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30-07-2009, 05:07 PM
Post: #1
CDMA (Download Full Seminar Report)
(Code Division Multiple Access) A method for transmitting real-time signals over a shared portion of the spectrum. The foremost application of CDMA is the digital cellular phone technology that operates in the 800MHz band and 1.9GHz . Unlike GSM and TDMA, which divides the spectrum into different time slots CDMA uses a spread spectrum technique to assign a code to each conversation. After the speech codec converts voice to digital, CDMA spreads the voice stream over the full 1.25MHz bandwidth of the CDMA channel coding each stream separately so it can be decoded at the receiving end. The rate of the spreading signal is known as the chip rate, as each bit in the spreading signal is called a chip voice conversations use the full bandwidth at the same time. One bit from each conversation is multiplied into 128 coded bits by the spreading techniques, giving the receiving side an enormous amount of data it can average just to determine the value of one bit.

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20-08-2010, 10:31 PM
Post: #2
RE: CDMA (Download Full Seminar Report)
cdma report for manvendra so
27-09-2010, 10:51 AM
Post: #3
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.doc  CDMA.doc (Size: 893 KB / Downloads: 533)
INTRODUCTION

Mobile communications are rapidly becoming more and more necessary for everyday activities. With so many more users to accommodate, more efficient use of bandwidth is a priority among cellular phone system operators. Equally important is the security and reliability of these calls. One solution that has been offered is a CODE DIVISION MULTIPLE ACCESS SYSTEM.

CDMA is one method for implementing a multiple access communication system. MULTIPLE ACCESS is a technique where many subscribers or local stations can share the use of the use of a communication channel at the same time or nearly so despite the fact originate from widely different locations. A channel can be thought of as merely a portion of the limited radio resource, which is temporarily allocated for a specific purpose, such as someone’s phone call. A multiple access method is a definition of how the radio spectrum is divided into channels and how the channels are allocated to the many users of the system.
Since there are multiple users transmitting over the same channel, a method must be established so that individual users will not disrupt one another. There are essentially three ways to do this.


Code Division Multiple Access is a new technology used in wireless communication devices. This technology made its commercial debut in the early nineties. Significant advantage of the CDMA is the fact that unlike other modulation schemes it does not have to allocate part of the frequency for each user. It allocates whole frequency spectrum to each user, distinguishing each signal with the unique pseudo-random sequence.

CDMA stands for "Code Division Multiple Access." It is a form of spread-spectrum, an advanced digital wireless transmission technique. Instead of using frequencies or time slots, as do traditional technologies, it uses mathematical codes to transmit and distinguish between multiple wireless conversations. Its bandwidth is much wider than that required for simple point-to-point communications at the same data rate because it uses noise-like carrier waves to spread the information contained in a signal of interest over a much greater bandwidth. However, because the conversations taking place are distinguished by digital codes, many users can share the same bandwidth simultaneously.


Code Division Multiple Access (CDMA) is a digital cellular spread-spectrum modulation technique that implements distributed voice and data networks.
CDMA works by converting speech into digital information, which is then transmitted as a radio signal over a wireless network. CDMA does not assign a specific frequency to each user, but the full available spectrum. Each signal is encoded differently using a unique code. This way CDMA enables a large number of users to share the same frequency band at the same time, without interference.
The receiving device is instructed to use the code to extract the data out of the received signal.


29-09-2010, 01:36 PM
Post: #4
RE: CDMA (Download Full Seminar Report)

.docx  COMPARISON OF CDMA AND TDMA SYSTEMS.docx (Size: 72.96 KB / Downloads: 170)
This article is presented by:
Malathy Elumalai
Advance topics in Communication
Spring 2010


COMPARISON OF CDMA AND TDMA SYSTEMS

ABSTRACT

In this report two candidates for high capacity cellular systems are simulated and analyzed, one CDMA and one TDMA system. Simulations of the CDMA example indicate a high sensitivity to variations in certain system parameters. The TDMA example is a GSM system using random frequency hopping and operating without frequency planning. The outage probabilities of both the systems that have been compared in the reference IEEE paper are also simulated in this project.
INTRODUCTION
In today’s world cell phone have become the single greatest tool in day today life. It has become a necessity that business associates should be able to communicate on the go. That’s why it has become so important to make choices in choosing which handheld device one should go for. A handheld device is selected according to its features and benefits, like does it provide access to internet and email or does it look slick and more.

