011 is represented by the vector (1, 0, 1, 1). Vectors can be multiplied by taking their dot product , by summing
360-573: A court order. A 2008 court case made web service providers responsible for reader comments, but that ruling is being appealed at the European Court of Human Rights. There have been instances of content removal involving civil court orders to remove inappropriate or off-topic reader comments from online news, discussion forums, and other sites. In 2012, over 80,000 videos were removed from YouTube and other streaming services for possible copyright infringement. The Personal Data Protection Act (PDPA) restricts
432-401: A different code to modulate their signal. Choosing the codes used to modulate the signal is very important in the performance of CDMA systems. The best performance occurs when there is good separation between the signal of a desired user and the signals of other users. The separation of the signals is made by correlating the received signal with the locally generated code of the desired user. If
504-505: A fixed number of orthogonal codes, time slots or frequency bands that can be allocated for CDM, TDMA, and FDMA systems, which remain underutilized due to the bursty nature of telephony and packetized data transmissions. There is no strict limit to the number of users that can be supported in an asynchronous CDMA system, only a practical limit governed by the desired bit error probability since the SIR (signal-to-interference ratio) varies inversely with
576-417: A mobile environment, each time slot must have a guard time, which reduces the probability that users will interfere, but decreases the spectral efficiency. Similarly, FDMA systems must use a guard band between adjacent channels, due to the unpredictable Doppler shift of the signal spectrum because of user mobility. The guard bands will reduce the probability that adjacent channels will interfere, but decrease
648-464: A spread-spectrum signal is generated. The data signal with pulse duration of T b {\displaystyle T_{b}} (symbol period) is XORed with the code signal with pulse duration of T c {\displaystyle T_{c}} (chip period). (Note: bandwidth is proportional to 1 / T {\displaystyle 1/T} , where T {\displaystyle T} = bit time.) Therefore,
720-514: A take-up rate of 87%, which is on par with the EU average. However, the country faces challenges in 5G deployment, having not allocated any spectrum for 5G as of April 2022. This lack of spectrum allocation contrasts with the EU average of 56%. Additionally, 5G coverage in Estonia's populated areas is only 18%, significantly lower than the EU average of 66%. Estonia is recognized for its leadership in digital public services, as evidenced by its top ranking in
792-401: A transmission bandwidth that is several orders of magnitude greater than the minimum required signal bandwidth. One of the initial reasons for doing this was military applications including guidance and communication systems. These systems were designed using spread spectrum because of its security and resistance to jamming. Asynchronous CDMA has some level of privacy built in because the signal
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#1732869718244864-568: A very short sequence length of typically 8 to 32). For space-based communication applications, CDMA has been used for many decades due to the large path loss and Doppler shift caused by satellite motion. CDMA is often used with binary phase-shift keying (BPSK) in its simplest form, but can be combined with any modulation scheme like (in advanced cases) quadrature amplitude modulation (QAM) or orthogonal frequency-division multiplexing (OFDM), which typically makes it very robust and efficient (and equipping them with accurate ranging capabilities, which
936-416: Is (2, −2, 2, 2), but the receiver interprets this as (1, 0, 1, 1). Values of exactly 0 mean that the sender did not transmit any data, as in the following example: Assume signal0 = (1, −1, −1, 1, 1, −1, 1, −1) is transmitted alone. The following table shows the decode at the receiver: When the receiver attempts to decode the signal using sender1's code, the data is all zeros; therefore the cross-correlation
1008-400: Is 26th, facing particular challenges in 5G and Fixed Very High Capacity Network (VHCN) deployment. Estonia's digitalization priorities include enhancing digital infrastructure and cybersecurity . In Estonia, fixed broadband infrastructure exhibits a mixed performance in comparison to the EU. The fixed broadband take-up stands at 83%, which is higher than the EU's average of 78%. However,
1080-461: Is a binary sequence that appears random but can be reproduced in a deterministic manner by intended receivers. These spreading sequences are used to encode and decode a user's signal in asynchronous CDMA in the same manner as the orthogonal codes in synchronous CDMA (shown in the example above). These spreading sequences are statistically uncorrelated, and the sum of a large number of spreading sequences results in multiple access interference (MAI) that
