gsm flex abis solution

8/19/2019 GSM Flex Abis Solution

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GSM Flex Abis Solution White Paper

1 Background Introduction

Under the intense competition situation, operators are eager for the solution that can reduce

OPEX and increase profits. Transmission resources cover one fourth of the whole operating

expenditure. To help reduce the expenditure of transmission resources, Huawei provides the Flex

Abis solution to improve the transmission efficiency.

For the common BSC, the transmission resources on the Abis interface are distributed in a fixed

way, that is, the timeslot resources on the Abis interface correspond to the TCH resources on the

Um interface based on configurations.

In actual situations, the CS service and PS service in different BTSs and cells may be busy in

different time periods. Sometimes one BTS is busy and another BTS is idle, or sometimes the PS

service is busy and the CS service is idle. Therefore, the resource utilization can be improved if

the Abis resources are shared between different BTSs/cells or between different types of services.

Especially for multi-cell large capacity BTSs, cascaded BTSs, and the cells configured with the

EDGE function, the dynamic Abis resource allocation can greatly improve resource utilization.

For this purpose, Huawei provides the Flex Abis solution to share the Abis resources among

different BTSs, cells, and services. When the transmission resources are limited, this solution

helps operators to reduce operating expenditure.

2 Huawei Flex Abis Solution

2.1 Principles

In Huawei Flex Abis solution, the Abis transmission resources corresponding to the PS service

and CS service in all the cells under a BTS and in all the cascaded BTSs are included in a

resource pool for centralized management and sharing. This can greatly improve the utilization of

transmission resources.

The following describes the Flex Abis solution:

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GSM Flex Abis Solution Whitepaper For internal use only

2009-3-26 Huawei Technologies Proprietary of 5

1. Flex Abis used in PS domain

Site Type: S4/S4/S4, Transmission:1 E1, Site Slave TS: 27, Cell:1 Static PDCH, 8 Dynamic PDCH

9.05

13.4

15.6

21.4

Abis Transmission Cost

Kbits/s 50 40 30 20 1060

MCS1

MCS2

MCS3

MCS4

MCS5

MCS6

MCS7

MCS8

MCS9

CS1

CS3

CS4

CS2

8.4

11.2

14.8

17.6

22.4

29.6

44.8

54.4

59.2

0 16 32 48 64 80

User data rate A-bis data rate

HUAWEIGMSK

Others

8PSK

Um Interface Requirement

Site Type: S4/S4/S4, Transmission:1 E1, Site Slave TS: 27, Cell:1 Static PDCH, 8 Dynamic PDCH

9.05

13.4

15.6

21.4

Abis Transmission Cost

Kbits/s 50 40 30 20 1060

MCS1

MCS2

MCS3

MCS4

MCS5

MCS6

MCS7

MCS8

MCS9

CS1

CS3

CS4

CS2

8.4

11.2

14.8

17.6

22.4

29.6

44.8

54.4

59.2

0 16 32 48 64 80

User data rate A-bis data rate

HUAWEIGMSK

Others

8PSK

Um Interface Requirement

Figure 1 Flex Abis (PS)

In PS domain, the transmission resources on the Abis interface are allocated based on 16 kbit/s

sub-timeslot. A main timeslot is allocated to the PDCP, and then additional timeslots are allocated

in steps of 16 kbit/s based on the required coding rate on the Um interface. Under normal

conditions in the industry, the transmission resources are allocated based on 64 kbit/s or 32 kbit/s

timeslot, while Huawei uses the 16 kbit/s timeslot, which greatly improves the bandwidth

utilization.

For example, as shown in Figure 1, if the Um interface uses the GMSK modulation mode and

MCS2 coding scheme, 16 kbit/s transmission resources on the Abis interface are required in

Huawei Flex Abis mode, while in other resource allocation mode, 32 kbit/s or 64 kbit/s

bandwidth is required. As shown in the red circle in Figure 1, about 50% transmission resources

are saved in Flex Abis mode.

