Vinay Chande

Benefits of transmit and receive diversity in enterprise femtocell deployments

In this paper, we study the benefits of transmit and receive diversity for enterprise UMTS femtocell deployments. Indoor enterprise femtocell deployments face a single-path slow fading wireless environment that may lead to frequent hard handovers in the boundary region of neighboring femtocells and consequent degradation in the voice quality experienced by the users. In the absence of soft-handover (SHO) support, transmit diversity at the femtocell can combat single-path fading channel. We demonstrate through over-the-air tests that transmit diversity is very effective in reducing the number of hard handovers and therefore results in significant improvement in voice quality for enterprise users. On the uplink, we study system stability using an analytical approach. We derive analytical conditions for system stability with and without receive diversity at the femtocells. Using this analytical framework, benefits of receive diversity in maintaining system stability and preventing uplink power racing between neighboring femtocells are quantified. It is shown that, in the absence of SHO, receive diversity is very effective in maintaining system stability by preventing potential uplink power racing caused by inter-femto interference.

Transmit power self-calibration for residential UMTS/HSPA+ femtocells

Downlink transmit power calibration is critical for femtocell deployment to achieve a good tradeoff between downlink coverage and interference impact to a co-channel macrocell network. In this paper, we study the performance of a femtocell power calibration algorithm that uses mobile reports to learn key information such as required coverage region for its own users and amount of interference to non-allowed users to fine-tune the femtocell downlink transmit power. It is shown that such a scheme is able to adapt to different deployment scenarios and provides better control of coverage-interference tradeoff than that provided by algorithms based on Network Listen Module alone.

Performance of VoIP services over 3GPP WCDMA networks

We analyze the performance of voice services over 3GPP WCDMA networks for Release 99 and Release 7 deployments. We show, by using simulations, that the system capacity of Release 7 VoIP is significantly higher than the Release 99 circuit-switched voice under similar system conditions and voice quality. These results are obtained under the 3GPP simulation assumptions where uplink and downlink constraints for power, code and interference are considered. Both AMR 12.2 and 5.9 as well as different types of mobile receivers (Rake and equalizer, single and dual receive antennas) are considered. We also show that the capacity and performance can be increased significantly further by using uplink interference cancellation at the base station. The performance of best effort traffic in the presence of voice users is also analyzed.

Circuit-Switched Voice Services Over HSPA

Circuit-Switched (CS) Voice Services over HSPA (CSoHS) was recently introduced for 3GPP WCDMA Release 7/8 systems. The benefits of this feature include improving voice and data system capacity by utilizing the enhancements offered by the shared packet transport of HSPA air interface while preserving the already widely deployed core networks. In this paper, we discuss the operation and implementation of CSoHS and analyze its performance via simulations. We show that the system capacity of CSoHS is significantly higher than Release 99 CS voice under similar system conditions and voice quality.

Performance Analysis of 64-QAM and MIMO in Release 7 WCDMA (HSPA+) Systems

Higher Order Modulation (HOM, 64-QAM) and Multiple Input Multiple Output (MIMO) transmissions are two key features introduced in the Release 7 (HSPA+) WCDMA systems to improve downlink performance. This paper focuses on the performance analysis of 64-QAM and MIMO in the WCDMA system. We describe the equalizer design for supporting these features as well as the simulation results demonstrating the higher system throughput and better user experience provided by these features.

Low complexity user loading emulation for 3G wireless systems testbeds

In a real-time test or demonstration environment/setup with support for only a few users, capturing the effects of large number of users in the system on a single user in terms of delay experienced and allocation of the shared resources is a challenge. In such a scenario, we propose a technique to emulate (or capture) the presence of large number of users with multiple QoS, resource constraints and channel conditions which we collectively refer to as load, without the load having to be present. We also implement the proposed loading emulation technique in Qualcomms prototype VoIP over HSPA system and compare the results of applying such a technique with results from Qualcomms network simulations supporting multiple users. We show that this emulation can be used to effectively capture load in a 3G HSPA+ test equipment.