Ultra Wide Band technology (UWB) has received increasing recognition in recent years for its potential applications beyond radar technology to communication networks. UWB is a spread spectrum technology that requires careful coordination among communicating nodes to jointly control link power and transmission rates. Here, we present U-MAC, an adaptive Medium Access Control (MAC) protocol for UWB in which nodes periodically declare their current state, so that neighbors can proactively assign power and rate values for new links locally in order to optimize global network performance. Simulations comparing U-MAC to the reactive approach confirm that U-MAC lowers link setup latency and control overhead, doubles the throughput and adapts better to high network loads. Simulations also reveal that the basic form of U-MAC favors nodes that are closer to the receiver. As a result, we also introduce novel mechanisms that control the radius around a receiver within which nodes can have fair access to it. We show through simulations the effect of the mechanisms on the tradeoff between network throughput and fair access.  Ultra Wide Band technology (UWB) is a spread spectrum technology that is based on the modulation of short nanosecond low power pulses. This technology has been used for radar applications for over half a century. In recent years, UWB has received increasing recognition for its applicability to short to medium range communication networks because of desirable features such as high data rates, low power consumption, precise ranging capabilities, resistance to multi-path fading, and penetration of dense objects. UWB is currently a candidate technology for short range high transfer rate applications such the simultaneous transfer of multiple video streams in a Wireless Personal Area Network (WPAN A central problem in UWB networks is the joint optimization of transmission power and transmission rates for active links. The joint rate and power assignment problem in UWB involves complex tradeoffs between fair rate assignment, network efficiency, and Quality of Service (QoS). A high power link may achieve high transmission rates, but it also causes high interference which limits the rate available to neighboring links. On the other hand, a low power link promotes fair access to the wireless medium but yields lower transmission rates. Thus, nodes must collaboratively determine the optimal rate and power values for new links in the network. Another important consideration for rate and power assignments in UWB networks is fair access among nodes at different distances from a common receiver, especially in ad hoc networks with dynamic topologies. An inherent property of wireless communications is that transmission rates drop with increasing distance. This effect is even more pronounced in UWB communications, where the strong correlation of transmission rates with multiuser interference levels further increases the impact of relative distances on transmission rates. This impact may be unsuitable for applications that require all the network nodes to have fair access to the medium regardless of distance. The fair access requirement in such applications imposes an additional constraint on the choice of transmission power. So far, UWB research has been primarily confined to the investigation of the behavior of the physical layer [3, 4] . Research at higher layers of the network stack has been somewhat limited. Previous research proposals for higher layers considered an underlying Radio Frequency (RF) physical layer, so most of these proposals are not suitable for UWB networks. For instance, the existing wireless MAC protocols [5] for RF networks do not meet the need of UWB networks for joint rate and power assignment, hence the need for new UWB MAC protocols. There have been recent attempts to develop mechanisms for UWB networks at the MAC layer. The work in [6] proposes a simple reactive multiple access protocol that defines the handshaking procedure to establish a new link. The work in [7, 8] discusses a protocol that uses periodic state updates to allow nodes to jointly assign rate and power assignment values locally at each node. Here, we propose a new MAC protocol U-MAC (Ultra
In REF , an adaptive medium access control protocol for UWB is proposed, in which nodes periodically declare their current state, so that neighbors can proactively assign power and rate values for new links locally in order to optimize global network performance.
U-MAC: a proactive and adaptive UWB medium access control protocol
Wireless Comm. and Mobile Comp
Computer Science