Giovanni Giambene

Hetnets - a new paradigm for increasing cellular capacity and coverage [Guest Editorial]

Wireless data traffic has been increasing exponentially in recent years. Driven by a new generation of devices (smart phones, MIDs, netbooks, etc.), capacity demand increases faster than spectral efficiency improvement, particularly at hotspots/areas. Also, as services migrate from voice centric to data centric, more users operate indoors, which requires increased link budget and coverage extension to provide uniform user experience. Traditional networks optimized for homogeneous traffic face unprecedented challenges to meet the demand cost effectively. Most recently, Third Generation Partnership Project (3GPP) Long Term Evolution (LTE)-Advanced has started a new study item to investigate heterogeneous network (HetNet) deployments as an efficient way to improve system capacity as well as effectively enhance network coverage. Unlike traditional heterogeneous networks that deal with the interworking of wireless local area networks and cellular networks, which the research community has already studied for more than a decade, in this new paradigm in the cellular network domain, a HetNet is a network containing nodes with different characteristics such as transmission power and radio frequency (RF) coverage area. Low-power micro nodes and high-power macro nodes can be maintained under the management of the same operator. They can share the same frequency band, provided by the operator. In this case, joint radio resource/interference management needs to be provided to ensure the coverage of low-power nodes. In some other cases, the low- and highpower nodes can use discontinuous bands of an operator separately (e.g., through carrier aggregation) so that strong interference with each other can be avoided. Macro network nodes with large RF coverage areas are deployed in a planned way for blanket coverage of urban, suburban, and rural areas. Local nodes with small RF coverage areas aim to complement the macro network nodes for coverage extension or throughput enhancement. In addition to this, global coverage can be provided by satellites (macrocells) according to an integrated system concept. The objective of Het-Nets targets the improvement of overall capacity as well as a cost-effective coverage extension and green radio solution by deploying additional network nodes within the local area range, such as low-power micro/pico network nodes, home-evolved Node-Bs (HeNBs)/closed subscriber group (CSG) cells, and femto and relay nodes.

Cross-layer protocol optimization for satellite communications networks: a survey

Satellite links are expected to be one important component of the next-generation Internet. New satellite system architectures are being envisaged to be fully IP based and support digital video broadcasting and return channel protocols (e.g. DVB-S, DVB-S2 and DVB-RCS). To make the upcoming satellite network systems fully realizable, meeting new services and application requirements, a complete system optimization is needed spanning the different layers of the OSI, and TCP/IP protocol stack. This paper deals with the cross-layer approach to be adopted in novel satellite systems and architectures. Different cross-layer techniques will be discussed, addressing the interactions among application, transport, MAC and physical layers. The impacts of these techniques will be investigated and numerical examples dealing with the joint optimization of different transport control schemes and lower layers will be considered referring to a geostationary-based architecture. Our aim is to prove that the interaction of different layers can permit to improve the higher-layer goodput as well as user satisfaction. Copyright

Satellite component of NGN: Integrated and hybrid networks

Future mobile networks are expected to involve systems that are based on different technologies, such as WiFi, WiMAX, 2G/3G/3G+, LTE, and satellite. To address this scenario, ITU has defined integrated and hybrid networks in the framework of Next-Generation Networks. The interest is to exploit the cooperation of different wireless communication systems (segments) to provide service to mobile users in the most efficient way, taking into account signal quality (coverage), traffic congestion conditions, and cost issues. Integrated and hybrid networks have the potential to be an efficient and cost-effective solution to employ satellite communications for mobile users. In the view of this, our paper focuses on the design of integrated/hybrid systems taking into account physical, MAC, and network layers issues. System examples and standards are described as well. Then, cooperative diversity techniques and traffic engineering issues for overflow traffic are discussed. This paper concludes identifying some possible future trends. Copyright

Dynamic resource allocation based on a TCP‐MAC cross‐layer approach for DVB‐RCS satellite networks

Satellite communication networks can provide multimedia broadband services to fixed and mobile users in several scenarios where terrestrial networks are not present or where they need to be complemented. Moreover, satellite links can be useful to bypass crowded terrestrial networks, thus helping in reducing congestion. In such a scenario, characterized by a high propagation delay and a radio channel affected by losses, standard bandwidth allocation schemes prove to be inefficient when Transmission Control Protocol (TCP) is running. Hence, we propose a novel resource allocation scheme based on the cross-layer interaction between TCP and Medium Access Control (MAC) layers. The interest is here in achieving an efficient transfer of files by means of the FTP application protocol. Our scheme permits to avoid network congestion, to reduce the average file transfer time and to achieve a fair sharing of resources among competing flows. The allocation technique has been applied to an Interactive Satellite Network (ISN) based on the DVB-RCS standard with a group of fixed satellite terminals, which communicate with a Netivork Control Center (NCC) through a geostationary bent-pipe satellite, according to a classical star topology. Results are obtained through a network simulator. Copyright (c) 2006 John Wiley & Sons, Ltd.

