Showing papers on "Telecommunications link published in 2003"

Transmit power adaptation for multiuser OFDM systems

Abstract: In this paper, we develop a transmit power adaptation method that maximizes the total data rate of multiuser orthogonal frequency division multiplexing (OFDM) systems in a downlink transmission. We generally formulate the data rate maximization problem by allowing that a subcarrier could be shared by multiple users. The transmit power adaptation scheme is derived by solving the maximization problem via two steps: subcarrier assignment for users and power allocation for subcarriers. We have found that the data rate of a multiuser OFDM system is maximized when each subcarrier is assigned to only one user with the best channel gain for that subcarrier and the transmit power is distributed over the subcarriers by the water-filling policy. In order to reduce the computational complexity in calculating water-filling level in the proposed transmit power adaptation method, we also propose a simple method where users with the best channel gain for each subcarrier are selected and then the transmit power is equally distributed among the subcarriers. Results show that the total data rate for the proposed transmit power adaptation methods significantly increases with the number of users owing to the multiuser diversity effects and is greater than that for the conventional frequency-division multiple access (FDMA)-like transmit power adaptation schemes. Furthermore, we have found that the total data rate of the multiuser OFDM system with the proposed transmit power adaptation methods becomes even higher than the capacity of the AWGN channel when the number of users is large enough.

Sum capacity of the vector Gaussian broadcast channel and uplink-downlink duality

Abstract: We characterize the sum capacity of the vector Gaussian broadcast channel by showing that the existing inner bound of Marton and the existing upper bound of Sato are tight for this channel. We exploit an intimate four-way connection between the vector broadcast channel, the corresponding point-to-point channel (where the receivers can cooperate), the multiple-access channel (MAC) (where the role of transmitters and receivers are reversed), and the corresponding point-to-point channel (where the transmitters can cooperate).

MIMO WLAN system

Abstract: A multiple-access MIMO WLAN system that employs MIMO, OFDM, and TDD. The system (1) uses a channel structure with a number of configurable transport channels, (2) supports multiple rates and transmission modes, which are configurable based on channel conditions and user terminal capabilities, (3) employs a pilot structure with several types of pilot (e.g., beacon, MIMO, steered reference, and carrier pilots) for different functions, (4) implements rate, timing, and power control loops for proper system operation, and (5) employs random access for system access by the user terminals, fast acknowledgment, and quick resource assignments. Calibration may be performed to account for differences in the frequency responses of transmit/receive chains at the access point and user terminals. The spatial processing may then be simplified by taking advantage of the reciprocal nature of the downlink and uplink and the calibration.

Downlink capacity evaluation of cellular networks with known-interference cancellation

Abstract: Recently, the capacity region of a multiple-input multiple-output (MIMO) Gaussian broadcast channel, with Gaussian codebooks and known-interference cancellation through dirty paper coding, was shown to equal the union of the capacity regions of a collection of MIMO multiple-access channels. We use this duality result to evaluate the system capacity achievable in a cellular wireless network with multiple antennas at the base station and multiple antennas at each terminal. Some fundamental properties of the rate region are exhibited and algorithms for determining the optimal weighted rate sum and the optimal covariance matrices for achieving a given rate vector on the boundary of the rate region are presented. These algorithms are then used in a simulation study to determine potential capacity enhancements to a cellular system through known-interference cancellation. We study both the circuit data scenario in which each user requires a constant data rate in every frame and the packet data scenario in which users can be assigned a variable rate in each frame so as to maximize the long-term average throughput. In the case of circuit data, the outage probability as a function of the number of active users served at a given rate is determined through simulations. For the packet data case, long-term average throughputs that can be achieved using the proportionally fair scheduling algorithm are determined. We generalize the zero-forcing beamforming technique to the multiple receive antennas case and use this as the baseline for the packet data throughput evaluation.

