一种针对超短波电台接入网的混合信道接入方案

为超短波电台接入网提供了一种混合信道接入方案,方案借鉴了民用接入技术的一些先进理念,并结合军用跳频电台网络的特殊业务应用需求,采用了一种静态TDMA、动态TDMA和频分多址FDMA的混合信道接入策略,实现了多用户多业务传输的QOS保障,满足了军用业务的特殊传输需求。     

A distributed radio channel allocation scheme for WLANs with multiple data rates

For IEEE 802.11 wireless LANs (WLAN) with multiple access points (AP), it is critical to allocate the limited number of radio channels dynamically and efficiently. In this paper, we present a new radio channel allocation (RCA) scheme for WLANs with multiple data rates. First, we propose a new algorithm to dynamically estimate the number of active stations by using the least square estimator (LSE), which is unbiased and has minimum variance. Second, we derive an expression to evaluate the impact of the co-channel stations of an AP on the channel utilization of the AP based on the number of equivalent co-channel stations, which is the difference between the numbers of stations that are sensed by and associated with the AP. Third, we develop a new distributed RCA (DRCA) that considers the changing number of active stations, the impact of co-channel interference (CCI), and different traffic demands for different APs, which have not been considered by the existing RCA schemes. Simulation results have demonstrated that DRCA quickly finds optimal or suboptimal channel assignments and improves overall channel utilization for about 15 ~ 50% for different AP layouts, as compared to the existing schemes.     

A note on optimal input control policy for an Aloha access scheme

Input control policies had been proposed previously (e.g. in Lam and Kleinrock, 1975; and Fayolle et al., 1977) to improve the delay-throughput performance of Aloha access schemes. Through simulation results, Lam and Kleinrock observed that the optimal control policies were in general of control limit type. The authors discuss input control policies for one such Aloha access scheme and prove analytically that the optimal policy is indeed of the control limit type. The optimal policy is found to be extremely simple for the access scheme discussed. This policy is to accept the newly arrived packet if the present system state is either zero or one, and to reject the packet otherwise     

Partially overlapping channel assignment for WLANs using SINR interference model

The use of multiple channels in 802.11 wireless local area networks can improve network performance. Many efforts have been done to better exploit multiple non‐overlapped channels. However, the number of orthogonal channels in the Institute of Electrical and Electronics Engineers 802.11 standards is very much limited. Recent studies indicate that we can improve the full‐range channel utilization and the network throughput by properly utilizing the partially overlapping channels. However, little work was focused on channel assignment for partially overlapping channels. In this paper, we investigate the problem of partially overlapping channel assignment to improve the performance of 802.11 wireless networks based on the Signal to Interference–Noise Ratio interference model. Using the Signal to Interference–Noise Ratio model, we deduce a direct relationship between maximizing system throughput and minimizing total interference when partially overlapping channels are employed. After that, we propose a greedy method to minimize the total interference for throughput maximization. We evaluate our algorithm through extensive simulations and compare its performances with those of the state‐of‐the‐art. Copyright © 2013 John Wiley & Sons, Ltd.     

iVoIP: an intelligent bandwidth management scheme for VoIP in WLANs

Voice over Internet Protocol (VoIP) has been widely used by many mobile consumer devices in IEEE 802.11 wireless local area networks (WLAN) due to its low cost and convenience. However, delays of all VoIP flows dramatically increase when network capacity is approached. Additionally, unfair traffic distribution between downlink and uplink flows in WLANs impacts the perceived VoIP quality. This paper proposes an intelligent bandwidth management scheme for VoIP services (iVoIP) that improves bandwidth utilization and provides fair downlink–uplink channel access. iVoIP is a cross-layer solution which includes two components: (1) iVoIP-Admission Control, which protects the quality of existing flows and increases the utilization of wireless network resources; (2) iVoIP-Fairness scheme, which balances the channel access opportunity between access point (AP) and wireless stations. iVoIP-Admission Control limits the number of VoIP flows based on an estimation of VoIP capacity. iVoIP-Fairness implements a contention window adaptation scheme at AP which uses stereotypes and considers several major quality of service parameters to balance the network access of downlink and uplink flows, respectively. Extensive simulations and real tests have been performed, demonstrating that iVoIP has both very good VoIP capacity estimation and admission control results. Additionally, iVoIP improves the downlink/uplink fairness level in terms of throughput, delay, loss, and VoIP quality.     

