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In this paper, the problem of reducing the peak-to-average power ratio (PAPR) of a discrete Fourier transform-spread orthogonal frequency-division multiplexing signal is considered for the transmission of constellation-rotated QPSK symbols. In particular, a joint optimization of the constellation-rotation angle and the pulse-shaping vector is conducted, where the number of allocated subcarriers is larger than the number of QPSK symbols. To avoid the exponential complexity required to evaluate the exact PAPR, a computationally efficient upper bound on the worst-case PAPR is presented and adopted as the objective function. The signal-to-interference-plus-noise ratio (SINR) at the output of a constellation-derotating matched filter is also presented. Then, joint optimizations are conducted through numerical search for various target SINRs. Surprisingly, the optimal rotation angle is close to but not exactly equal to π/4. Numerical results show that the proposed technique is not only applicable to QPSK symbols but also to QAM symbols to significantly reduce the PAPR.

In this paper, the problem of further reducing the peak-to-average power ratio (PAPR) of a discrete Fourier transform-spread orthogonal frequency-division multiplexing signal is considered for the transmission of $\pi/2$ -BPSK symbols in the 5G New Radio specifications. In particular, a joint optimization of the constellation-rotation angle and the pulse-shaping vector is conducted. To avoid the exponential complexity required to evaluate the PAPR, a computationally efficient upper bound on the worst-case PAPR is presented and adopted as the objective function. The signal-to-interference-plus-noise ratio (SINR) at the output of a constellation-derotating matched filter is also presented. Then, joint optimizations are conducted through numerical search for various target SINRs. Surprisingly, the optimal rotation angle is close to but not exactly equal to $\pi/2$ . It is shown that the proposed combinations significantly outperform the existing combinations of the rotation angle and the shaping vector when the signal is amplified by a nonlinear PA.

New waveform design is one of the prominent 5G research directions which aims to increase spectrum efficiency and replace conventional cyclic prefixed orthogonal frequency division multiplexing (CP-OFDM) in 4G LTE systems. In particular, filter bank multi-carrier system (FBMC) is recognized as a promising post-OFDM candidate. Like other candidates, it sacrifices subcarrier orthogonality for improved spectrum confinement. In this paper, we show that a QAM based FBMC (QAM-FBMC) space-time block code (STBC) system can achieve close to CP-OFDM performance with a linear receiver only, settling the conventional perception of the necessity of non-linear equalizers in FBMC to support multiple-input multiple-output. The contribution of this paper is two-fold: (1) in terms of complexity and error rates performance our proposed QAM-FBMC system outperforms conventional OQAM-FBMC scheme; (2) a performance lower bound is shown numerically that QAM-FBMC attains close to CP-OFDM error rates.

As a promising candidate to replace cyclic prefixed orthogonal frequency division multiplexing (CP-OFDM), a new quadrature amplitude modulation filter-bank multi-carrier (QAM-FBMC) has been proposed for enabling spectral efficiency increase and spectrum confinement while keeping near orthogonality. QAM transmission can combat intrinsic interference of conventional offset-QAM (OQAM)-FBMC, which is main bottleneck in channel estimator and multiple antenna transceiver design. Compared to existing single filter based QAM-FBMC, the new QAM-FBMC has more optimization freedom in multiple prototype filters to increase self signal-to-interference ratio (SIR). In this paper, the possibility of per-tone multiple input multiple output (MIMO) reception in the new QAM-FBMC system is exploited. Our MIMO receiver is constructed with per-tone MIMO equalization in oversampled signal domain and its soft-demapper in symbol domain. Not only the separate log likelihood ratio (LLR) calculation per stream but also joint LLR calculation (i.e., soft maximum likelihood (ML) detection) is implemented with pre-processing. Simulation results show that the per-tone MIMO reception in QAM-FBMC is comparable to that of CP-OFDM.

Multiple filter-banks enable QAM transmission and reception in filter-bank multi-carrier (FBMC) systems. In this paper, we propose a new method to design a set of simultaneously used base filters for QAM-FBMC by optimizing the trade-off between spectrum confinement and self-interference. The increased freedom in multiple base filter designs brings merits of a tailor-made spectrum confinement and desirable bit error performance simultaneously. Simulations results show the superiority of the proposed QAM-FBMC systems to other post-OFDM waveform candidates.

Recently, as asynchronous heterogeneous network scenario becoming one of the key features for next generation wireless communications, superior spectrum confinement as well as higher spectral efficiency compared to cyclic prefixed orthogonal frequency division multiplexing (CP-OFDM) has been taken into consideration for future radio access technologies. In this paper, we propose a new quadrature amplitude modulation based filter-bank multi-carrier (QAM-FBMC) system that provides with an inherent spectral efficiency gain against CP-OFDM, which comes from reduction of the redundancies such as cyclic prefix (CP) and guard-band, while keeping the symbol rate same as in CP-less OFDM. We propose a new transceiver structure consisting of at least two different filter-bank bases at both transmitter and receiver sides. Practical algorithms including channel estimation and equalization to mitigate multi-path fading channel without CP are proposed. Various evaluation results show that the proposed system performs comparable to the CP-OFDM system even without CP and guard-band reduction is also available from the well-confined spectrum.

