LTE网络端MAC状态研究与设计

针对目前LTE系统网络端MAC子层状态划分的不明确性,提出了在LTE系统通信过程中网络端MAC层状态划分的方案.该方案将网络端MAC层划分为4个状态,设计了状态转移过程及随机接入流程,由此实现了MAC状态转移方案.通过TTCN与SDL协仿真的测试,证明了状态转移及随机接入流程设计的正确性,为LTE系统的通信实现提供有效方案.     

A Novel Medium Access Control for Ad hoc Networks Based on OFDM System

1IntroductionIn Ad hoc networks , the nodes share the wirelesschannel under the control of media access control proto-col . Currently,there are two types of MAC protocolsproposedfor Ad hoc networks . The first is hand-shak-ing protocol such as IEEE 802 .11 MAC protocol[1 ~4]and MACAW[5], which controls the access procedureby exchanging the control packets among the activenodes . The secondis busy-tone protocol that introducesadditional busy tone signal to control the medium ac-cess . S…     

基于OFDM系统的随机信道接入方案

双忙音多址信道接入(DBTMA)协议是一种信道利用率较高的无线局域网信道随机接入控制方案。但是, 该协议的硬件实现复杂度较高。该文在对DBTMA协议进行简单修改的基础上,结合节能意识多址接入(PAMAS) 协议提出了一种基于OFDM系统的DBTMA信道接入系统,并对此系统做了简要分析。分析结果显示,该文提出的随机信道接入系统的性能良好且实现方式简单。     

Adaptive random channel allocation scheme in HIPERLAN type 2

The MAC protocol of HIPERLAN type 2 is based on TDMA/TDD and resources in one MAC frame can be allocated dynamically by the access point (AP). We propose an adaptive random channel (RCH) allocation scheme for HIPERLAN type 2. The AP scheduler controls the number of RCHs in one MAC frame according to the transmission results of the previous MAC frame. The simulation results show that the proposed scheme achieves higher efficiency of resource and lower access delay than fixed RCHs allocation schemes     

Multiple feedback algorithm for RFID MAC protocols

This letter introduces a new tree-based anti-collision scheme using multiple feedbacks for uplink tag random access in a single-cell scenario. We examine MAC efficiency improvements that result from the proposed scheme in terms of uplink (UL) throughput for emerging radio frequency identification (RFID) networks, and compare it with the conventional tree based RFID MAC in ISO 18000-6 Type B standard.     

An OFDM-TDMA/SA MAC Protocol with QoS Constraints for Broadband Wireless LANs

Orthogonal frequency division multiplexing (OFDM) is an important technique to support high speed transmission of broadband traffic in wireless networks, especially broadband wireless local area networks (LANs). Based on OFDM, a new multiple access scheme, called OFDM-TDMA with subcarrier allocation (OFDM-TDMA/SA), is proposed in this paper. It provides more flexibility in resource allocation than other multiple access schemes such as OFDM-TDMA, OFDM-frequency division multiple access (OFDM-FDMA), and orthogonal frequency division multiple access (OFDMA). With OFDM-TDMA/SA, a medium access control (MAC) is designed for broadband wireless LANs. It optimizes bit allocation in subcarriers so that maximum bits are transmitted in each OFDM symbol under a frequency selective fading environment. The OFDM-TDMA/SA MAC protocol also supports three classes of traffic such as guaranteed, controlled-load, and best effort services. Based on the optimum subcarrier bit-allocation algorithm and considering heterogeneous QoS constraints of multimedia traffic, a hierarchical scheduling scheme is proposed to determine the subcarriers and time slots in which a mobile terminal can transmit packets. In such a way, the OFDM-TDMA/SA MAC protocol significantly increases system throughput in a frequency selective fading environment and guarantees QoS of multimedia traffic. Computer simulation is carried out to evaluate the performance of the OFDM-TDMA/SA MAC protocol. Results show that the new MAC protocol outperforms other MAC protocols for OFDM-based wireless LANs. This work was supported by the State of Georgia Yamacraw Project (E21-105).     

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。     

A distributed MAC scheme supporting voice services in mobile ad hoc networks

Future mobile ad hoc networks are expected to support voice traffic. The requirement for small delay and jitter of voice traffic poses a significant challenge for medium access control (MAC) in such networks. User mobility presents unique difficulties in this context due to the associated dynamic path attenuation. In this paper, a MAC scheme for mobile ad hoc networks supporting voice traffic is proposed. With the aid of a low‐power probe prior to DATA transmissions, resource reservation is achieved in a distributed manner, thus leading to small packet transmission delay and jitter. The proposed scheme can automatically adapt to dynamic path attenuation in a mobile environment. Statistical multiplexing of on/off voice traffic can also be achieved by partial resource reservation for off voice flows. Simulation results demonstrate the effectiveness of the proposed scheme. Copyright © 2009 John Wiley & Sons, Ltd.     

