Kiran K. Vanganuru

Architecture and protocols for LTE-based device to device communication

The evolution of cellular wireless communications has involved the introduction of technologies such as multiple antennas, OFDM, higher spectral efficiency through better modulation, denser deployments and carrier aggregation. A different approach to enhancing the cellular network by using direct communication between UEs is presented in this paper. Direct device-to-device (D2D) communication can be used for several purposes including network traffic offloading, public safety, and social applications such as gaming. The architectural and protocol enhancements required to extend the current 3GPP LTE-Advanced system to incorporate D2D communication are described, including the logical functions of a D2D server in the core network, the procedures for devices to discover each other and obtain D2D services, the steps involved in establishing and maintaining a D2D call and procedures for efficient mobility between a traditional cellular mode and a D2D mode of operation.

System capacity and coverage of a cellular network with D2D mobile relays

It has been predicted that the recent explosive growth in wireless data traffic will continue for the foreseeable future. To date, attempts to address this explosive growth have included increasing base station density through smaller cells, and to a lesser extent, by improving spectral efficiency using close-to-capacity channel coding and MIMO techniques. Providing further capacity and coverage improvements through ever shrinking cells could lead to large infrastructure costs and operating expenses. In this paper we propose a far less expensive alternate solution using a topology which employs mobile User Equipment (UE) nodes as virtual infrastructure to enhance the cellular capacity while also improving network coverage. The improvements in capacity and coverage are achieved by enabling cellular controlled direct Device to Device (D2D) links to carry relayed traffic. Each terminal UE (T-UE) with an active connection could potentially be assigned a Helper UE (H-UE), depending on the network conditions and traffic requirements to improve the system capacity. In addition, T-UEs which are out of coverage can also be assigned a H-UE, which would extend the typical coverage of a base station and lead to improved network coverage. In this paper, we present both coverage enhancement and system capacity results using Monte Carlo simulation techniques for both uplink and downlink communications. Our results indicate that cell edge percent throughput capacity improvements as well as percent throughput coverage improvements of more than 150% may be realized using idle UEs in the system as mobile relays.

System Architecture for a Cellular Network with Cooperative Mobile Relay

This paper describes a comprehensive system architecture that enables mobile-to-mobile communications for the purpose of enhancing the capacity of the cellular network. The architecture is developed using LTE Release-10 as the baseline. The impact on the protocol stack is discussed in detail. Neighbor discovery mechanisms are described to enable users to identify potential helper mobiles to enable a cooperative mobile relay. Resource partitioning for the mobile-to-mobile link is detailed and changes to the design of the HARQ entity structure and timing are discussed.

Uplink system capacity of a cellular network with cooperative mobile relay

This paper studies the performance of a hybrid cellular network with cellular controlled direct radio links between multiple mobile User Equipments (UEs). The main focus is on the uplink of the proposed system with multiple idle UEs acting as relays to assist the communication of any given UE with an active connection. In the presence of multiple UEs as relays, the Base Station (BS) dynamically chooses the best relay to maximize the throughput of each radio link. We present system capacity results using Monte Carlo system simulation techniques. Further, we compare results with and without the use of distributed beam forming techniques. Our results indicate that cell edge capacity could be improved by more than 99% by using idle UEs in the system as mobile relays. The performance improvement at cell edge is achieved while improving the mean cell throughput by more than 50%.

Performance evaluation of transmit diversity concepts for WCDMA in multipath fading channels

We analyse the performance of transmit diversity schemes in combination with receive antenna diversity on the downlink of a WCDMA system. The performance of maximum ratio combining and selection diversity combining schemes has been analysed for both open-loop and closed-loop transmit diversity schemes. The analytical framework developed can handle an arbitrary number of transmit and receive antennas. The framework is also used to study the effect of dissimilar received signal strengths at the mobile handset on the average symbol error rate performance of a multitude of digital modulation schemes in a generalized multipath fading environment. Simulation results obtained are shown to be in agreement with the analytical results.