Ad Hoc网络中一种具有优先控制的自适应协同MAC协议

ARQ(Auto Repeat reQuest)机制通常用来在传输失败后重传数据,但是在深衰落信道下,源节点多次重传有可能导致系统性能持续变坏,作为未来无线通信的重要技术,协同通信能够大大提高链路的可靠性,可以有效解决上述问题。本文针对Ad Hoc网络,提出了一种基于优先控制的自适应协同MAC(Media Access Control)协议。此协议采用ARQ机制,根据瞬时信道情况,自适应地选择信道质量更好的中继节点来重传数据,并且在优化的退避算法和中继选择算法的控制下,赋予中继节点相对源节点更高的优先级,协议中还在传统RTS/CTS分组交互基础上加入了新的握手交互机制,使得协议的性能进一步提升。本文还对经典二维Markov模型进行了改进,加入了协同机制并提出中继节点冲突模型,对所提协议进行了建模并推导出了吞吐量性能表达式。仿真结果表明,本文所提协议相对IEEE 80211 DCF协议和传统采用ARQ机制的协同MAC协议有着更好的性能。
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Performance analysis of multiple-antenna cooperative networks under Weibull fading

In wireless communications, cooperative relaying is well-known to enhance the overall system performance, but implementation and cost constraints stand against its wide deployment. This paper investigates the performance of cooperative relays with and without multiple antennas under independent and identically distributed (i.i.d.) Weibull faded channels in a two-hop wireless network. We consider the Weibull fading channel model due to its flexibility in describing the radio propagation environment more than the classical Rayleigh model. Our study relies on applying selection combining (SC) along with threshold decode and forward (TDF) protocol at the cooperative relays as a good compromise between cost and performance. In addition, maximal ratio combining (MRC) is used at the destination. We derive analytical expressions for the end-to-end (E2E) error performance of the network under such scenario and provide simulation results to confirm the validity of the obtained analytical expressions.     

Cooperative MAC Design in Multi-hop Wireless Networks: Part I: When Source and Destination are within the Transmission Range of Each Other

Cooperative communication is regarded as a promising technology in future 5G wireless networks to enhance network performance by exploiting time and/or space diversity via distributed terminals. In this paper, we propose a cooperative medium access protocol which addresses three key aspects of cooperative communications from MAC layer perspective, namely, when to cooperate, whom to cooperate with and how to protect ongoing cooperative transmissions. To further improve the protocol performance in dense networks, three techniques are investigated to avoid potential collision among multiple contending relays. Both analysis and simulation results demonstrate that significant improvement in terms of throughput and packet delivery ratio can be achieved by the proposed cooperative protocol.     

Cooperative communications with multilevel/AES-SD4-CPFSK in wireless sensor networks

In this paper, a new joint multilevel data encryption and channel coding mechanism is proposed, which is called ??multilevel/advanced encryption standard?Csystematic distance 4?Ccontinuous phase frequency shift keying?? (ML/AES-SD4-CPFSK). In the proposed scheme, we have not only taken advantage of spatial diversity gains but also optimally allocated energy and bandwidth resources among sensor nodes as well as providing high level of security and error protection for cooperative communications in wireless sensor networks. Relay protocols of cooperative communications, such as amplify-and-forward and decode-and-forward with/without adversary nodes, have been studied for 4CPFSK, 8CPFSK, and 16CPFSK of ML/AES-SD4-CPFSK. We have evaluated the error performances of multilevel AES for data encryption, multilevel SD-4 for channel coding, and various CPFSK types for modulation utilizing cooperative communications in wireless sensor networks. According to computer simulation results, significant diversity gain and coding gain have been achieved. As an example, bit error rate (BER) performance of 10^?5 value has been obtained at a signal-to-noise ratio (SNR) of ?6?dB for SD-4-CPFSK scheme in a compared related journal paper, whereas in our proposed system, we have reached the same BER value at a SNR of ?23?dB with amplify-and-forward with direct path signal protocol in 16-level AES, two-level SD-4 coded 16CPFSK, and at the same time, we have reached the same BER value at a SNR of ?22?dB with amplify-and-forward without direct path signal protocol in 16-level AES, two-level SD-4 coded 16CPFSK.     

