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66-492: Before the development and adoption of the POCSAG code, pagers used one of several codes such as binary Golay code . In the 1990s new paging codes were developed that offered higher data transmission rates and other advanced features such as European and network roaming . The POCSAG code originally transmitted at 512 bits per second. Faster transmission at 1200 or 2400 bits per second using so-called Super-POCSAG has mostly displaced

132-552: A soft-decision algorithm to demodulate digital data from an analog signal corrupted by noise. Many FEC decoders can also generate a bit-error rate (BER) signal which can be used as feedback to fine-tune the analog receiving electronics. FEC information is added to mass storage (magnetic, optical and solid state/flash based) devices to enable recovery of corrupted data, and is used as ECC computer memory on systems that require special provisions for reliability. The maximum proportion of errors or missing bits that can be corrected

198-401: A 25 kHz channel spacing, known as "wideband". Some jurisdictions require that all systems move to a "narrowband" configuration, using 12.5 kHz channels and ±2.5 kHz frequency shifts (for example, the U.S. Federal Communications Commission (FCC) has mandated this transition be completed prior to 2013.). Often single transmission channels contain blocks of data at more than one of

264-430: A code word produces its complement. Griess (p. 59) uses the labeling: PSL(2,7) is naturally the linear fractional group generated by (0123456) and (0∞)(16)(23)(45). The 7-cycle acts on T to give a subspace including also the basis elements and The resulting 7-dimensional subspace has a 3-dimensional quotient space upon ignoring the latter 2 octads. There are 4 other code words of similar structure that complete

330-433: A constrained telecommunications bandwidth. Color image transmission required three times as much data as black and white images, so the 7-error correcting Reed–Muller code that had been used to transmit the black and white Mariner images was replaced with the much higher data rate Golay (24,12,8) code. The MIL-STD-188 American military standards for automatic link establishment in high frequency radio systems specify

396-512: A fixed ECC method as long as the ECC can handle the error rate, then switch to ARQ when the error rate gets too high; adaptive modulation and coding uses a variety of ECC rates, adding more error-correction bits per packet when there are higher error rates in the channel, or taking them out when they are not needed. The two main categories of ECC codes are block codes and convolutional codes . There are many types of block codes; Reed–Solomon coding

462-908: A hard decision is made whether it corresponds to a one or a zero bit. In contrast, convolutional codes are typically decoded using soft-decision algorithms like the Viterbi, MAP or BCJR algorithms, which process (discretized) analog signals, and which allow for much higher error-correction performance than hard-decision decoding. Nearly all classical block codes apply the algebraic properties of finite fields . Hence classical block codes are often referred to as algebraic codes. In contrast to classical block codes that often specify an error-detecting or error-correcting ability, many modern block codes such as LDPC codes lack such guarantees. Instead, modern codes are evaluated in terms of their bit error rates. Most forward error correction codes correct only bit-flips, but not bit-insertions or bit-deletions. In this setting,

528-404: A large code-rate close to 1 implies a weak code. The redundant bits that protect the information have to be transferred using the same communication resources that they are trying to protect. This causes a fundamental tradeoff between reliability and data rate. In one extreme, a strong code (with low code-rate) can induce an important increase in the receiver SNR (signal-to-noise-ratio) decreasing

594-592: A limited number of errors. Therefore a reverse channel to request re-transmission may not be needed. The cost is a fixed, higher forward channel bandwidth. The American mathematician Richard Hamming pioneered this field in the 1940s and invented the first error-correcting code in 1950: the Hamming (7,4) code . FEC can be applied in situations where re-transmissions are costly or impossible, such as one-way communication links or when transmitting to multiple receivers in multicast . Long-latency connections also benefit; in

660-619: A mixture of paging and land mobile communications. The VHF low band (35/43 MHz) frequencies are mainly used for local hospital paging and in many areas are completely unused. Australia uses the following frequencies for localised paging, such as in hospitals, hotels and other facilities, and also as an Emergency communication system for fire services (such as the Victorian Country Fire Authority ) and for ambulances. Other paging systems for wide-area paging, such as commercial networks are licensed and operate anywhere in

726-443: A more uniform distribution of errors. Therefore, interleaving is widely used for burst error-correction . The analysis of modern iterated codes, like turbo codes and LDPC codes , typically assumes an independent distribution of errors. Systems using LDPC codes therefore typically employ additional interleaving across the symbols within a code word. For turbo codes, an interleaver is an integral component and its proper design

