Capacity Management and Its functions- WCDMA

Capacity Management is responsible for the control of the load in the cell.

It consists of 3 main functions:

1. Dedicated Monitored Resource Handling: tracks utilization of critical resources of the system.

2. Admission Control: accepts/refuses admission requests based on the current load on the dedicated monitored resources and the characteristics of the request

3. Congestion Control: detects/resolves overload situations.

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Is UMTS an Uplink limited or Downlink limited System?

Initially, A typical WCDMA network is Uplink Limited. Later a Loaded Network becomes Downlink Limites.

Downlaod Document on RRC KPIs

What is Cell Breathing and why?

The cell coverage shrinks as the loading increases, this is called cell breathing.

In the uplink, as more and more UE are served by a cell, each UE needs to transmit higher power to compensate for the uplink noise rise. As a consequence, the UE with weaker link (UE at greater distance) may not have enough power to reach the NodeB – therefore a coverage shrinkage.

In the downlink, the NodeB also needs to transmit higher power as more UE are being served. As a consequence UE with weaker link (greater distance) may not be reachable by the NodeB.

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What is Compressed Mode?

Compressed mode is a physical layer function that allows the UE to temporarily tune to another frequency, and measure the RF environment of another UMTS frequency (e.g. IFHO) or another technology (e.g. IRAT), while maintaining an existing dedicated channel.

Download WCDMA IRAT Handover Document.

What is Pilot Pollution?

Simply speaking, when the number of strong cells exceeds the active set size, there is “pilot pollution” in the area. Typically the active set size is 3, so if there are more than 3 strong cells then there is pilot pollution.

Definition of “strong cell”: pilots within the handover window size from the strongest cell. Typical handover window size is between 4 to 6dB. For example, if there are more than 2 cells (besides the strongest cell) within 4dB of the strongest cell then there is pilot pollution.

Download E Book on WCDMA for UMTS Networks.

What is “noise rise”? What does a higher noise rise mean in terms of network loading?

For every new user added to the service, additional noise is added to the network. That is, each new user causes a “noise rise”. In theory, the “noise rise” is defined as the ratio of total received wideband power to the noise power. Higher “noise rise” value implies more users are allowed on the network, and each user has to transmit higher power to overcome the higher noise level. This means smaller path loss can be tolerated and the cell radius is reduced. To summarize, a higher noise rise means higher capacity and smaller footprint, a lower noise rise means smaller capacity and bigger footprint.

What is SIR?

Define Active Set? Pros and Cons of having a small or longer Active Set

Active Set consists of group of cells that takes part in soft/softer handover & measure by UE.

Typical size of Active set is 3 or 4 & generally a standard practice in all WCDMA networks.

A small active set size may provide more resources available due to less soft/softer handover but at the expense of handover gain thereby reducing the capacity & link redundancy.

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