Outdoor-to-indoor signal propagation poses significant challenges to millimeter-wave link budgets. To gain insight into outdoor-to-indoor millimeter-wave at 28GHz, we conducted an extensive measurement campaign consisting of over 2,200 link measurements in West Harlem, New York City, covering seven highly diverse buildings. A path loss model constructed over all measured links shows an average of 30dB excess loss over free space at distances beyond 50m. We find the type of glass to be the dominant factor in outdoor-to-indoor loss, with 20dB observed difference between grouped scenarios with low-and high-loss glass. Other factors such as the presence of scaffolding, tree foliage, or elevated subway tracks, as well as difference in floor height are also found to have a 5–10dB impact. We show that for urban buildings with high-loss glass, outdoor-to-indoor downlink capacity up to 400Mb/s is supported for 90% of indoor customer premises equipment by a base station up to 40m away. For buildings with low-loss glass, such as our case study covering multiple classrooms of a public school, downlink capacity over 2.8/1.4Gb/s is possible from a base station 57/133m away within line-of-sight. We expect these results to help inform the planning of millimeter-wave networks targeting outdoor-to-indoor deployments in dense urban environments, as well as provide insight into the development of scheduling and beam management algorithms.

Outdoor-to-indoor (OtI) signal propagation further challenges link budgets at millimeter-wave (mmWave). To gain insight into OtI mmWave at 28 GHz, we conducted an extensive measurement campaign consisting of over 2,000 link measurements in West Harlem, New York City, covering seven highly diverse buildings. A path loss model constructed over all links shows an average of 30 dB excess loss over free space at distances beyond 50 m. We find the type of glass to be the dominant factor in OtI loss, with 20 dB observed difference between clustered scenarios with low- and high-loss glass. Other factors, such as difference in floor height, are found to have an impact between 5--10 dB. We show that for urban buildings with high-loss glass, OtI data rates up to 400 Mb/s are supported for 90% of indoor users by a base station (BS) up to 49 m away. For buildings with low-loss glass, such as our case study covering multiple classrooms of a public school, data rates over 2.8/1.4 Gb/s are possible from a BS 68/175 m away when a line-of-sight path is available. We expect these results to be useful for the deployment of OtI mmWave networks in dense urban environments and the development of scheduling and beam management algorithms.

Theory of normal mode propagation in a line-of-sight street scenario is extended to include propagation into buildings through coupling to a diffuse indoor field. Signal strength predictions are in close agreement with measurements, producing 2 dB and ≤ 3.5 dB root-mean-square model-data difference, in line-of-sight and outdoor-indoor scenarios, respectively. The full 3-D field model predicts actual signal directions and antenna correlations as a function of range, important for evaluating performance of directional antennas and spatial diversity. Only minimal description of the environment is needed, i.e., street width and representative building wall properties, without any interior details.

Based on measurements for a street-canyon-type femto-cell, we compare the downlink spectral efficiencies of various intra-cell interference mitigation systems. This includes zero-forcing (ZF), regularized ZF (RZF), and dirty-paper coding (DPC). As a reference for comparison, we consider subsectorization and time-division multiple access (TDMA). Outof-cell interference, treated as additive Gaussian noise, is included in two modes: 1) all cells transmit simultaneously and 2) neighboring cells transmit in alternated time slots. We find that ZF, RZF, and DPC can offer increases in spectral efficiency over subsectorization and TDMA by factors of ~4 under interference-limited conditions. This contrasts with the estimated gains of only ~2 when using a standard 3GPP mode instead of our measured data. This difference is due to the greater inter-cell isolation that characterizes our street-canyon-type test environment. We find that RZF achieves over 80% of the DPC's spectral efficiency under virtually all operating conditions.

We present an empirically based model for the gain of an indoor antenna array. This corresponds to the re-parametrization of the Greenstein-Erceg model, as applied to 5 m-50 m narrowband outdoor-indoor links. Our model is applicable to a few adjacent tones in an OFDM femtocell system such as LTE. We find that as much as 14 out of 16 dB of antenna-gain are attainable even in rich indoor scattering conditions. At the same time, no larger fade margin is required when using the array vs. the omnidirectional antenna. To provide a reference for the observed results we consider a simple propagation model, which is analyzed theoretically and via simulation. This model is found to match our empirical results very well.

