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Sternad, Mikael
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Publications (10 of 79) Show all publications
Apelfröjd, R., Zirwas, W. & Sternad, M. (2019). Low-Overhead Cyclic Reference Signals for Channel Estimation in FDD Massive MIMO. IEEE Transactions on Communications, 67(5), 3279-3291
Open this publication in new window or tab >>Low-Overhead Cyclic Reference Signals for Channel Estimation in FDD Massive MIMO
2019 (English)In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 67, no 5, p. 3279-3291Article in journal (Refereed) Published
Abstract [en]

Massive multiple input multiple output (MIMO) transmission and coordinated multipoint transmission are candidate technologies for increasing data throughput in evolving 5G standards. Frequency division duplex (FDD) is likely to remain predominant in large parts of the spectrum below 6 GHz for future 5G systems. Therefore, it is important to estimate the downlink FDD channels from a very large number of antennas, while avoiding an excessive downlink reference signal overhead. We here propose and investigate a three part solution. First, massive MIMO downlinks use a fixed grid of beams. For each user, only a subset of beams will then be relevant, and require estimation. Second, sets of coded reference signal sequences, with cyclic patterns over time, are used. Third, each terminal estimates its most relevant channels. We here propose and compare a linear mean square estimation and a Kalman estimation. Both utilize frequency and antenna correlation, and the later also utilizes temporal correlation. In extensive simulations, this scheme provides channel estimates that lead to an insignificant beamforming performance degradation as compared to full channel knowledge. The cyclic pattern of coded reference signals is found to be important for reliable channel estimation, without having to adjust the reference signals to specific users.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2019
Keywords
Radio channel estimation, frequency division duplex, antenna arrays
National Category
Signal Processing Telecommunications Communication Systems
Identifiers
urn:nbn:se:uu:diva-386180 (URN)10.1109/TCOMM.2019.2895059 (DOI)000468228900014 ()
Available from: 2019-06-19 Created: 2019-06-19 Last updated: 2019-06-19Bibliographically approved
Phan Huy, D.-T., Wesemann, S., Björsell, J. & Sternad, M. (2018). Adaptive massive MIMO for fast moving connected vehicles: It will work with predictor antennas!. In: : . Paper presented at 22nd International ITG Workshop on Smart Antennas (WSA 2018), Bochum, Tyskland.
Open this publication in new window or tab >>Adaptive massive MIMO for fast moving connected vehicles: It will work with predictor antennas!
2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Predicting the channel between a massive multiple input multiple output antenna and a car is a challenge, due to the short-term fading. It becomes essentially impossible by conventional extrapolation from past estimates if the car has moved by half a wavelength or more in space at the time when the channel estimate will be needed. This problem would prevent us from using the best fifth generation adaptive antenna downlink precoding schemes for very fast moving connected vehicles. A potential solution is to add another vehicle antenna, a "predictor antenna", which senses the channel in advance. In this paper, based on drive tests and channel measurements from a 64- element antenna to a car, we for the first time show that this concept works for massive MIMO downlinks. Thanks to the use of a predictor antenna, the complex OFDM downlink channels can be predicted with an accuracy that enables maximum ratio transmit beamforming with close to ideal beamforming gain for non-line-of-sight channels. Zero forcing transmission to two users results in a signal-to-interference ratio of 20 dB to 30 dB when predicting non-line-of-sight channels up to three wavelengths ahead in space. These first experiment shows that the predictor antenna concept is a potential solution to make fifth generation adaptive antennas work for very fast moving connected vehicles.

National Category
Signal Processing
Identifiers
urn:nbn:se:uu:diva-363241 (URN)
Conference
22nd International ITG Workshop on Smart Antennas (WSA 2018), Bochum, Tyskland
Available from: 2018-10-15 Created: 2018-10-15 Last updated: 2019-01-03Bibliographically approved
Apelfröjd, R., Björsell, J., Sternad, M. & Phan Huy, D.-T. (2018). Kalman smoothing for irregular pilot patterns: A case study for predictor antennas in TDD systems. In: 2018 IEEE 29th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC): . Paper presented at 29th IEEE Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC'18), SEP 09-12, 2018, Bologna, Italien.
Open this publication in new window or tab >>Kalman smoothing for irregular pilot patterns: A case study for predictor antennas in TDD systems
2018 (English)In: 2018 IEEE 29th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), 2018Conference paper, Published paper (Refereed)
Abstract [en]

