Showing papers on "Telecommunications link published in 2000"

Increase in capacity of multiuser OFDM system using dynamic subchannel allocation

Abstract: This paper investigates the problem of dynamic multiuser subchannel allocation in the downlink of OFDM systems. The assumptions are that the channel model is quasi-static and that the base station has perfect channel information. In traditional TDMA or FDMA systems, resource allocation for each user is non-adaptively fixed, and the water-filling power spectrum is known to be optimal. Since the subchannel allocations among the users are not optimized, a group of users is likely to suffer from poor channel gains resulting from large path loss and random fading. To resolve this problem, we derive a multiuser convex optimization problem to find the optimal allocation of subchannels, and propose a low-complexity adaptive subchannel allocation algorithm. Simulation results show that the proposed algorithm performs almost as well as the optimal solution. Also, a higher spectral efficiency is achieved for a larger number of users in a cell due to the multiuser diversity.

A generalized RAKE receiver for interference suppression

Abstract: Currently, a global third-generation cellular system based on code-division multiple-access (CDMA) is being developed with a wider bandwidth than existing second-generation systems. The wider bandwidth provides increased multipath resolution in a time-dispersive channel, leading to higher frequency-selectivity. A generalized RAKE receiver for interference suppression and multipath mitigation is proposed. The receiver exploits the fact that time dispersion significantly distorts the interference spectrum from each base station in the downlink of a wideband CDMA system. Compared to the conventional RAKE receiver, this generalized RAKE receiver may have more fingers and different combining weights. The weights are derived from a maximum likelihood formulation, modeling the intracell interference as colored Gaussian noise. This low-complexity detector is especially useful for systems with orthogonal downlink spreading codes, as orthogonality between own cell signals cannot be maintained in a frequency-selective channel. The performance of the proposed receiver is quantified via analysis and simulation for different dispersive channels, including Rayleigh fading channels. Gains on the order of 1-3.5 dB are achieved, depending on the dispersiveness of the channel, with only a modest increase in the number of fingers. For a wideband CDMA (WCDMA) system and a realistic mobile radio channel, this translates to capacity gains of the order of 100%.

System and method for re-routing communications based on wireless communication link quality

Abstract: A method for re-routing communications based on link quality includes establishing a first wireless communication link with a mobile station. The first wireless communication link is included in a first communication path used for communications between the mobile station and a destination device. The method also includes monitoring, from the mobile station, the link quality of the first wireless link and determining, at the mobile station, that the link quality of the first communication link has decreased below a low link quality threshold. The method further includes routing, using a router at the mobile station, communications between the mobile station and the destination device to a second communication path that includes a second wireless communication link to the mobile station. The second communication path is selected by the router based on one or more metrics.