MaxDiv: an optimal randomized spectrum access with maximum diversity scheme for cognitive radio networks

Cognitive radio network (CRN) is an emerging technology that can increase the utilization of spectrum underutilized by primary users (PUs). In the literature, most exiting investigations on CRNs have focused on how secondary users (SUs) can coexist harmlessly with the PUs. Despite the importance of such a coexistence issue, it is also crucial to investigate the coexistence of SUs because (i) the PUs usually rarely use the licensed spectrum and (ii) the advantages of CRN will significantly increase the number of SUs in the future. To address this challenging issue, we propose, in this paper, an optimal randomized spectrum access scheme, whose main ideas include the following: (i) an SU shares its sensing results with neighboring SUs and (ii) with the regional sensing results, an SU will access available channels with a non‐uniform probability distribution. We first formulate a multichannel optimal randomized multiple access (MC‐ORMA) problem that aims to maximize the throughput of the CRN; we then develop efficient distributed algorithms to solve the MC‐ORMA problem; we derive the closed‐form value of collision probability for each SU; and finally, we conduct extensive numerical experiments and compare our theoretical analysis with simulation results to demonstrate the advantages of our scheme. Copyright © 2011 John Wiley & Sons, Ltd.     

Near capacity multiple access scheme for interference channel usingcomplex-valued signals

A multiuser detection scheme is proposed for channels using non-spread signals. Trellis encoders and different random interleavers are employed for each user to remove the ambiguity in decoding each user's data from the composite received signal. With symbol-by-symbol soft decision, near channel capacity performance is obtained     

Decentralised learning MACs for collision-free access in WLANs

By combining the features of CSMA and TDMA, fully decentralised WLAN MAC schemes have recently been proposed that converge to collision-free schedules. In this paper we describe a MAC with optimal long-run throughput that is almost decentralised. We then design two schemes that are practically realisable, decentralised approximations of this optimal scheme and operate with different amounts of sensing information. We achieve this by (1) introducing learning algorithms that can substantially speed up convergence to collision free operation; (2) developing a decentralised schedule length adaptation scheme that provides long-run fair (uniform) access to the medium while maintaining collision-free access for arbitrary numbers of stations.     

Improved channel assignment scheme with access control for thecommon packet channel in WCDMA systems

We propose a channel assignment scheme with access control for obtaining better system performance within the common packet channel (CPCH) access procedure of wideband code-division multiple-access (WCDMA) systems. The proposed scheme is analyzed taking multiple access interference into consideration and is compared with other schemes in the 3rd Generation Partnership Project (3GPP): the basic scheme, the channel monitoring scheme, and the channel assignment scheme without access control. The results show that the proposed scheme provides high throughput, even under high-loading conditions, since the access control algorithm based on channel load prohibits excessive interference     

FastScan: a handoff scheme for voice over IEEE 802.11 WLANs

IEEE 802.11 Wireless LANs are increasingly being used in enterprise environments for broadband access. Such large scale IEEE 802.11 WLAN deployments implies the need for client mobility support; a mobile station has to be “handed off” from one Access Point to another. Seamless handoff is possible for data traffic, which is not affected much by the handoff delay. However, voice traffic has stringent QoS requirements and cannot tolerate more than 50ms net handoff delay. The basic IEEE 802.11 handoff scheme (implemented in Layers 1 & 2) only achieves a handoff delay of 300ms at best, leading to disrupted connectivity and call dropping. The delay incurred in scanning for APs across channels contributes to 90% of the total handoff delay. In this paper, the FastScan scheme is proposed which reduces the scanning delay by using a client-based database. The net handoff delay is reduced to as low as 20 ms for IEEE 802.11b networks. We next suggest “Enhanced FastScan” that uses the direction and relative position of the client with respect to the current AP to satisfy the latency constraint in IEEE 802.11a scenarios, which have significantly higher scanning delays due to the larger number of channels. The proposed schemes do not need any changes in the infrastructure (access points) and require only a single radio and a small cache memory at the client side.     

