Balamurali Natarajan

Dynamic point selection for LTE-advanced: Algorithms and performance

Dynamic Point selection (DPS) is a key Downlink (DL) Coordinated Multipoint (CoMP) technique that switches the serving data Transmission Point (TP) of a User Equipment (UE) dynamically among the UEs cooperating set of TPs without requiring a cell handover. It provides performance improvement due to TP selection-diversity gains and dynamic UE load balancing benefit. In this paper, we propose two simple DPS schemes that take into account the UEs current channel conditions and the cell loading conditions to make the UEs TP switching decisions. We show that these schemes improve the system performance under different practical and realistic settings, such as, cell handover margin, TP switching periods, bursty traffic conditions, and cooperation cell cluster sizes.

Coordinated Scheduling for Advanced UE Receivers Using Belief Propagation

The newly introduced Network Assisted Interference Cancellation and Suppression (NAICS) feature in LTE Release-12 facilitates autonomous cancellation/suppression of a user equipments (UEs) dominant interference. For one of the most-advanced UE receivers that benefit from NAICS, namely the interference-aware successive decoding (IASD) receiver, the achievable transmission rate is dependent on the dominant interferers transmission rate. Hence, cooperative scheduling among the neighboring basestations (BSs) can further enhance their performance. This paper proposes distributed coordination schemes for joint UE, rate and BS transmit power selection (power on/off) based on a belief-propagation framework.

Interference Penalty Algorithm (IPA) for inter-cell interference co-ordination in LTE uplink

In this paper, we develop a novel inter-cell interference co-ordination scheme that takes into account the interference cost on neighboring cells. We formulate a multi-cell utility maximization problem and subsequently decouple it into single-cell optimization problems by including an interference penalty. By solving this decoupled problem, we derive policies for user selection, resource allocation, and power-control. Since the coupling between cells is indirectly taken into account by means of the users channel gain to the neighboring cells, our simulation results show that this distributed solution has no degradation in performance while little or no inter-cell co-ordination is required. We present simulation results that show that the Interference Penalty Algorithm (IPA) provides significant improvement in sector and cell-edge throughputs.

Channel Orthogonality and Utility-Based UE Pairing Schemes for LTE Uplink MU-MIMO

Multi-User MIMO (MU-MIMO) is a useful technique to enhance uplink capacity in LTE because the base stations employ multiple receive antennas whereas the user equipments transmit with only a single antenna. In this paper we investigate several UE pairing schemes that maximize the total system utility while adhering to the LTE Release-8 constraint of allocating identical contiguous resource blocks (RBs) to the paired UEs. We design pairing decisions using either the wideband or sub- band channel cross-correlation values of the UEs. These mechanisms offer varying trade-offs between performance and complexity.We show that with appropriate modifications, these schemes work well even for finite queue traffic.