30-05-2013, 04:38 PM
Advanced Mobile Phone System (AMPS)
[attachment=54540]
INTRODUCTION
Advanced Mobile Phone System (AMPS) is an analog mobile phone system standard developed by Bell Labs, and officially introduced in the Americas in 1978, which became the first cellular network in the U.SAMPS is a first-generation cellular technology that uses separate frequencies, or "channels", for each conversation (see FDMA). It therefore required considerable bandwidth for a large number of users
Technology
AMPS is a first-generation cellular technology that uses separate frequencies, or "channels", for each conversation (see FDMA). It therefore required considerable bandwidth for a large number of users. In general terms, AMPS was very similar to the older "0G" Improved Mobile Telephone Service, but used considerably more computing power in order to select frequencies, hand off conversations to PSTN lines, and handle billing and call setup.
What really separated AMPS from older systems is the "back end" call setup functionality. In AMPS, the cell centers could flexibly assign channels to handsets based on signal strength, allowing the same frequency to be re-used in various locations without interference. This allowed a larger number of phones to be supported over a geographical area. AMPS pioneers coined the term "cellular" because of its use of small hexagonal "cells" within a system.[12][13]
AMPS suffered from many weaknesses when compared to today's digital technologies. As an analog standard, it was very susceptible to static and noise, and had no protection from eavesdropping using a scanner. In the 1990s, an epidemic of "cloning" cost the cellular carriers millions of dollars. An eavesdropper with specialized equipment could intercept a handset's ESN (Electronic Serial Number) and MIN (Mobile Identification Number, or cellular telephone number). The Electronic Serial Number was a 12 digit number sent by the handset to the cellular system for billing purposes, uniquely identifying that phone on the network. The system then allowed or disallowed calls and or features based on its customer file. If an ESN/MIN Pair was intercepted, it could then be cloned onto a different phone and used in other areas for making calls without paying.
Standards
AMPS was originally standardized by ANSI as EIA/TIA/IS-3. EIA/TIA/IS-3 was superseded by EIA/TIA-553 and TIA interim standard IS-91 (Narrowband Advanced Mobile Phone System). AMPS networks have been replaced by digital networks based on standards including Digital AMPS, GSM, and CDMA2000 which brought improved security as well as increased capacity. Though cloning is still possible even with digital technologies, the cost of wireless service is so low that the problem has virtually disappeared.
Frequency bands
AMPS cellular service operated in the 850 MHz Cellular band. For each market area, the United States Federal Communications Commission (FCC) allowed two licensees (networks) known as "A" and "B" carriers. Each carrier within a market used a specified "block" of frequencies consisting of 21 control channels and 395 voice channels. Originally, the B (wireline) side license was usually owned by the local phone company, and the A (non-wireline) license was given to wireless telephone providers.
Code division multiple access
Code division multiple access (CDMA) is a channel access method used by various radio communication technologies. It should not be confused with the mobile phone standards called cdmaOne, CDMA2000 (the 3G evolution of cdmaOne) and WCDMA (the 3G standard used by GSM carriers), which are often referred to as simply CDMA, and use CDMA as an underlying channel access method.
One of the concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a band of frequencies (see bandwidth). This concept is called multiple access. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency. CDMA is a form of spread-spectrum signalling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.
Steps in CDMA Modulation
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 XOR’ed 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]
Digital AMPS
IS-54 and IS-136 are second-generation (2G) mobile phone systems, known as Digital AMPS (D-AMPS). It was once prevalent throughout the Americas, particularly in the United States and Canada in the 1990s. D-AMPS is considered end-of-life, and existing networks have mostly been replaced by GSM/GPRS or CDMA2000 technologies.
This system is most often referred to as TDMA. That name is based on the abbreviation for time division multiple access, a common multiple access technique which is used by multiple protocols, including GSM, as well as in IS-54 and IS-136. However, D-AMPS has been competing against GSM and systems based on code division multiple access (CDMA) for adoption by the network carriers, although it is now being phased out in favor of GSM/GPRS and CDMA2000 technology.