A deterministic channel access scheme for multimedia streaming in WiMedia networks

WiMedia MAC is an attractive transmission technology for high rate multimedia streaming and high quality consumer electronic devices in wireless personal area networks. In this paper, we propose a deterministic channel access (DCA), where all the devices determine their transmission orders in a distributed manner by exchanging beacon frames in the beacon period. Since all of the devices follow a deterministic transmission order, collision-free channel access can be achieved and thus the throughput can be significantly improved. In addition, the DCA addresses unfairness problems found in channel access by using circulating reference points. The trace-driven simulation results demonstrate that the DCA outperforms the existing channel access schemes in WiMedia MAC under different situations, especially under bursty traffic.     

Enhancing the performance of medium access control for WLANs with multi-beam access point

Wireless LANs with multi-beam directional antennas have received intensive attention lately due to the potential gain in throughput performance. However, when the multi-beam directional antennas are introduced in this system, the ever popular contention-based medium access control protocol such as IEEE 802.11 MAC is no longer effective, and many challenging problems, such as beam-synchronization problem, beam-overlapping problem, mobility and receiver blocking problem (deafness problem), need to be resolved. In this paper, we propose a novel MAC protocol to carefully address these problems. In addition to improving communication efficiency, we also consider the backward compatibility in our design, whereby an IEEE 802.11 terminal can transparently access a multi-beam access point. Furthermore, we present an analytical model to evaluate the performance of multi-beam wireless LANs. Extensive simulation studies are used to validate the analytical model and show that our scheme can significantly improve the throughput performance     

Fast channel access and DCA scheme for connection andconnectionless-oriented services in UMTS

An efficient MAC protocol and flexible dynamic channel allocation (DCA) scheme for the UMTS-TDD mode is presented which exploits the characteristics of connectionless and connection-oriented services. The proposed protocol gives fast channel access and high bandwidth efficiency in any traffic scenario asymmetric between uplink and downlink channels, particularly in the presence of Internet traffic     

交通应急通信中信道自适应的业务接入机制

在高密度蜂窝车联网(cellular vehicle-to-everything,C-V2X)中,群集通信终端的有效阵列接入方法是多业务性能保障和有限频谱效率提升的前提。利用蜂窝车联网中终端计算能力,提出了信道自适应的业务接入机制。该机制由基站估计当前区域通信密度,生成通信密度关联的接入类别限制(access class barring,ACB)因子,并在通信区域内广播;随后,车载通信终端根据接收基站广播信号的信干噪比(signal to interference plus noise ratio,SINR)和ACB因子计算自适应信道状态的接入概率,并比较接入概率和ACB因子。当接入概率大于ACB因子时,通信终端以最小接入概率从前导码池中随机选择一个前导码上传到基站,以获得与信道状态匹配的接入机会。仿真结果表明,在高密度通信状态下,与S-ALOHA协议和M2M-OSA方案相比,所提方案平均接入碰撞概率降低了约5%~20%,有效地减小了平均接入时延。     

Distributed QoE-aware channel assignment algorithms for IEEE 802.11 WLANs

Wireless Networks - One of the challenging problems with deployment of IEEE 802.11WLANs in the same hotspot is assignment of appropriate channels to the Access Points (APs). As the number of...     

Improving replicator dynamic evolutionary game model for selecting optimal defense strategies

In terms of the existence of strategy dependency in the same game group,network attack-defense evolutionary game model based on the improved replicator dynamics was constricted by introducing the intensity coefficient,which completed the method of calculating replicator dynamic rate.The improved replicator dynamic equation was adopted to solve the evolutionary equilibrium for the situation that both attack and defense have two optional strategies.The stability of the equilibrium points was analyzed by the local stability analysis method of Jacobian matrix,and the optimal defense strategies were obtained under different conditions.The results show that the strategy dependency between the players in the same group has a certain influence on the evolution of the game,both the incentive and the inhibition.Finally,the accuracy and validity of the model and method are verified by the experimental simulation,which provides a new theoretical support for solving the information security problems in the real.     