1152-486: Is analogous to the last example where people speaking the same language can understand each other, but other languages are perceived as noise and rejected. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can communicate. In general, CDMA belongs to two basic categories: synchronous (orthogonal codes) and asynchronous (pseudorandom codes). The digital modulation method
1224-441: Is analogous to those used in simple radio transceivers. In the analog case, a low-frequency data signal is time-multiplied with a high-frequency pure sine-wave carrier and transmitted. This is effectively a frequency convolution ( Wiener–Khinchin theorem ) of the two signals, resulting in a carrier with narrow sidebands. In the digital case, the sinusoidal carrier is replaced by Walsh functions . These are binary square waves that form
1296-480: Is approximated by a Gaussian noise process (following the central limit theorem in statistics). Gold codes are an example of a spreading sequence suitable for this purpose, as there is low correlation between the codes. If all of the users are received with the same power level, then the variance (e.g., the noise power) of the MAI increases in direct proportion to the number of users. In other words, unlike synchronous CDMA,
1368-480: Is difficult without CDMA). Other schemes use subcarriers based on binary offset carrier modulation (BOC modulation), which is inspired by Manchester codes and enable a larger gap between the virtual center frequency and the subcarriers, which is not the case for OFDM subcarriers. The technology of code-division multiple access channels has long been known. In the US, one of the earliest descriptions of CDMA can be found in
1440-536: Is equal to zero and it is clear that sender1 did not transmit any data. When mobile-to-base links cannot be precisely coordinated, particularly due to the mobility of the handsets, a different approach is required. Since it is not mathematically possible to create signature sequences that are both orthogonal for arbitrarily random starting points and which make full use of the code space, unique "pseudo-random" or "pseudo-noise" sequences called spreading sequences are used in asynchronous CDMA systems. A spreading sequence
1512-504: Is not true for asynchronous CDMA; rejection of unwanted signals is only partial. If any or all of the unwanted signals are much stronger than the desired signal, they will overwhelm it. This leads to a general requirement in any asynchronous CDMA system to approximately match the various signal power levels as seen at the receiver. In CDMA cellular, the base station uses a fast closed-loop power-control scheme to tightly control each mobile's transmit power. In 2019, schemes to precisely estimate
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#17328697182441584-517: Is possible to achieve this increase at a low complexity and high bit error rate performance in flat fading channels, which is a major research challenge for overloaded CDMA systems. In this approach, instead of using one sequence per user as in conventional CDMA, the authors group a small number of users to share the same spreading sequence and enable group spreading and despreading operations. The new collaborative multi-user receiver consists of two stages: group multi-user detection (MUD) stage to suppress
1656-464: Is shown in the adjacent picture. These vectors will be assigned to individual users and are called the code , chip code , or chipping code . In the interest of brevity, the rest of this example uses codes v with only two bits. Each user is associated with a different code, say v . A 1 bit is represented by transmitting a positive code v , and a 0 bit is represented by a negative code −v . For example, if v = ( v 0 , v 1 ) = (1, −1) and
1728-410: Is spread using a pseudo-random code; this code makes the spread-spectrum signals appear random or have noise-like properties. A receiver cannot demodulate this transmission without knowledge of the pseudo-random sequence used to encode the data. CDMA is also resistant to jamming. A jamming signal only has a finite amount of power available to jam the signal. The jammer can either spread its energy over
1800-547: Is used as the access method in many mobile phone standards . IS-95 , also called "cdmaOne", and its 3G evolution CDMA2000 , are often simply referred to as "CDMA", but UMTS , the 3G standard used by GSM carriers, also uses "wideband CDMA", or W-CDMA, as well as TD-CDMA and TD-SCDMA, as its radio technologies. Many carriers (such as AT&T , UScellular and Verizon ) shut down 3G CDMA-based networks in 2022 and 2024, rendering handsets supporting only those protocols unusable for calls, even to 911 . It can be also used as
1872-615: The European Commission ranks Estonia first in Digital Public Services among 27 European Union (EU) countries. In Human Capital, Estonia is 8th, with a significant number of ICT specialists and graduates. The country is positioned 15th in the Integration of Digital Technology, displaying varying digital adoption levels between newer companies and traditional Small and Medium-sized Enterprises (SMEs). In Connectivity, Estonia
