Wireless Systems Design

Software Drives Ultra Wideband Home

This electronic-design-automation tool puts the full power and functionality of Ultra-Wideband communications within the reach of today's wireless-systems engineers.

Ultra Wideband (UWB) is used to transmit digital data over a wide spectrum of frequency bands with very low power. This wireless technology can carry huge amounts of data over a short distance. Thankfully, UWB is not prone to the signal interference caused by doors and other obstacles. Such obstacles tend to reflect signals at more limited bandwidths and higher power. This characteristic makes UWB ideal for a host of applications like smart homes, high-resolution radar, and precision (sub-centimeter) radio-location systems. As is true for any new technology, however, talking about UWB and actually implementing it are two totally different matters. Implementation requires a comprehensive understanding of both the technology and its potential usage model. It also calls for appropriate design tools and test equipment.

This issue is exactly the type of problem that Agilent EEsof EDA likes best. After all, this company's area of expertise lies in developing electronic-design-automation (EDA) software solutions for the electronics industry. Earlier this year, Agilent EEsof came to market with an Ultra Wideband (UWB) Design-Guide to help speed the development of baseband ASICs, RFICs, and modules for Ultra Wideband transceivers. It streamlined the design and verification process for designs using Ultra Wideband, pulse-based spectrums. Until the arrival of the company's latest offering, however, it didn't address multiband (MB) OFDM UWB design.

The MB-OFDM UWB Design-Guide works with Agilent's Advanced Design System (ADS) and RF Design Environment (RFDE) EDA software. It gives designers the models and verification testbenches that they need to analyze the RF effects in OFDM UWB-based communications devices. Simulations like baseband, signal processing, and digital control are all performed in a mixed-signal environment. In addition, preconfigured signal sources and tests enable the quick simulation of circuitry that's used in Ultra Wideband applications. Best of all, designers no longer need to create their own testbenches or models—a tedious and error-prone process. As a result, the product design and verification process is substantially faster and more accurate.

One of the forces behind Agilent EEsof's new MB-OFDM UWB Design-Guide was Innovative Wireless Technologies (IWT). This wireless-communications company provides system- and circuit-design services to wireless chip-set providers. It specializes in developing solutions that use UWB, Project 25 Land Mobile Radio, JTRS, GPS, and proprietary protocols for government and commercial applications. Agilent partnered with IWT to develop the MB-OFDM UWB Design-Guide.

IWT believed that establishing a solid system specification early in the design process was critical to successful transceiver-chip-set development. After all, the lack of a solid specification may result in a suboptimal combination of subcomponent specifications. This result, in turn, may lead to expensive and time-consuming design respins. The MB-OFDM UWB Design-Guide offers designers a viable way to bypass these obstacles.

Yet IWT also is a current user of the tool. According to the company, this tool has been extremely valuable in its development of custom MB-OFDM UWB for commercial, homeland-security, and military applications.

Currently, two main technologies are vying for the IEEE UWB specification: direct-sequencing UWB (DS-CDMA) and MB-OFDM. A key difference between these two options is that the DS-CDMA architecture—in combination with a Silicon/Germanium (Si/Ge) substrate—isn't currently able to integrate multiple radio front ends. MB-OFDM technology, on the other hand, is capable of this integration. It also can support the development of a multi-protocol baseband architecture to support the utilization of cognitive radio methodologies.

When it's used in conjunction with Agilent's ADS, the MB-OFDM UWB Design-Guide is specifically optimized to deal with the design issues that are associated with multiple radio front ends. Through simulation, the design guide can determine radio performance including transmit spectrum mask, data rate, range, multipath degradation, interference rejection, and system timing (FIG. 1). Those simulations enable the rapid optimization of transceiver subcomponent specifications. For example, ADS simulations help to determine the amplification stage gain, noise figure, dynamic range, and linearity specifications. They also can demonstrate frequency-offset specifications and synchronization-timing-accuracy requirements.

To transmit 500-MHz-wide symbols, MB-OFDM sends 122 subcarriers in parallel (FIG. 2). Each subcarrier is 4.125 MHz wide. With the design guide, designers can determine the amplitude, phase, and raw bit error rate (BER) on a subcarrier-by-subcarrier basis. Performance at this level is used to establish the performance that can be obtained by the overall system.

CHALLENGES AHEAD

MB-OFDM UWB also has another great strength: It provides the high-data-rate transfer of wireless data at low cost and with minimal power consumption. Additional benefits will be derived from the fabrication of MB-OFDM UWB transceiver chip sets in CMOS technology. Such positive results will include cost, help with power consumption, and radio performance.

Despite these benefits, however, cost and power consumption will continue to be a challenge for designers—especially when they are trying to achieve optimal system performance. Such efforts require a good understanding and the ability to optimize a chip set's various subcomponent specifications.

Within the Agilent EEsof environment, chip-set subcomponent specifications govern product-differentiating performance. These specifications are referred to as the "Money Specs." According to IWT's Steve Selby, "The full specification of PAN and WLAN chip sets involves defining hundreds of subcomponent requirements. A small set of performance characteristics will determine whether a chip set is preferred over its competitors by application designers. The performance in these critical areas is determined by how a few subcomponent specifications of the chip set are met. Achieving better performance on these few 'Money Specs' produces significantly superior utility for the end user."

It follows that by combining the "Money Specs" in an optimized manner, one can greatly increase the probability of a design's success. Of course, this task isn't as easy as it may sound. It's not always clear which specifications will provide the biggest challenges for the implementation of MB-OFDM. For obvious reasons, though, suspicion falls on the core radio.

In that core radio, the analog-transceiver and digital-demodulation functions convert received signals into bits. The radio lets Agilent EEsof's MB-OFDM UWB Design-Guide, ADS, and RF design environments truly shine. Both ADS and RFDE allow the engineer to create the individual subcomponents of the transceiver. Using the design guide, the engineer can then ensure that the individual subcomponents work together optimally as a system.

The MB-OFDM UWB Design-Guide's testbenches provide the direct simulation of regulatory conformance, performance versus range, performance versus synchronization-time accuracy, and interference rejection (FIG. 3). The user can quickly enhance this core foundation to determine the tradeoffs of a specific design. At the same time, the designer can take advantage of standard ADS features like amplifier noise and linearity, LO phase noise, and frequency offset. The Design Guide's simulations of "Money Specs" can later be used to predict overall system performance.

The MB-OFDM UWB Design-Guide is now available. It is accessible directly from ADS. It also is available to the RF Design Environment through the ADS design-export capability. Together, these tools provide today's designers with a process for thorough system-level design analysis. They should serve as a critical linchpin by allowing designers to successfully and quickly bring MB-OFDM UWB products to market.

Agilent EEsof EDA, 30699 Russell Ranch Rd., Suite 170, Westlake Village, CA 91362; (800) 829-4444, www.agilent.com.

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