Code Division Multiple Access - Wikipedia, The Free Encyclopedia

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de division multiple access - Wikipedia, the free encyclopedia

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Code division multiple access

Multiplex techniques

Anal og modul atio n

AMFM PMQAM SMSSB

Circuit mode (constant bandwidth)

TDMFDM/ WDM SDM

Polarization multiplexing

Spatial multiplexing OAM multiplexing

Statistical multiplexing (variable bandwidth)

Packet mode Dynamic TDM FHSS

DSSSOFDMASC-FDM MC-SS

Related top ics

Channel access methods

Media Access Control

VTE

From Wikipedia, the free encyclopedia

(Redirected fromCDMA)

This article is about a channel access method. For the mobile phone technology referred to as CDMA, see IS-95 and

CDMA2000.

Code division multiple access (CDMA) is a channel access method used by

various radio communication technologies.

CDMA is an example ofmultiple access, which is 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 to be achieved without undue interference between the users CDMA

employs spread-spectrum technology and a special coding scheme (where each

transmitter is assigned a code).

CDMA is used as the access method in many mobile phone standards such as

cdmaOne, CDMA2000 (the 3G evolution of cdmaOne), and WCDMA (the 3G

standard used by GSM carriers), which are often referred to as simply CDMA.

Contents [hide]

1 History

2 Uses

3 Steps in CDMA Modulation

4 Code division multiplexing (Synchronous CDMA)

4.1 Example

5 Asynchronous CDMA

5.1 Advantages of asynchronous CDMA over other techniques

5.1.1 Efficient practical utilization of fixed frequency spectrum

5.1.2 Flexible allocation of resources

5.2 Spread-spectrum characteristics of CDMA

6 Collaborative CDMA

7 See also

8 Further reading

9 References

10 External links

The technology of code division multiple access channels has long been known. In the USSR, the first work devoted to this

subject was published in 1935 by professor Dmitriy V. Ageev.[1] It 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 automaticmobile phone, called LK-1 by him, with a base station. LK-1 has a weight of 3 kg, 2030 km operating distance, and 2030

hours of battery life.[2][3] The base station, as described by 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, named by him as correllator.[4][5] 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 and was approximately 3 cubic meters in size[dubious discuss]. It 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.[citation needed]

One of the early applications for code division multiplexing is in GPS. Thispredates and is distinct from its use in mobile phones.

The Qualcommstandard IS-95, marketed as cdmaOne.

The Qualcommstandard IS-2000, known as CDMA2000. This standard is used

by several mobile phone companies, including the Globalstarsatellite phone

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network.

The UMTS3G mobile phone standard, which uses W-CDMA.

CDMA has been used in the OmniTRACS satellite system for transportation

logistics.

CDMA is a spread spectrum multiple access[6] technique. A spread spectrum

technique spreads the bandwidth of the data uniformly for the same transmitted

power. A spreading code is a pseudo-random code that has a narrow ambiguity

function, 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 via bitwise XOR(exclusive OR) with the faster code. The figure shows

how a spread spectrum signal is generated. The data signal with pulse duration of

(symbol period) is XORed with the code signal with pulse duration of (chip period). (Note: bandwidth is proportional

to where = bit time) Therefore, the bandwidth of the data signal is and the bandwidth of the spread spectrum

signal is . Since is much smaller than , the bandwidth of the spread spectrum signal is much larger than the

bandwidth of the original signal. The ratio 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.[7]

Each user in a CDMA system uses 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 will occur 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

correlatingthe received signal with the locally generated code of the desired user. If 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, 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. [8]

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 is analogous to the last example where people speaking the same language

can understand each other, but other languages are perceived as noiseand 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).

