The ideas related to coverage and sector overlap modeling are at the moment quite immature, and would hence require more attention. These parameters could be optimized and possibly implemented in planning or optimization tools to provide suggestions of the optimum overlap between cells. However, for that purpose, the model should be more general and not only applicable for WCDMA networks.
Regarding site location deviations, the ultimate target would be to have a plan-ning guideline between the coverage overlap and the maximum allowable site loca-tion devialoca-tion. Again, this informaloca-tion would be useful during the planning process.
Most of the simulation results in this thesis concentrated for a suburban or light urban macrocellular environment, and hence, an interesting question is: what hap-pens in dense urban or in microcellular environment? For example, how the an-tenna downtilt angles should be set in case of roof-top installations when the most strongest signal component in non-LOS situations becomes typically from over roof-top diffraction. In general, the impact of practical and different site locations for antenna deployment as roof-top, mast, and pole installations should be studied to
6.2. FUTURE WORK 75 find optimum solutions from the coverage and capacity point of view per site basis.
Moreover, the studies related to evaluation of the applicability of CAEDT with prac-tical user distributions, not only with moving hot-spots, would be needed in a real network.
Related to verification techniques of the radio network topology, different mod-els and methods could be developed, and furthermore, their utilization during the radio network optimization should be considered. In addition, the example study performed for the planning tool verification should be also extended to cover more suburban environments and also rural environments for possible implementation of lower frequency CDMA technologies as CDMA450 [120] or WCDMA900 [121].
Moreover, the possible utilization of the COST-231-Walfisch-Ikegami to model the propagation in urban environment should be considered also.
Part of the work introduced here of the repeaters and mobile positioning tech-niques have already been continued within the Radio Network Group. However, especially repeaters seem to create an attractive approach to cover the so-called cov-erage dead-spots in otherwise capacity-limited environment by taking advantage, e.g. from indoor distributed antenna (DAS) implementations. Moreover, the ten-dency of using even higher frequencies for cellular systems (e.g. [122]) will make the absolute coverage area from a single antenna smaller and smaller, and hence creating a need for intelligent repeater solutions.
The above mentioned points are mostly related to current evolution and direction of cellular networks. However, the evolution of cellular networks is continuous and hence the attention regarding the radio network topology should be also directed to-wards the future systems. For example, the next system released by the 3GPP will be based on orthogonal frequency division multiple access (OFDMA) technique [123], and hence, the impact of this new radio interface technology on the radio network topology planning should be studied. Another aspect related directly to different antenna configurations is multiple input multiple output (MIMO) systems where several antennas are used for transmission and reception. Hence, from the radio net-work topology point of view, one interesting question is that how much antenna po-sitions or configurations affect the correlation of different antenna elements, which heavily impacts the achievable capacity, in a MIMO system.
C HAPTER 7
Summary of Publications
7.1 Overview of Publications and Thesis Results
Basic radio network topology studies were conducted in [P1]-[P6]. The reference simulations of coverage overlap were provided in [P1]. However, all the required analyses were performed in this thesis only, and have not been published elsewhere.
The approach for modeling coverage overlap with a single parameter seems to be valid, even though more research is needed on that topic. Nevertheless, the results showed the importance of optimum coverage overlap a from system capacity point of view.
The impact of non-hexagonal site locations and non-uniform antenna directions on the system level performance was assessed in [P2]. The results indicate that the performance of WCDMA network is rather robust for moderate changes on hexago-nal site locations, and also on small changes of nomihexago-nal antenna directions. In [P2], some site evolution strategies were also presented, but the analysis was slightly ex-tended in the frame of the thesis.
The importance of the selection of antenna beamwidth for different sectoring schemes was studied in [P3]. For this thesis, the number of simulation scenarios was increased to cover also different degrees of overlap. As a result, it was observed that optimum sector overlap depends on coverage overlap.
Publication [P1] presented the results of simulation campaign regarding opti-mum downtilt angles for a suburban WCDMA network. The results indicated that downtilt is of great importance, and especially in dense networks. The measure-ments of the impact of the mechanical antenna downtilt were provided in [P4], which verified the capacity gain of downtilt also in practice. Moreover, [P5] emphasized the impact of different geographical user distributions on the optimum downtilt angle.
The results indicated that usage of rapidly changing downtilt angle is not worth de-ploying in a cellular WCDMA network.
Verification studies on the radio network topology were provided in [P7]-[P8].
A method for verifying the quality of a network plan was introduced in [P7]. Al-though a simple model, the Ec/N0 mapping method seems to be rather accurate for verifying the quality of the radio plan, and, moreover, extremely applicable for immediate use. Publication [P8] provided an initial assessment of the functionality and reliability of the static WCDMA radio network planning tool with two different propagation models. The results clearly indicate insufficient accuracy of the COST-231-Hata propagation model, whereas certain problems might also be observed with
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ray tracing models. However, the performance assessment was only performed only in an urban environment.
The impact of repeaters was simulated and measured in [P9] and [P10]. The assessment was carried out in a capacity-limited network, not in a coverage-limited one as is typical in the context of repeaters. The results clearly indicate the potential capacity gain of a repeater deployment.
Finally, [P11] and [P12] provide an accuracy assessment of cell ID+RTT with and without forced SHO for a WCDMA network. Clearly, the radio network topology partly defines the availability and attainable accuracy. Moreover, both of these per-formance indicators can be maximized with an non-optimum radio network topol-ogy configuration from the capacity point of view.