2/17/2014

Trường Đại học Bách Khoa Hà Nội
Viện Điện tử Viễn thông

Thông tin di động
Mobile Communications

TS. Đỗ Trọng Tuấn
Bộ môn Kỹ thuật thông tin

Hà Nội, 04-2011

1

2/17/2014

Phân cấp vùng phục vụ
trong mạng GSM

2


2/17/2014

Phân cấp vùng phục vụ GSM
Location Information-GSM Service Area Hierarchy

3

2/17/2014

Phân cấp vùng phục vụ GSM

Location Information-GSM Service Area Hierarchy
GSM Service Area

Service area = the area
in which a subscriber
an access the network.
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Vùng phục vụ PLMN

5

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Vùng định vị LAI và vùng phục vụ MSC/VLR

Vùng định vị LA là vùng gồm một số cell do nhà
quy hoạch ấn định tại đó MS có thể di chuyển tự
do mà không cần cập nhật lại vị trí.
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2/17/2014


Số nhận dạng vùng định vị LAI
3 digits

2 digits

Mobile country
Code (MCC)

Mobile
Network Code
(MNC)

2 Bytes
Location Area
Code (LAC)

Số LAI: Location Area Identity => Số nhận dạng vùng định vị
3 digits
Mobile country
Code (MCC)

2 digits

2 Bytes

2 Bytes

Mobile Network Location Area Global Cell
Code (MNC)
Code (LAC) Identity (GCI)


Số nhận dạng ơ tồn cầu GCI:
GCI = MCC + MNC + LAC + GCI = LAI + GCI

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Phân cấp vùng phục vụ GSM

Location Information-GSM Service Area Hierarchy

8


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Phân cấp vùng phục vụ GSM

Location Information-GSM Service Area Hierarchy

9

2/17/2014

Phân cấp vùng phục vụ GSM

Location Information-GSM Service Area Hierarchy

Số nhận dạng vùng định vị LAI được lưu giữ

ở đâu ?

10


2/17/2014

Phân cấp vùng phục vụ GSM

Location Information-GSM Service Area Hierarchy

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2/17/2014

Ví dụ

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Kênh tại giao diện vô tuyến Um

13

2/17/2014

Giao diện vô tuyến Um


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FDMA

Frequency

Channel

Time

15

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Kênh tần số trong hệ thống GSM và DCS

16


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TDMA

Time Slot

Frequency
Channel


0

1

2

3

4

5

6

7

Time

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Khái niệm


Kênh vật lý là phương tiện truyền tải thơng tin.




Tại Um:
• Kết hợp sử dụng 2 phương thức đa truy nhập
FDMA và TDMA.
• Kênh vật lý CH = TSi є ARFCNj

Kênh logic là thông tin mang trên kênh vật lý

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2/17/2014

Channels : differentiating between
Physical and Logical channels
Physical channels : The combination of an ARFCN
and a time slot defines a physical channel.
Logical channels : These are channels specified by
GSM which are mapped on physical channels.

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Kênh vật lý và kênh logic

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2/17/2014


Chế độ làm việc song công - Duplex
FDD: Frequency Division Duplex
TDD: Time Division Duplex

960 MHz

124

959.8MHz

123

GSM900 utilizesTS:
two
of 25 MHz. 890Timebands
slot

……
.

DOWNLINK

Downlink
(TDMA
frame)
= 8 the
TS
915 MHz band is
used for
uplink

while

……

is used for downlink.
0935-960
1 2 MHz
3 4 5 6 7

2

200KHz

935.2 Mhz

1

935 MHz

FDD
915 MHz
914.8 MHz

45 MHz

124
123
……
.


UPLINK
200KHz

The frequency bands are divided into 200
KHz wide channels called ARFCNs (Absolute
Radio Frequency
Channel
Numbers)
Data burst = 156.25
bit periods
= 576.9s i.e.
there are 124 ARFCNs are used.
TDD ARFCN supports 8 users with each user
Each
transmitting / receiving on a particular time
0 1 2 3 4 5 6 7
Delay
slot
(TS).