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792-464: A partition of the vector space. G 23 is a 12-dimensional subspace of the space F 2 . The automorphism group of the perfect binary Golay code G 23 (meaning the subgroup of the group S 23 of permutations of the coordinates of F 2 which leave G 23 invariant), is the Mathieu group M 23 {\displaystyle M_{23}} . The automorphism group of

858-457: A signal is close to a codeword by only looking at a small number of positions of the signal. Not all testing codes are locally decoding and testing of codes Not all locally decodable codes (LDCs) are locally testable codes (LTCs) neither locally correctable codes (LCCs), q-query LCCs are bounded exponentially while LDCs can have subexponential lengths. Interleaving is frequently used in digital communication and storage systems to improve

924-422: A sync codeword, defined in the standard as 0x7CD215D8, followed by 16 payload codewords that are either address or data. Any unused codewords are filled with the idle value of 0x7A89C197. Although the address (also referred to as a RIC - Radio Identity Code or CAP code - Channel Access Protocol code) is transmitted as 18 bits the actual address is 21-bits long: the remaining three bits are derived from which of

990-409: Is a relatively inefficient ECC. Better ECC codes typically examine the last several tens or even the last several hundreds of previously received bits to determine how to decode the current small handful of bits (typically in groups of 2 to 8 bits). ECC could be said to work by "averaging noise"; since each data bit affects many transmitted symbols, the corruption of some symbols by noise usually allows

1056-570: Is a slightly increased error-correcting code reliability for messages that span more than one POCSAG packet. Within a codeword 7-bit characters are packed from left to right ( MSB to LSB ). The LSB of an ASCII character is sent first (is the MSB in the codeword) as per standard ASCII transmission conventions, so viewed as bits inside a codeword the characters are bit reversed. In the UK , most pager transmissions are in five bands at The frequency 466.075 MHz

1122-407: Is a technique used for controlling errors in data transmission over unreliable or noisy communication channels . The central idea is that the sender encodes the message in a redundant way, most often by using an error correction code or error correcting code ( ECC ). The redundancy allows the receiver not only to detect errors that may occur anywhere in the message, but often to correct

1188-404: Is also used for the evolution of CDMA2000 1x specifically for Internet access, 1xEV-DO (TIA IS-856). Like 1x, EV-DO was developed by Qualcomm , and is sold by Verizon Wireless , Sprint , and other carriers (Verizon's marketing name for 1xEV-DO is Broadband Access , Sprint's consumer and business marketing names for 1xEV-DO are Power Vision and Mobile Broadband , respectively). Sometimes it

1254-627: Is an iterated soft-decoding scheme that combines two or more relatively simple convolutional codes and an interleaver to produce a block code that can perform to within a fraction of a decibel of the Shannon limit . Predating LDPC codes in terms of practical application, they now provide similar performance. One of the earliest commercial applications of turbo coding was the CDMA2000 1x (TIA IS-2000) digital cellular technology developed by Qualcomm and sold by Verizon Wireless , Sprint , and other carriers. It

1320-430: Is commonly referred to as 'alpha-paging', and 4-bit BCD is commonly referred to as 'numeric-paging'. BCD encoding packs 4 bit BCD symbols 5 to a codeword into bits 30-11. The most significant nibble (bits 30,29,28,27) is the leftmost (or most significant) of a BCD coded numeric datum. Values beyond 9 in each nibble (i.e. 0xA through 0xF) are encoded as follows: BCD messages are space padded with trailing 0xC's to fill

1386-430: Is completely lost and the missing letters can be recovered with minimal guesswork. Use of interleaving techniques increases total delay. This is because the entire interleaved block must be received before the packets can be decoded. Also interleavers hide the structure of errors; without an interleaver, more advanced decoding algorithms can take advantage of the error structure and achieve more reliable communication than

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1452-501: Is crucial for good performance. The iterative decoding algorithm works best when there are not short cycles in the factor graph that represents the decoder; the interleaver is chosen to avoid short cycles. Interleaver designs include: In multi- carrier communication systems, interleaving across carriers may be employed to provide frequency diversity , e.g., to mitigate frequency-selective fading or narrowband interference. Transmission without interleaving : Here, each group of

