Joint power and rate allocation for spectrum sharing cognitive radio multicast networks under service outage constraint

This letter considers a downlink spectrum sharing cognitive radio (CR) multicast network coexisting with a primary network. The problem of joint power and rate allocation to maximize the average sum rate is studied. In this regard, a joint power and rate allocation scheme is proposed, where the allocated rate can be higher than the lowest rate of all the secondary users (SUs) within the same group, which is different from the conventional multicast transmission scheme. To guarantee the quality of service (QoS) of the SU, the service outage probability defined as the probability that the maximum achievable rate of the SU is lower than the rate of the group, is constrained to be under a certain threshold, which is termed as the service outage constraint. The numerical results show that the proposed scheme provides significant improvement over the conventional scheme in terms of average sum rate.     

Joint power control and spectrum sensing for capacity maximisation in spectrum sharing systems

We study the problem of joint power control and spectrum sensing for maximising the capacity at the secondary user while protecting the primary user's transmissions in spectrum sharing cognitive radio systems. Power control regulates the transmission power of the secondary user and spectrum sensing regulates the sensing time and the sensing threshold that care for the primary user's protection. This problem is a capacity maximisation problem that we formulate and solve using an iterative greedy algorithm due to its complex form. The solution of the proposed algorithm leads to the global optimal solution that represents the optimal triplet values of transmission power, sensing time and threshold. The obtained results show the potential capacity maximisation that is achieved by the proposed joint design as long as the primary user's protection is provided. Finally the convergence behaviour of the proposed algorithm is assessed in terms of the needed iterations for enhancing the capacity of spectrum sharing systems.     

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.     

Transmission capacity of wireless ad hoc networks with outage constraints

In this paper, upper and lower bounds on the transmission capacity of spread-spectrum (SS) wireless ad hoc networks are derived. We define transmission capacity as the product of the maximum density of successful transmissions multiplied by their data rate, given an outage constraint. Assuming that the nodes are randomly distributed in space according to a Poisson point process, we derive upper and lower bounds for frequency hopping (FH-CDMA) and direct sequence (DS-CDMA) SS networks, which incorporate traditional modulation types (no spreading) as a special case. These bounds cleanly summarize how ad hoc network capacity is affected by the outage probability, spreading factor, transmission power, target signal-to-noise ratio (SNR), and other system parameters. Using these bounds, it can be shown that FH-CDMA obtains a higher transmission capacity than DS-CDMA on the order of M/sup 1-2//spl alpha//, where M is the spreading factor and /spl alpha/>2 is the path loss exponent. A tangential contribution is an (apparently) novel technique for obtaining tight bounds on tail probabilities of additive functionals of homogeneous Poisson point processes.     

Asymptotically tight bounds on the capacity and outage probabilityfor QAM transmissions over Rayleigh-faded data channels with CSI

In this article, novel quickly computable analytical upper and lower bounds are presented on the symmetric capacity for flat-faded Rayleigh channels with finite-size quadrature amplitude modulation constellations when perfect channel-state information at the receiving site is available; the proposed bounds are asymptotically tight both for high and low signal-to-noise ratios. Furthermore, an easily computable expression is also provided for a reasonably tight evaluation of the resulting outage probability     

多天线频谱共享认知网络保密中断概率分析

针对单输入多输出认知无线电网络,研究了瑞利衰落信道下采用最大比合并时保密中断性能。在所研究的系统中,次用户发射机发送机密信息给另一个次用户接收机,次用户接收机配备多个天线并且采用最大比例合并多个接收信号。同时,拥有多个天线窃听者也采用最大比合并方案偷听次用户发射机和次用户接收机之间传送的信息。频谱共享下次用户发射机工作时必须保证主用户的服务质量。推导了保密中断概率的精确表达式,分析了系统保密中断概率渐近性能。仿真结果验证了分析的正确性。     

Choosing from redundant designs of power systems using system outage rate and cost

The push for high availability is on. As customers keep telling computer manufacturers, any outage to their operations is unacceptable. For those involved at the design stage, this usually means that functions within a computer's subsystems, like power, must be made fault-tolerant, or redundant. In its simplest form, redundancy replaces one component with two, so that the first failure will have no impact on the customer. More generally, a K-out-of-N design calls for N components to do the job of N − K + 1, so that the first K − 1 failures can be tolerated but the K-th failure causes a system outage. In this paper, we relate our own experience with power subsystems: how we chose from among different shades of redundancy by concentrating on outage rate and cost. To further simulate real life, we also considered the service strategy, i.e. whether (and when) to preventively replace a component whose failure did not cause the system to go down. A key result of the paper shows that a redundant design coupled with a well-chosen service strategy yields advantages beyond what either one alone would provide. The combination not only decreases the design's already low system outage rate, it makes the outage rate essentially constant—so that ease of predictability is ensured. Three power subsystem designs are outlined, as are the reliability and outage rate functions associated with them. Cost and service strategy are then considered, to help decide which is the optimal design based on total program cost projections and reliability objectives.     

