Node-B

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Node-B is a term used in UMTS to denote the BTS (base transceiver station). In contrast with GSM base stations, Node B uses WCDMA as air transport technology. As in all cellular systems, such as UMTS and GSM, Node B contains radio frequency transmitter(s) and the receiver(s) used to communicate directly with the mobiles, which move freely around it. In this type of cellular networks the mobiles cannot communicate directly with each other but have to communicate with the BTSs. [1]

1 Functionality
2 Differences between a BTS and a Node B
- 2.1 Frequency use
- 2.2 Power requirements
3 Node B setup

[edit] Functionality

Traditionally, the Node Bs have minimum functionality, and are controlled by an RNC (Radio Network Controller). However, this is changing with the emergence of High Speed Downlink Packet Access (HSDPA), where some logic (e.g. retransmission) is handled on the Node B for lower response times.

[edit] Differences between a BTS and a Node B

[edit] Frequency use

The utilization of WCDMA technology allows cells belonging to the same or different Node Bs and even controlled by different RNC to overlap and still use the same frequency (in fact, the whole network can be implemented with just one frequency pair). The effect is utilized in soft handovers.

[edit] Power requirements

Since WCDMA often operates at higher frequencies than GSM, the cell range is considerably smaller compared to GSM cells, and, unlike in GSM, the cells' size is not constant (a phenomenon known as "cell breathing"). This requires a larger number of Node-Bs and careful planning in 3G (UMTS) networks. Power requirements on Node Bs and UE (user equipment) are much lower.

[edit] Node B setup

A full setup contains a cabinet, an antenna mast and actual antenna. An equipment cabinet contain e.g. power amplifiers, digital signal processors and back-up batteries. What you can see by the side of a road or in a city center is just an antenna. However, the tendency nowadays is to camouflage the antenna (paint it the color of the building or put it into an RF-transparent enclosure). Smaller indoor solutions may have a built-in antenna on the cabinet door.

A Node B can serve several cells, also called sectors, depending on the configuration and type of antenna. Common configuration include omni cell (360°), 3 sectors (3x120°) or 6 sectors (3 sectors 120° wide overlapping with 3 sectors of different frequency).