Planning UMTS base station location: optimization models with power control and algorithms

Abstract: Classical coverage models, adopted for second-generation cellular systems, are not suited for planning Universal Mobile Telecommunication System (UMTS) base station (BS) location because they are only based on signal predictions and do not consider the traffic distribution, the signal quality requirements, and the power control (PC) mechanism. We propose discrete optimization models and algorithms aimed at supporting the decisions in the process of planning where to locate new BSs. These models consider the signal-to-interference ratio as quality measure and capture at different levels of detail the signal quality requirements and the specific PC mechanism of the wideband CDMA air interface. Given that these UMTS BS location models are nonpolynomial (NP)-hard, we propose two randomized greedy procedures and a tabu search algorithm for the uplink (mobile to BS) direction which is the most stringent one from the traffic point of view in the presence of balanced connections such as voice calls. The different models, which take into account installation costs, signal quality and traffic coverage, and the corresponding algorithms, are compared on families of small to large-size instances generated by using classical propagation models.

Wireless downlink data channels: user performance and cell dimensioning

Abstract: We consider wireless downlink data channels where the transmission power of each base station is time-shared between a dynamic number of active users as in CDMA/HDR systems. We derive analytical results relating user performance, in terms of blocking probability and data throughput, to cell size and traffic density. These results are used to address a number of practically interesting issues, including the trade-off between cell coverage and cell capacity and the choice of efficient scheduling and admission control schemes.

Apparatus and method for transmitting/receiving serving HS-SCCH set information in an HSDPA communication system

Abstract: A communication system includes a shared channel occupied by a plurality of user equipments (UEs) and spread with a plurality of channelization codes to transmit user data, and a plurality of control channels for transmitting control information related to the shared channel in order to enable the UEs to receive the shared channel signal. The system generates a plurality of control channel sets by classifying the control channels into a predetermined number of control channels, and assigns the control channel sets so that each of the UEs monitors a particular control channel set among the control channel sets. Upon detecting necessity to modify a control channel set to be assigned to a particular UE among the UEs, a Node B determines to modify a control channel set assigned into the UE to a new control channel set at a predetermined point of time to come. After determining to modify the control channel set, the Node B transmits an indicator indicating expected modification of the control channel set and information on the control channel set to be modified to the UE over a downlink.

Apparatus and method for transmitting and receiving uplink power offset information in a mobile communication system supporting hsdpa

Abstract: A radio network controller (RNC) transmits a power offset for controlling transmission power of an uplink high speed dedicated physical control channel (HS-DPCCH) when a user equipment (UE) enters a handover region, in a mobile communication system including the RNC, a Node B connected to the RNC, and the UE located in one of at least two cell areas occupied by the Node B. The Node B transmits data to the UE over a high speed downlink shared channel (HS-DSCH) and the UE transmits information indicating reception of the data to the Node B over the uplink HS-DPCCH. The RNC informs the UE of a power offset for determining a transmission power increment of the uplink HS-DPCCH, if it is determined that the UE is located in the handover region. The RNC informs the Node B of the power offset so that the Node B can determine a threshold value for determining information indicating reception of the data, depending on the power offset.

Uplink pilot and signaling transmission in wireless communication systems

Abstract: Techniques to more efficiently transmit pilot and signaling on the uplink in an OFDM system. With subband multiplexing, M usable subbands in the system are partitioned into Q disjoint groups of subbands. Each subband group may be assigned to a different terminal for uplink pilot transmission. Multiple terminals may transmit simultaneously on their assigned subbands. The transmit power for the pilot may be scaled higher to attain the same total pilot energy even though S instead of M subbands are used for pilot transmission by each terminal. Pilot transmissions from the terminals are received, and a channel estimate is derived for each terminal based on the pilot received on the assigned subbands. The channel estimate comprises a response for additional subbands not included in the assigned group. Subband multiplexing may also be used for uplink signaling transmission.

Subsea communications system

Abstract: A subsea communications module includes an interface to communicate with a surface facility over a communications link using a packet-based protocol. The communications link can be implemented with a fiber optic line, wire-based line, and/or other types of communications lines.

