基于TDMA的LoRa通信网络设计

针对LoRa通信技术具有长距离传输和抗干扰能力强但只支持半双工通信的特点,提出一种基于TDMA的通信组网方法。该方法通过划分信道和时隙可在同一个信道下容纳多个通信设备,在信道资源有限的情况下可充分利用信道。基于LoRa的UE设备以星型组网的方式接入基于LoRa的中心基站,中心基站可以控制接入的设备以及对信道时隙管理,加上适当的网关还可以接入互联网。为提高信道时隙的利用率以及手持UE人员的活动范围,采用随机接入中心基站的方法。根据该通信组网方式的特性,设计出对应的上下行通信协议和对UE添加唯一标号,这很好地解决了接入基站过程中的竞争冲突。实验测试表明基于TDMA的LoRa组网能随机接入中心基站扩大使用人员的活动范围,并提高信道利用率。     

Uniform leader election protocols for radio networks

A radio network is a distributed system with no central arbiter, consisting of n radio transceivers, henceforth referred to as stations. We assume that the stations are identical and cannot be distinguished by serial or manufacturing number. The leader election problem asks to designate one of the stations as leader. In this work, we focus on single-channel, single-hop radio networks. We assume that time is slotted and all transmissions occur at slot boundaries. In each time slot, the stations transmit on the channel with some probability until, eventually, one of the stations is declared leader. A leader election protocol is said to be uniform if, in each time slot, every station transmits with the same probability. In a seminal paper, Willard (1986) presented a uniform leader election protocol for single-channel single-hop radio stations terminating in log log n+o(log log n) expected time slots. It was open for more than 15 years whether Willard's protocol featured the same time performance with "high probability." One of our main contributions is to show that, unfortunately, this is not the case. Specifically, we prove that for every parameter f∈e^O(n), in order to ensure termination with probability exceeding 1-1/f, Willard's protocol must take log log n+Ω(√f) time slots. The highlight of this work is a novel uniform leader election protocol that terminates, with probability exceeding 1-1/f, in log log n+o(log log n)+O(log f) time slots. Finally, we provide simulation results that show that our leader election protocol outperforms Willard's protocol in practice     

Energy-efficient permutation routing in radio networks

A radio network (RN, for short) is a distributed system populated by small, hand-held commodity devices running on batteries. Since recharging batteries may not be possible while on mission, we are interested in designing protocols that are highly energy efficient. One of the most effective energy-saving strategies is to mandate that the stations go to sleep whenever they do not transmit or receive messages. It is well known that a station is expending power while its transceiver is active, that is, while transmitting or receiving a packet. It is perhaps surprising at first that a station is expending power even if it receives a packet that is not destined for it. Since, in single-hop radio networks, every station is within transmission range from every other station, the design of energy-efficient protocols is highly nontrivial. An instance of the permutation routing problem involves p stations of an RN, each storing n/p items. Each item has a unique destination which is the identity of the station to which the item must be routed. The goal is to route all the items to their destinations while expending as little energy as possible. Since, in the worst case, each item must be transmitted at least once, every permutation routing protocol must take n/k time slots. Similarly, each station must be awake for at least n/p time slots to transmit and/or receive packets. Our main contribution is to present an almost optimal energy-efficient permutation routing protocol for a k-channel, a p-station RN that routes n packets in at most (2d+2b+1)n/k+k time slots with no station being awake for more than (4d+7b-1)n/p time slots, where d=[(logp/k)/(logn/p)], b=[(log k)/(logn/p)] and k⩽√(p/2). Since, in most real-life situations, the number n of packets to route, the number p of stations in the RN, and the number k of channels available satisfy the relation k≪p≪n, it follows that d and b are very small     

Efficiency-driven selection of bandwidth request mechanism in broadband wireless access networks

To avoid collisions in WiMAX networks, the connections in Subscriber Stations (SSs) use a request–grant process to acquire transmission resources from the Base Station (BS). In accordance with the IEEE 802.16 standard, the request–grant process is accomplished using either a unicast polling method or a contention request method. In WiMAX systems, the number of bandwidth-request (BR) slots per frame is limited. Thus, to enhance the network performance, the BR slots must be used in the most efficient manner possible. In practical WiMAX systems, the offered network load varies over time, and thus the strict use of either the unicast polling method or the contention request method results in a poor utilization efficiency of the BR slots. Accordingly, the present study proposes a scheme designated as Efficiency-Driven Selection of Bandwidth Request (EDSBR), in which the request–grant mechanism is adjusted dynamically on a frame-by-frame basis in accordance with the network conditions. The performance of the proposed scheme is evaluated by simulations. The results show that EDSBR achieves a more efficient utilization of the BR slots than the unicast polling scheme or the contention request scheme, and therefore yields an improved network performance.     