Synchronous CDMA exploits mathematical properties oforthogonality between vectors representing the data strings. For

example, binary string 1011 is represented by the vector (1, 0, 1, 1). Vectors can be multiplied by taking their dot product, by

summing the products of their respective components (for example, if u = (a, b) and v = (c, d), then their dot product uv =

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 and:

A CDMA2000 mobile phone

Steps in CDMA Modulation [edit source | edit beta ]

Code division multiplexing (Synchronous CDMA) [edit source | edit beta ]
http://en.wikipedia.org/wiki/UMTShttp://en.wikipedia.org/wiki/UMTShttp://en.wikipedia.org/wiki/W-CDMAhttp://en.wikipedia.org/wiki/Logisticshttp://en.wikipedia.org/wiki/Ambiguity_functionhttp://en.wikipedia.org/wiki/Ambiguity_functionhttp://en.wikipedia.org/wiki/Ambiguity_functionhttp://en.wikipedia.org/wiki/XOR#Bitwise_operationhttp://en.wikipedia.org/wiki/XOR#Bitwise_operationhttp://en.wikipedia.org/wiki/Bandwidth_%28signal_processing%29http://en.wikipedia.org/wiki/Cross-correlationhttp://en.wikipedia.org/wiki/Cross-correlationhttp://en.wikipedia.org/wiki/Noisehttp://en.wikipedia.org/wiki/Noisehttp://en.wikipedia.org/wiki/Orthogonalityhttp://en.wikipedia.org/wiki/Coordinate_vectorhttp://en.wikipedia.org/wiki/Dot_producthttp://en.wikipedia.org/wiki/Dot_producthttp://en.wikipedia.org/wiki/W-CDMAhttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&action=edit&section=3http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=3http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=3http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&action=edit&section=4http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=4http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=4http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=4http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=4http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&action=edit&section=4http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=3http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=3http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&action=edit&section=3http://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/File:Au_CDMA_1X_WIN_W31SAII_gravelly_silver_expansion.jpghttp://en.wikipedia.org/wiki/File:Au_CDMA_1X_WIN_W31SAII_gravelly_silver_expansion.jpghttp://en.wikipedia.org/wiki/W-CDMAhttp://en.wikipedia.org/wiki/Dot_producthttp://en.wikipedia.org/wiki/Coordinate_vectorhttp://en.wikipedia.org/wiki/Orthogonalityhttp://en.wikipedia.org/wiki/Noisehttp://en.wikipedia.org/wiki/Cross-correlationhttp://en.wikipedia.org/wiki/File:Generation_of_CDMA.svghttp://en.wikipedia.org/wiki/Bandwidth_%28signal_processing%29http://en.wikipedia.org/wiki/XOR#Bitwise_operationhttp://en.wikipedia.org/wiki/Ambiguity_functionhttp://en.wikipedia.org/wiki/Ambiguity_functionhttp://en.wikipedia.org/wiki/Logisticshttp://en.wikipedia.org/wiki/W-CDMAhttp://en.wikipedia.org/wiki/UMTS


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Each user in synchronous CDMA uses a code orthogonal to the others' codes to modulate their signal. An example of four

mutually orthogonal digital signals is shown in the figure. 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 are orthogonal to one another, 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 is shown in the picture on the left. 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 2 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, ifv = (v0, v1) = (1, 1) and the data that the user wishes to transmit

is (1, 0, 1, 1), then the transmitted symbols would be (v , v , v , v) = (v0, v1, v0,v1, v0, v1, v0, v1) = (1, 1, 1, 1, 1, 1, 1, 1). 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 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 the coding steps:

Step Encode sender0 Encode sender1

0 code0 = (1, 1), data0 = (1, 0, 1, 1) code1 = (1, 1), data1 = (0, 0, 1, 1)

1 encode0 = 2(1, 0, 1, 1) (1, 1, 1, 1)

= (1, 1, 1, 1)

encode1 = 2(0, 0, 1, 1) (1, 1, 1, 1)

= (1, 1, 1, 1)

2 signal0 = encode0 code0

= (1, 1, 1, 1) (1, 1)

= (1, 1, 1, 1, 1, 1, 1, 1)

signal1 = encode1 code1

= (1, 1, 1, 1) (1, 1)

= (1, 1, 1, 1, 1, 1, 1, 1)

