Performance evaluation of Passive Optical CDMA Networks using a linear parallel interference receiver in imperfect power cases

In this paper, we propose a transmission and reception block diagram to cancel interference in the case of multiuser Optical Code Division Multiple Access. We evaluate the performances of Passive Optical Networks using different transmitted powers. To highlight the problem and analyze imperfect power, we propose a new approach based on technical issues of two transmitter groups. These groups correspond to high and low multiple access interference issued from different power classes. A compensation factor is added to the linear parallel interference cancelation structure to improve channel propagation errors. Transmission errors are evaluated analytically and by simulation, considering synchronous and asynchronous cases. The error probabilities of the proposed optical code division multiple access system are estimated using Gaussian approximation. We show that the optimization of the compensation factor gives better performances in terms of bit error rate than other classical receivers. It also shows that this approach on the one hand, overcomes the problem of multiple services in a network source optical code division multiple access and on the other hand, it avoids the imperfect power effects for different users.     

Microcellular CDMA system with a linear multiuser interferencecanceler

In the paper, the authors suggest an asynchronous microcellular CDMA system with a matrix-based multiuser interference canceler for the reverse link, in which multiuser interference is completely removed on a symbol-by-symbol basis. The linear interference cancellation scheme, whose matrix order is equal to the number of active users, does not require knowledge of their received power levels, thereby resulting in high capacity and near/far resistance. In the paper, the influence of surrounding cell interference on a given base station receiver for various propagation path loss models is also analyzed and then the system performance is investigated theoretically. Provided the normalized capacity is defined by a required SNR (=E_b/N₀ ) of 7 dB at the binary DPSK detector, the CDMA system can provide capacity per cell of 46~54%     

5G室内密集立体覆盖的计算通信:架构、方法与增益

提出了一种新型的室内密集立体覆盖的计算通信一体化架构,通过挖掘信道计算、容量计算以及网络资源优化计算之间的内在联系,并利用基于云计算和雾计算的密集分布式接入网络的优势,该架构完成了计算电磁学、计算信息论与大规模优化理论到计算通信理论的深度融合.介绍了该架构的实现方法,即以密集异构分布式无线接入网络作为通信接入网络基础架构,利用分布式的计算资源结合计算电磁学理论实现并行化的信道计算,据此进一步依据计算信息论实现容量计算,并基于大规模优化理论完成多用户的网络资源优化计算,最终实现由传播环境到信道容量与资源分配的计算通信.     

Capacity in fading environment based on soft sensing information under spectrum sharing constraints

In this paper, the ergodic channel capacity for a secondary user is investigated using soft sensing information about primary user activity in a shared channel under joint peak transmit power and average received interference power constraints for Nakagami-m fading channel. The results of the proposed power adaptation scheme illustrate the effect of communication environment parameters and soft sensing information about primary user activity on the channel capacity of secondary user. In particular, the effect of cross link channel state information to maximize the channel capacity for the power adaptation scheme is emphasized by considering the Lagrangian optimization problem for joint peak transmit power and average interference power constraints. Moreover, the performance of the primary user is also investigated considering the interference of the secondary user to the primary in spectrum sharing environment in terms of transmission rate and average channel capacity.     

On the capacity of mobile ad hoc networks with delay constraints

Previous work on ad hoc network capacity has focused primarily on source-destination throughput requirements for different models and transmission scenarios, with an emphasis on delay tolerant applications. In such problems, network capacity enhancement is achieved as a tradeoff with transmission delay. In this paper, the capacity of ad hoc networks supporting delay sensitive traffic is studied. First, a general framework is . proposed for characterizing the interactions between the physical and the network layer in an ad hoc network. Then, CDMA ad hoc networks, in which advanced signal processing techniques such as multiuser detection are relied upon to enhance the user capacity, are analyzed. The network capacity is characterized using a combination of geometric arguments and large scale analysis, for several network scenarios employing matched filters, decorrelators and minimum-mean-square-error receivers. Insight into the network performance for finite systems is also provided by means of simulations. Both analysis and simulations show a significant network capacity gain for ad hoc networks employing multiuser detectors, compared with those using matched filter receivers, as well as very good performance even under tight delay and transmission power requirements.     

