Daiming Qu

Two novel nonlinear companding schemes with iterative receiver to reduce PAPR in multi-carrier modulation systems

Companding transform is an efficient and simple method to reduce the Peak-to-Average Power Ratio (PAPR) for Multi-Carrier Modulation (MCM) systems. But if the MCM signal is only simply operated by inverse companding transform at the receiver, the resultant spectrum may exhibit severe in-band and out-of-band radiation of the distortion components, and considerable peak regrowth by excessive channel noises etc. In order to prevent these problems from occurring, in this paper, two novel nonlinear companding schemes with a iterative receiver are proposed to reduce the PAPR. By transforming the amplitude or power of the original MCM signals into uniform distributed signals, the novel schemes can effectively reduce PAPR for different modulation formats and sub-carrier sizes. Despite moderate complexity increasing at the receiver, but it is especially suitable to be combined with iterative channel estimation. Computer simulation results show that the proposed schemes can offer good system performances without any bandwidth expansion.

Extended Active Interference Cancellation for Sidelobe Suppression in Cognitive Radio OFDM Systems With Cyclic Prefix

The sidelobe of noncontiguous orthogonal frequency-division multiplexing (OFDM) signals is required to be deeply suppressed in the licensed users band in cognitive radio (CR) systems. To this end, we propose a novel method of adding extended active interference cancellation (EAIC) signals to suppress sidelobes and to shape the spectrum of the CR-OFDM signal with a cyclic prefix (CP). For simplicity, we called the proposed scheme EAIC-CP. The key idea of the proposed EAIC-CP is to employ some cancellation signals consisting of tones spaced closer than the interval of OFDM subcarriers to cancel the sidelobes of OFDM signals. Moreover, we derive the optimal cancellation signals to minimize the total sidelobe power subject to a self-interference constraint. Numerical results show that, when the guard bandwidth is equal to one OFDM subcarrier interval, the EAIC-CP scheme offers more than a 45.0-dB sidelobe suppression with unnoticeable signal-to-noise ratio (SNR) loss at a symbol error rate (SER) from 10-2 to 10-3 for 64 quadratic-amplitude modulation (64QAM). Moreover, the EAIC-CP scheme can achieve high spectrum efficiency with low implementation complexity.

Multi-Block Joint Optimization for the Peak-to-Average Power Ratio Reduction of FBMC-OQAM Signals

Recently, the filter bank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) has attracted increasing attention. However, most peak-to-average power ratio (PAPR) reduction schemes developed for orthogonal frequency division multiplexing (OFDM) signals are not effective for FBMC-OQAM signals, due to the overlapping structure of FBMC-OQAM signals. In this paper, we propose an improved partial transmit sequence (PTS) scheme by employing multi-block joint optimization (MBJO) for the PAPR reduction of FBMC-OQAM signals, called as MBJO-PTS scheme. In PTS scheme, one data block is divided into several subblocks and each subblock is multiplied by a phase rotation factor for the subblock. The PTS scheme searches over all combinations of allowed phase factors to lower the PAPR. Unlike existing PAPR reduction schemes of independently optimizing the data blocks, the MBJO-based scheme exploits the overlapping structure of the FBMC-OQAM signal and jointly optimizes multiple data blocks. Moreover, we develop two algorithms for the optimization problem in the MBJO-PTS scheme, including a dynamic programming (DP) algorithm to guarantee the optimal solution and avoid exhaustive search. Theoretical analysis and simulations show that the proposed MBJO-PTS scheme could provide a significant PAPR reduction in the FBMC-OQAM system, by exploiting the overlapping structure of the FBMC-OQAM signal. Employing the proposed DP algorithm, the FBMC-OQAM system with the proposed MBJO-PTS scheme even outperforms the OFDM system with the conventional PTS scheme by 0.9 dB at CCDF of 10-3 in PAPR reduction, under the same number of subcarriers, modulation type and PTS parameters given in Section V.

