14 research outputs found
Modeling Asymmetric Slot Allocation for Mobile Multimedia Services in Microcell TDD Employing FDD Uplink as Macrocell
Abstract. This paper introduces an analytical approach which is provided to calculate the downlink and uplink capacities of the time division duplex (TDD) system utilizing the underused frequency division duplex (FDD) uplink which shares the same frequency band. Then the ratio of downlink and uplink slots in one frame is adjusted, so as to prevent the radio resource waste due to asymmetric traffic characteristic in mobile multimedia services. The computer simulation shows that the resource waste problem can be considerably solved through the asymmetric slot allocation. Thus, this paper can be useful as a guideline in the course of planning a two-layer hierarchical cell structure (HCS) employing the TDD system as a microcell and FDD system as a macrocell as well as a mean to increase the performance of such a system
Final report on the evaluation of RRM/CRRM algorithms
Deliverable public del projecte EVERESTThis deliverable provides a definition and a complete evaluation of the RRM/CRRM algorithms selected in D11 and D15, and evolved and refined on an iterative process. The evaluation will be carried out by means of simulations using the simulators provided at D07, and D14.Preprin
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Capacity and Throughput Optimization in Multi-cell 3G WCDMA Networks
User modeling enables in the computation of the traffic density in a cellular network, which can be used to optimize the placement of base stations and radio network controllers as well as to analyze the performance of resource management algorithms towards meeting the final goal: the calculation and maximization of network capacity and throughput for different data rate services. An analytical model is presented for approximating the user distributions in multi-cell third generation wideband code division multiple access (WCDMA) networks using 2-dimensional Gaussian distributions by determining the means and the standard deviations of the distributions for every cell. This model allows for the calculation of the inter-cell interference and the reverse-link capacity of the network. An analytical model for optimizing capacity in multi-cell WCDMA networks is presented. Capacity is optimized for different spreading factors and for perfect and imperfect power control. Numerical results show that the SIR threshold for the received signals is decreased by 0.5 to 1.5 dB due to the imperfect power control. The results also show that the determined parameters of the 2-dimensional Gaussian model match well with traditional methods for modeling user distribution. A call admission control algorithm is designed that maximizes the throughput in multi-cell WCDMA networks. Numerical results are presented for different spreading factors and for several mobility scenarios. Our methods of optimizing capacity and throughput are computationally efficient, accurate, and can be implemented in large WCDMA networks
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Study of continuous-phase four-state modulation for cordless telecommunications. Assessment by simulation of CP-QFSK as an alternative modulation scheme for TDMA digital cordless telecommunications systems operating in indoor applications
One of the major driving elements behind the explosive boom in wireless revolution is the advances in the field of modulation which plays a fundamental role in any communication system, and especially in cellular radio systems. Hence, the elaborate choice of an efficient modulation scheme is of paramount importance in the design and employment of any communications system. Work presented in this thesis is an investigation (study) of the feasibility of whether multilevel FSK modulation scheme would provide a viable alternative modem that can be employed in TDMA cordless communications systems. In the thesis the design and performance analysis of a non-coherent multi-level modem that offers a great deal of bandwidth efficiency and hardware simplicity is studied in detail. Simulation results demonstrate that 2RC pre-modulation filter pulse shaping with a modulation index of 0.3, and pre-detection filter normalized equivalent noise bandwidth of 1.5 are optimum system parameter values. Results reported in chapter 5 signify that an adjacent channel rejection factor of around 40 dB has been achieved at channel spacing of 1.5 times the symbol rate while the DECT system standards stipulated a much lower rejection limit criterion (25-30dB), implying that CP-QFSK modulation out-performs the conventional GMSK as it causes significantly less ACI, thus it is more spectrally efficient in a multi-channel system. However, measured system performance in terms of BER indicates that this system does not coexist well with other interferers as at delay spreads between 100ns to 200ns, which are commonly encountered in such indoor environment, a severe degradation in system performance apparently caused by multi-path fading has been noticed, and there exists a noise floor of about 40 dB, i.e. high irreducible error rate of less than 5.10-3. Implementing MRC diversity combiner and BCH codec has brought in a good gain.Higher Education Ministr
Soft handover issues in radio resource management for 3G WCDMA networks
PhDMobile terminals allow users to access services while on the move. This unique
feature has driven the rapid growth in the mobile network industry, changing it from a
new technology into a massive industry within less than two decades.
Handover is the essential functionality for dealing with the mobility of the mobile
users. Compared with the conventional hard handover employed in the GSM mobile
networks, the soft handover used in IS-95 and being proposed for 3G has better
performance on both link and system level.