Throughput and Energy-Efficiency-Aware Protocol for Ultrawideband Communication in Wireless Sensor Networks: A Cross-Layer Approach

In this paper, we propose an efficient MAC protocol: the throughput maximized MAC protocol (TM-MAC), inspired by the availability that a number of ultrawideband (UWB) transmission parameters can be tuned to better match the requirements of data flow. In TM-MAC, we implement a concurrent multiuser access scheme instead of a mutual exclusion method such as TDMA and random access. For multiuser interference, we establish a model to adaptively adjust the data transmission rate to generate the expected signal to interference noise ratio (SINR) at the receiver side for reliable communications. We also analyze the relationship among the theoretical maximum channel capacity, achievable maximum channel capacity, and data transmission rate. According to network topology, TM-MAC redivides each piconet into several subsets in which communication pairs can make communication simultaneously and achieve the maximum throughput using the highest data rate. In subset formation, we propose a general analytical framework that captures the unique characteristics of shared wireless channel and throughput variance, as well as allows the modeling of a large class of systemwide throughput maximization via the specification of the per-link utilization function. For algorithm essential parameters design, we consider the influence of traffic type on the system performance. Heavy tailed distribution, compared to Poisson distribution for most existing work, is exploited to accurately model the real traffic to achieve the adaptation of our algorithm. Simulation results show that our algorithm can maximize throughput to achieve short latency.     

Optimal power control for Rayleigh-faded multiuser systems with outage constraints

How can we achieve the conflicting goals of reduced transmission power and increased capacity in a wireless network, without attempting to follow the instantaneous state of a fading channel? In this paper, we address this problem by jointly considering power control and multiuser detection (MUD) with outage-probability constraints in a Rayleigh fast-fading environment. The resulting power-control algorithms (PCAs) utilize the statistics of the channel and operate on a much slower timescale than traditional schemes. We propose an optimal iterative solution that is conceptually simple and finds the minimum sum power of all users while meeting their outage targets. Using a derived bound on outage probability, we introduce a mapping from outage to average signal-to-interference ratio (SIR) constraints. This allows us to propose a suboptimal iterative scheme that is a variation of an existing solution to a joint power control and MUD problem involving SIR constraints. We further use a recent result that transforms complex SIR expressions into a compact and decoupled form, to develop a noniterative and computationally inexpensive PCA for large systems of users. Simulation results are presented showing the closeness of the optimal and mapped schemes, speed of convergence, and performance comparisons.     

TD-SCDMA集群系统中的干扰抑制策略

TD-SCDMA集群系统中会存在各种干扰,一些通过抑制干扰提高系统容量的技术被考虑采纳,如智能天线、多用户检测和功率控制等。传统的功控算法无法消除来自集群群组间的用户干扰。先用波束赋形进行主波瓣外干扰抑制,然后进行多群组联合检测消除波瓣内群组间干扰,从而降低系统对功率控制的要求,提高性能。仿真证明,上述算法能有效降低系统发射功率和抑制干扰。     

Capacity Maximization through Energy-Aware Multi-Mode Relaying

In future wireless mobile networks, data rate and quality of service are expected to be comparable to those of wired deployments. To achieve this target, novel architectures must be adopted, successfully countering the disadvantages of the wireless transmission. Inspired by that, cooperative relaying was proposed because of the various gains it introduces to the network. In this work we propose a scheme consisting of multi-mode decode and forward relays facilitating the communication between a base station and a user terminal (UT). By equipping the relays with two interfaces, we can exploit the plethora of the available wireless protocols. Also, instead of performing multi-relay transmissions, we adopt an opportunistic relaying scheme due to its simplicity and outage-optimality. Additionally, we incorporate successive transmissions to improve the spectral efficiency, thus recovering the half-duplex loss in capacity due to the two-hop transmission. However, as inter-relay interference arises from successive transmissions, we propose mitigation techniques through interference cancellation and out-band transmissions using the multi-mode relays. At the same time, an energy-aware mechanism is implemented in the selected relay’s transmission, opting for power reduction, as the channel state information is acquired prior to the signal’s forwarding to the UT. Finally, we give numerical results by comparing the proposed energy-aware multi-mode relaying (EA-MMR) scheme, with two other schemes in terms of average end-to-end capacity, outage probability, delay distribution and power gain.     

Interference-aware node access scheme in UAV-aided VANET

In vehicular Ad Hoc network (VANET),frequent link handovers and channel interference can lead to increased transmission delay and decreased network throughput.To address the issues,unmanned aerial vehicle (UAV) were introduced to cooperate with vehicles and construct UAV-assisted air-ground integrated VANET.An interference-aware node access scheme was proposed.The node access problem was formulated as a multi-objective optimization problem considering link transmission rate,link handovers and transmit power.Then the optimization problem was decomposed into two convex optimization sub-problems by dual decomposition method,the sub-problem jointly optimizes handovers and link transmission rate while the sub-problem optimizes the transmit power based on link reliability.Finally,simulation results show that the proposed mechanism can effectively improve data delivery ratio,average end-to-end delay and network throughput.     