This paper presents closed-form expressions for the space-frequency (SF) second-order statistics for the power gain of indoor wideband channels. These expressions hold for channel models in which multi-path components are clustered, both in their arrival angles and their arrival times. Assuming that the arrival times are independent of the angles of arrival, we derive a closed-form expression for the covariance between the channel power gains at two receiving antenna positions d meters apart, at any pair of frequencies ω1and ω2. This expression reveals that increasing d yields the same SF covariance asymptotic reduction attainable by increasing |ω1- ω2|, only if |ω1- ω2|≠0, and that the covariance is symmetric in its dependence with ω1- ω2and with ω1+ ω2. Thus, the channel power gain at higher frequency bands has less variation than at lower frequencies. Finally, we show that the variable part of the SF covariance decays approximately as 1/d.

We present empirical results on the achievable cellular system throughput gains stemming from the use of remote radio heads (RRH) in an urban environment. Our work is based on simultaneous path-loss measurements of the base station (BS) and RRH links to outdoor street-level users. We calculated the increase in received power, when a RRH is added to improve the coverage achieved by a BS. We consider diverse settings for the RRH and diverse expected coverage areas for the mobile station (MS), evaluating the effect of RRH height and position with respect to the intended users. We also compare the power gains that would be obtained in practice from combining schemes such as selection combining (SC) and maximum ratio combining (MRC). We conclude that under practical conditions, the benefits of using RRHs will depend very strongly on the existence of line-of-sight links between the RRH and the intended users. For RRHs placed at low heights, below the clutter, only users in a "street-canyon" position with respect to the RRH will obtain a significant benefit. Our data also shows that the gains in signal-to-noise ratio achieved when using MRC are only marginally better than those of the much simpler SC.

We present empirical results on the achievable gains stemming from the use of wireless remote radio heads (RRH) in a typical urban environment. Our work is based on simultaneous path-loss measurements of the base station and RRH links to outdoor street level users. We statistically characterize the increase in received power, when a RRH is added to improve the coverage achieved by a base station. We consider diverse expected coverage areas for the mobile terminal, evaluating the effect of RRH position with respect to the intended users. We also compare the power gains that would be obtained in practice from combining the signals from the base with those of the RRH, using schemes such as selection combining and maximum ratio combining. We conclude that under practical conditions, the benefits of using RRHs will depend very strongly on the existence of line-of-sight links between the RRH and the intended users. For RRHs placed at low heights, below the clutter, only users in a street-canyon position with respect to the RRH will obtain a significant benefit. Our data also shows that the gains in signal-to-noise ratio achieved when using maximum ratio combining are only marginally better than those of the much simpler selection combining.

Americanae nace como un proyecto conjunto que surge dentro de la Red Europea de Información y Documentación sobre América Latina (REDIAL), y que ha afrontado la Biblioteca de la Agencia Española de Cooperación Internacional para el Desarrollo (AECID). Esta nueva biblioteca virtual hace más accesibles los libros digitales de tema americanista a los investigadores y usuarios interesados de cualquier parte del mundo.

This study presents an empirical characterisation of the wireless channel observed by static users in settings that correspond to populated open public spaces, where wireless services are increasingly being deployed. Link stability is analysed in terms of the temporal K-factor of the Ricean distribution. Second-order statistics were parameterised in terms of the Doppler shift, coherence time and level crossing rates. The authors found that the volume of pedestrian traffic had a very significant effect on the temporal K-factor, overshadowing the influence of line-of-sight or lack of it in the link. On the other hand, the volume of pedestrian traffic in the environment had no detectable effect on the second-order statistics of the channel.

