As Uncrewed Aerial Vehicle (UAV) technology matures and spreads, non-cooperative UAV intrusions have significantly increased airspace safety risks. To achieve all-weather airspace awareness and multi-level threat response, integrating UAV detection and warning into existing cellular base stations is a promising solution. Currently, most UAV detection techniques involve extracting Micro-Doppler features during UAV movement. However, extracting salient Micro-Doppler motion features is challenging and requires complex mathematical algorithms. We present a novel detection network called the Shallow Brain Residual Network (SBRN) to address this critical need for timely detection and early warning systems. The SBRN is inspired by the Shallow Brain architecture, which emulates the parallel processing hierarchy of the human visual system and fundamentally differs from classical deep learning frameworks. To the best of our knowledge, the proposed SBRN model is the first architecture that systematically implements a complete shallow-brain biological architecture. Our framework achieves detection accuracy of 99.45% while eliminating complex data preprocessing requirements. The model demonstrates robust multi-class discrimination capabilities, distinguishing between six distinct UAV types and multiple avian species. Unlike conventional deep learning models, the SBRN with only 17 million parameters, enabling efficient deployment. The network exhibits fast convergence speed, achieving > 96% accuracy within the first training epoch.

We consider the distributed channel allocation problem in an asymmetrical opportunistic spectrum access (OSA) system where each secondary user possibly has different channel reward even in the same channel due to geographic dispersion. We formulate this problem as a Gale-Shapley stable theorem using game theory to optimize the sum reward of all secondary users. It is challenging to achieve the stable matching of user-channel pairs without centralized control and prior knowledge of channel availability statistics. In this paper, we present a novel decentralized order-optimal learning Gale-Shapley scheme (OLGS) in which secondary users learn from their local history data and individually adjust their behaviors in a time-varying OSA system. The proposed scheme eliminates collisions among secondary users by a one-to-one user-channel matching policy. It also achieves stable spectral allocations using learning method without assuming known channel parameters and independent of information exchange among secondary users. Simulation results show that the system regret of the OLGS solution grows with time at the logarithmic order with low complexity.

In this paper, we propose a distributed precoder design algorithm for suppressing the inter-cell interference(ICI) and maximizing the average throughput of a multi-cell multi-user multi-input multi-output(MU-MIMO) system. Motivated by the recent results of the distributed signal-to-leakage-plus-noise ratio(SLNR) model for ICI coordination(ICIC), we design a joint optimization algorithm to achieve the pareto-optimal average system throughput. Existed SLNR-based algorithms only consider downlink optimization problem of one optimized factor, which will bring a restriction to the further improvement of the system performance. In our proposed algorithm, the SLNR-based downlink precoder and the transmitting power factor will be designed from a joint optimization problem, and the closed-form pareto-optimal solutions of both optimized factors can be obtained through matrix analysis and decomposition techniques. Simulation results show that the proposed distributed joint precoder design algorithm can significantly increase the average cell throughput and improve the resource efficiency while effectively reducing the system overhead.

This paper addresses the impact of dynamic spatiotemporal variance of heterogeneous spectrum on the performance of the Cognitive Radio Ad Hoc Networks (CRAHNs). A dynamic heterogeneous spectrums Multiple Channels Reuse Areas (MCRA) model is set up for a Cognitive Radio (CR) node to characterize the interference from the other nodes, the variation of the traffic of Primary Users (PUs) and Secondary Users (SUs), as well as the variance of heterogeneous spectrum of Primary Channels (PCs) and Secondary Channels (SCs). The performance metrics of blocking probability, dropping probability, throughput and availability are evaluated for a CR node linked with another node located in various positions in the MCRA with the aid of a novel structured 3-D Markov-chain model with continuous time parameters, which also makes our model extendable and programmable for an arbitrary number of PCs and SCs. In addition, we obtain the performance metric of the throughput of a potential routing in CRAHNs. Extensive numerical results verify the validity of the proposed model and analysis method.

ABSTRACT In this paper, we consider the narrowband interference problem for orthogonal frequency division multiplexing (OFDM)‐based cognitive radio (CR) systems, in which parts of the OFDM subcarriers and parts of the data frame can be seriously interfered, resulting in significant performance degradation. We propose a scheme of iterative noise plus interference estimation and decoding (IED) to mitigate the performance degradation caused by the narrowband interference, which is based on expectation maximization (EM) algorithm. To reduce the number of OFDM symbols for time domain averaging required in the proposed scheme, and adapt the proposed scheme to rapid changing narrowband interference conditions, we also propose an IED scheme with frequency domain partial averaging (IED‐FPA). Moreover, we derive the Cramér‐Rao lower bounds for unbiased noise plus interference variance estimations, and they can be achieved via the proposed IED schemes. Simulation results show that the proposed IED‐FPA scheme can effectively achieve the same performance as that of the optimal maximum likelihood decoder with full knowledge of the power plus interference variances, and the proposed IED‐FPA scheme is very robust with respect to the number of the interfered subcarriers and positive errors of the knowledge of the interfered subcarriers' number. Copyright © 2010 John Wiley & Sons, Ltd.

We employ a multiuser detection (MUD) method using a novel genetic algorithm (GA) based on complementary error function mutation (CEFM) and a differential algorithm (DA) for ultra-wideband (UWB) systems. The proposed MUD method is termed CEFM-GA DA for short. We describe the scheme of CEFM-GA DA, analyze its algorithm, and compare its computational complexity with other MUDs. Simulation results show that a significant performance gain can be achieved by employing the proposed CEFM-GA DA, compared with successive interference cancellation (SIC), parallel interference cancellation (PIC), conventional GA, and CEFM-GA without DA, for UWB systems in lognormal fading channel. Moreover, CEFM-GA DA not only reduces computational complexity relative to conventional GA and CEFM-GA without DA, but also improves bit error rate (BER) performance.

