Showing papers on "Telecommunications link published in 1996"

System and method for flexible coding, modulation, and time slot allocation in a radio telecommunications network

Abstract: A system and method for dynamically adapting the user bit rate of a time division multiple access (TDMA) cellular telecommunication system to achieve optimum voice quality over a broad range of radio channel conditions are disclosed. The system continuously monitors radio channel quality on both the uplink and the downlink, and dynamically adapts the system's combination of speech coding (21), channel coding (22), modulation (23), a number of assignable time slots per call (27) to optimize voice quality of the measured conditions. Various combinations of the system's speech coding, channel coding, modulation, and assignable time slots are identified as combination types (1-5) and corresponding cost functions are defined. By idendifying and selecting the cost function with the lowest cost for the measured radio channel conditions, the system provides the maximum voice quality achievable within the limits of the system design.

Capacity and power control in spread spectrum macrodiversity radio networks

Abstract: What is the capacity of the uplink of a radio network of receivers? We consider a spread spectrum model in which each user is decoded by all the receivers in the network (macrodiversity). We use a carrier-to-interference performance criterion that we derive from Shannon theory; each user must find the right transmitter power level to satisfy its carrier-to interference constraint. Satisfying this requirement for all users is equivalent to solving a fixed point problem. We use this power control problem to derive the network capacity region and find that the feasibility of a configuration of users is independent of their positions in the network; each user can be assigned a bandwidth that is independent of the user's position in the network. Our capacity region is an upper bound over all schemes that treat the interference of other users as pure noise. To show that the capacity can be realized in practice, we propose a decentralized power adaptation algorithm and prove global convergence to the fixed point via a monotonicity argument.

Joint demodulation using spatial maximum likelihood

Abstract: Methods and systems for processing signals in radio communication systems are described which include processes for handling co-channel interference while reducing the number of Viterbi states being processed. A spatial analogy to the Viterbi MLSE process is provided. Both the uplink and downlink cases are described.

Performance of a joint CDMA/PRMA protocol for mixed voice/data transmission for third generation mobile communication

Abstract: A joint code-division multiple-access/packet-reservation multiple-access (CDMA/PRMA) technique is proposed and investigated as a candidate for an uplink protocol for third generation mobile communication systems. Access to the radio channel is controlled such that compared to random access CDMA, interference variance is reduced and throughput increased. Mixed voice/data traffic is investigated for an isolated cell only, whereas voice-only traffic is also investigated in a cellular environment with a regular hexagonal cell structure. Intercell interference is assumed to be Gaussian, and only the average interference level is considered.

Channel quality management in a cable telephony system

Abstract: A method and apparatus in a communication system (100) for allocating and controlling data transmissions to and from communications unit (134) in communications system (100). The communication systems (100) includes a cable distribution network (106) with a base communications unit (102) and a number of downstream communications units (134) all connected to the cable distribution network (106). A plurality of channels are used to transmit data transmissions between the base communications unit (100) and the downstream communications unit (134). Uplink and downlink channels are monitored to determine channel quality for each of the channels in communications system (100). The determined channel quality is used to both initiate transfers of communications links to other frequencies and for assigning channels to various communications units (134).

Medium access control scheme for data transmission on code division multiple access (cdma) wireless systems

Abstract: A synchronous discontinuous transmission medium access control (SDTX-MAC) method and apparatus for more efficiently using existing uplink channels by sharing these uplink channels between multiple terminals engaged in bursty data transmission. This is accomplished by assigning each mobile terminal an individual time slot and by not requiring each mobile terminal to broadcast its identity. This results in a reduction in the number of receivers on each base station and a reduction in the length of the synchronization message.

