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Software-Defined Radio (SDR) is a hardware-software co-design of digital radio revolution.
The concept of SDR architecture is to push the antenna as the only analogous component at the front-end, with the fully-programmable digital component (either a uP, uC, FPGA, DSP, or mix of these) to implement the digital baseband processing such as digital multiplexer, digital filters, digital frequency synthesizer, digital mixer, digital modulator, digital coding/decoding etc.
Note: ADC is a mixed-signal component. In SDR, sigma-delta modulator is used.
WARNING!
A true SDR is very hard or quite impossible to realise with current know-how.
At present, most research results can only implement a 1/2 or 1/3 SDR, because with current technologies, we are still unable to replace analogue components like amplifier and mixer with digital substitutes.
Why SDR?
1. Programmability or Flexibility - SDR can be programmed to function as W-CDMA, WLAN, WiMax, Bluetooth, ZigBee or even a simple FM radio in one common hardware. This favours multi-mode, multi-protocol, tunable band, selectable channel design in one system. Hence this favours the realisation of UMTS. It is this programmability or flexibility that gives SDR the name of Software-Defined Radio
2. Low-cost - Digital components can easily be mass-produced with high yield in very short time-to-market. Everyone can afford a cheap and reliable digital radio.
3. Stability and Reliability - Unlike analogue components, digital components don't suffer from temperature variation (drift), bias, offset, more immuned to noise. Digital components can be calibrated, better than analogue components that require fine-tuning.
4. IP protection - Digital components can be protected by patents much easier than analogue ones.
5. Testability - Design-for-Test is very established for digital. Mixed-signal and analogue requires expensive equipment and manpower cost for testing.
6. Remedy to the shortage of analogue expertise - The entire world faces a global shortage of experienced analogue designers. Analogue designers are more expensive to hire and pull from a strong rivaling company. Statistics show that more fresh graduates prefer to work in digital because it is easier to learn and work with. USA faces this problem since 1995. Despite the rising numbers of analogue experts from Asia, such as Taiwan, China, India, Japan, Israel, Pakistan, Iran, Turkey, Singapore, Malaysia, Thailand, it is still not enough to meet the increasing need for analogue engineers to engage in sensors and actuators, power electronics, control engineering, instrumentations etc.
7. Size - Analogue IC designs hover above 0.13-µm due to poor performance with down-scaling, therefore device and interconnect size limits area reduction.
8. Technology - At very high frequency designs, analogue components require Bipolar technology, which is more costly than CMOS technology.
9. Power Consumption - It is very difficult to reduce power consumption in analogue, even with the use of SC, current-mode or current-steering instead of voltage-mode. Whereas in digital, ultra-low-power design techniques are very matured and proven successfully.
10. Internet and Wireless Convergence 2010 - The leading players like NTT DoCoMo (Japan), Motorola(USA), Nortel(Canada), Alcatel(France), Huawei (China) and Intel, IBM, Samsung are pushing for I-W Convergence. SDR is a vehicle to realise this by porting multi-protocol platform into a single programmable hardware.
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