Due to the popularity of unmanned aerial vehicles (UAVs), UAV detection technology has attracted considerable attention. In order to widely deploy UAV detection for preventing civil UAVs, a UAV detection method that can be used with any transceiver and operate in parallel with any communication system is proposed in this paper. UAV flights influence electromagnetic environments during signal propagation, and the proposed method detects UAVs based on the variance of higher-order cumulants. In this paper, the principle of the method is deduced and proven, and the detection performance is analysed. Explicit expressions for the detection and false alarm probabilities are obtained, and the influencing factors are investigated. Finally, the feasibility of the proposed method is verified experimentally, and the detection distance, signal-to-noise ratio and detection height are analysed. The results give the effective detection distance and show that the proposed method has superior anti-noise performance.

In single-input single-output (SISO) systems, transmitting the expected signals with artificially generated noise can effectively enhance the physical layer security (PLS). However, the traditional noise suppression at the intended receivers will increase algorithm complexity, particularly over multi-path fading channels, which poses challenges for some massive Internet-of-Things (IoT) networks that take advantage of low-cost and resource-constrained nodes. In this paper, we design a novel self-noise (SN) waveform for transmission security. The transmitter stacks the signal segments periodically, and the additive SN in the current signal period derives from the previous signal periods. Based on this, SN can be completely suppressed at intended receivers by differential operations between two adjacent signal periods. Both analysis and simulation results confirm that the proposed scheme can significantly reduce the complexity of noise suppression and its performance is not affected by multi-path channel environments. Besides, the proposed scheme can effectively worsen the signal-to-noise ratio (SNR) of eavesdroppers while having negligible impacts on intended receivers.

The reconfigurable intelligent surface (RIS), which consists of many low-cost reflecting elements, can enhance the reception of the desired signal and suppress the interference. Considering the above advantages, this paper investigates the RIS-assisted wireless communication in the presence of an interferer, where a receiver receives the desired signal and interference from a transmitter and an interferer, respectively, and the RIS is deployed to assist this system. First, an interference-limited channel capacity maximization problem is formulated, and a numerical algorithm based on the fraction programming and optimality conditions is proposed to obtain the optimal solution. Then, this paper shows the upper boundary of the maximal capacity with interference and discusses what kind of channel conditions can achieve the upper boundary and the corresponding optimal phase shifts. Next, this paper analyzes the asymptotic behaviors of the maximal capacity in the scenarios that some or all of the number of reflecting elements, antennas at the transmitter, and interferer go to infinity. Finally, this paper generalizes the above results to the multiple interferers scenario.

Nonlinear self-interference (SI) cancellation is crucial for eliminating the impact of the transmitter-side nonlinearity on the comprehensive SI cancellation performance in full-duplex radios. However, in the propagation environment with rich reflection paths of signals, the number of the delayed taps required for time-domain nonlinear SI cancellation booms exponentially with the increase of the multi-path number, leading to unacceptable complexity. In this paper, a novel frequency-domain nonlinear SI canceller based on successive interference cancellation (SIC) technique is proposed for orthogonal frequency division multiplexing (OFDM) modulated full-duplex systems subjected to both transmitter nonlinearity and receiver nonlinearity. The proposed frequency-domain nonlinear SIC (FD-NSIC) cancels nonlinear components one by one via separately estimating the channel frequency response suffered by each order nonlinear component, which significantly relaxes the computational cost. Besides, to avoid the influence of the strong correlation between nonlinear components, orthogonalization is operated before SIC to white basis functions, which accelerates the convergence speed of the proposed FD-NSIC. Simulations are explicitly performed, showing that compared with the conventional frequency-domain nonlinear canceller based on recursive least squares (RLS) channel estimation, the proposed FD-NSIC is capable of canceling the SI to the noise floor with only 52% computational cost under 50 dB interference-to-noise ratio.

Network function virtualization (NFV) implements mobile edge computing (MEC) services as software appliances, and allows resources to be adaptively allocated to accommodate demand variations. Scalability and network cost (including operational cost and response latency) are key challenges. This paper presents a new game-theoretic approach to minimizing the network cost, where access points (APs) select MEC servers and routes in a decentralized manner, and unloaded routers and links are deactivated for cost saving. The key idea is that we interpret the minimization of network cost as a mixed game with a non-monotonic cost function capturing both the operational cost and response latency. We prove that the game is conditionally an ordinary potential game and converges to$\alpha $-approximate equilibriums. A closed-form expression is derived for the convergence delay. Another important aspect is that we integrate Stackelberg routing into the proposed mixed game to avoid inefficient equilibriums (with high cost or latency). We prove that the mixed game can converge faster to better equilibriums under linear response latency models. Extensive simulations corroborate the new game-theoretic approach can significantly outperform existing techniques in terms of efficiency, convergence, and scalability.

In full-duplex multipath self-interference (SI), each of the resolvable multipath SI components consists of a group of non-resolvable (NR) components with similar delays. Since the transceiver cannot distinguish the NR components in reality, the canceller can only generate the approximate constructed SI to imperfectly cancel the received SI. This leads to residual SI remaining. This paper analyzes the effect of the NR components on the SI cancellation, and proposes a practical scheme to eliminate the residual SI caused by the NR components. First, a closed-form expression of the residual SI is obtained. Next, the average power of the residual SI and the SI cancellation ratio are derived to characterize the effect of NR components on SI cancellation in the multipath SI channel. Last, a switch scheme is proposed to eliminate the residual SI.