Exact outage performance of small-cell network relying device-to-device and non-orthogonal multiple access under perfect and imperfect CSI

Wireless Networks - This paper investigates a non-orthogonal multiple access (NOMA) technique by employing device-to-device (D2D) transmission in small-cell networks. More specifically, the D2D...     

Ergodic capacity and outage probability optimization for secondary user in cognitive radio networks under interference outage constraint

This paper considers a cognitive radio network where a secondary user (SU) coexists with a primary user (PU). The interference outage constraint is applied to protect the primary transmission. The power allocation problem to jointly maximize the ergodic capacity and minimize the outage probability of the SU, subject to the average transmit power constraint and the interference outage constraint, is studied. Suppose that the perfect knowledge of the instantaneous channel state information (CSI) of the interference link between the SU transmitter and the PU receiver is available at the SU, the optimal power allocation strategy is then proposed. Additionally, to manage more practical situations, we further assume only the interference link channel distribution is known and derive the corresponding optimal power allocation strategy. Extensive simulation results are given to verify the effectiveness of the proposed strategies. It is shown that the proposed strategies achieve high ergodic capacity and low outage probability simultaneously, whereas optimizing the ergodic capacity (or outage probability) only leads to much higher outage probability (or lower ergodic capacity). It is also shown that the SU performance is not degraded due to partial knowledge of the interference link CSI if tight transmit power constraint is applied.     

Impact of the secondary service transmit power constraint on the achievable capacity of spectrum sharing in rayleigh fading environment

The two main constraints on the transmit power allocation of the secondary service in a spectrum sharing scheme are the received interference threshold at the primary receiver, and the maximum transmit power of the secondary user. We obtain a critical system parameter which relates these two constraints and enables the system designer to eliminate the interference threshold constraint by adjusting the maximum transmit power of the secondary users. Eliminating the interference threshold constraint significantly reduces the system complexity by making the power allocation of the secondary service independent from the channel state information between the secondary transmitter and the primary receiver; thus removes the need for signaling between primary and secondary systems.     

Joint power allocation and multi-relay selection scheme based on system outage probability

An amplify-and-forward （AF） based multi-relay network is studied. In order to minimize the system outage probability with a required transmission rate, a joint power allocation （PA） and multi-relay selection scheme is proposed under both total and individual power constraints （TIPC）. In the proposed scheme, the idea of ordering is adopted to avoid exhaustive search without losing much system performance. Besides the channel quantity, the ordering algorithm proposed in this article also takes relays＇ maximal output ability into consideration, which is usually ignored in traditional relay ordering algorithms. In addition, simple power reallocation method is provided to avoid repetitive PA operation during the process of searching all possible relay subsets. By Adopting the idea of ordering and using the proposed power reallocation method lead to remarkable decrease of the computation complexity, making the scheme easier and more feasible to implement in practical communication scenarios. Simulations show that the proposed multi-relay selection scheme provides similar performance compared to the optimal scheme with optimal PA and exhaustive search （OPAES） but with much lower complexity.     

Protocol design and resource allocation for power optimization using spectrum sharing for 5G networks

Telecommunication Systems - In this paper, we propose a spectrum sharing protocol wherein the sharing is performed in a situation without introducing a secondary transmitter in assisting the...     

Time dynamics of outage of fiber optic local system employingspread spectrum

A model is developed for ascertaining the robustness of operation of the random-carrier-code-division multiple-access (RC-CDMA) method of implementing optical frequency division multiple access. The unwanted wander (i.e. the supersensitivity of carrier frequencies to physical perturbations) of each channel is parameterized by σ, of dimensions gigahertz per square root second. Channel outage comes about when, by chance, too many channels crowd into the same part of the optical band, causing overwhelming adjacent channel interference. In this study a lower bound is derived on the mean time between outages (units of years), as a function of bit rate (~10 Mbit/s), chip rate (units of gigabits per second), required signal-to-interference-ratio (~3-30 dB), population size (on the order of ten thousand), and σ. While the technology has not matured to give a clear prognosis of the ability to limit σ, the `payoff', in terms of performance for a given σ, is discussed. Constraints on σ are found that, if met, imply that RC-CDMA can be used to achieve networks with throughput exceeding 100 Gbit/s     

Cognitive relay network with several primary receivers and outdated CSI: a new spectrum sharing constraint

