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- System CapacityPublication . Velez, Fernando J.; Nazir, Muhammad Kashif; Aghvami, A. Hamid; Holland, Oliver; Robalo, DanielIn Fixed WiMAX, the contribution from each transmission mode can be incorporated into an implicit formulation to obtain the supported throughput as a function of the carrier-to-interference ratio. This is done by weighting the physical throughput in each concentric coverage ring by the size of the ring. In this paper, multi-hop cells are formed by a central coverage zone and three outer coverage zones served by cheaper low-complexity relays. It is assumed that line of sight propagation to the bases station is achieved in a high percentage of the cell, reducing the impact of selective fading, through allowing dimensioning to be done by GIS cellular planning tools. By using tri-sectorised equipment there is a need for three times more bandwidth, while hardware costs are higher. In our proposal for relays, the FDD mode is considered and the frames need to guarantee resources for BS-to-MS communications but also for BS-to-RS and RS-to-MS communications. These requirements leads to a 1/5 asymmetry factor between the UL and DL in the omnidirectional BS case and to a 3/7 asymmetry factor in the case of tri-sectored BSs. Although the reuse distance is augmented by a factor, we show that with the use of relays in FDD mode only the consideration of tri-sectored BSs with reuse pattern K = 3 (at the cost of extra channels, corresponding to 9 channels) enables to obtain values for the throughput comparable to cases without the use of relays. The presence of sub-channelisation only improves the results for the highest values of R. The consideration of tri-sectored BS antennas with K = 1 (whilst keeping the number of required channels – equal to 3) did not enable to obtain values of the throughput comparable to the ones without using relays, although frame format is more favourable. Relays can be cheaper than BS with full functionalities. As the use of relays may lead to lower costs it is worthwhile to analyse the impact of using them on costs and revenues.
- Business Models and Cost/Revenue OptimizationPublication . Velez, Fernando J.; Nazir, Muhammad Kashif; Aghvami, A. Hamid; Holland, Oliver; Robalo, DanielThis Chapter starts by covering general aspects about the business models for WiMAX and then addresses the cost/revenue optimization for these networks, for cellular configurations without and with relays. In Fixed WiMAX, radio and network planning can be optimised by tuning a cost/revenue function which incorporates de the cost of building and maintaining the infrastructure and the effect of the available resources on revenues. From the cost-benefit analysis, one conclusion of this work is that given today’s hypothesis of price per MByte of information transfer of somewhere between 0.0025 € and 0.010 €, it is clear that, without considering the use of relays, the choice of reuse patterns 3 or 4 with sectorial cells is preferable to the use of omnidirectional cells with reuse pattern, K, of 7, as three times more resources are available in each cell. Besides, in nowadays networks, if there is a need for sparse BS deployments whilst reducing costs, K = 1 may be a solution, as it presents higher profit for the longest coverage distances. In future networks, when costs will be lower, the advantage of sectorization is kept and will drive the deployment of tri-sectorization forward. Nevertheless, in this case K = 1 will not be advantageous with tri-sectorization for the longest coverage distances anymore. This study also concludes that cell radii in the range 1000–1500m is preferable, corresponding to profit in percentage terms of near the achievable maximum, while keeping costs acceptable. The WiMAX cost-benefit optimization is also explored for the case where relays are used to help on improving coverage while mitigating the interference. Results show that the use of relays with no sectorization in the BS leads to a lower profit (K = 3). Also the use of sectorization (an example is presented for K = 1) does not seem to enable larger profit. The optimum (maximum) values occur for coverage distances up to 1,000 m. In the DL, when the price per MB, R144, increases from 0.0025 €/min to 0.005 €/min the profit increases more than 100%.
- Cost/Revenue Tradeoff in the Optimization of Fixed WiMAX Deployment With RelaysPublication . Velez, Fernando J.; Nazir, Muhammad Kashif; Aghvami, A. Hamid; Holland, Oliver; Robalo, DanielIn fixed Worldwide Interoperability for Microwave Access (WiMAX), the contribution from each transmission mode can be incorporated into an implicit formulation to obtain the supported throughput as a function of the carrier-to-interference ratio. This is done by weighting the physical throughput in each concentric coverage ring by the size of the ring. In this paper, multihop cells are formed by a central coverage zone and three outer coverage zones, which are served by cheaper low-complexity relays. Although the reuse distance in this case is augmented by a factor of √3, we show that, with the use of relays in frequencydivision duplexing (FDD) mode with an adapted time-division duplexing (TDD) uplink (UL) subframe structure to accommodate communication from/to the relay station (RS) to/from subscriber station (SS), only the consideration of trisectored base stations (BSs) with a reuse pattern of K = 3enables attainment of values for the cell per sector throughput that is comparable with cases without the use of relays. Cost/revenue optimization results show that trisectored BSs in topologies with relays enable us to achieve more profitable reuse configurations than with omnidirectional BSs and no relays. Under the same total bandwidth and with the coverage distance set at R ∼ 500 m, we show that it is preferable to consider K = 1 with three carriers per sector instead of K = 3with one carrier per sector, whereby the profit in this case is increased from ∼1000% to ∼1450%. Furthermore, if the price [in (C/MB)] is increased from 0.0025 to 0.005, the achievable profit more than doubles.