What is a Handover Test System?
Handover Test Systems are devices that are used to simulate the process of handover of signals from one base station to the next in cellular or WLAN networks within the controlled space of laboratories. These devices fade/attenuate the strength of RF signals using numerous variable attenuators which act as various RF paths (channels) that are available between the base station/access point to the mobile device. This helps network engineers to predict the performance of the systems in real-world situations and make necessary updates to the network design.
Handover test systems can be classified into two categories depending on the method in which the device can be controlled:
- Programmable Handover Test Systems
- Manual Handover Test Systems
These systems can also be classified based on their configurations. They are
- Full Fan-out Handover Test Systems
- Limited Fan-out Handover Test Systems
Programmable Handover Test Systems
Programmable handover test systems utilize programmable attenuators/matrix which can be controlled from the physical control panel or remotely over Ethernet or RS232 using the control commands or graphical user interface (GUI). These test systems can operate over both AC and DC power supplies.
Manual Handover Test Systems
Manual handover test systems use manual step attenuators to provide varying attenuation to individual channels. Each attenuator can be controlled through their physical controls (usually knobs or toggle switches). These handover test systems do not require an AC supply.
Full Fan-out Handover Test Systems
These handover test systems are used to test multiple access points and mobile devices. Full fan-out systems are designed with power dividers/combiners on both halves of the matrix with a step attenuator on every path through the matrix. Every RF path through the matrix can have its own unique attenuation value and this allows the signal between each access point and mobile device to be in individually faded up or down as required.
Limited Fan-out Handover Test Systems
These handover test systems are used to test multiple access points with a single mobile device. They are designed with a step attenuator on each input port with a power divider/combiner to combine all RF signals to a common path. This design requires as many step attenuators and the number of input ports and can fade RF signals from each access point to the mobile device.
How does a Handover Test System work?
Handover test systems consist of at least two base stations and one mobile device, which will simulate handover of the mobile device within these base stations (cells). Each base station is connected to the input of a step attenuator (programmable or manual) and the output of the step attenuator is connected to the transceiver port of the mobile device (DUT) through one of the ports of RF power divider/combiner.
To begin with, one of the variable attenuators (A1) will be set to provide minimum attenuation while the remaining attenuators will provide maximum attenuation. This implies the signal from the corresponding base station (BS1) will be the strongest and the mobile device will be connected to this base station (cell).
Gradually, the attenuation of this variable attenuator will be increased which will act as an increasing fading effect on the RF signal from the base station to DUT. Simultaneously, the attenuation of another variable attenuator (A2) – corresponding to another base station (BS2) – will be reduced step by step, simulating the process of the mobile device moving from one base station to another (BS1 to BS2).
As the attenuation of A1 increases and A2 decreases, the RF signal from BS1 continues to get weaker and the RF signal from the BS2 steadily gets stronger. Eventually, RF signal from BS2 becomes significantly stronger than BS1 and the process of handover begins from BS1 to BS2.
This process can be repeated using different attenuation levels, multiple base station and mobile devices. It can also be used to simulate multiple fading channels for testing of mesh networks using MIMO switching circuits.
