A new preamble structure is designed for wireless LAN based on MIMO OFDM systems, which can be used for both synchronization and channel estimation. Modulatable orthogonal polyphase sequence is utilized in training sy...A new preamble structure is designed for wireless LAN based on MIMO OFDM systems, which can be used for both synchronization and channel estimation. Modulatable orthogonal polyphase sequence is utilized in training symbol design regarding its correlation properties. The time synchronization and channel estimation are achieved by measuring the correlation between the received training sequence and the locally generated training sequence. Repeated training symbols are used to get carrier frequency offset （CFO） estimation. It is shown from the analysis that the accuracy of frequency synchronization is close to the Cramer-Rao lower bound. The training sequences are optimal for channel estimation based on the minimum mean square error （MMSE）.展开更多
It is wise for fixed operators to make use of broadband wireless access technologies,such as IEEE802.16d,to develop mobile access based on their existing fixed broadband IP networks.Mobile operators have to evolve the...It is wise for fixed operators to make use of broadband wireless access technologies,such as IEEE802.16d,to develop mobile access based on their existing fixed broadband IP networks.Mobile operators have to evolve their networks from 2G to 3G for making full use of their current resources. However,the AII-IP core network will be a general trend since broadband wireless access adopts the connectionless statistical packet multiplexing technology.Based on the introduction of IEEE802.16d,High Speed Downlink Packet Access (HSDPA) and CDMA2000 1x EV-DV technologies,this paper discusses the development trend of broadband wireless access technologies, and concludes that 3G's packet access technologies are the same as IEEE802.16d/e,and AII-IP is the goal.It emphasizes that Chinese TD-SCDMA should develop toward connectionless statistical packet multiplexing as early as possible.展开更多
1 IntroductionWith the rapid development of backbonenetworks,the subscriber accessnetwork,a major component of publictelecom network equipment and so-called the“last kilometer”,has turned out to bethe focus of atten...1 IntroductionWith the rapid development of backbonenetworks,the subscriber accessnetwork,a major component of publictelecom network equipment and so-called the“last kilometer”,has turned out to bethe focus of attention.Among various access technologies,thebroadband wireless access system featuresquick network construction,rapid investmentreturn and large bandwidth.It enables newnetwork operators to provide services quickly展开更多
Broadband Wireless Access (BWA) has become one of the major evolution trends in the fields of broadband access and mobile communications. However,some difficulties emerged during the application and industrialization ...Broadband Wireless Access (BWA) has become one of the major evolution trends in the fields of broadband access and mobile communications. However,some difficulties emerged during the application and industrialization of the BWA system,which calls for typical service models,key technology innovations and backbone support from broadband Internet. This article introduces a Broadband Wireless Multimedia (BWM) access system. It aims to build a new-type "triple play" BWA network by integrating terrestrial digital TV system and the BWA system,and by taking broadband Internet as its core network platform. A primary research shows that the new BWA system is an effective solution to the existing difficulties of BWA system. Moreover,it is quite competitive in service provision,service coverage,frequency planning,terminal power consumption and cost for network construction.展开更多
Hybrid Distributed Coordination Function (HDCF),a modified medium access control pro-tocol of IEEE 802.11 standard,is proposed in this paper to support both smart adaptive array anten-nas and normal omni-directional a...Hybrid Distributed Coordination Function (HDCF),a modified medium access control pro-tocol of IEEE 802.11 standard,is proposed in this paper to support both smart adaptive array anten-nas and normal omni-directional antennas simultaneously in one wireless LAN. Omni-directional an-tennas follow the standard Distributed Coordination Function (DCF) and smart antennas follow the Directional DCF (DDCF). The proposed DDCF is based on Hybrid Virtual Carrier Sense (HVCS) mechanism,which includes Omni-directional Request-To-Send/Clear-To-Send (ORTS/OCTS) hand-shake mechanism and directional data transmission. HDCF is compatible with DCF. When a node transmits in a directional beam,the other nodes can multiplex the physical channel. Hence,HDCF supports Space Division Multiple Access (SDMA). Simulation results show that HDCF can support hybrid antennas effectively and provide much higher network throughput and lower delay and jitter than DCF does.展开更多
This paper utilizes the cross-layer architecture to implement adaptive resource allocation in Orthogonal Frequency Division Multiple Access （OFDMA） based on the broadband wireless access system. According to the cro...This paper utilizes the cross-layer architecture to implement adaptive resource allocation in Orthogonal Frequency Division Multiple Access （OFDMA） based on the broadband wireless access system. According to the cross-layer architecture, the information in link layer is used for adaptive resource allocation in OFMDA. A new cross-layer adaptive resource allocation algorithm is developed which can guarantee the users to be in minimum average waiting time in link-layer and get the better spectrum utilization. Numerical results show that our scheme is appealing and can get about half of average waiting time less and 0.5 bps/Hz spectrum utilization more than the scheme in 1EEE802.16a.展开更多
Performance of fixed relays in orthogonal frequency division multiple access （0FDMA） systems, especially the coverage and capacity performance at the cell edge, is evaluated in this paper. Two methods, theoretical a...Performance of fixed relays in orthogonal frequency division multiple access （0FDMA） systems, especially the coverage and capacity performance at the cell edge, is evaluated in this paper. Two methods, theoretical analysis and calculation and Monte Carlo simulation, are used for the evaluations. By theoreti- cal analysis and calculation, frequency efficiency equation of a relay is introduced and numerical results are calculated. Monte Carlo simulation results also verify that the calculation method is reasonable. The evaluation shows that a relay can increase system performance to a certain level if it is designed appropriately, otherwise it will be harmful for the system performance, even to reduce it.展开更多
文摘A new preamble structure is designed for wireless LAN based on MIMO OFDM systems, which can be used for both synchronization and channel estimation. Modulatable orthogonal polyphase sequence is utilized in training symbol design regarding its correlation properties. The time synchronization and channel estimation are achieved by measuring the correlation between the received training sequence and the locally generated training sequence. Repeated training symbols are used to get carrier frequency offset （CFO） estimation. It is shown from the analysis that the accuracy of frequency synchronization is close to the Cramer-Rao lower bound. The training sequences are optimal for channel estimation based on the minimum mean square error （MMSE）.
