Effective Air-Interface Schemes For Carrier Aggregation In LTE-Advanced Systems

Previously, the primary focus of mobile communication technologies has been on voice communication. However, the rise in data content has shifted this emphasis to the provision of systems optimized for all-inclusive multimedia messages, such as:video-on-demand (VoD), television (TV), broadband internet access, video streaming and many more. The underlining technology responsible for this trend began with wideband code division multiple access (WCDMA) system otherwise known as 3rd generation networks (3G) engineered by 3rd generation partnership project (3GPP). Continuous enhancement of mobile communication technologies in stages has recently given birth to new mobile communication technologies known as long-term evolution (LTE) showcased as 3.9G and LTE-Advanced (LTE-A) which is widely accepted as the true 4G. The birth of LTE technology came with awesome rewards in the computing world, although it also has a number of accompanied challenges. Some of these challenges identified are:hardware design, protocol stack and dynamic air-interface just to name a few. Out of the major challenges LTE faces, air-interface remains one of the most dynamic challenges. This is majorly because of scarce network resources and the scenario-dependent air-interface. In this respect, radio resource scheduling has been identified as one of the effective techniques for improving the performance of air-interfaces.While, resource scheduling systems can be considered as flexible and rewarding, the considerably large number of criteria to be considered in scheduling makes the resource allocation (RA) in LTE-Advanced systems very complex, especially for carrier aggregation systems. In fact, the optimum RA that will be applicable to all LTE-Advanced network deployments has been described as practically infeasible. Consequently, suboptimal, efficient and simple RA scheduling strategies are required in order to allocate the frequency, time, and space resources of the system to network users. This thesis deals with suboptimal resource scheduling techniques in the downlink of LTE-Advanced systems. It primarily aims at maximizing users’throughput, ensuring fairness and increasing network spectral efficiency. In order to realize effective air-interface schemes via resource scheduling, we have approached the problem from four perspectives/scenarios, namely; resource scheduling within interference-limited environment, resource scheduling for carrier aggregation (CA) systems, frequency selective scheduling and control channel resource scheduling.With respect to interference-limited environment, an analytical model of interference-limited environment in a wireless network and how it relates with our study is first provided. Based on this study, we proposed a mechanism for reducing the overhead for feedback reporting during scheduling using the concept of Markov-Chain to estimate interference level being experienced by users. Furthermore, in order to facilitate resource allocation for users experiencing worst-case of interference, we proposed the worst-case fair weighted fair queuing (WF2Q) for scheduling procedure, which ensures fairness during resource allocation.In the case of carrier aggregation systems, it has been established that, because of difference in behaviors for selected frequencies, frequency selectivity is capable of impacting resource scheduling by attenuating certain frequencies while enhancing others. Likewise, users’ capability may also differ in terms of the number of carriers they can support. Moreover, the Release 10 UEs is perceived to having a higher advantage over legacy UEs because of their ability to access more than one frequency band at a time. The situation becomes more prominent in the case where the legacy UEs falls within a frequency band that is highly impacted. To tackle this issue, we proposed a technique that effectively schedules the UEs within frequency selective environment in carrier aggregation systems. Our proposed resource allocation paradigm is built on proportional fair (PF) algorithm with resource aggregation control mechanism. We provide a simplified analytical model to prove the effectiveness of our proposed method. Numerical simulation of the proposed technique has shown that overall system fairness and users’ throughput can be improved.Also, the evolution of LTE systems to LTE-A resulted in changing the features of air-interfaces which then necessitate the need for effective scheduling and expanding of Physical Downlink Control Channel (PDCCH)’s resources. The limited PDCCH resources usually result to some users being blocked from accessing network resources because they have not been scheduled for resource access by PDCCH. Using transformation matrix, we developed a new strategy for remapping users control signaling messages. Our scheme remaps the users’ search spaces (where users look for their control messages) using a transformation function derived from their previous search spaces and the available resources. Simulation results showed that our new scheme can reduce users’ average blocking probability in addition to significantly improving PDCCH resource utilization.Finally, the new enhanced PDCCH (EPDCCH) which also functions like PDCCH is multiplexed with data channels. The key challenge of EPDCCH is the mapping out of its resources from the Physical Downlink Shared Channel (PDSCH) and the scheduling of its resources. Using a combined method of binary combination and CQI reporting, we have proposed a dynamic EPDCCH mapping to the data channel. Furthermore, we outlined an algorithm for adaptive search space for the users. Our simulation results exhibited superior better performance to benchmarks in terms of EPDCCH mapping overhead, blocking probability and resource utilization.