LTE Advanced: 3GPP Solution for IMT-Advanced

13.1 Introduction

The peak data rates provided by LTE radio are substantially higher than the average data rates or the cell edge data rates – the difference can be a factor of 10 or more. The main reason is inter-cell interference, which limits signal-to-interference ratios and consequently also achievable data rates. While GSM systems apply frequency reuse (for example reusing the same resources only every seven or 12 cells), LTE uses a frequency reuse factor of one, meaning that inter-cell interference is particularly high. While this interference has traditionally been minimized by careful RF planning with antenna selections, antenna tilt and parameter settings, LTE radio brings further tools to mitigate interference in frequency and time domain in 3GPP Releases 8 and 10, as discussed in Chapter 8. A completely different view on multi-cell interference paths is now being enabled through the option of coordinated or cooperative signal processing across multiple cells. Such techniques, often referred to as Coordinated Multipoint (CoMP) Transmission and Reception and addressed in a work item for LTE Release 11 in 3GPP, are able to exploit interference paths between cells, rather than seeing them as problematic. Consequently, they can lead to higher capacity per area and, more importantly, offer an increased and homogeneous quality of service across cell areas. CoMP concepts, network architecture implications, and performance gains are described in this chapter.