Satellite Systems for Personal and Broadband Communications

Abstract: I. Basics.- 1. Introduction.- 1.1 Mobile and Personal Satellite Communications.- 1.1.1 Applications of Mobile Satellite Communications.- 1.1.2 Personal Satellite Communications.- 1.1.3 UMTS, IMT-2000.- 1.2 Broadband Multimedia Satellite Communications.- 1.3 Frequency Bands.- 1.4 Key Aspects of Satellite Communication Systems.- 2. Satellite Orbits, Constellations, and System Concepts.- 2.1 Satellite Orbits.- 2.1.1 Elliptical and Circular Orbits.- 2.1.2 Satellite Velocity and Orbit Period.- 2.1.3 Orientation of the Orbit Plane.- 2.1.4 Typical Circular Orbits.- 2.1.5 Orbit Perturbations.- 2.1.6 Ground Tracks.- 2.2 Satellite - Earth Geometry.- 2.2.1 Geometric Relations between Satellite and Earth Terminal.- 2.2.2 Coverage Area.- 2.3 Satellite Constellations.- 2.3.1 Inclined Walker Constellations.- 2.3.2 Polar Constellations.- 2.3.3 Asynchronous Polar Constellations.- 2.4 GEO System Concept.- 2.4.1 Inmarsat-3.- 2.4.2 EAST (Euro African Satellite Telecommunications).- 2.5 LEO System Concept.- 2.5.1 Globalstar.- 2.5.2 Intersatellite Links and On-Board Processing.- 2.5.3 Iridium.- 2.6 MEO System Concept.- 2.6.1 ICO.- 2.7 Satellite Launches.- 3. Signal Propagation and Link Budget.- 3.1 Satellite Link Budget.- 3.1.1 Antenna Characteristics.- 3.1.2 Free Space Loss and Received Power.- 3.1.3 Link Budget.- 3.1.4 Spot Beam Concept.- 3.2 Peculiarities of Satellite Links.- 3.2.1 Dependence on Elevation.- 3.2.2 Time Dependence of Satellite Links.- 3.2.3 Faraday Rotation.- 3.3 Signal Shadowing and Multipath Fading.- 3.3.1 Narrowband Model for the Land Mobile Satellite Channel.- 3.3.2 Satellite Channels at Higher Frequencies.- 3.3.3 Wideband Model for the Land Mobile Satellite Channel.- 3.4 Link Availability and Satellite Diversity.- 3.4.1 Concept of Satellite Diversity.- 3.4.2 Correlation of Channels.- 3.4.3 Link Availability and Satellite Diversity Service Area.- 3.5 System Implications.- 4. Signal Transmission.- 4.1 Speech Coding.- 4.1.1 Quality of Coded Speech.- 4.1.2 Overview of Speech Coding Schemes.- 4.2 Modulation.- 4.2.1 Modulation Schemes for Mobile Satellite Communications.- 4.2.2 Bandwidth Requirement of Modulated Signals.- 4.2.3 Bit Error Rate in the Gaussian Channel.- 4.2.4 Bit Error Rate in the Ricean and Rayleigh Fading Channel.- 4.3 Channel Coding (Forward Error Correction, FEC).- 4.3.1 Convolutional Coding.- 4.3.2 Block Coding.- 4.3.3 Error Protection with Cyclic Redundancy Check (CRC).- 4.3.4 RS Codes.- 4.3.5 Performance of Block Codes.- 4.3.6 Performance of Block Codes in Fading Channels.- 4.4 Automatic Repeat Request (ARQ).- 4.4.1 Stop-and-Wait ARQ.- 4.4.2 Go-Back-N ARQ.- 4.4.3 Selective-Repeat ARQ.- 4.5 Typical Error Control Schemes in Mobile Satellite Communications.- II. Satellite Systems for Mobile/Personal Communications.- 5. Multiple Access.- 5.1 Duplexing.- 5.1.1 Frequency-Division Duplexing (FDD).- 5.1.2 Time-Division Duplexing (TDD).- 5.2 Multiplexing.- 5.3 Multiple Access.- 5.4 Slotted Aloha Multiple Access.- 5.4.1 The Principle of Slotted Aloha.- 5.4.2 Throughput of Slotted Aloha.- 5.4.3 Mean Transmission Delay for Slotted Aloha.- 5.4.4 Pure Aloha Multiple Access.- 5.5 Frequency-Division Multiple Access, FDMA.- 5.5.1 Adjacent Channel Interference.- 5.5.2 Required Bandwidth for FDMA.- 5.5.3 Intermodulation.- 5.5.4 Pros and Cons of FDMA.- 5.6 Time-Division Multiple Access, TDMA.- 5.6.1 Bandwidth Demand and Efficiency of TDMA.- 5.6.2 Burst Synchronization in the Receiving Satellite.- 5.6.3 Slot Synchronization in the Transmitting TDMA Terminals.- 5.6.4 Pros and Cons of TDMA.- 5.7 Code-Division Multiple Access, CDMA.- 5.8 Direct-Sequence CDMA (DS-CDMA).- 5.8.1 Generation and Characteristics of Signature Sequences.- 5.8.2 Investigation of Asynchronous DS-CDMA in the Time Domain.- 5.8.3 Investigation of Asynchronous DS-CDMA in the Frequency Domain.- 5.8.4 Multi-Frequency CDMA, MF-CDMA.- 5.8.5 Qualcomm Return Link CDMA (Globalstar).- 5.8.6 Synchronous Orthogonal DS-CDMA with Coherent Detection.- 5.9 CDMA Receivers.- 5.9.1 PN Code Synchronization in the CDMA Receiver.- 5.9.2 Rake Receiver.- 5.9.3 CDMA Multiuser Detection.- 5.10 Characteristics of CDMA.- 5.11 CDMA for the Satellite UMTS Air Interface.- 5.11.1 The ESA Wideband CDMA Scheme.- 5.11.2 The ESA Wideband Hybrid CDMA/TDMA Scheme.- 6. Cellular Satellite Systems.- 6.1 Introduction.- 6.1.1 Concept of the Hexagonal Radio Cell Pattern.- 6.1.2 Cell Cluster and Frequency Reuse.- 6.2 Co-Channel Interference in the Uplink.