Error propagation analysis for underwater cooperative multi-hop communications

The potential gains of cooperative communication and multi-hopping in underwater acoustic communication channels is examined. In particular, performance of such systems is compared to a comparable single hop system (direct transmission) with a common transmission distance. The effects of error propagation with decode and forward at each relay are explicitly treated and it is shown that strong gains can be achieved by multi-hopping (an effective SNR gain) as well as cooperation, which contributes to a diversity gain. We observe that cooperative diversity gains are retained even when considering error propagation. The analysis is done via a Markov chain analysis for both regular linear and grid networks. Our initial analysis is for single path channels; the effects of inter-symbol interference as well as multi-user interference are examined. It is found that due to the strong decay of signal power as a function of transmission distance, multi-user interference is not as significant as inter-symbol interference. In both cases, cooperative and multi-hopping gains are observed.     

Power Control Based on Maximum Power Adaptation in Two-Tier Femtocell Networks

In recent years, femtocells are receiving considerable attention in mobile communication as a cost-effective means of improving indoor coverage and capacity. A significant technical challenge in the deployment of a large number of femtocells is the management of interference from the underlay of femtocells onto the overlay of macrocell. In this paper, a reasonable and effective interference suppression scheme based on the adaptive adjustment of femtocell users’ maximum transmission power is proposed. The highlight of the scheme is the joint design of macrocell users’ uplink communication protection and femtocell users’ optimal power allocation. The scheme restricts the cross-tier interference at macrocell base station below a given threshold and ensures the optimization of femtocell users’ power allocation at each adjustment phase. Last, admission control is also considered, aiming to exploit the network resources more effectively. Simulation results show the superiority of the proposed scheme over the scheme based on the Signal-to-Interference-Plus-Noise Ratio adaptation. We also give some reference on utility function selection by setting different coefficients in the utility function, and show the effectiveness of admission control in both fixed and random network topologies.     

Power-Efficient Spatial Reusable Channel Assignment Scheme in WLAN Mesh Networks

Interference has strong effect on the available bandwidth of wireless local area network (WLAN) based mesh networks. The channel assignment problem for multi-radio multi-channel multihop WLAN mesh networks is complex NP-hard, and channel assignment, routing and power control are tightly coupled. To mitigate the co-channel interference and improve capacity in multi-channel and multi-interface WLAN mesh networks, a power-efficient spatial reusable channel assignment scheme is proposed, which considers both channel diversity and spatial reusability to reduce co-channel interference by joint adjusting channel, transmission power and routing. In order to assign channel appropriately, an efficient power control scheme and a simple heuristic algorithm is introduced to achieve this objective, which adjust the channel and power level of each radio according to the current channel conditions so as to increase the opportunity of channel spatial reusability. The proposed channel assignment scheme also takes load, capacity and interference of links into consideration. Simulation results show the effectiveness of our approach and demonstrate that the proposed scheme can get better performance than other approaches in terms of throughput, blocking ratio, energy consumption and end-to-end delay.     

Energy Efficiency-Delay Tradeoffs in CDMA Networks: A Game-Theoretic Approach

A game-theoretic approach for studying energy efficiency-delay tradeoffs in multiple-access networks is proposed. Focusing on the uplink of a code-division multiple-access (CDMA) network, a noncooperative game is considered in which each user seeks to choose a transmit power that maximizes its own utility while satisfying its (transmission) delay requirements. The utility function measures the number of reliable bits transmitted per joule of energy and the user's delay constraint is modeled as an upper bound on the delay outage probability. The Nash equilibrium for the proposed game is derived, and its existence and uniqueness are proved. Using a large-system analysis, explicit expressions for the utilities achieved at equilibrium are obtained for the matched filter, decorrelating and (linear) minimum-mean-square-error (MMSE) multiuser detectors. The effects of delay quality-of-service (QoS) constraints on the users' utilities (in bits per joule) and network capacity (i.e., the maximum number of users that can be supported) are quantified. Using the proposed framework, the tradeoffs between energy efficiency and delay are quantified in a competitive multiuser setting.     

一种基于准奇异子空间传输的MIMO多用户群检测方法

在多用户MIMO系统中,共享信道用户之间干扰是系统噪声的主要来源.基于压制用户间干扰的考虑,本文提出一种类似奇异子空间传输的多用户检测的方法.这种方法由于在发送端只需要得到部分信道状态信息.从而大大的减轻了回馈链路的通信负担.这在系统内用户数量很多的时候对系统资源的节省尤为明显.为了使这种传输方法能够获得更好的总体信道容量,进一步给出了与此传输系统相匹配多用户调度准则.另外由于这个传输方法中只用到了信道的左右奇异向量,因此系统性能将不受到信道自相关的影响.最后通过仿真的方法证明了这种传输方法能够提供很理想的系统性能.     

