Large-scale multi-objective optimization problems (LSMOPs) face computational challenges due to high-dimensional search spaces and variable correlations. Existing algorithms often struggle to balance convergence, diversity, and efficiency in high-dimensional scenarios. We propose ATSPCA, a two-stage adaptive algorithm employing PCA-guided perturbation. The first stage uses PCA-based dynamic variable screening to identify key decision variable groups, applying adaptive Gaussian perturbation to guide optimization. The second stage enhances convergence and diversity through an improved competitive swarm optimizer (CSO) and reference pointbased environmental selection. An adaptive transition mechanism bridges the two stages. Tested on LSMOP and WFG benchmarks against state-of-the-art large-scale multi-objective evolutionary algorithms(LSMOEAs), ATSPCA demonstrates superior performance.

In this paper, a new four-antenna based structure (FAS) is introduced for capacity improvement in future cellular networks with frequency reuse factor of 1. In FAS, each cell consists of one omni-directional antenna located at the cell center and three 120-degree directional antennas located at the cell edge. In order to achieve effective system bandwidth allocation among four antennas, novel spectrum planning schemes for both downlink (DL) and uplink (UL) are proposed. Theoretical analysis and simulation demonstrate that the proposed cellular structure can significantly improve the system capacity in both DL and UL, especially at the cell edge.

In this paper, the throughput performance of the access links (i.e., base station to mobile station and relay station to mobile station) is analyzed for the wireless relay networks based on IEEE 802.16j. An isolation band based frequency reuse scheme (IBFRS) is proposed, which introduces an isolatio

Bandwidth allocation, in terms of distributing available data slots among different users, is studied for QoS provisioning in IEEE 802.16 networks. By considering the Automatic Repeat reQuest with Selective Acknowledgement (ARQ-SA) scheme for erroneous wireless channels, a mathematical model is established to theoretically analyze the delay performance of transmitting Service Data Unit (SDU) under a multiuser environment. The analytical results indicate that the delivery delay of the SDU is dominated by the time spent for the first transmission of all its Protocol Data Units (PDUs). Based on this observation, a novel dynamic bandwidth allocation algorithm is proposed and a detailed performance analysis is provided. Simulation results show that the proposed bandwidth allocation algorithm can significantly improve the delay performance of SDUs and ensure the fairness among different users.

Reuse partitioning (RP), a promising technique for constructing high efficient multi-cell OFDM systems, has brought a lot of attentions from both industry and academia. In this paper, by considering the characteristics of various service flows, we first introduce a new performance metric, called flow-satisfaction-degree (FSD), and then formulate an optimization problem for maximizing the FSD over the whole system. We then propose a FSD-based scheduling (FSDS) algorithm for the static RP system. Simulation results demonstrate that the proposed algorithm greatly outperforms the traditional static allocation scheme in terms of FSD and system throughput for the fully loaded system.

The IEEE 802.16e broadband wireless access (BWA) system is developed to cater for the rapidly growing requirement for multimedia wireless services. Since the heterogeneous services provided by the system are connection-oriented, admission control and associated resource reservation (RR) mechanisms are needed to achieve desired quality of service (QoS). In this paper, we develop a dynamic bandwidth reservation admission control scheme for the IEEE 802.16e system. In the proposed scheme, we set some overall reserved resource as admission guard bandwidth, which is dynamically adjusted according to the bandwidth request of on-going real-time variable-bit rate (VBR) services in addition to guaranteeing the resource requirement of potential handoff services. We also propose an analytical traffic model to evaluate the scheme. The results prove that our scheme can satisfy the bandwidth request of real-time VBR services and improve the system bandwidth utilization efficiently while guaranteeing the QoS requirements of all services at the same time.

The IEEE 802.16e standard is a rapidly developing technology for broadband wireless access system. Its PHY OFDMA mode defines two subchannel building methods: diversity permutation and contiguous permutation (AMC subchannel). In this paper we propose a joint packet scheduling and subchannel allocation scheme applicable for the IEEE 802.16e OFDMA AMC subchannel. Since it is a multiuser, multi-service and multichannel packet-switched system, we define a distinct scheduling priority for each packet on each subchannel that integrates MAC QoS requirements, service type and PHY channel state information (CSI). Based on these scheduling priorities and specific scheduling mechanism, efficient QoS guaranteed resource allocation is achieved in our scheme. Intensive simulations show that our scheme outperforms throughput-oriented maximum C/I (MCI) and QoS-oriented priority schemes under various conditions.

