SON Self Healing Networks

- Self healing aspects of Self Organising Networks, SON, how they work, and their effect on the cellular networks.

The self-healing aspects of SON self-organizing networks is an increasingly important element of the overall cellular network. Self-healing capability enables faults to be detected and their effects masked to users while repairs are effected on the cellular network.

Today, cellular networks are extremely large and very complicated. It is therefore not surprising that failures occur from time to time.

While some failures may not be noticed by mobile users, many are. Accordingly self-healing network technology has become increasingly important to ensure the proper operation of the overall cellular network even when failures occur.

Self-healing network basics

All areas of the cellular network can display faults from time to time. Many can be overcome without a major problem and in many cases backup hardware may be available.

However it is the radio access network is the most critical domain with respect to faults. Each base station has its own coverage area.

Any loss of service within the base station will result in users not experiencing lack of availability or significantly degraded service in terms of availability, and degraded performance. This can result in loss of revenue for the operator and the possibility of an increased level of churn.

Within the current understanding of cellular self-healing networks there are a number of main areas that are addressed:

  • Self recovery of software - the ability to return to a previous software version should issues arise.
  • Self-healing of board faults - this often involves redundant circuits where a spare can be switched in.
  • Cell outage detection - it must be possible to remotely detect when there is an issue with a particular cell.
  • Cell outage recovery - routines to assist with cell recovery, this may include detection and diagnosis and along with an automatic recovery solution, together with a report of the outcome of the action.
  • Cell outage compensation - methods of maintaining the best service to users while repairs are effected.
  • Return from cell outage compensation - this action, while obvious needs to be included as it must be possible to easily return to the pre fault status, removing any compensation actions that may have been initiated.

To enable these use cases to be auctioned a number of elements must be included into the network to detect and manage the faults that may occur. The self-healing network functionality can be broken down into a number of areas. These incorporate many techniques such as built in test and monitoring solutions as well as advanced data collection and analysis. Dependent upon these the self-healing network functions can flag the problem so that repairs can be effected, and reduce the impact of the problem in the interim period.

Cell degradation

The detection and management of cell degradation forms a major part of the cellular self-healing network functionality.

The first stage of this part of the self-healing network is the detection of any fault. Without a knowledge of a fault it is not possible to do anything about it.

When monitoring the performance of the base station, it is necessary to have in place measurements for some of the key performance indicators, KPIs. While parameters such as power output, and other key base station parameters can be monitored, key performance indicators that assess the actual performance of the network itself also need to be monitored as these may indicate a wider problem.

One a failures is detected an alarm is flagged to the operation, administration and management centre where automated and manual action can be initiated.

Alarm flags may be set for definitive hardware and software failures within the cell, i.e. base station, or when wider network key performance indicators fall outside acceptable limits.One of the key issues with any fault detection system is to set the limits for acceptable performance. Set too wide and faults will not be detected; set too narrow and there will be false alarms. Neither of these scenarios is acceptable and therefor optimisation of the limit setting will be required.

Cell outage compensation

One of the key elements of the self-healing network is the compensation when a cell outage occurs.

One of the key requirements for any cell outage compensation is that the overall network should respond quickly so that immediately the fault is detected and the impact quantified, compensation is introduced. As this needs to be implemented quickly this cannot be adjusted manually and therefore automated means are required.

In the first instance any means within the base station itself will be sought to alleviate the situation whatever the fault may be. However if this is not possible because of a complete cell outage, then the compensation must come from other neighbouring cells.

Neighbouring cell compensation is achieved increasing the size of the neighbouring cells to try to cover the area of the failed one. The same routines that are used for the coverage and capacity optimisation re used. Techniques include titling the antenna and also increasing the power of the base station.

Cellular self-healing network technology can be used to mitigate the effects of a complete cell outage or other failure. However there is likely to be an impact on performance and therefore a fast response once the fault is diagnosed is required to ensure that the network can return to its pre-fault condition.

By Ian Poole

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