P. Karlsson

University of Bristol, Bristol, ENG, United Kingdom

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Publications (55)17.04 Total impact

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    G.P. Koudouridis, P. Karlsson
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    ABSTRACT: In alignment to an "always best experience" scenario, we assess gains on user traffic in the context of a multi-radio access environment where heterogeneous radio technologies are integrated at link layer and users are jointly scheduled across multiple radio accesses (RAs). Such integration allows for an implementation of multi-radio transmission diversity (MRTD) which switches transmission of a user's data over the available RAs. The RA selection is based on measurements of radio link quality as reported by the radio interface. The application of an ARQ scheme utilising multiple RAs (MR-ARQ) in conjunction with MRTD provides added gains on user delay and neutralizes parts of degradations in spectral efficiency caused by reporting delays. Such multi-radio ARQ mechanism exploits the diversity across independent RAs, and results in gains in throughput over those achieved by RA-specific ARQ. MRTD when combined with MR-ARQ shows gains of up to 35% in spectral efficiency compared to the case where the radio accesses operate independently.
    Vehicular Technology Conference, 2007. VTC-2007 Fall. 2007 IEEE 66th; 11/2007
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    ABSTRACT: This paper outlines key aspects that operators need to consider when expanding their radio access infrastructure to get a cost efficient production of wireless services. Two promising expansion paths are analyzed with respect to the achievable area throughput for an urban scenario. The first is considering a cellular evolution based on high speed packet access (HSPA) with multiple input multiple output (MIMO) technology in macro base stations. The other is a multi radio access (multi-access) environment where a HSPA macrocell layer without MIMO is complemented with IEEE 802.11a wireless local area network (WLAN) access points. When accounting for the difference in total cost for complementary base stations, the cellular evolution supports a higher average area throughput in downlink for low and moderate hot spot densities. The advantage decreases with macro base station site density so for higher hot spot and macrocell site densities the multi-access system is more favourable. For uplink the multi-access network in general supports higher capacity thanks to that the cellular evolution is limited by penetration losses for indoor users. Thus, depending on how densely an existing macrocell network is deployed and the targeted capacity in downlink and uplink, different expansion paths would bring the lowest cost of infrastructure.
    Personal, Indoor and Mobile Radio Communications, 2007. PIMRC 2007. IEEE 18th International Symposium on; 10/2007
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    ABSTRACT: Ambient networks multi-radio access technology for efficient multi-operator multi-radio resource management can provide large advantages in terms of improved services to users, new business opportunities, and cost savings. This paper quantifies the potential infrastructure cost savings through a number of techno-economic infrastructure cost comparisons. The results indicate clear potential cost savings with integrated deployment in suburban and urban areas and additional cost savings with multi-operator cooperation when using the ambient networks multi-radio access technology
    Vehicular Technology Conference, 2006. VTC 2006-Spring. IEEE 63rd; 06/2006
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    ABSTRACT: Integration of heterogeneous access technologies to provide multi-radio access allows for dynamic access selection. The "always best connected" paradigm can increase system capacity and end user throughput, as well as, reduce the network deployment costs for multi-radio wireless networks. In this paper we present the functional entities generic link layer and multi-radio resource management, and describe their interactions for access selection. A focus of the paper is to show - with an example given for 3G and WLAN - how existing wireless networks can be migrated to provide multi-radio access functionality. This will be explained for a single operator integrating different radio access standards, as well as, for multiple cooperating network operators.
    Proceedings of the 64th IEEE Vehicular Technology Conference, VTC Fall 2006, 25-28 September 2006, Montréal, Québec, Canada; 01/2006
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    ABSTRACT: Future technologies for network co-operation, such as those proposed within the Ambient Networks (AN) project, will increase the openness of interfaces and open up new business opportunities for new players on the global market. This paper investigates in what way regulatory support and compensation schemes are needed to support new business models and value chains. Our view is that Ambient Network concept like network composition including advertising, dynamic roaming and compensation together with new interfaces will enable the de-coupling of business roles of the traditionally vertically integrated value chain. This contributes to increased competition since any user will "more easily" be able to use any service using "any" network.