IEEE 802.16, also known as WiMax (worldwide interoperability for microwave access), introduces the automatic repeat request with selective acknowledgement (ARQ-SA) scheme to improve the reliability of the wireless link. For ARQ-SA, packets or protocol data units (PDUs), several of which compose one service data unit (SDU) from the upper layer, are transmitted orderly, but only those negatively acknowledged packets are retransmitted. We analyze the delay performance of SDU under ARQ-SA in a multiuser network environment. Our analysis shows that the SDU delay is mainly determined by the first transmission of all its PDUs. Further more, we propose a simple scheme to reduce the delivery delay of SDU. Simulation results are given to demonstrate the accuracy of the analytical one.

To provide a reliable transmission in 3GPP WCDMA systems, in the Radio Link Control (RLC) sublayer of the WCDMA, an Acknowledgement Mode (AM) is defined where an ACK frame is sent to indicate the data frame receiving status. In order to design a well-performed AM scheme, in this paper, we first investigate the AM protocol behavior and present the delay performance of the standard periodical AM-RLC scheme in the Bernoulli channel. Then, based on the observation from the performance above, we propose a dynamic AM scheme in RLC over a more general time-varying Markov channel. It is demonstrated that a much better delay performance can be achieved compared with the standard AM scheme with periodical acknowledgements.

This paper addresses the throughput optimization problem in multihop ultra-wideband (UWB) networks by jointly considering network topology formation and routing. Given a spatial distribution of UWB devices and traffic requirement, we want to form piconets and select paths to maximize the network throughput. Although there have been several works considering the problem of selecting paths to achieve the optimal throughput in multihop wireless networks, to the best of our knowledge, none of them takes the topology formation into the consideration. In this paper, we use Boolean matrices to model role assignment in UWB networks and formulate the throughput optimization problem as a nonlinear programming (NLP) problem. Since the throughput optimization problem is NP-hard, we give an upper bound of the optimal throughput by relaxing some constraints and using pseudo-Boolean optimization to linearize the NLP. We prove that the solution of the upper bound is at most three times of the optimal throughput. Based on the topology formed by solving the upper bound, we formulate a lower bound of the optimal throughput as a linear programming problem and use column generation to solve the lower bound. Numerical results show that the lower bound is very close to the upper bound. Simulation results demonstrate the effectiveness of the scheme.

Multimedia decoding is one of the key parts of many popular mobile multimedia applications, such as video telephony, streaming, and video playback. Since the multimedia decoding consumes a significant amount of energy on processors, it is crucial to lower the power consumption and prolong the battery life. In this paper, the statistical analysis of more than 600 processor load trace files is first presented. From the analysis, we found that it is feasible to predict the processor load of multimedia applications accurately using a low order linear time series model if the load is sampled using the feature period, which is obtained with Fast Fourier Transformation. Based on the analysis, we propose a novel interval-based DVS scheme to achieve penalty controllable energy reduction. The DVS scheme does not need any task profile or involvement of application program, and it is compatible with the service model of general purpose mobile operating systems. In addition, the proposed DVS scheme can handle the nonstationary behavior using an efficient online change detector, and important parameters, such as coefficients of the linear time series model, are estimated on the fly. More importantly, the proposed scheme can keep the Overscaling Rate (OSR) around a certain predefined value. Since the OSR has a simple and stable relationship with the Deadline Miss Rate (DMR), the penalty incurred by DVS is effectively controlled. Experimental results show that the proposed DVS scheme achieves a much smaller prediction error than previous approaches and achieves a significant processor energy reduction with adjustable and controlled penalty.

The life of battery power available time is a crucial character of the battery powered mobile device. In this paper, we investigate the performance issues of upper layer protocol, such as TCP, in IEEE 802.11 LAN's power saving mode. We discuss the tradeoff of energy saving, networking throughput and response time at the points of user experience. A novel power efficiency scheme is proposed to control the traffic transmission in power saving mode, which takes the QoS requirements of applications into account. Finally, we show that the proposed schema achieves higher user experience in our experiment.

The software codec on mobile device introduces significant power consumption because the energy efficiency of general processor based system is much lower than that of the dedicated hardware such as ASIC based accelerator. Dynamical Voltage Scaling (DVS) is one of the most efficient techniques to promote the energy efficiency. Most existing papers on this topic use simple heuristics to predict processor load, and poor prediction accuracy is observed in experiments. We advocate intensive analysis on processor load before designing DVS framework and algorithm. Hence, we conduct load analysis on more than 600 processor load trace files for 57 test sequences and 98 representative clips from Internet. Basic statistical analysis and time series analysis are applied intensively to identify major characteristics of the processor load. The analysis shows that it is feasible to predict processor load using low order linear time series model if the load is sampled using feature period. Moreover, there is indeed significant potential to reduce the energy consumption. Based on the analysis results, we develop a fully adaptive DVS technique to adjust supply voltage online with controllable penalty.