Power and timing control methods and apparatus

Abstract: The use of multiple states of mobile communication device operation to allow a single base station to support a relatively large number of mobile nodes is described. The various states require different amounts of communications resources, e.g., bandwidth. Four supported states of operation are an on-state, a hold-state, a sleep-state, and an access-state. Each mobile node in the on-state is allocated communication resources to perform transmission power control signaling, transmission timing control signaling and to transmit data as part of a data uplink communications operation. Each mobile node in the hold-state is allocated communication resources to perform transmission timing control signaling and is provided a dedicated uplink for requesting a state transition and a shared resource for transmitting acknowledgements. In the sleep state a mobile node is allocated minimal resources and does not conduct power control signaling or timing control signaling. Data may be received in the on and hold states.

Methods and apparatus for operating mobile nodes in multiple states

Abstract: The use of multiple states of mobile communication device (14) operation to allow a single base station (12) to support a relatively large number of mobile nodes (14, 16) is described. The various states require different amounts of communications resources, e.g., bandwidth. Four supported states of operation are a on-state (404), a hold-state (410), a sleep-state (408), and an access-state (402). Each mobile node in the on-state (404) is allocated communication resources to perform transmission power control signaling, transmission timing control signaling and to transmit data as part of a data uplink communications operation. Each mobile node in the hold-state (410) is allocated communication resources to perform transmission timing control signaling and is provided a dedicated uplink for requesting a state transition and a shared resource for transmitting acknowledgements. In the sleep state (408) a mobile node is allocated minimal resources and does not conduct power control signaling or timing control signaling.

Power constrained and delay optimal policies for scheduling transmission over a fading channel

Abstract: An optimal power and rate scheduling problem for a single user transmitting to a base station on a fading wireless link with the objective of minimizing the mean delay subject to an average power constraint is considered. The base station acts as a controller which, depending upon the transmitter buffer lengths and the signal power to interference ratio (SIR) on the uplink pilot channel, allocates transmission rate and power to the user. We provide structural results for an average cost optimal stationary policy under a long run average transmitter power constraint. We obtain a closed form expression relating the optimal policy when the SIR is the best, to the optimal policy for any other SIR value. We also obtain lower and upper bounds for the optimal policy.

Non-reciprocal transceivers in OFDM/SDMA systems: impact and mitigation

Abstract: Channel reciprocity is needed in SDMA or MIMO downlink pre-filtering when the channel knowledge is acquired in the uplink. We first show analytically that the non-reciprocity of the base station analog hardware, which is part of the channel, introduces a very high level of multi-user interference and quantify the effect of the non-reciprocity by means of simulations. We then propose a novel calibration technique at the base station that enables to compensate for the non-reciprocity and reduce the MUI to a negligible value while having a low implementation cost.

Low complexity CDMA downlink receiver based on frequency domain equalization

Abstract: This paper proposes a new approach to apply frequency domain equalization (FDE) in the downlink of broadband CDMA cellular systems. Equalization has been recognized as a better receiving method than the RAKE receiver for CDMA downlink systems, especially in cells with a high number of users. By performing the equalization in the frequency domain, the complexity of the equalization algorithm can be significantly reduced with the help of the FFT operation. Three methods of implementing FDE in the CDMA downlink are described: the cyclic prefix method, the zero padding method, and the overlap-cut method. In addition to its simplicity and good performance, the FDE also offers the possibility to build a multimode receiver for singlecarrier and multicarrier signals. Simulation results are presented in a TD-CDMA system with parameters taken from the UTRA-TDD standard.

Channel calibration for a time division duplexed communication system

Abstract: Techniques are described to calibrate the downlink and uplink channels to account for differences in the frequency responses of the transmit and receive chains at an access point and a user terminal. In one method, pilots are transmitted on the downlink and uplink channels and used to derive estimates of the downlink and uplink channel responses, respectively. Correction factors for the access point and correction factors for the user terminal are determined based on (e.g., by performing matrix-ratio computation or minimum mean square error (MMSE) computation on) the downlink and uplink channel response estimates. The correction factors for the access point and the correction factors for the user terminal are used to obtain a calibrated downlink channel and a calibrated uplink channel, which are transpose of one another. The calibration may be performed in real time based on over-the-air transmission.

