Performance evaluation of preemptive polling schemes and ARQtechniques for indoor wireless networks

This paper examines a radio-based indoor communication network with a single radio channel shared by several data terminals. By enabling the terminals to communicate with each other and access the resources of a wired network, the system is a potential provider of in-building LAN-like services. In this indoor fading environment, a base-station approach is assumed. In the analysis, a two-state Markov chain model is used to model the nonstationary transmission channel. Two preemptive polling multiple-access schemes combine with ARQ error-control schemes to counteract the effects of a nonstationary transmission channel. The main idea devised is that of making the service interruption dependent on the propagation conditions of the transmission channel by monitoring the outcomes of the data packet transmission attempts. A performance comparison reveals the superiority of the preemptive polling systems with respect to a classical TDMA scheme     

Performance evaluation of polling systems for wireless localcommunication networks

This paper evaluates the performance of different polling systems used in wireless local networks where the transmission channel exhibits a nonstationary behavior. Many spatially dispersed data user terminals have been assumed to share a common short-range radio uplink channel to access a hub station. We have specifically considered cyclic polling systems with M queues (terminals), having the same general packet arrival process and general switchover period. The gated and exhaustive disciplines have been considered in ordering the transmission of the packets buffered at each terminal. By appropriately modeling the uplink channel, we propose analytical approaches to derive the average packet waiting time and the average cycle length for gated polling systems, combined with stop-and-wait (SW) and go-back-N (GBN) automatic repeat request (ARQ) techniques to control errors. A gated cyclic polling scheme combined with the selective-repeated (SR) stutter ARQ technique as well as an exhaustive cyclic polling scheme combined with SW, GBN, or SR stutter ARQ techniques, respectively, have also been considered In order to give an in-depth knowledge of the behavior of suitable polling alternatives for applications in wireless local communication networks     

Spread‐spectrum CDMA packet radio MAC protocol using channel overload detection and blocking

An analytical and simulation performance evaluation is presented for a multi‐access protocol for a data packet radio network with a limited user capacity. The network employs direct‐sequence code division multiple access (DS‐CDMA) in a centralised channel load‐sensing scheme with channel overload (collision) detection and blocking via a separate ancillary channel state information broadcast system. Traffic models that incorporate both a finite population and an infinite population and variable length data messages are considered. Results show that an improved throughput/delay performance can be obtained by implementing a channel overload detection (message dropping) scheme as well as a channel overload avoidance (message blocking) scheme. The channel overload threshold β is fixed at the system's maximum user capacity whereas it is shown that the overload avoidance blocking threshold α should be variable and dependent on the mean message arrival rate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Two-step multipolling MAC protocol for wireless LANs

The IEEE 802.11 standard defines two coordination functions: distributed coordination function (DCF) and point coordination function (PCF). These coordination functions coordinate the shared wireless medium. The PCF uses a centralized polling-based channel access method to support time-bounded services. To design an efficient polling scheme, the point coordinator (PC) needs to obtain information about the current transmission status and channel condition for each station. To reduce overhead caused by polling frames, it is better to poll all stations using one polling frame containing the transmission schedule. In this paper, we propose an efficient polling scheme, referred to as two-step multipolling (TS-MP), for the PCF in wireless local area networks (WLANs). In this new scheme, we propose to use two multipolling frames with different purposes. The first frame is broadcast to collect information such as the numbers of pending frames and the physical-layer transmission rates for the communication links among all stations. The second frame contains a polling sequence for data transmissions designed based on the collected information. This frame is broadcast to all stations. Extensive simulation studies show that TS-MP not only overcomes the aforementioned deficiencies, but also help to implement rate adaptation over time-varying wireless channel.     