An important question when designing and standardizing cellular systems is the
Selection of the multiple access schemes. Multiple Access methods address the problem of how many users can share the same spectrum resources in an efficient manner. We distinguish between them as follows
• Multiple access within one cell, i.e., a fixed assignment of resources in time or bandwidth to specific users
• Random access, i.e., a dynamic assignment of spectrum resources in time or bandwidth to users, according to their needs
• Frequency reuse, i.e., assignment of spectrum resources considering the location of users and the attenuation of radio signals that travel over sufficiently large distances
Examples of multiple access schemes are FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access), and CDMA (Code Division Multiple Access). All three principles allow
Multiple users to share the same physical channel. But the two competing technologies differ in the way user sharing the common resource. TDMA allows the users to share the same frequency channel by dividing the signal into different time slots. Each user takes turn in a round robin fashion for transmitting and receiving over the channel. CDMA uses a spread spectrum technology that is it spreads the information contained in a particular signal of interest over a much greater bandwidth than the original signal. In TDMA users can only transmit in their respective time slot. Unlike TDMA, in CDMA several users can transmit over the channel at the same time.


01-10-2010, 03:56 PM
Post: #5
Thumbs Up RE: CDMA (Download Full Seminar Report)

.pptx  C D M A.pptx (Size: 2.67 MB / Downloads: 257)
This article is presented by:

SABYASACHI RANA
SAPTARSHI CHATTERJEE
AVIK MODAK
ANURAN ROY CHOUDHARY


C D M A
What is Multiple Access?
Simultaneous private use of a transmission medium by multiple, independent users.

Advantages of Multiple Access

Increased capacity: serve more users
Reduced capital requirements since fewer media can carry the traffic
Decreased per-user expense
Easier to manage and administer

MOST POPULER MULTIPLE ACCESS TECHNOLOGIES THAT ESTABLISHED CHANNELS

FDMA (Frequency Division Multiplex Access)
each user on a different frequency
a channel is a frequency

TDMA (Time Division Multiplex Access)
each user on a different window period
in time (“time slot”)
a channel is a specific time slot on a specific frequency

CDMA (Code Division Multiplex Access)
each user uses the same frequency all the time
, but mixed With different distinguishing code patterns
a channel is a unique set of code patterns

06-10-2010, 05:48 PM
Post: #6
RE: CDMA (Download Full Seminar Report)

.pdf  CDMA.pdf (Size: 123 KB / Downloads: 123)
CDMA Tutorial


CDMA (Download Full Seminar Report)


(Code Division Multiple Access) A method for transmitting real-time signals over a shared portion of the spectrum. The foremost application of CDMA is the digital cellular phone technology that operates in the 800MHz band and 1.9GHz . Unlike GSM and TDMA, which divides the spectrum into different time slots CDMA uses a spread spectrum technique to assign a code to each conversation. After the speech codec converts voice to digital, CDMA spreads the voice stream over the full 1.25MHz bandwidth of the CDMA channel coding each stream separately so it can be decoded at the receiving end. The rate of the spreading signal is known as the chip rate, as each bit in the spreading signal is called a chip voice conversations use the full bandwidth at the same time. One bit from each conversation is multiplied into 128 coded bits by the spreading techniques, giving the receiving side an enormous amount of data it can average just to determine the value of one bit.

for more http://www.seminarprojects.com/Thread-cd...nar-report
17-12-2010, 04:43 PM
Post: #7
RE: CDMA (Download Full Seminar Report)
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17-12-2010, 09:19 PM
Post: #8
RE: CDMA (Download Full Seminar Report)
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31-12-2010, 01:56 PM
Post: #9
RE: CDMA (Download Full Seminar Report)
SUBIMITTED TO:-

ms. Neelam Arya
Deptt. Of EC
ITM GWALIOR


SUBIMITTED BY:-

Rajendra ku. Bansal




.ppt  printout.PPT (Size: 564.5 KB / Downloads: 69)

Why CDMA?


CDMA is extremely robust and provides excellent audio quality

CDMA is the technology of choice for both 800 MHz Cellular and 1900 MHz PCS service providers
CDMA satisfies CTIA Users’ Performance Requirements
CDMA provides high capacity (many times the capacity of AMPS)
CDMA provides privacy through its coding scheme

What is Multiple Access?


Multiple Access: Simultaneous private use of a transmission medium by multiple, independent users.

Since the beginning of telephony and radio, system operators have tried to squeeze the maximum amount of traffic over each circuit
Types of Media
Twisted pair - copper
Coaxial cable
Fiber optic cable
Air interface (radio signals)
Advantages of Multiple Access
Increased capacity: serve more users
Reduced capital requirements since fewer media can carry the traffic
Decreased per-user expense
Easier to manage and administer


Each pair of users enjoys a dedicated, private circuit through the transmission medium, unaware that the other users exist.