Abstract In this paper, we first propose a simplified tone reservation (STR) method with low computational complexity which is based on the Fourier series expansion. Then, we analyze how to combine the STR method with the cross antenna rotation and inversion method to reduce the peak‐to‐average power ratio (PAPR) for multi‐input multi‐output orthogonal frequency division multiplexing (MIMO‐OFDM) system. To validate the analytical results, extensive simulations are conducted and the numerical results show the efficiency of the proposed schemes including the PAPR reduction and low computational complexity for MIMO‐OFDM system. Copyright © 2010 John Wiley & Sons, Ltd.

This paper considers the multi-user MIMO collaborative spatial multiplexing uplink scheduling scheme in multi-cell time-division duplexing system. An transmitter centric (TC) beamforming and scheduling scheme has been proposed to reduce the inter-cell interference opportunistically. Most previous works in the area of mimo beamforming and scheduling are aiming at improve the signal to interference plus noise power ratio at receiver directly. These receiver centric (RC) schemes requires interference covariance at receiver. However, in multi-user system, the uplink interference at base station (BS) is fluctuant and can't be acquired for scheduling due to the dynamics of the scheduled user set in other cells. It makes the uplink scheduling problem challenging. Our proposed TC scheme considers the pollution which is defined as the sum power of user signal arriving at other BSs. User selects the transmit beamforming vector with highest signal to pollution plus noise ratio (SPR) and informs its home BS. To enhance the signal and suppress the pollution, a scheduling criterion is derived based on SPR metric with awareness of intra-cell interference. The proposed scheduling scheme is compared with conventional RC and single-user TC spatial multiplexing in the scenarios with various antenna configurations, BS and user numbers. The simulation result shows that our proposed TC scheme can better reduce the pollution and significantly improve the system capacity.

In this paper, we consider the problem of the capacity limits of the cellular network, which is modeled as a network consisting of two mutually interfering multiple access channel with multiple antennas at each receiver (e.g. the Base Station). By developing a tight outerbound (in the sense of DoF) and an achievable scheme which exploits the idea of interference alignment, we are able to exactly characterize the degrees of freedom (DoF) of the network when the channel coefficients are time- or frequency-varying, which is, the DoF per cell is $\frac{{KM}}{{K + \min (M,K)}}$ (where $M$ and $K$ denotes the number of receiver antennas and number of users in a cell, respectively). From the DoF result, it can be observed that when the number of users is large, we can nearly achieve the interference-free DoF of a multi-antenna cell!

In this paper, we propose an iterative data detection scheme to combat unknown narrowband interference for orthogonal frequency division multiplexing (OFDM) systems. The key idea of the proposed scheme is to joint channel estimation, noise plus interference power estimation and decoding together to enhance both the estimation accuracy and bit error ration (BER) performance. We derive the Cramér-Rao Bounds (CRB) for mean square errors of channel estimation and noise plus interference estimations, and the CRBs can be achieved via the proposed scheme with very few iteration numbers, hence, the complexity of the proposed scheme is very low. Moreover, simulation results show that the decoding performance of the proposed scheme substantially approaches to that of the maximum likelihood decoder with perfect channel estimation and full knowledge of interference distribution.

We propose an efficient low bit error rate (BER) and low complexity multiple-input multiple-output (MIMO) multiuser detection (MUD) method for use with multiuser MIMO orthogonal frequency division multiplexing (OFDM) systems. It is a hybrid method combining a multiuser-interference-cancellation-based decision feedback equalizer using error feedback filter (MIMO MIC DFE-EFF) and a differential algorithm. The proposed method, termed ‘MIMO MIC DFE-EFF with a differential algorithm’ for short, has a multiuser feedback structure. We describe the schemes of MIMO MIC DFE-EFF and MIMO MIC DFE-EFF with a differential algorithm, and compare their minimum mean square error (MMSE) performance and computational complexity. Simulation results show that a significant performance gain can be achieved by employing the MIMO MIC DFE-EFF detection algorithm in the context of a multiuser MIMO-OFDM system over frequency selective Rayleigh channel. MIMO MIC DFE-EFF with the differential algorithm improves both computational efficiency and BER performance in a multistage structure relative to conventional DFE-EFF, though there is a small reduction in system performance compared with MIMO MIC DFE-EFF without the differential algorithm.

We investigate the bandwidth allocation and power control schemes in orthogonal frequency division multiplexing (OFDM) based multi-hop cognitive radio networks, and the color-sensitive graph coloring (CSGC) model is viewed as an efficient solution to the spectrum assignment problem. We extend the model by taking into account the power control strategy to avoid interference among secondary users and adapt dynamic topology. We formulate the optimization problem encompassing the channel allocation, power control with the interference constrained below a tolerable limit. The optimization objective with two different optimization strategies focuses on the routes rather than the links as in traditional approaches. A heuristic solution to this nondeterministic polynomial (NP)-hard problem is presented, which performs iterative channel allocation according to the lowest transmission power that guarantees the link connection and makes channel reuse as much as possible, and then the transmission power of each link is maximized to improve the channel capacity by gradually adding power level from the lowest transmission power until all co-channel links cannot satisfy the interference constraints. Numerical results show that our proposed strategies outperform the existing spectrum assignment algorithms in the performance of both the total network bandwidth and minimum route bandwidth of all routes, meanwhile, saving the transmission power.

