I was trying to understand the frame structure importance and its requirement along with the cyclic prefix attachment.
I have basic two questions here:
Why is a frame structure requires in sending traffic and control signals in 5G/LTE?
Can’t we send just series of symbols as it is? Why is a frame structure defined in first place?
Why is cyclic prefix for 1st and 7th symbol more when compared to other symbols in the slots. The time/length of cyclic prefix for 1st and 7th symbol is more. Why can’t it be same for all the symbols? What is the purpose.
For a digital communication system that has Networked nodes (e.g. gNodeBs, RANs, PGW, SGW, UE Clients, etc..) a Frame Structure is key to ensuring that Signalling and Payload messages can be constructed to a protocol specification and can be delivered.
If there are any errors an ARQ – Automatic Request – is made so that the message can be re-sent for processing. CRC – Cyclic Redundancy Check – is used to ensure that transmission errors have not “crept in”.
Frame structure and CRC, or check sums, are not new. They have been with SS7 / C7, ISDN, GSM, 3G, etc.. Network nodes for Wireless and Wireline solutions.
Having a Frame Structure helps with debugging and this helps to understand which node is not “aligned” to the interface specification.
The reason for choosing the symbols 0 and 7 (0 and 14 for 30kHz etc. ) is to synchronize the start of these symbols with time at 0, 0.5ms, 1ms, 1.5ms and so on. If you simply divide the available cyclic prefix to the number of symbols, the symbol at the middle will not start at multiple of 0.5ms. That’s why the first and middle symbol are given larger CP. Some of these symbols should have to receive larger CP so they are the chosen ones.
The frame structure is defined so that the receiver can synchronize in time with the transmitter. It’s easier if everyone knows that a frame has 10ms, a subframe 1ms and certain symbols start at multiple of 0.5ms
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