For the sake of the performance improvement of soft-switching inverters, the paper designs an efficient resonant pole inverter. Main switches in the designed inverter can attain zero-voltage switching with the low peak voltage and current stress, which is conducive to the low loss of main switches. Moreover, the striking feature of the designed inverter different from existing resonant pole inverters is that two sets of independent symmetrical auxiliary circuits on each bridge arm are not jointly involved in the operation in a switching cycle, and that they are alternately involved in the operation based on the different direction of load current, not only providing the condition of zero-voltage switching for main switches but also improving the reliability of soft-switching of main switches in the case of open failure of any auxiliary device. The paper provides the detailed interpretation on each working status during a switching cycle. Experimental waveforms manifest that main switches can attain zero-voltage switching. The efficiency test at rated operation state also manifests that the efficiency of the designed inverter is up to 99.1% without any failure of auxiliary devices and 98.2% with open failure of an auxiliary switch on each bridge arm, confirming that the designed inverter has superiority over the comparison object in the field of efficiency even if open failure of an auxiliary switch on each bridge arm occurs in both of them. Hence, the alternate operation of symmetrical double auxiliary circuits based on different direction of load current in the designed inverter is especially beneficial to reliability improvement of soft-switching with open failure of any auxiliary device.

The paper conducts research on an efficient three-phase soft-switching inverter with simplified asymmetric single auxiliary circuit on each bridge arm to achieve miniaturization and light weight of soft-switching inverters. Main switches can realize zero-voltage switching, bringing about efficient operation of the studied inverter. Since auxiliary switches and resonant inductors are necessary for resonant pole zero-voltage switching inverters, only one auxiliary switch and one resonant inductor, along with two auxiliary diodes and three resonant capacitors, constitute simple auxiliary circuits of each phase. In the designed inverter, few auxiliary switches and auxiliary diodes are beneficial to the use of heat sinks with small volume, thereby achieving the miniaturization of the inverter; the weight of auxiliary circuits mainly depends on resonant inductors, so few resonant inductors can also make the inverter lightweight. The paper conducts a detailed analysis on each working status in one switching cycle and puts forward corresponding design requirements. The experimental waveforms verify the advantage that switches can realize soft-switching. The efficiency comparison in the same experimental conditions demonstrates that the efficiency of the studied inverter reaches 99.2% at rated output power, which is 0.5% and 0.7% higher than that of the two comparison objects with symmetric double auxiliary circuits on each bridge arm, respectively. Thus, the novel asymmetric single auxiliary circuit composed of fewer auxiliary devices on each bridge arm is beneficial for optimizing and popularizing resonant pole zero-voltage switching inverters.

To meet the urgent demand for high efficiency and high power density inductive power transfer (IPT) system in key applications such as electric vehicles, deep-sea intelligent equipment and consumer electronics, this article proposes a novel IPT system with full range soft-switching operation and magnetic integrated structure based on the dual-decoupling concept. With the help of the novel active auxiliary network, the switching tubes in the high-frequency inverter can achieve zero-voltage switching (ZVS)-ON and ZVS-OFF within the full power range. Meanwhile, the proposed magnetic integrated structure based on the dual-decoupling concept integrates the resonant inductor in the auxiliary circuit and compensation network into the transmitter coil, sharing a set of magnetic core. It can achieve the decoupling between the auxiliary resonant inductor and the compensation resonant inductor, as well as the decoupling between the two resonant inductors and the power transfer coils, with the effect of suppressing leakage flux and reducing the proximity effect of high-frequency currents. The proposed dual-decoupling concept can be extended to other high-order compensation IPT topologies with multiple resonant inductors. The above schemes can effectively reduce the system’s switching losses and the overall core losses of the system, improve the transfer efficiency of the system across the entire power range, and possess many advantages such as high power density, efficiency, and magnetic flux balance. Eventually, the advantages of the proposed scheme are validated through the construction of a 1kW experimental prototype.

