Tuesday, June 02, 2009

Software Defined Radio


[Here is an article on SDR compiled by my students Shijesh, Sibil, Shyju and John by browsing the internet, books and journals]

The rapid growth of technology and changing trends in the Communication techniques has paved way for the introduction of many telecommunication devices, many of which are not feasible to modify cost effectively due to lack of flexibility in their implementation. Software Defined Radio (SDR) technology mitigates this problem by providing the flexibility through software.

Software-Defined Radio (SDR) is a rapidly evolving technology that is receiving enormous recognition and generating widespread interest in the telecommunication industry. Over the last few years, analog radio systems are being replaced by digital radio systems and programmable hardware modules are increasingly being used in digital radio systems at different functional levels. SDR technology aims to take advantage of these programmable hardware modules to build open-architecture based radio system software.

An SDR system is a radio communication system where components that have typically been implemented in hardware are instead implemented using software on embedded computing devices. In other words SDR is a Radio in which some or all of the physical layer functions are software defined.

A Radio is any kind of device that wirelessly transmits or receives signals in the radio frequency (RF) part of the electromagnetic spectrum to facilitate the transfer of information.

In today's world, radios exist in a multitude of items such as cell phones, computers, car door openers, vehicles, and televisions.

While the concept of SDR is not new, the rapidly evolving capabilities of digital electronics are practical enabling many processes that were once only theoretically possible.

In the past, radio systems were designed to communicate using one or two waveforms [waveform here refers to any specific standard like Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), and Time Division Multiple Access (TDMA) or it can be as simple as Frequency or Amplitude Modulation (FM or AM)].

As a result, two groups of people with different types of traditional radio were not able to communicate due to incompatibility problems. The need to communicate with people using different types of equipment can only be solved using software programmable radios because of its flexible architecture.

Traditional hardware based radio devices limit cross-functionality and can only be modified through physical intervention. This results in higher production costs and minimal flexibility in supporting multiple waveform standards. By contrast, software defined radio technology provides an efficient and comparatively inexpensive solution to this problem, allowing multi-mode, multi-band and/or multi-functional wireless devices that can be enhanced using software upgrades

The primary goal of SDR is to replace as many analog components and hardwired digital VLSI devices of the transceiver (radio) as possible with programmable devices.

Some of the advantages of SDR are:

  1. Multifunctionality. The same piece of hardware i.e. the radio set can be used to transmit, receive and process different communication signals that adhere to different air interface standards. This can be done simply by reconfiguring the software.
  2. Global Mobility. The same piece of hardware i.e. the radio set can be used in different parts of the world that endorse different air interface standards. This can again be done simply by reconfiguring the software.
  3. Compactness and power efficient design. Unlike traditional non-SDR systems, which require multiple hardware sets for multi-functional communication, the same piece of SDR hardware can be reduced for such a purpose. This results in compact and power –efficient design, especially as the number of systems increases.
  4. Ease of manufacture. A SDR comprises of fewer hardware parts than a traditional radio since most processing is done in software within a general-purpose microprocessors or special purpose microprocessors like the DSP, or in reconfigurable hardware including FPGAs. This eases the production cycle for the manufacturer with lesser parts to standardize and produce.
  5. Ease of upgrades. Any service upgrade can be easily introduced through the release of new software versions without the expense of recalling or replacing the hardware units. A user can simply download the software off the internet and load it into the SDR.

The most significant asset of SDR is versatility. Wireless systems employ protocols that vary from one service to another. Even in the same type of service, for example wireless fax, the protocol often differs from country to country. A single SDR set with an all-inclusive software repertoire can be used in any mode, anywhere in the world. Changing the service type, the mode, and/or the modulation protocol involves simply selecting and launching the requisite program, and making sure the batteries are adequately charged if portable operation is contemplated.

The ultimate goal of SDR engineers is to provide a single radio transceiver capable of playing the roles of GSM phone, CDMA phone, Wimax terminal, wireless fax, wireless Web browser, Global Positioning System (GPS) unit, and other functions still in the realm of science fiction.





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