    01/2006;
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    ABSTRACT: 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
    Proceedings of the 63rd IEEE Vehicular Technology Conference, VTC Spring 2006, 7-10 May 2006, Melbourne, Australia; 01/2006
  • R. Stridh, Kai Yu, B. Ottersten, P. Karlsson
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    ABSTRACT: Multiple transmitters and receivers can be used to provide high link capacity in future wireless systems. Herein, an analysis of indoor environment multiple-input-multiple-output (MIMO) measurements in the industrial, scientific, and medical (ISM) band at 5.8 GHz is performed and the possible increase in capacity, utilizing multiple transmitters and receivers is examined. The investigation shows that in the measured indoor environment, the scattering is sufficiently rich to provide substantial link capacity increases. Furthermore, the effect of intra-element spacing on the channel capacity is studied. Our investigation also shows that the envelope of the channel coefficients for this obstructed-line-of-sight (OLOS) indoor scenario is approximately Rayleigh distributed and the MIMO channel covariance matrix can be well approximated by a Kronecker product of the covariance matrices describing the correlation at the transmitter side and the receiver side, respectively. A statistical narrowband model for the OLOS indoor MIMO channel based on this covariance structure is presented.
    IEEE Transactions on Wireless Communications 06/2005; · 2.42 Impact Factor
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    ABSTRACT: A simple method for estimating the costs of building and operating a cellular mobile network is proposed. Using the empirical data from a third generation mobile system (WCDMA), it is shown that the cost is driven by different factors depending on the characteristics of the base stations deployed. When the site density increased, the operational and transmission costs tend to dominate rather than the radio equipment and site costs. The results also show how, for different capacity requirements, the costs can be minimized by a proper selection of macro, micro and pico base stations. In many scenarios, the macro base stations yield the lowest cost, indicating that the coverage (cell range) is an important parameter when designing wireless systems.
    Personal, Indoor and Mobile Radio Communications, 2004. PIMRC 2004. 15th IEEE International Symposium on; 10/2004
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    ABSTRACT: At present, wireless local area networks (WLANs) such as HiperLAN2 and 802.11a are being developed and deployed around the world. In this letter, the use of sectorized antennas is considered as a means to improve the physical layer performance of WLANs. Results demonstrate that throughput and range can be enhanced and/or the transmit power can be reduced. However, these benefits are achieved with a small increase in multiple access protocol overhead. Simulations are performed using measured wideband channels in the 5-GHz band. In cases where the channel exhibits strong Rician characteristics, gains as high as 13 dB are demonstrated. These benefits substantially outweigh the associated medium access control overhead.
    IEEE Transactions on Wireless Communications 10/2004; · 2.42 Impact Factor
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    ABSTRACT: The most prominent problem in providing anywhere, anytime wideband mobile access is the towering infrastructure cost as it is basically proportional to the bandwidth provided. We provide a simple, initial, analysis of the various infrastructure cost factors. This analysis shows that, contrary to what one may expect, the infrastructure cost is not dominated by electronic equipment, but rather by other deployment related costs (towers, wiring, building, network connections) and maintenance costs. In the paper some novel architectural approaches for future wideband mobile access focusing on these dominant cost factors are described and the related key research issues are discussed.