To meet the charging requirements of constant current output (CCO) and constant voltage output (CVO), and maintain constant output when the couplers are misaligned in inductive power transfer (IPT) system, a hybrid three-coil IPT topology with high misalignment tolerance is presented. Two mode conversion switches, one inductor and two capacitors are added on the receiver side of the conventional series series (SS) topology to realize the switching SS and S/LCC topologies, so as to achieve the CCO and CVO. The system combines all the advantages of the two topologies, does not need to switch frequency, and has simple control. Moreover, it gets rid of the wireless communication between the receiver and the transmitter. The transmitter adopts two coils connected in reverse series to improve system’s misalignment tolerance. The operating principle of the topology is introduced in detail, and the main idea of parameter design is also given. Ultimately, a 100W experimental prototype is built to verify the effectiveness and superiority of the proposed hybrid IPT topology.

Non-orthogonal multiple access (NOMA) is a promising technology for handling massive connectivity in future 5G wireless networks. Even though the spectral efficiency can be promoted, the transmission reliability is sometimes poor, due to the introduced multiple access interference (MAI), and the computational complexity for multiuser detection is usually high in NOMA. To solve this problem, we investigate the NOMA regime with sparse multiple-access sequences, so as to leverage sparse signal processing methods, e.g., the message passing algorithm (MPA) for low-complexity and highly- reliable multiuser detection. Particularly, we formulate an optimization problem to design the sparsity of spreading sequences, while maximizing the efficiency of NOMA subject to the allowable symbol error rate (SER) constraint as well as the affordable detection complexity constraint. To evaluate the detection performance of MPA, we give the large-system limit analysis and derive the density evolution method. The impact of variable and function sparsity on the performance is then analyzed. Based on the uncovered characteristics of the optimization problem, an efficient algorithm is proposed to derive the optimal sparsity achieving the desired trade-off between efficiency, reliability and complexity.

This paper addresses the problem of dynamic resource control and scheduling algorithms in multi-hop wireless networks with power constrained nodes and time-varying channels. Subject to different per-flow end-to-end delay requirements, a new queue management policy is designed and then, a delay parameter is introduced by combining both delay constraints and path length to destination nodes. By taking advantage of the delay parameter and the queue management policy, this paper proposes a distributed congestion control, routing and scheduling back-pressure algorithm. The proposed algorithm not only achieves high throughput, but also adaptively selects favorable routes according to per-flow delay constraints. Simulation results show our algorithm effectively achieves well- performed delay performance while ensuring the throughput.

In this paper, the ergodic capacity (EC) of a land mobile satellite (LMS) system using dual-polarized antennas for transmit diversity is analysed. Three key channel parameters, i.e. cross-polarization discrimination (XPD), transmit and receive correlation coefficients and Ricean K-factor are included in channel modeling and their effects on the EC are investigated. In particular, we derive the estimated expression and approximation at high SNR of EC for Rayleigh fading and fairly tight upper bound for Ricean fading. Simulation results corroborate the theoretic analyses. About 1.5dB power gain is estimated to be obtained in high SNR regime by using dual-polarized antennas, compared with non-polarized antennas. It is found that the EC benefits from poorer XPD but degrades with higher transmit and receive correlation coefficients. Besides, the EC grows logarithmically with K-factor, which indicates that more fixed part of channel will enhance the communication performance.

Quality of service (QoS) guarantees play a significant role in next-generation wireless networks and the concept of effective capacity is proposed to characterize the maximum arrival rate that a time-varying fading channel can support under a delay-QoS constraint. However, the probability density function (PDF)-based analysis of effective capacity over generalized fading channels suffers from mathematical intractability in some situations of interest. In this paper, an approach based on the moment generating function (MGF) is introduced, which is suitable to deduce the closed-form expression for effective capacity computation. We start with the general case of adaptation transmission policy under the assumption of channel side information (CSI) only at the receiver, and then extend it to other adaptation policies. In addition, we derive unified and concise expressions of effective capacity by means of Fox's H function, which can be easily calculated, accommodating a wide variety of fading scenarios. Finally, the formulas of effective capacity are verified by numerical and simulation results.