In the timing asynchronous self-interference cancellation (TASIC) of full-duplex (FD) orthogonal frequency division multiplexing (OFDM) systems, the relative delay between the signal of interest (SoI) and the self-interference (SI) may be greater than the length of the cyclic prefix (CP) due to the long distance transmission of the SoI and the access timing control, which causes a loss in the orthogonality of the SI when performing SI cancellation (SIC) in the frequency domain directly. In order to maintain the orthogonality of the SI pilots and estimate the channel response without the interference caused by the SoI, a channel estimation method is given utilizing either the complete or incomplete subcarriers. Based on it, a TASIC method is proposed to cancel the SI, where the expression of the time-domain SI is derived considering the influence of the multi-path channel and the relative delay between the SoI and the SI. The theoretical and simulation results show that the value of the residual interference (RI) power is stable and the SIC ratio (SICR) increases with the increase of the interference to signal ratio (ISR), and the proposed TASIC method can largely avoid the impairment brought by the relative delay between the SoI and the SI.

Full duplex radio is one of the most promising techniques for the fifth-generation (5G) wireless networks. It usually includes a feedback loop to capture the nonlinear distortion of the transmitted signal for linearization of power amplifiers (PAs) and nonlinear self-interference (SI) cancellation. This paper presents an FD transceiver architecture consisting of the digital predistortion (DPD), radio frequency (RF)-tapping SI cancellation, and baseband (BB)-tapping SI cancellation. In particular, the issue of high sampling rate required in the feedback loop is addressed, and a BB-tapping method, which adopts a nonlinear modeling method with a low-rate aliasing transmitted signal, is proposed to significantly reduce the required feedback sampling rate. Numerical results verify that by using the proposed BB-tapping cancellation, a sampling rate of 25 MSPS is enough for the feedback loop in the scenario of a 100 MHz source signal.

The reconfigurable intelligent surface (RIS), which consists of a large number of passive and low-cost reflecting elements, has been recognized as a revolutionary technology to enhance the performance of future wireless networks. This paper considers an RIS assisted multicast transmission, where a base station (BS) with multiple-antenna multicasts common message to multiple single-antenna mobile users (MUs) under the assistance of an RIS. An equivalent channel model for the considered multicast transmission is analyzed, and then an optimization problem for the corresponding channel capacity is formulated to obtain the optimal covariance matrix and phase shifts. In order to solve the above non-convex and non-differentiable problem, this paper first exploits the gradient descent method and alternating optimization, to approach the locally optimal solution for any number of MUs. Then, this paper considers a special case, which can obtain the global optimal solution, and shows the sufficient and necessary condition for this special case. Finally, the order growth of the maximal capacity is obtained when the numbers of the reflecting elements, the BS antennas, and the MUs go to infinity.

This paper considers a point-to-point communication system which is protected by a cooperative jammer from being eavesdropped. Previous works in this field always assume that the cooperative jamming is cancelled perfectly at the receiver, without considering any imperfections in the jamming cancellation of practical systems. In this paper, by taking into account the residual jamming caused by frequency offset at the receiver, a power allocation scheme is proposed to maximize the secrecy capacity over the additive white Gaussian noise (AWGN) channel, which is derived as an exact closed-form solution. In addition, the relationship between the optimal jamming power and the relative channel quality is analyzed under imperfect jamming cancellation. Simulation results confirm that the proposed power allocation scheme outperforms the power allocation scheme without considering any imperfections in the jamming cancellation, and illustrate that the frequency offset significantly degrade the security performance. Specially, for small frequency offset, the total power consumption increases with the frequency offset, which means the frequency offset consumes extra power to achieve the secrecy capacity target. However, for large frequency offset, the secrecy capacity may fail to meet its preset goal no matter how sufficient the power budget is. More seriously, when the frequency offset is remarkable, the secrecy capacity may drop to 0, which implies that the eavesdropper can always overhear the confidential information.

In full-duplex (FD) systems, time alignment error between the received self-interference (SI) and the reconstructed one results in performance degradation of the SI cancellation. As a crucial part of SI cancellation, nonlinear interference (NI) cancellation is usually invested in the ideal situation, and the impact of the time alignment error on NI cancellation performance is rarely considered. In this paper, a robust NI cancellation algorithm is proposed to tackle the time alignment error in FD systems. At first, the impact of the time alignment error on NI cancellation is analyzed. The approximate expression of the residual NI power with time alignment error is derived to predict the NI cancellation performance. Then, an improved memory polynomial (IMP) model is derived to describe both time alignment error and nonlinearity. Finally, based on the IMP model, a novel NI cancellation algorithm with robustness to the time alignment error is proposed. Simulations present the impact of the time alignment error on NI cancellation capability, in which the theoretical value is coincident with the actual value. Besides, the proposed algorithm significantly enhances the NI cancellation performance. Specifically, when the time alignment error is 10% of the sampling interval and the interference to noise ratio is 60 dB, the proposed algorithm outperforms the conventional algorithm by 33 dB.

To further enhance the security of the wireless communication systems, an architecture of the cooperative jamming (CJ) assisted slow frequency-hopping (FH) systems is proposed in this paper. Then, after the CJ cancellation operation, the residual CJ raised from synchronization error is analyzed, where the inter-symbol interference (ISI) is employed to depict the time misalignment between the received signal and the local reference CJ at the receiver, and the inter-hop interference (IHI) is introduced to describe the frequency misalignment. In addition, the closed-form expression of the jamming cancellation ratio (JCR) is derived to evaluate the CJ cancellation performance. Theoretical analyses and simulation results show that in the slow FH systems, both the proportions of the ISI and IHI components in the residual CJ are jointly determined by the synchronization error and the hop length. Besides, the JCR increases with the increase of the hop length and the jamming-to-noise ratio (JNR), and decreases with the increase of the synchronization error.

