Siddharth Mohan

Enhanced HSDPA Mobility Performance: Quality and Robustness for Voice over HSPA Service

Legacy High Speed Downlink Shared Channel (HS-DSCH) Serving Cell Change (SCC) procedures in deployed HSPA networks (3GPP Release 5 and 6) may lead to unacceptably high call drop rates in realistic Urban Canyon conditions when Signaling Radio Bearers (SRBs) are mapped on the HS-DSCH. Mapping SRB on HS-DSCH is necessary to enable high capacity voice over HSPA (Circuit Switched Voice or VoIP over HSPA) since it eliminates the code limitation that arises when SRBs are mapped on DCH. To address the above robustness issue, Enhanced SCC (ESCC) was introduced in 3GPP Release 8. In this paper we highlight the first ever implementation of the E-SCC algorithm in a HSPA prototype system. A comprehensive evaluation of the E-SCC algorithm for voice over HSPA is performed through measurements made over a prototype network. We show that under tough urban canyon conditions, the ESCC procedure provides significant gains compared to the legacy USCC procedure in terms of call drop rates, packet drops and duration of serving cell change, thus allowing robust high quality voice service under mobility conditions. To conclude, this paper provides evidence that E-SCC algorithm implementation is feasible and when implemented, robust mobility for voice over HSPA can be achieved.

Dual Cell HSDPA Application Performance

Dual Cell HSDPA (DC-HSDPA), which was introduced in Release 8 of the WCDMA specifications, enables the User Equipment (UE) to receive downlink data on two adjacent carriers simultaneously. Although the user physical layer throughput is expected to double compared to a single carrier HSDPA (SC-HSDPA) system, it is not quite clear how this would translate to user experience for realistic applications in various operating scenarios, i.e. channel conditions and loading. We implemented DC- HSDPA functionality in a prototype and evaluated its performance for various applications in comparison with SC-HSDPA. Our results show that, with DC-HSDPA, realistic applications such as web browsing and video streaming see significant gains in lab as well as OTA environments compared to SC-HSDPA with or without loading due to other users. Our results also highlight the ability of DC-HSDPA UEs to improve application performance by taking advantage of uneven loading across carriers, which may result due to UEs operating on a single carrier.

Dual Cell HSDPA System Benefits and User Experience Gains

Dual Cell-High Speed Downlink Packet Access (DC-HSDPA), which was introduced in Release 8 of the WCDMA specifications, enables the User Equipment (UE) to receive downlink data on two adjacent carriers simultaneously. Previous papers, including [1] [2] have shown how the doubling of physical layer rate of DC-HSDPA UEs translates to user experience gain for real applications such as web browsing and video streaming in unloaded systems. In this paper, using a real prototype implementation, we focus on gains of DC-HSDPA over two carriers of Single Cell HSDPA (SC-HSDPA) in terms of number of additional supportable users. For a given user experience, we show how many more users DC-HSDPA can support compared to two carriers of SC-HSDPA; we show these results for the two applications, file download and web browsing. In addition, our results show the impact of the TCP Slow Start algorithm on the user experience gains of DC-HSDPA for the application of file download.

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.