Transmission algorithms for a multi-channel packet radio system with priority users

In multi-channel systems such as multi-station packet radio networks or cellular radio, various user categories arise. In this paper, we propose that one portion of the users, named low-priority, each be assigned a specific channel for their transmissions, whereas another portion, named high-priority, may transmit through any of the channels via some channel selection policy. The main objective is to reduce delays of the high-priority users without imposing heavy penalties on the delays of the low-priority group. For the described system, we adopt a previously studied limited sensing random access algorithm and introduce two dynamic channel selection policies. We study the stability region and the delays induced by the system. The selection policies present the high-priority users with a significant delay advantage and induce fair utilization of the transmission channels, without requiring any knowledge about the system state by the users. One of the selection policies induces high system throughput at the expense of implementation complexity and increased delays for the low-priority users. The second policy is easier to implement but, although it does not penalize the delays of the low-priority users, it reduces the system thoughput.     

Non-saturated throughput analysis of IEEE 802.11-based cognitive radio networks

Technology of cognitive radio networks has emerged as an effective method to enhance the utilization of the radio spectrum where the primary users have priority to use the spectrum,and the secondary users try to exploit the spectrum unoccupied by the primary users.In this paper,considering the non-saturated condition,the performance analysis for the IEEE 802.11-based cognitive radio networks is presented with single-channel and multi-channel,respectively.For the single-channel case,an absorbing Markov chain model describing the system transitions is constructed,and one-step transition probability matrix of the Markov chain is given.By using the method of probability generating function,the non-saturated throughput of the secondary users is obtained.For the multi-channel case,taking into account the negotiation-based sensing policy,the mean number of unused channels perceived by the second users is given,and then the non-saturated aggregate throughput of the secondary users is derived.Finally,numerical examples are provided to show the influences of the non-saturated degree,the number of the secondary users and the channel utilization of the primary users on the performance measures for the non-saturated throughput with single-channel and the non-saturated aggregate throughput with multi-channel.     

无线Ad Hoc网络中基于业务感知的多信道MAC协议(英文)

Existing multi-channel Medium Access Control (MAC) protocols have been demonstrated to significantly increase wireless network performance compared to single channel MAC protocols. Traditionally, the channelization structure in IEEE 802.11 based wireless networks is pre-configured, and the entire available spectrum is divided into subchannels and equal channel widths. In contrast, this paper presents a Traffic-Aware Channelization MAC (TAC-MAC) protocol for wireless ad hoc networks, where each node is equipped with a single half duplex transceiver. TAC-MAC works in a distributed, fine-grai-ned manner, which dynamically divides variable-width subchannels and allocates subchannel width based on the Orthogonal Frequency Division Multiplexing (OFDM) technique according to the traffic demands of nodes. Simulations show that the TAC-MAC can significantly improve network throughput and reduce packet delay compared with both fixed-width multi-channel MAC and single channel 802.11 protocols, which illustrates a new paradigm for high-efficient multi-channel MAC design in wireless ad hoc networks.     

Adhoc多信道技术及安全性分析

无线网络中多信道技术是解决无线相干性,提高网络容量的有效技术。以单接口多信道为分析对象,对多信道协议进行分类并分析各类的优缺点。根据不同分类的多信道技术分析其存在的安全性问题,进一步提出针对多信道MAC协议特有的攻击行为,通过实验显示该攻击可以对多信道网络性能带来明显的负面效果。     

