GSM

Các thông số kỹ thuật

GSM

• Dải tần số:

-P-GSM-900: uplink 890 - 915 MHz và downlink 935 - 960 MHz (124 kênh mỗi kênh cách nhau200KHz – khoảng duplex(đường up và down cho 1 thuê bao) 45MHz)- E-GSM:uplink 880 - 915 MHz và uplink 925 - 960 MHz (thêm 50 kênh tần số)- R-GSM: uplink 876 - 915 MHz và uplink 921 - 960 MHz (thêm 20 kênh nữa)- GSM-1800: 1710 - 1785 MHz và 1805 - 1880 MHz. (374 kênh mỗi kênh cách200KHz – khoảng duplex(đường up và down cho 1 thuê bao) 95MHz) - GSM-1900: 1850-1910 MHz và 1930-1990 MHz.

GSM

• Kỹ thuật đa truy cập: FDMA kết hợp TDMA, mỗi kênh tần số mang 8 kênh lưu lượng trên 8 khe thời gian.

• Phân chia song công: phân chia tần số (FDD - Frequency Division Duplexing)

GSM

mobile station

(MS) base station

(BS)

Um Abis

Abis

Abis

base station controller

(BSC)

BSC

TRAU

Transcoder Rate Adaptor Unit (TRAU)

A

Home Location Register (HLR)

Visitor Location Register (VLR)

Equipment Identity Register (VLR)

MSC

Mobile Switching

Center (MSC)

GMSC

GatewayMobile

Switching Center (GMSC)

Uplink (Tx)

Downlink (Rx)

GSM

GSM

Name Exchange Description

Um MS - BS Radio interface between mobile and base station

Abis BS - BSC Communication transfer base station - controller

A BSC - MSC Communication transfer controller – switch center

B MSC - VLR Visitor information communication

C GMSC - HLR Request HLR for incoming call

D VLR - HLR Subscriber localization

E MSC - MSC Handover

F MSC - VLR Mobile station identity verification

GSM

DCS 1800

1710 1785 1805

Tx

1880

Rx f(MHz)

MS=mobile station1-2WattsBS=base

station100-200 Watts

Uplink (Tx)

GSM

890 915 935

Tx

960

Rx f(MHz)

Downlink (Rx)

Frequency-power

GSM

• ARFCN = Absolute Radio Frequency Number • GSM : ARFCN=1-124

– Frequency (Downlink) = 935.2 + 0.2*(n-1) MHz, – Frequency (uplink) = 890.2 + 0.2*(n-1) MHz

• DSC 1800 : ARFCN=512-885 – Frequency (Downlink) = 1805.2 + 0.2*(n-512) MHz – Frequency (Uplink) = 1710.2 + 0.2*(n-512) MHz

• Extended GSM : ARFCN=975-1023– Uplink (880.4-890.0 MHz) – Downlink (925.4- 935.0 MHz) – Frequency (Downlink) = 935.2 + 0.2*(n-1024) MHz– Frequency (Uplink) = 890.2 + 0.2*(n-1024) MHz

• SFR 75 - 124, 721-764 channels• ORANGE 1-50, 765 - 809 channels• Bouygues 51-74, 811 – 885 channels

GSM

890 Frequency(MHz)

200KHz

Amplitude

Time

R1

T1

577µs

935

890

935

T1

4.61ms

T8

200KHz

Time domain multiple access (TDMA)

Duplex distance45MHz

Duplex & TDMA

GSM

0 1 2 3 4 5 6 7

« Burst » description

Data bits Data bits (same)

3 bits 58 bits 26 bits 58 bits 3 bits

546 µs Training sequence00100 10111 000010 00100 10111

BS000010

GSM data rate

GSM

Regular Pulse Excitation (60 parameters, 188 bits)

Parameter computing

F0Long Term Prediction (8 parameters, 26 bits)

Short term prediction (8 parameters, 36 bits)

Compression 1/10

2080 bits 260 bits

20 ms of sampled signal

LTE-RTP Algorithm – University of Berkeley, USA