VLSIimplementationOFDMmodem - VLSI implementation of OFDM...

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VLSI implementation of OFDM modem Authors: Aseem Pandey, Shyam Ratan Agrawalla & Shrikant Manivannan WHITE PAPER Abstract OFDM is a multi-carrier system where data bits are encoded to multiple sub-carriers, while being sent simultaneously. This results in the optimal usage of bandwidth. A set of orthogonal sub-carriers together forms an OFDM symbol. To avoid ISI due to multi-path, successive OFDM symbols are separated by guard band. This makes the OFDM system resistant to multi-path effects. Although OFDM in theory has been in existence for a long time, recent developments in DSP and VLSI technologies have made it a feasible option. Many wired and wireless standards like DVB- T, DAB, xDSL and 802.11a have adopted OFDM. This paper first lists various approaches to implement an OFDM system. It then describes the VLSI implementation of OFDM in details. Specifically the 802.11a OFDM system has been considered in this paper. However, the same considerations would be helpful in implementing any OFDM system in VLSI. Wipro Technologies Innovative Solutions, Quality Leadership
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White Paper © Wipro Technologies Page : Table of Content INTRODUCTION. ............................................................................................. OFDM transceiver. ............................................................................................ Different implementation techniques. .................................................................. DSP based implementation. ......................................................................... DSP with hardware accelerators . .................................................................. VLSI implementation. ................................................................................... Design Methodology . ...................................................................................... Architecture definition. ...................................................................................... Specifications of the OFDM transceiver . ........................................................ Design trade-offs . ........................................................................................ Algorithm survey & simulation . ......................................................................... Fixed point simulation . ................................................................................. Simulation setup. ......................................................................................... Hardware design. ............................................................................................. Interface definition. ....................................................................................... Interface to MAC. .................................................................................... Radio. .................................................................................................... Clocking strategy. ........................................................................................ Design of crucial blocks. .............................................................................. FFT. ....................................................................................................... Viterbi . .................................................................................................. NCO . ..................................................................................................... Arctan. ................................................................................................... Optimize usage of hardware resources by reusing different blocks. ................... Optimize the widely used circuits . ................................................................. Multipliers. .............................................................................................. ACS unit. ................................................................................................ Debug support. RTL Simulations . ............................................................................................. Acronyms and definitions. ................................................................................. VLSI implementation of OFDM modem Page: Table of Content 01 02 03 03 04 05 05 06 06 07 07 08 09 09 09 09 09 11 12 12 15 16 17 17 18 18 18 19 19 21
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White Paper © Wipro Technologies Page : Page : 01 of 22 Introduction OFDM is a multi-carrier system where data bits are encoded to multiple sub-carriers. Unlike single carrier systems, all the frequencies are sent simultaneously in time. OFDM offers several advantages over single carrier system like better multi-path effect immunity, simpler channel equalization and relaxed timing acquisition constraints. But it is more susceptible to local frequency offset and radio front-end non-linearities. The frequencies used in OFDM system are orthogonal. Neighboring frequencies with overlapping spec- trum can therefore be used. This property is shown in the figure where f1, f2 and f3 orthogonal. This results inefficient usage of BW. The OFDM is therefore able to provide higher data rate for the same BW OFDM is fast gaining popularity in broadband standards and highspeed wireless LAN.
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VLSIimplementationOFDMmodem - VLSI implementation of OFDM...

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