- 6.2.1 Co-Channel Interference for FDMA and TDMA Uplinks.- 6.2.2 Co-Channel Interference for an Asynchronous DS-CDMA Uplink.- 6.3 Co-Channel Interference in the Downlink.- 6.3.1 Co-Channel Interference for FDMA and TDMA Downlinks.- 6.3.2 Co-Channel Interference for CDMA Downlinks.- 6.4 Bandwidth Demand and Traffic Capacity of Cellular Satellite Networks.- 6.4.1 Total System Bandwidth.- 6.4.2 Traffic Capacity per Radio Cell.- 6.4.3 Traffic Capacity of the System.- 6.4.4 Required User Link Capacity of a Satellite.- 6.4.5 Overall Network Capacity Considerations.- 7. Network Aspects.- 7.1 Architecture of Satellite Systems for Mobile/Personal Communications.- 7.2 Network Control.- 7.2.1 Tasks of Network Control.- 7.2.2 Signaling Channels of the Air Interface.- 7.3 Mobility Management.- 7.3.1 Service Area of a Gateway Station.- 7.3.2 Location Area.- 7.3.3 Registration and Location Update.- 7.4 Paging.- 7.5 Call Control.- 7.5.1 Setup of a Mobile Originating Call.- 7.5.2 Setup of a Mobile Terminating Call.- 7.6 Dynamic Channel Allocation.- 7.6.1 C/I-Based DCA.- 7.6.2 DCA Using a Cost Function.- 7.7 Handover.- 7.7.1 Handover Decision.- 7.7.2 Handover Procedure.- 7.7.3 Channel Allocation at Handover.- 7.8 Call Completion Probability.- 7.9 Routing.- 7.9.1 Routing in LEO/MEO Satellite Networks.- 7.9.2 Off-Line Dynamic ISL Routing Concept.- 7.9.3 On-line Adaptive ISL Routing.- 7.10 Integration of Terrestrial and Satellite Mobile Networks.- 8. Satellite Technology.- 8.1 Satellite Subsystems.- 8.2 Antenna Technology.- 8.2.1 GEO Antennas for Mobile Links with Spot Beams.- 8.2.2 LEO/MEO Antennas.- 8.3 Payload Architecture.- 9. Regulatory, Organizational, and Financial Aspects.- 9.1 Allocation of Frequency Bands.- 9.2 Licensing/Regulation.- 9.2.1 Granting a System License.- 9.2.2 Licensing in the USA.- 9.2.3 Licensing in Europe.- 9.2.4 Common Use of Frequency Bands by Several Systems.- 9.2.5 Global Licensing and Political Aspects.- 9.3 Financing and Marketing of S-PCN Systems.- 9.4 Operation of S-PCN Systems.- III. Satellite Systems for Broadband Multimedia Communicat ions.- 10. Multimedia Communications in Satellite Systems.- 10.1 Types of Broadband Communication Networks.- 10.1.1 Traditional Circuit-Switched Networks and the Packet-Switched Internet.- 10.1.2 New Multimedia Satellite Systems Using New Satellite Orbits.- 10.2 Multimedia Services and Traffic Characterization.- 10.2.1 Video Traffic and MPEG Coding.- 10.2.2 Self-Similar Traffic.- 10.3 ATM-Based Communication in Satellite Systems.- 10.3.1 Principles of ATM.- 10.3.2 Implications for ATM-Based Satellite Networks.- 10.4 Internet Services via Satellite Systems.- 10.4.1 Principles of TCP/IP.- 10.4.2 Internet Protocol (IP).- 10.4.3 Transport Control Protocol (TCP).- 10.4.4 TCP/IP in the Satellite Environment.- 10.4.5 IP over ATM in the Satellite Environment.- 11. ATM-Based Satellite Networks.- 11.1 System Architecture.- 11.2 Services.- 11.3 Protocol Architecture.- 11.4 ATM Resource Management.- 11.4.1 Connection Admission Control and Usage Parameter Control.- 11.4.2 Congestion Control, Traffic Shaping, and Flow Control.- 11.5 Multiple Access for ATM Satellite Systems.- 11.5.1 TDMA-Based Multiple Access.- 11.5.2 CDMA-Based Multiple Access.- 11.6 Radio Resource Management.- 11.7 Error Control.- 12. Network Dimensioning.- 12.1 Spot Beam Capacity Dimensioning for GEO Systems.- 12.1.1 Motivation and Approach.- 12.1.2 Market Prediction.- 12.1.3 Generic Multiservice Source Traffic Model.- 12.1.4 Calculation of the Spot Beam Capacity Requirements.- 12.1.5 System Bandwidth Demand Calculation.- 12.1.6 Applied Spot Beam Capacity Dimensioning: A Case Study.- 12.2 ISL Capacity Dimensioning for LEO Systems.- 12.2.1 Topological Design of the ISL Network.- 12.2.2 ISL Routing Concept.- 12.2.3 Network Dimensioning.- 12.2.4 Numerical Example.- 12.2.5 Extensions of the Dimensioning Approach.- A. Satellite Spot Beams and Map Transformations.- A.1 Map Projections and Satellite Views.- A.2 Generation of Satellite Spot Beams.- B. Parameters of the Land Mobile Satellite Channel.- B.1 Narrowband Two-State Model at L Band.- B.2 Narrowband Two-State Model at EHF Band.- B.3 Wideband Model at L Band.- C. Existing and Planned Satellite Systems.- C.1 Survey of Satellite Systems.- C.2 ACeS (Asia Cellular Satellite).- C.3 Astrolink.- C.4 EuroSkyWay.- C.5 Globalstar.- C.6 ICO (Intermediate Circular Orbits).- C.7 Inmarsat-3/Inmarsat mini-M.- C.8 Iridium.- C.9 Orbcomm.- CIO SkyBridge.- C.11 Sky Station.- C.12 Spaceway.- C.13 Teledesic.- References.