    Vehicular Technology Conference, 2004. VTC 2004-Spring. 2004 IEEE 59th; 06/2004
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    ABSTRACT: In this paper, we first verify a previously proposed Kronecker-structure-based narrow-band model for nonline-of-sight (NLoS) indoor multiple-input-multiple-output (MIMO) radio channels based on 5.2-GHz indoor MIMO channel measurements. It is observed that, for the narrow-band case, the measured channel coefficients are complex Gaussian distributed and, consequently, we focus on a statistical description using the first- and second-order moments of MIMO radio channels. It is shown that the MIMO channel covariance matrix can be well approximated by the Kronecker product of the covariance matrices, seen from the transmitter and receiver, respectively. A narrow-band model for NLoS indoor MIMO channels is thus verified by these results. As for the wide-band case, it is observed that the average power-delay profile of each element of the channel impulse response matrix fits the exponential decay curve and that the Kronecker structure of the second-order moments can be extended to each channel tap. A wide-band MIMO channel model is then proposed, combining a simple COST 259 single-input-single-output channel model and the Kronecker structure. Monte Carlo simulations are used to generate indoor MIMO channel realizations according to the models discussed. The results are compared with the measured data using the channel capacity and good agreement is found.
    IEEE Transactions on Vehicular Technology 06/2004; · 2.06 Impact Factor
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    M. Beach, B. Allen, P. Karlsson
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    ABSTRACT: This paper introduces a novel metric for determining the spatial decorrelation between the up- and down-link wireless bearers in frequency division duplex (FDD) networks. This metric has direct relevance to smart or adaptive antenna array base-station deployments in cellular networks, which are known to offer capacity enhancement when compared to fixed coverage solutions. In particular, the results presented were obtained from field trial measurement campaigns for both urban and rural scenarios, with the observations having a direct impact on the choice of down-link beamforming architecture in FDD applications. Further, it is shown that significant spatial decorrelation can occur in urban deployments for bearer separations as small as 5 MHz. Results are presented in terms of both instantaneous characteristics as well as time averaged estimates, thus facilitating the appraisal of smart antenna solutions in both packet and circuit switched networks.
    IEEE Transactions on Antennas and Propagation 02/2004; · 2.33 Impact Factor
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    ABSTRACT: In multiple-input multiple-output (MIMO) systems the horizontal orientation of a linear array has, in some situations a large influence on the available channel capacity. In this paper, we investigate the effect of horizontal array orientation on channel capacity, eigenvalue distribution and antenna complex correlation coefficient in such systems. We present channel measurements in an office corridor environment for a 6×6 MIMO system and compare the capacity results to those of a physical and non-physical model based on the measurements. The results show that under LOS conditions the channel capacity can vary significantly depending on the receiver array orientation in the horizontal plane.
    Vehicular Technology Conference, 2003. VTC 2003-Spring. The 57th IEEE Semiannual; 05/2003
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    ABSTRACT: In this paper, we present results of 5.2 GHz wideband indoor multiple input multiple output (MIMO) channel measurements under the EU IST SATURN project . First we show the average power delay profile for the single input single output (SISO) channel. Furthermore, our investigation shows that for non-line-of-sight (NLOS) indoor scenarios, the MIMO channel covariance matrix of each normalized tap of channel impulse response can be be well approximated by the Kronecker product of the covariance matrices seen from the transmitter and receiver respectively. Based on the above results, a wideband statistical model for HiperLAN/2 MIMO channel is presented. Monte-Carlo simulations show reasonably good agreement between the measured data and our model. Finally, we use this model to show the capacity characteristics of the HiperLAN/2 channel in NLOS indoor scenarios.
    12/2002;
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    ABSTRACT: Smart antennas promise to provide range extension and capacity enhancements crucial to the successful deployment of Universal Mobile Telecommunications System (UMTS) networks. The frequency offset between the uplink and downlink in the frequency division duplex (FDD) air interface gives rise to a frequency dependency in the channel responses and potential problems in downlink beamforming. In order to investigate this, a highly novel dual-band, dual-polarised channel sounding trial was performed in the UMTS FDD bands by the University of Bristol. The wideband measurements were conducted in the City of Bristol, encompassing urban city and sub-urban residential scenarios and subsequent post processing was performed to extract channel parameters across the two bands. This paper presents the results and analysis done for the single polarisation static measurements. It was observed that in most instances, there was a higher degree of scattering in the higher frequency band, resulting in larger angular spreads and delay spreads. The channels also exhibited a strong degree of de-correlation when viewed from the spatial and temporal domains.
