Signal Analysis that Stays Ahead of Wireless Technologies

1. Introduction
2. Addressing Signal/System Complexity
3. New Display Types
4. Enhanced Tools for Enhanced Displays
5. Unparalleled Display Flexibility
6. Custom OFDM Modulation Analysis
7. LTE-Advanced Demodulation
8. Summary
9. Related Information

Engineers working with today's continually changing modulated signals and standards require constant improvement in their analysis tools just to keep up. For over a decade, the industry standard tool for addressing the challenge of advanced signal analysis has been Agilent Technologies' 89600 PC-based vector signal analysis (VSA) software. This software takes data from a wide variety of front ends, beginning with RF and baseband/IF analyzers and extending to logic analyzers, oscilloscopes, optical analyzers, and even simulation software and mathematical programs such as MATLAB®.

While the analysis capability of the VSA software has expanded through more than a dozen major versions to handle the widest variety of modulation types and communication standards, and focus on the leading-edge techniques like OFDM and MIMO, continuous and dramatic increases in signal and system complexity have stretched the limits of its architecture. Today's engineers demand a new approach to signal analysis, one that embodies not only extensions and improvements in signal analysis capability, but a simpler user interface as well.

Agilent Technologies' next-generation VSA software, the 89600B, offers just such a solution for advanced signal analysis--one that stays ahead of wireless technologies. With new measurement, display and user-interface capabilities, it speeds the engineer's time-to-insight. Its ability to display up to 20 traces at once, with up to 20 markers for each trace, provides engineers with simultaneous views of every facet of a signal, helping them to see the "why" behind system interactions and problems (Figure 1). Running on a PC Windows® platform allows the VSA software to stay ahead of R&D challenges by taking advantage of increased processing power, algorithm innovations, display size, and flexibility. It also enables fast delivery of the latest updates and enhancements. Whether operating inside an instrument or an attached PC, the VSA software provides engineers with an unmatched window into what's happening inside complex wireless devices.

The 89600B VSA software delivers this functionality thanks to a number of key innovations, including: new types of displays, enhanced tools for enhanced displays, unparalleled display flexibility, custom OFDM modulation analysis and new analysis tool for LTE-Advanced modulation.

The transient nature of many signals and their faults (errors) and the increasing prevalence of complex time-varying signals has led to the development of trace types beyond the traditional spectrum and signal envelope (time-domain) displays. For example, designers are now taking advantage of displays that compile statistics and signal history in one form or another, such as with the popular spectrogram and complementary cumulative distribution function (CCDF). There is also growing interest in variable (or digital) persistence displays and statistical displays comprised of signal frequency/amplitude versus probability data.

While the 89600B features the same spectrogram and CCDF offered by the 89600, it also adds cumulative history and digital persistence displays of any measurement type. The new displays make it easier to visualize how signals change over time and, in the case of cumulative history, to not only spot rare events but measure how rare they are. For spectrum measurements, each point in the cumulative history display is associated with a frequency, amplitude and frequency of occurrence or density figure. The relationship of these views is illustrated in Figures 2 and 3.

Advanced display types are most useful when they can be generated from any data source. In the 89600B, any display or trace type can be generated from live or recorded measurement data, in either a free-run or triggered mode. The triggering includes adjustable pre-trigger delays (analyzing signals before the trigger event) or post trigger delays. Trigger enhancements include time holdoff with above/below level selection and polarity, which allow full independence of the triggered and measured elements of the signal under test.

Some of the trace types that are new to spectrum/signal analyzers and VSAs are primarily visual tools, while others are a visual representation of a database of measurement traces. Obtaining quantitative data after being steered by the visual assessment of traces (of any kind), markers and trace downloads can be very useful. With the 89600B, up to 20 markers can be used on a single measurement trace (up to 20 measurement traces), whether separate or overlaid. These markers can be placed on the trace or set to any display position, allowing bit-map displays (e.g., cumulative history) to be examined in detail for signal statistics (Figure 4).

