1. 
 Almers, Peter, et al.
(författare)

Exercises
 2005

Ingår i: Wireless Communications.  John Wiley & Sons Ltd.  047084888X  9780470848883  139780470848876  0470848871 ; s. 561593

Bokkapitel (övrigt vetenskapligt)


2. 
 Dahman, Ghassan, et al.
(författare)

On the probability of nonshared multipath clusters in cellular networks
 2015

Ingår i: IEEE Wireless Communications Letters.  IEEE.  21622337 . 21622345. ; :99

Tidskriftsartikel (refereegranskat)abstract
 In Space Division Multiple Access (SDMA) systems, users are separated based on their positions. The basestation (BS) signals typically reach the users through multipath clusters. The goal of this work is to find the probability that a randomly selected user will receive the signal from the BS via at least one nonshared (by any other user) multipath cluster. This probability, referred to as PSuccess, provides (under some conditions) the limit of the probability that the BS is able to communicate successfully with a randomly selected user using SDMA without causing significant interference to other users. In order to find PSuccess, we first derive a model describing the probability distribution function (pdf) of the nonoverlapping area of a set of circles, that have the same radius and are spatially distributed according to a Poisson distribution. Then, the proposed model for this pdf is used to express PSuccess as a function of the user’s intensity and the clusters’ intensity. Simulations, using the COST 2100 model, for outdoor and indoor scenarios, are used to validate the derived expression for PSuccess with a very good agreement, where the maximum error was 0:04.


3. 
 Flordelis, Jose, et al.
(författare)

Spatial Separation of CloselySpaced Users in Measured Massive MultiUser MIMO Channels
 2015

Konferensbidrag (refereegranskat)abstract
 Fullysynchronous measurements of a massive multiuser multipleinput multipleoutput (MUMIMO) radio propagation channel are presented. We evaluate the ability of a massive MIMO system to spatially separate users located close to each other in lineofsight (LOS) propagation conditions. The system consists of a basestation (BS) antenna array equipped with 64 dualpolarized antenna elements (128 ports) arranged in a cylindrical configuration, and eight singleantenna users. The users are confined to a fivemeter diameter circle and move randomly at pedestrian speeds. The BS antenna array is located on top of a 20 m tall building and has LOS to the users. We examine user separability by studying singular value spread of the MUMIMO channel matrix for several subsets of BS antenna array ports, along with sumrate capacity and achievable sumrates with both zeroforcing and matchedfiltering linear precoders. We also analyze the performance of the user with the lowest rate. Finally, a comparison between the performance offered by the massive MIMO system and that of a conventional MUMIMO system is provided. To the best of our knowledge, this is the first report of fullysynchronous dynamic measurements of a massive MIMO system. Our investigation shows that even users located close to each other in LOS propagation conditions can be spatially separated in a massive MIMO system.


4. 
 Gao, Xiang, et al.
(författare)

Channel behavior for verylarge MIMO systems  initial characterization
 2012

Konferensbidrag (övrigt vetenskapligt)abstract
 Wireless communication using verylarge multipleinput multipleoutput (MIMO) antennas is a new research field, where base stations are equipped with a very large number of antennas as compared to previously considered systems. Unlike the conventional small and compact antenna arrays, the verylarge arrays may span many wavelengths in space, thus they can experience largescale fading over the array. This power variation over the antenna array may be critical to algorithm design and performance evaluations for verylarge MIMO systems, and it is thus important that it is included in channel models. Based on channel measurements using a 128antenna linear array in a semiurban area, we characterize and model the largescale fading properties. We focus on clusterbased modeling which can be seen as an extension of the current COST 2100 channel model. In the paper, we report our latest channel behavior modeling progress for verylarge MIMO systems.


5. 
 Gao, Xiang, et al.
(författare)

Extension of the COST 2100 channel model for massive MIMO
 2015

Konferensbidrag (övrigt vetenskapligt)abstract
 Massive MIMO has been shown, both in theory and through experiments, to offer very promising properties. These include the possibility to decrease output power by at least an order of magnitude while still achieving large gains in spectral efficiency, as compared to today’s access schemes. To efficiently design communication algorithms and evaluate massive MIMO schemes, channel models that capture important massive MIMO channel characteristics are needed. We pursue this by extending a wellknown clusterbased MIMO channel model  the COST 2100 model. In the paper, we suggest a model extension for massive MIMO, and we discuss main concepts, parameters and implementation issues. The modeling work is based on measurement data from a measurement campaign in the 2.6 GHz frequency range using a physicallylarge array with 128 elements.