D-AMPS uses existing AMPS channels and allows for smooth transition between digital and analog systems in the same area. Capacity was increased over the preceding analog design by dividing each 30 kHz channel pair into three time slots (hence time division) and digitally compressing the voice data, yielding three times the call capacity in a single cell. A digital system also made calls more secure because analog scanners could not access digital signals. Calls were encrypted, although the algorithm used (CMEA) was later found to be weak.[1]
IS-136 added a number of features to the original IS-54 specification, including text messaging, circuit switched data (CSD), and an improved compression protocol. SMS and CSD were both available as part of the GSM protocol, and IS-136 implemented them in a nearly identical fashion.
History
The evolution of mobile communication has been almost wholly in 3 different geographic regions. The standards that were born in these regions were quite independent. The 3 regions are North America, Europe and Japan. The earlier mobile or wireless technologies were wholly analog and are collectively known as 1st Generation (1G) technologies. In Japan, the 1G standards were Nippon Telegraph and Telephone (NTT) and the high capacity version of it (Hicap). The European systems were not common and the 'European Union' viewpoint that is visible in the later technologies was absent. Various 1G standards that were in use in Europe include C-Netz (in Germany and Austria), Comviq (in Sweden), Nordic Mobile Telephones/450 (NMT450) and NMT900 (both in Nordic countries), NMT-F (French version of NMT900), Radiocom 2000 (RC2000) (in France), and TACS(Total Access Communication System) (in the United Kingdom and Ireland). North American standards were Advanced Mobile Phone System (AMPS) and Narrow-band AMPS (N-AMPS).
Technology specifications
IS-54 employs the same 30 kHz channel spacing and frequency bands (824-849 and 869-894 MHz) as AMPS. Capacity was increased over the preceding analog design by dividing each 30 kHz channel pair into three time slots and digitally compressing the voice data, yielding three times the call capacity in a single cell. A digital system also made calls more secure because analog scanners could not access digital signals.
The IS-54 standard specifies 84 control channels, 42 of which are shared with AMPS. To maintain compatibility with the existing AMPS cellular telephone system, the primary forward and reverse control channels in IS-54 cellular systems use the same signaling techniques and modulation scheme (binary FSK) as AMPS. An AMPS/IS-54 infrastructure can support use of either analog AMPS phones or D-AMPS phones.
[attachment=54540]
INTRODUCTION
Advanced Mobile Phone System (AMPS) is an analog mobile phone system standard developed by Bell Labs, and officially introduced in the Americas in 1978, which became the first cellular network in the U.SAMPS is a first-generation cellular technology that uses separate frequencies, or "channels", for each conversation (see FDMA). It therefore required considerable bandwidth for a large number of users
Technology
AMPS is a first-generation cellular technology that uses separate frequencies, or "channels", for each conversation (see FDMA). It therefore required considerable bandwidth for a large number of users. In general terms, AMPS was very similar to the older "0G" Improved Mobile Telephone Service, but used considerably more computing power in order to select frequencies, hand off conversations to PSTN lines, and handle billing and call setup.
What really separated AMPS from older systems is the "back end" call setup functionality. In AMPS, the cell centers could flexibly assign channels to handsets based on signal strength, allowing the same frequency to be re-used in various locations without interference. This allowed a larger number of phones to be supported over a geographical area. AMPS pioneers coined the term "cellular" because of its use of small hexagonal "cells" within a system.[12][13]
AMPS suffered from many weaknesses when compared to today's digital technologies. As an analog standard, it was very susceptible to static and noise, and had no protection from eavesdropping using a scanner. In the 1990s, an epidemic of "cloning" cost the cellular carriers millions of dollars. An eavesdropper with specialized equipment could intercept a handset's ESN (Electronic Serial Number) and MIN (Mobile Identification Number, or cellular telephone number). The Electronic Serial Number was a 12 digit number sent by the handset to the cellular system for billing purposes, uniquely identifying that phone on the network. The system then allowed or disallowed calls and or features based on its customer file. If an ESN/MIN Pair was intercepted, it could then be cloned onto a different phone and used in other areas for making calls without paying.
Standards
AMPS was originally standardized by ANSI as EIA/TIA/IS-3. EIA/TIA/IS-3 was superseded by EIA/TIA-553 and TIA interim standard IS-91 (Narrowband Advanced Mobile Phone System). AMPS networks have been replaced by digital networks based on standards including Digital AMPS, GSM, and CDMA2000 which brought improved security as well as increased capacity. Though cloning is still possible even with digital technologies, the cost of wireless service is so low that the problem has virtually disappeared.