In this paper, a multiple-input multiple-output (MIMO) full-duplex (FD) transceiver design is proposed, which can mitigate the impact of phase noise and provide an enhanced self-interference cancellation capability. This design is featured by finely tuning the delay of the transmit oscillator signal and using it as the receive oscillator signal. To maximize the cancellation capability, a delay selection principle is developed to calculate the optimal oscillator delay. To further reduce the number of parameters needed in the delay calculation, a simplified principle is also developed with acceptable loss of cancellation capability. Compared to the traditional transceiver with a shared oscillator for its transmitter and receiver, the proposed design achieves an obvious improvement about 10 dB in terms of cancellation capability.

Compared with the conventional mobile edge cloud (MEC) network, the network function virtualization (NFV)-enabled MEC network provides new flexibility on the MEC service deployment. Resource wastage owing to dynamic workloads in traditional MEC networks can be overcome through adaptive resource allocation. In this paper, we investigate the resource allocation problem to minimize the operational cost (e.g., energy consumption, capital expenditure) and the average response time in the NFV-enabled MEC network. We consider the problem from the perspective of MEC service deployment, assignment, and routing among the access points (APs) and MEC servers. We propose an user-network cooperation-based algorithm with low-complexity. In the proposed algorithm, the network announces a path-switching rule (i.e., α-approximate deviation) with proportionally shared operational cost, while the APs selfishly choose their paths with the least cost accordingly. We analyze the selfish behaviors of APs with game theory. We prove existence and convergence of α-approximate equilibriums. Also, we evaluate the efficiency of the equilibriums with the price of stability (POS). Furthermore, an enhanced algorithm based on public service advertising (PSA) is proposed to improve the convergence performance and equilibriums efficiency. Through simulations, we show the superiority of the proposed algorithms over existing algorithms (e.g., BnB-SD and greedy routing) on the accuracy and convergence performance (measured by the overall path switching).

Mobile edge computing (MEC) is a promising technique which enables the user equipment (UE) to leverage the vast computation resources on the clouds (or cloudlets). The redundant design and dynamic nature of traffic raise an energy inefficiency issue in MEC network. In this paper, we aim to minimize the energy consumption and average response time in the MEC network. We jointly consider the cloud selection and routing optimization on both wired and wireless links. Based on the game theory, we propose a low-complex resource allocation algorithm, which can achieve the global optimal solution. Further, to reduce the number of re-routing (routing times), an improved algorithm is proposed, which introduces an approximate factor (i.e., β). The β represents the additional cost during the re-routing, such as session migrations, energy consumption. We demonstrate the convergence of the improved algorithm. The simulations show that the proposed algorithms outperform the other conventional algorithms.

In wireless full-duplex communication systems, selfinterference (SI) cancellation is a key technique to ensure simultaneous transmission and reception on the same carrier frequency. During the SI cancellation, it has been shown that the oscillator phase noise dramatically affects the cancellation capability and thus needs consideration and suppression. In this paper, a novel time-domain digital SI cancellation approach is proposed to cancel the transmitter and receiver phase noises along with the incoming SI signal, without estimating either the SI channel response or the phase noise associated coefficients. For proofof-concept evaluation, simulations are performed on orthogonal frequency division multiplexing (OFDM)-modulated signals of 20 MHz bandwidth with 16 QAM constellations to verify the effectiveness of the proposed method. It is demonstrated that the proposed approach provides at least 3 dB improvement on the SI cancellation capability and at least 5 dB increase on the interference tolerance over the conventional cancellation approach that uses the frequency domain SI channel estimation.

In this paper, we address the multi-user scheduling problem of the multi-user two-way full-duplex (FD) decode-and-forward relay system. According to the availability of the channel state information (CSI) and system state information (SSI), three scheduling schemes are investigated in terms of the system outage performance. Specifically, for the non-CSI case, we analyze the random scheduling scheme, which serves as a baseline for comparison. For the full CSI case, we propose the Max-Min scheduling scheme, which is theoretically proved to be sub-optimal in the low signal-to-interference-plus-noise ratio (SINR) regime but optimal in the high SINR regime. To minimize the outage probability, we propose the optimal scheduling scheme, which involves the full SSI. In addition, the exact closed-form outage probability expressions corresponding to different schemes are derived under the general independent but not identically distributed channels. The residual self-interference incurred by the FD mode is taken into account. Moreover, independent and identically distributed channels are also considered as special cases. Finally, numerical simulations are performed to corroborate the theoretical results. The results reveal that the Max-Min scheduling and optimal scheduling schemes significantly improve the outage performance compared with the random scheduling scheme.

This paper proposes a simple hybrid decode- compress- and-forward and compress-and-forward (DCF&CF) relay scheme for the coordinated multipoint (CoMP) uplink transmission. In particular, we consider a scenario that two mobile users (MUs) transmit signal to two access points (APs), which are linked to the central unit (CU) via lossless capacity-limited fronthaul. To characterize the achievable rate region of the considered system, a rate maximization problem is formulated and solved by exploiting the monotonicity and convexity of its objective function. Furthermore, maximum sum rate of the two MUs is obtained according to the maximized rate region boundary. Finally the analysis is validated by numerical results.

