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Fast acquisition is the major challenge for DS (direct sequence)/FH (frequency hopping) spread spectrum system. A DS/FH acquisition circuit which implements a digital noncoherent correlation scheme is studied extensively. The closed-form expressions of the mean acquisition time by single dwell decision and two-dwell decision are obtained with the state diagram respectively. The results show that,...
In this paper, we propose a novel automatic gain control (AGC) algorithm as a solution to improve the signal reception performance based on the IEEE 802.15.4a chirp spread spectrum (CSS) over indoor fading channels. The CSS signals are composed of low-band and high-band signals whose frequency characteristics are different because of multipath fading in indoor environment. It is not appropriate to...
Spread spectrum communication system with high bit rate, has bad performance of acquisition sensitivity, since the coherent integration time is short. The bad performance can be improved by the method of non-coherent integration processing after coherent integration. But in low SNR environment, the performance is not satisfying because of the large SNR loss of noncoherent integration. This paper describes...
In this paper, we present short communication schedules for broadcast, data aggregation, data gathering, and gossiping in multihop wireless networks subject to physical interference. We assume that all communications proceed in synchronous time-slots, each node can transmit at most one packet of fixed size in each time-slot, and all nodes have fixed and equal transmission power. Under mild assumptions,...
This paper investigates the invariant detection problem of quadrature phase-shift keying (QPSK) direct sequence spread spectrum (DS-SS) signals in additive white Gaussian noise (AWGN). Using the complex Gaussian mixture signal model and invariance principle, we consider the constant-false-alarm-rate (CFAR) invariant detectors and other sub-optimal invariant tests, including the uniformly-most-powerful-invariant...
Iterative signal processing has gained in popularity over the last decade as a way of reducing the effects of interference in a communication system. In previous work, the expectation maximization (EM) algorithm was used to estimate the parameters and data of colliding transmissions in a slow frequency-hopping spread-spectrum (FHSS) system using binary frequency-shift keying (BFSK). As in many FHSS...
In this paper, an algorithm reprocessing of the power spectrum density (RPSD) is proposed to detect and estimate the PN code's period of the multipath direct sequence spread spectrum (DS/SS) signal in low SNR, which develops the previous processing method based on the single path environment. It can solve the difficult problem of PN code's period detection and estimation in multipath environment....
Ultra-wideband (UWB) communication systems are usually implemented by baseband spreading schemes relying either on time hopping (TH) or direct sequence (DS) codes. However these schemes are not suitable to cancel narrow band interference (NBI). Other approaches rely on digital single carrier spreading (SC) or multi-carrier (MC) spreading codes, offering flexibility in NBI cancellation.
We present pre-filtering methods of self-encoded spread spectrum (SESS) in dense multipath channels. SESS eliminates the need for traditional transmit and receive pseudo noise (PN) code generators. In this paper, we propose multipath management of SESS in dense multipath urban environments. We propose a transmitter pre-filtering method that retains only good paths that contribute to the data decision...
This paper targets multicast transmission where the same data is destined to many users simultaneously. Although multicast allows bandwidth saving, it prevents a precise link adaptation over radio links. Indeed, users are subject to the same bitrate despite their different and variable radio conditions. Neither operators nor 3 GPP standard offer solutions to support link adaptation in a multicast...
In this work, we propose a novel combined set-membership (SM) reduced-rank interference suppression scheme and consider its application to spread-spectrum multiuser direct sequence ultra-wideband (DS-UWB) systems. In the proposed scheme, the theory of set-membership filtering is applied to the training-based powers of R (PoR) multi-stage Wiener filter (MSWF) reduced-rank process and the reduced-rank...
Spectrum sensing is a key technology in cognitive radio (CR) and cooperative spectrum sensing is derived due to the effects of channel fading. In this paper, we focus on the optimal number of secondary users in cooperative spectrum sensing to maximize the utility in CR network. By considering both the detection error probability and the resource used by the secondary users in cooperation, we derive...
The main objective of this paper is to describe and simulate the application of an interference cancelling technique named Amplitude Domain Processing (ADP) in navigation. ADP is the simplified algorithm of locally optimum detection theory. According to statistical theory, ADP is a non-linear and digital technology and it can eliminate interferences according to the statistical characteristics of...
This paper focuses on optimal detection of quadrature phase-shift keying (QPSK) and binary phase-shift keying (BPSK) direct sequence spread spectrum (DS-SS) signals in additive white Gaussian noise (AWGN) with unknown spreading sequence and other parameters. Using complex Gaussian mixture signal model and invariance principle, we derive constant-false-alarm-rate (CFAR) invariant detectors such as...
This paper proposes a computationally efficient spreading-waveform-estimation method for the non-symbol-periodic Direct Sequence Spread Spectrum (DS-SS) signals. The method is a low SNR unconditional maximum likelihood (UML) estimation algorithm. It works under the assumption of uniformly distributed transmission delay, which may cause mismatch in the real-world model. Equivalence exists between the...
In this paper, a novel method combining cooperative spectrum sensing with quantized soft decision combining is introduced. In order to allow cognitive radios and cognitive networks to opportunistically use spectrum, it is a prerequisite that the license owner or primary user of the spectrum will not be harmfully interfered and the spectrum band will be vacated as soon as the primary user starts its...
Cognitive radio (CR) is a promising technology for the efficient use of available spectrum. Reliable detection of primary user (PR) signals and spectrum sensing are the most important challenges which meet the implementation of the CR. In CR's communications, the PR user must be protected from the interference from the CR users. This can be achieved only by using an optimal spectrum sensing. In this...
The performance of a cooperative multiuser direct-sequence code-division multiple-access (DS-CDMA) system is analyzed in the asymptotic regime where both the spreading codes and the number of users grow large with the same ratio. A simple signal-to-interference-plus-noise ratio (SINR) expression is derived that is independent from the spreading codes and explicitly accounts for the effects of the...
As M-ary orthogonal code spread-spectrum dispreading method is based on maximum correlation rule, a false dispreading result will be computed out in the situation of false alarm. Moreover, this false result will be handed down to the following units, which of course causes a waste of resources. In this essay, a dispreading method based on confidence analysis is proposed, and the simulation results...
This paper deals with characteristics and theory of code division multiple access (CDMA), orthogonal frequency division multiplexing (OFDM) and variable spreading factor orthogonal ferquency and code division multiplexing (VSF-OFCDM) systems. As comparison and evaluation of VSF-OFCDM with various 2D spreading factor (SF) as frequency and time dispersive transmission channel according to ETSI standard...
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