CDMA系统中一种新的基于MMSE多用户检测的自适应功率控制算法

功率控制技术是CDMA通信系统中克服“远一近效应”，降低多址干扰、增大系统容量的一项关键技术。第三代移动通信系统对功率控制提出了新的研究课题。在本文提出CDMA系统中一种新的白适应功率控制和MMSE多用户检测的联合优化的算法，仿真结果表明，这种新的联合优化算法对提高系统容量，改善系统性能有很大的作用。     

Differentially-Encoded Di-Symbol Time-Division Multiuser Impulse Radio in UWB Channel

Ultra-wideband (UWB) communication systems are expected to operate in a highly frequency-selective multipath fading environment. To exploit multipath diversity gains in a multiuser scenario, we developed a differentially-encoded, di-symbol time-division multiuser impulse radio (d²TD-IR) system with delay-sum autocorrelation receivers. In traditional time-division multiple access systems, each user transmits a single pulse during a symbol duration in a pre-assigned chip which is longer than maximum excess delay of the channel. However, due to the exponential decay property of UWB channel, we proposed the use of much shorter chip duration, which significantly increases the transmission rate. Because dense pulse transmission will induce multiuser interference, two time-hopping access sequences, which alternately encode the odd- and even-index symbols, are employed with delay-sum autocorrelation receivers to maximally suppress the interference. It was shown that when the chip duration is properly chosen, the proposed system outperforms the conventional time-hopping impulse radio system at high signal-to-noise ratio. This paper also proposed a method to estimate the optimal chip duration when only the average power decay profile of the UWB channel is known.     

Distributed Cooperative Control Algorithm for Topology Control and Channel Allocation in Multi-radio Multi-channel Wireless Sensor Network: From a Game Perspective

With the development of wireless communication technology, the spectrum resource is becoming more and more scarce, which results in the increase of network co-interference and then incurs the increase of data retransmission probability. Hence, the single channel based algorithms are facing a myriad of challenges. Moreover, reducing the energy consumption and prolonging the network lifetime is the key issue for wireless sensor network. In order to alleviate the interference while reducing and balancing the energy consumption, we tend to design a multi-radio multi-channel algorithm that joint the topology control and channel allocation. Firstly, we study the interactions between topology control and channel allocation, which lay the basis for the further reduction of transmission power and interference. We take account of the radio power, node residual energy and node interference to construct a cooperative control game model of topology and channel allocation. This game model has proven to guarantee the existence of Nash equilibrium. And then based on this game model, a distributed Cooperative Control Algorithm of Topology and Channel allocation (CCATC) is developed, which can converge to Nash Equilibrium and preserve the network connectivity. Furthermore, the simulation results demonstrate that CCATC can not only greatly reduce the interference but also prolong the network lifetime by balancing the energy consumption of nodes. The reduction of interference comes with the improvement of network throughput. Besides, CCATC has many other attractive features such as the higher channel utilization, the better robustness, the fairer channel allocation and the less end-to-end delay.     

An uplink power control based on truncated channel inversion fordata traffic in a cellular CDMA system

A power control scheme, called truncated channel inversion, in which a mobile suspends transmission when the wireless channel is in a bad condition in order to reduce out-cell interference is examined. It is found that capacity is improved and battery power consumption is reduced as a consequence of suspending transmission, but extra queuing delay is introduced. It is shown that the extra queuing delay depends on how fast the channel characteristics change and that the truncated scheme works well, even for moderate mobile velocities     

Multiuser two‐way relay processing and power control methods for cognitive radio networks

We consider a cognitive radio system where a secondary network shares the spectrum band with a primary network. Aiming at improving the frequency efficiency of the secondary network, we set a multiantenna relay station in the secondary network to perform two‐way relaying. Three linear processing schemes at the relay station based on zero forcing, zero forcing‐maximum ratio transmission, and minimum mean square error criteria are derived to guarantee the quality of service of primary users and to suppress the intrapair and interpair interference among secondary users (SUs). In addition, the transmit power of SUs is optimized to maximize the sum rate of SUs and to limit the interference brought to PUs. Numerical results show that the proposed multiuser two‐way relay processing schemes and the optimal power control policies can efficiently limit the interference caused by the secondary network to primary users, and the sum rate of SUs can also be greatly improved. Copyright © 2011 John Wiley & Sons, Ltd.