GBC 006 E1 1 GSM Advanced Technology-49

8/13/2019 GBC 006 E1 1 GSM Advanced Technology-49

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GBC_006_E1_0 GSM Advanced Technology

ZTE University

GSM-BSS Team


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Objectives

At the end of this course, you will be able to:

Understand HR services and implementation

methodsUnderstand principles of ZTE ultra-distance

coverage technology

Understand concepts, features and specifications of

EDGE technology

Grasp satellite Abis transmission configurations


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Contents

HR Services

Ultra-Distance Coverage Technology

EDGE Technology

Satellite Abis Technology


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Basic Concepts

According to the switching mode, TCHs are divided into

circuit switching channels and data switching channels.

According to the transmission rate, TCHs are divided intoFull Rate (FR) channels and Half Rate (HR) channels.

The rate of GSM FR channel is 13 kbps while the rate of

GSM HR channel is 6.5 kbps. In addition, the Enhanced

FR channel has the same rate (13 kbps) as the FR

channel, but has better compression encoding scheme

than the FR channel, thus it has better voice quality.

HR service


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HR Frame Structure

If the HR voice channel is adopted, the air interfaces frame

structure does not change. The multi-frames odd-numbered

frames are allocated to a user, even-numbered frames are

allocated to another user, and the 26th idle frame functions as

SACCH of the second user. Therefore, the channel capacity

doubles, that is, the channel bears two TCH/H services rather

than the original one TCH/F service.

HR service


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HR Frame Structure

ZTE equipments support both static HR and dynamic HRservice

Static HR service

Static HR service means that the system HR channels aredecided in network planning, and the static configuration is

made on the system OMCR equipments. During the system

running, the HR channel occupies fixed carrier and timeslots,

and each timeslot on the carrier maintains its status as HR orFR that is set when being allocated, and the status can not be

changed. Fine adjustment can be made to the static

configuration in later network optimization.

HR service


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HR Frame Structure

Dynamic HR service

Dynamic HR service means that only FR service is provided during the

systems initial running, and the ratio of commissioned HR channels

depends on the traffic change during system running.

When the traffic increases, the reserved dynamic HR auxiliary timeslots

of Abis interface are used to start the conversion from idle FR channels

to HR channels. In this way, HR channels are used to increase the

system traffic capacity and reduce the congestion rate.

When the traffic decreases, the conversion from idle HR channels to FR

channels is started, to guarantee the system voice quality with FR

channels. With dynamic HR service, the advantages of HR service can

be fully utilized in handling traffic burst and network capacity expansion.

HR service


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HR Service Implementation

In ZXG10-BSS system, the HR service implementation process

in uplink direction is as follows:

The HR frame is processed by BTS first and then sent to RMM

through Abis interface. BIPP performs the internal conversion

from 8 kbps channel to 16 kbps channel and then sends the

frame to Bit-Oriented Switching Network (BOSN). After being

processed by BOSN, the HR frame enters the TC unit and the

rate adaptation unit that handle the HR service. Finally, the

frame is sent to MSC from A-interface at the speed of 64 kbps.

in downlink direction, just reverse of that in uplink direction.

HR service


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Uplink: conversion from 8 kbps to 16 kbps

Downlink: conversion from 16 kbps to 8 kbps

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MS supporting

HR-service

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OMC-R Server OMC-R Client

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Processing HR frame

A-interface 64

kbps voice channel

Configuring HR,

performance measurement,

and service flow processing

16 kbps

HR channel

16 kbps

HR channelAbis interface 8

kbps HR channel

Uplink: decode HR frame to 64 kbps voice

channel

Downlink: encode 64 kbps voice channel into

16 kbps HR channel

Configuring HR,

performance measurement,

and relevant O&M

processing

HR Service Implementation

HR service


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HR Channel Allocation Strategies

ZXG10-BSS system can automatically recognize whether the terminal

supports HR , and can decide whether the terminal accesses HR, FR,

EFR channel according to parameter configurations.

The system decides the allocation priority for HR, FR, and EFRchannels according to the users voice channel priority issued by MSS.

Priority allocation parameters for HR, FR, and EFR channels are

supported. For terminals that support HR service, if MSS does not

specify the priority, the system decides to allocate HR, FR, or EFRchannel according to priority allocation parameters. After adopting this

allocation strategy, if a resource is unavailable, the system will

automatically allocate another resource instead.