For future large-scale multi-antenna systems, channel orthogonal downlink pilots are not feasible due to extensive overhead requirements. Instead, channel reciprocity can be utilized in time division duplex (TDD) systems so that the downlink channel estimates can be based on pilots transmitted during the uplink. User mobility affects the reciprocity and makes the channel state information outdated for high velocities and/or long downlink subframe durations. Channel extrapolation, e.g. through Kalman prediction, can reduce the problem but is also limited by high velocities and long downlink subframes. An alternative solution has been proposed where channel predictions are made with the help of an extra antenna, e.g. on the roof of a car, so called predictor antenna, with the primary objective to measure the channel at a position that is later encountered by the rearward antenna(s). The predictor antenna is not directly limited by high velocities and allows the channel in the downlinks to be interpolated rather than extrapolated. One remaining challenge here is to obtain a good interpolation of the uplink channel estimate, since a sequence of uplink reference signals (pilots) will be interrupted by downlink subframes. We here evaluate a Kalman smoothing estimate of the downlink channels and compare it to a cubic spline interpolation. These results are also compared to results where uplink channels are estimated through Kalman filters and predictors. Results are based on measured channels and show that with Kalman smoothing, predictor antennas can enable accurate channel estimates for a longer downlink period at vehicular velocities. The gaps in the uplink pilot stream, due to downlink subframes, can have durations that correspond to a vehicle movement of up to 0.75 carrier wavelengths in space, for Rayleigh-like non-line-of-sight fading.

National Category
Telecommunications
Identifiers
urn:nbn:se:uu:diva-371938 (URN)10.1109/PIMRC.2018.8581030 (DOI)000457761900206 ()978-1-5386-6009-6 (ISBN)
Conference
29th IEEE Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC'18), SEP 09-12, 2018, Bologna, Italien
Note

Received a PIMRC2018 Best Paper Award

Available from: 2019-01-03 Created: 2019-01-03 Last updated: 2019-02-27Bibliographically approved
Zirwas, W., Sternad, M. & Apelfröjd, R. (2017). Key solutions for a massive MIMO FDD system. In: 2017 IEEE 28TH ANNUAL INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR, AND MOBILE RADIO COMMUNICATIONS (PIMRC): . Paper presented at IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), OCT 08-13, 2017, Montreal, Kanada. IEEE
Open this publication in new window or tab >>Key solutions for a massive MIMO FDD system
2017 (English)In: 2017 IEEE 28TH ANNUAL INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR, AND MOBILE RADIO COMMUNICATIONS (PIMRC), IEEE, 2017Conference paper, Published paper (Refereed)
Abstract [en]

The ongoing standardization within 3GPP for the so called new radio (NR) system has identified massive multiple-input multiple output (MIMO) transmission, also called full dimension MIMO, as one of the main contributors to higher spectral efficiency for the mobile broadband case. In particular for radio frequencies below 6 GHz, channel estimation has to be supported in frequency division duplex (FDD) as well as time division duplex (TDD) operation. In TDD we may obtain downlink channels by estimating uplink channels, assuming reciprocity. For FDD, codebook based design as well as some type of explicit feedback is under discussion. Separately, there are also ongoing discussions of the question if massive MIMO in combination with FDD is a reasonable choice at all. Here we highlight some of our recent results obtained within several 5G research projects. To our understanding they overcome some of the inherent limitations of massive MIMO for FDD. As indicated by simulations, the resulting concept enables a grid of beam (GoB) and reference signal design with a reasonable downlink reference signal overhead of around 10 percent, together with reasonable feedback overhead of several hundred kbit/s per UE. Such a design attains around 90 percent of the massive MIMO system performance with ideal channel state information.

Place, publisher, year, edition, pages
IEEE, 2017
National Category
Signal Processing
Identifiers
urn:nbn:se:uu:diva-330698 (URN)10.1109/PIMRC.2017.8292395 (DOI)000426970901083 ()978-1-5386-3531-5 (ISBN)
Conference
IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), OCT 08-13, 2017, Montreal, Kanada
Funder
EU, European Research Council, ICT-671660
Available from: 2017-10-03 Created: 2017-10-03 Last updated: 2018-08-09Bibliographically approved
Björsell, J., Sternad, M. & Grieger, M. (2017). Predictor antennas in action. In: 2017 IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC): . Paper presented at IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), 8-13 Oct. 2017, Montreal, Kanada. IEEE
Open this publication in new window or tab >>Predictor antennas in action
2017 (English)In: 2017 IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), IEEE, 2017Conference paper, Published paper (Refereed)
Abstract [en]

