123 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
Topology and interference analysis in macrocellular environment
In the present day, mobile based data services have become increasingly popular among end users and businesses and thus considered as one of the important issues in the telecommunication network, because of its high demand. The telecommunication industry is continuously striving to fulfil this demand in a cost-efficient manner. Fundamentally, the performance of a mobile communication network is constrained by the propagation environment and technical capabilities of the network equipment. The target of radio network engineers is to design and deploy a mobile network that provides effective coverage and capacity solution with a profitable implementation cost. In order to reach this target, careful examination of radio network planning and choosing the right tools are the key methods. Network densification is considered as a feasible evolutionary pathway to fulfil the exponentially increasing data capacity demand in mobile networks.
The objective of this thesis work is to study and analyse the densification of classical macrocellular network, which is still the dominant form of deployment worldwide. The analysis is based on deep ray-tracing based propagation simulations in the outdoor and indoor environment, and considers two key performance metrics; cell spectral efficiency and area spectral efficiency. For analysing the impact of network densification, different cell densities, obtained from varying the inter-site distances are considered. Furthermore, the network is assumed to be operating in a full load condition; an extreme condition in which the base stations are transmitting at full power. From the simulations, it has been illustrated that as a result of densifying the network, the inter-cell interference increases, which reduce the achievable cell spectral efficiency. The system capacity, on the other hand, is shown to improve due to the increase in the area spectral efficiency, as a result of high-frequency re-use, in the outdoor settings. Nevertheless, it is observed that the densification of macrocellular network experience inefficiency in the indoor environment; mainly arising from coverage limitation due to extreme antenna tilt angles. This calls for sophisticated methods such as base station coordination or inter-cell interference cancellation technique to be employed for future cellular network. For fulfilling the indoor capacity demand in a cost-efficient manner, the operators will be required to deploy dedicated indoor small cells based solutions
IST-2000-30148 I-METRA: D6.2 Implications in re-configurable systems beyond 3G (Part 2)
This activity evaluates the extension of the bandwidth of the UTRA MIMO HSDPA concept to 20 MHz, which is precisely the bandwidth of HIPERLAN/2. This would allow a fair comparison between the performance of UTRA MIMO HSDPA and the enhanced HIPERLAN/2. The bandwidth expansion would be the consequence of multiplying the chip rate of the W-CDMA spreading by four, i.e., 3.84 x 4 = 15.36 Mcps. A higher bandwidth MIMO channel model is necessary and this will be developed based on the channel model already developed in WP2. High data rates are required to satisfy the ever-increasing application requirements in future wireless communication systems. Recent investigations have indicated that a peak data rate of up to 20Mbps per user in the DL may be required for satisfactory reception of bursty traffic. As the transmission powers (of both mobile terminals and base stations) are limited, higher data rates lead to the reduction of the effective coverage area of a cell. That is, only users that are close to the base station will be able to communicate with high data rates, while users far away from the base station will only be able to use low data rates.Preprin
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
Prestasi dan perlaksanaan kawalan kuasa untuk sistem W-CDMA
Pa >aran perhubungan bersel telah berkembang secara raendadak pada beberapa tahun
kebelakangan ini. Matlamat utama sistem perhubungan bersel ini adalah untuk
menyediakan perkhidmatan perhubungan tanpa perlu memilih masa dan tempat.
Teknologi antaramuka udara ' Wideband Code Division Multiple Access' ataupun
secara ringkas W-CDMA telah dipilih untuk kebanyakan pengendali perkhidmatan
perhubungan bersel di dalam merealisasikan perlaksanaan sistem perhubungan bersel
generasi baru ini. Sistem W-CDMA diharapkan sebagai langkah pertama ke arah
sistem bersel digit Generasi Ketiga. Salah satu daripada pengurusan sumber-sumber
radio W-CDMA yang kritikal ialah kawalan kuasa. Tanpa kehadiran kawalan kuasa,
kesan fenomena gangguan hujung-dekat-hujung-jauh menjadi perusa dan muatan
sistem bergerak W-CDMA adalah sangat rendah. Takrifan kawalan kuasa yang baik
adalah penting untuk sistem W-CDMA berfungsi dengan betul dan membolehkan
pengguna-pengguna untuk berkongsi sumber-sumber sistem W-CDMA secara
bersama di antara mereka. Tambahan lagi, dengan kawalan kuasa yang betul
membolehkan jumlah penghantaran kuasa sistem bergerak dikurangkan kepada tahap
minimum supaya tiada kuasa berlebihan yang diperlukan telah disinarkan dan
melanjutkan hayat bated. Disertasi ini adalah hasil kajian ke atas prestasi algoritma
kawalan kuasa sistem W-CDMA melalui simulasi komputer yang telah dibangunkan.