On the performance of adaptive TDMA protocols in WDM passive star networks with fixed transmitters and tunable receivers

An adaptive time division multiple access (TDMA) protocol for WDM passive star networks using fixed transmitters and tunable receivers is presented. The proposed optical adaptive TDMA (OATDMA) protocol is capable of operating efficiently under bursty and correlated traffic. According to the proposed protocol, the stations which are granted permission to transmit at each time slot, are selected by taking into account the network feedback information. In this way, the number of idle slots is minimized and the network performance is significantly improved. Furthermore, although the traffic parameters are unknown and time-variable, the portion of the bandwidth assigned to each station is dynamically adapted to the station’s needs.     

SCPS: A self-configuring power-saving protocol for wireless ad hoc networks

SCPS is a novel self-configuring power-saving protocol for wireless one-hop ad hoc networks. According to IEEE 802.11 WLAN standard, a station may enter a special power-saving (PS) mode. SCPS allows all stations in the PS mode to adjust their wakeup schedules whenever a station enters or exits the PS mode. The adjustment can balance the number of wakeup stations in each beacon interval so that the contention for transmission medium and the collisions in transmission will be ameliorated, which results in more efficient energy usage. Simulation results show that SCPS successfully balances the number of stations that wake up in each beacon interval, increases the sleep ratio, and reduces the collision probability. The combined effect reduces total energy consumption.     

An energy-efficient permutation routing protocol for single-hop radio networks

A radio network (RN) is a distributed system where each station or node is a small hand-held commodity device called a station. Typically, each station has access to a few channels for transmitting and receiving messages. By RN(p, k), we denote a radio network with p stations, where each station has access to k channels. In a single-hop RN, every station is within the transmission range of every other station. Each station consumes power while transmitting or receiving a message, even when it receives a message that is not destined for it. It is extremely important that the stations consume power only when it is necessary since it is not possible to recharge batteries when the stations are on a mission. We are interested in designing an energy-efficient protocol for permutation routing, which is one of the most fundamental problems in any distributed system. An instance of the permutation routing problem involves p stations of an RN, each storing n/p items. Each item has a unique destination address which is the identity of the destination station to which the item should be sent. The goal is to route all the items to their destinations while consuming as little energy as possible. We show that the permutation routing problem of n packets on an RN(p, k) can be solved in 2n/k+(p/k)/sup 2/+p+2k/sup 2/ slots and each station needs to be awake for at most 6n/p+2p/k+8k slots. When k/spl Lt/p/spl Lt/n, our protocol is more efficient, both in terms of total number of slots and the number of slots each station is awake compared to a previously published protocol by Nakano et al. (2001).     

A wavelength division multiple access protocol for high-speed local area networks with a passive star topology

In this paper a multiple access protocol is proposed for a system consisting of many high-speed bursty traffic stations interconnected via an optical passive star coupler. Each station has access over a range of wavelengths. Time is divided intp fixed-sized slots. A station must reserve a wavelength first, then transmits the data on that wavelength. New stations can join the system anytime without any system reconfiguration. Broadcast and multicast traffic can also be easily supported. The performance of both the infinite and finite population cases has been modeled and analyzed. Numerical results show that low delay and high throughput (larger than the electronic speed of a single station) can be achieved. The analysis also shows that the best performance is obtained when the capacities of the reservation channels and the data channels are balanced.     

