Marta Gatnau Sarret

The Potential of Flexible UL/DL Slot Assignment in 5G Systems

5th Generation (5G) small cells are expected to satisfy the increasing demand for wireless data traffic. In the presence of large scale dense and randomly deployed cells, autonomous and distributed configuration mechanisms are highly desirable. However, small cells typically serve a small number of users, such that sudden traffic imbalances between downlink (DL) and uplink (UL) are expected in the new 5G system. We exploit the flexibility of time-division duplex (TDD) to deal with such imbalances by adapting swiftly to instantaneously varying traffic needs. In this paper we propose a distributed algorithm to deal with these varying traffic requirements. We also exploit the availability of interference rejection capable receivers. Simulation results show that in the presence of the aforementioned features, we can approximately double the session throughput and halve the packet delay in a large number of cases.

Can Full Duplex Boost Throughput and Delay of 5G Ultra-Dense Small Cell Networks?

Given the recent advances in system and antenna design, practical implementation of full duplex (FD) communication is becoming increasingly feasible. In this paper, the potential of FD in enhancing the performance of 5th generation (5G) ultra-dense small cell networks is investigated. The goal is to understand whether FD is able to boost the system performance from a throughput and delay perspective. The impact of having symmetric and asymmetric finite buffer traffic is studied for two types of FD: when only the base station is FD capable, and when both the user equipment and base station are FD nodes. System level results indicate that there is a trade- off between multiple-input multiple-output (MIMO) spatial multiplexing and FD in achieving the optimal system performance. Moreover, results show that FD may be useful for asymmetric traffic applications where the lightly loaded link requires high level performance. In such cases, FD can provide an average improvement of up to 116% in session throughput and 77% in packet delay compared to conventional half duplex transmissions.

Improving link robustness in 5G ultra-dense small cells by hybrid ARQ

A new 5th generation (5G) radio access technology is expected to cope with an estimated factor of ~x1000 growth in mobile data traffic in the upcoming years. Such system will be optimized for a massive uncoordinated deployment of small cells, where autonomous operation of the individual nodes may bring unpredictable and fast varying link quality. In this paper, Hybrid Automatic Repeat Request (HARQ) is studied as a solution to cope with such unpredictability. An operational mode of HARQ for our 5G system definition is proposed, and its performance is evaluated for two different scheduling options. Simulation results confirm the capability of HARQ of improving the final throughput and solving outage problems, with limited impact on the end delay.

Can Full Duplex reduce the discovery time in D2D Communication

Device-to-device (D2D) communication is considered as one of the key technologies to support new types of services, such as public safety and proximity-based applications. D2D communication requires a discovery phase, i.e., the node awareness procedure prior to the communication phase. Conventional half duplex transmission may not be sufficient to provide fast discovery and cope with the strict latency targets of future 5G services. On the other hand, in-band full duplex, by allowing simultaneous transmission and reception, may complete the discovery phase faster. In this paper, the potential of full duplex in providing fast discovery for the next 5th generation (5G) system supporting D2D communication is investigated. A design for such system is presented and evaluated via simulations, showing that full duplex can accelerate the discovery phase by supporting a higher transmission probability compared to half duplex. Simulation results show that, in order to meet the strict 5G control plane latency target, advanced receivers are required. In that case, full duplex can reduce the latency up to 80%.

Full Duplex Communication under Traffic Constraints for 5G Small Cells

Full duplex (FD) communication promise of doubling the throughput of half duplex (HD) communication makes such type of system an attractive solution to cope with the expected mobile data traffic increase. Nevertheless, simultaneous transmission and reception in dense deployment scenarios increases the inter- cell interference compared to a traditional HD communication, due to a larger number of nodes simultaneously transmitting. Moreover, FD communication can only be exploited when there is traffic in both uplink and downlink directions simultaneously. In this paper, FD communication is studied within the framework of 5th generation (5G) small cell systems in order to address its effective gain in such specific scenarios. The factors that affect FD performance are analysed, and its performance is evaluated against a traditional HD communication. System level simulations show that the gain of FD over HD in the considered scenarios is lower than the expected 100% gain, with a strong dependency on the traffic and the interference conditions.

