Improving Spectrum Usage on Full-Duplex Communications with an Innovative Channel Reservation

A full-duplex MAC technique to improve spectrum-efficiency on 5G mobile wireless networks

In-band full-duplex (FD) communications have been optimistically promoted to improve the spectrum utilization and efficiency. However, the penetration of FD communications to the cellular networks domain is challenging due to the imposed uplink/downlink interference. This paper presents a tractable framework, based on stochastic geometry, to study FD communications in cellular networks. Particularly, we assess the FD communications effect on the network performance and quantify the associated gains. This paper proves the vulnerability of the uplink to the downlink interference and shows that FD rate gains harvested in the downlink (up to 97%) come at the expense of a significant degradation in the uplink rate (up to 94%). Therefore, we propose a novel fine-grained duplexing scheme, denoted as the α-duplex scheme, which allows a partial overlap between the uplink and the downlink frequency bands. We derive the required conditions to harvest rate gains from the α-duplex scheme and show its superiority to both the FD and half-duplex (HD) schemes. In particular, we show that the α-duplex scheme provides a simultaneous improvement of 28% for the downlink rate and 56% for the uplink rate. Finally, we show that the amount of the overlap can be optimized based on the network design objective.

Recent advances in self-interference cancellation techniques enable in-band full-duplex (FD) transmission in which a wireless node can simultaneously transmit and receive in the same frequency band. However, to fully exploit the benefits of FD technology in a wireless network, in addition to the physical (PHY) layer issues, medium access control (MAC) layer issues such as inter-node collisions, fairness between halfduplex (HD) and FD users, opportunistic selection of different modes of FD transmission, and synchronization issues need to be resolved. To this end, this article first discusses the fundamental concepts, potential benefits, and primary network topologies of FD transmission. We then highlight immediate challenges (both in the PHY and MAC layers) that need to be addressed in designing FD wireless systems. A qualitative comparison among the existing full-duplex MAC (FD-MAC) protocols is then provided. Finally, the primary requirements and research issues for the design of FD-MAC protocols are discussed, and implications of FD technology in cellular wireless networks are highlighted.

Device-to-device (D2D) communication has been regarded as a promising technique for content dissemination in the fifth generation wireless network. To improve the efficiency of content dissemination, in this paper, we propose a content dissemination mechanism with proactive content fetching (PCF) and full-duplex (FD) D2D communication, referred to as PCF-FD mechanism. This mechanism is characterized by the proactive content requests of partial users that don’t request contents originally. FD communication is utilized to establish more D2D links and increase the area spectral efficiency (ASE). Based on stochastic geometry, we derive the recursive formula of content caching probability from the evolutionary perspective. In addition, the expressions of successful offloading probability (SOP), ASE and average energy consumption are also obtained. Computer experiments show that the analytical results match well with simulation results and our scheme outperforms the conventional scheme without PCF and FD communication by 45% in terms of SOP in a scenario with small user density and light load.

In this paper we propose a decentralized medium access control (MAC) scheme to coordinate the access of multiple transmitters adopting a multi-packet reception (MPR) physical (PHY) layer. MPR receivers are able to decode multiple transmissions, and depending on the technique adopted at the PHY-layer, there is an optimal number of simultaneous transmissions that maximize the number of packets successfully decoded in a simultaneous way. The proposed MAC scheme admits an MPR PHY-layer and is divided in two stages. In the first one the nodes indicate their willingness to transmit, while in the second one they jointly transmit. Adopting a generic model for the PHY-layer, we characterize the throughput achieved by the proposed MAC when both MAC and PHY layers are considered. The formal characterization of the throughput is then used to optimize the duration of the first stage of the MAC scheme in order to optimize the throughput. In this way, the number of transmitters is regulated to optimize the cross-layer operation, taking into consideration the features of the MPR PHY-layer and the maximum performance achieved with the proposed MAC design. Several results obtained through simulation are presented, which validate the numerical results obtained with the proposed characterization. The proposed scheme is a first step to develop MAC protocols specifically designed to distributed MPR systems that operate in a cross-layer and improve the exploitation of current and future MPR techniques proposed for the PHY-layer.

Communication for control-centric industrial applications is characterized by the requirements of very high reliability, very low and deterministic latency and high scalability. Typically, IEEE 802.11-based wireless local area networks (WLANs), also known as Wi-Fi networks, are deemed ineligible for industrial control applications owing to insufficient reliability and non-deterministic latency. This paper proposes a novel solution for providing reliable and deterministic communication, through Wi-Fi, in industrial environments. The proposed solution, termed as $\mathsf{HAR}^{\mathsf{2}}\mathsf{D-Fi}$ ( H ybrid channel A ccess with R edundancy for R eliable and D eterministic Wi- Fi ), adopts hybrid channel access mechanisms for achieving deterministic communication. It also provides temporal redundancy for enhanced reliability. $\mathsf{HAR}^{\mathsf{2}}\mathsf{D-Fi}$ implements different medium access control (MAC) designs that build on the standard physical (PHY) layer. Such designs can be classified into two categories: (a) MAC designs with pre-defined (physical) time-slotted schedule, and (b) MAC designs with virtual time-slotted schedule. Performance evaluation, based on analysis and system-level simulations, demonstrates the viability of $\mathsf{HAR}^{\mathsf{2}}\mathsf{D-Fi}$ for control-centric industrial applications.