1518-413: Is determined by the design of the ECC, so different forward error correcting codes are suitable for different conditions. In general, a stronger code induces more redundancy that needs to be transmitted using the available bandwidth, which reduces the effective bit-rate while improving the received effective signal-to-noise ratio . The noisy-channel coding theorem of Claude Shannon can be used to compute

1584-454: Is encoded as POCSAG and broadcast on these frequencies: In Switzerland the following frequencies are used: The Belgium POCSAG is used for paging over the A.S.T.R.I.D. network: In Italy , the 26.225-26.935 MHz band (AM/FM, odd frequency steps) and 40.0125-40.0875 MHz (in 25 kHz steps) may be used for local pagers. These frequencies are often used for on-site hospital paging systems, including voice paging. Use of POCSAG on

1650-709: Is noteworthy for its widespread use in compact discs , DVDs , and hard disk drives . Other examples of classical block codes include Golay , BCH , Multidimensional parity , and Hamming codes . Hamming ECC is commonly used to correct NAND flash memory errors. This provides single-bit error correction and 2-bit error detection. Hamming codes are only suitable for more reliable single-level cell (SLC) NAND. Denser multi-level cell (MLC) NAND may use multi-bit correcting ECC such as BCH or Reed–Solomon. NOR Flash typically does not use any error correction. Classical block codes are usually decoded using hard-decision algorithms, which means that for every input and output signal

1716-458: Is obtained from the extended binary Golay code by deleting one coordinate position (conversely, the extended binary Golay code is obtained from the perfect binary Golay code by adding a parity bit ). In standard coding notation, the codes have parameters [24, 12, 8] and [23, 12, 7], corresponding to the length of the codewords, the dimension of the code, and the minimum Hamming distance between two codewords, respectively. In mathematical terms,

1782-425: Is only necessary to decode single bits of the message, or to check whether a given signal is a codeword, and do so without looking at the entire signal. This can make sense in a streaming setting, where codewords are too large to be classically decoded fast enough and where only a few bits of the message are of interest for now. Also such codes have become an important tool in computational complexity theory , e.g., for

1848-422: The Hamming distance is the appropriate way to measure the bit error rate . A few forward error correction codes are designed to correct bit-insertions and bit-deletions, such as Marker Codes and Watermark Codes. The Levenshtein distance is a more appropriate way to measure the bit error rate when using such codes. The fundamental principle of ECC is to add redundant bits in order to help the decoder to find out

1914-434: The "best single published page" in coding theory . There are two closely related binary Golay codes. The extended binary Golay code , G 24 (sometimes just called the "Golay code" in finite group theory) encodes 12 bits of data in a 24-bit word in such a way that any 3-bit errors can be corrected or any 4-bit errors can be detected. The other, the perfect binary Golay code , G 23 , has codewords of length 23 and

1980-683: The 26 MHz and 27 MHz band has been logged by several listeners in Europe, specifically frequencies 26.350 MHz, 26.500 MHz, 26.705 MHz, 26.725 MHz, 26.755 MHz, 27.005 MHz, 27.007 MHz, 27.255 MHz (see note below regarding legal use of 27.255 MHz for paging in the United States). It appears that US-specification paging systems operating on 27.255 MHz have been sold in Italy and other European countries. The former monopoly operator SIP (which later became TIM) used

2046-441: The 450-470 MHz band (plus 421-430 or 470-512 MHz in certain cities). In larger metropolitan areas with congested frequency spectrum, paging services will often share the same frequency as land mobile stations, or operate on an adjacent channel. For example, a department store may operate handheld walkie-talkies on 462.7625 MHz while there are high power pager transmitters on 462.7500 MHz and/or 462.7750 MHz in

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2112-427: The 8 pairs of codewords in the batch the address is sent in. This strategy allows the receiver to turn off for a considerable percentage of the time as it only needs to listen to the pair that applies to it, thus saving a significant amount of battery power. Before a burst of data there will always be a preamble of at least 576 bits of data containing alternating 1s and 0s, allowing the receiver to synchronize itself to

2178-556: The POCSAG in the developed world but the transition is still in progress. In 1976 an international group of engineers began to meet to explore the possibility of developing a new code for wide area paging; paging networks covering regions of entire countries. These meetings were successful and in February 1981 the CCIR (Comité consultatif international pour la radio) the forerunner of the ITU-R accepted

