IJCSNS International Journal of Computer Science and Network Security, VOL.7 No.4, April 2007 87 Manuscript received April 5, 2007 Manuscript revised April 25, 2007 Analysis of Frequency Offsets and Phase Noise Effects on an OFDM 802.11 g Transceiver Mourad MELLITI + , Salem HASNAOUI + , Ridha BOUALLEGUE ++ (+) SYSCOM Laboratory, National School of Engineering of Tunis TUNISIA (++) SYSTEL Laboratory SUP’COM, National School of Engineering of Sousse TUNISIA Summary Since WLAN OFDM Transceiver on both IEEE 802.11a and IEEE 802.11b is the most usable technique to achieve a high performance communication, we can, by means of some modifications evaluate an IEEE 802.11g Transceiver behavior against some link impairments as frequency offset, Inter-carrier interference, phase noise, etc. In this paper, we focus on the analysis of simulation results of a link impairments applied on a WLAN OFDM Modulation. More specifically, we use the power of ADS 1 2005A simulation techniques to evaluate phase noise and Frequency Offsets Effects on an OFDM 802.11 g Transceiver. Key words: OFDM, WLAN Transceiver, IEEE 802.11g, Frequency Offset, Phase Noise. Introduction Needs for wireless communications grow in domains of our daily life and particularly in industrial domain. The near future shows new industrial equipments, connected together, within wireless networks that permit to have an increased versatility in the management of disparate equipments[1], [10]. As a consequence, researchers are developing technologies that will eventually lead to a fully integrated single chip OFDM transceiver based on CMOS technology [7]. On The other hand OFDM symbol is sensitive to many link impairments as frequency offset, Inter- carrier interference, phase noise, average ratio, IFFT/FFT complexity, intersymbol Interference, etc. In this paper we propose an all detailed analysis of frequency offset and phase noise effects on an OFDM IEEE 802.11g Transceiver using an integrated design and simulation environment. The simulation results of the transceiver behavior against those impairments will be presented and access simulation techniques, transceiver architecture and design methodology will be discussed. 1 Advanced Design System (ADS) is an electronic design automation software system produced by Agilent EEsof EDA [11], a unit of Agilent Technologies. It provides an integrated design and simulation environment to designers of RF electronic products such as mobile phones, pagers, wireless networks, satellite communications, and radar systems. 2. Concept of OFDM OFDM is a type of multi-carrier modulation in which single high-rate bit stream is converted to low-rate N parallel bit streams. Each parallel bit stream is modulated on one of N sub-carriers. Each sub-carrier can be modulated differently. For example, BPSK, QPSK or QAM. To achieve high bandwidth efficiency, the spectrum of the sub-carriers is closely spaced and overlapped. Nulls in each sub-carrier’s spectrum land at the center of all other sub-carriers (orthogonal). OFDM symbols are generated using IFFT. 3. Advantages of OFDM OFDM prove robustness in multi-path propagation environment [1]. Due to the use of many sub-carriers, OFDM is more tolerant of delay spread. In fact the symbol duration on the sub-carriers is increased, relative to delay spread so it’s clear that the inter-symbol interference is avoided through the use of guard interval. It Simplified or eliminate equalization needs, as compared to single carrier modulation. It is also more resistant to fading. FEC is used to correct for sub-carriers that suffer from deep fade. 4. Design challenges of OFDM modulation Practically, OFDM symbol is sensitive to frequency offset (need frequency offset correction in the receiver) [4]. It is also sensitive to oscillator phase noise (“clean” and stable oscillator required). That is not the only challenge; OFDM presents a large peak to average ratio (amplifier back-off, reduced power efficiency), an IFFT/FFT complexity (fixed point implementation to optimize latency and performance) and an intersymbol Interference (ISI) due to multi-path-use as shown in figure 1.