WiMAX Network Entry Procedure

This page details the WiMAX network entry procedure between a Subscriber Station (SS) and a Base Station (BS). This process allows a WiMAX subscriber to connect to a WiMAX-compliant base station.

The following steps outline the network entry process as per the IEEE 802.16-2004 OFDM PHY and MAC layer specifications. This version of WiMAX is often called “fixed WiMAX” because the subscriber stations are not mobile.

The mobile WiMAX procedure is similar, but it includes modifications to MAPs/channel descriptors, header formats, and additional MAC messages.

Network Entry Steps

1. Downlink Channel Scanning and Synchronization: The WiMAX Subscriber Station (SS) scans for a downlink RF channel frequency and synchronizes with the WiMAX Base Station (BS).

2. Uplink Transmission Parameter Acquisition (UCD Message): The Subscriber Station obtains information about when it can transmit in the WiMAX frame based on the UCD (Uplink Channel Descriptor) message. The Base Station broadcasts the UCD message. The modulation and coding rate information for the broadcast message is in the FCH (Frame Control Header) or DLFP (Downlink Frame Prefix). Therefore, the SS must decode the FCH, which is always BPSK1/2, to get the broadcast message information.

   

3. Ranging: The Subscriber Station performs ranging to maintain the RF link between the BS and SS. Different types of ranging messages exist. The messages used are RNG-REQ (from SS to BS) and RNG-RSP (from BS to SS). A dedicated slot is reserved for these ranging messages in the WiMAX frame structure.

4. Basic Capability Negotiation: The WiMAX SS informs the BS of its basic capabilities. The BS adjusts parameters based on the SS’s information. The messages used are SBC-REQ (from SS to BS) and SBC-RSP (from BS to SS). The position for SBC in the frame is sent to the SS in response to the bandwidth request message received at the BS. The BS provides this information in the subsequent broadcast message.

5. Authorization: The BS authorizes the SS, and a key is exchanged for encryption using PKM-REQ and PKM-RSP messages.

6. Registration: The SS follows the registration procedure, becoming manageable by the BS. REG-REQ and REG-RSP messages are used.

7. Secondary Management Connection and IP Configuration: A managed SS establishes a secondary management connection and configures its IP connectivity. The SS uses the DHCP protocol to obtain its IP address and other parameters required for the IP connection. This step assumes a provisioned service flow has been created between the BS and SS using DSA-REQ, DSA-RSP, and DSA-ACK messages.

8. Time of Day Establishment: The SS establishes the time of day to retrieve time-stamped logged events.

9. Operational Parameter Transfer: Operational parameters are transferred between the BS and SS. When the SS successfully downloads the configuration file, it notifies the BS by transmitting a TFTP-CPLT message on its primary management connection. The BS responds with a TFTP-RSP message (Configuration File TFTP Complete Response).

10. Data Transfer: Data transfer now occurs between the BS and SS.

    

Figure 2 illustrates the messages logged in the event log screen of a popular WiMAX-compliant base station device. It shows the following WiMAX network entry messages in sequence:

1. Initial Ranging Success
2. Basic Capability Success
3. SS Registered
4. Service Flow Creation success for downlink (example)
5. Service Flow Creation success for uplink

For more information, refer to the article on WiMAX MAC protocol. This article describes WiMAX MAC layers, including the convergence sublayer, MAC common part sublayer, and security sublayer. It covers various MAC layer messages exchanged between BS and SS, including:

• Broadcast message (DLMAP, ULMAP, UCD, and DCD)
• Ranging request (RNG-REQ)
• Bandwidth request (BW-REQ)
• DSA-REQ and DSA-ACK