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All ears?
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09/10/2006
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The proliferation of standards – including wide area 3G, 2.5G, and local area 802.11 networks – means future wireless devices will need to support multiple air interfaces and modulation formats. Software defined radio (SDR) enables such functionality in wireless devices by using a reconfigurable hardware platform.
With the evolution of fpga and data converter technology, SDR is becoming a reality. Programmable logic devices, a portfolio of intellectual property (IP) cores and state of the art design software offer a way to implement SDR technology efficiently.
Figure 1 illustrates the hardware partitioning of an SDR based 3G basestation that can be reconfigured to support multiple standards. To reconfigure the entire system, an ideal SDR basestation would perform all signal processing tasks in the digital domain. However, current generation wideband data converters cannot support the processing bandwidth and dynamic range required across different wireless standards. As a result, the a/d and d/a converters are usually operated at intermediate frequencies (IF), with separate wideband analogue front ends used for subsequent signal processing to the rf stages.
Digital IF extends the scope of digital signal processing beyond the baseband domain to the antenna – the rf domain. This increases the flexibility of the system whilst reducing manufacturing costs. Moreover, digital frequency conversion provides greater flexibility and higher performance (in terms of attenuation and selectivity) than traditional analogue techniques.
Altera’s Stratix II fpgas, with their embedded digital signal processing blocks, embedded soft processors, TriMatrix memory architecture and high speed interfaces, provide a flexible and integrated platform on which to implement computationally intensive digital IF functions – including digital up/down converters – whilst reducing the risk involved in introducing new techniques such as digital predistortion (dpd), crest factor reduction (cfr) and smart antennas.
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Author
Jean-Charles Bouzigues
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