V. Hassel

Norwegian University of Science and Technology, Trondheim, Sor-Trondelag Fylke, Norway

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Publications (12)4.84 Total impact

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    ABSTRACT: Offering throughput guarantees for cellular wireless networks, carrying real-time traffic, is of interest to both the network operators and the customers. In this article, we formulate an optimization problem which aims at maximizing the throughput that can be guaranteed to the mobile users. By building on results obtained by Borst and Whiting and by assuming that the distributions of the users' carrier-to-noise ratios are known, we find the solution to this problem for users with different channel quality distributions, for both the scenario where all the users have the same throughput guarantees, and the scenario where all the users have different throughput guarantees. Based on these solutions, we also propose two simple and low complexity adaptive scheduling algorithms that perform significantly better than other well-known scheduling algorithms. We further develop an expression for the approximate throughput guarantee violation probability for users in time-slotted networks with the given cumulants of the distribution of bit-rate in a time-slot, and a given distribution for the number of time-slots allocated within a time-window.
    Eurasip Journal on Wireless Communications and Networking - EURASIP J WIREL COMMUN NETW. 01/2011; 2011(1).
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    V. Hassel, G.E. Oien, D. Gesbert
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    ABSTRACT: In this letter we develop an expression for the approximate throughput guarantee violation probability (TGVP) for users in time-slotted networks for any scheduling algorithm with a given mean and variance of the bit-rate in a time-slot, and a given distribution for the number of time-slots allocated within a time-window. Based on this general result, we evaluate closed-form expressions for the TGVPs for four well-known scheduling algorithms. Through simulations we also show that our TGVP approximation is tight for a realistic network with moving users with correlated channels and realistic throughput guarantees.
    IEEE Transactions on Wireless Communications 01/2008; · 2.42 Impact Factor
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    ABSTRACT: For cellular wireless networks carrying real-time traffic, it is in the interest of both network operators and customers that throughput guarantees can be offered. In this paper, we formulate an optimization problem which aims at maximizing the throughput that can be guaranteed to the mobile users. By building on results obtained by Borst and Whiting and by assuming that the distributions of the users' carrier-to-noise ratios are known, we find the solution to this problem for users with different channel quality distributions, both for the scenario where all the users have the same throughput guarantee, and for the scenario where all the users have different throughput guarantees. Based on these solutions, we propose an adaptive scheduling algorithm that performs significantly better than other well-known scheduling algorithms.
    Wireless Communication Systems, 2007. ISWCS 2007. 4th International Symposium on; 11/2007
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    ABSTRACT: In this paper we propose a channel state feedback algorithm that uses multiple feedback thresholds to reduce the number of users transmitting feedback to a minimum. The users are polled with lower and lower threshold values and only the users that are above a threshold value transmit feedback to the base station. We show how this feedback algorithm can be used for any scheduling algorithm and show how closed-form expressions for the optimal threshold values can be obtained for two well-known scheduling algorithms. Finally, we propose a two-step optimization procedure for optimizing the feedback algorithm for real-life cellular standards.
    IEEE Transactions on Wireless Communications 08/2007; · 2.42 Impact Factor
  • V. Hassel, G.E. Oien, D. Gesbert
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    ABSTRACT: In this paper we analyze achievable throughput guarantees in wireless time-division multiplexing (TDM) networks. Approximations of the throughput guarantee violation probability (TGVP) for users communicating in time-slotted systems are obtained for any scheduling algorithm with a given mean and variance of the number of bits transmitted in a time- slot and a distribution for the number of time-slots allocated to a user within a time-window. We investigate the corresponding TGVPs for three scheduling algorithms, namely (i) Round Robin Scheduling, (ii) Maximum Carrier-to-Noise Ratio Scheduling, and (iii) Opportunistic Round Robin Scheduling, when the users' channels are independently and identically distributed.
    Global Telecommunications Conference, 2006. GLOBECOM '06. IEEE; 01/2007
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    V. Hassel, G.E. Oien, D. Gesbert