6. 
 Gao, Xiang, et al.
(författare)

Large antenna array and propagation environment interaction
 2014

Konferensbidrag (refereegranskat)abstract
 In conventional MIMO, propagation conditions are often considered widesense stationary over the entire antenna array. In massive MIMO systems, where arrays can span over large physical dimensions, the situation is quite different. For instance, significant variations in signal strength, due to shadowing, can be experienced across a large array. These effects vary with propagation environment in which the array is placed, and influence achievable sumrates. We characterize these variations for several measured propagation scenarios in the 2.6 GHz frequency range and illustrate how power variations and correlation properties change along the array.


7. 
 Gao, Xiang, et al.
(författare)

Linear precoding performance in measured verylarge MIMO channels
 2011

Ingår i: Proc. of the 74th IEEE Vehicular Technology Conference.  IEEE.

Konferensbidrag (refereegranskat)abstract
 Wireless communication using verylarge multipleinput multipleoutput (MIMO) antennas is a new research field, where base stations are equipped with a very large number of antennas as compared to previously considered systems. In theory, as the number of antennas increases, propagation properties that were random before start to become deterministic. Theoretical investigations with independent identically distributed (i.i.d.)\ complex Gaussian (Rayleigh fading) channels and unlimited number of antennas have been done, but in practice we need to know what benefits we can get from very large, but limited, number of antenna elements in realistic propagation environments. In this study we evaluate properties of measured residentialarea channels, where the base station is equipped with 128 antenna ports. An important property to consider is the orthogonality between channels to different users, since this property tells us how advanced multiuser MIMO (MUMIMO) precoding schemes we need in the downlink. We show that orthogonality improves with increasing number of antennas, but for two singleantenna users there is very little improvement beyond 20 antennas. We also evaluate sumrate performance for two linear precoding schemes, zeroforcing (ZF) and minimum mean squarederror (MMSE), as a function of the number of base station antennas. Already at 20 base station antennas these linear precoding schemes reach 98\% of the optimal dirtypaper coding (DPC) capacity for the measured channels.


8. 
 Gao, Xiang, et al.
(författare)

Massive MIMO performance evaluation based on measured propagation data
 2015

Ingår i: IEEE Transactions on Wireless Communications.  IEEE.  15361276. ; 14:7, s. 38993911

Tidskriftsartikel (refereegranskat)abstract
 Massive MIMO, also known as verylarge MIMO or largescale antenna systems, is a new technique that potentially can offer large network capacities in multiuser scenarios. With a massive MIMO system, we consider the case where a base station equipped with a large number of antenna elements simultaneously serves multiple singleantenna users in the same timefrequency resource. So far, investigations are mostly based on theoretical channels with independent and identically distributed (i.i.d.) complex Gaussian coefficients, i.e., i.i.d. Rayleigh channels. Here, we investigate how massive MIMO performs in channels measured in real propagation environments. Channel measurements were performed at 2.6 GHz using a virtual uniform linear array (ULA) which has a physically large aperture, and a practical uniform cylindrical array (UCA) which is more compact in size, both having 128 antenna ports. Based on measurement data, we illustrate channel behavior of massive MIMO in three representative propagation conditions, and evaluate the corresponding performance. The investigation shows that the measured channels, for both array types, allow us to achieve performance close to that in i.i.d. Rayleigh channels. It is concluded that in real propagation environments we have characteristics that can allow for ef?cient use of massive MIMO, i.e., the theoretical advantages of this new technology can also be harvested in real channels.


9. 


10. 
 Harrysson, Fredrik, et al.
(författare)

Efficient experimental evaluation of a MIMO handset with user influence
 2010

Ingår i: IEEE Transactions on Wireless Communications.  IEEE.  15361276. ; 9:2, s. 853863

Tidskriftsartikel (refereegranskat)abstract
 The immediate environment of handset antennas, including the casings and the users holding the handsets, has a strong impact on the radio channel in mobile communication. In this paper we investigate a composite channel method that synthetically combines doubledirectional measurements of the userless propagation channel with measured superantenna patterns, i.e., patterns of the combined antennacasinguser arrangement. We experimentally evaluate the method by comparing results (power, capacity, and eigenvalue distribution) obtained from this composite method with direct measurements in the same environment. The measurements were done in two static 8 × 4 MIMO scenarios at 2.6 GHz, with the user indoors and the base station located outdoors and indoors, respectively. A realistic user phantom together with a “smartphone” handset mockup with four antenna elements was used, and different configurations and orientations were tested. The method gives statistical distributions of the MIMO eigenvalues, that are close to the measured. By using the composite method, we found that the user, apart from introducing hand and body loss that mainly decreases the SNR of the channel, slightly increases the correlation between the fading at the antenna elements.

