2 research outputs found
Analysis and Validation of The Effect of Various Queueing Configurations to the End-to-end Throughput of Multi-Hop Wireless Network
A multi-hop wireless network is created by connecting multiple wireless access points (APs) as the backhaul of the network to increase the network coverage. The issue of spatial bias, unbalanced network performance of end-to-end throughput and delay occurs when the total offered load of the associated stations to the backhaul exceeds the wireless link capacity. Station associated to the access point with more hops away from the gateway will experience a significant amount of delay and lower end-to-end throughput compared to the station with fewer hops to the gateway. The equality of local successful transmit probability and mesh successful transmit probability in congested APs, which is the main root cause of the spatial bias problem, is modelled and validated. If the packet arrival ratio of local over mesh ingress interface is larger than the respective queue length ratio, the mesh ingress interface successful transmit probability will be higher than the local ingress interface successful transmit probability and vice-versa. By controlling the ratio of queue lengths, stations associated to the access point with more hops away from the gateway are given higher transmit opportunity, and therefore the spatial bias problem in multi-hop wireless network can be alleviate
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