A theoretical analysis is presented to show that in orthogonal frequency division multiplexing systems, the peak-to-average power ratio (PAPR) can be reduced by performing a unitary matrix transformation on the input vector of N symbols. The authors also prove that this transformation does not degrade the bit error rate (BER) or power spectral density (PSD) performance. Based on this, the inverse discrete Fourier transform matrix is proposed as the unitary matrix to reduce the PAPR. The simulation results show that the proposed scheme can obtain significant PAPR reduction while maintaining good performance in the BER and the PSD. To further evaluate the performance of the proposed scheme, the authors compare it with some well known PAPR reduction techniques by simulations. It is demonstrated that the proposed scheme can offer better system performance and achieve a better compromise with regard to the PAPR reduction, BER, spectral efficiency and computational complexity.

Bianchi's 2-Dimesional Markov model has laid the foundation for analysis of 802.11 CSMA/CA mechanism. However, the assumption that every station is saturated significantly degrades the accuracy of it since it is quite possible that the network exists in heterogeneous saturation status where some types of traffics are extremely saturated while other types of traffics are far from saturation. Although there are several analytical models under non-saturated assumption by introducing a constant probability that the station has packets awaiting transmission, they share two common weaknesses: the possibility of multiple packets arriving and the constant probability that a station has packet to send. Thus we establish a 3-Dimensional Markov model that introduces an additional Dimensional, the queue length, to solve them. We validated our analytical results of performance metrics of 802.11 under homogeneous and heterogeneous traffics by extensive simulations.

Abstract Long propagation delay is one of the most important characteristics in underwater wireless sensor networks (UWSNs) and poses a great challenge for medium access control (MAC) protocol design, especially for contention‐based MAC protocols due to intolerable delay caused by unpredictable retransmissions in UWSNs. Recently, some MAC protocols for UWSNs have been suggested in the literature, and most of them are based on random access with their capabilities to compensate propagation delay. However, two issues should still be resolved in these protocols: (a) they need to make measurements to realize duty cycle synchronization and (b) packet collisions exist, which not only reduce the throughput (thus increasing delays) but also waste energy. In this paper, we propose a novel MAC protocol explicitly designed for UWSNs, which makes the best use of the propagation delay to resolve collision problem and reduce overhead of control‐packet to save energy. The proposed MAC protocol can assure that the number of retransmissions is not more than one. To validate the analytical results, simulations have been conducted to show that the proposed MAC protocol can offer a low energy consumption while avoiding collisions in UWSNs. Copyright © 2008 John Wiley & Sons, Ltd.

Voice over Internet Protocol (VoIP) over wireless local area network (WLAN) is becoming a widely used technique. However, several technical problems exist in this application: First, voice delay is unacceptable in the presence of coexisting with other applications. Second, the inherent characteristic of WLAN causes low voice capacity. To address the problems, in this paper we propose and analyze two schemes, slotted TXOP and time-slot reuse scheme, that can significantly advance the voice capacity in WLAN. In the proposed scheme, with interaction with application layer, the delay of voice packets can reach its minimum value. In addition, with the help of time-slot reuse, the network capacity is significantly advanced. We also show the performance analysis and simulation of our proposed schemes in various PHY rates and over various voice codecs. The simulation results show that the proposed schemes greatly enhance the system capacity for VoIP compared with HCCA of 802. lie.

E-limited (or K-limited) scheduling is attractive because its performance is close to that of the exhaustive scheduling which is proven to be the optimal polling scheme for symmetric systems (same traffic offered to all queues) by some researches. If the parameter K is chosen properly, E- limited scheduling can avoid the unfairness, which is an inherent problem for the exhaustive service on a short time scale. In this paper, M-gated scheduling which is superior to E- limited is proposed to be used in wireless networks. With the method of the imbedded Markov points and the probability generating function, we develop a model for this novel scheduling algorithm with vacations, where the vacations represent the time periods in which the resource sharing mechanism used is a non-polling mode. The theoretical analyses are consistent with the simulation results. We also use the derived quality of service parameter as the basis for cross- layer design and then analyze its performance.

In cluster-based storage systems, the metadata server cluster must be able to adaptively distribute responsibility for metadata to maintain high system performance and long-term load balance, due to workload skew and metadata servers' heterogeneity. In this paper, we describe a simple and adaptive metadata load management scheme, called self-balancing uniform (SBU) randomization, to efficiently and continually adapt the metadata distribution to current demands in heterogeneous metadata server cluster. We implement our system within a discrete event driven simulation environment, along with two other systems, simple randomization (SR) and performance aware distribution (PAD) to serve as points of comparison, and evaluate the performance of our SBU algorithms against SR and PAD algorithms by both a trace workload and a synthetic workload. Simulation results verify that our SBU algorithm achieves load self-balance, provides consistent response latencies and resource utilization. Simulation results also indicate that SR cannot cope with skew and heterogeneity and PAD requires a larger shared state to achieve optimal performance.

Most video coding standards broadly used in the world such as MPEG series and H.26x are established based on rate-distortion theory. The spatial, temporal and statistic redundancies are reduced by using transform, prediction and entropy coding technologies. However, another important factor, which is named as perceptual redundancy, is ignored or not much developed in recent video coding technologies. In this paper, the authors research the human visual model and propose a perceptual coding method aiming at reducing the energy of luma residual coefficients in pixel domain. Our experiment results prove that this perceptual coding method can reduce the output bitrate of H.264 by 10%-34% without losing the subjective quality of video stream.

IEEE 802.11 distributed coordination function (DCF) is the most popular medium access control (MAC) protocol in distributed wireless networks, in which the wireless medium is shared. But the throughput of the network is restrained because of collisions and the idle time slots wasted for competition. In this paper, we present a new medium access protocol with a busy tone (MABT)1. In this protocol, the backoff procedure is executed in the busy tone instead of the data channel, so there is almost no wasted time slot in the data channel. Besides, this paper also introduces a modified backoff algorithm different with that of IEEE 802.11 DCF. By this backoff algorithm, the probability of packet collision can be significantly reduced. A remarkable characteristic of this protocol is that it does not require extra transceiver for the busy tone, which doesn't increase the hardware cost of the mobile station. We study the performance of MABT protocol through simulated experiments. The results show that MABT protocol is more efficient than the one discussed in the IEEE 802.11e task group.

