combining blocks & motorola's architecture

Combining blocks for GSM900/1800

Twin Duplexing Filter (TDF)

Twin Duplexing Filter (TDF): A module that can filter 2 TRX from the same cell or from different cell to provide maximum output power in rural area. Also provides duplexing of the transmit output with 1 receive input each.

This equipment provides the final stage of filtering in either an GSM900 or GSM1800 Base station transmitter lineup. Due to this positioning, the filter provides a guaranteed performance over the whole frequency band defined for spurious emissions in GSM900/GSM1800. Both inputs are separately filtered with a Bandpass filter before being routed to the output ports of the unit.

The Twin TDF is capable of proper operation with an average signal power of 60 watts incident upon each of its input, and its output being presented with a termination of VSWR.

This element is particularly adapted for air combining

Twin Duplexing Filter (TDF)

The TDF transmit insertion is typically 1.4 dB for GSM900.The TDF transmit insertion is typically 1.1 dB for GSM1800.

Motorola Confidential & Proprietary of 16 Nov 2002

Duplexer/Bandpass

Filter

Ant1

Tx2 Tx1

Duplexer/Bandpass

Filter

Ant2Rx1Rx2

TRX Hybrid combining

This can be achieved using the three following elements: the 2 input Duplexed Combining Filter module (DCF), and the 3 input Dual-stage Duplexed Combining Filter (DDF), and the 2 Input Hybrid Combiner Unit (HCU). By connecting the output of the Hybrid combiner module to the “ input 3 ” of the 3 Input DDF, 4 TRXs can be coupled on one antenna.

Two input Duplexed Combining Filter module (DCF)

This combining filter block provides the final stage of filtering in either an GSM900 or GSM1800 Basestation transmitter lineup. Due to this positioning, the combining filter provides a guaranteed performance over the whole frequency band defined for spurious emissions in GSM900/GSM1800.

The unit consists of one 3dB hybrid coupler, which provides the combining properties with the unused port of the coupler being terminated with a suitable load capable of dissipating power.

The output is filtered with a bandpass filter which is part of the receive duplexer. A single receive input is fed into the duplexer and combined with the two transmit feeds.

Two input Duplexed Combining Filter module (DCF)

The DCF transmit insertion is typically 4.4 dB for GSM900.The DCF transmit insertion is typically 4.1 dB for GSM1800.


Hybrid Combiner

Duplexer/Bandpass Filter

Rx Ant

Tx2 Tx1

Load

Three input Dual-stage Duplexed Combining Filter (DDF)

This combining filter block provides the final stage of filtering in either an GSM900 or GSM1800 Basestation transmitter lineup. Due to this positioning, the combining filter provides a guaranteed performance over the whole frequency band defined for spurious emissions in GSM900/GSM1800.

The unit consists of two 3dB hybrid coupler, which provides the combining properties with the unused ports of each coupler being terminated with a suitable load capable of dissipating power.

The output is filtered with a bandpass filter which is part of the receive duplexer. A single receive input is fed into the duplexer and combined with the two transmit feeds.

Three input Dual-stage Duplexed Combining Filter (DDF)

At GSM 900 the DDF transmit insertion loss is typically 7.6 dB for Tx1, Tx2, and 4.4 dB for Tx3.At GSM 1800 the DDF transmit insertion loss is typically 7.5 dB for Tx1, Tx2, and 4.3 dB for Tx3.


Hybrid Combiner

Duplexer/Bandpass Filter

Rx Ant

Tx2 Tx1

Tx3

Hybrid Combiner

Load

Load

Two Input Hybrid Combiner Unit (HCU)

The output of this module connects into the Input 1 of the three input CBF. Inputs are through the

roof cut outs as in the original two input CBF.

At GSM 900 the HCU transmit insertion loss is typically 3.3 dB.At GSM 1800 the HCU transmit insertion loss is typically 3.25 dB.

The transmit combining filters are capable of proper operation with an average signal power of 60 watts incident upon each of its input, and its output being presented with a termination of VSWR.


Hybrid Combiner

Output(to Tx3 of DDF block)

Tx2 Tx1

Load

Different Configurations and Diagrams

1/1/1 DCF Combining (proposed):


2/2/2 DCF Combining (proposed):


2/2/2 TDF Combining:


3/3/3 DCF & Air Combining (proposed):


3/3/3 DDF (Three RF Cabinets):


4/4/4 DCF & Air:


4/4/4 DDF & HCU:

1/3/2 DCF & TDF (non-standard config):


Motorola’s A rchitecture and its Advantages


Cellular operators have consistently reported that transmission accounts for a significant proportion (perhaps 20-30%) of operating costs. With increasing network capacity requirements and adoption of smaller cell size technologies this proportion is unlikely to decrease. Accordingly optimizing transmission costs is an important area and one in which Motorola has placed considerable emphasis.

Motorola’s strategy has two dimensions:

An efficient network architecture that minimizes the required bandwidth and length of links.