2244-454: The Shannon limit. However, capacity achieving ECCs are usually extremely complex to implement. The most popular ECCs have a trade-off between performance and computational complexity. Usually, their parameters give a range of possible code rates, which can be optimized depending on the scenario. Usually, this optimization is done in order to achieve a low decoding error probability while minimizing

2310-545: The VHF/UHF bands. Binary Golay code In mathematics and electronics engineering , a binary Golay code is a type of linear error-correcting code used in digital communications . The binary Golay code, along with the ternary Golay code , has a particularly deep and interesting connection to the theory of finite sporadic groups in mathematics. These codes are named in honor of Marcel J. E. Golay whose 1949 paper introducing them has been called, by E. R. Berlekamp ,

2376-576: The basis of 12 code words for this representation of W. W has a subspace of dimension 4, symmetric under PSL(2,7) x S 3 , spanned by N and 3 dodecads formed of subsets {0,3,5,6}, {0,1,4,6}, and {0,1,2,5}. Error correction was vital to data transmission in the Voyager 1 and 2 spacecraft particularly because memory constraints dictated offloading data virtually instantly leaving no second chances. Hundreds of color pictures of Jupiter and Saturn in their 1979, 1980, and 1981 fly-bys would be transmitted within

2442-426: The bit error rate, at the cost of reducing the effective data rate. On the other extreme, not using any ECC (i.e., a code-rate equal to 1) uses the full channel for information transfer purposes, at the cost of leaving the bits without any additional protection. One interesting question is the following: how efficient in terms of information transfer can an ECC be that has a negligible decoding error rate? This question

2508-443: The case of satellites orbiting distant planets, retransmission due to errors would create a delay of several hours. FEC is also widely used in modems and in cellular networks . FEC processing in a receiver may be applied to a digital bit stream or in the demodulation of a digitally modulated carrier. For the latter, FEC is an integral part of the initial analog-to-digital conversion in the receiver. The Viterbi decoder implements

2574-411: The code as Radiopaging Code No.1 (RPC No.1),(Rec, 584). The meetings were chaired by R.H.Tridgell and were attended by representatives of British, European, and Japanese pager manufacturers The modulation used is frequency-shift keying (FSK) with a ±4.5  kHz shift on the carrier. The high frequency represents a 0 and the low frequency a 1. The ±4.5  kHz frequency shift is used along with

2640-508: The code can detect and correct up to 2 errors in a codeword. The generating polynomial g ( x ) for the BCH (31, 21) code is: The codewords are either address or data, which is indicated by the first bit transmitted, bit 31. An address codeword contains 18 bits of address (bit 30 through to 13), and 2 function bits (12 & 11). Each data codeword carries 20 bits of data (bits 30 through to 11). Codewords are transmitted in batches that consist of

2706-442: The codeword. There is no POCSAG specified restriction on message length, but particular pagers of course have a fixed number of characters in their display. Alphanumeric messages are encoded in 7-bit ASCII characters packed into the 20 bit data area of a message codeword (bits 30-11). Since three seven bit characters are 21 rather than 20 bits and the designers of the standard did not want to waste transmission time, they chose to pack

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2772-809: The constituent SPC codes in parallel. LDPC codes were first introduced by Robert G. Gallager in his PhD thesis in 1960, but due to the computational effort in implementing encoder and decoder and the introduction of Reed–Solomon codes, they were mostly ignored until the 1990s. LDPC codes are now used in many recent high-speed communication standards, such as DVB-S2 (Digital Video Broadcasting – Satellite – Second Generation), WiMAX ( IEEE 802.16e standard for microwave communications), High-Speed Wireless LAN ( IEEE 802.11n ), 10GBase-T Ethernet (802.3an) and G.hn/G.9960 (ITU-T Standard for networking over power lines, phone lines and coaxial cable). Other LDPC codes are standardized for wireless communication standards within 3GPP MBMS (see fountain codes ). Turbo coding

2838-462: The convolutional decoder. Single pass decoding with this family of error correction codes can yield very low error rates, but for long range transmission conditions (like deep space) iterative decoding is recommended. Concatenated codes have been standard practice in satellite and deep space communications since Voyager 2 first used the technique in its 1986 encounter with Uranus . The Galileo craft used iterative concatenated codes to compensate for

