【網(wǎng)絡(luò)工程】nokia-gsm原理介紹-在線瀏覽
2025-02-23 13:15本頁(yè)面
【正文】 and Downlink use different bands(45MHz apart for GSM900) Frequency Hopping M O D Coupler Switch Synth Register Control Uplink BS 1 BS 2 Monitoring RX Lev RX Qual Downlink 1 65 124 1 65 124 Home BS 20ms Blocks Speech Coder Bits Ordered 260 Bits 260 Bits 50 132 78 . RELP and LTP Coder RELP ResidualExcited Linear Prediction Coder LTP Long Term Prediction . Converts Speech to Low Data Rate . 20ms Speech makes 260Bits . Output 13kbit/s Very Important Bits Important Bits Other Bits Speech Coder Error Correction Type Ia 50 Type Ib 132 Type II 78 50 132 78 3 Type Ia CRC Type Ib Type II Block Code 25 66 25 66 3 4 78 Reordering 378 78 Half rate convolutional code 456 Bits from 20ms of Speech Type Ia Type Ib Type Ib Type Ia Tail Type II CRC 262 Bits In 456 Bits Out Diagonal Interleaving 456 Bits from 20ms of Speech 456 Bits from 20ms of Speech 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 TCH Traffic Channel (TCH) Bursts Carry Two 57 Bits Blocks (114) Each 120ms of Speech = 456x6 = 2736 bits 2736/114 = 24 bursts . 24frames(mobile transmits once per frame) Multiframe has 26 frames in 120ms There are 2 spare frames厖 One SACCH, one Idle Speech to Radio / Radio to Speech Channel coding Speech Digitizing and Source coding Interleaving Burst formatting Ciphering Modulation Channel decoding Speech Source decoding Deinterleaving Burst formatting Deciphering Demodulation MS Camp on Flow Chart MS Turn On MS searches channels and orders by signal strength MS Stongest BCCH FCCH on BCCH and adjusts timebase SCH on BCCH and fine tunes timebase timing Decode BCCH store info Is BCCH in PLMN ? MS Next Stongest BCCH YES NO
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