A user-centric no-cell (UCNC) framework has been proposed which enables different level coordination over a large number of TRPs. This paper presents some key technologies in UCNC framework with the focus on PoC of UL grant- free transmissions in UCNC architecture. Massive connectivity support is one of the three important scenarios in 5G networks. The challenges to support massive connectivity lie in the cost of signaling overhead and transmission latency. An uplink grant- free transmission based on SCMA (sparse code multiple access) design is proposed. The proposed scheme can provide different levels of overloading to efficiently meet the massive connectiv- ity requirements. Extensive lab tests have been conducted to verify the performance matrices. Taken LTE as a baseline for comparison purpose, it is shown that the signaling overhead by using uplink grant-free transmission can be reduced by around 80% and the user plane transmission latency in ECO state can be reduced by around 93%. Moreover, massive connectivity is efficiently supported with SCMA scheme that yields around 230% gain over OFDMA in terms of supported active users.

A 5G mobile network has evolved from a cell centric radio access network to a user centric one. A user-centric no-cell (UCNC) framework has been proposed, which enables physical layer coordination over a large number of transmission and reception points for each mobile user to always experience cell-center-like communications. This paper presents some key technologies in the UCNC framework. The focus is on proof of concept of UL grant-free transmissions in the UCNC architecture. Massive connectivity supporting a huge number of devices is one of the three important scenarios in 5G networks. The challenges to support massive connectivity lie in the cost of signaling overhead and transmission latency. An uplink grant-free transmission based on sparse code multiple access (SCMA) design is proposed. The proposed scheme can provide different levels of overloading to efficiently meet the massive connectivity requirements. Grant-free transmission conducted in RRC connected state can reduce signaling overhead, while in energy conserved operation (ECO) state, it can significantly reduce the user plane transmission latency. Extensive laboratory testing has been conducted in a collaborative project of Huawei and Telefonica to verify the performance matrices. Taking LTE as a baseline for comparison purposes, it is shown that the signaling overhead by using uplink grant-free transmission can be reduced by around 80% and the user plane transmission latency in ECO state can be reduced by around 93%. Moreover, massive connectivity is efficiently supported with the SCMA scheme that yields around 230% gain over OFDMA in terms of supported active users.

Sparse code multiple access (SCMA) is a code domain non-orthogonal multiple-access technique introduced for future 5G wireless networks. This paper describes the basic ideas of SCMA, the SCMA codebook design, the encoder and decoder, as well as the SCMA enabled transmission schemes for different application scenarios, including uplink grant-free contention-based transmission, downlink multi-user superposition, and downlink open-loop CoMP for ultra-dense networks even with moving users. We shall show from design principles and application examples that SCMA can resolve some major issues of current wireless systems and establish itself as a strong candidate for 5G networks.

Applying 6-100 GHz spectrum to mobile communications is a promising topic in 5G. In this paper, a hybrid network is presented where LTE system at low frequency works for seamless coverage and a mmWave system at 72 GHz works in hotspots for capacity enhancement. The scheme for the hybrid network includes: 1) frame structure and OFDM-based numerology for 72 GHz; 2) time-space beam switching method for beamforming; 3) zero-forcing MIMO precoding for interference cancellation; 4) a channel model based on measurements in [1] for simulation. System-level simulations show that the hybrid network can achieve the system throughput over 1600 times higher than that in 2 GHz frequency band in case of two streams. MIMO precoding is not mandatory for capacity enhancements because the effect of intra-cell interference is not severe. Thus, 72 GHz is a promising spectrum band that can well meet 5G requirements from the aspects of capacity and maximum data rate.

The spectral efficiency enhancement for 5G air interface represents a technical challenge. In addition to the higher capacity requirement, 5G system will also address massive connectivity demand for 5G applications, such as IoT. A straightforward re-design of OFDM based LTE by using different radio parameter set cannot meet the challenges from the diverse 5G usage scenarios. In this paper, we present 5G radio access technologies by exploiting inter-block non-orthogonality and Intra-block non-orthogonality. The interblock non-orthogonality is achieved by block filtering of OFDM sub-block, and the Intra-block non-orthogonality is achieved by Sparse Code Multiple Access based on optimized sequence design. Such a framework can unify the large numbers of radio links for very diverse services and also provides increased spectral efficiency. In particular, when combined with emerging polar codes, we can further increase the spectral efficiency for smaller packets and support excessive number of connection links. Several design details for this novel air-interface will be presented.