Design of high-efficiency power amplifier (PA) is one of the key challenges to realize green radios, wherein digital predistortion (DPD) is deployed to reduce the PA's power back-off and thus increase its power efficiency. As the bandwidth of the transmit signal increases, stringent requirements are posed on the DPD linearization performance with limited sampling rate and dynamic range for the analog-to-digital converter (ADC) in the DPD feedback channel. In this paper, under a fixed ADC sampling rate, novel DPD architecture is proposed to compensate for the PA nonlinearity with limited ADC dynamic range. In the feedback channel of the proposed architecture, an extra radio frequency (RF) cancellation chain is introduced to eliminate the linear component of the PA amplified signal, and thus the requirement on the ADC dynamic range can be significantly reduced. Subsequently, by accurately estimating the loop delay and attenuation of the cancellation chain, the baseband replica of the RF cancelling signal is recovered, and the original PA output signal is rebuilt to estimate the DPD coefficients. Finally, experiments show that for the long term evolution (LTE)-advanced signals, the proposed architecture can achieve an adjacent channel leakage ratio lower than -47.6 dBc, which outperforms the conventional DPD by about 3.4 dB, with the effective bits of the ADC being reduced by 4.4 and a power added efficiency of 43.8% with 7.3 dB power back-off being observed for a fabricated Doherty PA with 50-dBm saturation power.

This paper presents the nonlinear effects of the analog self-interference (SI) canceller and a practical solution to suppress the nonlinear distortions in multiple-input multiple-output (MIMO) full-duplex wireless communication systems. Due to the inherent nonlinearities of the active radio frequency (RF) components used to tune the attenuations and the phase shifts in the analog SI cancellers, nonlinear distortions are introduced to the residual SI signal by the analog cancellation and enter the receive chain. In this paper, we build an extra feedback chain for each analog canceller to obtain the reference signal coupled from the transmitted RF signal and observe the characteristics of the canceller. Using the observations, we develop a nonlinear model including all the cancellers at each receive antenna with the presence of MIMO SI channel to estimate the nonlinear components. By subtracting the model estimates from the received signal instantaneously, the corresponding nonlinear distortions are effectively mitigated. After the nonlinearity mitigation, a linear digital cancellation scheme based on the Maximum Likelihood Estimation is applied to further reduce the residual SI signal caused by the MIMO SI channel to the noise floor. Experiments are performed on a 2x2 MIMO full-duplex testbed to validate the effectiveness of the proposed nonlinearity modeling and suppression method using Long Term Evolution signals of 20-MHz bandwidth.

In this paper, we propose a novel approach to cancel Self-interference (SI) signal in analog domain in Full-duplex (FD) communication system. This approach is based on self-mixing and called Self-Mixed Self-Interference Analog Cancellation (SM-SIAC) where three feedback loops are employed for auto-tuning. In condition that these loops converge, we analyze the cancellation performance.

Oscillator phase noise in a full duplex radio causes the mismatch between the self-interference (SI) signal and the cancelling signal, and thus degrades performance of the digital SI cancellation (SIC). In this paper, we analyze the effect of phase noise on digital SIC in wireless full duplex. We consider an OFDM-based full duplex radio corrupted by the phase noise at both the transmitter and the receiver, which are modeled as independent Wiener processes. A closed-form expression for the cancellation ability of a common digital SIC scheme is derived, in terms of the interference-to-noise ratio (INR), the SI subcarrier spacing and the oscillator's 3dB coherence bandwidth. The theoretical analysis and simulations reveal that the digital SIC ability degrades with the increase of the ratio of the oscillator's 3dB coherence bandwidth to the signal bandwidth, which determines the upper bound of the digital SIC ability.

Considering the radio frequency (RF) self-interference cancellation of the full duplex transceiver, which can transmit and receive simultaneously at the same frequency band. The current studies mainly focus on the feasibility verification, most of which are realized by manual adjustment of the self-interference parameters, and lack of the theoretical analysis of the interference cancellation capability. To solve this problem, an adaptive least mean square (ALMS) algorithm for the self-interference cancellation at the RF stage is presented in this paper. Besides, the convergence and steady state performances of the ALMS algorithm are proved and analyzed, respectively. Analysis and simulation results show that the ALMS algorithm can achieve significant cancellation of the self-interference at the RF stage. Moreover, it is revealed that the interference cancellation performance and convergence speed of the ALMS algorithm are related with the following parameters: the duration per iteration, normalized step size, as well as the ratio of the interference power and total power of the desired signal plus noise.

The sampling clock accuracy of the digital predistortion (DPD) feedback path is limited by nonideal electronic components, which introduces random clock jitter and thus degrades the linearization performance. In this paper, we propose a new DPD architecture capable of estimating and mitigating the sampling clock jitter. The theoretical analysis reveals that the sampling clock jitter has a adverse effect on the signal-to-noise ratio (SNR) of the samples received and hence degrades the DPD performance. By applying the proposed reference injection method, the clock jitter can be estimated and mitigated, effectively. Simulation results demonstrate that the proposed DPD architecture can improve the normalized mean square error (NMSE) and the adjacent channel leakage ratio (ACLR) performances, compared with conventional DPD architecture when feedback sampling clock jitter is considered.