In the wireless networks, the power saving is highly important. The way of power saving by resource allocation and scheduling is attached more attention on recently. This paper explores optimal and suboptimal scheduling strategy for a multi- carrier system over fading channels. The scheduling objective is to minimize the average system power under the delay constraint. Specifically, we study the trade-offs between the total transmit power of an orthogonal frequency division multiplexing (OFDM) system and the buffering delay of the packets in a transmission buffer. We formulate this optimization problem as a MDP and use dynamic programming techniques to obtain the optimal solution. Since finding the optimal policies becomes complex and practically un-realizable for large number of carriers in the system, we offer a suboptimal power allocation and bit loading algorithm using the results of the single carrier system and a greedy approach. Simulations show that the sub-optimal algorithm, which has reduced complexity, has performance close to the optimal one.

IEEE 802.11e standard has defined EDCA to guarantee prioritized QoS by service differentiation. However, it induces significant performance deterioration in both delay performance and collision probability at heavy load due to inherent drawbacks of binary exponential backoff (BEB) scheme. In this paper we proposed a novel backoff scheme, channel collision based adaptive backoff (CCBAB)1 scheme which compels each station to react to channel collisions irrespective of whether or not it is involved in, to combat the deterioration problem. CCBAB selectively forces some uncollided traffics to reduce their transmission probability and grants collided real time traffics larger transmission probability to ensure them be successfully transmitted in a shorter time. Simulations demonstrate that CCBAB scheme achieves more stable channel collision probabilities, smaller delay and jitter for real time traffics than EDCA and its enhanced variation AEDCF schemes and proves to be more resistant towards collisions and delay deterioration at high congestion level.

In the 802.11e protocol, voices traffic takes a higher priority than other services. However, there are still some technical problems existing in VoIP services over WLAN: (a) low voice capacity caused by the inherent characteristic of WLAN and heavy packet headers from upper layers and (b) unacceptable voice delay in the presence of coexisting with other applications. To address these problems, in this paper we propose several schemes to better manage the limited network capacity of VoIP network. In the proposed schemes, every voice stream occupies a fixed bandwidth to avoid collision between packets. With the Packet Header Compression technology, the overhead of voice packets is greatly reduced. Under various PHY rates, we investigate the performance of our proposed scheme over various voice codecs. Compared to HCCA, the proposed scheme greatly advances the maximum throughput of voice streams.

IEEE 802.11 standard is the most popular medium access control (MAC) protocol in distributed wireless networks. But the throughput of the network is restrained because of collisions and the idle slots wasted for competition. In this paper, we present a new Distributed Medium Access protocol with a busy tone (DMABT). In this protocol, a new backoff procedure is executed in the busy tone instead of the data channel and collision is reduced, so the throughput of the network is improved. A remarkable characteristic of this protocol is that it does not require extra transceiver for the busy tone, which does not increase the hardware cost of the mobile station. We study the performance of DMABT protocol through simulated experiments. The results show that DMABT protocol is more efficient than the one discussed in the IEEE 802.11e task group.

In non-infrastructure WLANs low network capacity and lack of QoS guarantee are the bottlenecks of commonly used contention access protocols. In this paper, we proposed a novel MAC protocol, the Delegate Polling Hybrid Access (DPHA)1protocol, which uses a distributed polling-based access scheme, delegate polling access scheme, to avoid collisions and adopt contention access scheme as a complement when wrong polling decisions occur. We designed a feasible delegate polling access scheme in non-infrastructure networks, which lets the current transmitting Traffic Stream (TS) delegate the AP to select the next transmitting TS based on a polling algorithm and announce it in the data packet header. The elaborately designed polling algorithm employs conditional service differentiation to improve fairness for best effort traffics and overcomes the drawbacks of existing polling algorithms. Simulation results demonstrate that DPHA protocol can significantly improve network capacity and QoS performance for all kinds of traffics.

In traditional ad hoc networks, the hidden-terminal and the exposed-terminal problems can reduce the network capacity severely on the MAC layer. To address the problem, many MAC schemes have been proposed such as RTS/CTS dialogue and DBTMA protocol. Among these protocols, the DBTMA protocol has solved the hidden- and the exposed- terminal problems perfectly. However, the DBTMA protocol occupies two separate busy tone channels to address the hidden- and the exposed-terminal problems, and therefore causes a waste of channel. In this paper, we propose a new MAC protocol, termed the combined dual busy tone multiple access (CDBTMA). In our proposed CDBTMA protocol, the DBTMA protocol is modified, using only one busy tone channel to implement all functions which the DBTMA protocol has, without significant loss on performance.

With the development of numerous imaging sensors, many images can be simultaneously pictured by various sensors. However, there are many scenarios where no one sensor can give the complete picture. Image fusion is an important approach to solve this problem and produces a single image which preserves all relevant information from a set of different sensors. In this paper, we proposed a new image fusion method using the support value transform, which uses the support value to represent the salient features of image. This is based on the fact that, in support vector machines (SVMs), the data with larger support values have a physical meaning in the sense that they reveal relative more importance of the data points for contributing to the SVM model. The mapped least squares SVM (mapped LS-SVM) is used to efficiently compute the support values of image. The support value analysis is developed by using a series of multiscale support value filters, which are obtained by filling zeros in the basic support value filter deduced from the mapped LS-SVM to match the resolution of the desired level. Compared with the widely used image fusion methods, such as the Laplacian pyramid, discrete wavelet transform methods, the proposed method is an undecimated transform-based approach. The fusion experiments are undertaken on multisource images. The results demonstrate that the proposed approach is effective and is superior to the conventional image fusion methods in terms of the pertained quantitative fusion evaluation indexes, such as quality of visual information (Q(AB/F)), the mutual information, etc.

