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Interference Challenges at 700 MHz
Unique to 700 MHz, the close proximity of multiple broadcast type signals creates a potentially challenging RF environment. Specifically, the use of a FDD version of LTE results in a scenario where very low power base station receive channels are in close proximity to high power broadcast channels like DTV, MediaFLO, and Public Safety.
Without adequate receive filtering, the presence of these high power signals can cause the base station receiver to desensitize and degrade, threatening cell coverage, data throughput and quality of service. In some cases, as with AT&T’s lower C band which is adjacent to MediaFLO transmitters in the D block, the level of filtering required can be quite substantial. This interference environment can be compared to today’s 850 MHz network. There, 850 MHz base station receive channels are in close proximity to SMR transmit signals with A and B prime bands at 850 MHz, causing a variety of interference problems. However, the potential interference problems at 700 MHz are more acute. Guardbands which help mitigate interference and offset strict filter requirements are limited at 700 MHz, leaving these base stations vulnerable.
Broadband emissions generated by DTV, MediaFLO, and Public Safety transmitters are other sources of interference. High order transmit filters would need to be implemented to eliminate the affects of these emissions. Without transmit filtering, these emissions add noise to the receiver which compromise network performance. Mitigating these interferors and using every possible kHz of valuable spectrum without compromising the link budget will be a high priority for carriers in order to maximize the potential of the new 700 MHz network.
STI's Role at 700 MHz
Based on ABI Research’s recent 2008 LTE report, carriers will deploy over 185,000 base stations to complete their network build over the next 5 to 10 years. As an integral resource, STI has been in direct contact with its customers; helping carriers understand the interference challenges from pre-auction studies to current network planning. STI is a recognized expert in providing front-end receiver solutions which include low loss, brick wall filtering while simultaneously improving sensitivity. Combined with our unique field proven technology – over 6,000 SuperLink units deployed today, 230 million cumulative runtime hours, and an MTBF of well over 500,000 hours, STI is well positioned to meet the challenges faced by the carriers to optimize their return on investment of the valuable 700 MHz space.
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