Rainer Schoenen - Academia.edu (original) (raw)

Papers by Rainer Schoenen

Cellular networks face severe challenges due to the expected growth of application data rate dema... more Cellular networks face severe challenges due to the expected growth of application data rate demand with an increase rate of 100% per year. Over-provisioning capacity has been the standard approach to reduce the risk of overload situations. Traditionally in telephony networks, call blocking and overload probability have been analyzed using the Erlang-B and Erlang-C formulas, which model limited capacity communication systems without or with session request buffers, respectively. While a closed-form expression exists for the blocking probability for constant load and service, a steady-state Markov chain (MC) analysis can always provide more detailed data, as long as the Markov property of the arrival and service processes hold. However, there is a significant modeling advantage by using the stochastic Petri net (SPN) paradigm to model the details of such a system. In addition, software tool support allows getting numeric analysis results quickly by solving the state probabilities in the background and without the need to run any simulation. Because of this efficiency, the equivalent SPN model of the Engset, Erlang-B and Erlang-C situation is introduced as novelty in this paper. Going beyond the original Erlang scenario, the user-in-the-loop (UIL) approach of demand shaping by closed-loop control is studied as an extension. In UIL, demand control is implemented by a dynamic usage-based tariff which motivates users to reduce or postpone the use of applications on their smart phone in times of light to severe congestion. In this paper, the effect of load on the price and demand reduction is modeled with an SPN based on the classical Erlang Markov chain structure. Numeric results are easily obtained and presented in this paper, including probability density functions (PDF) of the load situation, and a parameter analysis showing the effectiveness of UIL to reduce the overload probability.

2009 5th International Conference on Wireless Communications, Networking and Mobile Computing, 2009

Future cellular radio systems aim at maximizing the spectral efficiency. OFDMA radio resources ar... more Future cellular radio systems aim at maximizing the spectral efficiency. OFDMA radio resources are the scarce good with their dimensions bandwidth, time and space. Due to frequency selective fading the effective pathloss varies in all dimensions. Adaptive algorithms are available which allocate the best modulation and coding scheme depending on the expected SINR, as well as dynamic subchannel assignment which aims to choose the best subchannel for each user. This already boosts the performance of OFDMA system. However, these algorithms alone do not touch the transmitted power per subchannel. On the cell edge this is fine, but large areas are covered with a transmitted power exceeding the usually required SINR. In this paper we introduce a power control which saves power on the users within the cell. This leads to a reduced interference into neighbor cells, especially for future reuse one systems. Also some of the saved power can be used to boost transmissions at the cell edge. In this paper we introduce an adaptive power control concept and arrange it into a closed loop control system which contains blocks for all adaptive algorithms for modulation, power, subchannel usage and channel quality indication.

2010 European Wireless Conference (EW), 2010

4G cellular systems and the IMT Advanced candidates will provide broadband wireless access with Q... more 4G cellular systems and the IMT Advanced candidates will provide broadband wireless access with QoS. Especially in multihop configurations of these systems the base station controls resources centrally while relays can take over a part of the responsibility on the second hop. To make this work on layer two, scheduling is the most important task. However, many dimensions of the problem lead to much confusion. In this paper we approach this complexity inside the MAC layer. First, we propose that Packet and Resource Scheduling are two distinct tasks inside the medium access control layer of a wireless system. Due to the frequency selective channel and huge path loss ranges dynamic subcarrier assignment and adaptive power control are important. Proper resource scheduling also relies on accurate channel quality indication so there is a natural loop from base station to user terminal and back.

2011 Ninth Annual Communication Networks and Services Research Conference, 2011

As the increase of data traffic is expected to grow faster than wireless capacity, dealing with c... more As the increase of data traffic is expected to grow faster than wireless capacity, dealing with congestion is unavoidable in the future. The capacity imbalance between wired and wireless links leaves a bottleneck on the wireless link while traffic keeps coming in through the bigger pipe. In current systems, the dynamics of a wireless channel and the variations in the higher priority real time traffic both make full link utilization impossible. Either the buffers are full, giving a full link but resulting in packet losses in the queues or the link is underutilized.

