Turbo soft combining hybrid ARQ techniques: Theory and application to 3G wireless networks

This paper deals with the application of Hybrid Automatic Repeat reQuest (h-arq) techniques to allow reliable data communications in wireless 3G networks. Basically, retransmission of coded data is endowed with soft combining schemes applied, respectively, to packet replicas, or to decoding algorithm outputs. In particular, the proposed coding scheme takes advantage of error correction capabilities of the turbo codes, while the combining algorithm follows the diversity approach. The performance of the proposedh-arq schemes has been derived by means of a suitable analytical approach and numerical simulations in the case of a typical umts environment. The results highlight the good behavior of the proposed scheme in term of error rate, throughput, packet delivery delay and power reduction.     

Cross‐layer design for energy efficient communication in wireless sensor networks

There is a plethora of recent research on high performance wireless communications using a cross‐layer approach in that adaptive modulation and coding (AMC) schemes at wireless physical layer are used for combating time varying channel fading and enhance link throughput. However, in a wireless sensor network, transmitting packets over deep fading channel can incur excessive energy consumption due to the usage of stronger forwarding error code (FEC) or more robust modulation mode. To avoid such energy inefficient transmission, a straightforward approach is to temporarily buffer packets when the channel is in deep fading, until the channel quality recovers. Unfortunately, packet buffering may lead to communication latency and buffer overflow, which, in turn, can result in severe degradation in communication performance. Specifically, to improve the buffering approach, we need to address two challenging issues: (1) how long should we buffer the packets? and (2) how to choose the optimum channel transmission threshold above which to transmit the buffered packets? In this paper, by using discrete‐time queuing model, we analyze the effects of Rayleigh fading over AMC‐based communications in a wireless sensor network. We then analytically derive the packet delivery rate and average delay. Guided by these numerical results, we can determine the most energy‐efficient operation modes under different transmission environments. Extensive simulation results have validated the analytical results, and indicates that under these modes, we can achieve as much as 40% reduction in energy dissipation. Copyright © 2008 John Wiley & Sons, Ltd.     

Efficient broadcasting in multi-hop wireless networks with a realistic physical layer

Almost all existing broadcasting algorithms assume an ideal physical layer, in which a successful transmission is guaranteed if the distance between communicating nodes is less than a certain threshold, e.g., a transmission range. However, wireless communication links normally suffer from the characteristics of realistic physical layer, which significantly reduce the reliability of broadcasting among the nodes. This work addresses the minimal broadcasting problem in multi-hop wireless networks with a realistic physical layer. Given a probability p^*, the problem is to design a distributed broadcasting algorithm such that each node in the network receives the broadcasting packet with probability no less than p^* and the number of retransmissions is minimized. We show that this problem is NP-hard and propose a distributed greedy algorithm which maximizes the gain cost ratio at each node. We prove that the proposed algorithm guarantees that each node receives the broadcasting packet with probability no less than p^*, and analyze upper bound on the number of total retransmissions in the network. Simulation results show that our algorithm can provide near 100% coverage to the wireless network with a realistic physical layer, and reduce the number of retransmissions compared with modified traditional flooding schemes k-Flooding (pure flooding with multiple times) and ACK-Flooding (pure flooding with acknowledgement). We believe our algorithmic solution is efficient and practical for general existing multi-hop wireless networks.     

Packet access using DS-CDMA with frequency-domain equalization

The next-generation mobile communications system is anticipated to support very high-speed data rates exceeding several tens megabits per second. In this paper, we consider high-speed downlink packet access for direct-sequence code-division multiple access (DS-CDMA) as in third-generation wideband code-division multiple-access systems. Adaptive modulation and coding (AMC), multicode operation and hybrid automatic repeat request (HARQ) will be the enabling technologies. With such high-speed data transmissions, however, multicode operation severely suffers from the loss of orthogonality among the spreading codes since the wireless channel becomes severely frequency-selective. In this paper, we apply frequency-domain equalization (FDE) based on minimum mean-square error (MMSE) criterion instead of conventional rake combining for receiving the packet. A new MMSE-FDE weight is derived for packet combining. The throughput in a frequency-selective Rayleigh-fading channel is evaluated by computer simulation for Chase combining and incremental redundancy (IR) packet combining. It is shown that the use of MMSE-FDE for the reception of multicode DS-CDMA packet gives an improved throughput irrespective of the channel's frequency-selectivity.     