This paper presents an empirical study of the achievable data rates of network multiple-input multiple-output (MIMO) techniques including zero-forcing (ZF), zero-forcing dirty paper coding (ZF-DPC) and dirty paper coding (DPC) using actual 4-by-4 indoor wireless channel measurements at 3.5 GHz. Their performances are contrasted with those of conventional techniques, in which either the base stations are not coordinated (NC), or their interference is avoided using frequency division (FD) multiplexing. The measurements were taken in aisle-to-office and large unobstructed hall scenarios. The study of these results reveals that, at high signal-to-noise ratios (SNRs), DPC and ZF-DPC can yield more than a three-fold increase in attainable data rates when compared to NC and FD. The gains obtained using ZF are smaller, but still significant. At low SNRs the system is noise-(rather than interference-) limited, and only DPC exhibits gains. The evaluations in this paper also show that collaborative systems such as DPC can benefit from interference-prone environments to yield increased transmission capacity. With regard to the propagation channel, the classical log-normal plus Rayleigh/Ricean fading model, with parameters fitted to the scenario type, was found to be good at predicting the statistics of the achievable data rates of all the strategies considered.

We derive closed form expressions for the second-order statistics of the spectral power gain of wide-band microwave indoor channels. We obtain our results within a framework general enough to be compatible with several popular channel models, such as those proposed by the IEEE 802.15.3a task group, as well as the Saleh-Valenzuela channel model. As all these models, our channel description is based upon clusters and rays with Poisson arrivals and random amplitudes. Our results consist of closed form expressions for the second-order statistics of the channel power frequency response, where statistical averages involve expectations over ray amplitudes and arrival times. We first express the auto-covariance of this frequency response in closed-form. We then use this result to obtain an analytical expression for the variance and second-order moment of the channel power within any given interval of frequencies. This allows us to express the channel spectral diversity as a function of model parameters and bandwidth. From this function, we determine the range within which diversity scales approximately linearly with bandwidth and its upper limit.

We present a summary of results based on several years of measurements for urban fixed wireless (FW) channels. Our results are aimed at providing reference data for practical applications in FW services. We discuss temporal stability and fade dynamics of outdoor-outdoor single-input single-output (SISO) channels with and without spatial diversity, a relevant aspect when considering the types of modulations that such a channel can support. Our main findings are that nearby vehicular traffic is the main source of temporal variations, but that in most practical situations temporal fades are very shallow. Spatial fades are quite significant and are stable over time. Diversity has the twofold effect of mitigating these fades and increasing temporal stability. We also present practical results on outdoor- indoor multiple-Input multiple-output (MIMO) channels. Based on empirical data we contrast spectral efficiencies for diverse types of systems, ranging from those that only use multiple antennas for beamforming to those that take full advantage of channel state information. We find that for low signal to noise ratio (SNR), beamforming achieves in practice spectral efficiencies comparable to that of MIMO and that it retains a significant proportion of such spectral efficiency at higher SNR, with the benefit of considerably lower complexity.

In this paper we develop closed form approximations for the probability density function (PDF) of the reliability metrics (L-values) in bit-interleaved coded modulation (BICM). The expressions are valid for M2-ary quadrature amplitude modulations (M2-QAM) with binary reflected Gray mapping when the metrics are calculated using the so-called max-log approximation. Based on the developed expressions, we also propose two simple Gaussian mixture approximations that are analytically tractable. We apply our developments to efficiently calculate the BICM capacity, and to develop bounds on the coded bit-error rate when a convolutional code is used. The coded performance of a hybrid automatic repeat request (HARQ) based on constellation rearrangement is also evaluated.

In this letter we derive closed-form expressions for the probability density functions (PDFs) of the bits' reliability metrics (L-values) in bit-interleaved coded modulation (BICM) transmission over fully-interleaved fading channels. The expressions are valid for the relevant case of quadrature amplitude modulation (QAM) with Gray mapping when the metrics are calculated via the so-called max-log approximation. Using the developed expressions, the performance of coded BICM transmissions is efficiently evaluated, i.e., without resorting to otherwise required two-dimensional numerical integration. The BICM capacity for different fading channels and constellation sizes is also evaluated.

In this paper we consider hybrid automatic repeat request transmission based on binary phase shift keying modulation. Our objective is to improve the performance of the retransmissions, keeping at the same time the complexity and the performance of the first transmission unaltered. We conclude that the so-called mapping rearrangement (MR) may considerably improve the performance if multi-dimensional modulation is applied. We evaluate the theoretical limits of bit-interleaved coded modulation with MR, verify the functioning of the practical coding scheme, and propose to improve the performance via iterative detection-decoding (BICM-ID) which brings considerable gains. In particular, for high coding rates, a 4 dB SNR gain over transmission without MR may be achieved.

