Multiple-Access Trellis-Coded Modulation using chirp signalling

Multiple-Access (MA) techniques in communication systems enable several transmitters to send information simultaneously over a single communications channel. They are an enabling factor in wireless communications, where the transmission medium is shared and corresponding resources such as bandwidth, time and power are limited. The choice of MA scheme is the first and foremost challenge for defining and developing any radio communications system, such as: cellular systems, wireless local area networks (WLANs) and wireless sensor networks (WSNs). With an increased demand for supporting large numbers of users and enhanced data rates, the design of new, more efficient, MA techniques is a pertinent topic in today's radio systems research. Since the implementation of MA schemes is constrained by ubiquitous bandwidth- and power-efficiency limitations of the existing modulation schemes, it is of interest to balance the requirements of interference-free transmissions in MA schemes with an acceptable BER performance for users.;This thesis introduces a novel Trellis Coded Modulation (TCM) based MA technique which takes advantage of CDMA approaches. The proposed MA TCM scheme exploits signal redundancy and modulation with memory principles to provide flexibility of CDMA schemes. The advantage of the novel MA technique is that it uses narrow-band modulation schemes and allows higher bandwidth utilization. Data associated with individual users in MA TCM are received reliably, even in the presence of a controllable amount of Multiple-Access Interference (MAI). This is because users are assigned unique, code-based trellises employing distinct signal sub-sets. This thesis focuses on the applicability of chirp signalling in MA TCM, even though the proposed system can use other types of narrowband modulations such as Frequency Shift Keying. Specifically, the MA scheme proposed in this thesis features the assignment of overlapping, dissimilar signal trellises that efficiently occupy the system bandwidth and allow for (i) user identification and (ii) reliable data recovery. Careful design of a chirp signalling scheme and the trellis arches guiding the frequency hopping patterns is conducted to reduce MAI. The bandwidth efficiency of chirp signalling is further exploited by providing multiple chirp rates to each user. An efficient demodulation algorithm is developed using the Viterbi decoder incorporated with an MAI cancellation scheme. It is demonstrated with simulations that the proposed scheme achieves a targetted bit error rate performance of 10-4 for different system configurations.;Code-Division Multiple-Access (CDMA) is one of the newer MA methods, where users transmitting in the same time and frequency band are separated by an assignment of signalling codes rather than an assignment of time and frequency slots, as practised in more traditional MA techniques. To counter the interference of other users in CDMA, signals are spread in the frequency domain so that the system bandwidth is larger than what is required by narrow-band modulation schemes. Conventional time- and frequency-division MA schemes set up many distinct, non-overlapping slots in time or frequency to be cycled through by users. Where these techniques rely on avoidance, code-based MA schemes allow controllable collisions to occur in a manner that can be reversed at the receiver.