Fundamentals of wireless communications

Radio Frequency (RF) communications are an important smart grid enabler for functions such as volt/VAR control, recloser control, and feeder restorations and isolation. This paper will give a basic tutorial on the types of radio frequency communications and the benefits and liabilities of each. Specific topics to be explored will be licensed versus unlicensed frequencies, distance between remote radios and base stations, and communications architectures. Radio technology is often referred in numerical ranges or frequencies. The decision on which frequency to employ in a network depends on a few key variables. Prior to deciding which frequency for a network, the application for the radio use will assist with dictation of which frequency range to utilize. Applications such as recloser control and volt/Var control may require a radio device that can provide a high bandwidth/fast speed solution. Other SCADA applications such as sensor monitoring may only require small bandwidth and for data delivery to be at a much slower speed. Another variable when deciding on a radio network is the distance from the main SCADA hosts to end remote devices such as RTUs or PLCs. Lower end frequencies (100 MHz-900 MHz) provide further coverage and greater distance from base stations/Access Points to remote end devices, whereas higher frequencies (2.4 GHz-5.8 GHz) provide shorter distance coverage, but higher bandwidth and relay data back to SCADA hosts much faster. Determining a network's architecture should focus on either the desire of a private, licensed network or the notion of an unlicensed, less expensive network. The lower licensed frequency ranges (100 MHz, 200 MHz, 400 MHz and upper 900 MHz bands) are often referred to as MAS (Multiple Address Systems) networks and require license acquisition from the FCC once geographical coverage is determined. These licenses are granted for the lower frequencies as mentioned previously but are considered the proprietary use of the owner. Anyone operating in these frequencies will be fined/cited by the FCC. The less expensive, unlicensed network is allowable for frequencies ranging from 902MHz-928MHz, which is defined as the ISM (Industrial, Scientific, and Medical) bands. Within the unlicensed frequency band, there exist registered bands (3.65 GHz) that employ WiMax (Wireless Microwave Access for Broadband) technology that provide shorter coverage for remote devices, however, the bandwidth and speed provided by these frequencies make them just as popular for networks. Further analysis and discussion of licensed versus unlicensed radio wireless communications is proposed in this paper.