An Algorithm for Radio Resource Management in UWB Ad Hoc Networks with Concurrent Guaranteed QoS and Best Effort Traffic Tomaso Erseghe, Nicola Laurenti, Pietro Nicoletti, and Andrea Sivieri Department of Information Engineering, University of Padova, Via Gradenigo 6/B - 35131 Padova, Italy E-mail: {erseghe,nil}@dei.unipd.it, pietro.nicoletti@fracarro.com, andrea.sivieri@icn.siemens.com Abstract— In the framework of ultra-wide-band impulse-radio (UWB-IR) systems and networks, little has been discussed so far about radio resource management issues. On the other hand, results for general multiple-access spread-spectrum systems can be a basis for developing techniques suited to UWB-IR features. On the basis of a recent work by Cuomo et al., we propose a distributed algorithm for radio resource management in UWB-IR ad-hoc networks where two traffic classes (guaranteed QoS and best effort) coexist. We evaluate its performance partly by analysis, partly by simulations. I. I NTRODUCTION Ultra-wide-band (UWB) systems, and in particular Impulse Radio (IR) technology, have recently attracted wide interest as they are potentially able to support high data rates in indoor dense multipath environments, with low power consumption and low complexity in terms of transmission and reception operations. UWB-IR works efficiently in an asynchronous environment, a feature that is particularly suitable for ad-hoc networks where it could be exploited as a promising and flexible transmission technology [1]. However, little has been discussed so far about radio resource management issues for UWB-IR networks. The problem of assigning radio resources to different traffic flows in an UWB ad-hoc network was first addressed in [2]. There, two management techniques are introduced separately, each corresponding to a different traffic type. Traffic type is classified depending on whether it requires a minimum degree of QoS throughout the connection, which we call guaranteed QoS (GQ), or not, called best effort (BE). Although the technique proposed in [2] for GQ traffic proves to be very effective, that for BE traffic, which aims at maximizing the overall throughput of the network, leads the authors to conclude that either transmitting at maximum power or silencing are the only resulting policies. On the grounds of these results, we explore in this paper the possibility to manage radio resources for simultaneous GQ and BE traffic, since in a realistic environment co-existence of both types (e.g. real-time multimedia applications and WEB browsing) should be assumed. We also aim at improving the flexibility of the BE management protocol, by focusing on a minimization of the average transmitted power, in a way that it is consistent with the states of the queue and the physical channel usage which dictate the resulting transmission urge. To this end, we make use of the power control multiple access (PCMA) approach introduced by Bambos [3] for power management of the BE links. With our solution, the QoS requirements for GQ traffic are rapidly achieved at the start of the connection and consistently maintained throughout, even in the presence of a manic activity of BE traffic. In the paper, we describe our algorithm in detail, providing the signaling procedure and the algorithms for power update (both This work was supported by the Italian Ministry of University and Research (MIUR) within the framework of the PRIMO project FIRB RBNE018RFY. Pietro Nicoletti is now with Fracarro Radioindustrie, Italy. Andrea Sivieri is now with Siemens ICN, Italy. for GQ and BE services), then derive analytically the statistics of the signaling traffic involved in our approach. We also present the results of simulations for a specific traffic scenario. Our technique performs satisfactorily also for BE traffic both in terms of overall transmitted power and packet re-transmission rate. The paper is organized as follows. In Section II we prelim- inarily discuss specific features of UWB transmission, such as the modulation format, the use of time hopping (TH) codes, the reference signal to interference ratio (SIR) expression for evaluating performances. On the basis of these characteristics, in Section III we present the signaling procedures for network access and power control in both cases of GQ and BE traffic. Performances are finally evaluated in Section IV both by mathematical analysis and by simulations. II. PHYSICAL LAYER: UWB FEATURES According to the most recent FCC regulations [4], UWB devices for communication and measurement applications must operate with their 10 dB bandwidth in the frequency band 3.1 − 10.6 GHz with a −41.3 dBm/Hz effective isotropic radiated power spectral density (EIRP). This implies the use of ultra-narrow pulses w(t), with an extension which is less than a nanosecond, and a low power consumption, typically with a maximum radiated power of 1 mW or less. The UWB communication system that we take as our reference is Impulse Radio, proposed by Scholtz in 1993 [5]. In UWB- IR, multiple access is achieved through a TH spread spectrum technique and pulse position modulation (PPM) is used for data transmission. The signal sent by user i can thus be expressed as si (t)= +∞  n=-∞ w  t − Tn,i − bn,i T  (1) where Tn,i is the TH sequence associate with user i, {bn,i } is the incoming binary stream adequately encoded for reliable transmission, and T is the sub-nanosecond PPM spacing. The TH sequence identifies the times available for transmission to user i, with an average rate of 1 transmitted pulse every Ts seconds, which we call symbol period. Typically, for an indoor environment where multipath propagation has a maximum delay spread of the order of few tens of nanoseconds [6], the frame time can be of the order of Ts = 250 ns to avoid severe self-interference. This makes UWB-IR a transmission with an extremely low duty cycle and allows to implement a full-duplex UWB-IR link, since the time dedicated to transmission (hence to power emission) is only a fraction of the available time, and the remaining time can be dedicated to reception [7]. Moreover, TH allows for the simultaneous transmission and reception of packets, and even for the transmissions and reception over multiple links (but with different TH sequences associated to each link), at the cost of a small increase in computational