Previous work on soft handover has led to several algorithms being proposed and
extensive research has been conducted on the performance analysis and parameters
optimisation of these algorithms. Most of the previous analysis focused on the uplink
direction. However, in future mobile networks, the downlink is more likely to be the
bottleneck of the system capacity because of the asymmetric nature of new services,
such as Internet traffic.
In this thesis, an in-depth study of the soft handover effects on the downlink
direction of WCDMA networks is carried out, leading to a new method of optimising
soft handover for maximising the downlink capacity and a new power control
approach
Spatio-Temporal processing for Optimum Uplink-Downlink WCDMA Systems
The capacity of a cellular system is limited by two different phenomena, namely
multipath fading and multiple access interference (MAl). A Two Dimensional (2-D)
receiver combats both of these by processing the signal both in the spatial and temporal
domain. An ideal 2-D receiver would perform joint space-time processing, but at the
price of high computational complexity. In this research we investigate computationally
simpler technique termed as a Beamfom1er-Rake. In a Beamformer-Rake, the output of a
beamfom1er is fed into a succeeding temporal processor to take advantage of both the
beamformer and Rake receiver. Wireless service providers throughout the world are
working to introduce the third generation (3G) and beyond (3G) cellular service that will
provide higher data rates and better spectral efficiency. Wideband COMA (WCDMA)
has been widely accepted as one of the air interfaces for 3G. A Beamformer-Rake
receiver can be an effective solution to provide the receivers enhanced capabilities
needed to achieve the required performance of a WCDMA system.
We consider three different Pilot Symbol Assisted (PSA) beamforming techniques,
Direct Matrix Inversion (DMI), Least-Mean Square (LMS) and Recursive Least Square
(RLS) adaptive algorithms. Geometrically Based Single Bounce (GBSB) statistical
Circular channel model is considered, which is more suitable for array processing, and
conductive to RAKE combining. The performances of the Beam former-Rake receiver are
evaluated in this channel model as a function of the number of antenna elements and
RAKE fingers, in which are evaluated for the uplink WCDMA system. It is shown that,
the Beamformer-Rake receiver outperforms the conventional RAKE receiver and the
conventional beamformer by a significant margin. Also, we optimize and develop a
mathematical formulation for the output Signal to Interference plus Noise Ratio (SINR)
of a Beam former-Rake receiver.
In this research, also, we develop, simulate and evaluate the SINR and Signal to Noise
Ratio (Et!Nol performances of an adaptive beamforming technique in the WCDMA
system for downlink. The performance is then compared with an omnidirectional antenna
system. Simulation shows that the best perfom1ance can be achieved when all the mobiles
with same Angle-of-Arrival (AOA) and different distance from base station are formed in
one beam
Hybrid generalized non-orthogonal multiple access for the 5G wireless networks.
Master of Science in Computer Engineering. University of KwaZulu-Natal. Durban, 2018.The deployment of 5G networks will lead to an increase in capacity, spectral efficiency, low latency
and massive connectivity for wireless networks. They will still face the challenges of resource and
power optimization, increasing spectrum efficiency and energy optimization, among others.
Furthermore, the standardized technologies to mitigate against the challenges need to be developed
and are a challenge themselves. In the current predecessor LTE-A networks, orthogonal frequency
multiple access (OFDMA) scheme is used as the baseline multiple access scheme. It allows users to
be served orthogonally in either time or frequency to alleviate narrowband interference and impulse
noise. Further spectrum limitations of orthogonal multiple access (OMA) schemes have resulted in
the development of non-orthogonal multiple access (NOMA) schemes to enable 5G networks to
achieve high spectral efficiency and high data rates. NOMA schemes unorthogonally co-multiplex
different users on the same resource elements (RE) (i.e. time-frequency domain, OFDMA subcarrier,
or spreading code) via power domain (PD) or code domain (CD) at the transmitter and successfully
separating them at the receiver by applying multi-user detection (MUD) algorithms. The current
developed NOMA schemes, refered to as generalized-NOMA (G-NOMA) technologies includes;
Interleaver Division Multiple Access (IDMA, Sparse code multiple access (SCMA), Low-density
spreading multiple access (LDSMA), Multi-user shared access (MUSA) scheme and the Pattern
Division Multiple Access (PDMA). These protocols are currently still under refinement, their
performance and applicability has not been thoroughly investigated. The first part of this work
undertakes a thorough investigation and analysis of the performance of the existing G-NOMA
schemes and their applicability.