Multiple Access Technologies


Channel: An individually-assigned, dedicated pathway through a transmission medium for one user’s information
The physical transmission medium is a resource that can be subdivided into individual channels according to different criteria depending on the technology used:
Here’s how the three most popular technologies establish channels:
FDMA (Frequency Division Multiplex Access)
each user on a different frequency
a channel is a frequency
TDMA (Time Division Multiplex Access)
each user on a different window period in time (“time slot”)
a channel is a specific time slot on a specific frequency
CDMA (Code Division Multiplex Access)
each user uses the same frequency all the time, but mixed with different distinguishing code patterns
a channel is a unique set of code patterns




31-12-2010, 02:03 PM
Post: #10
Thumbs Up RE: CDMA (Download Full Seminar Report)
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so i want suggestions about my new project.
01-01-2011, 10:01 AM
Post: #11
RE: CDMA (Download Full Seminar Report)
okey, let us know about your topic.
29-01-2011, 04:17 PM
Post: #12
RE: CDMA (Download Full Seminar Report)
please send me the CDMA full seminar report
31-01-2011, 08:08 PM
Post: #13
RE: CDMA (Download Full Seminar Report)
Thank u [/size][/font]
22-02-2011, 05:33 PM
Post: #14
RE: CDMA (Download Full Seminar Report)
Nice one Smile
Thank u..
26-02-2011, 03:14 PM
Post: #15
RE: CDMA (Download Full Seminar Report)

.pptx  cdma mobile system.pptx (Size: 456.19 KB / Downloads: 59)
The CDMA Mobile System
 Its origin and its technique
CDMA Mobile Functions
 Service Resource Functions
 Service Control Functions
 Service Management Functions
SERVICE RESOURCE FUNCTIONS
 Transmission and Synchronization
 Power Control
 Signaling
Transmission and Synchronization
Power Control
Signaling
Service control and Management Functions

∫ Call control
 Voice Service
 Data Service
 Short Message Service
∫ Handoff
∫ Authentication
∫ Location Management
∫ Resource Management
∫ OAM Management
∫ Cell boundary Management
∫ Performance Management
Voice Service
Data Service
Short Message Services
CMS Structure
System Configuration
01-03-2011, 04:56 PM
Post: #16
RE: CDMA (Download Full Seminar Report)
presented by:
Tejas V. Shah


