The commercialization of 5G is planned by multiple operators worldwide in the coming few years around 2020. 5G is expected to support new services and higher frequency bands. In particular, the use of higher frequency bands above 6 GHz for mobile communications is one new and important technical challenge tackled by 5G. However, in the initial deployments of 5G, higher frequency bands would only be used for limited areas, e.g., small cell deployments, or fixed wireless access. To further extend the benefits of higher frequency bands to wider coverage and usage, it is important to enable a wide use of higher frequency bands to a similar level as those of existing low frequency bands in terms of coverage, power consumption, etc. In this paper, we present our outdoor experimental trials of long range mobile communications using 39 GHz band. The trial results demonstrate the potential of higher frequency bands to support Gbps class data rates while still providing coverage and supporting mobility over a coverage area of above 1 km.

Non-orthogonal multiple access (NOMA) is a novel multi-user multiplexing scheme that improves spectral efficiency for LTE enhancements and 5G. By overlapping radio resources (e.g., time/frequency/code), but assigning different powers to the multiplexed users, NOMA is able to improve the system performance and fairness. To assess the performance of downlink NOMA under realistic conditions and confirm its feasibility with real hardware, we conducted experimental trials in outdoor environments using smartphone-sized NOMA chipset-embedded devices. This paper introduces our trial setup and trial results of NOMA combined with closed-loop 4×2 SU-MIMO.

The fifth generation mobile communications (5G) system will need to support ultra-reliable and low-latency communications (URLLC) to enable future mission-critical applications, e.g., self-driving cars and remote control. In this paper, we clarify coverage and mobility performance of URLLC by field experimental trials. To achieve URLLC requirements in 5G, we use a new frame structure, which adopts wider subcarrier spacing and acknowledgement/negative acknowledgement-less (ACK/NACK-less) retransmission to reduce the user-plane latency and improve the packet success probability, in this trial. We evaluate the URLLC coverage for several packet sizes using our prototype test-bed. The results show that URLLC requirement in 3GPP can be achieved in UL even when SNR is approximately -3.1 dB. Furthermore, we clarify that the requirement can be satisfied with 25 km/h mobility.

Three 5G enabling technologies, i.e, sparse code multiple access (SCMA), Polar codes and filtered OFDM (f-OFDM), are implemented into a massive MIMO system in the field trial conducted by HUAWEI and NTT DOCOMO to investigate their impacts on the system spectral efficiency. Taking massive MIMO with OFDMA and Turbo codes as the baseline, we observe about 30% downlink spectral efficiency improvement in the trial. Results from test field are summarized and analyzed in this paper, which verified that SCMA, Polar codes and f- OFDM are also feasible for massive MIMO systems in terms of spectral efficiency improvement.

Massive multiple-input multiple-output (MIMO) has been considered as one of the key technologies in 5G communication, owing to its promising potential to increase the spectrum efficiency significantly. The capacity grows rapidly with the increasing number of antennas. However, in real-time environment, the more antennas are employed, the more computing resources are required, and this increase is even in a nonlinear progression. In this work, radio computing architecture (RCA) with multiple parallel general purpose processors (GPPs) and automatic distribution system (ADS) are utilized to overcome the strict real-time constraints and establish a highly flexible prototype platform for massive MIMO research. The feasibility and performance of the GPP-based prototype has been investigated through field trial. A collocated 64-RF-channel base station (BS) with each RF channel driving 3 antennas can simultaneously serve twelve 8-antenna user equipments (UEs). The maximum overall bandwidth is 200 MHz, and the maximum flow number is pre-defined as 24. In this field trial, a peak total user throughput of 11.29 Gbps and a cell spectrum efficiency of 79.82 bps/Hz are achieved. As far as we know, this is the world's highest throughput ever achieved in the sub 6 GHz band. Furthermore, apart from multi-user MIMO, single-user MIMO is also tested in this field trial.

This paper presents a field experimental trial on frequency-domain multiplexing of a mixture of multiple numerologies. The goal is to support diverse applications and services in the fifth generation mobile communications (5G) system. Frequency-domain multiplexing of mixed numerology has been discussed for 5G in order to flexibly support the variety of requirements introduced by future applications. However, frequency-domain multiplexing of mixed numerology causes inter sub-band interference. In this paper, we apply filtered-orthogonal frequency division multiplexing (f-OFDM), which is a new waveform, in order to reduce the inter sub-band interference. Through the field trial, we show that f-OFDM realizes mixed numerology while reducing the impact from inter sub-band interference compared to conventional cyclic prefix OFDM. The field trial results show that f-OFDM has no throughput degradation when using more than one guard subcarrier.

