Optimization of Power Allocation for Multiusers in Multi-Spot-Beam Satellite Communication Systems

In recent years, multi-spot-beam satellite communication systems have played a key role in global seamless communication. However, satellite power resources are scarce and expensive, due to the limitations of satellite platform. Therefore, this paper proposes optimizing the power allocation of each user in order to improve the power utilization efficiency. Initially the capacity allocated to each user is calculated according to the satellite link budget equations, which can be achieved in the practical satellite communication systems. The problem of power allocation is then formulated as a convex optimization, taking account of a trade-off between the maximization of the total system capacity and the fairness of power allocation amongst the users. Finally, an iterative algorithm based on the duality theory is proposed to obtain the optimal solution to the optimization. Compared with the traditional uniform resource allocation or proportional resource allocation algorithms, the proposed optimal power allocation algorithm improves the fairness of power allocation amongst the users. Moreover, the computational complexity of the proposed algorithm is linear with both the numbers of the spot beams and users. As a result, the proposed power allocation algorithm is easy to be implemented in practice

Study of Rain Attenuation Calculation and Strategic Power Control for Ka-Band Satellite Communication in India

The tremendous worldwide growth in the use of Internet and multimedia services prompted the ambitious planning for evolution of commercial and broadband satellite communication systems. The traditional C and Ku bands in satellite communications are getting crowded, So the systems are moving towards higher frequency ranges above 20 GHz. The Ka-band (18-40 GHz) frequency spectrum has gained attention for satellite communication. The inherent drawback of Ka-band satellite system is that increase in signal distortion resulting from propagation effects. Atmospheric attenuation in Ka-band is always severe, especially in the presence of rain. Thus, New technologies are required for Ka-band systems, such as multiple hopping antenna beams and regenerative transponders to support aggregate data rates in the range of 1 - 20 Gbps per satellite, which can provide DTH, HDTV, mobile and fixed Internet users with broadband connection. Currently in India C and Ku-band frequencies are being used for commercial satellite communications. In future Ka-band will be used for wideband applications. Keeping in view of the socio-economic and geographical diversities of India. Propagation studies are essential for estimation of attenuation, so that Ka-band satellite links operating in different parts of Indian region can be registered appropriately. Ka-band system is recognized as a new generation in communication satellites that encompasses a number of innovative technologies such as on board processing (OBP) for multimedia applications and switching to provide two way services to and from small ground terminals. To do this efficiently multiple pencil like spot beams are used. One distinct feature of this propagation being used to address this problem is Satellite Spot-Beam. To design effective satellite communication system, the arrangement of spot beam locations in Indian subcontinent, the study and analysis of link availability for Kaband satellite communication in various geographically separated spot beams in India using statistical data is necessary. Based on global rain models integrated with the link budget, the study allows us to examine major system design issues encountered in Ka-band satellite communication that are susceptible to propagation impairments. This system can be flexible enough to increase power on specific transmissions to compensate for local weather conditions. This can make better use of the available bandwidth than C or Ku-band satellite, and more users can get higher level of services

Demand-based optimization for adaptive multi-beam satellite communication systems

Satellite operators use multiple spot beams of high throughput satellite systems to provide internet services to broadband users. However, in recent years, new mobile broadband users with diverse demand requisites are growing, and satellite operators are obliged to provide services agreed in the Service Level Agreements(SLA) to remote rural locations, mid-air aeroplanes and mid-ocean ships. Furthermore, the expected demand is spatio-temporal which varies along the geographical location of the mobile users with time and hence, creating more dynamic, non uniformly distributed, and time sensitive demand profiles. However, the current satellite systems are only designed to perform similarly irrespective of the changes in demand profiles. Hence, a practical approach to meet such heterogeneous demand is to design adaptive systems by exploiting the advancements in recently developed technologies such as precoding, active antenna array, digital beamforming networks, digital transparent payload and onboard signal processing. Accordingly, in this work, we investigate and develop advanced demand-based resource optimization modules that fit future payload capabilities and satisfy the satellite operators’ interests. Furthermore, instead of boosting the satellite throughput (capacity maximization), the goal is to optimize the available resources such that the satellite offered capacity on the ground continuously matches the geographic distribution of the traffic demand and follows its variations in time. However, we can introduce adaptability at multiple levels of the transmission chain of the satellite system, either with long term flexibility (optimization over frequency, time, power, beam pattern and footprint) or short term flexibility (optimization over user scheduling). These techniques can be optimized as either standalone or in parallel or even jointly for maximum demand satisfaction. However, in the scope of this thesis, we have designed real time optimizations only for some of the radio resource schemes. Firstly, we explore beam densification, where by increasing the number of beams, we improve the antenna gain values at the high demand hot-spot regions. However, such increase in the number of beams also increase the interbeam interference and badly affects SINR performance. Hence, in the first part of Chapter 2 of this thesis, we focus on finding an optimal number of beams for given high demand hot-spot region of a demand distribution profile. Also, steering the beams towards high demand regions, further increase the demand satisfaction. However, the positioning of the beams need to be carefully planned. On one hand, closely placed beams result in poor SINR performance. On the other hand, beams that are placed far away will have poor antenna gain values for the users away from the beam centers. Hence, in the second part of Chapter 2, we focus on finding optimized beam positions for maximum demand satisfaction in high demand hot-spot regions. Also, we propose a dynamic frequency-color coding strategy for efficient spectrum and interference management in demand-driven adaptive systems. Another solution is the proposed so-called Adaptive Multi-beam Pattern and Footprint (AMPF) design, where we fix the number of beams and based on the demand profile, we configure adaptive beam shapes and sizes along with their positions. Such an approach shall distribute the total demand across all the beams more evenly avoiding overloaded or underused beams. Such optimization was attempted in Chapter 3 using cluster analysis. Furthermore, demand satisfaction at both beam and user level was achieved by carefully performing demand driven user scheduling. On one hand, scheduling most orthogonal users at the same time may yield better capacity but may not provide demand satisfaction. This is majorly because users with high demand need to be scheduled more often in comparison to users with low demand irrespective of channel orthogonality. On the other hand, scheduling users with high demand which are least orthogonal, create strong interbeam interference and affect precoding performance. Accordingly, two demand driven scheduling algorithms (Weighted Semi-orthogonal scheduling (WSOS) and Interference-aware demand-based user scheduling) are discussed in Chapter 4. Lastly, in Chapter 5, we verified the impact of parallel implementation of two different demand based optimization techniques such as AMPF design and WSOS user scheduling. Evidently, numerical results presented throughout this thesis validate the effectiveness of the proposed demand based optimization techniques in terms of demand matching performance compared to the conventional non-demand based approaches