ABSTRACT Increasing cellular traffic is the driving force for innovations in wireless communicati... more ABSTRACT Increasing cellular traffic is the driving force for innovations in wireless communications. While voice traffic is not expected to increase much and does not require 4G systems, traffic for video and data applications is expected to grow with a rate of 100% per year. Smart mobile devices, tablets and laptop dongles will certainly make this a reality. On the other hand the supply side cannot grow with the same rate. Base stations, eNB, pico- and femtocells will bring more heterogeneity in space and new applications will bring more heterogeneity in demand over time. Designing for over-provisioning capacity has been the standard approach to stabilize traffic, but is will be harder and harder, with more congestion situations in time (busy hour) and space (crowded cell) which will break application traffic and give bad quality-of-experience of users. Furthermore, over-provisioning comes with more power consumption and higher financial expenditures for infrastructure and operating costs. The user-in-the-loop (UIL) approach offers a solution orthogonal to the traditional supply-only view. In addition to technical improvements, having a temporal demand control can alleviate the severity of busy-hour situations which formerly caused congestion and connection failures. Demand shaping is implemented by a dynamic usage-based tariff and adaptive rates depending on the load condition. The users in a cell are part of a closed control loop which reacts in cases of severe demand overload. In this paper three different service classes are controlled individually and results from analysis and simulation show the performance in stationary and dynamic scenarios. The economics of tariffs and dynamic prices and the resulting operator revenue on one side is compared to the dissatisfaction of rejected users and this gives decision indicators for the investment into new infrastructure. Overall this saves money, energy and turns situations of hard congestion into an elastic stationarity whi- h is in the interest of both users and operators.

... Rainer Schoenen and Roman Hying Institute for Integrated Signal Processing Systems, Aachen Un... more ... Rainer Schoenen and Roman Hying Institute for Integrated Signal Processing Systems, Aachen University of Technology schoenen@ert.rwth-aachen.de, http ... 58.6% [4]. The Virtual Output Queueing (VOQ) can avoid blocking by bypassing cells destined for free output ports [15]. ...

Seamless Interconnection for Universal Services. Global Telecommunications Conference. GLOBECOM'99. (Cat. No.99CH37042), 2000

New generations of cellular radio systems are currently being developed based on OFDM transmissio... more New generations of cellular radio systems are currently being developed based on OFDM transmission with OFDMA as the multiple access scheme. The demand for high data rates in reasonably large areas is omnipresent, but the conventional cellular architecture offers does not only a maximum rate depending on the distance. Close to the base station, the higher received SIN R valueallows the highest Modulation&Coding scheme (PhyMode), which offers the highest data rate. In this paper we user the mutual information approach to calculate the maximum data rate based on the SIN R at all positions in an interference-limited radio cell.

ICC Workshops - 2008 IEEE International Conference on Communications Workshops, 2008

Broadband wireless access will be deployed in a cellular way with 3GPP-LTE [1]. For the first rol... more Broadband wireless access will be deployed in a cellular way with 3GPP-LTE [1]. For the first rollout the main demand is a huge area coverage. With only few available base station sites that are connected to an access fiber, multihop (relaying) techniques can be used well to fill the coverage gaps. Later with increasing offered traffic, the demand shifts to higher capacity over the area. Even for this purpose relays are beneficial. There is an area around relays where they provide better overall capacity to the user terminal, taking into account all resources used for the first and second hop (the relaying overhead). Relaying or Multihop operation therefore massively improves the coverage as well as the capacity goals at low cost, without the need of a cable or fiber access. This paper analyzes a realistic urban scenario on the island of Jersey. We study the coverage and capacity over the area in three cases. One base station (BS) only, one BS with four relay nodes (RNs), and the latter plus another ring of nine RNs. The BS has fiber access for rates beyond 100 Mbit/s, while the first hop of Relays (H1) is fed over the air from BS using shared resources in the same LTE band. The second hop H2 is fed by the relays of group H1. In this paper we provide the results from numeric analysis based on models we explain here. It is shown that huge gains in coverage and capacity are obtained by relaying.