A CSMA/CD compatible MAC for real-time transmissions based on varying collision intervals

This paper suggests a CSMA/CD compatible MAC protocol for real-time transmissions in a shared Home or Small Office Local Area Network. The new MAC is based on the distributed assignment of special TAG numbers to the stations transmitting real-time traffic. These TAG numbers determine a Round Robin order of transmissions among the real-time stations. They also help in resolving collisions among real time stations by setting the length of the Jam signal, transmitted in case of a collision, to be a function of the TAG number. In a collision the station with the highest TAG number, and so with the longest Jam, is persisting with its Jam transmission for the longest until all the other stations defer. Thus, the collision terminates and the longest persisting station can transmit its packet successfully. The new protocol enables stations implementing the IEEE 802.3 MAC standard to transmit on the same network with stations implementing the new protocol. After introducing the protocol, we compute an upper bound on the access delay that the protocol guarantees and prove the correctness of the distributed TAG assignment procedure. Finally, we simulate the protocol in a network consisting stations implementing the new protocol together with stations implementing the standard IEEE 802.3 MAC. We show that the access delays of the stations transmitting real-time traffic are indeed bounded as predicted.     

A New Contention Resolution Procedure for HFC Access Networks and its Performance Evaluation

Bidirectional Cable TV networks using hybrid fiber coaxial (HFC) systems are good examples of broadcast environments where a contention resolution algorithm is needed in order to allocate the multiaccess medium among various customers. The medium access control (MAC) scheme, proposed by DAVIC/DVB, IEEE 802.14 and DOCSIS for the upstream channel of HFC access networks is based on a mixable contention-based/contentionless time slot assignment. Contention-less (CL) slots are assigned by the head-end (HE) to end stations according to a reservation scheme. Contention-based slots (CB) are randomly accessed by active terminals without any prelimanry allocation and so collisions may occur. To resolve contention the contention tree algorithm has been widely accepted by the DVB/DAVIC, IEEE 802.14 and DOCSIS standards for MAC because of higher throughput and lower access delay. In this paper we propose a simple modification to the existing protocol and analyze its performance. We propose to have one slot in the frame exclusively reserved for the new arrivals that wish to access the channel capacity using contention resolution and atleast one more slot reserved for resolving their contention if there was a contention in the arrival slot. This assumption simplifies the protocol to a queuing mechanism and we use the results of the queue to analyze the protocol. The queuing analysis method is used to determine the throughput of the channel and waiting times of the arbitrary customers. Furthermore, we present numerical results and compare that with simulations.     

DeviceNet现场总线中轮询协议的性能研究

基于DeviceNet协议生产者/消费者通信模型特点构建了其轮询通讯方式模型,轮询命令报文由主站广播至生产从站,轮询响应报文由生产从站通过主站周期地轮询每个生产从站广播至所有消费从站;文章采用Petri网的过程变迁TPN混合方法对DeviceNet总线协议进行了分析和研究,对其轮询通讯方式进行了模拟,讨论了响应时间、吞吐量等参数,分析了性能差异和响应快慢,根据文章的结论,现场总线的设计者可以很好的选择和设计满足自己需要的设计方案.     

Runtime optimization of IEEE 802.11 wireless LANs performance

IEEE 802.11 is the standard for wireless local area networks (WLANs) promoted by the Institute of Electrical and Electronics Engineers. Wireless technologies in the LAN environment are becoming increasingly important and the IEEE 802.11 is the most mature technology to date. Previous works have pointed out that the standard protocol can be very inefficient and that an appropriate tuning of its congestion control mechanism (i.e., the backoff algorithm) can drive the IEEE 802.11 protocol close to its optimal behavior. To perform this tuning, a station must have exact knowledge of the network contention level; unfortunately, in a real case, a station cannot have exact knowledge of the network contention level (i.e., number of active stations and length of the message transmitted on the channel), but it, at most, can estimate it. We present and evaluate a distributed mechanism for contention control in IEEE 802.11 wireless LANs. Our mechanism, named asymptotically optimal backoff (AOB), dynamically adapts the backoff window size to the current network contention level and guarantees that an IEEE 802.11 WLAN asymptotically achieves its optimal channel utilization. The AOB mechanism measures the network contention level by using two simple estimates: the slot utilization and the average size of transmitted frames. These estimates are simple and can be obtained by exploiting information that is already available in the standard protocol. AOB can be used to extend the standard 802.11 access mechanism without requiring any additional hardware. The performance of the IEEE 802.11 protocol, with and without the AOB mechanism, is investigated through simulation. Simulation results indicate that our mechanism is very effective, robust, and has traffic differentiation potentialities.     

