937 research outputs found
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
Performance Evaluation of Hyperbolic Position Location Technique in Cellular Wireless Networks
This study addresses the wireless geolocation problem that has been an attractive subject for the last few years after Federal Communications Commission (FCC) mandate for wireless service providers to locate emergency 911 users with a high degree of accuracy -within a radius of 125 meters, 67 percent of the time by October 2001. There are a number of different geolocation technologies that have been proposed. These include, Assisted GPS (A-GPS), network-based technologies such as Enhanced Observed Time Difference (E-OTD), Time Difference of Arrival (TDOA), Angle of Arrival (AOA), and Cell of Origin (COO). This research focuses on network based techniques, namely the more prominent TDOA which is also called hyperbolic position location technique. The main problem in time-based positioning systems is solving nonlinear hyperbolic equations derived from set of TDOA estimates. Two algorithms are implemented as a solution to this problem: A closed form solution and a Least Squares (LS) algorithm. Accuracy and computational efficiency performances are compared in a wireless system established using DGPS measurements in Dayton, OH area
Soft handover parameter optimisation for DS-CDMA downlink design.
DS-CDMA - Direct Sequence Code Division Multiple AccessAvailable from British Library Document Supply Centre-DSC:DX189702 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo
An Intelligent Mobility Prediction Scheme for Location-Based Service over Cellular Communications Network
One of the trickiest challenges introduced by cellular communications networks is mobility prediction for Location Based-Services (LBSs). Hence, an accurate and efficient mobility prediction technique is particularly needed for these networks. The mobility prediction technique incurs overheads on the transmission process. These overheads affect properties of the cellular communications network such as delay, denial of services, manual filtering and bandwidth.
The main goal of this research is to enhance a mobility prediction scheme in cellular communications networks through three phases. Firstly, current mobility prediction techniques will be investigated. Secondly, innovation and examination of new mobility prediction techniques will be based on three hypothesises that are suitable for cellular communications network and mobile user (MU) resources with low computation cost and high prediction success rate without using MU resources in the prediction process. Thirdly, a new mobility prediction scheme will be generated that is based on different levels of mobility prediction.
In this thesis, a new mobility prediction scheme for LBSs is proposed. It could be considered as a combination of the cell and routing area (RA) prediction levels. For cell level prediction, most of the current location prediction research is focused on generalized location models, where the geographic extent is divided into regular-shape cells. These models are not suitable for certain LBSs where the objectives are to compute and present on-road services. Such techniques are the New Markov-Based Mobility Prediction (NMMP) and Prediction Location Model (PLM) that deal with inner cell structure and different levels of prediction, respectively. The NMMP and PLM techniques suffer from complex computation, accuracy rate regression and insufficient accuracy.
In this thesis, Location Prediction based on a Sector Snapshot (LPSS) is introduced, which is based on a Novel Cell Splitting Algorithm (NCPA). This algorithm is implemented in a micro cell in parallel with the new prediction technique. The LPSS technique, compared with two classic prediction techniques and the experimental results, shows the effectiveness and robustness of the new splitting algorithm and prediction technique.
In the cell side, the proposed approach reduces the complexity cost and prevents the cell level prediction technique from performing in time slots that are too close. For these reasons, the RA avoids cell-side problems. This research discusses a New Routing Area Displacement Prediction for Location-Based Services (NRADP) which is based on developed Ant Colony Optimization (ACO). The NRADP, compared with Mobility Prediction based on an Ant System (MPAS) and the experimental results, shows the effectiveness, higher prediction rate, reduced search stagnation ratio, and reduced computation cost of the new prediction technique
A comparative investigation on the application and performance of Femtocell against Wi-Fi networks in an indoor environment
Due to the strenuous demands on the available spectrum and bandwidth, alongside the ever increasing rate at which data traffic is growing and the poor quality of experience QoE) faced with indoor communications, in order for cellular networks to remain dominant in areas pertaining to voice and data services, cellular service providers have to reform their marketing and service delivery strategies together with their overall network rchitecture. To accomplish this leap forward in performance, cellular service operators need to employ a network topology, which makes use of a mix of macrocells and small cells, effectively evolving the network, bringing it closer to the end-Ââuser. This investigation explores the use of small cell technology, specifically Femtocell technology in comparison to the already employed Wi-ÂâFi technology as a viable solution to poor indoor communications.The performance evolution is done by comparing key areas in the
every day use of Internet communications. These include HTTP testing, RTP testing and VoIP testing. Results are explained and the modes of operation of both technologies are compared
Interference analysis of and dynamic channel assignment algorithms in TDâCDMA/TDD systems
The radio frequency spectrum for commercial wireless communications has become an expensive
commodity. Consequently, radio access techniques are required which enable the efficient
exploitation of these resources. This, however, is a difficult task due to an increasing diversity
of wireless services. Hence, in order to achieve acceptable spectrum efficiency a flexible airâ
interface is required.