Estimation of capacity and required transmission power of WCDMA downlink based on a downlink pole equation

Abstract: A simple method is derived for estimating the downlink capacity and required base station transmission power in a WCDMA system. This is based on a downlink pole equation which is mostly similar with the well known CDMA uplink pole equation. It is shown that the total downlink transmission power is composed of two terms. The first term is equal to what would be needed in the absence of interference and the second one shows the increase due to multiple access interference which is inversely proportional to 1-/spl eta//sub DL/ where /spl eta//sub DL/ is called the downlink loading. The method can be used in radio network dimensioning where extensive simulations can not be run. Usage of the method is demonstrated by some examples.

Onboard control of demand assigned multiple access protocol for satellite ATM networks

Abstract: An onboard DAMA protocol for use in connection with a processing satellite communications network, where multiple users are assigned to a common transmission resource as part of a sharing set. A media access controller (30) on the satellite maintains a reservation log which identifies the frequencies and number of uplink time slots in the resource that are currently reserved by one or more members of the sharing set. To reserve a time-frequency slot on the transmission resource for a non-contentious transmission of data, a user of the sharing set will transmit a reservation request to the satellite on a contentious uplink resource. If a return message is not received, the user knows that the reservation request collided with another reservation request, and a retransmission strategy of the reservation request is employed. When the media access controller (30) receives the reservation request, it decides whether to grant, deny or delay the request based on the service and price class of the user, the amount of data already sent by the user, the number and type of other users with reservation requests in the queue, and the congestion state of the destination downlink port and subsequent nodes in the network. When the user receives a reservation grant message from the media access controller (30) on the satellite in the downlink, it will then wait for its reservation time frequency slot, and transmit its data in a non-contentious basis on the transmission resource at that time. If the user needs additional bandwidth to transmit more data, it may piggyback a reservation request on the data transfer.

Generalised sphere decoder for asymmetrical space-time communication architecture

Abstract: A generalised sphere decoding (GSD) algorithm is presented. Its application to the detection of information symbols in a multiantenna cellular system with N antennas at the mobile and M/spl ges/N antennas at the base station is explored. The GSD algorithm has the maximum likelihood (ML) performance for both the uplink and downlink with moderate complexity.

Monitoring network performance using individual cell phone location and performance information

Abstract: A system and method of collecting call data from a Mobile Telephone Switching Office and combining this data with location information of a wireless device (or devices) to generate information reports concerning the electromagnetic coverage of a cell site. The collection of call data from a switch permits consideration of uplink information in the analysis of system performance. This information combined with location information obtained using a time difference of arrival (TDOA) technique allows the cell site to be evaluated and to remove transient effects associated with, for example, local terrain and other physical impairments.

Single-user and multiuser adaptive maximal ratio transmission for Rayleigh channels

Abstract: In maximal ratio transmission, the base station adjusts the complex weights of its transmit antennas to compensate for downlink channel gains in order to produce signal reinforcement-diversity-at a desired mobile that may have only a single antenna. To make the method adaptive, the complex weights are obtained from the instantaneous complex gains in the uplink; however, delay and frequency offset between uplink measurements and downlink transmission reduce the correlation between the gains in the two directions. This paper provides an analysis of the effects of gain decorrelation and of the number of antennas, and an assessment of the effect of fading when the method supports multiple users. It demonstrates that large reductions in downlink transmit power are achievable, and it examines simple transmission models to see how well they support the technique.