……

Uplink (TDMA frame)

2
890.2 MHz

1

890 MHz


Duplex methods

Therefore 1 TDMA frame = 156.25 x 8 = 1250 bits
and has a duration of 576.92s x 8 = 4.615 ms

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2/17/2014

Time Slot & Burst
P (dB)

 148

bits = 542,8 µs

+4 dB
- 6 dB
± 1 dB

34 dBm

- 30 dB

- 70 dB

 156,25 bits = 577 µs

t (µs)


Mức cơng suất phát của MS biến thiên theo thời gian



Time Slot: khe thời gian

 Busrt: Cụm thông tin
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2/17/2014

Phân cấp cấu trúc khung - Frame hierarchy
1 hyperframe = 2048 superframes = 2715648 TDMA frames

0

1

2

……

3

2044

2045


2046

2047

3 h 28 min 53.76 s
1 superframe = 51 (26frame) multiframes

OR

26 (51 frame) multiframes

6.12 s

0

1

2

0

……….

3

47

48

……….


1

49
24

50
25

26 * 51 = 1326 TDMA Frames
1 trafic multiframe = 26TDMA frames
T0

T1

…..

T11

S

T12

…..

1 control multiframe = 51TDMA frames

T24

I


T0

T1

T2

T3

….

…..

…..

T48

T49

T50

235.4 ms

120 ms
0

1

...


slot

577 µs

burst

6

7

4.615 ms

TDMA Frame

23

2/17/2014

Cấu trúc cụm bình thường NB – Normal Burst

Power p(t)

useful part
f2
f1

0 1 2 ... 7 0 1 ...
0 1 2 ... 7 0 1 ...

t


156.25 Bits in 576.923 s
(3.6923 s/Bit)

Stealing Flag

3 Tail Bits

26 Training Bits
2 x 57 Encrypted Bits

3 Tail Bits
8.25 Bits Guard Period

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Normal Burst
4.615ms

0

1

2

3


4

5

6

7
TB: tail bit

TB
3

Data
57

S
F
1

Training
26

S
F
1

Data
57

TB

3

148 bits
156.25 bits = 0.577ms

• To carry information on the TCH and all control channels except
for RACH, SCH and FCCH
• The two sets of encrypted 57 bits are data or speech

…….
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Normal Burst
•The stealing flag (SF) indicates whether the burst was
stolen for signaling or not.
•The 3 tail bits are (0,0,0) and is used as the start/stop
pattern.
• The GP (guard period of 8.25 is used to prevent
overlapping of frames
•The 26 training bits is a known bit sequence to get an
estimate of how the channel is affected by interference

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Synchronization Burst

MTS

4.615ms

0

TB
3

1

2

Encrypted
Bits 39

3

4

5

Extended training bits
64

6

Encrypted
Bits 39


BTS

7

TB
3

148 bits
156.25 bits = 0.577ms

• This burst is used for time synchronization of the mobile
• The long training sequence is a synchronization sequence
• The encrypted 78 bits carry the information of the TDMA frame
number and the BSIC (Base Tranceiver Station Identity Code)
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2/17/2014

Frequency Correction Burst
MTS

4.615ms

0

1

TB
3


2

3

4

Fixed all zeros
142

5

6

BTS

7

TB
3

148 bits
156.25 bits = 0.577ms

• This burst is used for frequency synchronization of the mobile
• The sequence of fixed zeros is equivalent to an unmodulated
carrier.

28



2/17/2014

Access Burst
4.615ms

0

1

TB
8

2

Syn.
Sequence
41

3

4

Encrypted
message
36

5

TB
3


6

7

Additional
guard time
60

148 bits
156.25 bits = 0.577ms

• The random access burst has a longer guard period since the mobile
does not know the timing advance when it randomly accesses the
system

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2/17/2014

Cấu trúc cụm tại giao diện vô tuyến

NB
FB
SB
DB
AB

30



2/17/2014

Kênh logic

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2/17/2014

Kênh lưu lượng - TCH

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2/17/2014

Kênh lưu lượng TCH


TCH/FS : for speech digitized at raw data
rate of 13 kbps (FS: Full Speech): Bm



TCH/HR: for speech digitized at raw data
rate of 6.5 kbps (HS: Half Speech):Lm



TCH/9.6 -> data transfer rate at 9.6 kbps




TCH/4.8, TCH/2.4 . . .