A portfolio of interconnection technologies to minimize costs in every situation.

Motorola advantages: a combination of Mobis interface, Distributed BSC Approach, and Drop and Insert.

The Mobis interface

The Motorola defined BSC-to-BTS interface is a modification of the Abis standard called Mobis. It distributes functionality between the BSC and the remote BTS equipment, and offers several advantages:

• Reduced signaling link traffic, which permits efficient use of E1/T1 links. The BTS performs handover data processing. This reduces the amount of data sent to the BSC over the signaling link. This significantly reduces the amount of processing required in the BSC.

• Better Synchronization of the BSC and BTS. This ensures better handover from one traffic channel to another.

• Improved overload control and fault recovery algorithms.

• Efficient use of the paging and access grant channels.

• Control of more than one BTS (sectors) on a single control link.

Table 1 shows the significant reduction in the number of 64 kbit/s signaling channels that can be achieved by using the Motorola BTS-BSC interface compared to the current GSM A-bis. It has been assumed that 25% of the sites are 3 sector sites and the remainder omni configures sites.

Number of sites GSM BTS/BSC

Motorola BTS/BSC

64 kbit/sChannel saving


Signaling Channels

Signaling Channels

100 150 100 50200 300 200 100400 600 400 200

Table 1. - Comparison of the GSM A-bis and the Motorola A-bis.

The reduction in control and signaling on the 2.048 Mbit/s links provides better traffic utilization, reduced blocking and increased grade of service to the subscriber. It allows a more efficient and cost effective BSC traffic concentration through the use of distributed BSC’s and passes cost savings onto the customer which ultimately provides a higher quality of network.

Distributed BSC and Remote Transcoding

Installation and rental charges for ‘Leased Lines’ and many other transmission products are related to the length of the circuit involved. By distributing the BSC away from the MSC but closer to the deployed cell sites the number of long links is greatly reduced. This translates directly into monthly cost savings. The approach is made feasible by Motorola’s BSC products that are much smaller and less expensive than competitive equivalents.

A further feature is to retain the Transcoder at the MSC (i.e. ‘Remote’ Transcoding) by this means the required bandwidth to the switching site is reduced by a factor of four.

In the example below a conventional arrangement (shown below left) requires 20 long links. The Motorola solution (shown below right) requires just 5 long links and 19 short links.

XCDR

BSCMSC XCDR

BSC

20 long links5 long links19 short links

Not only do short links equate to lower monthly charges but they also enable alternate technologies, such as HDSL and Free Space Optical Links, to be deployed. These are covered later in this document.

Further savings may be made by exploiting trunking efficiency between the Transcoder and BSC. This would involve equipping the link with less than the specified full bandwidth requirement but accepting a modest level of blocking.

Daisy Chaining Loops and Forks


BTSs connected in a star topology lead to high transmission costs due to the longer link length. The Motorola BTS products can be connected in ‘Daisy Chains’, ‘Forks’ and, if redundancy is required, ‘Loops’. Where possible a BTS multiplexes its own traffic with that of downstream BTSs onto a single transmission link. At each stage the transmission link becomes more fully utilized. The real example below shows how these techniques can benefit a network.

Simulated star network with co-locatedBSC/MSC

100 E1 links, total link distance 860 km

Equivalent network with distributed BSC,remote Transcoding and daisy chaining111 E1 links, total link distance 295 km= 68% reduction in transmission length

25 k

m

In this example the transmission costs were reduced by 48% due to the reduced link lengths and bandwidths required.

Note that, using the appropriate procedures, BTSs may be added (insert) and removed (drop) from the network without disruption to services.

Timeslot Reservation and Nailed Connection

Timeslot reservation enables configurable blocks of timeslots within a link to be excluded from use by cellular traffic. This allows unrelated data, such as from a paging network, to share the transmission bandwidth using external multiplexer equipment.

A complementary feature is ‘Nail Connects’ where the BTS’s themselves perform the function of the multiplexer and demultiplexer removing the requirement for additional external equipment.


NetworkElement

NetworkElement

NetworkElement

NetworkElement Mux/

Demux

Mux/Demux

GSM/DCSRF Network

Paging SystemRF Network

SharedTransmission

Network

The outcome is two (or even three) networks implemented for the transmission costs of one network.

Summary of Advantages:

Motorola BSS architectural features minimize backhaul transmission costs through the following:

Support for distributed BSC Remote Transcoding with 4:1 sub-multiplexing BTS daisy chaining, loops, forks Minimal site signaling to intelligent BTS’s Sharing transmission lines using

Timeslot reservation Nailed Connects

Transmission represents a major proportion of a GSM network’s operating cost, Motorola offer a competitive network architecture leading to:

Fewer expensive long links Fewer timeslots required Shorter links required (opens up technology choice and reduces costs) Less bandwidth required


combining blocks & motorola's architecture

Documents

combining filter

filter ddf

input ddf

bandpass filter

combining properties

filter block

filter module dcf

input dualstage