Embedded Wireless Design

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Embedded systems designers are quickly realizing the benefits of going wireless, including reductions in cable costs, aesthetics and ease of installation. Unfortunately, wireless solutions often come with barriers or challenges such as reliability of wireless connectivity, distance limitations due to signal range, complexity of designing-in or attaching a wireless solution, and the dire need for low-power consumption to maximize battery life. In response, a plethora of wireless technologies has evolved. Data encoding techniques such as Direct Sequence Spread Spectrum (DSSS) are used to maximize reliability (Figure 1). Channel hopping is used to avoid interference (Figure 2). Signal amplification, through both in-chip and off-chip amplifiers, addresses range issues. And extremely low-power transceivers that have low sleep, receive and transmit power ratings have evolved to extend battery life.

 

Figure 1. Direct Sequence Spread Spectrum

Figure 2. Channel Hopping

 

While many wireless solutions in the market today address one or two of these design challenges, the problem for designers has been finding a single solution that incorporates all of these technologies. For example, many proprietary 2.4GHz wireless solutions focus on providing ultra low transceiver power ratings, but these solutions fall short in terms of reliability and/or range.

Cypress’s new CyFi Low-Power RF solution, however, addresses all of these challenges in an uncompromising way. It provides a highly reliable, longer range solution that is extremely simple to design and operate, and offers the best system power-efficiency in the market.

 

Reliability Technologies

DSSS and hopping technologies have evolved to directly address the challenge of wireless reliability. DSSS is a radio transmission technology that essentially applies a robust forward error correction scheme to the data-in-transit in order to minimize the effect of data loss due to signal interference. Specifically, DSSS encodes a set of data into a larger bit stream, or chips. As you can see in Figure 1, 8-bits of data are encoded into 32 chips. The chips are then modulated onto the RF signal and transmitted. The receiver demodulates the chips from the received signal and then reverses the DSSS encoding scheme. Even with demodulation errors due to signal noise or interference, the original data can still be recovered.

Channel hopping is an often complex technique of moving around the available RF spectrum to avoid interference. Some technologies are designed to constantly hop following an established and shared hopping algorithm, while others hop only as needed, or when facing overwhelming signal noise or interference. Finally, the smaller the channel size the greater the number of channels to hop to and, thus, the greater the spectrum agility to avoid interference.

These benefits in reliability directly correlate to system power savings: the higher the reliability, the less power-intensive retransmits are required, and the more time spent in power conserving sleep modes. In addition, the higher the reliability, the further the signal can transmit and still be clearly deciphered, boosting the signal range.

 

Power Efficiency vs. Low-Power

The driving feature in the world of embedded wireless has long been minimizing sleep, transmit and receive power ratings of the transceivers. This focus has been so great that the efforts to minimize these power ratings have come at the expense of system reliability, which adversely affects the system’s power rating. A wireless system with low reliability will result in many more inefficient re-transmits when compared to a reliable system and thus will expend more energy despite having lower per-component power ratings - thus the push to focus on system-level power consumption, or “power efficiency.”

Power efficiency is the power savings contributed to by all of the different features and components of the wireless solution. The transceiver and its low sleep, transmit and receive current are only one of the many variables within the overall measure of system power efficiency. Other attributes include the level of system reliability (average number of transmits and re-transmits) and any power management controls embedded in the solution’s protocol.

Cypress’s new CyFi Low-Power RF solution uniquely conserves power using Active Power Management functions. CyFi dynamically switches DSSS reliability on or off depending on the interference levels present — with DSSS on, it provides reliable but reduced-throughput transmission and less retransmissions; with DSSS off, it minimizes on-air time using the fastest available system throughput (see Figure 3). CyFi also dynamically manages power output by measuring receive signals and using bi-directional communication to minimize output power to only what is required (see Figure 4).

 

Figure 3. CyFi Low-Power RF and Active Power Management

Figure 4. Dynamic Output Power Management

 

 Featured Products

Part Number		Description	Data Sheet	App. Notes
CY3210-CyFi		CyFi Development Kit
CY3271		PSoC First Touch™ Kit with CyFi Low-Power RF
CY3271-RFBOARD		RF Expansion Kit for the PSoC FirstTouch Starter Kit

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