In this paper, a 4-transmit-antenna space time block coding (STBC) scheme with 1-bit differential feedback is proposed. This scheme gives full transmit diversity and spatial coding rate over time-selective fading channels by rotating the signal constellations for certain angles determined by the differential feedback information. By utilizing differential feedback, our method can provide much better channel orthogonality and track the variation of the channel more accurately and timely under time-selective fading circumstances, comparing to recent works presenting other quantized feedback schemes. Simulation results show that the 1-bit differential feedback scheme achieves near-optimum performance and outperforms existing algorithms without adding more overhead or complexity.

In this paper, we investigate the relaying scheme for multi-antenna cooperative networks without channel state information at the transmitters. It is shown that the classic opportunistic relaying scheme, which allows only one relay node to forward the message, may lead to significant loss when it is extended to the corresponding multi-antenna relay scenarios. A generalized opportunistic relaying approach, which selects more transmit antennas distributed on multiple relay nodes to transmit data simultaneously, is proposed to maximize the network throughput via balancing the source-relay and the relay-destination channels. Numerical examples show the large impact of multiple antennas and relays on the network throughput, and the significant gains obtained through the proposed opportunistic cooperation scheme.

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 individual QoS requirement. We investigate joint power allocation, relay selection and subcarrier assignment to maximize overall system rates with considerations 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 significant outperforms previous works in terms of both services support and QoS satisfaction.

In this paper, we focus on the capacity sensitivity of the cooperative MIMO relay network over spatially correlated channels. We study and compare the capacity loss of MMSE, MF, SVD, AF and ZF relaying schemes over Rayleigh flat fading channels where antennas of the source or destination terminal are correlated. Simulation results show that the MF relaying scheme is most sensitive for all existing relaying schemes. In order to improve the performance of capacity sensitivity for the MF relaying scheme, this paper proposes a modified MF relaying scheme, which is analogous to the MF relaying scheme but has much less capacity sensitivity.

Adaptive network coded cooperation (ANCC) scheme has been shown to have better performance than the conventional repetition-based schemes and the space-time coded cooperation (STCC) frameworks for data transmissions from a large collection of terminals to a common destination in large wireless networks. However, the random selection strategy for ANCC protocol may generate many short cycles in the distributed low-density generator-matrix(LDGM) codes, which may cause error-floor and performance degradation. In this paper, an optimized relay selection strategy for ANCC is proposed. By exploiting information interaction between destination and terminals before data communication, and matching the instantaneous network topology, the proposed method generates ensembles of distributed LDGM codes free of short cycles. Simulation results demonstrate that the proposed relay selection protocol significantly outperforms the random relay selection strategy for various network sizes and different fixed numbers of selected terminals.

This paper considers an OFDMA relay network and proposes an auction algorithm for the subchannel allocation to balancing efficiency and fairness with service differentiation. This algorithm allows users to fairly compete for the using of the subchannel through a new bidding strategy. We use the second-price sealed auction mechanism under which the dominant strategy of the bidder is bidding the true valuation of the subchannel. The users' valuations to the subchannel are estimated by considering their minimum rate requirements, current channel conditions and the long term average data rates. The active index which can be chosen from the set provided by the system is introduced to differentiate the user's willingness to pay for different services. For each subchannel, the user bids highest will be allocated the subchannel. The auction procedure can naturally realize a competitive fairness from the perspective of the users. Simulation results show that the proposed algorithm can achieve different degrees of tradeoff between the system efficiency and fairness by using different active index set, satisfy the users' minimum rate requirements and also provide differentiated services for different users.

This paper considers a joint subcarrier and power allocation in an orthogonal frequency division multiple access (OFDMA) cellular system with base station (BS) cooperation. The problem is formulated as an average utility maximization subject to the per-antenna power constraint. Existing algorithms to solve similar problem in a single-sell system are shown not so efficient in the cooperative multi-cell system. Therefore, we specially design a method which contains a greedy search algorithm for subcarrier allocation and a Lagrange dual based algorithm for power allocation. Simulation results reveal that the proposed method achieves near-optimal performance and outperforms the counterpart derived originally for a single-cell system by 52% on average, yielding good tradeoff between system efficiency and fairness with proper utility functions.

