The Physical Uplink Control Channel (PUCCH), which is mainly used to transmit Uplink Control Information (UCI), is a key component to enable the 5G NR system. Compared to LTE, NR specifies a more flexible PUCCH structure to support various applications and use cases. In the literature, however, an optimized solution that exploits those degrees of freedom is missing and fixed-heuristic solutions are just implemented in current 5G networks. Consequently, the predefined PUCCH format configuration is inefficient because it proposes a one-size-fits-all solution. In short, the number of symbols dedicated to PUCCH resources are often pre-determined and fixed without considering the UE’s specific needs and requirements. Failure to exploit the diversity of PUCCH format configurations and sticking to the one-size-fits-all solution, translates into a poor PUCCH resource allocation in the physical grid. To overcome this, a solution is presented by introducing a more efficient PUCCH re-distribution algorithm that exploits the same Physical Resource Block (PRB) domain. This leads into a combinatorial optimization problem with the objective of minimizing the PRBs utilization while maximizing the number of resources allocated and, in essence, the number of UEs “served”. For this purpose, we utilize a Monte Carlo Tree Search (MCTS) method to find the optimal puzzle on the grid, which offers clear advantages in search time benchmarked against an exhaustive search method. A wide variety of cases and scenario-dependent solutions are allowed using this puzzling technique. Overall results indicate that the optimal solutions devised by MCTS in conjunction with the new resource allocation algorithm bring substantial improvement compared to the one-size-fits-all baseline. In particular, this novel implementation, nonexistent to date in the 3GPP standard, reduces the dedicated PUCCH resource region by 1=6 without sacrificing any user’s allocation, while reusing the remaining PRBs (an increase of up to 11:36%) for the UL data channel or PUSCH. As a future work, we expect to observe similar improvements in higher layers metrics and KPIs, once link-level reception details are implemented and simulated for UL control channels based on our resource allocation solution. / PUCCH, som huvudsakligen används för att överföra UCI, är en nyckelkomponent för att möjliggöra 5G NR-systemet. Jämfört med LTE specificerar NR en mer flexibel PUCCH-struktur för att stödja olika tillämpningar och användningsfall. I litteraturen saknas dock en optimerad lösning som utnyttjar dessa frihetsgrader, och fasta heuristiska lösningar har bara implementerats i nuvarande 5G-nät. Följaktligen är den fördefinierade konfigurationen av PUCCH-formatet ineffektiv eftersom den föreslår en lösning som passar alla. Kort sagt, antalet symboler som är avsedda för PUCCH-resurser är ofta förutbestämda och fastställda utan att man tar hänsyn till UE:s specifika behov och krav. Om man inte drar nytta av den mångfald av PUCCH-formatkonfigurationer och håller sig till en lösning som passar alla, kommer det att leda till en dålig PUCCH-resursallokering i det fysiska resursnätet. För att lösa detta presenteras en lösning genom att införa en effektivare algoritm för omfördelning av PUCCH som utnyttjar samma PRB-domän. Detta leder till ett kombinatoriskt optimeringsproblem med målet att minimera PRB-utnyttjandet och samtidigt maximera antalet tilldelade resurser och, i huvudsak, antalet betjänadeänvändare. För detta ändamål använder vi en MCTS-metod för att hitta det optimala pusslet på rutnätet, vilket ger klara fördelar i söktid jämfört med en uttömmande sökmetod. En mängd olika fall och scenarioberoende lösningar tillåts med hjälp av denna pusselteknik. De övergripande resultaten visar att de optimala lösningarna som MCTS har tagit fram tillsammans med den nya resursfördelningsalgoritmen ger avsevärda förbättringar jämfört med den grundläggande lösningen med en enda lösning som passar alla. Denna nya implementering, som hittills inte funnits i 3GPP-standarden, minskar det dedikerade PUCCH-resursområdet med 1=6 utan att offra någon användarallokering, samtidigt som de återstående PRB:erna återanvänds (en ökning med upp till 11:36%) för UL-datakanalen eller PUSCH. Som ett framtida arbete förväntar vi oss att observera liknande förbättringar i mätvärden och KPI:er på högre nivåer, när mottagningsdetaljer på länknivå har genomförts och simulerats för uplink-kontrollkanaler baserade på vår resursallokeringslösning.

Reliability of data transmission is a fundamental problem in wireless communications. Fading in wireless channels causes the signal strength to vary at the receiver and this results in loss of data packets. To improve the reliability, automatic repeat request (ARQ) schemes were introduced. However these ARQ schemes suffer from a reduction in the throughput. To address the throughput reduction, conventional ARQ schemes were combined with forward error correction (FEC) schemes to develop hybrid-ARQ (HARQ) schemes. For improving the reliability of data transmission, HARQ schemes are included in the present wireless standards like LTE, LTE-Advanced and WiMAX. Conventional HARQ systems use the same transmission power and the same number of channel uses in different ARQ rounds. However this is not optimal in terms of minimizing the average transmit power or the average energy spent for successful transmission of a data packet. We address this issue in the first part of the dissertation, where we consider optimal resource allocation in HARQ systems with a limit on the maximum number of allowed transmissions for a data packet. Specifically, we consider the problem of minimizing the packet drop probability (PDP) under an average transmit power constraint or equivalently minimizing the average transmit power under a fixed PDP constraint. We consider both incremental redundancy (IR)-based and Chase combining (CC)-based HARQ systems in our work. For an IR-HARQ system, for the special case of two allowed transmissions for each packet, we provide a solution for the optimal number of channel uses and the optimal power to be used in each ARQ round. For a CC-HARQ system, we solve the problem of optimal power allocation in i.i.d. Rayleigh fading channels as well as correlated Rayleigh fading channels. For the CC-HARQ case, we also provide a low complexity geometric programming (GP) solution using an approximation of the outage probability expression. HARQ systems conventionally use one bit acknowledgement (ACK)/negative ACK (NACK) feedback from the receiver to the transmitter. In the 3GPP-LTE systems, one method for sending these HARQ acknowledgement bits is to jointly code them with the other control signaling information using a specified Reed-Muller code consisting of 20 coded bits. Even though the resources used for sending this control signaling information can inherently provide a diversity gain, the Reed-Muller code with such a short block size is not good at extracting all of the available diversity. To address this issue, in the second part of this dissertation, we propose two new methods: i) based on complex-field coding (CFC), and ii) using repetition across frequency bands, to extract the inherent diversity available in the channel resources and improve the error protection for the HARQ acknowledgement bits along with the other control signaling information. In the second part of the dissertation, we also propose a new signal space diversity (SSD) scheme, which results in transmit signals having constant envelope (CE). The proposed CE-SSD scheme results in a better overall power efficiency due to the reduced back-off requirements on the radio frequency power amplifier. Moreover, the proposed CE-SSD technique can be useful for application scenarios involving transmission of small number of information bits, such as in the case of control signaling information transmission. In conventional HARQ systems, during the retransmission phase, the channel resources are exclusively used for the retransmitted data packet. This is not optimal in terms of efficient resource utilization. For efficient utilization of channel resources during the retransmissions, a superposition coding (SPC) based HARQ scheme was proposed in the literature. In an SPC based HARQ system, an erroneous packet is transmitted together with a new data packet by superposition in the Euclidean space. In the final part of this dissertation, we study performance of different bits-to-symbol mappings for such an SPC based HARQ system.