.doc  46_CDMA.doc (Size: 658 KB / Downloads: 85)
Generally a fixed amount of frequency spectrum is allocated to a cellular system by the national regulator (e.g. in the United states,the Federal communication commission). Multiple-access techniques are then deployed so that many users can share the available spectrum in an efficient manner. Multiple access systems specify how signals from different sources can be combined efficiently for transmission over a given radio frequency band and then separated at the destination without mutual interference.The three basic multiple access methods currently in use in cellular systems are:
• Frequency division multiple access (FDMA)
• Time division multiple access (TDMA)
• Code division multiple access (CDMA)
In case of FDMA ,users share the available spectrum in the frequency domain,and user is allocated a part of the frequency band called the traffic channel.
In TDMA techniques that are utilized in many digital cellular systems,the available spectrum is partitioned into narrow frequency bands or frequency channels (as in FDMA),which in turn are divided into a number of time slots.An individual user is assigned a time slot that permits access to the frequency channel for the duration of the time slot.
The CDMA systems utilizes the spread spectrum technique,whereby a spreading code(called a pseudo-random noise or PN code) is used to allow multiple users to share a block of frequency spectrum.In CDMA cellular systems (e.g. IS-95 in the United States) that use direct sequence spread (DSS) spectrum techniques,the(digital) information from an individual user is modulated by means of the unique PN code (spreading sequence) assigned to each user.All the PN –code-modulated signals from different users are then transmitted over the entire CDMA frequency channel (e.g.,1.23 MHZ in case of IS-95).Since the signal in the case of CDMA utilize the entire allocated block of spectrum,no guard bands of any kind are necessary within the allocated block.
CDMA permits a more uniform distribution of energy in the emitted bandwidth Short for Code Division Multiple Access, a digital cellular technology that uses spread-spectrum techniques. Unlike competing systems, such as GSM that use TDMA, CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence. The older version of the CDMA technology and now it is now known as cdmaOne as well as IS-95. The other types of CDMA technology has CDMA2000,WCDMA (Wideband CDMA). The spread spectrum may be viewed as a kind of modulation scheme in which the modulated(spread spectrum) signal bandwidth is much greater than the message(baseband) signal bandwidth. Thus, spread spectrum is a wideband scheme.
The final assessment on the potential superiority of CDMA systems over TDMA systems,in terms of capacity,cost, and speech quality,will emerge only after both systems have been in operation in dense,urban areas with full complements of subscribers and services.
A CDMA system is clearly not a collision avoidance system like FDMA and TDMA. The opposite is true and explains the differences in the behavior of CDMA systems compared to FDMA and TDMA. In general, the collisions at the channel is a disadvantage of CDMA system and can be mitigated by careful selection of the sequence and power control that is close to perfect. CDMA is restricted to a short distance charging area(SDCA). Currently, there are 2600 SDCAs within the country. A CDMA-based phone can thus ‘roam’ only within its SDCA. This is NOT a technological restriction. In India, Reliance Infocom and Tata Indicom use CDMA technology to provide WILL services. In remote rural areas, where installing cables is difficult as well as expensive, CDMA-based WILL networks can be deployed quickly. A CDMA doesn’t have a SIM card, which makes m-commerce difficult.
Daily application possible with CDMA is daily downloading, text communication such as chat,e-mail,sms,member search etc.sending photo on the air,entertainment and games.
INTRODUCTION
This paper is intended to provide an introduction to CDMA use in wireless telephone systems. The focus is on explaining, in generally non-technical language, both the key aspects of CDMA technology, and the primary benefits the technology offers to wireless communication system operators and their subscribers. There is a tremendous amount of detailed technical information which is intentionally not covered in this forum.
It has been necessary, though, to assume at least a rudimentary familiarity with cellular telephone systems, including the basic characteristics of radio and the RF spectrum, as well as fundamental system design concepts such as frequency re-use.