Interference reduction in shared-frequency wireless communication systems

Abstract: An apparatus and method for reducing interference between an uplink transmitter of a fixed satellite service (FSS) system (150) and an uplink or downlink receiver of a local multipoint distribution service (LMDS) system (100) are described An ordered list of the preferred uplink transmission frequencies is assigned to all FSS uplinks located in a particular cell of the LMDS system (100) Different ordered lists are used in different cells (105-1 -105-3) of the LMDS system (100), while uplinks located in the same cell can utilize the same order list Further, the ordered list may be selected by the LMDS service provider such that the impact of interference from FSS uplinks can be readily predicted and minimized Therefore, the system allows simultaneous access to a shared frequency band for both LMDS and FSS systems (100 and 150)

Voice over data conferencing for a computer-based personal communications system

Abstract: A personal communications system enables the operator to simultaneously transmit voice and data communication to a remote site. The personal communications system is equipped with two telephone line interfaces to allow connection over a communications link between two remote sites. The personal communications system incorporates advanced priority statistical multiplexing of non-time-critical data with time-critical data over the communications link to increase channel throughput without a reduction in quality of the time-critical data. The personal communications system may be networked in different topological configurations to enable conferencing in a variety of time-critical and non-time-critical communications.

Performance of an OFDM-TDMA mobile communication system

Abstract: The multicarrier transmission technique (OFDM) is considered in combination with a TDMA/TDD multiple access scheme for a cellular mobile communication system. Performance analysis is presented for the uncoded and coded (TCM) case. It is shown that OFDM systems have a large potential concerning the flexible allocation of the total given bandwidth to different users. This flexibility can be exploited to adapt to the impairments of the radio channel, thus increasing the overall performance. Two methods, namely (1) a simple principle to leave out weak subcarriers, and (2) the individual modulation of each subcarrier (adaptive modulation) are studied (for the up-/downlink case in a frequency selective and time-variant radio channel), and results with respect to throughput and BER performance are discussed.

Communications system and method of operation

Abstract: A method of operation of a radio communications system having a controller controlling communications of a plurality of communicating units on a plurality of communication channels. The method includes the steps of a first communications unit transmitting a call request (100) to the controller and the controller reserving a first communications channel for a communications unit required in the requested call. The controller allocates the first communications channel for temporary communications to other communicating units whilst waiting for the availability of a second communications channel for the requested call, wherein the second communications channel is to be allocated to a second communications unit required in the requested call. A communications system having a channel allocation controller (12) having a list of communications channels (16) with reserved indicators (18) indicative of the status of reserved communications channels.

System for transmitting radio signals from mobile terminals to provide space diversity for uplink signals via geostationary communication satellites

Abstract: The invention concerns a system for transmission of spatial diversity radio signals via a geostationary main communication satellite and one or more auxiliary satellites "colocated" in the same orbit. The distance between an auxiliary satellite and the main satellite is in the range from 200 km to 400 km. The system includes conventional bidirectional transmission links between terrestrial mobile terminals and the main satellite and between the latter and a terrestrial station. Additionally, unidirectional transmission links are provided between the auxiliary satellites and the main satellite. Applications include a mobile communication service with portable terminals via a geostationary satellite.

Apparatus and method of synchronizing a transmitter in a subscriber terminal of a wireless telecommunications system

Abstract: A wireless telecommunications system (1) includes a central terminal (10) for transmitting and receiving radio frequency signals to and from a subscriber terminal (20). A downlink communication path is established from a transmitter (200) of the central terminal (10) to a receiver (202) of the subscriber terminal (20). A downlink signal (212) is transmitted from the transmitter (200) to the receiver (202) during setup and operation of the wireless telecommunications system (1). The downlink signal (212) includes an overhead channel (224) having a code synchronization signal (234). The code synchronization signal (234) is capable of adjusting a phase of a transmitter (204) in the subscriber terminal (20). A receiver (206) in the central terminal (10) monitors an uplink signal (214) transmitted by the transmitter (204) in the subscriber terminal and provides changes to the code synchronization signal (234) such that the transmitter (204) is synchronized to the receiver (206). Synchronization of the transmitter (204) in the subscriber terminal (20) to the receiver (206) in the central terminal (10) facilitates establishment of an uplink communication path from the subscriber terminal (20) to the central terminal (10).

