What exactly is Wi-Fi? Wireless network options.

During my professional life in telecommunications I often come across different ways of perceiving wireless connections. The word Wi-Fi, or "wifi", is mostly a symbol of a connection outside the expensive data service of an LTE operator, where the young members of the family can finally watch videos from their friends. The classic connection at home. So, a positive thing. On the other hand, I often hear from various xDSL sellers that a Wi-Fi connection does not work in bad weather, has many "buts", and that nothing beats proper cables. 

Time for a technical aside. Everything revolves around two indicators from which the transmission speed is calculated. The first is bandwidth, and the second is the modulation scheme. To avoid going into too much technical detail, I will simplify this relationship a lot. Modulation is the number of states during one cycle of the signal. With four-state amplitude modulation, the signal can take 4 values, and the transmitted data word has some variation of four bit characters, for example 0101, 1101... Try to imagine the rest. The higher the modulation, the higher the transmission capacity, but at the same time the demands on the transmission medium grow. You know this from practice: you are far from your home Wi-Fi and the speed drops until it finally disconnects. It is the same with the exchange of a copper network, or with the distance from a mobile operator's base station. 

Another fundamentally important factor is bandwidth. The number of data words grows as many times as you have MHz available. Popularly, this can be explained by the number of subchannels in one medium. Why is it so complicated?

The reason lies in how things developed. In the past, nobody planned for a society-wide data network. The construction of the telephone network, based on copper wire and covering the whole country, took several decades. It was designed for voice transmission, even analogue, and for such small capacities it was enough to use thin wires in wide cable bundles. Every house had a suitably dimensioned branch line, and such a home line terminated at an exchange somewhere in the catchment area, perhaps several kilometres from the subscriber's home. That was enough for telephone calls, and after the switch to digital exchanges there was still no problem. Because of crosstalk between wires, a low carrier frequency was used, so the usable bandwidth was just enough for telephony, and when someone did need a data service, they used a dial-up (DIAL-UP) connection. But without going into too much detail: the gradual development of technology for this old, long-established telephone network led to higher carrier frequencies on the medium, and thanks to that, to higher modulation rates and, above all, greater bandwidth. Today these parameters are quite excellent at the locations of digital exchanges. For example, modern VDSL2 can use 35 MHz of bandwidth at a fairly high modulation rate. When you transmit data over a good-quality cable over a short distance, say up to 300 metres, the transmission speed can be a brisk 100 Mbps. With further methods of reducing crosstalk, calculating crosstalk in modems and controlling vectors in the cable bundle, the xDSL network has a chance of reaching a theoretical 250 Mbps.

There are two significant "buts": 

a) by the very principle of the copper medium, you do not get substantial capacity for uploading data to a server

b1) the speed drops significantly, quite literally falls, with increasing distance from the exchange

b2) the speed drops significantly with poor quality of the copper connection 

So even in modernised parts of the network, some people have it, and others will never have it... 

So where does Wi-Fi fit in? 

Regional internet providers do not use old copper lines for the connection from the exchange to the customer. Firstly, in earlier times they did not have access to them, and there was not much reason to either. The wireless medium served well for connecting customers. And the analogy used earlier in the article also applies to wireless access to the fixed network. Wi-Fi is a standardised way of communication between wireless devices. Wi-Fi, short for Wireless Fidelity, is the name of the Wi-Fi Alliance organisation and denotes a particular standard, or protocol, that manufacturers use so that their devices can understand each other. For this kind of communication, the community of regulators set aside a frequency band where such devices can operate as long as the rules are followed. First it was the 2.4 GHz band, and later a much wider section in the 5 GHz band. And the Institute of Electrical and Electronics Engineers, IEEE, began defining standards, depending on the possibilities of the technology of the time. This is how the 802.11 standard came about.

Overview of IEEE 802.11 standards

Note that the original speed of the ancient 802.11 standard is 2 Mbps. That is roughly the line speed of an ISDN line, which in many cases is the only option for connecting to the copper network. The 802.11n and 802.11ac standards are established in the wireless access network. (The 802.11ad standard is not yet permitted for outdoor installations.) 

So what about these wireless networks? The access points themselves, which look like small transmitters, as in an LTE network, often use a proprietary extension of the Wi-Fi protocols from various manufacturers. They can afford to, because these are devices built specially for infrastructure purposes. Their designers use various methods to increase capacity and make them more robust against mutual interference. They are equipped with mitigation techniques to avoid collisions with radar systems, and powerful processors for calculations that correct crosstalk during operation. 

When operated with the right antennas and well-set capacity control, today's wireless networks are able to provide services without problems at the same or higher capacities than the copper network. But to be fair, this again comes with two conditions:

a) when the spectrum is loaded, the customer's receiver must not be too far from the access point

b) both the receiver and the transmitter must work with an adequate energy budget for rain loss, that is, suitable antennas

The transmission speed in the medium, at the same modulation, grows in direct proportion to bandwidth. The modulation rate in wireless Wi-Fi technologies can no longer be increased much. Top devices reach 256 QAM, and thanks to the MIMO and OFDM methods, which are not described here, the 802.11n/ad protocol achieves high transmission speeds. The future of wireless networks, whether Wi-Fi or LTE, lies precisely in increasing bandwidth. In the near future, wireless operators will use even the millimetre 60 GHz bands, where the directionality of antennas means there is no risk of mutual interference. At the same time, European spectrum regulators are responding to market demands and negotiating the allocation of some further sections in the upper part of the 5 GHz band to increase service capacity. At the same time, the optical parts of networks are being expanded. 

But more on that next time. 

Sufficient capacity brought to the access point

A professionally built network must have many connection points, and these connection points must be linked with quality infrastructure. But that belongs to a somewhat different technical part of the internet infrastructure, the access network. 

In the next article we will look at the access network. I will describe radio links in professional bands, that is, ones that have nothing to do with Wi-Fi at all, except for the word "radio". And optical fibres are also part of the access and backbone infrastructure. 

To be continued... 

Author: Jakub Moník