Radio frequency (RF) channel reciprocity calibration is one of the most important technologies in massive multiple-input multiple-output (MIMO) system. With the increasing of the antenna size, the calibration procedure becomes much more challenging. In this paper, wired- and wireless-calibration schemes have been proposed and investigated through field-trial test based on a real-time massive MIMO prototype with 64 independent RF channels. The prototype is capable of supporting 12 200-MHz user equipments (UEs) simultaneously. The field trial test results validate both schemes can significantly improve the overall system throughput. For single-user (SU) MIMO scenario, the throughput can be enhanced from 0.71 Gbps to 1.46 Gbps and 1.54 Gbps with wireless- and wired-calibration schemes, respectively. For multi-user (MU) MIMO scenario, the corresponding enhancement can be from 0.26 Gbps to 9.18 Gbps and 11.29 Gbps, respectively. In terms of calibration accuracy, the wired-calibration scheme has better performance, but the wireless one has lower system complexity and cost. To the best of our knowledge, this is the first field trial investigation of wireless-calibration scheme and comparison with wired calibration in a real-time high-throughput massive MIMO prototype.

The 5th generation of mobile communications system (5G) is nowadays expected to support very diverse applications, devices, and services such as enhanced mobile broadband (eMBB) and the Internet of things (IoTs). In order to meet the future requirements, new 5G candidate radio access technologies have been proposed and studied. For example, Massive multiple-input multiple-output (MIMO) is an attractive technology to further improve the spectrum efficiency and to boost system capacity. This paper presents a large scale field experimental trial of downlink time division duplex (TDD) Massive MIMO using the developed 5G test bed at the 4.5 GHz band. Specifically, the system performance of multi-user (MU) Massive MIMO with different numbers of sets of user equipment (UEs) and spatial layers is investigated, including the impact of different inter-UE separations and UE deployments, which have not been well investigated compared to the previous studies. The experimental results show that the throughput performance for a wide UE separation linearly increases as the number of layers and UEs increases, while the performance improvement is diminished when inter-UE separation narrows. In addition, the maximum total user throughput of 11.29 Gbps, which corresponds to a spectrum efficiency of 79.82 bps/Hz/cell, was achieved with 24 layers. The results indicate that TDD Massive MIMO using the developed 5G test bed greatly improves the spectrum efficiency for large scale MU-MIMO.

Service diversity is expected in the upcoming fifth-generation (5G) cellular networks, which poses great challenges to the underlying waveforms to accommodate heterogeneous service requirements in a flexible way. By dividing the bandwidth into several subbands, each having a different numerology, this paper reports a field trial in time division duplex downlink conducted on a configurable test bed in a real-world environment for the performance evaluations of orthogonal frequency-division multiplexing (OFDM)-based 5G waveform candidates, i.e., cyclically prefixed OFDM (CP-OFDM), windowing OFDM (W-OFDM), and filtered OFDM (f-OFDM), in the presence of mixed numerologies. Field trial results confirm the feasibility of mixed numerologies and reveal the impact of several important system parameters, e.g., guard bandwidth, data bandwidth, signal-to-noise ratio (SNR), and transmit power. The results also suggest that f-OFDM outperforms CP-OFDM and W-OFDM in terms of both the spectrum efficiency and robustness in a high SNR regime, and the gain increases with a higher inter-numerology out-of-band interference. In some specific scenarios, ideal spectrum utilization can be realized by f-OFDM which completely removes the guard band.

