In order to improve the throughput performance of the secondary users （SUs） in the cognitive radio （CR） environment, a quality of service （QoS） based media access control （MAC） protocol is proposed. In this pr...In order to improve the throughput performance of the secondary users （SUs） in the cognitive radio （CR） environment, a quality of service （QoS） based media access control （MAC） protocol is proposed. In this protocol, the CR node maps the channel state as a vector, and the transmitter and the receiver obtain the final channel map through an AND operation to prepare for an optional channel set. Data from the upper application layer are classified into two priority levels according to the QoS requirement. The data of each level relate to different contention windows so that the priority of real time data can be guaranteed. A two-dimensional discrete-time Markov chain is utilized to evaluate the system performance, and mathematical expressions of the system throughput are derived. Simulation results show that compared with the IEEE 802. 11 distributed coordination function （DCF）, the proposed MAC protocol can achieve higher throughput.展开更多
The characteristics of underwater acoustic channel such as long propagation delay and low bit rate cause the MAC(Medium Access Control) protocols designed for radio channels to be either inapplicable,or have low effic...The characteristics of underwater acoustic channel such as long propagation delay and low bit rate cause the MAC(Medium Access Control) protocols designed for radio channels to be either inapplicable,or have low efficiency for UWSN(Underwater Sensor Network).We propose a hierarchical and distributed code assignment algorithm based on divisive probability function which can avoid conflict between spread codes with high probability,and provide a statebased MAC protocol for UWSN.Without RTS/CTS(Request To Send/Clear To Send) handshaking,each node maintains a neighbor table including state field,and packages are forwarded according to the state of the receiver,so it can avoid the interference caused by transmitting to a sending node in a half-duplex system and improve channel utilization.The design of power control minimizes the nearfar effect inherent in CDMA.Simulation results reveal that state-based CDMA protocol shows outstanding performance in throughput,delivery ratio and resource-consumption.展开更多
This paper proposes a new multi-channel Medium Access Control (MAC) protocol named as Dual Reservation Code Division Multiple Access (CDMA) based MAC protocol with Power Control (DRCPC). The code channel is divided in...This paper proposes a new multi-channel Medium Access Control (MAC) protocol named as Dual Reservation Code Division Multiple Access (CDMA) based MAC protocol with Power Control (DRCPC). The code channel is divided into common channel,broadcast channel and several data chan-nels. And dynamic power control mechanism is implemented to reduce near-far interference. Compared with IEEE 802.11 Distributed Coordination Function (DCF) protocol,the results show that the pro-posed mechanism improves the average throughput and limits the transmission delay efficiently.展开更多
This paper proposes a cross-layer dual adaptive coded modulation architecture using turbo codes for mobile multimedia communication, which adapts to both the varying channel characteristics and the QoS of various mult...This paper proposes a cross-layer dual adaptive coded modulation architecture using turbo codes for mobile multimedia communication, which adapts to both the varying channel characteristics and the QoS of various multimedia services simultancously to increase the average system throughput substantially. A pragmatic channeladaptive turbo coded modulation schcme, which comes within 2.5 dB of the Shannon limit, is optimally designed, and then a QoS-adaptive scheme is superimposed to build the dual adaptive architecture. Simulation results show that the novel dual adaption reduces the gap from the fading channel capacity to 2 dB when assuming different services occur in equal probability and the service duration follows exponential distribution.展开更多
Brown envelop syndrome （BES） has remained a controversial issue in any debate centred on the Nigerian press, media professionalism and media ethics. It is one of the major setbacks of media growth in Nigeria. BES is...Brown envelop syndrome （BES） has remained a controversial issue in any debate centred on the Nigerian press, media professionalism and media ethics. It is one of the major setbacks of media growth in Nigeria. BES is a system whereby journalists collect money or other material gifts from news sources, company executives or event organizers to cover such events and probably give it the wildest publicity as the case may be. It symbolizes the rot that has plagued the Nigerian media industry since the early 1980s to date. This paper therefore builds from an empirical study by the same authors, as well as literature materials to argue that media professionalism and the enforcement of the various ethical codes that preach professionalism are the practical ways to ensure ethical conduct and behaviour amongst journalists and other categories of media practitioners, especially in Nigeria where these are missing. This, according to the paper, is the missing link in the quest to rid the media industry in Nigeria from the monster called BES.展开更多