Delay models for contention trees in closed populations

In this paper we consider some models for contention resolution in cable networks, in case the contention pertains to requests from a finite population of stations and is carried out by means of contention trees. More specifically, we study a number of variants of the standard machine repair model, that differ in the service order at the repair facility. Considered service orders are first come first served, random order of service, and gated random order of service. For these variants, we study the sojourn time at the repair facility. In the case of the free access protocol for contention trees, the first two moments of the access delay in contention are accurately represented by those of the sojourn time at the repair facility under random order of service. In the case of the blocked access protocol, gated random order of service is shown to be more appropriate.     

基于IEEE 802.11b无线网络的MAC协议改良冲突解决算法

研究基于介质访问控制协议(MAC)的分布式争用问题的主要焦点就是设计有效的具有高吞吐量性能的MAC协议。该文提出在无线局域网中基于MAC协议的有效争用方法,即改良的冲突解决算法(DCR)。该算法主要做了以下几方面的改良和创新:对所有现用网点主动的分配补偿时间,提高解决冲突的速度;当确定固定数量的连续空闲时间片被探测到时,对成功包传输的站点使用较小的争用窗口,以指数级速度减少补偿时间片和减少空闲时间片的平均数。该文提出的改良冲突解决算法提供了高吞吐量性能和在局域网中的低执行时间。     

Energy-efficient initialization protocols for single-hop radionetworks with no collision detection

A radio network (RN, for short) is a distributed system consisting of n radio stations. We assume that the stations are small, bulk-produced, hand-held devices running on batteries and cannot be distinguished by serial or manufacturing number. Since recharging batteries may not be possible while on mission, we are interested in designing protocols that are highly energy-efficient. The initialization problem is to assign each of the n stations in the RN a unique ID. The initialization problem is nontrivial since the stations are assumed to be indistinguishable. The problem is fundamental, since practically all communication protocols for RNs proceed under the assumption that the RN has been initialized in advance. The main contribution of this work is to propose energy-efficient randomized initialization protocols for single-hop RNs lacking collision detection capabilities. First, we show that if the number n of stations is known beforehand, the single-channel RN can be initialized by a protocol that terminates, with probability exceeding 1-¹/_n in O(n) time slots, with no station being awake for more than O(log log n) time slots. We then go on to address the multichannel case and show that if k, (k⩾1), channels are available, an n-station RN can be initialized, with probability exceeding 1-¹/_n, in O(ⁿ/_k+log n) time slots, with no station being awake for more than O(log log n) time slots     

Broadcasting in UDG radio networks with unknown topology

The paper considers broadcasting in radio networks, modeled as unit disk graphs (UDG). Such networks occur in wireless communication between sites (e.g., stations or sensors) situated in a terrain. Network stations are represented by points in the Euclidean plane, where a station is connected to all stations at distance at most 1 from it. A message transmitted by a station reaches all its neighbors, but a station hears a message (receives the message correctly) only if exactly one of its neighbors transmits at a given time step. One station of the network, called the source, has a message which has to be disseminated to all other stations. Stations are unaware of the network topology. Two broadcasting models are considered. In the conditional wake up model, the stations other than the source are initially idle and cannot transmit until they hear a message for the first time. In the spontaneous wake up model, all stations are awake (and may transmit messages) from the beginning. It turns out that broadcasting time depends on two parameters of the UDG network, namely, its diameter D and its granularity g, which is the inverse of the minimum distance between any two stations. We present a deterministic broadcasting algorithm which works in time O (D g) under the conditional wake up model and prove that broadcasting in this model cannot be accomplished by any deterministic algorithm in time better than ${\Omega (D \sqrt{g})}The paper considers broadcasting in radio networks, modeled as unit disk graphs (UDG). Such networks occur in wireless communication between sites (e.g., stations or sensors) situated in a terrain. Network stations are represented by points in the Euclidean plane, where a station is connected to all stations at distance at most 1 from it. A message transmitted by a station reaches all its neighbors, but a station hears a message (receives the message correctly) only if exactly one of its neighbors transmits at a given time step. One station of the network, called the source, has a message which has to be disseminated to all other stations. Stations are unaware of the network topology. Two broadcasting models are considered. In the conditional wake up model, the stations other than the source are initially idle and cannot transmit until they hear a message for the first time. In the spontaneous wake up model, all stations are awake (and may transmit messages) from the beginning. It turns out that broadcasting time depends on two parameters of the UDG network, namely, its diameter D and its granularity g, which is the inverse of the minimum distance between any two stations. We present a deterministic broadcasting algorithm which works in time O (D g) under the conditional wake up model and prove that broadcasting in this model cannot be accomplished by any deterministic algorithm in time better than W(D ?g){\Omega (D \sqrt{g})} . For the spontaneous wake up model, we design two deterministic broadcasting algorithms: the first works in time O (D + g ²) and the second in time O (D log g). While neither of these algorithms alone is optimal for all parameter values, we prove that the algorithm obtained by interleaving their steps, and thus working in time O ( min{ D + g², D logg}){ O \left( \min\left\{ D + g^2, D \log{g}\right\}\right) }, turns out to be optimal by establishing a matching lower bound.     