Cell‐loss control in multiplexing of VBR video over ATM networks

In this article we investigate the impacts of interspacing and source polling policies on the cell‐loss rates in transmission of variable bit rate video sources over Asynchronous Transfer Mode networks. We present a mathematical model that finds the approximate optimal starting times of the video sources that minimize the congestion at the multiplexer. Combined with the approximate optimal source starting times, we propose a source ordering and polling policy for reducing the cell‐loss rates. The proposed policy is tested against alternative policies using simulation of pre‐recorded video data. This revised version was published online in June 2006 with corrections to the Cover Date.     

Satellite‐PCS channel simulation in mobile user environments using photogrammetry and Markov chains

In this paper, we present a system that models the land‐mobile satellite communication channel with a Markov chain approach supported by images of the mobile Earth station's (MES) environment. Our method employs a video camera with a fish‐eye lens capturing image sequences of the user environment from the position of the moving MES, image and signal processing algorithms to recognize propagation path states and extract their duration and transition probabilities, and modeling of the communication channel characteristics using the theory of Markov stochastic processes combined with statistical fade distributions appropriate for given path states. The results demonstrate that the procedure provides a full statistical characterization of the narrow‐band land‐mobile satellite propagation channel in several environments. This revised version was published online in June 2006 with corrections to the Cover Date.     

RIM-MAC：一种适用于水下传感网接收者发起的多会话MAC协议

声通信是水下传感网的主要通信方式之一,但是它具有长延迟和低带宽的特点,这是水下传感网MAC（media access control）协议研究面临的主要挑战。为提高网络吞吐量,提出了一种接收者发起的多会话MAC协议（RIM-MAC）。它利用接收者发起会话,通过一次会话的4次握手完成所有邻居数据分组的传输,有效地减少握手次数。同时利用侦听到的本地信息（邻居延迟图和邻居的传输调度）避免信道冲突并发起多个会话,这解决了长传播延迟带来的信道利用率低的问题。RIM-MAC通过增强节点间并行传输的能力,在接收者和发送者两端提高时空复用率,与经典水下MAC协议比,网络吞吐量提高了至少36%。除此之外,基于自适应数据轮询策略提出了一种网络负载公平算法（FTA）,它保证了网络中竞争节点间的信道访问的公平性。仿真实验表明,在长传播延迟的场景下,RIM-MAC取得了比典型的水下传感网MAC协议更好的吞吐量性能。     

The time‐dependent Erlang loss model with retrials

We consider a generalization of the classical Erlang loss model with both retrials of blocked calls and a time‐dependent arrival rate. We make exponential‐distribution assumptions so that the number of calls in progress and the number of calls in retry mode form a nonstationary, two‐dimensional, continuous‐time Markov chain. We then approximate the behavior of this Markov chain by two coupled nonstationary, one‐dimensional Markov chains, which we solve numerically. We also develop an efficient method for simulating the two‐dimensional Markov chain based on performing many replications within a single run. Finally, we evaluate the approximation by comparing it to the simulation. Numerical experience indicates that the approximation does very well in predicting the time‐dependent mean number of calls in progress and the times of peak blocking. The approximation of the time‐dependent blocking probability also is sufficiently accurate to predict the number of lines needed to satisfy blocking probability requirements. This revised version was published online in June 2006 with corrections to the Cover Date.     

A novel adaptive hybrid ARQ scheme for wireless ATM networks

This paper describes the design and performance of a novel adaptive hybrid ARQ scheme using concatenated FEC codes for error control over wireless ATM networks. The wireless links are characterized by higher, time‐varying error rates and burstier error patterns in comparison with the fiber‐based links for which ATM was designed. The purpose of the hybrid ARQ scheme is to provide a capability to dynamically support reliable ATM‐based transport over wireless channels by using a combination of our ARQ scheme (called SDLP) and the concatenated FEC scheme. The key ideas in the proposed hybrid ARQ scheme are to adapt the code rate to the channel conditions using incremental redundancy and to increase the starting code rate as much as possible with the concatenated FEC, maximizing the throughput efficiency. The numerical results show that our proposed scheme outperforms other ARQ schemes for all SNR values. This revised version was published online in July 2006 with corrections to the Cover Date.     

