36 research outputs found
QoS and energy efficient resource allocation in downlink OFDMA systems
In this paper we present and evaluate the performance of a resource allocation algorithm to enhance the Quality of Service (QoS) provision and energy efficiency of downlink Orthogonal Frequency Division Multiple Access (OFDMA) systems. The proposed algorithm performs resource allocation using information on the downlink packet delay, the average delay and data rate of past allocations, as well as the downlink users' buffer status in order to minimize packet segmentation. Based on simulation results, the proposed algorithm achieves significant performance improvement in terms of packet timeout rate, goodput, fairness, and average delay. Moreover, the effect of poor QoS provision on energy efficiency is demonstrated through the evaluation of the performance in terms of energy consumption per successfully received bit
Resource allocation software algorithms for AMC-OFDM systems
PhD ThesisIn recent years, adaptive modulation and coding (AMC) technologies,
resource allocation strategies and user scheduling for single-cell downlink
orthogonal frequency division multiplexing (OFDM) and orthogonal
frequency division multiple access (OFDMA) systems have been
widely researched in order to ensure that capacity and throughput are
maximised. In terms of AMC technologies, the correlation between the
channel coefficients corresponding to the transmitted sub-carriers has
not been considered yet. In the literature of resource allocation and user
scheduling, either channel coding is not considered or only a fixed code
rate is specified. Consequently, with a fixed number of data sub-carriers
for each user, all these criteria restrict the flexibility of exploiting the
available channel capacity, which reflects negatively on system throughput.
At the same time, the presented scheduling algorithms so far managed
the data of each user regardless the fair services of all users. The
philosophy of this thesis is to maximise the average system throughput
by proposing novel AMC, resource allocation and user scheduling
strategies for OFDM and OFDMA systems based on developed software
engineering life cycle models. These models have been designed to
guarantee the scalability, extendibility and portability of the proposed
strategies. This thesis presents an AMC strategy that divides the transmitted
frame into sub-channels with an equal number of sub-carriers and
selects different modulation and coding schemes (MCSs) amongst them
rather than considering the same MCS for the entire frame. This strategy
has been combined with a pilot adjustment scheme that reduces the
pilots used for channel estimation in each sub-channel depending on the
measured coherence bandwidth, signal to noise ratio (SNR), and SNR
fluctuation values. The reduced pilots are replaced with additional data
sub-carriers in order to improve the throughput. Additionally, a novel
resource allocation strategy has been introduced in order to maximise
the system throughput by distributing the users, transmission power and
information bit streams over the employed sub-channels. The introduced
method utilises the proposed AMC strategy in combination with pilot
adjustment scheme to tackle the problem of channel capacity exploiting
efficiently. It presents the throughput as a new cost function in terms
of spectral efficiency and bit-error rate (BER), in which both convolutional
coding rates and modulation order can be varied. The investigated
throughput maximisation problem has been solved by producing two approaches.
Firstly, optimised approach that solves the adopted problem
optimally using the well known Lagrange multipliers method. This approach
requires a huge search processes to achieve the optimal allocation
of the resources, which yields a high computational complexity. To overcome
the complexity issue, the second approach decouples the considered
maximisation problem into two sub-problems based on the decomposition
method on the cost of performance particularly for low SNR values.
The proposed resource allocation strategy has been developed to
work with multi-input-multi-output (MIMO) based AMC-OFDMA systems.
In this project, two MIMO transmission criteria are considered,
i.e. traditional and eigen-mode. In contrast, a user scheduling algorithm
combined with the proposed resource allocation and AMC strategies is
presented. The user scheduling algorithm aims to maximize the average
system throughput by arranging the users in distinct queues according
to their priorities and selecting the best user of each queue individually
in order to guarantee a fair user service amongst different priority levels.
When the involved users are scheduled, the scheduled users have been
passed to the resource allocation to implement the distribution of the
available resources. The proposed strategies have been tested over different
international telecommunication union (ITU) channel profiles. The
obtained simulation results show the superior performance of the introduced
approaches in comparison with the related conventional methods.
