Broadband OFDM using 16-bit precision on a SDR platform

This paper discusses our development of a robust broadband model of OFDM using 16-bit fixed-point ANSI C code that can be easily ported to a variety of software defined radio (SDR) platforms. The fixed-point model allows fast runtime, low power consumption, and low cost implementation. The receiver analog to digital converter (ADC) resolution and 16-bit fixed-point issues are explored. The OFDM system consists of DQPSK encoded data symbols, pilot symbols and null symbols to minimize aliasing and reduce filter requirements. The total number of OFDM subchannels is set to 256. A cyclic extension scheme is used to reduce the intersymbol interference (ISI) caused by long multipath delay spreads. The channel model consists of additive white Gaussian noise (AWGN) and continuously variable channel delay. The fixed-point OFDM algorithm was optimized with a system that uses no compensation for peak to average ratio (PAR). The model supports post-detection spatial diversity, which can be easily implemented by the multi-channel architecture provided by many SDRs.

[1]  M. Lott.  Comparision of frequency and time domain differential modulation in an OFDM system for wireless ATM , 1999, 1999 IEEE 49th Vehicular Technology Conference (Cat. No.99CH36363).

[2]  Nelson Ray Sollenberger,et al.  Beyond 3G: wideband wireless data access based on OFDM and dynamic packet assignment , 2000, IEEE Commun. Mag..

[3]  J.E.M. Nilsson,et al.  Wideband multi-carrier transmission for military HF communication , 1997, MILCOM 97 MILCOM 97 Proceedings.

[4]  John E. Kleider,et al.  Robust time-frequency synchronization for OFDM mobile applications , 1999, ISSPA '99. Proceedings of the Fifth International Symposium on Signal Processing and its Applications (IEEE Cat. No.99EX359).

[5]  Kevin L. Baum.  A synchronous coherent OFDM air interface concept for high data rate cellular systems , 1998, VTC '98. 48th IEEE Vehicular Technology Conference. Pathway to Global Wireless Revolution (Cat. No.98CH36151).

[6]  H. Rohling,et al.  Reducing the peak-to-average power ratio in OFDM radio transmission systems , 1998, VTC '98. 48th IEEE Vehicular Technology Conference. Pathway to Global Wireless Revolution (Cat. No.98CH36151).

[7]  Preben Mogensen,et al.  Performance analysis for UMTS downlink receiver with practical aspects , 1999, Gateway to 21st Century Communications Village. VTC 1999-Fall. IEEE VTS 50th Vehicular Technology Conference (Cat. No.99CH36324).

[8]  Hideki Ochiai,et al.  Channel capacity of clipped OFDM systems , 2000, 2000 IEEE International Symposium on Information Theory (Cat. No.00CH37060).

[9]  Masato Mizoguchi,et al.  The performance of a packet mode OFDM modem for 5 GHz band high-data-rate wireless LANs , 1999, 1999 IEEE International Workshop on Mobile Multimedia Communications (MoMuC'99) (Cat. No.99EX384).