Design of power control mechanisms with PCM realization for the uplink of a DS-CDMA cellular mobile radio system

Abstract: Power control (PC) is an important issue in a direct sequence-code division multiple access (DS-CDMA) cellular mobile radio system. Higher link performance and greater system capacity cannot be achieved unless an appropriate PC mechanism is employed. In previous research, a delta-modulation (DM) realization of strength-based and SIR-based PC mechanisms for uplink communication has been studied by simulation. In order to obtain higher PC trackability, we study a pulse-code-modulation (PCM) realization of the above two PC mechanisms for the uplink of a DS-CDMA cellular mobile radio system. The simulation results presented indicate that the PC mechanisms with PCM realization for the uplink can achieve a lower outage probability and thus higher link performance than the PC mechanisms with DM realization. We also obtain optimal design parameters such as the stepsize and the control mode for the two PCM PC mechanisms. In addition, we compare the two PCM PC mechanisms in terms of their outage probability and stability and find that the strength-based mechanism has a higher outage probability but greater stability than the SIR-based mechanism.

Apparatus and method of controlling transmitting power in a subscriber terminal of a wireless telecommunications system

Abstract: A wireless telecommunications system (1) includes a central terminal (10) for transmitting and receiving radio frequency signals to and from a subscriber terminal (20). A downlink communication path is establised from a transmitter (200) of the central terminal (10) to a receiver (202) of the subscriber terminal (20). A downlink signal (212) is transmitted from the transmitter (200) to the receiver (202) during setup and operation of the wireless telecommunications system (1). The downlink signal (212) includes an overhead channel (224) having a power control signal (236). The power control signal (236) is capable of adjusting a transmitting power of a transmitter (204) in the subscriber terminal (20). Adjustment of the transmitting power of the transmitter (204) facilitates establishment and maintenance of an uplink communication path between the transmitter (204) of the subscriber terminal and a receiver (206) of the central terminal (10).

A real time downlink channel allocation scheme for an SDMA mobile radio system

Abstract: In SDMA mobile radio systems where only base stations, but no mobiles are equipped with antenna arrays, co-channel interference on the downlink has to be kept down by beamforming. The performance of the beamformer is determined by the directions of arrival (DOAs) of the users operating in the same frequency/time/code slot. Thus the full capacity of an SDMA cell can only be made use of by an effective channel allocation scheme. In this paper, a real time concept for channel allocation is presented. Furthermore, several criteria to quickly evaluate the spatial separability of subsets of users, were defined and then compared to each other by means of simulations.

Worldwide telecommunications system using satellites

Abstract: A satellite telecommunications system that is operative in conjunction with an existing terrestrial telecommunications system. The satellite telecommunications system includes at least one satellite in earth orbit, at least one terrestrial communications gateway for coupling the at least one satellite to the terrestrial telecommunications system, a plurality of satellite telecommunications system subscriber transceivers operative for conducting communications through the at least one satellite with subscribers of the terrestrial telecommunications system, and a terrestrial network coordinating gateway (NCG) in communication with the at least one satellite. The NCG includes a satellite receiver for receiving access requests from individual ones of the plurality of subscriber transceivers and a controller for assigning satellite channels on behalf of the subscriber transceivers and for selecting terrestrial communications gateways to create call set-up links on behalf of the subscriber transceivers. The NCG further logs-in roaming subscriber transceivers.

Increasing the capacity of GSM cellular radio using adaptive antennas

Abstract: The capacity of mobile cellular radio networks can be considerably increased if a higher level of cochannel interference can be tolerated. An adaptive antenna combines the outputs of an array of elements to maximise the wanted signal and suppress interfering signals. The author proposes an adaptive antenna algorithm suitable for GSM and the urban multipath environment. The algorithm is based on iterative reference signal reconstruction from the GSM training sequence. The average error rate is obtained by simulation for four equal power interfering signals and an urban GSM multipath model. An adaptive antenna can only practically be deployed at the base station. Realising its gains in a real network on both the up and downlinks requires, for the downlink, a number of techniques. This is discussed and a concept of how the full capacity gains can be achieved in an evolutionary manner on both links is proposed. The concept is equally applicable to the DCS 1800 and DCS 1900 systems based on GSM.

