Narrow Band Interference Channel Research Articles

Peak-to-Average-Power Ratio Reduction Using Low-Complexity MIMO SFBC CI–OFDM System

This paper presents MIMO SFBC CI---OFDM on two-transmit and two-receive antennas. First, STBC---DPC is used for avoiding interference and improving the transmitter diversity. Next STBC---DPC with modulo operation i.e Tomlinson---Harashima precoding (THP) is proposed to reduce peak-to-average-power ratio. In narrow band interference channel MIMO SFBC CI---OFDM achieves considerable BER improvement. Compared with STBC---DPC/THP technique, the proposed MIMO SFBC CI---OFDM can provide low PAPR and excellent BER performance.

Performance of a Frequency-Domain OFDM-Timing Estimator

A frequency-domain algorithm for OFDM-timing estimation is considered useful when the OFDM system is to operate in a known narrowband interference channel, e.g., in a cognitive radio OFDM-based overlay system. We generalize a recently proposed frequency-domain algorithm for OFDM-timing estimation and then analyze the performance of the algorithm. The algorithm is based on a complex timing metric that has the mean of which the angle depends in an affine manner on the time offset. By computing the mean of the metric and the mean square of the metric component orthogonal to the mean, from the power-delay profile and noise condition of the channel, the channel-induced bias of the estimator is quantified and the root-mean-square of the estimation error is estimated. The discrepancy between analysis and simulation results on the root-mean-square error is less than one nominal sampling interval for a useful range of operating conditions.

System design and analysis of MIMO SFBC CI-OFDM system against the nonlinear distortion and narrowband interference

The CI-OFDM (carrier interferometry orthogonal frequency division multiplexing) system has been widely studied in the multi-carrier communication system. This CI-OFDM system spreads each information symbol across all N sub-carriers using orthogonal CI spreading codes. The CI-OFDM system can show the advantage of PAPR (peak to average power ratio) reduction and frequency diversity gains without any loss in the communication throughput. On the other hand, a great attention has been devoted to MIMO (multiple input multiple output) antenna array systems and space-time-frequency processing. In this paper, focusing on the two Tx (transmit) / one Rx (receive) antennas and two Tx / two Rx antennas configuration, we evaluate the performance of MIMO OFDM and MIMO CI- OFDM system. SFBC (space frequency block coding) coding is applied into both MIMO OFDM system and MIMO CI-OFDM system. For CI-OFDM realization, digital implemented CI-OFDM structure is used in which CI code spreading operation and carrier allocation are separately processed by simple IFFT type operation. From the simulation results, it is shown that MIMO SFBC CI-OFDM reduces PAPR significantly compared with MIMO SFBC-OFDM system. The out-of band re-growth of signal spectrum in MIMO SFBC CI-OFDM system is much smaller than MIMO SFBC OFDM. In the NBI (narrow band interference) channel MIMO SFBC CI-OFDM system achieves considerable BER improvement, compared with the MIMO SFBC-OFDM system in which error floor occurs in most of SNR range. So, it can be expected that MIMO SFBC CI-OFDM system is very useful for the high speed communication system in the situation of nonlinear HPA (high power amplifier) and NBI channel.

Sensitivity of multiple-access techniques to narrow-band interference

This paper investigates the sensitivity of several multiple-access techniques to narrow-band interference. The analysis covers time-division multiple access (TDMA), code-division multiple access (CDMA), and orthogonal frequency-division multiple access (OFDMA). The study is carried out under the assumption that all the considered multiple-access systems occupy the same total bandwidth, and the bit rates of all active users are identical. A major finding of this study is that CDMA with pseudonoise spreading sequences is more sensitive to narrow-band interference than TDMA. We point out that the signal-to-jammer power ratio at the decision device input is in fact identical for both multiple-access techniques, but the amplitude distribution of the jammer term at the threshold detector input is more favorable to TDMA, which turns out to be more robust in terms of bit-error rate. Another finding is that in terms of sensitivity to narrow-band interference, orthogonal CDMA (OCDMA) is closer to TDMA than to CDMA with pseudonoise sequences, because the degradation is not the same for all users. Finally, we discuss the relationship of OCDMA and TDMA and highlight the superiority, in terms of capacity over the narrow-band interference channel, of TDMA to the other multiple-access techniques considered in this paper.