System Design Tradeoff for Supporting Soft Handoff for Packet Data Calls using cdma2000 Cellular Simulator

The 2G CDMA IS-95A cellular networks have been deployed for almost 8 years. Although the system design rules and operating procedures for voice services (i.e., IS-95A services) are well established and understood, with the launch of cdma2000 1x high-rate data service worldwide in year 2002, these rules and procedures need to be re-examined. We have built a complete 3G cdma2000 1x cellular simulator, which simulates the physical layer using Signal Processing WorkSystem (SPW) and networking layers using OPNET Modeler, to investigate various design issues of cdma2000 1x networks. In this paper, we perform system design trade-off study for supporting soft handoff for packet data calls using cdma2000 1x cellular simulator. Soft handoff provides diversity for the link (switched diversity for the reverse link and combined diversity for the forward link); as a result, the link quality can be improved. However, soft handoff also introduces overhead on the forward link; specifically transmit power, channel element and Walsh code. As a result, the soft handoff regions in IS-95A networks must be engineered to achieve a delicate balance between call quality and network capacity. Soft handoff has always been performed for voice calls (in both IS95A and cdma2000 1x networks) to enhance the call quality with the understanding that there would be some degradation of the forward link capacity. However, this design rule needs to be reexamined for data calls since the QOS requirement for data calls is different from that for voice calls. For example, soft handoff can potentially be disabled for packet data calls. In this paper, we discuss the pros and cons of supporting soft handoff for data calls. In addition, we propose a new concept of supporting soft handoff for packet data calls by dynamically enabling soft handoff based on system and user conditions.