1944-587: The USSR , Ural-1 , was set up in the town of Nõo . Mass usage of computing networks first came with FidoNet , the first Estonian node of which appeared in 1989. The first Internet connections in the country were introduced in 1992 at academic facilities in Tallinn and Tartu . The national domain ( .ee ) was registered in the middle of 1992. By virtue of its geographical location, the country played important role in transporting Internet culture to neighbouring Russia . One of
2016-521: The Bürokratt AI network and the 3D digital twin project to improve public service efficiency and accessibility. In healthcare, Estonia has achieved a digitalization rate of 99% for prescriptions and offers a broad range of online health services. As outlined in the Digital Agenda 2030, Estonia has prioritized a 90% satisfaction rate for their digital public services. In 1965 the first school computer in
2088-524: The EU's 2022 Digital Economy and Society Index (DESI). With an adoption rate of 89% for e-government services among its population, it exceeds the EU average of 65%. The quality of digital services offered to citizens and businesses is demonstrated by scores of 92/100 and 98/100, respectively, both surpassing the EU averages of 75 for citizens and 82 for businesses. The country's digital framework enables public service access, with 90% of its citizens holding digital IDs . It has invested in technologies such as
2160-475: The Wikimedia System Administrators, please include the details below. Request from 172.68.168.150 via cp1114 cp1114, Varnish XID 495847761 Upstream caches: cp1114 int Error: 429, Too Many Requests at Fri, 29 Nov 2024 08:41:58 GMT CDMA CDMA optimizes the use of available bandwidth as it transmits over the entire frequency range and does not limit the user's frequency range. It
2232-512: The adoption of broadband speeds of at least 100 Mbps is only at 20%, which lags behind the EU average of 41%. Estonia aligns with the EU in Fast Broadband (NGA) coverage at 90%. Its Fixed Very High Capacity Network (VHCN) coverage at 73% slightly exceeds the EU average of 70%, and Fibre to the Premises (FTTP) coverage is noteworthy at 73%, exceeding the EU's average of 50%. Mobile broadband has
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2304-416: The amplitude of each signal, but if they are out of phase, they subtract and give a signal that is the difference of the amplitudes. Digitally, this behaviour can be modelled by the addition of the transmission vectors, component by component. If sender0 has code (1, −1) and data (1, 0, 1, 1), and sender1 has code (1, 1) and data (0, 0, 1, 1), and both senders transmit simultaneously, then this table describes
2376-555: The author, could serve several customers. In 1958, Kupriyanovich made the new experimental "pocket" model of mobile phone. This phone weighed 0.5 kg. To serve more customers, Kupriyanovich proposed the device, which he called "correlator." In 1958, the USSR also started the development of the " Altai " national civil mobile phone service for cars, based on the Soviet MRT-1327 standard. The phone system weighed 11 kg (24 lb). It
2448-400: The bandwidth of the data signal is 1 / T b {\displaystyle 1/T_{b}} and the bandwidth of the spread spectrum signal is 1 / T c {\displaystyle 1/T_{c}} . Since T c {\displaystyle T_{c}} is much smaller than T b {\displaystyle T_{b}} ,
2520-431: The bandwidth of the data uniformly for the same transmitted power. A spreading code is a pseudo-random code in the time domain that has a narrow ambiguity function in the frequency domain, unlike other narrow pulse codes. In CDMA a locally generated code runs at a much higher rate than the data to be transmitted. Data for transmission is combined by bitwise XOR (exclusive OR) with the faster code. The figure shows how
2592-417: The bandwidth of the spread-spectrum signal is much larger than the bandwidth of the original signal. The ratio T b / T c {\displaystyle T_{b}/T_{c}} is called the spreading factor or processing gain and determines to a certain extent the upper limit of the total number of users supported simultaneously by a base station. Each user in a CDMA system uses
2664-586: The coding steps: Because signal0 and signal1 are transmitted at the same time into the air, they add to produce the raw signal This raw signal is called an interference pattern. The receiver then extracts an intelligible signal for any known sender by combining the sender's code with the interference pattern. The following table explains how this works and shows that the signals do not interfere with one another: Further, after decoding, all values greater than 0 are interpreted as 1, while all values less than zero are interpreted as 0. For example, after decoding, data0
2736-401: The collection and public dissemination of an individual's personal data. No personal information that is considered sensitive—such as political opinions, religious or philosophical beliefs, ethnic or racial origin, sexual behavior, health, or criminal convictions—can be processed without the consent of the individual. Prior to the blocking of remote gambling sites in 2010 the Internet in Estonia