Load-aware channel hopping protocol design for mobile ad hoc networks

Using multiple channels in wireless networks improves spatial reuse and reduces collision probability and thus enhances network throughput. Designing a multi-channel MAC protocol is challenging because multi-channel-specific issues such as channel assignment, the multi-channel hidden terminal problem, and the missing receiver problem, must be solved. Most existing multi-channel MAC protocols suffer from either higher hardware cost or poor throughput. Some channel hopping multi-channel protocols achieve pretty good performance in certain situations but fail to adjust their channel hopping mechanisms according to varied traffic loads. In this paper, we propose a load-aware channel hopping MAC protocol (LACH) that solves all the multi-channel-specific problems mentioned above.LACH enables nodes to dynamically adjust their schedules based on their traffic loads. In addition to load awareness, LACH has several other attractive features: (1) Each node is equipped with a single half-duplex transceiver. (2) Each node’s initial hopping sequence is generated by its ID. Knowing the neighbor nodes’ IDs, a node can calculate its neighbors’ initial channel hopping sequences without control packet exchanges. (3) Nodes can be evenly distributed among available channels. Through performance analysis, simulations, and real system implementation, we verify that LACH is a promising protocol suitable for a network with time-varied traffic loads.     

基于网络分割的无线传感器网络多信道MAC协议

无线传感器网络中,可用正交信道数目较少和噪声干扰问题制约着多信道MAC协议性能的提升,结合数据采集应用的特点,提出一种基于网络分割的多信道MAC协议。在最小化网络总干扰值的基础上,网络分割引入碰撞因子进一步优化子树结构、降低树内干扰。并利用基于图着色理论的分配策略为每棵子树分配一条高质量信道。仿真实验结果表明,该协议显著提高了网络吞吐量,并且大幅降低了传输延迟和分组丢失率。     

A Distributed MAC Protocol Using Virtual Control Channels for CRSNs

A cognitive radio sensor network (CRSN) is a promising fusion network that combines conventional wireless sensor network (WSN) with cognitive radio (CR) functionalities. With abilities to sense for available channels and to adapt to the radio environment, a CRSN is able to be more opportunistic in accessing spectrums than a WSN, but it also has problems due to hardware constraints and energy limitations. In many studies on distributed CR MAC protocols, establishing dedicated control channels (DCCs) has been considered as an important problem because it is essentially used for coordination and negotiation of spectrum assignments. However, directly applying DCCs into CRSNs is impractical, due to its high-cost complexity in hardware and deployment. To solve it, in this paper we propose a distributed MAC protocol using virtual control channels for CRSNs, in which CR sensor nodes called secondary users are grouped into clusters, and commonly shared available channels are utilized as virtual DCCs. In addition, a channel selection scheme is developed, based on an approximated partially observable Markov decision process. Our numerical simulation results indicate that the proposed MAC protocol can not only improve the throughput rate but also reduce the energy consumption under no DCCs.     

Multi-channel support for DMAC in WSNs

Currently most wireless sensor network applications assume the presence of single-channel medium access control (MAC) protocols. However, lower sensing range result in dense networks, single-channel MAC protocols may be inadequate due to higher demand for the limited bandwidth. In this paper we proposed a method of multi-channel support for DMAC in Wireless sensor networks (WSNs). The channel assignment method is based on local information of nodes. Our multi-channel DMAC protocol implement channel distribution before message collecting from source nodes to sink node and made broadcasting possible in DMAC. Analysis and simulation result displays this multi-channel protocol obviously decreases the latency without increasing energy consumption.     

Cognitive medium access control protocols for secondary users sharing a common channel with time division multiple access primary users

The unused time slots in a primary time division multiple access (TDMA) network are regarded as the potential channel access opportunities for secondary users (SUs) in cognitive radio (CR). In this paper, we investigate the medium access control protocols that enable SUs to access a common TDMA channel with primary users (PUs). The primary traffic is assumed to follow a Bernoulli random process. A two‐state Markov chain is used to model the secondary traffic, and two different scenarios are considered. The first scenario assumes that the secondary packet arrivals are independent and follow a Bernoulli random process and a cognitive carrier sensing multiple access (Cog‐CSMA) protocol is proposed. A Rayleigh fading channel is considered in evaluating Cog‐CSMA, and its throughput expression is derived in this paper. The second scenario assumes that the packet arrivals follow a correlated packet arrival process and a cognitive packet reservation multiple access (Cog‐PRMA) protocol is proposed. A Markov chain is used to model the different system states in Cog‐PRMA and derive the throughput. Numerical results show that the Cog‐CSMA and Cog‐PRMA protocols achieve the objective of supporting secondary transmissions in a TDMA network without interfering the PUs' transmissions and improve the network bandwidth utilization. Copyright © 2012 John Wiley & Sons, Ltd.     