In this paper, we investigate the effect of shadowing on optimal power allocation of amplify- and-forward cooperative relaying systems. Considering the joint effects of path loss, correlated shadowing and flat Rayleigh fading, the approximate outage probability at high signal-to- noise ratio (SNR) is first derived. Then we solve the power allocation problem by minimizing the approximate outage probability subject to a total power constraint. It is shown by the analytical results that the correlation coefficients and the standard deviations of shadowing have a significant impact on the optimal power allocation. The simulation results show that the proposed power allocation scheme yields about 2dB SNR gain compared to the equal power allocation in the high SNR regime.

SUMMARY Because of the increasing energy consumption in radio access networks, a new radio access network called Cloud radio access network (C‐RAN) has attracted increasing attention. In C‐RAN, the distributed radio remote units (RRUs) are located in different sites and the placement of RRUs will influence the system performance. However, few researches investigate the optimal RRU placement from the perspective of energy efficiency, which is one of the most important characteristics of C‐RAN. In this paper, we first derive the energy efficiency of C‐RAN to achieve certain QoS requirements considering the circuitry energy consumption. Then, we obtain the optimal placement of RRUs by minimizing the consumed energy per bit. Numerical results are also presented to validate the analysis. Copyright © 2012 John Wiley & Sons, Ltd.

Iterative clipping and filtering (ICF) is a well-known technique to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. Recently, Wang and Luo investigated the clipped signal and proposed a modified algorithm called optimized ICF (OICF). This is an optimal algorithm since it can achieve the required PAPR reduction with minimum in-band distortion and far fewer iterations. However, OICF needs to solve a convex optimization problem with O(N3) complexity, where N represents the number of subcarriers. In this paper, instead of analyzing the clipped signal, we study the clipping noise and propose a simplified OICF algorithm. In the new algorithm, solving the convex optimization problem is approximated by some simple algebraic operations and the computational complexity reduces to O(N). Simulation results show that after three iterations, the original OICF algorithm can achieve the desired PAPR while the simplified one exhibits almost the same performance: for a 128-subcarrier and quadrature phase shift keying (QPSK) modulated OFDM system, the PAPR-reduction performance difference between the two algorithms are 5×10-3dB at a 10-4clipping probability and the bit-error-rate performance difference is 6×10-3dB at a 10-7error probability.

SUMMARY Cognitive radio is always based on spectrum sensing to cognize the physical characteristics of the wireless channel and carry out wireless communication resource scheduling. This kind of method makes it hard for cognitive radio to respond to a change in the radio environment in advance. Therefore, both the predictive ability and cognitive contents are limited. This paper proposes a new system called visual cognitive radio, which uses visual information to cognize the radio environment. Visual observation has a good predictive ability and abundant cognitive information, which enables the visual cognitive radio to react to the frequent change in the radio environment and make optimal configurations to the process of wireless communication. This paper presents a typical communication scene as an example to explain the advantages of visual cognitive radio, and also makes a preliminary analysis of its applications and challenges. Copyright © 2011 John Wiley & Sons, Ltd.

This paper focus on how to design the location of transmit antennas for Multiple-Input Multiple-Output (MIMO) space-time coding architecture with distributed transmit antennas. Considering the effects of path loss, correlated shadowing, multipath fading and white Gaussian noise, we first derive the approximate area averaged symbol error rate (AASER) in a circular cell at high signal-to-noise ratio (SNR) with M-PSK for orthogonal space-time block coded (OSTBC) systems with distributed transmit antennas. Then, we obtain the transmit antenna location by minimizing approximate AASER. Theoretical and numerical results show that the transmit antenna location depends on the cross-correlation coefficient and the standard deviation of shadow fading, and that the transmit antennas should be symmetrical with respect to the cell center.

To obtain the receive diversity of timing acquisition, the cooperative processing of multiple distributed received antennas is considered in this paper. In the flat Rayleigh channels, we assume two remote antennas at the base station for receiving the signal transmitted from the mobile station with a single antenna. By utilizing the coverage range of each remote antenna, a constraint is exploited to associate the time-delays from the mobile station to the two remote antennas. With this constraint, we propose a maximum likelihood-based cooperative timing acquisition method to improve the probability of correct acquisition for each remote antenna. Also, a lower bound of the probability of correct acquisition is derived to evaluate the performance of the proposed method. Compared to the independent timing acquisition, the analysis and simulations show that the probability of correct acquisition for each remote antenna can be improved by the cooperation of the two remote antennas.

This paper investigates the cooperative timing acquisition (CTA) for distributed antenna systems (DAS). As a preliminary study, the path loss and additive white Gaussian noise (AWGN) channel are considered without assuming multipath fading and shadowing. In the DAS coverage region, two remote antennas (RA) are assumed at base station (BS) for receiving the signal transmitted from the mobile station (MS) with a single antenna. Under the constraint that is derived from the known locations of the two RAs, a maximum-likelihood (ML)-based CTA method is proposed. By the analysis and simulation, it is shown that the probability of correct acquisition for each RA can be improved by the cooperation of the two RAs.

In this paper, an asynchronous layered space-time architecture is proposed to realize the spatial multiplexing over the Ricean multiple-input multiple-output (MIMO) channels. Based on reducing the correlation of spatial shaping pulses between the multiplexed streams, this approach can be used to solve the problem of detection in the ill-conditioned channel matrix. It is shown that at the receiver, the reduction of the correlation enables the requirement on the number of the receive antennas to be removed by the zero forcing (ZF) detector compared with the conventional synchronous layered space-time architecture. First, this paper presents how to exploit the correlation of spatial shaping pulses between the multiplexed streams. Then deriving the exact closed-form expression of error rate for the proposed scheme, this paper finds that the maximum possible diversity gain can be achieved based on the independent layered architecture by the ZF detector at the cost of limited multiplexing gain.

