Theoretical Performance Evaluation and Optimization of UW-OFDM

Abstract

Abstract-Unique-word (UW) OFDM is a new OFDM variant that offers several advantages over cyclic prefix OFDM, such as better bit-error-rate (BER) performance in frequency selective channels and much lower out-of-band radiation. However, all results with respect to the BER performance are based on MonteCarlo simulations only, and offer little insight in the behaviour of the system performance as function of its parameters. In this paper, we theoretically analyse the performance of the UW-OFDM system for both a deterministic channel and a fading channel, and offer a systematic way to generate the UW-OFDM signal to optimize the performance of the system. When the fading channel is known at the transmitter, we show that we can obtain a diversity order that is of the same order of magnitude as the theoretically maximum diversity order, but when the channel is not known at the transmitter, it will be very hard to achieve maximum diversity order, although the obtained diversity order is larger than one.

Precoding for PAPR Reduction in UW-OFDM

“…Because although the constraint (5) guarantees to have full diversity at very high SNRs, the true diversity gain at moderate SNR levels will depend on the eigenvalues of the matrix G H B H H H HBG, where H is the diagonal matrix with as diagonal elements the frequency response of the channel [5].…”

“…In practical systems, often the transmitted energy per data symbol is normalized, leading to trace G H G = N d . Further, in [1], [5], it is shown that the condition…”

“…minimizes the mean-squared error of the linear minimum mean square error and the best linear unbiased estimator (BLUE) data detectors. Moreover, the condition (5) also turns out to be a sufficient condition to optimize the diversity gain [5]. Substituting the decomposition (4) into the condition (5), and taking into account that Y H Y = I (N dr −Nu) , we find that the matrix C must satisfy C H C = I N d .…”

“…Moreover, the condition (5) also turns out to be a sufficient condition to optimize the diversity gain [5]. Substituting the decomposition (4) into the condition (5), and taking into account that Y H Y = I (N dr −Nu) , we find that the matrix C must satisfy C H C = I N d . In the next section, we will propose a method to select the matrix C, in order to minimize the PAPR.…”

“…To make the insertion of the UW possible, a TD data block is generated that contains zeros at the positions of the UW by adding redundancy in the frequency domain using a generator matrix. This redundancy results in several advantageous properties such as inherent diversity gain resulting in outstanding bit error rate (BER) performance [5], and lower out-of-band radiation (OOBR) than for CP-OFDM [6]. Yet, these advantageous properties come at some cost: to fully exploit the introduced diversity gain, UW-OFDM needs more sophisticated data detectors compared to conventional CP-OFDM [1], [7].…”