Kesan perubahan beberapa parameter masukan terhadap mutu dan muatan sistem telah
dianalisis berdasarkan beberapa andaian. Dua algoritma kawalan kuasa yang berlainan
juga dibandingkan untuk menentukan prestasi algoritma yang menghasilkan
keputusan yang lebih baik. Keputusan simulasi menunjukkan bahawa kawalan kuasa
berupaya mengatasi masalah pemudaran isyarat dan gangguan hujung-dekat-hujung�jauh dengan menghasilkan tahap gangguan yang minimum bagi semua pengguna.
Algoritma DSSPC (Dynamic Step Size Power Control) menunjukkan prestasi yang
lebih baik berbanding algoritma FSSPC {Fixed Step Size Power Control) berdasarkan
kepada keputusan simulasi yang telah dilakukan
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
Wireless digital point to multipoint link utilizing wideband CDMA
One of the proposed techniques for multiple access communications for the third generation is code division multiple access (CDMA). This has been shown to be a viable alternative to both TDMA and FDMA. While there does not appear to be a single multiple accessing technique that is superior to others in all situations, there are characteristics of CDMA that give it a distinct advantage over the other multiple access techniques. In CDMA each user is provided with an unique, orthogonal code. If these K codes are orthogonal and uncorrelated with each other, than K independent users can transmit at the same time and in the same radio bandwidth. The receivers decorrelate the information and regenerate the original transmitted signal. It must be noted that the term "Wideband CDMA" is used comparatively to the only existing commercial CDMA system, IS-95 which uses a spectral bandwidth of only 1.2288 MHz. This thesis examines and evaluates a good set of orthonormal codes (orthogonal and normalized to have equal power) and their application to providing accessing for a point to multipoint (PMP) stationary system. The correlation properties, design and constellation properties of these codes are investigated. The system model is then simulated using Systemview and then evaluated in terms of it's bit error rate, user capacity and Erlang with addition of users to the system
On the modeling of WCDMA system performance with propagation data
The aim of this study was to develop calculation methods for estimating the most important system level performance characteristics of the WCDMA radio network (i.e. network capacity and coverage) in the presence of interference from various sources. The calculation methods described in this work enable the fast design of radio systems with a reasonable degree of accuracy, where different system parameters, propagation conditions and networks as well as frequency scenarios can be easily tested. The work also includes the development and verification of a propagation model for a microcellular environment.
Traditionally, system level performance figures have been retrieved using system simulations where the radio network has been modeled as accurately as possible. This has included base stations and mobile stations, propagation models, traffic models and mobility models. Various radio resource management (RRM) algorithms, such as power controls and handovers have also been modeled. However, these system simulations are very complex and time consuming and typically the models are difficult to modify. The idea behind this work is to use the main statistical parameters retrieved from accurate, case specific propagation models and to use these statistics as input for the developed analytical radio network models. When used as output from these analytical models we are able to obtain the performance measures of the network.
The specific application area for the developed methods is the evaluation of the effect of the interference from the adjacent frequency channels. Adjacent channel interference decreases the efficiency of the usage of the electromagnetic spectrum i.e. the spectral efficiency. The aim of a radio system design is to ensure that the reduction in the spectral efficiency is as low as possible. This interference may originate from the same or a different radio system and from the same or another operator's network. The strength of this interference is dependent on the system parameters and the network layout.
The standard questions regarding adjacent system interference between different operators' network are what guard band is needed between the radio carriers in order to maintain the quality of the network or what are the main mobile and network parameters, such as adjacent channel emission levels or adjacent channel selectivity, required in order to achieve satisfactory network performance. With the developed method proposed here it is possible to answer these questions with reasonable accuracy.
One important aspect of network performance is the radio wave propagation environment for which the radio systems are designed. This thesis presents methods evaluating radio wave propagation, especially for cases where the base station antenna is below the rooftops, i.e. in the case of microcellular network environments. The developed microcellular propagation model has been developed for network planning purposes and it has been verified using numerous field propagation measurements. The model can be used in cases where the mobile station is located either indoors or outdoors.reviewe
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