With the emergence of self-interference cancellation techniques, wireless full-duplex communication at the same frequency channel and time slot has become possible. The gain of full-duplex communication over half-duplex depends on the success of self-interference cancellation or the amount of residual self-interference. In this paper, we propose a medium access control (MAC) protocol, named Synchronized Contention Window Full-Duplex (S-CW FD) protocol for enabling full duplex in wireless local area networks (WLANs) and we evaluate its performance under a realistic self-interference model and a realistic network model with hidden nodes. The proposed S-CW FD protocol can not only work both in ad hoc and infrastructure modes of IEEE 802.11 WLANs, but with the legacy nodes as well. Our performance analysis considering various network scenarios and different self-interference cancellation levels show that, when there are no hidden nodes in the network, the S-CW FD protocol can at most double the throughput of half-duplex IEEE 802.11. In the presence of hidden nodes, the advantages of full-duplex are further emphasized, as the throughput gain can get as high as an order of magnitude even for moderate SI cancellation levels.

Machine-to-Machine (M2M) networks require more elaborate design of medium access control (MAC) due to their higher complexity in system management. In many applications of M2M networking, the major traffic pattern consists of data collected from several source nodes to a sink through a unidirectional tree. Earlier prevalence of Carrier-Sense Multiple Access (CSMA) has continuously been being switched to Time-Division Multiple Access (TDMA). The main drawback of CSMA is idle listening, which refers to the fact that the nodes have to unnecessarily wake up due to lack of schedule. Energy inefficiency of a network gets higher as the number of nodes committed to idle listening, which seriously limits the scalability of a network. Recent enhancement of hardware has been enabling sufficiently accurate synchronization while keeping energy consumption low enough, which mitigates the main drawback of TDMA. This paper proposes a TDMA-based MAC protocol that achieves higher energy efficiency in centralized M2M communications. As a TDMA-based protocol, the proposed protocol is fully scheduled and hence no idle listening occurs. Moreover, the protocol reduces the length of a multi-hop transaction which results in higher energy efficiency as well as lower latency. Simulation results show that the proposed MAC protocol outperforms the conventional CSMA and other popular MAC schemes, in terms of energy consumption, delay, and packet delivery ratio (PDR).

In this paper, we propose a novel adaptive scheme for full-duplex communication of secondary users (SUs) in a cognitive radio network. The secondary network operates adaptively in three modes; cooperative sensing (CS), full duplex transmit and sensing (FDTS), and in-band bidirectional full duplex transmit and receive (FDTR). In the CS mode, the secondary nodes will detect the signal of a primary user (PU) through a novel cooperative medium access control (MAC) protocol and will decide the system's mode of operation in the subsequent spectrum hole. This adaptive decision is based on dual-threshold detection introduced for the first time. When the PU's signal at SU's receivers is weak, the system switches to the FDTS mode to avoid higher collisions probability and long or endless collision durations. In the FDTS mode, one of SUs senses the PU activity continuously while transmitting to another node. When the channel conditions allow, the system switches to the FDTR mode, in which the SUs would communicate bidirectionally in an asynchronous full duplex manner. The novel idea of asynchronous transmission in this mode will result in decreased maximum and average collision durations. Analytical closed forms for probability of collision, average collision duration, and cumulative collision duration, as well as throughput of the SU network are derived, and performance of the proposed scheme in terms of the above-mentioned metrics, effectiveness, and advantages over conventional methods of sensing and transmission are verified via simulations.

Full-duplex (FD) communication transmits and receives packets simultaneously at the same channel. The FD communication is possible thanks to self-interference cancellation (SIC) technology that has developed. However, in the asymmetric FD pair, the interference should be carefully considered to fully utilize FD communication. In this paper, we propose a power control algorithm to improve throughput performance. The access point (AP) controls the transmission power of the AP and the uplink (UL) node. The simulation results show that the throughput performance of the proposed algorithm is higher than that of other algorithms.