There is considerable pressure to define the key requirements of 5G, develop 5G standards, and perform technology trials as quickly as possible. Normally, these activities are best done in series but there is a desire to complete these tasks in parallel so that commercial deployments of 5G can begin by 2020. 5G will not be an incremental improvement over its predecessors; it aims to be a revolutionary leap forward in terms of data rates, latency, massive connectivity, network reliability, and energy efficiency. These capabilities are targeted at realizing high-speed connectivity, the Internet of Things, augmented virtual reality, the tactile internet, and so on. The requirements of 5G are expected to be met by new spectrum in the microwave bands (3.3-4.2 GHz), and utilizing large bandwidths available in mm-wave bands, increasing spatial degrees of freedom via large antenna arrays and 3-D MIMO, network densification, and new waveforms that provide scalability and flexibility to meet the varying demands of 5G services. Unlike the one size fits all 4G core networks, the 5G core network must be flexible and adaptable and is expected to simultaneously provide optimized support for the diverse 5G use case categories. In this paper, we provide an overview of 5G research, standardization trials, and deployment challenges. Due to the enormous scope of 5G systems, it is necessary to provide some direction in a tutorial article, and in this overview, the focus is largely user centric, rather than device centric. In addition to surveying the state of play in the area, we identify leading technologies, evaluating their strengths and weaknesses, and outline the key challenges ahead, with research test beds delivering promising performance but pre-commercial trials lagging behind the desired 5G targets.

Spectral efficiency is always a key factor to be improved and optimized along mobile communication networks evolving generation by generation. 5G enabling technologies must take spectral efficiency into consideration. In this paper, we show the performance of three key 5G technologies in sense of spectral efficiency improvement. Sparse code multiple access, polar codes, and filtered orthogonal frequency-division multiplexing are novel multiple access technology, channel coding scheme, and waveform, respectively. The combination of them is implemented in a 5G field trial testbed by NTT DOCOMO and Huawei for the first time. According to the field test results, we achieve over 100% spectral efficiency improvement comparison with baseline, where orthogonal frequency-division multiple access and turbo coding as LTE are used.

Recently, NTT DOCOMO and Huawei conducted a large-scale experimental trial of key technologies for the 5th generation (5G) mobile systems. Downlink multi-user (MU) transmission with massive MIMO in the time-division duplex (TDD) mode is one of the technologies evaluated in this trial. With linear and non-linear downlink precoding schemes, we investigated the practical performance of MU massive MIMO systems under different numbers of users, user distributions, and different radio frequency channel calibration settings with up to 24 users deployed. When linear precoding is used, the cell spectrum efficiency reaches 39 bit/s/Hz, and it reaches 43 bit/s/Hz when non-linear precoding is used. In term of the cell throughput, up to 1.35 Gbps cell throughput was observed with a linear precoder and 100 MHz bandwidth; and 343 Mbps cell throughput was observed with a non-linear precoder and 20 MHz bandwidth. Based on these investigations, we verified the feasibility and performance of a TDD massive MIMO system for 5G mobile systems, and studied the impact of key factors on the system performance.

As a promising downlink multiple access scheme for further cellular enhancements toward 5G, non-orthogonal multiple access (NOMA) improves both cell average and cell-edge user throughput compared to orthogonal multiple access (OMA). Our previous work showed that NOMA can improve system performance compared with OMA even when combined with multiple-input multiple-output (MIMO). However, for NOMA with MIMO, the inter-user interference becomes a dominant part of the signal-to-interference-and-noise ratio (SINR). Thus, the conventional channel information feedback scheme, which is based on channel quality indicator (CQI) feedback for OMA, is insufficient for base station (BS) to perform accurate modulation and coding scheme (MCS) selection for NOMA users. In this paper, we propose two enhanced channel feedback schemes to improve performance of channel feedback for NOMA systems. One is based on outer loop link adaptation (OLLA), which controls the feedback update by a predefined time window to improve the accuracy. No extra feedback signaling is needed in the scheme. The other one improves the original channel feedback by an extra quantized increment feedback from user equipment (UE) to BS, which benefits BS with more information for MCS selection. The performance improvements of NOMA with closed-loop (CL) single-user (SU) MIMO are investigated by system-level simulations with practical assumptions. Simulation results show that the performance gains of NOMA for both cell average and cell-edge user throughputs improve with the proposed channel feedback schemes.

Emerging new applications, such as Internet of Things (IoT), gigabit wireless connectivity, tactile internet, and many more are expected to impose new and diverse requirements on the design of the fifth generation (5G) of cellular communication systems. In recent years, many alternative multicarrier waveforms are being investigated with the aim to identify to what extent it would be possible to better address these diverse requirements compared to Cyclic Prefix (CP) OFDM, which is currently adopted by LTE/LTE-Advanced. However, most of these investigations considered in many research activities have focused on theoretical considerations or simulations and mainly with emphasis on only one alternative waveform. In this paper, we present ongoing work based on measurement results where real hardware experiments are conducted to investigate the performance of three waveform families: CP-OFDM, filter bank multicarrier with offset quadrature amplitude modulation (FBMC/OQAM) and universal-filtered OFDM (UF-OFDM). FBMC/OQAM has the benefit of very low sidelobes leading to less inter-carrier interference in asynchronous and high mobility scenarios, whereas the typically long filter leads to low efficiency for short blocks and the use of OQAM makes it nontrivial to adopt certain schemes well-developed for CP-OFDM. UF-OFDM combines the benefits of CP-OFDM with the advantage of significantly lower out-of-band radiation while avoiding the drawbacks of FBMC/OQAM. In this paper we compare the performance of these alternative waveforms under several 5G targeted scenarios.

