Two new developments in cellular technology could potentially transform the way cellular operators work with spectrum – with the emergence of LAA, Licensed-Assisted Access and LWA – WiFi Aggregation – raising questions about potential difficulties between licensed and unlicensed spectrums. This article takes a closer look at the two new terms – and just why they may be of such significance to the industry.
Defining LAA and LWA
LAA and LWA are both terms for similar technologies – essentially, Licensed-Assisted Access. This can be seen as an evolution of a prior technology known as LTE-U, Long Term Evolution in the Unlicensed spectrum. The main principle behind their use is that they enable unlicensed Wi-Fi spectrums, as well as others, to be used for cellular data to be transferred.
Using the unlicensed spectrum could enable operators to capitalize on growing the extent of cellular service, by opening a large portion of bandwidth for use across a number of channels. These may allow high-speed data offloading, by using carrier grade Wi-Fi, as well as helping to refine future cellular standards.
Benefits and risks associated
Despite the potential benefit offered by the technology, one of the main concerns they pose – and why they raise important questions for the industry to consider – is of potential interference with existing connections. LAA could have the scope to interfere with Wi-Fi points and hot spots, leading to a serious impact for a vast majority of cellular operators and their customers.
The risk of interference also raises another important issue – the impact of LTE deployment in an unlicensed spectrum, without regulation. As well as creating greater congestion of Wi-Fi channels, the lack of guidelines around them could lead to conflict between different carriers.
As the amount of spectrum available becomes increasingly limited, the options available to develop and improve data speed, or enhance user capacity for data intensive use such as video streaming, have also greatly reduced. Although 2016 will see an FCC spectrum auction, this will come at a high financial cost, for a relatively small amount of spectrum.
Unlicensed spectrums do carry the tempting possibility of boosting cellular service and improving growth, but there remains a fine line between that and the risk of major interference.
While some initial tests, such as those conducted by Qualcomm, have claimed that the use of unlicensed spectrum has not led to any adverse issues, there is a still extensive research that needs to be carried out.
Some industry experts who are raising concerns with the move to the unlicensed spectrum suggest that LAA, or its predecessor, LTE-U, is not designed to share the Wi-Fi spectrum, and hence could only lead to greater congestion. It also poses questions about other potential risks that could emerge from cellular operators being enabled to subvert spectrum intended for established, pre-existing Wi-Fi.
This will only be explored through more developed testing – as further investigations into LAA are carried out later this year, they may provide more of a clearer view into this industrial debate.
But regardless of what these debates may reveal, some providers have already decided to press ahead and implement LAA anyway, in order to see what may happen.
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Vector Network analyzers (VNAs) are an essential part of RF testing, as they allow designers to assess signal parameters and measure the performance of components and circuits across a variety of complex systems.
With a wide variety of analytical functions available across different models of vector network analyzers, they enable a number of components to be tested in detail — from high end VNAs that allow for amplifier and mixer measurements, to affordable handheld devices that provide support for spectrum analysis and power measurements.
This blog post takes a closer look at the wider testing options introduced by a new generation of vector network analyzers.
Using vector network analyzers
Vector network analyzers have been widely used across the industry for component testing and help to achieve more accurate characterization through measuring the amplitude and phase of swept-frequency test signals.
VNAs can be used to plot the amplitude and phase of a signal over a period of time – this information allows troubleshooters to assess a signal’s behavior and identify how it is being transmitted and reflected. Doing this can help to characterize signal scattering – a key issue that can impact the performance of a component.
Finding greater precision
Existing VNAs have a high degree of accuracy already, but with the addition of lasers, their function can be improved to enable greater precision in measuring signal strength and phase in components.
With a more complex structure, the new generation of prototype analyzers exceeds frequencies of 1THz. The enhanced precision of new network analyzers is due to the use of a femtosecond laser to generate test signals – using short and precise voltage pulses that are passed down a short gold strip of 4mm length, the electric field of a gallium arsenide chip can be changed. Another laser beam subsequently tracks and measures changes in phase and amplitude as the signal progresses.
This technique allows for greater precision in measurement, as it can resolve both signals travelling up and down, and additionally measure their reflection. By measuring voltage pulses at different positions, designers are able to separate voltage signals in both directions, even when signals are temporarily overlapped. Taking these values over a range of frequencies enables designers to characterize the device under test comprehensively.
However, while femtosecond lasers are low in price and simple to install, the new generation of analyzers is not entirely free of drawbacks. Its most obvious limitation is a smaller dynamic range – while conventional VNAs have a range of 120 dB, these are restricted to 40 dB, despite having a measurement bandwidth of 500 GHz.
Nevertheless, their overall simplicity and the broad frequency range accessible through a single piece of hardware is a significant advantage, and they are likely to continue to grow in usage.
What are your thoughts on the new generation of VNAs? Do you prefer to use more standard analyzers, or will these give you an advantage? We’d love to read your thoughts – share them with us in the comments!