Femtocells: Opportunities and Challenges for Business and Technology

4

Radio Issues for Femtocells

Simon Saunders

4.1 Introduction

One of the defining characteristics of a femtocell is its use of licensed spectrum. Typically this spectrum is already in use for delivering services using the existing macrocells. Some of the individual frequency channels may be unused by macrocells where operators have sufficient spectrum, but this is not generally the case, so operators need to have confidence that femtocells can operate without creating harmful interference to the existing network, even when deployed entirely by the end-user.

Over the air, femtocells produce identical signals to those which would be produced by a conventional base station. However, there are three respects in which radio issues may differ for femtocells compared with base stations:

• The required coverage area is deliberately limited to the area of a house or small office associated with a given user group.
• Interference between femtocells and macrocells is controlled via entirely automated means rather than via manual planning.
• The cost of femtocells must be minimised, so radio specifications which drive excessive cost without significant performance benefits must be avoided.

This chapter concentrates on the operation of femtocells in wideband CDMA (WCDMA) systems, since these present some of the most challenging cases as well as being candidates for early deployments of femtocells. However, the same general principles and outcomes apply to CDMA systems (e.g. cdma2000) and to OFDMA ...