HR service


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HR Channel Allocation Strategies

The TC that supports HR service also supports FR and

EFR. After TCs related to FR and EFR are occupied, the

system will allocate TCs that support HR service to satisfy

FR and EFR requirements. After TCs that support HR

service are occupied, the system stops allocating HR

radio resource, and allocates the FR channel and EFR

channel until the TC resource that supports HR service is

available.

HR service


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HR Service Applications

HR applications in area with burst traffic

The HR service is most effective in handling burst traffic in areas

such as the stadium, campus, or rendezvous. These areas all

have the common feature that the heavy traffic occurs

periodically or suddenly. For example, the traffic increases

suddenly during a match in a stadium, and the traffic on campus

increases suddenly after class. The dynamic HR service is most

appropriate to apply in such situations. In normal cases, the

traffic is low, and the channel is in FR status. When the traffic

increases suddenly, the channel automatically converts to HR

status, relieving the traffic congestion and avoiding the waste

that is usually caused by the common capacity expansion.

HR service


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HR applications in area with dense traffic

The traffic is dense in areas such as the dense urban area, airport,

railway station, and plaza. In order to avoid frequent network

adjustment, the HR service can be adopted to temporarily relieve

the pressure of capacity expansion. Before the next capacity

expansion is performed, commissioning the dynamic HR or static

HR can handle the emergent capacity increase. The HR service,

combined with a long-term planning and capacity expansion,

provides a flexible choice for operators in capacity expansion.

Moreover, the HR service is also a solution for network capacity

expansion for dense urban area where the frequency resource is

limited and the site expansion is infeasible.

HR service


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HR applications in area with low-end users

In some areas with low-end users such as the remote rural

area, operators also provide the coverage to enhance their

competition power. These low-end users do not have high

requirement for the voice quality. Thus the HR service

(static HR or dynamic HR) can be adopted together with

some wide-coverage technologies to realize a low-cost

coverage.

HR service


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Contents

HR Services


EDGE Technology



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Technological Background

It is specified in GSM protocols that the maximum access

radius of GSM 900 MHz system is 35 km, and the

corresponding Time Advance (TA) is 63. Such restrictions

in GSM protocols are mainly due to that the coverage

larger than 35 km is difficult to realize in the GSM 900

MHz environment, and can be realized only in some

special propagation environments.


Ult Di t C T h l


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Technological Background

With the evolution of GSM protocols, there are more

frequency bands. Because the propagation loss of GSM

400 MHz system is less that that of GSM 900 MHz

system, it is specified that the coverage radius of the

former can be larger than 35 km, the maximum access

radius of the former can be 120 km, and the

corresponding TA is up to 219. For the time being, except

for GSM 400 MHz system, other GSM systems do not

support TA that is larger than 63.


Ult Di t C T h l


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Radio Interface Restrictions

In GSM system, each carrier adopts the TDMA mode,

that is, eight timeslots constitute a frame, and the eight

timeslots correspond to eight physical channels

respectively, as shown in Figure.

TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0TS0TS7 TS1

Frame

Time Axis


Ult Di t C T h l


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During the call process, one user occupies one timeslot (time

window), and at the base station, each timeslot corresponds to

a user. Thus the MS-sent data that is received by the base

station can only fall into the users time window, otherwise, the

next channel will be influenced.

If MS is in the idle status, it does not know the distance from it

to BTS. Therefore, when sending the first access request, MS

takes its own time window as reference. Because delay exists

in space transmission, the time window has a certain offset

when the MS signal actually reaches BTS, that is, delay exists .


Ult Di t C T h l


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The length of a TA is one byte. As specified in GSMprotocols, both GSM 900 MHz system and GSM 1800

MHz system uses six bits to send the TA and the other

two bits are reserved. Thus the maximum TA value is 63,

i.e. 63 bits, of which each bit equals 3.69 ms.

The space transmission delay includes uplink delay and

downlink delay (the uplink distance equals the downlink

distance). The signal is transmitted at the velocity of light.

The maximum coverage radius is calculated as follows:

(63 3.69 10-6) 3 10 8/ 235 km



Ultra Distance Coverage Technology


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Thus for GSM 900 MHz system and GSM 1800 MHz system,

the maximum coverage radius is specified as 35 km in GSM

protocols. The following lists the restrictions:

1. Restrictions of Access Burst (AB) For the AB of MS, MS sends it according to its own time

reference TA = 0. If the distance between MS and BTS exceeds

35 km, then even the significant bits (0~87) of AB can not fall into

the same timeslot completely. According to the common methodsspecified in GSM protocols, BTS can not decode the AB. In other

words, if MS is more than 35 km away from BTS, it can not

access the network, which then causes subsequent ABs unable

to be decoded.




