Price-based max-min fair rate allocation in wireless multi-hop networks

The interaction between links in wireless multihop networks introduces extra constraints on the combinations of achievable flow rates. Algorithms have been proposed to achieve max-min fairness under these additional constraints. This letter provides a simple price-based max-min fair rate allocation scheme, building on a utility maximization scheme recently proposed for such networks.     

Packet combining with adaptive retransmission control in DS-CDMA random access networks

Packet combining with adaptive retransmission control (ARC) in DS-CDMA random access networks has been investigated. The proposed system uses diversity packet combining while adaptively adjusting the retransmission probability of backlog users to optimize packet retransmissions. A soft decision DS-CDMA analysis is used to derive the optimum channel input for ARC. Simulation results show that packet combining with ARC can significantly increase the throughput and maintain the performance very close to its optimum in the high traffic region.     

Multipacket reception in random access wireless networks: fromsignal processing to optimal medium access control

There has been considerable interest in the idea of cross-layer design of wireless networks. This is motivated by the need to provide a greater level of adaptivity to variations of wireless channels. This article examines one aspect of the interaction between the physical and medium access control layers. In particular, we consider the impact of signal processing techniques that enable multipacket reception on the throughput and design of random access protocols     

Multichannel random access in OFDMA wireless networks

Orthogonal frequency-division multiple access (OFDMA) systems are considered promising candidates for implementing next-generation wireless communication systems. They provide multiple channels that can be accessed via random access schemes. However, traditional random access schemes could result in an excessive amount of access delay. To address this issue, we develop a fast retrial scheme that is based on slotted Aloha and exploits the structure of OFDMA. A salient feature of this scheme is that when collisions occur instead of retrials occuring randomly in time, they occur randomly in frequency, i.e., the scheme randomly selects the subchannels for retrial. To further achieve fast access, retrials are designed to follow the 1-persistent type, i.e., no exponential backoff. To achieve the maximum throughput, we limit the maximum number of allowed retrials according to the load condition. We also consider the issue of designing for an appropriate reuse factor for random access channels in order to overcome the intercell interference problem in OFDMA multicell environments. Our finding is that full sharing, i.e., a reuse factor of one, performs best for given random access channels. Through analysis and simulation, we confirm that our fast retrial algorithm has the advantage of high throughput and low access delay, and the full sharing policy for random access channels shows high throughput as well as low collision.     

Network-assisted diversity for random access wireless networks

A novel viewpoint to the collision resolution problem is introduced for wireless slotted random access networks. This viewpoint is based on signal separation principles borrowed from signal processing problems. The received collided packets are not discarded in this approach but are exploited to extract each individual user packet information. In particular, if k users collide in a given time slot, they repeat their transmission for a total of k times so that k copies of the collided packets are received. Then, the receiver has to resolve a k×k source mixing problem and separate each individual user. The proposed method does not introduce throughput penalties since it requires only k slots to transmit k colliding packets. Performance issues that are related to the implementation of the collision detection algorithm are studied. The protocol's parameters are optimized to maximize the system throughput     

Joint random access and power control game in ad hoc networks with noncooperative users

We consider a distributed joint random access and power control scheme for interference management in wireless ad hoc networks. To derive decentralized solutions that do not require any cooperation among the users, we formulate this problem as noncooperative joint random access and power control game, in which each user minimizes its average transmission cost with a given rate constraint. Using supermodular game theory, the existence and uniqueness of Nash equilibrium are established. Furthermore, we present an asynchronous distributed algorithm to compute the solution of the game based on myopic best response updates, which converges to Nash equilibrium globally. Finally, a link admission algorithm is carried out to guarantee the reliability of the active users. Performance evaluations via simulations show that the game-theoretical based cross-layer design achieves high performance in terms of energy consumption and network stability.     

Sensor networks with mobile access: optimal random access and coding

We consider random access and coding schemes for sensor networks with mobile access (SENMA). Using an orthogonal code-division multiple access (CDMA) as the physical layer, an opportunistic ALOHA (O-ALOHA) protocol that utilizes channel state information is proposed. Under the packet capture model and using the asymptotic throughput as the performance metric, we show that O-ALOHA approaches the throughput equal to the spreading gain with an arbitrarily small power at each sensor. This result implies that O-ALOHA is close to the optimal centralized scheduling scheme for the orthogonal CDMA networks. When side information such as location is available, the transmission control is modified to incorporate either the distribution or the actual realization of the side information. Convergence of the throughput with respect to the size of the network is analyzed. For networks allowing sensor collaborations, we combine coding with random access by proposing two coded random access schemes: spreading code dependent and independent transmissions. In the low rate regime, the spreading code independent transmission has a larger random coding exponent (therefore, faster decay of error probability) than that of the spreading code dependent transmission. On the other hand, the spreading code dependent transmission gives higher achievable rate.     

