Radio Access Networks for UMTS: Principles and Practice

The Node B conﬁguration deﬁnes characteristics such as the number of sectors and the number of

RF carriers. The most common conﬁguration for initial network deployment is three sectors with one

RF carrier. This is known as a 1þ1þ1 Node B conﬁguration. It requires at least three antennas to be

connected to the Node B cabinet, i.e. at least one antenna serving each sector. If uplink receive diversity

or downlink transmit diversity is used then either six single element antennas or three dual element

antennas are required. If six single element antennas are used then there should be spatial isolation

between the two antennas belonging to each sector. This tends to be less practical than using three dual

element antennas. It is common to use cross polar antennas which accommodate two antenna elements

within each antenna housing. In this case, isolation is achieved in the polarisation domain rather than

the spatial domain. Figure 1.5 illustrates an example 1þ1þ1 Node B conﬁguration using cross polar

antennas.

When diversity is used then a separate RF feeder is required for each diversity branch. A 1þ1þ1

Node B with uplink receive diversity requires six RF feeders to connect the antennas to the Node B

cabinet. Likewise, if Mast Head Ampliﬁers (MHA) are used then six of them would be required. The

þ1þ1 Node B conﬁguration has three logical cells, i.e. a logical cell is associated with each sector of

the Node B. When the capacity of a single RF carrier becomes exhausted then it is common to upgrade

to a second RF carrier. The Node B conﬁguration is then known as a 2þ2þ2. This conﬁguration has

three sectors, but now has two RF carriers and six logical cells. Alternatively, a six sector single RF

carrier conﬁguration could be deployed which would be known as a 1þ1þ1þ1þ1þ1. This conﬁguration

also has six logical cells but has six sectors and 1 RF carrier.

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