Browsing by Author "Aghvami, A. Hamid"
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- Basic Limits for System Capacity and Cost/Revenue Optimisation: a formulation for Fixed WiMAXPublication . Velez, Fernando J.; Camino Noguera, Maria del; Aghvami, A. Hamid; Holland, OliverIn Fixed WiMAX, the cost/revenue radio and network planning optimisation function incorporates the cost of building and maintaining the infrastructure and the effect of the available resources on revenues. Supported throughput typically decreases with larger cells due to the implied greater average distance of users from the base station, although the use of subchannelisation can keep it steady up to a larger cell radius. Sectorization facilitates the use higher order modulation and coding schemes in the cell and may improve the throughput; however, sectorization equipment is more expensive, and there is the need for three times more spectrum bandwidth, increasing costs. In turn, the use of Relay Stations (RSs) may significantly reduce the deployment cost of the system. With relays, only the consideration of trisectored Base Station (BS) antennas with K=3 (at the cost of extra channels, where 9 channels corresponds to a bandwidth of 31.5 MHz) enables to obtain values of throughput comparable to the ones without using relays. This is due to the more favourable frame format. With no RSs and sectorization with K=3 the economic performance is weak, as only one carrier may be used. However, with omnidirectional BSs with K=3, under the same total bandwidth, three carriers may be used and the profit in percentage varies between ~900 and 800% for coverage distances lower than 1000 m. With RSs, the use of tri-sectored BSs corresponds to a clear advantage relatively to the “no RS” case up to R~1300 m. When the price per MB, R144, increases from 0.0025 to 0.005 €/MB the profit in percentage increases more than 100%.
- 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 performance in an IMT-Advanced scenario with Spectrum Aggregation over non-contiguous frequency bandsPublication . Acevedo Flores, Jessica Elizabeth; Velez, Fernando J.; Cabral, Orlando; Robalo, Daniel Luís Silveira; Holland, Oliver; Aghvami, A. Hamid; Meucci, Filippo; Mihovska, Albena Dimitrova; Prasad, Neeli R.; Prasad, RamjeeThis paper determines the cost/revenue performance of a mobile communication system in an IMT-Advanced scenario with integrated Common Radio Resource Management (iCRRM). The iCRRM performs classic CRRM functionalities jointly with Spectrum Aggregation (SA), being able to switch users between non-contiguous frequency bands. The SA scheduling is obtained with an optimized General Multi-Band Scheduling (GMBS) algorithm with the aim of cell throughput maximization. In particular, we investigate the dependence of the throughput on the cell coverage distance for the allocation of users over the 2 and 5 GHz bands for a single operator scenario under a constant average Signal to Interference-plus-Noise Ratio (SINR), for the same type of Radio Access Technology and both frequency bands. The operator has the availability of a non-shared 2 GHz band and has access to part (or all) of a shared frequency band at 5 GHz. An almost constant gain near 30 % was obtained with the proposed optimal solution compared to a system where users are first allocated in one of the two bands and later not able to handover between the bands. It is shown that the profit in percentage terms decreases as the cell radius increases. These results allow for evaluating the impact of the revenue from the channel in the total revenue and in the profit, defined as the difference between revenues and costs, in percentage. Maximum profits of about 1270, 585 and 240 % have been obtained for prices of 0.10, 0.05 and 0.025 €/MByte, respectively, when iCRRM is employed, while profits of 990, 440, and 170 % have been reached with no iCRRM, i.e., simple CRRM. Finally, an energy efficiency strategy is proposed and analyzed, showing that there is significant transmission power saving potential through the opportunistic reallocation scheme.
- 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.
