How to speed up application development of WiMAX-ready subscriber stations

Within the WiMAX systems development community, the delivery of subscriber station equipment for carrier deployment is considered by many to be the primary revenue opportunity.

Typically deployed at a ratio of dozens or hundreds of subscriber units to each base station installed, they represent the majority of mass market sales available to systems companies.

In order to speed deployment, Fujitsu Microelectronics America recently developed a WiMAX reference kit that can be used for either the popular Time Division Duplexing (TDD) scheme or the prevalent legacy Half Duplex Frequency Division Duplexing (HDX-FDD) scheme.

The kit consists of a development board and complete MAC-layer software, also includes Fujitsu’s MB87M3400 802.16-2004 WiMAX SoC and all other hardware resources required for a typical subscriber station.

This article provides a how-to overview of the steps involved in leveraging the reference kit to create self-configurable indoor or outdoor subscriber stations that operate in licensed or license-exempt bands from 2 to 11 GHz.

The reference kit is provided with the mandatory MAC and PHY functions as outlined in IEEE802.16-d standard. If the developer plans to roll out product with the mandatory features included in the kit, time-to-market can be reduced from one year to as little as three months, while the margin of error is substantially reduced and ease of implementation greatly improved.

TDD or HDX-FDD reference design
As shown in Figure 1, the WiMAX reference design board provides a radio module, a baseband daughter-board incorporating the Fujitsu WiMAX SoC, Ethernet and serial ports, power module and clock-generation circuitry. The SoC integrates MAC and PHY blocks that comply with the fully ratified IEEE 802.16-2004 standard.

Click here for Figure 1
Figure 1: Subscriber Station Reference Design in TDD Mode.

The PHY implements Orthogonal Frequency Division Modulation (OFDM) with 256 carriers. Under OFDM, the PHY supports various modulation schemes (including BPSK, QPSK, QAM16 and QAM64) in Time Division Duplex and Frequency Division Duplex modes using all channel bandwidths as specified by the WiMAX forum.

The reference kit’s complete subscriber station MAC-layer software consists of upper and lower MAC layers (UMAC and LMAC, respectively). This software runs on the SoC’s two embedded processors, but can also run on external processors under multiple operating systems.

The upper MAC software implements the MAC management layer, service-specific convergence sub-layers, and multiple service classes to differentiate the service quality. The UMAC also provides common-part sub-layer, privacy, authentication and key-management services.

Running on another of the SoC’s embedded processors, the lower MAC firmware implements time-critical lower-level 802.16 MAC functions, including PHY setup and control. Key blocks of this UMAC firmware include PHY Service Access Point (PSAP) management, PSAP scheduler, data control processor and OFDM PHY driver.

To assist in application development and customization of the upper MAC software, Fujitsu’s reference kit provides detailed documentation on the application program interfaces (APIs) to the upper and lower MAC software as well as the PSAP block.

Application design
Application software for the host processor must manage and monitor wireless-centric network parameters, including:

• Channel selection
• Network association
• Data rate
• Number of Ethernet packets and PHY frames received/transmitted
• Receiver Sensitivity Signal Strength (RSSI)
• Bit Error Rate (BER)
• Site survey (local as well as remote to minimize maintenance costs)

Click here for Figure 2
Figure 2: Indoor CPE design.