Narrow Band Advanced Mobile phone service (NAMPS)
Motorola developed a system which covers a large AMPS areas and this help in increasing the capacity in larger areas .This is known as Narrow Band Advanced Mobile phone service (NAMPS).It is similar to AMPS.
Features of NAMPS
- NAMPS can service three MS in a 30 KHz bandwidth
- Uses 10 KHz channels and FDMA (increases the capacity of AMPS by a factor of 3)
- In more congested areas, service providers could provide more trunked radio channels hence increase cell capacity and provide a better GOS
- NAMPS also uses SAT ST and blank and burst signaling just like AMPS, but signaling was done in sub-audible band
- The max frequency deviation is decreased, to reduce the signal BW, hence it increase S/ (N I) ratio.
- To counteract that NAMPS uses Companding to provide synthetic voice channel queuening.
- NAMPS uses 200 Hz SAT and ST, and a 300 Hz high pass band audio filter is used
- SAT and ST signaling is sent using 200 bps NRZ, which is FSK modulated
- Since SAT and ST signals are sent repetitively in small predefined code blocks (Called DSAT and DST) each 24 bits long
- There are 7 different 24 bit blocks DSAT codeword which may be selected by MSC,
- A DSAT word is constantly repeated by MS and BS
- DST signal is binary complement of DSAT
- The 7 code words specially designed to provide a sufficient number of alternating “1” and “0” so that the code can pass thru even when DC blocking implemented by the receivers