33

2/17/2014

Kênh điều khiển - CCH

34


2/17/2014

Control Channels
Functions:
• To help the MS find the control channels.
• To provide information about
- voice and control channel repetition cycle.
- parameters in the cell.
- surrounding cells.
- paging.
• To allow random access attempts by the MS.

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2/17/2014


Nhóm kênh điều khiển quảng bá BCH


In general mapped to BCCH ARFCN on TS0.



Broadcast control channels consist of:

-

Kênh điều khiển quản bá: BCCH - Broadcast Control
Channel .

-

Kênh hiệu chỉnh tần số FCCH – Frequency Correction
Channel.

-

Kênh đồng bộ SCH - Synchronization Channel

36


2/17/2014

Broadcast Control Channel (BCCH)



Serves as a Beacon for the Cell



Country Code (CC) and the Network Code (NC)



Location Area Identity (LAI) and



List of neighboring cells which should be

Cell identity

monitored by MS


List of frequencies used in the cell

37

2/17/2014

Frequency Correction Channel-FCCH


Allows each user unit to synchronize its

internal frequency standard with BTS



Repeated each 10 frame in control
multiframe

38


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Synchronization Channel (SCH)
Contains:
• Identification of base station for mobile
(BSIC).
• Frame synchronize with BTS ( 0 to 2715647)
• Timing advancement command


Transmitted just after FCCH , i.e. after
each 10 frames in control multiframe.

39

2/17/2014

Các kênh điều khiển chung CCCH



In general mapped to BCCH ARFCN on TS0.



Common control channels consist of:

-

Kênh tìm gọi: PCH ( Paging CHannel, forward channel),

-

Kênh truy nhập ngẫu nhiên RACH ( RANDOM Access
CHannel, reverse channel).

-

Kênh cho phép truy nhập AGCH ( Access Grant
CHannel, forward channel).

40


2/17/2014

Kênh tìm gọi PCH


functions:
• Paging signal from BS to to all mobile in the

cell.
• Notifies one mobile of an incoming call, by
sending IMSI/TMSI to target subscriber along
with request for ack on RACH.

41

2/17/2014

Common control channels, CCCH


RACH
• RACH is reverse channel for user to BTS ack
for a Page.
• Also used by mobiles to originate a call.
• The BTS responds by assigning a Stand
Alone Dedicated channel (SDCCH) for
signalling during a call. This is done on
AGCH.

42


2/17/2014

Common control channels, CCCH


AGCH ( Access Grant CHannel)

• AGCH is the final CCCH mesg to subscriber
before it moves off from Control Channel.

43

2/17/2014

Dedicated Control Channels


Three types of Dedicated Channel,
Bidirectional like traffic channels.



Like TCH, they exist on any channel
except TS0 of BCCH ARFCN



Used for providing signaling service
required by a particular user during a
call.

44


2/17/2014

Dedicated Control Channels



SDCCH ( stand alone dedicated control
channel)
• This ensures that MS and BS remain
connected while BS and MSC verify
subscriber identity before BS allocate
resource ( TCH assignmnet) to MS.
• SDCCH may be assigned their own physical
channel

45

2/17/2014

What function does Stand-Alone Dedicated Control channel
(SDCCH) serve?


Used by MS for call setup

 Authentication


Location Updating



Short message service (SMS)


BTS
MTS

(Bi-directional)

Back

46


2/17/2014

Dedicated Control Channels


Slow Associated Control Channel
• Always associated with a traffic channel TCH
or maps to a SDCCH phy channel.



SACCH of transmitted every 13 (26 for
half rate) TDMA frames i.e on each
speech multiframe, 8 TS is used for 8
users ( or 16 users for half rate).

47

2/17/2014


A Slow Associated Control channel (SACCH) is associated
with both a TCH and a SDCCH
DOWNLINK:



Power control
Timing Advance information

UPLINK


Receive Signal Strength Indicator



Quality reports

BTS
MTS

(Bi-directional)

Back

48


2/17/2014


Dedicated Control Channels







FACCH: Fast Associated Control Channels:
FACCH contains same type of signaling data
(but urgent, like handoff request) and used
when SDCCH has not been dedicated for a
particular user.
This is done by stealing frames from TCH
forward channel burst.
Two special bits called S bits in one TS, When
set indicates that data is FACCH data and not
user data.
49

2/17/2014

ξ3. Tổ hợp kênh
và cấu trúc đa khung

50