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RF / Bluetooth – Standards Based vs Proprietary Design

For wireless connectivity applications a fundamental decision that needs to be made, is whether to go with a standards based RF interface like Wi-Fi, Bluetooth, or ZigBee, or a proprietary RF design.

There are many reasons and tradeoffs to consider, such as cost, security, power consumption, interoperability, design time, and certification requirements. Many of these issues are interrelated so designers must first determine the design requirements, to make the best decision..

Proprietary RF design is generally considered when an application requires high security, low power, and a small footprint.

Security - proprietary designs may offer “security-through-obscurity.” That is, an RF interface which isn’t generally known is harder to hack. There’s also the tendency for proprietary interfaces to be point-to-point, or to operate in closed systems that don’t connect to wider networks. Designers of proprietary interfaces are free to develop their own advanced encryption algorithms or tweak established ones, without concern for interoperability with security algorithms from other manufacturers.

Interoperability - proprietary designs can ensure a more robust connection (considering interference from Wi-Fi networks, other electronic products/systems), or other low-power wireless networks as designers have flexibility to optimize the wireless spectrum using direct-sequence spread spectrum (DSSS) or frequency hopping spread spectrum (FHSS). In addition, one can utilize coding schemes to increase throughput or lower power consumption.

The same flexibility also applies to data packet structure. Without the packet overhead required to ensure interoperability with established protocol standards, the packet structure can be streamlined to meet needs of a specific application.

From a hardware design point of view, performance requirements may allow designers of a proprietary RF interface to optimize for space, power, and performance.

While proprietary RF has many advantages, there are a number of factors/tradeoffs to consider. The first is cost. Generally, to justify the non-recurring engineering (NRE) cost of a custom RF IC design and software development requires a very high volume application. Other key considerations, are design time, and time-to-market goals.

Bluetooth was originally conceived as a point-to-point cable replacement technology for HIDs and other devices. It soon became a wireless audio and device-to-device connectivity solution. Bluetooth is well understood and designers can be confident their devices will connect and be interoperable with other Bluetooth enabled devices, regardless of the hardware source.

Bluetooth operates in the 2.4 GHz industrial, scientific, and medical (ISM) band with throughput of 1 Mbit/s (Bluetooth Basic Rate). Its adaptive FHSS encoding scheme allows it to continue to remain robust in the face of interferers. To get to higher data rates, Bluetooth 2.0+Enhanced Data Rate (EDR) uses π/4-DQPSK (differential quadrature phase shift keying) and 8DPSK modulation, yielding rates of 2 and 3 Mbits/s, respectively.

While Bluetooth is tightly controlled, further changes came about with the introduction of Bluetooth 4.0 Core Specification in 2010 which has to be considered. This introduced Bluetooth low energy (BLE), formerly marketed as Bluetooth Smart, but is not backward compatible with Bluetooth Classic.

The primary goal of BLE is low power consumption. This is accomplished by moving from Bluetooth Classic’s connection-oriented approach (devices always connected), to an unconnected approach where only connected when needed.

The latest version, Bluetooth 5, doubles the BLE data rate to 2 Mbits/s from 1 Mbit/s, and increases the range of a 128 kbit/s connection by 4x to up to 50 m by using stronger forward error correction (FEC). The higher data rate allows more packets to be transmitted for a given time slot. Power consumption is reduced as the device can stay in low-power or idle mode for extended periods.

The longer range gives designers more flexibility to trade-off data rate for distance for any Bluetooth device such as beacons. Beacons are battery driven BLE devices that broadcast their identifier to nearby mobile devices so those devices can perform certain actions when close to the beacon.

What started as a simple cable replacement technology has now morphed into something much more useful. As a result, designers are now more apt to look for a quick and easy Bluetooth solutions rather than go through the cost and expense of designing their own RF interface.

This inclination to opt for a Bluetooth interface is turning into a necessity as time-to-market windows narrow and design budgets shrink.

Antenna matching and placement is one of the finer arts of RF design, so off-loading it from the designer saves time and helps ensure optimal signal coupling. Off-the-shelf modules provide a complete solution with established regulatory approvals. On-board DC-DC converter, intelligent power control, efficient size and integrated antenna options are all potential benefits.

When mounting a module in an enclosure, make sure there’s no metal near the antenna or it will impact performance. As it is designed and tuned for free-air operation, potting, epoxy, over-molding, or conformal coatings can affect performance, requiring additional measurements after application to ensure the link budget is within specification.

Proprietary vs. Bluetooth sweet spot

Between a full custom proprietary radio design and standard Bluetooth, there is another option: an off-the-shelf radio transceiver around which designers can develop their own protocol and coding schemes, or adopt off-the-shelf versions such as Ant, Thread, or ZigBee. These offer reduced costs and a wide range of software support, and may be the “sweet spot” for designers looking for differentiation, latitude for optimization, and enhanced security options, all while keeping costs low and design schedules intact.

Proprietary vs. Bluetooth sweet spot

In summary there are many reasons to choose either a full proprietary RF design, a standard Bluetooth radio, or flexible solutions enabling some level of proprietary differentiation.