In this paper, we provide the design criteria of the nonlinear companding transforms for reduction in peak-to-average power ratio (PAPR) of multi-carrier modulation (MCM) signals, which can enable the original MCM signals to be transformed into the desirable distribution. As examples, some novel nonlinear companding transforms have been proposed to transform the amplitude or power of the original MCM signals into uniform distribution, which can effectively reduce the PAPR for different modulation formats and subcarrier sizes without any complexity increase and bandwidth expansion. It has been shown by computer simulations that the proposed schemes can significantly improve the performance of MCM systems including bit-error-rate and PAPR reduction.

H.264 defines 7 different coding modes for macroblocks (MBs) in P slices. In order to achieve a coding performance as high as possible, the H.264 encoder calculates rate distortion costs of all possible modes to determine the best mode of a MB. The computation complexity is so large that make it difficult to be used in practical applications especially in real time environment. In this paper, a fast adaptive inter modes decision method is proposed to reduce the complexity of H.264 encoder. The candidate inter modes used in rate distortion optimization can be limited in a small mode group (MG) by using the characteristics of the motion compensated residual image. The overlapped mode groups and dynamic adjusted thresholds adopted in the proposed method can make the best mode lies within the chosen MG with great possibility which leads to extensively computation reduction without any perceivable loss in quality. The experimental results show that the proposed method can save the encoding time up to 52% on average with -0.05dB performance degradation that is negligible. Keywords-H.264; inter modes; mode group; adaptive; overlapped

Efficient load balancing algorithm is indispensable to serve more mobile stations in the heterogeneous wireless networks. In this paper, we propose a load balancing algorithm based on the velocity and position of mobile station for heterogeneous multitier wireless networks consisting of macrocell system and microcell system. This algorithm is able to balance load by transferring some mobile stations with longer sojourn time from overloaded cells to overlapping heterogeneous under-loaded cells. In addition, velocity, direction of motion and local position can be used to decrease unnecessary handoffs, and high-speed mobile stations can also connect to microcell system. Simulation results of three models show that blocking probability, dropping probability and overall system utilization using the proposed load balancing algorithm are improved significantly.

In this paper, we propose a novel nonlinear transform scheme to reduce the Peak-to-Average Power Ratio (PAPR) in multi-carrier modulation (MCM) systems. The key idea of the proposed scheme is to transform the original MCM signals such that the amplitude or the power of the companded signals follows uniform distribution. In this manner, the proposed scheme can effectively reduce the PAPR for different modulation formats and sub-carrier sizes without increasing the system complexity and signal bandwidth. Extensive simulation results show that the proposed schemes can significantly improve the performance of MCM systems.

Layered video multicasting can be used to accommodate the heterogeneity of users and their receive channels in wired and wireless system. In a wireless system using adaptive modulation and coding (AMC), total utility of all users can be increased by transmitting the video layers over different AMC modes and allocating proper bandwidth to these video layers. In this paper, it is shown that when the utility function is convex, the utility maximization problem can be formulated into a convex optimization problem. Then several important practical issues like limitation of layer numbers and operational layer rates are considered. With these limitations and no convex constraint on utility function, a genetic algorithm (GA) is proposed to maximize the total utility by layer rate allocation and selecting AMC modes to transmit the video layers. A 7-cell cdma2000 HDR system is used in the simulation to show the performance of the proposed methods.

H.264 defines 7 different coding modes for macroblocks (MBs) in P slices. In order to achieve a coding performance as high as possible, the H.264 encoder calculates rate distortion costs of all possible modes to determine the best mode of a MB. The computation complexity is so large that make it difficult to be used in practical applications especially in real time environment. In this paper, a fast adaptive intermodes decision method is proposed to reduce the complexity of H.264 encoder. Firstly the candidate inter modes used in rate distortion optimization can be limited in a small mode group (MG) by using the characteristics of the motion compensated residual image. Then the two most probable modes of the chosen MG are obtained on the basis of the modes of the up MB and the left MB. By calculating and comparing the rate distortion cost of the two modes, the optimum mode of the MB is determined. The overlapped mode groups and dynamic adjusted thresholds adopted in the proposed method can make the best mode lie within the chosen MG with great possibility which leads to extensive computation reduction with acceptable loss in quality. The experimental results show that the proposed method can save the encoding time up to 65% on average with -0.24dB performance degradation.

Space-time block code (STBC) provides full diversity gain but does not achieve any coding gain. To provide a significant coding gain, STBC needs to be concatenated with an outer code. Turbo product code (TPC) is a kind of high-efficient coding scheme with low latency decoding. Moreover, TPC does not have an error floor. In this paper, we investigate the performance of a TPC-based STBC coded MIMO-OFDM system under several IMT2000 channel environments.

Conventional entropy coding such as UVLC (universal variable length coding) usually uses variable length coding (VLC) based on static codeword table mechanism to code syntax elements which are partitioned from motion vectors and residual coefficients. UVLC employs half-variable length code (HVLC) such as kth order Exp-Golomb-Rice code to code syntax elements. However, static tables which indicate the average probability can not adapt the real-time probability distribution satisfactorily, so there are some needs to construct a probability updating mechanism in the codeword tables. If the real-time probability could be evaluated, Huffman code is undoubtedly the best choice for its approximation to source entropy. In PUAHC, dynamic Huffman code which is based on probability updating and Golomb code are joined together to code different source information for their adaptations to different kinds of probability distributions. In the experiment, it is proved that when PUAHC is used, the bit rate can be decreased by 3.9% and the computational complexity of decoder is also acceptable compared to UVLC