Downlink scheduling in CDMA data networks

Abstract: Packet data is expected to dominate third generation wireless networks, unlike current generation voice networks. This opens up new and interesting problems. Physical and link layer issues have been studied extensively, while resource allocation and scheduling issues have not been addressed satisfactorily.In this work, we address resource management on the downlink of CDMA packet data networks. Network performance (for example, capacity) has been addressed, but user centric performance has not received much attention. Recently, various non-traditional scheduling schemes based on new metrics have been proposed, and target user performance (mostly without reference to wireless). We adapt these metrics to the CDMA context, and establish some new results for the offline scheduling problem. In addition, we modify a large class of online algorithms to work in our setup and conduct a wide range of experiments. Based on detailed simulations, we infer that: Algorithms which exploit “request sizes” seem to outperform those that do not. Among these, algorithms that also exploit channel conditions provide significantly higher network throughput.Depending on continuous or discretized bandwidth conditions, either pure time multiplexing or a combination of time and code multiplexing strikes an excellent balance between user satisfaction and network performance.Discrete bandwidth conditions can lead to degraded user level performance without much impact on network performance. We argue that the discretization needs to be fine tuned to address this shortcoming.

Orthogonal frequency division multiplexing based spread spectrum multiple access

Abstract: In an orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access system the entire bandwidth is divided into orthogonal tones, and all of the orthogonal tones are reused in each cell. To reduce peak-to-average ratio at the mobile transmitter, each voice user is allocated preferably a single one, but no more than a very small number, of the orthogonal tones for use in communicating with the base station. Data users are similarly allocated tones for data communication, however, the number of tones assigned for each particular data user is a function of the data rate for that user. The tone assignment for a given user is not always the same within the available band, but instead the tones assigned to each user are hopped over time. More specifically, in the downlink, the tones assigned to each user are change relatively rapidly, e.g., from symbol to symbol, i.e., the user fast "hops" from one tone to another. However, in the uplink, preferably slow hopping is employed to allow efficient modulation of the uplink signal which necessitates the employing of additional techniques, such as interleaving, to compensate for the reduction in the intercell interference averaging effect. For data communication power control is employed in the uplink and/or downlink so that the transmission rate is increased, e.g., by increasing the number of symbols transmitted per tone per unit time or the coding rate, as a function of allocated power per tone and the corresponding channel attenuation.

Low-cost multi-mission broadband communications payload

Abstract: A method and system for communicating using satellites in a constellation in LEO, MEO or GEO orbits is disclosed. The system comprises a receive system, a downlink system, and a data processing system. The receive system receives an uplink signal comprising at least one data packet from at least one user in an uplink cell. The ground programmable downlink system transmits the data packet to a specific downlink cell and adjusts a power used to transmit the data packet to the specific downlink cell. The ground programmable data processing system processes and routes the data packet to an input of the downlink system such that the downlink system transmits the data packet to the specified downlink cell. The method comprises receiving at the satellite an uplink signal comprising at least one data packet from at least one user in an uplink cell, processing the data packet on the satellite, routing the data packet to a transmit antenna on the satellite, adjusting a power level of a transmitter used to transmit the data packet from the satellite to a specific downlink cell, and transmitting the data packet to the specified downlink cell.

All-digital PAM impulse radio for multiple-access through frequency-selective multipath

Abstract: Impulse radio (IR) is an ultra-wideband system with attractive features for baseband asynchronous multiple-access (MA), multimedia services, tactical wireless communications and networking. Implemented with analog components, the continuous-time IRMA model utilizes pulse-position modulation (PPM) and random time-hopping codes to alleviate multipath effects and suppress multiuser interference (MUI). We develop here a novel all-digital IRMA scheme and its discrete-time equivalent model that relies on pulse-amplitude modulation (PAM) and judiciously designed orthogonal user codes to eliminate MUI deterministically and account for frequency-selective multipath in the downlink. We also design a time-division-duplex access protocol and low-complexity linear multichannel receivers that we compare and test both analytically and by simulation.

Analysis of the uplink of an asynchronous multi-user DMT OFDMA system impaired by time offsets, frequency offsets, and multi-path fading

Abstract: We study through analysis the joint effect of time offsets, frequency offsets, and multi-path fading in the uplink of an asynchronous multi-user system for wireless communications deploying discrete multi-tone modulation and demodulation. We derive analytical expressions for the multiple access interference, and we quantify its detrimental effects through the evaluation of both the average SINR, and the symbol-error-rate performance. As a result it is shown that the MAI strongly depends not only on the aforementioned impairments but also on the tone assignment algorithm used to multiplex the users. Based on our analysis, the insertion of appropriate time and frequency guard intervals and the accurate selection of the tone assignment algorithm effectively reduce the MAI, so that a proper trade off with spectral efficiency can be met to optimize system performance.