基于移动信道中速数据流的高健壮性二元网络传输编码调制方案研究

在第三代及第四代移动通信技术中,通信网内数据存量及流量主要以中速数据为主。但由于移动通信技术的特性,在数据传输过程中,信道干扰因素非常强烈,从而直接导致网络数据传输的可靠性大大的降低。而当前网络编码调制技术主要采用了单一的网络编码矢量量化技术,不仅忽略了信道干扰因素,而且对全部的中速数据采用等级保护模式,在移动信道中速数据传输过程误码率性能不强。对此,本文设计了基于移动信道中速数据流的高健壮性二元网络传输编码调制方案。将信道干扰因素和分级保护思想加以引入,提出了联合最佳准则ROBS-C(The Rule Of Based Source And Channel) 分级保护DLP(Divided Level of Protection)的调制方案,兼顾了量化性能和误码性能两个方面。仿真实验表明：本文方案在低信道扰码的场合下量化性能优良;且在强信道扰码情况下,比单一因素的时候误码率低,从而有效的可以面对实际的移动信道下低 /高信道扰码交替的信道状况,能够更好的适应移动通信的要求。     

Design and analysis of an algorithm for fair service in error‐prone wireless channels

In order to support diverse communication‐intensive real‐time and non‐real‐time data flows over a scarce, varying and shared wireless channel with location‐dependent and bursty errors, we define a service model that has the following characteristics: short‐term fairness among flows which perceive a clean channel, long‐term fairness for flows with bounded channel error, worst‐case delay bounds for packets, short‐term throughput bounds for flows with clean channels and long‐term throughput bounds for all flows with bounded channel error, expanded schedulable region, and support for both delay sensitive and error sensitive data flows. We present the wireless fair service algorithm, and show through both analysis and simulation that it achieves the requirements of the service model in typical wireless network environments. The key aspects of the algorithm are the following: (a) an enhanced fair queueing based service scheme that supports decoupling of delay and bandwidth, (b) graceful service compensation for lagging flows and graceful service degradation for leading flows, (c) support for real‐time delay sensitive flows as well as non‐real‐time error sensitive flows, and (d) an implementation within the framework of the simple and robust CSMA/CA wireless medium access protocol. This revised version was published online in July 2006 with corrections to the Cover Date.     

Performance analysis of fractal modulation transmission over fast-fading wireless channels

Fractal modulation schemes have been under investigation for signal transmission over time-varying channels because of their advantages in data transmission at different frequency bands. This also allows efficient reception when channel conditions are varying by selecting the optimal frequency/time resolution based on the current channel condition. We present a performance analysis of fractal modulation transmission over Rician fast-fading channels in the presence of AWGN. A quadrature transmission scheme is simulated and compared, in terms of error robustness, to a QAM transmission system. Other papers analysing fractal modulation system performance do not consider time-varying channels, which are important as they represent the main configuration for communication systems based on this modulation technique. The novelty of our paper lies in the comparison of a fractal modulation system to a QAM one (core of the OFDM modulation technology, extensively used in broadcasting) using a testbed simulation environment where additive noise and fast fading are considered as typical error sources for transmission over wireless channels. Several wavelet families for a fractal modulation scheme have been considered and performance for each one measured; results reported show the effectiveness of the fractal modulation paradigm and confirm its effective utilization in data broadcasting.     

