Cooperative Scheme in SFN Positioning System

Jun Yan, Lenan Wu, Feng He, Man Feng

School of Information Science and Engineering, Southeast University, Nanjing, 210096, China

application is limited by the network coverage. Therefore, Abstract—In order to solve the problem of cooperative issue in development of new solutions by use of existing networks is of single frequency network (SFN) positioning system, in this paper, great interest [4]. a cooperative positioning scheme using the fundamental Digital television (DTV) network is a relatively new characteristic of SFN is proposed. Some different signal levels are technology that greatly enhances television performance. described for cooperative signal selection. According to the Positioning using DTV signals has some notable advantages difference between the cooperative signal levels, the proper signal from the point of theory comparison with respect to the can be selected for cooperative positioning in different scenarios. The cooperative positioning strategies for different cooperative received signal power level, signal bandwidth, and modulation signal levels are also proposed to improve the positioning type. DTV signal has a power advantage over GPS signal of performance. These methods can be considered as a feasible more than 40dB and can be employed to realize robust indoor solution for actual applications. positioning [5]. Further, the DTV signal has roughly three times the bandwidth of GPS signal and thus can provide a more Index Terms—mobile positioning; cooperative signal selection; accurate position estimation result with wider signal cooperative positioning strategy; single frequency network (SFN) bandwidth. The modulation type of most DTV standards is based on orthogonal frequency division multiplexing (OFDM). It has an inherent capability to mitigate multipath effects and I. INTRODUCTION fading on particular frequencies. Therefore it can ensure robust obile positioning using radio signals has received signal reception at different environments. Hence, DTV M considerable attention in recent years [1]. The U.S. network can be considered as a feasible and desirable platform Federal Communications Commission (FCC) requirements and for positioning especially indoors. Note that because all the position information applications have boosted research in base stations (BSs) in a DTV network transmit the same DTV wireless location techniques. The government authorities signal in the same signal frequency at the same time, it is a require all wireless service providers to provide location single-frequency network (SFN). With the development of the position techniques, information for Emergency 911 (E-911) public safety services. cooperative will become a research trend. Compared with the On the other hand, reliable location estimation is a critical traditional cooperative positioning systems, the cooperative component for a diverse set of applications including medical scheme for SFN positioning system faces greater challenge, services, search and rescue operations and intelligent transport owing to the characteristics of DTV network. To the best of the system (ITS), as well as a large set of location-based authors’ knowledge, there exists no literature addressing this applications in cognitive radio (CR) [2]. issue. This paper intends to fill up this gap. Global Positioning System (GPS) can achieve centimeter The rest of the paper is organized as follows. Section II accuracy in outdoor environments when the ground-based briefly presents the problem formulation in SFN positioning reference stations are used to form differential GPS. However, system. Section III proposes the cooperative signal selection because the GPS signals are transmitted at relatively low power approach in different scenarios. Section IVstudies the levels and the received signal strength is rather weak over great cooperative strategy among the cooperative signal levels. distances, the signal can not be detected by normal GPS Finally, Section V draws our conclusion. receivers in urban canyons or indoor environments, since the weak signal is blocked by buildings. Alternative practicable ROBLEM FORMULATION position location systems were recently proposed based on II. P cellular networks or wireless local area network (WLAN). Although positioning using DTV signal can provide more Owing to the low transmission power and narrow signal available, accurate and rapid position information service [6]- bandwidth, positioning in cellular networks can only achieve [9], it brings some difficulties when no more than one kind of very limited accuracy [3]. Although the position estimation in DTV signals are received. For instance, the DTV can receive WLAN is more accurate within the service area of network, its different DTV programs in a given SFN or different DTV standard signals in the overlapped region with multiple SFNs. The work was supported by the Cultivation Fund of the Key Scientific and Hence, it gives many opportunities for cooperative positioning. Technical Innovation Project of Ministry of Education of China (No. 706028) On the other hand, from the traditional cooperative system, the and the National Natural Science Foundation of China (No. 61174205). SFN positioning system can also take advantage of satellite and wireless radio signals to perform better position estimation.

