RF Signals & Modulation
※ RF Signals ※
Absolute Value Formula:
Compare Formula:
- Law of Zero: P1 = P2
- Law of 3: Double / Half
- Law of 10: Ten times / one-tenth
For example:
mW = 200 x 2 x 2 x 10
dB = 23 = 7 + 3 + 3 + 10
Rx Signal:
EIGP:
Transmitter: EIRP (100mW to 1mW) (+20dBm to 0dBm)
Receiver: RSSI (1mW to 0mW) (0dBm to -100dBm)
Signal to Noise Ratio in dBm: 愈大愈好
Frequency Sense:
Broadband: 包好多frequency
Narrowband: 包好少frequency
Channel: 包好多frequency
Theoretical data rate: frequency
Modulation data rate 愈快, repeated date 愈少
※ Modulation ※
FHSS:
- 1 bit Data 用1個channel行, 每次都轉channel
- 每個channel 1-MHz闊
- 速度: 1 or 2 Mbps
DSSS:
- 有14 channels, 常用1, 6, 11
OFDM:
- 48 sub-channels 同時發data
分數代表chip有的data, 剩下都是repeated data
For example:
QPSK: 4個組合, 即2bits
DQPSK: 8個組合, 即3bits
