Mohammad Z. Siam

Energy-Efficient Clustering/Routing for Cooperative MIMO Operation in Sensor Networks

Employing multi-input multi-output (MIMO) links can improve energy efficiency in wireless sensor networks (WSNs). Although a sensor node is likely to be equipped with only one antenna, it is possible to group several sensors to form a virtual MIMO link. Such grouping can be formed by means of clustering. In this paper, we propose a distributed MIMO-adaptive energy-efficient clustering/routing scheme, coined cooperative MIMO (CMIMO), which aims at reducing energy consumption in multi- hop WSNs. In CMIMO, each cluster has up to two cluster heads (CHs), which are responsible for routing traffic between clusters (i.e., inter-cluster communications). CMIMO has the ability to adapt the transmission mode and transmission power on a per-packet basis. The transmission mode can be one of four transmit/receive configurations: 1 times 1 (SISO), 2 times 1 (MISO), 1 times 2 (SIMO), and 2 times 2 (MIMO). We study the performance of CMIMO via simulations. Results indicate that our proposed scheme achieves a significant reduction in energy consumption, compared to non-adaptive clustered WSNs.

Clustering and power management for virtual MIMO communications in wireless sensor networks

Abstract Multi-input multi-output (MIMO) is a well-established technique for increasing the link throughput, extending the transmission range, and/or reducing energy consumption. In the context of wireless sensor networks (WSNs), even if each node is equipped with a single antenna, it is possible to group several nodes to form a virtual antenna array , which can act as the transmitting or receiving end of a virtual MIMO (VMIMO) link. In this paper, we propose energy-efficient clustering and power management schemes for virtual MIMO operation in a multi-hop WSN. Our schemes are integrated into a comprehensive protocol, called cooperative MIMO (CMIMO), which involves clustering the WSN into several clusters, each managed by up to two cluster heads (CHs); a master CH (MCH) and a slave CH (SCH). The MCH and SCH collect data from their cluster members during the intra-cluster communications phase and communicate these data to neighboring MCHs/SCHs via an inter-cluster VMIMO link. CMIMO achieves energy efficiency by proper selection of the MCHs and SCHs, adaptation of the antenna elements and powers in the inter-cluster communications phase, and using a cross-layer MIMO-aware route selection algorithm for multi-hop operation. We formally establish the conditions on the transmission powers of CHs and non-CHs that ensure the connectivity of the inter-cluster topology. Simulations are used to study the performance of CMIMO. The simulation results indicate that our proposed protocol achieves significant reduction in energy consumption and longer network life time, compared with non-adaptive clustered WSNs.

Coexistence Problem in IEEE 802.22 Wireless Regional Area Networks

IEEE 802.22 wireless regional area network (WRAN) is an emerging cognitive radio-based system. One of the major challenges for WRANs is how to efficiently schedule both channel sensing and data transmission for multiple adjacent WRAN cells. This challenge is known as coexistence problem. In this paper, we propose four schemes that aim at reducing the coexistence-problem effect. These schemes are based on a well-known operation mode of IEEE 802.22, namely dynamic frequency hopping (DFH). The first and second schemes are based on using omni-directional antennas at the base stations (BSs), whereas the BSs in the other two schemes use directional antennas. The first scheme, coined fixed-scheduling DFH (FDFH), bases upon a fixed scheduling of working channels for adjacent WRAN cells. The second scheme, called cooperative DFH (CDFH), cooperatively selects working channels. The third scheme, namely sectoral DFH (SDFH), is proposed to reduce the coordination overhead of CDFH via dividing a WRAN cell into sectors to decrease the chances of collisions between adjacent cells. Finally, we integrate FDFH and SDFH into a new scheme, called fixed-scheduling sectoral DFH (FSDFH), which exploits the advantages of both schemes with no additional overhead. Computer simulations are used to demonstrate the performance gain of the proposed schemes.

An overview of MIMO-oriented channel access in wireless networks

The integration of MIMO technology in WLANs has recently been the locus of extensive research. The main objectives of this technology are to improve channel reuse and or reduce energy consumption. In this article, we give an overview of MIMO systems and their use in WLANs. We highlight the different types of gains that MIMO offers and then discuss some of the work that has been done on MAC design. We conclude by outlining several open issues thai must be addressed for MIMO-based systems.

