In this paper, we study the performance of loss-tolerant multiuser large-scale multiple-input multiple-output (LS-MIMO) system with rateless space time block code (RSTBC). Since large number of low-power antenna elements are deployed in LS-MIMO systems, there is always a possibility of transmission losses, which may degrade the system performance significantly. In such cases, packets may get lost or not decodable at the receiver resulting in wireless erasure channels. Hence, RSTBC is introduced in LS-MIMO downlink transmission to tackle this problem. Performance analysis and simulation results are provided to demonstrate the feasibility of the proposed scheme in such cases. It has been shown that RSTBC guarantees the reliability of lossy LS-MIMO system with low overhead and complexity.

This paper presents propagation path loss channel models developed from real-field measurement campaigns that were conducted in indoor and outdoor Line-of-Site (LOS) propagation environments in Riyadh city, Saudi Arabia, using highly directional antennas at 60 GHz. The setup used in these measurements emulates the future fifth-generation (5G) cellular systems for both access and backhaul services, as well as for Machine-to-Machine (M2M) communications. We used our measurement data to develop the corresponding large-scale propagation path loss models at 60 GHz, using the log-distance and the floating intercept modeling approaches. It is shown that cellular radio links can be established in short-range distances up to 134 m indoors, and up to 77 m outdoors, when employing highly directional antennas at both the transmitter and receiver sides. It is also shown that path loss at 60 GHz in hot and sunny weather during the day, is higher than those obtained in cool and clear weather at night. This is partly due to solar radio noise effect arising from the intense solar radiation that characterizes summer afternoon in Riyadh city, which can cause a decrease in carrier-to-noise ratio at the input of receiving antennas. It is also partly due to the increase in thermal noise when electronics components in the measurement device become hot. The results presented here are thus very useful in 5G cellular design and infrastructure planning in the gulf region, where daytime temperature could reach 43° C or more.

This paper studies the performance of rateless space time block code (RSTBC) in massive multiuser MIMO systems with antenna element failure. The paper illustrates the basis for rateless space time codes deployments in massive MIMO transmission over wireless erasure channels, where packets may get lost or are not decodable at the receiver due to antenna element failure. Since a large number of antenna elements are deployed in massive MIMO systems, there is always a possibility of failure of some antenna elements, which may degrade the system performance significantly. The results show that RSTBC guarantees the reliability of the system in such cases even when the failure rate is 25%. Simulation results are provided to demonstrate the feasibility of the proposed scheme.

Massive multiple‐input multiple‐output (MIMO) is a breakthrough wireless transmission technique proposed for future wireless standards due to its spectrum and energy efficiencies. However, pilot contamination constitutes a particularly significant impairment in multi‐cell systems that utilise reciprocity‐based channel estimation. This phenomenon results from the non‐orthogonality of the pilot sequences in different cells. Given a large number of antennas employed in massive MIMO systems, conventional channel estimation schemes cannot mitigate this problem effectively without high computational complexity. In this study, a simple rateless space–time block code (RSTBC) is employed in the downlink transmission of a lossy multi‐cell massive MIMO system to mitigate the effects of signal‐to‐interference‐and‐noise ratio (SINR) degradation resulting from pilot contamination. Specifically, a robust optimisation problem is formulated to maximise the minimum downlink SINR among all users. Simulation and analytical results for large numbers of antenna elements at the base station (BS) are provided to demonstrate the usefulness of the proposed scheme. The SINR and spectral efficiency analyses indicate that RSTBC can effectively mitigate downlink SINR degradation that is caused by pilot contamination. Experimental results for the proposed scheme are also included for a 2 × 2 MIMO system, and it agrees closely with the simulation.

