RF tests tendencies

Wireless communications are evolving rapidly, mostly from voice to data, and to the new modulation schemes in WiFi, WiMAX, 3G and LTE,

all creating new demands on RF test systems.

La tecnología de radio comercial en muchas vías ciertamente ha llegado a un punto de inflexión. The market demand for wireless communications continues to accelerate,

the shift to data-intensive applications such as text messaging, web browsing and video. Customers are always on the lookout for higher bandwidth and wireless service providers

want to sell high value services beyond voice, this is a given market.

To support these new customer demands, the underlying technology that provides voice and data services is evolving. These applications require high speed transmission

for easy use, this is creating new access roads for use of limited frequency spectrum. More types of spectrally efficient modulation and digital encoding schemes have been used,

improved-bandwidth from 200 kHz in the 90 to 40 MHz today.


Trends in Communication Technologies
Perhaps the most important trend in wireless is the change from single-carrier modulation OFDM (Orthogonal Frequency Domain Modulation) and the passing of the configurations SISO

(Single-Input Single-Output) to structures MIMO (Multiple-Input Multiple -Output). The carrier modulation formats only transmit a data symbol each time in a single frequency carrier.

To increase data transmission rates with this type of modulation is increased speed of command data. However, as the symbol transmission rate increases, issues such as signal fading of the multiple

paths are increasing their effect, especially in high mobility applications. In OFDM, many carriers are used and data are transmitted in parallel on all carriers.

This allows for transmission speeds slower symbol per carrier reduce the impact of issues such as signal fading multiple paths. OFDM modulation requires a higher level of DSP (digital signal processing)

on mobile devices. However, with the advancement of DSP technology, this level of performance can now be included in a mobile device to a reasonable price and consumption. The OFDM modulation

is used in WiFi, WiMAX and the emerging standard LTE (Long Term Evolution) mobile phones.
The transition from SISO to MIMO technology allows multiple data streams are transmitted simultaneously using the same frequency spectrum. These parallel data streams can be

used either to increase data transfer by transmitting different data on each antenna or to increase coverage by sending the same data on all antennas.
This change has been driven largely by consumer demand for mobile services and the reduction of DSP technology costs required to deploy wireless high bandwidth. MIMO

technology can now be used in wide range of commercial communications devices including mobile phones, PDAs and laptops. The net result is high data transmission rates with

these consumer devices.


Trends and challenges in testing
MIMO spectral efficiency acquires a new level by allowing transmission and reception Multiseñal. However, with high spectral efficiency reaches a high level of complexity.
There are a number of challenges involved in moving from SISO-based systems in MIMO to be considered by test engineers and technicians.
Another challenge created by the complexity of MIMO and OFDM is the number of streams in the same space of time that can be supported by the test system. For example, wireless LAN (WLAN)

and LTE support four stream configurations, and current WiMAX technology supports two streams.
A final challenge in the test receiver is to decompose mixed signal into multiple separate signals or streams. However, the biggest challenge relates to timing. Instrumentacion2-3N54.

The transmission of multiple signals requires accurate synchronization of multiple channels and adjust the sampling phase. Thus, signal analyzers and signal generators must have precise adjustment so you

can make accurate measurements and repetitive.Another challenge for test equipment is the bandwidth (BW). For example, WiMAX and LTE have a need for bandwidth of 20 MHz and WLAN 802.11,

the 40 MHz is, thus, the test equipment they need the flexibility to handle bandwidths, ideally without requiring acquisition of additional instrumentation.
There is growing use of multiple standards in many wireless devices, or a manufacturer can produce multiple devices using different standards. Therefore, the test equipment need to host the largest number

of formats (eg, GSM, GPRS, EDGE, WCDMA, cdmaOne and cdma2000). The implementation should allow the extent necessary for them all and, with precision, for example with small error vector

magnitude (EVMS). When a manufacturer adopts new standards, it creates migration of test equipment. Ideally, one would like to improve test equipment for cellular and new modulation formats, easily

and profitably, perhaps with only software changes.


Industry response to cost sensitivity
As wireless devices become increasingly complex, there is growing competitive pressure positioning the profit margins low. At the same time, the tests are becoming more difficult, pushing up unit costs.

Face of shrinking margins, manufacturers seek to reduce its costs wherever possible, including test equipment and test cost. This applies not only to the production facility, also in the R & D In both

environments, the need is growing for test equipment cost with increased functionality, high yield and ease of use.
Regarding the number of streams in the same space of time in WLAN, LTE and WiMAX, a main objective is to keep down the cost per stream without sacrificing performance.

However, the costs of test equipment, especially for MIMO systems, can multiply rapidly.
Equipment designs has never been aimed at these issues. For example, the MIMO test platform next generation of simple and inexpensive ago Keithley add support for new

signal standards and MIMO configurations. It consists of the new signal generator Model 2920 RF Vector, vector signal analyzer Model 2820 MIMO synchronization unit

and the 2895 model creation software SignalMeisterTM waveforms. This system supports up to 8x8 MIMO and measures is a commonly used wireless standards such as 802.11n WiFi, 802.16e Mobile

WiMAX Wave 2, and future as 3GPP Release 8 LTE and UMB (Ultra Mobile Broadband).
These possibilities are the result of some recent innovations in the industry. For example, a DSP architecture based on software defined radio (SDR) simply adapting to changing test needs. SDR-based

instruments can generate and analyze virtually any signal with just a simple extension of software. This extends the longevity of the team making it easy to extend the test system. The DSP technology also

provides exceptional performance. Ensures accurate, repeatable signals that help to minimize measurement errors. Similarly, vector signal analyzers can measure DSP-based low EVM at a per channel

basis and per symbol.
The DSP technology also contributes to increased production. Tuning allows faster frequency switching in less than a millisecond to more frequent steps. Similarly, the settling time after changing signal

amplitudes are also a few milliseconds. A typical DSP platform is complemented by a relatively large memory waveforms. This allows memory simultaneously in many waveforms to call them immediately.
Combining all these technologies in the most cost effective form of cost, the latest generation of RF test equipment helps wireless device manufacturers to control the lower their total cost of test. They can

carry out more tests, more quickly, and get a shorter time out of their products to market, while ensuring that critical parameters are appropriate.


About the author
Mark Elo ( This e-mail address is being protected from spambots. You need JavaScript enabled to view it ) is director of marketing at Keithley Instruments (www.keithley.com). He joined the company in 2006 after working for Agilent Technologies in management of marketing and R & D. Elo graduated with honors in engineering from the University of Salford, Lancashire, England, and an MBA from Herriot Watt University in Edinburgh, Scotland.

Keithley Instruments is represented in Spain by the Measuring Instruments Company, Ltd.

Author: Mark Elo. Keithley Instruments, Inc. Cleveland, Ohio (USA)