Non-orthogonal multiple access (NOMA) utilizing transmit power difference and advanced successive interference canceller (SIC) receivers has been considered as a candidate radio access technology for future wireless communication systems. Single-user multiple-input multiple-output (SU-MIMO) is one of the key technologies in Long-Term-Evolution (LTE) systems. Thus, it has been proved to combine with NOMA for further system performance improvement. In previous studies, SIC receiver is adopted at cell center users (UEs), while SIC processing is not taken into account at cell-edge UEs, considering the feasibility of UE receiver and control signaling overhead. However, it may put limitation on the performance of NOMA. To further enhance the performance of NOMA with SU-MIMO, advanced receiver can be considered at cell-edge UEs. In this paper, we investigate the impact of applying the SIC receiver at cell-edge UEs in downlink NOMA with SU-MIMO. The detail SIC detection schemes at cell-edge UE will be discussed, including ideal SIC processing and non-ideal SIC processing. The simulation results show that performance gains of NOMA can be improved with SIC processing at cell-edge UEs. It indicates that more advanced receiver can be considered for cell-edge UE to achieve upper-bound performance.

Non-orthogonal multiple access (NOMA) utilizing power domain and advanced receiver has been considered as a very promising candidate radio access technology for future wireless communication systems. Hybrid automatic repeat request (HARQ), as an indispensable part of link adaptation, plays a very important role in reliable high speed packet data service through exploiting retransmission diversity and channel coding gain. In this paper, we investigate HARQ design for downlink NOMA with single user-multiple input multiple output (SU-MIMO). The impacts of user pairing, precoding matrix adaptation and transmission power assignment (TPA) ratio adaptation in retransmission on NOMA performance are investigated. An enhanced HARQ algorithm is proposed, where opportunistically HARQ combining is applied and the TPA of retransmission considers HARQ combining gain of the retransmission user. It is found that HARQ probability of NOMA is much higher than that of OMA and flexible retransmission strategies could increase performance gain of NOMA. Furthermore, it found the (wrong, correct) is the dominate case in NOMA HARQ and thus is of most importance for enhanced NOMA HARQ design. Simulation results show the proposed HARQ algorithm is effective and can achieve better performance than the existing algorithm.

This paper presents the link-level performance of downlink non-orthogonal multiple access (NOMA) with successive interference cancellation (SIC) receiver, considering the influence of error vector magnitude (EVM). In our evaluations, for the case of a 1-by-2 transmission and the number of NOMA multiplexed users is two, we clarify the performance of NOMA for cell-center user equipment (UE) with codeword level SIC (CWIC) receiver and the performance of the cell-edge UE, which does not apply SIC. Based on link-level performance evaluations, we show that the performance of CWIC receiver is almost the same as that of ideal SIC when the allocated transmit power ratio to cell-center UE is less than 0.35, the modulation and coding scheme (MCS) of cell-center UE is 16QAM (R = 0.51) or 64QAM (R = 0.47), and the MCS of cell-edge UE is QPSK (R = 0.51). Furthermore, we also show that, when EVM value is 4 % and the allocated power ratio to cell-center UE is between 0.2 and 0.37, the level of degradation due to the influence of EVM is below 0.6 dB, which is almost the same level of degradation as that of orthogonal frequency division multiple access (OFDMA) for the EVM value required by 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE). On the other hand, we show that the influence of EVM is marginal for cell-edge UE compared to cell-center UE. However, when the cell-center UE uses a higher order modulation such as 64QAM, we show that the required SNR of cell-edge UE increases due to the increase in inter-user interference. Based on these results, we clarify that it is important for the base station (BS) to take into account the target BLER and influence of EVM when selecting the MCS and allocated transmit power ratio of NOMA UEs.