LMDS/LMCS hub interconnection alternatives and multiple access issues

LMDS/LMCS is a broadband wireless local loop, millimeter‐wave alternative to emerging integrated multiservice access networks. Significantly large amounts of bandwidth – in the order of one GHz of spectrum – are made available to residential subscribers or supported business users respectively that employ highly directional antennas and signal polarization to establish communication with a central hub. Besides the requirement for dynamic bandwidth allocation capabilities, these networks should be able to guarantee negotiated quality of service (QoS) levels to a number of constant‐length (ATM) – and possibly variable length (TCP/IP) – packet streams. In this context, we analyze the performance of contention, polling/probing and piggybacking mechanisms that will be used by the LMDS MAC protocol for the dynamic support of both real‐time and non‐real‐time traffic streams. More specifically, we focus on the end‐to‐end performance of a real‐time variable bit rate connection for which the LMDS link is only the access component of a multi‐link path through an ATM network. Results are presented on maximum end‐to‐end cell delays under a Weighted Round Robin service discipline and buffer requirements are calculated for no‐loss conditions. In parallel, we also consider the case in which variable length IP packet traffic is supported as such by the same wireless access network. Backbone interconnection alternatives of LMDS hubs, multiple access proposals and scheduling algorithms are addressed in this framework. This revised version was published online in July 2006 with corrections to the Cover Date.     

Performance evaluation of a finite buffer generalized selectiverepeat ARQ scheme for satellite communications

This article presents a new generalized selective repeat automatic repeat request (ARQ) scheme for error control in broadcast and point-to-point satellite communication systems. In the proposed scheme, each bit in a packet is repeated m times consecutively to increase the transmission reliability. Finite capacity buffers have been assumed at the earth stations. The throughput, theoretically derived for the proposed scheme, is optimized with respect to the number of copies transmitted per bit. A suitable algorithm to adaptively choose this number in relation to the transmission channel propagation conditions can also be used. In comparison with classical and modified versions of the selective repeat ARQ scheme as described in the literature, the proposed scheme provides enhanced throughput, especially with poor channel conditions and a high number of receiving earth stations     

Design and evaluation of multicast GFR for supporting TCP/IP over hybrid wired/wireless ATM

The major challenges of designing multicast traffic control protocols for a combined wired/wireless network are the varying transmission characteristics (bandwidth, error, and propagation delay) of the wireless and wired media, and the different, possibly conflicting frame rate requests from multiple sources. To address these issues, in this paper we design and evaluate new unicast and multicast guaranteed frame rate (GFR) schemes for supporting TCP/IP traffic over a combined wired/wireless ATM network. We first propose a new, flexible weighted buffer management, and a frame‐based virtual spacing (VS) mechanism implementing weighted fair queueing. The unicast GFR scheme is based on the integration of the new weighted buffer management, and either cell‐based or frame‐based VS. It is then extended to support multicast GFR flows. The multicast scheme presented in this paper is the first multicast GFR scheme appeared in the literature. These schemes are carefully evaluated over several network configuration, supporting heterogeneous TCP/IP traffic with various frame rates. Simulation results show that the new schemes guarantee the minimum rates requested, provide excellent fairness, and achieve reasonably high efficiency. The new schemes may be extended to provide differentiated service in both IP and mobile IP frame work. This revised version was published online in July 2006 with corrections to the Cover Date.     

On properties of read and write sets in the Awerbuch–Peleg scheme for tracking mobile users

An important issue in the design of a wireless network is the scheme used for tracking the locations of its mobile users. A formal scheme for efficient location tracking proposed by Awerbuch and Peleg uses a locality‐preserving distributed directory server whose construction is based on the graph‐theoretic notion of a regional matching. Although this scheme has been theoretically shown to have low worst‐case communication complexity, its implementation behavior is not known. We have implemented the Awerbuch–Peleg scheme in order to evaluate its performance and practicality. This paper, which stems from our implementation, examines properties of the read and write sets that are a key component of the hierarchical directories used in the scheme. We are particularly interested in read set size since it directly influences the scheme’s communication cost and performance. Our experimental results indicate that read set sizes in randomly‐generated networks are much smaller than the theoretical bound. We derive some analytical results that help explain this behavior. In particular, we establish tight constant bounds for read set size in linear, grid and uniform degree balanced tree networks that are independent of the number of network nodes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Performance of Double-Tier Access-Control Schemes Using a Polling Backbone for Metropolitan and Interconnected Communication Networks

We consider a double-tier communication network architecture for metropolitan area and packet radio networks for controlling the access of network terminals into a single shared broadcast channel. Terminals are organized into local groups in accordance with their geographical proximity or other criteria. Each local group can be associated with a primary station. The latter can serve as an unbuffered repeater for terminal transmissions unto the multiple-access channel. A polling policy is used by the primary stations to gain access into the shared communications backbone. Once a primary station is provided access into the channel, it initiates a local access control procedure. Message delay performance results and bounds are obtained for general reservation local-access procedures. In particular, we analyze and present performance results for a polling/tree-random-access procedure which can be effectively used for many packet radio and cellular digital radio networks, as well as for a polling/positionalpriority scheme for CATV and fiber-optic based networks.     

