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46-567: The functions of the MINTERM are similar to those of the TACTERM; its updated design includes an improved modular architecture, and it has been reduced in size. The MINTERM is lightweight, low-power, single channel, half-duplex, narrowband/wideband/wireline terminal providing secure voice and data communications with full key distribution and remote rekey capabilities. The MINTERM is certified to secure traffic up to TOP SECRET. The MINTERM improvements include

92-419: 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

138-517: A common frequency for all members of the network to verify that the equipment is operational. During initial net activation, all operators in the net tune to the manual frequency. After communications are established, the net switches to the FH mode and the NCS transfers the hopping variables to the outstations. More than 570,000 radios have been purchased. There have been several system improvement programs, including

184-485: 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 a soft-decision algorithm to demodulate digital data from an analog signal corrupted by noise. Many FEC decoders can also generate

230-512: 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

276-908: 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,

322-404: 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

368-426: A modular basis to achieve maximum commonality among various ground, maritime, and airborne configurations. A common receiver/transmitter (RT) is used in the ground configurations. The modular design also reduces the burden on the logistics system to provide repair parts. The SINCGARS can operate in either the single-channel (SC) or frequency hopping (FH) mode, and stores both SC frequencies and FH loadsets. The system

414-443: 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

460-457: 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

506-409: 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

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552-404: 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

598-627: 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

644-481: Is compatible with all current U.S. and allied VHF-frequency modulation (FM) radios in the SC, nonsecure mode. The SINCGARS operates on any of 2320 channels between 30 and 88 megahertz (MHz) with a channel separation of 25 kilohertz (kHz). It accepts either digital or analog inputs and superimposes the signal onto a radio frequency (RF) carrier wave. In FH mode, the input changes frequency about 100 times per second over portions of

690-430: 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

736-501: 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

782-413: 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

828-709: 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

874-425: 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

920-499: 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 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

966-471: 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

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1012-404: 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 the case of satellites orbiting distant planets, retransmission due to errors would create

1058-706: The Integrated Communications Security (ICOM) models, which have provided integrated voice and data encryption, the Special Improvement Program (SIP) models, which add additional data modes, and the advanced SIP (ASIP) models, which are less than half the size and weight of ICOM and SIP models and provided enhanced FEC ( forward error correction ) data modes, RS-232 asynchronous data, packet data formats, and direct interfacing to Precision Lightweight GPS Receiver (PLGR) devices providing radio level situational awareness capability. In 1992,

1104-518: The SINCGARS’ primary role is voice transmission between surface and airborne command and control (C2) assets. The SINCGARS family replaced the Vietnam War-era synthesized single frequency radios ( AN/PRC-77 and AN/VRC-12 ), although it can work with them. The airborne AN/ARC-201 radio is phasing out the older tactical air-to-ground radios (AN/ARC-114 and AN/ARC-131). The SINCGARS is designed on

1150-454: 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

1196-491: The U.S. Air Force awarded a contract to replace the AN/ARC-188 for communications between Air Force aircraft and Army units. Forward error correction In computing , telecommunication , information theory , and coding theory , forward error correction ( FEC ) or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels . The central idea

1242-426: 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

1288-501: The capability to control output power; however, most airborne SINCGARS are fixed power. Those RTs with power settings can vary transmission range from approximately 200 meters (660 feet) to 10 kilometers (km) (6.2 miles). Adding a power amplifier increases the line of sight (LOS) range to approximately 40 km (25 miles). (These ranges are for planning purposes only; terrain, weather, and antenna height can affect transmission range.) The variable output power level allows users to operate on

1334-809: 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

1380-462: 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

1426-444: 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

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1472-655: The following: The AIRTERM is a lightweight, self-contained secure voice and data terminal that provides secure half-duplex voice, digital data, analog data, and remote-keying capabilities for transmission over radio circuits or wireline media. It is a wideband/narrowband terminal that interoperates with the TACTERM, MINTERM, VINSON, and Single Channel Ground and Airborne Radio System ( SINCGARS ). AIRTERM accepts classified analog voice information and uses LPC-10 at 2.4 kbit/s in narrowband voice modes and continuously variable slope delta (CVSD) modulation at 12 kbit/s and 16 kbit/s in wideband voice modes. The AIRTERM provides

1518-501: 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

1564-419: 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

1610-400: The minimum power necessary to maintain reliable communications, thus lessening the electromagnetic signature given off by their radio sets. This capability is of particular importance at major command posts, which operate in multiple networks. SC CNR users outside the FH network can use a hailing method to request access to the network. When hailing a network, a user outside the network contacts

1656-469: The network control station (NCS) on the cue frequency. In the active FH mode, the SINCGARS gives audible and visual signals to the operator that an external subscriber wants to communicate with the FH network. The SINCGARS operator must change to the cue frequency to communicate with the outside radio system. The network can be set to a manual frequency for initial network activation. The manual frequency provides

1702-435: 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

1748-510: 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

1794-408: 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

1840-496: The same connectors, with similar functional pinouts, as the VINSON for the wideband operational modes. This cryptography-related article is a stub . You can help Misplaced Pages by expanding it . SINCGARS Single Channel Ground and Airborne Radio System ( SINCGARS ) is a very high frequency combat network radio (CNR) used by U.S. and allied military forces. In the CNR network,

1886-584: 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

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1932-612: The tactical VHF-FM range. These continual changes in frequency hinder threat interception and jamming units from locating or disrupting friendly communications. The SINCGARS provides data rates up to 16,000 bits per second. Enhanced data modes provide packet and RS-232 data. The enhanced data modes available with the System Improvement Program (SIP) and Advanced System Improvement Program (ASIP) radios also enable forward error correction (FEC), and increased speed, range, and accuracy of data transmissions. Most ground SINCGARS have

1978-411: 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

2024-413: 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

2070-463: 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

2116-443: 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

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