223 research outputs found
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
TD-SCDMA Relay Networks
PhDWhen this research was started, TD-SCDMA (Time Division Synchronous Code
Division Multiple Access) was still in the research/ development phase, but
now, at the time of writing this thesis, it is in commercial use in 10 large cities in
China including Beijing and Shang Hai. In all of these cities HSDPA is enabled.
The roll-out of the commercial deployment is progressing fast with installations
in another 28 cities being underway now.
However, during the pre-commercial TD-SCDM trail in China, which started
from year 2006, some interference problems have been noticed especially in the
network planning and initialization phases. Interference is always an issue in
any network and the goal of the work reported in this thesis is to improve
network coverage and capacity in the presence of interference.
Based on an analysis of TD-SCDMA issues and how network interference arises,
this thesis proposes two enhancements to the network in addition to the
standard N-frequency technique. These are (i) the introduction of the concentric
circle cell concept and (ii) the addition of a relay network that makes use of
other users at the cell boundary. This overall approach not only optimizes the
resilience to interference but increases the network coverage without adding
more Node Bs.
Based on the cell planning parameters from the research, TD-SCDMA HSDPA
services in dense urban area and non-HSDPA services in rural areas were
simulated to investigate the network performance impact after introducing the
relay network into a TD-SCDMA network.
The results for HSDPA applications show significant improvement in the TDSCDMA
relay network both for network capacity and network interference
aspects compared to standard TD-SCDMA networks. The results for non-
HSDPA service show that although the network capacity has not changed after
adding in the relay network (due to the code limitation in TD-SCDMA), the
TD-SCDMA relay network has better interference performance and greater
coverage
Multi-hop relaying networks in TDD-CDMA systems
The communications phenomena at the end of the 20th century were the Internet and mobile
telephony. Now, entering the new millennium, an effective combination of the two should
become a similarly everyday experience. Current limitations include scarce, exorbitantly priced
bandwidth and considerable power consumption at higher data rates.
Relaying systems use several shorter communications links instead of the conventional
point-to-point transmission. This can allow for a lower power requirement and, due to the
shorter broadcast range, bandwidth re-use may be more efficiently exploited. Code division
multiple access (CDMA) is emerging as one of the most common methods for multi user
access. Combining CDMA with time division duplexing (TDD) provides a system that
supports asymmetric communications and relaying cost-effectively. The capacity of CDMA
may be reduced by interference from other users, hence it is important that the routing of
relays is performed to minimise interference at receivers.
This thesis analyses relaying within the context of TDD-CDMA systems. Such a system was
included in the initial draft of the European 3G specifications as opportunity driven multiple
access (ODMA). Results are presented which demonstrate that ODMA allows for a more
flexible capacity coverage trade-off than non-relaying systems. An investigation into the
interference characteristics of ODMA shows that most interference occurs close to the base
station (BS). Hence it is possible that in-cell routing to avoid the BS may increase capacity.
As a result, a novel hybrid network topology is presented. ODMA uses path loss as a metric
for routing. This technique does not avoid interference, and hence ODMA shows no capacity
increase with the hybrid network. Consequently, a novel interference based routing algorithm
and admission control are developed. When at least half the network is engaged in in-cell
transmission, the interference based system allows for a higher capacity than a conventional
cellular system. In an attempt to reduce transmitted power, a novel congestion based routing algorithm is introduced. This system is shown to have lower power requirement than any other analysed system and, when more than 2 hops are allowed, the highest capacity.
The allocation of time slots affects system performance through co-channel interference. To
attempt to minimise this, a novel dynamic channel allocation (DCA) algorithm is developed
based on the congestion routing algorithm. By combining the global minimisation of system
congestion in both time slots and routing, the DCA further increases throughput. Implementing
congestion routed relaying, especially with DCA, in any TDD-CDMA system with in-cell calls
can show significant performance improvements over conventional cellular systems
Performance evaluation of mobile relays in CDMA system
In this thesis we consider the uplink direction of DS-CDMA (Direct Sequence, Code Division Multiple Access) network with multihop transmission. For the purpose, we discussed simple conditions by which we can understand whether single hop or multihop is better. One promising direction that the current wireless network moves toward is multihopping that allows mobiles to relay packets of other mobiles to their destinations. A major reason for adopting such multihopping is in capacity and range enhancement, which may pay off its increased complexity. Here, we focus on the non-real-time (NRT) services in the uplink of a DS-CDMA cell. Mobiles are moving around the cell, trying to send NRT packets to the base station, possibly by multihopping. Our goal is to derive a per-hop based multihop scheduling algorithm that is easily applicable in a cellular network with high mobility. For the purpose, we utilize the similarity between the basketball game and our multihop uplink packet scheduling problem. By regarding players, the basket and the ball as mobiles, the base station and data packet, respectively, we can mimic passing (multihopping) patterns of the basketball players. A major difference between the two is that in the multihopping problem, there are many packets (balls) while in the basket ball game, there is only one ball to shoot into the basket
Cooperative control of relay based cellular networks
PhDThe increasing popularity of wireless communications and the higher data
requirements of new types of service lead to higher demands on wireless networks.
