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What is Paging Occasion and Paging Frame in LTE?

Updated: Apr 29, 2023

Introduction to Paging Occasion and Paging Frame

Paging is a fundamental mechanism used in 4G networks to locate a User Equipment (UE) that is in an idle mode, i.e., not actively transmitting or receiving data. The paging procedure involves paging a UE to request its presence in the network, initiating a service request, or transmitting data. Paging is an important procedure in 4G networks because it enables network operators to efficiently utilize network resources while maintaining the desired Quality of Service (QoS) for their customers. In this article, we will discuss the paging procedure in 4G networks.

Paging Occasion and Paging Frame
Paging Occasion and Paging Frame

Background of Paging Occasion and Paging Frame

In 4G networks, a UE is typically in one of two states: idle or connected. When a UE is idle, it is not actively transmitting or receiving data, and its radio interface is in a low-power consumption mode to conserve battery life. In this state, the UE is not assigned to any specific cell, but it periodically monitors a paging channel to detect incoming calls or messages. When a UE receives a paging message, it enters the connected state to establish a connection with the network and initiate a service request.


Paging Procedure in 4G Networks

The paging procedure in 4G networks involves several steps, as shown in the figure below:

Step 1: UE Enters Idle Mode

When a UE is not actively transmitting or receiving data, it enters the idle mode. In this mode, the UE periodically monitors the paging channel to detect incoming calls or messages.

Step 2: Network Initiates Paging

When the network needs to communicate with a UE that is in idle mode, it initiates a paging message. The paging message is sent to the paging channel of the cell where the UE is most likely to be located. The paging message includes the Temporary Mobile Subscriber Identity (TMSI) or the International Mobile Subscriber Identity (IMSI) of the UE being paged.

Step 3: UE Receives Paging Message

When the UE receives a paging message, it decodes the message and checks whether it is the intended recipient of the message. If the UE is the intended recipient, it proceeds to the next step. If the UE is not the intended recipient, it returns to monitoring the paging channel.

Step 4: UE Establishes Connection with the Network

After receiving a paging message, the UE establishes a connection with the network by transmitting a Radio Resource Control (RRC) connection request. The RRC connection request includes the TMSI or the IMSI of the UE.

Step 5: Network Assigns Resources to UE

When the network receives the RRC connection request from the UE, it assigns resources to the UE to establish a connection. The network also initiates the necessary procedures to set up the connection, such as Authentication and Key Agreement (AKA) and Radio Bearer Establishment (RBE).

Step 6: UE Sends Service Request

After the connection is established, the UE sends a service request to the network. The service request includes the type of service being requested, such as voice or data.

Step 7: Network Responds to Service Request

After receiving the service request, the network responds with the necessary information to initiate the requested service. For example, if the UE is requesting a data service, the network may provide the necessary IP address and access point name (APN) information.

Step 8: UE Transmits or Receives Data

After the necessary resources are assigned and the service request is approved, the UE can transmit or receive data with the network.


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What is Paging Occasion and Paging Frame in LTE?

In LTE, the paging occasion and paging frame are two key parameters used in the paging procedure to locate a User Equipment (UE) that is in idle mode.

Paging Occasion:

A paging occasion is a specific time interval during which a UE in idle mode is expected to monitor the paging channel for incoming paging messages. In LTE, the paging occasion is defined as a subframe in the radio frame structure. Each subframe is 1 millisecond in duration, and each radio frame contains 10 subframes. The paging occasion is specified by the network in the System Information Block Type 2 (SIB2) that is broadcasted periodically by the serving cell. The UE uses the paging occasion to synchronize its monitoring of the paging channel with the network.

Paging Frame:

A paging frame is a group of subframes that are used by the network to send paging messages to a UE in idle mode. In LTE, the paging frame is a 10-millisecond period consisting of one or more subframes. The number of subframes in a paging frame can vary depending on the network configuration and the number of UEs being paged. The paging frame is also specified in the SIB2 and is synchronized with the paging occasion.

When the network needs to page a UE in idle mode, it selects a paging frame and a paging occasion based on the UE's location and mobility pattern. The paging message is then transmitted on the paging channel during the selected paging frame and paging occasion. The UE monitors the paging channel during the specified paging occasion and, if it receives a paging message, it responds by establishing a connection with the network to initiate the requested service.

In summary, the paging occasion and paging frame are important parameters in the paging procedure in LTE. The paging occasion is a subframe interval used by the UE to monitor the paging channel, while the paging frame is a group of subframes used by the network to transmit paging messages. The selection of the paging occasion and paging frame is critical in ensuring efficient use of network resources and timely delivery of paging messages to the UEs in idle mode.

What is Paging Cycle DRX?

In LTE, the paging cycle is the time interval between successive paging occasions during which a User Equipment (UE) in idle mode is expected to monitor the paging channel for incoming paging messages. The Discontinuous Reception (DRX) mechanism is used to reduce the power consumption of the UE by enabling it to periodically switch off its receiver during idle periods.


Paging Cycle DRX refers to the use of DRX in conjunction with the paging cycle to further reduce the UE's power consumption. With Paging Cycle DRX, the UE only needs to monitor the paging channel during specific DRX periods within each paging cycle, instead of monitoring the channel continuously throughout the cycle.


The Paging Cycle DRX mechanism is implemented by defining two parameters: the DRX cycle and the paging cycle. The DRX cycle is the time interval during which the UE's receiver is switched off, while the paging cycle is the time interval between successive paging occasions. The DRX cycle duration is typically shorter than the paging cycle, and it is expressed as a multiple of the subframe duration.


During the Paging Cycle DRX operation, the UE turns off its receiver during the DRX period and wakes up briefly at the end of each DRX period to check if there is any paging message on the paging channel. If there is no paging message, the UE goes back to sleep and repeats the DRX cycle until the end of the current paging cycle. If there is a paging message, the UE will wake up fully and initiate a connection with the network to receive the message and respond as needed.


The Paging Cycle DRX mechanism enables the UE to save power by reducing the amount of time it needs to monitor the paging channel during idle periods. This results in longer battery life and improves overall UE performance. However, it is important to note that the use of Paging Cycle DRX can also increase the latency of the paging procedure, since the UE may not receive the paging message immediately if it is sleeping during the DRX period.


In summary, Paging Cycle DRX is a mechanism used in LTE to reduce power consumption in UEs by enabling them to periodically switch off their receivers during idle periods. This mechanism is implemented by defining two parameters, the DRX cycle and the paging cycle, and enabling the UE to monitor the paging channel only during specific DRX periods within each paging cycle. While Paging Cycle DRX can help save power, it can also increase the latency of the paging procedure.


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