Wireless Communications
Wireless radiocommunications operate in the licensed and unlicensed frequency bands. In Australia, there are three categories of radiocommunications licenses: apparatus licenses, spectrum licenses, and class licenses.
An apparatus license authorizes the user to operate a transmitter or receiver within a specific frequency band at a designated location. In contrast, a spectrum license permits the use of a range of radio devices across a specific geographic area within the designated frequency band.
The class license serves as a cost-free option that enables users to operate common radio equipment on shared frequencies. There is no application process or associated costs for obtaining a class license. However, it is imperative that users ensure that their equipment complies with the regulations prescribed by the appropriate regulatory body in their country of use.
Regulatory Bodies for different countries are as follows:
Australian Communications and Media Authority (ACMA) – Australia
Federal Communications Commission (FCC) – United States of America
European Telecommunications Standards Institute (ETSI) – Europe
Radio Spectrum Management (RSM) – New Zealand
Ministry of Internal Affairs and Communications (MIC) – Japan
Industry Canada (IC) – Canada
In Australia, short-range devices (SRDs) operate under the Low Interference Potential Devices (LIPD) class licence 2015 and adhere to the performance requirements outlined in AS/NZS 4268 standards. This class licence permits the operation of these devices without the need for an individual licence, allowing them to function in an unlicensed frequency band. However, it is important to note that SRDs share the radio spectrum with other communication devices, and they do not receive any protection from interference caused by other radiocommunication services.
Fundamentals of a Wireless Link
A radiocommunications link is made of a transmitter and a receiver with antennas on both ends. The transmitter transmits the radio signal via the transmitting antenna and the receiver receives the radio signal via the receiving antenna. The maximum operating distance achievable is based on several factors including the transmitter power, receiver sensitivity, operating frequency, antenna gain, operating environment, and radio frequency interference.
Transmitter Power
Transmitter power is an important characteristic of a wireless communication link. The maximum permissible transmit power for SRDs, as defined by the AS4268 standards, is expressed in terms of their effective isotropic radiated power (EIRP). The EIRP refers to the power level of the transmitter, measured in dBm, that is applied to the antenna, in addition to the gain, expressed in dBi, of a directional antenna directed toward the direction of maximum radiation. Consequently, a well-designed gain antenna can be used with a reduced transmitter power to achieve the same EIRP.
Elsema transmitters are designed to radiate optimal power while minimizing energy consumption, ensuring maximum operational range while complying to the regulatory standards.
Receiver Sensitivity
Receiver sensitivity is a crucial factor in determining the maximum operating distance of a wireless link. It is typically measured in decibels-milliwatts (dBm) and indicates the weakest signal a receiver can reliably decode while maintaining acceptable performance. A receiver with higher sensitivity can detect weaker signals, leading to an improved operating range. For example, a receiver with a sensitivity of -110 dBm can detect weaker signals than one with a sensitivity of -80 dBm, resulting in a better operating range.
All Elsema receivers have a sensitivity range of -115 dBm to -120 dBm, depending on the specific model. The sensitivity of each Elsema receiver is individually tested and verified during production, reflecting our commitment to quality and precision.
Operating Frequency
The International Telecommunication Union (ITU) standardizes frequency bands into different groups. The main frequency bands of interest for SRDs are Very High Frequency (VHF) that ranges from 30 MHz to 300MHz and Ultra High Frequency (UHF) that ranges from 300MHz to 3GHz.
The operating frequency is important for wireless communications as it also determines the operating distance that can be achieved in different operating environments. Typically, VHF have better penetration properties hence they are suitable for long range communications. The Elsema FMT151 series of transmitters operate in the VHF band and are suitable for long range communication.
The ability to penetrate through walls and vegetation decreases as the operating frequency increases. However higher frequencies do provide wider bandwidth which allows more data to be transmitted and also the implementation of techniques like frequency hopping which significantly reduces co-channel interference issues. Elsema’s PentaCODE® (PCK), PentaFOB® (FOB) and Multicode (MCT) series of transmitters operate in the UHF frequency band and use Frequency Hopping Spread Spectrum (FHSS) technology which allow multiple transmitters to be utilised in the same area.