The underlying waveform has always been a shaping factor for each generation of the cellular networks, such as orthogonal frequency division multiplexing (OFDM) for the 4th generation cellular networks (4G). To meet the diversified and pronounced expectations upon the upcoming 5G cellular networks, here we present an enabler for flexible waveform configuration, named as filtered-OFDM (f-OFDM). With the conventional OFDM, a unified numerology is applied across the bandwidth provided, balancing among the channel characteristics and the service requirements, and the spectrum efficiency is limited by the compromise we made. In contrast, with f-OFDM, the assigned bandwidth is split up into several subbands, and different types of services are accommodated in different subbands with the most suitable waveform and numerology, leading to an improved spectrum utilization. After outlining the general framework of f-OFDM, several important design aspects are also discussed, including filter design and guard tone arrangement. In addition, an extensive comparison among the existing 5G waveform candidates is also included to illustrate the advantages of f-OFDM. Our simulations indicate that, in a specific scenario with four distinct types of services, f-OFDM provides up to 46% of throughput gains over the conventional OFDM scheme.

Cooperation among network nodes at one side and terminal nodes on the other side are the two main enablers of radio access virtualization to establish scalable and dynamically adjustable data pipes to the users in the 5G mobile networks. User cooperation requires careful design to address cooperation incentive, battery life, user discovery, security and privacy. Dummy user, a network-aware terminal, can facilitate the implementation of user cooperation and leverage its benefits. Dummy users can offer a low cost alternative for the enhancement of the network performance to address persistent or temporary demand such as a hotspot created by an outdoor festival. Proper deployment of dummy users provides fairness and ubiquity of the network while enabling many advanced transmission and reception schemes that require more accurate channel state knowledge at the network.

An adjustable pulse bandwidth single carrier waveform for asynchronous low-cost low-power 5G M2M applications is proposed. The solution uses ultra narrow-band pulse to improve coverage, which is a much more efficient coverage enhancement solution than existing repetition solutions. Frequency localized pulse shaping is used, which allows asynchronous transmission and packing more machine-type devices (MTDs) for the same spectrum resources. In addition, bandwidth of each MTD is configurable based on long term channel quality and system load, which supports higher throughput and lower power consumption. Performance comparison with the repetition solution of 3GPP LTE demonstrates significant gain in terms of number of supported connections.

The weighted circularly convolved OFDM/OQAM (WCC-OFDM/OQAM), a variant of OFDM/OQAM without time-domain tail overhead, is investigated in a doubly dispersive fading environment. A new receiver is proposed that resolves the self-interference present at a regular WCC-OFDM/OQAM receiver when the channel variations are too fast compared to the signal burst duration. This is achieved by exploiting the channel state information (CSI) available at the receiver to compensate for the channel discontinuity that appears in the receiver's circular operations. The proposed receiver is universal in two regards: first, it performs equally well for a wide range of speeds and modulation and coding schemes (MCSs), and second, it does not require any change to the WCC-OFDM/OQAM signal structure, and thus, is transparent to the transmitter.

A virtualized radio access network (VRAN) is envisaged in next generation wireless networks. Therein, users experience a seamless ubiquitous service without cell-specific signaling through transparent grouping of densely deployed transmit points (TPs) and helping UEs. Aiming at reducing the Carbon footprint as well as the operational expenditure while maintaining users' QoS, we propose an energy/cost-aware dynamic wideband muting and traffic offloading scheme for the VRAN. The proposed scheme favors muting hypotheses with greater energy/cost savings from TPs with relatively light traffic loads. Such loads are opportunistically offloaded to adjacent TPs to improve their energy efficiency. This is achieved by employing a low-complexity joint wideband muting and multi-point scheduling algorithm optimizing a novel energy-aware utility. The utility accounts for the power consumption models of different TPs, the current cost per unit energy and the TP's predicted 'Soft Loading Ratio'. Operator controls the energy savings-performance tradeoff in individual network regions regardless of the topology. Simulation results show significant energy efficiency and system capacity gains.