Generally, G-NOMA schemes perceives overloading by non-orthogonal spectrum resource
allocation, which enables massive connectivity of users and devices, and offers improved system
spectral efficiency. Like any other technologies, the G-NOMA schemes need to be improved to
further harvest their benefits on 5G networks leading to the requirement of Hybrid G-NOMA
(G-NOMA) schemes. The second part of this work develops a HG-NOMA scheme to alleviate the
5G challenges of resource allocation, inter and cross-tier interference management and energy
efficiency. This work develops and investigates the performance of an Energy Efficient HG-NOMA
resource allocation scheme for a two-tier heterogeneous network that alleviates the cross-tier
interference and improves the system throughput via spectrum resource optimization. By considering
the combinatorial problem of resource pattern assignment and power allocation, the HG-NOMA
scheme will enable a new transmission policy that allows more than two macro-user equipmentâs
(MUEs) and femto-user equipmentâs (FUEs) to be co-multiplexed on the same time-frequency RE
increasing the spectral efficiency. The performance of the developed model is shown to be superior to
the PD-NOMA and OFDMA schemes
Spatio-Temporal processing for Optimum Uplink-Downlink WCDMA Systems
The capacity of a cellular system is limited by two different phenomena, namely
multipath fading and multiple access interference (MAl). A Two Dimensional (2-D)
receiver combats both of these by processing the signal both in the spatial and temporal
domain. An ideal 2-D receiver would perform joint space-time processing, but at the
price of high computational complexity. In this research we investigate computationally
simpler technique termed as a Beamfom1er-Rake. In a Beamformer-Rake, the output of a
beamfom1er is fed into a succeeding temporal processor to take advantage of both the
beamformer and Rake receiver. Wireless service providers throughout the world are
working to introduce the third generation (3G) and beyond (3G) cellular service that will
provide higher data rates and better spectral efficiency. Wideband COMA (WCDMA)
has been widely accepted as one of the air interfaces for 3G. A Beamformer-Rake
receiver can be an effective solution to provide the receivers enhanced capabilities
needed to achieve the required performance of a WCDMA system.
We consider three different Pilot Symbol Assisted (PSA) beamforming techniques,
Direct Matrix Inversion (DMI), Least-Mean Square (LMS) and Recursive Least Square
(RLS) adaptive algorithms. Geometrically Based Single Bounce (GBSB) statistical
Circular channel model is considered, which is more suitable for array processing, and
conductive to RAKE combining. The performances of the Beam former-Rake receiver are
evaluated in this channel model as a function of the number of antenna elements and
RAKE fingers, in which are evaluated for the uplink WCDMA system. It is shown that,
the Beamformer-Rake receiver outperforms the conventional RAKE receiver and the
conventional beamformer by a significant margin. Also, we optimize and develop a
mathematical formulation for the output Signal to Interference plus Noise Ratio (SINR)
of a Beam former-Rake receiver.
In this research, also, we develop, simulate and evaluate the SINR and Signal to Noise
Ratio (Et!Nol performances of an adaptive beamforming technique in the WCDMA
system for downlink. The performance is then compared with an omnidirectional antenna
system. Simulation shows that the best perfom1ance can be achieved when all the mobiles
with same Angle-of-Arrival (AOA) and different distance from base station are formed in
one beam
Efficient radio resource management for future generation heterogeneous wireless networks
The heterogeneous deployment of small cells (e.g., femtocells) in the coverage area of the traditional macrocells is a cost-efficient solution to provide network capacity, indoor coverage and green communications towards sustainable environments in the future fifth generation (5G) wireless networks. However, the unplanned and ultra-dense deployment of femtocells with their uncoordinated operations will result in technical challenges such as severe interference, a significant increase in total energy consumption, unfairness in radio resource sharing and inadequate quality of service provisioning. Therefore, there is a need to develop efficient radio resource management algorithms that will address the above-mentioned technical challenges. The aim of this thesis is to develop and evaluate new efficient radio resource management algorithms that will be implemented in cognitive radio enabled femtocells to guarantee the economical sustainability of broadband wireless communications and users' quality of service in terms of throughput and fairness. Cognitive Radio (CR) technology with the Dynamic Spectrum Access (DSA) and stochastic process are the key technologies utilized in this research to increase the spectrum efficiency and energy efficiency at limited interference. This thesis essentially investigates three research issues relating to the efficient radio resource management: Firstly, a self-organizing radio resource management algorithm for radio resource allocation and interference management is proposed. The algorithm considers the effect of imperfect spectrum sensing in detecting the available transmission opportunities to maximize the throughput of femtocell users while keeping interference below pre-determined thresholds and ensuring fairness in radio resource sharing among users. Secondly, the effect of maximizing the energy efficiency and the spectrum efficiency individually on radio resource management is investigated. Then, an energy-efficient radio resource management algorithm and a spectrum-efficient radio resource management algorithm are proposed for green