The following thoughts from an article by Mark Bole CEO of Talu Investee, Mesaplexx Pty Ltd. The time is right for disruptive radio filter technology…..
Delivering LTE Coverage and Capacity Gains –
Why Radio Filters Matter
Unprecedented growth in mobile data traffic continues to increase expectations on LTE technology. The pressure is on the operator and supporting vendor community to maximise spectrum efficiency to recoup substantial financial investment and sustain profitability. However, few industry experts expect LTE to carry the data burden in isolation; with many pointing to a collaboration of supporting technologies and techniques, to drive spectral efficiency and maximise network coverage and capacity to meet rising demand.
Active antenna systems (AAS), small cells and other compact radio systems are good examples of these supporting technologies. All are focused on generating additional network coverage and capacity and targeting it towards congested areas of the network. These technologies will become commonplace across next generation networks as part of a heterogeneous network layer.
Given the complexities of next generation network architectures, technologies such as AAS and carrier grade small cells must overcome some technical challenges if they are to reach their full potential. This means removing some of the existing limitations that stem from their existing radio components, and in particular, their radio filters.
Radio filters critical in achieving spectral efficiency
All filters share the same purpose and function – driving spectral efficiency. In the radio access node or base station, the filter selects which signals, in which band, reach the radio receiver, whilst rejecting unwanted frequencies. They achieve this by enabling radio systems to share the same spectrum within the same geographic area. Filters enable mobile operators to partition available spectrum and reduce the need for guard bands to be used to protect against interference caused by adjacent bands. By achieving this, and by blocking spectrum at the band boundaries, filters can maintain a greater number of channels in the band, thus maximising spectrum usage.
Three key challenges facing filter design – size, weight and performance
Equipment vendors are striving to improve the performance of their radio systems whilst making them smaller, lighter and more efficient. Other system components are being successfully miniaturised but infrastructure vendors continue to struggle when it comes to effectively shrinking radio filters. This is a significant obstacle in creating system architectures that meet the needs of the market. This is especially true given that the filters may have to offset any deficiencies caused by the miniaturisation of the other radio components.
Existing filters in AAS and small cells are too large and too heavy. AAS require multiple transceivers to facilitate advanced beam steering techniques and support multiple network technologies on multiple bands (multimode). This means several filters need locating in the antenna housing, and to achieve this without increasing the overall size and weight of the antennas, they need to be made smaller and lighter. It is also critical that filters do not absorb too much signal power. Doing so increases loss and weakens critical signal strength while generating too much heat. Many of these challenges also apply to small cells, limiting performance, coverage and capacity.
A breakthrough in radio filter design
The challenge of effective filter miniaturisation has now been overcome. A new compact, cool running, low loss, high isolation filter has now been developed that improves sensitivity and handles much more power than existing technologies. This filter uses multimode resonators, joined together by sophisticated coupling techniques to optimise performance. In fact, these coupling techniques effectively enable the re-use of the same resonator many times. This dramatically reduces the size of the filter.
Increasing capacity and coverage
The technology will enable operators to enjoy significant capacity improvements. This is achieved by reducing the insertion loss of filters and duplexers, reducing interference and improving the signal to noise ratio. By reducing insertion loss, the filter also improves network coverage by maximising the power amplifier throughput radiated from the base station, increasing the downlink range. It also improves the sensitivity of the system and the maximum range at which a mobile signal can be received and the range at which a device can be used. Handsets will also be able to negotiate a higher throughput at any given range or be able to reduce their transmitted power, thereby extending battery life. This enables better signal strength across wider distances, reducing the number of small cells and macro base stations required.
Power – delivering more with less
Conventional compact filter technologies are often unable to handle more than a few watts of power. This is unsuitable for a significant proportion of cellular networks, including many carrier grade small cells. However, increasing the amount of power causes unwanted heat within the system. This heat can limit overall performance and be expensive to remove. The latest filter technology is capable of reducing this heat by up to 50 per cent – it dissipates a much lower proportion of its input power (just 20 per cent) as heat. This not only leads to an increase in base station capacity but also increases power handling capability and reduces the cost and complexity of dissipating heat. By wasting less of the input power, more power is transmitted in the network. This enables power amplifiers to operate more efficiently, enabling cleaner, greener and more efficient networks and devices.
The ability to successfully miniaturise radio filters has significant implications for the vendor and operator community. The commercial reality at present is that existing radio systems are suffering from a variety of issues that can all be traced back to the performance of the filter. Some face heat challenges, while others are struggling with power output or achieving true multi-band capability. New filter innovation, such as xCube™ from Mesaplexx, enables network vendors to achieve the best possible network architecture by simultaneously solving a variety of challenges. The benefits include increased network coverage or capacity, improving power handling, enhancing sensitivity, reducing heat, lowering power usage, enabling multiband capability and delivering lighter, more environmentally friendly systems. These filters give the mobile industry real cause for optimism.