Georgios P. Koudouridis

Generic link layer: a solution for multi-radio transmission diversity in communication networks beyond 3G

With the advent of multi-radio access (MRA), an integration of differentradio access technologies (RATs) into a heterogeneous radio access network(RAN) becomes feasible. Such integration allows a user to be at any instantof time served by one or multiple radio accesses (RAs) concurrently, where anRA constitutes an independent radio resource, such as a carrier or a channel,implemented by a single RAT. It also allows a user´s service demands to bemapped onto the aggregated network resources in a transparent and efficientway. An approach for the realization of such multi-radio integrated environmentsis through a unifying generic link layer (GLL) that provides joint radiolink processing and enables communication between nodes and devices acrossdifferent radio accesses.Based on the requirements on multi-access, an architecture that supportsMRA is suggested and the functions of GLL that aims at integrating andutilising multiple RATs are defined. We explore the potential for performanceimprovements through novel extensions of the transmission diversityparadigm which builds on GLL functions that enable multi-radio access selection.Multi-radio transmission diversity (MRTD) is defined as the dynamicselection of radio access for the transmission of a user´s data and it can bethought of as consisting of a packet scheduler operating across multiple radiointerfaces. Different MRTD schemes may be envisaged through combinationsof access re-selection rate, transmission parallelism and transmission redundancy.The re-selection rate refers to the rate at which radio access selectionis performed. It may range from multiple IP packets to one single MACframe. Switched MRTD corresponds to an access selection scheme where auser transmits via one RA at a time, while parallel MRTD corresponds to ascheme where simultaneous transmissions over multiple RAs are scheduled.Finally, redundancy refers to the transmission of copies of the same data overmultiple RAs to increase the possibility of correct reception.The benefits of MRTD are investigated by simulation studies on two multiradiocase scenarios, based on generic RATs and on specific RATs respectively.In the RAT generic scenario, switched MRTD has been evaluated for networktopologies of collocated and non-collocated RAs consisting of macroand pico-cells. In the case of collocated RAs, spectral efficiency is increasedby exploiting diversity in multi-path fading while in non-collocated RAs, thespectral efficiency increase is due to diversity exploitation in both shadowingand multi-path fading. Simulation results show that switched MRTD is mostadvantageous when the RAs provide comparable throughputs. Furthermore,when combined with multi-radio ARQ, MRTD significantly reduces packetloss and packet transmission delays. This is also shown in the specific radioaccesssimulation scenario where a delay sensitive voice service is studied. Inaddition, switched MRTD provides comparable gains to parallel MRTD interms of average packet transmission delay and packet loss, while using lessradio resources. In all cases, it is concluded that maximum performance isconditioned on the reporting delays of the channel quality indicator (CQI).Reporting delays of CQI that are half the channel coherence time render sucha complex MRTD mechanism less effective.

Switched multi-radio transmission diversity in future access networks

In this paper we study packet scheduling algorithms which exploit multi-radio transmission diversity in a multi-radio access network. We view the packet scheduling process as a combination of user ...

A Centralised Approach to Power On-Off Optimisation for Heterogeneous Networks

The design of centralized algorithms and techniques allowing for an efficient utilisation of infrastructure in terms of energy consumption is one of the key challenges in heterogeneous networks (HetNets). In this study the energy efficiency in the HetNet scenario is formulated as an optimisation problem and an iterative improvement algorithmic approach to power on-off of network cells is devised and evaluated. The algorithm is based on the simulated annealing search approach and the obtained network configuration solutions are compared to a baseline configuration scenario where all cells are powered on. The optimization search is guided by an objective function which is defined on outage throughput and energy efficiency. Simulation results show that significant energy reductions gains can be achieved by switching off macro cells and with no loss of the cell edge user throughput. In some scenarios the algorithm generates solutions which considerably increase network throughput. The gains are more pronounced in configurations where pico cells are deployed at hot zones of user clusters.

Distributed power on-off optimisation for heterogeneous networks - A comparison of autonomous and cooperative optimisation

The design of distributed algorithms and techniques allowing for an efficient utilisation of infrastructure in terms of energy consumption is one of the key challenges in heterogeneous networks or HetNets. In this study the energy efficiency in the HetNet scenario is formulated as an optimisation problem and an iterative improvement algorithmic approach to power on-off of network cells is devised and evaluated. The network is divided into clusters of cells, and the algorithm, which employs simulated annealing search, is executed by the clusters in a distributed manner. Four different variations of autonomous and cooperative optimisation are devised and the obtained network configuration solutions are compared to a baseline configuration scenario where all cells are powered on. The optimization search is guided by an objective function which is defined on outage throughput and energy efficiency. Simulation results show that the distributed cooperative algorithms perform better than the baseline in nearly all cases both in terms of outage throughput and energy efficiency. Furthermore, coordination among clusters has a strong impact on the speed and the performance of the obtained solutions.