It has been demonstrated that code division multiple access (CDMA) provides flexibility by
enabling efficient multi user access in a cellular environment. In addition, time division duplex
(TDD) as compared to frequency division duplex (FDD) represents an appropriate method to
cater for the asymmetric use of a duplex channel. However, the TDD technique is subject to
additional interference mechanisms in particular if neighbouring cells require different rates of
asymmetry. If TDD is combined with an interference limited multiple access technique such as
CDMA, the additional interference mechanism represents an important issue. This issue poses
the question of whether a CDMA/TDD airâinterface can be used in a cellular environment.
The problems are eased if a hybrid TDMA (time division multiple access) / CDMA interface
(TDâCDMA) is used. The reason for this is that the TDMA component adds another degree
of freedom which can be utilised to avoid interference. This, however, requires special channel
assignment techniques.
This thesis analyses cellular CDMA/TDD systems used in indoor environments. A key parameter
investigated is the interference in such systems. In the interference analysis a special
focus is placed on adjacent channel interference since the jamming entity and victim entity can
be in close proximity. The interference analysis shows that coâlocation of BSâs using adjacent
channels is not feasible for an adjacent channel protection factor that is less than 40 dB
and frame synchronisation errors of more than 10%. Furthermore, it is demonstrated that ideal
frame synchronisation does not necessarily yield the highest capacity. As a consequence, a new
technique termed âTSâopposingâ is introduced. This method is intended to enable a cellular
TDâCDMA/TDD system to apply cell independent channel asymmetry. For this purpose, a
centralised DCA is developed. It is found that this algorithm indeed enables neighbouring cells
to adopt different rates of asymmetry without a significant capacity loss.
Moreover, a decentralised DCA algorithm based on the TSâopposing principle is developed.
In this context, a novel TS assignment concept is proposed which reduces the complexity associated
with the TSâopposing technique. In addition, the TS assignment plan allows for full
spatial coverage. It is shown that the capacity of a TDâCDMA/TDD interface can be greater
than the capacity of an equivalent FDD interface. The performance of the decentralised DCA
algorithm is limited by the interference in the uplink. Therefore, additional methods which assist
in reducing the interference in the uplink are envisaged to further improve the performance
of the decentralised DCA algorithm.
The exploitation of the TSâopposing technique in two different ways demonstrates that this
method can be used to improve the performance of a TDâCDMA/TDD system significantly
Antenna arrays for the downlink of FDD wideband CDMA communication systems
The main subject of this thesis is the investigation of antenna array techniques for improving
the performance of the downlink of wideband code division multiple access (WCDMA) mobile
communication systems. These communication systems operate in frequency division duplex
(FDD) mode and the antenna arrays are employed in the base station. A number of diversity,
beamforming and hybrid techniques are analysed and their bit error ratio (BER) versus signalto-
noise ratio (SNR) performance is calculated as a function of the eigenvalues of the mean
channel correlation matrix, where this is applicable. Also, their BER versus SNR performance
is evaluated by means of computer simulations in various channel environments and using
different numbers of transmit antenna elements in the base station. The simulation results
of the techniques, along with other characteristics, are compared to examine the relationship
among their performance in various channel environments and investigate which technique is
most suitable for each channel environment.
Next, a combination of the channel correlation matrix eigenvalue decomposition and space-time
processing is proposed as a possible open loop approach to the downlink data signal transmission.
