EMI suppression technique for ISM-band WLANs using multicode transmission and EMI observation channel

It is well known that the electromagnetic interference (EMI) radiated from industrial, scientific and medical (ISM) apparatus seriously degrades the p erformance of wireless communication systems. In this paper, an ISM-band wi reless local area network (WLAN) which employs a direct sequence spread spe ctrum (DS-SS) system is designed to be sufficiently robust and reliable to operate in the presence of this EMI. To satisfy this goal, a technique to s uppress EMI in the DS-SS system using a multicode transmission and an EMI o bservation channel is proposed. In the study, thf EMI radiated from switchi ng-type microwave ovens (MWO interference) which are ISM apparatus is conce rned, and for a tractable investigation, a statistical model to represent M WO interference based on experimental measure ment results is employed. As well known that MWO interference exhibits a bursty impulsive characteristic in time, a technique to transmit multiple long spreading codes (multicode transmission) is introduced for the DS-SS system to overcome the burstness of the interference. Moreover, inspired by the broadband in frequency of MW O interference, a technique to estimate the channel MWO interference by mea ns of observing its levels in an adjacent channel is proposed, and this tec hnique is applied to construct a multicode DS-SS receiver which can suppres s the channel MWO interference. An evaluation of the Lit error rate perform ance of the proposed multicode DS-SS system is conducted bg computer simula tion, and the numerical results demonstrate that the proposed DS-SS system can operate effectively even in the presence of MWO interference.