Rajarajan Balraj

Bio: Rajarajan Balraj is an academic researcher from Intel. The author has contributed to research in topics: Signal & Interference (communication). The author has an hindex of 11, co-authored 78 publications receiving 475 citations. Previous affiliations of Rajarajan Balraj include Intel Mobile Communications & Apple Inc..

MU-MIMO in LTE Systems

Abstract: A relatively recent idea of extending the benefits of MIMO systems to multiuser scenarios seems promising in the context of achieving high data rates envisioned for future cellular standards after 3G (3rd Generation). Although substantial research has been done on the theoretical front, recent focus is on making Multiuser Multiple-Input Multiple-Output (MUMIMO) practically realizable. This paper presents an overview of the different MU-MIMO schemes included/being studied in 3GPP standardization from LTE (long-term evolution) to LTE Advanced. MU-MIMO system concepts and implementation aspects have been studied here. Various low-complexity receiver architectures are investigated, and their performance assessed through link-level simulations. Appealing performance offered by low-complexity interference aware (IA) receivers is notably emphasized. Furthermore, system level simulations for LTE Release 8 are provided. Interestingly, it is shown that MU-MIMO only offers marginal performance gains with respect to single-user MIMO. This arises from the limited MU-MIMO features included in Release 8 and calls for improved schemes for the upcoming releases.

On the Equivalence of MMSE and IRC Receiver in MU-MIMO Systems

Abstract: In order to combat the residual interference in multiuser multiple-input and multiple-output systems (MU-MIMO), a number of low-complexity interference aware type of receivers have been considered. In this letter, single layer Minimum Mean Square Error (MMSE) and Interference Rejection Combiner (IRC) are applied in MU-MIMO transmission. Based on some very simple but extremely useful matrix manipulations, their equivalence is proven analytically and demonstrated via Monte Carlo simulations.

User equipment generation and signaling of feedback for supporting adaptive demodulation reference signal transmission

Abstract: Disclosed are UE-feedback techniques to support the adaptive DMRS transmission. A UE and eNB support adaptive DMRS transmission in which an eNB adjusts (i.e., selects) a DMRS pattern based on information describing channel conditions perceived by the UE. The UE may explicitly provide the channel conditions, or implicitly provide them by selecting a desired DMRS pattern.

Multi-user MIMO and Carrier Aggregation in 4G systems: The SAMURAI approach

Abstract: The market success of broadband multimedia-enabled devices such as smart phones, tablets, and laptops is increasing the demand for wireless data capacity in mobile cellular systems. In order to meet such requirements, the introduction of advanced techniques for increasing the efficiency in spectrum usage was required. Multi User -Multiple Input Multiple Output (MU-MIMO) and Carrier Aggregation (CA) are two important techniques addressed by 3GPP for LTE and LTE-Advanced. The aim of the EU FP7 project on “Spectrum Aggregation and Multi-user-MIMO: real-World Impact” (SAMURAI) is to investigate innovative techniques in the area of MU-MIMO and CA with particular focus on the practical, real-life, implementation and system deployment aspects. In the present paper, we provided an overview of the up-to-date SAMURAI contributions together with a description of the SAMURAI demonstrators developed as core part of the project.

Methods and devices for mitigating interference

Abstract: A method includes receiving a signal including a two-dimensional signal pattern in a time-frequency representation, wherein the two-dimensional signal pattern includes a first reference signal at a predetermined first position in the two-dimensional signal pattern and at least one second reference signal at a predetermined second position in the two-dimensional signal pattern The first reference signal includes cell identification information of a target cell of a cellular radio system and the at least one second reference signal includes cell identification information of at least one interfering cell of the cellular radio system The method further includes determining a first noise covariance measure based on the first reference signal, determining at least one second noise covariance measure based on the at least one second reference signal, and mitigating an interference included in the received signal based on the first noise covariance measure and the at least one second noise covariance measure

Radio base station, user terminal, and radio communication method

Abstract: The present invention is designed to improve spectral efficiency in a radio communication system which can use non-orthogonal multiple access (NOMA). Steps are provided in which a radio base station configures one of a plurality of transmission mode including a first transmission mode, which groups a plurality of transmission methods including a transmission method to employ non-orthogonal multiple access (NOMA) and multiple-user multiple-input and multiple-output (MU-MIMO), and a second transmission mode, which groups a plurality of transmission methods including a transmission method to employ this NOMA and open-loop transmit diversity, and transmits a downlink signal for this user terminal based on the configured transmission mode.

User terminal and radio communication method

Abstract: The present invention is designed to enable adequate transmission power control when inter-base station CA is employed. When inter-base station CA is employed, radio base stations detect when a user terminal's transmission power reaches the maximum transmission power, and execute control to cancel this. For example, a user terminal has a transmission section that transmits an uplink physical channel to each component carrier, a power headroom generating section that generates power headroom, which is extra transmission power of the subject terminal, and a control section that, when the value of the power headroom becomes 0 or less, executes control so that the power headroom is triggered and reported to the radio base stations.

System and methods for planned evolution and obsolescence of multiuser spectrum

Abstract: A system and method are described which enable planned evolution and obsolescence of multiuser wireless spectrum. One embodiment of such a system includes one or multiple centralized processors and one or multiple distributed nodes that communicate via wireline or wireless connections. The distributed nodes may share their identification number and other reconfigurable system parameters with the centralized processor. The information about all distributed nodes may be stored in a database that is shared by all centralized processors. The reconfigurable system parameters may comprise power emission, frequency band, modulation/coding scheme. The distributed nodes may be software defined radios such as FPGA, DSP, GPU and/or GPCPU that run algorithms for baseband signal processing and may be reconfigured remotely by the centralized processor. A cloud wireless system may be used wherein the distributed nodes are reconfigured periodically or instantly to adjust to the evolving wireless architecture.

Systems and methods for wireless power distribution allocation

Abstract: Systems and methods for power distribution allocation are provided. A system may establish a first wireless connection between the system and a first mobile device. The system may receive a first power request from the first mobile device, the first power request associated with a first minimum energy charge of the first mobile device, and may determine an available charging capacity of the charging system. The system may determine a first energy charge to provide wirelessly to the first mobile device, and may establish a second wireless connection with a second mobile device. The system may receive a second power request from the second mobile device, and may receive a first charge indicator from the first mobile device associated with a present charging status of the first mobile device. The system may determine a second energy charge to provide wirelessly to the second mobile device.

System and methods to compensate for Doppler effects in multi-user (MU) multiple antenna systems (MAS)

Abstract: A system and methods are described which compensate for the adverse effect of Doppler on the performance of DIDO systems. One embodiment of such a system employs different selection algorithms to adaptively adjust the active BTSs to different UEs based by tracking the changing channel conditions. Another embodiment utilizes channel prediction to estimate the future CSI or DIDO precoding weights, thereby eliminating errors due to outdated CSI.