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84-472: Airspan was originally a product division of DSC Communications, a manufacturer of telephone switching equipment. Original products included a CDMA -based radio platform used for the fixed wireless market. In 1998, the company separated from DSC Communications and announced Eric Stonestrom as CEO and President. Airspan originally focused its product line on the small cell and mini-macro equipment market, used by mobile operators to extend wireless services. Through

168-439: A channel access method or multiple access method allows more than two terminals connected to the same transmission medium to transmit over it and to share its capacity. Examples of shared physical media are wireless networks , bus networks , ring networks and point-to-point links operating in half-duplex mode. A channel access method is based on multiplexing , which allows several data streams or signals to share

252-474: A subsidiary of Aspen Wind Corporation, to send radios to Kabul , Afghanistan. In the fourth quarter of 2005, the company released its WiMAX product line. In September 2006, Oak Investment Partners made a $ 29 million investment in the company. In 2010, the company teamed with LightSquared to market LightSquared's 1.4 GHz wireless spectrum in the United States. The spectrum is targeted primarily at

336-575: 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

420-425: 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,

504-452: 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

588-401: 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

672-508: 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

756-454: A half-duplex system, communication only works in one direction at a time. A walkie-talkie is an example of a half-duplex system because both users can communicate with one another, but not at the same time, someone has to finish transmitting before the next person can begin. In a full-duplex system, both users can communicate at the same time. A telephone is the most common example of a full-duplex system because both users can speak and be heard at

840-417: 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

924-523: A partnership with Google in support of CBRS services. In August 2021, Airspan completed a business combination with New Beginnings Acquisition Corp. The newly-renamed "Airspan Networks Holdings Inc. then began trading on the NYSE American under the ticker symbol MIMO . The company was founded in January 1998. In May 1998, Eric D. Stonestrom was named president and chief executive officer of

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1008-400: 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

1092-464: 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,

1176-401: 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

1260-568: 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

1344-778: Is modulated on a specific carrier frequency . A related technique is wavelength division multiple access (WDMA), based on wavelength-division multiplexing (WDM), where different data streams get different colors in fiber-optical communications. In the WDMA case, different network nodes in a bus or hub network get a different color. An advanced form of FDMA is the orthogonal frequency-division multiple access (OFDMA) scheme, for example, used in 4G cellular communication systems. In OFDMA, each node may use several sub-carriers, making it possible to provide different quality of service (different data rates) to different users. The assignment of sub-carriers to users may be changed dynamically, based on

1428-416: 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

1512-666: Is CSMA/CD, which is used in Ethernet . Although today's Ethernet installations use full-duplex connections directly to switches . CSMA/CD is still implemented to achieve compatibility with older repeater hubs . In satellite communications , multiple access is the capability of a communications satellite to function as a portion of a communications link between more than one pair of ground-based terminals concurrently. Three types of multiple access presently used with communications satellites are code-division , frequency-division , and time-division multiple access. In cellular networks

1596-461: 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

1680-510: Is a sub-layer in the data link layer of the OSI model and a component of the link layer of the TCP/IP model . Several ways of categorizing multiple-access schemes and protocols have been used in the literature. For example, Daniel Minoli (2009) identifies five principal types of multiple-access schemes: FDMA , TDMA , CDMA , SDMA , and random access . R. Rom and M. Sidi (1990) categorize

1764-486: 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

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1848-441: 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

1932-483: 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,

2016-491: Is based on spread spectrum , meaning that a wider radio channel bandwidth is used than the data rate of individual bit streams requires, and several message signals are transferred simultaneously over the same carrier frequency, utilizing different spreading codes. Per the Shannon–Hartley theorem , the wide bandwidth makes it possible to send with a signal-to-noise ratio of much less than 1 (less than 0 dB), meaning that

2100-905: Is based on using variable transmission power between users in order to share the available power on the channel. Examples include multiple SCPC modems on a satellite transponder, where users get on demand a larger share of the power budget to transmit at higher data rates. Packet mode channel access methods select a single network transmitter for the duration of a packet transmission. Some methods are more suited to wired communication while others are more suited to wireless. Common statistical time-division multiplexing multiple access protocols for wired multi-drop networks include: Common multiple access protocols that may be used in packet radio wireless networks include: Where these methods are used for dividing forward and reverse communication channels, they are known as duplexing methods. A duplexing communication system can be either half-duplex or full duplex . In

