SoC vs SDR For Wireless Product Design

Written By: Steve Hawkins

Steve is the Senior RF Engineer at LSR. Steve has over 30 years of experience in the development of wireless and CATV systems. Steve has a BSEE from the Missouri Institute of Technology.

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. So which one is preferable when designing your product? On today's blog, we'll cover the SoC solution.  

GPS receivers, Wi-Fi, Bluetooth®, and Zigbee are common solutions in a vast variety of wireless products. GPS is found in everything from cars, airplanes, boats, trains, phones and has many other uses. Wi-Fi enables wireless networks, Bluetooth enables wireless headsets for cell phones and Zigbee is in numerous smart energy and home automation products.

Bluetooth, Zigbee, Wi-Fi and even cellular solutions have been reduced to one SoC transceiver design. But, they come with a rigid set of specifications that my not solve or meet the design or cost requirements. Although SDR allows flexibility, they generally come at a higher cost. Some designs start as a multi-chip and evolve over time into single or higher integrated designs.

Licensed VS. License-free Spectrum

Communications can take place over privately licensed spectrum or license-free spectrum. Cell companies have spent billions on new licensed spectrum for deploying their 4G networks. Paging networks, satellite television, AM, FM and television broadcasting are all users of licensed spectrum. Many of the license spectrum users are able to have a transmitter that broadcasts with an output power of several watts to thousands of watts, enabling long range communications.

Government, military, marine, railroad, and aircraft also utilize licensed communication in everything from voice and data communications to radar.

With licensed spectrum, companies purchase spectrum licenses from the FCC, giving them exclusive access to certain frequencies within a geographic area. The FCC allows licensed radio systems to use high-power transmissions (usually greater than 1 watt) on their assigned frequencies. Licensed spectrum is a scarce resource that is difficult and expensive to acquire in large blocks. Because of these constraints, these vendors often possess just several hundred kHz of spectrum, providing only a handful of channels. The licensed spectrum is normally only useful for narrow band communications. Cellular 4G and WiMax spectrum is an exception.

FCC spectrum licenses are not permanent. In addition, the FCC can reallocate spectrum for other uses and has done so in the past.

Unlicensed spectrum for commercial use is available for no cost. Unlicensed spectrum includes the CB, FRS, and the industrial, scientific and medical (ISM) band, at 13.5, 27, 40, 433, 915 MHz, and 2.4, 5.8, 24.1, 61.2, 122.5, and 245 GHz bands. To minimize interference, the FCC restricts the maximum transmit power for unlicensed devices and requires the use of spread spectrum technologies. SoC transceiver solutions are available for most of these frequency bands with the exception of CB and FRS bands. The CB and FRS bands are special cases and limited to only this type of transceiver modulation.

SoC Radio Solutions

SoC solutions come in many different forms. Many are standards based: Wi-Fi, Bluetooth, Zigbee, RFID, NFC, and GPS. Proprietary solutions also exist when a standards based solution doesn’t meet the requirements. Samplings of SoC transceivers that are available are shown below:

 

The SoC transceivers are very highly integrated and very cost effective. Most require very little support circuits other than a microprocessor for controlling, power supply and an antenna. Below is a simplified Block Diagram.

The receivers usually are direct conversion architecture. This architecture is the ideal choice for highly integrated receivers, reducing the bill of materials by fully integrating all inter-stage filtering. The front end includes low noise amplifiers (LNAs) feeding mixer for down-converting to a low or zero-frequency intermediate frequency. Integrated receiver filters usually offers selectable bandwidth and data rates. Analog to digital converters complete the RF signal to digital data translation.

Majority of the transmitters offer direct conversion modulators. They may integrate a transmit amplifier and filter.

Integrated phase lock loops (PLLs) provide high performance frequency synthesis for both receive and transmit sections. Some VCO and loop filter components are fully integrated.

Adding an antenna as the air interface, a MPU for control and data decision with a power source such as a battery make a very highly integrated, low cost system.

Range Extension

Many SoC designs can be improved with the addition of external transmit power amplifiers (PA) and receive low noise amplifiers (LNA). They increase the transmitter output power and receiver sensitivity respectively (See Figure 3). Many times these are realized with a module or IC, which integrates these functions. 

The range extension increases output power and sensitivity as show below.

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

 
 
 
 

 

 Discrete components can form the major building blocks of an HDR or SDR which include:
  • Amplifiers (low, medium, and high power)

  • frequency mixers

  • modulators

  • demodulators

  • filters

  • phase lock loops (PLL)

  • transistors

  • diodes

  • voltage regulators

  • couplers

  • frequency oscillators

  • analog and RF switches

  • Analog to Digital Converters (ADC)

  • Digital to Analog Converters (DAC)

  • Digital Signal Processors (DSP)

  • Microprocessors (MPU)

 

Conclusion

System on a chip radios provide a low cost radio solution path that solve many radio wireless connection requirements. They usually meet requirements for the following applications:

Applications

 

  • Consumer electronics

  • Wireless computer peripherals

  • Wireless gaming accessories

  • Wireless Audio

  • Sport equipment

  • Remote controls

  • Alarm and Security monitoring equipment

  • Smart Energy

  • Industrial Controls

  • Building automation

 Software Defined Radios have significant utility for the military, and public services, both of which must serve a wide variety of changing radio protocols in real time.

 A software-defined radio can be flexible enough to avoid the "limited spectrum" assumptions of designers of previous kinds of radios, in one or more ways including:

 Spread spectrum techniques allow several transmitters to transmit and receivers to receive in the same place on the same frequency with very little interference.

 An SDR can be reprogrammed with different protocols, operating frequencies, demodulation techniques and still use the same hardware.

 One SDR receiver can cover 10 MHz to 1 GHz and with software demodulators become a FM receiver, TV receiver, shortwave receiver, and a multi channel public service scanner.

 A credit-card-sized board can be used to send and receive wireless data using a wide range of secure modulation schemes, including quadrature amplitude modulation (QAM), frequency-shift-keying (FSK), and Gaussian minimum-shift-keying (GMSK) modulation.