In many applications wireless communication has dominated the market. Can we now even live without the mobile services and Wi-Fi ? What about our Bluetooth-enabled smartwatches and gadgets? Do we want to go back to wired connections? Surely not. But there are many applications where going wireless is still considered to be risky and not worth the effort. So what exactly is the effort, where are the risks and what are the potential benefits? Let’s try to find out.
Wireless communication channel is less deterministic.
Let’s start with the obvious. Wireless communication is by design more prone to external effects – mainly affecting the communication channel. In case of wire the channel is well defined. In case of radio communication the channel is less deterministic and its properties vary in time. It’s one of the reasons why radio engineers don’t like to give range estimates so much. Since the channel may vary, the range of effective radio transmission may also vary and it is certainly not a constant property. But it’s manageable. The range of radio transmission depends on signal attenuation between a transmitter and receiver. In general increasing the distance between them increases the signal attenuation and after reaching some value the signal is so low that it is hardly distinguishable from noise. This is where communication error start to occur – the link becomes unreliable, some data is lost, packets are dropped, connections are broken etc. But this is the case when the link is working at its limits. In a properly designed link there is some attenuation margin and most channel attenuation changes do not push the link into its limits. What’s more is
Wired connections have better throughput.
Next, let’s consider throughput. It will usually be much lower in wireless than in wired connections. This is a practical limitation due to the principle of operation. The signal emitted by the transmitter is heavily attenuated when going through a typical air channel. Once it reaches the receiver its magnitude is very low. How low ? Well an exemplary radio link may attenuate the signal power by 100dB and still be useful. That is 10 000 000 000 times (!) less than the power that was transmitted. In case of wired connections the attenuation is much much lower – for example 2-5 times. Now how does this affect throughput? Well, we have to consider noise. Electrical noise is an omnipresent phenomena in electronic circuits. Especially thermal noise that is caused by random generation of charge due to temperature. The power of thermal noise scales with the bandwidth – the more bandwidth the more thermal noise we get in the receiver. And large bandwidth is needed to carry more information per second. So if we want to have large throughput, we need high bandwidth but that also means that we get larger noise power. So the receiver will have to distinguish weak signal coming from the transmitter from the noise. Whether it will succeed or not depends on the Signal to Noise Ratio (SNR). So in reality if you want to reach higher throughput you need to either increase transmitter power (but that is usually not feasible) or reduce distance. Some radio links like those used in mobile and Wi-Fi connections manage the throughput automatically adapting it to the channel attenuation. As user we see that the closer we are to the base station or Wi-Fi router the better throughput we get.
Wireless links are less secure.
In this post I’ve assumed that wireless connection is a radio connection which is most often the case. But there are other options like infrared or ultrasound. These are however much less common.