Maximizing Spectral Efficiency at 700 MHz
Hello, and welcome to STI’s third installment of our LTE eNOTE series. As you are aware, billions of dollars have been spent on 700 MHz spectrum, so maximizing this investment is essential. In this segment, I would like to focus on the value of this spectrum and discuss an alternative approach to maximizing LTE spectral capacity.
The 3GPP standards body has laid out particular recommendations for worldwide LTE spectrum usage. This table from Standard Release 8, shows the number of resource blocks allowed for specified channel bandwidths. Simply stated, LTE resource blocks are “groups of sub-carriers or intervals, that are assigned to transport data.”
Now, I would like to walk you through an example of how a carrier may allocate these resource blocks within their spectrum. For this example let’s consider a typical 6 MHz band in the U.S. 700 MHz spectrum. One way in which a carrier can allocate resource blocks is to use a 5 MHz transmission bandwidth configuration which permits 25 resource blocks. In this scenario, 1 MHz of valuable spectrum is left unused. This spectrum may be reserved to provide adequate guardband to protect against high power, out-of-band interferers like Qualcomm’s MediaFLO and Digital Television. STI sees this as an opportunity for carriers to reclaim a large portion of this unusable spectrum.
As you all know, high performance and low loss receive filtering is required to protect against high power interferers. Unfortunately, standard, low loss, receive filtering uses large amounts of spectrum in order to achieve the desired rejection that mitigates interference. In comparison, high-order, low loss, sharp filtering, uses much less spectrum to offer the same protection against interference, resulting in more usable spectrum. So how can the carrier take advantage of sharp filtering and still stay within the 3GPP standards?
Well, carriers could potentially reconfigure their channel bandwidths by combining two 1.4 MHz channels with a 3 MHz channel. As you can see, this would allow for a total of 27 resource blocks rather than the 25 permitted by a single 5 MHz allocation. This net gain of 2 additional resource blocks translates into an 8% capacity improvement.
So what does this additional capacity mean in terms of the carrier’s spectral investment?
The 700 MHz auction raised a total of $19B in winning bids on 52 MHz of spectrum. This translates into approximately $365M spent per MHz, or $2.2B spent for a 6 MHz license. This means that for a typical 6 MHz band, using a 25 resource block configuration, each resource block can be valued at about $88M. Therefore, the 2 additional resource blocks or 8% additional capacity can be valued at about $176M. The actual value of this reconfiguration could be even greater, when accounting for the benefits from additional traffic and customer satisfaction.
Something to consider, is that in order to effectively use these additional resource blocks, some adjustments may have to be made to the handset and base station. However, given the large benefits, these possible changes may be more than justified. In conclusion, maximizing spectral usage is essential to capitalize on the billions of dollars that have been invested. With STI’s unique high-order sharp filtering carriers could potentially reallocate their channel bandwidths within 3GPP standards and gain the use of additional resource blocks. This capacity improvement could restore unused spectrum valued in the hundreds of millions of dollars.
We hope you find this approach to be insightful, and we look forward to sharing new ways to improve LTE at 700. Thank you for your time, and please feel free to contact us with any questions or comments.
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