Radio-Resource Management and Access-Control Mechanism Based on a Novel Economic Model in Heterogeneous Wireless Networks

In this paper, we first investigate the radio-resource management and network-selection schemes in heterogeneous wireless networks. Then, we propose a novel economic model to allocate radio resources for both code-division multiple-access (CDMA) networks and wireless local area networks (WLANs). Particularly, the resource-usage constraint is deduced in the CDMA uplink, where the radio resource is allocated with the aim of maximizing the total welfare of the CDMA network while satisfying the signal quality requirement of all mobile users. Moreover, we formulate and solve the optimization problem in the WLAN to maximize the network welfare when the maximum throughput in the WLAN is achieved by controlling the optimum collision probability. An approximated closed-form expression for the network welfare is also given when the assigned bandwidth for each user is close to the bandwidth request. Finally, we design the joint access-control mechanism under different load conditions in coupled heterogeneous networks. Numerical results show that the proposed scheme can achieve approximately 20% more users and 10% more network social welfare, which outperforms the utility-function-based access selection and single network access-control mechanisms in the literature for heterogeneous wireless networks.

Sliding Window Tone Reservation Technique for the Peak-to-Average Power Ratio Reduction of FBMC-OQAM Signals

The filter bank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) has attracted increasing attention recently. In this paper, we address the problem of PAPR reduction for FBMC-OQAM systems using Tone Reservation (TR) technique. Due to the overlapping structure of FBMC-OQAM signals, directly applying TR schemes of OFDM systems to FBMC-OQAM systems is not effective. We improve the tone reservation (TR) technique by employing sliding window for the PAPR reduction of FBMC-OQAM signals, called sliding window tone reservation (SW-TR) technique. The proposed SWTR technique uses the peak reduction tones (PRTs) of several consecutive data blocks to cancel the peaks of the FBMC-OQAM signal inside a window. Furthermore, we propose a method to overlap the sliding windows to control the out-of-window peak regrowth caused by the peak-canceling signal.

Joint Channel Estimation and PTS to Reduce Peak-to-Average-Power Radio in OFDM Systems Without Side Information

In this letter, we propose a novel scheme to reduce the PAPR of OFDM signals, and its key idea is that the side information of partial transmit sequence is considered as a part of channel frequency response. Therefore, the proposed scheme does not need to reserve bits for submitting side information, resulting in an increase in the data rate. Furthermore, we propose a novel pilot arrangement, in which pilot tones are independently inserted into each subblock. Simulations show that the proposed scheme with the novel pilot arrangement could offer good performances of bit error rate and PAPR reduction.

Time Domain Channel Estimation for OQAM-OFDM Systems: Algorithms and Performance Bounds

In this paper, we first present a general time domain model for the channel estimation in the orthogonal frequency division multiplexing system with offset quadrature amplitude modulation (OQAM-OFDM), and utilize the frequency domain pilots to estimate the time domain channel impulse responses. Different form the conventional methods, there is no specific requirement for the length of the symbol interval compared to the the maximum channel delay spread in the proposed scheme. Furthermore, with the proposed time domain model, the channel statistic information could be utilized to improve the performance of the channel estimation. Then, we propose two channel estimation schemes, i.e., linear minimum mean square error (LMMSE) and weighted least square (WLS), and we also derive their corresponding Bayesian Cramér-Rao Bound (BCRB) and Cramér-Rao Bound (CRB) bounds, respectively. Simulation results demonstrate that the BCRB and CRB bounds could be achieved by the proposed LMMSE and WLS methods, respectively. Moreover, simulation results show that the proposed methods are much robust to the time synchronization error compared to the conventional frequency domain methods, and imply that the pulse shaping filter with waveforms concentrated in the time domain could be employed in OQAM-OFDM systems to improve the channel estimation performance and spectral efficiency.

Prototype Filter Optimization to Minimize Stopband Energy With NPR Constraint for Filter Bank Multicarrier Modulation Systems

Recently, filter bank multicarrier (FBMC) modulations have attracted increasing attention. The filter banks of FBMC are derived from a prototype filter that determines the system performance, such as stopband attenuation, intersymbol interference (ISI) and interchannel interference (ICI). In this paper, we formulate a problem of direct optimization of the filter impulse-response coefficients for the FBMC systems to minimize the stopband energy and constrain the ISI/ICI. Unfortunately, this filter optimization problem is nonconvex and highly nonlinear. Nevertheless, observing that all the functions in the optimization problem are twice-differentiable, we propose using the

Coded Auxiliary Pilots for Channel Estimation in FBMC-OQAM Systems

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Spectral Sculpting for OFDM Based Opportunistic Spectrum Access by Extended Active Interference Cancellation

-based Branch and Bound (