Logical Channels Research Articles

Effect of the sampling rate of the tracking system on free-space laser communications

Lasers play an ever-increasing role in aerospace communication systems by providing the most logical connectivity channels. They drive the advancements in modern optoelectronics; however, successful implementation of this technology hinges on having an equally advanced beam-steering system for tracking the communication counterpart in the presence of complex maneuvers and the resident vibration of the airframe. The work presented in this paper concentrates on the development of agile acousto-optic beam-steering systems for laser communication terminals, which use constant-gain controllers augmented with an adaptive Kalman filter. Experimental results are presented to demonstrate communication performance as a function of the sampling rate in the tracking loop.

Phase estimation in data channelization for video transmitting

Channelization is one of the important techniques for sharing a single physical channel among the multiple videos. In channelization, the videos are partitioned into segments and the bandwidth of the physical channel is partitioned into logical channels. The first segment of each video is transmitted through the first logical channel, the second segment of each video is transmitted through the second logical channel, and so forth. The segments are transmitted periodically through the logical channels. In this paper, the video signals to be transmitted through the logical channels are estimated. Furthermore, the phase is estimated in terms of jitter delays that occur among the video segments, while transmitting them through the logical channels. The phase is an important parameter in video communication latency. Using the phase, the group delay can be estimated and based on the group delay, the storage space required at the client's site can be determined so that the continuous and jerk-free delivery of the videos is provided to the users.

Storage space estimation for videos using fading channels

In this paper, we propose a model for estimating the buffer storage for providing continuous delivery of the video data to users. The model incorporates the jitter delay, which is a switching delay between two consecutive video segments being transmitted through a logical channel. The jitter delay is assumed to be Rayleigh distributed as it characterizes the channel fading.

The Software Architecture for Module-based Robot System Supporting Heterogeneous Network Interfaces

On developing modern robot systems, intellectual robots can be designed as multiple modules, where the module means the autonomous hardware units performing robot specific tasks. Further, each module can be connected with non-unified network interfaces due to a heterogeneous feature of robot system. In this manner, one of technical challenges is interoperability to support stable and effective communication between such disparate devices. Focusing on this issue, this paper proposes a middleware named HERM (Heterogeneous nEtwork-based Robot Middleware). HERM is divided into three layers; (i) Network Interface Layer, which abstracts various heterogeneous network interfaces as logical channels, (ii) Network Adaptation Layer, which provides addressing strategies and routing service for communication between modules, and (iii) Application Support Layer, which manages robot applications and transforms application data into a standard format for transmitting over a network. By this layered design, HERM provides standardized interfaces to control various heterogeneous network devices, supporting transparent and facilitates integration of different module which constitute a robot system. The results of implementation and experiment show that HERM is suitable for a module-based robot.

Connection data rate optimisation of IEEE 802.15.3 scatternets with multirate carriers

Designed for high rate Wireless Personal Area Networks (WPANs), the IEEE 802.15.3 Medium Access Control (MAC) protocol supports peer-to-peer communications in a piconet. In this paper, we analyse the link rate distribution of an 802.15.3 piconet employing multirate carriers at the physical layer, and show that the Expected Piconet Link Rate (EPLR) decreases gradually with the piconet radius. Furthermore, the Effective Scatternet Connection Rate (ESCR) is defined to minimise the stream connection cost in a scatternet by optimising the piconet coverage. Analytical and simulation results show that direct peer-to-peer communications in 802.15.3 piconets bring a huge gain in the expected data rate of intra-piconet links. While the maximum piconet size minimises the number of piconets in the scatternet and the number of hops for a randomly chosen connection, a medium sized piconet radius optimises the scatternet connection data rate. Thus, configuration of scatternets needs to consider the piconet size and channel reuse given the number of logical channels available.