2904-444: The design of probabilistically checkable proofs . Locally decodable codes are error-correcting codes for which single bits of the message can be probabilistically recovered by only looking at a small (say constant) number of positions of a codeword, even after the codeword has been corrupted at some constant fraction of positions. Locally testable codes are error-correcting codes for which it can be checked probabilistically whether

2970-437: The extended binary Golay code G 24 consists of a 12-dimensional linear subspace W of the space V = F 2 of 24-bit words such that any two distinct elements of W differ in at least 8 coordinates. W is called a linear code because it is a vector space. In all, W comprises 4096 = 2 elements. The binary Golay code, G 23 is a perfect code . That is, the spheres of radius three around code words form

3036-557: The extended binary Golay code is the Mathieu group M 24 {\displaystyle M_{24}} , of order 2 × 3 × 5 × 7 × 11 × 23 . M 24 {\displaystyle M_{24}} is transitive on octads and on dodecads. The other Mathieu groups occur as stabilizers of one or several elements of W . There is a single word of weight 24, which is a 1-dimensional invariant subspace. M 24 {\displaystyle M_{24}} therefore has an 11-dimensional irreducible representation on

3102-409: The field with 2 elements. In addition, since the binary golay code is a 12-dimensional subspace of a 24-dimensional space, M 24 {\displaystyle M_{24}} also acts on the 12-dimensional quotient space , called the binary Golay cocode . A word in the cocode is in the same coset as a word of length 0, 1, 2, 3, or 4. In the last case, 6 (disjoint) cocode words all lie in

3168-420: The first 20 bits of an ASCII message into the first code word, the next 20 bits of a message into the next codeword and so forth. What this means that a 7-bit ASCII character of a message that falls on a boundary can and will be split between two code words, and that the alignment of character boundaries in a particular alpha message code word depends on which code word it is of a message. The side benefit of this

3234-555: The following frequencies for their pager service, called Teledrin: In France , POCSAG is operated by E*Message over the AlphaPage network on the 466 MHz frequency: In addition to the bands listed above, paging may be authorized on any frequency in the land mobile bands authorized under Part 90 of the FCC rules, including frequencies in the 72-76 MHz band as well as the usual 30.56-49.58 MHz, 150.775-162.000 MHz VHF bands and

3300-501: The impact to the data rate. Another criterion for optimizing the code rate is to balance low error rate and retransmissions number in order to the energy cost of the communication. Classical (algebraic) block codes and convolutional codes are frequently combined in concatenated coding schemes in which a short constraint-length Viterbi-decoded convolutional code does most of the work and a block code (usually Reed–Solomon) with larger symbol size and block length "mops up" any errors made by

3366-419: The maximum achievable communication bandwidth for a given maximum acceptable error probability. This establishes bounds on the theoretical maximum information transfer rate of a channel with some given base noise level. However, the proof is not constructive, and hence gives no insight of how to build a capacity achieving code. After years of research, some advanced FEC systems like polar code come very close to

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3432-435: The original user data to be extracted from the other, uncorrupted received symbols that also depend on the same user data. Most telecommunication systems use a fixed channel code designed to tolerate the expected worst-case bit error rate , and then fail to work at all if the bit error rate is ever worse. However, some systems adapt to the given channel error conditions: some instances of hybrid automatic repeat-request use

3498-510: The output are systematic , while those that do not are non-systematic . A simplistic example of ECC is to transmit each data bit 3 times, which is known as a (3,1) repetition code . Through a noisy channel, a receiver might see 8 versions of the output, see table below. This allows an error in any one of the three samples to be corrected by "majority vote", or "democratic voting". The correcting ability of this ECC is: Though simple to implement and widely used, this triple modular redundancy

3564-408: The performance of forward error correcting codes. Many communication channels are not memoryless: errors typically occur in bursts rather than independently. If the number of errors within a code word exceeds the error-correcting code's capability, it fails to recover the original code word. Interleaving alleviates this problem by shuffling source symbols across several code words, thereby creating

3630-416: The rates. Transmission uses 32-bit blocks called codewords. Each codeword carries 21 bits of information (bits 31 through 11), 10 bits of error-correcting code (bits 10 through 1), and an even parity bit (bit 0). Bits 31 through 1 are a binary BCH code (31, 21). The error-correcting code has a 6-bit Hamming distance : each 31-bit codeword differs from every other codeword in at least 6 bits. Consequently,