2808-445: The correlation should be as close to zero as possible. This is referred to as auto-correlation and is used to reject multi-path interference. An analogy to the problem of multiple access is a room (channel) in which people wish to talk to each other simultaneously. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA
2880-450: The country had over 2,440 free, certified Wi-Fi areas meant for public use, including at cafes, hotels, hospitals, schools, and gas stations. A countrywide wireless internet service based on CDMA technology has been deployed. Three mobile operators offer mobile 3G and 3.5G services, and as of May 2013, 4G services covered over 95 percent of the territory. Computerization and digital connection for people are encouraged and supported by
2952-508: The country's obligations as an EU member state. Anonymity is unrestricted, and there have been extensive public discussions on anonymity and the respectful use of the Internet. Work is underway to bring Estonian law into compliance with the European Council Framework on "combating certain forms and expressions of racism and xenophobia by means of criminal law". Restrictions on Internet content and communications in Estonia are among
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3024-443: The data that the user wishes to transmit is (1, 0, 1, 1), then the transmitted symbols would be For the purposes of this article, we call this constructed vector the transmitted vector . Each sender has a different, unique vector v chosen from that set, but the construction method of the transmitted vector is identical. Now, due to physical properties of interference, if two signals at a point are in phase, they add to give twice
3096-467: The entire bandwidth of the signal or jam only part of the entire signal. CDMA can also effectively reject narrow-band interference. Since narrow-band interference affects only a small portion of the spread-spectrum signal, it can easily be removed through notch filtering without much loss of information. Convolution encoding and interleaving can be used to assist in recovering this lost data. CDMA signals are also resistant to multipath fading. Since
3168-412: The first backbone links for Russia was built in 1991 by Relcom through Estonia to Finland . In 1996 Estonian president Lennart Meri started the four-year state program " Tiigrihüpe " to computerize and internetize all of the country's schools. The first public Wi-Fi area was launched in 2001 and a system of mobile data networks that enable widespread wireless broadband access has developed. In 2011,
3240-477: The largest functioning public-key infrastructure in Europe. All radio channels and TV productions, including news, of Estonian Public Broadcasting are available over the Internet in real time and archives of its radio and television programs are available at no charge. The country's most popular search engine in Estonia is Google , although a not so common, but still existing alternative is the local Neti.ee . Estonia
3312-708: The lightest in the world. ISPs and other communications companies are required to register with the Estonian Technical Surveillance Authority (ETSA), a branch of the Ministry of Economic Affairs and Communications, though there is no registration fee. Electronic communications companies are required to preserve traffic and location data for one year, as defined by the EU Data Retention Directive . They may only provide this data to surveillance agencies or security authorities when presented with
3384-423: The multipath to appear uncorrelated with the intended signal, and it is thus ignored. Some CDMA devices use a rake receiver , which exploits multipath delay components to improve the performance of the system. A rake receiver combines the information from several correlators, each one tuned to a different path delay, producing a stronger version of the signal than a simple receiver with a single correlation tuned to
3456-463: The number of users. In a bursty traffic environment like mobile telephony, the advantage afforded by asynchronous CDMA is that the performance (bit error rate) is allowed to fluctuate randomly, with an average value determined by the number of users times the percentage of utilization. Suppose there are 2 N users that only talk half of the time, then 2 N users can be accommodated with the same average bit error probability as N users that talk all of
3528-416: The original pseudo-random code, and will thus appear as another user, which is ignored at the receiver. In other words, as long as the multipath channel induces at least one chip of delay, the multipath signals will arrive at the receiver such that they are shifted in time by at least one chip from the intended signal. The correlation properties of the pseudo-random codes are such that this slight delay causes
