Sharad Deepak Sambhwani

HSUPA Scheduling Algorithms Utilizing RoT Measurements and Interference Cancellations

This paper discusses several important aspects in the HSUPA scheduling algorithms. First, it clearly demonstrates the benefit of explicitly utilizing the directly measured Rise-over- Thermal(RoT) values in term of capacity and robustness improvement. This paper also briefly presents the RoT measurement schemes designed specifically for the asynchronous systems such as WCDMA/HSUPA. If pilot and traffic interference cancellation (IC) schemes are implemented at the Node B receiver, this paper presents a scheduling algorithm that attains IC benefit in such a way that the capacity enhancement is maximized while fairness and link budget are maintained. The presented algorithm defines the effective RoT by monitoring the IC performance in real time and adjusts its grants accordingly. In addition, the user priority function used here optimizes the sum utility functions and provides multi-user diversity.

Introducing heterogeneous networks in HSPA

In heterogeneous networks, low power nodes may be deployed within macro cells for coverage and capacity improvement. Due to transmit power difference between low power nodes and macro cells, downlink (DL) and uplink (UL) coverage of the low power nodes can be very different. This DL-UL coverage difference could negatively affect system performance on both the DL and the UL. We describe a few techniques to alleviate this problem in HSPA. We present simulation results to show the effectiveness of these techniques as well as the system performance improvement of heterogeneous networks over traditional macro cell only deployments in HSPA.

System performance of Inter-NodeB MF-HSDPA with RLC and MAC enhancements

In this paper, we study the feature of Multi-Flow HSDPA (MF-HSDPA), which allows simultaneous transmission of separate data packets from two or more serving cells (across different sectors or NodeBs) to a UE. This new feature brings challenges for system design, especially for the Inter-NodeB case, in which the serving cells reside in different NodeBs. To address these challenges, we propose enhancements to the Radio Link Control (RLC) layer and Media Access Control (MAC) layer. Simulation results show significant performance gain can be achieved by the MF-HSDPA feature.

Non-Parametric Interference Cancellation for CDMA Uplink System

Uplink capacity of a code division multiple access (CDMA) system is limited by the mutual interference among users. It is well known that interference cancellation can significantly increase the CDMA uplink capacity. In this paper, we present a new interference cancellation scheme based on non-parametric channel estimation and waveform reconstruction. Compared with the traditional parametric scheme, the new scheme can effectively solve the model mismatch problem caused by a multipath channel. We also propose channel estimation cleaning methods to further improve the performance.

Performance analysis of HSPA Multi-carrier heterogeneous networks

Heterogeneous networks (HetNets), consisting of Macro NodeBs (macros) and low power Pico NodeBs (picos), can increase system capacity by offloading some users to the picos. However, this offloading may be limited due to intercell interference from macros to picos that reduces their coverage. HSPA Multi-carrier HetNets allow the use of range expansion techniques to achieve more offloading, such as power reduction from the macros on one carrier. This paper provides a system level analysis of the gain provided by power reduction on one carrier of the macros in a HetNet environment. As the interference from the macros is reduced, more capacity offloading to picos occurs and higher system capacity can be achieved. By considering cell biasing in serving cell selection, further gains can be observed.

Design aspects of closed loop beamforming transmit diversity in HSUPA

Closed loop beamforming transmit diversity is a promising technique to improve the uplink transmission performance in cellular networks. This technique was recently incorporated into the 3GPP HSPA standard. This paper reflects on several design aspects of closed loop beamforming transmit diversity, including: precoded pilot channels design, precoding information determination when UE is in soft handover, and enhanced symmetric beamforming implementation.

Iterative Soft Interference Cancelation for HSPA Uplink

Interference cancelation (IC) has been well studied in literature as a potential capacity approaching scheme for uplink code-division multiple-access (CDMA) systems. With the advance of silicon technology, it is becoming implementationally feasible. In this paper, we study a soft IC algorithm which could be iteratively concatenated with Turbo decoding. The algorithm only relies on a conventional single user Rake receiver. We study the IC efficiency as well as optimal soft decision methods. We compare different types of add-back operations between iterations. Finally we provide both link level as well as system level simulation results.

MIMO in HSDPA and Legacy-MIMO Co-Existence

Multiple Input Multiple Output (MIMO) transmission improves downlink spectral efficiency and is a key feature of Release 7 High Speed Downlink Packet Access (HSDPA). When the Node-B is configured in the MIMO mode with secondary common control pilot channel (S-CPICH), the power amplifiers (PAs) for the two transmit antennas are not balanced. A common pre-coder is required to balance the PAs for legacy and dual-stream MIMO transmissions. In addition, codebook restriction is needed to balance the PAs for single-stream MIMO transmissions. Despite codebook restriction, MIMO performance degradation is small. Legacy user performance in a MIMO cell suffers due to power and interference penalties associated with the Secondary Common Pilot Channel (S-CPICH). By reducing the S-CPICH transmit power, this degradation can be reduced, without significantly compromising the channel estimation quality for MIMO users in the cell.