Kamyar Rohani

Bio: Kamyar Rohani is an academic researcher from Motorola. The author has contributed to research in topics: Communication channel & Signal. The author has an hindex of 24, co-authored 48 publications receiving 1619 citations.

Method and system in a transceiver for controlling a multiple-input, multiple-output communications channel

Abstract: The present invention makes it possible to increase a data rate between a transmitter and receiver using a multiple-input, multiple-output radio frequency channel. A multiple-stream, multiple-antenna receiver measures a composite channel between a multiple-antenna transmitter and a multiple-antenna receiver to produce a composite channel measurement. The receiver selects a plurality of antenna array weight sets for use in the multiple-antenna transmitter in response to the composite channel measurement, where each antenna array weight set is associated with one of multiple data streams. Information describing the plurality of antenna array weight sets for use in the multiple-antenna transmitter are then transmitted.

Apparatus and method for transmitting signals in a communication system

Abstract: Orthogonal transmit diversity is implemented by employing a data splitter (803) to subdivide channel information (801) into at least a first portion of bits (802) and a second portion of bits (804). Each portion is spread with its own Walsh code for eventual transmission to a mobile station via a predetermined carrier frequency. When the number of bits in the first and second portion (802, 804) are small, separate Walsh codes are used to maintain orthogonality. When the number of bits in the first and second portion (802, 804) are relatively large, a time-division multiplex transmission is used to maintain orthogonality. A controller (809) controls the subdivision of the channel information and also an interleaver (308) to further enhance the effects of the diversity transmission. Control information related to the subdivision is transmitted to the mobile station so the channel information can be accurately reconstructed prior to decoding.

Method and system for transmitting and receiving signals transmitted from an antenna array with transmit diversity techniques

Abstract: In a method for wireless data communication between a base station and a subscriber unit in a wireless communication system, groups of symbols of an input data stream are commutated to produce a plurality of commutated data streams. The plurality of commutated data streams are then transformed to produce a plurality of transformed data streams. Next, each transformed data stream is spread with a selected one of a plurality of spreading codes to produce a plurality of antenna signals. Finally, each of the plurality of antenna signals is transmitted using a selected one of a plurality of spaced apart antennas, wherein the plurality of spaced apart antennas are spaced apart to provide transmit diversity. In one embodiment, the transform is a space-time transform.

Method and system for generating a power control command in a wireless communication system

Abstract: In a wireless communication system using a power control command to control power of a transmitted traffic channel (58), a signal from a transmitter (64) is received (104) via a channel. A channel quality is measured (70, 108) using the signal from the transmitter. In response to the measured channel quality (70) exceeding (80, 110) a channel quality threshold (82), a decrease traffic channel power command is sent (112) to the transmitter, and a channel quality threshold is increased (114). In response to the channel quality threshold (82) exceeding (80, 110) the measured channel quality (70), an increase traffic channel power command is sent (116) to the transmitter, and the channel quality threshold is decreased (118). A traffic signal quality may be measured (72) and compared (88) to a traffic signal quality threshold (86). The result of the comparison (132) may be used to adjust (134) the channel quality threshold (82). The traffic signal quality threshold may be adjusted (90, 126, 128) in response to whether or not a frame error is detected (74, 124).

A comparison of base station transmit diversity methods for third generation cellular standards

Abstract: Code division multiple access (CDMA) is a common access scheme among all major proposals for third generation cellular standards. The objective of this paper is to show the performance benefits of open loop (which do not adapt transmission based on the channel to the mobile) and closed loop (which do adapt based on the channel to the mobile) transmit diversity methods for CDMA. We examine orthogonal transmit diversity (OTD) (an open loop method), and transmit adaptive arrays (TXAA) (a closed loop method).

On the capacity of a cellular CDMA system

Abstract: It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

Communication system and methods for enhanced information transfer

Abstract: A communication system (20) is provided with multiple purpose personal communication devices (50 and 150). Each communication device (50 and 150) includes a touch-sensitive visual display (60 and 160) to communicate text and graphic information to and from the user and for operating the communication device (50 and 150). Voice activation (78) and voice control capabilities (76) are included within communication devices (50 and 150) to perform the same functions as the touch-sensitive visual display (60 and 160). The communication device includes a built-in modem (82), audio input and output (52 and 53), telephone jacks (86), and wireless communication (90). A plurality of application modules (100) are used with personal communication devices (50 and 150) to perform a wide variety of communication functions such as information retrievable, on-line data base services, electronic and voice mail. Communication devices (50 and 150) and application modules (100) cooperate to allow integrating multiple functions such as real time communication, information storage and processing, specialized information services, and remote control of other equipment into an intuitively user friendly apparatus. The system (20) includes both desktop (150) and hand-held communication devices (50) with the same full range of communication capabilities provided in each type of communication device (50 and 150).

System and method for providing and using universally accessible voice and speech data files

Abstract: A system and method provides universal access to voice-based documents containing information formatted using MIME and HTML standards using customized extensions for voice information access and navigation. These voice documents are linked using HTML hyper-links that are accessible to subscribers using voice commands, touch-tone inputs and other selection means. These voice documents and components in them are addressable using HTML anchors embedding HTML universal resource locators (URLs) rendering them universally accessible over the Internet. This collection of connected documents forms a voice web. The voice web includes subscriber-specific documents including speech training files for speaker dependent speech recognition, voice print files for authenticating the identity of a user and personal preference and attribute files for customizing other aspects of the system in accordance with a specific subscriber.

Differential space-time modulation

Abstract: Space-time coding and modulation exploit the presence of multiple transmit antennas to improve the performance on multipath radio channels Thus far, most work on space-time coding has assumed that perfect channel estimates are available at the receiver In certain situations, however, it may be difficult or costly to estimate the channel accurately, in which case it is natural to consider the design of modulation techniques that do not require channel estimates at the transmitter or receiver We propose a general approach to differential modulation for multiple transmit antennas based on group codes This approach ran be applied to any number of transmit and receive antennas, and any signal constellation We also derive low-complexity differential receivers, error bounds, and modulator design criteria, which we use to construct optimal differential modulation schemes for two transmit antennas These schemes can be demodulated with or without channel estimates This permits the receiver to exploit channel estimates when they are available The performance degrades by approximately 3 dB when estimates are not available

Method and apparatus for high-rate packet data transmission

Abstract: In a data communication system capable of variable rate transmission, high rate packet data transmission improves utilization of the forward link and decreases the transmission delay. Data transmission on the forward link is time multiplexed and the base station transmits at the highest data rate supported by the forward link at each time slot to one mobile station. The data rate is determined by the largest C/I measurement of the forward link signals as measured at the mobile station. Upon determination of a data packet received in error, the mobile station transmits a NACK message back to the base station. The NACK message results in retransmission of the data packet received in error. The data packets can be transmitted out of sequence by the use of sequence number to identify each data unit within the data packets.