System and method for sharing uplink bandwidth among satellites in a common orbital slot

Abstract: A system for transmitting data to a plurality of satellites is provided A first satellite (320) in an orbital slot has an associated receive antenna, and is configured to receive signals in a first range of frequencies A second satellite (316) in the orbital slot has an associated receive antenna The second satellite (316) is separated from the first satellite (320) by at least a first separation angle, and is configured to receive signals in the first range of frequencies A first earth uplink antenna (308b), located at a first earth location, is capable of transmitting a first uplink beam ((328a) at the receive antenna of the first satellite (320) A second earth uplink antenna (308b), collocated at the first earth location, is capable of transmitting a second uplink beam (324a) at the receive antenna of the second satellite (316) The first uplink beam (328a) includes first signals at the first range of frequencies, and the second uplink beam (324a) includes second signals at the first range of frequencies Further, the first uplink beam (328a) is substantially attenuated beyond the first separation angle in the direction of the second satellite (316), and the second uplink beam (324a) is substantially attenuated beyond the first separation angle in the direction of the first satellite (320)

Method of mapping data for uplink transmission in communication systems

Abstract: A method of mapping data for uplink transmission in a communication system maps data to a transport channel for uplink transmission in accordance with a selected transmission mode for uplink transmission. In the method, a transmission parameter may be extracted from a received signaling message, and a transmission mode for uplink transmission selected based on the extracted transmission parameter. The data, which may be high data rate uplink data, may me mapped from logical channels in a MAC layer to transport channels in a physical layer for transmission on the uplink. The transmission on the uplink may be performed from one of an autonomous transmission mode and a scheduled transmission mode, and the transmission parameter may be at least one of a priority indication parameter related to class priority of a service class of data to be transmitted on the uplink, and a radio channel condition.

High Speed Downlink Packet Access: WCDMA Evolution

Abstract: This article gives an overview of the high speed downlink packet access (HSDPA) concept; a new feature which is coming to the Release 5 specifications of the 3GPP WCDMA/UTRA-FDD standard. To support an evolution towards more sophisticated network and multimedia services, the main target of HSDPA is to increase user peak data rates, quality of service, and to generally improve spectral efficiency for downlink asymmetrical and bursty packet data services. This is accomplished by introducing a fast and complex channel control mechanism based on a short and fixed packet transmission time interval (TTI), adaptive modulation and coding (AMC), and fast physical layer (L1) hybrid ARQ. To facilitate fast scheduling with a per-TTI resolution in coherence with the instantaneous air interface load, the HSDPA-related MAC functionality is moved to the Node-B. The HSDPA concept facilitates peak data rates exceeding 2 Mbps (theoretically up to and exceeding 10 Mbps), and the cell throughput gain over previous UTRA-FDD releases has been evaluated to be in the order of 50-100% or even more, highly dependent on factors such as the radio environment and the service provision strategy of the network operator.

Enhancing wirelass lan capacity using transmission power control

Abstract: A method for mobile communication by access points (22, 23, 25, 27) in a wireless local area network (WLAN) includes transmitting a first downlink signal on a common frequency channel from a first access point to a first mobile station (24), at a first downlink power level, which is adjusted responsively to a first uplink power level transmitted from the first mobile station to the first access point. If the first downlink signal received at a second access point is below a predetermined interference threshold, the second access point may transmit a second downlink signal on the common frequency channel to a second mobile station (29), simultaneously with transmission of the first downlink signal from the first access point to the first mobile station. The capacity of the WLAN may thus be substantially increased.

Prototype experience for MIMO BLAST over third-generation wireless system

Abstract: In this paper, a multiple-input-multiple-output (MIMO) extension for a third-generation (3G) wireless system is described. The integration of MIMO concepts within the existing UMTS standard and the associated space-time RAKE receiver are explained. An analysis is followed by a description of an actual experimental MIMO transmitter and receiver architecture, both realized on digital signal processors (DSPs) and FPGAs within a precommercial OneBTS base station. It uses four transmit and four receive antennas to achieve downlink data rates up to 1 Mb/s per user with a spreading factor of 32 and the UMTS chip rate of 3.84 MHz. Furthermore, different MIMO detectors are evaluated, comparing their performance and complexity. System performance is evaluated through simulations and indoor over-the-air measurements. Capacity and bit-error rate measurement results are presented.