DDOR: Destination discovery oriented routing in?highway/freeway VANETs+

The emerging adoption of wireless communications on surface transportation systems has generated extensive interest among researchers over the last several years. Innovative inter-vehicular communications and vehicle-to-infrastructure communications achieve road traffic safety, ecstatic driving and delightful travelling experiences. Multi-hop information dissemination in vehicular ad hoc networks is challenged by high mobility and frequent disconnections of wireless nodes. This paper presents a new routing scheme for Highway/Freeway VANETs, which consists of a unicast destination discovery process, a robust forward node selection mechanism and a positional hello mechanism. In this paper, no dedicated path is framed in order to prevent frequent path maintenance. In addition, the avoidance of flooding and location services substantially reduces the control overhead. Positional hello scheme ensures connectivity and diminishes control overhead concurrently. Simulation results signify the benefits of the proposed routing strategy (i.e. DDOR) has higher packet delivery ratio, reduced routing overhead and shorter delay compared with previous works.     

Clustering and power management for virtual MIMO communications in wireless sensor networks

Multi-input multi-output (MIMO) is a well-established technique for increasing the link throughput, extending the transmission range, and/or reducing energy consumption. In the context of wireless sensor networks (WSNs), even if each node is equipped with a single antenna, it is possible to group several nodes to form a virtual antenna array, which can act as the transmitting or receiving end of a virtual MIMO (VMIMO) link. In this paper, we propose energy-efficient clustering and power management schemes for virtual MIMO operation in a multi-hop WSN. Our schemes are integrated into a comprehensive protocol, called cooperative MIMO (CMIMO), which involves clustering the WSN into several clusters, each managed by up to two cluster heads (CHs); a master CH (MCH) and a slave CH (SCH). The MCH and SCH collect data from their cluster members during the intra-cluster communications phase and communicate these data to neighboring MCHs/SCHs via an inter-cluster VMIMO link. CMIMO achieves energy efficiency by proper selection of the MCHs and SCHs, adaptation of the antenna elements and powers in the inter-cluster communications phase, and using a cross-layer MIMO-aware route selection algorithm for multi-hop operation. We formally establish the conditions on the transmission powers of CHs and non-CHs that ensure the connectivity of the inter-cluster topology. Simulations are used to study the performance of CMIMO. The simulation results indicate that our proposed protocol achieves significant reduction in energy consumption and longer network life time, compared with non-adaptive clustered WSNs.     

Error performance of hybrid wireless-power line communication system

This paper considers a hybrid wireless-power line communication system for smart meter and grid interaction. The performance of the considered system is evaluated for different switching schemes such as threshold based switching, random switching, and selection combining. The power line channel is characterized using the log-normal random variable, whereas the channel response for the wireless link is modeled as the Nakagami-m distributed random variable. The expressions for average bit-error-rate (BER) for the considered switching/combining schemes are obtained, and the average BER performances of all the considered combining schemes are compared. The results are verified through simulations.     

Modeling and comparative analysis of Forward Error Correction in the context of multipath redundancy

In recent years mobile devices have shown increased computational power as well as simultaneous access to multiple wireless networks that combined with advanced modulation schemes that make better use of the available bandwidth has resulted in faster transmission rates. These facts are the bases that allow for efficient mechanisms to provide more reliable communications; namely through both, Forward Error Correction and the Multipath Real-Time Protocol. In this paper, a mathematical model that accounts for the playback success of media in the context of Real Time Communications is presented. The analytical model relies on a two-state Markov process that is typical of impaired wireless environments subjected to fading. Moreover, the model is validated through an experimental framework that emulates the different loss, latency and burstiness conditions introduced in the Markov process. Specifically both, theoretical and experimental, probabilities of successful playback are compared and contrasted against media quality scores.     