Joint logical topology design, interface assignment, channel allocation, and routing for multi-channel wireless mesh networks

A multi-channel wireless mesh network (MC-WMN) consists of a number of stationary wireless routers, where each router is equipped with multiple network interface cards (NICs). Each NIC operates on a distinct frequency channel. Two neighboring routers establish a logical link if each one has an NIC operating on a common channel. Given the physical topology of the routers and other constraints, four important issues should be addressed in MC-WMNs: logical topology formation, interface assignment, channel allocation, and routing. Logical topology determines the set of logical links. Interface assignment decides how the logical links should be assigned to the NICs in each wireless router. Channel allocation selects the operating channel for each logical link. Finally, routing determines through which logical links the packets should be forwarded. In this paper, we mathematically formulate the logical topology design, interface assignment, channel allocation, and routing as a joint linear optimization problem. Our proposed MC-WMN architecture is called <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TiMesh</i> . Extensive ns-2 simulation experiments are conducted to evaluate the performance of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TiMesh</i> and compare it with two other MC-WMN architectures <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Hyacinth</i> [1] and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLICA</i> [2]. Simulation results show that <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TiMesh</i> achieves higher aggregated network throughput and lower end-to-end delay than <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Hyacinth</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLICA</i> for both TCP and UDP traffic. It also provides better fairness among different flows.

Throughput Analysis for Parallel ARQ over Correlated MIMO Channels

We treat the throughput analyses of parallel ARQ schemes over correlated MIMO channels with adaptive modulation and coding (AMC). To describe the packet transmission over multiple parallel logic channels, we extend the existing burst- error model for single channel to multiple parallel logic channels. Based on such a packet error model, we derive the throughput of different parallel ARQ protocols. Moreover, to describe the temporally correlated physical channel fading, we generalize the existing Markov model for single channel to multiple parallel channels for MIMO systems. Then we develop a method for calculating the packet-level model parameters from the parameters of the physical-layer model and the MIMO transceiver. Using the above hierarchical throughput analysis framework, we investigate the potential throughput gain or throughput loss of parallel ARQ over the conventional serial ARQ in MIMO systems. Our results reveal that as SNR increases, parallel ARQ can achieve higher throughput gain or less throughput loss compared to serial ARQ; parallel SW can achieve throughput gain in most of the MIMO scenarios but increasing the number of antennas does not always bring higher gain; parallel GBN with large number of antennas and independent buffers can achieve throughput gain; parallel SR incurs throughput loss.

Novel radio resource allocation strategy for multimedia content delivery over satellite multicast/broadcast systems

The provisioning of multimedia applications requires wireless networks to optimally allocate radio resource and efficiently adapt to dynamically changing wireless environment. Radio Resource Allocation (RRA) strategy is an important issue in the design of the Satellite Digital Multimedia Broadcasting (SDMB) system, aiming at providing more efficient and cost-effective delivery of broadcast/multicast (BC/MC) services to a wide range of audience. Based on the single-level channel multiplexing framework, the existing RRA strategy only performs transport channel multiplexing and assumes one-to-one ideal mapping between logical and transport channels. However, the bit rates of the logical channels do not always exactly match those of the transport channels, and this leads to inefficient usage of radio resource. To solve this problem, in this paper, a novel RRA strategy, which is capable of optimally performing both logical and transport channel multiplexing, is proposed for the SDMB system. In order to improve the resource utilisation and reduce the power consumption, two new algorithms, namely Optimum Estimation Algorithm (OEA) and Power-Oriented Adaptation (POA) algorithm, are developed to optimize the proposed 2-level channel multiplexing scheme. In comparison with the existing single-level channel multiplexing scheme, simulation results show that the proposed 2-level channel multiplexing scheme achieves significantly better performance in terms of transport/physical channel utilisation, transmission power consumption as well as total transmission capacity.

