Abstract A possible problem of orthogonal frequency division multiplexing (OFDM) is its high peak-to-average power ratio (PAPR). Recently, the single carrier (SC) transmission system with frequency-domain equalization is attracting much attention. In this paper, a novel approach to alleviate the PAPR problem of OFDM is proposed. A generalized OFDM (GOFDM) with frequency-domain equalization is presented and its performance in a frequency-selective fading channel is evaluated and compared with those of conventional OFDM and single carrier (SC) systems.

I. INTRODUCTION Orthogonal frequency-division multiplexing (OFDM) [1] is one of the promising techniques for very high-speed data transmissions in a severe frequency-selective fading channel [2]. However, since OFDM uses a numerous number of narrowband orthogonal subcarriers to transmit data in parallel, the problem of high peak-to-average power ratio (PAPR) arise. To alleviate the PAPR problem, a novel technique called generalized OFDM (GOFDM) is presented, in which OFDM symbols with less number of subcarriers are serially concatenated. Frequency-domain equalization (FDE) is applied to eliminate the intersymbol and inter-subcarrier interference. This paper evaluates the BER performance of generalized OFDM.

In the “good old days” before automation became a way of life in the clinical laboratory, hand methods of analysis were sometimes capable of producing accurate as well as precise results-a highly gratifying situation to all concerned, especially the patient. Today in the U. S., 12,000 to 15,000 laboratories (depending upon the criteria used to define a clinical laboratory) are practicing clinical chemistry and turning out more than two billion results per year, according to a recent report from the Center for Disease Control (CDC). Somewhere in the transition from the widely used manual methods of yesterday to the extensive use of automated methods of today, accuracy as the predominant requirement for valid results was displaced by repeatability. Does one blame the engineers who adapted clinical methods to their ingenious machines in such a way as to produce highly replicable results, often at the expense of accuracy? Or does some of the fault lie with the professional clinical chemist who, under great pressure, started thinking more in terms of quantity than of quality? No matter what the historical reasons, there is little to be gained at this time in assigning blame. The goal in clinical chemistry today must be to reemphasize and recapture accuracy in analysis. At this point one may ask, “Why is accuracy in clinical chemistry necessary, anyway?” In all complex measurement systems, results, if they are to be comparable across time and distance, must be based on accuracy and not only on precision. Accuracy in measurement is related directly to the “true” value, the value that reflects reality in the most meaningful possible way. A measuring process is accurate (although not necessarily precise) if the average of a large number of replicate measurements obtained by this process is very close to the “true” value. Thus, accuracy involves traceability to the base system of units. If all practitioners agree on that base system of units, then results will be directly comparable and the bias of different methods becomes self-evident. Precision, by contrast, is only an expression of the reproducibility of a measurement system; it is not necessarily related to accuracy in any systematic way.

Analog network coding (ANC) as a simple implementation of physical layer network coding based on orthogonal frequency division multiplexing (OFDM) has been proposed to increase the network capacity and reliability of bi-directional link between a pair of users. In ANC protocol, an information between a pair of users is exchanged through two orthogonal time phases (i.e., multiple-access and broadcast phases). On the other hand, the phase noise (PN) introduces phase offset and inter carrier interference (ICI) to the useful signal. Thus, in ANC scheme PN will affect the useful signal during both multiple-access and broadcast phases. In this article, we present a performance analysis of ANC scheme using OFDM in the presence of PN in frequency-selective fading channel. We derive the total composite variance of ANC scheme in the presence of PN to obtain the signal-to-interference-plus-noise ratio (SINR) expression. Then, we evaluate the system's performance in terms of bit error rate (BER), SINR degradation, and ergodic capacity through both numerical and computer simulations. Computer simulated average BER has been consistent with the numerical results, validating the presented analysis. Our results have shown that the ANC scheme is more sensitive to the PN introduced during the broadcast phase (i.e., at destination) than during the multiple-access phase (i.e., at relay). This is because of the higher ICI to the useful signal and enhanced noise due to the imperfect self-information removal at the destination. In addition, the performance degradation of ANC scheme based on OFDM in the presence of PN is highly expressed for the PN linewidth values up to 20 Hz.