This paper presents comprehensive findings on the characterization of Indoor Hotspot channel parameters, derived from an extensive experimental campaign conducted at 6.9, 8.3, and 14.5 GHz in a commercial office building. Extensive measurements were carried out in diverse indoor office settings, including cubicles, conference rooms, hallways, and laboratory spaces across four floors. The path loss, shadow fading, delay spread, and angular spread was modeled. Our results offer significant insights into the attenuation and dispersion characteristics of wireless signals in diverse indoor settings in the centimeter-wave frequency band, and can be used for improving indoor network design and performance in commercial buildings.

In this paper, we present an advanced channel sounding system designed for sensing and propagation experiments in all types of cellular deployment scenarios. The system’s exceptional adaptability, high resolution, and sensitivity makes it an invaluable tool for utilization in a variety of indoor and outdoor measurement campaigns. The sounder has a 2.5 ns delay resolution, 170 dB path loss measurement capability and is able to measure a 360° power-angular delay profile of the channel in less than 0.9 ms. Additionally, the system can be easily reconfigured to measure different frequency bands by changing the RF front-end antennas. This versatile sounder is suitable for double directional channel sounding, high-speed vehicular experiments such as vehicle-to-vehicle and vehicle-to-infrastructure communications, and integrated communication and sensing experiments.

Communication in millimeter wave spectrum is an integral component to meet the ever increasing user throughput demand in fifth generation and beyond wireless cellular networks. Current millimeter wave basestation deployments typically use active phased array antennas which employ a codebook of predetermined directional beams to service cellular users. Highly directional beams are needed to overcome the high pathloss of the wireless medium in millimeter wave spectrum. However, drawbacks of such antenna systems include the signaling and measurement overhead required to select appropriate beams from the codebook for each user, as well as grouping users that can be covered by the same beam across the operating band of the array. Digital and hybrid beamforming systems are being actively researched to overcome these issues, however there is a scarcity of multi-antenna channel measurements in the millimeter wave spectrum needed to effectively optimize digital beamforming design parameters. In this paper, we present a novel fully digital 32 channel uniform planar array testbed, that is capable of performing wideband outdoor channel measurement in millimeter wave spectrum. Our testbed can also be calibrated to maintain precise phase and amplitude synchronization across all elements of the antenna array. Preliminary results from an outdoor channel sounding campaign show that digital beamforming receive algorithms provide significantly higher beamforming gain over traditional directional beamforming.

Wireless communication in millimeter wave spectrum is poised to provide the latency and bandwidth needed for advanced use cases unfeasible at lower frequencies. Despite the market potential of vehicular communication networks, investigations into the millimeter wave vehicular channel are lacking. In this paper, we present a detailed overview of a novel 1 GHz wide, multi-antenna vehicle to vehicle directional channel sounding and measurement platform operating at 28 GHz. The channel sounder uses two 256-element phased arrays at the transmitter vehicle and four 64-element arrays at the receiver vehicle, with the receiver measuring 116 different directional beams in less than 1 millisecond. By measuring the full multi-beam channel impulse response at large bandwidths, our system provides unprecedented insight in instantaneous mobile vehicle to vehicle channels. The system also uses centimeter-level global position tracking and 360 degree video capture to provide additional contextual information for joint communication and sensing applications. An initial measurement campaign was conducted on highway and surface streets in Austin, Texas. We show example data that highlights the sensing capability of the system. Preliminary results from the measurement campaign show that bumper mounted mmWave arrays provide rich scattering in traffic as well a provide significant directional diversity aiding towards high reliability vehicular communication. Additionally, potential waveguide effects from high traffic in lanes can also extend the range of mmWave signals significantly.

