1. Chapter 3 Analog Cellular Communications AMPS System
This chapter covers the first-generation cellular technology focusing on AMPS (Advanced Mobile Phone System).
AMPS delivers basic telephony and supplement services (voice mail and call forwarding).
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2. Network Elements
The AMPS specification refers to terminals as mobile stations and to base station as land stations.
The common terminology for an AMPS switch is mobile telephone switching office (small and large MTSO).
The communication links between the base stations and switch are labeled land lines (copper wires, optical fibers or microwave systems)
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4. AMPS Identification Codes
Mobile Identification Number (MIN)
Area code (3 digits), Exchange number (3 digits) and subscriber number (4 digits)
Electronic Serial Number (ESN)
System Identifier (SID)
Station Class Mark (SCM)
Indicates capabilities of a mobile station
Supervisory Audio Tone (SAT)
Digital Color Code (DCC)
Help mobile stations distinguish neighboring base stations from one another
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5. Frequency Bands and Physical Channels
The band for forward transmissions, from cell site to mobile station, is MHz.
The reverse band, for transmissions by mobiles, is 45 MHz lower.
An AMPS physical channel occupies two 30 KHz frequency bands, one for each direction.
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7. Radiated Power
An AMPS terminal is capable of radiating signals at 6 or 8 different power levels (6 mW to 4W).
10 log 4000 = 36 dBm
The radiated power at a a base station is typically 25 W.
Discontinuous transmission (DTX)
Speech activity detector
ON-OFF state
Power saving and Interference reducing
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8. Analog Signal Processing
Compression and pre-emphasis are established techniques for audio signal transmission.
An amplitude limiter confines the maximum excursions of the frequency modulated signal to 12 KHz.
Low pass filter Attenuates signal components at frequencies above 3 KHz, refer to Fig. 3.5.
The notch (at 6KHz) removes signal energy at the frequencies associated with the 3 SAT of the AMPS system.
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12. SAT and ST
The SAT (Supervisory Audio Tone) transmitted with user information serves to identify the base station assigned to a call.
Each base station has its own SAT- at 5970 Hz, 6000 Hz, or 6030 Hz.
An analog signals from AMPS terminals can also contain a 10 KHz sine wave referred to as a ST (Supervisory Tone).
On-hook and Off-hook indications signaling
The channel reuse principles (Section 9.3.2)
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13. Digital Signals
AMPS also transmits important network control information in digital form.
AMPS digital signal are sine waves either 8 KHz above or 8 KHz below the carrier.
The signal format is Manchester coded binary frequency shift keying at a rate of 10 Kbps
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15. Spectrum Efficiency Frequency modulation in 30 KHz physical channels
Signal-to-Interference ratio (SIR)
SIR >= (SIR)req = 18 dB
Reuse factor N = 7 (Figure 9.9)
Spectrum efficiency
E=395 /7*25 = 2.26 conversations/cell/MHz
395 traffic channels, 25 MHz/system, 7 cells in a cluster
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17. Logical Channel Categories
FOCC: Forward (Downlink) Control Channel
Carries the same information from one base station to all of the mobile terminals (Broadcast)
RECC: Reverse (Uplink) Control Channel
Carries information from many mobile terminals that do not have voice channel (Random access)
FVC: Forward Voice Channel (Dedicated)
RVC: Reverse Voice channel (Dedicated)
Forward and reverse traffic channel
User information (Dedicated)
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26. Tasks Performed by Terminals
Initialization mode
The terminal turns the power on
A conversation ends
Loses contact with the current base station
Idle mode
Access mode (from Idle mode)
The terminal presses the SEND button
An incoming call request detected (MIN)
A registration event stimulated
Conversation mode
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31. Capacity There are 3 ways to increase the capacity
Operate with smaller cells
Obtain additional spectrum allocations
Improve spectrum efficiency
NAMPS (Narrowband-AMPS)
Messages similar to AMPS
Synchronization sequences
Digital versions of the SAT and ST
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33. Review Exercises
What is the purpose of the busy / idle bits in the FOCC? Why are they not used in the other control channel formats?
Explain how the AMPS system users supervisory audio tones (SAT) and a digital color code (DCC). Why are both required?
Explain why it is sometimes desirable for the AMPS system to set up a call through a base station that is not the nearest base station to the terminal. How does the AMPS system achieve this effect?
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