Initiating and scaling massive concurrent data transactions

Abstract: An interactive multi-player computer hosted game employs an unstructured telecommunications link, such as the Internet, between a game server and a plurality of game clients. A game server, associated with a game driver, performs a performance monitoring function to determine an optimal bandwidth for each connection to a game client. Each information packet generated by the game driver is prioritized and queued for transmission in order of relevance for the game client. The game server then optimizes the transmission of information packets through the telecommunication network to the game client. Processed user input is received through the telecommunication network from the game client and transmitted to the game driver.

Joint transmission (JT), an alternative rationale for the downlink of time division CDMA using multi-element transmit antennas

Abstract: In the 3/sup rd/ Generation Partnership Project (3GPP) time division CDMA (TD-CDMA) has been selected as the air interface for the TDD (time division duplexing) bands of 3/sup rd/ generation (3G) mobile radio systems. In the case of TDD the same channel impulse responses are valid for both the uplink and the downlink. In state-of-the-art TD-CDMA characterized by joint data detection (JD) this equality cannot be exploited for enhancing the system performance and reducing system complexity. A novel TD-CDMA downlink transmission scheme is proposed. This scheme is termed joint transmission (JT). It utilizes the knowledge of the channel impulse responses gained by channel estimation at the base station in such a way that channel estimators are no longer required at the mobile stations and the computational expense of data detection is dramatically reduced. The scheme easily lends itself to the utilization of multi-element transmit antennas. Further, its application is not restricted to systems of the type TD-CDMA.

System and method for monitoring incoming communications to a telecommunications device

Abstract: A system for notifying an Internet-accessible device of a communication placed from a first telecommunications device to a second telecommunications device by a calling party is disclosed. The system includes a switch and a node in communication with the switch. The switch is for detecting the communication. The node is configured for communication with the Internet-accessible device and includes a first module and a second module. The first module is for determining information about the calling party. The second module is for determining information about the Internet-accessible device.

Downlink signal processing in cdma systems utilizing arrays of antennas

Abstract: The present invention is a method for operating a base station (BS) for transmitting information to a subscriber unit (SU) in a cellular communication system. The information is included in a downlink signal sent from a signal processing circuit through an array of antennae. The processing depends on a weight set that is utilized in generating individual signals to be sent on individual antennae in the array to the SU. The weight set is determined by transmitting a plurality of pilot downlink signals from BS to the SU, each pilot downlink signal being processed with a different weight set than that used to process the other pilot downlink signals. Report signals are received for each of the pilot downlink signals and are compared to determine which weight set should be utilized. The present invention may be practiced within existing CDMA cellular standards such as the IS-95 standard.

Data detection techniques for DS/CDMA mobile systems: a review

Abstract: As system requirements in terms of the BER performance and capacity increase, so will the need for more advanced detection techniques. The application of advanced receiver structures is optional for phase 2 of the UMTS FDD mode, while it is mandatory for the time-division duplex mode. Layer 1 of both modes is based on wideband direct sequence code-division multiple access technology, where a physical channel is characterized by the code, frequency, and, in the uplink, the relative phase (I/Q). Furthermore, in the TDD mode the physical channel is also characterized by the time slot (TDMA component).

All-digital PPM impulse radio for multiple-access through frequency-selective multipath

Abstract: Impulse radio (IR) is an ultra-wideband system with attractive features for baseband asynchronous multiple access (MA), multimedia services, and tactical wireless communications. Implemented with analog components, the continuous-time IRMA model utilizes pulse-position modulation (PPM) and random time-hopping codes to alleviate multipath effects and suppress multiuser interference (MUI). We introduce a novel continuous-time PPM-IRMA model, deduce a low-complexity approximate one, and derive its discrete-time equivalent model. Relying on a time-division-duplex access protocol and orthogonal user codes, we design composite linear/non-linear receivers for the downlink. The linear step eliminates MUI deterministically and accounts for frequency-selective multipath while a maximum likelihood (ML) receiver achieves symbol detection.