Millimeter wave wireless spectrum deployments will allow vehicular communications to share high data rate vehicular sensor data in real-time. The highly directional nature of wireless links in millimeter spectral bands will require continuous channel measurements to ensure the transmitter (TX) and receiver (RX) beams are aligned to provide the best channel. Using real-world vehicular mmWave measurement data at 28 GHz, we determine the optimal beam sweeping period, i.e. the frequency of the channel measurements, to align the RX beams to the best channel directions for maximizing the vehicle-to-infrastructure (V2I) throughput. We show that in a realistic vehicular traffic environment in Austin, TX, for a vehicle traveling at an average speed of 10.5 mph, a beam sweeping period of 300 ms in future V2I communication standards would maximize the V2I throughput, using a system of four RX phased arrays that scanned the channel 360 degrees in the azimuth and 30 degrees above and below the boresight. We also investigate the impact of the number of active RX chains controlling the steerable phased arrays on V2I throughput. Reducing the number of RX chains controlling the phased arrays helps reduce the cost of the vehicular mmWave hardware while multiple RX chains, although more expensive, provide more robustness to beam direction changes at the vehicle, allowing near maximum throughput over a wide range of beam sweep periods. We show that the overhead of utilizing one RX chain instead of four leads to a 10% drop in mean V2I throughput over six non-line-of-sight runs in real traffic conditions, with each run being 10 to 20 seconds long over a distance of 40 to 90 meters.

Characterization of the millimeter wave wireless channel is needed to facilitate fully connected vehicular communication in the future. To study the multipath-rich, rapidly varying nature of the vehicular propagation environment, fast millimeter wave channel sounders are required. We present a channel sounder design capable of covering 360 degrees in azimuth and 60 degrees in elevation with 200 individual beam directions in 6.25 ms by using four phased arrays simultaneously. The channel measurements are accompanied by high resolution positioning and video data, allowing channel sounding to be conducted while either the transmitter, or the receiver, or both are moving. Channel sounding campaigns were conducted at multiple urban locations with light traffic conditions in Austin, Texas. Preliminary results show that beam selection at the receiver can lower the effective pathloss exponent to 1.6 for line-of-sight and 2.25 for non line-of-sight.

For the development of new 5G systems to operate in bands up to 100 GHz, there is a need for accurate radio propagation models at these bands that currently are not addressed by existing channel models developed for bands below 6 GHz. This document presents a preliminary overview of 5G channel models for bands up to 100 GHz. These have been derived based on extensive measurement and ray tracing results across a multitude of frequencies from 6 GHz to 100 GHz, and this document describes an initial 3D channel model which includes: 1) typical deployment scenarios for urban microcells (UMi) and urban macrocells (UMa), and 2) a baseline model for incorporating path loss, shadow fading, line of sight probability, penetration and blockage models for the typical scenarios. Various processing methodologies such as clustering and antenna decoupling algorithms are also presented.

In this paper, we investigate the service coverage for interweaving cognitive radio networks with cooperative relays in shadowed areas within the metropolitan region. We highlight the influence of relays on the primary and secondary systems in severe shadow fading channels. The outage probability is utilized as a comprehensive performance metric to characterize the coverage quality for the cognitive radio system with relays. We show that cooperative spectrum sensing among the secondary transmitter and relays can improve the vacant spectrum detection probability and the false alarm probability, thereby making the additionally introduced interference by relays to be constrained within a tolerable limit. Overall, our analysis unveils that both the spectrum utilization rate and the spatial coverage can be significantly improved through the use of the relays, and there exists the spatial selectivity phenomena for both the primary and secondary systems.

We consider beam selection using a fixed beamforming network (FBN) at a base station withMarray antennas. In our setting, a Butler matrix is deployed at the RF stage to formMbeams, and then the best beam is selected for transmission. We introduce some properties of the noncentral chi-square distribution and prove the resulting properties of the beam selection gain verifying that beam selection is superior to antenna selection in Rician channels with anyK-factors. Furthermore, we find asymptotically tight stochastic bounds of the beam selection gain, which yield approximate closed form expressions of the expected selection gain and the ergodic capacity. Beam selection has the order of growth of the ergodic capacity Θ(logM) regardless of user location in contrast to Θ(log(logM)) for antenna selection.

We describe a channel sounding system designed for small outdoor cell (~400 meter radius) wireless channel characterization. We report on a program of path loss measurements using a 2×2 MIMO configuration and data reduction in the frequency range of 5.7-5.75 GHz. The results are based on over 10,000 independent complex frequency responses collected in residential neighborhoods in northern New Jersey. We characterize and report on key path loss parameters such as path loss exponent and shadowing for low base station antenna heights. Based on our data analysis, we propose a statistical model for path loss in neighborhood area networks in suburban environments.

