4.3 Channel Estimation C 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology 7.4.4 Precoding Strategy 7.4.5 COOPA HARQ 7.5 Conclusions References Abstract The 3rd Generation Partnership Project (3GPP) long tem evolution (LTE) release 8 specification defines the basic functionality of a new high-performance air interface providing high user data rates in combination with low latency based on MIMO (multiple input, multiple output), OFDMA (orthogonal frequency division multiple access), and an optimized system architecture evolution (SAE) as main enablers. At the same time, in the near future, increasing numbers of users will request mobile broadband data access everywhere-for example, for synchronization of e-mails, Internet access, specific applications, and file downloads to mobile devices like per- sonal digital assistants (PDAs) or notebooks. In the future, a 100-fold increase in mobile data traffic is expected [1], making further improvements beyond LTE release 8 necessary and possibly ending up in new LTE releases or in a so-called international mobile telecommunications (IMT) advanced system [2-4]. IMT- advanced is a concept from the ITU (International Telecommunication Union) for mobile communication systems with capabilities that go further than that of IMT- 2000. IMT-advanced was previously known as systems beyond IMT-2000. The main enemy in today's cellular radio systems is interference. Although intra- cell interference is of minor importance for OFDMA systems like LTE, intersector as well as intersite interference reduces achievable spectral efficiency by factors. Multiuser MIMO (MU-MIMO) and OFDMA partly help to combat interference by beam forming gains and due to selection of resources less affected by interfer- ence. In the interference-limited case-meaning small cell sizes like pico or urban macrocells and high-transmission power-the performance of multicell systems is remarkably smaller than that of a single interference-free site. At the same time, it i