HSPA+ Evolution to Release 12: Performance and Optimization

4 Continuous Packet Connectivity and High Speed Common Channels

Harri Holma and Karri Ranta-aho

4.1 Introduction

WCDMA Release 99 was designed for large file transfers, not for frequent and bursty transmission of small packets such as those created by smartphones, see Chapter 13. The WCDMA air interface design is circuit switched like dedicated channels that are not optimized for efficiency, for latency, nor for terminal power consumption. High Speed Downlink Packet Access (HSDPA) in Release 5 and High Speed Uplink Packet Access (HSUPA) in Release 6 improved the efficiency, data rates, and latency considerably by providing a true packet channel-based radio interface. The limitation was still that a Dedicated Physical Control Channel (DPCCH) was required and setting up and releasing DPCCH takes time, adding to the connection setup latency and limiting the number of users with simultaneously active radio connections. We could say that the Release 6 solution was still circuit-switched from the control channel point of view.

Release 7 brings Continuous Packet Connectivity (CPC) which enables Discontinuous Transmission (DTX) for the control channel. Release 8 brings for the first time a true packet-switched channel type in HSPA with High Speed Random Access Channel (HS-RACH) for the uplink direction, called Enhanced Cell_FACH in 3GPP. The corresponding downlink channel High Speed Forward Access Channel (HS-FACH) was defined in Release 7. The evolution of the packet transmission ...