An enhanced XOR‐based scheme for wireless packet retransmission problem

Solving wireless packet retransmission problem (WPRTP) using network coding (NC) is increasingly attracting research efforts. However, existing NC‐based schemes for WPRTP are with high computational complexity resulting from computation on larger Galois field (GF(2^q)), or the solutions on GF(2) found by the schemes are less efficient. In this paper, combining the basic ideas in two existing schemes, denoted as ColorNC and CliqueNC, respectively, we present a new scheme named as ColorCliqueNC. The advantages of ColorCliqueNC include the following: (i) it is suitable for all kinds of WPRTP instances; (ii) it works on GF(2); thus, it is computationally efficient than the schemes working on larger Galois fields; and (iii) the solutions found by ColorCliqueNC usually have fewer packet retransmissions than those by ColorNC and CliqueNC despite that they all work on GF(2). Theoretical analysis indicates that ColorCliqueNC is superior to ColorNC and CliqueNC. Simulation results show that ColorCliqueNC generally outperforms ColorNC and CliqueNC. Compared with ColorNC, ColorCliqueNC can save up to 10% packet retransmissions. Copyright © 2013 John Wiley & Sons, Ltd.     

On reducing the rate of retransmission in time-varying channels

For data communications in time-varying channels such as wireless channels, the dynamic channel fluctuations often cause high frame-error rates. When the link layer detects that a frame is in error, conventionally, the frame is dropped and retransmission of the frame is requested. Based on the fact that the erroneous frames still contain useful information, several schemes have been proposed, such as packet combining and incremental redundancy, which retain and utilize the erroneous frames to improve retransmission performance. In this paper, we address two questions: 1) how much information is still useful in the erroneous frame; and 2) how to design a retransmission scheme to make efficient use of such information. We model this scenario (retransmission with an erroneous frame available at the receiver) as communication with side information at the receiver, and for a class of time-varying channels, the compound block interference channels, we derive with information-theoretic arguments the minimum information rate sufficient for retransmission to recover the erroneous frame. Motivated by the theoretical results, we propose an embedded channel coding/modulation structure together with a rate-adaptive retransmission scheme. Performance results indicate significant improvements over existing retransmission schemes in both additive white Gaussian noise and quasi-static Rayleigh fading channels.     

大气无线光通信调制方式性能分析

在对三种典型大气无线光通信调制方式--OOK、PPM和DPIM的调制结构进行分析的基础上,结合大气无线光信道特点,分析比较了这三种调制方式的带宽需求、传输容量、功率需求和差错性能.理论分析与仿真结果表明,OOK方式实现简单,不需要符号同步,带宽需求最小,但功率利用率太低;PPM方式大大提高了功率利用率,但带宽利用率最低,而且需要符号同步;DPIM相比于OOK具有更高的功率利用率,相比于PPM具有更高的带宽利用率,而且不需要符号同步,应用于无线光通信系统具有显著的优势.     

Highly Efficient Voice—Data Integration over Medium and High Capacity Wireless TDMA Channels

A new medium access control (MAC) protocol for mobile wireless communications is presented and investigated. We explore, via an extensive simulation study, the performance of the protocol when integrating voice and data traffic over two wireless channels, one of medium capacity (referring mostly to outdoor microcellular environments) and one of high capacity (referring to an indoor microcellular environment). Data message arrivals are assumed to occur according to a Poisson process and to vary in length according to a geometric distribution. We evaluate the voice packet dropping probability and access delay, as well as the data packet access and data message transmission delays for various voice and data load conditions. By combining two novel ideas of ours with two useful ideas which have been proposed in other MAC schemes, we are able to remarkably improve the efficiency of a previously proposed MAC scheme [5], and obtain very high voice sources multiplexing results along with most satisfactory voice and data performance and quality of service (QoS) requirements servicing. Our two novel ideas are the sharing of certain request slots among voice and data terminals with priority given to voice, and the use of a fully dynamic low-voice-load mechanism.     