2184-483: 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

2268-536: 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

2352-504: 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

2436-517: 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

2520-464: 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

2604-410: 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

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2688-646: Is the spreading code, and each message signal (for example each phone call) uses a different spreading code. Another form is frequency-hopping CDMA (FH-CDMA), based on frequency-hopping spread spectrum (FHSS), where the channel frequency is changed rapidly according to a sequence that constitutes the spreading code. As an example, the Bluetooth communication system is based on a combination of frequency-hopping and either CSMA/CA statistical time-division multiplexing communication (for data communication applications) or TDMA (for audio transmission). All nodes belonging to

2772-577: Is typically also based on time-domain multiplexing, but not in a cyclically repetitive frame structure. Due to its random character, it can be categorized as statistical multiplexing methods and capable of dynamic bandwidth allocation . This requires a media access control (MAC) protocol, i.e. a principle for the nodes to take turns on the channel and to avoid collisions. Common examples are CSMA/CD , used in Ethernet bus networks and hub networks, and CSMA/CA , used in wireless networks such as IEEE 802.11 . The code-division multiple access (CDMA) scheme

2856-485: The frequency-division multiplexing (FDM) scheme, which provides different frequency bands to different data streams. In the FDMA case, the frequency bands are allocated to different nodes or devices. An example of FDMA systems were the first-generation 1G cell-phone systems, where each phone call was assigned to a specific uplink frequency channel, and another downlink frequency channel. Each message signal (each phone call)

2940-541: The MAI between the groups and a low-complexity maximum-likelihood detection stage to recover jointly the co-spread users' data using minimal Euclidean-distance measure and users' channel-gain coefficients. An enhanced CDMA version known as interleave-division multiple access (IDMA) uses the orthogonal interleaving as the only means of user separation in place of signature sequence used in CDMA system. Channel access method In telecommunications and computer networks ,

3024-545: The acquisition of Mimosa Networks in 2018, the company entered the market for fixed wireless solutions which are used in commercial, enterprise and operator networks for wireless backhaul and access applications. Airspan's 5G NR development program is focused on mmWave , Sub 6GHz, Massive MIMO , and Open Virtual RAN architectures. The company also offers fixed wireless access and backhaul solutions for PTP (point-to-point) and PTMP (point-to-multi-point) applications through its Mimosa Products. In March, 2019, Airspan announced

3108-416: 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

3192-566: 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

3276-400: 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}} ,

3360-431: 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

3444-417: 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

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3528-407: The capacity of spectrum. Qualcomm knew that CDMA would greatly increase the efficiency and availability of wireless, but the wireless industry having already invested millions of dollars into TDMA was skeptical. Jacobs and Qualcomm spent several years improving infrastructure and performing tests and demonstrations of CDMA. In 1993, CDMA became accepted as the wireless industry standard. By 1995, CDMA

3612-586: 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

3696-408: The company. Its first product, AS4020 platform, was based on CDMA radio technology adapted for fixed wireless access points . In July 2000, as the dot-com bubble was bursting, the company became a public company and raised $ 82.5 million in an initial public offering . Its stock price rose 113% in its first day of trading. In 2004, the company made an agreement with Neda Telecommunications,

3780-445: 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

3864-500: The current radio channel conditions and traffic load. Single-carrier FDMA (SC-FDMA), a.k.a. linearly-precoded OFDMA (LP-OFDMA), is based on single-carrier frequency-domain-equalization (SC-FDE). The time-division multiple access (TDMA) channel access scheme is based on the time-division multiplexing (TDM) scheme. TDMA provides different time slots to different transmitters in a cyclically repetitive frame structure. For example, node 1 may use time slot 1, node 2 time slot 2, etc. until

3948-443: 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

4032-667: The deal. Airspan's industry recognition and awards date back to 2007 when the company won the 'Best of WiMAX World USA Award'. Airspan & Jio won the SCF 2020 Award for Excellence in Commercial Deployment (Urban). Sprint and Airspan won the SCF 2019 Small Cell Award for Excellence in Commercial Deployment. Sprint & Airspan Netlworks – Sprint LTE Magic Box won the SCF Award 2018 Excellence in Commercial Deployment (Residential). Airspan and Sprint were selected as

4116-467: 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

4200-535: The last transmitter when it starts over. An advanced form is dynamic TDMA (DTDMA), where an assignment of transmitters to time slots varies on each frame. Multi-frequency time-division multiple access (MF-TDMA) combines time and frequency multiple access. As an example, 2G cellular systems are based on a combination of TDMA and FDMA. Each frequency channel is divided into eight time slots, of which seven are used for seven phone calls, and one for signaling data. Statistical time-division multiplexing multiple access

