Experimental Evaluation of Transmitted Signal Distortion Caused by Power Allocation in Inter-Cell Interference Coordination Techniques for LTE/LTE-A and 5G Systems

Error vector magnitude (EVM) and out-of-band emissions are key metrics for evaluating in-band and out-band distortions introduced by all potential non-idealities in the transmitters of wireless systems. As EVM is a measure of the quality of the modulated signal/symbols, LTE/LTE-A and 5G systems specify mandatory EVM requirements in transmission for each modulation scheme. This paper analyzes the influence of the mandatory satisfaction of EVM requirements on the design of radio resource management strategies (RRM) (link adaptation, inter-cell interference coordination), specifically in the downlink (DL). EVM depends on the non-idealities of the transmitter implementations, on the allocated power variations between the subcarriers and on the selected modulations. In the DL of LTE, link adaptation is usually executed by adaptive modulation and coding (AMC) instead of power control, but some flexibility in power allocation remains being used. LTE specifies some limits in the power dynamic ranges depending on the allocated modulation, which ensures the satisfaction of EVM requirements. However, the required recommendations concerning the allowed power dynamic range when inter-cell interference coordination (ICIC) and enhanced ICIC (eICIC) mechanisms (through power coordination) are out of specification, even though the EVM performance should be known to obtain the maximum benefit of these strategies. We perform an experimental characterization of the EVM in the DL under real and widely known ICIC implementation schemes. These studies demonstrate that an accurate analysis of EVM is required. It allows a better adjustment of the design parameters of these strategies, and also allows the redefinition of the main criteria to be considered in the implementation of the scheduler/link adaptation concerning the allocable modulation coding scheme (MCS) in each resource block. © 2013 IEEE

Performance of power control in inter-cell interference coordination for frequency reuse

To mitigate inter-cell interference in 3G evolution systems, a novel inter-cell interference coordination scheme called soft fractional frequency reuse is proposed in this article, which enables to improve the data rate in cell-edge. On this basis, an inter-cell power control is presented for the inter-cell interference coordination, and the inter-cell balanced signal to interference plus noise ratio (SINR) among users is established for power allocation, which enables mitigation of inter-cell interference. Especially, the power control is based on a novel exponential kernel equation at higher convergence speed than the traditional arithmetic kernel equations. Numerical results show that the proposed scheme improves the throughput and reduces the blocking rate compared to the existing power control algorithms

Advanced Techniques for Future Multicarrier Systems

Future multicarrier systems face the tough challenge of supporting high data-rate and high-quality services. The main limitation is the frequency-selective nature of the propagation channel that affects the received signal, thus degrading the system performance. OFDM can be envisaged as one of the most promising modulation techniques for future communication systems. It exhibits robustness to ISI even in very dispersive environments and its main characteristic is to take advantage of channel diversity by performing dynamic resource allocation. In a multi-user OFDMA scenario, the challenge is to allocate, on the basis of the channel knowledge, different portions of the available frequency spectrum among the users in the systems. Literature on resource allocation for OFDMA systems mainly focused on single-cell systems, where the objective is to assign subcarriers, power and data-rate for each user according to a predetermined criterion. The problem can be formulated with the goal of either maximizing the system sum-rate subject to a constraint on transmitted power or minimizing the overall power consumption under some predetermined constraints on rate per user. Only recently, literature focuses on resource allocation in multi-cell networks, where the goal is not only to take advantage of frequency and multi-user diversity, but also to mitigate MAI, which represents one of the most limiting factor for such problems. We consider a multi-cell OFDMA system with frequency reuse distance equal to one. Allowing all cells to transmit on the whole bandwidth unveils large potential gains in terms of spectral efficiency in comparison with conventional cellular systems. Such a scenario, however, is often deemed unfeasible because of the strong MAI that negatively affects the system performance. In this dissertation we present a layered architecture that integrates a packet scheduler with an adaptive resource allocator, explicitly designed to take care of the multiple access interference. Each cell performs its resource management in a distributed way without any central controller. Iterative resource allocation assigns radio channels to the users so as to minimize the interference. Packet scheduling guarantees that all users get a fair share of resources regardless of their position in the cell. This scheduler-allocator architecture integrates both goals and is able to self adapt to any traffic and user configuration. An adaptive, distributed load control strategy can reduce the cell load so that the iterative procedure always converges to a stable allocation, regardless of the interference. Numerical results show that the proposed architecture guarantees both high spectral efficiency and throughput fairness among flows. In the second part of this dissertation we deal with FBMC communication systems. FBMC modulation is a valid alternative to conventional OFDM signaling as it presents a set of appealing characteristics, such as robustness to narrowband interferers, more flexibility to allocate groups of subchannels to different users/services, and frequency-domain equalization without any cyclic extension. However, like any other multicarrier modulations, FBMC is strongly affected by residual CFOs that have to be accurately estimated. Unlike previously proposed algorithms, whereby frequency is recovered either relying on known pilot symbols multiplexed with the data stream or exploiting specific properties of the multicarrier signal structure following a blind approach, we present and discuss an algorithm based on the ML principle, which takes advantage both of pilot symbols and also indirectly of data symbols through knowledge and exploitation of their specific modulation format. The algorithm requires the availability of the statistical properties of channel fading up to second-order moments. It is shown that the above approach allows to improve on both frequency acquisition range and estimation accuracy of previously published schemes

Improving Frequency Reuse and Cochannel Interference Coordination in 4G HetNets

This report describes my M.A.Sc. thesis research work. The emerging 4th generation (4G) mobile systems and networks (so called 4G HetNets) are designed as multilayered cellular topology with a number of asymmetrically located, asymmetrically powered, self-organizing, and user-operated indoor small cell (e.g., pico/femto cells and WLANs) with a variety of cell architectures that are overlaid by a large cell (macro cell) with some or all interfering wireless links. These designs of 4G HetNets bring new challenges such as increased dynamics of user mobility and data traffic trespassing over the multi-layered cell boundaries. Traditional approaches of radio resource allocation and inter-cell (cochannel) interference management that are mostly centralized and static in the network core and are carried out pre-hand by the operator in 3G and lower cellular technologies, are liable to increased signaling overhead, latencies, complexities, and scalability issues and, thus, are not viable in case of 4G HetNets. In this thesis a comprehensive research study is carried out on improving the radio resource sharing and inter-cell interference management in 4G HetNets. The solution strategy exploits dynamic and adaptive channel allocation approaches such as dynamic and opportunistic spectrum access (DSA, OSA) techniques, through exploiting the spatiotemporal diversities among transmissions in orthogonal frequency division multiple access (OFDMA) based medium access in 4G HetNets. In this regards, a novel framework named as Hybrid Radio Resource Sharing (HRRS) is introduced. HRRS comprises of these two functional modules: Cognitive Radio Resource Sharing (CRRS) and Proactive Link Adaptation (PLA) scheme. A dynamic switching algorithm enables CRRS and PLA modules to adaptively invoke according to whether orthogonal channelization is to be carried out exploiting the interweave channel allocation (ICA) approach or non-orthogonal channelization is to be carried out exploiting the underlay channel allocation (UCA) approach respectively when relevant conditions regarding the traffic demand and radio resource availability are met. Benefits of CRRS scheme are identified through simulative analysis in comparison to the legacy cochannel and dedicated channel deployments of femto cells respectively. The case study and numerical analysis for PLA scheme is carried out to understand the dynamics of threshold interference ranges as function of transmit powers of MBS and FBS, relative ranges of radio entities, and QoS requirement of services with the value realization of PLA scheme.1 yea