On energy efficiency of geographic opportunistic routing in lossy multihop wireless networks

Geographic opportunistic routing (GOR) is an emerging technique that can improve energy efficiency in lossy multihop wireless networks. GOR makes local routing decision by using nodes?? location information, and exploits the broadcast nature and spatial diversity of the wireless medium to improve the packet forwarding reliability. In this paper, our goal is to fully understand the principles and tradeoffs in GOR, thus provide insightful analysis and guidance to the design of more efficient routing protocols in multihop wireless networks. We propose a local metric, one-hop energy efficiency (OEE), to balance the packet advancement, reliability and energy consumption in GOR. We identify and prove important properties about GOR on selecting and prioritizing the forwarding candidates in order to maximize the expected packet advancement. Leveraging the proved properties, we then propose two localized candidate selection algorithms with O(N ³) running time to determine the forwarding candidate set that maximizes OEE, where N is the number of available next-hop neighbors. Through extensive simulations, we show that GOR applying OEE achieves better energy efficiency than the existing geographic routing and blind opportunistic routing schemes under different node densities and packet sizes.     

移动数据通信

本文介绍了移动通信发展的概况以及在现有模拟与数字移动网上进行数据通信的原理。同时还介绍了专用的无线分组交换数据网如ＣＤＰＤ和Ｄａｔａ ＴＡＣ。     

On the application of the sum of generalized Gaussian random variables: maximal ratio combining

In most wireless communication systems, the additive noise is assumed to be Gaussian. However, there are many practical applications where non-Gaussian noise impairs the received signal. Examples include co-channel and adjacent channel interference in mobile cellular systems, impulsive noise in wireless and power-line communications, ultra-wide-band interference and multi-user interference in wireless systems, and spectrum sensing. To cover this issue, we consider in this paper the application of the sum of generalized Gaussian (GG) random variables (RVs). To this end, we consider single-input multiple-output (SIMO) systems that operate over Nakagami-m fading channels in the presence of an additive white generalized Gaussian noise (AWGGN). Specifically, we derive a closed-form expression for the bit error rate (BER) of several coherent digital modulation schemes using maximal ratio combining diversity in the Nakagami-m fading channels subject to an AWGGN. The derived expression is obtained based on the fact that the sum of L GG RVs can be approximated by a single GG RV with a suitable shaping parameter. In addition, the obtained BER expression is valid for integer and non-integer value of the fading parameter m. Analytical results are supported by Monte-Carlo simulations to validate the analysis.     

Detailed simulation of the physical level in a simulator of wireless sensor networks

The general architecture of a simulator of wireless sensor networks and a detailed model of a wireless communications channel that involves various models of the radio-wave propagation are presented. It is demonstrated that the model of the radio-wave propagation significantly affects the connectivity of the wireless sensor network. It is shown that the radio-wave-propagation model based on the parabolic-equation method yields more accurate results for the packet reception rate as a function of distance and the width of the transition region. The results are in good agreement with experimental data, thus indicating that the effective and reliable simulation of a wireless communications channel can be implemented in practice.     

Providing deterministic packet delays and packet losses in multimedia wireless networks

‘Anytime, anywhere’ communication, information access and processing are much cherished in modern societies because of their ability to bring flexibility, freedom and increased efficiency to individuals and organizations. Wireless communications, by providing ubiquitous and tetherless network connectivity to mobile users, are therefore bound to play a major role in the advancement of our society. Although initial proposals and implementations of wireless communications are generally focused on near‐term voice and electronic messaging applications, it is recognized that future wireless communications will have to evolve towards supporting a wider range of applications, including voice, video, data, images and connections to wired networks. This implies that future wireless networks must provide quality‐of‐service (QoS) guarantees to various multimedia applications in a wireless environment. Typical traffic in multimedia applications can be classified as either Constant‐Bit‐Rate (CBR) traffic or Variable‐Bit‐Rate (VBR) traffic. In particular, scheduling the transmission of VBR multimedia traffic streams in a wireless environment is very challenging and is still an open problem. In general, there are two ways to guarantee the QoS of VBR multimedia streams, either deterministically or statistically. In particular, most connection admission control (CAC) algorithms and medium access control (MAC) protocols that have been proposed for multimedia wireless networks only provide statistical, or soft, QoS guarantees. In this paper, we consider deterministic QoS guarantees in multimedia wireless networks. We propose a method for constructing a packet‐dropping mechanism that is based on a mathematical framework that determines how many packets can be dropped while the required QoS can still be preserved. This is achieved by employing: (1) An accurate traffic characterization of the VBR multimedia traffic streams; (2) A traffic regulator that can provide bounded packet loss and (3) A traffic scheduler that can provide bounded packet delay. The combination of traffic characterization, regulation and scheduling can provide bounded loss and delay deterministically. This is a distinction from traditional deterministic QoS schemes in which a 0% packet loss are always assumed with deterministically bounding the delay. We performed a set of performance evaluation experiments. The results will demonstrate that our proposed QoS guarantee schemes can significantly support more connections than a system, which does not allow any loss, at the same required QoS. Moreover, from our evaluation experiments, we found that the proposed algorithms are able to out‐perform scheduling algorithms adopted in state‐of‐the‐art wireless MAC protocols, for example Mobile Access Scheme Based on Contention and Reservation for ATM (MASCARA) when the worst‐case traffic is being considered. Copyright © 2002 John Wiley & Sons, Ltd.     