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    ABSTRACT: In this paper we analyze achievable throughput guarantees for different opportunistic scheduling algorithms operating in wireless time-division multiplexing networks. We consider a scenario where the average carrier-to-noise ratios of the users' channels are different from user to user. An approximation of the throughput guarantee violation probability for users communicating in time-slotted systems are obtained for any scheduling algorithm with a given mean and variance of the number of bits transmitted in a time-slot, and a given distribution for the number of time-slots allocated to a user within a time window. We investigate the corresponding throughput guarantees for three different scheduling algorithms: (i) Maximum Carrier- to-Noise Ratio Scheduling, (ii) Normalized Carrier-to-Noise Ratio Scheduling, and (iii) Opportunistic Round Robin Scheduling.
    Telecommunications Symposium, 2006 International; 10/2006
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    V. Hassel, M.R. Hanssen, G.E. Oien
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    ABSTRACT: In this paper we analyze the Opportunistic Round Robin (ORR) scheduling algorithm [1], [2]. This algorithm is able to exploit multiuser diversity (MUD) and at the same time provide short-term fairness between the users in a wireless cellular network. We analyze the spectral efficiency and the fairness for two scenarios. In the first scenario all the users have the same average carrier-to-noise ratios (CNR) and for the second scenario the users have different average CNRs. For the first scenario the absolute MUD is exploited while we exploit the so-called relative MUD between the users for the second scenario. The advantages and disadvantages of the different ORR implementations are highlighted by analyzing plots of our closed-form expressions.
    Communications, 2006. ICC '06. IEEE International Conference on; 07/2006
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    ABSTRACT: In this paper we propose a multiuser scheduling al- gorithm that has the maximum average system spectral efficiency, but obtains a significant reduction in feedback load compared to full feedback by using a feedback threshold. An expression for the threshold value that minimizes the feedback load has been found. Another novel result shows that when using M - ary quadrature amplitude modulation, the spectral efficiency will increase significantly by using power adaptation. The impact of scheduling delay and outdated channel estimates is also analyzed.
    01/2006;
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    H. Koubaa, V. Hassel, G.E. Ien
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    ABSTRACT: Not Available
    Vehicular Technology Conference, 2005. VTC-2005-Fall. 2005 IEEE 62nd; 10/2005
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    H. Koubaa, V. Hassel, G.E. Oien
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    ABSTRACT: Multiuser diversity (MUD) underlies much of the recent work on scheduling design in wireless networks. This form of diversity can be exploited by choosing the receiver with the best quality in order to obtain a higher system spectral efficiency. In systems having MUD based scheduling algorithms the sender will query receivers for their channel conditions. The process of obtaining channel state information will be performed within a guard time. The length of the guard time will depend on what feedback mechanism is implemented. In this context, it has already been shown that the number of users giving feedback can be significantly decreased by applying multiple carrier-to-noise ratio thresholds. However, publications on MUD have not yet taken into account guard time reduction and possibility for contention between users that want to feed back channel state information. In this paper we reduce the guard time and resolve the feedback contention problem by proposing two different solutions: (i) a ranked feedback algorithm and (ii) a tailored version of the exponential backoff algorithm. Closed-form expressions are found for the guard time duration and the spectral efficiency for both feedback schemes. Plots show that the ranked protocol yields a better performance than the exponential backoff protocol when we have a small number of thresholds and long packet duration.
    Signal Processing Advances in Wireless Communications, 2005 IEEE 6th Workshop on; 07/2005
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    ABSTRACT: This paper describes a novel scheduling algorithm that takes advantage of multiuser diversity to obtain the maximum system spectral efficiency and uses multiple feedback thresholds to reduce the feedback load to a minimum. In this scenario the relevant users are probed with a set of carrier-to-noise ratio (CNR) thresholds. The users are first probed with the highest threshold. If none of the users are above this threshold the threshold value is sequentially lowered until one or more users are found. A closed-form expression for the average, normalized feedback load (NFL) is found. It can be argued that it is wise to minimize this average NFL to minimize the guard time needed for the feedback process. Consequently, the optimal CNR thresholds which minimize the average NFL are found. We also develop closed-form expressions for the overall capacity using quantized feedback. Plots show that the number of transmitted symbols between feedback queries has great impact on the overall capacity and that one bit feedback is optimal in all cases. The scheduling outage probability has also been analyzed, and the results show that the scheduling outage probability increases dramatically when a scheduling deadline is exceeded.
    Vehicular Technology Conference, 2005. VTC 2005-Spring. 2005 IEEE 61st; 01/2005
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    Vegard Hassel, Hend Koubaa, Geir E Øien