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HO (Hand Over)

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Handover (HO) is a critical feature in wireless communication networks, allowing the transfer of a mobile device's connection from one base station (BS) to another. This transfer is necessary to maintain a seamless communication experience as the mobile device moves through the network's coverage area. HO is a complex process, and various factors can affect its effectiveness, such as the network topology, mobility patterns, and radio channel conditions. In this article, we will provide a detailed explanation of HO, including its types, procedures, and challenges.

Types of Handover

There are two types of handovers: hard handover and soft handover.

Hard handover (HHO) is a type of handover that involves breaking the connection with the current base station before establishing a connection with the new base station. This process is also known as a make-before-break (MBB) handover. In this case, the mobile device loses its connection with the old BS and searches for a new BS to establish a connection. HHO is a simple and efficient technique used in early wireless communication networks.

Soft handover (SHO) is a type of handover that enables a mobile device to maintain a connection with multiple base stations simultaneously. This technique is also known as a break-before-make (BBM) handover. SHO is an essential feature in cellular networks that use Code Division Multiple Access (CDMA) technology. In CDMA networks, the mobile device can receive signals from multiple base stations simultaneously, and it can combine these signals to improve the communication quality. SHO is a more complex and challenging technique to implement than HHO.

Handover Procedures

The handover procedure involves several steps that allow the mobile device to move from one BS to another while maintaining the connection. These steps can vary depending on the type of handover and the network's specific configuration. Generally, the handover procedure involves the following steps:

  1. Measurement: The mobile device measures the signal strength and quality of the current BS and the surrounding BSs. The mobile device sends these measurements to the network's Radio Resource Management (RRM) system.
  2. Decision: The RRM system uses the measurements to determine if a handover is necessary. The decision is based on several factors, such as the signal strength, the quality of the connection, and the available resources in the current and surrounding BSs.
  3. HO Trigger: If the RRM system determines that a handover is necessary, it sends a trigger message to the mobile device to initiate the handover procedure.
  4. Preparation: The mobile device starts preparing for the handover by allocating resources in the target BS and establishing a connection with it.
  5. Execution: The mobile device breaks the connection with the current BS and establishes a connection with the target BS. This step can involve either a hard handover or a soft handover, depending on the type of handover.
  6. Verification: Once the handover is complete, the mobile device verifies the connection's quality with the target BS. If the quality is not sufficient, the mobile device can initiate another handover procedure.

Handover Challenges

Handover is a complex process that can face several challenges. These challenges can impact the communication quality, delay the handover procedure, or even cause a complete communication failure. Some of the main challenges of handover are:

  1. Network Congestion: A high number of mobile devices and BSs in the network can cause network congestion, leading to delays in the handover procedure.
  2. Interference: Interference from other devices or networks can affect the quality of the signal and impact the handover decision.
  3. Signal Strength Variation: The signal strength can vary depending on the distance between the mobile device and the BS. This variation can lead to incorrect handover decisions.
  4. Mobility: High mobility of the mobile device can also impact the handover procedure. A fast-moving device may switch between BSs frequently, causing delays and instability in the communication.
  5. Radio Resource Management: Radio resource management (RRM) is a critical component of the handover procedure. Poor RRM algorithms or improper configuration can lead to suboptimal handover decisions.
  6. Handover Trigger: The handover trigger is a crucial step in the handover procedure. An incorrect or delayed trigger can lead to poor communication quality or even a complete failure of the handover.
  7. Handover Latency: The time required to complete the handover procedure can impact the user experience. A high handover latency can lead to call drops or poor communication quality.
  8. Handover Failure: Handover failure occurs when the mobile device cannot establish a connection with the target BS. Handover failure can be caused by several factors, such as poor signal quality or insufficient resources in the target BS.

Conclusion

In summary, handover is a critical feature in wireless communication networks that enables mobile devices to maintain a seamless connection as they move through the network's coverage area. Handover involves several steps, including measurement, decision, trigger, preparation, execution, and verification. There are two types of handover: hard handover (HHO) and soft handover (SHO). While HHO is simpler, SHO enables the mobile device to maintain a connection with multiple BSs simultaneously. Handover faces several challenges, such as network congestion, interference, signal strength variation, mobility, and RRM. Proper planning, configuration, and optimization can help overcome these challenges and ensure a smooth handover procedure.