Introduction to Software Defined Radio

What is SDR?

As the capabilities of analog to digital converters (ADCs) and signal processors expand, there are new ways for system designers to overcome chronic design challenges. Software defined radio (SDR) is a concept that has grown in popularity over the last few years, not only for broadcasting receivers, but also for portable mobile handsets. The principle behind SDR is to run software on a multi-purpose processor to handle the functions of the radio reception path that are typically realized in hardware, as for example, the demodulation and audio decoding. Effectively, the software defines what kind of processing is applied to the signal coming in from the antenna, enabling both analog and digital radio reception in the radio with a minimum of components.

A software-defined radio is characterized by its flexibility: Simply modifying or replacing software programs can completely change its functionality. This allows easy upgrade to new modes and improved performance without the need to replace hardware. An SDR can also be easily modified to accommodate the operating needs of individual applications. There is a distinct difference between a radio that internally uses software for some of its functions and a radio that can be completely redefined in the field through modification of software. The latter is a software-defined radio.

This SDR convergence is occurring because of advances in software and silicon that allow digital processing of radio-frequency signals. Many of these designs incorporate mathematical functions into hardware to perform all of the digitization, frequency selection, and down-conversion to baseband.

Advantages of SDR

One of the biggest advantages of SDR is the increased flexibility gained by converting hardware blocks into software which allows the car infotainment system to be updated at the service point (such as when the customer stops by for regularly scheduled maintenance), adding new functions and removing bugs. Also, we can expect the new digital broadcasting standards to change after a few years, so the infotainment system, which is installed in an automobile with a much longer life span as compared to consumer goods, has to be easily upgradable. For example, new audio compression schemes (as currently introduced with the transition from DAB to DAB+) as well as some specific news and data services can only be supported if a particular decoder is implemented in the receiver. With SDR, this could be achieved with a simple software upgrade. Along with that, support can be guaranteed for the latest portable media players and mobile phones over the entire lifetime of the car, which creates a real value for the end customer.

Another advantage important for system designers is that a single, future-proof hardware platform in theory could be re-used for different customer applications simply by adding application specific software. This saves both time and cost in the design phase creating a real competitive advantage.

Summary of advantages when using a SDR concept:

· Reuse hardware for different customer requirements leads to reduced hardware qualification and development effort

· Software updates to fit new/changing broadcasting standards, fix bugs, support latest external devices, and not penalize early adopters

· Compact hardware platform requiring less space in the head unit

· Shorter time to market because the hardware is less complex. Development effort moves to software design while hardware stays the same for different customer requirements

· Lower bill of materials by eliminating hardware components and re-using hardware platforms

· Allows last-minute design changes because functionality is mainly determined by software

References:

Software Defined Radio – the next-generation automotive radio platform

By Harald Koch, Automotive Marketing Manager, Microtune®, Inc.

Software Radio: A Modern Approach to Radio Engineering by Jeffrey H. Reed

ESPAR Antenna - For Commercial Adaptive Technology

Signal to Interference Noise Ratio (SINR) for Wireless Local Area Network (WLAN) systems and cellular networks can be improved by using adaptive antenna systems. Conventionally phased array antennas have been used for beam and null steering but the problem with them is that they are intentionally not made compact to avoid mutual coupling between elements. To overcome this limitation and due to many other advantages, ESPAR Antenna has become very popular recently. ESPAR stands for Electronically Steerable Parasitic Array Radiator. Conceptual overview of ESPAR antenna structure is shown in Fig. 1*. There is an active monopole in center surrounded by several parasitic elements in circular configuration. This active monopole induces voltage in the surrounding elements. By theory of arrays, if somehow the current through individual array elements can be controlled, the overall radiation pattern can be controlled. For this purpose, each parasitic element is loaded by a varactor, whose variable reactance (capacitance) is varied by changing the applied DC voltage.

Each phase shifter in the phased array is replaced by a cheap varactor. Moreover, since there is a single feed element, only one transmitter and receiver circuit is required*. Since a varactor diode operates under reverse bias, almost no current flows through it which accounts for low energy consumption. Due to it's low cost, compact size, uncomplicated structure and low power requirements, the antenna has immense potential to be massively embedded in handheld devices.

* Takashi Ohira and Kyouichi Iigusa, Electronically Steerable Parasitic Array Radiator Antenna, Electronics and Communications in Japan (Part II: Electronics), Volume 87, Issue 10, pages 25–45, October 2004.