Fifth-generation (5G) cellular systems are likely to operate in the centimeter-wave (3-30 GHz) and millimeter-wave (30-300 GHz) frequency bands, where a vast amount of underutilized bandwidth exists world-wide. To assist in the research and development of these emerging wireless systems, a myriad of measurement studies have been conducted to characterize path loss in urban environments at these frequencies. The standard theoretical free space (FS) and Stanford University Interim (SUI) empirical path loss models were recently modified to fit path loss models obtained from measurements performed at 28 GHz and 38 GHz, using simple correction factors. In this paper, we provide similar correction factors for models at 60 GHz and 73 GHz. By imparting slope correction factors on the FS and SUI path loss models to closely match the close-in (CI) free space reference distance path loss models, millimeter-wave path loss can be accurately estimated (with popular models) for 5G cellular planning at 60 GHz and 73 GHz. Additionally, new millimeter-wave beam combining path loss models are provided at 28 GHz and 73 GHz by considering the simultaneous combination of signals from multiple antenna pointing directions between the transmitter and receiver that result in the strongest received power. Such directional channel models are important for future adaptive array systems at millimeter-wave frequencies.

This study presents the symbol error probability (SEP) analysis of relay‐multiplexing scheme in relay‐assisted cellular systems such as the IEEE 802.16j and upcoming fifth generation (5G) systems. The availability of multiple relay paths in these systems motivates two relay configurations: (i) relay diversity and (ii) relay multiplexing. Available works in the literature have focused on the relay diversity methods. In this study, we explore the relay‐multiplexing alternative whereby relay stations (RSs) act as independent data pipes for transmitting multiple independent data streams from the base station (BS) to the mobile station (MS). We examine the case when the BS is equipped with massive multiple‐input multiple‐output (MIMO) antennas, transmitting independent data streams to several MS simultaneously via different relay paths. We derive analytical expressions for the SEP performance of the proposed scheme, and also complement the analysis with simulations. The results show that parallel relaying of independent data streams via different RSs has acceptable SEP performance while boosting the capacity of the system linearly with the number of parallel RSs available in the system. The results also show that when this relaying approach is combined with the emerging massive MIMO techniques, a tremendous boost in data rate can be achieved.

ABSTRACT The demand for higher data rate has spurred the adoption of multiple‐input multiple‐output (MIMO) transmission techniques in IEEE 802.11 products. MIMO techniques provide an additional spatial dimension that can significantly increase the channel capacity. A number of multiuser MIMO system have been proposed, where the multiple antenna at the physical layer are employed for multiuser access, allowing multiple users to share the same bandwidth. As these MIMO physical layer technologies further evolve, the usable bandwidth per application increases; hence, the average service time per application decreases. However, in the IEEE 802.11 distributed coordination function‐based systems, a considerable amount of bandwidth is wasted during the medium access and coordination process. Therefore, as the usable bandwidth is enhanced using MIMO technology, the bandwidth wastage of medium access and coordination becomes a significant performance bottleneck. Hence, there is a fundamental need for bandwidth sharing schemes at the medium access control (MAC) layer where multiple connections can concurrently use the increased bandwidth provided by the physical layer MIMO technologies. In this paper, we propose the MIMO‐aware rate splitting (MRS) MAC protocol and examine its behavior under different scenarios. MRS is a distributed MAC protocol where nodes locally cooperate with one another to share bandwidth via splitting the spatial channels of MIMO systems. Simulation results of MRS protocol are obtained and compared with those of IEEE 802.11n protocol. We show that our proposed MRS scheme can significantly outperform the IEEE 802.11n in medium access delay and throughput. Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents the analysis of the impact of circuit nonlinearities on the transmission rate of a communication system. We consider a general transmission model that includes transmitter- and receiver-side nonlinearities, environmental thermal noise and receiver chain noise. Using this model we establish lower and upper bounds for the capacity of nonlinear additive white Gaussian noise channels in various thermal noise and receiver noise regimes.

The bit‐error‐rate (BER) performance of orthogonal frequency division multiplexing (OFDM) systems in mobile multi‐hop relaying (MMR) system is severely degraded by the effect of Doppler shift and the severity of this degradation increases with the number of hops traversed by the OFDM signal. In this study, the authors propose a method to mitigate the effect of Doppler shift in MMR system (such as the IEEE 802.16j system) using directional antennas. It is shown that the effect of the resulting inter‐carrier interference (ICI) because of the phase noise generated by the Doppler shift over multi‐hop relaying channels, can be reduced by employing directional antennas at both the mobile and relay stations. Consequently, the BER performance of MMR system is significantly enhanced. Analysis and simulation results show that the BER enhancements using the proposed approach are strongly related to the orientation and beamwidth of the directional antenna employed. As the antenna beamwidth is reduced, the BER enhancement increases for both the perpendicular and parallel antenna orientations, and comparing these two orientations, the parallel orientation case provides slightly better BER enhancements.

