Showing papers on "Communication channel published in 1989"

Packet reservation multiple access for local wireless communications

Abstract: Simulation work is reported indicating that packet reservation multiple access (PRMA) allows a variety of information sources to share the same wireless access channel. Some of the sources, such as speech terminals, are classified as periodic and others, such as signaling, are classified as random. Packets from all sources contend for access to channel time slots. When a periodic information terminal succeeds in gaining access, it reserves subsequent time slots for uncontested transmission. Both computer simulations and a listening test reveal that PRMA achieves a promising combination of voice quality and bandwidth efficiency. >

The multitone channel

Abstract: The maximum bit rate of multitone QAM (quadrature amplitude modulation) over a general linear channel is found. First, the overall bit rate for an AWGN channel with a two-level transfer function is maximized, using a multitone QAM system. The power distribution between the tones and the number of bits/symbol per tone is optimized for a given symbol error rate. Extending these results to the general channel, it is shown that the optimum power division for multitone signals is similar to the water-pouring solution of information theory. Furthermore, multitone QAM performance is about 9 dB worse than the channel capacity, independent of the channel characteristics. The multitone results throughout are compared to those of an equivalent single-tone linearly equalized system. The comparison shows that the multitone system is useful for some channels, e.g. those with deep nulls in the transfer function. The maximum bit error rate over a twisted-pair channel which is performance dominated by near-end crosstalk (NEXT) is also found. >

Capacity and coding for the gilbert-elliott channels

Abstract: The Gilbert-Elliott channel, a varying binary symmetric channel, with crossover probabilities determined by a binary-state Markov process, is treated. In general, such a channel has a memory that depends on the transition probabilities between the states. A method of calculating the capacity of this channel is introduced and applied to several examples, and the question of coding is addressed. In the conventional usage of varying channels, a code suitable for memoryless channels is used in conjunction with an interleaver, with the decoder considering the deinterleaved symbol stream as the output of a derived memoryless channel. The transmission rate is limited by the capacity of this memoryless channel, which is often considerably less than the capacity of the original channel. A decision-feedback decoding algorithm that completely recovers this capacity loss is introduced. It is shown that the performance of a system incorporating such an algorithm is determined by an equivalent genie-aided channel, the capacity of which equals that of the original channel. The calculated random coding exponent of the genie-aided channel indicates a considerable increase in the cutoff rate over that of the conventionally derived memoryless channel. >

Two-layer coding of video signals for VBR networks

Abstract: Two-layer conditional-replenishment coding of video signals over a variable-bit-rate (VBR) network is described. A slotted-ring network based on an Orwell protocol is assumed, where transmission of certain packets is guaranteed. The two-layer coder produces two output bit streams: the first bit stream contains all the important structural information in the image and is accommodated in the guaranteed capacity of the network, while the second adds the necessary quality finish. The performance of the coder is tested with CIF standard sequences and broadcast-quality pictures. The portion of the VBR channel allocated to the lower layer as guaranteed bandwidth is examined. Using broadcast-quality pictures, statistics were obtained on the performance of this system for different choices of bit rate in the lower layer. The effect of lost packets is shown on CIF standard picture sequences. It is shown that the coder performs well for a guaranteed channel rate as low as 10-20% of the total bit rate. >

The Role of Trust and Co‐operation in Marketing Channels: A Preliminary Study

Abstract: There exists at present a gap in channel theory on the role of co‐operation and trust in the functioning of interfirm relationships. These variables have not featured as major factors in the explanations of how channels co‐ordinate their activities, survive and grow. This article introduces trust as an important determinant of channel behaviour, indicates the importance of trust in co‐operative behaviour and presents the results of an introductory study on trust in marketing channels.

