It’s 7 am and you awake to the sound of classic rock from your radio alarm clock. Gosh, what’s that song? Your radio, equipped with the RDS standard, shows the words “Wanted Dead or Alive - John Bon Jovi” in digital text that scrolls across the screen. While you sip your morning coffee, a WLAN tranceiver lets you check your e-mail from the den. Ready for work, you enter the garage and use a 315MHz FSK transmitter to unlock your car doors. Another burt from a 43MHz ASK transmitter opens your garage door. As you back out of your driveway, you’re thankful that satellite radio provides you commercial-free entertainment. One song and it’s time for work. Moments later, a bluetooth transceiver is in your ear and a 3G cellphone is in your hand. It’s time for marching orders from your boss, and it looks like you’ll be traveling today. Within moments, your GPS navigation system has acquired a 3D position fix and you’re already well on your way. The voice on your GPS receiver is telling you to use the toll road, where an RFID reader will be used to charge your car the appropriate amount.There is no doubt that RF technology is everwhere. However, the explosion of wireless technology adoption by consumers has not come without increasing challenges to the engineers involved in creating these products. In fact, the RF test market has in many ways evolved in parallel with the wireless consumer market – with new consumer products defining the features on new test instruments.
This article will explain three trends in the wireless world that are both influencing the design of RF test instruments and the ways that engineers use these tools. These trends are:
• Increasing system-on-chip (SoC) integration
• New standards using advanced modulation techniques
• Increasing pressure to reduce test time
As a result of understanding each of these three trends, we will see why general-purpose, software-defined, and inherently flexible test platforms are necessary to meet each of these industry demands. Twenty years ago, we at National Instruments pioneered the term “Virtual Instrumentation” to describe test systems that use customizable software and modular measurement hardware to create user-defined measurements. While that idea might have been controversial at the time, today we observe this exact approach to measurements being driven by the RF and communications industry.
TREND 1: SOC INTEGRATION
Over the several years, consumer demand for more functional products has resulted in more and more wireless standards being integrated on the same device. Whether the device is a modern handset or even your car, the chances of it having more than one RF transceiver is increasing
How we know it’s here: Five years ago, I was impressed when my cellphone had a Bluetooth transceiver in addition to quad-band GSM support. Today, any cellphone without Bluetooth connectivity and 3G network support would seem antiquated. In fact, it’s likely that the next-generation Smartphones will support an even broader range of standards including GSM, EDGE, W-CDMA, WiMAX, WLAN, DVB-H, Bluetooth, and even GPS. Of course, integration of multiple standards isn’t limited to the cellular world. In the automotive world, today’s infotainment systems are designed not only to supply users with traditional AM/FM radio, but also to provide navigation services through GPS and video entertainment through either ATSC or DVB-T broadcast video.
Some of the best examples of increasing SoC integration are occurring in the Wireless LAN (WLAN) world, where the RF front end, WLAN baseband, and Bluetooth baseband are all integrated onto the same chip. In addition, there are many more “multi-standard” consumer devices which allow users to access multiple wireless technologies. For example, while the only RF receiver on a traditional GPS device was the GPS RF front-end, today’s GPS receivers may offer Bluetooth and even AM/FM capabilities.
As one might expect, increasing levels of multi-standard integration at the consumer level have slowly tricked down the value chain to the semiconductor world as well. In order to offer both lower costs and smaller footprints, many chip vendors now offer SOC architectures which integrate multiple transceivers onto the same piece of silicon.
What it means: While the transition to higher levels of integration at both the semiconductor and consumer product level is beneficial to consumers, it also proves to be a significant test challenge for engineers. In the past, engineers were able to rely on using a different box instrument for each standard they needed to test. There were GPS simulators for navigation devices, radio test sets for cellular devices, and even dedicated WLAN and Bluetooth test sets for those products as well. However, with the increasing integration of wireless devices, the old approach is simply too expensive. As a result, the wireless test world has fundamentally changed.
The predominant trend is for vendors to offer general-purpose RF generators and analyzers that are capable of testing a wide range of wireless standards. For example, with PXI RF measurement systems based on LabVIEW, the same hardware can be used to test AM, FM, RDS, XM/Sirius, ATSC, DVB, ISDB-T, UHF RFID, GPS, GSM, EDGE, W-CDMA, WiMAX, WLAN and other standards. As a result, engineers testing multiple wireless standards no longer have to purchase a new box for every new standard designed into their product. In addition, many general-purpose instruments can be upgraded over time to offer testing capabilities for new or emerging wireless standards.
TREND 2: NEW STANDARDS
The past decade has seen continuous innovation in the wireless communications industry with new wireless handsets and networking devices achieving higher data rates than ever before. However, the cost of this innovation also produces a significant challenge for today’s test engineers. Not only are next-generation communications devices more complex, but they also require more demanding measurement quality.
How we know it’s here: One recent mainstream innovation for wireless communications systems is the emergence of MIMO-OFDM (Multiple Input Multiple Output – Orthogonal Frequency Division Multiplexing). In 1949, Claude Shannon proposed what later became known as “Shannon’s Law,” which stated that maximum channel capacity was bounded by bandwidth and signal to noise ratio (SNR). This relationship is shown in the Equation below.