Satellite-based direct access telecommunications systems

Abstract: A direct-access satellite telecommunications system employs one or more telecommunications satellites in geosynchronous orbit. Small, low-cost user terminals are located at the user's premises and permit two-way telecommunications via user links. Access links provide satellite telecommunications to larger gateway stations as well as a network control center. Gateway stations store user information and provide connection to terrestrial telecommunications networks. In operation, the network control center allocates satellite bandwidth and power to setup the access and user links, with a minority of the satellite's power being allocated to the access links, and a majority of the power being available for the user links.

Personal communications access networks using subcarrier multiplexed optical links

Abstract: One of the major challenges for future personal communication systems (PCS) and personal communication networks (PCN) is the capacity needed to meet the growing demand. In this paper, fiber optics and wavelength division multiplexing (WDM) technology is proposed, and shown to be a cost-effective solution to this problem. In particular, it is shown that the mature fiber-optics and WDM technology could be used in conjunction with subcarrier multiplexing in microcells in order to transmit messages from subscribers to central base station (uplink) and in the opposite direction too. The access backbone network architecture of such a PCN is also investigated and key problems associated with it are highlighted.

Link state routing device in ATM communication system

Abstract: A link state routing device reduces amount of link state information exchanged in a network irrespective of number of links connecting between adjacent switches. Hello protocol portion detects adjacent switches in the network, to which respective of links are connected. A link abstracted portion obtains an abstracted link by virtually aggregating a plurality of links connected to the same switch, and generates a link state with respect to abstracted link with uniting link state information of a plurality of links. The link state update protocol portion has link topology information synchronized in the network by distributing the abstracted link state information with flooding mechanism. Since the abstracted link represents a plurality of links, information amount to be distributed can be reduced.

Translator for time division multiple access wireless system having selective diversity circuits

Abstract: In this approach to implementing a wireless communication system, in band translator components are located in the center of remote cells which would normally contain a base transceiver system (BTS). Selective diversity processing is implemented in the translators by providing for at least two spatially separated receive antennas and two receive path circuits in the up link direction. A diversity circuit is time synchronized to the downlink signal to provide for proper detection and selection of the appropriate signal to be forwarded to a centralized BTS. As a result, a separate diversity path need not be maintained for the remainder of each backhaul link, and radio frequency components such as a second upconverter, synthesizer and power amplifier associated with the range extender can be eliminated.

Multiuser detection for multirate CDMA communications

Abstract: We study ways of devising multirate channels for wireless CDMA communications with a focus on asynchronous uplink reception. Methods based on parallel and serial transmission are reviewed. We consider a serial transmission scheme in which the data rate is increased by varying the processing gain. In this transmission concept the processing gain is changed for multirate transmission while maintaining a fixed chip rate and symbol alphabet. A spatio-temporal multistage multiuser receiver is introduced for providing acceptable service quality in a cell where multiple users with different data rates coexist. First, it is argued that multiuser detection is imperative, when the information capacity is maximized for mixed services. Second, it is shown that the proposed multirate multiuser receiver is considerably less complex than a low rate system with comparable information capacity. The simulations carried out in the pico and micro cellular channel models developed in the European CODIT project verify the performance of the considered concept. Simulation results are provided for antenna diversity reception with closed loop power control in a 5.12 MHz band with data rates ranging from 165 kbit/s to 2.62 Mbit/s.

An antenna downlink beamsteering arrangement

Abstract: A base station arrangement including an antenna array is disclosed, wherein the uplink signals are weighted with complex array weights and the downlink signals are steered, wherein the downlink signals are steered using data from directional information derived from the uplink signals. A method of operation is also disclosed.

