Paired and Unpaired Spectrum
Nicholas Anderson · 2009
As suitable radio spectrum for the deployment of cellular radio systems becomes increasingly scarce, a key design goal of LTE was to enable deployment in a diverse range of spectrum environments in terms of bandwidth, duplex spacing and uplink-downlink asymmetries. This chapter focuses first on the particular design challenges posed by operation in unpaired spectrum which had to be addressed during the design of LTE. These include unique interference issues, for which a thorough analysis is provided, co-existence with other systems, switching times between transmit and receive modes, and the design of control signalling. The second half of the chapter addresses the principle of reciprocity, a specific feature of deployments in which both directions of the radio link operate on the same frequency (i.e. TDD). The conditions under which reciprocity exists are identified, together with practical limitations. This leads on to an examination of which specific features of LTE may be able to benefit from reciprocity in appropriate scenarios; the validity of reciprocity is discussed for aspects such as scheduling, power control, link adaptation and MIMO schemes.