Channel parameters estimation in an orthogonal for the receiver station is a multi-dimensional （MD） frequency division multiple access （OFDMA） system optimization problem, because every user node has a separate lo...Channel parameters estimation in an orthogonal for the receiver station is a multi-dimensional （MD） frequency division multiple access （OFDMA） system optimization problem, because every user node has a separate local oscillator and every transmitter to receiver link has individual carrier frequency offset （CFO） and channel impulse response （CIR） parameters. In order to reduce the computational complexity for MD optimization, a time domain CFOs and CIRs estimation algorithm over the OFDMA based wireless multimedia sensor networks （WMSN） is proposed in this paper. In this algorithm, the receiver station can decouple the signal from every node by correlation based on specially designed training sequences, so that the MD optimization problem is simplified to an 1-D optimal problem. It is proved that the multiple CFOs can be identified from the correlation result using the phase shift of the consecutive training se- quences. Based on the CFOs estimation result, the CIRs can then he estimated according to the minimum mean square error （MMSE） criterion. The theoretic analysis and simulation results show that the proposed algorithm can effectively decouple the signal from different user nodes and the bit error rate （BER） per- formance curves are close to the ideal estimation when the user number is not large.展开更多
In VSF-OFCDM wireless communication, wireless channel is divided into component channels with the same frequency space according to the frequency, and the carriers on component channels are mutually orthogonal. When t...In VSF-OFCDM wireless communication, wireless channel is divided into component channels with the same frequency space according to the frequency, and the carriers on component channels are mutually orthogonal. When there are enough subcarriers, the bandwidth efficiency of the system is close to nyquist limit, which can ensure the utilization ratio of system frequency. Therefore, under the premise of ensuring orthogonal division of channels, the channels received a secondary division according to data rate requirements and power limit of business to make the frequency resource fully used and makes the total power minimal, which realizes the optimal distribution of wireless-communication system resources. The secondary division is represented by bit loading algorithm the best bit number of subcarrier allocation in symbol period. For the characteristics of wide-band multi-media services and granular division of VSF-OFCDM wireless communication, the subject proposes the idea of business-oriented subcarrier allocation, which means that the subcarriers are divided in symbol period with the business as the dominant. Based on the idea, the paper designs service-oriented bit loading algorithm of subcarrier, byte and power combined with distribution based on channel detection, and makes verification and performance analysis on the algorithm.展开更多
基金The National Science and Technology Major Project( No. 2010ZX03006-002-01 )the National Basic Research Program of China ( 973 Program) ( No. 2011CB302905)the Science and Technology Support Program of Jiangsu Province ( No. BE2011177)
文摘In order to improve the throughput performance of the secondary users （SUs） in the cognitive radio （CR） environment, a quality of service （QoS） based media access control （MAC） protocol is proposed. In this protocol, the CR node maps the channel state as a vector, and the transmitter and the receiver obtain the final channel map through an AND operation to prepare for an optional channel set. Data from the upper application layer are classified into two priority levels according to the QoS requirement. The data of each level relate to different contention windows so that the priority of real time data can be guaranteed. A two-dimensional discrete-time Markov chain is utilized to evaluate the system performance, and mathematical expressions of the system throughput are derived. Simulation results show that compared with the IEEE 802. 11 distributed coordination function （DCF）, the proposed MAC protocol can achieve higher throughput.
基金supported by the Program for New Century Excellent Talents in University of China(NCET-11-1025)the NationalNatural Science Foundation of China(No.61162003,61163050,6126104)+1 种基金Qinghai office of science and technology(grant No.2012-Z-902)the Natural Science Foundation of Tianjin(No.10JCYBJC00600)
文摘The characteristics of underwater acoustic channel such as long propagation delay and low bit rate cause the MAC(Medium Access Control) protocols designed for radio channels to be either inapplicable,or have low efficiency for UWSN(Underwater Sensor Network).We propose a hierarchical and distributed code assignment algorithm based on divisive probability function which can avoid conflict between spread codes with high probability,and provide a statebased MAC protocol for UWSN.Without RTS/CTS(Request To Send/Clear To Send) handshaking,each node maintains a neighbor table including state field,and packages are forwarded according to the state of the receiver,so it can avoid the interference caused by transmitting to a sending node in a half-duplex system and improve channel utilization.The design of power control minimizes the nearfar effect inherent in CDMA.Simulation results reveal that state-based CDMA protocol shows outstanding performance in throughput,delivery ratio and resource-consumption.
