user in an adjacent cell may generate interference that will reduce the signal-to-noise-plus-interference ratios (SINR) of an existing user SO much that it no longer meets its QoS requirements. 8.4 Radio Resource Allocation that Considers Spectrum Sharing The definition of QoS can be quite complex considering factors such as bandwidth, through- put, latency, and loss. Cisco has published [34] a detailed assessment of QoS requirements for different types of service. However, this section is about radio resource allocation and spectrum sharing; such resource allocation can either be blocks of spectrum or time slots. Here, the same approach as found in much of the literature [35] is taken, whereby ser- vices are differentiated by the required bitrate and the requirements on different types of QoS requirement must be mapped into allocation of spectrum. This mapping is generally a well-known problem. For example, a simple loss-sensitive sliding-window ARQ protocol needs to have extra bandwidth allocated to allow for retransmission of errored packets; the allocated bitrate is given by ralloc = 1-WDW where r is the desired bit rate, W the window size, and Pwe the probability of a packet being in error. Figure 8.8 summarizes the different methods of sharing the spectrum between slices for three slices. Static resource assignment: A slice operates with a fixed resource. This provides a guaran- teed resource allocation to the slices but does not allow for changing demand. ICI means that there can be intra-slice interference. 8.4 Radio Resource Allocation that Considers Spectrum Sharing Available spectrum (a) Fixed allocation per slice Slice 1 Slice 2 Slice 3 but not same BW per slice (b) Partial resource Slice 1 Slice 2 Slice 3 Shared reservation (c) Full resource sharing: all spectrum is available to all Shared users Figure 8.8 Types of network slicing. Partial resource reservation: This is introduced in Guo and Arnott [31] and combines a fixed allocation with a sharing region (Figure 8.8b). In [36], the authors propose a