Request based data delivery in video-on-demand services

In unified video-on-demand (UVoD) architecture, the logical channels are classified as multicast and unicast channels. The multicast channels provide services periodically and are independent of the user requests, whereas the unicast channels are used to provide services to the individual users. In that architecture, the optimal number of unicast channels has been reported to be independent of the request arrival rate. This result seems to be less accurate as the number of logical channels is affected by the request arrival rate. In this paper, we propose a more accurate study in which the number of unicast channels is shown to be explicitly dependent on the request arrival rate. In addition, for providing immediate services to the users, the number of unicast channels is much less than that of the UVoD architecture. The other important point of this study is that it can provide services for both less popular and more popular videos. However, for more popular videos all channels should be multicast channels

Understanding the key performance issues with MAC protocols for multi‐hop wireless networks

AbstractMulti‐hop wireless networks arise in the context of ad hoc networks, sensor networks, and mesh networks, and their performance depends critically on the underlying medium access control (MAC) protocol. Inspite of the large body of work devoted to MAC protocols and associated problems, the relative importance of these problems is still not well understood. This is because most of the previous work focuses on designing a protocol to solve a particular problem, or on identifying scenarios where a protocol will not work well. In addition, most of the work is also based on simplistic assumptions about the physical wireless medium, like fixed ranges for communication and interference, or concepts like capture threshold where the desired signal strength is compared with interference from a single node at a time, rather than cumulatively.Our paper seeks to address these issues. We believe it is extremely critical that (i) we develop an understanding of the relative significance of the problems affecting MAC protocols, and that (ii) we use a realistic model for the physical channel for design and performance evaluation. Towards this end, we evaluate the performance of three currently proposed MAC protocols, IEEE 802.11 [1], RI‐BTMA [2], and DUCHA [3] under a realistic channel model with additive interference. Since these protocols solve or suffer from different sets of problems, our evaluation provides a differential diagnosis of the severity of these problems. Based on our observations, we propose a simple and robust two channel MAC protocol (entitled 2CM) that is based on IEEE 802.11 augmented with a busy‐tone channel. The 2CM protocol (i) mitigates the hidden node problem considerably, (ii) does not waste bandwidth in terms of logical control channels, and (iii) provides a reliable link layer acknowledgment. Through extensive simulations, we show that 2CM offers a consistently high throughput performance while not sacrificing link layer reliability in a variety of scenarios, thereby vindicating our approach. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Information Transmission Availability in WDM Networks

This paper deals with the system availability estimation schemes in WDM (Wavelength Division Multiplexing) optical networks and it provides for each network topology analysis of the availability. The methodology to calculate the reliability of the optical network logical connections is introduced here. Possibilities of interferences in the connection have been calculated while assessing the amount of the reserved ways and the amount of elements in the network in every logical channel. We consider single or multiple link protection scenarios. Availability models and formulas are followed by some numerical examples that allow us to estimate availability and compare data for the different network topologies. Ill. 8, bibl. 5. (in English; summaries in English, Russian and Lithuanian).

Joined MAC Scheduling and Transport Format Choice for UMTS Uplink Transmission

This paper deals with the description of the QoS architecture developed in the framework of the IST VIRTUOUS and SAILOR projects, especially targeting at the design of an UMTS MAC scheduling algorithm in charge of managing several uplink parallel active logical channels at User Equipment side. The joined approach to the packet scheduling and transport format choice proposed in this paper shows better performances respect to the 3GPP standard solution, mainly when the number of logical channels of different types --- i.e. logical channels with different needs in terms of maximum allowed delay --- handled by the same User Equipment increases. Furthermore, the proposed MAC design introduced in this paper allows a better exploitation of the available bandwidth in the uplink UMTS Radio Access Network, also increasing fairness between IP datagrams belonging to different sources.