Communication system employing reuse of satellite spectrum for terrestrial communication

Abstract: A terrestrial communication system using satellite uplink and downlink frequencies is disclosed. A terrestrial cell site produces a signal at a satellite uplink frequency that is transmitted to a terrestrial user terminal. The terrestrial cell site receives a signal at a satellite downlink frequency that was transmitted by a terrestrial user terminal. The terrestrial cell site may include a signal nulling means in the direction of a satellite producing signals at the uplink and downlink frequencies.

Performance characteristics of cellular systems with different link adaptation strategies

Abstract: In this paper, the theoretical performance of cellular systems with different types of link adaptation is analyzed. A general link and system performance analysis framework is developed to enable the system-level performance characteristics of the various link adaptation strategies to be studied and compared. More specifically, this framework is used to compare the downlink performance of fully loaded cellular systems with fixed power and modulation/coding, adaptive modulation/coding (AMC), adaptive power allocation (APA) with system-level AMC, and water-filling (WF). Performance is studied first for idealized methods, and then for cases where some practical constraints are imposed. Finally, a hybrid link adaptation scheme is introduced and studied. The hybrid scheme is shown to overcome most of the performance loss caused by the practical constraints. Moreover, the hybrid scheme, as opposed to WF, enables the system to be tuned to meet the most important performance objective for the system under consideration, such as coverage reliability, capacity, or data rate distribution. The algorithms and the framework presented in this paper can be used to improve the link adaptation performance of modern cellular systems such as HSDPA.

Radio communication scheme for providing multimedia broadcast and multicast services (mbms)

Abstract: A radio communication scheme applicable to UMTS providing packet data services, such as multimedia broadcast and multicast services (MBMS), to one or more users by modifying (augmenting) certain existing radio communication protocols while employing a new transport channel (a point-to-multipoint DSCH), and/or by establishing new physical downlink shared channels (C-PDSCH and D-PDSCH). An RLC layer is provided in a single CRNC so that the same MBMS can be transmitted to a plurality of terminals via a point-to-multipoint DSCH, without having to repetitively provide many RLC layers in many SRNCs. Alternatively, a C-PDSCH (physical downlink shared channel for control) and a D-PDSCH (physical downlink shared channel for data) are established to allow periodic transmission of MBMS, permitting users to simultaneously access one or more MBMS.

Method and apparatus for distributed signaling for uplink rate control

Abstract: A method and associated equipment for use by a first entity (17) of a radio access network (101), such as a node B, in communicating with a UE (18) so as to control an uplink rate used by the UE (18) in communicating with the first entity (17), the method characterized by: a step in which the first entity (17) transmits to the UE (18) a rate control signal (RA) conveying information regarding the uplink rate. The rate control signal may be used to command the UE (18) to adjust the maximum uplink rate in a range or set of uplink rates; alternatively, it may be used to command the UE (18) to adjust the uplink rate. The rate control signal (RA) may be sent as a response to a rate change request signal (RR) received from the UE (18) by the first entity (17).

Non-reciprocal Transceivers in OFDMKDMA Systems: Impact and Mitigation'