Motorola welcomes your comments and feedback on this paper.
What is CDMA?
One of the most important concepts to any cellular telephone system is that of "multiple access", meaning that multiple, simultaneous users can be supported. In other words, a large number of users share a common pool of radio channels and any user can gain access to any channel (each user is not always assigned to the same channel). A channel can be thought of as merely a portion of the limited radio resource which is temporary allocated for a specific purpose, such as someone's phone call. A multiple access method is a definition of how the radio spectrum is divided into channels and how channels are allocated to the many users of the system.
The CDMA Cellular Standard
With CDMA, unique digital codes, rather than separate RF frequencies or channels, are used to differentiate subscribers. The codes are shared by both the mobile station (cellular phone) and the base station, and are called "pseudo-Random Code Sequences." All users share the same range of radio spectrum.
For cellular telephony, CDMA is a digital multiple access technique specified by the Telecommunications Industry Association (TIA) as "IS-95".
In March 1992, the TIA established the TR-45.5 subcommittee with the charter of developing a spread-spectrum digital cellular standard. In July of 1993, the TIA gave its approval of the CDMA IS-95 standard.
IS-95 systems divide the radio spectrum into carriers which are 1,250 KHz (1.25 MHz) wide. One of the unique aspects of CDMA is that while there are certainly limits to the number of phone calls that can be handled by a carrier, this is not a fixed number. Rather, the capacity of the system will be dependent on a number of different factors. This will be discussed in later sections.
CDMA - Code Division Multiple Access
IS-95 uses a multiple access spectrum spreading technique called Direct Sequence (DS) CDMA.
Each user is assigned a binary, Direct Sequence code during a call. The DS code is a signal generated by linear modulation with wideband Pseudorandom Noise (PN) sequences. As a result, DS CDMA uses much wider signals than those used in other technologies. Wideband signals reduce interference and allow one-cell frequency reuse.
There is no time division, and all users use the entire carrier, all of the time.
CDMA Technology
Though CDMA application in cellular telephony is relatively new, it is not a new technology. CDMA has been used in many military applications, such as anti-jamming (because of the spread signal, it is difficult to jam or interfere with a CDMA signal), ranging (measuring the distance of the transmission to know when it will be received), and secure communications (the spread spectrum signal is very hard to detect).
Spread Spectrum
CDMA is a "spread spectrum" technology, which means that it spreads the information contained in a particular signal of interest over a much greater bandwidth than the original signal.
The standard data rate of a CDMA call is 9600 bits per second (9.6 kilobits per second). This initial data is "spread," including the application of digital codes to the data bits, up to the transmitted rate of about 1.23 megabits per second. The data bits of each call are then transmitted in combination with the data bits of all of the calls in the cell. At the receiving end, the digital codes are separated out, leaving only the original information which was to be communicated. At that point, each call is once again a unique data stream with a rate of 9600 bits per second.
Traditional uses of spread spectrum are in military operations. Because of the wide bandwidth of a spread spectrum signal, it is very difficult to jam, difficult to interfere with, and difficult to identify. This is in contrast to technologies using a narrower bandwidth of frequencies. Since a wideband spread spectrum signal is very hard to detect, it appears as nothing more than a slight rise in the "noise floor" or interference level. With other technologies, the power of the signal is concentrated in a narrower band, which makes it easier to detect.
Increased privacy is inherent in CDMA technology. CDMA phone calls will be secure from the casual eavesdropper since, unlike an analog conversation, a simple radio receiver will not be able to pick individual digital conversations out of the overall RF radiation in a frequency band.
02-03-2011, 09:29 AM
Post: #17
RE: CDMA (Download Full Seminar Report)