In this paper, an asynchronous layered space-time architecture is proposed to realize the spatial multiplexing over the Ricean multiple-input multiple-output (MIMO) channels. Based on reducing the correlation of spatial shaping pulses between the multiplexed streams, this approach can be used to solve the problem of detection in the ill-conditioned channel matrix. It is shown that at the receiver, the reduction of the correlation enables the requirement on the number of the receive antennas to be removed by the zero forcing (ZF) detector compared with the conventional synchronous layered space-time architecture. First, this paper presents how to exploit the correlation of spatial shaping pulses between the multiplexed streams. Then deriving the exact closed-form expression of error rate for the proposed scheme, this paper finds that the maximum possible diversity gain can be achieved based on the independent layered architecture by the ZF detector at the cost of limited multiplexing gain.

This paper focuses on the compensation of carrier frequency offsets (CFO) in multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems with distributed transmit antennas, where the CFOs are possibly different for each transmit antenna. Considering macroscopic fading and multipath Rayleigh fading, the average power of the intercarrier interference (ICI) caused by the CFOs is derived. The optimal CFO compensation value is then obtained by maximizing the signal-to-interference-and-noise ratio (SINR) before MIMO detection. It is shown that the optimal CFO compensation value should be located between the minimum and maximum value of the CFOs and depends on the CFOs and the macroscopic fading of all the transmit antennas. The performance of the CFO compensation is evaluated for a MIMO OFDM system with two transmit antennas and two receive antennas using zero-forcing (ZF) detection. Simulation results show that the symbol error rate (SER) performance is significantly improved by using the proposed optimal CFO compensation value to compensate for the CFOs.

In [1], a modified Vertical-Bell Labs layered space- time (V-BLAST) system has been proposed, where different delay offsets are intentionally applied to the spatially multiplexed data streams. Compared with the conventional synchronous V- BLAST system, the modified system with only a simple linear detection under zero-forcing(ZF) criterion can achieve Mrth- order diversity(where Mris the number of receive antennas), therefore giving a reasonable tradeoff between complexity and performance. In this paper, we focus on how to find the optimum linear detection of the Modified V-BLAST Systems. Simulations demonstrate that the optimum linear detection is superior to the ZF detection algorithm used in [Shihai Shao et al., 2007], especially when the number of transmit antennas is large.

This paper focuses on a modified Vertical-Bell Labs Layered Space-Time (V-BLAST) system, where different delay offsets are intentionally applied to the spatially multiplexed data streams. We consider a multiuser MIMO uplink environment, where each user carries Mttransmit antennas, but is allocated only one signature sequence. Compared with the conventional V-BLAST, the modified scheme gains advantage mainly in two aspects: firstly, it is able to recover the transmitted information from only one receive antenna, whereas the conventional V- BLAST requires that Mrges Mt(Mris the number of receive antenna); secondly, the modified system could achieve the maximum possible diversity gain Mrof V-BLAST at the cost of limited multiplexing gain, whereas the diversity gain is only Mr- Mt+ 1 in conventional V-BLAST with ZF detector. The exact closed-form expression of bit error rate (BER) is derived for an Mttimes Mrmodified system with ZF strategy. And further explanation for the performance difference between the modified and conventional scheme is given from the spatial correlation point of view. Finally, we compare the performance of our proposed system with the conventional scheme by computer simulations which validate the analytical results.

Partial transmit sequence (PTS) with pseudo-random sub-block partition can achieve lower Peak-to-Average Power Ratio (PAPR) performance. Based on the correlation of the candidate signals, we can prove that the performance is uncorrelated with the input signal. In general, the correlation of the candidate signals will increase with the number of candidate signals. As a result, the performance improvement will decrease evidently. In this paper, we provide a novel method to design the phase factor for PTS scheme, so as to achieve quasi orthogonal candidates to get better PAPR reduction performance. Simulation results prove it is more efficient than the traditional one.

In this paper, we propose a new list-based detection algorithm to achieve near maximum likelihood (ML) performance with low computational complexity for multiple-input multiple-output (MIMO) systems. First, we use the minimum mean square error (MMSE) detection to yield an initial bit decision and the corresponding bit log-likelihood ratio (LLR) for a specified layer. Next we construct a list of LLR-based candidate error vectors for the specified layer, and then apply independent reduced-complexity sub-detectors to the remaining layers after cancelling the contribution of each candidate vector of the list. Finally the most likely vector is returned among all visited decisions. Simulation results show that the proposed method can approach identical performance to that of ML detection but only 0.15% complexity for (4,4) system using uncoded 16-QAM.

In this paper, we address the problem of carrier frequency offset estimation for multiple-input multiple-output (MIMO) correlated fading channels. A maximum likelihood (ML) carrier frequency offset estimator based on the average likelihood function is proposed, which can make use of the channel correlation information by averaging the conditional likelihood function over all realizations of the channel and can exploit both transmit and receive spatial diversity as well. The Cramer-Rao bound (CRB) for the problem is also derived, and simulation results are given to illustrate the performance of the proposed estimator and compare it with the CRB. It is shown that the proposed estimator can provide satisfactory frequency offset estimates in MIMO correlated fading channels.