A cross-layer protocol for exploiting cooperative diversity in multi-hop wireless ad hoc networks

Cooperative communication has emerged to reap the benefits of spatial diversity. To fully exploit cooperative diversity, we propose a medium access control and routing enabled cross-layer cooperative transmission (MACR-CCT) protocol for improving the performance in multi-hop wireless ad hoc networks (MWAN). Different from previous cooperative protocols that determine a receiver in one hop according to a non-cooperative routing protocol first and then select a cooperative relay, MACR-CCT selects the cooperative relay together with the receiver in one hop to exploit fully cooperative diversity, so that the receiver is selected for higher cooperative gain and closer distance to destination, and the relay is selected to achieve the better throughput performance while considering transmission error. Furthermore, considering that there are multiple source–destination pairs in MWAN, MACR-CCT takes interference mitigation into account to further improve network throughput when selecting the cooperative relay. Besides, we propose a theoretical model to analyze the throughput performance. Finally, we take advantage of simulation results to validate the effectiveness of our analytical model and show that our proposed MACR-CCT protocol can significantly outperform existing packet transmission mechanisms in terms of throughput and delay under the multi-hop multi-flow network scenario.     

无线中远程通信系统设计

针对传统中远距离通信系统的精度不高、传输数据不稳定、实时性差等缺点,文中提出了一种基于STM32单片机和RS485总线网络的无线中远程通信系统的方案。STM32低功耗、高性能,且接口丰富,适合便携式通信领域。利用STM32的标准通信接口实现了基于MODBUS协议的RS485总线和NRF24L01无线接收芯片的无线远程通信系统设计。经多次试验数据分析,系统传输出错率约为0.015,且系统的可靠性、稳定性均得到了大幅提升。     

Error modeling schemes for fading channels in wireless communications: A survey

Network system designers need to understand the error performance of wireless mobile channels in order to improve the quality of communications by deploying better modulation and coding schemes, and better network architectures. It is also desirable to have an accurate and thoroughly reproducible error model, which would allow network designers to evaluate a protocol or algorithm and its variations in a controlled and repeatable way. However, the physical properties of radio propagation, and the diversities of error environments in a wireless medium, lead to complexity in modeling the error performance of wireless channels. This article surveys the error modeling methods of fading channels in wireless communications, and provides a novel user-requirement (researchers and designers) based approach to classify the existing wireless error models.     

Cooperative MAC Design in Multi-Hop Wireless Networks—Part II: When Source and Destination are Two-Hops Away from Each Other

Ubiquitous and pervasive computing and networking are envisaged as part of the future 5G wireless communication landscape where devices which are multi-hops away from each other are connected in a cooperative way. In this paper, we investigate a challenging case in cooperative communications where source and destination are two-hops away from each other. From the perspective of MAC design, we propose a novel MAC protocol which enables two-hop cooperative communications by involving one or more one-hop neighbors of both source and destination as the relays for cooperative communication. To do so, a concept referred to as Multiple Relay Points (MRPs) has been introduced and the MRPs are selected by jointly considering the link quality of both hops. In addition to employing a static scheme which always uses a fixed number of relays for cooperative communication, we have also proposed an adaptive scheme which can optimally adjust the number of relays flexibly according to channel conditions. Through performance evaluation and comparison with the original IEEE 802.11 based scheme, we demonstrate that more reliable communications, reduced transmission power and significant throughput improvement can be achieved by using our two-hop cooperative MAC protocol, especially when operated in the adaptive mode.     

一种基于GPRS无线通信的远程I/O控制终端实现

GPRS无线通信已经广泛地运用于现实生活中。针对GPRS无线通信远程终端I/O口控制问题,提出了一个从硬件设计到软件控制的整体方案。在该方案中,完成了GPRS模块GTM900的硬件连接设计和软件驱动,规范了GPRS模块与LPC2214处理器之间串口通信的MODBUS协议标准格式,实现了GPRS无线通信。实验结果证明,所提出来的方案成本低,且稳定可靠。     

Performance of amplify-and-forward cooperative networks with differential unitary space time coding

In wireless communications, multi-input multi-output technology has been appreciated for its high transmission rate and diversity gain. These can also be exploited in cooperative networks by using network nodes as virtual antenna arrays. In this paper, we analyze the performance of cooperative networks with differential unitary space-time modulation under high signal-to-noise ratio. Relaying protocol is based on amplify-and-forward. The effect of relay location and energy allocation as well as the comparison with a conventional cooperative network is also addressed.     