Abstract: AEISTRACI Channel reciprocity is needed in SDMA or MIMO downlink pre-filtering when the channel knowledge is acquired in the n link We first show analytically that the non-reci roeity ofthe .&e station anal hardware which is part of the channel, introduces a veqxgh level ok multiuser interference and quantify the effect of the nonreciproeit by means of simulations We then prop a novel caliiratinn technique at the base station that enables to compensate for the non-reciprocity and reduce the MU to a negligible value while having a low implementation cat I. INTRODUIXION OFDM-SDMA is an attractive technique to enhance the capacity of future wireless LANs since it allows mitigating the frequency selective channel fading (OFWM) and increasing the spectral efficiency by accommodating several users in the same time-frequency slots (SDMA). In the downlink, pre-filtering at the base station (BS) side allows to pre-compensate the phase (and amplitude) of the channel in such a manner that all simultaneous users receive their own signal free of MLn 01, [4l. It is in fact this interference Cancellation property that makes SDMA possible in the downlink. Since the terminals have only one antenna, they have no means IO mitigate the spatial MUI. When the channel is estimated in the uplink, the downlink channel matrix is just the transpose of the uplink matrix, assuming the channel is reciprocal. However, the "channel" is actually made up of the propagation channel (the medium between the antennas), the antennas and the transceiver RF, IF and baseband circuits at both sides of the link. The transceiver circuits are usually not reciprml (the TX and RX frequency responses are different) and this can jeopardise the performance of the SDMA system. In this paper, we depart from the reciprocity assumption, analyse the impact of channel non-reciprocity and propose a mitigation method. The document is organised as fdlows. Section 2 introduces the OFDM-SDMA Uplink and Downlink model, including the impact of the composite channel. In section 3, the effects of non-reciprocities are estimated by simulations. Seaion 4 proposes a simple yet effective calibration method with minimal additional hardware requirement. Then, the conclusions are drawn. 11. SYSTEM MODEL

TDD-CDMA for the 4th generation of wireless communications

Abstract: This article discusses an evolutionary TDD mode of CDMA-based path for 3.5G/4G systems. This technology has already been the basis of two 3G standards: TD-CDMA and TD-SCDMA with a synchronous uplink. Several techniques have been developed that allow TDD-CDMA-based systems to transmit at rates usually associated with 3.5G to 4G, up to 10-20 Mbit/s with wide area coverage. The present TDD-CDMA-based 3G standards are evolving to provide these higher rates, while fully retaining the coverage and mobility associated with, and expected from, the present mobile communications systems. This article discusses how TDD-CDMA specific techniques facilitate delivering services at data rates associated with 3.5G and 4G. We review how TDD-CDMA can provide for asymmetric uplink and downlink transmissions, facilitate deployment of advanced antennas for improved downlink coverage, and enable provision of advanced receiver techniques in base stations and mobiles. We also discuss how these techniques affect systems capacity in full packet-switched IP-based systems. We then discuss 4G TDD CDMA systems: those with different modulation techniques for uplink and downlink communications. These are generally based on a multicarrier mode of CDMA, and may incorporate OFDM technique.

Method for channel quality prediction for wireless communication systems

Abstract: A method of improved performance through channel quality prediction for communications systems employing link adaption techniques includes a receiver which makes selective measurements (210) on downlink transmissions, and then stores one or more of the measurements or a channel quality indicator derived therefrom (212). The receiver then retrieves one or more of the past measurements (or the past channel quality estimates themselves), and combines it with current measurements (or the current channel quality estimate), to predict what the channel quality will be at some future time and derive a predictive channel quality indicator (CQI). This predictive CQI, derived from both current channel measurements and at least one past channel measurement, is then sent to the transmitter for use in updating transmission parameters (220).

Impact of multiuser diversity and channel variability on adaptive OFDM

Abstract: A downlink radio interface for cellular packet data systems with wide area coverage and high spectral efficiency is evaluated. A slotted OFDM radio interface is used, in which time-frequency bins are allocated adaptively to different mobile users within a downlink beam, or sector, based on their channel quality. Frequency division duplex (FDD) is assumed, which requires channel prediction in the terminals and feedback of this information to a packet scheduler. The adaptive modulation scheme is optimized by a novel approach which maximizes the throughput, including also the ARQ part of the transmission. A theoretical evaluation of the resulting multiuser diversity under some idealized assumptions shows that the spectral efficiency increases significantly with the number of active users. The simulations indicate that the loss of performance due to channel variability within the bins for vehicular users in frequency-selective fading environments is rather small.

An uplink common channel for sending feedback information

Abstract: A wireless/radio communication scheme uses a particular uplink common channel for each particular terminal group. Terminals within the particular terminal group receive a particular data service, such as a multimedia broadcast/multicast service (MBMS). Terminals in a particular terminal group use at least one particular uplink common channel that has been specifically established for transmitting feedback information regarding the particular data service to be provided. Each uplink common channel can be specifically configured according to the characteristics of the feedback information of a particular terminal group, and uplink channel resources are not wasted.