A low-complexity, near-optimal transmit antenna selection algorithm is proposed for multi-relay networks where all nodes are equipped with multiple antennas. We first establish a system model and a unified capacity maximization framework for a two-hop opportunistic relaying scheme where the source node (S) transmits signals to multiple relay nodes (R) in the first time slot, and the selected relay antennas and their corresponding relay nodes receive, decode and forward the messages to the destination (D) in the second time slot. Based on the system model, we develop a transmit antenna selection algorithm that maximizes the network capacity assuming that the channel state information is available at the receivers but not available at the transmitters, and total transmit power constraints are imposed on source/relay transmitters. The proposed algorithm first constructs a sorted list of relay antennas with decreasing S-R capacities, then iteratively maximizes the R-D capacity over a candidate antenna set using a low-complexity, near-optimal antenna selection scheme. The candidate set is reduced in the next iteration according to the selected antenna set of the current iteration. The overall network capacity is computed for the selected antenna sets of all iterations, and the set yielding the highest S-R-D capacity is the solution to the maximization problem. We show that this novel iterative algorithm achieves near-optimal solution and has a polynomial-time complexity. We also derive the lower and upper bounds of the achievable network capacity for both average capacity and outage capacity. Numerical examples show the significant performance gains obtained via the proposed scheme compared to its conventional counterparts.

Two major techniques are used to embed pilots into data, time-division multiplexed (TDM) and superimposed (SIP). In this paper, we compare these two techniques in an informative consideration under time varying fading channels. Besides the ordinary SIP without dealing with the interference, we also study two different kinds of performance improved iterative SIP: interference subtraction (IS) and interference exploitation (IE). Using Wiener filtering and accounting estimation error, the capacity lower bounds and BER expressions are derived. Numerical results show that great potential benefits are brought by SIP if the interference is utilized properly. With this potential exploited, SIP shows great superior to PSAM, especially in high speed environments.

In time varying relay networks, imperfect channel estimation deteriorates the performance and must be accounted for system design. By doing this, this paper derives the achievable rate expressions first, and then studies the training optimization problem based on those rates for both Amplify-and-Forward (AF) and Decode-and-Forward (DF) relay networks. There are two kinds of training designs for relay networks. One is remaining the design just optimal for source-destination (SD) channel as if there is no relay node (we name it SD design). Another is optimizing over the whole relay network. The former way is simple but is shown to have a great degradation, while the latter one is optimal but too complex to get closed-form optimal solutions. In this paper, we simplify the latter way and propose new sub-optimal training designs in closed-forms. Simulations show that our proposed designs for both AF and DF can achieve considerable gains compared with SD design and have negligible performance degradation compared to the optimal design.

This paper considers joint schedule and resource allocation in downlink cooperative OFDMA systems with multiple sources, multiple relays and a single destination. Each user has individual QoS requirements and the relays operate in amplify-and-forward and half-duplex mode. We try to find optimal power allocation, relay selection and subcarrier assignment to maximize overall system rates. The problem is formulated as a Mixed Binary Integer Programming (MBIP). Although the original problem is comprehensive in nature, a novel two-level dual-primal decomposition based algorithm is proposed to tackle the problem. Optimal solutions are given in closed-form and the algorithm has a polynomial complexity in general. The efficiency of the algorithm is finally illustrated by numerical results.

Low-complexity tree search based exact maximum-likelihood (ML) detectors have gained attention for optimum signal detection in multiple-input multiple output (MIMO) wireless systems. In this paper, taking a fresher look at the closet lattice point search problem, we propose a new fast exact ML sphere decoder with ever-increasing radius (IR-SD). It is shown that IR-SD visits minimum number of tree nodes and is more computationally efficient than existing sphere decoders. IR-SD is also faster and requires less storage than ML stack detector. An upper-bound of expected computation and storage complexity of IR-SD independent of tree radius is derived. Numerical results validate that IR-SD greatly speeds up the ML detection than other sphere detectors while requiring less storage than ML stack algorithm. A factor-of-2.5 speed-up is observed over the depth-first Schnorr-Euchner sphere decoders when utilizing IR-SD in 16-QAM 10/spl times/10 complex MIMO system.

