802.11ac has seen a tremendous uptake in 2014 and the industry expects this technology to be adopted much more quickly than the previous standards.
IEEE 802.11ac has proven popularity now. That's because service providers have a critical need to offload their traffic and because the industry doesn't foresee any other major standards emerging in the near future. Capacity management came about as a big challenge as the industry sees a tremendous increase in demand for it, especially because many new devices don't have wired internet access. Furthermore, many users like to bring all of their devices to work – the BYOD (bring-your-own-device) phenomena -- sometimes up to a total of five connected devices at the same time. This demand for capacity is partially driving the demand for 802.11ac as well.
Although many 802.11ac products have appeared on the market, there is still hesitation on when to schedule 802.11ac deployments. Some of the challenges associated with this are cost of deployment, identifying the right product, and a steep learning curve. The good thing, though, is that 802.11ac is now an approved IEEE standard and Wi-Fi Alliance has a Wi-Fi Certified ac certification program available. 802.11ac opens up new possibilities for throughput, capacity, improved price-to-performance ratio, as well as the ability to use 5-GHz bands.
Several testing challenges emerged while testing 802.11ac standard, though.
Bandwidth: The 802.11ac standard functions at the 5 GHz license-free bands in the 80 MHz or 160 MHz bandwidth, which is much greater than earlier WLAN standards. According to Aeroflex, a single capture of the full signal bandwidth is required for conducting transmitter tests to measure EVM (error vector magnitude), frequency, power and spectrum flatness. The spectrum mask measurement provides the analysis of a significantly wide bandwidth; this operation is executed via spectrum stitching by recording and capturing snapshots of the signal and stitching, them in the frequency domain. For receiver tests, generating a full bandwidth signal waveform is necessary to stimulate the device under test (DUT). This allows receiver sensitivity tests during various modes of operation.
The spectrum specification of an 802.11ac channel is 160 MHz wide.
Multiple spatial streams: The 802.11ac standard increases MIMO (multiple input, multiple output) support up to eight spatial streams, allowing a terminal to transmit and receive a signal to and from several users on the same frequency band simultaneously. In the R&D application, MIMO requires test equipment to perform encoding or decoding of composite signals with multi-path channel emulation. At the manufacturing stage, the WiFi testing focus shifts to RF component calibration and quality assurance.
High-density modulation: The 802.11ac release highlights modulation schemes at up to 256 QAM (quadrature amplitude modulation), that is four times greater than 64 QAM used in previous WLAN standards. As a result, obtaining the required signal quality for high-rate transmission became more challenging. To accurately measure 802.11ac signals, the remaining EVM of the test equipment must be better than the lowest EVM requirement or negative 32 dB at 256 QAM, to avoid jeopardizing production numbers, according to Aeroflex.
Challenges in WiFi offload testing: Apart from the challenges mentioned, WiFi offload testing is expected to extend from performance tests in the laboratory to OTA (over-the-air) field tests for network assessment. Network equipment vendors do most of the testing in the lab using cabled RF to simulate network loads. With WiFi offload, mobile operators will ensure that site assessment will be an integral aspect of testing, and this will require expertise in OTA tests.