Improving LTE uplink sensitivity at 700 MHz
Hello, my name is Abhijit Karandikar, a Sr. Product Manager here at STI. In this second installment of our LTE E-Note, I would like to talk briefly about the benefits of improving uplink basestation receiver sensitivity.
Rapid growth in mobile data traffic has driven operators to invest in LTE. LTE can have downlink speeds two to three times greater than uplink speeds. This is good today because the majority of data traffic comes from users who download large amounts of web contact to their handsets.
Yet as mobile peer to peer communication, multimedia sharing, and 2-way video conferencing gains popularity, there will be a greater need for higher uplink data speeds and capacity. One way in which carriers can maximize data speeds and capacity on the uplink is by improving the signal to noise ratio. This can be done by adding low noise gain to the receiver. To illustrate this concept consider this example of a receiver chain.
As shown, each component of the chain degrades the signal to noise ratio of the signal as it passes through it. The amount the signal to noise ratio degrades is called the noise figure. Using the Friis equation, the receiver chain’s overall system noise figure can be calculated, which in this example is 4.5 dB. Now, if we add a low noise amplifier or LNA with 12 dB of gain to the front of the receiver chain, the noise figure of the system improves by 3dB. This 2X improvement of the signal to noise ratio reduces the need for data redundancy and provides a higher quality transmission. This frees up network capacity and enables higher data speeds and throughput.
Adding an LNA to the receiver chain can have potential drawbacks. Additional gain can make components like mixers and LNA’s more susceptible to blocking, which can degrade system performance. However, by adding a high order filter, the blocking problem is solved. A high-order, sharp filter reduces the power of the signals, especially near the passband, which dramatically reduces the component’s susceptibility to blocking. In band, the signals are generally power controlled by the BTS, so the probability of blocking is very low.
To summarize, by adding a low noise amplifier and sharp filter, the receiver's signal to noise ratio can be improved to maximize data throughput. We hope you find this update to be helpful, and please contact us if you have any questions. Thank you, and we look forward to speaking with you again.
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