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2. Restrictions of MSs TA adjustment capability

After MS accesses the network successfully, Normal Burst

(NB) is sent on the traffic/signaling channel. If the distance

between MS and BTS exceeds 35 km, BTS can not adjust

the MSs sending time, which inevitably interferes the

running of other MSs on other timeslots.




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Restriction of upper-layer signaling:

In layer-3 signaling, TA is used by some messages. The

GSM 900 MHz system and GSM 1800 MHz system only

support TA 63, thus when TA > 63, the handling for

abnormal signaling flow is initiated.

The messages are restricted by the condition TA 63, thus

if TA > 63, the normal signaling processing will be

influenced.




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Breakthrough Methods

There are two methods to break the restriction of coverage distance

specified in GSM protocols (i.e. the maximum TA is 63, or the maximum

coverage radius of GSM 900 MHz system and GSM 1800 MHz system is

35 km). Breakthrough method 1

Adopts GSM 400 MHz system, or realizes the method specified in GSM 400

MHz system in GSM 900 MHz system.

Breakthrough method 2

BTS adopts the special radio channel mapping technology and improved

BTS receiving technology at radio interface, to guarantee there is no mutual

interference between BTSs.




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Breakthrough method 1:

According to GSM protocols, only the GSM 400 MHz system can

have TA that is larger than 63 and the maximum TA value is 219.

For GSM 400 MHz system, two frequency bands are defined in

GSM protocols: GSM 450 MHz and GSM 480 MHz. As to date,

the GSM 400 MHz system has not been commercialized.

The following lists the advantage and disadvantage of

breakthrough method 1:




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Advantage

Since the specification in GSM protocol is broken through,

there is no capacity limit when realizing a coverage

distance larger than 35 km.

Disadvantage

Because the GSM 900 MHz MS does not adapt to GSM

400 MHz system, appropriate MS is required, but it is

difficult to realize in actual applications.




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Breakthrough method 2:

If the coverage radius exceeds 35 km, then MS must

support TA > 63. However, the maximum TA recognized by

GSM 900 MHz MS is 63 bits. It is impossible to upgrade all

MSs, thus the restriction that the maximum coverage radius

is 35 km can be broken through by applying special radio

channel mapping technology and improved BTS receivingtechnology at the radio interface. In other words, BSS

should be upgraded.




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The following lists the advantage and disadvantage of

breakthrough method 2:

Advantage

It is easy to be applied because no change should be made

in MS and the cost is low.

Disadvantage

A certain system capacity is sacrificed. In normal cases,one carrier provides eight channels. If the coverage area is

very large, there might not be eight channels. The number

of channels depends on specific networking solutions.



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Contents

HR Services


EDGE Technology


EDGE Technology


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Definition

Enhanced Data for GSM Evolution (EDGE) includes Enhanced

General Packet Radio Service (EGPRS) and Enhanced Circuit

Switched Data (ECSD). EDGE is a method used to improve the data

transmission rate during GSM radio connection.

Essentially, EDGE is only a new modulating and channel encoding

technology, which can be used to transmit Packet switching (PS)

and Circuit Switching (CS) data/voice. As an evolved GPRS-to-

UMTS solution, EDGE enables the network operator to use currentradio network equipments to the maximum extent. It also provides

PC multimedia communication services ahead of time before the

third generation mobile network become commercialized.

EDGE Technology

EDGE Technology


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Feathers

The system architecture of EDGE network is similar to

that of GSM network. The following lists features of the

EDGE technology in the access service and network

establishment:

1. Access service

The bandwidth is increased greatly. The peak transmission

rate of mobile data service is up to 384 kbps.

It provides more precise network-layer positioning service.

EDGE Technology

EDGE Technology


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Feathers

2. Network establishment

As a modulating and encoding technology, EDGE changes

the transmission rate at the air interface.

EDGEs air interface features, including the air channel

allocation mode and TDMA frame structure, are the same

as those of GSM.

EDGE does not change the architecture of GSM network or

GPRS network, and does not have new NEs. It only

updates BSS

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EDGE Technology


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Feathers

The core network adopts the three-layer model: service

application layer, communication control layer, and

communication connection layer. The interface between

layers is standard. The hierarchical architecture makes

the call control and communication connection mutually

independent. It also fully uses advantages of the packet

switching network, making the bandwidth allocation

closely related to the traffic. It especially suits the VoIP

service.