Relay based cellular networks have been seen as an effective way to meet users’
increased data rate requirements while still retaining the benefits of a cellular
structure. However, maximizing the probability of providing service and spectrum
efficiency are still major challenges for network operators and engineers because of
the heterogeneous traffic demands, hard-to-predict user movements and complex
traffic models.
In a mobile network, load balancing is recognised as an efficient way to increase
the utilization of limited frequency spectrum at reasonable costs. Cooperative
control based on geographic load balancing is employed to provide flexibility for
relay based cellular networks and to respond to changes in the environment.
According to the potential capability of existing antenna systems, adaptive radio
frequency domain control in the physical layer is explored to provide coverage at
the right place at the right time.
This thesis proposes several effective and efficient approaches to improve
spectrum efficiency using network wide optimization to coordinate the coverage
offered by different network components according to the antenna models and
relay station capability. The approaches include tilting of antenna sectors,
changing the power of omni-directional antennas, and changing the assignment of
relay stations to different base stations. Experiments show that the proposed
approaches offer significant improvements and robustness in heterogeneous traffic
scenarios and when the propagation environment changes. The issue of predicting
the consequence of cooperative decisions regarding antenna configurations when
applied in a realistic environment is described, and a coverage prediction model is
proposed. The consequences of applying changes to the antenna configuration on
handovers are analysed in detail. The performance evaluations are based on a
system level simulator in the context of Mobile WiMAX technology, but the
concepts apply more generally
Interference mitigation and interference avoidance for cellular OFDMA-TDD networks
In recent years, cellular systems based on orthogonal frequency division multiple access – time
division duplex (OFDMA-TDD) have gained considerable popularity. Two of the major reasons
for this are, on the one hand, that OFDMA enables the receiver to effectively cope with multipath
propagation while keeping the complexity low. On the other hand, TDD offers efficient
support for cell-specific uplink (UL)/downlink (DL) asymmetry demands by allowing each cell
to independently set its UL/DL switching point (SP). However, cell-independent SP gives rise
to crossed slots. In particular, crossed slots arise when neighbouring cells use the same slot in
opposing link directions, resulting in base station (BS)-to-BS interference and mobile station
(MS)-to-MS interference. BS-to-BS interference, in particular, can be quite detrimental due to
the exposed location of BSs, which leads to high probability of line-of-sight (LOS) conditions.
The aim of this thesis is to address the BS-to-BS interference problem in OFDMA-TDDcellular
networks. A simulation-based approach is used to demonstrate the severity of BS-to-BS interference
and a signal-to-interference-plus-noise ratio (SINR) equation for OFDMA is formulated
to aid system performance analysis. The detrimental effects of crossed slot interference in
OFDMA-TDD cellular networks are highlighted by comparing methods specifically targeting
the crossed slots interference problem. In particular, the interference avoidance method fixed
slot allocation (FSA) is compared against state of the art interference mitigation approaches,
viz: random time slot opposing (RTSO) and zone division (ZD). The comparison is done based
on Monte Carlo simulations and the main comparison metric is spectral efficiency calculated
using the SINR equation formulated in this thesis. The simulation results demonstrate that
when LOS conditions among BSs are present, both RTSO and ZD perform worse than FSA for
all considered performance metrics. It is concluded from the results that current interference
mitigation techniques do not offer an effective solution to the BS-to-BS interference problem.
Hence, new interference avoidance methods, which unlike FSA, do not sacrifice the advantages
of TDD are open research issues addressed in this thesis.