Wireless Optical Communication Systems

Abstract: Wireless Optical Communication Systems addresses the problem of designing efficient signaling and provides a link between the areas of communication theory and modem design for amplitude constrained linear optical intensity channel. Topics include historical perspective, channel impairments, amplitude constraints and the characteristics of popular optoelectronic components. A variety of wireless optical channel topologies are presented along with a survey and analysis of present day signalling techniques employed for these channels. The author provides a unifying framework for signalling design which allows the channel constraints to be represented geometrically and permits the use of modem design principles from electrical channels. Modulation schemes are designed using the formalism of lattice codes and a design process for signalling sets is specified. The use of multiple-input/multiple-output (MIMO) wireless optical channels to improve the spectral efficiency of links is explored. The basic spatio-temporal modem design problem is specified and a spatial multiplexing gain is quantified. New spatial discrete multitone modulation is proposed and the unique features are discussed. Based on measurements on an experimental prototype, a channel model is formulated and a realizable spatio-temporal coding scheme is simulated to quantify performance gains. This volume is organized for professional and academic readers engaged in modem design for wireless optical intensity channels. Significant background material is presented on both the properties as well as on fundamental communications principles. Wireless Optical Communication Systems can be used by physicists and experimentalists as an introduction to signalling design as well as communication systems designers.

Digital sound broadcasting to mobile receivers

Abstract: The authors describe a system that combines the orthogonal frequency-division multiplexing technique and a coding strategy associated with diversity in the frequency domain. The system is suitable for digital broadcasting through a particularly hostile urban radio channel. The general principles of COFDM (coded orthogonal frequency-division multiplexing) are explained, and a detailed representation of the signals and the decoding procedure is given. The performance of the system in the selective Rayleigh channel is presented, and the behavior of the system when the conditions of temporal and frequency coherence of the channel are not fully met (very high-speed reception and abnormally extended channel delay spread) is described. The first implementation of a 4-PSK-COFDM systems has been demonstrated at the WARC-ORB 88 conference in Geneva, validating this concept of digital sound broadcasting. >

Distributed assignment algorithms for multihop packet radio networks

Abstract: New distributed dynamic channel assignment algorithms for a multihop packet radio network are introduced. The algorithms ensure conflict-free transmissions by the nodes of the network. The basic idea of the algorithms is to split the shared channel into a control segment and a transmission segment. The control segment is used to avoid conflicts among nodes and to increase the utilization of the transmission segment. It is shown how these algorithms can be used in order to determine time-division multiple access (TDMA) cycles with spatial reuse of the channel. >

Performance analysis of cellular mobile communication systems with dynamic channel assignment

Abstract: The traffic analysis of small-cell mobile networks with dynamic channel assignment is investigated to determine their blocking performance, using a hybrid method of analysis and simulation. The authors particularly focus on the performance problems presented by networks with heterogeneous cell traffic loads, the impact of traffic volatility among the cells, and the impact of multichannel traffic on the channel blocking probabilities. Significant improvement in network performance with dynamic channel assignment is established by numerical results. >

Three-dimensional turbulent structure in straight open channel flows

Abstract: Secondary currents are generated and modified as a result of the anisotropy of turbulence, which is caused by the boundary conditions of the bed, the side-wall and the free surface, as well as the aspect ratio of the channel and the channel geometry. Secondary currents affect the primary mean flow, producing threedimensional structures. Such a generation mechanism for secondary currents in closed and open channel flows can be explained well by using the longitudinal vorticity equation. The secondary motions in open channel flows are quite different from those in closed channel flows.

The capacity region of the symbol-asynchronous Gaussian multiple-access channel

Abstract: An equivalent discrete-time Gaussian channel parametrized by the signal cross-correlations is derived to obtain an equivalent channel model with discrete-time outputs. The main feature introduced by the lack of symbol synchronism is that the channel has memory. This is due to the overlap of each symbol transmitted by a user with two consecutive symbols transmitted by the other user. It is shown that if the transmitters are assigned the same waveform, symbol asynchronism has no effect on the two-user capacity region of the white Gaussian channel which is equal to the Cover-Syner pentagon, whereas if the assigned waveforms are different (e.g., code division multiple access), the symbol-asynchronous capacity region is no longer a pentagon. An alternative representation of the capacity region which results in a particularly compact characterization of the fundamental limits of the multiple-access channel in the region of signal-to-noise ratios is also considered. >

Modulation and demodulation system employing AM-PSK and FSK for communication system using digital signals

Abstract: A communication network having a first broadband communications channel or transmitting bus and a second broadband communications channel or receiving bus, wherein the first broadband communications channel is for passing information upstream to a head end and the second broadband communications channel is for passing information downstream from the head end to remote nodes. All nodes of the system are coupled to both the first communications channel and the second communications channel. According to the invention, modulation of signals applied to the first communication channel is optimized for burst communication from a plurality of sources to central control at the head end, and modulation applied to the second communications channel is optimized for continuous communication from the central source to a target node.