3696-628: The same city. Or, a restaurant will use 467.7500 MHz to alert customers when their table is ready (using so-called "coaster pagers") while a department store nearby uses 467.7500 MHz for their in-store communications. In both of these examples, the department store is forced to use a squelch system such as CTCSS or DCS . In many areas in the United States, these frequencies are used for land mobile (two-way) radio communications services in addition to paging. The VHF (152/157-158 MHz) and UHF (454/459 MHz) frequencies are often used for

3762-433: The same coset. There is an 11-dimensional invariant subspace, consisting of cocode words with odd weight, which gives M 24 {\displaystyle M_{24}} a second 11-dimensional representation on the field with 2 elements. It is convenient to use the " Miracle Octad Generator " format, with coordinates in an array of 4 rows, 6 columns. Addition is taking the symmetric difference. All 6 columns have

3828-584: The same letter represents a 4-bit one-bit error-correcting codeword. The codeword cccc is altered in one bit and can be corrected, but the codeword dddd is altered in three bits, so either it cannot be decoded at all or it might be decoded incorrectly . With interleaving : In each of the codewords "aaaa", "eeee", "ffff", and "gggg", only one bit is altered, so one-bit error-correcting code will decode everything correctly. Transmission without interleaving : The term "AnExample" ends up mostly unintelligible and difficult to correct. With interleaving : No word

3894-526: The same parity, which equals that of the top row. A partition of the 6 columns into 3 pairs of adjacent ones constitutes a trio . This is a partition into 3 octad sets. A subgroup, the projective special linear group PSL(2,7) x S 3 of a trio subgroup of M 24 is useful for generating a basis. PSL(2,7) permutes the octads internally, in parallel. S 3 permutes the 3 octads bodily. The basis begins with octad T: and 5 similar octads. The sum N of all 6 of these code words consists of all 1's. Adding N to

3960-530: The signal, and is another mechanism that enables the receiver to be turned off for a large percentage of the time. A message will start with an address codeword followed by a number of data codewords and will continue until another address, a sync, or an idle codeword is sent. When the data bits are extracted they will be in one of two formats. There are two message coding formats for the data messages. Numeric messages are sent as 4 bit BCD values, and alphanumeric messages are sent as 7-bit ASCII . The 7-bit ASCII

4026-411: The theoretical maximum given by the Shannon channel capacity under the hypothesis of an infinite length frame. ECC is accomplished by adding redundancy to the transmitted information using an algorithm. A redundant bit may be a complicated function of many original information bits. The original information may or may not appear literally in the encoded output; codes that include the unmodified input in

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4092-413: The true message that was encoded by the transmitter. The code-rate of a given ECC system is defined as the ratio between the number of information bits and the total number of bits (i.e., information plus redundancy bits) in a given communication package. The code-rate is hence a real number. A low code-rate close to zero implies a strong code that uses many redundant bits to achieve a good performance, while

4158-429: The use of an extended (24,12) Golay code for forward error correction . In two-way radio communication digital-coded squelch (DCS, CDCSS) system uses 23-bit Golay (23,12) code word which has the ability to detect and correct errors of 3 or fewer bits. Error-correcting code In computing , telecommunication , information theory , and coding theory , forward error correction ( FEC ) or channel coding

4224-463: The very high error rate conditions caused by having a failed antenna. Low-density parity-check (LDPC) codes are a class of highly efficient linear block codes made from many single parity check (SPC) codes. They can provide performance very close to the channel capacity (the theoretical maximum) using an iterated soft-decision decoding approach, at linear time complexity in terms of their block length. Practical implementations rely heavily on decoding

4290-443: Was answered by Claude Shannon with his second theorem, which says that the channel capacity is the maximum bit rate achievable by any ECC whose error rate tends to zero: His proof relies on Gaussian random coding, which is not suitable to real-world applications. The upper bound given by Shannon's work inspired a long journey in designing ECCs that can come close to the ultimate performance boundary. Various codes today can attain almost

4356-406: Was previously used by Hutchison Paging, but the network was shut down in 2000. The frequency is still reserved for paging but is not used. In Germany , well known transmissions are at Licensed paging is possible in any other VHF/UHF bands. In Spain , nationwide service was provided by Telefónica Mensatel but the network was shut down in 2012. The Swedish pager network marketed as "Minicall"

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