认知无线网络中应用空闲认知用户的联合随机频谱检测策略

针对认知网络中主用户状态的不确定性和随机检测策略无法保证认知用户准确地寻找可用信道的问题,该文提出一种利用认知无线网络中空闲认知用户进行联合随机检测的策略。在加入空闲认知用户进行检测后,利用马尔科夫模型对认知基站获得的可用信道数进行描述,推导出此时认知网络的检测性能。理论分析和仿真结果表明,利用空闲认知用户可以减少服务时延,提高认知网络的吞吐量。在考虑认知用户汇报检测信息所占用的时长后,通过优化算法得出最优的参与联合检测的空闲认知用户数。     

Remote locations coverage analysis with wireless mesh networks based on IEEE 802.16 Standard

This article analyzes the wireless coverage problem of remote regions with low user density and propagation problems due to irregular terrain and high tree density. The use of a wireless mesh network is proposed as a solution where user data is transmitted directly to a base station when it is possible or relayed through other nodes in a multi-hop manner when there is not a direct link. The mesh topology uses short links with higher capacity instead of long links with low capacity. We analyze radio propagation and MAC protocols, including random sources, queues, and packet delays. The article is based on the coverage of a realistic rural region near Medellin, a mid size city in Colombia, and it shows that a wireless mesh network is an alternative to a typical cell based solution. It includes propagation analysis and MAC protocol behavior, so it is not limited to a radio coverage problem but also traffic, scheduling, and routing analysis     

Decentralized cognitive MAC for opportunistic spectrum access in ad hoc networks: A POMDP framework

We propose decentralized cognitive MAC protocols that allow secondary users to independently search for spectrum opportunities without a central coordinator or a dedicated communication channel. Recognizing hardware and energy constraints, we assume that a secondary user may not be able to perform full-spectrum sensing or may not be willing to monitor the spectrum when it has no data to transmit. We develop an analytical framework for opportunistic spectrum access based on the theory of partially observable Markov decision process (POMDP). This decision-theoretic approach integrates the design of spectrum access protocols at the MAC layer with spectrum sensing at the physical layer and traffic statistics determined by the application layer of the primary network. It also allows easy incorporation of spectrum sensing error and constraint on the probability of colliding with the primary users. Under this POMDP framework, we propose cognitive MAC protocols that optimize the performance of secondary users while limiting the interference perceived by primary users. A suboptimal strategy with reduced complexity yet comparable performance is developed. Without additional control message exchange between the secondary transmitter and receiver, the proposed decentralized protocols ensure synchronous hopping in the spectrum between the transmitter and the receiver in the presence of collisions and spectrum sensing errors     

A hybrid multi-channel MAC protocol for wireless ad hoc networks

In a regular wireless ad hoc network, the Medium Access Control (MAC) protocol coordinates channel access among nodes, and the throughput of the network is limited by the bandwidth of a single channel. The multi-channel MAC protocols can exploit multiple channels to achieve high network throughput by enabling more concurrent transmissions. In this paper, we propose a hybrid and adaptive protocol, called H-MMAC, which utilizes multi-channel resources more efficiently than other multi-channel MAC protocols. The main idea is to adopt the IEEE 802.11 Power Saving Mechanism and to allow nodes to transmit data packets while other nodes try to negotiate the data channel during the Ad hoc Traffic Indication Message window based on the network traffic load. The analytical and simulation results show that the proposed H-MMAC protocol improves the network performance significantly in terms of the aggregate throughput, average delay, fairness and energy efficiency.     

