双网卡多信道无线MAC协议

多收发器多信道技术能够有效提高无线多跳网络的带宽和吞吐量,成为学术界的研究热点。多收发器多信 道MAC协议研究主要涉及信道资源的分配与管理问题。在现有多信道MAC协议的研究基础上,提出一种基于 IEEE802. 11标准W iFi网卡的双收发器多信道MAC协议—DIM(Dual-Interface Management)。协议采用信道冲 突模型来分配信道资源,以优化网络的信道分布;同时,DIM协议在较少的硬件配置下,充分利用IEEE802. 11标准提 供的信道资源,提高了信道利用率。仿真实验表明,DIM协议具有较大的网络吞吐量和较小的分组传输延迟。     

WLAN Mesh网络多信道速率自适应MAC协议

针对多种传输速率的链路共存于同一信道时引发的性能瓶颈,以及单接口多信道网络中接收端忙的问题,在DCF协议的框架内提出一种适用于WLAN Mesh网络的分布式多信道速率自适应媒体控制接入(MAC)协议。该协议允许发送节点的邻居节点通过协作应答的方式告知相应接收节点所处信道,接收节点根据当前信道质量合理选择传输速率和传输信道反馈给发送节点。通过上述机制,将不同传输速率的链路分配在不同的信道上。仿真结果证明,该协议能避免不同传输速率链路之间的相互干扰,解决接收端忙问题。与现有典型多信道速率自适应MAC协议相比,能有效提高网络的总吞吐量。     

一种面向用电信息采集系统的WSNs多信道MAC协议

由于无线传感器网络（WSNs）单信道介质访问控制（MAC）协议无法满足用电信息采集系统的数据量大和并发性强的特点,提出了一种面向分簇网络的多信道MAC协议.网络簇间通信采用多信道并行传输方式,簇内通信采用基于信道质量实时评估的自适应信道切换机制.基于OMNeT＋＋的仿真结果表明：与单信道MAC协议相比,该MAC协议可以有效提高网络吞吐量和抗干扰能力.     

HM-MAC:一种支持广播的多信道传感器网络MAC协议

针对单Radio多信道MAC协议需要全网时间同步、占用大量正交信道、多信道隐终端较多以及单跳多信道广播数据大量丢失等问题,提出了一种基于竞争的多信道MAC协议--HM-MAC.该协议无需全网时间同步,通过动态预约技术降低了正交信道占用量,利用握手机制减少了多信道隐终端数目,同时,HM-MAC采用基于概率的广播发送者协调机制,减少了广播数据丢失,提高了广播效率.在理论上分析了所用信道数目、多信道隐终端数目以及广播效率等性能参数.实验结果表明:HM-MAC可以有效地解决多信道隐终端数目较多的问题,显著地提高了广播效率和网络吞吐量.     

一种应用于分布式网络的新型私有多信道UWB MAC协议设计

目前,单信道MAC协议在网络负载较重时的冲突和退避,造成信道带宽浪费而使得协议效率不高.本文主要针对UWB应用在无线个域网络中的特定场景,提出了一种新的应用于分布式网络的私有多信道UWB MAC协议,既可以解决隐藏终端和暴露终端问题,又可以有效地分配信道资源,提高网络性能.     

一种适用于Ad Hoc网络的多信道能量高效MAC协议

对多信道条件下MAC协议功率控制机制进行了分析,提出一种能够根据各个接收节点的通信状况,动态地调整数据信道上数据帧的传输功率和控制信道上CTS帧的发送功率的多信道Ad Hoc网络能量高效的MAC协议(MPEMAC).仿真表明,该协议有效的节省了节点能耗,延长了网络节点的生存时间,同时还能够增大空间信道的利用率,从而进一步提高网络的平均吞吐量.     

面向多跳无线网络的无冲突MAC协议

多跳无线网络中隐藏节点导致节点之间的冲突频繁、数据重传率高、网络吞吐量下降.而802.11 DCF 中的RTS/CTS(ready-to-send/clear-to-send)机制不能有效地防止隐藏节点,特别是随着网络中节点通信速率的提高,由 于节点的信噪比要求也相应提高,接收节点受到更大范围内隐藏节点的干涉,RTS/CTS 机制防止隐藏节点的效率急剧降低.首先,在考虑网络积累干涉以及环境噪音的情况下分析了多跳无线网络中的隐藏节点问题.然后,提出一种双信道无冲突MAC(media access control)协议DCCFMA(double channel collision free media access).DCCFMA 协议采用双信道结构,接收节点根据数据信道中发送节点的信号强度动态调节控制信道的发射功率,以完全覆盖接收节点周围所有的隐藏节点,保证接收节点在接收过程中不受干涉.DCCFMA 协议能够有效地解决多跳无线网络中的隐藏节点问题.仿真结果表明,与802.11DCF 相比,DCCFMA 机制下的平均网络吞吐量增加了24%.     