Because signal0 and signal1 are transmitted at the same time into the air, they add to produce the raw signal:

(1, 1, 1, 1, 1, 1, 1, 1) + (1, 1, 1, 1, 1, 1, 1, 1) = (0, 2, 2, 0, 2, 0, 2, 0)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 receiver combines it with the codes of the senders. The

following table explains how this works and shows that the signals do not interfere with one another:

Step Decode sender0 Decode sender1

0 code0 = (1, 1), signal = (0, 2, 2, 0, 2, 0, 2, 0) code1 = (1, 1), signal = (0, 2, 2, 0, 2, 0, 2, 0)

1 decode0 = pattern.vector0 decode1 = pattern.vector1

2 decode0 = ((0, 2), (2, 0), (2, 0), (2, 0)).(1, 1) decode1 = ((0, 2), (2, 0), (2, 0), (2, 0)).(1, 1)

3 decode0 = ((0 + 2), (2 + 0), (2 + 0), (2 + 0)) decode1 = ((0 2), (2 + 0), (2 + 0), (2 + 0))

4 data0=(2, 2, 2, 2), meaning (1, 0, 1, 1) data1=(2, 2, 2, 2), meaning (0, 0, 1, 1)

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 is (2, 2, 2, 2), but the receiver interprets this as (1, 0, 1, 1). Values of exactly 0 means

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:

Step Decode sender0 Decode sender1

Example [edit source | edit beta ]

An example of four mutually orthogonal

digital signals.
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0 code0 = (1, 1), signal = (1, 1, 1, 1, 1, 1, 1, 1) code1 = (1, 1), signal = (1, 1, 1, 1, 1, 1, 1, 1)

1 decode0 = pattern.vector0 decode1 = pattern.vector1

2 decode0 = ((1, 1), (1, 1), (1, 1), (1, 1)).(1, 1) decode1 = ((1, 1), (1, 1), (1, 1), (1, 1)).(1, 1)

3 decode0 = ((1 + 1), (1 1),(1 + 1), (1 + 1)) decode1 = ((1 1), (1 + 1),(1 1), (1 1))

4 data0 = (2, 2, 2, 2), meaning (1, 0, 1, 1) data1 = (0, 0, 0, 0), meaning no data

When the receiver attempts to decode the signal using sender1's code, the data is all zeros, therefore the cross correlation

is equal to zero and it is clear that sender1 did not transmit any data.

See also: Direct-sequence spread spectrum and near-far problem

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"

(PN) sequences are used in asynchronous CDMA systems. A PN code is a binary sequence that appears random but can

be reproduced in a deterministic manner by intended receivers. These PN codes 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 PN sequences are statistically uncorrelated, and the sum of a large number of PN sequences results in

multiple access interference (MAI) that is approximated by a Gaussian noise process (following the central limit theorem in

statistics). Gold codesare an example of a PN 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, the signals of other users will appear as noiseto the signal of interest and interfere slightly with the desired signal in proportion to number of users.

All forms of CDMA use spread spectrumprocess gain to allow receivers to partially discriminate against unwanted signals.

Signals encoded with the specified PN sequence (code) are received, while signals with different codes (or the same code

but a different timing offset) appear as wideband noise reduced by the process gain.

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 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 theory, CDMA, TDMA and FDMA have exactly the same spectral efficiency but practically, 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 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 shiftof the

signal spectrum because of user mobility. The guard-bands will reduce the probability that adjacent channels will interfere,

but decrease the utilization of the spectrum.

Asynchronous CDMA offers a key advantage in the flexible allocation of resources i.e. allocation of a PN codes 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 number of simultaneous users is limited.