Adaptive power-controlled MAC protocols for improved throughput in hardware-constrained cognitive radio networks

Cognitive radios (CRs) are emerging as a promising technology to enhance spectrum utilization through opportunistic on-demand access. Many MAC protocols for cognitive radio networks (CRNs) have been designed assuming multiple transceivers per CR user. However, in practice, such an assumption comes at the cost of extra hardware. In this paper, we address the problem of assigning channels to CR transmissions in single-hop and multi-hop CRNs, assuming one transceiver per CR. The primary goal of our design is to maximize the number of feasible concurrent CR transmissions, and conserve energy as a secondary objective, with respect to both spectrum assignment and transmission power subject to interference constraint and user rate demands. The problem is formulated under both binary-level and multi-level spectrum opportunity frameworks. Our formulation applies to any power-rate relationship. For single-hop CRNs, a centralized polynomial-time algorithm based on bipartite matching that computes the optimal channel assignment is developed. We then integrate this algorithm into distributed MAC protocols that preserve fairness. For multi-hop ad hoc CRNs, we propose a novel distributed MAC protocol (WFC-MAC) that attempts to maximize the CRN throughput, assuming single transceiver radios but with “dual-receive” capability. WFC-MAC uses a cooperative assignment that relies only on information provided by the two communicating users. The main novelty in WFC-MAC lies in requiring no active coordination with licensed users and exploiting the dual-receive capability of radios, thus alleviating various channel access problems that are common to multi-channel designs. We conduct theoretical analysis of our MAC protocols, and study their performance via simulations. The results indicate that compared with CSMA/CA variants, our protocols significantly decrease the blocking rate of CR transmissions, and hence improve network throughput.     

Artificial bee colony–based spectrum handoff algorithm in wireless cognitive radio networks

In this work, we proposed a new artificial bee colony–based spectrum handoff algorithm for wireless cognitive radio systems. In our wireless cognitive radio system, primary users, secondary users, and related base stations exist in the same communication environment. For our artificial bee colony–based algorithm, secondary users that always struggle to discover an idle channel have a leading role. While honey bees work hard to find the best‐quality nectar source for foraging, secondary users try to find idle channels for making communication. In this way, secondary users are organized for different missions such as sensing and handoff similar to honey bees to minimize spectrum handoff delay by working together. In the spectrum handoff stage, some secondary users must sense the spectrum so that the interrupted secondary user may perform the spectrum handoff process. In our developed spectrum handoff algorithm, the spectrum availability characteristic is observed on the basis of the missions of the bees in the artificial bee colony algorithm with the aim of minimizing the spectrum handoff delay and maximizing probability of finding an idle channel. With the help of the algorithm that is developed using the artificial bee colony, spectrum handoff delay of secondary users is considerably decreased for different number of users without reducing probability of finding an available channel.     

A joint sensing and transmission power control policy for RF energy harvesting cognitive radio networks

We consider a radio frequency energy harvesting cognitive radio network in which a secondary user (SU) can opportunistically access channel to transmit packets or harvest radio frequency energy when the channel is idle or occupied by a primary user. The channel occupancy state and the channel fading state are both modeled as finite state Markov chains. At the beginning of each time slot, the SU should determine whether to harvest energy for future use or sense the primary channel to acquire the current channel occupancy state. It then needs to select an appropriate transmission power to execute the packet transmission or harvest energy if the channel is detected to be idle or busy, respectively. This sequential decision‐making, done to maximize the SU's expected throughput, requires to design a joint spectrum sensing and transmission power control policy based on the amount of stored energy, the retransmission index, and the belief on the channel state. We formulate this as a partially observable Markov decision process and use a computationally tractable point‐based value iteration algorithm. Section 5 illustrate the significant outperformance of the proposed optimal policy compared with the optimal fixed‐power policy and the greedy fixed‐power policy.     