基于时分复用的车载自组织网多信道MAC协议

为解决车载自组织网络负载较重时控制信道拥塞和IEEE1609.4标准中信道利用率低的问题,提出一种使用时分复用机制的VANET多信道MAC协议。协议采用节点分时段接入控制信道的机制来降低冲突概率,规定每个节点使用两部收发机来避免数据信道空闲;使用一个优化模型确定退避过程参数,以最大化饱和吞吐量。仿真结果表明该协议具备优良的吞吐量性能,能给出较低的,稳定的安全信息时延。     

基于接收方信道质量的Ad Hoc网络多信道MAC协议

在分析当前Ad Hoc网络多信道MAC协议的基础上,提出了一个衡量信道质量的度量参数CQ（Channel Quality）作为信道选择的依据。并提出了一个基于接收方信道质量的多信道MAC协议MMCQ（Multi-channel MAC protocol with Channel Quality of receiver）,以解决多信道MAC协议常见的控制信道瓶颈和信道分配公平性问题。仿真表明：该协议在降低控制信道开销的前提下,能显著增加网络的平均吞吐量,并降低端到端平均时延。     

认知无线电网络双天线多信道MAC协议

在认知无线电网络中,媒体接入控制(MAC)协议的主要功能包括信道感知、选择和接入控制,其中感知时间和传输时间的长度对网络的性能有着重要的影响。在动态无线网络环境下,如何合理分配感知时间和传输时间是个挑战性问题。提出了一种双天线多信道分布式认知无线电MAC（TM-MAC）协议,不需要在传输之前对信道进行感知。节点可以在其它节点传输数据的同时对频谱资源进行检测,然后利用空闲的频谱资源通信。建立了数学模型分析在饱和网络状况下MAC协议的吞吐量。仿真分析表明TM-MAC协议能够有效提高网络的吞吐量。     

An adaptive random access strategy for multi-channel relaying networks

In this paper, an adaptive random access strategy is presented for multi-channel relaying networks to address the issue of random access of the non-real-time (NRT) services. In the proposed scheme, NRT services access the base station (BS) by first accessing the nearest relay node (RN). When collision occurs, for the sake of fast and efficient access, the user will begin a frequency domain backoff rather than randomly retry in time domain. A remarkable feature of this scheme is that the RN will adaptively determine the maximum allowed frequency backoff window at each access period. This is achieved according to the new arrival rate as well as the number of available access channels. Moreover, to alleviate the interference caused by sub-channel reuse among RNs, a fractional frequency reuse scheme is also considered. The analysis and numerical results demonstrate that our scheme achieves higher throughput, lower collision probability and lower access delay than conventional slotted Aloha as well as the scheme without frequency backoff window adaptation.     

超密集网络中子信道和功率分配研究

超密集网络中,严重的小区间干扰制约了终端用户的数据速率,针对该问题,提出一种基于簇优先级的资源分配方案。该方案分为3个步骤:首先,采用基于图论的染色算法为毫微微接入点(Femtocell Access Points,FAPs)分簇;然后,以簇内每个毫微微用户(Femtocell User Equipments,FUEs)的待发送数据量、排队等待时延以及受干扰强度等作为优先级,计算每个簇的优先级,高优先级的簇可最先获得信道增益好的子信道;最后,利用卡罗需-库恩-塔克(Karush-Kuhn-Tucker,KKT)条件和注水算法为FUEs分配功率。仿真实验表明该方案能够有效地减小Femtocell间的干扰,并能够极大地满足用户的需求,同时提升系统的吞吐量和频谱效率。     

Run-time optimization of heterogeneous media access in a multimediaserver

Discrete media (DM) data throughput is vital to systems that need to support the heterogeneity and variety of data found in interactive hypermedia and digital library applications. Therefore, a multimedia server's ability in delivering a high DM data throughput without degrading its CM data throughput deserves more attention. In this paper, we address this issue by optimizing the use of disk bandwidth spent on CM service at run-time and redirecting the saved bandwidth to service DM requests. Based on a new cost model of disk access incurred in CM service, we formulate strategies to control the size of each disk read at run time. These strategies improve the efficiency of each disk access and improve the DM data throughput of a multimedia server, without jeopardizing the CM throughput. Through experimental evaluations, the improvements achieved are demonstrated. Furthermore, efficient control of the allocation of disk bandwidth between DM and CM services over a wide range is also demonstrated     

同步令牌通信方式及其扩展应用

本文提出一种新的网络访问方式。它引入了同步时钟和令牌链，使得各点可共享一条通信数据线而访问控制电路却简单到仅用几个Ｄ触发器即可实现。它具有传统令牌方式所没有的一些优点。在通信量较少，速度要求不高的场合，其效果很好。文中讨论的一种应用方式。     

Using SDRAM Memories for High-Performance Accesses to Two-Dimensional Matrices Without Transpose

The data throughput of SDRAMs is significantly reduced by the control overhead required for access or transposition of large two-dimensional data matrices stored in SDRAM memories. In this paper, a new address mapping scheme is introduced, taking advantage of multiple banks and burst capabilities of modern SDRAMs. In this way, the data throughput is maximized when reading or writing rows or columns of a two-dimensional data matrix. Other address mapping strategies minimize the total number of SDRAM page-opens while traversing the two-dimensional index-space in row or column direction. In order to achieve a higher data throughput, the new approach uses an alternative bank interleaving method to hide additional wait cycles. In this way, the number of data bus wait cycles do not depend on the overall number of page-opens directly any more. It is shown, that the data bus utilization can be increased significantly. In particular, the new mapping strategy is optimized for access of parallel samples, distributed among a number of SDRAM chips. Therefore, double buffering can be omitted. As a special operation, 2D-FFT processing for radar applications is considered. Depending on SDRAM parameters and dimensions, a continuous bandwidth utilization of 96–98 % is achieved for accesses in both matrix dimensions, including all page-opens and refresh operations.     