Fig.1 shows the schematic diagram of the cooperative multiple SFNs (3) other related DTV networks and (4) other positioning in SFN. In the following, these problems about positioning systems. Compared with different cooperative cooperative positioning are described in detail. signal levels, the application analysis is described in Table 1. In order to effective channel resource usage, there exists more than one DTV programs for broadcasting in a given SFN. It means that, at the reception, many kinds of DTV programs can be received. Therefore, the DTV program transmitted from different BSs can be utilized for cooperative positioning, according to the cooperative principle. There are many DTV terrestrial transmission standards around the world, such as Advanced Television System Committee (ATSC) standard, Digital Video Broadcasting- Terrestrial (DVB-T) standard, Integrated Service Digital Broadcasting-Terrestrial (ISDB-T) standard and Chinese Digital Television Terrestrial Broadcasting (DTTB) standard [10] [11]. Owing to government policy and deployment layout, it may adopt more than one DTV standard for a given region. For example, two DTV standards, Chinese DTTB and DVB-T, are coexisting in Nanjing China. The DTV receiver may obtain different standard DTV signals in some areas of Nanjing. Fig.2. Block diagram of the cooperative signal levels Hence, cooperative positioning between different SFNs may occur in the overlapped region of multiple SFN coverage. TABLE I In order to extend the convergence, DTV network usually THE APPLICATION ANALYSIS BETWEEN DIFFERENT COOPERATIVE SIGNAL makes use of satellite network to broadcast DTV signals in the LEVELS desert and remote countryside areas. Many DTV standards for 1 2 3 4 satellite transmission are established, such as DVB-S for DVB detection transport DTV DTV signal standard. Hence, cooperative positioning should also consider rule stream (TS) standard standard features this kind of DTV signal similarly in the above areas. parameters parameters In the previous work of [5], the authors pointed out that reception DTV receivers special positioning using DTV signals can be considered as a potential equipmen receivers t supplement for GPS in urban and indoor positioning. Hence, it complexit low high means that the SFN positioning system can work with other y system for cooperative positioning. typical different different DVB-S; GPS signals; example DTV DTV ISDB-S wireless programs standard network signals

First, the detection rule of each cooperative signal level is different. First, second and third cooperative signal levels can be detected, according to the transport stream (TS) or the DTV standard parameters. These three cooperative signal levels are also received by the DTV receiver itself. After channel estimation/equalization, signal demodulation, and channel decoding, the TS and DTV signal standard parameters can be obtained. In the case where the signals are transmitted from different BSs in the same SFN, the detection rule of the first cooperative signal level is to compare the received TSs. On the other hand, the signal standard parameters or received TS can be utilized to distinguish the second and third cooperative signal levels when the signals are transmitted from different Fig.1. Schematic diagram of the cooperative positioning in SFN SFNs or other related DTV networks. For the fourth cooperative signal level, because they are beyond the DTV III. COOPERATIVE SIGNAL SELECTION network, the detection rule is very easy. By using a special In order to carry out cooperative positioning, receiver with multi-reception, it can be found whether the cooperative signal selection is an essential step in SFN fourth cooperative signal level exists or not. positioning system. In this section, different cooperative signal Second, the fourth signal level is the most complicated for levels are presented first and then some application analysis on practical applications among all the cooperative signal levels. these different signal levels are discussed. Owing to the mature hardware of DTV receivers, the first, Fig.2 shows a block diagram of the cooperative signal second and third cooperative signal levels are cost-effective. levels which consists of four main components: (1) one SFN (2) However, it should make use of special receiver to capture the

3 fourth cooperative signal level. Hence, this system complexity the first, the second and the third cooperative signal levels, i.e. is much higher. the measurements have different sampling frequencies and are not arrive at the same time. Hence, the strategy selection IV. COOPERATIVE STRATEGY SELECTION between this cooperative signal level and other cooperative Because the position estimation accuracy depends on the signal level is only the distributed cooperative strategy, number of the observed DTV signals, the mobile should make according to the above discussion. use of all possible DTV signals. According to the knowledge of TABLE2 THE COOPERATIVE STRATEGY SELECTION FOR EACH COOPERATIVE SIGNAL positioning estimation algorithm, the cooperative strategy LEVELS contains centralized cooperative positioning and distributed cooperative signal centralized distributed cooperative positioning which are illustrated in Fig. 3. For levels central cooperative positioning, all the positioning parameters 1and 2 Yes Yes after proper time delays are sent to the position estimator at the 1and 3 Yes Yes 1and 4 No Yes same time. The position estimator estimates the mobile position 2 and 3 Yes Yes with all the positioning parameters. This kind of position 2 and 4 No Yes estimation is calculated only one time. However, for the 3 and 3(different DTV Yes Yes standard) distributed cooperative positioning, the position estimation 3 and 4 No Yes process contains two steps. First, the intermediate position 4 and 4 (different No Yes estimation is obtained with some positioning parameters. Then network) all the intermediate position estimations are fused to obtain the final result by some data fusion criterion. V. CONCLUSION In this paper, a cooperative scheme for SFN positioning system is proposed. Based on the fundamental characteristic of SFN, the cooperative signal levels for signal selection are presented and some application analysises about different cooperative signal levels are also discussed. It can guide the cooperative signal selection in different scenarios. To incorporate the entire selected cooperative signals, the cooperative positioning strategies between different cooperative signal levels are also proposed. It can be considered as a feasible solution for actual application.

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