Q: For line of sight near-field bidirectional wireless communication applications would you rather use IrDA light-based methodologies or RF?
Since IrDA technology is small and easily incorporated into such devices as handheld test equipment, calculators, PDAs and cellular phones, it provides a cost-effective solution in allowing these devices access to a nearby computer or network. IrDA also has security advantages over RF. But even in ideal conditions, IrDA can have its problems depending on the placement of the equipment and the location of the IR detectors. For instance, a computer and piece of test equipment located next to each other on the same shelf may have no way to align the IR to communicate properly.
RF technology is more costly to implement into a device, but it frees the device from many of the problems found with IrDA. It allows a device to communicate to adjacent equipment through walls, into multiple rooms or even outside buildings. The effective distance of RF in real world applications is much farther than IrDA. The bandwidth of RF and IrDA as implemented today is comparable — although in theory, IrDA could have an advantage. For multiple devices operating in the same environment, RF has a real advantage but also its own set of problems. Antenna alignment can be critical, especially in buildings with many people walking around as they can create multipath problems resulting in unreliable signal connections. Depending on the frequency allocation of the devices used, other RF devices such as cordless phones, cell phones, high power communications equipment or even other RF-like devices operating nearby can cause issues with signal reliability
A ZigBee based wireless mesh RF network can be used to provide network and communication coverage throughout a facility. Each wireless sensor can act as a router for its neighboring devices. Self-installation, self-healing and redundant communication paths result from the mesh topology.
Unlike point-to-point or point-to-multipoint communication, if the communication path fails, or if the signal quality decreases or the infrastructure changes, a mesh RF system can automatically establish an alternative route.
This self-healing network feature enables continuous contact even in harsh environments or when structures change. If a piece of heavy equipment gets moved into the transmission path, or if there is a change in environmental conditions, the wireless mesh network can send a signal around the problem.
This inherent network integrity minimizes false alarms and ultimately trims operational costs. To further enhance the reliability, periodic ‘heartbeat’ signals ensure that all transmitters are continuously active and guarantee full network and building coverage.
In addition, by using a low-power Routing (LPR) communication stack, the devices do not require powering from the mains power supply, which allows for battery operation. This is achieved by using smart power-up/power-down and synchronization techniques that enable all mesh nodes to operate in a low-power mode without a battery or power cabling.
If the application can maintain alignment of 15° and up to one meter in distance between devices, then IrDA is a good choice. The limitations of IrDA can outweigh the complexities of RF, but customer expectations and ease of use should play a major role in making the final decision between IrDA and RF. Here are some pros and cons of IrDA to consider:
Pros of IrDA:• Does not require individual country radio agency certifications (for example, United States FCC, Europe ETSI) • Simpler design (no RF or antenna design expertise) • The SIR-type transceivers are inexpensive relative to RF components • Microcontroller manufacturers offer on-chip IrDA peripherals and free software stacks • The IrDA stack software is easier to integrate into an application; plus it is a fraction of the size of many RF protocol stacks • Less energy required (battery friendly) • For RF, the 2.4 GHz frequency range is quite crowded with wireless phones, security systems, Wi-Fi, ZigBee and microwave ovens, which are all causing interference with each other.
Cons of IrDA:• Degrades in very bright outdoor sunlight • Slower maximum data speeds than RF • Membership in IrDA Data Association required (but still less trouble than all of the global RF radio regulations) • Does not have security as part of its native protocol • Must have line of sight, have 15° alignment, be within one meter, and have no obstructions • IrDA is a point-to-point only protocol
