TABLE OF CONTENTS Although HSPA as defined in Release 6 is a significant enhancement to the packet-data functionality in WCDMA, the performance is further enhanced in Release 7 and beyond. Herein, this is referred to as HSPA Evolution and consists of both the introduction of new major features, such as MIMO, and many smaller improvements to existing structures which, when taken together as a package, represents a major increase in performance and capabilities. In the following sections, some of these enhancements are discussed.
MIMO is one of the major new features in Release 7, introduced to increase the peak data rates through multi-stream transmission. Strictly speaking, MIMO, Multiple Input Multiple Output, in its general interpretation denotes the use of multiple antennas at both transmitter and receiver. This can be used to obtain a diversity gain and thereby increase the carrier-to-interference ratio at the receiver. However, the term is commonly used to denote the transmission of multiple layers or multiple streams as a mean to increase the data rate possible in a given channel. Hence, MIMO, or spatial multiplexing, should mainly be seen as a tool to improve the end-user throughput by acting as a data-rate booster . Naturally, an improved end-user throughput will to some extent also result in an increased system throughput.
As discussed in Chapter 6, MIMO schemes are designed to exploit certain properties in the radio propagation environment to attain high data rates by transmitting multiple data streams in parallel. However, to achieve these high data rates, a correspondingly...