There are 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 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 2N users that only talk half of the time, then 2N users can be

accommodated with the same average bit error probability as N users that talk all of 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 arandom

quantity (with the same mean)for 2N 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 the underutilized resources inherent to bursty traffic due to the fixed number oforthogonal 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

Asynchronous CDMA [edit source | edit beta ]

Advantages of asynchronous CDMA over other techniques [edit source | edit beta ]

Efficient practical utilization of fixed frequency spectrum [edit source | edit beta ]

Flexible allocation of resources [edit source | edit beta ]
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Wikimedia Commons has mediarelated to: CDMA

and 2N 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 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 don't, keeping the same PN 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 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 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 the entire bandwidth of the signal or jam only part of the entire signal. [9]

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

encodingand interleavingcan be used to assist in recovering this lost data. CDMA signals are also resistant to multipath

fading. Since 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 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 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 the path delay of the

strongest signal.[10]

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, 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.[11]

Since adjacent cells use 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 the soft

hand off, which is undetectable and provides a more reliable and higher quality signal. [11]

In a recent study, a novel collaborative multi-user transmission and detection scheme called Collaborative CDMA[12] 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 multiple access interference (MAI) limited environment. The authors show that it

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 the MAI between the groups and a low complexity maximum-likelihood detection stage to

recover jointly the co-spread users data using minimum Euclidean distance measure and users channel gain coefficients. In

CDM signal security is high.

cdmaOne

CDMA2000

W-CDMA

Orthogonal variable spreading factor(OVSF), an implementation of CDMA

Spread-spectrum characteristics of CDMA [edit source | edit beta ]

Collaborative CDMA [edit source | edit beta ]

See also [edit source | edit beta ]
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[hide]VTE

[show]VTE

Pseudo-random noise

Spread spectrum

CDMA Spectral Efficiency

Comparison of mobile phone standards

Viterbi, Andrew J . (1995). CDMA: Principles of Spread Spectrum Communication (1st ed.). Prentice Hall PTR. ISBN0-

201-63374-4.

"CDMA Spectrum" . Retrieved 2008-04-29.

1. ^ Ageev, D. V. (1935). "Bases of the Theory of Linear Selection. Code Demultiplexing". Proceedings of the Leningrad

Experimental Institute of Communication: 335.

2. ^ Nauka i Zhizn8, 1957, p. 49

3. ^ Yuniy technik 7, 1957, p. 43-44

4. ^ Nauka i Zhizn 10, 1958, p. 66

5. ^ Tekhnika Molodezhi 2, 1959, p. 18-19

6. ^ Ipatov, Valeri (2000). Spread Spectrum and CDMA. J ohn Wiley & Sons, Ltd.

7. ^ Dubendorf, Vern A. (2003). Wireless Data Technologies. J ohn Wiley & Sons, Ltd.

8. ^ "CDMA Spectrum" . Retrieved 2008-04-29.

9. ^ Skylar, Bernard (2001). Digital Communications: Fundamentals and Applications (Second ed.). Prentice-Hall PTR.

10. ^ Rapporteur, Theodore S. (2002). Wireless Communications, Principles and Practice. Prentice-Hall, Inc.

11. ab Harte, Levine, Kikta, Lawrence, Richard, Romans (2002). 3G Wireless Demystified. McGowan-Hill.12. ^ Shakya, Indu L. (2011). "High User Capacity Collaborative CDMA". IET Communications.

CDMA Development Group

Spread spectrum in Digital Communications

Main articlesSpread spectrumCode division m ultiple access (CDMA)

History: Hedy LamarrCommercial useMore...

Spread spectrum MethodsDirect-sequence spread spectrum(DSSS) Frequency-hopping spread spectrum(FHSS)

Chirp spread spectrum (CSS) Time-hopping spread spectrum(THSS)

CDMA Schemes W-CDMATD-CDMA TD-SCDMADS-CDMAFH-CDMA MC-CDMA

Major implementationsSpace Network (NASA) GPS GalileoGLONASS Bluetooth Cordless phones:DECT

Cellular:EV-DO Mobile IS-95(aka cdmaOne) CDMA2000(aka IS-2000) Als o: Qualcomm Verizon

Major conceptsPN (pseudorandom noise) code ChipNear-far problemPower spectral density (PSD) Process gain