基金Supported by the Science Foundation of Shanghai Mu-nicipal Commission of Science and Technology under contract 045115012.
文摘This paper proposes a new multi-channel Medium Access Control (MAC) protocol named as Dual Reservation Code Division Multiple Access (CDMA) based MAC protocol with Power Control (DRCPC). The code channel is divided into common channel,broadcast channel and several data chan-nels. And dynamic power control mechanism is implemented to reduce near-far interference. Compared with IEEE 802.11 Distributed Coordination Function (DCF) protocol,the results show that the pro-posed mechanism improves the average throughput and limits the transmission delay efficiently.
基金This work is supported by the High Technology Research and Development Program of China(No. 2001AA121031)the National Natural Science Foundation of China (No. 60072028)
文摘This paper proposes a cross-layer dual adaptive coded modulation architecture using turbo codes for mobile multimedia communication, which adapts to both the varying channel characteristics and the QoS of various multimedia services simultancously to increase the average system throughput substantially. A pragmatic channeladaptive turbo coded modulation schcme, which comes within 2.5 dB of the Shannon limit, is optimally designed, and then a QoS-adaptive scheme is superimposed to build the dual adaptive architecture. Simulation results show that the novel dual adaption reduces the gap from the fading channel capacity to 2 dB when assuming different services occur in equal probability and the service duration follows exponential distribution.
文摘Brown envelop syndrome （BES） has remained a controversial issue in any debate centred on the Nigerian press, media professionalism and media ethics. It is one of the major setbacks of media growth in Nigeria. BES is a system whereby journalists collect money or other material gifts from news sources, company executives or event organizers to cover such events and probably give it the wildest publicity as the case may be. It symbolizes the rot that has plagued the Nigerian media industry since the early 1980s to date. This paper therefore builds from an empirical study by the same authors, as well as literature materials to argue that media professionalism and the enforcement of the various ethical codes that preach professionalism are the practical ways to ensure ethical conduct and behaviour amongst journalists and other categories of media practitioners, especially in Nigeria where these are missing. This, according to the paper, is the missing link in the quest to rid the media industry in Nigeria from the monster called BES.
基金supported by the National High Technology Research and Development Programme of China(No.2006AA01Z216)
文摘Channel parameters estimation in an orthogonal for the receiver station is a multi-dimensional （MD） frequency division multiple access （OFDMA） system optimization problem, because every user node has a separate local oscillator and every transmitter to receiver link has individual carrier frequency offset （CFO） and channel impulse response （CIR） parameters. In order to reduce the computational complexity for MD optimization, a time domain CFOs and CIRs estimation algorithm over the OFDMA based wireless multimedia sensor networks （WMSN） is proposed in this paper. In this algorithm, the receiver station can decouple the signal from every node by correlation based on specially designed training sequences, so that the MD optimization problem is simplified to an 1-D optimal problem. It is proved that the multiple CFOs can be identified from the correlation result using the phase shift of the consecutive training se- quences. Based on the CFOs estimation result, the CIRs can then he estimated according to the minimum mean square error （MMSE） criterion. The theoretic analysis and simulation results show that the proposed algorithm can effectively decouple the signal from different user nodes and the bit error rate （BER） per- formance curves are close to the ideal estimation when the user number is not large.
文摘In VSF-OFCDM wireless communication, wireless channel is divided into component channels with the same frequency space according to the frequency, and the carriers on component channels are mutually orthogonal. When there are enough subcarriers, the bandwidth efficiency of the system is close to nyquist limit, which can ensure the utilization ratio of system frequency. Therefore, under the premise of ensuring orthogonal division of channels, the channels received a secondary division according to data rate requirements and power limit of business to make the frequency resource fully used and makes the total power minimal, which realizes the optimal distribution of wireless-communication system resources. The secondary division is represented by bit loading algorithm the best bit number of subcarrier allocation in symbol period. For the characteristics of wide-band multi-media services and granular division of VSF-OFCDM wireless communication, the subject proposes the idea of business-oriented subcarrier allocation, which means that the subcarriers are divided in symbol period with the business as the dominant. Based on the idea, the paper designs service-oriented bit loading algorithm of subcarrier, byte and power combined with distribution based on channel detection, and makes verification and performance analysis on the algorithm.