.ppt  10-cdma.ppt (Size: 116.5 KB / Downloads: 231)
CDMA Mobile Communication & IS-95
Most of the slides are stolen from Prof. Abhay Karandikar’s lecture
Spread Spectrum Priniciples
Does not attempt to allocate disjoint frequency or time slot resources
Instead, this approach allocates all resources to simultaneous users, controlling the power transmitted by each user to the minimum required to maintain a given SNR
Each user employs a noise-like wideband signal occupying the entire frequency allocation
Each user contributes to the background noise affecting all users, but to the least extent possible.
Spread Spectrum Priniciples
This restriction on interference limits capacity, but because time and bandwidth resource allocations are unrestricted, the resulting capacity is significantly higher than the conventional system
Spread Spectrum Priniciples
Suppose each user use a wideband Gaussian noise carrier
Suppose each user’s transmission is controlled so that all signals received at the BS are of equal power
Let Ps be the power of each user, and the background noise be negligible.
Then the total interference power, I, presented to each user’s demodulator is
I = (K-1) Ps (1) where K is the number of users
Spread Spectrum Priniciples
Let’s say demodulator of each user operates at bit-energy-to-noise-density level of Eb/N0.
So the noise density received by each user’s demodulator is N0 = I/W (2), where W Hz is the bandwidth of the wideband noise carriers
The received energy per bit is the received signal power divided by the data rate R (bits/s), i.e., Eb = Ps/R (3)
Spread Spectrum Priniciples
Combining (1), (2) and (3) we get
K – 1 = I/Ps = (W/R) / (Eb/N0) (4)
If W >> R then the capacity of the system can be large
i.e., transmission bandwidth should be much larger than the message bandwidth
If Eb/N0 is small, then also the capacity can be large. (since Eb/N0 α SNR, this means SNR should be as small as possible)
Code Division Multiple Access - CDMA
Multiple users occupying the same band by having different codes is known as CDMA - Code Division Multiple Access system
Let
W - spread bandwidth in Hz
R = 1/Tb = Date Rate
S - received power of the desired signal in W
J - received power for undesired signals like multiple access users, multipath, jammers etc in W
Eb - received energy per bit for the desired signal in W
N0 - equivalent noise spectral density in W/Hz
In conventional systems W/R  1 which means, for satisfactory operation J/S < 1
Example Let R = 9600; W = 1.2288 MHz
(Eb/N0)min = 6 dB (values taken from IS-95)
Jamming margin (JM) = 10log10(1.2288*106/9.6*103) - 6
= 15.1 dB  32
This antijam margin or JM arises from Processing Gain (PG) = W/R = 128
If (Eb/N0)min is further decreased or PG is increased, JM can be further increased
CDMA (contd…)
JM can be used to accommodate multiple users in the same band
If (Eb/N0)min and PG is fixed, number of users is maximized if perfect power control is employed.
Capacity of a CDMA system is proportional to PG.
Spreading Codes
A noise-like and random signal has to be generated at the transmitter.
The same signal must be generated at the receiver in synchronization.
We limit the complexity by specifying only one bit per sample, i.e., a binary sequence.
Desirable Randomness Properties
Relative frequencies of “0” and “1” should be ½ (Balance property)
Run lengths of zeros and ones should be (Run property):
Half of all run lengths should be unity
One - quarter should be of length two
One - eighth should be of length three
A fraction 1/2n of all run lengths should be of length n for all finite n
Desirable Randomness Properties (contd…)
If the random sequence is shifted by any nonzero
number of elements, the resulting sequence
should have an equal number of agreements and
disagreements with the original sequence
(Autocorrelation property)
PN Sequences
A deterministically generated sequence that nearly satisfies these properties is referred to as a Pseudorandom Sequence (PN)
Periodic binary sequences can be conveniently generated using linear feedback shift registers (LFSR)
If the number of stages in the LFSR is r, P  2r - 1 where P is the period of the sequence
PN Sequences (contd…)
However, if the feedback connections satisfy a specific property, P = 2r - 1. Then the sequence is called a Maximal Length Shift Register (MLSR) or a PN sequence.
Thus if r=15, P=32767.
MLSR satisfies the randomness properties stated before
Randomness Properties of PN Sequences
Balance property - Of the 2r - 1 terms, 2r-1 are one and 2r-1–1 are zero. Thus the unbalance is 1/P. For r=50; 1/P10-15
Run length property - Relative frequency of run length n (zero or ones) is 1/ 2n for n  r-1 and 1/(2r - 1) for n = r
One run length each of r-1 zeros and r ones occurs. There are no run lengths for n > r
Autocorrelation property - The number of disagreements exceeds the number of agreements by unity. Thus again the discrepancy is 1/p
PN Sequences Specified in IS-95
A “long” PN sequence (r =42) is used to scramble the user data with a different code shift for each user
The 42-degree characteristic polynomial is given by:
x42+x41+x40+x39+x37+x36+x35+x32+x26+x25+x24+x23+x21+x20+x17+x16+x15+x11+x9+x7+1
The period of the long code is 242 - 1  4.4*102 chips and lasts over 41 days
PN Sequences Specified in IS-95 (contd…)
A short PN sequence (r = 15) is specific to a base station and its period is (215−1)Tc = 27ms.
Two “short” PN sequences (r=15) are used to spread the quadrature components of the forward and reverse link waveforms
Power Control in CDMA
CDMA goal is to maximize the number of simultaneous users
Capacity is maximized by maintaining the signal to interference ratio at the minimum acceptable
Power transmitted by mobile station must be therefore controlled
Transmit power enough to achieve target BER: no less no more
Two factors important for power control
Propagation loss due to propagation loss, power variations up to 80 dB
a high dynamic range of power control required
Channel Fading
average rate of fade is one fade per second per mile hour of mobile speed
power attenuated by more than 30 dB
power control must track the fade
Power Control in IS-95A
At 900 MHz and 120 km/hr mobile speed Doppler shift =100Hz
In IS 95-A closed loop power control is operated at 800 Hz update rate
Power control bits are inserted (‘punctured’) into the interleaved and encoded traffic data stream
Power control step size is +/- 1 dB
Power control bit errors do not affect performance much
Rake Receiver
Mobile station receives multiple attenuated and delayed replicas of the original signal (multipath diversity channels).
Two multipath signals are resolvable only if their relative delay exceeds the chip period Tc
Amplitudes and phases of multipath components are found by correlating the received waveform with multiple delayed versions of the signal (delay = nTc).
Searcher performs the above task for up to 3 different multipath signals.
3 parallel demodulators (RAKE fingers) isolate the multipath components and the RAKE receiver combines them.
Handoff in CDMA System
In GSM hard handoff occurs at the cell boundary
Soft Handoff
Mobile commences Communication with a new BS without interrupting communication with old BS
same frequency assignment between old and new BS
provides different site selection diversity
Softer Handoff
Handoff between sectors in a cell
CDMA to CDMA hard handoff
Mobile transmits between two base stations with different frequency assignment
Soft Handoff- A unique feature of CDMA Mobile
Advantages