Channel Access Scheme for MIMO-Enabled Ad Hoc Networks with Adaptive Diversity/Multiplexing Gains

Transmission power control (TPC) is used in wireless networks to improve channel reuse and/or reduce energy consumption. It has been often applied to single-input single-output (SISO) systems, where each node is equipped with a single antenna. Multi-input multi-output (MIMO) systems can improve the throughput or the signal-to-noise ratio (SNR) by providing multiplexing or diversity gains, respectively. In this paper, we incorporate a power-controlled MAC protocol for a wireless network with two antennas per node. Our protocol, coined CMAC, combines different types of MIMO gains, allowing for dynamic switching between diversity and multiplexing modes so as to maximize a utility function that depends on both energy consumption and throughput. CMAC adapts the “antenna mode,” the transmission power, and the modulation order on a per-packet basis. By “antenna mode” we mean one of five possible transmit/receive antenna configurations: 1 × 1 (SISO), 2 × 1 (MISO-D), 1 × 2 (SIMO-D), 2 × 2 (MIMO-D), and 2 × 2 (MIMO-M). The second, third, and fourth configurations offer a diversity gain, whereas the last configuration offers a multiplexing gain. By using control packets to bound the transmission power of potentially interfering terminals, CMAC allows for multiple interference-limited transmissions to take place in the vicinity of a receiving terminal. We study via simulations the performance of CMAC in ad hoc topologies. Our results indicate that relative to non-adaptive protocols, CMAC achieves a significant improvement in both the overall energy consumption and the throughput.

Throughput-Oriented Power Control in MIMO-Based Ad Hoc Networks

Transmission power control (TPC) has been used in wireless ad hoc networks to improve channel reuse and/or reduce energy consumption. It has been mainly applied to single-input single-output (SISO) systems, in which each node is equipped with a single antenna. In this paper, we study MAC protocols for mobile ad hoc networks (MANETs) with MIMO (multi-input multi-output) capability. In particular, we consider the integration of MIMO into two MAC protocols. The first protocol is the IEEE 802.11 standard, which is a conservative protocol that does not use TPC. The second protocol is POWMAC, which exploits TPC to maximize the perceived throughput. We refer to these protocols when applied to MIMO systems as MIMO-802.11 and MIMO-POWMAC. We compare the performance of MIMO-802.11 and MIMO- POWMAC with SISO-802.11 and SISO-POWMAC, in terms of the perceived throughput and energy consumption. Our simulations reveal that although the MIMO system doubles the bit rate per link over the SISO system, the network throughput is not necessarily doubled due a reduction in the number of concurrent transmissions. In addition, the throughput gains in the MIMO system come at a non-negligible energy cost.

A combined power-controlled protocol with adaptive MIMO gains for wireless networks

Transmission power control (TPC) is used in wireless networks to improve channel reuse and/or reduce energy consumption. It has been applied mainly to single-input single-output (SISO) systems, where each node is equipped with a single antenna. Multi-input multi-output (MIMO) systems can improve the throughput or the signal-to-noise ratio (SNR) by providing multiplexing or diversity gains, respectively. In this paper, we propose a power-controlled MAC protocol that combines different types of MIMO gains in a wireless network with two antennas per node. Our protocol, coined CMAC, allows for dynamic switching between diversity and multiplexing modes so as to maximize a utility function that depends on both the energy consumption and throughput. CMAC adapts the “antenna mode,” the transmission power, and the modulation order on a per-packet basis. By “antenna mode“ we mean one of the five possible transmit/receive antenna configurations: 1×1 (SISO), 2×1 (MISO-D), 1×2 (SIMO-D), 2×2 (MIMO-D), and 2×2 (MIMO-M), where the second, third, and fourth configurations offer a diversity (D) gain, whereas the last configuration offers a multiplexing (M) gain. By using control packets to bound the transmission power of potentially interfering terminals, CMAC allows for multiple interference-limited transmissions to take place in the vicinity of a receiving terminal. We study via simulations the performance of CMAC in ad hoc topologies. Our results indicate that relative to non-adaptive protocols, CMAC achieves a significant improvement in both the overall energy consumption and the throughput.