Question: What is the RF spectrum and what considerations regarding it do we need to take as we expand our implementation of wireless networks?
Answer: There is an extremely important asset that you own and control. However, if you don’t manage this asset effectively, it could turn into your greatest liability. This asset is your airwaves — the radio-frequency spectrum that is available in and around your facility. As you begin to deploy wireless applications at your facility, you will need a solid, spectrum management strategy in order to reduce or eliminate issues, such as slow network performance, security vulnerabilities and network instability. In addition, the strategy must continue to be managed and updated as the network grows and changes. A wireless application network ensures that an effective spectrum management strategy can be designed and maintained.
The radio frequency (RF) spectrum refers to the organization and mapping of electromagnetic waves. These waves travel through space at different frequencies. The frequency range that we are concerned with is referred to as the radio spectrum, which refers to the 3 kHz to 300 GHz range that can be used for wireless communication. Management and regulation at the national, regional, and global levels is designed to avoid and solve frequency interference, design long- and short-term frequency allocations, advance the introduction of new wireless technologies, coordinate communication with neighbors and so on.
At the corporate level, wireless network management requires the same level of discipline. Failure to create a solid RF spectrum strategy will most certainly result in interference and co-existence issues. A solid spectrum strategy reduces or eliminates issues, such as slow network performance, security vulnerabilities and network instability.
Diversity
Diversity is the key element in RF spectrum management. There are seven key types of wireless and network diversity that need to be addressed in the design, deployment, and management of a wireless infrastructure. These will also impact the selection of specific wireless devices and applications.
Application diversity: To achieve maximum return on investment, multiple spectrum users and applications must be considered when defining a spectrum strategy. Cooperation is an inherent requirement of any approach intending to balance the needs of many users.
Frequency diversity: Frequency diversity refers to the segregation of network data across different frequencies. Frequency segregation can be implemented by network type, application, or data type. No matter the technique, frequency diversity is a core strategy for improving network reliability.
Protocol diversity: Protocol diversity encourages further segregation of traffic by allowing for different applications to be transported using different protocols. Protocol diversity is particularly effective when considering the backhaul section.
Time diversity: Multiple versions of the same signal are transmitted at different times. Alternatively, a redundant, forward error-correction code is added and the message is spread in time by means of bit-interleaving before transmission. This helps to avoid error bursts and aids in error correction.
Space diversity: Here, the signal is transferred over several different paths. This can be achieved by antenna diversity using multiple transmitter antennas (transmit diversity) and/or multiple receiving antennas (reception diversity). In industrial environments, there is typically no clear line-of-sight (LOS) between the transmitter and the receiver. The signal is reflected along multiple paths before being received. Each bounce can introduce phase shifts, attenuations, and time delays.
Vendor diversity: Vendor diversity benefits users by encouraging price/performance competition. In addition, vendor diversity reduces risk by enabling second-source providers.
Polarization Diversity Multiple versions of a signal are transmitted and received via antennas with different polarization. This is accomplished through the use of separate vertically and horizontally polarized receiving antennas.
Understanding the trade-offs these diversity options represent and providing insight and controls on how to tune them to their optimum advantage is a fundamental requirement of a wireless application network. From the system engineering and design, through deployment and ongoing management, a wireless application network must be optimized for performance, reliability, and scalability without limitations or compromise.
Stephen Lambright is the vice president of marketing and customer service at Apprion (Mountain View, Calif.; www.apprion.com), a leading provider of industrial wireless application networks.
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