A utility-based resource allocation scheme for IEEE 802.11 WLANs via a machine-learning approach

The problem of allocating resources in IEEE 802.11 wireless local area networks (WLAN) is challenging due to limited bandwidth, time-varying channel conditions, and especially the distributed channel-access manner. In this paper we propose an intelligent resource allocation scheme that dynamically adjusts medium-access-control (MAC) parameters to tune channel-access opportunities and maximize the total utility. “Intelligent” refers to the capability of our approach to regulate each 802.11 node’s parameters automatically according to the changes of surrounding situations, e.g. channel conditions and number of nodes. Our intelligent allocation scheme uses neural networks to on-line learn the nonlinear function between the adopted MAC parameters and allocated throughput. Based on the learned knowledge, MAC parameters can therefore be dynamically adjusted toward the desired throughput allocation and consequently the maximal WLAN utility. Simulations results demonstrate the effectiveness of our allocation scheme in maximizing the system utility in a varying 802.11 WLAN environment.     

Joint optimal channel base station and power assignment forwireless access

The provision of personal communication services is the goal of the evolution of integrated communication systems. The fundamental problem underlying any phase (hand-off, new connection, etc.) of a dynamic resource allocation algorithm in a wireless network is to assign transmission powers, forward (downstream) and reverse (upstream) channels, and base stations such that every mobile of the system can establish a connection. Each one of these problems separately has been studied extensively. We consider the joint problem in a system with two base stations. An algorithm that achieves the optimal assignment is provided. It involves the computation of a maximum matching in a graph that captures the topological characteristics of the mobile locations. The traffic capacities, in terms of expected number of connections per channel, of the forward and reverse channel are obtained and compared, for both cases of power control and nonpower control. It turns out that when the transmission power is fixed, the capacities of the forward and reverse channel are different, while when power control is allowed they are the same. For systems with two mobiles the capacities of the forward and reverse channels are studied analytically. Finally, several versions of the two-way channel assignment problem are studied     

Resource allocation scheme for orthogonal frequency division multiple access networks based on cooperative game theory

Cooperative game theory can be applied to orthogonal frequency division multiple access (OFDMA) networks for fair resource allocation. In this work, we consider a comprehensive cross‐layer framework including physical and medium access control layer requirements. We apply two cooperative games, nontransferable utility (NTU) game and transferable utility (TU) game, to provide fairness in OFDMA networks. In NTU game, fairness is achieved by defining appropriate objective function, whereas in TU game, fairness is provided by forming the appropriate network structure. For NTU game, we analyze the Nash bargaining solution as a solution of NTU game taking into account channel state information and queue state information. In a TU game, we show that coalition among subcarriers to jointly provide rate requirements leads to better performance in terms of power consumption. The subcarrier's payoff is determined according to the amount of payoff which that subcarrier brings to the coalition by its participation. We show that although NTU and TU games are modeled as rate adaptive and margin adaptive problems, respectively, both solutions provide a fair distribution of resources with minimum fairness index of 0.8. Copyright © 2012 John Wiley & Sons, Ltd.     

Design and performance evaluation of an RRA scheme for voice‐data channel access in outdoor microcellular environments

In PCS networks, the multiple access problem is characterized by spatially dispersed mobile source terminals sharing a radio channel connected to a fixed base station. In this paper, we design and evaluate a reservation random access (RRA) scheme that multiplexes voice traffic at the talkspurt level to efficiently integrate voice and data traffic in outdoor microcellular environments. The scheme involves partitioning the time frame into two request intervals (voice and data) and an information interval. Thus, any potential performance degradation caused by voice and data terminals competing for channel access is eliminated. We consider three random access algorithms for the transmission of voice request packets and one for the transmission of data request packets. We formulate an approximate Markov model and present analytical results for the steady state voice packet dropping probability, mean voice access delay and voice throughput. Simulations are used to investigate the steady state voice packet dropping distribution per talkspurt, and to illustrate preliminary voice-data integration considerations. This revised version was published online in June 2006 with corrections to the Cover Date.