Non-orthogonal multiple access (NOMA) is a promising multiple access scheme for further improving the spectrum efficiency compared to that for orthogonal multiple access (OMA) in the 5th Generation (5G) mobile communication systems. All of the existing evaluations for NOMA focus on the macrocell deployment since NOMA fully utilizes the power domain and the difference in channel gains, e.g., path loss, between users, which is typically sufficiently large in macrocells. Currently, small cells are becoming important and being studied for future Long-Term Evolution (LTE) enhancements in order to improve further the system performance. Thus, it is of great interest to study the performance of NOMA for small cell deployment under various environments. This paper investigates the system level performance of NOMA in small cells considering practical assumptions such as the single user multiple-input multiple-output (SU-MIMO) technique, adaptive modulation and coding (AMC), feedback channel quality indicator (CQI). Some of the key NOMA specific functionalities, including multi-user paring and transmit power allocation are also taken into account in the evaluation. Based on computer simulations, we show that for both macrocell and small cell deployments, NOMA can still provide a larger throughput performance gain compared to that for OMA.

Non-orthogonal multiple access (NOMA) is one of the promising radio access techniques for further cellular enhancements toward 5G. Compared to orthogonal multiple access (OMA) such as orthogonal frequency-division multiple access (OFDMA), large performance gains were confirmed via system-level simulations. However, NOMA link-level simulations and the design of the receiver remain of great importance to validate NOMA performance gains. In this paper, we evaluate downlink NOMA link-level performance with multiple receiver designs and propose a novel NOMA transmitter and receiver design, where the signals of multi-users are jointly modulated at transmitter side and detected at receiver side. The predominant advantage of the proposed scheme is that at receiver side interference cancellation to the interference signal is not needed, thus low complexity is achieved. The performances of codeword-level SIC, symbol-level SIC and the proposed receiver are evaluated and compared with ideal SIC. Simulation results show that compared with ideal SIC, downlink NOMA link-level performance depends on actual receiver design and the difference in the power ratio split between the cell edge user and cell center user. In particular, it is shown that codeword-level SIC and the proposed receiver can both provide a good performance even when the power ratio difference between the cell center user and cell edge user is small and with real channel estimation.

Non-orthogonal multiple access (NOMA) has been attracting a lot of attention as a promising downlink multiple access scheme for LTE enhancements and 5G. This paper introduces an overview of the concept, performance evaluation gains and our experimental trials related to NOMA. The goal is to clarify the benefits of NOMA over orthogonal multiple access (OMA) such as OFDMA adopted by Long-Term Evolution (LTE), also its combination with MIMO is discussed. Using computer simulations, NOMA performance gains are assessed from both link-level and system-level perspectives. Also, our NOMA test-bed and the measurement results are explained. Our evaluation results and measurements show that NOMA provides higher gains compared to OFDMA. These gains are more than 30%.

Non-orthogonal multiple access (NOMA) is a promising radio access technique for further cellular enhancements toward 5G. Single-user multiple-input multiple-output (SU-MIMO) is one of the key technologies in LTE /LTE-Advanced systems. Thus, it is of great interest to study how to efficiently and effectively combine NOMA and SU-MIMO techniques together for further system performance improvement. This paper investigates the combination of NOMA with open-loop and closed-loop SU-MIMO. The key issues involved in the combination are presented and discussed, including scheduling algorithm, successive interference canceller (SIC) order determination, transmission power assignment and feedback design. The performances of NOMA with SU-MIMO are investigated by system-level simulations with very practical assumptions. Simulation results show that compared to orthogonal multiple access system, NOMA can achieve large performance gains both open-loop and closed-loop SU-MIMO, which are about 23% for cell average throughput and 33% for cell-edge user throughput.

Non-orthogonal multiple access (NOMA) is a promising radio access technique for LTE release 13 and beyond. In this paper, we focus on the investigation of the system performance for uplink NOMA with an advanced successive interference cancellation (SIC) receiver applied in the base station side. In NOMA, more than one user can be multiplexed simultaneously in the same frequency bandwidth, which demands multi-user scheduling. In our study, we propose an enhanced proportional fair (PF) based scheduling scheme for non-orthogonal multiplexed users with contiguous resource allocation to retain the SC-FDM property. In order to reduce the scheduling complexity for non-orthogonal multiple access, a greedy consecutive resource allocation method is adopted. Moreover, since the interference condition becomes more complicated in NOMA, we consider the application of fractional frequency reuse (FFR) to NOMA to further enhance the performance of cell-edge users. In simulation results, the system performance of NOMA by using the proposed PF-based scheduling algorithm is evaluated. The results show that NOMA significantly enhances the uplink system performance compared to the conventional orthogonal multiple access.