Contact with new base station is made before the call is switched
Diversity combining is used between multiple cell sites
Diversity combining is the process of combining information from multiple transmitted packets to increase the effective SNR of received packets
additional resistance to fading
If the new cell is loaded to capacity, handoff can still be performed for a small increase in BER
Neither the mobile nor the base station is required to change frequency
09-03-2011, 09:31 PM
Post: #18
Star RE: CDMA (Download Full Seminar Report)
I WANT WIDEBAND CDMA PROJECT REPORT
15-03-2011, 12:09 PM
Post: #19
RE: CDMA (Download Full Seminar Report)

.doc  cdma.doc (Size: 103.5 KB / Downloads: 91)
CODE DIVISION MULTIPLE ACCESS
INTRODUCTION:-

Mobile communications are rapidly becoming more and more necessary for everyday activities. With so many more users to accommodate, more efficient use of bandwidth is a priority among cellular phone system operators. Equally important is the security and reliability of these calls. One solution that has been offered is a CODE DIVISION MULTIPLE ACCESS SYSTEM.
CDMA is one method for implementing a multiple access communication system. MULTIPLE ACCESS is a technique where many subscribers or local stations can share the use of the use of a communication channel at the same time or nearly so despite the fact originate from widely different locations. A channel can be thought of as merely a portion of the limited radio resource, which is temporarily allocated for a specific purpose, such as someone’s phone call. A multiple access method is a definition of how the radio spectrum is divided into channels and how the channels are allocated to the many users of the system.
Since there are multiple users transmitting over the same channel, a method must be established so that individual users will not disrupt one another. There are essentially three ways to do this.
1. FREQUENCY DIVISION MULTIPLE ACCESS
In this technique, the available bandwidth is split up into non-overlapping frequency bands and these disjoint sub bands of frequency are allocated to the different users on a continuous time basis. In order to reduce interference between users allocated adjacent channel bands, channel bands are used to act as buffer zones, as illustrated in figure(1). These guard bands are necessary because of the impossibility of achieving ideal filtering for separating the different users. It could be compared to AM or FM broadcasting radio where each station has a frequency assigned.
1. TIME DIVISION MULTIPLE ACCESS
In this technique, each user is allocated the full spectral occupancy of
The channel, but only for a short duration of time called time slot. Buffers zones are in the form of guard times are inserted between the assigned time slots. This is done to reduce interference between users by allowing for time uncertainty that arises due to system imperfections, especially in synchronization scheme.
DRAWBACKS:
In both FDMA and TDMA, only one subscriber at a time is assigned to a channel. No other conversion can access this channel until the subscriber’s call is finished or until that original call to handed off to a different channel by the system. Voice data tends to be burst in nature. So much of the time, no data is being sent over the channel. This inefficiency tends to limit the capacity of the system.
3. CODE DIVISION MULTIPLE ACCESS
The above drawbacks are overcome in this third technique in which the users are spread across both frequency and time in the same
Channel. This is a hybrid combination of FDMA and TDMA. For example, frequency hopping may be employed to ensure during each successive time slot, the frequency bands assigned to the users are recorded in random manner. During time slot 1, user 1 occupies frequency band 1, user 2 occupies frequency band 2, user 3 occupies band 3 and so on. During time slot 2, user 1 hops to frequency band 3, user 2 hops to band 1, user 3 hops to band 2, and so on. An important advantage of CDMA over FDMA and TDMA is that it can provide for secure communication.
MEANING OF CDMA:
Here, the users are spread across both frequency and time in the same channel. Here, unique digital codes, rather than separate RF frequencies or channels are used to differentiate subscribers. The codes are shared by both the mobile stations (cellular phone) and the base station, and are called “pseudo random code sequences” or “pseudo-noise code sequences”.
PN – SEQUENCE:
A PN – sequence is a periodic binary sequence with a noise like waveform that is usually generated by means of a feedback shift register. ”pseudo” word is used, as these are not real noise. These are noise like.
BASIS OF CDMA:
Basis of CDMA is the spread spectrum technology.
SPREAD SPECTRUM is a means of transmission in which the data sequence occupies a bandwidth in excess of the minimum bandwidth necessary to send it. Spread spectrum is accomplished before transmission through the use of a code that is independent of the data sequence (PN).
It can provide secure communication in hostile environment such that the transmitted signal is not easily detected or recognized by unwanted listeners. It can reject interference whether it is the unintentional interference by another user simultaneously attempting to transmit through the channel, or the intentional interference by a hostile transmitter attempting to jam the transmission. Another application is in multiple access communication in which a number of independent users can share a common channel without an external synchronizing mechanism.
TYPES OF SPREAD SPECTRUM
1. DIRECT SEQUENCE SPREAD SPECTRUM

DS sequence allows each station to transmit over the entire frequency
Spectrum all the time. Multiple simultaneous transmissions are separated using some sort of coding technique that is each user is assigned a chip sequence. The sender and receiver synchronize by the receiver locking into the chip sequence and the sender and receiver locking into the chip sequence of the sender. All the other (unsynchronized) transmission is then seen as random noise. So with CDMA each user uses the full frequency spectrum.
They employ a high speed code sequence along with the basic information being sent, to modulate their RF carriers. The high speed code sequence is used directly setting the transmitted RF bandwidth.
Binary phase shift keying (BPSK) is the most common technique used in DS system. Direct sequence is, in essence, multiplication of a more conventional communication waveform by PN sequence in the transmitter.
2. FREQUENCY HOPPING SPREAD SPECTRUM
FH – CDMA is a kind of spread spectrum technology that enables many users to share the same channel by employing a unique hopping pattern to distinguish different users’ transmission. The type of spread spectrum in which the carrier hops randomly from one frequency to another is called FH spread spectrum. A common modulation format for FH system is that of M-ary frequency shift keying (MFSK).the combination is referred to as FH/MFSK.
A major advantage of frequency hopping is that it can be implemented over a much larger frequency band than it is possible to implement DS- spreading, and the band can be noncontiguous. Another major advantage is that frequency hopping provides resistance to multiple – access interference while not requiring power control to prevent near – far problems. In DS – systems , accurate power control is crucial but becomes less effective as the carrier frequency is increased.
Frequency hopping does not cover the entire spread spectrum
Instantaneously, we are led to consider the rate at which the hops occur. So, we may identify two basic characterizations of frequency hopping.
1. Slow frequency hopping, in which the symbol rate Rs of MFSK signal is an integrator multiple of the hop rate Rh . that is, several symbols are transmitted on each frequency hop
2. Fast frequency hopping, in which the hop rate Rh is an integrator multiple of the MFSK symbol rate Rs. that is, the carrier frequency will change or hop several times during the transmission of one symbol.
03-04-2011, 11:48 AM
Post: #20
RE: CDMA (Download Full Seminar Report)
pls send me the following report urgently
14-04-2011, 10:02 AM
Post: #21
RE: CDMA (Download Full Seminar Report)
PRESENTED BY:
LAKPA BITTU TAMANG
JITENDRA KUMAR RAI


