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A new oversampled orthogonal frequency division multiplexing (OFDM) system operating in doubly selective fading environment is proposed in this paper. The oversampled OFDM structure employs oversampling in time domain and linear signal processing in frequency domain. The time-frequency processing enables a two dimensional Doppler-frequency grid that allows each data symbol be transmitted at multiple...
We study a cognitive network consisting of multiple cognitive users communicating in the presence of a single primary user. The primary user is located at the center of the network, and the cognitive users are uniformly distributed within a circle around the primary user. Assuming a constant cognitive user density, the radius of this circle will increase with the number of users. We consider a scheme...
In this paper, we analyze the performance of the optimal maximum likelihood (ML) receiver for a concatenated space-frequency block coded orthogonal frequency division multiplexing (CSFBC-OFDM) system over frequency-selective Rayleigh fading channels. First, we derive a simple expression to approximate the theoretical BER performance of the optimal ML receiver for CSFBC-OFDM systems. The accuracy of...
Joint iterative channel and covariance estimation with sufficient-statistics (SS)-based chip combining is studied for a multicarrier code division multiple access (MC-CDMA) system operating under partial-band noise jamming (PBNJ). The expectation maximization (EM) algorithm, which exploits the log- likelihood ratio (LLR) from the decoder, is employed to estimate the channel impulse response and interference-plus-noise...
In this paper we consider a multicell and multi- antenna E-UTRA system as conforming to 3GPP recommendation. Focusing on the downlink, the system performance is severely hampered by the intercell interference due to the frequency reuse. For this reason, 3GPP is currently studying some policies to mitigate the interference impairments. We compare here two main approaches: interference coordination...
This paper proposes new techniques for acquisition of hybrid DS-SFH spread-spectrum systems in the presence of partial-band interference in fading channels. The proposed techniques include differential detection followed by maximizing the circular cross correlation with a known PN sequence. This is extremely robust against tone interference. An interference rejection method is used to improve the...
In this paper, we propose a technique for predicting the traffic pattern of primary users in cognitive radio systems. Cognitive radios enable sharing the frequency bands that are licensed to primary users. By forecasting the traffic pattern of primary users, secondary users can estimate the utilization of frequency bands and select one for radio transmission to reduce the frequency hopping rate (the...
Subcarrier allocation for multiuser MC-DS-CDMA systems is much more complicated when compared to OFDM systems due to the presence of multiple access interference (MAI) when multiple users transmit simultaneously on the same subcarrier. In this paper, we propose a novel suboptimal algorithm to adaptively allocate subcarriers for MC-DS-CDMA systems, with the effect of MAI taken into consideration. An...
In IEEE 802.16 uplinks, the permutation of data on a frequency domain is performed when logical subchannels are transformed to physical subchannels to scatter deterioration of the radio propagation environment via inter-cell interference. However, it is ideal from the viewpoint of evading interference to completely divide the radio resource between the interfering cells, when there is comparatively...
Multi-channel multi-radio WMNs are promising solutions for overcoming the limited capacity problem in multi- hop wireless networks. In these WMNs, each mesh router is equipped with multiple radios and each radio operates in a distinct frequency band. Channel assignment is the key issue that should be addressed in these networks. In this paper we propose a channel assignment scheme with the objective...
Recently, multi-cell joint transmission and joint detection schemes have been identified as promising features of next generation mobile communications systems, as they enable to actively exploit inter-cell interference rather than treating it as noise. Both for uplink and downlink, concrete algorithms have been proposed, and strong increases in spectral efficiency and system fairness have been predicted...
The poor performance of TCP in wireless networks is further diminished in IEEE 802.11-based ad hoc networks networks due to the unnecessary actions of on-demand routing protocols when interference-induced packet drops happen at the medium access control (MAC) layer. In this paper, we present a cross-layer hop-by-hop congestion control scheme designed to improve TCP performance in multihop wireless...
The microwave oven (MWO) is a commonly available appliance that does not transmit data but still radiates signals in the unlicensed 2.4 GHz Industrial, Scientific and Medical (ISM) band. The MWO thus acts as an unintentional interferer for IEEE 802.11 Wireless Fidelity (Wi-Fi) communication signals. An analytic model of the MWO signal is developed and studied in this paper. The model's efficacy is...
Partially overlapped channel (POC) based design, has been identified recently as a promising technique to overcome the capacity bottleneck facing wireless engineers in various networks, such as WLAN, wireless mesh network (WMN) and ad hoc networks. However, considerable confusions still exist as to the actual power of POCs to improve network capacity, especially since traditional communication system...
The IEEE 802.11 and Low Rate WPAN (LR-WPAN) wireless networks can provide complimentary services and are likely to be installed within the same environments. Coexistence between the networks would be impaired, if the probability of packet collision between the networks is sufficiently large. This paper presents the results of an empirical study examining the impact of IEEE 802.11 on the LR-WPAN. The...
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