B3G/TDD系统中随机接入方案研究

提出了一种应用于B3G TDD系统的随机接入方案。该方案结合了媒体接入层的包调度和物理层的信号处理技术,可以有效地避免数据包的碰撞。分析比较和仿真表明,该方案较传统的时隙ALOHA随机接入方案在吞吐率和时延方面都有较大的改善。     

面向mMIMO系统的模式分割随机接入方案

为提升海量机器类通信（massive machine-type communication,m MTC）设备的随机接入（random access,RA）性能,提出一种面向大规模多输入多输出（massive multiple-input multiple-output,m MIMO）系统的模式分割随机接入（pattern division random access,PDRA）方案。该方案将导频竞争空间扩展到模式域,通过叠加同一ZC(Zadoff-Chu）根序列的L个不同循环移位序列,设计基于“图样叠加”的模式域导频,在不增加物理资源的前提下扩大导频集合。仿真结果表明,在不影响信道估计和数据检测性能的前提下,与传统RA方案相比,PDRA方案能够显著降低导频碰撞概率,提高接入成功率。     

A novel MAC protocol for IDMA‐based multi‐beam satellite communication systems

Considering the limitations of satellite communication systems and advantages of new emerging interleave‐division multiple access (IDMA) technology, IDMA is introduced into the satellite systems, providing a new solution for multiple access techniques of satellite systems. To further validate the IDMA into satellite systems, a novel medium access control (MAC) scheme is proposed. In the random access channel, the interleave‐division slotted ALOHA method is adopted to alleviate the collision of access requests. Furthermore, a novel minimum power allocation scheme based on signal‐to‐interference‐plus‐noise ratio (SINR) evolution is proposed to maximize the capacity of such an interference‐sensitive system. By virtue of SINR evolution, our proposed scheme can accurately estimate multi‐user detection efficiency with low computational cost and further reduce the transmitted power, illustrating the high power efficiency of IDMA. To further enhance the performance of the MAC protocol, an effective call admission control scheme considering the effect of power control error is designed and combined into our MAC protocol. Analysis and simulation results show that, by taking full advantage of the chip‐by‐chip multi‐user detection technique, the proposed IDMA MAC protocol achieves high throughput and low average packet delay simultaneously, with low onboard processing complexity in the multi‐beam satellite communication systems. Copyright © 2013 John Wiley & Sons, Ltd.     

卫星通信系统两步随机接入技术研究

为了实现卫星通信系统低延迟高可靠接入,研究了两步随机接入技术中的信道设计及接收端检测算法.针对卫星场景提出了一种两步随机接入信道设计方案,对两步随机接入信道中数据部分的信道结构以及前导和数据之间的映射方式进行了设计.针对传统最小均方串行干扰消除(Minimum Mean Squared Error-Successive Interference Cancellation,MMSE-SIC)算法中存在误差传播问题导致解码性能降低的问题,提出了一种多判决排序串行干扰消除(Multi-decision Ordered Successive Interference Cancellation,MD-OSIC)算法,以提升多用户发起接入时数据部分检测的可靠性.仿真结果验证了所设计信道及检测算法在典型卫星通信场景下应用的可行性.     

一种基于CoMP的随机接入方案

提出了一种新的基于协作多点传输和接收（CoMP）技术的多发随机接入流程,并根据 随机接入的目的和业务类型设计了接入优先级,在此基础上设计了一种新的随机接入方案, 对 不同类型的随机接入请求提供不同的接入机制,以保证边缘用户的接入性能和满足不同业务 的QoS需求。仿真结果表明,与LTE标准随机接入方案相比,该方案对系统整体接入性能略有 提高,且大大提高了边缘高优先级用户的接入性能。     

Effects of Ad Hoc MAC Layer Medium Access Mechanisms under TCP

Mobile computing is the way of the future, as evident by such initiatives as Bluetooth, Iceberg and HomeRF. However, for mobile computing to be successful, an obvious layer, the MAC layer, must be efficient in channel access and reservation. Therefore, in-depth understanding is needed of the wireless MAC layer if wireless computing is to takeoff. Many random access wireless MAC protocols have been proposed and even standardized. However, there has yet been an attempt to understand why certain designs are used and what makes certain protocols better than others. In this paper, we survey several popular, contemporary, wireless, random access MAC protocols and determine the effects behind the design choices of these protocols.     