Antennas
Antennas are fundamental components in wireless communications, and antenna gain is crucial for ensuring reliable performance. It is essential to use antennas precisely tuned to the correct frequency. Antennas designed for a specific frequency will perform poorly if used outside their intended frequency band.
Miniaturized PCB antennas are commonly used in portable applications for SRDs and are housed in compact enclosures. However, the design of these antennas significantly affects their reliability. Poorly designed antennas may become detuned when exposed to changing environments, such as when positioned near metallic materials. This highlights the critical importance of ensuring the system’s reliability. Elsema incorporates several miniaturized PCB antennas in its products. These antennas have been engineered to optimize performance, ensuring high efficiency and reliability.
Antennas for fixed base station units and receivers, which are typically external and installed on poles, play a crucial role in the system. The bandwidth of the antennas used for receivers should fully cover the operational frequency band. Additionally, antennas provide some degree of selectivity to the receiver, so it’s important that their bandwidth is not excessively wide.
Elsema’s range of antennas is specifically designed for the frequencies used by its SRD products, ensuring optimum performance and maximum operating range.
Operating Environment
Wireless communications are profoundly influenced by the extent of obstruction encountered in their operating environment. VHF frequencies exhibit superior penetration properties, thereby making them less vulnerable to interference from obstacles.
In wireless communication, a direct line of sight between the transmitter and receiver is essential for achieving optimal range. Non-line-of-sight communications, which are impeded by obstacles, experience multipath interference that adversely affects both range and reliability.
The three primary environments; rural, suburban, and urban are critical factors in this context. Rural environments, characterized by minimal obstruction, consistently enable wireless systems to achieve optimal operating ranges. Conversely, urban environments, marked by a high density of buildings and other structures, significantly restrict the range of these systems. Elsema offers a range of transmitters and receivers that are suitable for use in all operating environments.
Radio Frequency Interference
Interference within the SRD bands is a complex challenge that can arise from various sources and take on different forms. The main contributors to this interference include co-channel interference, adjacent channel interference, spectral noise, and intermodulation noise. These factors can complicate the maintenance of a reliable and efficient communication system within the SRD band, disrupting intended signals and adversely affecting the performance of devices operating in this frequency range.
Electromagnetic Compatibility (EMC) is a critical consideration that addresses the unintentional generation, transmission, and reception of electromagnetic energy, which can lead to harmful effects such as electromagnetic interference (EMI). For SRD receivers, EMI can significantly impact performance, impairing sensitivity and reducing the operational range of these devices. It is essential to note that SRDs that do not meet regulatory requirements can cause electromagnetic interference, disrupting other devices operating within the same frequency bands.
Elsema products are designed to fully comply with regulatory requirements and relevant standards, ensuring their reliability and efficiency in operation. In addition, Elsema’s PentaCODE® (PCK), PentaFOB® (FOB) and Multicode (MCT) series of transmitters and receivers are designed with advanced Frequency Hopping Spread Spectrum (FHSS) techniques. This technology works by rapidly changing the transmission frequency among several predetermined channels, significantly reducing the likelihood of interference from other devices operating on the same frequencies. As a result, multiple transmitters can operate simultaneously in the same geographical area without significantly disrupting their signals.
This innovative approach not only enhances the reliability of wireless communications but also provides a robust solution to the persistent challenge of co-channel interference. Users can enjoy improved performance and a more stable connection, allowing critical applications to function smoothly even in crowded communication environments. Overall, this advancement instils confidence in maintaining clear communication amidst the complexities of wireless environments.
Conclusion
The effective operation of a wireless communication link is dependent on several critical factors. As SRDs operate under a class license, compliance with the requirements established by the regulatory authority in the respective country is imperative. Furthermore, careful consideration must be given to various elements that influence the performance of the wireless communication link. These elements include transmitter power, receiver sensitivity, operating frequency, antenna gain and the operating environment. Additionally, adherence to electromagnetic compatibility (EMC) standards, which mitigate electromagnetic interference, is essential to ensure that the device does not disrupt the functionality of other devices utilising the same frequency band.