We study the impact of nonlinearities on the transmission rate of a communication system by establishing lower and upper bounds on the channel capacity. Our analysis is based on a general transmission model that includes transmitter and receiver nonlinearities, environmental thermal noise, and receiver chain noise. Using this model, we derive lower and upper bounds for the channel capacity of additive white Gaussian noise channels, fading channels, and multiple input multiple output channels in various thermal noise and receiver noise regimes.

ABSTRACT This paper analyzes the bit error rate performance of orthogonal frequency‐division multiplexing systems in mobile multihop relaying channels. We considered the uplink scenario and quantified the effects of mobile channel impairments such as Doppler shift due to user mobility per hop, high power amplifier distortions when amplifying the transmitted/relayed orthogonal frequency‐division multiplexing symbol per hop, and the cumulative effects of these impairments on multihop relaying channels. It was shown that the resulting intercarrier interference due to the cumulative effects of the phase noise generated by these impairments per hop becomes very significant in a multihop relaying communication system and severely degrades the bit error rate performance of the system. Simulation results agree well with and validate the analysis. Copyright © 2011 John Wiley & Sons, Ltd.

This study presents the analysis of a constellation partition (CP) algorithm for multiple-input multiple-output–maximum-likelihood detection (MIMO–MLD) systems. The authors consider an Nt by Nr MIMO system, where MLD algorithm is employed at the receiver side for MIMO signal detection. The authors show that for the case of orthogonal space-time block codes and MIMO beamforming (MIMO-BF) systems, the proposed CP algorithm achieves the same error-rate performance as the optimum MLD algorithm while cutting back significantly on the complexity of MIMO–MLD scheme. Thus complexity reduction is not achieved at the expense of the optimum MLD performance in these cases, unlike the existing simplified MLD schemes in the literature. For the case of MIMO-multiplexing system, however, it is observed that the complexity reduction is achieved at the expense of the optimum MLD performance, similar to the existing simplified MLD schemes. Thus the proposed algorithm is especially attractive in real-time implementation of space-time block code and MIMO-BF systems.

Orthogonal frequency division multiplexing (OFDM) system has been proposed as a technique for broadcasting digital signals and for wireless communication. The bit-error-rate (BER) performance of the OFDM system is severely affected by the nonlinearity of the high power amplifier and by the Doppler effect impairments. In this paper, we analyze the effects induced on the OFDM signal by the amplifier non-linearity and by the Doppler effect over multi-hop relaying channels. Moreover, simulation results are presented to validate the analysis. It is shown that the resulting inter-carrier interference (ICI) due to the cumulative effects of the phase noise generated by these impairments per hop becomes very significant in a multi-hop relaying communication system, and severely degrades the BER performance of the system. Theoretical results show perfect agreement with those obtained by simulation.

This paper presents the analysis of the throughput enhancements using threshold-based PUSC in WiMAX OFDMA system. We consider a point-to-multipoint (PMP) WiMAX network where base station (BS) schedules downlink packets for simultaneous transmissions to multiple users. Using the OFDMA option in the WiMAX standard, users are assigned different subchannels for reception of their data using the same OFDM symbol. In the proposed threshold-based scheduling scheme, the BS scheduler selects at any time instant users whose channel gains in the available subchannels equal or exceed a predetermined energy threshold. Thus, only users who can maximize BS throughput on the available subchannels are assigned data transmission opportunities. We quantify the throughput enhancement of the system, and illustrate its benefits by numerical simulations.

