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RISS 인기검색어
- 검색키워드
- 저자 : Nazar A. Saqib (검색결과 2 건)
- 무료
- 기관 내 무료
- 유료
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Bandwidth-Efficient Selective Retransmission for MIMO-OFDM Systems
Muhammad Zia,Nazar A. Saqib,Tariq Shah,Hasan Mahmood,Tamoor Kiani 한국전자통신연구원 2015 ETRI Journal Vol.37 No.1
In this work, we propose an efficient selective retransmission method for multiple-input and multiple-output (MIMO) wireless systems under orthogonal frequency-division multiplexing (OFDM) signaling. A typical received OFDM frame may have some symbols in error, which results in a retransmission of the entire frame. Such a retransmission is often unnecessary, and to avoid this, we propose a method to selectively retransmit symbols that correspond to poor-quality subcarriers. We use the condition numbers of the subcarrier channel matrices of the MIMO-OFDM system as a quality measure. The proposed scheme is embedded in the modulation layer and is independent of conventional hybrid automatic repeat request (HARQ) methods. The receiver integrates the original OFDM and the punctured retransmitted OFDM signals for more reliable detection. The targeted retransmission results in fewer negative acknowledgements from conventional HARQ algorithms, which results in increasing bandwidth and power efficiency. We investigate the efficacy of the proposed method for optimal and suboptimal receivers. The simulation results demonstrate the efficacy of the proposed method on throughput for MIMO-OFDM systems.
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Protocol-Aware Radio Frequency Jamming in Wi-Fi and Commercial Wireless Networks
Abid Hussain,Nazar A. Saqib,Usman Qamar,Muhammad Zia,Hassan Mahmood 한국통신학회 2014 Journal of communications and networks Vol.16 No.4
Radio frequency (RF) jamming is a denial of serviceattack targeted at wireless networks. In resource-hungry scenarioswith constant traffic demand, jamming can create connectivityproblems and seriously affect communication. Therefore, the vulnerabilitiesof wireless networks must be studied. In this study, weinvestigate a particular type of RF jamming that exploits the semanticsof physical (PHY) andmedium access control (MAC) layerprotocols. This can be extended to any wireless communication networkwhose protocol characteristics and operating frequencies areknown to the attacker. We propose two efficient jamming techniques:A low-data-rate random jamming and a shot-noise basedprotocol-aware RF jamming. Both techniques use shot-noise pulsesto disrupt ongoing transmission ensuring they are energy efficient,and they significantly reduce the detection probability of the jammer. Further, we derived the tight upper bound on the durationand the number of shot-noise pulses for Wi-Fi, GSM, and WiMaxnetworks. The proposed model takes consider the channel accessmechanism employed at the MAC layer, data transmission rate,PHY/MAC layer modulation and channel coding schemes. Moreover,we analyze the effect of different packet sizes on the proposedjamming methodologies. The proposed jamming attack modelshave been experimentally evaluated for 802.11b networks on an actualtestbed environment by transmitting data packets of varyingsizes. The achieved results clearly demonstrate a considerable increasein the overall jamming efficiency of the proposed protocolawarejammer in terms of packet delivery ratio, energy expenditureand detection probabilities over contemporary jammingmethodsprovided in the literature.
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