In a protocol assisted switched diversity (PASD) system, the time separated repetition blocks are accumulated in order to increase decoding reliability. In this paper, we consider transmit antenna selection (TAS) protocols in a PASD system. To minimize system complexity we assume the feedback information is limited to the SNR of the current pair of antennas. We propose three TAS protocols : the random TAS (R-TAS) protocol which selects antennas randomly, the threshold TAS (T-TAS) protocol which keeps the current selection if the predetermined SNR threshold level requirement is met and the minimum number of transmission TAS (MNT-TAS) protocol which determines the selection of a new antenna set or keeping the current set based on the evaluation of expectation of the number of necessary remaining transmissions. We analyze the average number of transmissions of three proposed protocols in a Rayleigh fading channel and compare numerical evaluations to simulation results under different system conditions.

We consider on the move satellite systems with geostationary satellites. Using the antenna pointing distribution of Weerackody and Gonzalez, we derive tight upper and lower bounds of the interference between adjacent satellites from/to the on-the-move platforms. We then compute the distribution of the interference and the outage probability of the system. Simulation results are provided demonstrating that the analytical estimates are accurate.

For a multiple-antenna system, we find a simple and accurate expression for the asymptotic distribution of the antenna selection gain when the transmitter selects the transmit antenna with the strongest channel. We use this to estimate the underlying channel capacity distributions and obtain the approximate ergodic capacity. This estimate is compared with upper and lower bounds. This analysis demonstrates that unlike multiple-input/multiple-output (MIMO) systems, the channel for antenna selection systems hardens at a slower rate, and thus a significant multiuser scheduling gain can exist-Theta (1/logm) for channel selection as opposed to Theta (1/radicm) for MIMO, where m is the number of transmit antennas.

Fixed wireless multipoint communication systems are increasingly being deployed in suburban macrocell environments, either to provide voice and data services to residences (wideband systems) or to supply automated meter reading and related supervisory control and data acquisition services (narrowband systems). Here, we show that a particularly simple yet complete first-order statistical characterization of two-branch diversity reception over fixed wireless channels can be given in terms of just five channel parameters: the average path gains and Ricean K-factors for each branch and the complex envelope correlation coefficient between the time-varying parts of the two path gains. We further show that all five parameters can be estimated from amplitude-only measurements of path gain vs. time, subject only to the assumption that the time-varying component of the path gain is complex Gaussian. We present representative sets of model parameters based upon data collected in typical suburban macrocell environments over time, location, and/or frequency using polarization diversity antennas. Because each of the model parameters, or its logarithm, is close to Gaussian, the set may be cast as a five-element vector of jointly random Gaussian processes. Despite obvious physical differences between the environments, the results show a remarkable consistency.

We consider a wireless transmission scenario, when a base station is endowed with a fixed beamforming network, where M antennas are employed at the base station to point beams to predetermined azimuthal angles. In our setting, a Butler matrix is deployed at the RF stage to form M beams, and then the best beam is selected for transmission. We derive the distribution of the beam selection gain for this scenario under a Rician channel assumption as a function of both the azimuthal location of the remote unit and the Rician A'-factor. Using some key properties of the noncentral chi-square distribution, we prove that beam selection outperforms antenna selection.

In this paper, we analyze the performance of a communication system that employs Protocol Assisted Switched Diversity (PASD) antennas under Rayleigh fading channel conditions. The PASD system accumulates time-displaced blocks, each with the same information but using different antennas, and then combines their symbols using maximal ratio combining (MRC). In the PASD system, quality of service (QoS) is ensured by comparing the available signal-to-noise ratio (SNR) at the output of the combiner against a preset threshold value. Our analysis shows that this method reduces the number of transmissions significantly as the channel deteriorates as compared with ARQ without memory while it can satisfy the symbol error rate (SER) requirement for most of blocks. It is also shown that deploying more than one antenna is important to stabilize the system when the channel becomes static.

We study a cognitive network consisting of multiple cognitive users communicating in the presence of a single primary user. The primary user is located at the center of the network, and the cognitive users are uniformly distributed within a circle around the primary user. Assuming a constant cognitive user density, the radius of this circle will increase with the number of users. We consider a scheme in which the primary transmitter sends a beacon signaling its own transmission. The cognitive users, upon receiving this beacon, stay silent. Because of channel fading, however, there is a non-zero probability that a cognitive user misses the beacon and hence, with a certain activity factor, transmits concurrently with the primary user. Given the location of the primary receiver, we are interested in the total interference caused by the cognitive users to this receiver. In particular, we provide closed-form bounds on the mean and variance of the interference, and relate them to the outage probability on the primary user. These analytical results can help in the design of a cognitive network with beacon.