In the distributed space time block coded (DSTBC) orthogonal frequency division multiplexing (OFDM) system (DSTBC-OFDM), since the transmit antennas belong to different nodes that are distributed, there may exist multiple carrier frequency offsets (CFOs) to the transmitters at the receiver. Several kinds of equalization techniques, which intend to mitigate the intercarrier interference (ICI) when detecting symbols, are compared in terms of the BER performance. And an equalization method based on iterative ICI cancellation is proposed. Simulation results show that when the difference of normalized CFOs (with respect to the subcarrier spacing) between distributed transmitters is not more than 0.2, the proposed iterative ICI cancellation method could combat ICI effectively at very low computational cost. However, in case of large difference of normalized CFOs, i.e., 0.4, the frequency offsets could cancel the space diversity gain of distributed STBC totally even when ideal ICI cancellation is assumed, and the performance is close to that of OFDM system using single transmit antenna without space time block coding

In this paper, the performance of distributed space-time block coded (DSTBC) orthogonal frequency-division multiplexing (OFDM) system (DSTBC-OFDM) with the presence of carrier frequency offsets is investigated. Since the transmit antennas belong to different nodes that are distributed, there may exist multiple carrier frequency offsets to the transmitters at the receiver of DSTBC-OFDM system. The system model of DSTBC-OFDM with multiple carrier frequency offsets is given. Then we propose a frequency-domain detector to cancel the inter-symbol interference and the inter-carrier interference when detecting the symbols. The proposed detector has a reasonable performance and a moderate computational complexity. Simulation results show that the detector works very well when the carrier frequency difference between the distributed transmitters is small

Efficient load balancing algorithm is indispensable to serve more mobile stations in the heterogeneous wireless networks. In this paper, we propose a dynamic load balancing algorithm based on sojourn time for heterogeneous multitier wireless networks consisting of macrocell cellular network and microcell cellular network. The sojourn time is calculated by the velocity, direction of motion and position of mobile station. This algorithm is able to balance load by transferring some ongoing calls with longer sojourn time from overloaded cells to overlapping under-loaded heterogeneous cells. The number of transferred ongoing calls per load balancing period is calculated by the new calls arrival rate of overloaded cells and the workload states of overlapping cells. In addition, high-speed mobile stations can hand off from macrocells to microcells and slow mobile stations can hand off from microcells to macrocells, which can decrease the call dropping probability. Simulation results show that call blocking probability, call dropping probability and overall system utilization using our proposed dynamic load balancing algorithm are improved significantly.

Layered video multicasting can be used to accommodate the heterogeneity of users in wired and wireless system. In a wireless system with adaptive modulation and coding (AMC) scheme, total utility of all users can be increased by transmitting the video layers over different AMC modes and allocating proper bandwidth to these video layers. The utility maximization problem can be formulated into a convex optimization when the utility function is convex. When considering the limit of number of layers, a 2-step convex optimization algorithm is proposed to maximize the total utility by properly selecting the AMC modes to transmit the video layers and allocating bandwidth. A 7-cell cdma2000 HDR system is used in the simulation to show the performance of the proposed methods.

In this paper, a novel method is presented to guarantee the predefined quality-of-service (QoS) requests such as handoff-dropping probability by forecasting the next possible number of handoff dropping calls, using auto regressive moving average (ARMA) model, to update threshold through a close-loop control, while increasing the statistical multiplexing gain (the number of users provided service in a wireless/mobile system at a time) in providing acceptable QoS grades for every connections. We have tested our algorithm through simulations on a wide variety of traffic input. Our simulation results suggest that the forecasting-based approach enables us to achieve a higher level of statistical multiplexing gain while still reliably meeting the target handoff-dropping probability.

In this paper, we investigate the performance of distributed space-time block coded (DSTBC) orthogonal frequency-division multiplexing (OFDM) system (DSTBC-OFDM) with the presence of carrier frequency offsets. Since the transmit antennas belong to different nodes that are distributed, there may exist multiple carrier frequency offsets to the transmitters at the receiver of DSTBC-OFDM system. Received signal model of DSTBC-OFDM system with multiple carrier frequency offsets is given. Then a frequency-domain equalization technique is proposed to mitigate the inter-carrier interference (ICI) and the inter-symbol interference (ISI) when detecting the symbols. The proposed equalizer has a reasonable performance and low computational complexity. Simulation results show that the equalization technique is quite effective when the carrier frequency difference between the distributed transmitters is small, and moreover, by setting the receiver's frequency to the mean value of the transmitters' frequencies, a better performance can be obtained

This letter addresses the carrier frequency offsets and channel gains estimation problem for MIMO channels with multiple carrier frequency offsets that are not assumed to be equal for all transmit-receive antenna pairs. Training sequences are proposed for both flat fading and frequency selective fading MIMO channels. Under the proposed training sequences, sub-optimal performance of parameter estimation can be achieved by a subspace-based method with reasonable computational complexity. The method can also provide flexible tradeoff between complexity and performance

In this paper, a H.264 compatible spatially scalable video coding method with in-band prediction is proposed which taking advantages from both the high coding efficiency of H.264 coding scheme and the attractive performance of in-band overcomplete discrete wavelet transform (ODWT) in wavelet-domain motion estimation and motion compensation. Four MV prediction modes are proposed for INTER prediction of high frequency subbands. The intra prediction modes of H.264 are also simplified for each high band according to the directional features inherited inside. Finally, a H.264 compatible scheme based on one of the MV prediction modes is presented to provide better tradeoff among standard compatibility, low complexity and high performance.