This paper proposed a modified vertical-Bell Labs layered space-time (V-BLAST) system, where different delay offsets are intentionally applied to the spatially multiplexed data streams in order to improve bit error rate (BER) performance. The proposed system can use only one receive antenna to recover the transmitted information by zero forcing (ZF) detection, whereas the conventional synchronous V-BLAST system requires that Mrges Mt(where Mtand Mrare the number of transmit and receive antennas, respectively). Compared with the conventional synchronous V-BLAST system, the modified system can achieve Mrth-order diversity using ZF detection. Although delay offsets in the system introduce an attenuation factor which decreases the instantaneous signal-to-noise ratio (SNR), the BER performance of the modified system with proper system parameters demonstrates a performance improvement over the conventional synchronous V-BLAST system.

Space-time block codes are known to be a powerful tool to achieve full spatial diversity gain while maintaining a very simple receiver structure. In this paper, the authors analyze the asymptotic error performance of orthogonal space-time block codes over flat Nakagami-m fading channels. Both identical and non-identical m-distributions are considered. Based on the moment generation function (MGF) approach, the closed-form asymptotic symbol error probabilities over Nakagami-m fading channels are derived. Compared to the previous works in literature, our results are more accurate and more general. Simulation results are provided to verify our analytical results.

This paper is concerned with the design and performance evaluation of a time and frequency domain chip-level differential detection (TF-CLDD) technique for two-dimension spread spectrum system. Unlike the conventional chip-level differential encoding/detection performed either time domain or frequency domain, such a technique envisages differential detection of the time domain and frequency domain spreading code chips to counteract both the time-selective and frequency-selective fading at the same time. The bit error rate performance of the receiver is analytically evaluated as a function of the relevant system parameters.

A novel differential detection method in frequency domain spread spectrum systems, called multicarrier spread spectrum chip-level differential detection (MC-SS-CLDD), is proposed. The moment generating function (MGF) of the decision variable and a saddlepoint approximation method are exploited to analyze the BER performance of MC-SS-CLDD. The results of analysis and simulation indicate that, if the coherent bandwidth of the channel does not exceed the occupied bandwidth of two subcarriers, MC-SS-CLDD exhibits a better performance in making the system resistant to frequency-selective fading in the case of narrower channel coherent bandwidth.

Abstract Orthogonal frequency division multiplexing (OFDM) is very attractive for next generation high‐speed wireless communication because of its various advantages in lessening the severe effects of frequency‐selective fading. When using pilot symbol assisted (PSA) M‐ary quadrature amplitude modulation (M‐QAM) in OFDM systems, if the power of pilot is too low, the channel parameters cannot be accurately estimated, whereas, high pilot power will lead to less power left for data symbols under the condition that the total transmitted power is constrained to be a constant. In this paper, we present how pilot power affects the demodulation performance in Rayleigh fading propagation environments. Consequently, the pilot‐to‐data power ratio (PDR) is optimized analytically, and degradation of system performance due to inaccurate channel estimation is also evaluated. The theoretical and simulation results show that the optimum PDR is affected by the signal‐to‐noise ratio (SNR), Doppler frequency and interpolation size etc. When the optimum PDR is adopted for an OFDM system, the total transmission power will be minimal for certain bit error rate (BER) target. Copyright © 2005 John Wiley & Sons, Ltd.

The TDD pre-equalized OFDM systems have a mighty significant advantage of saving system resource by omitting the pilot symbols. Along with that, there is a limitation that the timing error can not be revised in the absence of pilot symbols. In this paper we investigate the impact of timing error on the receiver's BER performance of TDD pre-equalized OFDM systems. We obtain the analytic BPSK BER expressions of ideally and nonideally pre-equalized OFDM systems in multipath Rayleigh fading environment. The corresponding simulations verify the analytic expressions. Compared with the theoretical system performance bound, the performance of ideal and nonideal pre-equalization entail loss of 1db and 3db respectively when the normalized timing error is 1/8. When it is 1/4, both of the two systems' performances degrade severely. At the same time, the gap between them diminishes. In that case, timing error becomes dominant among those elements which would affect system performance.

The paper proposes a new method, minimum clipping power loss scheme (MCPLS), to control the clipping noise based on the relationship between the power of clipped portion and the clipping noise power of OFDM signals. First, the transmitter generates multi-route signals that carry the same information then estimates the clipping noise power of every route under the same clipping threshold. The transmitter then selects the signal with the lowest clipping noise power to clip and transmits the signal. The simulation results proved that this method can mitigate clipping noise and improve the performance of the system. The signal-to-noise ratio is gained 8 dB to achieve 10/sub -3/ symbol-error-rate when the number of subcarriers is 256, the modulation mode is 16-QAM, the clipping threshold is 1.5 and the redundancy of system is 0.59%. The floor of symbol-error-rate is reduced from 10/sub -3/ to 3/spl middot/10/sub -5/. The arithmetic achieves better effect if the threshold is lower.

In this paper, the bit error rate (BER) performance of orthogonal frequency division multiplexing (OFDM) system in multipath fading channels using the frequency domain differential demodulation (FDDD) and time domain differential demodulation (TDDD) is analyzed. The results indicate that in frequency-nonselective fading channel, the BER performance of FDDD is better than that of TDDD. In frequency-selective fading channel, if the time delay doesn't exceed the guard time, the BER performance of TDDD is not affected by the multipath and time delay, but it is affected by the Doppler frequency; the BER performance of FDDD is affected by the time delay and the Doppler frequency at the same time. With the increase of Doppler frequency, the BER performance of FDDD is better than that of TDDD demodulation.