A filter-bank multicarrier - quadrature amplitude modulation (FBMC-QAM) system with two prototype filters for transmitting QAM signal is proposed. The proposed transmitter performs separate filtering for the even-numbered sub-carrier symbols and the odd-numbered sub-carrier symbols. We derive the orthogonality conditions for a FBMC-QAM system without the intrinsic interference. In order to satisfy the suggested orthogonality conditions, we perform a kind of block interleaving for the odd-numbered sub-carrier filtering. The receiver structure is the counterpart to the transmitter. Numerical results showed that the proposed FBMC-QAM system has almost the same bit error rate (BER) performance compared to the FBMC-OQAM and the orthogonal frequency division multiplexing (OFDM) system. with the proposed FBMC-QAM, multiple-input multiple-output transmission schemes and channel estimation schemes can be utilized similarly as in OFDM.

Along with the attention drawn to the millimeter-wave frequency bands for the drastically increased data rate support for the next generation (5G) mobile communications, the hybrid beamforming architectures combining analog beamforming and digital precoding have been investigated as potential candidates to provide good compromise between the complexity and the performance. Among the different hybrid beamforming architectures, the architecture with so-called shared array antenna is analyzed with respect to the peak-to-mean envelope power ratio over antenna elements and the total average transmission power constraint upon multi-beam transmissions. It is shown that the non-trivial normalization coefficients should be applied to the hybrid beamforming architecture under consideration to achieve the average transmission power within the total power constraint. Taking into account the total power normalization for the hybrid beamforming architecture with shared array antenna, various simulation results are provided to show the performance of the multi-beam transmission diversity against the single-beam analog beamforming.

The ever-increasing traffic crunch for the wireless communication has drawn attention to the large spectrum available in the millimeter-wave bands as a potential means to achieve several fold mobile data traffic increase. While the channel characteristics at the millimeter-wave bands are known to be unfavorable for the mobile wireless communication purpose, the high gain available from massive array antenna facilitated by the short wavelength makes it possible to overcome the large path-loss. In this paper, we propose a hybrid beamforming architecture that combines an analog beamforming with array antennas and a digital precoding with multiple RF chains. Furthermore, we propose a multi-beam transmission diversity scheme for single stream transmission for single user MIMO operation. It is shown through various simulation results that the proposed hybrid beamforming scheme leads to considerable performance improvements even with limited feedback.

Adaptive modulation is a link adaptation technique that dynamically adjusts modulation level and code rate to the time-varying channel conditions in order to obtain considerably high data rates. In this paper, we propose a new adaptive modulation algorithm in which an modulation and coding scheme level is selected by the received SNR plus the offset value obtained from the transmission results. Simulations, which are done in the IEEE 802.11n environment, show that the proposed algorithm performs better than the well-known adaptive modulation algorithms such as auto rate fallback and general SNR-based techniques. Particularly, the proposed algorithm has more robust throughput performance while satisfying the target packet error ratio for fast fading channels.

In this paper, we analyze channel quality indicator (CQI) mismatch probabilities of multiuser orthogonal random beamforming (ORBF) systems. First, we derive the CQI mismatch probability of the ORBF system with M transmit antennas and K users equipped with one receive antenna. Using that result, we also derive the upper and lower bounds of the per user unitary and rate control (PU2RC) system with 2 transmit antennas and K users equipped with one receive antenna, which is being adopted in the IEEE 802.16m standard. Finally, we compare theoretical results with numerical results from simulation.

In this paper, we present and analyze a rate-adaptive multiuser orthogonal random beamforming (ORBF) system. The goal is to maximize the average spectral efficiency (ASE) while satisfying a target bit error ratio (BER) constraint. We first derive the cumulative distribution function of the post-scheduling signal-to-interference-plus-noise ratio (SINR) with a new approach. The average BER and the ASE are derived as closed-form expressions. Finally, we obtain the optimal switching SINR thresholds maximizing the ASE under average BER constraint. Simulation results show performance improvement in terms of ASE.

This paper presents closed-form expressions of the distribution of signal-to-interference-plus-noise ratios (SINRs) and the average bit error rate (BER) for an orthogonal random beamforming system in multiple-antenna Gaussian broadcast channels. First, we derive the statistical distribution of the SINR of the scheduled transmit signals and confirm that the approximate form of the cumulative distribution function (cdf) of the SINR is equivalent to the formula in \cite{sharif} and \cite{letaief}. We then obtain a closed-form expression for the total average BER of the system by using the approximate cdf. Our theoretical results are compared to the Monte Carlo simulation results.

Multiple-input multiple-output (MIMO) systems give high data rates through spatial multiplexing or diversity using space-time codes. We propose a rate-adaptive modulation scheme combined with mode switching between spatial multiplexing and orthogonal space-time block coding. We first find out which modulation level and mode maximize the spectral efficiency with a given target bit error ratio (BER). If the rates of the two MIMO modes are the same, we select one mode which gives lower BER than the other. We also propose a simple mode switching algorithm using effective SNR and constellation specific constant. Numerical results demonstrate improvement over each fixed mode with adaptive modulation in terms of average spectral efficiency.