The computation complexity of H.264 is so large that make it difficult to be used in practical applications especially in real time environment. In this paper, a fast adaptive inter modes decision method is proposed to reduce the complexity of H.264 encoder. Firstly the candidate inter modes can be limited in a small mode group (MG) by using the characteristics of the motion compensated residual image. Then the most probable mode (MPM) of the MB is predicted on the basis of the modes of the neighboring macroblocks. The overlapped mode groups and dynamic adjusted thresholds adopted in the proposed method can make the best mode lies within the chosen MG with great possibility which leads to extensively computation reduction with acceptable loss in quality. The experimental results show that the proposed method can save the encoding time up to 64% on average with -0.45dB performance degradation.

This paper discusses the problem of antenna subset selection in multiple-input multiple-output systems. Based on sub-optimal sorting and QR decomposition, we propose a transmit antenna selection criterion that is applicable for V-BLAST systems with ordered successive interference cancellation detection. Unlike most of the existing works, this criterion takes into account the impacts of ordering and cancellation. Simulations show that the proposed strategy achieves near-optimal outage capacity and outperforms several existing schemes in performance with reasonable complexity

In this paper, the subcarrier allocation problems for downlink transmission of spatial multiplexing based OFDM systems are investigated. With the goal of maximizing the instantaneous capacity, two categories of subcarrier assignment criteria are derived, that is, exclusive manner based criteria which allocate each subcarrier to a single user, and shared manner based criteria which allow multiple users to share a subcarrier. Simulation results demonstrate that both the presented criteria are capable of utilizing the multiuser diversity to enhance the capacity of spatial multiplexing based OFDM systems significantly. Furthermore, via experiments we find that compared with shared criteria, allocating each subcarrier to a single user is a feasible choice to achieve tradeoff among complexity, overhead, and capacity enhancement.

There are now great interests in antenna selection strategy for spatial multiplexing systems for the reason that it can reduce cost and complexity yet retain a large part of benefits of multiple antennas. In this paper, we focus on the transmit antenna selection criterion which is applicable to V-BLAST systems with OSIC detection. Based on sub-optimal sorting and QR decomposition, an approximate performance analysis of each sub-stream for V-BLAST transmission is done, and a new solution to the transmit antenna selection problems is suggested. Unlike most of the existing works, this criterion takes into account the impacts of ordering and cancellation. Simulation results show that the proposed algorithm behaves well both in outage capacity and in BER performance. Furthermore, due to the nature of QR decomposition, the implemental complexity can be reduced further by utilizing Gram-Schmidt orthogonalization.

In this paper a VBLAST-OFDM system with linear constellation precoding (LCP) is proposed for wideband wireless communications. Frequency diversity is obtained through the LCP precoding across OFDM subcarriers. Also a joint VBLASTLCP decoder which combines classical V-BLAST successive interference cancellation with Maximum Likelihood decoding for the precoding is proposed. Computer simulation shows that VBLAST-OFDM-LCP has a performance gain of at least 8.5dB at a certain symbol error rate compared with VBLAST-OFDM.

In wireless networks, bandwidth is extremely valuable resource. Therefore, an effective call admission control is urgent for bandwidth allocation with the occurrence of handoff increasing. The main challenges with multiple types of traffic are that each has its own requirements of bandwidth, traffic characteristic, QoS guarantee and handoff rate. Moreover, the computational complexity is another challenge. To meet these challenges, we set up a fictitious stochastic model to study the actual system so as to avoid coping with the complex multiple dimensions stochastic problem. On one hand, it can turn the multiple steps of state transition into single step, which is a necessary condition for ideal birth-death processes. On the other hand, it can provide a simple and effective method to compute a little larger approximation of the call dropping probabilities for multiple services, which facilitate our estimation for the acceptance ratio vector subject to QoS requirement. In addition, the boundary conditions are also considered in order to improve the control precision. Furthermore, a fast numerical method has been found to decrease the computation complexity greatly. As a result, we get an effective multiservices dynamic call admission scheme called EMDCA to adapt for multiple types of services in broadband wireless networks. Numerical results of simulation show that our scheme steadily satisfies the hard constraint on call dropping probability of multiservices while maintaining a high channel throughput.

Subcarrier and bit allocation schemes for SISO-OFDM systems in multiuser downlink scenario are well-documented. In this paper, we extend it to MIMO-OFDM systems and design a transmit scheme as a concatenation of dynamic subcarrier assignment, adaptive modulation and beamforming. With the goal of minimizing the overall transmit power required to meet the target BER, we develop an adaptive OFDM subcarrier allocation approach based on perfect and partial channel information. Simulation results show that our proposed algorithm outperforms the multiuser MIMO-OFDM with static FDMA technique considerably, and can lessen the performance loss caused by feedback delays. We have also evaluated the performance of the presented system under various number of transmit- and receive-antennas.

One of the key techniques in ensuring the quality of service in wireless networks is call admission control. The traditional well-known guard channel (GC) scheme and its numerous variants give preferential treatment to the handoff calls over new arrivals by reserving a number of radio channels exclusively for handoffs. However, this scheme is not able to adapt to changes in traffic pattern due to the static nature. The SDCA (stable dynamic call admission) control mechanism proposed by S. Wu (2002) can overcome that shortcoming, and improve the control precision and stability greatly because of its stochastic nature. Unfortunately, it is only suitable for single-service. In this paper, call admission control mechanism is extended by setting up a fictitious stochastic model to study the actual system so as to void meeting the complicated multiple dimensions stochastic problem and propose a new scheme called multiservices dynamic call admission (MDCA) to adapt for multiservices in the broadband wireless networks. Numerical results of simulation show that our scheme steadily satisfies the hard constraint on call dropping probability of multiservices while maintaining a high channel throughput.