The major contribution of this thesis is a novel cooperative resource balancing technique that
offers a solution to the crossed slot problem. The novel concept, termed asymmetry balancing,
is targeted towards next-generation cellular systems, envisaged to have ad hoc and multi-hop
capabilities. Asymmetry balancing completely avoids crossed slots by keeping the TDD SPs
synchronised among BSs. At the same time, the advantages of TDD are retained, which is
enabled by introducing cooperation among the entities in the network. If a cell faces resource
shortage in one link direction, while having free resources in the opposite link direction, the
free resources can be used to support the overloaded link direction. In particular, traffic can
be offloaded to near-by mobile stations at neighbouring cells that have available resources. To
model the gains attained with asymmetry balancing, a mathematical framework is developed
which is verified by Monte Carlo simulations. In addition, asymmetry balancing is compared
against both ZD and FSA based on simulations and the results demonstrate the superior performance
of asymmetry balancing. It can be concluded that the novel interference avoidance
approach is a very promising candidate t
Cross layer optimization in 4G Wireless mesh networks
Wireless networks have been rapidly evolving over the past two decades. It is foreseen that Fourth generation (4G) wireless systems will involve the integration of wireless mesh networks and the 3G wireless systems such as WCDMA. Moreover their wireless mesh routers will provide service to wireless local networks (WLANs) and possibly incorporate MIMO system and smart admission control policies among others. This integration will not only help the service providers cost effectiveness and users connectivities but will also improve and guarantee the QoS criteria. On the other hand, cross layer design has emerged as a new and major thrust in improving the quality of service (QoS) of wireless networks. Cross layer design involves the interaction of various layers of the network hierarchy which could further improve the QoS of the 4G integrated networks. In this work we seek new techniques for improving the overall QoS of integrated 4G systems. Towards this objective we start with the local low tier WLAN access. We then investigate CDMA alternatives to the TDMA access for wireless mesh networks. Cross layer design in wireless mesh networks is then pursued. In the first phase of this thesis a new access mechanism for WLANs is developed, in which users use an optimum transmission probability obtained by estimating the number of stations from the traffic conditions in a sliding window fashion, thereby increasing the throughput compared to the standard DCF and RTS/CTS mechanism while maintaining the same fairness and the delay performance. In the second phase we introduce a code division multiple access/Time division duplex technique CDMA/TDD for wireless mesh networks, we outline the transmitter and receiver for the relay nodes and evaluate the efficiency, delay and delay jitter performances. This CDMA based technique is more amenable to integrating the two systems (Mesh networks and WCDMA or CDMA 2000 of3G). We compare these results with the TDMA operation and through analysis we prove that the CDMA system outperforms the TDMA counterparts. In the third phase we proceed to an instance of cross layer optimized networks, where we develop an overall optimization routine that finds simultaneously the best route and the best capacity allocation to various nodes. This optimization routine minimizes the average end to end packet delay over all calls subject to various contraints. In the process we use a new adaptive version of Spatial TDMA as a platform for comparison purposes of the MAC techniques involved in the cross layer design. In this phase we also combine CDMA/TDD and optimum routing for cross layer design in wireless mesh networks. We compare the results of the CDMA/TDD system with results obtained from the STDMA system. In our analysis we consider the parallel transmissions of mesh nodes in a mesh topology. These parallel transmissions will increase the capacity resulting in a higher throughput with a lower delay. This will allow the service providers to accommodate more users in their system which will obviously reduce the colt and the end users will enjoy a better service paying a lower amount
Performance analysis of 4G wireless networks using system level simulator
Doutoramento em Engenharia ElectrotécnicaIn the last decade, mobile wireless communications have witnessed an explosive
growth in the user’s penetration rate and their widespread deployment around the
globe. In particular, a research topic of particular relevance in telecommunications
nowadays is related to the design and implementation of mobile communication
systems of 4th generation (4G). 4G networks will be characterized by the support
of multiple radio access technologies in a core network fully compliant with the
Internet Protocol (all IP paradigms). Such networks will sustain the stringent
quality of service (QoS) requirements and the expected high data rates from the
type of multimedia applications (i.e. YouTube and Skype) to be available in the
near future. Therefore, 4G wireless communications system will be of paramount
importance on the development of the information society in the near future.
As 4G wireless services will continue to increase, this will put more and more
pressure on the spectrum availability. There is a worldwide recognition that
methods of spectrum managements have reached their limit and are no longer
optimal, therefore new paradigms must be sought. Studies show that most of the
assigned spectrum is under-utilized, thus the problem in most cases is inefficient
spectrum management rather spectrum shortage. There are currently trends
towards a more liberalized approach of spectrum management, which are tightly
linked to what is commonly termed as Cognitive Radio (CR).
Furthermore, conventional deployment of 4G wireless systems (one BS in cell and
mobile deploy around it) are known to have problems in providing fairness (users
closer to the BS are more benefited relatively to the cell edge users) and in
covering some zones affected by shadowing, therefore the use of relays has been
proposed as a solution.
To evaluate and analyse the performances of 4G wireless systems software tools
are normally used. Software tools have become more and more mature in recent
years and their need to provide a high level evaluation of proposed algorithms and
protocols is now more important. The system level simulation (SLS) tools provide
a fundamental and flexible way to test all the envisioned algorithms and protocols
under realistic conditions, without the need to deal with the problems of live
networks or reduced scope prototypes. Furthermore, the tools allow network
designers a rapid collection of a wide range of performance metrics that are useful
for the analysis and optimization of different algorithms.
This dissertation proposes the design and implementation of conventional system
level simulator (SLS), which afterwards enhances for the 4G wireless technologies
namely cognitive Radios (IEEE802.22) and Relays (IEEE802.16j). SLS is then
used for the analysis of proposed algorithms and protocols.FC
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