8 Topologies of the Macro NodeB

About This Chapter

The topology of the macro NodeB refers to the topology of the transmission over the Iubinterface, that is, the topology of the transmission channels between the NodeB and the RNC.The macro NodeB supports multiple topologies, such as star, chain, tree, cascading RRUs, hubNodeB, and co-transmission with 2G and 3G equipment to meet the requirements of differentscenarios.

8.1 Star TopologyAs the most commonly used topology, the star topology applies to most areas, especially todensely populated areas.

8.2 Chain TopologyThe chain topology applies to the belt-shaped and sparsely populated areas, such as highwaysand railways.

8.3 Tree TopologyThe tree topology applies to complicated networks and sites such as a large area withconcentrated hot spots.

8.4 2G/3G Co-transmissionThe NodeB supports the Fractional ATM and CES, which enables 2G/3G co-transmission andreduces investment in transmission resources.

8.5 Topology of the Hub NodeBThe NodeB supports the topology with the hub NodeB. The hub NodeB converges thetransmission bandwidth of the lower-level NodeBs.

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8.1 Star TopologyAs the most commonly used topology, the star topology applies to most areas, especially todensely populated areas.

Figure 8-1 shows this topology.

Figure 8-1 Star topology

Advantages:

l The NodeB is directly connected to the RNC. Therefore, the star topology featuressimplicity, convenience in maintenance, engineering, and capacity expansion.

l Direct data transmission is built between the NodeB and RNC and signals travel throughfewer nodes, which gives higher transmission reliability.

Disadvantage: Compared with other topologies, the star topology requires more transmissionresources.

8.2 Chain TopologyThe chain topology applies to the belt-shaped and sparsely populated areas, such as highwaysand railways.

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Figure 8-2 shows this topology.

Figure 8-2 Chain topology

Advantage: The chain topology can reduce costs in transmission equipment, engineering,construction, and transmission link lease.

Disadvantages:

l Signals travel through many nodes, so the transmission reliability is low.

l Faults in the upper-level NodeB may affect the lower-level NodeB(s).

l The number of levels in the chain topology cannot exceed five.

8.3 Tree TopologyThe tree topology applies to complicated networks and sites such as a large area withconcentrated hot spots.

Figure 8-3 shows this topology.

Figure 8-3 Tree topology

Advantage: The tree topology requires fewer transmission links than star topology.

Disadvantages:

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l Signals travel through many nodes, which causes low transmission reliability andconstruction and maintenance difficulties.

l Faults in the upper-level NodeB may affect the lower-level NodeB(s).

l Capacity expansion is difficult because it may involve major modification to the networkarchitecture.

l The number of levels in the tree topology cannot exceed five.

8.4 2G/3G Co-transmissionThe NodeB supports the Fractional ATM and CES, which enables 2G/3G co-transmission andreduces investment in transmission resources.

Fractional ATM

In the Fractional ATM mode, some of the 32 timeslots in an E1/T1 link are used for ATM celltransmission. That is, the ATM cells are mapped to some of the 30 timeslots (timeslots 0 and 16already reserved) at the TX end and then recovered from those timeslots at the RX end.

The scenarios of 2G/3G co-transmission in the Fractional ATM mode are as follows:

l The operators have GSM mobile networks. It is possible to use current transmissionnetwork resources to build 3G networks.

l The RNC and NodeB support the Fractional ATM.

l The BSC and BTS or external timeslot cross devices support timeslot cross connection.

Figure 8-4 shows the 2G/3G co-transmission in Fractional ATM mode.

Figure 8-4 2G/3G co-transmission in Fractional ATM mode

Advantages: The 2G/3G co-transmission helps operators speed up WCDMA construction andoffering services. It saves the transmission resources and reduces investment in the initial phaseof WCDMA construction.

Disadvantages: The 3G equipment is dependent on the 2G equipment, whose stability andupgrade affect the stability of 3G services.

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CES

The Circuit Emulation Service (CES) uses the technology that emulates the TDM circuit in theATM network. The CES enables the narrowband signals to be transmitted in the widebandsystem. In the CES mode, 2G systems may use the 3G ATM transmission devices to transmit2G services.

The scenarios of 2G/3G co-transmission in CES ATM mode are as follows:

l When the transmission resources of the 2G network are insufficient, 2G systems can usethe ATM transmission devices to transmit services through CES mode.

l The RNC and NodeB must support the CES.

Figure 8-5 shows the 2G/3G co-transmission in the CES mode.

Figure 8-5 2G/3G co-transmission in the CES mode

Advantages:

l The 2G/3G co-transmission in CES mode reduces costs of transmission and networkmaintenance.

l No timeslot cross device is required on the NodeB side, which reduces the costs andenhances system reliability.

l The transmission over the ATM network enhances the usage of the transmission resourcesand ensures the performance of the CS real time services as well as the sequence of thetimeslot data.

Disadvantages:

l The CES mode applies to mature 3G networks with enough bandwidth on the Iub interfacebecause it occupies more bandwidth on the interface.

l The CES port resource is limited on the RNC side.

l The 2G equipment is dependent on the 3G equipment, whose performance affects thestability of the 2G services.

l The encapsulation and decapsulation during the circuit emulation introduces delay anddelay variation, which affect the QoS of the 2G services.

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8.5 Topology of the Hub NodeBThe NodeB supports the topology with the hub NodeB. The hub NodeB converges thetransmission bandwidth of the lower-level NodeBs.

The hub NodeB integrates the functions of transmission device. Thus the hub NodeB canconverge the transmission data of the lower-level NodeBs. Figure 8-6 shows the topology withthe hub NodeB.

Figure 8-6 Topology of the Hub NodeB

Advantage: The hub NodeB converges the transmission data of the lower-level NodeBs. Thusthe transmission resources are more effectively used.

Disadvantage: Faults in the hub NodeB may affect the running of the lower-level NodeBs.

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