Subramanian Vasudevan

Enhanced capacity and coverage by Wi-Fi LTE integration

Wi-Fi provides cost-effective data capacity at hotspots in conjunction with broadband cellular networks. The hotspots are required to capture a large number of users and provide high data rates. Data rates, over the Wi-Fi interface, are influenced by the media access protocol, which loses throughput due to contention based protocol delays and unintended collisions when a large number of users are active. The hotspot range that determines the number of users that can associate is limited by the lower power of the client rather than the access point. By diverting the traffic destined to the access point via another access network, both range and efficiency can be improved. This uplink redirection or diversion is achieved by simultaneous use of the Wi-Fi and LTE radio interfaces. Three options, loose, tight, and hybrid integration, are presented to providing enhanced capacity and coverage.

Performance Gains of a Hybrid Wi-Fi/LTE Architecture

Wi-Fi is providing hotspot capacity in conjunction with broadband cellular networks. We propose to divert uplink 802.11 MAC layer traffic to the cellular uplink towards improving range and downlink efficiency. This architecture uses the large unlicensed spectrum on the downlink, and the higher power and other advanced media access and physical layer techniques of the LTE uplink. Initial measurements show an improvement in Wi-Fi efficiency of about 30 percent due to the otherwise large airtime spent on TCP acknowledgements. Based on propagation and 802.11n receiver models, indoor area coverage at high bit rate (100 Mbps) is improved by a factor of 20. Maximum range is improved by a factor of 4 for indoor-to-outdoor scenarios. These are examples of gains beyond the federation of bandwidth.

Enabling Data Offload and Proximity Services Using Device to Device Communication over Licensed Cellular Spectrum with Infrastructure Control

The viability of device to device (D2D) communication on uplink resources [1] as also the benefits accruing from network control over such communication, on licensed spectrum [2], are quite well understood today. We investigate the merits of a particular system instantiation based on these two tenets. The challenge of scheduling communication between two devices using remote schedulers at one or more base stations is addressed with minimal changes to the current signaling mechanisms in a 3GPP LTE based framework. This system maintains as tight a control over device to device communication as is currently maintained over device to infrastructure communication. Furthermore the benefits of such a system range from optimized routing and resource allocation to metered charging for data exchanged on the D2D link to lawful intercept to dynamic local broadcast. We also provide a comparison of this system with the available option of D2D communications over unlicensed spectrum using Wi-Fi.

Co-operative scheduling for balancing throughput gains and fairness in cell-edge enhancement schemes for wireless networks

Multi-point reception techniques for enhancing cell-edge throughput are currently under standardization in cellular wireless standards as Single Frequency Dual Cell (SFDC) [1] in 3GPP and as Single Carrier Multi Link(SCML) [2] in 3GPP2. Unlike soft-handover operation, User Equipment(UEs) at cell-edge (handover zone) can independently request data from adjacent cells in multi point operation. Although the cell-edge UEs are benefited, there is a trade-off with fairness towards the in-cell UEs that get served only by a single serving cell, and the overall cell throughput and this paper proposes a joint scheduling algorithm to address this trade-off. To support practical implementation of such a scheme in current multi-vendor wireless networks, the cells participating in multi-point operation need to share throughput feedback via standards based mechanisms. Numerical results through computer simulation based on system parameters conforming to 3GPP2 evaluation methodology is presented. The results show that the proposed scheme can provide higher throughput for cell-edge users while maintaining the fairness towards other users in the system.