MIMO systems are usually associated with high scattering isotropic propagation while the use of directive antennas is associated with free space conditions. We found outdoor-indoor channels to be in between these two extremes, in the sense that we observed directivity - and - MIMO gain, for the same ensemble of channels. Our observation is based on measurements with directive (8 dB) and dipole antennas. Median MIMO capacities were found to be about 80% of the ideal (Rayleigh i.i.d.), at 5 dB signal to noise ratio (SNR), for both types of antennas. Using properly aimed directive antennas, the SNR was found on average to be 5.4 dB above that obtainable with dipoles, somewhat less than the 7 dB antenna gain difference. Thus, isotropic propagation, which would have negated directivity gains, cannot be justified in general. We empirically established that aiming for largest received power is the best array pointing strategy with directive antennas. Combining MIMO processing and angular search resulted on average in gains of 70% over the median capacities obtained with dipoles. Therefore it may in some cases be convenient to arrange subgroups of antennas for beamforming, and then process the thus reduced number of radio channels for MIMO gain.

We present an empirically based comparative study of spectral efficiency for a variety of transmission systems applicable to a fixed or repositionable wireless environment, in the context of Wi-Fi, WiMAX or MuniNet systems. A narrowband 4times4 multiple input multiple output (MIMO) channel sounder was constructed and a series of outdoor to indoor measurements were carried out, in multiple locations and with different array configurations. The channel measurements were used to compute the efficiency of different systems that could be deployed in such scenarios, ranging from a full MIMO system with perfect channel state information (CSI) at both ends to simple diversity schemes such as classical beamforming. We show comparisons of efficiency for the different transmit/receive configurations operating in a representative variety of locations. Our results indicate that for low values of signal to noise ratio (SNR), in the range of 5 dB, such as found in strong interference scenarios, simple schemes can achieve median spectral efficiencies as high as 80% of that of MIMO with complete CSI.

In this paper we consider hybrid automatic repeat request transmission based on binary phase shift keying modulation. Our objective is to improve the performance of the retransmissions, keeping at the same time the complexity and the performance of the first transmission unaltered. We conclude that the so-called mapping rearrangement (MR) may considerably improve the performance if multidimensional modulation is applied. We evaluate the theoretical limits of bit-interleaved coded modulation with MR, verify the functioning of the practical coding scheme, and propose to improve the performance via iterative detection-decoding (BICM-ID) which brings considerable gains. In particular, for high coding rates, a 4 dB SNR gain over transmission without MR may be achieved.

We present an empirically based comparative study of spectral efficiency for a variety of transmission systems applicable to a fixed or repositionable wireless environment, in the context of Wi-Fi, WiMAX or MuniNet systems. A narrowband 4times4 Multiple Input Multiple Output (MIMO) channel sounder has been constructed and a series of outdoor to indoor measurements have been carried out, in multiple locations and with different array configurations. The channel measurements have been used to compute the spectral efficiency of different systems that could be deployed in such scenarios, ranging from a full MIMO system with perfect Channel State Information (CSI) at both ends to simple diversity schemes such as classical beamforming. We show comparisons between the different transmit/receive configurations operating in a representative variety of indoor receive locations. Our results indicate that for low values of Signal to Noise Ratio (SNR, in the range of 5dB), simple schemes can achieve capacities as high as 80% of that of MIMO with complete CSI.