Capacity = Bandwidth x log2 (1 + SNR)
Within the past decade, we’ve observed significant innovation in techniques to maximize the efficiency of a wireless communications channel. While many traditional channels such as ATSC (broadcast video) and GSM (cellular) use a single-carrier modulation scheme, greater efficiency can be achieved using techniques such as OFDM (orthogonal frequency division multiplexing). In fact, standards such as DVB-T and IEEE 802.11a/g already use OFDM to maximize channel efficiency.
While Shannon’s law can be used to describe the maximum throughput for single antenna systems, multiple antenna systems can be used to produce even greater throughput. In fact, the demand for faster data rates in both fixed and mobile applications has produced a new generation of communications standards which use MIMO-OFDM. In Figure 1, we observe emerging standards such as WiMAX, 3GPP LTE, and IEEE 802.11n.
With consumers demanding faster and faster data rates in both fixed and mobile applications, it’s likely that we’ll see widespread adoption of next-generation communications standards such as WiMAX and IEEE 802.11n over the next couple of years.
What it means: For engineers testing next-generation communications devices, the use of MIMO-OFDM standards produces several critical requirements on test instrumentation. First, OFDM signals have some of the most demanding RF requirements. Not only do many of these signals typically use wider bandwidths, but they also have higher peak-to-average ratios (a characteristic of OFDM), requiring instruments with greater dynamic range. Second, the development of MIMO systems requires engineers to test devices with synchronized RF generators and analyzers. Finally, with new standards emerging at such a rapid pace, engineers also require instrumentation that can not only test today’s wireless standards, but can also be updated to test tomorrow’s standards.
TREND 3: PRESSURE TO REDUCE TEST TIME
While many of the wireless markets may actually shrink in 2009, we will continue to observe increasing pressure to reduce the cost of test. In fact, the need to reduce production test cost and reduce time-to-market for RFICs (RF integrated circuits) has placed increasing emphasis on lowering test time.
How we know it’s here: One of the biggest indicators of the need to reduce test times comes from the demands of our customers. Whether the product is a WLAN device, a cellular handset, or even a TPMS (tire pressure monitoring system) transceiver, engineers are continually finding new ways to reduce total test time. In many ways, the need to reduce test time is a natural result of products having lower material costs. As the cost of materials drops, production test time actually becomes a driver of product COGS (cost of goods and services). In the RF test world, two changes in measurement technology also suggest that many vendors face requirements to lower test times.
First, we’ve begun to see a systematic shift in RF vector signal generators and analyzers using VCO (voltage controlled oscillator) based synthesizers instead of the traditional YIG (Yttrium Iron Garnet). While YIG-based synthesizers traditionally offer better phase noise, VCO-based synthesizers offer significantly faster tuning speeds. With faster tuning times than YIG-based alternatives, VCO-based products such as the NI PXIe-5663 RF vector signal analyzer and NI PXIe-5673 RF vector signal generator are able to perform multi-band RF measurements more quickly.
A second indicator of the need for faster measurement times is the increasing number of “fast measurement mode” options on today’s RF vector signal analyzers. For example, many analyzers used for cellular devices offer a “FAST ACP” mode, in which measurements such as adjacent channel power (ACP) are performed in the time domain instead of in the frequency domain. While users generally tradeoff dynamic range, the options allow engineers to choose speed vs. accuracy.
What it means: The increasing focus on reducing measurement time means that engineers must find more efficient ways to test wireless devices. In some instances, this means using parallel test techniques in order to maximize the utilization of their instruments. In other situations, it means that RF analyzers must perform measurements faster than ever before. Fortunately, one of the benefits of software-defined PXI instrumentation is that measurement speed is a function of the PXI controller. As we observe in Figure 2, the measurement time of a PXI RF vector signal analyzer (NI PXIe-5663) for a 50MHz span is dependent on the CPU used in the system. Thus, measurement time can actually be reduced simply by using a faster CPU. For example, a 50MHz span spectrum measurement with a 100kHz RBW can be reduced from 3.3ms to 2.1ms by simply upgrading from an AMD Turon CPU to the latest Intel Core 2 Duo.
Thus, engineers using software-defined measurement systems can actually improve measurement speed in the future with faster CPUs.
While instrument measurement speed is important, it is not the only factor that can affect overall measurement time for automated test systems. In many cases, the efficiency of the test code can significantly affect test time as well. We’ve seen many customers use software tools such as LabVIEW and NI Teststand test executive to automate testing with both PXI and traditional benchtop instrumentation. With both of these tools, observation of proper programming practices can often significantly improve test time.
CONCLUSION
No matter what happens in the wireless market in 2009, three significant trends will continue to change the world of RF instruments. With the increasing integration of wireless products, the emergence of new standards, and the increasing pressure to reduce test time, RF instruments are changing. As a result, today’s RF vector signal generators and analyzers are not only more flexible than those of the past, but they also perform measurements faster than ever before. With the inherent need for fast and flexible measurements, we can only wonder if software-defined RF virtual instruments are the wave of the future.
About the author
David Hall is a product marketing manager at National Instruments, David Hall is responsible for driving the growth of RF and wireless communications hardware and software. He holds a bachelor’s degree with honors in computer engineering from Penn State University.
Click here for the illustrations: Figure 1, Figure 2 |