Utility driven cooperative spectrum sensing scheduling for heterogeneous multi-channel cognitive radio networks

Owing to the spectrum scarcity and energy constrained devices in wireless networks arises the demand for an efficient spectrum sensing technique which improves both sensing performance and energy efficiency for cognitive radio networks. This paper proposes a cooperative spectrum sensing scheduling (CSSS) scheme for heterogeneous multi-channel cognitive radio networks with the objective of finding an efficient sensing schedule to enhance network utility while keeping the energy depletion at a lower level. We start with formulating the CSSS problem as an optimization problem, which captures both the energy-performance and performance opportunity trade-offs. We prove that the formulated CSSS problem is non-deterministic polynomial hard (NP-hard). To tackle the higher computational complexity of the formulated problem, we propose a greedy-based heuristic solution, which produces a sub-optimal result in polynomial time. To reduce energy consumption during spectrum sensing, we make secondary users to adaptively decide on the sensing duration based on the received signal-to-noise ratio (SNR), where higher SNR leads to lower sensing duration and vice-versa. For enhancing network throughput, SUs sense multiple channels in the order of their suitability for data transmission to explore as many numbers of channels as possible within the permitted maximum sensing time. We consider erroneous nature of reporting channel to make the cooperative decision robust against errors during reporting. Simulation based results show the effectiveness of the proposed scheme in terms of utility, energy overhead, and the number of channels explored compared to similar schemes from literature.

     

Replacement of Spectrum Sensing in Cognitive Radio

Two major challenges exist in the development and deployment of cognitive radio networks: spectrum sensing and hidden terminal problem. In this research, we consider a network structure where the spectrum sensing task is separated from the unlicensed users (secondary users). The service provider for the secondary users needs to place sensing devices within the networks of licensed users (primary users). These sensing devices sense the primary users? activity. The sensing devices also decide whether to admit a secondary user?s transmission. A new cognitive cycle is proposed accordingly. The proposed protocol is analyzed using the theory of Lamé curve. The problem of optimally locating sensing devices and the properties of the proposed system are studied for single-user case and multi-user case. For the case without a separate control channel, a lowtemperature handshake technique is proposed for handshakes between the secondary users and the sensing devices. The other advantage of the proposed scheme is from the business model point of view: the expensive sensing devices will be implemented by the cognitive radio service provider, instead of being built in the secondary user devices which are usually consumer products demanding low cost.     

Cluster‐based adaptive multispectrum sensing and access in cognitive radio networks

Spectrum sensing and access have been widely investigated in cognitive radio network for the secondary users to efficiently utilize and share the spectrum licensed by the primary user. We propose a cluster‐based adaptive multispectrum sensing and access strategy, in which the secondary users seeking to access the channel can select a set of channels to sense and access with adaptive sensing time. Specifically, the spectrum sensing and access problem is formulated into an optimization problem, which maximizes the utility of the secondary users and ensures sufficient protection of the primary users and the transmitting secondary users from unacceptable interference. Moreover, we explicitly calculate the expected number of channels that are detected to be idle, or being occupied by the primary users, or being occupied by the transmitting secondary users. Spectrum sharing with the primary and transmitting secondary users is accomplished by adapting the transmission power to keep the interference to an acceptable level. Simulation results demonstrate the effectiveness of our proposed sensing and access strategy as well as its advantage over conventional sensing and access methods in terms of improving the achieved throughput and keeping the sensing overhead low. Copyright © 2012 John Wiley & Sons, Ltd.     

Prediction‐based MAC‐layer sensing in cognitive radio networks

We consider a cognitive radio network which coexists with multiple primary users (PUs) and secondary users (SUs) transmit over time‐varying channels. In this scenario, one problem of the existing work is the poor performances of throughput and fairness due to variances of SUs' channel conditions and PUs' traffic patterns. To solve this problem, we propose a novel prediction‐based MAC‐layer sensing algorithm. In the proposed algorithm, the SUs' channel quality information and the probability of the licensed channel being idle are predicted. Through the earlier predicted information, we schedule the SUs to sense and transmit on different licensed channels. Specifically, multiple significant factors, including network throughput and fairness, are jointly considered in the proposed algorithm. Then, we formulate the prediction‐based sensing scheduling problem as an optimization problem and solve it with the Hungarian algorithm in polynomial time. Simulation results show that the proposed prediction‐based sensing scheduling algorithm could achieve a good tradeoff between network throughput and fairness among SUs. Copyright © 2014 John Wiley & Sons, Ltd.