Jan Nilsson

Cost drivers and deployment scenarios for future broadband wireless networks - key research problems and directions for research

The most prominent problem in providing anywhere, anytime wideband mobile access is the towering infrastructure cost as it is basically proportional to the bandwidth provided. We provide a simple, initial, analysis of the various infrastructure cost factors. This analysis shows that, contrary to what one may expect, the infrastructure cost is not dominated by electronic equipment, but rather by other deployment related costs (towers, wiring, building, network connections) and maintenance costs. In the paper some novel architectural approaches for future wideband mobile access focusing on these dominant cost factors are described and the related key research issues are discussed.

A comparison of access methods for multi-hop ad hoc radio networks

For mobile radio networks without guaranteed connections to fixed infrastructure, simple non-centralized network control is desirable in order to reduce the administrative traffic in the network. In this paper, we analyze and compare two asynchronous non-centralized access schemes in the case of multi-hop ad hoc networks. The first is a new protocol based on time-hopping code division multiple access (TH-CDMA), and the second is based on carrier-sense multiple access (CSMA). The new ultra-wideband (UWB) impulse radio technique makes the first scheme an interesting option. A third scheme, a synchronous spatial time-division multiple access (STDMA) scheme is also included in the comparison as a reference.

Robust MPR-based flooding in mobile ad-hoc networks

The paper investigates robust MPR-based broadcasting in a highly dynamic scenario. There are several methods, or combinations of methods, that can be used to increase the robustness of MPR-based flooding. We investigate the use of a reduced HELLO interval, a fading margin or additional MPRs. It is also important to consider the cost of implementing these methods. To investigate which method to choose, and when, a dynamic urban scenario is used, that is based on a channel model that mimics real radio transmissions. Results show, among other things, that using a reduced HELLO interval does not provide sufficient robustness. Moreover, the choice of method depends on the network connectivity. For sparse networks, using additional MPRs is a good choice, but for dense networks, using a fading margin is more efficient. This latter method, however, requires physical layer information. Furthermore, an MPR relay assistance method is proposed that is robust for both sparse and dense networks at a reasonable cost.

Coding of spread spectrum signals for HF communications

Problems connected with HF communications are atmospheric noise, multipath propagation and interfering signals from other users. In military applications also intentional jamming should be considered. A method used to cope with these problems is wideband transmission combined with coding techniques. We investigate and compare the efficiency of coding applied in two well-known wideband techniques; direct sequence (DS) signaling, and orthogonal frequency division multiplexing (OFDM) or multicarrier transmission. We let the channel be disturbed by both Gaussian noise and narrowband interfering signals according to the Laycock-Gott (1988) model.

Architectural issues for integrating tactical radio access networks in civilian infrastructure

We investigate architectures where a tactical radio subsystem can integrate in civilian systems. The idea is that civilian communication infrastructure should be used wherever it is available. One such possibility may be found in the proposed next generation wireless communication system UMTS, where the definition of a radio network subsystem (RNS), encapsulating all the features of wireless mobile communication has been proposed. We adopt this design paradigm to see if it is possible to find a low cost military network (by maximal use of civilian network technology and communication applications). The idea is to within the framework of an RNS, encapsulate also features specific to tactical wireless communications, a tactical radio access network (TRAN). Based on UMTS we describe two system concepts for designing a TRAN and analyze the architectures.

Performance of MPR-based broadcast methods in mobile ad hoc networks for rural terrains

With the aim of achieving robust broadcasting, the paper explores how the terrain affects different MPR-based broadcast methods. As a reference we consider the MPR selection method in OLSR and investigate methods for increasing robustness by the using of physical layer information and additional MPRs. It is also important to consider the overhead of these methods. To assess how terrain properties influence performance we consider mobile scenarios in different rural terrains. A channel model that mimics real radio transmissions and includes terrain effects is employed. The plane earth model is also tested. The terrain has a large influence on overall performance, and the results obtained with the plane earth model can produce misleading results. However, when determining how to select MPR nodes, network connectivity is the main criteria to use.

Spectrum and waveform relations of multicarrier communications

The paper treats spectrum and signal waveform relations of M-ary PSK multicarrier communications. We propose new codes resulting in constant, or near constant, modulus (envelope) time-domain baseband signals.

A realistic military scenario and emulation environment for experimenting with tactical communications and heterogeneous networks

Emulation environments are an effective approach to experimenting with and evaluating network protocols, algorithms, and components. This paper describes a joint effort by the NATO Science & Technology Organizations IST-124 task group to develop and distribute an emulation environment and scenario. The most significant contribution is a vetted and militarily-realistic scenario that provides a rich combination of elements for experimentation. The scenario includes detailed mobility patterns for a battalion-sized operation over the course of two hours, which has been developed by military experts in planning and performing real exercises. The mobility patterns are used to drive the network emulation.

Scenario based comparison of cellular and ad-hoc tactical radio networks

Two types of tactical radio networks are analyzed and compared. Firstly we consider a multi-hop ad-hoc network and secondly a WCDMA cellular network based on the new UMTS terrestrial radio access network called UTRAN. We are interested in how an ad-hoc network behaves and compares to a cellular network with a limited number of base stations, in a mobile scenario. For the assessment, two tactical scenarios involving a Swedish mechanized battalion are drawn up for armed combat on Swedish ground. They are characterized by different mobility, where in the first we have constant movements over a large area and in the second only a high speed movement within a limited area at the end of the scenario. We test a service mix consisting of situation awareness data, group calls and intranet connections. We use a digitized terrain database for propagation modeling in the 300 MHz and the 1.5 GHz frequency bands. As a scenario elapses, at each time instant, the probability that the network can provide a service for an arbitrarily chosen radio terminal is estimated. Based on these results we finally assess the different network solutions.

Link and Network Capacity Gains in Ad Hoc Networks Utilizing MIMO-Techniques

Multiple-Input Multiple-Output (MIMO) antenna systems is a promising technique for achieving substantially increased capacities and robustness in future tactical wireless networks. The purpose of this work has been to investigate the theoretical link and network capacity gains that can be achieved by employing MIMO-techniques in wireless ad hoc networks. We study these gains from a theoretical viewpoint and derive a closed-form expression of the network capacity for a reservation based MAC protocol that utilizes traffic adaptation. The link and network capacities are thereafter examined in urban environments, using two different MIMO channel models. Furthermore, the effect of utilizing MIMO-systems on the mean route lengths and the number of used links are investigated.