Frequency bands
AMPS cellular service operated in the 850 MHz Cellular band. For each market area, the United States Federal Communications Commission (FCC) allowed two licensees (networks) known as "A" and "B" carriers. Each carrier within a market used a specified "block" of frequencies consisting of 21 control channels and 395 voice channels. Originally, the B (wireline) side license was usually owned by the local phone company, and the A (non-wireline) license was given to wireless telephone providers.
Code division multiple access
Code division multiple access (CDMA) is a channel access method used by various radio communication technologies. It should not be confused with the mobile phone standards called cdmaOne, CDMA2000 (the 3G evolution of cdmaOne) and WCDMA (the 3G standard used by GSM carriers), which are often referred to as simply CDMA, and use CDMA as an underlying channel access method.
One of the concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a band of frequencies (see bandwidth). This concept is called multiple access. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency. CDMA is a form of spread-spectrum signalling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.
Steps in CDMA Modulation
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 XOR’ed 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]
Digital AMPS
IS-54 and IS-136 are second-generation (2G) mobile phone systems, known as Digital AMPS (D-AMPS). It was once prevalent throughout the Americas, particularly in the United States and Canada in the 1990s. D-AMPS is considered end-of-life, and existing networks have mostly been replaced by GSM/GPRS or CDMA2000 technologies.
This system is most often referred to as TDMA. That name is based on the abbreviation for time division multiple access, a common multiple access technique which is used by multiple protocols, including GSM, as well as in IS-54 and IS-136. However, D-AMPS has been competing against GSM and systems based on code division multiple access (CDMA) for adoption by the network carriers, although it is now being phased out in favor of GSM/GPRS and CDMA2000 technology.
D-AMPS uses existing AMPS channels and allows for smooth transition between digital and analog systems in the same area. Capacity was increased over the preceding analog design by dividing each 30 kHz channel pair into three time slots (hence time division) and digitally compressing the voice data, yielding three times the call capacity in a single cell. A digital system also made calls more secure because analog scanners could not access digital signals. Calls were encrypted, although the algorithm used (CMEA) was later found to be weak.[1]
IS-136 added a number of features to the original IS-54 specification, including text messaging, circuit switched data (CSD), and an improved compression protocol. SMS and CSD were both available as part of the GSM protocol, and IS-136 implemented them in a nearly identical fashion.
History
The evolution of mobile communication has been almost wholly in 3 different geographic regions. The standards that were born in these regions were quite independent. The 3 regions are North America, Europe and Japan. The earlier mobile or wireless technologies were wholly analog and are collectively known as 1st Generation (1G) technologies. In Japan, the 1G standards were Nippon Telegraph and Telephone (NTT) and the high capacity version of it (Hicap). The European systems were not common and the 'European Union' viewpoint that is visible in the later technologies was absent. Various 1G standards that were in use in Europe include C-Netz (in Germany and Austria), Comviq (in Sweden), Nordic Mobile Telephones/450 (NMT450) and NMT900 (both in Nordic countries), NMT-F (French version of NMT900), Radiocom 2000 (RC2000) (in France), and TACS(Total Access Communication System) (in the United Kingdom and Ireland). North American standards were Advanced Mobile Phone System (AMPS) and Narrow-band AMPS (N-AMPS).
Technology specifications
IS-54 employs the same 30 kHz channel spacing and frequency bands (824-849 and 869-894 MHz) as AMPS. Capacity was increased over the preceding analog design by dividing each 30 kHz channel pair into three time slots and digitally compressing the voice data, yielding three times the call capacity in a single cell. A digital system also made calls more secure because analog scanners could not access digital signals.
The IS-54 standard specifies 84 control channels, 42 of which are shared with AMPS. To maintain compatibility with the existing AMPS cellular telephone system, the primary forward and reverse control channels in IS-54 cellular systems use the same signaling techniques and modulation scheme (binary FSK) as AMPS. An AMPS/IS-54 infrastructure can support use of either analog AMPS phones or D-AMPS phones.