For a multiple antenna system, we compute the asymptotic distribution of antenna selection gain when the transmitter selects the transmit antenna with the strongest channel. We use this to asymptotically estimate the underlying channel capacity distributions, and demonstrate that unlike multiple- input/multiple-output (MIMO) systems,the channel for antenna selection systems hardens at a slower rate, and thus a significant multiuser scheduling gain can exist. Additionally, even without this scheduling gain, it is demonstrated that transmit antenna selection systems outperform open loop MIMO systems at low signal-to-interference-plus-noise ratio (SINR) regimes, particularly for small number of receive antennas. This may have some implications on wireless system design, because most of the users in modern wireless systems have low SINRs.

We compare three approaches for modeling the ultra-wideband (UWB) indoor channel delay profile, including the one adopted by the IEEE 802.15.3a Task Group. We do this using a large database we collected (and have reported on previously) spanning numerous indoor environments. Where appropriate, we recalculate model parameters so as to be compatible with the database. We test the models against the database and against each other by computing certain statistical `attributes' of the ensemble of channel delay profiles, e.g., the probability distribution, across the ensemble, of the root-mean-square (rms) delay spread. We show that each of the modeling approaches yields reasonable agreement with the database for most or all of the attributes tested, and we discuss the relative merits of the three approaches

We construct nonuniform phase-shift keying (PSK) constellations that provide unequal error protection for multiclass traffic such as compressed voice and video data. Then closed-form expressions expression for the exact bit-error rate (BER) of the nonuniform PSK constellations is derived in multiple receive-antenna systems over Rayleigh fading channels. Based on this BER analysis, we optimize the nonuniform PSK constellations such that the BERs of all the bits of each class are equalized or such that the total transmission power is minimized subject to the average BER constraints. In particular, we demonstrate that even for transmitting single-class traffic, the optimized nonuniform PSK constellations can be better than the conventional uniform PSK. Finally, we extend the nonuniform PSK constellations to space-time coded communications systems with multiple transmit and multiple receive antennas.

In this study we consider the challenge of reliable communication over a wireless Rayleigh flat-fading channel using multiple transmit and receive antennas. Since modern digital communication systems employ signal sets of finite cardinality, we examine the use of the quadrature amplitude modulation (QAM) constellation to approach the capacity of this channel. By restricting the channel input to the M-QAM subset of the complex-plane, the maximum achievable information rate (C/sub M-QAM/) is strictly bounded away from the channel capacity (C). We utilize a modified version of the Arimoto-Blahut algorithm to determine C/sub M-QAM/ and the probability distribution over the channel input symbols that achieves it. The results of this optimization procedure numerically indicate that the optimal input symbol distribution factors into the product of identical distributions over each real dimension of the transmitted signal. This is shown to vastly reduce the computational complexity of the optimization algorithm. Furthermore, we utilize the computed optimal channel input probability mass function (pmf) to construct capacity approaching trellis codes. These codes are implemented independent across all antennas and symbol dimensions and, if used as inner codes to outer low-density parity check (LDPC) codes, can achieve arbitrarily small error rates at signal-to-noise ratios very close to the channel capacity C/sub M-QAM/. Examples are given for a 2-transmit/2-receive antenna (2 /spl times/ 2) system.

In order to improve the throughput of the opportunistic beamforming, we generalize the opportunistic beamforming by using multiple random weighting vectors at each time slot. The base station chooses the best weighting vector and performs the opportunistic beamforming with this optimum vector. For the case of equally strong independent fast Rayleigh fading channels, we analytically approximate the throughput of the proposed scheme and obtain the optimum number of random weighting vectors per time slot. Numerical results demonstrate that the proposed scheme considerably improves the throughput compared to the conventional opportunistic beamforming for a low/realistic number of users.

In order to improve the throughput of the opportunistic beamforming, the authors generalize the opportunistic beamforming by using multiple random weighting vectors at each time slot. The base station chooses the best weighting vector and performs the opportunistic beamforming with this optimum vector. For the case of equally strong independent fast Rayleigh fading channels, the throughput of the proposed scheme is analytically approximated and the optimum number of random weighting vectors per time slot is obtained. Numerical results demonstrate that the proposed scheme considerably improves the throughput compared to the conventional opportunistic beamforming for a low/realistic number of users.

