Test different wireless standards with the same platform

Engineers engaged in wireless communication design and testing are now facing unprecedented challenges. There are so many wireless communication standards that it is dizzying. With the rapid advancement of technology, new standards will emerge even more rapidly. Since various technologies have their own advantages and characteristics, it seems that no standard can monopolize the market. This article aims to point out how engineers can achieve testing of multiple standards through a single, software-centric platform in the case of multiple standards coexisting, so as to keep up with the pace of technological development.

Although wireless technology has traditionally been considered a vertical part of the telecommunications industry, it is expanding horizontally into many non-traditional markets. Wireless technology has now become a default device feature, for example: chips integrate multiple wireless technologies onto boards, wireless remote meter reading systems using ZigBee or GSM, cars use Bluetooth technology for non-band communications, tire pressure monitoring through wireless communications, widespread use of RFID technology, PC peripherals using wireless connections, industries rely on wireless sensors to monitor and control various operations, and so on.

Classification of existing wireless technologies

Looking back at wireless networks, we can see that wireless technologies can be roughly categorized into: wireless personal area networks, local area networks, metropolitan area networks, and regional area networks. Among them, wireless wide area networks can also be classified as cellular technologies. Figure 1 compares the ranges corresponding to different networks, and Figure 2 compares the ranges corresponding to different wireless standards.

Wireless Personal Area Network (WPAN) includes many different technologies and is the core of wireless home. Ultra-wideband, which is currently widely used to solve the problem of excessive home cables, uses the UWB protocol in this technology. Through it, users can get rid of complicated cables and freely place flat-screen TVs anywhere in the home. ZigBee targets the industrial sector and allows HVAC, lighting and sensor controls to be placed anywhere without cables.

Wireless Local Area Network (WLAN) is an extension of Personal Area Network. The main technology is 802.11, among which 802.11a/b/g is more familiar to people.

Wireless Metropolitan Area Networks (WMANs) include the upcoming WiMAX. 802.16-2004 includes two fixed-point standards, one below 11 GHz and another line-of-sight standard extending to 66 GHz. Since 802.16e adds roaming capabilities to WiMAX, it is foreseeable that it will be a very promising technology.

Wireless Regional Area Network (WRAN) has the widest range. Among them, 802.22 is a new standard under development that can work in the frequency range of 54-862MHz standard TV channels. Since the range of WRAN can exceed 40km, 802.22 will most likely provide support for WiMAX.

Future wireless technology brings hope

If we use a timeline to represent the various standards, the evolution of many standards will become very clear, and the development of new standards is proceeding at an unprecedented speed, as shown in Figure 3. Before 2000, there were only four or five coexisting standards, and they had a long life span, but today, this situation has been completely reversed. As new standards emerge like mushrooms after rain, the life cycle of each standard has been greatly shortened.

Here are some emerging wireless standards that are currently in the development phase:

◆ OFDM (Orthogonal Frequency Division Multiplexing) – This technology is becoming increasingly popular and is being implemented in many new standards

◆ 4G cellular technology

◆ Cognitive radio – As part of the 802.22 standard, this technology searches for empty spectrum to use when there is a conflict or traffic, and moves traffic to other unused spectrum

◆ Ad Hoc and sensor networks

◆ Software Defined Radio (SDR) – SDR uses reconfigurable hardware, such as FPGAs, to adapt the hardware to changing network requirements.

◆ Multiple-Input Multiple-Output (MIMO) systems – in this system, multiple antennas are used to increase system capacity

◆ Ultra-Wideband (UWB) - On first generation devices (3.1 to 4.8 GHz), each channel can use the full 528 MHz and transmit data at 480 Mbit/s

Corequisite Standards Challenge Test Difficulty

With all these new and old standards emerging and coexisting, equipment manufacturers, test engineers and designers will face many challenges. The usual purchase cycle for RF equipment is 5 to 7 years, but new standards and new technologies are introduced every two years, so the purchased RF equipment will soon become obsolete.

Software-centric testing platform can handle the situation with ease

Faced with such challenges, more and more companies are adopting a software-centric platform in combination with modular hardware to meet the evolving technology needs. Software-centric platforms can help users test new standards as soon as possible and accelerate the time to market for their products or solutions; they can meet the requirements of testing new standards by simply adjusting the software, which is extremely flexible; for engineers themselves, they can add their own intellectual property technology to the system to gain technical initiative, and technology will no longer be held only by standard manufacturers or institutions.

National Instruments (NI) has always advocated the concept of "software-centric test and measurement architecture". Since launching its flagship software LabVIEW in 1986, NI has been helping engineers improve their work efficiency through this innovative graphical programming language. Later, NI launched the PC-based industry standard test platform PXI in 1997. In 1998, NI and other test and measurement companies jointly formed the PXI System Alliance. So far, the alliance has more than 70 member companies and more than 1,200 PXI products, with functions ranging from power supply, DMM to RF, allowing users to select and combine according to specific test needs.

Today, LabVIEW, PXI, and modular instruments have become essential tools for engineers and scientists to develop and test new technologies, including wireless standards. In the following two cases, you will see researchers at the University of Texas at Austin using this technology to develop a 4G-based system in just 6 weeks; and a local company's successful solution for developing and testing 1C2G RFID systems.