Application of soft computing techniques to adaptive user buffer overflow control on the Internet

Two novel expert dynamic buffer tuners/controllers, namely, the neural network controller (NNC) and the fuzzy logic controller (FLC) are proposed in this paper. They use soft computing techniques to eliminate buffer overflow at the user/server level. As a result they help shorten the end-to-end service roundtrip time (RTT) of the logical Internet transmission control protocol (TCP) channels. The tuners achieve their goal by maintaining the given safety margin Delta around the reference point of the {0,Delta}2 objective function. Overflow prevention at the Internet system level, which includes the logical channels and their underlying activities, cannot shorten the service RTT alone. In reality, unpredictable incoming request rates and/or traffic patterns could still cause user-level overflow. The client/server interaction over a logical channel is usually an asymmetric rendezvous, with one server serving many clients. A sudden influx of simultaneous requests from these clients easily inundates the server's buffer, causing overflow. If this occurs only after the system has employed expensive throttling and overflow management resources, the delayed overflow rectification could lead to serious consequences. Therefore, it makes sense to deploy an independent user-level overflow control mechanism to complement the preventative effort by the system. Together they form a unified solution to effectively stifle channel buffer overflow

Filtering strategies for TFC selection schemes in 3GPP W-CDMA systems

The selection of a suitable transport format combination (TFC) according to the system load condition is one important issue of the radio resource management (RRM) in 3GPP W-CDMA systems. Different TFCs specify different ways of transmitting user data input from logical channels. It is observed that data transmission with a higher data rate will suffer a higher bit error rate (BER). This paper investigates the impact of BER on the selection of optimal TFC for transmitting the user data. Two filtering strategies are proposed to filter out infeasible TFCs so that the optimal TFC can be selected to achieve high performance. Moreover, an imbedded Markov chain is developed to evaluate the proposed strategies. From the simulation results, the feasibility and the effectiveness of the proposed strategies are demonstrated as well. We are suggesting that, for the design of an optimal TFC selection algorithm, the proposed TFC filtering strategy shall be taken into consideration.

How fast is too fast? [Super-fast Internet access

This paper discusses how super-fast Internet access can be achieved with a new technology that involves channel bonding to take access speeds over cable into the hundreds of megabits per second. A key element of this cable broadband service technology is DOCSIS 3.0, which allows several downstream and upstream radio frequency carriers to be bundled into a single logical channel to multiply capacity. It has been estimated that speeds up to 1 Gbit/s could theoretically be achieved by bonding an n number of RF channels. Apart from an obvious marketing advantage, operators can use the technology as a way of increasing network efficiency since statistical multiplexing works more effectively with wider channels.

Differential space-frequency modulation via smooth logical channel for broadband wireless communications

In this letter, a differential space-frequency modulation (DSFM) scheme is proposed for multiple input multiple-output (MIMO)-orthogonal frequency-division multiplexing (OFDM) systems in broadband wireless communications. We assume that the fading channels keep constant only within each OFDM block, and may change independently from one OFDM block to another. The differential schemes proposed for MIMO-OFDM systems in the literature cannot successfully decode with such a rapidly fading channel, since the successful decoding of the previously existing schemes relies on the assumption that the fading channel keeps constant within a period of several OFDM blocks, and it changes slowly from a period of several OFDM blocks to another. In our proposed DSFM scheme, the transmitted signals are differentially encoded in the frequency domain within each OFDM block. Thus, the differential decoding can be performed over subcarriers within each single OFDM block. Furthermore, if a statistical channel power-delay profile (PDP) is known at the transmitter, we propose to create a smooth logical channel to improve the performance of the DSFM scheme. We obtain the smooth logical channel by sorting the channel frequency responses over subcarriers from a statistical point of view. If the logical channel is not smooth enough, we further consider a pruning process in which we use only the good part of the channel and get rid of the bad part of the channel. Simulation results show that the proposed DSFM scheme over a smooth logical channel (with pruning, if necessary) performs well for various channel PDPs.