Optimal decentralized control in the random access multipacket channel

Abstract: A decentralized control algorithm is sought that maximizes the stability region of the infinite-user slotted multipacket channel and is easily implementable. To this end, the perfect state information case in which the stations can use the instantaneous value of the backlog to compute the retransmission probability is studied first. The vest throughput possible for a decentralized control protocol is obtained, as well as an algorithm that achieves it. These results are then applied to derive a control scheme when the backlog is unknown, which is the case of practical relevance. This scheme, based on a binary feedback, is shown to be optimal, given some restrictions on the channel multipacket reception capability. >

Narrowband/wideband packet data communication system

Abstract: The best features of narrowband and wideband signaling are merged to provide a simple and reliable multiple-access network. This is done by transmitting the header of the packet using narrowband signaling coupled with an associated channel access protocol such as carrier-sense multiple-access. The data portion of the packet is then sent as a spread-spectrum signal with a spreading sequence that is common to all nodes in the network. The narrowband headers allow easy monitoring of channel loading and busy nodes while acting as a synchronization aid to the wideband signal. The multiple-access capability of spread-spectrum signaling increases channel throughput dramatically over a conventional narrowband-only system, and the anti-multipath feature allows increased data transmission rates on a multipath-prone channel. Common spreading sequences simplify transceiver design and allow packet broadcasting on the network.

Dependence balance bounds for single-output two-way channels

Abstract: If in a transmission the inputs of a single-output two-way channel exhibit some interdependence, this dependence must have been created during earlier transmissions. The idea that no more dependence can be consumed than is produced is used to obtain new upper bounds to the capacity region of the discrete memoryless single-output two-way channel. With these upper bounds it is shown that C.E. Shannon' (1961) inner bound region is the capacity region for channels in a certain class, and the Zhang-Berger-Schalkwijk upper bound (1986) for Blackwell's multiplying channel is improved upon. >

A systematic approach to carrier recovery and detection of digitally phase modulated signals of fading channels

Abstract: The problem of optimal carrier recovery and detection of digitally phase modulated signals on fading channels by using a nonstructured approach is presented, i.e. no constraint is placed on the receiver structure. First, the optimal receiver is derived for digitally phase-modulated signals when transmitted over a frequency-nonselective fading channel with memory. The memory results from the fact that usually the coherence time of the channel is larger than the symbol period. Symbols adjacent in time cannot be detected independently and therefore the well-known quadratic receiver is not optimal in this case. A maximum a posteriori (MAP) detector is derived and explicitly utilizes the channel memory for carrier recovery. The derivation shows that the optimal carrier recovery is, under certain conditions, a Kalman filter. Some attractive properties of this carrier recovery unit (including the absence of hang up) are discussed. Then the error rate of several digital modulation schemes is calculated taking the performance of the filter into account. The differences in susceptibility of the modulation schemes to carrier phase jitter are specified. >

Multiple-access channels with memory with and without frame synchronism

Abstract: The capacity region of frame-synchronous and frame-asynchronous, discrete, two-user multiple-access channels with finite memory is obtained. Frame synchronism refers to the ability of the transmitters to send their code words in unison. The absence of frame synchronism in memoryless multiple-access channels is known to result in the removal of the convex hull operation from the expression of the capacity region. It is shown that when the channel has memory, frame asynchronism rules out nonstationary inputs to achieve any point in the capacity region, thereby allowing only coding strategies that involve cooperation in the frequency domain but not in the time domain. This restriction drastically reduces the capacity region of some multiple-access channels with memory, and in particular the total capacity of the channel, which is invariant to frame asynchronism for memoryless channels. >

The analysis of river basins and channel networks using digital terrain data

Abstract: 2 Acknowledgement 3 Table of

Efficient digital frequency division multiplexed signal receiver

Abstract: A digital intermediate frequency (IF) receiver for frequency division multiplexed (FDM) signals including analog circuitry for receiving FDM signals and an analog-to-digital (A/D) converter for converting the received signals to a sampled digital received signal. A digital complex mixer responsive to the digital output of the A/D converter translates the spectrum of the sampled digital received signal to center the desired FDM channel at zero frequency (DC). Digital low pass filtering isolates the desired channel centered at DC, and a digital complex mixer can be used to translate the isolated selected channel to a predetermined IF frequency. The in-phase portion of the digital IF centered selected channel or the DC centered complex envelope selected channel can then be provided to appropriate demodulation or decoder networks.