4284-423: 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

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4368-463: 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

4452-416: 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

4536-421: 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

4620-402: 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,

4704-509: 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

4788-400: The protocols into Conflict-free access protocols , Aloha protocols , and Carrier Sensing protocols . The Telecommunications Handbook (Terplan and Morreale, 2000) identifies the following MAC categories: Channel access schemes generally fall into the following categories. The frequency-division multiple access (FDMA) channel-access scheme is the most standard analog system, based on

4872-466: 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

4956-422: The same communication channel or transmission medium. In this context, multiplexing is provided by the physical layer . A channel access method may also be a part of the multiple access protocol and control mechanism, also known as medium access control (MAC). Medium access control deals with issues such as addressing, assigning multiplex channels to different users and avoiding collisions. Media access control

5040-462: 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

5124-414: 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

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5208-400: The same frequency, allowing more conversations to be transmitted over the same amount of spectrum; this is one reason why CDMA eventually became the most widely adopted channel access method in the wireless industry. The origins of CDMA can be traced back to the 1940s where it was patented by the United States government and used throughout World War II to transmit messages. However, following

5292-429: 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

5376-413: 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

5460-583: The same time on each end. Some types of full-duplexing methods are: Note that hybrids of these techniques are frequently used. Some examples: Different channel access constraints and schemes apply to different applications. In local area networks (LANs) and metropolitan area networks (MANs), multiple access methods enable bus networks, ring networks, star networks, wireless networks and half-duplex point-to-point communication, but are not required in full-duplex point-to-point serial lines between network switches and routers. The most common multiple access method

5544-791: The same user (to the same piconet ) use the same frequency hopping sequence synchronously, meaning that they send on the same frequency channel, but CDMA/CA or TDMA is used to avoid collisions within the virtual personal area network (VPAN). Frequency-hopping is used by Bluetooth to reduce the cross-talk and collision probability between nodes in different VPANs. Other techniques include OFDMA and multi-carrier code-division multiple access (MC-CDMA). Space-division multiple access (SDMA) transmits different information in different physical areas. Examples include simple cellular radio systems and more advanced cellular systems that use directional antennas and power modulation to refine spatial transmission patterns. Power-division multiple access ( PDMA ) scheme

5628-401: 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,

5712-405: 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

5796-402: 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

5880-481: 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

5964-406: 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

6048-559: 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

6132-462: 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

6216-435: The transmission power can be reduced to a level below the level of the noise and co-channel interference from other message signals sharing the same frequency range. One form is direct-sequence CDMA (DS-CDMA), based on direct-sequence spread spectrum (DSSS), used for example in 3G cell phone systems. Each information bit (or each symbol) is represented by a long code sequence of several pulses, called chips. The sequence

6300-409: The two most widely adopted technologies are CDMA and TDMA. TDMA technology works by identifying natural breaks in speech and utilizing one radio wave to support multiple transmissions in turn. In CDMA technology, each individual packet receives a unique code that is broken up over a wide frequency spectrum and is then reassembled on the other end. CDMA allows multiple people to speak at the same time over

6384-473: 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

6468-580: 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. 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

6552-481: The utility industry for Smart Grid deployments. In 2009, the company's stock was delisted from the NASDAQ. In March 2021, the company announced that it would be re-listed on NYSE American through a reverse merger with New Beginnings Acquisition Corporation, a special-purpose acquisition company . In August 2021, the company completed the reverse merger with New Beginnings Acquisition Corporation. The parent company

6636-413: 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

6720-404: The war the patent expired and the use of CDMA diminished and was widely replaced by TDMA. That was until Irwin M. Jacobs an MIT engineer, and fellow employees from the company Linkabit founded the telecommunications company Qualcomm . At the time Qualcomm was founded, Jacobs had already been working on addressing telecommunications problems for the military using digital technology to increase

6804-500: The winners for the “Best Mobile Technology Breakthrough” at GLOMO 2018 Awards. Airspan and Qualcomm won the SCF 2021 Small Cell Award for Excellence in Commercial Deployment for 5G OpenRANGE mmWave outdoor small deployment. 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

6888-575: Was hence renamed "Airspan Networks Holdings Inc." and began trading on the NYSE American under the ticker symbol MIMO . In May 2023, Glenn Laxdal was announced as the new CEO. In March 2024, the company announced that it would become private after receiving up to $ 95 million in new equity financing. The company's stock was soon delisted from the NYSE, and the company filed for a voluntary prepackaged Chapter 11 bankruptcy filing in order to implement

6972-569: 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

7056-483: 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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