Capacity analysis of reservation-based random access for broadband wireless access networks

In this paper we propose a novel model for the capacity analysis on the reservation-based random multiple access system, which can be applied to the medium access control protocol of the emerging WiMAX technology. In such a wireless broadband access system, in order to support QoS, the channel time is divided into consecutive frames, where each frame consists of some consequent mini-slots for the transmission of requests, used for the bandwidth reservation, and consequent slots for the actual data packet transmission. Three main outcomes are obtained: first, the upper and lower bounds of the capacity are derived for the considered system. Second, we found through the mathematical analysis that the transmission rate of reservationbased multiple access protocol is maximized, when the ratio between the number of mini-slots and that of the slots per frame is equal to the reciprocal of the random multiple access algorithm?s transmission rate. Third, in the case of WiMAX networks with a large number of subscribers, our analysis takes into account both the capacity and the mean packet delay criteria and suggests to keep such a ratio constant and independent of application-level data traffic arrival rate.     

Medium access control in ultra-wideband wireless networks

Ultra-wideband (UWB) transmission is an emerging wireless communication technology with unique potential merits such as high-rate, low-transmission power, immunity to multipath propagation, and capability in precise positioning. It has received significant interests for future wireless communications from both academia and industry. In UWB wireless networks, medium access control (MAC) is essential to coordinate the channel access among competing devices. The unique UWB characteristics not only pose significant challenges but also offer great opportunities in efficient UWB MAC design. This paper presents a comprehensive overview of UWB MAC development on four important aspects: multiple access, overhead reduction, resource allocation, and quality of service (QoS) provisioning, and identifies some future research issues.     

A unique beamforming-based equilibrium in multi-user random access SIMO networks

In this letter, we tackle the problem of competitive single antenna transmitters accessing a multiple antenna access point using a random access protocol. We show that the access point can help the system to reach a unique Stackelberg equilibrium and prevent network collapse due to the selfish nature of the transmitters.     

Analysis and optimization of duty-cycle in preamble-based random access networks

Duty-cycling has been proposed as an effective mechanism for reducing the energy consumption in wireless sensor networks (WSNs). Asynchronous duty-cycle protocols where the receiver wakes up periodically to check whether there is a transmission and the sender transmits preambles to check if the receiver is awake are widely used in WSNs due to the elimination of complex control mechanisms for topology discovery and synchronization. However, the intrinsic simplicity of the asynchronous mechanism has the drawback of smaller energy saving potential that requires the optimization of the duty cycle parameters. In this paper, we propose a novel method for the optimization of the duty-cycle parameters in preamble-based random access networks based on the accurate modeling of delay, reliability and energy consumption as a function of listen time, sleep time, traffic rate and medium access control (MAC) protocol parameters. The challenges for modeling are the random access MAC and the sleep policy of the receivers, which make it impossible to determine the exact time of data packet transmissions, and thus difficult to investigate the performance indicators given by the delay, reliability and energy consumption to successfully receive packets. An analysis of these indicators is developed as a function of the relevant parameters of the network and it is used in the minimization of the energy consumption subject to delay and reliability requirements. The optimization provides significant reduction of the energy consumption compared to the previously proposed protocols in the literature.     

Twelve random access strategies for the fiber optic networks

Twelve random-access strategies that do not constrain the distance or transmission rate of a network, and can use the capabilities of fiber-optic components, are described and compared. The twelve strategies consist of three protocols, each of which can use two timing arrangements and two network-access devices. The three protocols are the standard ALOHA protocol, LCSMA, and LCSMA/CD. The last two protocols operate on linear-unidirectional networks and use local information at the transmitter to increase the throughput of the system. The networks considered have a common point that all transmitted signals pass through before being received. This makes two timing arrangements possible; a slotted system or an unslotted system. The taps on the network can be either passive or active     

基于ALOHA的无线网络随机接入协议研究

针对无线网络中的随机接入问题,详细介绍了ALOHA,时隙ALOHA及相关改进协议的基本原理和方法,介绍并讨论了多种常用的冲突解决算法,同时结合数学推导,对基于ALOHA的多种随机接入协议的特点和性能进行了分析。     

A random access channel resources allocation approach to control machine-to-machine communication congestion over LTE-advanced networks

The Internet of Things (IoT) is becoming a reality, and one of the core elements to make this reality come true is machine-to-machine (M2M) communication. With the fast-growing rate in which devices are being deployed, communication among them has become crucial to support the development of IoT applications. The Long-Term Evolution-Advanced (LTE-A) is a potential access network for these M2M devices. However, the LTE-A inherited characteristics from older cellular network standards, which were designed for human-to-human (H2H) and human-to-machine (H2M) communication. Accordingly, supporting M2M communication poses some challenges to LTE-A, with a highlight of the congestion and overload problems in the radio access network (RAN) during the random access channel (RACH) procedure. Such a problem arises due to the large number of devices sending access-request messages to the network and the limited number of resources to satisfy this new demand. In this paper, we introduce a solution to mitigate the impact of M2M communication in the LTE-A network. Precisely, we model how to divide the random access resources into different types of devices as a bankruptcy problem. Then, we propose two solutions: (i) A game theory approach to formulate the bankruptcy problem as a transferable utility game, and (ii) an axiomatic method where some elements are considered for judging the amount of resources each class should receive. The simulation results show that our approaches present improvements in terms of energy efficiency, impact control of M2M over H2H accesses, and priority respect among the different classes of devices.     

