Antennas can recieve data (bits) because RF signals induce an analog signal into it in a serial format, essentially a voltage that varies over time. My question is can we have an antenna that can process bits in parallel by having a specific voltage level on each wire using RF signals? Or RF signals have an all or nothing effect, where you either get the same induced signal on all of them or none?
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- 2\$\begingroup\$ "Each wire" where? Are you envisioning multi-level symbols (PCM, QAM, etc.) through one antenna? Or a "diversity" of antennas? \$\endgroup\$Tim Williams– Tim Williams2024-07-18 03:00:23 +00:00Commented Jul 18, 2024 at 3:00
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2 Information is sent over RF (or any medium, really) as a series of symbols. It possible for a symbol to represent more than one bit at a time. For example, QAM-256 is a widely used coding system which sends symbols that each represent one of 256 states, or 8 bits.
The ability to send more bits per symbol depends on the signal/noise ratio of the channel. The noisier the channel, the fewer bits/symbol can be used. This is why WiFi slows down as you get farther from the access point: the coding used (MCS) shifts downward as the signal gets weaker.
The principle that governs this is expressed in the Shannon-Hartley Channel Capacity Theorem.
According to this theorem, Channel Capacity \$C\$ is expressed as:
$$C = W *log_2(1 + SNR)$$ Where \$W\$ represents the bandwidth and \$SNR\$ is the signal to noise ratio.
So when it comes to channels, you don’t get ‘all or nothing’, you get faster or slower, depending on the channel SNR and of course, its bandwidth.
Related: Can we get higher internet speeds even with low BW message signals?
A channel encoder like QAM will accept 8-bit parallel input and serialize it into symbols. These are de-serialized by a receiver. So while it's not isolating the bits to wires per se, the effect is the same: multiple bits in a single electromagnetic 'wave' (symbol.)
In the spirit of your question, it’s also possible to use MIMO (spatial multiplexing) to increase throughput over the existing channel, in a way that physically isolates the 'wires'. MIMO divides the channel payload over multiple antennas, each antenna with its own phase orientation, and with some clever math (such as what's described in the linked paper) it's all re-assembled at the receiver into the total payload.
- \$\begingroup\$ The antenna part was just an example, my main question was if we can induce different voltage levels on different wires using 1 single electromagnetic wave, like inducing a voltage of 3.3 V on D0, 0 V on D1, 0 V on D2, 3.3 V on D3, and so on. my doubts where that if I wanted to achieve that I'd probably have to send individual signals that are directed towards each wire, but I didn't know if that was true \$\endgroup\$19216811– 192168112024-07-18 03:30:47 +00:00Commented Jul 18, 2024 at 3:30
- \$\begingroup\$ That’s the point of channel coding: one electromagnetic ‘wave’ (that is, a symbol) can encode multiple bits. QAM-256 does exactly that at 8 bits per ‘wave’. \$\endgroup\$hacktastical– hacktastical2024-07-18 04:27:20 +00:00Commented Jul 18, 2024 at 4:27