A Multi-QoS Aggregation Mechanism for Improved Fairness in WLAN

The 802.11e and subsequently the 802.11n amendments brought Quality of Service (QoS) into the Wireless Local Area Network (WLAN) arena, in order to provide higher access priority to certain types of traffic such as video and voice. Unfortunately these improvements are not enough, since in very dense and highly loaded network conditions they can provide more harm than benefits, by making the lower priority traffic starve and increasing the average collision rate. This lack of performance in the Medium Access Control (MAC) layer is where we focused our work. We propose a solution that avoids the starvation of the lowest priority Access Categories (AC), taking into account the priority defined by the 802.11e amendment and at negligible or extremely low cost for the high priority ones. Simulation results presented in this paper prove the effectiveness of the method by showing delay improvements up to 92% in overcrowded and overloaded networks.

Full duplex communications in 5G small cells

Full duplex communication promises system performance improvement over conventional half duplex communication by allowing simultaneous transmission and reception. However, such concurrent communication results in strong self interference and an increase in the overall network interference, and can only be exploited when traffic is available in both directions. The potential throughput gains of full duplex communication over conventional half duplex transmission in a small cell network with asymmetric traffic conditions is investigated in this contribution. The throughput performance gains are analysed using tools from stochastic geometry, and further confirmed through extensive system level simulations. Our findings explicitly quantify how the gains from full duplex communication depend on the traffic profile and the inter-cell interference coupling. The demonstrated throughput gains and delay reduction make full duplex communication an attractive potential technology component for the fifth generation dense small cell cellular system.

On the potential of full duplex performance in 5G ultra-dense small cell networks

Full duplex allows a device to transmit and receive simultaneously in the same frequency band, theoretically doubling the throughput compared to traditional half duplex systems. However, several limitations restrict the promised full duplex gain: non-ideal self-interference cancellation, increased inter-cell interference and traffic constraints. In this paper, we first study the self-interference cancellation capabilities by using a real demonstrator. Results show that achieving ~110 dB of cancellation is already possible with the current available technology, thus providing the required level of isolation to build an operational full duplex node. Secondly, we investigate the inter-cell interference and traffic constraints impact on the full duplex performance in 5th generation systems. System level results show that both the traffic and the inter-cell interference can significantly reduce the potential gain of full duplex with respect to half duplex. However, for large traffic asymmetry, full duplex can boost the performance of the lightly loaded link.

Impact of Transport Control Protocol on Full Duplex Performance in 5G Networks

Full duplex (FD) communication has attracted the attention of the industry and the academia as an important feature in the design of the future 5th generation (5G) wireless communication system. Such technology allows a device to simultaneously transmit and receive in the same frequency band, with the potential of providing higher throughput and lower latency compared to traditional half duplex (HD) systems. In this paper, the interaction between Transport Control Protocol (TCP) and FD in 5G ultra- dense small cell networks is studied. TCP is a well- known transport layer protocol for providing reliability, which comes at the price of increased delay and reduced system throughput. FD is expected to accelerate the TCP congestion control mechanism and hence mitigate such consequences. System level results show that FD can outperform HD and alleviate the TCP drawbacks when the inter-cell interference is not the main limiting factor. On the other hand, under strong inter-cell interference, results show that the capabilities of the system to cope with such interference dictates the gain that FD may provide over HD.

Flexible UL/DL in Small Cell TDD Systems: A Performance Study with TCP Traffic

Time division duplex (TDD) systems offer a substantial amount of freedom to deal with downlink (DL) and uplink (UL) traffic asymmetries. Most TDD-based systems define either multiple static configurations or adaptive approaches to deal with such asymmetries. Our envisioned 5G concept embraces the flexibility brought along by TDD, and allows us to switch the link direction on a slot by slot basis. In this paper we study the interaction of Transmission Control Protocol (TCP) traffic, with a fully flexible UL/DL TDD allocation scheme. We show that flexibility is not only beneficial for exploiting the different instantaneous UL and DL traffic variations, but also performs well with TCP traffic, where the protocol behaviour plays an important role in throughput performance. The advantages of full flexibility compared to fixed static allocations for TCP traffic are reported for both small and large payloads, and for multi-cell scenarios where both DL and UL traffic are present.