Furthermore, the gradually improvement in the throughput performance
of the AMC-OFDM/ODMA system throughout the combination of the
proposed strategies is clearly explained.Ministry of Higher Education and Scientific
Research/IRAQ
Device-to-Device Communication and Multihop Transmission for Future Cellular Networks
The next generation wireless networks i.e. 5G aim to provide multi-Gbps data traffic, in order to satisfy the increasing demand for high-definition video, among other high data rate services, as well as the exponential growth in mobile subscribers. To achieve this dramatic increase in data rates, current research is focused on improving the capacity of current 4G network standards, based on Long Term Evolution (LTE), before radical changes are exploited which could include acquiring additional/new spectrum. The LTE network has a reuse factor of one; hence neighbouring cells/sectors use the same spectrum, therefore making the cell edge users vulnerable to inter-cell interference. In addition, wireless transmission is commonly hindered by fading and pathloss.
In this direction, this thesis focuses on improving the performance of cell edge users in LTE and LTE-Advanced (LTE-A) networks by initially implementing a new Coordinated Multi-Point (CoMP) algorithm to mitigate cell edge user interference. Subsequently Device-to-Device (D2D) communication is investigated as the enabling technology for maximising Resource Block (RB) utilisation in current 4G and emerging 5G networks. It is demonstrated that the application, as an extension to the above, of novel power control algorithms, to reduce the required D2D TX power, and multihop transmission for relaying D2D traffic, can further enhance network performance. To be able to develop the aforementioned technologies and evaluate the performance of new algorithms in emerging network scenarios, a beyond-the-state-of-the-art LTE system-level simulator (SLS) was implemented. The new simulator includes Multiple-Input Multiple-Output (MIMO) antenna functionalities, comprehensive channel models (such as Wireless World initiative New Radio II i.e. WINNER II) and adaptive modulation and coding schemes to accurately emulate the LTE and LTE-A network standards. Additionally, a novel interference modelling scheme using the ‘wrap around’ technique was proposed and implemented that maintained the topology of flat surfaced maps, allowing for use with cell planning tools while obtaining accurate and timely results in the SLS compared to the few existing platforms.
For the proposed CoMP algorithm, the adaptive beamforming technique was employed to reduce interference on the cell edge UEs by applying Coordinated Scheduling (CoSH) between cooperating cells. Simulation results show up to 2-fold improvement in terms of throughput, and also shows SINR gain for the cell edge UEs in the cooperating cells. Furthermore, D2D communication underlaying the LTE network (and future generation of wireless networks) was investigated. The technology exploits the proximity of users in a network to achieve higher data rates with maximum RB utilisation (as the technology reuses the cellular RB simultaneously), while taking some load off the Evolved Node B (eNB) i.e. by direct communication between User Equipment (UE). Simulation results show that the proximity and transmission power of D2D transmission yields high performance gains for a D2D receiver, which was demonstrated to be better than that of cellular UEs with better channel conditions or in close proximity to the eNB in the network. The impact of interference from the simultaneous transmission however impedes the achievable data rates of cellular UEs in the network, especially at the cell edge. Thus, a power control algorithm was proposed to mitigate the impact of interference in the hybrid network (network consisting of both cellular and D2D UEs). It was implemented by setting a minimum SINR threshold so that the cellular UEs achieve a minimum performance, and equally a maximum SINR threshold to establish fairness for the D2D transmission as well. Simulation results show
an increase in the cell edge throughput and notable improvement in the overall SINR distribution of UEs in the hybrid network. Additionally, multihop transmission for D2D UEs was investigated in the hybrid network: traditionally, the scheme is implemented to relay cellular traffic in a homogenous network. Contrary to most current studies where D2D UEs are employed to relay cellular traffic, the use of idle nodes to relay D2D traffic was implemented uniquely in this thesis. Simulation results show improvement in D2D receiver throughput with multihop transmission, which was significantly better than that of the same UEs performance with equivalent distance between the D2D pair when using single hop transmission