This paper presents the analysis of a constellation-partition (CP) algorithm for multiple input multiple output-maximum likelihood detection (MIMO-MLD) system. We consider an Ntby NrMIMO system where MLD algorithm is employed at the receiver side for MIMO signal detection. We show that the proposed CP algorithm achieves same error rate performance as the optimum MLD algorithm while cutting back significantly on the complexity of MIMO-MLD system. Thus the proposed algorithm is very attractive in real-time implementation of MIMO-MLD systems.

In this paper, we quantify the expected symbol loss probability in mobile multi-hop relaying systems employing Orthogonal Frequency Division Multiple Access (OFDMA) Techniques. We obtain the expected number of collisions and calculate the probability of symbol loss when a conflict occurs between subcarriers of two or more non-transparent relay stations, as well as we calculate the average symbol loss probability in the system. Also, the proportion of symbol with degraded SNR is measured and the collision rate is calculated. Our analysis shows that the resulting collision due to the simultaneous use of a subcarrier in different non-transparent relay stations can be very significant in a multi-hop relaying communication system, and severely degrades the SNR, and affects the QoS support in the system.

This paper presents a capacity-aware linear minimum mean square error (MMSE) detector for orthogonal frequency-division multiplexing/space-division multiple access (OFDM-SDMA) applications. We derive closed-form expressions for the signal-to-interference plus noise ratio (SINR) performance of OFDM-SDMA systems with linear MMSE detection method, where capacity enhancements have been introduced in the transmit/receive weight computations. Using the derived expressions, we compare the performance of the proposed scheme with the regular multiple-input multiple-output (MIMO)-MMSE system in OFDM-SDMA applications. It is shown that in enhancing the system capacity, the capacity-aware MIMO-MMSE scheme also enhances the SINR, resulting in lower symbol error rate (SER) compared to the conventional MIMO-MMSE beamforming schemes.

This paper presents the symbol error rate (SER) performance of a capacity-aware adaptive MIMO beamforming scheme, which seeks iteratively, the beamforming weight vectors that enhance the capacity of OFDM-SDMA systems. We derive closed-form expressions for the SER performance of OFDM-SDMA systems, with MIMO-MRC and the proposed capacity-aware MIMO beamforming scheme. It is shown that the capacity-aware MIMO beamforming scheme enhances the SER performance of OFDM-SDMA systems, and outperforms conventional beamforming schemes such as the MIMO-MRC system.

This paper presents the symbol error rate (SER) performance of a capacity-aware adaptive MIMO beamforming scheme, which seeks iteratively, the optimum beamforming weights that enhance the capacity of OFDM-SDMA systems. We derive closed-form expressions for the SER performance of OFDM-SDMA systems, with MIMO-MRC and the proposed capacity-aware MIMO beamforming scheme. It is shown that the capacity-aware MIMO beamforming scheme enhances the SER performance of OFDM-SDMA systems, and outperforms conventional beamforming schemes such as the MIMO-MRC system.

One of the main challenges for metro-scale WiMAX mesh network deployments is related to capacity scaling. In a full mesh mode, a WiMAX node acts as a mesh router as well as a client access node. To improve latency and speed performance, typical dual- and multi-radio mesh solutions use different radio channels to create separate links for access and mesh relaying services. The available spectrum is therefore split between mesh and client access services. Network operators operating the WiMAX system over the licensed spectrum are not keen to provide separate radio channels for access and mesh relay services, as this reduces the total number of users serviced per spectrum allocation. MIMO-multiplexing relaying approach however provides separate links for access and mesh relaying services on the same radio channel. In this paper, we discuss the multi-hop capacity of OFDM-based MIMO-multiplexing relaying in WiMAX networks. For an NxN MIMO-multiplexing relaying with amplification factor alpha at relay nodes, R-hops relaying degrade the capacity by at most -Nlog2(alpha2R/(1 +SigmaRr-1alpha2rNr)) +RN/log2(N) bits/sec/Hz. Therefore, greater capacity loss is experienced in networks employing high-order MIMO- multiplexing relaying. We also show that the capacity loss is independent of the OFDM configurations employed; thus network operators could employ higher OFDM configurations to compensate data rate loss in access services when some of the MIMO-multiplexing links are dedicated to mesh relay. This analysis provides useful guidelines for operators planning MIMO-multiplexing option for mesh support in WiMAX network.