IEEE 802.15.3 is designed for short-distance wireless connectivity within a wireless personal area network (WPAN). It has great significance for applications such as home networking. Security is one of the fundamental issues in IEEE 802.15.3 WPAN. Although several security mechanisms have been defined in the standard, there are many others open and left for implementation. Therefore, in this paper, by utilizing the unique characteristics of the IEEE 802.15.3 WPAN, we propose a certificate-based trust management (including device initialization and certificate management) and key establishment scheme to protect the IEEE 802.15.3 WPAN.

The Dly-ACK scheme in IEEE 802.15.3 is designed to reduce the overhead of the ACK and improve the channel utilization. However, the way to use the Dly-ACK is open for implementation. In this paper, we first investigate the problems of applying the fixed Dly-ACK scheme to the TCP stream and show that the TCP performance is rather poor. Then, we propose two enhancement mechanisms for TCP with Dly-ACK over the 802.15.3 system. The first one is to request the Dly-ACK frame adaptively or change the burst size of Dly-ACK according to the queue size. The second is a retransmission counter to enable the destination DEV to deliver the packets to the upper layer timeously and in orderly fashion. Simulation results show that, with our enhancements, the TCP throughput can be improved more than 40% compared with the conventional Imm-ACK. We also investigate the impacts of some important system parameters such as the buffer size on the TCP performance. Some guidelines for the Dly-ACK design are given. Finally, it is worth pointing out that our enhancements are compatible with the standard.

Roaming across heterogeneous wireless networks such as wireless wide area network (WWAN) and wireless local area network (WLAN) poses considerable challenges, as it is usually difficult to maintain the existing connections and guarantee the necessary quality-of-service. This paper proposes a novel seamless and proactive end-to-end mobility management system, which can maintain the connections based on the end-to-end principle by incorporating an intelligent network status detection mechanism. The proposed system consists of two components, connection manager (CM) and virtual connectivity (VC). The CM, by using novel media access control-layer and physical-layer sensing techniques, can obtain accurate network condition, while at the same time reducing the unnecessary handoff and ping-pong effect. The VC can make mobility transparent to applications without additional network-layer infrastructure support using a local connection translation, and can handle mobility well in the network address translator and simultaneous movement cases using a subscription/notification service. The proposed system enjoys several unique advantages: 1) capable of reacting to roaming events proactively and accurately; 2) maintaining the connection's continuity with small handoff delay; and 3) being a unified end-to-end approach for both IPv4 and IPv6 networks. We have built a prototype system and performed experiments to demonstrate the advantages of the proposed system.

An M-ary orthogonal pulse polarity modulation (OP/sup 2/M) using modified orthogonal variable spreading factor codes (OVSF), i.e., a set of orthogonal Walsh codes, for time hopping ultra wideband (TH-UWB) communication systems is proposed. Under FCC power spectrum density (PSD) constraint for UWB, the proposed M-ary OP/sup 2/M system proves to be more power efficient than traditional bi-phase shift-keying (BPSK) modulation, binary and M-ary pulse position modulation (PPM) systems. OVSF codes are modified in OP/sup 2/M to smooth the signal PSD for meeting FCC PSD mask for UWB system. Reduced complexity receiver architecture provides tractable system complexity. Analytical and simulation results show that the proposed 32-ary OP/sup 2/M TH-UWB system is more power efficient than previous PPM and BPSK modulations.

In current WLAN system that is designed for best-effort communications, there is not any quality of service (QoS) differentiation support. In this paper, we propose a fully distributed medium access control (MAC) adaptation method for service differentiation. It is implemented by dynamically updating the MAC layer parameters (such as contention window) to adapt to the network conditions in a class-based fashion. In this sense, the QoS classes are differentiated and the system performance is significantly improved in terms of delay, packet loss and throughput while ensuring fairness and stability. The key idea of our scheme is the introduction of a mapping function and a target contention window. It is demonstrated that our proposed adaptive MAC can outperform both the basic 802.11 MAC and the fixed differentiation scheme with very low complexity.

Orthogonal frequency division multiplexing (OFDM) with multiple antennas makes it possible for efficient transmission of high-speed multimedia over wireless channels. This paper proposes an approach for power-efficient video transmission of MPEG-4 fine granularity scalable (FGS) bit-stream over OFDM systems with multiple antennas at both transmitter and receiver. Our proposed approach minimizes the total distortion while satisfying the constraint of transmission power, which is achieved by optimal power allocation and transmission rate control of power efficient assignment of scalable source to spatial subchannels. The performance of our proposed scheme is compared with one using fixed transmission rate or power allocation. Simulation results show significant performance gain of our approach.