This paper introduces a new spectrum sharing constraint which facilitates outage analysis for the cognitive relay networks with multiple primary receivers (PR)s and under outdated channel state information (CSI). The pivotal idea in spectrum sharing paradigm is controlling the interference generated due to the coexistence of primary and secondary users. In a realistic scenario, interference management is hampered by several parameters. In this context, this paper targets the influence of the CSI accuracy and the number of PRs. In a cognitive network with multiple PRs, the best approach to shielding the receivers from intolerable interference is to limit the maximum inflicted interference. Although being effective, this strategy has two drawbacks. First: it measurably affects mathematical tractability of the outage analysis. Second: it requires substantial resources to find the strongest interference channel which may be unaffordable in certain applications, especially when there are many PRs. In this paper, we propose the total interference (TI) constraint as the spectrum sharing criterion and investigate the outage behavior of the secondary network. A simple back-off power control method is adopted so as to mitigate the harmful effect of the outdated CSI. Considering decode-and-forward relays and partial relay selection strategy, we derive exact expressions for the end-to-end outage probability. Monte-Carlo simulations are made and results corroborate correctness of the mathematical derivations. The findings suggest that: first, outage assessment under the TI constraint is more tractable than under the maximum interference (MI) constraint as it leads to simple closed-form expressions. Second, the secondary network under the TI constraint is more resilient against the outdated CSI because the interference probability arising from the outdated CSI is smaller under the TI constraint than MI.     

Variable power adaptive MIMO OFDM system under imperfect CSI for mobile ad hoc networks

Future high speed mobile applications require diverse Quality of Service (QoS). To provide flexible data rate services while satisfying the low delay requirements, adaptive MIMO OFDM is a promising technique over time varying channels. In this paper a variable power adaptive MIMO OFDM system under imperfect CSI using cross layer design for mobile ad hoc networks is proposed. Data throughput is maximized while maintaining the delay QoS requirements in the presence of channel estimation errors. Numerical results show that the variable power adaptive MIMO OFDM system provides better spectral efficiency than its constant power counterpart.     

Effects of the BS power and soft handoff on the outage and capacity in the forward link of an SIR-based power-controlled CDMA system

In the forward link of a signal-to-interference ratio (SIR)-based fast power-controlled CDMA system, the fraction of base station (BS) power allocated to a mobile station (MS) is considered as a key factor affecting the system performance. By using our proposed macrodiversity non-orthogonality factor, we establish a unified analytical model to characterize the distribution of the fraction of BS power allocated to an MS in either the non-soft handoff mode or the soft handoff mode. By using that distribution and limiting the maximum fraction of BS power available to an MS, a closed-form expression of the capacity at a certain outage probability is obtained. The effects of system parameters, such as the available Rake fingers, the soft handoff threshold, the unbalance of the BS power, and the power control error, on the capacity are investigated from the viewpoint of the limitation on the fraction of BS power allocated to an MS. Simulation results show that soft handoff does not always improve capacity and the capacity gain may result depending on the choice of the system parameters.     

Investigation on multiuser diversity in spectrum sharing based cognitive radio networks

A new form of multiuser diversity, named multiuser interference diversity, is investigated for opportunistic communications in cognitive radio (CR) networks by exploiting the mutual interference between the CR and the existing primary radio (PR) links. The multiuser diversity gain and ergodic throughput are analyzed for different types of CR networks and compared against those in the conventional networks without the PR link.     

Optimal energy-efficiency capacity and sensing tradeoff for hybrid spectrum sharing in CRN

This paper investigates the tradeoff between energy-efficiency capacity and spectrum sensing under hybrid spectrum sharing model,where the spectrum sharing method is based on sensing results of seconda...     

非理想功率控制下WCDMA系统中的业务速率与系统容量

根据 WCDMA系统单小区功率分配算法有解的充要条件,通过将目标信干比抽象为对数正态随机变量的方法,该文得出了非理想功率控制条件下系统容量的定量关系式,为研究非理想功率控制下,VBR(Variable Bit Rate)业务的速率与 CBR(Constant Bit Rate)和 VBR业务的用户容量间的关系提供了一条有效的途径。分析和数值计算结果表明,非理想功率控制对系统性能有着显著的影响,业务速率和系统容量之间存在的互换关系。可以根据不同业务的性能要求,通过改变业务参数来提高系统的适应性,从而提高系统的资源利用率和服务质量。     

Dynamic power and subcarrier allocation for downlink OFDMA systems under imperfect CSI

Wireless Networks - In this paper, we investigate the joint power and subcarrier allocation for the downlink of orthogonal frequency division multiplexing access systems, with various practical...