Cooperative network implementation using open-source platforms

Cooperative networking, by leveraging the broadcast nature of the wireless channel, significantly improves system performance and constitutes a promising technology for next-generation wireless networks. Although there is a large body of literature on cooperative communications, most of the work is limited to theoretical or simulation studies. To impact the next generation of wireless technologies and standards, it is essential to demonstrate that cooperative techniques indeed work in practice. This article describes two programmable cooperative communication testbeds built at Polytechnic Institute of NYU to achieve this goal. The testbeds are based on opensource platforms and enable implementation of cooperative networking protocols in both the physical and the medium access control layer. Extensive experiments carried out using the testbeds suggest not only that cooperative communication techniques can be integrated into current wireless technologies, but also that significant benefits of cooperation can be observed in terms of network throughput, delay, and video quality in real applications.     

Dynamic framework with adaptive contention window and multipath routing for video-streaming services over mobile ad hoc networks

The number of portable electronic devices capable of maintaining wireless communications increases day by day. Such mobile nodes may easily self-configure to form a Mobile Ad Hoc Network (MANET) without the help of any established infrastructure. As the number of mobile devices grows, the demand of multimedia services such as video-streaming from these networks is foreseen to increase as well. This paper presents a proposal which seeks to improve the experience of the end users in such environment. The proposal is called dCW-MMDSR (dynamic Contention Window-Multipath Multimedia Dynamic Source Routing), a cross-layer multipath routing protocol which includes techniques to achieve a dynamic assignment of the Contention Window of the IEEE 802.11e MAC level. In addition, it includes multipath routing suitable for layered coded video to improve the performance of the service. The operation is simple and suitable for low capacity wireless devices. Simulations show the benefits under different scenarios.     

CoopMAC: A Cooperative MAC for Wireless LANs

Due to the broadcast nature of wireless signals, a wireless transmission intended for a particular destination station can be overheard by other neighboring stations. A focus of recent research activities in cooperative communications is to achieve spatial diversity gains by requiring these neighboring stations to retransmit the overheard information to the final destination. In this paper we demonstrate that such cooperation among stations in a wireless LAN (WLAN) can achieve both higher throughput and lower interference. We present the design for a medium access control protocol called CoopMAC, in which high data rate stations assist low data rate stations in their transmission by forwarding their traffic. In our proposed protocol, using the overheard transmissions, each low data rate node maintains a table, called a CoopTable, of potential helper nodes that can assist in its transmissions. During transmission, each low data rate node selects either direct transmission or transmission through a helper node in order to minimize the total transmission time. Using analysis, simulation and testbed experimentation, we quantify the increase in the total network throughput, and the reduction in delay, if such cooperative transmissions are utilized. The CoopMAC protocol is simple and backward compatible with the legacy 802.11 system. In this paper, we also demonstrate a reduction in the signal-to-interference ratio in a dense deployment of 802.11 access points, which in some cases is a more important consequence of cooperation     

Real-time mixed-traffic wireless networks

In this paper we introduce a new protocol, prioritized carrier sense multiple access with collision avoidance, for real-time wireless local area networking. Wireless networks increasingly will be called upon to carry mixed traffic, some portion of which will be devoted to real-time control and monitoring. Our protocol, based upon the IEEE 802.11 wireless standard, mixes real-time traffic with standard multimedia data in a way which assures loop stability. Scheduling the real-time traffic is the primary issue considered. Under our framework, we propose and validate several new algorithms for dynamically scheduling the traffic of wireless networked control systems: constant penalty, estimated error order and lag first-order schemes. All algorithms are compared via simulation and the results show that dynamic scheduling algorithms achieve better system performance on average than static scheduling algorithms like fixed-order polling. The results of a real experiment involving two dryer plants and three IEEE 802.11 nodes are reported with static scheduling employed as it lower bounds the closed-loop behavior     

Dynamic cooperative media access control for wireless networks

Cooperative communications can obtain spatial diversity, high channel capacity, and reliable transmission without multiple antennas, and thus, it has become a hot topic in recent years. Different from existing research, this paper pays attention on cooperative media access control (MAC) mechanism, which considers both physical gain and MAC overhead caused by cooperation. To this end, a dynamic cooperative MAC mechanism for wireless networks, called DCMAC, is proposed. DCMAC can obtain the useful channel state information through broadcasting characteristic of wireless channel, choose the suitable helpers to relay data with our proposed helpers selection algorithm, and reserve wireless channel efficiently and dynamically. Numerical results show the effectiveness of DCMAC to improve the system performance.     

