Channel Access Using Opportunistic Reservations and Virtual MIMO - eScholarship
Jose Joaquin Garcia-Luna-Aceves · 2009
Computer Networks 53 (2009) 883–895 Contents lists available at ScienceDirect Computer Networks journal homepage: www.elsevier.com/locate/comnet Channel access using opportunistic reservations and virtual MIMO q Xin Wang a, * , J.J. Garcia-Luna-Aceves a,b , Hamid R. Sadjadpour c a b c Department of Computer Engineering, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, United States Palo Alto Research Center (PARC), 3333 Coyote Hill Road, Palo Alto, CA 94304, United States Department of Electrical Engineering, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, United States a r t i c l e i n f o Article history: Received 23 October 2007 Received in revised form 21 July 2008 Accepted 8 October 2008 Available online 1 November 2008 Responsible Editor: L. Lenzini Keywords: Channel access Reservation Virtual MIMO a b s t r a c t We propose ORCHESTRA, a channel-access protocol that uses reservations and virtual MIMO to provide high throughput and bounded channel-access delays. The channel-access process is divided into a contention-based access period and a scheduled access period. To attain high throughput, nodes build a channel schedule using the contention-based access period, and utilize the spatial multiplexing gain of virtual MIMO links in the scheduled access period. To attain bounded channel-access delays, nodes reserve time slots through opportunistic reservations. We evaluate the performance of ORCHESTRA through numeri- cal analysis and simulations, and show that it results in much better throughput, delay, and jitter characteristics that simply using MIMO nodes together with scheduled access (i.e., NAMA) or contention-based access (i.e., IEEE 802.11 DCF). O 2008 Elsevier B.V. All rights reserved. 1. Introduction Recent advances in ad hoc networks have stimulated the support of voice-related applications such as voice over wireless IP. These applications need to coexist with data- centric applications. To better support such integrated voice and data traffic in an ad hoc network, the underlying channel-access protocol needs to satisfy two require- ments: high channel utilization and bounded channel-ac- cess delay. Multiple-input multiple-output (MIMO) techniques can increase channel capacity significantly through the use of q This work was partially sponsored by the US Army Research Office under Grants W911NF-04-1-0224 and W911NF-05-1-0246, by the National Science Foundation under Grant CNS-0435522, by DARPA through Air Force Research Laboratory (AFRL) Contract FA8750-07-C- 0169, and by the Baskin Chair of Computer Engineering. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Defense Advanced Research Projects Agency or the US Government. * Corresponding author. Tel.: +1 831 4595436; fax: +1 831 4594829. E-mail addresses: [email protected] (X. Wang), [email protected] (J.J. Garcia-Luna-Aceves), [email protected] (H.R. Sadjadpour). 1389-1286/$ - see front matter O 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.comnet.2008.10.010 multiple antennas. In a point-to-point MIMO channel, the multiple antenna arrays increase the spatial degrees of freedom (DOF) and can provide spatial multiplexing gain or spatial diversity gain [1]. Consider a system with N transmit and M receive antennas, in order to achieve the spatial multiplexing gain, the incoming data are demulti- plexed into N distinct streams and each stream is transmit- ted from a different antenna with equal power at the same frequency. Foschini et al. [2] has shown that the multiplex- ing gain can provide a linear increase in the asymptotic link capacity as long as both transmit and receive antennas increase. In rich multipath environments, the transmitted data streams fade independently at the receiver and the probability that all data streams experience a poor channel at the same time is reduced. This contributes to the spatial diversity gain of the MIMO channel. In order to achieve spatial diversity gain, each stream is transmitted using dif- ferent beamforming weights to achieve a threshold gain at the specified receiver while at the same time nulling coex- isting, potentially interfering transmitter–receiver pairs. The spatial diversity gain can be used to reduce the bit er- ror rate (BER) or increase the transmission range of the wireless links [3]. We denote by H ij the channel coefficient