CDMA
CDMA (Code Division Multiple Access) is a spread spectrum technology that allow multiple user to occupy same radio channel.
Characteristics:
- every user using unique code.
- Every data will be spreaded before it emitted so its enabling multiple access.
- Transmition bandwidth larger than information bandwidth. The ratio between of them is called processing gain (Gp).
- Interference insensitive
- Using soft handoff because all system using same frequency.
- Anti jamming.
IS-95 CDMA specification:
- bandwidth : 1.25 MHz
- chip rate : 1.2288 Mcps
- freq. uplink : 869 – 894 MHz 1930 – 1990 Mhz
- freq. downlink : 824 – 849 MHz 1850 – 1910 MHz
- frame length : 20 ms
- bit rates: 9.6 Kbps 14.4 Kbps
- speech code: QCELP 8 KBps, ACELP