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EDGE Technology


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Feathers

Media Gateway (MGW) is adopted in EDGE. MGW has

the same functions as Signaling Transfer Point (STP),

and can realize the signaling network establishment in IP

network. Moreover, MGW is not only the interface

between GSM circuit switching service and PSTN but

also the interface between Radio Access Network (RAN)

and 3G core network.

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EDGE Technology


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Feathers

EDGE supports two data transmission modes: packet

switching and circuit switching. With the packet data

service, a rate of 11.2 kbps ~ 69.2 kbps per timeslot can

be realized. EDGE supports the circuit switching service

with a rate of 28.8 kbps. EDGE also supports

symmetric/asymmetric data transmission, which is very

important for the mobile equipment to access network.

For example, in EDGE system, the user can have a

higher rate in downlink than in uplink.

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EDGE Technology


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Specifications

The EDGE standardization involves the following three

aspects:

Standardizes the relevant change in physical layer (the

definition of modulation and coding method)

Standardizes the change in ECSD protocol

Standardize the change in EGPRS protocol

EDGE Technology


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Specifications

EDGE is realized in two phases:

Phase 1: provides the single/multiple-timeslot packet

switching service with a rate of less than 64 kbps and the

single/multiple-timeslot circuit switching service.

Phase 2: provides real-time services not included in phase

1 and adopts the new modulating technology.

EDGE Technology


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Key technologies

EDGE modulation mode

EDGE adopts 8-PSK as its modulation mode. 8-PSK has

the same modulation quality as GMSK, considering the

interference generated from adjacent channels. It enables

EDGE channels to be completely integrated in the current

frequency planning, and can allocate the new EDGE

channel as standard GSM channel.

EDGE Technology


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Key technologies

Radio block structure

EDGE Technology


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Key technologies

Channel coding

The nine MCSs of EDGE are categorized into three groups

according to their characteristics:

Family A (MCS-3, MCS-6, MCS- 8, MCS-9)

Family B (MCS-2, MCS-5, MCS-7)

Family C (MCS-1, MCS-4)

For coding scheme structures in the same group, either one

structure includes another or being included by another, which

makes it easy to realize conversion between coding rates.

EDGE Technology


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Key technologies

In practical applications, balance should be kept between

the transmission rate of valid information and the valid

transmission quality. The low-rate channel coding

scheme, which contains many redundancy error

correction codes but without transmitting much valid

information, is suitable for an environment with poor

transmission quality.

EDGE Technology


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Key technologies

For example, on the edge of a cell, the low-rate GMSK

modulation method MCS1 ~ 4 is more suitable for

compensating poor link quality; in the central area of a

cell where propagation conditions are good, the high-rate

MCS is often adopted.


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Contents

HR Services


EDGE Technology




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Satellite Transmission Features and Solutions

The following problems will be encountered when the

satellite link is used to realize transmission between BTS

and BSC.

The delay of Abis link is long. The information sent from

the satellite ground station is transferred through the

satellite and then received by another ground station. The

end-to-end delay is not less than 260 ms, which does not

have much to do with the ground stations position.



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BER The satellite links BER is much larger than that of the ground

link. Because of this factor and the influence of fading, the BER

change is very large. On the other hand, the large delay and

BER on the transmission link will cause the message throughput

to drop.

Clock

The precision of the satellite Abis clock is not very good. The above problems do not occur when the ground link is used

to realize transmission between BTS and BSC, thus they should

be resolved first.



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Solution:

BTS clock

Because the precision of the clock extracted from Abisinterface is much less than the clock precision specified in

GSM protocols, such a clock is not used to synchronize

BTS any more. Instead, when using the satellite link to

connect Abis interface, the high-precision clock source

inside BTS is often used as BTS clock source. In other

words, the inner clock of BTS is used for synchronization.



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Protocol timer

Adjust the interval of timers in some BTS/BSC protocols to

make these protocols to adapt to large delay. The LAPD

timer of Abis is influenced most.



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ZXG10-BSS Satellite Abis Principles

ZXG10-BTS realizes the satellite Abis by setting

transmission modes through setting DIP switches at BTS.

According to the DIP switch setting, BTS sets

corresponding inner processing modes. BSC

automatically identifies the BTS processing mode and

performs relevant processing.

In order to save the cost of satellite transmission, the

satellite Abis often adopts Abis multiplexing mode to

reduce the number of timeslots at Abis interface.


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Thank you

GBC 006 E1 1 GSM Advanced Technology-49

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