Logical channels: using web services for cross‐organizational workflow

PurposeThis paper seeks to establish a design for cross‐organizational workflow based on logical channels of communication. A set of scenarios is established which can be used to test the effectiveness of future architectures.Design/methodology/approachStarting with scenarios based on cross‐organizational business transactions, designs a set of sequence diagrams, analyzes these diagrams, and then deduces the need for certain system capabilities.FindingsCurrent approaches to web services focus on just one channel – that of invocation. In order to handle the full gamut of cross‐organizational workflow, channels devoted to flow, monitoring, negotiation, and interpersonal interaction are also necessary.Research limitations/implicationsExtensions to this research might include designs for integrating these multiple channels. Such designs can be tested against the scenarios discussed in the paper. In particular, research related to the semantic web might extend the ideas raised here.Practical implicationsCompanies implementing web services may want to augment the current technology with enhancement of their own in order to avoid inadvertently reducing their channels of communication with trading partners. A properly constructed monitoring channel has the potential to change the nature of complex workflow.Originality/valueThose designing and implementing web service technology may find value in the articulation of a set of complex scenarios which can be used to test alternative designs and implementations. The discussion of cross‐organizational monitoring is new, and has broad implications for business.

Managing logical channel configurations in complex satellite architectures

AbstractAs a result of the increased switching complexity of many communications satellites, often transponders are available with a variety of configuration options offering flexibility in power, bandwidth, and coverage. Many of these configurations share resources that prevent them from being simultaneously active, making it a challenge to understand and manage the satellite capacity inventory. In this paper we define the logical channel configuration (LCC) as an unambiguous unit of the inventory and present a novel method of modelling the interdependencies between these LCCs using linear algebra. In particular, a projector matrix is defined which can be used to update the activation state of all LCCs when the state of one or more of these is changed. As a result, a number of valid LCC scenarios can be easily generated and evaluated for optimal use of the satellite resources. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Adaptive Resource Sharing Strategies for UMTS Multiservice Mobiles

In this paper, a multiservice transmission scheme which joints voice, video, interactive game and signaling is evaluated for the dedicated channel of the Universal Mobile Telecommunications System. The transmission rate for each service is determined by means of an adaptive transport format selection. In the UMTS standard, this selection is based on power allocation provided by radio resource controller, trying to match the Eb/No requirements of the individual services. An appropriate selection of the individual rates of each multiplexed service, taking into account its particular QoS requirements, will provide a more efficient resource management than the transmission only restricted to power allocation. For this purpose, we propose and evaluate a new selection strategy based on buffer occupation, delay requirements and target bit rate keeping power constraints that intends to improve the basic operation trying to minimize the impact of the whole network. Video and game services are multiplexed in upper layers (logical channels) sharing a common transmission rate (transport channel). In this paper, it is proposed a new strategy to share the transmission rate set for this transport channel between both services taking into account their particular requirements. Results show that considering delay constraints provides a more balanced performance of the multiplexed services.

A Packet Scheduling Approach to QoS Support in Multihop Wireless Networks

Providing packet-level quality of service (QoS) is critical to support both rate-sensitive and delay-sensitive applications in bandwidth-constrained, shared-channel, multihop wireless networks. Packet scheduling has been a very popular paradigm to ensure minimum throughput and bounded delay access for packet flows. This work describes a packet scheduling approach to QoS provisioning in multihop wireless networks. Besides minimum throughput and delay bounds for each flow, our scheduling disciplines seek to achieve fair and maximum allocation of the shared wireless channel bandwidth. However, these two criteria can potentially be in conflict in a generictopology multihop wireless network where a single logical channel is shared among multiple contending flows and spatial reuse of the channel bandwidth is possible. In this paper, we propose a new scheduling model that addresses this conflict. The main results of this paper are the following: (a) a two-tier service model that provides a minimum "fair" allocation of the channel bandwidth for each packet flow and additionally maximizes spatial reuse of bandwidth, (b) an ideal centralized packet scheduling algorithm that realizes the above service model, and (c) a practical distributed backoff-based channel contention mechanism that approximates the ideal service within the framework of the CSMA/CA protocol.