Standards Expand For Enhanced Performance

Dec. 16, 2011
Wireless communications standards continue to evolve by expanding channel bandwidths and extending the use of advanced technology, including higher orders of modulation.

Wireless communications standards are constantly in flux, with standards bodies such as the Institute of Electrical and Electronics Engineers (IEEE) and the International Telecommunications Union (ITU) seeking to test the limits of different operating frequencies, bandwidths, and modulation formats. Some standards currently awaiting finalization include LTE Advanced, IEEE 802.11ac, and IEEE 802.11ad.

The Long-Term-Evolution (LTE) cellular communications standard was meant to be a candidate for fourth-generation (4G) cellular services, but fell short in terms of certain requirements for 4G systems. LTE Advanced, which is sometimes referred to as Evolved Universal Terrestrial Radio Access (E-ULTRA), represents an improved version of LTE. It is designed to be backward compatible with both conventional LTE systems and earlier generations of cellular communications technologies; in addition, it also meets the full ITU performance requirements of a 4G cellular system, including the capability to operate at peak data rates to 1 Gb/s and beyond. LTE Advanced is structured to share frequency bands with the original LTE release.

Several proposals have been circulated for LTE Advanced. These include formats with scalable bandwidths from 20 to 100 MHz; with interference suppression and forward error correction (FEC); using cognitive radio techniques and multiple-input, multiple-output (MIMO) antenna architectures; and employing advanced modulation techniques, such as a hybrid combination of orthogonal frequency division multiple access (OFDMA) and single-carrier FDMA (SC-FDMA) in the uplink. Leading test-equipment suppliers such as Agilent Technologies and Rohde & Schwarz have already demonstrated test solutions for lte advanced.

In terms of wireless networks, the IEEE 802.16 standard known as WiMAX has gone through several revisions since 2001, all aimed at adding speed. The original standard, for example, was meant for fixed users. It was modified for mobile use via mobile WiMAX standard IEEE 802.16e-2005, with the speed increased to 1 Gb/s earlier this year via IEEE 802.16m-2011 for 4G usage.

Like LTE Advanced, the latest version of WiMAX (or WiMAX 2) is designed to use MIMO technology in antenna arrays as large as 8 x 8 and to use quadrature amplitude modulation (QAM) at levels as high as 128-state QAM (128QAM). As with many wireless standards, WiMAX 2 is designed for backwards compatibility with its earlier versions. Expectations for WiMAX 2 using a 4 x 2 MIMO configuration are for upstream data rates to 60 mb/s and downstream data rates to 120 mb/s, depending upon separation distance between transmitter and receiver.

Two extensions to the IEEE 802.11 family of wireless-local-area-network (WLAN) standards, IEEE 802.11ac and IEEE 802.11ad, are seeking to extend composite data rates to as high as 7 Gb/s. The former standard will operate within the existing WLAN frequency bands while the latter will make use of millimeter-wave bands freed for commercial use by the United States Federal Communications Commission (FCC), including the 60-GHz band. The IEEE 802.11ac standard, which is also referred to as IEEE 802.11 VHT (for very high throughput), will extend the channel bandwidth to 80 and 160 mHz from a bandwidth of 40 mHz for the current IEEE 802.11n WLAN standard. the VHT standard will also support as many as eight MIMO spatial streams as well as higher density modulation (256QAM) compared to 64QAM in IEEE 802.11n. Very recently, the first IEEE 802.11ac chipset, the model QAC2300, was introduced by Quantenna Communications for IEEE 802.11ac WLAN developers.

Lastly, by using higher frequencies and their readily available bandwidths, IEEE 802.11ad seeks to achieve data rates to 7 Gb/s at 60 GHz for distances from 1 to 5 m. Initially considered as a "high definition wire replacement," IEEE 802.11ad included support for beamforming techniques and the use of SC-FDMA and OFDMA modulation technologies. Earlier this year, Qualcomm Atheros and Wilocity announced the availability of the AR9004TB chipset for developers of 60-GHz IEEE 802.11ad WLAN products.

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