l. CHAPTER 4.3 High data rates in mobile communications 4.3.2 Higher data rates within transmitted signal is, at least in principle, independent of a limited bandwidth: Higher-order the size of the modulation alphabet and mainly depends on the modulation rate, i.e. the number of modulation modulation symbols per second. The maximum bandwidth utiliza- tion, expressed in bits/s/Hz, of 16QAM and 64QAM are As discussed in the previous section, providing data rates thus, at least in principle, two and three times that of larger than the available bandwidth is fundamentally QPSK, respectively. in-efficient in the sense that it requires un-proportionally It should be pointed out that there are many other high signal-to-noise and signal-to-interference ratios at the possible modulation schemes, in addition to those illus- receiver. Still, bandwidth is often a scarce and expensive trated in Figure 4.3-2. One example is 8PSK consisting of resource and, at least in some mobile-communication eight signaling alternatives and thus providing up to 3 bits scenarios, high signal-to-noise and signal-to-interference of information per modulation symbol. ratios can be made available, e.g. in small-cell environ- The use of higher-order modulation provides the ments with a low traffic load or for mobile terminals close possibility for higher bandwidth utilization, that is the to the cell site. Future mobile-communication systems, possibility to provide higher data rates within a given including the evolution of 3G mobile communication, bandwidth. However, the higher bandwidth utilization should be designed to be able to take advantage of such comes at the cost of reduced robustness to noise and scenarios, that is should be able for offer very high interference. Alternatively expressed, higher-order data rates within a limited bandwidth when the radio modulation schemes, such as 16QAM or 64QAM, conditions SO allow. require a higher Eb/No at the receiver for a given bit-error A straightforward means to provide higher data rates probabil