In general, MIMO systems are associated with high scattering isotropic propagation while the use of directive antennas is associated with free space or narrow angular spread conditions. We found outdoor-indoor channels to be in between these two extremes, in the sense that we observed directivity - and - MIMO gain, for the same ensemble of channels. Our observation is based on measurements with directive (8 dB gain) and dipole antennas. Median MIMO capacities were found to be 80% of the ideal (Rayleigh i.i.d.), at 5 dB signal to noise ratio (SNR), with no significant difference resulting from the choice of antenna. On the other hand, using properly aimed directive antennas, the SNR was found on average to be 5.4 dB above that obtainable with dipoles, somewhat less than the 7 dB antenna gain difference. Thus, isotropic propagation, which would have negated directivity gains, cannot be justified in general. The combination of MIMO processing and angular search with directive antennas resulted on average in gains of 69% over the median capacities obtained with dipoles. Since MIMO and directivity can combine effectively, it may in some cases be convenient to arrange subgroups of antennas for beamforming, and then process the thus reduced number of radio channels for MIMO gain.

In the popular bit-interleaved coded modulation (BICM) the output of the channel encoder and the input of the modulator are separated by a bit-level interleaver. From the decoder's point of view, the modulator, the transmission channel, and the demodulator (calculating bits' reliability metrics) become a memoryless BICM channel with binary inputs and real outputs. In unfaded channels, the BICM channel's outputs (reliability metrics) are known to be Gaussian for binary- or quaternary phase shift keying but their probability density function (PDF) is not known for higher-order modulation. We fill this gap by presenting an algorithmic method to calculate closed-form expressions for the PDF of reliability metrics in BICM with arbitrary modulation and bits-to-symbol mapping when the so-called max-log approximation is applied. Such probabilistic description of BICM channel is useful to analyze, from an information- theoretic point of view, any BICM constellation/mapping design.

In this paper we develop formulas for the probability density function (PDF) of the reliability metrics in bit- interleaved coded modulation (BICM) for arbitrary M2-ary quadrature amplitude modulation (M2-QAM) with Gray mapping. The advantage of this approach over an entirely general one proposed previously, is that the resulting formulas are obtained without resorting to any algorithmic steps. We also propose Gaussian mixture approximations that are analytically tractable, and we analyze their accuracy when evaluating uncoded bit error rate (BER) and BICM capacity.

Hybrid ARQ with packet combining for high-order modulations (such as 16-QAM) may be significantly enhanced if the bits-to-symbols mappings are appropriately changed throughout the transmissions. In this paper, we analyze the relationship between such mapping rearrangement (or mapping diversity) and channel coding. We calculate the capacity of the popular bit-interleaved coded modulation (BICM) to draw qualitative and approximate quantitative conclusions that are valid for strong codes approaching the capacity limits. We conclude that the choice/design of the appropriate mapping depends on the targeted spectral efficiency and we demonstrate that certain forms of mapping rearrangement may be counterproductive. We also show that iterative demapping may be successfully applied to significantly reduce the gap between the BICM and coded modulations capacities. The analysis presented is illustrated with the results obtained when the mapping rearrangement is combined with practical turbo codes.

In bit interleaved coded modulation (BICM), the probability density function (PDF) of the reliability metrics (L- values) fully defines the BICM transmission and may be used to analyze it from an information-theoretic point of view. In this paper, the closed-form expressions for the PDF of the L-values in Rayleigh fading channels for 16-QAM with Gray mapping are derived and contrasted with histograms of the L-values obtained via numerical simulations. The obtained closed-forms show that the PDF is either a sum of exponentials or is bounded by such a sum.

In this paper we address the issue of probabilistic modelling of the extrinsic L-values, used as reliability metrics in the context of bit interleaved coded modulation with iterative demapping (BICM-ID). Starting with a simple piece-wise linear model of the L-values obtained via the max-log approximation, we derive the expressions for the cumulative distribution functions of the L-values, that differentiated produce the desired forms of the probability density functions for Gray-mapped 16-QAM. To illustrate the usefulness of our analytical expressions we applied them to efficiently compute the so-called EXIT functions of the demapper for different values of SNR. The proposed analytical expressions are also compared to thehistograms of the L-values obtained through time-consuming simulations.

