# LoRa Communication Using TVWS Frequencies: Range and Data Rate
## 2 LoRa, TVWS, and Related Work  
LoRa, a physical layer technology promoted by LoRa Alliance, employs chirp spread spectrum (CSS) modulation, improving link budget and interference resilience. It uses the 433, 868, and 915 MHz ISM bands and the medium access control (MAC) layer protocol (LoRaWAN). The data sent by a LoRa node in a LoRaWAN star topology network may be received by multiple nearby gateways that relay the data via an IP interface to a network server, as illustrated in Figure 1.  
CSS modulation spreads the information signal spectrum by a continuously varying frequency chirp carrier signal. The extent of spreading that happens to the original data signal is termed the spreading factor (_SF_) [1]. One LoRa symbol can encode _SF_ bits of information, and one symbol's duration depends on _SF_ and the bandwidth as given in,  
\[T_{s}=\frac{2^{SF}}{BW} \tag{1}\]  
where \(T_{s}\) is the symbol duration, _SF_ is the spreading factor, and _BW_ is the bandwidth. LoRa uses the forward error correction (FEC) method, and the code rate (CR) is {4/5, 4/6, 4/7, or 4/8}. Typically, bandwidth supported is {125, 250, 500} kHz and _SF_ = {7, 8, 9, 10, 11, 12}. Transmit power values usually chosen are {2, 5, 8, 11, 14} dBm [7]. The channel frequency selected depends on the region of operation. Bandwidth, spreading factor, code rate, channel frequency, and transmit power are important parameters that can be chosen for LoRa modulation and influence the modulation bit rate and resistance to interference [8, 9]. The communication range for higher SF values increases, but time on air (ToA) also increases, reducing the data rate. The symbol duration affects the time on air; as time on air increases, the energy required to transmit the data packet also increases. Thus, the _SF_ value, the channel frequency, and transmit power decide the range and energy requirement. LoRa nodes communicate using pure ALOHA, and the LoRa network uses adaptive data rate (ADR) at the gateway, ensuring good network throughput. Different spreading factors result in orthogonal signals and data rate changes. The gateway can simultaneously receive several data rates on the same channel [10]. TVWS refers to broadcast frequency bands in certain parts of the spectrum that are unused due to the digitization of TV services and bands free at different times, as presented in Figure 2. The lower frequency ranges of TVWS (50-698 MHz) penetrate well through obstacles making them less prone to fading and multipath, thus enabling indoor and consumer applications. The bandwidth offered by TVWS is large, thus supporting various high-bit-rate applications too. In contrast to ISM bands, enough TVWS may be generally accessible, especially in rural regions, since there are fewer TV stations than in metropolitan areas [11]. TVWS has good propagation characteristics, excellent indoor penetration, and higher spectral efficiency, making it a good prospect for a wide range of significant indoor  
Figure 1: Basic LoRa network architecture. and outdoor wireless applications. TVWS is appropriate for applications that need a wide transmission range. The Federal Communications Commission (FCC) permitted the unlicensed use of TVWS in 2008 [12]. Most countries have rules for the licensed or unlicensed use of TVWS. The United States, United Kingdom, Canada, Singapore, Mozambique, Japan, and Hong Kong have regulations for the use of TVWS for fixed and mobile wireless communications. The United States has enabled licensed access to TVWS for wireless broadband and mobile data services. The Indian government has issued experimental licenses in the 470-590 MHz band to perform trials at several places using TVWS, unlocking prospects for using the TVWS spectrum in India in either an unlicensed or lightly licensed manner. Literature studies show several TVWS use cases dedicated to rural wireless broadband access, home networks, WLAN applications, and smart metering. Several pilot projects, mostly in rural areas using TVWS, are demonstrated in Africa, Europe, Asia, North America, and Germany.