Apparatus for and method of controlling the opening and closing of channel for liquid

Abstract: An apparatus for controlling the opening and closing of a channel for a liquid is arranged such that a liquid channel is closed by causing a controller to control one heat absorbing and generating part of a cooling/heating element to execute heat absorption and cooling a heat transmitting element to solidify the liquid in the channel. The apparatus is also arrangement such that the channel is opened first by causing the controller to control the same heat absorbing and generating part to execute heat generation and heating the heat transmitting element to melt the liquid solidified in the channel. A method of controlling the opening and closing of a channel according to the invention includes the steps of: solidifying a liquid in a channel by cooling it from the outside to close the channel; and opening the channel thus closed by melting the liquid solidified in the channel by the application of heat.

Dependence balance bounds for single-output two-way channels

Abstract: If in a transmission the inputs of a single-output two-way channel exhibit some interdependence, this dependence must have been created during earlier transmissions. The idea that no more dependence can be consumed than is produced is used to obtain new upper bounds to the capacity region of the discrete memoryless single-output two-way channel. With these upper bounds it is shown that C.E. Shannon' (1961) inner bound region is the capacity region for channels in a certain class, and the Zhang-Berger-Schalkwijk upper bound (1986) for Blackwell's multiplying channel is improved upon. >

Packet-switched communications network with parallel virtual circuits for re-routing message packets

Abstract: In a packet-switched communications network, each of a plurality of terminals sequentially transmits control packets in response to a request for call before sequentially transmitting message packets. A switching node of the network is responsive to the control packets for establishing first and second logical channels through the network. Message packets are propagated through the first logical channel. The established logical channels are monitored to detect an abnormal condition. In the event of an abnormal condition in the first logical channel the message packets are re-routed to the second logical channel.

Method and apparatus for determining audience viewing habits by jamming a control signal and identifying the viewers command

Abstract: A method and apparatus for determining the channel of a plurality of predetermined channels to which a remotely controlled receiver is tuned. A viewer transmitter device includes a keyboard for receiving viewer entered selections and a remote transmitter which transmits infrared, ultrasonic, radio frequency or other radiated control signals for each of the viewer selections. A receiver device in a channel detection system receives a signal in the selected transmission medium, and immediately signals a jamming device to broadcast interference which precludes the remotely controlled receiver from identifying and acting upon the transmitted control signal. The receiver device applies the received signal to a processor device that performs a stored program to determine if the received signal corresponds to a transmitted control signal from the viewer transmitter device and, if so, to identify the channel to which the monitored receiver is to be tuned. An associated memory device is used for storing the identified channel reception data. The processor device identifies the user selection and either applies a corresponding control signal to a second transmitter device which transmits a control signal of sufficient strength to overcome the interference, or instructs the jammming device to cease the broadcasting of interfering signals. In either case, the remotely controlled receiver will now receive and implement the viewer selection. The processor device will periodically broadcast a command to the remotely controlled receiver containing the last identified channel data to ensure that a viewer does not manually adjust the channel being viewed.

Performance analysis of spread spectrum packet radio network with channel load sensing

Abstract: A continuous-time Markov-chain model for an asynchronous communication spread-spectrum code-division-multiple-access (CDMA) packet radio network is developed. The network is composed of mutually independent users. The receiver-based code is considered; a terminal with a packet to send looks up the destination's code and transmits on that code. Each user senses the channel load and refrains from transmission if the channel load exceeds the channel threshold. The model makes it possible to study the threshold effect of channel load on the performance of the CDMA packet radio network. Improvements in performance of spread-spectrum packet radio networks due to channel-load sensing are shown. Steady-state results for throughput are obtained. >

