Quantum Computing and Communications: An Engineering Approach

8

Quantum-based Multi-user Detection

Every telecommunication system designed to provide services for more than one subscriber has to cope with the problem of medium access control (MAC), which regulates how to share the common medium (channel) among the users. Unlike traditional solutions where subscribers are separated in time, frequency or space, state of the art third/fourth generation mobile systems differentiate the users based on special individual codes assigned to each customer. Unfortunately performing optimal detection proves to be a hard task classically, therefore suitable suboptimal solutions are the focus of international research. However, quantum computing offers a direct way to the optimal solution because of its parallel processing capabilities.

Hence we introduce a mobile telecommunication oriented application based on quantum counting in this chapter: Section 8.1 explains the theoretical background of code division multiple access systems, highlights the related detection problem and gives the most trivial answer to it. Optimal detection criteria and their complexity are summarized and classical optimum detectors are discussed in Section 8.2. Finally we trace the optimal detection to quantum counting in Section 8.3.

8.1 INTRODUCTION TO CODE DIVISION MULTIPLE ACCESS AND CLASSICAL MULTI-USER DETECTION

Traditional telecommunication systems share the channel among the users in different ways:

TDMA Time Division Multiple Access ensures separation by assigning time ...