Wireless Products: SoC VS. SDR, Part 2

The requirements of a wireless product design should drive the technology and solution. Numerous technology solutions have been optimized in an all on one System-on-Chip (SoC), while a Software Defined Radio (SDR) allows a great deal of flexibility. As we discussed in Part 1, the advantages of SoC designs is standard availability, reduced BOM cost and reduced RF design complicity which results in reduced manufacturing cost. When SoC designs don’t meet the requirements, a designer is left to develop a system with discrete components.

In multi-channel RF systems, hardware defined radio (HDR) implementations require a significant amount of analog signal processing, leading to larger board size, increased analog design complexity, limited flexibility, and RF interference susceptibility. Figure 5 shows a hardware defined radio.

• High Analog Complexity

• Susceptibility for RF interference (intermodulation)

• Limited flexibility

• Hardware and Software redesign required for additional features

• DC power increases as features increase

• High BOM count and recurring cost

 

Software Defined Radio

In a ideal design, an SDR radio generally doesn’t have an IF, Modulator, or Demodulator stages as we generally understand those terms: a receive RF preamp feeds directly into an A-to-D converter (ADC), which is connected to a computer DSP/CPU to tune a signal and extract the modulated audio or data. On the transmit side, the CPU and DSP generate the modulation directly, and feed it to a digital to analog converter (DAC) and then to an RF power amplifier.

Do to hardware limitations of CPU, ADC/DAC speed, amplifier compression limitations, some hardware blocks are usually included to reduce to required speed and spurious signals but add demodulation and modulation limitations.

A software-defined radio receiver uses an analog-to-digital converter (ADC) to digitize the analog signal in the receiver as close to the antenna as practical. Once digitized, the signals are filtered, demodulated, and separated into individual channels. Similarly, a software-defined radio transmitter performs coding, modulation, etc. in the digital domain, in the final output IF stage, a digital-to-analog converter (DAC) is used to convert the signal back to an analog format for transmission.

Software-defined radio (SDR) is a radio communication technology that is based on software defined wireless communication protocols instead of hardwired implementations. In other words, frequency band, air interface protocol and functionality can be upgraded with software download and update instead of a complete hardware replacement. SDR provides an efficient and secure solution to the problem of building multi-mode, multi-band and multifunctional wireless communication devices.

An SDR is capable of being re-programmed or reconfigured to operate with different waveforms and protocols through dynamic loading of new waveforms and protocols. These waveforms and protocols can contain a number of different parts, including modulation techniques, security and performance characteristics defined in software as part of the waveform itself.

With a Software Defined Radio (SDR) approach, signal processing is moved to the digital domain—providing various benefits:

• Low Analog Complexity

• Less susceptibility for RF interference (less intermodulation effects)

• Unlimited flexibility

• DC power does not increase with features

• Low BOM count and lower recurring cost