Method and apparatus for deriving uplink timing from asynchronous traffic across multiple transport streams

Abstract: A communication apparatus that shares precise return channel uplink timing information includes a common symbol timing reference and one or more control stations that each transmit independent asynchronous DVB data streams which evenly share the common symbol timing. The control stations each include respective delay trackers to determine broadcast transmission delays associated with the particular control station and transmission path. Each broadcast data stream includes the same non real-time frame marker and a transmission delay message particular to the respective control station. A remote receiver receives one of the broadcast streams and timestamps the non real-time frame marker with a local time of receipt. A timing recovery circuit determines an upcoming return channel frame start time by adjusting the local time of receipt by the particular broadcast transmission delay and a unique receiver offset time. A local transmitter subsequently uplinks a TDMA message in a predetermined time-slot after the return channel frame start time. The method for transmitting a frame synchronized message includes receiving a non real-time frame reference marker in a receiver, timestamping the received frame reference marker with a reception time, and subsequently receiving a control node timing differential at the receiver. The local reception time of the non real-time frame marker is corrected to determine the proper return channel frame transmit start time by applying the control node timing differential and the local offset time. Users then uplink a message during an assigned period after the return channel frame transmit start time.

Interference considerations for the time division duplex mode of the UMTS Terrestrial Radio Access

Abstract: The air interface of the UMTS Terrestrial Radio Access (UTRA) covers both a frequency division duplex (FDD) part for the paired bands and a time division duplex (TDD) part for the unpaired bands of the UMTS spectrum. The Universal Mobile Telecommunication System (UMTS) is the 3rd-generation mobile communication system. This paper presents an interference evaluation of the UTRA TDD. Since both uplink and downlink share the same frequency in TDD, the signals of the two transmission directions can interfere with each other. This interference can occur between two mobile stations or between two base stations within one carrier or between two operators. The interference between uplink and downlink is evaluated by system simulations. Synchronization and coordination requirements of UTRA TDD are evaluated based on the results.

Method and apparatus for compressed mode communications over a radio interface

Abstract: A system and corresponding method for utilizing Code Division Multiple Access (CDMA) techniques in compressed modes. In certain embodiments, radio frames on an uplink data channel are formed and transmitted to include at least one transmission gap (TG) therein in a compressed mode. This may be achieved by reducing the spreading factor (e.g., by a factor of two). In combination with reducing the spreading factor, the TG may be tailored or adjusted to its desired length (TGL) by using bit repetition (or reduction of puncturing). This enables the TG length to be tailored to a desired length, without having to increase output power more than necessary. In other embodiments of this invention, frames on an uplink control channel are formed or formatted so as to repeat format indicator (e.g., TFCI) bits therein in compressed mode. Optionally, format indicator bit(s) immediately or directly following the TG may be repeated later in the frame since these bits may sometimes suffer from slightly worse power control than other TFCI bits in the frame. Moreover, any embodiment of this invention is also applicable to downlink channel communications.

Energy-efficient TDMA medium access control protocol scheduling

Abstract: In this paper we study the energy efficiency and channel efficiency of TDMA MAC protocol scheduling mechanisms. Most MAC protocols are based on phase grouping that basically has three phases in a frame: uplink, downlink and reservation. We propose a new mechanism in which we have multiple uplink and downlink phases. These phases are grouped per mobile in a frame. Although this has a negative effect on the capacity of the channel, it allows the mobile to turn the power off from the wireless interface for a longer period. We made this choice since in a mobile multimedia environment it is more important that connections have a certain QoS, than highest possible bandwidth. We present an analysis in which these two basic mechanisms are compared in respect to bandwidth efficiency and energy efficiency. We have developed and implemented a novel MAC protocol based on mobile grouping that provides Quality of Service (QoS) support for diverse traffic types.

Methods and arrangements for locating a mobile telecommunications station

Abstract: In a mobile telecommunications network, a mobile station (MS) (12) is configured to generate and uplink transmit position measuring data (54, 70) prior to and/or during a call connection, without noticeably interrupting the user or degrading the quality of service provided Position measuring data (54, 70) can be uplink transmitted over an idle traffic channel during a call set up operation for a brief moment while the call connection is being completed Position measuring data (54, 70) can also be uplink transmitted during a call by selectively stealing data positions or burst positions in the uplink signal The position measuring data (54, 70) is received by a plurality of base stations (14) and uplink signal characteristics are measured and collected The measured uplink signal characteristic data from several base stations (14) is then used to determine a current approximate geographical location of the mobile station (12)

Null deepening for an adaptive antenna based communication station

Abstract: A method and apparatus is described for modifying a smart antenna processing strategy determined from a set of signals received at an array of antenna elements of a wireless station, such as a set of weights for processing received antenna signals or forming a set of antenna signals for transmission. The method and apparatus uses the signatures of one or more interferers to produce a modified processing strategy that improves the nulling to the one or more interferers in that, when the modified strategy is applied on the downlink, the transmit signal strength in the direction of the one or more interferers is decreased, and, when the modified strategy is applied on the uplink, the sensitivity to signals from the direction of the one or more interferers is decreased.

