Initial Scanning for Channel in WiMAX point-to-multipoint (PMP)

When Subscriber Station (SS) wants to join a WiMAX in point-to-multipoint (PMP) network, it must follow a set of procedure as IEEE 802.16 Standard. The set of essential routine steps is as outlined below:

1. Scan for downlink channel and establish synchronization with the BS.
2. Acquire transmit parameters.
3. Perform ranging.
4. Negotiate basic capabilities.
5. Authorize subscriber station and perform key exchange.
6. Perform registration.
7. Establish IP connectivity.

Network Entry and Initialization, part 3.

Upon the network entry of a client into the network, the BS scans through its frequency list attempting to synchronize with a BS. The BS performs the admission control algorithm to make a decision whether to admit the SS, based on the QoS requirements requested by the SS and the existing resource availability of the BS. If admitted, the BS generates a set of connection and Connection Identifier (CIDs), together with the management and transport connections, to connect with the SS. Three pairs of management connections are established for control packets, and the transport connection is used for data transmission.

Along with the new CIDs, the BS also assigns new service flow identifiers (SFIDs) to the new data flows linked with the station. A service flow (SF) is a unidirectional flow of MAC SDUs between a pair of BS and SS, of which is provided with a particular set of QoS parameters, and a SFID uniquely identifies the service flow.

WiMAX Network Entry and Initialization, part 2.

The network entry process can be separated into a few phases. Within each phase, particular MAC management messages  are exchanged among Base Station (BS) and Subscriber Station. On the establishment of process, the SS scans individual DL channels searching in favor of the DL-MAP and DCD messages broadcasted by the BS.

Using these messages, the SS get synchronize with the BS and obtains DL paremeters. As successfully synchronized, the SS wait for the UL-MAP and UCD messages to acquire UL parameters.

WiMAX Network Entry and Initialization, part 1.

Once a SS senses a BS, for a network entry, it will first scans for downlink channel (DL) and trying synchronizes itself with the BS. After that, SS shall obtain transmit parameters, which are integrated in the Uplink Channel Descriptor (UCD), Uplink (UL)-MAP, and Downlink (DL)-MAP. The final step would be to complete initial ranging.

The BS is required to discover different received ranging codes, approximate the timing offset and the power for every user that bears and initial ranging code. The BS then broadcast the detected ranging codes with some change instruction for the proper timing and power level. Other than that, the status notifications of either ranging successful or retransmission are also broadcasted.

WiMAX Point-to-Multipoint and Mesh Network

In Point-to-Multipoint (PMP) mode, a single-hop network contains a central unit as a Base Station (BS) to makes decision to the entire nodes such as Subscriber Station (SS) within its cell that is a central geographic entity of a cellular structure.

In a mesh network, a number of SS are not in direct contact through the BS where a relay system is necessary on intermediary SS that resolve relay information toward other SS that are not in direct contact with the BS.

WiMAX MAC Layer

One of the important aspects of WiMAX is the MAC layer supports more than one physical layer (PHY) mode. This characteristic not only enable companies to differentiate their product from each other, but also makes WiMAX to be an adaptive technology that can suit special requirements depending on application.

The WiMAX MAC layer performs the standard function of providing a medium independent interface to the PHY layer. The major focal point of the MAC layer is handling resource of air-link proficiently.

MAC layer is responsible on the whole connection to arrange packet transmission among multiple Point-to-Multipoint (PMP) and mesh network models.

The MAC layer is separated into three sub layers. There are called specific convergence sub layer (CS), MAC common part sub layer (CPS), and the security sub layer.

The MAC CS support asynchronous transfer mode (ATM) service and packet service used for packet-switched networks. The MAC CPS provides utilities to facilitate both types of service in the CS.

The security sub layer is the third sub layer within the MAC layer. It is designed for privacy, authentication, and confidentiality used for the SSs in the network.

The MAC is capable to grant differentiated service to users on the equivalent medium throughout a range of method. MAC design plays an essential role in WiMAX networks. A MAC protocol defining rules for orderly access to the physical shared medium is vital when it comes to efficient utilization and fair sharing of resources to desired system performance such as high throughput and short delay.

Reduce Scanning Time and Optimization of Ranging Process in WiMAX Network Entry

Reduce the channel scan approaches during the scanning time are able to achieve a fast scanning process but this approaches may not guarantee Subscriber Station (SS) to acquire a precise information for the purpose of association with Base Station (BS).

While optimization of ranging process may improve the connection but it will sometimes disregard the performance of WiMAX network traffic flow.