Rake receiverLow probability of intercept

See also :Digital communicationModulation Statistical multiplexing Waveform

Channel access methods and Media access c ontrol (MAC)/Multiple-access protocols

Categories: Channel access methods Code division multiple access Multiplexing Radio resource management

Media access control

Further reading [edit source | edit beta ]

References [edit source | edit beta ]

External links [edit source | edit beta ]
http://wikimediafoundation.org/wiki/Privacy_policyhttp://en.wikipedia.org/wiki/Wikipedia:Abouthttp://en.wikipedia.org/wiki/Wikipedia:General_disclaimerhttp://en.wikipedia.org/wiki/Wikipedia:Contact_ushttp://en.m.wikipedia.org/wiki/Code_division_multiple_accesshttp://en.wikipedia.org/wiki/Wikipedia:Text_of_Creative_Commons_Attribution-ShareAlike_3.0_Unported_Licensehttp://en.wikipedia.org/wiki/Wikipedia:Text_of_Creative_Commons_Attribution-ShareAlike_3.0_Unported_Licensehttp://wikimediafoundation.org/wiki/Terms_of_Usehttp://wikimediafoundation.org/wiki/Terms_of_Usehttp://wikimediafoundation.org/wiki/Terms_of_Usehttp://wikimediafoundation.org/wiki/Privacy_policyhttp://wikimediafoundation.org/wiki/Privacy_policyhttp://www.wikimediafoundation.org/http://en.wikipedia.org/wiki/Template:Cdmahttp://en.wikipedia.org/wiki/Template:Cdmahttp://en.wikipedia.org/wiki/Template_talk:Cdmahttp://en.wikipedia.org/wiki/Template_talk:Cdmahttp://en.wikipedia.org/w/index.php?title=Template:Cdma&action=edithttp://en.wikipedia.org/w/index.php?title=Template:Cdma&action=edithttp://en.wikipedia.org/wiki/Template:Channel_access_methodshttp://en.wikipedia.org/wiki/Template:Channel_access_methodshttp://en.wikipedia.org/wiki/Template_talk:Channel_access_methodshttp://en.wikipedia.org/wiki/Template_talk:Channel_access_methodshttp://en.wikipedia.org/w/index.php?title=Template:Channel_access_methods&action=edithttp://en.wikipedia.org/w/index.php?title=Template:Channel_access_methods&action=edithttp://en.wikipedia.org/wiki/Pseudo-random_noisehttp://en.wikipedia.org/wiki/Spread_spectrumhttp://en.wikipedia.org/wiki/CDMA_Spectral_Efficiencyhttp://en.wikipedia.org/wiki/Comparison_of_mobile_phone_standardshttp://en.wikipedia.org/wiki/Andrew_Viterbihttp://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/Special:BookSources/0-201-63374-4http://en.wikipedia.org/wiki/Special:BookSources/0-201-63374-4http://en.wikipedia.org/wiki/Special:BookSources/0-201-63374-4http://www.activexperts.com/asmssrvr/cellular/cdmaspectrum/http://en.wikipedia.org/wiki/Nauka_i_Zhiznhttp://en.wikipedia.org/wiki/Nauka_i_Zhiznhttp://en.wikipedia.org/wiki/Tekhnika_Molodezhihttp://www.activexperts.com/asmssrvr/cellular/cdmaspectrum/http://www.cdg.org/http://en.wikipedia.org/wiki/Spread_spectrumhttp://en.wikipedia.org/wiki/Spread_spectrumhttp://en.wikipedia.org/wiki/Spread_spectrumhttp://en.wikipedia.org/wiki/Hedy_Lamarr#Frequency-hopping_spread-spectrum_inventionhttp://en.wikipedia.org/wiki/Hedy_Lamarr#Frequency-hopping_spread-spectrum_inventionhttp://en.wikipedia.org/wiki/Spread_spectrum#Commercial_usehttp://en.wikipedia.org/wiki/Spread_spectrum#Commercial_usehttp://en.wikipedia.org/wiki/Spread_Spectrum#Historyhttp://en.wikipedia.org/wiki/Spread_Spectrum#Historyhttp://en.wikipedia.org/wiki/Direct-sequence_spread_spectrumhttp://en.wikipedia.org/wiki/Frequency-hopping_spread_spectrumhttp://en.wikipedia.org/wiki/Frequency