Performance evaluation of a reservation TDMA protocol for voice/data transmissions in a LEO satellite communication system

In this paper, the capability is investigated of a reservation TDMA‐based protocol to support constant bit rate and best‐effort traffics in Low Earth Orbit (LEO) satellite communication systems under typical propagation conditions. Differently from several previous papers on the same subject, we focus here on a communication channel affected by multipath fading and characterized by a high round trip delay. In our protocol, a higher priority is given to constant bit rate terminals with respect to best‐effort data terminals. The performance for constant bit rate and best‐effort terminals was derived by means of a suitable analytical approach and computer simulations. The results shown herein permits to evaluate the influence of the channel propagation conditions on the system performance. Moreover, they highlight that the reservation TDMA protocol exhibits a good behaviour for the communication channel under consideration and in comparison with a recent protocol based on the classical PRMA scheme. Copyright © 2003 John Wiley & Sons, Ltd.     

ATM cell encryption and key update synchronization

This paper presents a data compaction/randomization based approach as a mode of block encryption for ATM (Asynchronous Transfer Mode) cells. The presented approach converts a plaintext into pseudo‐random plaintext before ciphering to conceal patterns in the plaintext. The underlying idea behind this scheme is the Shannon's principles of “confusion” and “diffusion” which involve breaking dependencies and introducing as much randomness as possible into the ciphertext. In this scheme, confusion and diffusion are introduced into the system by first compressing the ATM cell payload and then spreading a continuously changing random data over the entire content of the cell. As a mode of operation for block ciphering, this scheme offers the following attractive features:(i) plaintext patterns are pseudo‐randomized and chained with ciphertext (thereby, preventing against “dictionary”, “known plaintext”, and “statistical analysis” attacks), (ii) it is self‐synchronizing, (iii) cell loss has no additional negative effect, (iv) no IV (Initialization Vector) storage is required, (v) it is encryption‐algorithm independent, (vi) there is no cell‐to‐cell dependency (no feedback from previous cells), and (vii) it is highly scalable (i.e., cells from the same stream can be ciphered and deciphered in parallel). This paper also presents a secure mechanism for in‐band synchronization of encryption/decryption key updates using a “marker‐cell” that is carried within the data channel. An important aspect of both the above mechanisms is that they do not require any changes to the ATM cell header or ATM infrastructure. This revised version was published online in June 2006 with corrections to the Cover Date.     

TCP extensions for space communications

The space communication environment and mobile and wireless communication environments show many similarities when observed from the perspective of a transport protocol. Both types of environments exhibit loss caused by data corruption and link outage, in addition to congestion‐related loss. The constraints imposed by the two environments are also similar – power, weight, and physical volume of equipment are scarce resources. Finally, it is not uncommon for communication channel data rates to be severely limited and highly asymmetric. We are working on solutions to these types of problems for space communication environments, and we believe that these solutions may be applicable to the mobile and wireless community. As part of our work, we have defined and implemented the Space Communications Protocol Standards‐Transport Protocol (SCPS‐TP), a set of extensions to TCP that address the problems that we have identified. The results of our performance tests, both in the laboratory and on actual satellites, indicate that the SCPS‐TP extensions yield significant improvements in throughput over unmodified TCP on error‐prone links. Additionally, the SCPS modifications significantly improve performance over links with highly asymmetric data rates. This revised version was published online in June 2006 with corrections to the Cover Date.