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CdmaOne
Interim Standard 95 (IS-95) was the first ever CDMA-based digital cellular technology. It was developed by Qualcomm and later adopted as a standard by the Telecommunications Industry Association in TIA/EIA/IS-95 release published in 1995. The proprietary name for IS-95 is cdmaOne. It is a 2G mobile telecommunications standard that uses code-division multiple access (CDMA), a multiple access scheme for digital radio, to send voice, data and signaling data (such as a dialed telephone number) between mobile telephones and cell sites. CDMA transmits streams of bits ( PN codes). CDMA permits several radios to share the same frequencies. Unlike TDMA "time division multiple access", a competing system used in 2G GSM, all radios can be active all the time, because network capacity does not directly limit the number of active radios. Since larger numbers of phones can be served by smaller numbers of cell-sites, CDMA-based standards have a significant economic advantage over ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Code-division Multiple Access
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). 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 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. It can be also used as a chan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comparison Of Mobile Phone Standards
This is a comparison of standards of mobile phones. A new generation of cellular standards has appeared approximately every tenth year since 1G systems were introduced in 1979 and the early to mid-1980s. Issues Global System for Mobile Communications (GSM, around 80–85% market share) and IS-95 (around 10–15% market share) were the two most prevalent 2G mobile communication technologies in 2007. In 3G, the most prevalent technology was UMTS with CDMA-2000 in close contention. All radio access technologies have to solve the same problems: to divide the finite RF spectrum among multiple users as efficiently as possible. GSM uses TDMA and FDMA for user and cell separation. UMTS, IS-95 and CDMA-2000 use CDMA. WiMAX and LTE use OFDM. * Time-division multiple access (TDMA) provides multiuser access by chopping up the channel into sequential time slices. Each user of the channel takes turns to transmit and receive signals. In reality, only one person is actually using th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Qualcomm
Qualcomm () is an American multinational corporation headquartered in San Diego, California, and incorporated in Delaware. It creates semiconductors, software, and services related to wireless technology. It owns patents critical to the 5G, 4G, CDMA2000, TD-SCDMA and WCDMA mobile communications standards. Qualcomm was established in 1985 by Irwin M. Jacobs and six other co-founders. Its early research into CDMA wireless cell phone technology was funded by selling a two-way mobile digital satellite communications system known as Omnitracs. After a heated debate in the wireless industry, the 2G standard was adopted with Qualcomm's CDMA patents incorporated. Afterwards there was a series of legal disputes about pricing for licensing patents required by the standard. Over the years, Qualcomm has expanded into selling semiconductor products in a predominantly fabless manufacturing model. It also developed semiconductor components or software for vehicles, watches, laptops, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Radio
Digital radio is the use of digital technology to transmit or receive across the radio spectrum. Digital transmission by radio waves includes digital broadcasting, and especially digital audio radio services. Types In digital broadcasting systems, the analog audio signal is digitized, compressed using an audio coding format such as AAC+ ( MDCT) or MP2, and transmitted using a digital modulation scheme. The aim is to increase the number of radio programs in a given spectrum, to improve the audio quality, to eliminate fading problems in mobile environments, to allow additional datacasting services, and to decrease the transmission power or the number of transmitters required to cover a region. However, analog radio (AM and FM) is still more popular and listening to radio over IP (Internet Protocol) is growing in popularity. In 2012 four digital wireless radio systems are recognized by the International Telecommunication Union: the two European systems Digital Audio Broadca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CDMA2000
CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards for sending voice, data, and Signaling (telecommunication), signaling data between mobile phones and cell sites. It is developed by 3GPP2 as a backwards-compatible successor to 2G, second-generation cdmaOne (IS-95) set of standards and used especially in North America and South Korea. CDMA2000 compares to UMTS, a competing set of 3G standards, which is developed by 3GPP and used in Europe, Japan, China, and Singapore. The name CDMA2000 denotes a family of standards that represent the successive, evolutionary stages of the underlying technology. These are: *Voice: CDMA2000 1xRTT, 1X Advanced *Data: CDMA2000 1xEV-DO (Evolution-Data Optimized): Release 0, Revision A, Revision B, Ultra Mobile Broadband (UMB) All are approved radio interfaces for the International Telecommunication Union, ITU's IMT-2000. In the United States, ''CDMA2000'' is a registered trademark of the Tel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IS-2000
CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards for sending voice, data, and signaling data between mobile phones and cell sites. It is developed by 3GPP2 as a backwards-compatible successor to second-generation cdmaOne (IS-95) set of standards and used especially in North America and South Korea. CDMA2000 compares to UMTS, a competing set of 3G standards, which is developed by 3GPP and used in Europe, Japan, China, and Singapore. The name CDMA2000 denotes a family of standards that represent the successive, evolutionary stages of the underlying technology. These are: *Voice: CDMA2000 1xRTT, 1X Advanced *Data: CDMA2000 1xEV-DO ( Evolution-Data Optimized): Release 0, Revision A, Revision B, Ultra Mobile Broadband (UMB) All are approved radio interfaces for the ITU's IMT-2000. In the United States, ''CDMA2000'' is a registered trademark of the Telecommunications Industry Association (TIA-USA). 1X CDMA2000 1X ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Autocorrelation