The temporal behavior of fixed wireless (FW) links is usually described in terms of fade depth distribution, level crossing rates and average fade duration. This knowledge is needed for the optimization of transceiver parameters such as modulation format, frame length, automatic gain control dynamics, etc. We present analytic and empirical results on the level crossing rate (LCR) and average fade duration (AFD) in FW links. We show that under certain conditions the LCR and AFD do not depend on the shape of the Doppler spectrum and that with a proper choice of parameters, expressions that have been justified for mobile wireless links are also applicable to FW. Results of extensive measurements validate the assumptions that sustain our model

Diversity techniques can be very effective against fading. For fixed wireless terminals, antenna diversity increases spatial coverage by reducing the likelihood of all antennas being at a faded location. At the same time, temporal fade depth is reduced, as time variations are normally uncorrelated for the antennas. The analysis of temporal fade in fixed wireless applications must take into account that the standard assumption made in mobile applications, namely equal average power across the diversity branches, is no longer justified, as a given antenna may be at a faded location for an extended time. In this paper we quantify the benefits of diversity receivers for fixed wireless links in terms of reductions in temporal fluctuation and outages, including the effect of power unbalance among diversity branches which is typical for these links. We specifically consider the case where the time varying multipath fade components are independent but identically distributed random processes for all branches, while due to spatial fades, the time invariant components may be different. A statistical description that includes the average level crossing rate (LCR) of the output signal of a maximal ratio combiner is derived in closed form. Simplified expressions, applicable for the case of links with high Ricean X-factors, as occurs in fixed wireless, are derived for both maximal ratio and equal gain combining. It was found that the combiner output statistics essentially depend on the value of sum of the branch K-factors, with the number of branches having virtually no effect. Extensive measurements at 3.5 GHz are used to compare, and found to match well, the theoretical expressions derived in this work. The results are useful for link design, by providing theoretical tools and empirical data for the calculation of the fade margin reduction and fade duration that results from the use of diversity combiners in the case of fixed wireless links with unequal power across the diversity branches.

An analytical method to predict accurately the performance of iterative demapping in bit-interleaved coded modulation (BICM-ID) is presented. It is based on the analytical evaluation of the bit error rate at the output of the demapper and, in comparison with previously known methods (e.g., those based on EXIT charts), considerably reduces the need for simulations. The results obtained with the proposed method are compared with those obtained by EXIT analysis and through simulations.

In the popular bit-interleaved coded modulation (BICM) the output of the channel encoder and the input of the modulator are separated by a bit-level interleaver. From the decoder's point of view, the modulator, the transmission channel, and the demodulator (calculating bits' reliability metrics) become a memoryless BICM channel with binary inputs and real outputs. The BICM channel's outputs (reliability metrics) are known to be Gaussian for binary- or quaternary phase shift keying but no expression for their probability density function (PDF) is known for higher-order modulation. We fill this gap presenting an algorithmic method to calculate closed-form expressions for the PDF of reliability metrics in BICM with arbitrary modulation and bits-to-symbol mapping. Such probabilistic description of BICM channel provides a useful tool to analyze, from an information- theoretic point of view, any BICM constellation/mapping design.

In this paper we present a novel performance analysis of bit-interleaved coded modulation (BICM) over AWGN channel for different modulation schemes considering a finite block length and suboptimal metrics calculation. Using the known BICM capacity analysis as well as the Gallager bound, we show that among many known modulations, only three M-ary quadrature amplitude modulation (QAM) are necessary to ensure the maximization of the channel capacity. We analyze the maximum throughput and the switching thresholds of the system, and we compare the theoretical analysis with simulation results of practical strong codes, i.e., turbo codes. We show that if the modulation and code are well adapted, the optimal throughput decreases by less than 1% when suboptimal metrics are used. We show also, that the turbo codes throughput is within 1.5 dB of the new bound, and the SNR switching thresholds, are shifted by 1.5 dB with respect to the theoretical analysis.

We present a statistical model for the dynamics of the envelope of the received signal in narrowband urban fixed wireless links, with applications to the performance evaluation of diversity receivers. The model is based on a straightforward analytical treatment based on simplifying assumptions. The assumptions are validated by an extensive empirical study of a broad range of urban settings representative of realistic deployment scenarios for fixed wireless service. The results are useful for system designers and for the efficient selection of error control mechanisms that need to adjust to the dynamics of the propagation channel. We find that in practice, the autocovariance of the combiner branch input signals are similar and also similar to the autocovariance of the output of the diversity combiners.