This paper analyzes the bit error rate (BER) performance of orthogonal frequency division multiplexing (OFDM) system. We derive the BER performance of OFDM system, and quantify the effects of channel impairments such as Doppler shift due to user mobility and high-power amplifier (HPA) distortion when amplifying the transmitted OFDM symbol. It is shown that the resulting inter-carrier interference (ICI) generated by these impairments becomes very significant in OFDM system, and severely degrades its BER performance. Simulation results match well and verify the analysis.

This paper derives the multi-hop capacity of OFDM-based MIMO-multiplexing relaying systems. MIMO-multiplexing relaying presents a spectrally efficient means of realizing mesh supports in wireless networks operating over licensed bands by providing separate links for access and mesh relaying services on the same broadband radio channel. We show that for an NtimesN MIMO-multiplexing relaying system with amplification factor alpha at relay nodes, R-hops relaying degrade the capacity by at most -Nlog2(alpha2R/ (1 + Sigmar=1Ralpha2rNr)) + RNlog2(N) bits/sec/Hz. Therefore, greater capacity loss is experienced in MIMO-multiplexing relaying involving high order MIMO systems. We also illustrate that the capacity loss is independent of the OFDM configurations employed; thus network operators could employ higher OFDM configurations to compensate for data rate loss in access services when some of the MIMO-multiplexing links are dedicated to mesh relay. This pioneering analysis provides useful guidelines for network operators planning to employ MIMO-multiplexing option for mesh relay supports.

MIMO systems using multiple transmit and receive antennas on both ends of a linear wireless communications link are by now well studied. Several axes of these schemes have been explored with the underlying MIMO channel assumed linear. In this work, we investigate the effect of non-linearity in the MIMO channel. New results on symbol error rate performances of several M-QAM constellations in linear and non-linear MIMO channels are presented. The results show that for any MIMO configuration, performance degradation due to non-linearity reduces as the fading gets more severe, and for a particular fading channel, the degradation increases as the MIMO dimension is increased. Optimum ring-ratios for circular QAM constellations in MIMO channels are also reported, and compared with existing results where applicable.

Central features of future 4G mobile communication systems are high-speed data transmission (up to 1 Gb/s) and interactive multimedia services. For effective delivery of these services, the network must satisfy some stringent QoS metrics, defined typically in terms of maximum delay and/or minimum throughput. Mobile satellite systems will be fully integrated with the terrestrial cellular systems to provide ubiquitous global coverage to diverse users. The challenges for future broadband satellite systems, therefore, lie in the proper deployment of state-of-the-art satellite technologies to ensure seamless integration of the satellite networks into the cellular systems and its QoS frameworks, while achieving, as far as possible, efficient use of satellite link resources. The paper presents an overview of future high-speed satellite mobile communication systems, the technologies deployed or planned for deployment, and the challenges. Focusing in particular on nonlinear downlink channel behavior, shadowing and multipath fading, various physical channel models for characterizing the mobile satellite systems are presented. The most prominent technologies used in the physical layer, such as coding and modulation schemes, multiple-access techniques, diversity combining, etc., are then discussed in the context of satellite systems. High-speed and QoS-specific technologies, such as onboard processing and switching, mobility and resource management, IP routing and cross-layer designs, employed in the satellite systems are also discussed.

The severity of fading on mobile communication channels calls for the combining of multiple diversity sources to achieve acceptable error rate performance. Traditional approaches perform the combining of the different diversity sources using either: the conventional selective diversity combining (CSC), equal-gain combining (EGC), or maximal-ratio combining (MRC) schemes. CSC and MRC are the two extremes of compromise between performance quality and complexity. This paper presents a generalized diversity selection combining (GSC) scheme in which only those diversity branches whose energy levels are above a specified threshold are combined. Doing so, the proposed scheme will have a bit error (BER) performance that is upper- and lower-bounded by those of the CSC and MRC schemes respectively. Simulation results for the performances of this scheme over Nakagami (1960) fading channels are shown.