Product: Spartan-II FPGAs

Product Description: The Spartan-II family offers some of the most advanced FPGA technologies available today, including programmable support for multiple I/O standards (including 5V tolerance), on-chip block RAM and digital delay lock loops for both chip-level and board-level clock management at low-costs. In addition, the Spartan-II devices provide superior value by eliminating the need for many simple ASSPs such as phase lock loops, FIFOs, I/O translators and system bus drivers that in the past have been necessary to complete a system design. Article Description: Spartan-II FPGAs provide the flexibility needed in the wireless LAN market and products to update specifications and standards, and to interface with other technologies.

Introduction

Wireless local area networks (WLANs) are a rapidly emerging market. WLANs combine data connectivity with user mobility and provide a connectivity alternative for a broad range of consumers and business customers. They have a strong popularity in vertical markets such as telecommuting, SOHOs, health-care, retail, manufacturing, warehousing, and academia, where productivity gains are realized by using hand-held terminals and notebook PCs to transmit real-time information to centralized hosts for processing. Business Research Group, a leading market researcher, predicts that revenues from WLAN products will exceed $2 billion in the year 2000, and show a steady growth of unit shipments and revenue. Demand for computing and telephony mobile devices will be one of the most influential market drivers, along with end users demanding higher data rates and ease of use to sustain growing Internet and data applications.

However, several issues remain unsolved for the industry. Although vendors have made great strides in achieving interoperability, a common wireless standard is far from reality (today, there are seven standards). Interference from competing 2.4GHz technologies (like Bluetooth and HomeRF) threatens the already crowded band. In addition, uncertainties exist with several technologies migrating to the evolving 5GHz frequency band.

Technology, Types and Chaos

WLANs focus on the PHY (physical) layer and the data-link layer (with the medium access control (MAC) and logical link control (LLC) sub-layers) of the OSI model. The physical layer defines the electrical, mechanical and procedural specifications, which provides the transmission of bits over a communication medium or channel. WLAN PHY layer technologies used are narrowband radio, infrared (IR), OFDM (orthogonal frequency division multiplexing) and spread spectrum (frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS)). The MAC layer, which is part of the data link layer, ensures error control and synchronization between the physically connected devices communicating over a channel. It is also responsible for determining priority and allocation to access the channel. Some of the popular WLAN technologies are IEEE 802.11a, IEEE 802.11b and HiperLAN2.

IEEE 802.11

IEEE 802.11 is the IEEE standard addressing the 2.4 and 5GHz WLAN market. The IEEE 802.11b extension employs a modulation scheme called complementary code keying (CCK) and operates in the 2.4GHz ISM (industrial, scientific, medical) band. It is designed to enable data rates of 1Mbps to 11Mbps for DSSS systems and interoperability with both DSSS and FHSS networks operating at 1Mbps or 2Mbps. The MAC uses the popular CSMA/CA (carrier sense multiple access/collision avoidance) technique. IEEE 802.11a, a recently formalized extension to 802.11, will prove attractive to vendors looking for speed and compatibility with existing standards. IEEE 802.11a employs the OFDM modulation scheme in the 5GHz band, with a maximum optional speed of 40Mbps and a range of 150m.

HiperLAN2

HiperLAN2 is an OFDM-based, variable bit rate PHY layer technology operating at 5GHz. It has FEC error control, with dynamic sub-channel modulation allowing data transmission at higher rates with a strong SNR at lower throughputs in adverse conditions. HiperLAN2 provides high bandwidth w/ QoS: 54 Mbps with a range of over 150 meters. It has a generic architecture and supports Ethernet, 1394, ATM, PPP, 3G. The HiperLAN2 data-link layer/MAC provides QoS via dynamic fixed time slots. The time slotted structure allows simultaneous communication in both downlink and up-link in the same period. It is also a connection-oriented technology that allows negotiation of QoS parameters like bandwidth, bit error rate, latency, jitter & delay requirements and this assures that other terminals will not interfere with subsequent transmissions. It provides ARQ (Automatic Repeat reQuest), dynamic frequency selection, power control and power save, cellular hand-over and security (authentication and encryption).