On optimizing backoff counter reservation and classifying stations for the IEEE 802.11 distributed wireless LANs

In this paper, we propose a novel contention-based protocol called backoff counter reservation and classifying stations for the IEEE 802.11 distributed coordination function (DCF). In the proposed scheme, each station has three states: idle, reserved, and contentious. A station is in the idle state if it has no frame ready to transmit. A station is in the reserved state if it has a frame ready to transmit and this frame's backoff counter has been successfully announced through the previous successfully transmitted frame so that other stations know this information. A station is in the contentious state if it has a frame ready to transmit, but this frame's backoff counter has not been successfully announced to other stations. All the stations in the idle state, the reserved state, and the contentious state form an idle group, a reserved group, and a contentious group, respectively. Two backoff schemes are proposed in the BCR-CS protocol based on the number of stations in the contentious group including the optimal pseudo-p-persistent scheme. The proposed schemes are compared with the DCF and the enhanced collision avoidance (ECA) scheme in the literature. Extensive simulations and some analytical analysts are carried out. Our results show that all proposed schemes outperform both the DCF and the ECA, and the BCR-CS with optimal pseudo-p-persistent scheme is the best scheme among the four schemes.     

Dynamic accommodation of the permission probability over the joint voice/data frame reservation multiple access

Some schemes are proposed for dynamic accommodation of the permission probability based on frame reservation multiple access protocol, a variant of PRMA, where the base station broadcasts the acknowledgements for all the slots in a frame which occurs at the end of the frame. One is by adjusting the permission probability with regard to the available slots, once in every frame. Another is to set the permission probability individually, based on the contending number of retrials for each active voice terminal. For the integration of voice and data users, to combine the above mentioned schemes, the speech packet dropping probability and mean data delay techniques are superior to the original PRMA with fixed permission probability, as indicated from the simulation results obtained here.     

Orthogonal signaling-based queue status investigation method in IEEE 802.11

IEEE 802.11 specifies four different medium access control (MAC) protocols to coordinate multiple access in a wireless local area network (WLAN). Since several tens of stations can operate in a WLAN, the performance of MAC protocols is important for overall network efficiency. It has been observed that the IEEE 802.11 MAC protocols can be improved by knowing which station has a non-empty queue, i.e., queue status. The point coordination function (PCF) can use this information to avoid polling a station that has no pending data. The HCF controlled channel access can adapt polling parameters based on queue status information, especially when scheduling a bursty and variable bit-rate traffic. Previously suggested methods are rather limited in terms of accuracy and efficiency.In this paper, we propose a novel method to investigate the queue status of multiple stations by exploiting orthogonal signaling. With synchronous transmission of orthogonal codes and symbol level signal processing, the method allows all of the associated stations to report their queue status at the same time. Challenges that can arise in the implementation of the proposed method are identified, and their solutions are suggested. The feasibility of detecting orthogonal signals is thoroughly tested on a realistic channel model. To demonstrate the performance improvement of a MAC protocol, we applied the proposed method to PCF. Both analysis and simulation show that the modified PCF significantly outperforms not only the original PCF but also other previously suggested PCF enhancements.     

无线传感器网络能量异构非均匀分簇路由协议

基于分簇的无线传感器网络路由协议,采用多跳路由方式传输数据至基站,容易造成靠近基站的节点转发大量数据而过早失效。另外,分簇协议通常假定网络节点是能量同构的,不能有效解决节点能量异构的问题。因此,从非均匀分簇的角度出发,结合局部竞争簇首机制,提出了一种基于能量异构的分簇协议（EHUC）。仿真结果表明该协议能够有效应用于能量异构的无线传感器网络,并延长网络的生命周期。