3600-421: The orthogonal-code, time-slot or frequency-channel resources. By comparison, asynchronous CDMA transmitters simply send when they have something to say and go off the air when they do not, keeping the same signature sequence as long as they are connected to the system. Most modulation schemes try to minimize the bandwidth of this signal since bandwidth is a limited resource. However, spread-spectrum techniques use
3672-449: The path delay of the strongest signal. Frequency reuse is the ability to reuse the same radio channel frequency at other cell sites within a cellular system. In the FDMA and TDMA systems, frequency planning is an important consideration. The frequencies used in different cells must be planned carefully to ensure signals from different cells do not interfere with each other. In a CDMA system,
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#17328697182443744-509: The products of their respective components (for example, if u = ( a , b ) and v = ( c , d ), then their dot product u · v = ac + bd ). If the dot product is zero, the two vectors are said to be orthogonal to each other. Some properties of the dot product aid understanding of how W-CDMA works. If vectors a and b are orthogonal, then a ⋅ b = 0 {\displaystyle \mathbf {a} \cdot \mathbf {b} =0} and: Each user in synchronous CDMA uses
3816-466: The required length of the codes in dependence of Doppler and delay characteristics have been developed. Soon after, machine learning based techniques that generate sequences of a desired length and spreading properties have been published as well. These are highly competitive with the classic Gold and Welch sequences. These are not generated by linear-feedback-shift-registers, but have to be stored in lookup tables. In theory CDMA, TDMA and FDMA have exactly
3888-462: The same frequencies, CDMA systems have the ability to perform soft hand-offs. Soft hand-offs allow the mobile telephone to communicate simultaneously with two or more cells. The best signal quality is selected until the hand-off is complete. This is different from hard hand-offs utilized in other cellular systems. In a hard-hand-off situation, as the mobile telephone approaches a hand-off, signal strength may vary abruptly. In contrast, CDMA systems use
3960-414: The same frequency can be used in every cell, because channelization is done using the pseudo-random codes. Reusing the same frequency in every cell eliminates the need for frequency planning in a CDMA system; however, planning of the different pseudo-random sequences must be done to ensure that the received signal from one cell does not correlate with the signal from a nearby cell. Since adjacent cells use
4032-429: The same sequences but different timing offsets) appear as wideband noise reduced by the spreading factor. Since each user generates MAI, controlling the signal strength is an important issue with CDMA transmitters. A CDM (synchronous CDMA), TDMA, or FDMA receiver can in theory completely reject arbitrarily strong signals using different codes, time slots or frequency channels due to the orthogonality of these systems. This
4104-413: The same spectral efficiency, but, in practice, each has its own challenges – power control in the case of CDMA, timing in the case of TDMA, and frequency generation/filtering in the case of FDMA. TDMA systems must carefully synchronize the transmission times of all the users to ensure that they are received in the correct time slot and do not cause interference. Since this cannot be perfectly controlled in
4176-401: The signal matches the desired user's code, then the correlation function will be high and the system can extract that signal. If the desired user's code has nothing in common with the signal, the correlation should be as close to zero as possible (thus eliminating the signal); this is referred to as cross-correlation . If the code is correlated with the signal at any time offset other than zero,
4248-405: The signals are channelized into 64 orthogonal signals. The following example demonstrates how each user's signal can be encoded and decoded. Start with a set of vectors that are mutually orthogonal . (Although mutual orthogonality is the only condition, these vectors are usually constructed for ease of decoding, for example columns or rows from Walsh matrices .) An example of orthogonal functions
4320-402: The signals of other users will appear as noise to the signal of interest and interfere slightly with the desired signal in proportion to number of users. All forms of CDMA use the spread-spectrum spreading factor to allow receivers to partially discriminate against unwanted signals. Signals encoded with the specified spreading sequences are received, while signals with different sequences (or
4392-475: The soft hand-off, which is undetectable and provides a more reliable and higher-quality signal. A novel collaborative multi-user transmission and detection scheme called collaborative CDMA has been investigated for the uplink that exploits the differences between users' fading channel signatures to increase the user capacity well beyond the spreading length in the MAI-limited environment. The authors show that it
