While wireless markets have exploded, fundamental aspects such as coding have received relatively little attention. There is a lack of suitable coding standards for remote control and telemetry applications. Encryption algorithms have evolved quickly, mostly driven by the data-security fears of the GSM, Bluetooth and WLAN communities. In control and telemetry, speed of operation as well as prevention of interference are far more pressing concerns. Eavesdroppers are highly unlikely to be interested in decoding data transmissions from the controller of a piece of sports equipment. However, a suitable coding algorithm should provide sufficient protection against false triggering by a nearby device, without requiring complex decoding that introduces delay and thereby impairs the responsiveness of the equipment.
A great deal of investment has been made in developing protocols for wireless data security, but there has been relatively little investment in protocols that satisfy the data-integrity and reliability requirements of wireless telemetry, industrial switching and remote control applications. Between raw RS-232RS-232 transmission and the far more complex Keeloq encryption, Holtek remains the only standard encoding algorithm. Holtek is a decidedly first-generation technology that provides only 256 different code combinations.
Keeloq, by contrast, supports 64 million combinations, and also implements code-hopping. To all practical purposes the code is unbreakable, and has been adopted almost universally for protecting high-value assets such as cars. But although Keeloq is superb for security applications such as vehicle RKE, it is far too slow for a vast number of wireless opportunities that will require simple, speedy operation.
Wireless telemetry products need the coding algorithm to provide an optimal balance between reliability, immunity to interference and responsiveness. Examples include systems such as remotely controlled garden lights, which are required turn on and off effectively instantaneously. Systems with a safety aspect, such as a stairlift, must stop as soon as the command is given. This is particularly important, as the motor will take a finite time to halt in any case: an extra quarter- or half-second delay as the system decodes Keeloq packets is unacceptable and potentially dangerous. In other areas, radio-controlled photographic flashguns are a large potential market, but must be made to fire within 10ms of each other. To achieve these goals, designers need an effective solution enabling them to optimise packet overheads in terms of security overhead.
In the absence of standards, developers must typically rely on proprietary protocols to provide the appropriate level of protection for new designs. This is not necessarily a bad situation, but it does require engineers to have a certain level of RF design knowledge. In turn, this tends to contradict the vision of turnkey RF design using off the shelf modules, conceived to allow engineers without specialist RF skills to successfully get new designs up and running.
Companies seeking a solution must consider developing their own protocols to embed into wireless receivers. This is not a trivial challenge, at least in part because of the integrative behaviour of the radio receiver. Since the incoming bitstream is decoded using a comparator with feedback, the input is compared with an analogue voltage that constantly fluctuates according to previously received data. If the data becomes dominated either by 1s or 0s, the receiver becomes less able to “see” opposing bits. Hence skilful coding is required to limit these fluctuations so that the receiver can reliably decode the bitstream.
If the skills to develop a suitable algorithm are not available in house, or if a faster solution is required, many companies are forced to engage a specialist design consultant. Clearly this involves cost in terms of the consultant’s fee, as well as investment by the company to identify a suitable specialist if none are already known.
A lower cost solution may be achieved using a receiver with an optimised coding algorithm already embedded. Currently this is the only turnkey solution that properly addresses requirements for reliability and responsiveness in industrial, telemetry and remote-control applications, without imposing cumbersome security-oriented processing overheads. These chips provide up to 16 bits of encoding, giving a maximum of 65,536 different combinations for high interference performance, but can be quickly decoded by the embedded CPU. Without the need for high data security, the added complexity of code hopping is avoided and the system can respond quickly to commands from the user.
Systems built using solutions such as these are now proving effective in allowing engineers to quickly and cost-effectively achieve a suitable coding strategy. This should enable companies to devote more time and creative energy to unleashing more of the power of wireless in new markets and applications.