Practice is the key to success

MIMO-OFDM 4G System Prototype Design

This is a representative example of how to quickly prototype and develop a system through this platform. OFDM (Orthogonal Frequency Division Multiplexing) is a multi-carrier digital communication modulation technology that selects mutually orthogonal carrier frequencies as subcarriers and uses multiple subcarriers for parallel transmission. OFDM technology can overcome the problem of increased interference between signals when supporting high-speed data transmission in CDMA, and has the advantages of high spectrum efficiency and simple hardware implementation. Therefore, OFDM is regarded as the core technology in the fourth-generation mobile communication system. MIMO (Multiple Input Multiple Output) uses multiple antennas to achieve multiple transmissions and multiple receptions, which can increase the channel capacity exponentially without increasing spectrum resources and antenna transmission power.

MIMO-OFDM combines the advantages of MIMO and OFDM, and can simultaneously improve the speed, range and reliability of wireless communication systems. It has now been written into the WLAN 802.11n and WiMAX 802.16 standards. The research on the fourth-generation mobile communication, which has attracted widespread attention in the industry, is still in its early stages, and its basic functions and core technologies are still in the conceptual stage. MIMO-OFDM is also one of the popular solutions for building 4G systems.

The University of Texas in Austin developed a MIMO-OFDM 4G system. Under the guidance of Professor Robert Heath of the UT Wireless Networking and Communications Laboratory, three students designed a prototype of a 4G system in six weeks.

The lab chose a software-based modular test platform because the readily available NI RF vector signal generator, RF vector signal analyzer, LabVIEW software, and modem toolkit allow researchers to start from a high starting point and focus on the development of the core parts. When completing the design process, it is necessary to build a prototype for the MIMO wireless communication system and provide practical verification for theoretical research. The traditional way is to use expensive dedicated hardware, which is time-consuming to program and difficult to maintain. After integrating NI software and wireless products, researchers at the University of Texas at Austin can create a wireless communication system, including various elements such as modulation, synchronization, and equalization. In addition, the hardware is also fully programmable, which facilitates new development and test requirements.

The hardware used by these researchers is a rugged, PC-based measurement and automation platform called PXI. PXI combines the electrical bus characteristics of PCI with the ruggedness, modularity, and mechanical packaging characteristics of CompactPCI, adds a dedicated synchronization bus, and the PXI controller runs the Windows operating system, making it a high-performance, low-cost carrier platform for measurement and automation systems. Figure 4 shows the PXI bus structure. In addition to the high-speed data throughput of 133MB/s, the PXI bus also has a precise trigger bus, a synchronous clock, and a local bus for data transmission between devices, which greatly improves the performance of the system.

A software-based modular test platform requires a flexible software platform. LabVIEW is a graphical programming language designed specifically for engineers. The LabVIEW front panel can be customized to display various user interfaces. In this case, on the front panel diagram (upper right corner of Figure 5), you can see two pictures of the campus - the top one is the original photo, and the bottom one is the restored picture after being transmitted by the 4G system. In addition, you can also see the constellation diagram and some measurements. The University of Texas at Austin successfully obtained a 4G solution using this technology, and now relevant personnel at the University of California, Berkeley are also using the same equipment for similar research.

C1G2 RFID Tag Test Solution

The Class 1, Generation 2 (C1G2) RFID standard is a recently launched standard by the international RFID standards organization EPCglobal, which specifies the communication protocol between RFID tags and readers operating in the ultra-high frequency (UHF), that is, the frequency range of 860-960MHz. C1G2 provides a faster, more secure, globally recognized and less expensive specification to deploy. So far, Europe and North America have accepted this standard.

C1G2 increases the tag reading speed to about 1,500 times per second in the United States and 600 times per second in Europe, compared to 100 to 300 times with current technology. When using C1G2, the writing speed is twice that of current products. This algorithm and spread spectrum technology allow readers to selectively communicate with different tags at acceptable distances and different frequencies. In addition, the standard solves the problem of interference between readers, and the reading distance of open space UHF can reach 10 to 20 feet. In terms of protecting tag information and user privacy, C1G2 includes password-protected read access and permanent memory content lock functions, and increases the password length from 8 bits to 32 bits. C1G2 uses a complex anti-collision algorithm to greatly improve the reader's ability to read a large number of tags in the reading area at one time. At present, when shopping and checking out in large supermarkets, it is necessary to take out the goods one by one in order to read the barcode information, which often causes congestion at the checkout during busy hours. If C1G2 technology is used, as long as the cart passes through the sensing area, the information of all the goods in the cart can be read, and this process may only take an incredible second.

While the C1G2 standard RFID brings many advantages, it also poses a problem for manufacturers in standardization testing. Since the standard is relatively new and the protocol is complex, it has high performance requirements for test equipment, especially RF real-time response capabilities. For semiconductor manufacturers that produce RFID products, this is undoubtedly a major obstacle to delaying the launch of products. When major companies have not yet launched test solutions on the market, a Chinese engineering company, Shanghai Juxing Instruments, took the lead in developing test equipment that supports all instructions of the C1G2 standard.

As shown in Figure 6, the test solution is based on NI RF modular instrument hardware. The intermediate frequency processing hardware is the software radio platform NI RF RIO (Reconfigurable I/O) with a powerful FPGA embedded in it. The software is implemented based on the LabVIEW graphical programming environment. Each RFID tag's response communication time can be completed within 400 to 500 microseconds. Currently, the test solution is being verified by the RFID standardization organization.

In summary, in the face of more and more wireless application standards appearing in the market, the software-centric test platform adopts high-performance modular hardware and flexible software platform to provide engineers with a unified platform to test various standards and easily meet the ever-changing market needs. On the one hand, this allows technology innovators to no longer be restricted by the restrictions of test manufacturers, and on the other hand, it helps those small-scale but strong companies to have high competitiveness in the rapidly developing market and become market pioneers.