Allowing for asynchronous access and very high carrier frequencies, 5G presents a major challenge for OFDM-based waveforms not originally designed to deal with these cases. In this paper, we present the benefits of Static Sequence Assisted DFT-spread OFDM (SS-A DFT-s-OFDM) waveform for 5G networks. Through theoretical arguments and numerical results, we show that SS-A DFT-s-OFDM exhibits good properties to be competitive regarding the out-of-band emissions. SS-A DFT-s-OFDM also offers support for tracking of phase noise which becomes a problem in high frequency. The spectral efficiency is then improved with respect to the conventional DFT-s-OFDM making SS-A DFT-s-OFDM an attractive candidate for 5G.

A novel static sequence assisted discrete Fourier transform (DFT)-spread-orthogonal frequency division multiplexing (OFDM) waveform is proposed to suppress out-of-band (OoB) emission. In the proposed scheme, a deterministic sequence, which functions as cyclic prefix (CP), is used to suppress OoB emission. A measure of continuity is proposed to determine the location of the static sequence to maximize the amount of OoB suppression. Perturbation is added to the static sequence to further improve phase continuity at block transitions. It is shown that the spectra of the proposed static sequence assisted waveforms are more compact that those of the conventional waveforms. A frequency offset estimation method using the static sequence is described and its performance is evaluated by simulations.

SC-OFDM (single carrier orthogonal frequency division multiplexing) has received considerable attention in recent years due to its low peak power and robust performance against multipath fading channels. There are emerging demands in a variety of wireless communication systems to transmit multiple SC-OFDM signals in different channels to improve bandwidth efficiency. However, the peak power of such multi channel SCOFDM (MCH-SC-OFDM) signals increases as more signals are multiplexed. In this paper, we present two techniques which can lower the peak power of MCH-SC-OFDM signals by applying phase rotation to SC-OFDM signals in the frequency domain. It is shown through simulation results that the proposed techniques do not introduce any penalties on error performance of the receivers.

This paper introduces novel frame synchronization methods which require lower computational complexity than conventional methods. There are two contributions in this paper. First, a low-complexity method to compute signal estimation error is introduced. Second, an algorithm is proposed to search frame timing candidates efficiently for an estimation error minimizing timing candidate. The simulation results indicate that the proposed algorithm yields a computation reduction of nearly 80% when compared to the conventional method, while it maintains the error performance of a conventional method.

In this letter, a design metric of the interleaver is derived from the union bound of the bit error rate (BER) of linearly precoded orthogonal frequency division multiplexing (OFDM) systems, assuming that the power-delay profile of the channel is known at the transmitter. A new cyclic shift interleaving scheme is proposed to improve the BER performance of OFDM systems. The proposed interleaving scheme is parameterized, and it incorporates existing interleaving schemes. The simulation results indicate that the proposed interleavers outperform the existing interleavers by up to 1.5 dB in a practical scenario.

This paper introduces a precoder design for wireless receivers with imperfect fading channel state information (CSI). Imperfect CSI arises from inaccurate channel modelling or suboptimum channel estimation procedure. Precoders at transmitters are considered here as the means to reduce detection error. To that end, a new lower bound for pairwise error probability (PEP) is introduced. Using the proposed lower bound, precoders are optimized to improve the bit error rate (BER) performance of a receiver which uses basis expansion models (BEM) to estimate time varying channel coefficients without statistical information about the channel. Two precoder design criteria, namely pairwise coding and diversity gain are introduced through the proposed lower bound. Experimentation and theoretical analysis reported here indicate significant improvement in the BER performance of the BEM based receiver when it is used with the precoder in fading channels.

In this letter, we compare the complexity and efficiency of several methods used for multiuser detection in a synchronous code-division multiple-access system. Various methods are discussed, including decision-feedback (DF) detection, group decision-feedback (GDF) detection, coordinate descent, quadratic programming with constraints, space-alternating generalized EM (SAGE) detection, Tabu search, a Boltzmann machine detector, semidefinite relaxation, probabilistic data association (PDA), branch and bound (BBD), and the sphere decoding (SD) method. The efficiencies of the algorithms, defined as the probability of group detection error divided by the number of floating point computations, are compared under various situations. Of particular interest is the appearance of an "efficient frontier" of algorithms, primarily composed of DF detector, GDF detector, PDA detector, the BBD optimal algorithm, and the SD method. The efficient frontier is the convex hull of algorithms as plotted on probability of error versus computational demands axes: algorithms not on this efficient frontier can be considered dominated by those that are.

A strategy of user ordering and time labeling for a decision feedback (DF) detector in asynchronous code-division multiple-access communications is proposed and is proved to be optimal for the ideal DF detector. The proposed algorithm requires O(K/sup 4/) offline operations, where K is the number of users. Although error propagation complicates the analysis of the actual DF detector, computer simulations show that, with the proposed user ordering and time labeling, the performance of an actual DF detector overlays the theoretical bound in most cases.

A strategy for user ordering and time labeling for a decision feedback (DF) detector in asynchronous Code-Division Multiple Access (CDMA) communications is discussed. Ordering and labeling would at first appear to be of a complexity exponential in K, the number of users. Surprisingly, optimal sequencing requires only O(K4) operations, and is needed only once per packet: it is thus a cheap way to obtain an often marked improvement in performance, compared to power-ordering and chronological labeling.

A probabilistic data association (PDA) method is proposed in this paper for multiuser detection over synchronous code division multiple access (CDMA) communication channels. PDA models the undecided user signals as binary random variables. By approximating the interuser interference (IUI) as Gaussian noise with an appropriately elevated covariance matrix, the probability associated with each user signal is iteratively updated. Computer simulations show that the system usually converges within 3-4 iterations, and the resulting probability of error is very close to that of the optimal maximum likelihood (ML) detector. Further modifications are also presented to significantly reduce the computational cost.

We (2001) previously showed that for solutions of the binary quadratic programming problem there exists an "efficient frontier" in the performance/speed domain among the algorithms which characterizes the relative performance of each algorithm. Here, in addition to the algorithms implemented previously, the Boltzmann machine, genetic algorithm and space alternating generalized EM (SAGE) receiver are implemented and results are given for much larger scale problems. Simulation results show that these and several other of the proposed methods can significantly outperform the decision feedback detector or its group counterpart.

We (2001) previously showed that for solutions of the binary quadratic programming problem there exists an "efficient frontier" in the performance/speed domain among the algorithms which characterizes the relative performance of each algorithm. Here, in addition to the algorithms implemented previously, the Boltzmann machine, genetic algorithm and space alternating generalized EM (SAGE) receiver are implemented and results are given for much larger scale problems. Simulation results show that these and several other of the proposed methods can significantly outperform the decision feedback detector or its group counterpart.