An energy efficiency model for adaptive and custom error control schemes in Bluetooth sensor networks

This paper analyzes the effect of custom error control schemes on the energy efficiency in Bluetooth sensor networks. An analytical model is presented to evaluate the energy efficiency metric, which considers in just one parameter the energy and reliability constraints of wireless sensor networks. New packet types are introduced using some error control strategies in the AUX1 packet, where custom coding can be implemented. Two adaptive techniques are proposed that change the error control strategy based on the number of hops traversed by a packet through the network. A packet selection strategy based on channel state is proposed for sensor networks with different channel conditions. Performance results are obtained through analysis and simulation in Nakagami-m fading channels for networks with different number of hops and channel conditions.     

Reliable data transfer Rendezvous protocol in wireless sensor networks using 2D-SEC-DED encoding technique

Many applications in Wireless Sensor Networks (WSNs) require all data to be transmitted with minimal or without loss, what implies that reliability is an important characteristic. In any WSN, there are two basic approaches to recover erroneous packets. One way is to use Automatic Repeat reQuest (ARQ), and another is Forward Error Correction (FEC). The error-control systems for applications based on ARQ use error detection coupled with retransmission requests to maximize reliability at some cost to throughput. Error detection is generally provided by the lower protocol layers which use checksums (e.g. Cyclic Redundancy Checksums (CRCs)) to discard corrupted packets and trigger retransmission requests. In these solutions event a single erroneous bit can render a packet useless to the end user. Having in mind that in WSNs the power is scarce and is primarily consumed by wireless transmission and reception, we propose to use FEC rather than ARQ. FEC is a way of correcting packets by transmitting additional information bits with aim to reduce the frequency of retransmission requests. During this, data bytes are optionally encoded after being fragmented with Error Correcting Code (ECC) to recover data bits in case of small number of bit errors. Various FEC encoding schemes such as erasure and Hamming based codes are available. The choice of the encoding schemes depends on the applications and error characteristics (error models/patterns) of the wireless channel. Erasure encoding is preferable for usage when the error pattern is burst dominated, while Hamming encoding when noise causes random errors. Our observations show that most bit errors are single-bit or double-bit errors and burst errors are present but rare. In this work, an efficient Hamming based FEC encoding scheme of relatively low complexity called Two Dimensional-Single Error Correcting-Double Error Detecting (2D-SEC-DED), intended to minimize packet retransmissions and to save energy, has been developed. Such FEC scheme can be used to correct all single-bit and 99.99%of double/multiple-bit errors. Since the radio block is dominant energy consumer within a Sensor Node (SN), we focus our attention to answer the question: which is the adequate metric to use, and under what conditions to accurately characterize the quality of the communication, related to reliable data transfer, with minimal energy consumption. To this end, as first, in a case when the bit error is not high and most errors are single-bit, we show that 2D SEC-DED encoding scheme is more energy efficient in comparison to erasure encoding. As second, the advantages of using 2D-SEC-DED in respect to CRC (NO-FEC) encoding, concerning decreasing the energy consumption and increasing the reliability of the radio block are derived through implementation of two versions of the Rendezvous Protocol for Long Living (RPLL) referred as Modified-RPLL (M-RPLL as FEC based) and Ordinary-RPLL (O-RPLL as NO-FEC), respectively.