G. Giancola

(UWB) 2 : uncoordinated, wireless, baseborn medium access for UWB communication networks

A MAC protocol for Ultra Wide Band (UWB) radio networks named (UWB)2 is proposed. The algorithm exploits typical features of impulse radio such as large processing gain, and is conceived in conjunction with a synchronization strategy which foresees the presence of a synchronization sequence in each transmitted packet. (UWB)2 adopts a pure Aloha approach; Performance analysis of the synchronization tracking mechanism showed in fact that under the preliminary simplistic hypothesis of an AWGN channel, and for a sufficient number of pulses in the synchronization sequence, a fairly high probability of successful synchronization can be achieved, even in the presence of several users and Multi User Interference (MUI). The multiple access scheme is based on the combination of a common control channel provided by a common Time Hopping (TH) code with dedicated data channels associated to transmitter specific TH codes.Results obtained by simulation indicate that (UWB)2 can be successfully applied when the number of users spans from a few tens to about one hundred, for data rates ranging from a few thousands to a few hundreds of bits per second. Network throughput was above 99.8% in all considered simulation settings. Such achievement confirms that (UWB)2 is a suitable and straightforward solution for large networks of terminals using impulse radio for transmission at low bit rates.

A novel approach for estimating multi-user interference in impulse radio UWB networks: the pulse collision model

Modeling multi-User Interference (MUI) is crucial in the design of wireless networks. In the case of Impulse Radio (IR)- Ultra Wide Band (UWB) networks, most of the adopted models are inspired by the legacy of the reference literature on spread spectrum communications, and do not address specific features for IR systems, where spectrum spreading is basically obtained by the radiation of very short time-limited pulses. The problem of conceiving a specific model for MUI in IR-UWB networks is addressed in this paper. The reference scenario consists of multiple asynchronous users transmitting IR-UWB signals using Pulse Position Modulation (PPM) in combination with Time Hopping (TH) coding. We provide a novel analytical expression for the average BER based on the observation that interference in IR is provoked by collisions occurring between pulses belonging to different transmissions. The proposed method requires specification of a similar set of system parameters as Gaussian-based approaches, but shows improved accuracy in estimating BER.

Multi user interference in power-unbalanced ultra wide band systems: analysis and verification

Validity of the standard Gaussian approximation (SGA) for modeling multi user interference (MUI) in impulse radio ultra wide band (IR-UWB) systems which do not implement power control is investigated. Analysis focuses on the case of UWB systems adopting binary pulse position modulation (2PPM) with a time hopping (TH) code division multiple access scheme. Theoretical predictions are compared vs. simulation outputs in order to quantify limitations of the SGA hypothesis.

Radio resource management in infrastructure-based and ad hoc UWB networks

Summary Modeling the resource manager of an ultra wide band (UWB) network is the main object of this paper. The model is tested in two different application scenarios: (i) a UWB WLAN access network to a backbone where the resource management module is implemented at the access points (APs); (ii) a UWB ad hoc network for either local communications or data exchange among sensors, with peer-to-peer links with distributed management. The design must include a quality of service (QoS)-aware strategy and must take into account coexistence issues raised by the use of UWB at the physical layer. Link quality is represented by the maximum end-to-end delay and minimum percentage of correct packets. From these parameters, the resource manager jointly selects the values of power and rate which must be adopted at the physical layer. In the model, radiated power by each device is supposed to be limited by an upper bound, reflecting thus the limitation imposed by regulation. QoS awareness and power constraints are satisfied, thanks to the implementation of an admission control function, which is centralized in the AP in the WLAN case and distributed in the ad hoc case. Major innovative aspects include: (i) taking into account UWB specific features; (ii) introducing QoS awareness based on network layer parameters rather than physical layer parameters; (iii) incorporating error protection functionalities for the optimization of transmission efficiency; (iv) considering both centralized and distributed resource management. Performance of the proposed resource manager module is evaluated in the presence of different classes of traffic, that is multimedia, voice, and data traffic. For each class of traffic, performance is expressed in terms of the maximum possible number of simultaneous connections for the WLAN case, and in terms of the effective achievable throughput for the ad hoc case. Results of simulations indicate that the behavior of the proposed scheme is strongly dependent upon the class of traffic in the WLAN scenario, while it is slightly affected by changes in traffic characteristics in the ad hoc case. Copyright # 2005 John Wiley & Sons, Ltd.