Connected vehicles in large numbers will be expensive in terms of power and bandwidth unless advanced transmit schemes are employed. These would rely on channel state information at transmitter (CSIT), which rapidly becomes outdated for fading vehicular channels. We here evaluate the predictor antenna concept, that solves this problem by using antennas on the outside of vehicles, with one extra antenna in front of the others. Its estimated channel is a scaled prediction for the channels encountered by rearward antennas when they reach that position. We evaluate this concept on a large set of channel sounding measurements from an urban environment. Recent investigations of the correlations of these measurements indicate that the average normalized mean squared errors (NMSEs) of the complex valued channel predictions should be around -10 dB for prediction horizons in space of up to 3 wavelengths. This represents an extension of the attainable prediction horizon by an order of magnitude, as compared to Kalman or Wiener extrapolation of past channel measurements. It represents an accuracy that would enable e.g. accurate massive multiple input multiple output (MIMO) downlink beamforming to vehicles. We here perform predictions on a subset of the measurements with good channel-to-estimation error power ratio (SNR). The approximate true channels are here available and we evaluate the performance on a validation data set. The results confirm that the distribution of the NMSE, over all investigated propagation environments, is close to that obtained by correlation-based models and outperforms the use of outdated channel measurements.

Place, publisher, year, edition, pages
IEEE, 2017
National Category
Signal Processing
Identifiers
urn:nbn:se:uu:diva-330699 (URN)10.1109/PIMRC.2017.8292235 (DOI)000426970900072 ()978-1-5386-3531-5 (ISBN)
Conference
IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), 8-13 Oct. 2017, Montreal, Kanada
Available from: 2017-10-03 Created: 2017-10-03 Last updated: 2018-08-10Bibliographically approved
Björsell, J., Sternad, M. & Grieger, M. (2017). Using predictor antennas for the prediction of small-scale fading provides an order-of-magnitude improvement of prediction horizons. In: : . Paper presented at IEEE International Conference on Communications, ICC, Workshop WDN-5G, Paris, Frankrike.
Open this publication in new window or tab >>Using predictor antennas for the prediction of small-scale fading provides an order-of-magnitude improvement of prediction horizons
2017 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Our aim is to investigate long range predictions (up to several wavelengths) of the small-scale fading of radio channels. The purpose is to enable advanced 5G downlink transmission schemes that require accurate channel state information at transmitters, such as massive MIMO and coherent joint transmission, for vehicular users. We here present a proof of concept for the recently introduced predictor antenna scheme which promises a significant increase in prediction horizon compared to conventional techniques. Predictor antennas utilize the exterior of moving vehicles by placing antenna arrays on top of their roofs. They are used to estimate the fading radio channels that are encountered later by the following antennas. The level of predictability is determined by the correlation between the channel measured at the predictor antenna and the channel that is later encountered by the following antennas when they move to that position. That correlation, and the resulting prediction errors, are assessed on a large set of measurement data sampled at vehicular velocities, at a carrier frequency of 2.53 GHz, from a multitude of urban fading environments. These represent a wide variety of propagation environments, including narrow and wide roads, intersections, dense urban environments and residential areas. Using low-pass filtered predictor antenna measurements, the obtained average prediction Normalized Mean Squared Error (NMSE) is -11 dB for prediction horizons of 0.25 wavelengths and -8.5 dB for horizons of 3 wavelengths. This represents an order of magnitude increase of the prediction horizons as compared to time-series prediction that typically, in practice, fails to work for prediction beyond 0.3 wavelengths in space. As a result, we have a tool that enables advanced 5G transmit schemes for vehicular users and vehicle-to-infrastructure links.

National Category
Telecommunications
Identifiers
urn:nbn:se:uu:diva-330704 (URN)000464321500010 ()978-1-5090-1525-2 (ISBN)
Conference
IEEE International Conference on Communications, ICC, Workshop WDN-5G, Paris, Frankrike
Available from: 2017-10-03 Created: 2017-10-03 Last updated: 2019-08-22Bibliographically approved
Phan-Huy, D.-T., Sternad, M., Svensson, T., Zirwas, W., Villeforceix, B., Karim, F. & El-Ayoubi, S.-E. -. (2016). 5G on Board: How Many Antennas Do We Need on Connected Cars?. In: 2016 IEEE GLOBECOM WORKSHOPS (GC WKSHPS): . Paper presented at IEEE-Communications-Society Global Communications Conference (IEEE GLOBECOM), DEC 04-08, 2016, Washington, DC. New York: IEEE
Open this publication in new window or tab >>5G on Board: How Many Antennas Do We Need on Connected Cars?
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2016 (English)In: 2016 IEEE GLOBECOM WORKSHOPS (GC WKSHPS), New York: IEEE, 2016Conference paper, Published paper (Refereed)
Abstract [en]