OFDMA中继系统中基于速率约束的资源调度算法

针对无线资源调度算法中系统吞吐率与用户公平性之间的矛盾,研究了OFDMA多用户多中继系统中的比例公平调度算法,并提出了基于速率约束的资源调度方案,该方案充分考虑不同用户对传输速率的最小约束,通过给不能满足速率要求的用户增加优先权,使其优先分配子信道,保证了用户的速率QoS要求。仿真结果表明,该方案在满足系统吞吐率的同时能更好地保证用户的公平性。     

Performance analysis of trigger frame in enhanced UL and DL MU MIMO transmissions

In an Internet-of-Things (IoT) environment, congestion and scarcity problems may occur because many mobile stations (STAs) access wireless networks simultaneously. The IEEE 802.11ax/802.11be standards for large-scale wireless communications have defined a trigger frame (TF) to control multiple STAs. During resource allocation, the downlink (DL) transmission is divided in a control period from the access point (AP) to multiple STAs. The resource allocation (RA) is then assigned to an uplink (UL) transmission by a TF and a DL period from the AP to STAs. However, because the DL transmission should be considered separately in terms of the control and DL periods, it is necessary to analyze the DL transmission. We propose a scheduled MU transmission (SMT) algorithm for enhanced UL and DL MU MIMO transmissions. In this study, we analyze and systematically model medium access control (MAC) performance when the DL transmission is divided in the control and data periods when the UL coexists with the DL data transmission. To achieve this, we mathematically analyze the time-efficient throughput, estimate the transmission and collision probabilities for wireless local area network (WLAN) STAs, and generalize the transmission interval. In addition, we propose an access category (AC) for the TF that is defined in the DL transmission. All data transmissions are defined as the ACs for basic channel access, but the AC is not defined for the TF. Therefore, we clarify the transmission by defining the AC of the TF to control the UL transmissions of various STAs. Evaluation results demonstrate that the SMT algorithm can improve the MAC throughput by up to 70% – 87% compared to UL and DL MU MIMO transmissions.

     

Characterizing Concurrency Control Performance for the PIOUS Parallel File System

Parallel file systems employ data declustering to increase I/O throughput. However, because a single read or write operation can generate data accesses on multiple independent storage devices, a concurrency control mechanism must be employed to retain familiar file access semantics. Concurrency control negates some of the performance benefits of data declustering by introducing additional file access overhead. This paper examines the performance characteristics of the transaction-based concurrency control mechanism implemented in the PIOUS parallel file system. Results demonstrate that linearizability of file access operations is provided without loss of scalability or stability.     

一种基于移动自组网的联合检测MAC协议性能分析

在ad hoc移动自组网中,隐藏终端和暴露终端问题严重影响着MAC层的网络吞吐量性能。为了更好的解决隐藏／暴露终端问题,文献[3,4]提出了一种信道接入方法,即联合检测法。论文对此算法进行了改进,对RTS／CTS控制分组采用了载波侦听／冲突检测（CSMA／CD）策略,而对数据分组采用了基于发射端的码分配法。通过理论分析和仿真,表明提出的信道接入策略可获得较大吞吐量增益。     

An energy-efficient,transport-controlled MAC protocol for wireless sensor networks

In wireless sensor networks (WSNs), one major cause of wasted energy is that the wireless network interface is always on to accept possible traffic. Many medium access control (MAC) protocols therefore adopted a periodic listen-and-sleep scheme to save energy, at sacrifice of end-to-end latency and throughput. Another cause is packet dropping due to network congestion, necessitating a lightweight transport protocol for WSNs. In this paper, we suggest a transport-controlled MAC protocol (TC-MAC) that combines the transport protocol into the MAC protocol with the aims of achieving high performance as well as energy efficiency in multi-hop forwarding. Although TC-MAC also works through a periodic listen-and-sleep scheme, it lowers end-to-end latency by reserving data forwarding schedules across multi-hop nodes during the listen period and by forwarding data during the sleep period, all while increasing throughput by piggybacking the subsequent data forwarding schedule on current data transmissions and forwarding data consecutively. In addition, TC-MAC gives a fairness-aware lightweight transport control mechanism based on benefits of using the MAC-layer information. The results show that TC-MAC performs as well as an 802.11-like MAC in end-to-end latency and throughput, and is more efficient than S-MAC in energy consumption, with the additional advantage of supporting fairness-aware congestion control.