Testing Times in the Continuing Evolution of WLAN
By atesmeh | July 29, 2014
The 802.11 WLAN standard continues to evolve, making comprehensive design and test capability critical to the successful development and implementation of new amendments.
We're all part of the tsunami of data in our world, where we seem to have developed the need to stay connected to everything all the time. We have multiple devices that need to be connected together including: computers, smartphones, tablets, printers, games consoles, media servers, and scanners. The Internet of Things (IoT) — forecast by some companies to host up to 50 billion wirelessly-connected devices by 2020 — demands yet more network capability and capacity. Equipment based on the 802.11 wireless LAN (local area network) standard is forecast to fulfill a major part of this need.
IEEE 802.11-2012
IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specifications for implementing wireless LAN (WLAN) communication. The standard was created, and is maintained, by the IEEE LAN/MAN Standards Committee (IEEE 802). It provides the basis for wireless network products using the Wi-Fi brand under the Wi-Fi Alliance.
As far as the IEEE Standards Association is concerned, there is only one current standard, IEEE 802.11-2012, which is denoted by IEEE 802.11 followed by the date it was published. It is the version currently in publication and is updated by means of amendments, which are created by task groups (TG). Both the TG and the finished document are denoted by 802.11 followed by a non-capitalized letter. While each amendment is officially revoked when it is incorporated in the latest version of the standard, the industry tends to market the amendments because they concisely denote capabilities of its products. Therefore, in the marketplace, each amendment (e.g. 802.11ac) tends to become the accepted means of differentiating product capability. Updating 802.11 is the responsibility of task group m (TGm). In order to create a new version, TGm combines the previous version of the standard and all published amendments. It also provides clarification and interpretation to the industry on published documents. The Wi-Fi Alliance is the trade association that holds the Wi-Fi trademark under which most products are certified and sold.
WLAN Adoption
Because WLAN is being integrated into more consumer products such as high-definition video cameras and smart TVs, the demand for higher rates and more simultaneous connections is increasing. Adoption of WLAN in the enterprise environment to simplify office wiring layout and reduce costs has raised the bar on system security and quality. In an expanding effort to enable the "always connected everywhere" world of people and IoT, IEEE 802.11 is expanding its reach into niche applications, unused spectrum, and evolving use models. In addition to the 2.4 and 5 GHz frequency bands originally used, and the later addition of 3.6 GHz, there are active amendments to the standard for WLAN for vehicular applications (802.11p), TV white space frequencies (802.11af), sub-1 GHz applications (802.11ah), and very high throughput versions (802.11ac at 5 GHz and 802.11ad at 60 GHz) to support extended applications.
Redomain
While 802.11 is an international standard, devices need to meet local regulations. IEEE uses the phrase "regdomain" to refer to a legal regulatory region. Different countries define different levels of allowable transmitter power, time that a channel can be occupied, and different available channels. Domain codes are specified for the United States, Canada, ETSI (for Europe), Japan, and China. Most certified devices default to regdomain 0, which means least common denominator settings, i.e. the device will not transmit at a power above the allowable power in any nation, nor will it use frequencies that are not permitted in any nation. The regdomain setting in an individual device is often made difficult or impossible to change so that the end user does not conflict with local regulations.
New Amendments for VHT
To keep pace with evolving user expectations, two new amendments for very high throughput (VHT) have been specified. 802.11ac is a higher speed and capacity extension to the general-use capability of 802.11n, providing a minimum of 290 Mbps with single spatial stream and maximum 6.9 Gbps throughput with multiple spatial streams, running in the existing 5 GHz band. The physical layer is a superset of the existing 802.11n standard and is fully backward compatible with it. Table 1 shows the physical layer features of 802.11ac and highlights the mandatory and optional extensions from 802.11n.
These two changes are the optional move to higher-density 256 QAM modulation and the increase in the number of spatial streams (i.e. separate transmit/receive channels carrying separate data that is re-combined after reception). Both aim to increase throughput by increasing the capability of the physical layer. The much wider 160 MHz and 80+80 MHz channel bandwidth modes are both included as optional features, and will be a focus for chip and device development.
For test equipment suppliers, new simulation models, and signal generation and analysis tools must include scenarios of non-contiguous frequency blocks, as well as being able to cope with the need for 160 MHz modulation bandwidth at 5 GHz. For transmitter design and development, today's vector signal analyzer (VSA) must be able to cope with the correct demodulation, analysis, and display of a wireless signal that uses two frequency blocks, OFDM modulation, and may comprise up to the eight MIMO data streams allowed in the standard. Figure 1 is an example display of 802.11ac demodulation result, showing each of the eight MIMO transmit streams and a summary table of the results.
The receiver needs to recover multiple simultaneous signals and adequately demodulate and decode them. The signal generation equipment needed for receiver design and development has the same overall frequency, bandwidth, and multiple data stream requirements as for the transmitter. In addition, it needs to provide a wide range of stress-test conditions, including repeatable, deterministic dynamic fading of each MIMO path, as well as interference scenarios to ensure the receiver is designed to cope with the worst scenarios. A modular-based multi-channel signal generator, or up to eight separate signal generators, may be needed to produce the required MIMO channel, along with additional generators to provide interference.
While 802.11ac is an extension of the existing 802.11n specification, 802.11ad represents a completely new paradigm aimed at very short range and very high rate applications. The 802.11ad amendment defines a backwards-compatible extension to the IEEE 802.11-2012 specification. It extends the MAC and PHY definitions, as necessary, to support short-range (less than 10 m) wireless interchange of data between devices over an ad-hoc network at data rates up to approximately 7 Gbps in the 60 GHz unlicensed band, where 2 GHz modulation bandwidths are practical. It has been specified by Working Group TGad in partnership with the Wireless Gigabit Alliance (WiGig).
WiGig & Wi-Fi Alliances
In 2013, WiGig Alliance and Wi-Fi Alliance united, consolidating WiGig technology and certification development in the Wi-Fi Alliance. The ITU-R specified global channelization and corresponding spectrum mask for the occupying signal for 802.11ad comprises four channels, each 2.16 GHz wide, centered on 58.32, 60.48, 62.64, and 64.80 GHz. Channel 2 is the globally available default channel for equipment operating in this frequency band. Multiple-antenna configurations using beam-steering are an optional feature of the specification. Beam-steering is employed to circumnavigate minor obstacles like people moving around a room, or a piece of furniture blocking line-of-sight transmission. The 802.11 specification also supports session switching between the 2.4, 5, and 60 GHz bands.
Major differences from other wireless communications systems are the wider modulation bandwidth and the physical construction of the devices, where the antenna is bonded directly to the RF components and a direct metallic connection is not possible. The system shown in Figure 2 combines all the equipment needed for transmitter and receiver design and development in one software-controlled package, providing signal generation and analysis capability tailored to high-bandwidth applications running in the 60 GHz band. The system allows the use of calibrated horn antennae to overcome the lack of physical connection.
The 802.11 WLAN standard continues to evolve. The need for reliable, and in some cases, mission-critical connectivity is driving development to meet the needs of new applications. Comprehensive design and test capability is critical to the successful development and implementation of new amendments, and to their acceptance by both corporate and end user customers.
This article originally appeared in the January/February print issue. Click here to read the full issue.
Filed Under: Aerospace + defense, M2M (machine to machine)