Autocorrelation, sometimes known as serial correlation in the discrete time case, is the correlation of a signal with a delayed copy of itself as a function of delay. Informally, it is the similarity between observations of a random variable as a function of the time lag between them. The analysis of autocorrelation is a mathematical tool for finding repeating patterns, such as the presence of a periodic signal obscured by noise, or identifying the missing fundamental frequency in a signal implied by its harmonic frequencies. It is often used in signal processing for analyzing functions or series of values, such as time domain signals. Different fields of study define autocorrelation differently, and not all of these definitions are equivalent. In some fields, the term is used interchangeably with autocovariance. Unit root processes, trend-stationary processes, autoregressive processes, and moving average processes are specific forms of processes with autocorrelation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
OQPSK
Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at a precise time. It is widely used for wireless LANs, RFID and Bluetooth communication. Any digital modulation scheme uses a finite number of distinct signals to represent digital data. PSK uses a finite number of phases, each assigned a unique pattern of binary digits. Usually, each phase encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the particular phase. The demodulator, which is designed specifically for the symbol-set used by the modulator, determines the phase of the received signal and maps it back to the symbol it represents, thus recovering the original data. This requires the receiver to be able to compare the phase of the received signal to a reference signal such a system is term ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Walsh Codes
The Hadamard code is an error-correcting code named after Jacques Hadamard that is used for error detection and correction when transmitting messages over very noisy or unreliable channels. In 1971, the code was used to transmit photos of Mars back to Earth from the NASA space probe Mariner 9. Because of its unique mathematical properties, the Hadamard code is not only used by engineers, but also intensely studied in coding theory, mathematics, and theoretical computer science. The Hadamard code is also known under the names Walsh code, Walsh family, and Walsh–Hadamard code in recognition of the American mathematician Joseph Leonard Walsh. The Hadamard code is an example of a linear code of length 2^m over a binary alphabet. Unfortunately, this term is somewhat ambiguous as some references assume a message length k = m while others assume a message length of k = m+1. In this article, the first case is called the Hadamard code while the second is called the augmented Had ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Viterbi Decoder
A Viterbi decoder uses the Viterbi algorithm for decoding a bitstream that has been encoded using a convolutional code or trellis code. There are other algorithms for decoding a convolutionally encoded stream (for example, the Fano algorithm). The Viterbi algorithm is the most resource-consuming, but it does the maximum likelihood decoding. It is most often used for decoding convolutional codes with constraint lengths k≤3, but values up to k=15 are used in practice. Viterbi decoding was developed by Andrew J. Viterbi and published in the paper There are both hardware (in modems) and software implementations of a Viterbi decoder. Viterbi decoding is used in the iterative Viterbi decoding algorithm. Hardware implementation A hardware Viterbi decoder for basic (not punctured) code usually consists of the following major blocks: *Branch metric unit (BMU) *Path metric unit (PMU) *Traceback unit (TBU) Branch metric unit (BMU) A branch metric unit's function is to cal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Handoff
In cellular telecommunications, handover, or handoff, is the process of transferring an ongoing call or data session from one channel connected to the core network to another channel. In satellite communications it is the process of transferring satellite control responsibility from one earth station to another without loss or interruption of service. Terminology American English uses the term ''handoff'', and this is most commonly used within some American organizations such as 3GPP2 and in American originated technologies such as CDMA2000. In British English the term ''handover'' is more common, and is used within international and European organisations such as ITU-T, IETF, ETSI and 3GPP, and standardised within European originated standards such as GSM and UMTS. The term handover is more common in academic research publications and literature, while handoff is slightly more common within the IEEE and ANSI organisations. Purpose In telecommunications there may be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pseudo-random Noise
In cryptography, pseudorandom noise (PRN) is a signal similar to noise which satisfies one or more of the standard tests for statistical randomness. Although it seems to lack any definite pattern, pseudorandom noise consists of a deterministic sequence of pulses that will repeat itself after its period. In cryptographic devices, the pseudorandom noise pattern is determined by a key and the repetition period can be very long, even millions of digits. Pseudorandom noise is used in some electronic musical instruments, either by itself or as an input to subtractive synthesis, and in many white noise machines. In spread-spectrum systems, the receiver correlates a locally generated signal with the received signal. Such spread-spectrum systems require a set of one or more "codes" or "sequences" such that * Like random noise, the local sequence has a very low correlation with any other sequence in the set, or with the same sequence at a significantly different time offset, or with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