Instantly decodable network coding protocols with unequal error protection

This work aims at introducing two novel packet retransmission techniques for reliable multicast in the framework of Instantly Decodable Network Coding (IDNC). These methods are suitable for order- and delay-sensitive applications, where some information is of high importance for an earlier gain at the receivers side. We introduce hence an Unequal Error Protection (UEP) scheme, showing by simulations that the Quality of Experience (QoE) for the end-users is improved even without complex encoding and decoding.

Performance analysis of a PRMA protocol suitable for voice and data transmissions in low Earth orbit mobile satellite systems

Mobile satellite systems (MSSs) are expected to play a significant role in providing users with communication services worldwide. In such a context, low Earth orbit (LEO) satellite constellations seem to be a good solution to attain a global coverage and to allow the use of low-power lightweight mobile terminals. This paper analyzes the performance of a novel medium access control (MAC) scheme suitable for applications in LEO-MSSs, named packet reservation multiple access with hindering states (PRMA-HS), that has been derived by proper modifications of the well-known PRMA protocol. We envisage a mixed traffic with voice sources and data sources with different quality of service (QoS) requirements. The good behavior of the proposed PRMA-HS scheme is validated by extensive comparisons with the classical PRMA protocol. Finally, it is shown that PRMA-HS efficiently supports integrated voice and data traffic in LEO-MSSs.

Radio resource management across multiple protocol layers in satellite networks: a tutorial overview

Satellite transmissions have an important role in telephone communications, television broadcasting, computer communications, maritime navigation, and military command and control. Moreover, in many situations they may be the only possible communication set-up. Trends in telecommunications indicate that four major growth market/service areas are messaging and navigation services (wireless and satellite), mobility services (wireless and satellite), video delivery services (cable and satellite), and interactive multimedia services (fibre/cable, satellite). When using geostationary satellites (GEO), the long propagation delay may have great impact, given the end-to-end delay users requirements of relevant applications; moreover, atmospheric conditions may seriously affect data transmission. Since satellite bandwidth is a relatively scarce resource compared to the terrestrial one (e.g. in optical transport networks), and the environment is harsher, resource management of the radio segment plays an important role in the systems efficiency and economy. The radio resource management (RMM) entity is responsible for the utilization of the air interface resources, and covers power control, handover, admission control, congestion control, bandwidth allocation, and packet scheduling. RRM functions are crucial for the best possible utilization of the capacity. RRM functions can be implemented in different ways, thus having an impact on the overall system efficiency. This tutorial aims to provide an overview of satellite transmission aspects at various OSI layers, with emphasis on the MAC layer; some cross-layer solutions for bandwidth allocation are also indicated. Far from being an exhaustive survey (mainly due to the extensive nature of the subject), it offers the readers an extensive bibliography, which could be used for further research on specific aspects. Copyright

Dynamic Resource Allocation based on a TCP-MAC Cross-Layer Approach for Interactive Satellite Networks

DVB-RCS is an open standard for interactive broadband satellite services. According to the standard, interactive terminals communicate with the network control center through the return channel adopting MF-TDMA. In this scenario, classical bandwidth allocation schemes do not take into account TCP evolution, leading to sub-optimal performance when TCP-based traffic share the return link. A cross-layer approach, based on exchange of information between not-adjacent layers, can help to improve efficiency. This paper presents an innovative allocation algorithm based on a cross-layer interaction between TCP and MAC layers. Such an algorithm aims to synchronize the requests of resources with the TCP transmission window trend. The obtained results show that our scheme permits both to reduce the delay, to increase the utilization of air interface resource and to achieve a fair share of resources among competing flows

Broadband Satellite Multimedia

The broadband satellite multimedia (BSM) architecture standardised by ETSI defines a satellite independent service access point (SI-SAP) interface layer that separates the satellite independent features of the upper layers from the satellite dependant features of the lower layers, and provides a mechanism to carry IP-based protocols over these satellite dependent lower layers. This enables interoperability at the IP layer between satellite systems of different physical and link layers technologies that fully comply with the SI-SAP concept. This study reviews past and current standardisation activities including the BSM quality of service (QoS) architecture, security architecture, network management that have been carried out by the ETSI Technical Committee-Satellite Earth Stations and Systems (TC-SES)/BSM working group and looking into the future to extend current SI-SAP functions that can enhance existing QoS provision and security management capabilities as well as proposing a mobility management architecture that complies with the IEEE 802.21 media independent handover framework to support BSM mobility and to allow integration of satellite networks with fixed and mobile network infrastructures. A service-based network management architecture is also proposed to allow management flexibility and integration of business and operation support functions, paving the way for satellite integration into the Internet of the future.

Optimization of power control parameters for DS-CDMA cellular systems

This paper envisages a cellular system based on code-division multiple access and investigates the performance of a strength-based closed-loop power control (CLPC) scheme on the basis of different parameters, such as the number of bits of the power command, the quantization step size, and the user speed. On the basis of a log-linear CLPC model, an analytical approach has been developed that has allowed to determine the optimum quantization step size to be used for each value of the number of power command bits. Simulation results have permitted to support the analytical framework developed in this paper.