Usa Vilaipornsawai

Uplink contention based SCMA for 5G radio access

Fifth generation (5G) wireless networks are expected to support very diverse applications and terminals. Massive connectivity with a large number of devices is an important requirement for 5G networks. Current LTE system is not able to efficiently support massive connectivity, especially on the uplink (UL). Among the issues that arise due to massive connectivity is the cost of signaling overhead and latency. In this paper, an uplink contention-based sparse code multiple access (SCMA) design is proposed as a solution. First, the system design aspects of the proposed multiple-access scheme are described. The SCMA parameters can be adjusted to provide different levels of overloading, thus suitable to meet the diverse traffic connectivity requirements. In addition, the system-level evaluations of a small packet application scenario are provided for contention-based UL SCMA. SCMA is compared to OFDMA in terms of connectivity and drop rate under a tight latency requirement. The simulation results demonstrate that contention-based SCMA can provide around 2.8 times gain over contention-based OFDMA in terms of supported active users. The uplink contention-based SCMA scheme can be a promising technology for 5G wireless networks for data transmission with low signaling overhead, low delay, and support of massive connectivity.

Scattered-pilot channel estimation for GFDM

This work presents the channel estimation for Generalized Frequency Division Multiplexing (GFDM). GFDM can be considered as a filtered bank multicarrier scheme, where a spectrally-contained pulse shaping is applied over each subcarrier to reduce out of band radiation (OOB). However, due to pulse shaping, subcarriers in GFDM are no longer orthogonal and there is inherent interference. Due to such interference, the channel estimation for GFDM is not trivial. In this work, two channel estimation methods for GFDM are proposed, 1) Pilot Interference Cancellation (Pilot-IC) where interference is pre-canceled only at pilot symbols, 2) Transmitter IC (Tx-IC) where interference is pre-cancelled at both data and pilot symbols. With scattered pilots over frequency and time grid, this allows frequency selective and time varying fading channels to be estimated, with reduced overhead. The simulation results show that these two methods can provide the same MSE performance. Moreover, the Pilot-IC pairing with a Zero Forcing (ZF) receiver, and the Tx-IC pairing with a simple Matched Filter (MF) receiver, also provide the same BER performance. Hence, it is possible to cancel the interference either at the transmitter or the receiver.

SCMA for Open-Loop Joint Transmission CoMP

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.

Two-tier distributed and open loop multi-point cooperation using SCMA

The fifth generation of cellular wireless networks known as 5G is based on user-centric non-cellular concept where the users are surrounded by many network nodes cooperating to serve the users providing a “cell-center” experience throughout the network. Traditional multi point cooperation techniques often rely on centralized coordination and require different and often stringent requirement on the central controller, backhaul capacity and overall network synchronization. A novel two tiered, open loop and distributed cooperation technique is proposed in this paper where the lower tier with fixed or slowly changing parameters and preferably using SCMA provide a ubiquitous performance to mobile users and users exposed to multiple network nodes, while the higher tier provides service to the users close to the network nodes and maintain the overall network throughput. Users scheduled by the lower tier signaling use joint detection techniques from multiple network nodes. Other users scheduled to the higher tier jointly decode the lower tier signal from one or multiple network nodes before proceeding with the detection of their intended signal. The proposed algorithm is based on distributed scheduling and imposes limited requirements on the central controller and backhaul capacity and does not require stringent network time and frequency synchronization among network nodes. Unlike traditional cooperation techniques, the proposed method is open loop and requires very limited feedback and signaling overhead. Performance evaluations show that the proposed technique provides significant network coverage enhancement especially for high speed mobile users.

User-centric wireless access virtualization strategies for future 5G networks

User-centric wireless access virtualization (WAV) allows each user to be served by a set of carefully selected transmission points (TP)s forming a user-specific virtual basestation (uVBS) adapted to its environment and quality of service (QoS) requirement. In this way, this new concept breaks away from the conventional cell-centric architecture to provide boundaryless communications in future 5G networks. This fundamental structural 5G evolution alongside the ultra-dense multi-tier heterogenous context foreseen in such networks require an inevitable rethinking of efficient scalable TPs clustering. As such, this paper proposes three innovative low-cost clustering approaches that enable user-centric WAV and provide dynamic, adaptive, and overlapping TPs clusters while requiring not only negligible overhead and power costs, but also minimum signaling changes at both network and user sides. In contrast to existing clustering techniques, the new ones we propose better leverage 5G features such as extreme densification and massive connectivity as well as new concepts such as mmWave spectrum and massive MIMO. Furthermore, these approaches are flexible enough to be adapted to different network dimensions (i.e., space, time, etc.), thereby paving the way for achieving the dramatic performance improvements required by 5G networks to cope with the upcoming mobile data deluge.

Wireless Access Virtualization Strategies for Future User-Centric 5G Networks

User-centric wireless access virtualization (WAV) allows each user to be served by a set of carefully selected transmission points (TP)s forming a user-specific virtual base-station (uVBS) adapted to its environment and quality of service (QoS) requirement. In this way, this new concept breaks away from the conventional cell-centric architecture to provide boundaryless communications in future 5G networks. This fundamental structural 5G evolution alongside the ultra-dense multi-tier heterogenous context foreseen in such networks require an inevitable rethinking of efficient scalable TPs clustering. As such, this paper proposes three innovative low-cost clustering approaches that enable user-centric WAV and provide dynamic, adaptive, and overlapping TPs clusters while requiring not only negligible overhead and power costs, but also minimum signaling changes at both network and user sides. In contrast to existing clustering techniques, the new ones we propose better leverage 5G features such as extreme densification and massive connectivity as well as new concepts such as mmWave spectrum and massive MIMO. Furthermore, these approaches are flexible enough to be adapted to different network dimensions (i.e., space, time, etc.), thereby paving the way for achieving the dramatic performance improvements required by 5G networks to cope with the upcoming mobile data deluge.