Power consumption is one of the most stringent bottlenecks in mobile devices. In this paper, we investigate the joint effect of MAC and PHY layers on power efficiency in IEEE 802.11a WLAN. Specifically, we study the link adaptation for a power efficient transmission by selecting a proper transmission mode and power level with the aid of our derived power efficiency model. This study addresses the fundamental impact of the CSMA MAC protocol on the power efficiency of IEEE 802.11a WLANs. Some implications for system design are also discussed. In particular, we show that the non-radio-transmission power plays an important role in the power optimization of IEEE 802.11a WLAN.

The performance of multirate direct-sequence code-division multiple-access (CDMA) systems is considered. We compare two multirate schemes: variable spreading length (VSL-CDMA) and multicode (MC-CDMA). The performance in terms of asymptotic multiuser efficiency (AME) and near-far resistance (NFR) for various detectors are evaluated. Analytical and numerical results demonstrate that in multirate systems, MC-CDMA has a similar performance to that of VSL-CDMA employing low-rate detection in terms of multirate AME (MAME) and multirate NFR (MNFR). A lower bound for the optimal MNFR is also obtained and is shown to be that of the linear decorrelator in multirate systems. Thus, this implies that the decorrelator is no longer optimal in the sense of MNFR.

The minimum mean squared error (MMSE) receiver is a linear filter which can achieve optimal near-far resistance in direct-sequence code-division multiple-access communications. However, one of the main problems of this receiver is the required number of filter taps, which is typically large. This is especially true in systems with a large processing gain in which case the receiver's computation burden becomes very high. As a result, methods for reducing the complexity of the MMSE receiver have been of great interest in recent years. We propose an efficient partitioned MMSE receiver based on a classification algorithm. It is shown that the computational complexity (in terms of the filter taps) of the proposed receiver can be reduced significantly while good performance is maintained. Based on the special structure of our proposed receiver, we also propose a release-merge adaptive partition algorithm which can update the partition and the receiver's coefficients simultaneously. In particular, it is demonstrated that the proposed receiver can perform much better than previously proposed reduced-rank MMSE receivers, such as the partial despreading MMSE receiver and the cyclically shifted filter bank receiver, with even a smaller number of taps.

The minimum mean-squared error (MMSE) receiver is a linear filter which can suppress multiple access interference (MAI) effectively in direct-sequence code-division multiple-access (CDMA) communications. An antenna array is also an efficient scheme for suppressing MAI and improving the system performance. In this letter, we consider an adaptive MMSE receiver in conjunction with beamforming in CDMA systems employing an antenna array. The proposed structure is featured as a low complexity receiver, which adapts the MMSE filter coefficients and the beamforming weights simultaneously. However, it does require the channel state information and the direction of arrival (DOA) of the desired user signal. As a result, we propose two adaptation methods to perform joint channel estimation and signal detection without any training sequence. It is demonstrated that the two proposed methods achieve similar bit-error-rate performance. More importantly, their performance degradation compared with the case with perfect channel information is small.

In a wireless local area network (WLAN), medium access control (MAC) layer access parameters are usually differentiated for various classes of users to provide different quality of service (QoS). In particular, in this paper, we investigate the MAC layer performance of IEEE 802.11e based WLAN, where the traffic flows are classified and each class is assigned different MAC parameters, such as inter-frame space (IFS), and contention window (CW) size. These parameters play a critical role in determining the system performance. Thus, an appropriate mathematical model is desired to determine the QoS differentiation on these parameters and guide the system design. However, so far, little work was reported. We propose a novel model based on the Markov chain, which takes into account almost all the important MAC parameters, CW, IFS, class number, etc. Despite its simplicity, it is demonstrated that our proposed model agrees quite well with the results obtained with the time-consuming simulations.

We first consider the OFDM/SDMA system which admits several OFDM users simultaneously by reusing the same frequency band. With the linear minimum mean squared error (MMSE) receiver, it has been shown that such a system can improve the system capacity significantly compared to the single antenna OFDM system. However, the number of required linear filters is huge. Thus, in this paper, we propose two reduced-complexity MMSE receivers for OFDM/SDMA system; namely, interpolated MMSE and partial MMSE. We demonstrate that both methods perform much better than the previously proposed reduced-complexity receiver. Other than OFDM/SDMA, an alternative to support multiple users with high spectrum efficiency is to use orthogonal frequency division multiple access (OFDMA) with high-level modulation. With both theoretical analysis and simulation, we find that the relative BER performance of these two systems depends on the receiver design of OFDM/SDMA. In particular, when the MMSE receiver is used, OFDM/SDMA is usually worse than or comparable to OFDMA. However, the former has the potential to outperform the latter because when the optimal (and the most complicated) ML detector is used, it is superior to the latter. On the other hand, OFDMA has the advantage of a simple receiver structure.

