Handover is a function of mobility in mobile networks. In brief, whenever a mobile UE moves, it leaves and joins areas, the mobile cells. The process of handing over into the next cell is called Handover.
Handover has been around for more than 3 decades but has been discussed a lot since the start of 5G networks.
Has handover been mainly a function of the radio access type the mobile is currently connected to, since the start of 5G, we have got many more options, which I’ll try to explain in this post.
In 4G and 5G Non-Standalone (NSA) mode, handovers between cells are performed using a protocol called X2. X2 handover is a type of inter-eNodeB (eNB) handover which allows a mobile device to switch between cells controlled by different eNBs. When a mobile device moves from the coverage area of one eNB to another, the new eNB sends a handover request message to the current eNB, which then initiates the handover process.
In 5G Standalone (SA) mode, handovers between cells are performed using a protocol called Xn handover. Xn handover is similar to X2 handover, but it is used for inter-gNodeB (gNB) handover, which allows a mobile device to switch between cells controlled by different gNBs. This new protocol provides more flexibility and allows more advanced features such as dual connectivity, which allows the mobile device to connect to multiple cells simultaneously, and inter-frequency handover, which allows the mobile device to switch between different frequency bands within the 5G network during the handover process.
In summary, X2 Handover is used in 4G and 5G Non-Standalone (NSA) mode, and it’s used for inter-eNodeB (eNB) handover, while Xn Handover is used in 5G Standalone (SA) mode and it’s used for inter-gNodeB (gNB) handover, providing more flexibility and advanced features.
In 4G, handover scenarios between cells typically take place in one of two ways: hard handover or soft handover. In hard handover, the mobile device disconnects from the current cell before connecting to the new cell. In soft handover, the mobile device maintains a connection with both the current and new cells during the handover process.
In 5G Non-Standalone (NSA) mode, handovers are performed between 4G and 5G cells using the same techniques as in 4G. In addition, 5G also supports a feature called dual-connectivity, which allows a mobile device to be connected to both a 4G and 5G cell simultaneously, resulting in improved handover performance.
Let’s think of testing a handover.
As described, handovers will be initiated as soon the cell the phone is connected will become less significant, meaning less quality and signal strength.
The key in testing is to force the degradation in signal strength, which could happen in the cellular module or the RAN.
Whether you can modify the signal strength information on a cellular module to force a handover for testing depends on the specific module and its capabilities. Some cellular modules may allow you to manually adjust the signal strength, while others may not.
Modifying the signal strength information can be an effective way to test handover scenarios, as it allows you to simulate a change in radio conditions and observe how the module responds. However, it’s important to keep in mind that this method may not accurately reflect real-world conditions and may not be representative of the performance of the module under normal conditions.
An alternative way to test handover scenarios is to use a test setup that simulates a change in radio conditions. This can be done by using specialized test equipment, such as RF signal generators and RF power amplifiers, to simulate changes in signal strength and quality. This method can be more accurate than manually adjusting the signal strength on the module, but it can be more expensive and complex to set up.
Another way to test handover scenarios is by using drive test, which is a method of testing a wireless network by driving a vehicle equipped with a test device through different areas while collecting data on the network’s performance.
Drive test enables a comprehensive view of the network performance, it is widely used by network operators and equipment vendors to test the network under real-world conditions. This method captures the real-world conditions and usage scenarios, but it could be expensive and time-consuming.
Besides the Xn and X2 handovers, one will find additional handovers which are the following:
Intra-frequency handover, also known as a “frequency handover” or “frequency reselection,” is a type of handover that occurs when a mobile device moves between cells that operate on the same frequency band. This type of handover is used to provide a seamless service to the mobile device, by switching it to a new cell that provides better signal quality or capacity.
During an intra-frequency handover, the mobile device continuously monitors the signal strength and quality of the cells in its surrounding area. If the mobile device detects that the signal strength or quality of a neighboring cell is better than the current cell, it sends a handover request to the network. The network then performs a handover by reassigning the mobile device to the neighboring cell.
Intra-frequency handovers are less complex and faster than inter-frequency handovers, which occur when a mobile device moves between cells that operate on different frequency bands.
Intra-frequency handover is also used to support load balancing, which is the ability to distribute the traffic load among different cells within the same frequency band.
Inter-frequency handover, also known as “frequency change” or “frequency handoff,” is a type of handover that occurs when a mobile device moves between cells that operate on different frequency bands.
During an inter-frequency handover, the mobile device continuously monitors the signal strength and quality of the cells in its surrounding area. If the mobile device detects that the signal strength or quality of a neighboring cell is better than the current cell, it sends a handover request to the network. The network then performs a handover by reassigning the mobile device to the neighboring cell, which operates on a different frequency band.
Inter-frequency handovers are more complex and slower than intra-frequency handovers, which occur when a mobile device moves between cells that operate on the same frequency band. This is because different frequency bands may have different propagation characteristics and require different radio access technologies.
Inter-frequency handover is used to support the use of multiple frequency bands in the same network, which allows for better frequency reuse, capacity and coverage. It is also used to support the use of different frequency bands for different types of services and applications, such as low-band for coverage and high-band for capacity.
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