There is clearly chaos in the WLAN market place. There are several wireless technologies and standards trying to address the same problems. Each standard has its pros and cons and quite a few of them are in conflict with complementary technologies. Each technology has different specification versions and standards, and these keep changing from time to time for adding more functionality, bug fixing, and adaptation of new standards. The home network created of information appliances has islands of smart consumer devices, supporting varying technologies. Examples of these appliance islands include one that networks mobile devices such as cellular phones, PDAs and notebook PCs with Bluetooth, another island that uses USB/USB 2.0 to network PC-centric devices such as desk-top PCs, printers and scanners, and still another island that networks digital TVs, set-top boxes, gaming consoles and other bandwidth-heavy entertainment appliances using IEEE 1394.

WLAN Products and Spartan-II FPGAs

WLAN products include network interface cards (or NICs/PC adapters), access points (end-user-to-LAN and LAN-to-LAN) and technology bridges for communications. NICs provide an interface between the end-user device (desktop PC, portable PC, or handheld computing device) and the airwaves via an antenna on the access point. Access points act as transmitters/receivers between wired and wireless networks. They connect to the wired network via standard Ethernet cable (token ring is available, but less common) and use airwaves to transmit information to and from "connected" wireless end users. Technology bridges exist at the periphery of each product and are the most susceptible to constant change and evolution. These products need a flexible, re-programmable and low-cost platform to accommodate for time-to-market pressures, specification changes, lack of clear direction and short product lifecycles.

PLDs have always provided time-to-market advantage over ASICs and ASSPs. In this cost sensitive and quickly developing market, there is a need to develop products fast at low costs. Aggressive process technology adoption has allowed FPGAs to obtain more die per wafer, provide more logic, offer increased performance, and accommodate various ASIC-like features required to allow system integration. This has been fundamentally instrumental in narrowing the wide gap between FPGAs and ASSPs. FPGA vendors, by virtue of the benefits reaped through process technology now have the capability to bring traditional FPGA benefits to the cost-sensitive home networking and WLAN markets. Xilinx FPGAs are based on SRAM technology and can be re-programmed an unlimited number of times. Field upgradability provides the ability to update functionality of the FPGA requiring a simple update to the FPGA configuration bit-stream. FPGAs allow designers to gain market share by bringing them to market sooner than a stand-alone ASSP. Designers can also take advantage of the fact that the solution now allows them to upgrade their hardware and stay in the market-place longer, adapt to specification changes and thus maximize profitability.

With the introduction of Spartan-II FPGAs, in January 2000, Xilinx extended its playing field into the low cost market. The Spartan-II family provides increased densities (up to 200,000 system gates) and system-level features (such as DLLs, BlockRAM and SelectIO) at a much lower cost. FPGA gates left over from programming the MAC may be used to customize the end products, and be used for additional functionality such as memory (SRAM, DRAM and flash) controllers, PCI controller, UARTs, and forward error correction (FEC). While FPGAs help eliminate bugs and incompatibilities, Spartan-II FPGAs and Xilinx IRL (Internet Reconfigurable Logic) program allow remote specification updates.

Spartan-II FPGAs Enable WLAN Products

Figure 1: Spartan-II FPGAs in NIC/PC Cards

Figure 2: Spartan-II FPGAs in Wireless LAN Access Points

Figure 3: Spartan-II FPGAs in (Wireless LAN to Ethernet) Technology Bridges

NIC/PC Cards

Figure 1 shows the WLAN card, which consists of the antenna, radio/PHY, baseband controller and the MAC. The role of FPGAs is highlighted in Maroon. The block diagram of the PC Card shows that the Spartan-II FPGA provides functionality of a WLAN MAC (radio control, packet header generator, MAC protocol engine, DMA engine, RAM packet buffer, host interface, configuration storage and MAC management), memory controller and as an interface to the PC.