The adaptive minimum mean squared error (MMSE) based detector is one of the most attractive CDMA receivers because of its relatively simple structure and good performance. However, most of the previous research on such receivers was based on the assumption that the system traffic is fixed during the receiver processing. We propose the use of the MMSE filter in a dynamic traffic system, such as in packet transmission systems. With decision directed (DD) update of the filter coefficients, we can adapt to the dynamic traffic. Under some extreme cases when the user traffic increases significantly, the pure DD mode may fail or diverge and the condition under which it fails is also derived. To assure convergence, the blind PASTd (Projection Approximation Subspace Tracking) method is first used before switching to the DD mode. It is shown that the combined PASTd and DD based MMSE filter is a robust receiver and can achieve almost the same performance as a receiver with training sequences for every packet, both in the uplink and the downlink. We also show that the receiver behavior is quite different when the traffic increases or decreases.

We derive the optimal (minimal) power allocation and capacity for a multirate DS/CDMA system with various QoS requirements. Most of the previous work on power allocation only dealt with the conventional matched filter (MF) receiver and no multiuser detection (MUD) was considered. It is well known that MUD and in particular interference cancellation (IC) can be used to improve the system performance significantly. Hence, after proposing a novel graph-aided method to do optimal power allocation with the conventional MF receiver, parallel IC (P/C) is considered in multirate systems. We propose an iterative approach for optimal power allocation with PIC in multirate systems. It is shown that the proposed power allocation algorithm can converge to the optimal solution quickly. Furthermore, it is demonstrated that when PIC is combined with optimal power allocation, the power dissipation decrease and the system capacity increase significantly.

Multiuser detection (MUD) is a key technique for combating multiple access interference (MAI) in CDMA systems. We propose a simple and effective multiuser receiver, which we refer to as the objective function based multiuser detector (OFMUD). This is a successive multistage joint detector based on the statistical optimization of an objective function. Two objective functions are considered in this paper. The first one is based on a maximum likelihood solution, and the second one is based on the least squared error solution. A key feature of the proposed detector is that among all the K user bits, we update the estimate of one and only one bit (the one that is most likely to be wrong) in every stage. Analytical and numerical results show that significant performance improvement can be achieved compared with the conventional DS/CDMA receiver. At the same time, the near-far problem is alleviated. In addition, it is shown that the proposed receiver can outperform the popular multiuser parallel interference cancellation receiver in most cases with a smaller computational cost.

There has been a lot of interest in using multiuser detection (MUD) for combating the detrimental effects of multiple access interference (MAI) in DS/CDMA communication systems. In this paper, we propose a simple and effective MUD receiver over multipath fading channels. It is shown that the proposed receiver can easily take advantage of path diversity. By doing so, significant capacity and performance improvement can be achieved compared with the conventional DS/CDMA receiver. It is also shown that the proposed MUD receiver can outperform the popular parallel interference cancellation (PIC) detector which does not employ a RAKE receiver. Furthermore, it can achieve similar performance as that of the PIC receiver which employs a RAKE with less computation complexity.

In satellite DS/CDMA communication systems, power control (PC) is critical, and only open loop power control (OLPC) is feasible due to the large propagation delay. We propose an adaptive OLPC method for DS/CDMA satellite communication systems based on a Markov chain channel model. Then, under the assumption that multiuser interference cancellation (IC) is employed, we derive the Erlang capacity of the satellite DS/CDMA system with the OLPC scheme. It is shown that IC and power control error (PCE) affects the Erlang capacity significantly. In addition, dual-satellite diversity is considered and we show that diversity can improve the Erlang capacity of such a system greatly.

In most of the current image/video compression standard, such as JPEG, MPEG, H.263, etc, the DCT is used. The DCT coefficients for every AC frequency component usually have Laplacian distribution. Such a distribution is critical in the image or video transcoding system. Therefore, the parameter in the distribution should be well estimated. Different from the normal parameter estimation, in the transcoding system, the original DCT value is unavailable, and only the dequantized value is available. In this paper, we propose 3 estimation methods based on the dequantized value for the transcoding system. The simulation demonstrates that they can yield very good results. In addition, under a fixed bit rate, they can work even better than estimation with the original DCT value in the sense of image/frame's PSNR.