Communications Test

Emerging 4G mobile wireless radio technologies such as long term evolution (LTE) and WiMAX are focused on delivering higher levels of throughput.

Troubleshooting communications test systems can be made easier if the hardware and software development are separated from each other. Problems can be more readily found and corrected by following this approach.

The design and verification of today’s complex digital communications systems present a multitude of interesting challenges. A particularly difficult problem is the impairments caused by RF components such as filters and amplifiers included in the signal path as well as interfering signals that pass through the RF link. Linear devices such as filters typically add phase distortion and group delay to the signal, and nonlinear components such as amplifiers cause intermodulation (IM) products that generate additional harmonics.

Interest in nonlinear behavioral modeling continues to grow as evidenced by the recent formation of the OpenWave Forum. As stated on the forum website, "The … alliance of RF and microwave firms [was] formed to collaborate, create, and promote a unified and transparent data exchange format for large-signal simulations, measurements and models."¹

Expectations for devices in the rapidly expanding smartphone market segment are high. In addition to reliable voice calling, they must support data services over a range of cellular technologies (GPRS/EDGE, WCDMA/HSPA, CDMA) across multiple bands to enable global roaming as well as Wi-Fi and Bluetooth.

The mobile phone market is undergoing its next phase with the transition from largely single-connectivity cellular-only phones to multistandard connectivity or cellular + Bluetooth + Wi-Fi phones. The increasingly ubiquitous smartphone embodies this development.

Digital designers reach for an oscilloscope as the tool of first choice for debug. As products under development can have a myriad of issues to debug, oscilloscopes with versatility give faster insight to shorten development cycles and produce higher quality products. Additionally, a recent scope-based innovation provides three instruments in one: oscilloscopes with built-in logic and protocol analysis. What are the advantages and trade-offs of these tools vs. traditional scopes plus a separate protocol analyzer?

Looked at from several points of view, long-term evolution (LTE) is an apt name for the latest wireless initiative. Literally, it is the name of the 3GPP project to define the long-term evolution of the universal mobile telephone system (UMTS) to a true fourth-generation (4G) level.

In real estate, it’s location, location, location. In data and communications networks, it’s bandwidth. No matter how often the word is repeated, bandwidth remains smaller than the amount of data people want to transport. VoIP, video on demand, and Internet music file downloads are only three of many applications adding to network traffic. As more applications like these become popular and the cost of data communications continues to decrease, the volume will grow to occupy the available bandwidth however large it may be.

The bit error ratio (BER) of a serial data stream is impacted by both jitter and noise. There are several tools that allow the visualization and measurement of jitter, such as BER contours and BER vs. decision timing, also known as the bathtub curve.

If you had a 3G base station in your own home or office, wouldn’t life be wonderful? You could surf the Web at warp speed with high signal strength, watch streaming video all day long, and make unlimited phone calls all from your 3G phone. With a target price of only $100 or so, a femtocell will provide these capabilities and more just for you.

Phase coherence, that is a stable phase relationship between signals, is essential when making measurements that require more than one RF output. While this was once primarily required when evaluating the performance of phased-array antennas in military applications, it has become more and more important now that wireless systems are using MIMO and beamforming techniques to increase network performance.

Engineers preparing to measure long-term evolution (LTE) face many challenges. For one, LTE introduces orthogonal frequency division multiplexing (OFDM) into the cellular world. It also brings bandwidths of up to 20 MHz, significantly wider than those of earlier technologies such as GSM and WCDMA. Understanding the tests defined in the specification, knowing the issues associated with particular tests, ensuring that the equipment is in place, and training personnel are some of the considerations.

If you need to transfer data at rates above a couple hundred megahertz, use a serial link. There are several to choose among including the many Ethernet versions, PCI-Express (PCIe), SAS, SATA, USB, and DisplayPort. Most of these standards have been upgraded at least once and today operate at bit rates ranging from DisplayPort’s 3.2 Gb/s to 10 Gigabit Ethernet at 10.3125 Gb/s. Both 40-Gb/s and 100-Gb/s Ethernet are under development, so you can expect bus speeds to increase well beyond present values.

Mobile communications networks truly have changed the way we live. Many years ago, lots of dimes and a memorized list of public phone locations were critical to a big-city salesman’s success. You had no other way to inform a client that you were tied up in traffic or that your car had broken down. Today, cell phone service is ubiquitous. However, for network operators, meeting ever-higher expectations for both voice and data communications is a continuing challenge.

Long ago, verifying the performance of a digital communications system was straightforward. The entire network was installed and owned by a single company, and if the system worked, extensive testing of the subcomponents was unnecessary. But in this age of optical networks using components produced at many different sources, proper compliance testing must ensure that system-level specifications are met when all components are connected, no matter where the components came from.

Although the term DigRF may lead to initial impressions of a digital signal somehow integrated into an RF signal path, this is not the case. DigRF is a published standard that describes a digital interface between baseband and RFIC chips.

Protocols are sets of rules. In data and communications networks, they define how information must be organized for it to be correctly interpreted. There are thousands of protocols in use today, and they all have a life cycle.

Today’s digital systems, from the video game console to the complex switching elements in a communications network, rely on serial bus technology to do their job. Not surprisingly, a host of application-specific serial buses has emerged.

The rich availability of Wi-Fi connectivity and the universal demand for constant access to voice and data communications are driving consumer and enterprise demand for converged Wi-Fi/cellular applications and services. Under the banner of fixed-mobile convergence (FMC), these applications promise better access to voice and data services as well as lower communications costs.