Mobile Networks: Tutorial

With Precision Time Protocol (PTP), Operators can measure the network’s synchronisation performance from the Grand Master to a basestation, that is, up to the air interface. However, measuring the synchronisation signal when it is transmitted over the air to the end customer is more difficult.

When the PTP is recovered by the eNodeB/basestation, it generates a 1pps (measured physically to 1.1µs at reference point C and 1.35µs at reference point D, see diagram below) which is then amplified up to the air interface/antenna. ITU-T standards G.8271.1 and G.8271.2 specify that the timing of a radio signal at this point (reference point E) must be within ±1.5µs of a common time reference at the network output on the air side – the customer interface.

The difficulty with measuring sync performance at the customer interface is twofold: basestations can be difficult to access, and small cells don’t have physical 1pps outputs. Furthermore, small cells within a cluster interact with one another so that they can perform certain features of LTE-A deployments. If one of the small cells is out of sync, it can effectively act as a jammer or spoofer, throwing out the timing of the surrounding interacting cells.

The performance of the radio signal is clearly important to end users (the ‘customer experience’) and one method to ensure the radio signal is correctly synchronised is to measure both frequency accuracy and time error ‘over the air’. Not having to connect directly to network equipment simplifies the operator’s ability to determine the synchronisation performance at the output of each device.

How Calnex can help?

Calnex Sentinel’s Over-the-Air (OTA) option is the only solution available that allows the network to be tested non-invasively to the ±1.5µs ITU-T requirement for both FDD and TDD. Sentinel OTA can also measure two basestations in succession to ensure that they are within ±3µs of each other which is also part of the ITU-T standard. In short, Sentinel OTA can measure and validate phase accuracy where it really matters – between the air interface and the end user.

More information of Sentinel and Over-the-Air option, click here.