communication, to improve the probabilities of spectrum access and further increase the network capacity for sustainable environments. Also, a joint maximization of the energy efficiency and spectrum efficiency of the overall networks is considered since joint optimization of energy efficiency and spectrum efficiency is one of the goals of 5G wireless networks. Unfortunately, maximizing the energy efficiency results in low performance of the spectrum efficiency and vice versa. Therefore, there is an investigation on how to balance the trade-off that arises when maximizing both the energy efficiency and the spectrum efficiency simultaneously. Hence, a joint energy efficiency and spectrum efficiency trade-off algorithm is proposed for radio resource allocation in ultra-dense heterogeneous networks based on orthogonal frequency division multiple access. Lastly, a joint radio resource allocation with adaptive modulation and coding scheme is proposed to minimize the total transmit power across femtocells by considering the location and the service requirements of each user in the network. The performance of the proposed algorithms is evaluated by simulation and numerical analysis to demonstrate the impact of ultra-dense deployment of femtocells on the macrocell networks. The results show that the proposed algorithms offer improved performance in terms of throughput, fairness, power control, spectrum efficiency and energy efficiency. Also, the proposed algorithms display excellent performance in dynamic wireless environments
Resource and power management in next generation networks
The limits of todayâs cellular communication systems are constantly being tested by
the exponential increase in mobile data traffic, a trend which is poised to continue
well into the next decade. Densification of cellular networks, by overlaying smaller
cells, i.e., micro, pico and femtocells, over the traditional macrocell, is seen as an
inevitable step in enabling future networks to support the expected increases in data
rate demand. Next generation networks will most certainly be more heterogeneous
as services will be offered via various types of points of access (PoAs). Indeed, besides
the traditional macro base station, it is expected that users will also be able to
access the network through a wide range of other PoAs: WiFi access points, remote
radio-heads (RRHs), small cell (i.e., micro, pico and femto) base stations or even
other users, when device-to-device (D2D) communications are supported, creating
thus a multi-tiered network architecture. This approach is expected to enhance the
capacity of current cellular networks, while patching up potential coverage gaps.
However, since available radio resources will be fully shared, the inter-cell interference
as well as the interference between the different tiers will pose a significant
challenge. To avoid severe degradation of network performance, properly managing
the interference is essential. In particular, techniques that mitigate interference such
Inter Cell Interference Coordination (ICIC) and enhanced ICIC (eICIC) have been
proposed in the literature to address the issue. In this thesis, we argue that interference
may be also addressed during radio resource scheduling tasks, by enabling
the network to make interference-aware resource allocation decisions.
Carrier aggregation technology, which allows the simultaneous use of several
component carriers, on the other hand, targets the lack of sufficiently large portions
of frequency spectrum; a problem that severely limits the capacity of wireless networks.
The aggregated carriers may, in general, belong to different frequency bands,
and have different bandwidths, thus they also may have very different signal propagation
characteristics. Integration of carrier aggregation in the network introduces
additional tasks and further complicates interference management, but also opens
up a range of possibilities for improving spectrum efficiency in addition to enhancing
capacity, which we aim to exploit. In this thesis, we first look at the resource allocation in problem in dense multitiered
networks with support for advanced features such as carrier aggregation and
device-to-device communications. For two-tiered networks with D2D support, we
propose a centralised, near optimal algorithm, based on dynamic programming principles,
that allows a central scheduler to make interference and traffic-aware scheduling
decisions, while taking into consideration the short-lived nature of D2D links.
As the complexity of the central scheduler increases exponentially with the number
of component carriers, we further propose a distributed heuristic algorithm to tackle
the resource allocation problem in carrier aggregation enabled dense networks. We
show that the solutions we propose perform significantly better than standard solutions
adopted in cellular networks such as eICIC coupled with Proportional Fair
scheduling, in several key metrics such as user throughput, timely delivery of content
and spectrum and energy efficiency, while ensuring fairness for backward compatible
devices.
Next, we investigate the potentiality to enhance network performance by enabling
the different nodes of the network to reduce and dynamically adjust the
transmit power of the different carriers to mitigate interference. Considering that
the different carriers may have different coverage areas, we propose to leverage this
diversity, to obtain high-performing network configurations. Thus, we model the
problem of carrier downlink transmit power setting, as a competitive game between
teams of PoAs, which enables us to derive distributed dynamic power setting algorithms.
Using these algorithms we reach stable configurations in the network,
known as Nash equilibria, which we show perform significantly better than fixed
power strategies coupled with eICIC