From the course: 4G LTE: Architecture, Protocols, Call Flows, KPIs, Optimization, Performance Analysis

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LTE RACH preamble transmission

LTE RACH preamble transmission

From the course: 4G LTE: Architecture, Protocols, Call Flows, KPIs, Optimization, Performance Analysis

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LTE RACH preamble transmission

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Imagine you're in a large empty stadium. If you shout at someone close by, they hear you instantly. But if you yell to someone on the far side, your voice takes time to travel and echoes can make it garbled. A cell tower faces the same problem. How does it ensure a phone miles away is heard clearly? The answer lies in designing the very first shout which is the RATCH preamble. The key is in the preamble's guard period. Think of it as a buffer for the echo. We choose a preamble format based on the cell's maximum size. In a small dense urban cell, phones are close by and signals arrive quickly. We can use a short preamble with a small guard period in this case. But in a large rural area where the users are far away, signals from distant users are delayed. If the preamble is too short, these delayed signals will crash into the next time slot causing interference and making the message unreadable. The guard period in the preamble acts as a protective buffer against this delay. A longer…

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