.pptx  CDMA.pptx (Size: 2.08 MB / Downloads: 53)
INTRODUCTION:
 CDMA is a new technology in wireless communication.
 Spread Spectrum technique is used.
 Mathematical codes are used to transmit & distinguish the users.
 The great attraction of CDMA technology has been because of the extraordinary increase in the system capacity and the service capacity.
 CDMA is extremely robust and provides excellent audio quality.
HISTORY:
 1st generation cellular system introduced in 1980, uses Analog frequency modulation.
 Due to some drawbacks, increase in market demands led to the foundation of 2nd generation cellular system.
 2nd generation cellular system uses Digital modulation technique which includes CDMA, GSM & TDMA.
 CDMA was introduced by QUALCOMM in 1994.
 CDMA provides 10 times more capacity than other Analog system.
BASIS OF CDMA:
 Based on Spread Spectrum Technology.
 Spread Spectrum is independent of data sequence.
 It provides secure communication which is not easily detectable.
 It rejects unwanted interference that may be intentional or unintentional.
 Number of independent users can share a common channel without external SYNCHRONIZING mechanism.
COMPETITION:
 The Euro-Asian biggest competitive to CDMA is the GSM.
 CDMA is more advantageous to GSM due to less interference, low radiation level & more security.
 GSM uses modified version of TDMA.
 GSM increases the network strength using SIM card.
 CDMA is the fastest growing technology in wireless communication than GSM.
11-05-2011, 03:32 PM
Post: #22
RE: CDMA (Download Full Seminar Report)

.doc  cdma.doc (Size: 134 KB / Downloads: 56)

.doc  cdma.doc (Size: 134 KB / Downloads: 56)
INTRODUCTION
Code Division Multiple Access (CDMA) is a form of multiplexing and a method of multiple access to a physical medium such as a radio channel, where different users use the medium at the same time thanks to using different code sequences.
Use in mobile telephony
Coverage and applications
Technical details
Coverage and applications
The size of a cell depends on the power of the signal transmitted by the handset, the terrain and the radio frequency being used
Various companies use different variants of CDMA to provide fixed-line networks using wireless local loop (WLL) technology
Technical details
CDMA exploits mathematical properties of orthogonality between vectors representing the data strings. For example, binary string "1011" is represented by the vector (1, 0, 1, 1).
Example
Macro diversity usage
Soft handover
Hard handover
Roaming
Soft handover
Soft handoff (or soft handover) is an innovation in mobility
As a result, signal quality and handoff robustness is improved compared to TDMA systems
Hard handover
When there are frequency boundaries between different carriers or sub-networks, a CDMA phone behaves in the same way as TDMA or analog and performs a hard handoff in which it breaks the existing connection and tries to pick up on the new frequency where it left off.
Roaming
CDMA2000 bases its roaming capabilities on ANSI-41,Regional, National or International roaming all have several elements that are required in order for CDMA roaming to be facilitated:
CDMA Roaming Business Elements
CDMA Roaming Technical Elements
CDMA Roaming Service Features
Roaming Service Providers
CDMA Roaming Inter-carrier Implementation
CDMA Roaming Carrier Maintenance
Features of CDMA
Narrowband message signal multiplied by wideband spreading signal code
Soft handoff increases capacity
Near-far problem


Attached File(s)
.ppt  CDMA.ppt (Size: 1.45 MB / Downloads: 34)
17-07-2011, 05:53 PM
Post: #23
RE: CDMA (Download Full Seminar Report)
Heart thanks 4 this valuebale informations
24-04-2012, 10:10 AM
Post: #24
Wink RE: CDMA (Download Full Seminar Report)
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05-06-2012, 10:55 AM
Post: #25
RE: CDMA (Download Full Seminar Report)
Hai
will u send me the seminar report of cdma to my mail id nareshvangapati[at]gmail.com

Regards,
NARESH
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