18-12-2012, 02:30 PM
CODE DIVISION MULTIPLE ACCESS
[attachment=44209]
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.
What is CDMA?
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.
HISTORY
The first generation of cellular systems, which include the AMPS (Advanced Mobile Phone Systems), was introduced in the early 1980s. These systems used analog frequency modulation (FM) and have a frequency division multiple access (FDMA) based media access control (MAC) architecture.
Within a few years, market demands and capacity requirements began to grow hitting the practical limitations. These limitations motivated the development of the second generation cellular systems, which improved compatibility and accommodated higher capacity than the first generation systems. These systems use digital modulation and processing techniques.
TDMA (Time Division Multiple Access), GSM (Global System for Mobile Communication) and (narrowband) CDMA belong to the second generation systems. CDMA was introduced in 1994, by Qualcomm, Inc. Using direct sequence code division multiple access, it claimed to provide 10 times more capacity than analog systems � far more than TDMA or GSM.
Today, CDMA is the basis to the third generation market in the United States and other places in the world.
BACKGROUND
A cellular system is called so because it divides the service area into small transmission areas called cells. Each cell contains a base station (BTS), which consists of a transceiver and a receiver in order to connect to mobile phones in the cell. Each cell is assigned a group of radio channels (frequencies).
COMPETITION
The Euro-Asian biggest competitive to CDMA is the Global System for Mobile Communication (GSM).
For several years, the wireless world has been divided into two groups: GSM, in Western Europe, and CDMA, in North America and parts of Asia. Motorola, Lucent and Nextel chose CDMA, while Nokia and Ericsson are the dominant GSM players.Each technology has its own advantages. Comparing these two competing technologies can be done depending on the functionality required.
CDMAs main advantages over GSM are its bigger capacity (56Kps vs. over 64Kps), less interference, lower radiation level (10 times less than GSM) and security (CDMA uses pseudo-random code sequence).
GSM, on the other hand, has its strength in its core network. Is uses the SIM card, which provides more functionality and allows roaming capabilities.
GSM uses a modified version of TDMA, which maximizes the system�s usage and efficiency by allowing calls to jump between channels and timeslots.
In the past 8 years CDMA has grown from a small experiment to one of the worlds fastest growing wireless technology.It continues to grow world wide, but despite promising growth, CDMA use is well below the early expectations and still GSM is the dominant technology for mobile communication. According to Qualcomm, 147 million people worldwide use CDMA technology on their wireless devices.
[attachment=44209]
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.
What is CDMA?
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.
HISTORY
The first generation of cellular systems, which include the AMPS (Advanced Mobile Phone Systems), was introduced in the early 1980s. These systems used analog frequency modulation (FM) and have a frequency division multiple access (FDMA) based media access control (MAC) architecture.
Within a few years, market demands and capacity requirements began to grow hitting the practical limitations. These limitations motivated the development of the second generation cellular systems, which improved compatibility and accommodated higher capacity than the first generation systems. These systems use digital modulation and processing techniques.
TDMA (Time Division Multiple Access), GSM (Global System for Mobile Communication) and (narrowband) CDMA belong to the second generation systems. CDMA was introduced in 1994, by Qualcomm, Inc. Using direct sequence code division multiple access, it claimed to provide 10 times more capacity than analog systems � far more than TDMA or GSM.
Today, CDMA is the basis to the third generation market in the United States and other places in the world.
BACKGROUND
A cellular system is called so because it divides the service area into small transmission areas called cells. Each cell contains a base station (BTS), which consists of a transceiver and a receiver in order to connect to mobile phones in the cell. Each cell is assigned a group of radio channels (frequencies).
COMPETITION
The Euro-Asian biggest competitive to CDMA is the Global System for Mobile Communication (GSM).
For several years, the wireless world has been divided into two groups: GSM, in Western Europe, and CDMA, in North America and parts of Asia. Motorola, Lucent and Nextel chose CDMA, while Nokia and Ericsson are the dominant GSM players.Each technology has its own advantages. Comparing these two competing technologies can be done depending on the functionality required.
CDMAs main advantages over GSM are its bigger capacity (56Kps vs. over 64Kps), less interference, lower radiation level (10 times less than GSM) and security (CDMA uses pseudo-random code sequence).
GSM, on the other hand, has its strength in its core network. Is uses the SIM card, which provides more functionality and allows roaming capabilities.
GSM uses a modified version of TDMA, which maximizes the system�s usage and efficiency by allowing calls to jump between channels and timeslots.
In the past 8 years CDMA has grown from a small experiment to one of the worlds fastest growing wireless technology.It continues to grow world wide, but despite promising growth, CDMA use is well below the early expectations and still GSM is the dominant technology for mobile communication. According to Qualcomm, 147 million people worldwide use CDMA technology on their wireless devices.