Spatial fading correlation severely impairs the performance of an antenna array system that relies on space diversity capability. In this paper, we first reviewed the general closed-form expression for the fading correlation function which could be applied to various array geometries and energy distributions of angle-of-arrival (AOA) in a mobile radio environment. Then, we applied them in studying the fading correlation under the case of multi-cluster arriving, and analyzed the correlation matrix for different antenna array structure.

The stable adaptive routing protocol (SAR) is a novel on-demand stable adaptive routing protocol for ad hoc network proposed last year, which considers joint route hop counts, node stability and route traffic load balance as the route selection criteria in routes searching and maintain. This paper describes the performance evaluation of SAR protocol by a practical ad hoc network test-bed under typical indoor and outdoor environments. And compared to AODV routing protocol, SAR has better performance on system cost, successfully delivery ratio and average delay jitter, as shown in the measurement results.

In this paper, we propose a new MAC protocol for ad-hoc networks that uses multiple channels and a dynamic channel selection scheme. The proposed protocol, DCC-MAC (dual control channel based MAC), deploys two control channels (CH/sub R/C/ and CH/sub ACK/ and N data channels, where N is independent of the number of nodes in the network. Through RTS/CTS dialogues on CH/sub R/C/ senders and receivers negotiate the most robust channel for data transmission with maximum-CIR selection criterion. ACK transmission on CH/sub ACK/ contributes to the unidirectional transmission on data channels and therefore the decrease of the co-channel reuse distance. Performance evaluation has been carried out and the simulation results demonstrate the effectiveness of the proposed protocol.

Routing algorithm has been the challenge in the wireless ad-hoc network for a long time because of the quick mutability of the network topology introduced by the mobility of nodes. AODV is appealing for ad hoc networks as an efficient on-demand routing protocol because of the low routing overhead and high performance. As an optimization for the current AODV, a novel stable adaptive enhancement for AODV routing protocol was proposed in this paper, which considers joint route hop count, node stability and route traffic load balance as the route selection criteria. Comparing with AODV protocol, the new algorithm has better performance as shown with the simulations results.

The paper presents the average bit error rate (BER) of a maximal ratio combining (MRC) two-dimensional (2D)-RAKE receiver in correlated frequency selective Nakagami fading environments in the presence of multiple co-channel interferences. A closed-form expression of the simple approximated probability density function for the signal-to-interference-plus-noise ratio (SINR) is derived for the receiver with multiple correlated antennas and multiple RAKE branches in arbitrary fading environments. The effects of spatial and temporal diversity order, angular spread, antenna spacing, average multi-path strength and fading severity on the performance of the MRC 2D-RAKE receivers are all illustrated.

The closed-form expressions of signal-to-interference-plus-noise ratio (SINR) and the outage probability are derived for a maximal ratio combining (MRC) two-dimensional (2D)-RAKE receiver with imperfect power control in a frequency-selective Nakagami fading channel. The impact of power control error (PCE) on the performance of the receiver is analyzed for various fading environments. Numerical results show that the performance of 2D-RAKE receivers degrades due to imperfect power control. But when PCE is not serious, increasing the number of antennae and temporal diversity order can compensate for the performance loss. The exact performance improvement due to space-time processing varies with PCE and the fading environment.

In this paper, output SINR performance of a smart antenna and two kinds of 2D-RAKE technology - combined and joint spatial-temporal 2D-RAKE - is compared in the same single cell DS-CDMA system. Average output SINR expressions are derived, with the parameters analyzed and performance compared.

The smart antenna and spatial diversity-combining receiver are two of the most important spatial signal processing technologies. This paper studies the radio propagation characteristics of the transmission path, spatio-temporal channel model and channel characteristics in different environments. On the basis of those analyses, the authors analyzed the operating principle of the smart antenna and spatial diversity-combining technology, and especially showed the differences between these two technologies in several aspects.

Previously developed techniques for modulation classification have assumed that both the signal and noise power are known. However, the signal or noise power estimations require that modulation type is known. To solve the problem, this paper introduces a method for joint power estimation and modulation classification (JPEMC), whose key point is employing the relationships between the second- and higher moments of received signal and signal and noise power. Simulation results demonstrate the efficiency of modulation classification of JPEMC and indicate that the power estimation can be used by later demodulators.