Access Points

The access points are devices that provide a wireless hub or a gateway for non-wireless networks to wireless networks. They also act as the network police and perform network management. They receive, buffer and transmit data between wireless LAN and the wired network infrastructure. Access points function within a range of 100 to several hundred feet. They also connect WLANs to other technologies such as USB and Ethernet. In figure 2, Spartan-II FPGAs provide solutions in the access point such as memory controller, Ethernet MAC, USB device controller and IEEE 802.11 MAC.

Technology Bridges

Conflicting specifications and lack of a clear direction create the need for FPGA-based technology bridges. It is also quite likely that some of these conflicts may never get resolved. It would be nearly impossible and cost-prohibitive for a supplier of home networking and wireless LAN products to cater to all the various specifications and changing needs. At the same time betting on the success of one single product may preclude them from being successful in the marketplace. An example of a wireless LAN to Ethernet technology bridge is shown in Figure 3. In the technology bridge example, Xilinx Spartan-II FPGAs are at the heart of the technology bridges, which usually connect unlike technologies - such as wireless LANs to Ethernet. While the Ethernet MAC has been around for a long time, the IEEE 802.11 specification that defines the MAC and PHY layers continue to evolve. With IEEE 802.11a and HiperLAN2 specifications still not defined, it seems ideal for the MAC and MII (media independent interface) to be programmed in an FPGA. Similarly, the HomePNA, HomeRF, FireWire, USB, HiperLAN2, Bluetooth are all technologies with evolving specifications.

WLAN products will extend beyond NICs, access points and technology bridges, and will enable every device in the home, SOHO and enterprise with WLAN capabilities. For example, devices such as digital TV, residential gateways, set-top boxes, digital modems, PC peripherals, gaming consoles and other appliances. Spartan-II devices are used for:

• I/O Control: Multiple front end interfaces (DSL, cable, satellite, powerline, wireless, analog) and multiple back end interfaces (USB/USB 2.0, HomePNA, HomeRF, FireWire, Bluetooth and Ethernet)
• Hard disk drive interface
• Clock distribution using on-chip DLL circuits
• MPEG decoder
• MAC (Fast Ethernet)
• Forward error correction (FEC) algorithms: Reed-Solomon, Viterbi
• Memory solutions: On-chip memory (Distributed memory, BlockRAM) and Memory controllers (Flash controller, SRAM controllers, DRAM controllers)
• CPU (microprocessor and microcontrollers)
• HDLC controller, ADPCM
• PCI and interface to other system interconnectivity technologies
• Glue Logic (LCD controllers, UARTs, DMA controllers)

Summary

The WLAN market is growing fast with a promise to penetrate homes, SOHOs and enterprises in large volumes. Being a cost sensitive and evolving market, WLAN products require low-cost programmable logic solutions. Programmable logic solutions allow customers to realize time-to-market and time-in-market advantages. Spartan-II FPGAs with increased densities, system-level features, an extensive IP portfolio and low costs, provide an ideal solution for WLAN products such as NIC cards, access points, technology bridges and other products. Spartan-II FPGAs provide interoperability between different technologies, which is essential for the success of this market.

Amit Dhir is a System Architect, strategic applications at Xilinx Corporation. His primary responsibilities include technical and market research and analysis of new emerging markets. He has published several articles and white papers on topics covering the role for FPGAs in Wireless, Embedded, Telecom, Networking, and Consumer applications. He has a BSEE from Purdue University and a MSEE from San Jose State University. He can be reached at amit.dhir@xilinx.com .

Krishna Rangasayee, Sr. Manager, strategic applications is responsible for identifying new market opportunities for Xilinx and implementing the underlying strategy to offer complete programmable logic solutions to these end markets. Krishna has seven years experience in the Programmable Logic Industry and has held engineering and management positions at Cypress Semiconductor, Altera and Xilinx. Krishna holds multiple patents related to programmable logic and has published numerous papers for industry conferences and technical trade journals. He can be reached at krishna@xilinx.com .