This letter proposes a novel intercarrier interference (ICI) mitigation method for OFDM in time-varying multipath channels. By splitting an OFDM symbol into sub-symbols, ICI may be relieved but with price of increased inter-subsymbol-interference (ISI). The induced ISI is then cancelled by a linear filter with the use of null subcarriers. Simulations show that the proposed method may effectively mitigate ICI while improving OFDM with enhanced reliability against high Doppler spread.

Most existing works on resource allocation in cooperative OFDMA systems have focused on homogeneous users with same service and demand. In this paper, we focus on resource allocation in a service differentiated cooperative OFDMA system where each user has a different QoS requirement. We investigate joint power allocation, relay selection and subcarrier assignment to maximize overall system rates with consideration of QoS guarantees and service support. By introducing QoS price, this combinatorial problem with exponential complexity is converted into a convex one, and a two-level dual-primal decomposition based QoS-aware resource allocation (QARA) algorithm is proposed to tackle the problem. Simulation results reveal that our proposed algorithm significantly outperforms previous works in terms of both services support and QoS satisfaction.

This paper proposes a moving source localization method that combines TDOA, FDOA and doppler rate measurements. First, the observation equations are linearized by introducing nuisance variables and an initial solution of all the variables is acquired using the weighted least squares method. Then, the Taylor expression and gradient method is applied to eliminate the correlation between the elements in the initial solution and obtain the final estimation of the source position and velocity. The proposed method achieves CRLB derived using TDOA, FDOA and doppler rate and is much more accurate than the conventional TDOA/FDOA based method. In addition, it can avoid the rank-deficiency problem and is more robust than the conventional method. Simulations are conducted to examine the algorithm's performance and compare it with conventional TDOA/FDOA based method.

This letter studies cellular controlled short-range communication in OFDMA networks. The network needs to decide when to allow direct communication between a closely located device-to-device (D2D) pair instead of conveying data from one device to the other via the base station and when not to, in addition to subchannel and power allocation. Our goal is to maximize the total network throughput while guaranteeing the rate requirements of all users. For that purpose, we formulate an optimization problem subject to subchannel and power constraints. A scheme which combines a joint mode selection and subchannel allocation algorithm based on equal power allocation with a power reallocation scheme is proposed. Simulation results show that our proposed scheme can improve the network throughput and outage probability compared with other schemes.

Adaptive network coded cooperation (ANCC) scheme may have excellent performance for data transmission from a large collection of terminals to a common destination in wireless networks. However, the random relay selection strategy for ANCC protocol may generate the distributed low-density parity-check (LDPC) codes with many short cycles which may cause error floor and performance degradation. In this paper, an optimized relay selection strategy for ANCC is proposed. Before data communication, by exploiting low-cost information interaction between the destination and terminals, the proposed method generates good assembles of distributed LDPC codes and its storage requirement reduces dramatically. Simulation results demonstrate that the proposed relay selection protocol significantly outperforms the random relay selection strategy.

Orthogonal Signal Division Multiplexing (OSDM), also known as SD-OFDM, has been proposed for information transmission with high spectrum efficiency. In this paper, a new signal construction method named Adaptive Carrier Interferometry OSDM (ACI-OSDM) is proposed for time-frequency selective fading channel. Particularly, the Adaptive CI codes originated from CI-OFDM are employed in the frequency domain of OSDM signal. Compared with traditional OFDM, the ACI-OSDM improves the performance considerably of broadband transmission, i.e., spectrum efficiency, Peak-to-Average Power Ratio (PAPR) mitigation and interference cancelation in the high speed mobile environment with multipath emission, e.g. super express train with speed more than 250 km/h.

We propose a time-frequency interleave (TFI) structure of single carrier (SC) frequency domain equalization (FDE) to combat spectral nulls of wireless channels. Permuted copies of block data are transmitted in the TFI-FDE, providing the same diversity order as maximal-ratio receiver combining. The spectral nulls are compensated by uncorrelated spectral components of the same channel. It shows 4 dB diversity gains at BER of 10-2 over an indoor channel. The TFI-FDE is computationally-efficient in combination with fast Fourier transform. This TFI-FDE fits SC systems with single antenna. It needs no channel state information at the transmitter.

This paper proposes and analyses an improved direction finding (DF) method that uses a rotating interferometer. The minimum sampling frequency is deduced in order to eliminate the phase ambiguity associated with a long baseline, the influence of phase imbalance of receiver is quantitatively discussed and the Root Mean Square Error (RMSE) of both bearing angle and pitch angle are also demonstrated. The theoretical analysis of the rotating interferometer is verified by simulation results, which show that it achieves better RMSE performance than the conventional method.