A New Air Interface Concept for Wireless Multimedia Communications beyond the 3rd Generation

This paper presents a new air interface concept for wireless multimedia communications beyond the 3rd generation. The proposed air interface uses the same physical layer as that ofETSI HiperLAN/2 and IEEE 802.11a supporting transmission rate up to 54 Mb/sto form a W-CHAMB (Wireless CHannel-oriented Ad-hoc Multihop Broadband)network. Unlike HiperLAN/2, that is based on a central control, W-CHAMB is a self-organizing network without any central control. The responsibilities of organizing andcontrolling of W-CHAMB are fully distributed among wireless stations themselves.A channel-oriented MAC protocol that is based on the dynamic channel reservation (DCR) is proposed for W-CHAMB.Energy signals (E-signals) are used to realize distributed access priorities of wireless stations, to solve the hidden station problemand to achieve a MAC level acknowledgment (ACK) for a fast ARQ.The multihop traffic performance of IEEE 802.11a and W-CHAMB is intensively evaluated stochastically based on a prototypical implementation of the protocols. The superiority of the multihop traffic performance withW-CHAMB can be seen in comparison withIEEE 802.11a.     

COOPERATIVE ARQ PROTOCOL FOR CORRELATED WIRELESS CHANNELS

A novel Automatic repeat ReQuest （ARQ） protocol called cooperative ARQ is presented in this letter, where a relay terminal is requested to retransmit an erroneously received packet, instead of the source terminal. The data link layer Packet Error Rate （PER） performance of cooperative ARQ is derived in correlated wireless channel. The results show that even though the relay-destination channel is worse than the sourcedestination channel, the new protocol outperforms the traditional one as long as the average SNR of the relaydestination channel is better than a certain threshold. It is also demonstrated that a second order diversity gain can be achieved with the cooperative ARQ protocol.     

非对称协作分集通信中网络编码的应用

该文提出了网络编码在非对称三点协作传输系统中的应用。通过协作分集技术和网络编码技术的联合运用,不但可得到无线通信传输系统的分集增益,也可得到系统的编码增益。该文设计的方案,充分考虑无线通信环境的差异性,利用非对称调制方式,在保证较差通信环境中取得通信可靠性的同时,在较优链路采取较高速率进行传输,利用较优链路传输更多的信息,实现系统资源的充分利用。在方案的具体实现中,通过在中继链路的中继节点加入已知信息实现网络编码,使得系统的译码性能得到增加。仿真结果表明,将网络编码技术应用于非对称协作分集通信中,相对比非协作传输方案可增加分集增益,降低系统的误比特率。跟传统对称传输系统相比,可充分利用系统资源,提升了系统传输容量。     

Dynamic multiuser resource allocation and adaptation for wireless systems

Driven by the increasing popularity of wireless broadband services, future wireless systems will witness a rapid growth of high-data-rate applications with very diverse quality of service requirements. To support such applications under limited radio resources and harsh wireless channel conditions, dynamic resource allocation, which achieves both higher system spectral efficiency and better QoS, has been identified as one of the most promising techniques. In particular, jointly optimizing resource allocation across adjacent and even nonadjacent layers of the protocol stack leads to dramatic improvement in overall system performance. In this article we provide an overview of recent research on dynamic resource allocation, especially for MIMO and OFDM systems. Recent work and open issues on cross-layer resource allocation and adaptation are also discussed. Through this article, we wish to show that dynamic resource allocation will become a key feature in future wireless communications systems as the subscriber population and service demands continue to expand.     

基于EPON MAC层协议的无线接入研究

光通信与无线通信的融合实现宽带无线接入是将来网络接入最具竞争优势的解决方案之一。为了能应用PON结构的技术优势和实现基于PON的无线接入,提出在EPON MAC层中适当增加WiFi无线接入控制有关的协议帧的技术方案,实现了EPON的宽带无线接入。建立基于该方案的网络模型。通过仿真实验,表明适当修改EPON MAC层协议,可实现EPON与WiFi的无线接入。