Update: LTE Self-Organizing Networks

Putting cell towers in place is one thing, optimizing their coverage quite another. Today, a lot of planning is required in advance to make sure all required neighboring cell information and handover parameters are available, antennas are installed and configured with the correct angle in order not to create too much interference in the coverage area of neighboring cells, etc. etc. With adding yet another radio layer with LTE, things are not getting any easier if everything has to be done by hand and later-on check and refined with drive tests. Furthermore, networks are never static as new cells added, as frequency plans change, etc., so frequent quality checks like drive tests are required.

To reduce the amount of work required, 3GPP is working on a standard for LTE to be a bit more self-organizing, self-correcting and reporting issues that can't be fixed automatically to maintenance. A number of papers have been written to cover the current state in 3GPP on this topic, for example by Nomor back in 2008 (see here) and by 3G Americas recently (see here). In the 3GPP archives, the following technical report might be of interest to you on which the subsequent standardization is based on:

3GPP TR 36.902: Self-configuring and self-optimizing network (SON) use cases and solutions

With 3GPP Release 9, time has come to put things into Technical Specification (TS) documents. These can be found in the 3GPP 32-series starting with TS 32.500. Here's a list (no exhaustive) of documents that sound especially interesting:

• 3GPP TS 32.500: "Telecommunication management; Self-Organizing Networks (SON); Concepts and requirements"

• 3GPP TS 32.501 and 36.502: "Self-Configuration of Network Elements; Concepts and Integration Reference Point (IRP) Requirements" and "Information Service (IS)"

• 3GPP TS 32.503: A CORBA framework for SON

• 3GPP TS 32.511: Automatic Neighbour Relation (ANR) management

• 3GPP TS 32.521, 32.522, 32.523: SON stage 1, stage 2 and stage 3

• 3GPP TS 32.541, 32.542, 32.543: Self Healing stage 1, stage 2 and stage 3

Quite an impressive list and the whitepapers mentioned above list the following features that are thought of in 3GPP:

• Self-configuration: Retrieve basic operation parameters from a centralized configuration server when the cell is first activated.

• Automatic Neighbor Relation (ANR): Mobile devices can report cells to the base station they are currently served by that are not in the neighbor list. This information can then be used by the network to automatically establish neighbor relationships for handovers.

• Coverage and Capacity Optimization: Interference between cells due to too much overlap ov the coverage area and the opposite, coverage holes, are one of the main enemies of every network planner. Such conditions are usually detected with drive tests. Here SON aims to use mobile device and base station measurements to detect these issues. While interference can potentially be reduced automatically, unintended coverage holes can sometimes only be fixed with additional base stations. In such a case the equipment could at least notify the network operator.

• Energy Saving: Reduce transmission power in case it is not needed, automatic shutdown and re-initialization of femtocells when the user arrives in or leaves the coverage area of the femto.

• Physical Cell ID configuration: This is a very short id that mobile devices can read without decoding the full broadcast channel. Only 504 IDs are available so they are not unique. Therefore, an auto-configuration is highly desirable. Again, the mobile is required to report to the network which cells it sees for the configuration process.

• Handover optimization: By analyzing the failure causes of handovers, coverage holes or wrong handover decisions can be detected and changed.

• Load Balancing: If a cell already experiences high load from many users, send users at the cell edge to nearby cells.

• Random Access Channel Optimization: The random access channel (RACH) is needed for the initial communication between non synchronized mobile devices and the network. Depending on the load, the number of resources dedicated to the RACH can be changed dynamically.

Quite a list! Interesting though that for the moment, all actions pretty much focus on LTE only. Lots of potential therefore for the future to extend SON functionality to the interworking with GSM and UMTS networks. In that regard I wonder if in the future network vendors will manage to offer an integrated SON an general management functionality for GSM, UMTS and LTE.

Ideally in a world where base stations are (auto-) software configurable on the fly for whatever air interface technologies are required at a certain place at a certain time. Advanced multi-mode base stations, but that's another topic…