It decomposes the channel into M components in the form of eigenvectors (M is the
number of transmit antennas in the base station), and attempts to minimise the transmit power
that is needed to achieve a target BER at the mobile receiver by employing the optimum number
of these eigenvectors. The lower transmit power and the directional transmission by means
of eigenvectors are expected to lower interference levels to non-desired users (especially to
those users who are not physically close to the direction(s) of transmission). Theoretical and
simulation results suggest that this approach performs better than other presented open loop
techniques, while the performance gain depends on M and the channel environment.
In simulations it is usually assumed that the base and mobile station have access to perfect
estimates of all needed parameters (e.g. channel coecients). However, in practical systems
they make use of pilot and/or feedback signals to obtain estimates of these parameters, which
result in noisy estimates. The impact of the noisy estimates on the performance of various
techniques is investigated by computer simulations, and the results suggest that there is typically
some performance loss. The loss depends on the parameter that is estimated from pilot signals,
and may be a function of M, SNR and/or the channel environment.
In certain beamforming techniques the base station operates the transmit antenna array in an
open loop fashion by estimating the downlink weight vector from the directional information
of the uplink channel. Nevertheless, in FDD systems this results in performance loss due to
the separation between the uplink and downlink carrier frequencies (`FDD gap'). This loss is
quantified and the results show that it is a function of M and the FDD gap. Also, a very simple
technique for compensating this loss is proposed, and results obtained after its application suggest
that it eliminates most of the loss. Comparison of the proposed technique with an existing
compensation technique suggests that, even though the latter is more complex than the former,
it yields very little additional improvement
3G migration in Pakistan
The telecommunication industry in Pakistan has come a long way since the country\u27s independence in 1947. The initial era could be fairly termed as the PTCL (Pakistan Telecommunication Company Limited) monopoly, for it was the sole provider of all telecommunication services across the country. It was not until four decades later that the region embarked into the new world of wireless communication, hence ending the decades old PTCL monopoly. By the end of the late 1990\u27s, government support and international investment in the region opened new doors to innovation and better quality, low cost, healthy competition. Wireless licenses for the private sector in the telecommunication industry triggered a promising chain of events that resulted in a drastic change in the telecommunication infrastructure and service profile. The newly introduced wireless (GSM) technology received enormous support from all stakeholders (consumers, regulatory body, and market) and caused a vital boost in Pakistan\u27s economy. Numerous tangential elements had triggered this vital move in the history of telecommunications in Pakistan. Entrepreneurs intended to test the idea of global joint ventures in the East and hence the idea of international business became a reality. The technology had proven to be a great success in the West, while Pakistan\u27s telecom consumer had lived under the shadow of PTCL dominance for decades and needed more flexibility. At last the world was moving from wired to wireless! Analysts termed this move as the beginning of a new era. The investors, telecommunication businesses, and Pakistani treasury prospered. It was a win-win situation for all involved. The learning curve was steep for both operators and consumers but certainly improved over time. In essence, the principle of deploying the right technology in the right market at the right time led to this remarkable success. The industry today stands on the brink of a similar crossroads via transition from second generation to something beyond. With the partial success of 3G in Europe and the USA, the government has announced the release of three 3G licenses by mid 2009. This decision is not yet fully supported by all but still initiated parallel efforts by the operators and the vendors to integrate this next move into their existing infrastructure
Fuzzy Assisted Handoff Algorithm for Micro and Macro Cellular System
Handoff is an essential part of any Mobile Communication Network. Efficient handoff algorithms provide cost-effective way for enhancing the capacity and QOS of cellular system. The work reported here in presents multi-criteria based hard handoff algorithm for micro and macro-cellular architecture. Fuzzy technique has been used as optimization engine. The fuzzy handoff algorithm based on Received Signal Strength (RSS), absolute threshold value, hysteresis level, slope ratios and speed of Mobile Terminal (MT) have been previously developed for conventional cellular networks. In this work the handoff algorithm has been improved by considering two new parameter, signalling delay and angle of motion of MT along with velocity as our input criteria. Two fuzzy models named Mamdani and Sugeno have been used for processing the input criteria. Further, ANFIS has also been used to tune the Sugeno model for parameter adjustment. The proposed fuzzy inference scheme uses triangular and trapezoidal membership function for fuzzification. The types of defuzzification method used are centriod and weighted average formula for Mamdani and Sugeno model respectively. Extensive simulation analysis has been used to validate the proposed technique. The results show that fuzzy is a viable option for handoff
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