A position based routing strategy for UWB networks

In this paper a position based routing strategy which exploits the high precision ranging capabilities offered by ultra-wide band (UWB) is presented. It is shown that if a position-aware routing protocol and a power-aware routing metric based on ranging measurements are adopted, emitted power levels as well as multi-user interference are significantly reduced. The position-aware strategy is compared with standard solutions based on the minimization of the number of hops and on-demand routing. Results are presented for various transmission ranges, i.e. network connectivity conditions. Both power efficiency and routing performance are taken into account in the analysis and trade-offs between these two features are finally discussed.

Power limits fulfilment and MUI reduction based on pulse shaping in UWB networks

Pulse shaping in ultra-wide band (UWB) networks based on impulse radio (IR) is a viable way for adapting the power spectral density (PSD) of transmitted signals to spectral requirements. The proposed pulse shaping method is based on linear combination of a set of base waveforms obtained by differentiation of the Gaussian pulse. Strategies for selecting linear combination coefficients are proposed and approximation of emission masks for UWB indoor systems based on linear combination of the above base functions is analyzed. It is shown that linear combination of base waveforms fulfils spectral requirements with higher efficiency than that achieved by a single waveform. The adoption of pulse shaping in the reduction of multiuser interference (MUI) between different UWB networks is finally proposed and evaluated by means of simulations.

Power-aware design of MAC and routing for UWB networks

Ultra wide band (UWB) radio is considered as a valuable candidate for the deployment of large-scale, low data rate networks, thanks to its large bandwidth allowing for a high number of simultaneous communications. The specific characteristics of UWB, such as ranging capability and severe power limitations, call however for innovative solutions not only at the physical layer, but also at MAC and network layers as well. In this paper an integrated strategy for MAC and routing in UWB networks is proposed, which combines the multiple access capabilities and the ranging information provided by this transmission technique. The strategy exploits the distance information for reducing the power emission in the network, leading to a longer network lifetime and low multi user interference (MUI), thanks to the combination of a distance-based routing metric with a location-aware routing protocol, enabled by the adoption of a distributed positioning protocol. The effectiveness of the proposed solution is evaluated by means of simulations.

A novel approach to error protection in medium access control design

In this paper we analyze the problem of designing the medium access control (MAC) module under quality of service (QoS) constraints for real-time services. The attention is focused on the case of slowly time-varying channels, such as in wireless local area networks (WLAN), and an analytical approach for the optimization of transmission efficiency is presented. In the paper we also propose a novel automatic repeat on request (ARQ) protocol which allows reduction of protective overhead for each transmitted data unit, resulting in a minimum increase of reserved bandwidth.

Evaluating BER in Sparse IR UWB Networks under the Pulse Collision Model

In this paper, we provide a novel analytical expression for the average BER in impulse radio ultra wide band (IR UWB) networks affected by multi user interference (MUI). BER is evaluated based on the observation that interference in IR is provoked by collisions occurring between pulses belonging to different transmissions. The reference scenario consists of multiple asynchronous users transmitting IR-UWB signals using pulse position modulation (PPM) in combination with time hopping (TH) coding. The proposed method requires specification of a similar set of system parameters as Gaussian-based approaches, but shows improved accuracy in estimating BER, in particular when sparse network topologies are taken into account

Introducing consciousness in UWB networks by hybrid modelling of admission control

We formalize a model for a self-organizing network of nodes that operate according to the UWB principle based on hybrid modelling formalism. We design the rules that lead to the formation of the network and in particular an admission control procedure that is capable to handle both continuous and discrete perturbations, while maintaining the network in a condition of stability. Cognition is introduced in the model by allowing nodes to adjust their rules of operation based on the perception of the environment by an elected node, serving as the observer, that is aware of context, evaluates, and selects one strategy of operation.