- Dynamic Configuration and Optimization of WiMAX Networks with Relay Power Saving Modes: Measurement-Based Scenario in a Hilly RegionPublication . Robalo, Daniel; Oliveira, João R.; Velez, Fernando J.; Holland, Oliver; Aghvami, A. HamidThis paper investigates the performances achievable by WiMAX networks deployed in various sectorization configurations, with and without relay stations (RSs). Further, it studies the dynamic adjustment of the configuration to serve traffic loads at different times of the day while maximising the use of opportunistic sleep modes by relays in conjunction with cell zooming, thereby saving energy. The configuration changes and invocation of opportunistic sleep modes also take into account coverage constraints. This paper first reports extensive propagation measurements that have been undertaken in Covilha˜, a hilly area of Portugal which presents a realistic and challenging propagation scenario. Using this scenario as the topographical basis, practical cellular planning results are then obtained and compared, using the dominant path and ray tracing (RT) functionalities of WinpropTM. It is shown that without RSs present, the supported throughput is lower in practice because coverage is not 100 %. Further, for the case with omnidirectional cells, coverage reduces to only approximately 60 % if RSs go into sleep mode, and for the tri-sectored cells case coverage drops from 95.75 to 81.90 % (based on RT calculations) if RSs go into sleep mode. There is, however, still a reasonable economic performance in all cases. Additional results demonstrate that savings typically of 47.6 % in RSs’ average power consumption can be achieved. These savings are shown to result in a financial saving for the operator of 10 % of the combined operational and maintenance cost. However, it is observed that such solutions have to be used cautiously in hilly regions due to challenges in maintaining coverage.
- Energy saving in the optimization of the planning of fixed WiMAX with relays in hilly terrains: Impact of sleep modes and cell zoomingPublication . Velez, Fernando J.; Oliveira, João; Robalo, Daniel Luís Silveira; Holland, Oliver; Aghvami, A. HamidLayered and cooperative elements such as femto-cells and relays can improve performance or energy efficiency in mobile networks; however, they consume energy per se and their durations in operational state must therefore be minimised. This paper investigates the use of relays in WiMAX network deployments and concentrates on the cost/revenue performance and energy efficiency trade-off in such cases. Specifically, it investigates the performance achievable by networks that are deployed in various sectorization configurations with and without relays, and matches this to varying traffic loads at different times of the day to maximise the use of sleep modes, where possible, by relays, also in consideration of coverage requirements. It does this for scenarios based on pioneering propagation measurements in the hilly area of Covilhã, Portugal. Results show that through the maximal use of power saving by relays at low traffic times, considerable energy savings in the relays' power consumption are achievable, typically 47.6%. These savings are shown to map to a financial saving for the operator of 10% in the operation and maintenance cost. However, it is also demonstrated that such solutions have to be used cautiously so as to maintain coverage requirements and not decrease the profit in challenging propagation scenarios such as investigated in this paper.
- Fixed WiMAX Profit Maximisation with Energy Saving through Relay Sleep Modes and Cell ZoomingPublication . Velez, Fernando J.; del Camino Noguera, Maria; Holland, Oliver; Aghvami, A. HamidIn Fixed WiMAX, the cost/revenue optimisation function for radio and network planning incorporates the cost of building and maintaining the infrastructure and the impact of the available resources on revenues. Supported throughput typically decreases with larger cells due to the implied greater average distance of users from the base station, although the use of subchannelisation can keep throughput steady with a larger cell radius. The use of sectored base stations facilitates selection of higher order modulation and coding schemes in the cell and can improve throughput; however, sectored equipment is more expensive. Fortuitously, using Relay Stations (RSs) can reduce the deployment cost of such systems. In such a context, if RSs are put into sleep mode during the night and at weekends when they are not necessary, important energy savings can be achieved. With relays, only the consideration of tri-sectored Base Station (BS) antennas with K = 3 (at the cost of extra channels, where nine channels corresponds to a bandwidth of 31.5 MHz) obtains values of system throughput comparable to those without using relays. This is due to the more favourable frame format that is employed under the use of tri-sectored BS antennas. This paper shows that the application of cell zooming in conjunction with relays going into sleep mode at times of low load achieves a notable power saving, corresponding to 10% saving in operation and maintenance cost on average. Moreover, as it is assumed that the DL sub-frame format cannot be changed to a more favourable one, economic performance is better when RSs are deployed. It is however important to highlight that in the absence of RSs, economic performance is still reasonable (for tri-sectored and omnidirectional BSs, 700–800% and 400–450% profit, respectively), compared with the case where RSs are deployed (∼1000 and ∼900% profit, respectively).