-hopping_spread_spectrumhttp://en.wikipedia.org/wiki/Chirp_spread_spectrumhttp://en.wikipedia.org/wiki/Time-hoppinghttp://en.wikipedia.org/wiki/Time-hoppinghttp://en.wikipedia.org/wiki/W-CDMA_%28UMTS%29http://en.wikipedia.org/wiki/W-CDMA_%28UMTS%29http://en.wikipedia.org/wiki/TD-CDMAhttp://en.wikipedia.org/wiki/TD-SCDMAhttp://en.wikipedia.org/wiki/TD-SCDMAhttp://en.wikipedia.org/wiki/Direct-sequence_CDMAhttp://en.wikipedia.org/wiki/Direct-sequence_CDMAhttp://en.wikipedia.org/wiki/Frequency-hopping_spread_spectrumhttp://en.wikipedia.org/wiki/Multi-carrier_code_division_multiple_accesshttp://en.wikipedia.org/wiki/Multi-carrier_code_division_multiple_accesshttp://en.wikipedia.org/wiki/Space_Networkhttp://en.wikipedia.org/wiki/Global_Positioning_Systemhttp://en.wikipedia.org/wiki/Global_Positioning_Systemhttp://en.wikipedia.org/wiki/Galileo_%28satellite_navigation%29http://en.wikipedia.org/wiki/Galileo_%28satellite_navigation%29http://en.wikipedia.org/wiki/GLONASShttp://en.wikipedia.org/wiki/Bluetoothhttp://en.wikipedia.org/wiki/Cordless_telephonehttp://en.wikipedia.org/wiki/Cordless_telephonehttp://en.wikipedia.org/wiki/Digital_Enhanced_Cordless_Telecommunicationshttp://en.wikipedia.org/wiki/Digital_Enhanced_Cordless_Telecommunicationshttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Evolution-Data_Optimizedhttp://en.wikipedia.org/wiki/IS-95http://en.wikipedia.org/wiki/IS-95http://en.wikipedia.org/wiki/CDMA2000http://en.wikipedia.org/wiki/CDMA2000http://en.wikipedia.org/wiki/Qualcommhttp://en.wikipedia.org/wiki/Verizon_Wireless#Networkhttp://en.wikipedia.org/wiki/Verizon_Wireless#Networkhttp://en.wikipedia.org/wiki/Pseudorandom_noise#PN_Codehttp://en.wikipedia.org/wiki/Chip_%28CDMA%29http://en.wikipedia.org/wiki/Chip_%28CDMA%29http://en.wikipedia.org/wiki/Near-far_problemhttp://en.wikipedia.org/wiki/Near-far_problemhttp://en.wikipedia.org/wiki/Spectral_densityhttp://en.wikipedia.org/wiki/Process_gainhttp://en.wikipedia.org/wiki/Process_gainhttp://en.wikipedia.org/wiki/Rake_receiverhttp://en.wikipedia.org/wiki/Rake_receiverhttp://en.wikipedia.org/wiki/Low_Probability_of_Intercept_Radarhttp://en.wikipedia.org/wiki/Low_Probability_of_Intercept_Radarhttp://en.wikipedia.org/wiki/Data_transmissionhttp://en.wikipedia.org/wiki/Data_transmissionhttp://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Statistical_time_division_multiplexinghttp://en.wikipedia.org/wiki/Waveformhttp://en.wikipedia.org/wiki/Waveformhttp://en.wikipedia.org/wiki/Channel_access_methodhttp://en.wikipedia.org/wiki/Media_Access_Controlhttp://en.wikipedia.org/wiki/Media_Access_Controlhttp://en.wikipedia.org/wiki/Help:Categoryhttp://en.wikipedia.org/wiki/Category:Channel_access_methodshttp://en.wikipedia.org/wiki/Category:Code_division_multiple_accesshttp://en.wikipedia.org/wiki/Category:Multiplexinghttp://en.wikipedia.org/wiki/Category:Radio_resource_managementhttp://en.wikipedia.org/wiki/Category:Media_access_controlhttp://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&action=edit&section=13http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=13http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=13http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&action=edit&section=14http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=14http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=14http