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2. Flex Abis used in CS domain

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No

Flex Abis

With

Flex Abis

TRX1

TRX2

Fixed Dynamic

occupied Idle

Figure 2 Flex Abis (CS)

In CS domain, the TRXs correspond to the Abis resources in the traditional resource allocationmode. Abis resource must be allocated to a TRX even if this TRX is idle. In Flex Abis mode, the

timeslot transmission on the Abis interface uses the resource pool mode. Abis resource is

allocated to a TRX only when the TRX is busy. This can improve the utilization of Abis

resources. Except for synchronization timeslot (TS0), RSL timeslot (radio signaling link), and

OML timeslot (operation and maintenance link), all the other Abis resources are included in the

Abis Pool.

2.2

Features

1. Support for the resource allocation based on 16 kbit/s timeslot in the PS domain

2. Support for the HR assignment on the Abis interface in the CS domain

In Huawei Flex Abis solution, the assignment of half-rate channels on the Abis interface can be

triggered based on the load of the Abis resources in the CS service. The minimum transmission

resource for allocation is 8 kbit/s. When the resource utilization on the Um interface does not

reach the congestion threshold but the transmission resource utilization has reached the








congestion threshold, 8 kbit/s half-rate channels on the Abis interface are assigned to improve the

utilization of Abis resources.

3. Support for Abis timeslot resources shared by PS service and CS service

Huawei Flex Abis supports the sharing of Abis timeslot resources between the PS service and the

CS service. Special algorithm is designed to balance the Abis resources between the PS service

and the CS service. In Flex Abis solution, a certain number of Abis resources are allocated to the

PS service to ensure the Qos for some PS service users. These Abis resources can be assigned

with fixed timeslots or dynamically reserved. The latter is better in terms of resource utilization.

4. Support for dynamic allocation among BTSs or cells

Link 0 Link 1 Link 2

B

T

S

Site0

B

T

S

Site1

B

T

S

Site2

Pool 0Pool 1

Pool 2

B

S

C

Figure 3 Support for dynamic allocation among BTSs or cells

Huawei Flex Abis solution supports the dynamic allocation of Abis resource among the cells and

BTSs . Figure 3 shows the resource sharing among three BTSs in chain topology. The resource

sharing for other types of topologies is similar to the chain topology. The resources on links 0, 1,

and 2 form Pools 0, 1, and 2. Link0, Link1, and Link2 indicate the Abis transmission links

between the BSC and Site0, between Site0 and Site1, and between Site1 and Site 2 respectively.

The links can be in E1, T1, or satellite transmission mode Pool 0 is shared by the CS service and

PS service in sites 0, 1, and 2. Pool 1 is shared by the CS service and PS service in sites 1 and 2.

Pool2 is shared by the CS service and PS service in Site2.

2.3 Scenarios

To fully utilize the Flex Abis function and improve resource utilization to the largest extent,

Huawei recommends that the Flex Abis function be applied in the following scenarios:

1. Areas with limited transmission resources and high rents, such as satellite transmission

2. Cells sharing Abis resources and having different reaching peak hours

3. Cells with high ratio of PS service users. Under certain conditions, the PS service and the CS

have different peak hours. The resource utilization can be improved if the PS service and the CS

service share Abis resources.

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4. Scenarios where users are insensitive to the influence of Abis interface congestion to services

In Flex Abis solution, the BSC needs to notify the BTS of the resource allocation through

additional signaling. This increases the load of signaling on the Abis interface. In addition, the

reliability of dynamic allocation is lower than the fixed allocation. Therefore, Huawei

recommends that the Flex Abis function be used only when the transmission resources on the

Abis interface is very limited.

3 Latest Development

Nowadays, the telecommunication field tends to focus on how to improve the utilization of Abis

resources. Some vendors have offered similar solutions in the PS domain, but not in the CS

domain. Some vendors have offered similar solutions in both the PS domain and the CS domain,

but not in multiple BTSs.

Huawei Flex Abis solution achieves the resource sharing in the PS domain, CS domain, and

multiple BTSs in different scenarios. This can greatly improve the utilization of Abis resources,

reduce the network construction and maintenance costs, and avoid transmission congestion on the

Abis interface.

In September 2007, Huawei BTS series, such as BTS3012, BTS3012AE, BTS3006C, and

BTS3002E of version GBSS7.0 will support the Flex Abis solution.

Copyright2007 Huawei Technologies Co., Ltd. All Rights Reserved.

The information contained in this document is for reference purpose only, and is subject to

change or withdrawal according to specific customer requirements and conditions.




gsm flex abis solution

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