The 89600B offers a great deal of marker flexibility with features suited to individual point measurements, as well as to the use of markers as a data-harvesting tool when combined with traces devoted to marker tables. Markers can be constrained to the measured trace in the traditional manner or set to any fixed point. The readout of specific display points by these fixed markers is especially useful for statistical or history traces as it enables easy readout of particular parameters desired by the engineer.

One way to enhance productivity and insight when dealing with complex signals is to present different signal measurements at the same time. Often times, this allows problems that may be obscured in one domain to be seen in another. With large format, high-resolution displays and multi-display setups now inexpensive and commonly available, it is much easier to take advantage of this capability.

The 89600B's display enhancements deliver this functionality, but with dramatic improvement, offering support for 20 active traces, each with a full complement of markers (Figure 5). Any trace can be configured for any measurement, in any window (attached or detached) and at any time. Flexibility in overlaying trace data (no matter the trace type) for composite displays further enhances the engineer's insight and ability to document phenomena.

The 89600B's display flexibility extends to complete freedom of aspect ratio and placement of the traces or display windows. This enables optimal viewing of measurement results since time domain and RF envelope traces are often landscape format, while constellation displays are normally square. Spectrogram displays are typically portrait format (tall and narrow) to show how signal spectrum changes over a significant length of time.

The 89600B's support for a large number of traces offers a number of critical benefits. It makes it

• easy to examine many different measurement results (e.g., constellation and symbol or error tables) at the same time, to correlate phenomena (e.g., RF envelope and spectrum) and get engineering insight; and
• allows multiple traces to be organized into different groups, each of which can be optimized for viewing different phenomena related to time, frequency or modulation. This eliminates reconfiguration of the analyzer display setup when switching from one type of analysis to another.  Traces can also be grouped by transmit chain and/or stream for MIMO measurements or other multi-antenna techniques such as space-time coding or beam steering.

Measurement setup and adjustment is more convenient as well, with support for multiple control windows on the display at the same time, streamlining the user interface for today's complex measurements.

The OFDM modulation scheme is today used in a wide variety of telecom and data communication applications, and is written into many of the newest standards (WiMAX™, LTE and 802.11n). It has even been chosen as the transport layer for a number of non-standard and custom wireless communication services, both commercial and noncommercial. As a consequence, R&D engineers need a powerful and flexible analysis tool for both general signal and modulation analysis.

The 89600B, with its flexible OFDM option, meets this need. The option allows engineers to specify all OFDM characteristics (e.g., number of carriers, carrier spacing, pilot locations, modulation types, power, and frame structure) and then provides the usual set of modulation metrics through the 89600B user interface. While not as simple as pressing a button to select a standard, the incremental configuration required to access the OFDM functionality need only be made once.

The newest version of the LTE standard—LTE Advanced—is a true 4th generation digital wireless technology. In support of this standard, the 89600B incorporates a new measurement/trace type called Antenna Beam Pattern (Figure 6). To produce the display, simultaneous measurements from multiple transmitters are used to derive the resulting radiation pattern. The two-user beamforming pattern displays radiation intensity versus azimuth, providing engineers with easy, independent visual confirmation of their multi-antenna transmitter setup. This display is made possible thanks to the 89600B’s support for the open Windows architecture and multiple-platforms, which enables it to be easily adapted to the latest communications standards and revisions.

The 89600B keeps designers at the leading edge of wireless technology through a host of new analysis and display features, and a user interface re-engineered to take advantage of the latest computing and display technology. Engineers get views into every facet of a signal, at any stage in the block diagram—from the digital baseband to the RF antenna. They also gain an analysis tool for every phase of development, from simulation in MATLAB and SystemView to single or multi-channel RF and microwave signal analysis. A single tool, with a consistent user interface and algorithms handles it all, eliminating multiple steep learning curves and providing the fastest and most direct path to a successful design.

Agilent Technologies Inc. (NYSE:A) is the world's premier measurement company and a technology leader in communications, electronics, life sciences and chemical analysis. The company's 19,000 employees serve customers in more than 110 countries. Agilent had net revenues of $5.4 billion in fiscal 2007. Information about Agilent is available on the Web at www.agilent.com.

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