Optimize your WiMAX subscriber station software stack design

The example software stack is not targeted for a specific application, and can therefore be used in all WiMAX-compliant systems to serve a wide variety of applications.

The example stack itself is partitioned into several components, including a board support package (BSP) with a real time operating system kernel, device drivers and boot loader, lower MAC (LMAC), intermediate MAC (IMAC) and upper MAC (UMAC), with configuration modules and the operating system (OS) wrapper.

These components are key in tailoring a range of subscriber station functions like security, buffer management, real-time/non-real-time operations, authentication, MAC management and a host of other capabilities.

Because the available API within the stack is capable of returning the values to all function calls made from a higher application layer, the subscriber station designer can save both time and money, as well as reduce the margin of error in developing user interfaces.

It should also be noted that a software stack is typically tested for fault-free performance by sending traffic to a commercial base station or receiving a stream from the WiMAX base station (i.e., actual field testing).

In this process, a variety of test equipment is used for measurement of parameters like range, throughput, packet loss, signal strength, noise and interoperability. Fujitsu offers its reference design boards as the test bed for lab or field testing, and customers can use them to test the performance of any other software stack, as well.

Fujitsu estimates time and money saving at a minimum of six to eight months of time saved in reduced system software development, which can translate to $700,000 to $1M in total system cost savings.

An example of the software architecture for Fujitsu's subscriber station reference kit is shown in Figure 1.

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Figure 1: Software architecture of a subscriber station.