    3G Mobile Communication Technologies, 2002. Third International Conference on (Conf. Publ. No. 489); 06/2002
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    Ralf E. Schuh, Peter Eneroth, Peter Karlsson
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    ABSTRACT: This paper presents an investigation of a radio receiver architecture to enable multi-standard (GPRS, WCDMA, HiperLAN2) implementation in mobile terminals. The architecture uses partial radio band digitisation at an intermediate frequency. Following circuit progress and industry trends (e.g. Moore's law) we estimate components for the proposed architecture with acceptable power consumption to be available within the next 5 years.
    06/2002;
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    ABSTRACT: At present, WLANs supporting broadband multimedia communication are being developed and standardized around the world. Standards include HIPERLAN/2, defined by ETSI BRAN, 802.11a, defined by the IEEE, and HiSWANa defined by MMAC. These systems provide channel adaptive data rates up to 54 Mb/s (in a 20 MHz channel spacing) in the 5 GHz radio band. An overview of the HIPERLAN/2 and 802.11a standards is presented together with software simulated physical layer performance results for each of the defined transmission modes. Furthermore, the differences between these two standards are highlighted (packet size, upper protocol layers etc.), and the effects of these differences on throughput are analyzed and discussed
    IEEE Communications Magazine 06/2002; · 3.66 Impact Factor
  • B. Allen, M. Beach, P. Karlsson
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    ABSTRACT: The outage occurring from beamformer-based smart antennas is analysed for an antenna array deployed in an urban macro-cell environment. Spatio-temporal channel data obtained from a small, urban cell and from within the UTRA frequency allocation has enabled beamforming performance to be determined from the measured uplink and downlink frequency bands. The analysis shows a sub-optimum uplink beamformer performance is observed for 8% of occasions and a 25% downlink beamforming outage for an eight-element uniformly spaced linear array
    Electronics Letters 02/2002; · 1.04 Impact Factor
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    ABSTRACT: Downlink beamforming in a WLAN-type system employing access points and mobiles equipped with multiple antennas and associated receivers and transmitters are considered. The beamforming aims at maximizing the performance under constraints on transmit power or equivalent isotropic radiated power (EIRP). Solutions for the two constraints are derived and investigated using simulated and measured channels. Our simulation and experimental results shows that performance gains of 8-10 dB when using four directional transmitter antennas and two receive antennas (as compared with a base-line one-transmit two-receive), are possible under both constraints. For simulated channels, a delay between channel estimation and use of the same channel of up to 10% of the (inverse of the) Doppler frequency only degrades performance some tenths of a dB. In our measurements, very small degradations are seen with delays of up to 130 ms. The measurements were made under relatively stationary conditions with only occasionally moving people. Two different strategies for updating the beamforming vectors: sounding and ping-pong, are also considered in the paper.
    Vehicular Technology Conference, 2002. VTC Spring 2002. IEEE 55th; 02/2002
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    ABSTRACT: Herein, results of 5.2 GHz wideband indoor multiple input multiple output (MIMO) channel measurements under the EU IST SATURN project are reported. Our investigation shows that for non-line-of-sight (NLOS) cases, the average power delay profiles fit the exponentially decaying curve quite well, therefore a simple wideband model for single-input single-output (SISO) proposed in COST259 has been used in our model. Furthermore, the investigations show that the MIMO channel covariance matrix of each normalized tap of the impulse response could be well approximated by the Kronecker product of the covariance matrices seen from the transmitter and receiver respectively. Based on the above results, a wideband statistical model is presented. Monte-Carlo simulations show reasonably good agreement between the measured data and our model. Finally, we use this model to show some capacity characteristics of Hiper-LAN/2 channels in NLOS indoor scenarios.
    Vehicular Technology Conference, 2002. VTC Spring 2002. IEEE 55th; 02/2002