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TDMA is long gone, and there are no "edges of packets" as you imagine them. I am not an expert, I only have little experience and knowledge from working in the area, but for example a few symbols are transmitted together using carriers at different phases. Those audio noises used to exist in the GSM area but no longer in 3G and 4G.

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It took a lot of Wikipedia reading, but I finally got to OFDMA[1], which apparently is used by my 4G phone to talk to the world. I had no idea it just kept spewing RF at all times. Though, it will be transmitting more or less signal depending on how many subchannels it is using.

There will be experiments with an RF sniffer later when I get to my friends repair shop.

[1] https://en.wikipedia.org/wiki/Orthogonal_frequency-division_...

It also has simple power control, making sure that all phones are received at the same power on the receiving antenna. Overall OFDMA is magic, if you can put your hands on a spectrum analyzer with constellation diagram you will be amazed.

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