On the Single-Chip Implementation of IEEE802.11a

1. On the Single-Chip Implementation of IEEE802.11a 長庚電機通訊組 碩一 張晉銓 指導教授:黃文傑博士

2. Outline • Software simulation of the C-code • The system concept and main parameters • Analog Front-End introduction • A scheme of synchronization blocks • SAW filter

3. IEEE 802.11a structure • Data rate ranging from 6-54 Mb/s • Bandwidth 20MHz • Modulation: BPSK, QPSK ,QAM. • Symbol duration : 4us including 0.8us guard interval • Why we use single-chip?

4. Computational Requirements of the Baseband Processor ●Software of the model (C-code) on a SUN Sparcstatsion 10 transmitted 1024 bytes 500 times at different bit rates from 6-54 Mb/s

5. Computational Requirements of the Baseband Processor 99.9% ●In the receiver, the Viterbi decoder consumes most of the calculation power ●Processing power of the 802.11a system is distributed in an asymmetric fashion between transmit and receive operations. The OFDM synchronization unit was not modeled

6. The system concept and mainparameters • The complete modem have three main blocks • Analog front- end • Digital baseband processor • DLC layer

7. The system concept and mainparameters (conventional)

8. Super-heterodyne transceiver • Require a narrowband filter (SAW surface acoustic wave). • The I/Q separation be done in the analog domain, which mean that two A/D converters with an analog BW of 10 MHz. • The IF chosen is 810 MHz. • Need to be routed off-chip which lead to an increase in power dissipation. • Two A/D converter resolution is 10 Bits. • Oversampling of 80 MHz. (A/D & D/A)

9. Super-heterodyne transceiver

10. Digital IF Receiver • Advantage: • Gain is distributed over several amplifiers • Good selectivity (due to the presence of preselect and channel filter • Conversion from a real to complex signal is done at one fixed freq. ●Disadvantage: ●A/D has to be least 20 MHz ●Numerically NCO ●The linearity of receiver hardware need be maintained

11. Homodyne (Zero IF) receiver • LO will translate the desired channel to 0 Hz • IF SAW filter are placed with low-pass filter • Research Issue: • DC offset • Maintenance of I/Q balance • Maintenance of low second order distortion

12. A scheme of synchronization blocks

13. SPW Model of baseband with synchronization • The estimator is mainly based on autocorrelation and crosscorrelation, and the preamble structure has to be optimized in order to minimize the estimator varience. • Symbol/frame timing offset • Carrier frequency offset • Sampling clock frequency offset

14. Approach for synchronization • Sampling clock freq. offset use a fixed clock and an interpolator filter and the filter factor that depend on some error signal. • Use pilot for channel estimation • A Gaussian or Lagrange interpolator filter • Due to the nearly independent behavior of correlation functions in time and freq. ,the problem is simplified by using two-dimension Wiener Filters

15. This SAW filter for the receiving RF circuit of GSM mobile communication equipment operating at 935 MHz ~ 960 MHz.

16. End • Thank you for your attention