In this paper, the current analysis focuses on the influence of demodulation performance in multipath fading propagation environments, which results from the pilot power variation of pilot symbol assisted modulation (PSAM) M-QAM in orthogonal frequency division multiplexing (OFDM) systems. The pilot-to-data power ratio (PDR) is optimized analytically, and the loss due to imperfect channel estimation is calculated. Theoretical and simulation results show that the optimum PDR is affected by the signal-to-noise ratio (SNR), Doppler frequency and interpolation size etc. When the optimization parameter of PDR is used, the power of the system transmission is minimum while still meeting a fixed bit error rate (BER) target.

In this paper, we derive closed-form expressions of the optimal interference cancellation weight (OICW) and evaluate bit error rate (BER) performance for multistage partial parallel interference cancellation (PPIC) over multipath fading channels in the case of perfect and imperfect channel estimation. The channel model assumes independent path with Rayleigh fading statistics. The effects of receiving BER of last stage, power ratio of pilot to date channels, multiple access and multi-path interference, additive white Gaussian noise (AWGN) and the factors affecting channel estimation error are analyzed. Then, the BER performance for multistage PPIC with complex spreading is evaluated by characteristic function method, indicating that all factors determining the optimal weight certainly affect the BER performance of PPIC. Performance of optimal weight PPIC (OW-PPIC), constant weight PPIC (CW-PPIC) and PPIC with perfect channel estimation (PCE-PPIC) is compared by analysis and simulation, indicating that OW-PPIC employing two stages achieves the performance near to PCE-PPIC with one stage.

This paper introduces an improved multistage parallel interference cancellation (PIC) whose weights are optimized by processing information from channel estimators. An expression determining the optimal interference cancellation weight (OICW) for partial parallel interference cancellation (PPIC) in multipath fading channels is derived and then a new weight-optimizing scheme for PPIC is proposed. Stage by stage, the proposed scheme can make the variance of residual interference less and less and is applicable to multi-rate CDMA systems. The simulation results in single-rate and multi-rate CDMA systems validate our reasonable assumption and show that the proposed scheme makes bit error rate (BER) at the following stage less than that at the previous stage. It is indicated that the proposed PPIC performs better than CW-PPIC with best interference cancellation weight (ICW), still more conventional PIC. Moreover, at a BER of 0.01. the performance loss of the proposed PPIC stage 2 is only 1.5dB, compared to PPIC with channel-known interference of one stage.

The performance of the system with partial transmit sequences is dominated by the side-information. On the premise of that the total transmitting power is limited, the authors investigate the effect of different power allocation schemes between the data and side-information. The arithmetic to obtain the optimal power allocation coefficient is proposed. Besides, the authors propose a new simple arithmetic to obtain the sub-optimal coefficient. The simulation results prove that when the number of carriers is large enough, reducing a little power on every data carrier will obtain large gain on the side-information. So the system is apt to averagely allocate the power to all carriers. Increasing signal noise ratio, the required additional power on the side-information decreases. The bit error rate with the optimal or sub-optimal coefficient is close to the ideal value.

Correct time and frequency synchronization is important for the performance of orthogonal frequency-division multiplexing (OFDM) system. While using the partial power training sequences to synchronize in orthogonal frequency-division multiplexing (OFDM) system, the received data signals will be interfered by the training sequences. In this paper, we give a method for suppressing the interference caused by the training sequence, and introduce an optimized formula for the partial interference canceling factor of partial power training sequence. The above technique is evaluated by means of pilot assistant coherent OFDM system under time-varying multipath Rayleigh fading channels, and the linear interpolation channel estimator is employed to exploit the frequency domain correlation. Especially we focus on only one OFDM symbol in a packet transmission, that is, both the OFDM data and the training sequences are included in one OFDM symbol, and there are no other symbols before or after it. Both theoretical and simulated results of the above technique are presented. It has been shown that the better BER performance can be achieved as compared with no separation, and only the one OFDM symbol can accomplish user data communication assignment.

We explore in this paper one novel deterministic simulation model for downlink multiple-input multiple-output (MIMO) fading channel in wireless communication. The von Mises function, which characterizes accurately the distribution of non-isotropic scattering around mobile station, is used to deterministic modeling process for both space-time codes (STC) scenario and downlink beam-forming (DBF) scenario. Statistical fading characteristics of the simulated MIMO channel, including level-crossing rate, average duration of fades and envelope cross-correlation, are studied. The impact of non-isotropic scattering on MIMO-link capacity is also investigated. The numerical results show that existence of non-isotropic scattering degraded ergodic capacity of MIMO channel by 1 bit/Hz/s in the case of STC scenario. And the maximum achievable capacity in the case of DBF scenario is always lower than that of STC scenario because transmit steering vector affected the transmit antenna correlation. The proposed MIMO channel simulation model has a universal structure and requires less parameter measurements. Hence, it can be used effectively for link-level simulation and capacity evaluation in MIMO wireless communication systems.

In this paper, we propose a novel method for orthogonal frequency-division multiplexing (OFDM) time and frequency synchronization by using PN sequence and barker code, time synchronization performance is improved by barker code, and we also propose a simple but effective method by setting the threshold during time synchronization. Improved frequency synchronization algorithm is presented in this paper too. The idea of multipath utilizing is the core of the frequency synchronization algorithm. The performance of the synchronization proposed here is better than that of conventional methods. Estimation precision is boosted from 10/sup -3/ to 10/sup -4/ for moderate SNR. The requirements of time and frequency synchronization for beyond 3G system based on OFDM can be well satisfied while using the proposed method.