Mobile networks will support increasing numbers of connected vehicles. Successive generations of mobile networks have reduced the cost of data rate, in terms of spectrum usage and power consumption at the base station, by increasingly exploiting the concept of channel state information at the transmitter. Unfortunately, beyond a limiting velocity (which depends on the carrier frequency), networks are no longer cost efficient, since such information is not usable. Recently, channel prediction techniques requiring several antennas on the car roof have been introduced to solve this problem. In this paper, for the first time, we determine the most cost efficient configurations, in terms of numbers of antennas on the car roof and carrier frequency, in various scenarios (highway and dense urban). Our studies show that with a simple prediction technique based on predictor antennas, the network can use twice less spectrum and around 20 dB less power, for cars with 3 antennas on their tops than for cars with the same number of antennas and not using prediction.

Place, publisher, year, edition, pages
New York: IEEE, 2016
Series
IEEE Globecom Workshops, ISSN 2166-0069
Keywords
5G, connected cars, predictor antenna, MIMO
National Category
Telecommunications
Identifiers
urn:nbn:se:uu:diva-332913 (URN)10.1109/GLOCOMW.2016.7848799 (DOI)000401921400002 ()978-1-5090-2482-7 (ISBN)
Conference
IEEE-Communications-Society Global Communications Conference (IEEE GLOBECOM), DEC 04-08, 2016, Washington, DC
Available from: 2017-11-03 Created: 2017-11-03 Last updated: 2018-11-08Bibliographically approved
Phan-Huy, D.-T., Svensson, T., Sternad, M., Zirwas, W., Villeforceix, B., Karim, F. & Sayrac, B. (2015). Connected vehicles that use channel prediction will fully take advantage of 5G. In: : . Paper presented at 22nd ITS World Congress, Bordeaux, Frankrike, 5-9 Oktober.
Open this publication in new window or tab >>Connected vehicles that use channel prediction will fully take advantage of 5G
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2015 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Research subject
Electrical Engineering with specialization in Signal Processing
Identifiers
urn:nbn:se:uu:diva-267315 (URN)
Conference
22nd ITS World Congress, Bordeaux, Frankrike, 5-9 Oktober
Available from: 2015-11-20 Created: 2015-11-20 Last updated: 2015-11-20
Brännmark, L.-J. & Sternad, M. (2015). Controlling the impulse responses and the spatial variability in digital loudspeaker-room correction. In: : . Paper presented at 2015 International Symposium on ELectroAcoustic Technologies (ISEAT), Shenzhen, Kina, november.
Open this publication in new window or tab >>Controlling the impulse responses and the spatial variability in digital loudspeaker-room correction
2015 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Research subject
Electrical Engineering with specialization in Signal Processing
Identifiers
urn:nbn:se:uu:diva-267314 (URN)
Conference
2015 International Symposium on ELectroAcoustic Technologies (ISEAT), Shenzhen, Kina, november
Available from: 2015-11-20 Created: 2015-11-20 Last updated: 2015-11-20
Phan-Huy, D.-T., Sternad, M. & Svensson, T. (2015). Making 5G Adaptive Antennas Work for Very Fast Moving Vehicles. IEEE Intelligent Transportation Systems Magazine, 7(2), 71-84
Open this publication in new window or tab >>Making 5G Adaptive Antennas Work for Very Fast Moving Vehicles
2015 (English)In: IEEE Intelligent Transportation Systems Magazine, ISSN 1939-1390, Vol. 7, no 2, p. 71-84Article in journal (Refereed) Published
Abstract [en]

Wireless systems increasingly rely on the accurate knowledge at the transmitter side of the transmitter-to-receiver propagation channel, to optimize the transmission adaptively. Some candidate techniques for 5th generation networks need the channel knowledge for tens of antennas to perform adaptive beamforming from the base station towards the mobile terminal. These techniques reduce the radiated power and the energy consumption of the base station. Unfortunately, they fail to deliver the targeted quality of service to fast moving terminals such as connected vehicles. Indeed, due to the movement of the vehicle during the delay between channel estimation and data transmission, the channel estimate is outdated. In this paper, we propose three new schemes that exploit the "Predictor Antenna" concept. This recent concept is based on the observation that the position occupied by one antenna at the front of the vehicle, will later on be occupied by another antenna at the back. Estimating the channel of the "front" antenna can therefore later help beamforming towards the "back" antenna. Simulations show that our proposed schemes make adaptive beamforming work for vehicles moving at speeds up to 300 km/h.

National Category
Transport Systems and Logistics Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-252960 (URN)10.1109/MITS.2015.2408151 (DOI)000353572400009 ()
Available from: 2015-05-20 Created: 2015-05-18 Last updated: 2016-01-06Bibliographically approved
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