This paper investigates inter-cell interference mitigation of non-orthogonal multiple access (NOMA) in the cellular downlink. A novel adaptive power and frequency resource allocation algorithm in the NOMA system is proposed for performance enhancement. The objective of the algorithm is to improve both the average cell throughput and cell-edge throughput through adaptive resource allocation in the power and frequency domains. The proposed algorithm improves the cell-edge throughput by providing better protection against inter-cell interference in the power domain while increasing the average cell throughput by providing more resources in the frequency domain. Numerical results show that the proposed algorithm yields significant improvements in the cell average throughput and cell-edge throughput by reducing the interference for cell-edge users and expanding the bandwidth for cell interior users.

Non-orthogonal multiple access (NOMA) utilizing power domain and advanced receiver is a promising technique for future radio access. Multi-antenna techniques have been deeply studied during the past decade to boost system performance by virtue of spatial multiplexing and/or spatial diversity. It is of great interest to study how to efficiently and effectively combine the two techniques together for further system performance improvement. This paper investigates on the combination of NOMA with opportunistic beamforming (OBF), which has been proposed as a practical multi-antenna transmission scheme with good performance and very limited feedback. The key design issues of NOMA with OBF are investigated including precoding, transmission power assignment, user feedback and scheduling. Furthermore, a method to improve the system performance with OBF is proposed by utilizing historical information. The performance of NOMA with OBF is investigated by system-level simulations with very practical assumptions and parameters in order to provide insights into the suitability of combining OBF with NOMA for future radio access. Simulation results show the proposed method is effective and NOMA with OBF is a promising scheme for future wireless communication systems.

As a promising downlink multiple access scheme for further LTE enhancement and future radio access (FRA), this paper investigates the system-level performance of non-orthogonal multiple access (NOMA) with a successive interference canceller (SIC) on the receiver side. The goal is to clarify the potential gains of NOMA over orthogonal multiple access (OMA) such as OFDMA, taking into account key link adaptation functionalities of the LTE radio interface such as adaptive modulation and coding (AMC), hybrid automatic repeat request (HARQ), time/frequency-domain scheduling, and outer loop link adaptation (OLLA), in addition to NOMA specific functionalities such as dynamic multi-user power allocation. Based on computer simulations, we show under multiple configurations that the system-level performance achieved by NOMA is superior to that for OMA.

This paper presents a non-orthogonal multiple access (NOMA) concept for cellular future radio access (FRA) towards the 2020s information society. Different from the current LTE radio access scheme (until Release 11), NOMA superposes multiple users in the power domain although its basic signal waveform could be based on the orthogonal frequency division multiple access (OFDMA) or the discrete Fourier transform (DFT)-spread OFDM the same as LTE baseline. In our concept, NOMA adopts a successive interference cancellation (SIC) receiver as the baseline receiver scheme for robust multiple access, considering the expected evolution of device processing capabilities in the future. Based on system-level evaluations, we show that the downlink NOMA with SIC improves both the capacity and cell-edge user throughput performance irrespective of the availability of the frequency-selective channel quality indicator (CQI) on the base station side. Furthermore, we discuss possible extensions of NOMA by jointly applying multi-antenna/site technologies with a proposed NOMA/MIMO scheme using SIC and an interference rejection combining (IRC) receiver to achieve further capacity gains, e.g., a three-fold gain in the spectrum efficiency representing a challenging target for FRA.

We consider the performance and improvement of Multi-User MIMO (MU-MIMO) in 3GPP LTE. In particular, we build on academic guidance, demonstrating the link between channel state information (CSI) accuracy and MU-MIMO performance, by considering MU-MIMO with practical CSI estimation and feedback within an actual system design under practical channels. Link-Level simulations are provided to model the interplay of such factors in the LTE design. We also propose a practical codebook structure to support increased CSI feedback. The results show that for some scenarios, in particular those with sufficient channel coherence and low antenna correlation, that MU-MIMO can be significantly improved by increased CSI feedback. Such conditions may be indicative of “small-cell” scenarios, an important scenario for future network capacity enhancement. The results also point to other issues that merit further consideration including CSI feedback granularity in frequency, CSI estimation, and improved MU-MIMO processing.