A high capacity assignment method for cellular mobile telephone systems

Abstract: The authors describe a channel assignment scheme for cellular mobile telephone systems in which assignment is based on actual field strength measurements performed dynamically on the functioning system. The scheme involves no rigid partitioning of the channel set into geographic patterns, as in conventional systems. A mutual interference criterion is applied to ensure that satisfactory service is maintained throughout the system. The system provides capacity improvements ranging from 100% to 300% depending on the complexity of the implementation. It is implementable using any of the current or proposed modulation schemes. >

Packet data transmission over mobile radio channels

Abstract: Since in mobile radio Rayleigh fading poses the main threat to accurate data transmission, a mathematical model of the dynamics of Rayleigh fading is used to explore the optimum duration of data packets. The performance criterion is the rate of information transfer through the mobile radio channel. In addition to packet size, the information rate depends on: the speed of the mobile terminal, the channel bit rate, the size of the packet header, and the fade margin of the modulation and coding techniques. In particular, attention is focused on line rates of 16 kb/s and 256 kb/s (which are representative of the rates proposed for digital mobile radio systems in North America and Europe, respectively). At 16 kb/s, the optimum packet size is approximately 17 B (8.5-ms duration). At 256 kb/s, maximum throughput occurs when the packet contains about 48 B (1.5-ms duration). The precise optimum depends on vehicle speed, header size, and fade margin. The optimum packets are considerably shorter than the 125-B packets customarily used in terrestrial and satellite systems. >

Optimum rate Reed-Solomon codes for frequency-hopped spread-spectrum multiple-access communication systems

Abstract: The authors consider a multiple-access frequency-hopped spread-spectrum communication system with Reed-Solomon codes. The performance measures of interest are an achievable region and the channel throughput. The achievable rate region is the set of all pairs of code rate and number of users for which communication is possible with error probability below a fixed value. The throughput measures the expected number of successful codeword transmissions per unit bandwidth. Two models of interference are considered. For these two models, the authors determine the optimal number of users for a given bandwidth and the optimal rate Reed-Solomon code that maximize the throughput. They also determine the achievable region for these models. >

A preliminary study of a diagonal channel-routing model

Abstract: The layout of two-terminal nets in a VLSI channel is realized in a new diagonal channel-routing model (DCRM), where the tracks are segments respectively displayed at +45 ° and −45 ° on the two layers of the channel. A new definition of channel density is introduced, and a lower bound to the channel width is derived by the application of an algorithm, whose complexity is evaluated as a function of the channel density, and other parameters of the problem. A simple linear-time algorithm is proposed, which produces an optimal layout (i.e., it requires a channel of minimum width) if the length of the longest net equals the lower bound for the channel width. In any case, the number of vias is at most one for each net. Some particular solutions are proposed for problems with long nets. Specific problems are much easier in DCRM than in the classical Manhattan model. For example, any shift-by-i can be realized in DCRM in a channel of widthi.

Signal distribution network system

Abstract: A signal distribution cable network system in which frequency division multiplexing is employed to provide a plurality of information channels. A channel allocation controller (CT) allocates free channels on request for the transport of signals from a local signal source (SS1, SS2, SS3) to a signal destination receiver (SR1, SR2, SR3) connected to the network. The local signal source includes a programmable modulator (CFS, VCO, MOD) which is set by the channel controller (CT) to operate at the carrier frequency of the selected channel. The signal level of the signals transmitted by the local signal source is measured in the controller and adjusted to compensate for signal attenuation by a command signal sent by the controlle to the programmable modulator in the local signal source.

Method and apparatus for recording and reproducing information including plural channel audio signals

Abstract: A method for recording and reproducing information including plural channel audio signals on and from a recording medium. A sampling operation at a predetermined sampling frequency is respectively performed against plural channel audio signals, a modulation operation of a predetermined modulation system is performed respectively for each of a plurality of channels of the sampled data, an identification code identifying each channel is added to each of plural channel coded information signals, and subsequently the coded information signals are multiplexed by a time division multiplexing operation and recorded on the recording medium together with one channel analog audio signal or by themselves. At the time of play-back, at least two of the plural channel coded information signals designated by a selection command or at least two of the plural channel coded information signals and the one channel analog audio signal designated by the selection command selectively decoded arbitrarily using the identification code, and a reproduction signal is generated by mixing the at least two channels of audio signal. With this feature, a single disc can be used for recording a program having multilingual audio signals.