As one of the promising approaches to increase the network capacity, Full-duplex (FD) communications have recently gained a remarkable attention. FD communication enables wireless nodes to simultaneously send and receive data through the same frequency band. Thanks to the recent achievements in the self-interference (SI) cancellation, this type of communication is expected to be potentially utilized in cellular systems, especially in small cell networks. In this paper, we integrate the FD communications into femtocell networks where femtocell users (FUs) share the same spectrum with macro users (MUs). In particular, aiming to maximize the number of admitted FUs in the network and satisfying the target rate for FUs, we jointly study the problem of sub-channel allocation, duplexing-mode selection, and power control for FUs in both uplink (UL) and downlink (DL) transmissions. Moreover, we address the power control problem for macro-tier where the main goal is to minimize the transmission power of prioritized MUs while guaranteeing a target rate for them. To jointly address these problems for both tiers, we propose a distributed algorithm in which FBSs and admitted FUs choose whether to operate in half-duplex (HD) or FD mode so as to meet their target rate. The convergence and performance of the proposed algorithm are evaluated through simulation where it is demonstrated that the average admission ratio of FUs in our proposed distributed scheme surpasses the existing traditional HD approaches.

Due to dynamic channel availability in cognitive radio networks (CRNs), rendezvous problem is known as the most challenging issue in the design of media access control (MAC) protocol, which is a key step for secondary users (SUs) to start communication. With the concept of blind rendezvous, numerous channel-hopping sequence (CHS) based rendezvous schemes have been proposed to solve this problem in these years. Currently, little attention is paid to the design of a carrier sensing multiple access/collision avoidance (CSMA/CA) MAC based on these rendezvous schemes and also the rendezvous de-synchronization problem brought by multiple rendezvous networking paradigm into MAC design. To this end, we propose a cooperative channel-hopping based CSMA/CA MAC (named CoCH-CSMA/CA MAC) which works on the top of existing CHS based rendezvous schemes. Resulting from the rendezvous de-synchronization problem, a new type of collision, named false collision, is identified. As a SU cannot discern the false collision by itself, we design a cooperative control feedback scheme which employs correlation-based signal detection to reduce the coordination overhead of cooperation and helps SUs to avoid backoff misbehavior. Moreover, we analyze the behavior of our MAC protocol and its advantage. Extensive simulations prove that the cooperative control feedback scheme can effectively alleviate the impact of rendezvous de-synchronization problem on backoff misbehavior and improve network performance.

The design of medium access control (MAC) protocols for Underwater Acoustic Sensor Networks (UASNs) pose many challenges due to low bandwidth and high propagation delay. In this paper, a new medium access control (MAC) protocol called Handshake Triggered Chained-Concurrent MAC (HTCC) is proposed for large-scale applications in UWSNs. The main idea of HTCC is to establish a chained concurrent transmission accomplishing spatial reuse. The novelties of HTCC lie in: firstly, the protocol allows multi-direction handshake with different nodes simultaneously; secondly, a random access mechanism is integrated with the handshake mechanism for improve channel utilization. Simulation results show that HTCC outperforms extended version of Slotted floor acquisition multiple accesses (Ext-sFAMA) in terms of network throughput, the RTS efficiency, as well as fairness in representative scenarios.

In this paper, we address the tradeoff between energy efficiency (EE) and spectral efficiency (SE) for cellular networks with full-duplex (FD) communications enabled base stations. To be backward compatible with legacy LTE systems, it is assumed that user devices still work in the conventional half-duplex (HD) mode. There usually exists residual self-interference (RSI) in FD communications after advanced interference suppression techniques are applied. In this paper, we consider two different RSI models: constant RSI model and linear RSI model. First, the necessary conditions for an FD transceiver to achieve better EE-SE tradeoff than an HD one are derived for both the RSI models. Then, for the constant RSI model, a closed-form EE-SE expression is obtained in the scenario of single pair of users. We further extend our result and prove that EE is a quasi-concave function of SE in the scenario of multiple user pairs. Accordingly, an optimal algorithm to achieve the maximum EE based on the Lagrange dual decomposition technique is developed. For the linear RSI model, the EE-SE relation is difficult to deal with and we develop a heuristic algorithm by decoupling the problem into two sub-problems: power control and resource allocation. Our analysis and algorithms are finally verified by comprehensive numerical results.

This paper explores some of the techniques and issues associated with the design of an effective medium access control (MAC) protocol for a geostationary satellite channel. Two satellite MAC schemes are described, combined free/demand assignment multiple access (CFDAMA) and burst targeted demand assignment multiple access (BTDAMA) and their performance is evaluated for both Poisson and self-similar data traffic. Simulation results show that the effectiveness of different MAC techniques is heavily dependent on the nature of the traffic to be supported. It is shown that the CFDAMA scheme can provide good delay/utilisation performance of a satellite channel for Poisson traffic but poorer performance for the highly bursty self-similar traffic. The BTDAMA scheme on the other hand provides good delay/utilisation performance for self-similar traffic but is less suited to handling Poisson traffic. (7 pages)