2008 14th European Wireless Conference, 2008

Multihop techniques are known as a practical solution for covering huge radio cell areas when the... more Multihop techniques are known as a practical solution for covering huge radio cell areas when there are only very few base stations (BS). This is the case when fiber access is limited and BS CAPEX and OPEX are very expensive. For WiMAX and 3GPP-LTE it is possible to operate relay stations which are only fed over the air link. While having some inherent overhead due to increased radio resource usage, there are nevertheless impressive gains in the coverage compared to a BS alone and also in the capacity of the whole radio cell. Near relay nodes (RN) there is not only better SINR to the user, which is obvious, but it is often more efficient to associate to a RN instead of the BS, taking into account all resources used for the first and second hop. Therefore this is a low cost measure to increase the system efficiency. This has been shown in the literature for artificial scenarios so far.

2011 Australasian Telecommunication Networks and Applications Conference (ATNAC), 2011

2007 International Conference on Wireless Communications, Networking and Mobile Computing, 2007

Next generation cellular radio systems will exceed the limitations of UMTS. The convergence of da... more Next generation cellular radio systems will exceed the limitations of UMTS. The convergence of data and voice traffic will be supported by a flexible OFDM-based PHY layer and an OFDMA-capable MAC layer. The long term evolution (LTE) successor of the 3G systems incorporates this. But problems concerning coverage and capacity at the cell border still remain for the classical cellular layout. Relaying or Multihop operation is an option to massively improve the coverage as well as the capacity issue at low cost, without the need of a cable or fibre access. For the performance analysis of such cellular systems models for ISO-OSI layers 1+2 (PHY+MAC) are needed. In this paper an analytic modelling framework and results are presented for the cellular LTE performance in two multihop scenarios.

2014 IEEE Global Communications Conference, 2014

2013 IEEE 77th Vehicular Technology Conference (VTC Spring), 2013

Future cellular communications faces a number of challenges. One of the trends is the ever increa... more Future cellular communications faces a number of challenges. One of the trends is the ever increasing demand for data rate due to smart mobile devices and laptop dongles with an estimated traffic growth of almost 100% per annum. Even with new cellular generation cycles every few years the same increase rate cannot be provided on the supply side. Neither anywhere nor anytime. The gap between supply and demand of wireless capacity will shorten and the conventional over-provisioning approach will not be possible anymore, especially during busy hours. The consequences are more frequent congestion situations with broken application traffic. The quality-of-experience will suffer as user expectations are high and steamed-up by advertising. An inadequate tariff system concentrating on flat-rates is also counterproductive for stability and energy-efficiency.

2010 16th Asia-Pacific Conference on Communications (APCC), 2010

OFDMA has become the key technology for future cellular wireless networks like the IMT-Advanced s... more OFDMA has become the key technology for future cellular wireless networks like the IMT-Advanced systems IEEE 802.16m and 3GPP LTE-A. The advantage of allowing different modulation&coding schemes (PhyModes) adaptively for each radio resource is at the same time a new disadvantage because the performance is now distance-dependent from the base station (BS) and the total spectral efficiency depends on how user terminals (UTs) are provided with service opportunities. Instead of increasing the effort to support cell-edge users with high data rates this paper investigates the chances of letting the user participate in the process such that his mobility becomes utilitydriven, in a similar way the user behaves in 802.11 hotspot areas. The user's willingness to move to regions of higher SINR must be supported by a display of the current situation (and indications where to move) plus a utility model (lower cost or higher data rate) which motivates moving a distance monotonic in the utility value. By giving input to the user and utilizing the output of his behavior the user becomes a member of the control loop, in a system theoretic sense. The paper shows numeric results of common scenarios and compares the old and new paradigms.

2009 IEEE International Conference on Communications Workshops, 2009

Cellular radio systems of the next generation aim to make the most out of the available radio res... more Cellular radio systems of the next generation aim to make the most out of the available radio resources in the dimensions bandwidth, time and space. The division of time into slots, frames and superframes is standard, both for TDD and FDD duplex modes. OFDMA allows the individual disposition of subchannels as a subdivision of the bandwidth but an aggregation of subcarriers. A basic resource unit is hence a brick in this two-dimensional grid. Space is important both as the location of the base station in whose surrounding the resources are used and in spatial diversity channels. These resources are the scarce good in future radio communications, because they are required proportionally to the traffic demand per area. Due to adaptive modulation and coding schemes and large ranges of possible SINR values, the required resources for a transmission may differ by a factor ten depending on the distances. In this paper we discuss the resource allocation and scheduling mission. We introduce a control system view on the topic, taking adaptive algorithms for modulation, power, subchannel usage and channel quality indication into account.