We compare single user digital multi-carrier spread spectrum (MC-SS) modulation with direct sequence (DS) SS (with a modified implementation) in the presence of narrowband interference (NBI) and multipath fading. We derive closed-form expressions for the symbol error probability for both the linear MMSE receiver as well as the conventional matched-filter receiver under different scenarios: additive white Gaussian noise (AWGN) channel with NBI, multipath channel with or without NBI. We show that DS-SS can achieve the same performance as MC-SS if the spreading code is carefully designed to have perfect periodic autocorrelation function (PACF). On the other hand, MC-SS is more robust to narrowband interference and multipath fading than is DS-SS with the widely used spreading codes that do not possess perfect PACE. Our analysis reveals that the performance improvement of MC-SS is precisely due to the implicit construction of an equivalent spreading, code having nonconstant amplitude but possessing perfect periodic autocorrelation.
Bibliographical noteFunding Information:
Paper approved by S. L. Miller, the Editor for Spread Spectrum of the IEEE Communications Society. Manuscript received October 17, 2000; revised July 15, 2001. This work was supported by ARL under Grant DAAL01-98-Q-0648 and by National Sceince Foundation under NSF Wireless Initiative Grant 99-79443. This paper was presented in part at the SPIE Digital Wireless Communications III, Orlando, FL, April 16–20, 2001, and at the International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Salt Lake City, UT, May 7–11, 2001.
- Frequency-selective fading
- Narrowband interference
- Periodic autocorrelation function
- Spread spectrum