Intersatellite communications systems

Abstract: An improved multi-beam bent-pipe communications satellite system and method includes a subchannel switching processor for extracting and switching subchannels of information to and from a plurality of uplink and downlink beams and an intersatellite link for routing certain of the extracted subchannels to another satellite in the system. The subchannel switching processor preferably employs a partial subchannelization processor that combines a coaxial switching network for switching some of the uplink channels at the channel level with an analog or digital transparent subchannel switching network connected to a portion of the uplink channels for extracting and switching at the subchannel level. The switched subchannels are combined to form channels, and then routed to either the downlink beams (where they are combined with other switched channels), or to the intersatellite link for transmission to another satellite. The system of the present invention could be a constellation of satellites, each satellite in the constellation connected to a plurality of other satellites using a plurality of intersatellite links.

Apparatus and method of establishing and maintaining communication paths in a wireless telecommunications system

Abstract: The receiver (202) of a subscriber terminal (20) compares a code and phase of a master code sequence in the downlink signal (212) to a code and phase of a slave code sequence of the receiver (202). The receiver (202) adjusts the phase of the slave code sequence until a match is obtained with the master code sequence. The downlink signal (212) includes an overhead channel (224) having a power control signal (236), a code synchronization signal (234), and a frame alignment signal (232). A receiver (206) in the central terminal (10) monitors an uplink signal (214) transmitted by the transmitter (204) in the subscriber terminal and provides changes to the code synchronization signal (234) such that the transmitter (204) is synchronized to the receiver (206). The receiver (202) monitors the downlink signal (212) to identify the frame alignment signal (232) and establishes the downlink communication path when two successive frame alignment signals (232) are identified. In an acquisition mode during establishment of the downlink communication path, the downlink signal (212) is transmitted at a high power level and a low transmit rate. In a standby mode after establishment of the downlink communication path, the downlink signal (212) is transmitted at a low power level and a low transmit rate. In a traffic mode upon a request for wireless communication transmission, the downlink signal (212) is transmitted at a high power level and a high transmit rate.

Method and apparatus for system synchronization in a messaging system

Abstract: A selective call messaging system comprises a control point satellite uplink (24) for transmission of source information to a satellite (12), the source information having timing information, a base station (16) for receiving the source information from the satellite and for retransmitting the source information to a receiver 18. A synchronization controller 29 is coupled to the receiver 18 and remotely coupled to the control point satellite uplink. The synchronization controller comprises a decoder (40) for decoding the timing information received from the base station to provide actual timing information, an absolute time source (28) that generates a reference time, a comparator (42) for comparing the actual timing information with the reference time to provide an offset signal (44) and a transmitter for forwarding the offset signal to the control point satellite uplink to adjust timing information at the control point satellite uplink.

Design study for a CDMA-based LEO satellite network: downlink system level parameters

Abstract: The performance analysis of a new concept of a code-division multiple-access (CDMA) based low Earth orbit (LEO) satellite network for mobile satellite communications is presented and discussed. The starting point was to analyze the feasibility of implementing multisatellite and multipath diversity reception in a CDMA network for LEO satellites. The results are used to specify the design parameters for a system experimental test bed. Due to the extremely high Doppler, which is characteristic of LEO satellites, code acquisition is significantly simplified by using a continuous wave (CW) pilot carrier for Doppler estimation and compensation. The basic elements for the analysis presented are: the channel model, the pilot carrier frequency estimation for Doppler compensation, and multipath and multisatellite diversity combining.

Capacity evaluation of a cellular CDMA uplink with multiuser detection

Abstract: The performance of a cellular CDMA uplink together with multiuser detection is evaluated. A system level simulator is built to utilise the link level simulation results and to derive the actual network capacity. A semistatic approach is chosen for the network simulator to model the special features in a CDMA system. The work is currently continued within the European Union ACTS program in the FRAMES project.

Telecommunications relay system

Abstract: A message initiated at a first terminal and transmitted over a first communications link to a relay interface may be relayed to a second terminal over a second communications link by converting the words in the message received at the relay interface into a format compatible for use by the second terminal. Then, the formatted words are individually analyzed so that corrections may be made prior to display at the second terminal. The formatted words may be corrected manually by a relay agent or automatically utilizing a computer program associated with a relay terminal at the relay interface. Then, the analyzed words are displayed at the second terminal. The relay interface may be used for unilateral and bilateral communication between a standard telephone set and a telecommunications device for the deaf (TDD).