- Intra-operator spectrum sharing concepts for energy efficiency and throughput enhancementPublication . Holland, Oliver; Attar, Alireza; Cabral, Orlando Manuel Brito; Velez, Fernando J.; Aghvami, A. HamidCognitive radio and other dynamic spectrum sharing paradigms have enjoyed the limelight recently for their potential to realize a number of benefits for communications systems. The majority of investigated solutions thus far have looked at primary/secondary access and sharing of spectrum among different spectrum owners. In contrast, this paper investigates solutions for spectrum sharing among different bands owned by the same entity, such as a mobile operator, and demonstrates considerable potential for such solutions to improve power efficiency for the network and to increase throughput. The paper utilizes four means to achieve this potential: spectrum sharing through the opportunistic movement of users between bands allowing radio network equipment in other bands to be switched off when possible, spectrum sharing to opportunistically improve links’ propagation characteristics therefore reducing necessary transmission power, better interference management in spectrum sharing to reduce necessary transmission power, and the opportunistic aggregation of spectrum bands to increase achievable throughput. Power consumption reductions of over 50%, both in terms of mains power draw and in terms of necessary transmission power, are demonstrated. Moreover, throughput enhancements of up to 20% are achieved.
- Opportunistic load and spectrum management for mobile communications energy efficiencyPublication . Holland, Oliver; Cabral, Orlando; Velez, Fernando; Aijaz, Adnan; Pangalos, Paul; Aghvami, A. HamidDynamic load and spectrum usage management techniques can significantly improve the energy efficiency of mobile communications systems. This paper considers: (i) the opportunistic reallocation of traffic loads between bands to allow radio network equipment in the bands that the traffic is originated from to be powered down, and (ii) the opportunistic selection of more appropriate spectrum based on propagation characteristics to minimize necessary transmission power through improving propagation and/or reducing power leaking into co-channel cells in frequency reuse cases. This paper addresses the simulation of video, FTP and HTTP (web browsing) traffic sources for configurations representing LTE and HSDPA telecommunications networks, and shows that the opportunistic reallocation of users between bands to power down radio equipment achieves a significant saving of 50% or more in from-the-socket power. Furthermore, it shows that the opportunistic reallocation of users/links to minimize transmission power through using more appropriate propagation spectrum leads to a further modest reduction in from-the-socket power consumption.
- Opportunistic spectrum and load management for green radio networksPublication . Holland, Oliver; Facchini, Christian; Aghvami, A. Hamid; Cabral, Orlando Manuel Brito; Velez, FernandoIntroduction Historically, the radio spectrum has been managed in a rather rigid fashion where systems have been constrained to very specific bands in order to avoid interference and maintain the spectrum's viability. This regime is extremely inefficient, because at any one time many systems are not being used thereby leaving their associated spectrum also unused. Alternative spectrum management, where systems not designated for a particular band may nevertheless use it if it is available, would greatly increase spectrumusage efficiency and capacity. Communications traffic has also historically been managed in a somewhat inefficient manner, whereby traffic load has usually only been carried on a specific band as directed by the “owner” of the user/device carrying the traffic. Improved traffic-load management techniques, where the traffic can be shared among bands and systems, would also increase efficiency or capacity. Although the end-user may sometimes have a limited choice of which band to receive traffic on (e.g. via a Wi-Fi interface using an ISM/UNII band, or via a 3G mobile communications interface using a UMTS band), centralized control of that choice, in a timely fashion, can far better manage efficiency and capacity than the end-user operating alone. Such opportunistic load and spectrum management between bands/systems is being made feasible by operators having an increasingly wide range of spectrum bands at their disposal, of very different frequencies and physical characteristics. Operators may typically operate a range of different systems on this range of spectrum bands.