Full duplex random access for multi-user OFDMA communication systemsAd Hoc Networks


Xudong Wang, Aimin Tang, Pengfei Huang
Computer Networks and Communications / Hardware and Architecture / Software


Opportunistic Spectrum Access in OFDMA Systems

Shehzad Ahmad, Adnan Shahid, Rao Munzir Ahmad, Adeel Akram, Muhammad Adnan Nasim

Multi-user frequency domain scheduling for WiMAX OFDMA

Alexander A. Maltsev, Andrey V. Pudeyev, Alexander A. Maltsev

Practical Secret Key Agreement for Full-Duplex Near Field Communications

Rong Jin, Xianru Du, Zi Deng, Kai Zeng, Jing Xu

Experimental demonstration of a GPON free space optical link for full duplex communications

S. Di Bartolo, A. Pizzoleo, S. Penna, G.M. Tosi Beleffi, F. Matera, S. Pompei



Accepted 1 September 2014

Available online xxxx


Full duplex communications

Medium access control cess paper, the capability of full-duplex communications is leveraged to propose novel mechan m mize different system utilities [4–6]. In data networks, traffic is bursty, so it is unreasonable to reserve wireless resources (e.g., subchannels). As a result, random access is a preferred option. a packet on one tus of other subre idle, tra be con immediately. Due to this drawback, the system th put is highly related to the number of subchannels the number of subchannels is smaller than the num contending nodes, the throughput drops quickly as the number of nodes increases, as a result of high collisions [8]. When the number of subchannels is larger than the number of nodes, the throughput also decreases due to http://dx.doi.org/10.1016/j.adhoc.2014.09.002 1570-8705/ 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author.

E-mail address: wxudong@ieee.org (X. Wang).

Ad Hoc Networks xxx (2014) xxx–xxx

Contents lists available at ScienceDirect

Ad Hoc Ne .e lsrandom access. The scheduled access mechanism is well suited for providing connection-oriented services with guaranteed quality of service (QoS). Based on optimization theories, many scheduling schemes are proposed to maxilems. Problem 1: When a node transmits of subchannels, it cannot sense the sta channels. Thus, even other subchannels a sions on these subchannels cannotPlease cite this article in press as: X. Wang et al., Full duplex random access for multi-user OFDMA communication systems, Ad Ho (2014), http://dx.doi.org/10.1016/j.adhoc.2014.09.002nsmisducted rough. When ber of(OFDMA) has been widely adopted by several next-generation wireless networks including WiMAX, 802:22 WRAN and LTE-A [1–3]. In an OFDMA system, multiple nodes share different set of subchannels (i.e., a block of subcarriers) simultaneously based on a certain medium access control (MAC) protocol, which is either scheduled access or low as a result of high collision probability. Based on carrier sense multiple access with collision avoidance (CSMA/CA), other subchannel random access protocols are proposed in [8,9]. These protocols can achieve much better performance than the multi-channel ALOHA protocol in [7]. However, there still remain several major prob-Orthogonal frequency division multiple access (OFDMA) 1. Introduction

Orthogonal frequency divisionisms such as full duplex carrier sensing, collision detection, and collision jamming. With these mechanisms, a full-duplex carrier sense multiple access with collision detection (FDCSMA/CD) protocol is developed for OFDMA wireless networks. It is based on a hierarchical design: (1) with full-duplex communications, operation of subchannels is decoupled, and a

CSMA/CD-like protocol is implemented in each subchannel as a random access scheme; (2) on top of random access per-subchannel, a simple but effective subchannel selection scheme is executed locally on each client to harvest multi-user diversity. Both theoretical analysis and simulations are carried out to validate the effectiveness and efficiency of our protocol.  2014 Elsevier B.V. All rights reserved. ultiple access

So far there exist a few random access protocols for

OFDMA wireless networks. In [7], a multi-channel ALOHA protocol is developed, but its throughput turns out to beReceived 19 March 2014

Received in revised form 23 July 2014 support services with bursty traffic. However, the existing OFDMA random access protocols suffer from low efficiency due to the constraints in half-duplex communications. In thisFull duplex random access for multi communication systems

Xudong Wang ⇑, Aimin Tang, Pengfei Huang

UM-SJTU Joint Institute, Shanghai Jiao Tong University, Shanghai, China a r t i c l e i n f o

Article history: a b s t r a c t

Random medium ac journal homepage: wwwer OFDMA control (MAC) plays a critical role in OFDMA wireless networks to tworks evier .com/locate /adhocc Netw. synchronized with each other, which is a default require2 X. Wang et al. / Ad Hoc Networks xxx (2014) xxx–xxxlow utilization of all subchannels [8]. In [9], the number of subchannels must be adjusted dynamically to be equal to the number of nodes, which is difficult in system implementation. Problem 2: Acknowledgement (ACK) cannot be returned without using an extra independent channel [8] or the ACK of an uplink (i.e., clients to access point (AP)) packet is delayed to the downlink (i.e., AP to clients) transmission period [9]. The delayed ACK is not suitable for random access protocols. Problem 3: Once a transmission collision happens, it lasts for the entire packet. Thus, the collision time is long. Problem 4: The downlink subframe and the uplink subframe (where random access is adopted) are operated in a time-division duplexing (TDD) fashion, which is not flexible to support fast time-varying unbalanced bursty traffic between downlink and uplink.

An approach to address the above issues is to make sure a radio of each node can transmit and receive signals at the same time in the same frequency. To facilitate this operation, the radio needs to have the capability of full-duplex communications. Recently, full-duplex wireless communications have become practical through a combination of antenna cancelation (AC), RF interference cancelation (RIC), and digital interference cancelation (DIC) [10–12].

Full-duplex radios bring two major benefits: (1) for a point-to-point link, its capacity can be significantly improved by up to twice [10]; (2) functions of a communication node are greatly enhanced, e.g., a node can transmit signals and sense the transmission status of other nodes simultaneously, which is a useful function for cognitive radios [13].

In this paper, by leveraging the capability of full-duplex communications in the physical (PHY) layer, a novel random access protocol, called full-duplex carrier sense multiple access with collision detection (FD-CSMA/CD) protocol, is designed for OFDMA wireless networks. It is distinguished by the following key features: (1) A radio operates in a full-duplex way: it can transmit signals on some occupied subchannels, and at the same time receive signals on all subchannels [12], i.e., transmissions on all subchannels are decoupled from each other. Thus, an idle subchannel can be detected and utilized in time whether another subchannel is in transmissionmode or not. Thus, Problem 1 is solved.Moreover, when a packet on one subchannel is received, an ACK can be returned immediately regardless of the status of other subchannels, which addresses Problem 2. To improve throughput, a novel virtual MAC header (VMAC-hdr) is designed and added in the PHY preamble of a packet. It serves two purposes. Firstly, it is an identifier used for a corresponding node to capture a full-duplex opportunity to improve the link throughput. Secondly, it is used for collision detection by all nodes. When a transmitting node detects a collision, it gives up the current transmission immediately. For hidden nodes, collision is detected by a third node like AP, and then the