On the capacity and energy efficiency of network scheduling in future ultra-dense networks

Massive densification of the radio network infrastructure is considered to be a promising solution to meet a rapidly increasing demand in future radio access networks. In this study we investigate the feasibility of a centralized approach for the allocation of radio network resources by studying the performance of a network scheduler that implements access node on/off scheduling in ultra-dense networks. The evaluation is performed by means of simulations for different distributions of mobile nodes and for different network densities. Simulation results show that considerable improvements in the network throughput and energy efficiency can be sought with an increasing network density. The improvements are independent of the mobile node distribution and diminish steadily as the network density increases. It is also shown that the gains are higher when mobile nodes are uniformly distributed as compared to a distribution where mobile nodes are clustered due to a higher number of mobile nodes per access node.

Utilization of Multi-Radio Access Networks for Video Streaming Services

In comparison to traditional voice based circuit switched mobile systems, the multimedia content puts forward significantly strict quality of service requirements. In this perspective, a noticeable proportion of contemporary research has been driven towards exploring the possibilities of simultaneously utilizing geographically co-existing mobile networks belonging to a wide range of wireless technologies. This paper evaluates such co-existence by means of a novel macro diversity scheme referred to as Multi Radio Transmission Diversity (MRTD) which exploits the dynamic cooperation between the networks at the radio link level. Relevant QoS parameters for an MPEG4 encoded video streaming service have been analyzed by means of simulations in a hybrid network topology consisting of IEEE 802.11b WLAN and UMTS HSDPA. The performance gains have been observed for various load and radio propagation conditions in comparison to a benchmark system which is not capable of utilizing such cooperation between multiple network interfaces.

Performance Evaluation of Multi-Radio Transmission Diversity for TCP Flows

The effect of the TCP congestion control mechanism over rapidly fluctuating wireless links is a deterioration of the TCP performance. The utilization of multi-radio accesses in future networks by means of packet scheduling and dynamic access selection enriches the arsenal of solutions that mitigate radio channel variations. Packet scheduling over multiple radio accesses at link level provides a novel diversity scheme referred to as Multi-Radio Transmission Diversity (MRTD). This work evaluates, through simulations, the effects of different MRTD schemes for TCP flows over heterogeneous radio links. Results indicate that MRTD schemes provide substantial gains in terms of goodput and show a significant reduction in file download times. These gains are due to the diversity obtained and the suppression of the unwanted duplicate acknowledgements that frequently cause degradation in TCP performance over a radio channel.

Performance Evaluation of Multi-Radio Transmission Diversity: QoS Support for Delay Sensitive Services

Integration and seamless networking of different wireless technologies is one of the driving scenarios in the contemporary research. In recent years, mobile phones have seen an influx of attractive on-demand multimedia services with strict QoS requirements. This work investigates the QoS for delay sensitive services under the design framework of a heterogeneous network. Multi Radio Transmission Diversity (MRTD), which exploits the benefits of dynamic usage of different access technologies, is tested using simulations for Voice-over-IP on multi-radio wireless devices. The network technologies in this study include HSDPA on UMTS and IEEE 802.11. By applying various MRTD schemes, gains in performance have been observed in terms of average packet delay, packet loss and goodput as compared to a legacy system which operates under only one network access for a given session. The MRTD schemes have been analyzed for various simulation scenarios characterized by varying traffic load and radio propagation conditions.

Switched Multi-Radio Transmission Diversity for Non-Collocated Radio Accesses

We evaluate the spectral efficiency gains observed through multi-radio transmission diversity (MRTD), whereby packets of data are jointly scheduled for downlink transmission over multiple independent radio accesses. We specifically address downlink switched MRTD employed across macro- and pico-cellular radio accesses with non-collocated base stations in a hierarchical cell structure. It is shown that while significant gains can be achieved via MRTD among collocated macro-cell (or pico-cell) base stations, tight cooperation across non-collocated macro-and pico-cell base stations is only beneficial for a small subset of possible geometries. The impact of CQI reporting delays is also investigated

Enablers for Energy-Aware Cooperative Decision and Control in Wireless Networks

Autonomic networking and cooperative communications paradigms have emerged as promising technologies that can pave the way for next generation networks. CONSERN project is focusing on cooperation and collaboration enablers, cooperative decision and control algorithms that will maximise the expected gains by utilising cooperative problem solving for improving energy efficiency in wireless networks. In this paper, cooperative and/or autonomous solutions are captured and a mapping to the envisaged technologies is made. Based on this mapping an initial analysis of the requirements for energy-efficient cooperation is presented. The cooperation deals with information exchange, actions coordination and decision making within and between different types of network nodes. Based on the requirements analysis a set of key cooperation enablers are identified and further elaborated upon.