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AMPS (Advanced Mobile Phone Service)

AMPS (Advanced Mobile Phone Service). AT&T Bell Labs developed the first cellular tel system in the late 70s. First system was deployed in Chicago in 1983. A total of 40 MHz spectrum in the 800 MHz band was allocated by FCC.

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AMPS (Advanced Mobile Phone Service)

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  1. AMPS (Advanced Mobile Phone Service) • AT&T Bell Labs developed the first cellular tel system in the late 70s. • First system was deployed in Chicago in 1983. • A total of 40 MHz spectrum in the 800 MHz band was allocated by FCC. • In 1989, additional 10 MHz (called “Extended Spectrum”) was allocated. • Large cells and omni-directional BS antennas were used.

  2. AMPS (Advanced Mobile Phone Service) • AMPS uses a 7-cell reuse pattern with cell splitting and sectoring (120 degrees). • It requires S/I of 18 dB for satisfactory system performance. • It uses frequency modulation (FM) for radio transmission. • Mobile-> BS (reverse link) uses frequencies between 824-849 MHz. • BS -> Mobile (forward link) uses frequencies between 869-894 MHz. • Separation for forward and reverse channels is 45 MHz.

  3. 1G ARCHITECTURE (AMPS) Home Location Register (HLR) BACKBONE TELEPHONE NETWORK Visitor Location Register (VLR) Mobile Switching Center MSC (MSC) VLR Mobile Terminal (MT)

  4. AMPS (Advanced Mobile Phone Service) • Each BS has one control channel transmitter (broadcasts on the forward control channel) • One control receiver (that listens on the reverse control channel for any cellular phone trying to set up a control) and 8 or more FM duplex voice channels. • BS supports as many as 57 voice channels.

  5. AMPS (Advanced Mobile Phone Service) • Forward Voice Channel (FVC) carries the portion of the tel conversation originating from the landline tel network caller and going to mobile user. • Reverse voice channels (RVC) carry the portion of the tel conversation originating from the mobile user and going to landline tel network caller. • The number of control and voice channels used at a BS varies based on load of the system.

  6. AMPS (Advanced Mobile Phone Service) • Each BS continuously transmits digital FSK data on the Forward Control Channel at all times so that idle mobile users can lock onto the strongest FCC wherever they are. • All users must be locked or “camped” onto an FCC in order to originate or receive calls. • The BS reverse control channel (RCC) receiver constantly monitors transmissions from mobile users that are locked onto the matching FCC. • There are 21 control channels and they are scanned to find the best serving base station.

  7. AMPS (Advanced Mobile Phone Service)CALL HANDLING A Wired User calls a Mobile User • The call arrives at MSC and a paging message is sent out with the mobile’s MIN (Mobile Identification Number) simultaneously on every BS forward control channel in the system. • When the target callee receives the page, it will respond with ACK transmission on reverse control channel. • The MSC then directs the BS to assign a FVC and RVC pair to the mobile so that this call can take place on a dedicated voice channel.

  8. AMPS (Advanced Mobile Phone Service) • The BS also assigns the mobile a Supervisory Audio Tone (SAT tone) and a Voice Mobile Attenuation Code (VMAC) as it moves the call to the voice channel. • The mobile automatically changes its frequency to the assigned voice channel pair.

  9. AMPS (Advanced Mobile Phone Service) Mobile User places a Call: • It transmits a message on the RCC containing its MIN, Electronic Serial Number (ESN), Station Class Mark (SCM) and the destination tel number. • If received correctly by the BS, this information is sent to the MSC which checks to see if the mobile is properly registered, connects the mobile to the PSTN, assigns the call to a forward and reverse voice channel pair with a specific SAT and VMAC and commences the conversation.

  10. AMPS (Advanced Mobile Phone Service) • Handoff decisions are made by the MSC when the signal strength on the reverse voice channel (RVC) of the serving BS drops below a preset threshold or when the SAT tone experiences a certain level of interference. • MSC uses scanning receivers called “locate receivers” in nearby BSs to determine the signal level of a particular user which needs a handoff. • In doing so, the MSC is able to find the best neighboring BS which can accept the handoff.

  11. AMPS (Advanced Mobile Phone Service) Autonomous Registration • Mobile notifies a serving MSC of its presence and location by periodically keying up and transmitting its identity information, which allows the MSC to constantly update its customer list. • Registration command is sent in the overhead message of each control channel at 5-10 minute intervals and includes a timer value which each mobile uses to determine the precise time at which it should respond to the serving BS with a registration transmission. • Each mobile reports its MIN and ESN during the brief registration transmission so that the MSC can validate and update the customer list.

  12. Multiple Access Duplexing Channel BW Reverse Channel Freq Forward Channel Freq Voice Modulation Data Rate on Control/Voice Channels Number of Channels Coverage radius by 1 BS FDMA FDD 30 KHz 824-849 MHz 869-894 MHz FM 10 kbps 666-832 2-25 km OVERVIEW

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