The case for SIMO random access in multi-antenna multi-hop wireless networks

In this paper, we demonstrate that multiple concurrent asynchronous and uncoordinated Single-Input Multiple-Output (SIMO) transmissions can successfully take place even though the respective receivers do not explicitly null out interfering signals. Hence, we propose simple modifications to the widely deployed IEEE 802.11 Medium Access Control (MAC) to enable multiple non-spatially-isolated SIMO sender-receiver pairs to share the medium. Namely, we propose to increase the physical carrier sense threshold, disable virtual carrier sensing, and enable message-in-message packet detection. We use experiments to show that while increasing the peak transmission rate, spatial multiplexing schemes such as those employed by the IEEE 802.11n are highly non-robust to asynchronous and uncoordinated interferers. In contrast, we show that the proposed multi-flow SIMO MAC scheme alleviates the severe unfairness resulting from uncoordinated transmissions in 802.11 multi-hop networks. We analytically compute the optimal carrier sense threshold based on different network performance objectives for a given node density and number of receive antennas.     

Achieving distributed user access control in sensor networks

User access control in sensor networks defines a process of granting user an access right to the stored information. It is essential for future real sensor network deployment in which sensors may provide users with different services in terms of data and resource accesses. A centralized access control mechanism requires the base station to be involved whenever a user requests to get authenticated and access the information stored in the sensor node, which is inefficient, not scalable, and is exposed to many potential attacks along long communication paths. In this paper, we propose a distributed user access control under a realistic adversary model in which sensors can be compromised and user may collude. We split the access control into local authentication conducted by a group of sensors physically close to a user, and a light remote authentication based on the endorsement of the local sensors. We implement the access control protocols on a testbed of TelosB motes. Our analysis and experimental results show that our schemes are feasible for real access control requirements.     

Analysis of frame-based reservation random access protocols formicrocellular radio networks

Reservation random access (RRA) protocols have been proposed for handling speech and data traffic on packet wireless networks. An interesting property of some RRA protocols is the capability of decoupling the speech access procedure from the data access procedure, so that speech access performances do not depend on actual data load. Frame-based protocols allow one to get the decoupling property easily. In this paper, we present a Markov model for analyzing the performances of frame-based RRA protocols that operate in a microcellular environment with channel errors. In the paper, this model is used for evaluating the performances of centralized RRA protocols, which use retransmissions for handling channel errors. Both in-slot access schemes, in which all the slots can be used for talkspurt setup and for user information transmission, and out-slot access schemes, with a separate reservation channel, are examined. Moreover, we present and analyze a new, stable, centralized RRA protocol, namely centralized-collision resolution access (C-CRA), which is based on collision resolution techniques     

Location‐aided medium access control for low data rate UWB wireless sensor networks

This paper presents a distributed medium access control (MAC) protocol for low data rate ultra‐wideband (UWB) wireless sensor networks (WSNs), named LA‐MAC. Current MAC proposal is closely coupled to the IEEE 802.15.4a physical layer and it is based on its Impulse‐Radio (IR) paradigm. LA‐MAC protocol amplifies its admission control mechanism with location‐awareness, by exploiting the ranging capability of the UWB signals. The above property leads to accurate interference predictions and blocking assessments that each node in the network can perform locally, limiting at the same time the actions needed to be performed towards the admission phase. LA‐MAC is evaluated through extensive simulations, showing a significant improvement in many critical parameters, such as throughput, admission ratio, energy consumption, and delay, under different traffic load conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

WCDMA随机接入信道的数学建模及性能分析

文章主要讨论了宽带码分多址(WCDMA)网络中无线小区随机接入信道(RACH)的数学建模方法及性能分析.首先介绍了WCDMA的RACH及信息发送方式,然后描述了RACH随机接入过程的时隙ALOHA接入方式,并在此基础上重点分析了RACH数学建模的方法和详细过程,给出了RACH吞吐量的计算公式,最后,对RACH的性能进行了分析.     

Near-far effects in land mobile random access networks withnarrow-band Rayleigh fading channels

The near-far effect of random access protocols in mobile radio channels with receiver capture is investigated. To this end, the probability of successful reception of a packet from a terminal at a known distance from the central receiver is obtained taking into account Rayleigh fading, UHF propagation attenuation, and the statistics of contending packet traffic in radio nets employing slotted ALOHA, carrier sense multiple access (CSMA) or inhibit sense multiple access (ISMA) protocols. Various models of receiver capture are compared, namely packet error rates for synchronous detection in slow- and fast-fading channels, and the probability that the signal-to-interference ratio is above a required threshold