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Millimeter wave fixed wireless systems in future backhaul and access network applications can be affected by weather conditions. The losses caused by rain attenuation and antenna misalignment due to wind-induced vibrations have greater impacts on the link budget reduction at E-band frequencies and higher. The current International Telecommunications Union Radiocommunication Sector (ITU-R) recommendation has been widely used to estimate rain attenuation, and the recent Asia Pacific Telecommunity (APT) report provides the model to estimate the wind-induced attenuation. This article provides the first experimental study of the combined rain and wind effects in a tropical location using both models at a frequency in the E band (74.625 GHz) and a short distance of 150 m. In addition to using wind speeds for attenuation estimation, the setup also provides direct antenna inclination angle measurements using the accelerometer data. This solves the limitation of relying on the wind speed since the wind-induced loss is dependent on the inclination direction. The results show that the current ITU-R model can be used to estimate the attenuation of a short fixed wireless link under heavy rain, and the addition of wind attenuation via the APT model can estimate the worst-case link budget during high wind speeds.

A directive fixed wireless link operating at a center frequency of 240 GHz achieves a data rate of 64 Gbit/s over a transmission distance of 850 m using QPSK and 8PSK modulation, in a single-channel approach without the use of spatial diversity concepts. The analog transmit and receive frontend consists of active monolithic integrated circuits including broadband RF amplification and quadrature subharmonic mixer channels. The analog frontend is addressed by 64 GSa/s ADC and DAC boards, which are amenable to real-time data transmission. A link budget calculation allows for the estimation of the performance under adverse weather conditions.

Adaptive spatial multiplexing (SM) Multiple Input Multiple Output (MIMO) techniques enhance the spectral efficiency of wideband wireless communications in favorable radio channel conditions. In this study, we show the benefits of combining a traditional fixed-beam scheme and multiuser opportunistic radio resource allocation in space-time-frequency domains. This combining is feasible in wideband Orthogonal Frequency Domain Multiple Access (OFDMA) systems such as the Universal Mobile Telecommunications System (UMTS) Long Term Evolution (LTE). This study brings novel knowledge which indicates that an orthogonal fixed beam approach benefits from opportunistic radio resource allocation clearly more than a conventional antenna domain approach in frequency-selective radio channels. It was found out that the fixed beam radio link performance is enhanced in wideband adaptive radio links due to the fact that orthogonal beams reduce correlation between the MIMO channels in the allocated sub-bands. Moreover, beamforming gains bring higher Eigenvalues of the MIMO channel matrix in the opportunistically selected sub-bands. It is shown that the fixed beam deployment changes the distribution of the MIMO channel correlation values and Eigenvalues in a manner which enhances opportunistic multiuser gains in wideband time-frequency-selective MIMO radio channels. Simulation results with 2 × 2 spatial multiplexing in an OFDMA uplink indicate that the proposed beam domain scheme gives up to 80% data throughput gain over the corresponding antenna domain scheme in a pedestrian microcell environment.

In this correspondence, the authors study the performance of multi-user transmitter preprocessing (MUTP)-assisted cooperative downlink (DL) transmission for multi-carrier code division multiple access (MC-CDMA) system, where multi-user interference (MUI) and inter-relay interference (IRI) are the principal channel impairments. Relaying is facilitated with the aid of fixed infrastructure-based relays that perform additional signal processing like formulating the preprocessing matrix for mitigating MUI in addition to forwarding the information they receive from the base station (BS). Specifically, in this study, the authors analyse the performance of cooperative communication-aided DL MC-CDMA system by employing three cooperation strategies: (i) all users supported by a single relay with dominant MUI at the relay and mobile stations (MSs); (ii) each user supported by a single relay where, MUI and IRI are dominant at the relays and MSs, respectively, as well as weak IRI at the MSs; and (iii) all users supported by L relays where MUI is dominant at the relays, and MUI and IRI are dominant at the MSs. Our simulation study shows that MUTP-aided cooperative DL transmission results in better achievable bit error rate than the multi-user detection-aided system as the MUI at the relays and MUI and IRI at the MSs are perfectly eliminated.

New physical–mathematical models for the calculation of the outage probability of the maximal ratio combining and selection combining dual branch spatial diversity schemes for broadband fixed wireless access networks operating above 10 GHz are presented. At these frequency bands and considering line-of-sight conditions, rain attenuation is the dominant fading mechanism, which should be taken into account in the radio communications system design. The models are based on bivariate inverse Gaussian (IG) distribution and on the adoption of a spatial correlation coefficient for the convergent terrestrial wireless links. IG distribution has been shown that models accurately the rain attenuation fading for both temperate and tropical climatic regions. The models are validated with numerical results and some useful conclusions are drawn.

As the complexity and applications of Fixed Wireless Loop (FWL) systems keeps growing, it is becoming less and less practical to fully compare their performance without resorting to simulations at some point. This paper introduces several common types of statistical relationships between links, analyzes some of their causes and effects, and shows ways to take them into account when running capacity simulations.