文摘It is wise for fixed operators to make use of broadband wireless access technologies,such as IEEE802.16d,to develop mobile access based on their existing fixed broadband IP networks.Mobile operators have to evolve their networks from 2G to 3G for making full use of their current resources. However,the AII-IP core network will be a general trend since broadband wireless access adopts the connectionless statistical packet multiplexing technology.Based on the introduction of IEEE802.16d,High Speed Downlink Packet Access (HSDPA) and CDMA2000 1x EV-DV technologies,this paper discusses the development trend of broadband wireless access technologies, and concludes that 3G's packet access technologies are the same as IEEE802.16d/e,and AII-IP is the goal.It emphasizes that Chinese TD-SCDMA should develop toward connectionless statistical packet multiplexing as early as possible.
文摘1 IntroductionWith the rapid development of backbonenetworks,the subscriber accessnetwork,a major component of publictelecom network equipment and so-called the“last kilometer”,has turned out to bethe focus of attention.Among various access technologies,thebroadband wireless access system featuresquick network construction,rapid investmentreturn and large bandwidth.It enables newnetwork operators to provide services quickly
文摘Broadband Wireless Access (BWA) has become one of the major evolution trends in the fields of broadband access and mobile communications. However,some difficulties emerged during the application and industrialization of the BWA system,which calls for typical service models,key technology innovations and backbone support from broadband Internet. This article introduces a Broadband Wireless Multimedia (BWM) access system. It aims to build a new-type "triple play" BWA network by integrating terrestrial digital TV system and the BWA system,and by taking broadband Internet as its core network platform. A primary research shows that the new BWA system is an effective solution to the existing difficulties of BWA system. Moreover,it is quite competitive in service provision,service coverage,frequency planning,terminal power consumption and cost for network construction.
文摘Hybrid Distributed Coordination Function (HDCF),a modified medium access control pro-tocol of IEEE 802.11 standard,is proposed in this paper to support both smart adaptive array anten-nas and normal omni-directional antennas simultaneously in one wireless LAN. Omni-directional an-tennas follow the standard Distributed Coordination Function (DCF) and smart antennas follow the Directional DCF (DDCF). The proposed DDCF is based on Hybrid Virtual Carrier Sense (HVCS) mechanism,which includes Omni-directional Request-To-Send/Clear-To-Send (ORTS/OCTS) hand-shake mechanism and directional data transmission. HDCF is compatible with DCF. When a node transmits in a directional beam,the other nodes can multiplex the physical channel. Hence,HDCF supports Space Division Multiple Access (SDMA). Simulation results show that HDCF can support hybrid antennas effectively and provide much higher network throughput and lower delay and jitter than DCF does.
基金Supported by the National Natural Science Foundation of China (No.60072048) the Doctoral Program Fund of Ministry of Education of China (No.20010561007).
文摘This paper utilizes the cross-layer architecture to implement adaptive resource allocation in Orthogonal Frequency Division Multiple Access （OFDMA） based on the broadband wireless access system. According to the cross-layer architecture, the information in link layer is used for adaptive resource allocation in OFMDA. A new cross-layer adaptive resource allocation algorithm is developed which can guarantee the users to be in minimum average waiting time in link-layer and get the better spectrum utilization. Numerical results show that our scheme is appealing and can get about half of average waiting time less and 0.5 bps/Hz spectrum utilization more than the scheme in 1EEE802.16a.
文摘Performance of fixed relays in orthogonal frequency division multiple access （0FDMA） systems, especially the coverage and capacity performance at the cell edge, is evaluated in this paper. Two methods, theoretical analysis and calculation and Monte Carlo simulation, are used for the evaluations. By theoreti- cal analysis and calculation, frequency efficiency equation of a relay is introduced and numerical results are calculated. Monte Carlo simulation results also verify that the calculation method is reasonable. The evaluation shows that a relay can increase system performance to a certain level if it is designed appropriately, otherwise it will be harmful for the system performance, even to reduce it.
