Search results for "Spread spectrum"
showing 7 items of 17 documents
Characterization of Radio Frequency Echo using frequency sweeping and power analysis
2014
International audience; Coupling between repeater's antennas, called Radio Frequency Echo (RFE) deteriorates signal quality and compromises system stability. If the channel insulation is insufficient, the power in the closed-loop raises with time according to the gain margin value. Multiple methods of echo cancellation exists. Generally, these techniques are based on correlation calculation and adaptive filtering. However, their efficiency and algorithm's convergence speed are calling into question under signal's modulation and real-time constraints, specially with narrow band signals having frequency hopping as GSM or TETRA. This paper describes a real time method of RFE detection and esti…
Performance of LoRa technology: link-level and cell-level performance
2020
Abstract LoRa is a chirp spread spectrum technology that is becoming very popular for low-power wide-area networks, with high-density devices. In this chapter, we study the capacity of LoRa in rejecting different interfering signals. First, we analyze LoRa modulation numerically demonstrating that channel captures appear easily and that collisions between packets modulated with different spreading factors (SFs) are not uncommon. We validate such findings in experiments based on commercial devices and software-defined radios. Second, we model the network capacity obtainable in a typical LoRa cell: we show that high SFs can be seriously influenced by inter-SF collisions and that fading has a …
Signal-to-Noise Ratio in Bandpass Direct-Sequence Spread-Spectrum Modulation Systems
1982
The effects of a linear transmission channel on the performance of a correlator receiver for a direct-sequence spreadspectrum system are analyzed and a complete treatment of the influence of a periodic spreading code is carried out. The output data signal is obtained as a function of the channel characteristic and the code sequence employed; this allows maximizing the output signal level and evaluation of the influence of the synchronization error of the local code. The asymptotic value of the correlation loss has also been derived together with the intersymbol inteference power. The general expression of a figure of merit of the effectiveness of the system is also obtained in simple terms …
Signal detection for spread spectrum communication systems with gradient algorithm
2012
Retrieval process of original symbols of a spread spectrum based communication system is tried to be improved by Gradient Algorithm (GA) and Blind Source Separation (BSS) principles. Two simple schemes, based on two energy functions are presented. Time correlation properties of the channel are used as advantages in developing the filter coefficients for the receiver. Direct Sequence - Code Division Multiple Access (DS-CDMA) technique based system setup is used for algorithm testing purposes. This is identified as one of the most stable spread spectrum communication technique where most of the technologies developed for that are highly compatible with High Speed Packet Access (HSPA) transmis…
Interference excision algorithm for frequency hopping spread spectrum based on undecimated wavelet packet transform
2002
An algorithm for reducing narrowband interference effects in frequency hopping spread spectrum is presented. The method is based on the undecimated wavelet packet transform. It improves the performance obtained by other methods. Experimental results demonstrate the suitability of the algorithm.
On Serving Cell Change Reliability in HSDPA Network
2009
In Wideband Code Division Multiple Access (WCDMA) networks the Signaling Radio Bearer (SRB) is transmitted downlink to inform the user i.a. when it needs to make a handover. When transmitting e.g. Voice over IP (VoIP) on High Speed Downlink Packet Access (HSDPA) SRB is mapped on HSDPA user data channel, High-Speed Downlink Shared Channel (HS-DSCH) in order to maximize voice capacity. The lack of support for soft handover (SHO) of HS-DSCH may compromise the reception of SRB and thus also a possible incoming serving HSDPA cell change command especially at the cell borders. This can lead to serious VoIP service degradation due to prolonged camping on a poor cell and in the worst case even to c…
Multi-hop D2D Communications with Network Coding : From A Performance Perspective
2019
Multi-hop device-to-device (D2D) communications play an important role in expanding D2D coverage. In this paper, we study a relay-based and network-coding-assisted (in particular, XOR coding) multi-hop D2D communication system. In the system, toward jointly considering the impact of interference and network traffic conditions on the quality of D2D communications, various channel fading models and traffic models are investigated, and the packet loss probability of D2D links is meticulously computed using these models. With the packet loss probability of D2D links, the general closed-form expressions of end-to-end packet loss probability (E2EPLP) of the system with the presence (or absence) o…