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Multi-carrier modulation (MCM) and especially orthogonal frequency division multiplexing (OFDM) are currently used in many radio transmission standards. Among these modulations, OFDM offset QAM (OFDM/OQAM) is an interesting alternative to OFDM. However, differently to OFDM, OFDM/OQAM modulation cannot directly use Alamouti coding scheme due to the remaining interference. In this paper, we propose...
We consider a two-hop infrastructure-based relay link with three transmit power allocation methods. Both amplify-and-forward and decode-and-forward protocols are studied. Fundamentally, a relay can operate either in a full-duplex or in a half-duplex mode. The performance in full-duplex relaying is degraded due to loop interference from the relay output to the relay input. On the other hand, the half-duplex...
Channel estimation for OFDM system using pilot carriers usually comprises time interpolation of the estimates across more OFDM symbols and then frequency interpolation. In order to improve estimate, the frequency response can be transformed into the time domain and windowed. To this end, an estimate of the channel duration is necessary and this process is particularly sensitive to the time interpolation...
In this paper we study the decentralized detection problem in wireless sensor networks when the sensors' observations have to be communicated to a fusion center through a fading channel subject to an energy constraint. We analyze the noncoherent case based on a simple on/off scheme combined with optimal sensor ldquocensoringrdquo. Interestingly we find that neither the PAC (parallel-access channel)...
In the commons model for spectrum usage, the cognitive (secondary) users are allowed to use the spectrum as long as the target performance in the primary system is not violated. In this paper we consider primary system that has a target outage performance and the transmission power of the secondary transmitter (STX) should be appropriately not to violate the target outage probability for the primary...
In this paper, we consider optimizing cooperative spectrum sensing in cognitive radio scenario, where two secondary users (SU) collaborate with each other via relaying scheme. Instead of directly assuming amplify-and-forward (AF) or decode-and-forward (DF) at each SU, the signal processing function is optimized via functional analysis considering both the average and the peak power constraints. We...
The cognitive radio paradigm is based on the ability to detect the presence of primary users in a given frequency band. In this scenario a spectrum monitor may estimate the signal power levels of all frequency channels in the band of interest, together with the background noise level. We address Maximum Likelihood estimation for this problem, exploiting apriori knowledge about the primary network,...
Efficient and reliable spectrum sensing plays a critical role in cognitive radio networks. This paper presents a cooperative sequential detection scheme to minimize the average sensing time that is required to reach a detection decision. In the scheme, each cognitive radio computes the Log-Likelihood ratio for its every measurement, and the base station sequentially accumulates these Log-Likelihood...
We propose a framework for designing an underlay secondary CDMA network. The objective is to select the secondary system's bit rate and spreading factor that improve the secondary network throughput given a required bit error rate and an allowable transmit power level acceptable to the primary network. The selection scheme is applied to both the case of random code assignment and an interference-minimizing...
In this paper we consider the problem of data-aided synchronization in the up-link of a multiple access (MA) orthogonal frequency division multiplexing (OFDM) system based on offset quadrature amplitude modulation (OQAM). In particular, the joint maximum-likelihood (ML) phase offset, carrier-frequency offset (CFO) and symbol timing (ST) estimator exploiting a short known preamble embedded in the burst...
The problem of interference alignment for K-user time-invariant multi-input multi-output (MIMO) interference channels is considered. A sufficient condition for perfect interference alignment is converted to a linear system of equations which is overdetermined for K ges 4. It is shown that this linear system is infeasible almost surely. To obtain the approximate solution to this problem, we use a least...
In this paper, we investigate the ergodic capacity of multiple-input multiple-output (MIMO) antenna systems with a single co-channel interferer in the low signal-to-noise-ratio (SNR) regime. Exact expressions for the minimum energy per information bit and wideband slope are derived, based on which, the impacts of the interference-to-noise-ratio (INR) and the number of receive antennas are examined...
In many communication protocols, small packets are aggregated into larger packets (bursts) at some layer of the protocol stack before being forwarded to the lower layer. Upon reception, the beginning of the burst has to be detected, and it has to be segmented to recover the small packets. Usually, this task is performed by hard decision on the received data. Obviously, if the burst is affected by...
We consider the problem of carrier phase offset estimation and propose two blind estimation techniques for low-density parity-check (LDPC) coded systems. The first technique is applied to a binary phase shift keying (BPSK) modulation while the second is applied to higher order modulations. These techniques are based on the calculation and minimization of functions of the log-likelihood ratios (LLR)...
In this paper, we analyze the effect of clock jitter on the performance of OFDM-based systems applying digital IF architecture. A bandpass SigmaDelta ADC is used for the analog to digital conversion process. An accurate and realistic model of the clock jitter in bandpass SigmaDelta ADC is implemented. Results from this paper show that clock jitter severely degrades OFDM system performance by introducing...
The problem of frame synchronization with equiprobable data symbols is widely analyzed in the literature and the optimum metric for AWGN channels has been derived both in the case of periodically and aperiodically embedded data symbols. On the contrary, the case of non-equiprobable data symbols has not been studied, although it can occur in many practical situations. An optimum metric for frame synchronization...
In this paper, low complexity linear network coordinated beamforming (N-CBF) algorithms under a zero inter-user interference constraint are proposed for the multi-cell downlink channel. We consider a downlink scenario with three base stations (BSs) equipped with one transmit antenna each and three mobile users, each of which has more than one receive antenna and is located on the cell-boundary. A...
Recent research have elucidated that significant performance gains can be achieved by exploiting the circularity/non-circularity property of the complex-valued signals. The generalized likelihood ratio test (GLRT) of circularity assuming complex normal (Gaussian) sample has an asymptotic chi-squared distribution under the null hypothesis, but suffers from its sensitivity to Gaussianity assumption...
The instantaneous capacity of multiple-input multiple-output (MIMO) systems over Rayleigh fading channel is known to follow a normal probability distribution when the number of transmit and receive antennas is large. In this paper, we extend this result for distributed MIMO (DMIMO) systems by deriving a closed-form approximation of the outage probability which becomes tighter as the rate or the number...
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