er modulation tech- station niques could therefore be used to deliver higher transmission rates to users closer to the base stations than users farther away. For example a user near the base station could use modulation schemes such as 16-QAM with an efficiency of 4 bits/s/Hz of capacity, whereas users near the cell edge would use QPSK modulation and experi- ence a capacity of 2 bits/s/Hz. This adaptive modulation technique increased the overall network efficiency. Case study Questions Why were the 2G and early 3G standards' focus on voice services? Why does voice service require equal bandwidth regardless of the location of the mobile device? Why does the received power get smaller as a mobile device gets further away from a base station? Why can data communications tolerate different transmission rates (in contrast to voice communications)? How do different modulation rates enable a higher resource utilisation efficiency? The Shannon channel capacity formula teaches that under favourable channel conditions, faster information transfer is possible. That is, a system's transmission rate in bits per second per unit of bandwidth (Hz) increases as the quality of the received signal improves. It is Broadband Telecommunications Technologies and Management impractical to take advantage of this capacity increase in analogue communications. In contrast, multi-level and multi-phase digital modulation techniques facilitate simultaneous transmission of multiple data bits, thereby realising channel transmission capacity as pre- dicted by Shannon. Hence, digital modulation provides a mechanism to realise Shannon capacity limits. This is one of the most important advantages of digital over analogue. Review Questions 1. Which parameters of a carrier wave may be used for transmission of discrete data? 2. How is ASK different from PSK? Which one is more efficient? 3. Where would you use ASK and why? 4. What is PAM-5 and where is it used? 5. How is the BER metric useful? 6. Why is QPSK superior to 8-PSK? 7. What is the value of hi