Cooperative spectrum sensing is an effective approach that utilizes spatial diversity gain to improve detection performance. Most studies assume that the background noise is exactly known. However, this is not realistic because of noise uncertainty which will significantly degrade the performance. A novel weighted hard combination algorithm with two thresholds is proposed by dividing the whole range of the local test statistic into three regions called the presence, uncertainty and absence regions, instead of the conventional two regions. The final decision is made by weighted combination at the common receiver. The key innovation is the full utilization of the information contained in the uncertainty region. It is worth pointing out that the weight coefficient and the local target false alarm probability, which determines the two thresholds, are also optimized to minimize the total error rate. Numerical results show this algorithm can significantly improve the detection performance, and is more robust to noise uncertainty than the existing algorithms. Furthermore, the performance of this algorithm is not sensitive to the local target false alarm probability at low SNR. Under sufficiently high SNR condition, this algorithm reduces to the improved one-out-of-N rule. As noise uncertainty is unavoidable, this algorithm is highly practical.

The channel noise in OFDM systems affects the accuracy of channel estimation, deteriorating the performance of equalization. We present a novel algorithm with MMSE (Minimum Mean Square Error) channel estimation based on Hadamard Transform, to mitigate the effects of noise. The performance of the proposed algorithm is proved to be better than that with LS (Least Square) estimation, and very close to that with the MMSE estimation based on Fourier Transform, while the computation required is pretty small due to the use of Hadamard Transform.

Base Station (BS) cooperation has been considered as a promising technology to mitigate co-channel interference (CCI), yielding great capacity improvement in cellular systems. In this paper, by combining frequency domain cooperation and space domain cooperation together, we design a new CCI mitigation scheme to maximize the total utility for a multi-cell OFDMA network. The scheme formulates the CCI mitigation problem as a mixture integer programming problem, which involves a joint user-set-oriented subcarrier assignment and power allocation. A computationally feasible algorithm based on Lagrange dual decomposition is derived to evaluate the optimal value of the problem. Moreover, a low-complexity suboptimal algorithm is also presented. Simulation results show that our scheme outperforms the counterparts incorporating BS cooperation in a single domain considerably, and the proposed low-complexity algorithm achieves near optimal performance.

Efficient resource allocation for delay-sensitive traffic, such as telephony and video streaming, in Orthogonal Frequency Division Multiple Access (OFDMA) networks is needed to increase system performance. In our system, users try to achieve a low queuing delay and buffer space usage by competing for transmission over the subchannels. We formulate this problem as a bargaining game and use the Nash Bargaining Solution (NBS) to realize a fair and efficient subchannel allocation for the users. Simulation results show performance improvements, with regard to packet dropping and delay distribution, over other algorithms.

Sequence set with Three Zero Correlation Zones (T-ZCZ) is applied in Quasi-Synchronized CDMA communication system to reduce the Multiple Access Interference (MAI) and Inter Symbol Interference (ISI). In this letter, we present a class of sequence set with Three Low Correlation Zones (T-LCZ), which has more sequences and flexibility than T-ZCZ sequence set. Moreover, the theoretical bound on T-LCZ sequences is derived for estimating the performance of such sequence set.

Doppler diversity has been proven effective to combat time variation caused by Doppler spread in single carrier systems. However, it is not efficient to directly apply Doppler diversity into Multi-Carrier Code Division Multiple Access (MC-CDMA) systems because Inter-Carrier-Interference (ICI) increases with the artificial frequency shifts in diversity branches. In this paper, a novel Doppler diversity scheme in MC-CDMA with Three Zero Correlation Zones (T-ZCZ) sequences is proposed to further improve the performance of Doppler diversity. Particularly, zero correlation zones are employed in frequency domain for ICI cancelation caused by Doppler spread, which confirms the validity of the contribution to the wideband wireless communications in high speed mobile environment.

Zero Correlation Zone (ZCZ) sequences have been confirmed the capability in interference mitigation in multipath fading channel. On the other hand, Orthogonal Variable Spreading Factor (OVSF) codes have been successfully applied in WCDMA for separating different channels with different transmission capacity. In this paper, novel OVSF-ZCZ sequences originated from LS and GO sequences have been proposed for CDMA systems with different service requirements. The construction method is discussed and the performance of the system is evaluated.