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#17328697182444464-406: The spread-spectrum signal occupies a large bandwidth, only a small portion of this will undergo fading due to multipath at any given time. Like the narrow-band interference, this will result in only a small loss of data and can be overcome. Another reason CDMA is resistant to multipath interference is because the delayed versions of the transmitted pseudo-random codes will have poor correlation with
4536-571: The state. The country has a digital ID card system, and in 2005 local elections were held with the official possibility to vote online – the first case of its kind in the world. In 2008, the North Atlantic Treaty Organization (NATO) established a joint cyberdefense center in Estonia to improve cyberdefense interoperability and provide security support for all NATO members. In 2009, the Estonian Internet Foundation
4608-543: The summary report of Project Hartwell on "The Security of Overseas Transport", which was a summer research project carried out at the Massachusetts Institute of Technology from June to August 1950. Further research in the context of jamming and anti-jamming was carried out in 1952 at Lincoln Lab . In the Soviet Union (USSR), the first work devoted to this subject was published in 1935 by Dmitry Ageev . It
4680-462: The time. The key difference here is that the bit error probability for N users talking all of the time is constant, whereas it is a random quantity (with the same mean) for 2 N users talking half of the time. In other words, asynchronous CDMA is ideally suited to a mobile network where large numbers of transmitters each generate a relatively small amount of traffic at irregular intervals. CDM (synchronous CDMA), TDMA, and FDMA systems cannot recover
4752-473: The underutilized resources inherent to bursty traffic due to the fixed number of orthogonal codes, time slots or frequency channels that can be assigned to individual transmitters. For instance, if there are N time slots in a TDMA system and 2 N users that talk half of the time, then half of the time there will be more than N users needing to use more than N time slots. Furthermore, it would require significant overhead to continually allocate and deallocate
4824-413: The utilization of the spectrum. Asynchronous CDMA offers a key advantage in the flexible allocation of resources i.e. allocation of spreading sequences to active users. In the case of CDM (synchronous CDMA), TDMA, and FDMA the number of simultaneous orthogonal codes, time slots, and frequency slots respectively are fixed, hence the capacity in terms of the number of simultaneous users is limited. There are
4896-512: Was established to manage Estonia's top level domain, ".ee". As a multi-stakeholder organization it represents the Estonian Internet community internationally with respect to various Internet governance issues. In 2013 there were over 200 operators offering electronic communications services, including six mobile phone companies and numerous Internet service providers. Voice over Internet Protocol (VoIP) services are widely available. Estonia has
4968-551: Was free of censorship. Early in 2010 Estonia started DNS filtering of remote gambling sites that violate the renewed Gambling Act (2008). The Gambling Act requires that servers for legal remote gambling must be physically located in Estonia. In March 2010 the Tax and Customs Board had compiled a blocking list containing 175 sites which ISPs are to enforce. As of September 2013 the list had grown to include over 800 sites. Statistics Estonia Too Many Requests If you report this error to
5040-561: Was placed in the trunk of the vehicles of high-ranking officials and used a standard handset in the passenger compartment. The main developers of the Altai system were VNIIS (Voronezh Science Research Institute of Communications) and GSPI (State Specialized Project Institute). In 1963 this service started in Moscow, and in 1970 Altai service was used in 30 USSR cities. CDMA is a spread-spectrum multiple-access technique. A spread-spectrum technique spreads
5112-690: Was rated as "Free" in the 2009, 2011 to 2015 Freedom on the Net reports from Freedom House with overall scores of 13, 10, 10, 9, 8 and 7 (top 2 in the world in 2015) on a scale where 0 is best and 100 is worst. Estonia has not been individually classified by the OpenNet Initiative (ONI), but is included in the ONI's regional overview for the Commonwealth of Independent States. Freedom of speech and freedom of expression are protected by Estonia's constitution and by
5184-483: Was shown that through the use of linear methods, there are three types of signal separation: frequency, time and compensatory. The technology of CDMA was used in 1957, when the young military radio engineer Leonid Kupriyanovich in Moscow made an experimental model of a wearable automatic mobile phone, called LK-1 by him, with a base station. LK-1 has a weight of 3 kg, 20–30 km operating distance, and 20–30 hours of battery life. The base station, as described by
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