Sparse Code Multiple Access (SCMA), a non-orthogonal multiple access scheme, has been introduced as a key 5G technology to improve spectral efficiency. In this work, we propose SCMA to enable open-loop coordinated multipoint (CoMP) joint transmission (JT). The scheme combines CoMP techniques with multi-user SCMA (MU-SCMA) in downlink. This scheme provides open-loop user multiplexing and JT in power and code domains, with robustness to mobility and low overhead of channel state information (CSI) acquisition. The combined scheme is called MU-SCMA- CoMP, in which SCMA layers and transmit power of multiple transmit points (TPs) are shared among multiple users while a user may receive multiple SCMA layers from multiple TPs within a CoMP cluster. The benefits of the proposed scheme includes: i) drastic overhead reduction of CSI acquisition, ii) significant increase in throughput and coverage, and iii) robustness to channel aging. Various algorithms of MU-SCMA-CoMP are presented, including the detection strategy, power sharing optimization, and scheduling. System level evaluation shows that the proposed schemes provide significant throughput and coverage gains over OFDMA for both pedestrian and vehicular users.

Sparse code multiple access (SCMA) is a new frequency domain non-orthogonal multiple-access technique which can improve spectral efficiency of wireless radio access. With SCMA, different incoming data streams are directly mapped to codewords of different multi-dimensional cookbooks, where each codeword represents a spread transmission layer. Multiple SCMA layers share the same time-frequency resources of OFDMA. The sparsity of codewords makes the near-optimal detection feasible through iterative message passing algorithm (MPA). Such low complexity of multi-layer detection allows excessive codeword overloading in which the dimension of multiplexed layers exceeds the dimension of codewords. Optimization of overloading factor along with modulation-coding levels of layers provides a more flexible and efficient link-adaptation mechanism. On the other hand, the signal spreading feature of SCMA can improve link-adaptation as a result of less colored interference. In this paper a technique is developed to enable multi-user SCMA (MU-SCMA) for downlink wireless access. User pairing, power sharing, rate adjustment, and scheduling algorithms are designed to improve the downlink throughput of a heavily loaded network. The advantage of SCMA spreading for lightly loaded networks is also evaluated.

Virtual radio access (VRA) technology wherein groups of cooperative transmit points (TPs) form virtual TPs (VTPs) to serve user equipments (UEs) continue to be a thriving subject of research in future generations of wireless networks. In this paper, we propose a technique that uses UE-centric metrics to provide multiple partitions of a wireless network into VTP sets. Our technique guarantees that all UEs enjoy a required gain in at least one VTP; effectively eliminating the edge UE experience in the network. To further enhance the performance of the proposed VRA technique in practical scenarios wherein there is a large load imbalance in the network, we also introduce a new concept of soft UE-TP association in which each UE is partially associated with multiple TPs. The use of our soft association concept when forming VTP sets facilitates load-balancing among various TPs. Finally, a technique is also offered to select the best VTP set at each scheduling resource unit. Numerical simulations are used to demonstrate the performance of our virtualization techniques.

A novel technique for removing the edge time transitions, a.k.a. tails, as well as the half symbol offset overhead of OFDM/OQAM signal is proposed. The proposed technique, which is called weighted circular convolution, totally removes the signal overheads, while preserving the real-orthogonality of the prototype filter, and as such, does not incur any ISI/ICI on the demodulated OQAM symbols. It is based on extension of the finite-length OQAM sequence to infinite-length such that the resulting signal is periodic. This periodicity together with special structure of OFDM/OQAM enables one to transmit only the desired overhead-removed portion of signal. This is equivalent to a weighted circular convolution instead of linear convolution in the OFDM/OQAM modulator/demodulator. The spectral sidelobe augmentation due to the sharp edge transitions of the overhead-removed signal is resolved by a weighted time-domain windowing. The proposed overhead-removal technique is applicable to an OFDM/OQAM burst of arbitrary length (either even or odd) and, among other benefits, significantly improves the spectral efficiency especially for short-burst signals.

Since video services are expected to constitute a major portion of the mobile downlink traffic, it is important to consider end users' perceptual quality of experience (QoE) for video traffic in the system design and performance evaluation of next generation mobile networks. We present a novel QoE-aware scheduling scheme for buffered video on demand (VoD). Therein, rebuffering is the critical attribute undermining users' QoE. Our scheduling scheme is based on `vacuum pressure scheduling'. We use playback buffer vacancy and apply the `backpressure' scheduling theory to schedule the VoD flows. The proposed scheme is further adjusted to enable joint scheduling of a mixture of VoD and best effort (BE) flows within the same band. A simple control knob is provided to operators to softly adjust the region in which BE flows contend on resources. Results demonstrate substantial user capacity gains compared to prior work without compromising the QoS of BE flows. Sensitivity analysis to feedback periodicity shows remarkable robustness and overhead savings compared to the baseline. Results even hold when requested videos are of heterogeneous qualities, i.e., encoding rates.