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Thursday, 02 July 2015 11:39

Ka vs. Ku - An Unbiased Review Featured

Ka-band is being touted by some as the next big thing for satellite technology, with smaller terminals and dramatically lower costs - but how does it really compare against both legacy and emerging Ku based solutions? Getting clear and concise information about the Ka and Ku bands and their respective strengths and weaknesses is no mean feat, and there continues to be a debate around which of the two provides a better foundation for communications services. 

Fundamentally, the discussion is based on the trade-offs between different RF frequencies. Ku-band occupies approximately 12-18 GHz, while Ka-band is allocated to the 26.5-40 GHz range of the electromagnetic spectrum. To get more granular in the debate, we must examine several important factors related to these different frequencies such as: antenna size, susceptibility to environmental interference, and geographical availability.

Figure 1. A Comparison of Frequency Bands and Corresponding Features

Antenna size

Antenna size has important implications for performance and is necessary to consider when calculating a link budget for a particular application. The higher frequency Ka-band allows use of antennas that are a quarter the size of their Ku counterparts in order to achieve the same gain characteristics. For example, the Skyware Global 1.8m Ka antenna has a transmit gain of 52.5 dBi at 30.0 GHz, compared to the same size 1.8m Ku antenna with a gain of 46.8 dBi at 14.3 GHz. This is almost four times more gain from the Ka antenna. The smaller antenna size for Ka systems vs Ku certainly has its advantages, dramatically reducing the space and weight needed for transportation, and allowing global mobility like never before. 

Environmental Interference, a.k.a. “Rain fade”

“Rain fade,” or interference caused by certain atmospheric conditions, is a frequently discussed topic in the Ka- vs. Ku-band arena, and is one of the biggest challenges affecting communications reliability. Rain fade is generally caused by wet snow and other moist precipitation (interestingly, dry snow has a minimal impact). The most significant attenuation due to rain is typically seen during relatively short periods of very intense rainfall.

With satellite bands, the higher the frequency/smaller the wavelength, the more susceptible it is to weather and atmospheric interference. Because Ka-band is at the top of the commercially available frequency range, it is somewhat more complex to provide high availability and reliable services as compared with lower frequencies. However, because the legacy Ku-band is also impacted by rain fade, an array technologies have been developed to help mitigate the effect of weather for systems across both frequency ranges.

For example, Newtec has announced a suite of hub and modem technologies that work in concert to overcome interference. Some of these technologies are known as FlexACM, Cross-Layer-Optimisation and Mx-DMA, which can be integrated into existing infrastructures. FlexACM works by optimising IP backbone and IP trunking, by automatically checking link conditions, anticipating degrading, and dynamically adjusting the satellite link parameters accordingly. Cross-Layer-Optimisation can be used in conjunction with this technology, and further improves performance by shaping both the IP and RF part of the network. 

For fixed bit rate services, Mx-DMA technology can ensure reliable bandwidth and service without the extra costs encountered with traditional outbound mitigation technologies such as ACM - in the case of rain, simply the baud rate of the carrier where it rains is increased, while dynamically the center frequency of the other carriers is moved, ensuring a fixed bit rate for all carriers. Combined, these bandwidth management technologies go far to reducing the impact of rain fade interference.

 In addition to this, new High Throughput Satellite (HTS) systems also better enable Ka- and Ku- alike to overcome weather issues, as compared to traditional wide beam systems. Spot beams are ‘hotter’ than conventional wide beams which must spread their energy across a wider area, and therefore have a greater ability to cut through weather. HTS systems are also designed to dynamically adjust their characteristics, such as individual beam power, to account for atmospheric conditions in a particular sub-region.

For applications with the most demanding needs for service availability, another solution is to combine Ka- or Ku-band systems with a lower frequency backup, such as L-band. This hybrid approach is becoming increasingly popular especially for mobility in maritime applications, and enables a terminal to maintain connectivity by using a ‘backup’ frequency during periods of particularly bad weather. The goal for hybrid terminal solutions is to allow for rapid and seamless switching between the L-band and K-band services, so that connectivity is not disrupted. 

Availability

Geographical availability is another important factor to consider when deciding on a Ku- or Ka- band system. As a legacy band, Ku has witnessed insatiable demand for global broadband services in recent years, and in some geographical regions the available capacity has become exhausted for particular application requirements. For those applications in areas that can’t gain access (or sufficient bandwidth) because services are saturated, Ka- band deployments unlock ‘new’ capacity. Currently, Ka-band services are not as globally available as Ku, however with the launch of new networks such as Inmarsat’s Global Xpress, the band will soon become available on a worldwide scale. 

Side Note: Ka Efficiencies for Military Customers

For Military users, Ka has arguably the most benefits and offers notable efficiencies over Ku. For example, Ka-band is the only frequency where the commercial and military bands have been allocated adjacent to each other (29.0-30.0 GHz and 30.0-31.0 GHz respectively), and as a result, military end users can more easily complement their MilSatCom capacity with commercial bandwidth using a single terminal, such as with Skyware Technologies’ ATOM and SKY terminals. Ka-band advocates say that this makes terminal development easier and more affordable, since a simplified terminal design can operate flexibly across a variety of commercial and military resources. 

Summary

In summary, the Ku- and Ka- frequency bands each have their merits, and it is clear there is no distinctive winner – in the end it is the application requirements and available services that should determine the appropriate band for your operations - be it military, remote office or media broadcast.

Ka-band can offer greater throughput than similar sized Ku systems. This is perfectly suited for customers on the move, and in other applications where terminal size and weight are important factors in making purchasing decisions, such as with military or media organisations.

For more dependable throughput in extreme weather conditions Ku-band wins the battle; the lower frequency range lends itself to a lesser impact by environmental factors. However, as discussed, due to the implementation of new mitigation technologies and availability of hybrid-band systems, Ka-band solutions are able to mitigate adverse weather conditions and maintain a similar level of reliability to their Ku-band counterparts.

As the more established technology platform, Ku is currently available in more regions around the world. However, today many Ku satellites are becoming saturated and so guaranteed levels of service performance may not be available where it is needed for a particular application. As a relatively new phenomenon, Ka-band service is only currently available in select regions, but the with the launch of more satellites and service offerings the situation will likely change in the coming years as Ka coverage catches up with its Ku competitor. 

 

 

Last modified on Thursday, 02 July 2015 12:04

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