Araceli Molina

Hotspot wireless LANs to enhance the performance of 3G and beyond cellular networks

At present, WLANs supporting broadband multimedia communications are being developed and deployed around the world. Standards include HIPERLAN/2 defined by ETSI BRAN and the 802.11 family defined by the IEEE. These systems provide channel adaptive data rates up to 54 Mb/s (in a 20 MHz channel spacing) over short ranges up to 200 m. The HIPERLAN/2 standard also specifies a flexible radio access network that can be used with a variety of core networks, including UMTS. It is likely that WLANs will become an important complementary technology to 3G cellular systems and will typically be used to provide hotspot coverage. In this article the complementary use of WLANs in conjunction with UMTS is presented. In order to quantify the capacity enhancement and benefits of cellular/hotspot interworking we have combined novel ray tracing, software-simulated physical layer performance results, and optimal base station deployment analysis. The study focuses on an example deployment using key lamppost mounted WLAN access points to increase the performance (in terms of capacity) of a cellular network.

The automatic location of base-stations for optimised cellular coverage: a new combinatorial approach

The cost and complexity of a network is closely related to the number of base-stations (BSs) required to achieve the system operators service objectives. The location of BSs is not an easy task and there are numerous factors that must be taken into account when deciding the optimum position of BSs. This paper discusses the performance of three different algorithms developed to solve the BS location problem: the greedy algorithm (GR), the genetic algorithm (GA) and the combination algorithm for total optimisation (CAT). These three methods are compared and results are given for a typical test scenario.

Cellular network capacity planning using the combination algorithm for total optimisation

The combination algorithm for total optimisation (CAT) is proposed to support smooth upgrading of third generation systems and to fulfil the requirements of current cellular networks. The CAT algorithm solves the problem of base-station location in different environments. Until now experiments were based on simple statistical propagation models such as Okumura-Hata. In this paper new results based on the use of a more complex ray-tracing approach combined with inhomogeneous capacity requirements are presented and discussed. Example results are given for various capacity and coverage targets.

The use of intelligently deployed fixed relays to improve the performance of a UTRA-TDD system

This paper examines the use of intelligently deployed fixed relays to improve the performance of an UTRA-TDD 3G system. In this study, the benefits of intelligent relaying in the form of enhanced capacity and/or coverage and reduced RF emissions relative to a traditional cellular network are quantified. Simulations are carried out in a microcellular environment using propagation data from a site-specific model and an optimisation algorithm to determine the locations of base stations (BSs) and relay nodes in the system. A system level simulation of an UTRA-TDD system is used to quantify the benefits of the relayed over the non-relayed system. Results show significant improvements in capacity, spectrum efficiency and reductions in mean terminal transmit power in the relayed system over conventional cellular BS-only operation. The effects of different code allocation strategies for the relay nodes are also investigated, revealing that benefits in relaying would only be realised if code re-use between the BSs and relay nodes is enabled or if relay nodes are allocated their own pool of spreading codes.

Cross-layer WLAN measurement and link analysis for low latency error resilient wireless video transmission

This work introduces a cross-layer measurement and link analysis strategy for video transport over IEEE 802.11. Field trial measurement data is presented for streamed H.264 video over ad-hoc 802.11g links. The data is used to analyze the interactions between the physical/network/transport and application layers. The development of cross layer optimized low latency error resilient video transmission schemes is discussed.

Automated W-CDMA microcellular deployment and coverage reconfiguration based on situation awareness

This paper examines the implementation of an automated W-CDMA microcellular deployment and coverage reconfiguration algorithm based on the concepts of situation awareness (SA). A deterministic microcellular propagation model (Citrus) is used to provide the detailed site-specific propagation data. An initial network deployment is performed over one square kilometre of central Bristol using the combination algorithm for total optimisation (CAT). Buildings are then added or removed from the microcell to represent realistic time variations in the geographic environment. A new situation awareness (SA) algorithm is developed and applied to the modified W-CDMA microcell to automatically reconfigure the networks coverage and capacity based on the new propagation environment. Optimisation of coverage and capacity is achieved through the use of a genetic algorithm (GA). This paper presents the details of the underlying SA algorithm and the results obtained for the above scenario. These new algorithms are shown to automatically sustain a high grade of service as the microcellular environment evolves over time. Gains of up 203% in spectral efficiency were observed for the 144 kbps service.

The effects of control node density in cellular network planning using the combination algorithm for total optimisation (CAT)

The combination algorithm for total optimisation (CAT) solves the problem of optimised base-station location and density for different cellular configurations and environments. The algorithm relies on two main user supplied databases for its operation. The first is an over specified list of possible base-station locations and the second is a database of control nodes. Coverage is defined by a distribution of control nodes in the area of study. The control nodes represent the operators capacity and coverage requirements at those points. This paper discusses the importance of control node distribution and density. A new approach based on introducing different classes of control node is proposed to improve the efficiency of the CAT algorithm. Results indicate that 400 control nodes per km/sup 2/ are required to ensure satisfactory operation. Introducing control node prioritisation is also shown to improve the quality and interpretation of the final solution.