Comparison of time slot allocation strategies for CDMA/TDD systems

Abstract: The traffic (load) asymmetry between uplink and downlink is a remarkable traffic characteristic in cellular mobile multimedia communications. The code division multiple access system with time division duplex mode (CDMA/TDD system), adopting unbalanced slot allocation between uplink and downlink, is a good solution for this traffic asymmetry. However, the level of traffic asymmetry may be significantly different from cell to cell. In this paper, we investigate a slot allocation strategy (DA strategy), by which each cell has its own slot allocation according to the level of traffic asymmetry. We compute the system capacity with DA strategy and find out the optimal slot allocation for the system. We also compare the maximum capacity to that with another strategy (SA strategy), by which all cells have the same slot allocation. As a result, this paper shows that the system with DA strategy outperforms the system with SA strategy in the aspect of capacity.

Method to put a mobile terminal into sleep when a frame control channel containing a location of slow broadcast channel does not include wakeup information

Abstract: In a WLAN where an AP and MTs use a duplex airlink having a MAC frame structure to communicate with each other, the AP places wakeup PDUs at different locations in a MAC frame to allow the MTs to conserve energy by maximizing sleep time. In other embodiments, the wakeup PDUs are sequenced by MAC-ID so that a MT can conclusively determine whether remaining wakeup PDUs in a sequence can contain its MAC-ID, and go to sleep early if they cannot. In another embodiment, a wakeup PDU type can indicate to a corresponding MT whether the MT can expect downlink data later in the same MAC frame. In addition, the wakeup PDU type can indicate to the MT that the MAC frame that it should awaken and remain awake to receive downlink data in the future.

On achievable rates in a multi-antenna broadcast downlink

Abstract: A Gaussian broadcast channel with r single-antenna receivers where the transmitter is equipped with t antennas and where both the transmitter and the receivers have perfect knowledge of the propagation channel is considered. This provides a very simple model for the downlink of a wireless system, but despite its apparent simplicity it is in general a nondegraded broadcast channel, for which the capacity region is not fully known. We propose a novel transmission scheme based on \ranked known interference". In brief, the transmitter decomposes the channel into an ordered (or ranked) set of interference channels for which the interference signal of the i-th channel is generated as a linear combination of the signals transmitted in channels j < i. In this way, known techniques of coding for non-causally known interference can be applied to make the interference in each channel harmless without further power penalty. We show that the proposed scheme is throughputwise asymptotically optimal for both low and high SNR. In the special case of 2-antenna and 2-users we propose a modi cation of the basic strategy achieving optimal throughput for all SNRs. Finally, the in nite-dimensional Rayleigh channel is considered and throughput closed-form expressions are provided in various cases. This analysis shows that a practical and sensible strategy to the downlink of a wireless system consists of hybrid TDMA and space-time multiplexing where only a subset of active users, whose optimal size depends on the available SNR, is served at any given channel use by using our ranked known interference scheme. TDMA is used for time-sharing between di erent active user subsets to give to all users the same average rate without penalty in the maximum throughput. Also, constant-power variablerate coding achieves practically the same throughput of variable-power variable-rate coding (water lling power allocation).

A unified wireless LAN architecture for real-time and non-real-time communication services

Abstract: This paper addresses how to support both real-time and non-real-time communication services in a wireless LAN with dynamic time-division duplexed (D-TDD) transmission. With D-TDD, a frequency channel is time-shared for both downlink and uplink transmissions under the dynamic access control of the base station. The base station (1) handles uplink transmissions by polling mobiles in a certain order determined on a per-connection (per-message) basis for transmitting real-time (non-real-time) traffic from mobiles and (2) schedules the transmission of downlink packets. To handle location-dependent, time-varying, and bursty errors, we adopt the channel-state prediction, transmission deferment, and retransmission. We consider the problems of scheduling and multiplexing downlink packet transmissions, and polling mobiles for uplink transmissions depending on the channel state. We also establish conditions necessary to admit each new real-time connection by checking if the connection's delivery-delay bound can be guaranteed as long as the channel stays in good condition without compromising any of the existing guarantees. Last, the performance of the proposed protocol is evaluated to demonstrate how the protocol works and to study the effects of various parameters of the protocol.