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2845 Lafayette Street, MS3201
Santa Clara, CA 95050
The wireless systems research laboratory (WSRL), formed in 2005, is the North American unit of the global telecommunications research and development activities in Hitachi Ltd. The current focus of WSRL is on research and standardization of next-generation wireless systems with emphasis on 4G LTE-Advanced cellular systems. WSRL contributes to Hitachi’s patent portfolio, participates actively in 3GPP standardization meetings, and closely collaborates with the product and business units through extensive algorithms and simulator development. WSRL members regularly publish in leading academic journals and conferences. A sample of various current projects in WSRL is,
Previously WSRL had participated in IEEE 802.11 standardization activities and played an active role in the formation of IEEE standard 802.11aa. WSRL had also worked on enabling reliable video transfer over wireless systems and organized a demonstration at global Consumer Electronics Show (CES) in 2008 under the umbrella of Hitachi, Ltd. The lab has a small and dedicated team of researchers co-located with Hitachi Data Systems, Corp. in Santa Clara, California and works closely with researchers in Hitachi's central research lab in Tokyo, Japan and research lab in Beijing, China. WSRL also promotes ties with leading academic institutions for research collaboration.
Overlaying small cells onto the legacy macro cell network is a well-established method of boosting cellular coverage as well as capacity. For LTE Release-12 and beyond, the focus is on deploying and optimizing very dense small cell networks, where issues such as interference coordination and frequent handover become critical. WSRL is actively involved in several aspects of efficient small cell operation at both PHY and higher layers, such as interference mitigation via small cell ON/OFF switching, robust over-the-air synchronization, coordinated resource allocation over non-ideal backhaul links, dynamic optimization of uplink/downlink TDD configurations, and seamless mobility by exploiting dual connectivity and RRC diversity. Upcoming areas of study will focus on how real-time small cell traffic conditions can be efficiently monitored and optimized by the core network, using enhanced self-organizing network mechanisms for fault diagnosis and avoidance.
Full-dimensional multiple input multiple output (FD-MIMO) is a practical implementation of massive MIMO in cellular systems. FD-MIMO relies on an active two-dimensional antenna grid at the base stations and harvests the benefits of both azimuth and elevation beamforming. To make the best out of the use of elevation beamforming and FD-MIMO, new three-dimensional channel models are currently being discussed in 3GPP Rel. 12. WSRL is actively involved in the standardization activities of FD-MIMO taking into account the three-dimensional placement of users and base stations. WSRLs’ research further covers several aspects of FD-MIMO concepts and applications. Areas of research range from analyzing the gains from vertical sectorization and multi-user vertical beamforming, to efficient multi-user precoding and FD-MIMO codebook design. WSRL’s research on FD-MIMO focuses in general on enhancing the performance of cellular networks, bringing together massive MIMO and small cell networks.
Base Station coordination technology also known as coordinated multipoint transmission reception (CoMP) can dramatically enhance the performance of cellular systems by coordinating the transmissions across several base stations and thus mitigating the interference. There are multiple ways to coordinate the base stations such as coordinated scheduling and beamforming and joint processing of UE data from multiple base stations. WSRL has worked extensively on 3GPP Release 10 and 11 topics such as precoders design, user selection, scheduling and resource allocation for the base station and feedback and receiver design at the UE side. With advent of Release 12, the area of work has been extended to proposing effective CoMP technologies when the base stations are connected via non-ideal backhaul.
Inter-Cell Interference Coordination (ICIC) is an important feature introduced in LTE Release 8, which allows two neighboring cells to coordinate their transmissions and interference in frequency domain via X2 backhaul interface. ICIC techniques were further enhanced in LTE-Advanced Releases 10 and 11 allowing for subframe-level interference coordination in time domain. WSRL has done extensive work in this area including topics such as Almost Blank Subframe (ABS), Reduced Power ABS, Cell Range Expansion (CRE), Common Reference Signal Interference Cancellation (CRS-IC), and weak cell detection. Since Release 12, our focus has been on efficient interference coordination mechanisms for dense small cell deployment scenarios.