We present a multiuser synchronization scheme for tracking the mobile's uplink time and frequency offsets. It uses the redundancy introduced by the cyclic prefix and does not need additional pilots. We show performance results of an orthogonal frequency division multiplexing (OFDM)-based radio interface based on universal mobile telecommunication system (UMTS) parameters. For a UMTS-typical mobile channel environment, the performance of a coherent system employing the scheme is virtually indistinguishable from the performance of a perfectly synchronized system. In a differentially modulated system, synchronization errors decrease the system performance by about 0.7 dB compared to a perfectly synchronized system.

We investigate the design of a broadcast system in order to maximize throughput. This task is usually challenging due to channel variability. Forty years ago, Cover introduced and compared two schemes: time sharing and superposition coding. Even if the second scheme was proved to be optimal for some channels, modern satellite communications systems such as DVB-SH and DVB-S2 rely mainly on a time sharing strategy to optimize the throughput. They consider hierarchical modulation, a practical implementation of superposition coding, but only for unequal error protection or backward compatibility purposes. In this article, we propose to combine time sharing and hierarchical modulation together and show how this scheme can improve the performance in terms of available rate. We introduce a hierarchical 16-APSK to boost the performance of the DVB-S2 standard. We also evaluate various strategies to group the receivers in pairs when using hierarchical modulation. Finally, we show in a realistic case, based on DVB-S2, that the combined scheme can provide throughput gains greater than 10% compared to the best time sharing strategy.

The use of Global Navigation Satellite System (GNSS) for positioning has grown significantly in recent years thanks in particular to the development of several mass-market applications, such as car navigation or mobile positioning. Unfortunately, in difficult environments such as dense urban or indoor areas, GNSS exhibits degraded performances in terms of precision and availability. The use of signals of opportunity is one of the solutions to replace or assist GNSS in those environments. These signals are communication signals that are usually designed to provide a service in dense environment and can thus be used in location where GNSS is unavailable. Several commercial positioning services based on signals of opportunity already exist such as ROSUM with ATSC digital TV signals, or Skyhook with Wi-Fi signals This paper investigates the potential of the digital TV European (but used worldwide) standard DVB-T, based on an OFDM air interface, to supply a navigation service. To support a previously proposed DVB-T receiver architecture, a DVB-T receiver simulator is presented that includes the principal blocks required for communication with enhanced navigation-oriented functionalities. In particular, this simulator includes a Delay Lock Loop (DLL) for accurate synchronization purpose. The theoretical expressions of pseudo-range sigma error and tracking threshold in case of Line-Of-Sight (LOS) signal are proposed and compared to simulation results, in order to validate the DLL module of the simulator. Then, performances in a more realistic Rayleigh multipath channel are presented. This paper also proposes description and explanations of impairments due to absence of LOS signal in urban environment and points out the limits of existing urban channel propagation models for a positioning solution.

In this paper, we study the Symbol Error Probability (SEP) performance of a hybrid/integrated satellite-terrestrial cooperative network. In particular, we focus on the case of mobile relays that forward the satellite signal to a masked mobile destination node. The Selective Decode-and-Forward (SDF) transmission scheme is implemented and only the relay nodes which can successfully decode the satellite message are selected to retransmit the signal. The destination node exploits the spatial diversity advantages by implementing a typical Maximum Ratio Combining (MRC) technique. The closed-form expressions for the exact average SEP of the arbitrary M-ary phase shift keying and M-ary quadrature amplitude modulation signaling with MRC diversity reception over independent but not necessarily identically distributed fading channels are derived using a Moment Generating Function (MGF) approach. These closed-form expressions are represented in terms of a finite sum of Lauricella hypergeometric functions. The analytical expressions show excellent agreement with the simulation results. Numerical results show that for a system using QPSK under the frequent heavy shadowed fading condition, the diversity gain of approximately 7 dB can be obtained at the SEP of 10 −1 with respect to the direct transmission, when only one relay is used. It increases to around 12 dB in the case of 3 relays.