Interference management is essential toward improving spectral efficiency in wireless networks. During the last decade inter-antenna interference management via multiple-input multiple output (MIMO) transmission has attracted attention for its capability to enhance link spectral efficiency. In a cellular environment, however, inter-cell interference imposes another limit on link spectral efficiency and for MIMO transmission in particular only a marginal portion of the expected gains is obtained. In this paper, as a candidate solution to reduce inter-cell interference and consequently enhance the gains achieved by MIMO, we investigate a coordinated wireless network where multiple base stations are connected to a central station that multiuser (MU)-MIMO precodes ongoing simultaneous transmissions from all coordinated base stations. Specifically, our main goal is to clarify the impact of coordination on spectral efficiency and evaluate user throughput with and without transmit power optimization, for both a hotspot scenario where all base stations can be coordinated (full coordination) and a cellular scenario where only the base stations grouped under the same cluster are coordinated (partial coordination).

In this paper we study pulse shaping with the goal of exploiting cyclostationarity to realize partially-coordinated flexible spectrum sharing. As a case study, we assume that two signals are sharing the same bandwidth, while having different symbol rates; the signals may not be completely coordinated when accessing the shared spectrum. To allow for spectrum sharing, cyclostationarity is induced by pulse shaping at the transmitter; it is exploited at the receiver for signal extraction by cyclic Wiener filtering. For several examples of coordination between the spectrum sharing signals, pulse shaping schemes are proposed and their corresponding signal extraction schemes are described and assessed using computer simulations

We study cyclic Wiener (CW) filtering based interference rejection to deal with unknown jamming interference. A desired wideband signal is assumed to spectrally overlap with an unknown narrowband interference. At the receiver, the CW filter exploits the spectral redundancy associated with pulse shaping the desired signal for rejecting the interference and recovering the desired signal. Its performance, however, largely depends on the carrier frequency offset between the desired and interfering signals and the amount of excess bandwidth associated with pulse shaping the desired signal. To alleviate these problems, we propose new pulses that we name as time-domain shrunk raised cosine pulses. Proposed pulses satisfy the Nyquist criterion and, compared to conventional raised cosine pulses, largely improve the ability of CW filtering at rejecting in-band interference, even for a less amount of excess bandwidth. Besides, the almost- flat shape of their frequency response is shown to entail a good performance for CW filtering irrespective of the carrier frequency offset between the desired and interfering signals.

MIMO wireless systems are able to realize communication links with high spectral efficiency and high performance. By the transmission of different data streams at the same time and on the same frequency but from different transmit antennas, the spectral efficiency of MIMO systems can be increased linearly with the number of transmit antennas. However, to achieve such enormous spectral efficiencies, one of the major limitations is the complexity of the receiver that needs to separate several overlapped cochannel signals whose number increases with the number of transmit antennas. We investigate the performance of low complexity ordered successive MMSE receivers with realistic channel estimations. Generation of nulling weights by both recursive and non-recursive approaches is studied. In order to compromise performance and complexity, novel ordered successive receivers where both approaches are combined are proposed. Those new receivers are named as semi-adaptive ordered successive receivers.

In recent years, a lot of attention has been drawn to the use of multiple antennas at both the transmitter and receiver sides. Such techniques are named here as space-time transmission and noted as STT. By their use of the available space dimension, STT techniques can achieve very high spectral efficiencies in Rayleigh fading channels with rich scattering. The use of STT techniques for indoor wireless systems with a huge number of antennas is considered. As a low complexity detection algorithm, ordered successive detection based schemes are considered. A scheme known as V-BLAST (vertical Bell Labs layered space-time) is proposed in the zero forcing (ZF) criterion (see Wolniansky, P.W. et al., Proc. ISSSE'98, 1998). In a previous work, it has been shown how this scheme can be much improved by the use of a backward iterative detection algorithm (see Benjebbour, A. et al., Proc. WPMC, p.819-24, 2000; Proc. VTC2001 Spring, 2001). An extension of the conventional V-BLAST algorithm to the minimum mean square error (MMSE) criterion is now proposed. For the proposed receiver, an ordering metric is defined. Then, the effect of ordering on both receivers is discussed. And finally, it is shown how the ordering metric in the MMSE criterion can be simplified.