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&action=edit&section=15http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=15http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=15http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=15http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=15http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&action=edit&section=15http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=14http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=14http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&action=edit&section=14http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=13http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&veaction=edit&section=13http://en.wikipedia.org/w/index.php?title=Code_division_multiple_access&action=edit&section=13http://en.wikipedia.org/wiki/Category:Media_access_controlhttp://en.wikipedia.org/wiki/Category:Radio_resource_managementhttp://en.wikipedia.org/wiki/Category:Multiplexinghttp://en.wikipedia.org/wiki/Category:Code_division_multiple_accesshttp://en.wikipedia.org/wiki/Category:Channel_access_methodshttp://en.wikipedia.org/wiki/Help:Categoryhttp://en.wikipedia.org/wiki/Media_Access_Controlhttp://en.wikipedia.org/wiki/Channel_access_methodhttp://en.wikipedia.org/wiki/Waveformhttp://en.wikipedia.org/wiki/Statistical_time_division_multiplexinghttp://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Data_transmissionhttp://en.wikipedia.org/wiki/Low_Probability_of_Intercept_Radarhttp://en.wikipedia.org/wiki/Rake_receiverhttp://en.wikipedia.org/wiki/Process_gainhttp://en.wikipedia.org/wiki/Spectral_densityhttp://en.wikipedia.org/wiki/Near-far_problemhttp://en.wikipedia.org/wiki/Chip_%28CDMA%29http://en.wikipedia.org/wiki/Pseudorandom_noise#PN_Codehttp://en.wikipedia.org/wiki/Verizon_Wireless#Networkhttp://en.wikipedia.org/wiki/Qualcommhttp://en.wikipedia.org/wiki/CDMA2000http://en.wikipedia.org/wiki/IS-95http://en.wikipedia.org/wiki/Evolution-Data_Optimizedhttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Digital_Enhanced_Cordless_Telecommunicationshttp://en.wikipedia.org/wiki/Cordless_telephonehttp://en.wikipedia.org/wiki/Bluetoothhttp://en.wikipedia.org/wiki/GLONASShttp://en.wikipedia.org/wiki/Galileo_%28satellite_navigation%29http://en.wikipedia.org/wiki/Global_Positioning_Systemhttp://en.wikipedia.org/wiki/Space_Networkhttp://en.wikipedia.org/wiki/Multi-carrier_code_division_multiple_accesshttp://en.wikipedia.org/wiki/Frequency-hopping_spread_spectrumhttp://en.wikipedia.org/wiki/Direct-sequence_CDMAhttp://en.wikipedia.org/wiki/TD-SCDMAhttp://en.wikipedia.org/wiki/TD-CDMAhttp://en.wikipedia.org/wiki/W-CDMA_%28UMTS%29http://en.wikipedia.org/wiki/Time-hoppinghttp://en.wikipedia.org/wiki/Chirp_spread_spectrumhttp://en.wikipedia.org/wiki/Frequency-hopping_spread_spectrumhttp://en.wikipedia.org/wiki/Direct-sequence_spread_spectrumhttp://en.wikipedia.org/wiki/Spread_Spectrum#Historyhttp://en.wikipedia.org/wiki/Spread_spectrum#Commercial_usehttp://en.wikipedia.org/wiki/Hedy_Lamarr#Frequency-hopping_spread-spectrum_inventionhttp://en.wikipedia.org/wiki/Spread_spectrumhttp://en.wikipedia.org/wiki/Spread_spectrumhttp://www.cdg.or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Code Division Multiple Access - Wikipedia, The Free Encyclopedia

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