• Journal of Communications and Networks
• /
• v.10 no.3
• /
• pp.301-307
• /
• 2008

In this paper, the impact of channel sensing methods to IEEE 802.15.4 under the interference of IEEE 802.11b are analyzed. Two different channel sensing methods, energy detection and carrier sense, are considered. An average transmission delay, a throughput, and a power drain rate are used as performance measures. Those performance measures of IEEE 802.15.4 under the interference of IEEE 802.11b are analyzed mathematically. The simulation results are shown to validate the analytic results.

• Journal of Communications and Networks
• /
• v.17 no.4
• /
• pp.362-369
• /
• 2015

This study addresses the effects of channel estimation error and mutual interference between licensed and unlicensed systems on outage performance of reactive relay selection in unlicensed systems over independent non-identical (i.n.i) Rayleigh fading channels and under both the maximum transmit power constraint and primary outage constraint. Toward this end, power allocation for unlicensed users is first recommended to satisfy both constraints and account for channel estimation error and mutual interference. Then, we derive an exact closed-form outage probability representation for unlicensed systems to quickly evaluate this effect in key operation parameters. Various results corroborate the derived expressions and provide useful insights into system performance.

• Journal of Communications and Networks
• /
• v.14 no.3
• /
• pp.273-279
• /
• 2012

In this paper, we propose an iterative interstream interference cancellation technique for system with frequency selective multiple-input multiple-output (MIMO) channel. Our method is inspired by the fact that the cancellation of the interstream interference can be regarded as a reduction in the magnitude of the interfering channel. We show that, as iteration goes on, the channel experienced by the equalizer gets close to the single input multiple output (SIMO) channel and, therefore, the proposed SIMO-like equalizer achieves improved equalization performance in terms of normalized mean square error. From simulations on downlink communications of $2{\times}2$ MIMO systems in high speed packet access universal mobile telecommunications system standard, we show that the proposed method provides substantial performance gain over the conventional receiver algorithms.

• Proceedings of the IEEK Conference
• /
• 2006.06a
• /
• pp.229-230
• /
• 2006

In this thesis, we analyze performance related to reduction scheme of inter-cell interference causing serious problems in portable internet system. Frequency reusing factor(FUF) is 1 in portable internet system, and it means that a adjacent cell uses same frequency band. This channel environment raises inter-cell interference problem, which provokes serious problems related to system performance and channel capacity. Consequently, it affects deterioration in system performance as a whole. We analyze inter-cell interference when appling a various schemes such as (DCA)Dynamic Channel Allocation, CS(Channel Segregation), IDMA(Interleave Division Multiple Access), FH-OFDM, CRSA(Conceptual Random Subcarrier Allocation), and HDD

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.20 no.5
• /
• pp.39-43
• /
• 2020

In this paper, we propose the multi-channel interference cancellation algorithm for visible light communication (VLC) in smart building. The VLC system is communication technology using visible rays that come out in Light Emitting Diode (LED) device. It has energy curtailment effect and possible to use in ubiquitous network service applications. When a large number of users communicate indoors, the performance can be reduced due to channel interference. To remove interference, at the first, the minimum mean square error (MMSE) scheme as interference cancellation methods used, and then the successive interference cancellation (SIC) is applied to obtain additional diversity gain and improve interference cancellation performance. Indoor VLC channel model is employed. The performance is evaluated in terms of bit error rate (BER). From the simulation results, it is confirmed that the proposed scheme has better BER performance compared to the previous systems. As a result, the proposed interference cancellation improves the signal quality of VLC systems by effectively removing the channel noise. The results of the paper can be applied to VLC for smart building and general communication systems.

• 한국정보통신설비학회:학술대회논문집
• /
• 2008.08a
• /
• pp.12-16
• /
• 2008

In this paper, we study precoding techniques for co-channel interference suppression in multiuser MIMO systems. DPC is optimal techniques to achieve the system capacity of multiuser MIMO downlink channels. DPC is not proper in practical wireless systems because complexity is very high. So block diagonal precoding for multiuser MIMO downlink channel is studied. The block diagonal precoding is used to suppress co-channel interference between multiuser. Block diagonal precoding method, whose complexity is reduced by modified null space operation, change multiuser MIMO channel to multiple single-user MIMO channel. We also use V-BLAST decoder in receiver. V-BLAST decoder can achieve increased system capacity in proportion to the number of users. We show improved system performance by using computer simulation.

• Journal of Communications and Networks
• /
• v.4 no.3
• /
• pp.189-198
• /
• 2002

Precoder has been shown to be able to provide source diversity and design flexibility. In this paper we employ precoding techniques for block transmission based on a multirate filterbank structure. To accommodate multiuser communication with variable data rates, different precoders with corresponding coefficients and up/down sampling rates are used. However, due to unknown multipath distortion, different interferences may exist in the received data, such as multiuser interference, intersymbol interference and interblock interference. To estimate channel parameters for a desired user, we employ all structured signature waveforms associated with different symbols of that user and apply subspace techniques. Therefore better performance of channel estimator can be achieved than the conventional subspace method based only on the signature of the current symbol. The delay for that user can also be jointly estimated. Channel identifiability conditions and asymptotic channel estimation error are investigated in detail. Numerical examples are provided to justify the proposed method. gest either multicode (MC) or multiple processing gain (MPG) mechanism [2], while requiring data rates to be integral multiples of some basic low-rate. In order to support variable rate transmission however, a comprehensive scheme needs to be investigated.

• Journal of IKEEE
• /
• v.23 no.2
• /
• pp.735-738
• /
• 2019

Recently, orthogonal non-orthogonal multiple access (O NOMA) with polar on-off keying (POOK) has been proposed to mitigate the severe effect of the superposition. However, it is observed that the performance of the O NOMA strong channel user is better than that of the perfect successive interference cancellation (SIC), i.e., the performance of a single user transmission with binary phase shift keying (BPSK). Can the performance of the BPSK modulation be better that that of itself? It is not normal. It should be clearly understood theoretically, with the ultimate bound, i.e., the channel capacity. This paper proves that the channel capacity of the O NOMA strong channel user is non-zero with zero power allocation. Thus, it is shown that the interference is transformed effectively into the meaningful signal.

• The Journal of the Acoustical Society of Korea
• /
• v.17 no.3E
• /
• pp.58-66
• /
• 1998

In this paper, we analyze the effects of interference canceller on the performance of multitone DS/CDMA system proposed by Vandendorpe[5]. There are various kinds of interference canceller suggested by different researchers including parallel and successive cancellers and we adopt a canceller used by Yoon et al.[9] which is a kind of parallel canceller. We consider three kinds of interferences, that is, multipath interference(MPI), interchannel interference(ICI) and multiple access interference(MAI). The ICI is the interference between multitones. The equations for variances. are derived for the inteferences and thermal noise used for signal to noise ratio calculation. We also consider RAKE reception over multipath channel which is modeled as lowpass equivalent linear filter and three stage interference canceller used for performance improvement. We show the performance results for number of canceller stage, diversity order and number of users and draw some conclusions that interference canceller is effective in multitone DS/CDMA system and the performance is further improved with the higher order of diversity and larger number of PN chips.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2001.10a
• /
• pp.753-756
• /
• 2001

Automatic Identification System(ALS) employed SOTDMA for the multiple access method. In SOTDMA systems, slot reuse may result in discrimination or garbling. Especially Gaussian Minimum Shift Keying(GMSK) Co-Channel Interference(CCI) resulted from the slot reuse in the Aloha zone degrades the system performance such as capacity In this paper we introduce some useful techniques to cancel the CCI and discuss the methodology which is applicable to AIS-SOTDMA