Small cell is an attractive and promising technology for improving capacity in traffic hotspots using cell densification. We consider the traffic load-balancing problem for a macro-assisted small cell architecture exploiting the flexible 3-D beamforming facilitated by the adoption of the active antenna system at base stations. Specifically, 3-D user equipment (UE)-specific beamforming is utilized for traffic load balancing due to its unique feature that the received signal is maximized, while the interference is limited with narrower beamwidth. We propose a novel traffic load-balancing algorithm based on cell association and cell sectorization using 3-D UE-specific beamforming, and the performance of the proposed algorithm is evaluated via system-level simulations. Results show that cell edge user throughput and cell average throughput both improve significantly with the proposed load-balancing algorithm compared with the conventional sectorization with fixed antenna down-tilt scheme. In addition, in denser small cell scenarios, our proposed scheme can further increase the load-balancing gain with reduced cell planning efforts compared with the conventional scheme.

Dynamic allocation of subframes to uplink (UL) or downlink (DL) in time division duplex (TDD), termed `Dynamic TDD,' has been studied by the 3rd Generation Partnership Project (3GPP) since the Long Term Evolution (LTE) Release 11 timeframe. At the same time, 3GPP is also standardizing macrocell-assisted small cell heterogeneous architectures for inclusion in LTE Release 12 as a solution offering high data rate to user terminals (UEs) along with high system capacity through spatial reuse of spectrum. In this paper, we focus on a particular small cell architecture proposed by DOCOMO, known as the Phantom Cell architecture, which provides the option to support dynamic TDD. For an arbitrarily-located UE in a small cell network, we apply results from stochastic geometry to derive expressions for the distribution of DL signal to interference plus noise ratio (SINR) at an arbitrary UE and the distribution of UL SINR at its serving base station (BS). The analytical results are verified by system level simulations. These results can be used to study aspects of system design for small cells, and the sensitivity of SINR to the extent of synchronization across small cells employing dynamic TDD. In order to deal with the severe inter-cell interference (ICI) problem in dynamic TDD, we further propose a frequency domain interference coordination technique. Finally, system level simulations based on more realistic system models and assumptions are conducted to evaluate the performance of dynamic TDD systems and the proposed interference coordination technique.

Full-duplex transmission is a promising technique to enhance the capacity of relay communications. In this paper, we investigate the power and location optimization for full-duplex decode-and-forward (DF) relaying systems. The outage probability is adopted as the optimization criterion and a two-dimensional (2D) optimization problem is formulated for systems with and without the direct source-destination link. Analytical and numerical results are provided to demonstrate advantages of the power and location optimization. More interestingly, the effect of residual self-interference (RSI) introduced by full-duplex transmission is investigated in terms of the optimal power allocation and relay location deployment and the outage probability performance improvement. Furthermore, we show that the minimal outage probability can be achieved via joint power-location optimization. The effect of power optimization on the outage performance is also compared between full-duplex and half-duplex relaying.

Small cell is an attractive and promising technology for improving capacity in traffic hotspots using cell densification. In this paper, we propose the capacity enhancement for small cells under macrocell-assisted architecture utilizing the flexible 3-dimensional (3D) beamforming facilitated by the adoption of the active antenna system (AAS) at base stations (BSs). In contrast to conventional macrocell network, more dynamic and flexible 3D beamforming with narrow beamwidth is feasible in the small cell layer because the service coverage and mobility robustness are basically supported in the macrocell layer. This dynamic beam adaptation in full dimensions can improve the received signal quality and at the same time control the interference more effectively, which is especially useful for the dense small cell deployment scenario where the interference issue is one of the major concerns. In particular, performance comparison between the conventional sectorization with fixed down-tilt scheme and UE (user equipment)-specific 3D beamforming is studied. Furthermore, a novel UE group-specific 3D beamforming is proposed as a more realistic operation compared to UE-specific beamforming. System level simulations demonstrate the significant gain of capacity enhancement with 3D beamforming over the conventional sectorization with fixed down-tilt in terms of both the cell average capacity (up to 124.8% gain) and the cell edge user throughput (up to 454.3% gain). It is also shown that UE group-specific beamforming can achieve performance comparable to that of UE-specific beamforming.

Small cell is an attractive and promising technology for improving capacity in traffic hotspots using cell densification. We consider the traffic load balancing problem for small cells under the enhanced Local Area (eLA) architecture utilizing the flexible 3-dimensional (3D) beamforming facilitated by the adoption of the active antenna system (AAS) at base stations (BSs). Different load balancing methods based on combinations of cell association algorithms and antenna tilt adjustment schemes are proposed and evaluated via system level simulations. Results show the potential gain of traffic load balancing with 3D beamforming in terms of cell edge user throughput. In particular, for the enhanced load balancing cell association combined with UE (user equipment)-specific tilting scheme, significant cell edge user throughput improvements can be achieved while good average cell throughput performance can still be maintained.

Full duplex transmission is a promising technique to enhance the capacity of relay communications. In this paper, we investigate the optimum transmit power allocation for full duplex decode-and-forward (DF) relaying systems. The outage probability is adopted as the optimization criterion and a transmit power optimization problem is formulated for systems with and without total power constraint. Analytical and numerical results are provided to show the advantages of the power optimization. More interestingly, the effect of residual self-interference introduced by full duplex transmission is examined in terms of optimal power allocation and outage probability performance improvement.

The Third Generation Partnership Project (3GPP) has been studying dynamic allocation of sub-frames to uplink or downlink in Time Division Duplex (TDD), since the Long Term Evolution (LTE) Rel. 11 timeframe. At the same time, 3GPP is also standardizing Enhanced Local Area (eLA) small-cell heterogeneous architectures for inclusion in 3GPP Rel. 12 as a solution offering high data rate to user terminals (UEs) along with high spatial reuse of spectrum. In this paper, we focus on a particular eLA architecture proposed by DOCOMO, called the Phantom Cell architecture, that has the option to support dynamic TDD. We evaluate the system performance of dynamic TDD in phantom cells and the corresponding inter-cell interference issues. Then we propose a frequency domain interference coordination technique for dynamic TDD in phantom cells. The superior performance of the proposed scheme over conventional frequency reuse technique and no interference coordination scenario is verified by system level simulations.

Gaussian frequency shift keying (GFSK) is a promising digital modulation scheme. The design of simple and high-performance receivers for GFSK systems is a challenging task. In this letter, we develop an optimized differential GFSK demodulator and investigate the phase wrapping issue in its implementation. Simulation results show bit-error-rate (BER) performance improvement in comparison with conventional differential demodulators in both AWGN and flat fading channels. We also compare our proposed demodulator with other existing alternatives in terms of BER performance.

Remote health monitoring by exploiting wireless communications technologies is an emerging area receiving increasing interests from academia, research labs and industry. This issue has also been brought up in the standardization process of IEEE 802.15 Task Group 6 Wireless Body Area Networks (WBAN). The challenge is to find the appropriate combination of medical data processing techniques and the wireless technology in order to meet the particularly stringent error, latency and power consumption requirements of healthcare applications. In this paper, we present the results of a case study on wireless electrocardiogram (ECG) monitoring over Bluetooth. Based on the special considerations of (processing and transmission) power consumption at wireless ECG sensors, we first propose a low complexity ECG compression method. Comparisons with existing approaches confirm the superior performance of our method. We then study the data reconstruction performance at the Bluetooth receiver and find that: i) the uncompressed ECG data transmission is not necessarily better than the compressed transmission; and ii) there exists an optimum ECG data compression ratio for the wireless link.