Mitigating tail latency in IEEE 802.11–based networks

Delay sensitive applications are being actively introduced with the advent of 5G and vehicular communications, and such applications are very sensitive to tail latency. However, tail latency has not been seriously considered so far, especially in IEEE 802.11–based networks. Channel access is scheduled by random Contention Window (CW) values in IEEE 802.11–based networks, and the node with the larger CW waits longer, and it may even observe multiple transmissions from a single contending node, which results in a long latency tail. In this paper, we propose a new decentralized MAC called SynchMAC to mitigate this latency tail. In SynchMAC, every competing node transmits exactly one packet within a virtual time slot without a centralized controller. Using the proposed approach, the maximum channel access latency is bounded by T×2N, where T is the time required for transmitting a single packet (including Inter‐Frame Space and CW) and N is the number of competing nodes. To maximize the system throughput, the proposed scheme optimizes the value of T by considering the probability of successful transmission. Our simulation study shows that SynchMAC reduces the maximum access latency by up to 94% and 53% compared with the conventional IEEE 802.11 MAC and the comparative scheme, respectively, without degrading throughput performance. We also show that SynchMAC is easily extended to support weighted access.     

A Hybrid Collision Avoidance Scheme for Ad Hoc Networks

A novel hybrid collision avoidance scheme that combines both sender-initiated and receiver-initiated collision-avoidance handshake is proposed for multi-hop ad hoc networks. The new scheme is compatible with the popular IEEE 802.11 MAC protocol and involves only some additional queue management and book-keeping work. Simulations of both UDP- and TCP-based applications are conducted with the IEEE 802.11 MAC protocol, a measurement-based fair scheme and the new scheme. It is shown that the new scheme can alleviate the fairness problem with almost no degradation in throughput. More importantly, it is shown that without explicit information exchange among nodes, the fairness problem cannot be solved conclusively if reasonable throughput is to be maintained. Hence it calls for further work to integrate the new collision avoidance scheme with other schemes that approximate fair queueing and use more contention information in channel access to achieve some QoS assurances in ad hoc networks.     

一种新的视点间预测结构

多视点视频编码除应具有较高的编码效率外,还应该包括后向兼容性、时间随机访问和视点可分级性等,这些都主要取决于所采用的预测结构。目前所提供的多视点视频编码(Joint Multi-view Video Coding, JMVC)采用固定的视点间预测结构,难以适应复杂情况的多视点视频编码。该文综合考虑编码效率和用户随机访问等因素,根据多视点视频相关性分析自适应调整视点间预测结构,以获得较好的编码综合性能。试验结果表明,与JMVC相比,该文的方法在提高编码效率的同时,有较好的随机访问性能。     

Stability analysis of an adaptive packet access scheme for mobile communication systems with high propagation delays

In this paper, we investigate a packet access scheme that is able to support mixed traffics in the presence of high propagation delays. Referring to a Time‐Code Division Multiple Access air interface, we propose a Medium Access Control (MAC) protocol based on a random access scheme. A successful attempt grants the use of a slot‐code resource. This protocol is named Adaptive Time Code‐Packet Reservation Multiple Access (ATC‐PRMA), since the access parameters are changed, depending on the traffic load conditions, so as to fulfil Quality of Service requirements. Numerical examples are carried out for the Low Earth Orbit (LEO)‐Mobile Satellite System (MSS) scenario, but all these considerations could be applied to High‐Altitude Platform Stations (HAPSs) as well. In both cases, high propagation delays prevent an immediate feedback to users. An analytical approach is proposed to study the stability of our MAC scheme. Accordingly, we define a criterion for optimizing system performance. The predicted ATC‐PRMA behaviour is supported by simulation results. Finally, we show the performance improvement of ATC‐PRMA with respect to a MAC protocol not employing adaptive parameters. Copyright © 2003 John Wiley & Sons, Ltd.     

卫星物联网混合随机接入技术

在卫星物联网(IoT)场景中,随着终端数量不断增加,频谱资源日益紧张。传统的随机接入技术频谱利用率较低,使得传统随机接入协议不适用于未来卫星IoT的高并发业务需求。同时,卫星通信链路长,开放性强,难以保证特种终端信号的安全性。对此,本文提出一种适用于卫星IoT的混合随机接入方案。该方案引入重叠传输的容量提升与安全性优势,利用扩频码对瞬时功率谱密度的控制能力,构造功率域非正交接入条件,并通过接收端的迭代分离实现稳健接收。对本文所提方案的吞吐量性能进行闭式解推导分析与计算机仿真,结果表明,与传统的随机接入协议相比,所提方案可提高系统吞吐量。同时,相较于常用信号隐藏方法,所提方法利用常规接入数据包的功率优势,强化了波形隐藏效果,提升了特种信息接入的安全性。