This paper describes the results of frequency-domain channel sounding in residential environments. It consists of detailed characterization of complex frequency responses of ultra-wideband (UWB) signals having a nominal center frequency of 5 GHz. A path loss model as well as a second-order autoregressive model is proposed for frequency response generation of the UWB indoor channel. Probability distributions of the model parameters for different locations are presented. Also, time-domain results such as root mean square delay spread and percent of captured power are presented.

In this study we provide a physical layer based analysis of the coexistence issues of ultra-wideband (UWB) with other devices in the same spectrum. Specifically, we have focused on the UWB interference to and from devices using the wireless local area network (WLAN) standard IEEE 802.11a. Our results indicate that a UWB interferer operating at the peak allowable power density induces minimal interference into such WLAN devices in line-of sight (LOS) scenarios, even at close range. However, in the non-LOS (NLOS) case, a UWB interferer can severely affect the data-rate sustainable by 802.11a systems. Moreover, 802.11a interference into UWB systems is shown to reduce the signal-to-interference ratio (SIR) by as much as 36 dB when the interferer is within LOS of the UWB receiver.

We present a statistical model for the multipath intensity profile (MIP) that can be used to construct an impulse response of a residential wireless channel. The model incorporates relevant parameters such as distance, global rms delay spread and the correlation between received multipaths. It describes the statistics of the MIP in detail. This model, together with a suitable path loss model, can be used to simulate residential wireless channels for performance evaluation of various communication systems. The MIP model is based on over 300,000 indoor frequency responses measured in a 1.25GHz bandwidth centered on 5-GHz, and simulation shows that it captures very well the main statistical properties of the measured data.

We describe a statistical model for the multipath intensity profile (MIP) in residential environments. The work is based on over 300,000 frequency response measurements at 712 locations in 23 homes. We show that, for non-line-of-sight (NLS) path, the MIP is well-modeled as a decaying exponential vs. delay, multiplied by a lognormal process over delay; and that a similar model applies to line-of-sight (LOS) paths. Moreover, we present simple statistical descriptions for the parameters of these functions.

We address issues concerning technology selection for non-real time, near real time and interactive data services for 3G W-CDMA systems. Specifically, we compare the packet mode of operation with the circuit mode of operation in UMTS W-CDMA. We show that the use of packet channels such as the common packet channel (CPCH) and forward access channel (FACH) lead to an order of magnitude higher spectrum efficiency as compared to use of the dedicated channels. We also show in an example and under a set of service mixture assumptions that their use lead to a factor of 3.3 higher spectrum efficiency in the downlink and 21 in uplink, and to more than two order of magnitude resource utilization efficiency gain in the range of 2-134. Finally, CPCH offers eightfold increase in throughput and capacity efficiency as compared to the random access channel (RACH). We find that the level of resource utilization gain is sensitive to the level of burstiness of traffic as is the case with the spectrum efficiency gain.

This paper deals with the measurement and modeling of multipath delay on fixed wireless paths at 1.9 GHz in suburban environments. The primary focus is on the delay profile, which is the normalized plot of received power versus delay in response to an RT "impulse." We describe measurement campaigns in the western suburbs of Chicago, IL, and in suburban north-central New Jersey. Our analysis of the data suggests to us that, for directive terminal antennas, the delay profile can be modeled as having a "spike-plus-exponential" shape, i.e., a strong return ("spike") at the lowest delay, plus a set of returns whose mean powers decay exponentially with delay. This delay profile can be characterized by just two parameters (both variable over the terrain), namely, the ratio (K/sub 0/) of the average powers in the "spike" and "exponential" components and the decay time constant (/spl tau//sub 0/) of the "exponential" component. No such simple structure appears to apply for delay profiles using omnidirectional antennas. For a directive antenna with a 32/spl deg/ beamwidth, we find that: (1) the statistical correlation between the profile parameters K/sub 0/ and /spl tau//sub 0/ is negligible; (2) these parameters are relatively insensitive to antenna height and path length; and (3) over each measured region (Illinois and New Jersey), K/sub 0/ and /spl tau//sub 0/ have median values close to 8 dB and just below 0.2 /spl mu/s, respectively. Moreover, we have found simple probability distributions that accurately portray the variability of K/sub 0/ and /spl tau//sub 0/ over the terrain.