Relying on amicable orthogonal design, we develop for multiple-antenna systems a general differential space-time block code (GDSTBC), which imposes no restrictions on underlying signal constellation compared with the existing differential space-time designs. This generalization potentially allows the spectral efficiency to be increased by carrying information not only on phases but also on amplitudes. We then derive a noncoherent decoder (NCD) for flat Rayleigh fading channels. We will show that NCD may recover data symbols with full antenna diversity and linear complexity at high signal-to-noise ratio. Particularly, while three kinds of conventional signal constellations (QAM, PSK and APSK) are used in GDSTBC, we derive simplified versions of NCDs which can effectively reduce the implementation cost.

Combining differential Alamouti space-time block code (DASTBC) with orthogonal frequency-division multiple access (OFDMA), this paper introduces a multiuser/multirate transmission scheme, which allows full-rate and full-diversity noncoherent communications using two transmit antennas over frequency-selective fading channels. Compared with the existing differential space-time coded OFDM designs, our scheme imposes 10 restrictions on signal constellations, and thus can improve the spectral efficiency by exploiting efficient modulation techniques such as QAM, APSK etc. The main principles of our design are s follows: OFDMA eliminates multiuser interference, and converts multiuser environments to single-user ones; Space-time coding achieves performance improvement by exploiting space diversity available with multiple antennas, no matter whether channel state information is known to the receiver. System performance is evaluated both analytically and with simulations.

This paper investigates the optimal access point (AP) placement (OAPP) in simultaneous broadcast system using orthogonal frequency division multiplexing (OFDM) for high data rate indoor wireless LAN. We aim to determine the best combination of multiple AP placements that minimizes average bit error rate (BER) of terminals when in put information including an indoor configuration, a number APs, and total transmission power is given a priori. Since OAPP is categorized as a hard combinatorial problem with many variables and constraints, we applied a nonlinear optimization scheme called uniform design simulated annealing (UDSA) to search for an approximate optimal solution and analyzed its performance in detail. The simulation results demonstrate that the UDSA algorithm has been successfully applied to OAPP and its effectiveness was also confirmed in comparison with very fast simulated annealing (VFSA) and local search (LS) algorithms.

We study the turbo equalization approach for OFDM system with combined error control coding and linear precoding. While previous literature: employed linear precoder of small size for complexity reasons, we propose use of a linear precoder of size larger than or equal to the maximum length of the equivalent discrete-time channel in order to achieve full frequency diversity and reduce complexities of the error control coder/decoder. A low complexity LMMSE turbo equalizer is also derived for the receiver. Through simulation and performance analysis, it is shown that the performance of our proposed scheme over frequency selective fading channel reaches the matched filter hound: compared with the same coded OFDM without linear preceding, the proposed scheme shows an SNR improvement of at least 6 dB at a bit error rate of 10/sup -6 /over a multipath channel with exponential power delay profile. Convergence behavior of the proposed scheme with turbo equalization using various types of linear precoder/transformer, various interleaver sizes and error control coders with various constraint lengths is also investigated.

As a consequence of the time-varying channel, the orthogonality between subcarriers is destroyed in conventional frequency-domain approaches for orthogonal frequency-division multiplexing (OFDM), resulting in interchannel interference, which increase's an irreducible error floor in proportion to the normalized Doppler frequency. In this paper, we propose a combined channel estimation in time domain and frequency domain. In time domain, the channel statistics like the channel correlation matrix can be achieved by PPS sequence, which may be used for frame synchronization in MIMO system. In frequency domain, in order to reduce the complexity of the estimator, we still apply theory of optimal rank-reduction to linear minimum mean-squared error (LMMSE) estimators, This enables us to achieve performance superior to any other structure without increasing bandwidth or incorporating redundancy. The performance is presented in terms of BER and MSE, and confirms that the estimator is robust to changes in channel characteristics.

In this paper, we propose an amicable-orthogonal-design-based differential space-time block code (ADSTBC) for multiple antennas. Compared with the existing differential modulation designs, our scheme imposes no restrictions on underlying signal constellation, and therefore can improve the spectral efficiency by exploiting efficient modulation techniques such as QAM, APSK, etc. We then derive a non-coherent maximum-likelihood decoder (MLD) with linear complexity for flat Rayleigh fading channels. Particularly, when the QAM constellation is used in ADSTBC, MLD can be further simplified to independently detect the real and imaginary parts of each modulated data symbol, and accordingly the implement cost can be greatly reduced; moreover, the computational amount for detecting single modulated data symbol is kept constant in MLD while the order of the QAM constellation increases.

Extraction of effective features plays a key role in pattern recognition. A large number of patterns, such as speech, radar signals, earthquake signals, handwriting, etc. are of non-stationary signals or exhibit time-varying behavior. The features of these patterns are often located in both the time and frequency domains. The traditional methods fail to extract such kind of features. Fortunately, wavelet packet transform (WPT) can provide an arbitrary time-frequency decomposition for the signals, because a wavelet packet (WP) library contains many WP bases, which can handle the different components of a signal. Therefore, by selecting a suitable basis, which is called "best basis", the effective features can be extracted. In this paper, three criteria are used to select the best WPT basis, namely: (1) distance criterion, (2) divergence criterion and (3) entropy criterion. Three algorithms to implement the above criteria are also provided. Experiments are conducted and the positive results are obtained.

SINCE quadrature amplitude modulation (QAM) was discovered in the early 1960s, more and more research (e.g. [1,2,3,4,5]) has been done on extracting more bandwidth and power efficiencies with QAM. Coded modulation, which combines modulation and coding, has been accepted as a more efficient transmission scheme in [2]. Multilevel coding (MLC), a coded modulation scheme proposed by Imai/Hirakawa in 1977, together with multistage decoding (MSD) has been known to be optimum in the sense of channel capacity over the A WGN channel model (see [1, 7, 8]). However, over Rayleigh fading channels Bit-Interleaved Coded Modulation (BICM), which was originally proposed by Zehavi. [4], gains much better performance [9, 10].