Use Of Subcarriers Research Articles

Improved autocorrelation method for time synchronization in filtered orthogonal frequency division multiplexing

Time synchronization is essential in multicarrier systems such as filtered orthogonal frequency division multiplexing (F-OFDM) because it determines the whole system’s performance. Differ with OFDM, where subcarrier allocation is not flexible. In F-OFDM, the subcarrier allocation is more flexible, and the whole subcarrier in one symbol can be grouped into several subbands. The use of subcarriers that are limited to only one subband can reduce the performance of time synchronization based on autocorrelation (AC) methods. In this study, we first compare the performance of the AC-based time synchronization algorithms used in F-OFDM when training symbols are limited to one subband. Secondly, we made improvements to the AC-based time synchronization with the averaging technique of its timing metric, thus increasing the accuracy of time estimates in the F-OFDM system. The averaging technique of the timing metric improved the performance of the AC method in cases where the training symbol is limited to one subband, as shown in the simulation results.

A Bandwidth Efficient Dual-Function Radar Communication System Based on a MIMO Radar Using OFDM Waveforms

A novel dual-function radar communication (DFRC) system is proposed, that achieves high communication rate, and can flexibly trade-off rate for improved sensing performance. The proposed system is a monostatic multiple-input multiple-output (MIMO) radar and transmits wideband, precoded, orthogonal frequency division multiplexing (OFDM) waveforms from its antennas. The system subcarriers are divided into two groups, i.e., shared and private. On a shared subcarrier, all antennas can transmit simultaneously, while on a private one only one antenna can transmit at a time. A novel target estimation approach with low complexity is proposed to overcome the coupling of transmitted symbols and radar target parameters in the target echoes, which arises due to the shared use of subcarriers by the transmit antennas. The proposed method first operates on all (shared and private) subcarriers to obtain coarse angle estimates, and then fine-tunes those estimates based on the signal received on the private subcarriers. The resolution of the coarse angle estimates is limited by the physical receive array, while the fine-tuning is enabled by effectively constructing a virtual array that has larger aperture than the receive array. The precoding matrix is optimally designed to optimize a weighted combination of the beampattern error with respect to a desirable beampattern, and the signal-to-noise ratio at the communication receiver.

Index Modulation Aided Uplink NOMA for Massive Machine Type Communications

Single-carrier frequency-division multiple access (SC-FDMA) based index modulation (IM), referred here as SC-IM, allows users to implicitly transmit a part of their data bits by switching on some of their allocated subcarriers, followed by ${M}$ -ary constellation symbols transmission over the activated subcarriers. This sparse use of subcarriers provides better energy efficiency and error rate. Using these benefits, this letter exploits SC-IM with uplink power domain non-orthogonal multiple access (NOMA), where all users with the same allocated subcarrier set can simultaneously transmit their SC-IM data with different power levels, which are exploited by the receiver to perform multi-user detection. Performance of the proposed technique is analyzed and compared with conventional NOMA. It is shown that the proposed scheme can achieve energy efficient massive connectivity, which is a primary requirement for massive machine-type communications.

ML Detection and PAPR Reduction of NC-OFDM Signals Based on Clipping Noise Suppression for Cognitive Radio

We propose a new scheme based on clipping noise suppression to effectively reduce the peak-to-average power ratio (PAPR) of non-contiguous orthogonal frequency division multiplexing (NC-OFDM) signals that are used in dynamic spectrum access networks such as cognitive radio. Applying the conventional clipping method to NC-OFDM presents a problem in that not only the subcarriers used by secondary users (SUs) are affected, but the subcarriers of primary users (PUs) are also affected. This paper proposes a method for improving PAPR reduction performance by dividing the subcarriers, depending on the use of subcarriers by the SU, and applying suppression of different types of clipping noise to the subcarriers used by the SU and other subcarriers. Simulation results show that the lower the suppression of the clipping noise for subcarriers not used by the SU, the lower the PAPR of the NC-OFDM signal becomes.

On the Achievable Rate of OFDM With Index Modulation

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a recently developed transmission technique that extends the principle of spatial modulation to OFDM subcarriers. In this paper, the performance of OFDM-IM is studied in terms of the achievable rate assuming an $M$ -ary constellation and that channel state information is available at the receiver. A closed-form lower bound is derived, based on which an interleaved grouping method is proposed for the use of subcarriers. In comparison with the existing grouping method, the proposed one can better benefit from the diversity effects over frequency-selective fading channels, especially when the spacing of any two subcarriers within a subcarrier group is larger than the coherence bandwidth. Through numerical results, it is revealed that OFDM-IM with interleaved grouping outperforms classical OFDM for small $M$ and certain ranges of signal-to-noise ratio. Finally, the effects of modulation types on the performance of OFDM-IM are studied. It is found that the superiority of OFDM-IM over classical OFDM is greater for phase-shift keying than for quadrature amplitude modulation.

Link Adaptation Considering Mobility in OFDMA Systems with Multiple Transmit Antennas

Link adaptation is investigated for OFDMA systems with multiple transmit antennas, where the transmission rate is adapted and where the subcarriers to be used and the multiple antenna transmission scheme to be applied are adaptively selected, according to instantaneous SNR and user mobility. The throughputs (defined as the transmission rate multiplied by 1-(outage probability)) of several transmission modes, which are differentiated by their use of subcarriers and multiple antennas, are compared. Numerical examples are presented showing that the best transmission mode depends on the instantaneous SNR, user mobility (or time-correlation of channel), and a rate adaptation scheme.

Use of subcarrier multiplexed acknowledgment tones for contention recovery in WDMA networks

Subcarrier multiplexed acknowledgment tones are used for contention recovery in connectionless WDMA networks with baseband data packets and subcarrier multiplexed control headers. By using this technique, an access node is allowed to retransmit a message (old or new) immediately after contention occurs, effectively increasing the data offered load, and the throughput of the networks is significantly improved.

Performance of WDMA networks with baseband data packets and subcarrier multiplexed control channels

The use of subcarrier multiplexed control channels for wavelength-division multiple access (WDMA) networks transporting baseband data packets is investigated. The contention problem is analyzed, and general expressions are derived for the throughput of slotted and random-arrival networks with N access nodes and Q subcarriers. The throughput of the networks is significantly increased by using multiple subcarriers for control channels. >

SMPTE Tutorial Paper: Stereo Audio in Television: The BTSC Multichannel Sound System

This article describes the work done in the industry on multichannel television sound standards for the reproduction of high-fidelity sound in TV receivers. The objectives for this improved television service are discussed, along with a short review of related laboratory tests and reports. The system devised by the EIA Broadcast Television Systems Committee (BTSC) is described in detail. In addition, some of the new FCC rules are explained which govern the use of subcarriers on TV for several purposes including stereophonic sound.